40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  ATF eLog, Page 36 of 56  Not logged in ELOG logo
ID Date Authorup Type Category Subject
  2602   Mon Jul 12 14:42:42 2021 StephenDailyProgressCryo vacuum chamberRTD attached to coldhead with spring clamp, Si mass to be installed this week

Brief summaries of the last week's progress and the coming week's plans (plots will be posted soon!):

- progress Friday 09 July: Opened the cryostat up at the cold head, and attached an RTD to the cold head with a spring clamp (instead of relying purely on the cryo varnish).

- progress Monday 12 July: Found 65 K workpiece temp and 63 K cold head temp. RTD was apparently held successfully by spring clamp, and we will continue to collect cold head temperature in future runs. Warmup was started, with old data collection completed (cooldown_20210709) and new data collection commenced (warmup_2021_07_12). Note that warmup started at 1:14 pm, and it took me ~ 5 minutes to stop and restart the script to changeover to the warmup data collection.

- table plan Wednesday 15 July: Complete in-air optical layout. Make one flat face of Si mass reflective.

- chamber plan Thursday 16 July: Open up main volume and drop in frame with Si mass. Connect RTDs. Start cooldown. Confirm cooldown is going ok (optical alignment, especially), and revert if necessary before things get too cold.

- table plan Friday 16 July: Maybe measure stuff, maybe better to wait till coming week and use controlled heating to hit different temperature setpoints.

 

  2608   Mon Jul 19 15:57:17 2021 StephenSummaryCryo vacuum chamberTemp Log 210716_2255

Uh oh, review of the cooldown plot from the previous cooldown (QIL/2603) shows workpiece temperature of ~92 K at conclusion, while a temperature of 65K was observed in the CTC100 readout (Attachment). The logging of the warmup is consistent with the CTC100 image, as the logging started a few minutes after the warmup was started, and the warmup "5 minutes after starting" temperature of ~ 71 K is a practical temperature.

Seems to be something weird going on here, we will need to have Radhika take a look on her return (and continue taking photos of the CTC100 whenever we stop by).

Quote:

Temperature log for the first 2 hours (Attachment 1)

I wonder why the temperatures displayed on CTC100 and the ones logged are different...?

 

 

  2626   Fri Jul 30 14:44:56 2021 StephenThings to BuyCryo vacuum chamberUpgrades and updates in advance of PD testing

(Aidan, Stephen, Koji)

Building off of QIL/2597 after more thorough discussion in Mariner meeting today. Aidan and I will confirm details today and make moves toward installation of PDs next week.

Necessary capabilities (note: no need to scavange anything from the IRLabs dewar):

 - Cold temperatures = ready (via conductive mounting we have seen workpiece ~ 80 K, workpiece heating and CTC100 temp control is demonstrated)

 - Optical interface = ready (existing 1700 nm AR-coated window will be used at 2 micron, input power will just be calibrated with a power meter)

 - Electrical interface = almost ready, pending cabling (the cryo vacuum chamber has RTDs instrumented, so we just need the leads for the PDs, and we can create Cu twisted pair leads with in-vac crimp/solder sockets a la Koji's OSEM cabling) (also need in-air cabling with DB9 plug - trivial)

Improvements in advance of PD testing:

 - RTD cabling and Heater cabling (in vacuum) should be split with in-vac pins and insulated with PTFE tube - Koji has the magic material recommendations

Desired improvements (not necessarily in advance of PD testing):

 - Cu solid linkage (being fabricated).

 - Inner radiation shield should be clamped well to cold plate (consistent with most recent trial, but do we want better/more clamps?).

 - RTD mounting option on shields without cryo varnish (new threaded hole, new clamps).

 - RTDs consistent with planned Mariner RTDs (ref. QIL/2590).

 - Heater mounting should be directly to the workpiece via an improved clamp on the 2" x 2" grid (rather than on unused Si cantilever workpiece holder).

  2630   Mon Aug 2 13:25:32 2021 StephenDailyProgressCryo vacuum chamberWarmup started 02 August

With Test Mass RTD at 119K, and with all of Koji's trials completed, I started the warmup this afternoon.

 - Cryocooler off at 12:41

 - Heater on at 13:05 (forgot to complete this task durming my initial visit).

Anticipated warmup duration of ~ 1 day, as improvements to cooldown (higher emissivity test mass, better conduction to inner shield) should also improve the efficiency of our active warming, which took a bit more than 30 hours last time (ref QIL/2615).

  2638   Thu Aug 5 14:12:36 2021 StephenDailyProgressCryo vacuum chamberloading cantilevers into megastat (and actions toward pumping down)

Actions on my to-do list, before we are able to pump down for Aaron and Shruti’s Si Cantilever Q measurement:

0. Confirm Aaron has completed cantilever mounting and is happy with shield alignment.
 - if needed, might have to rotate shields and/or clamp down workpiece holder.
[Done 2021.08.07] 1. Solder on new RTD, then mount RTD and heater to workpiece holder.
2. Verify electrical continuity of RTDs and heater.
3. Close up (shield lids, chamber lids).
4. (anytime, optional) complete RTD and Heater disconnection junctions with in-vac crimped pins.
[Koji indicated these were likely scavanged from DB connector kits, Stephen ordered more] - crimped plug pins were in 40m lab parts tower, but didn’t see any receptacle pins in the vicinity.

[update - Aaron indicated interest in deferring 1 week to establish more permanent setup. Likely to reattach outer shield RTD to cantilever clamp, allowing two different workpiece sensors] Planning to complete items on this list Friday, by Mariner meeting timeslot at the latest.We are in good shape to pump down Friday early afternoon, and for Aaron to collect data via controlled warmup on Monday/Tuesday (could run through Wednesday, if needed).  

  2639   Thu Aug 5 14:29:42 2021 StephenLaser2um PhotodiodesOptical design for 2um PD in new cryo chamber

Actions on my to-do list, once we are warm and up to air, before Aidan and I are able to run the JPL PD test. This list complements the optical setup tasks and data acquisition setup tasks that are also mentioned by Aidan in this thread.

Update 23 August - using this list to [comment on details] and highlight items which are still outstanding instead of duplicating in a daily progress log entry :)

0. Remove Aaron and Shruti’s Si cantilever clamp, and return to them for safekeeping [I set the clamp aside, need to coordinate return of cantilever to with Aaron!]
1. Solder a connector equivalent to the testpiece (ref. QIL/2465) but with the cryo wire, In-Ag solder on the connector end, and crimped plug pins on the free end. The crimped plug pins interface the with receptacle pins of the existing leads, which are connected to in-vac side of DB9 feedthrough).
 - need to locate some In-Ag solder! [done, and checked connectivity - used standard lead-tin solder following Rana's recommendation (ref. QIL/2418) born out by Koji's testing (ref. QIL/2462 and QIL/2465)]
2. Confirm which PD holder will be most useful for this effort (Koji’s newly machined holders might be useful?) and mount to cold baseplate. If using the tombstone from the IRLabs dewar, which is likely shorter than the beam height, it sounds like we would need to mount it on a pedestal or post. [Aidan used Koji's taller PD mount from the same purchase (ref. QIL/2459). The beam height required no modification, nice!]
3. Mount RTD to PD holder, likely with cryovarnish (unless there is a lucky extra hole for a screw/clamping post). [Radhika and Aidan's G2100807 demo shows the problem with the prior lug, not super stable mounting for the RTD as the same hole is being used to host two screws. Instead, I retrofitted the upper screw from the mount's retaining ring to host one of the trusty spring clamps, see Attachment 1. I checked for clipping or connector interference throughout, and found none.]
4. Mount heater to ___ (TBD, ideally on PD holder but possibly on cold baseplate nearby). [dog-clamped the heater to the baseplate, directly adjacent to the mount - see overview images in Attachment 2 and Attachment 3. We may go through some PID growing pains with this configuration, and we also need to learn whether the 22 W heater power locally applied can overcome the cryocooler's  ~50 W cooling power at our operating temperatures (ref. Radhika's QIL/2585). Might be necessary to intermittently power cycle the cryocooler.]
5. Confirm alignment of shields and PD. [aligned both shields, clamped inner shield, but could reposition if there is an issue.]
6. Verify electrical continuity of PD cable, RTDs, and heater. [note need to add indium and finalize clamping of PD holder, also note routing of pins to be connected to PD connector per Koji's QIL/2605 as described in Attachment 3]
7. Close up (shield lids, chamber lid). [note that in particular, the covering up (with foil sheets) of unused shield apertures is still WIP but wasn't originally mentioned!]
8. (anytime, optional) complete RTD and Heater disconnection junctions with in-vac crimped pins. [done, with mounting isolation achieved by kapton tape as ptfe tubing has not yet arrived. Attachment 4 shows one example, from the inner shield.]
 - crimped plug pins were in 40m lab parts tower, but didn’t see any receptacle pins in the vicinity. [ordered a few hundred new socket pins, I should share some with the 40m parts tower]

Pending Aaron and Shruti’s measurements, it is likely that heater-assisted warmup will occur starting Tuesday, in time for Wednesday/Thursday access. Friday 13th August could be the start of the cool down if everything goes to plan. [Nothing goes well on Friday the 13th. Aaron and Shruti do not need in-vacuum measurements anytime soon. The current plan is for cooldown to begin Tuesday and, if everything goes to plan, we will collect data through the week, then likely swap out the PDs on Monday for another run next week. The next experiment slated for the QIL Vacuum Cryostat is another Si mass radiative cooling run w/ black paint on inner surfaces of inner shield.]
 

Attachment 1: IMG_9685.JPG
IMG_9685.JPG
Attachment 2: IMG_9687.JPG
IMG_9687.JPG
Attachment 3: routing_markup_of_IMG_9688.png
routing_markup_of_IMG_9688.png
Attachment 4: IMG_9682.JPG
IMG_9682.JPG
  2650   Tue Aug 24 15:01:25 2021 StephenLaser2um Photodiodes2um PD in new cryo chamber

[Aidan, Stephen]

Worked toward aligning and characterizing beam on PD. Will complete next session.

Log:

Some difficulty aligning to the 2um beam, which is sensed by a thermal card. Aidan intends to upgrade with a fiber coupled visible laser, which could then be swapped interchangably for alignment.

The 1" mirror at the top of the periscope doesn't make sense, given larger apertures in shields and viewport. We looked for a nearby 2" replacement but did not have luck. Ended up swapping back in the gold-coated 2" mirror, even though it is thin enough to be a pain to mount.

Instrumented connector pins to DB9 pins using the following translation (ref Aidan's drawing for connector / PD pinout, ref drawing from QIL/2639)

            DB9   - 1 6 2 7 3 8 

    Connector - 2 3 4 5 6 7

 

  2654   Fri Aug 27 17:57:30 2021 StephenDailyProgress2um PhotodiodesStart of PD pumpdown

[Aidan, Stephen]

After Aidan validated that model inputs were creating physical parameter changes, we proceeded with some last few checks before closing up. Notes:

 - Aidan set up a helpful script turning laser power on and off, and strip tool to follow PD and monitor PD signals. A strip tool chart was used to confirm that there was no loss of functionality or alignment during pump down.

 - Checked Heater function and Workpiece RTD response - all good.

 - Confirmed alignment by steering at periscope output mirror and watching PD voltage.

At this point Aidan gave a green light for pumpdown prep, and to start pumpdown and start cooldown. Notes:

 - Stephen disconnected the PD connector accidentally while trying to add strain relief (the irony is palpable). Reattachment of connector didn't seem to affect any signal levels.

 - During installation of radiation shield lids, shields became misaligned and PD signal fell (presumably due to clipping). Recovered previous signal levels by realligning outer shield.

 - Double checked that everything seemed good to go, no issues!

 - Timeline of pumpdown and cooldown:

     17:32 - Pumpdown started.

     17:47 - Turbo spin up started (pump station delay parameter).

     17:55 - Pressure dropped below 1 mTorr, so I started cryocooler.

     18:05 - Healthy so far - Pressure had come down half a decade more, and Coldhead RTD was reading 235 K.

  2665   Tue Sep 14 15:17:03 2021 StephenDailyProgressCryo vacuum chamberChamber up to air, lids removed

Monday I completed the vent that Aidan had started by turning off the cryocooler. During the afternoon I turned off the pumps, unbolted the chamber lid, and removed the radiation shield lids.

Next, Aidan was going to run some characterization measurements and determine whether to swap the diode or repeat with A1.

  2674   Sat Oct 2 23:57:50 2021 StephenDailyProgressCryo vacuum chamberChamber pumping down, carbon paint flakes cleaned up

Pump down sequence executed tonight; Aidan plans to automate data collection during cooldown and warmup both, and the script will be activated early in the coming week.

- Carbon paint flakes (mentioned by Aidan in QIL/2667) were either picked up or scrubbed by IPA wipe, except the biggest, which were nudged near the closest 1/4-20 hole and picked up with tweezers for removal. There are still some small flakes of paint as there was less benefit to cleaning flakes closer to the PD or lens, and I opted not to risk any bumps. Aidan was correct, some areas of inner shield ID wall have flaked, but it seems the main location of delaminated paint is on the wrinkly foil excess covering the rim of the shield, an accidental paint location.

- While adding the lids, I monitored the PD outputs using Aidan's strip tool kindly left running. I never noticed any clipping in the trends - should I have been more skeptical?

- While adding the lids, I forgot to monitor the RTD outputs to the CTC100 controller, and the outer shield ended up shorting and ceasing to read any temperature. Didn't notice until I had turned on the roughing pump! Had to reopen and fix the short. Good reminder.

- Turbo came on at 12:07 am on 03 October at a pressure of 30 Torr - the setting is actually a timer and not a gauge reading.

  2701   Fri Dec 10 15:58:57 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity

Started a new run this afternoon, with the following goals:

   1) confirm that the first run (QIL/2695) went smoothly, by performing a visual inspection in the chamber while setting up for the first run.

      - kapton tape affixing inner shield RTD lead junctions to inner shield had fallen. These junctions were simply hanging - not ideal, but apparently not too harmful. Not likely to impact temperatures, in my opinion, but could have led to shorts or glitches in data.

      - all RTDs appeared to be fixed and well-contacted to surfaces

      - Everything seemed to be in good shape with the copper bar, no apparent issues

   2) obtain a second run with similar configuration, now that the rigid copper bar linkage has been implemented.

   3) vary a single important parameter relative to the first run, namely the inner surface emissivity of the inner shield, so that the impact of that parameter may be observed.

      - Added Aluminum foil (matte side visible) to the inner shield inner surfaces (lid and cylinder, both). Anywhere there was previously black Aquadag, there is now matte aluminum foil.

      - Kept the same apertures for viewport access and for electrical and thermal connection passthrough, basically attempted to achieve identical shield coverage.

      - There is one small sliver of black aquadag visible at the location of the electrical leads, but I didn't worry about patching that small area.

Run Details:

   - Pumps on at  ~3:40 pm

   - Cooling started at 4:13 pm (pressure ~6 mTorr, rapidly falling with turbo pump spinning up from ~70% to ~85% over a 1 minute interval). Coldhead RTD is responsive.

   - All photos will be posted to the QIL Cryo Vacuum Chamber photo album.

   - Note from check in on Monday afternoon, ~ 69 hours after start: everything looks good, and the workpiece temperature (~127 K) seems to reflect the emissivity change.

  2704   Tue Dec 21 15:33:39 2021 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - next run repeating

I opened the QIL cryostat today for a health check and visual inspection before the next run. Because I saw a couple of interesting issues, I decided to redo the same run with more attention to detail on the closeout. I'm worried the outer shield may have been linked to the inner shield and baseplate enough to affect comparability with the prior run.

issues with this  run, requiring redo:

  • RTD wire for outer shield was clamped under lid of inner shield - this might have created a conductive link between the inner shield and the outer shield
  • outer shield was more wobbly than usual, and could have possibly been off of the three spacers - this might have created a conductive link between the outer shield and the baseplate

run details:

  • pumping started at 3:45 pm
  • turbo started with 15 minute delay at 20 torr
  • cryocooler started at 4:15 pm with active ion gauge pressure at 3 e-4 torr.

And since I didn't get to implement any of the intended next runs, here are some notes on other future runs of interest:

  • Si mass covered with Al foil (matte side facing out) - interested in making the emissivity of the test mass equal to that of the inner shield in the new config, for modeling.
    • (of course, this emissivity equivalence would be an approximation, as there is a large area of the test mass which is bare silicon)
  • outer shield clamped/resting on baseplate - this is predicted by Koji to be the most efficient cooling configuration.
  • shielding attached to structure holding Si mass (electropolished aluminum, aquadag aluminum, bare aluminum surfaces are all available.
  2706   Fri Jan 7 14:54:58 2022 StephenDailyProgressCryo vacuum chamberFastest Radiative Cooling run started 14 Jan

As discussed during the 07 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling through the following configuration choices:

  • eliminate radiation leak apertures
  • maximize emissivity of test mass volume
  • improve conductivity to outer shield

Actions completed 14 Jan 2022

  • Vent
  • Cover up aperture to viewport with foil (on both shields).
  • Remove foil from inner shield inner surface.
  • Place outer shield directly onto cold plate (no clamping force).
    • A bit unsatisfying, because the outer shield is not flat relative to the cold plate, but the shield is resting quite firmly with only a slight wobble when pressed. As with any plane-plane contact, there are a limited number of true points of contact, and the contact area is increased somewhat by foil that is folded around the outer shield or the cold plate.
      • I would estimate the contact area at ~5% of the total area of the bottom flange.
    • 2x G10 spacer washers were dropped into the lower volume whild making this switch.
    • Note that bottom lid of outer shield is still not conductively cooled, and therefore will be approximately room temperature.
  • Tidy up aluminum foil collar around bottom lid of outer shield.
  • Tidy up mylar shield around conductive link after inner shield
  • Pump down, cool down.
    • Pump down started at ~15:35.
    • Cool down started at 16:10.
  2708   Tue Jan 18 16:11:35 2022 StephenDailyProgressCryo vacuum chamberStatus of Fastest Radiative Cooling run started 14 Jan

I ended the first cooldown of the run at 12:49 today, approximately 92 hours after it had started. Workpiece temperature was 100 K - more data and model fitting will reveal more insights on the results.

I started a 5 W injection through the heater (dog-clamped to baseplate with indium gasket), which I intend to leave running until steady state temperature is reached, at least overnight. This power level will not present a risk to the system, so I feel comfortable with this static power input even though it is not interlocked.

Update after 25 hours [ATTACHMENT 1]

The 5 W heating of the shields has not quite leveled off yet, and the workpiece temperature resumed falling, showing the temperature had not yet reached a steady state. I will leave 5 W on until I see a steady state, then I will plan to turn off 5 W and allow the workpiece trend to level off fully. Summary:

  • with no heater input, after 90+ hours the workpiece was slowly cooling at a rate of ~ 1 K per 6 hours, and the inner shield temperature was stable at about 76 K.
  • with 5W heater input, after about 25 hours the workpiece is (still) slowly cooling at a rate of ~ 1 K per 18 hours, and the inner shield temperature is about 88 K and slowly rising about 0.1 K per 7 hours

See attachment 1 for data viewer screenshot which reflects the above summary.

Update after 145 hours [ATTACHMENT 2]

Continued injecting 5 W for the whole weekend. Over the last 24 hours, the workpiece temperature seems to have leveled off into a new cooling rate, while both shields alternated between heating and cooling. I think this can be described as a steady-enough state that I'm ending the cooldown.

Now, I'll let the chamber come up to temperature with the help of the 5 W load.

Attachment 1: 5w_input_qil_cryostat_20220119.png
5w_input_qil_cryostat_20220119.png
Attachment 2: 5w_input_121_to_145_hours_qil_cryostat_20220124.png
5w_input_121_to_145_hours_qil_cryostat_20220124.png
  2713   Tue Jan 25 14:01:27 2022 StephenDailyProgressCryo vacuum chamberHeat transfer between grease joints and pressure joints

There's also a convention to write "50 kgf" to designate "kilograms of force" (implying the same conversion Rana describes, multiplying by g). I see kgf enough in the mechanical engineering world that I wouldn't have been confounded, so I wanted to pass that along.

Quote:

I think its least confusing to just replace 50 kg g with 500 N. Writing 50 g can be misleading, it seems like 50 grams.

 

 

  2715   Mon Jan 31 15:40:21 2022 StephenDailyProgress 31 Jan Fastest Radiative Cooling run started

As discussed during the 21 Jan 2022 meeting, the next cryostat run will seek the fastest radiative cooling (again, see QIL/2706) through the following configuration choices:

  • move heater to test mass
  • add thermal grease to inner shield - coldplate interface (clamped joint)

Actions completed 27, 28, and 31 Jan 2022

  • Vent.
  • Remove Test Mass in frame.
    • For simplicity, we snipped the RTD lead (we didn't want to have to redo the cryovarnish joint).
      • Of course, the joint failed during the repairs so we had to redo the workpiece RTD cryovarnish joint anyway!
  • Use cryovarnish to affix heater.
    • Removed aquadag in area of joint using IPA-soaked Alpha wipe and scrubbing motion.
    • First, varnished cigarette paper anchor pad, then added heater.
    • We allowed the cryovarnish to cure overnight between the 27th and 28th, then allowed the joint to hang in its vertical orientation over the weekend to confirm its integrity.
  • Use conventional pin-socket arrangement to add junction to heater leads and workpiece RTD leads.
    • Confirm all RTD leads are functional, and repair crimp joints and Kapton tape insulation where needed.
  • Clean up aquadag flakes on coldplate.
  • Remove inner shield, add Apiezon M thermal grease, and bolt down again.
  • Touch up position of mylar shield on cold linkage, aluminum foil aperture covers.
    • All apertures are covered except:
      • Inner Shield: cold linkage (not an issue - partially occluded by copper bar, mylar tube extends into cold head view and mylar mitten)
      • Outer Shield: electrical port, cold linkage (aperture has been extended to have additional area underneath the original circular aperture)
  • Insert Test Mass in frame. Dog clamp down frame.
  • Pump down, cool down.
    • Pump down started at ~15:15.
    • Cool down started at 15:44.

Model updates required to reflect new configuration:

  • estimate conductive leak from 24 AWG heater leads to test mass
  • model conductance of cryovarnish joint between heater and test mass - does cigarette paper make a difference?
  • model greased joint of inner shield - cold plate interface
    • confirm clamp load is adequate for effective greased joint, at room temp and cold temp!
  2717   Mon Feb 7 11:57:38 2022 StephenDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

[Stephen, Radhika]

The double copper bar configuration pictured in Attachment 1 has been implemented. We completed the updates within work sessions on Thursday and Friday. Here's a pseudo-log:

  • Removed all items from coldplate to make space for thermal linkage.
  • Prepared thermal linkage for installation.
    • ref. QIL/2694 for all preparations made.
  • Installed thermal linkage.
    • Removed thermal linkage to allow for regreasing
      • Discovered a single brass #4 washer sandwiched between coldhead and rigid copper bar (likely lost during efforts to install an RTD during intitial thermal linkage install); thermal grease was mostly indented at brass washer and at area opposite location of brass washer, suggesting non-uniform contact.
    • Applied Apiezon N thermal grease at joints: [coldhead - top copper bar], [top copper bar - bottom copper bar, near coldhead], [top copper bar - bottom copper bar, near thermal strap].
    • Sandwiched together top and bottom copper bars, to insert simultaneously.
    • Angled top and bottom copper bars to pass below coldhead, and overall passing the two bars in together went smoothly.
    • Bolted both copper bars into coldhead using long (1.25") 4-40 bolts threaded into coldhead. Access was from bottom port below cryocooler. Torqued using short arm of allen key (no access for long arm).
    • Borrowed one bolt location for RTD spring clamp mount. Confirmed continuity of coldhead RTD.
  • Repaired pins damaged in removal, and inserted sheaths intended to replace the previous scheme and hopefully prevent pin and socket damage. More detail later :).
  • Installed shields.
    • Applied new Apiezon N thermal grease to bottom flange of inner shield.
    • Re-clamped inner shield to cold plate using a dog clamp array.
    • Placed outer shield in contact with outer shield; rocking percieved when pressing on one quadrant of the annulus.
    • Confirmed continuity of shield RTDs.
  • Installed test mass, still with heater mounted to planar surface as in QIL/2715.
    • Confirmed suspension wires were contacting bare silicon OD surface in middle.
    • Confirmed continuity of heater and of workpiece RTD.
  • Closed up, pumped down, cooled down.
    • Roughing pump on at ~4:20 pm
    • Turbo on with no issues after 15 minute programmed delay
    • Cooling started at 5:15 pm, pressure was a few E-4 torr; no need to wait so long, that was just when we got around to it.

All images are (or soon to be) posted to the QIL Photo Dump.

Attachment 1: D2000310_y-004_section_double_linkage_20220207.png
D2000310_y-004_section_double_linkage_20220207.png
  2718   Mon Feb 7 16:06:36 2022 StephenDailyProgress 31 Jan Fastest Radiative Cooling run, ended 07 Jan

[Radhika, Stephen]

The heater was turned on at 3:13pm on Friday 2/4.

We specified a set temperature of 123K. However, the CTC100 PI control included a 1 W lower limit on the input to the heater, so there was a steady load of 1 W applied to the Silicon Workpiece over the weekend.

At 16:01 the cryocooler was turned off to start the warmup.

The CTC100 PI control was configured with a setpoint of 250 K on the Workpiece RTD, to aid in the warmup, and an allowable power range from 0 W to 22 W.

  2722   Wed Feb 16 11:35:18 2022 StephenDailyProgressCryo vacuum chamberDoubled Thermal Linkage Capacity run started 11 Feb 2022

[Stephen, Radhika]

The heater was turned on on Wed, 2/16 at 11:30am, with control setpoint 123K. The lower power limit was verified to be 0W.

The cryocooler was turned off on Thu, 2/17 at 12pm. The heater control setpoint was changed to 295K for warmup. The plan is to address the wacky cold head RTD on Monday.

  2737   Sat Mar 26 12:49:18 2022 StephenDailyProgressCryo vacuum chamberWarmup started, issue with steady state heating

25 March 2022 (Friday) at 21:00, went to QIL to start warmup.

 - Cryocooler was turned off at 21:21

 - Heater output was disabled - it seemed there was an issue, and therefore I opted for passive warmup only.

 

Heater Issue Troubleshooting

Symptom: Heater Output was enabled but reporting only .35 W and "Err" indicator.

Symptom: When output was disabled, a fan noise was terminated. When output was reenabled, the same fan kicked back on. The fan was driving much harder than I had ever heard it before.

Symptom: The output indicated .35 W but the test mass temperature was 66 K. Past heater power for steady state at 120 K was on the order of 1 W.

Per CTC 100 manual:

   - pg 9 (100W heater outputs) indicates: "If the temperature of either PCB exceeds 60°C, the CTC100 automatically shuts off the corresponding output" which was not the case.

   --> Apparently not an overtemperature situation.

   - pg 9 (Hardware faults) indicates a list of error conditions which are accompanied by pop up windows.

   --> This error had no pop up window, not quite sure what to make of that except that the controller doesn't think our issue is something it can identify.

   - pg 29 (The system fan) notes that "The main system processor reads the desired fan speed from each I/O card and sets the fan to the fastest requested speed".

   --> Suggests that the louder fan noise may have indicated higher temperature condition, even if not an over tempearature condition.

   - pg 41 (Numeric) describes that in the typical numerical view of the data channels, the message "Err" that I saw on the heater channel indicates "an internal error has occurred".

   --> No explanation of what an "internal error" is, but in this case I suspect it could reflect that the heater output is not coupled the input Workpiece temperature.

Best Guess: the symptoms and the lack of any apparent controller-identified fault suggests that the heater may have debonded. I didn't look at temperature history, so I'm not sure if there was a point where the heater was bonded to the test mass during this run.

Next Steps: We should open up and investigate.

  2752   Fri Apr 8 16:25:54 2022 StephenDailyProgress2um PhotodiodesRecovery of IR Labs dewar WIP

Quick log describing effort to recover leaky IR Labs dewar.

POC Steve Zoltowski - Stevez@irlabs.com

No fix yet, so I reached out to the vendor for more ideas.

I'll post another log with a summary of what leak(s) we suspect and what the current behavior of the leak is.

Fix Effort 1 - Valve Housing Seal (attachment 1)

The fix IR Labs recommended was to look at the seal of the valve housing.
 - There was no sign of any issue with oxidation at any visible location.
 - The fluoroelastomer valve seat looks like it has crept (plastically deformed in the shape of the sealing surface underneath) but not dramatically.
 - The o-ring looked fine, but I wiped all surfaces and added a bit of Krytox to o-ring and valve seat.
 - Photos - https://photos.app.goo.gl/oa4bCxm7xaWRJZDj7

Conclusion: No change to the behavior of the leak.

Fix Effort 2 - Feedthrough Seal

I had not yet explored the seal of the feedthrough to the chamber, except to note that the screws are tight.

 - The feedthrough wire leads are plugged in within the chamber, and there is not enough slack on the leads to examine the o-ring. I removed the screws, found I had inadequate access, and replaced the screws.

Conclusion: Cleaning / reseating is deferred.

Fix Effort 3 - Window Seal

I had not yet explored the seal of the window to the chamber, except to note that the screws are tight.

 - The window looked ok during removal, and I had no reason to be concerned.
 - Removed the o-ring and wiped down o-ring and groove thoroughly with IPA. 
 - Applied Krytox to chamber-side sealing surface.
 - Wiped down chamber sealing surface.

Conclusion: No change to the behavior of the leak

 

Attachment 1: IMG_1354.JPG
IMG_1354.JPG
  2753   Fri Apr 8 17:34:10 2022 StephenDailyProgressCryo vacuum chamberCooldown started, two copper bars; manual logging.

Restart, without vacuum incursion, of cooldown from QIL/2749. Hopefully we pull data this time, via manual logging while Radhika and Chris figure out how to get the channels uploading again.

 - Cryocooler on at ~2:30 pm with Workpiece Temp ~ 250 K.

 - Datalogging didn't start till ~5:40 pm because I forgot that manual logging was necessary!

  Draft   Mon May 9 09:45:17 2022 StephenDailyProgress2um PhotodiodesRecovery of IR Labs dewar WIP

[Jordan, Jancarlo, Stephen, Radhika]

The Helium leak testing setup from the 40m Bake Lab was transported to WB B265B and setup.

The connection to the cryostat was made to the intrinsic KF25 flex tube of the leak tester, at the location of the KF25 - KF40 adapter.

Leak testing found a strong Helium signature at one location of the bottom end cap o-ring seal. The location has been marked in black marker.

Forensics should continue, first with a

At this time, there is no reason to suspect that

 

 

  2797   Fri Jul 29 14:27:43 2022 StephenDailyProgressCryo vacuum chamberProgress - Heaters, RTDs, Maglite

Update to QIL/2795:

  • RTDs (Digi-key P/N 615-1123-ND) brought to lab (see pic).
  • Heaters (Digi-key P/N A102128-ND) brought to lab (see pic).
  • Maglite hole drilled; remains to be seen whether than improves solderability, but we could also look at a lug / ring connector as an alternative connection.
  2547   Thu Apr 1 18:42:55 2021 Stephen DailyProgressCryo vacuum chamberPreparations for Q measurements

2021.03.30, StephenA

1. Viewport swap to nozzle that is not occluded by cryo shield = complete. All bolts on both Active Ion Gauge and Viewport have been torqued gradually (about a half turn at a time, around the clock dial) until the conflat seal was metal-to-metal. Periscope on damped optical rod was rotated to make room for replacement.

Before viewport swap - IMG_8487

After viewport swap - IMG_8502

2. Cryo RTD repair = complete. Two RTDs had been damaged during prior mounting efforts by me. I was able to repair the clamped RTD at the single damaged solder joint. I was able to repair the former Al-Block RTD by replacing the RTD element, and making a new direct attachment (not preloaded, not varnished to the aluminum block anymore)

Materials and set-up for solder repair - IMG_8491

Repaired Clamp-2 RTD - IMG_8494

Damaged Al-Block RTD - IMG_8492 (note short length between kapton strain relief and aluminum block was not ideal, one lead had already fractured and the second soon followed at the slightest touch)

Repaired, remounted Al-Block RTD - IMG_8495 (heater sandwiched underneath threaded adapter, clamp threaded into adapter, sandwiching RTD at top plane)

Remounted Clamp-2 RTD - IMG_8496 (RTD clamped at cold flange, strap is mounted)

Remaining Clamp-1 and Varnish RTDs are free - IMG_8497

Current readouts of CTC-100 controller, with repaired RTDs now behaving (note need to rename the Al-Block RTD) - IMG_8501

3. Next steps:

 - Karthik to install clamps, align in-air relay, and confirm positition of radiation shield aperture.

 - Remaining free RTDs to be mounted; current RTDs are mounted at Heater and Cold Flange, would be good to mount RTD at Work Piece/Clamp and at Outer Radiation Shield.

 - Radiation shield lids to be installed (might be easiest to install Outer Radiation Shield RTD after installing lid)

 - Mount lid, install bolts, pump down, turn on cryo cooler, the usual!

Attachment 1: IMG_8487.JPG
IMG_8487.JPG
Attachment 2: IMG_8502.JPG
IMG_8502.JPG
Attachment 3: IMG_8491.JPG
IMG_8491.JPG
Attachment 4: IMG_8494.JPG
IMG_8494.JPG
Attachment 5: IMG_8492.JPG
IMG_8492.JPG
Attachment 6: IMG_8495.JPG
IMG_8495.JPG
Attachment 7: IMG_8496.JPG
IMG_8496.JPG
Attachment 8: IMG_8497.JPG
IMG_8497.JPG
Attachment 9: IMG_8501.JPG
IMG_8501.JPG
  2694   Fri Nov 12 14:21:32 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberUpgrade to Rigid Copper Bar, and assorted transitions from PD testing

This post describes upgrade efforts from 10 - 16 November, with the following goals:

 - introducing a solid copper bar thermal linkage

 - shifting the setup away from PD testing

 - preparing for the next test (radiative cooling of Si)

Here are some highlights of the effort:

  • While removing the shields we found contaminants had plated near the line of sight surfaces at the optical window and the electrical feedthrough [Attachment 1]. The film was removed by IPA wipe [Attachment 2] and was not evident in any other location (presumably these were the cold surfaces in line of sight, so they received the most contaminant, but there may be a thinner deposition throughout!).
  • In order to install the copper rod, we needed to cut out slots in the outer shield and inner shield. We used a reciprocating saw and held the piece stiffly on a table [Attachment 3] [Attachment 4].
    • We tried to use large snips, but that failed to provide enough cutting force, especially where it was necessary to use the tip to access into the flanged corner. We also damaged a few of the electrical leads to the feedthrough (formerly used to wire the OSEMs) - this will require attention at next opportunity.
  • The copper rod itself was found to have a few issues:
    • Outer surfaces were somewhat tarnished and greasy, so an 80 grit aluminum oxide paper was used to clean up all surfaces [Attachment 5]. The surfaces were then wiped with IPA using Alpha wipes.
    • Slot width was matching the long thermal strap instead of the short thermal strap, so a drill press was used to add cut away the correct areas of one pair of holes [Attachment 6]. Later, this modification required larger washers in the stack under the bolt head.
    • The cold head had a larger OD than designed, so we were unable to use the corner holes to mount the RTD. There was not enough space at the corners to host the nut or washer. Instead one of the bolt pattern holes was used to host the RTD stack [Attachment 7]
  • The installation of the copper rod required the following steps:
    • We documented the previous state of the table [Attachment 8].
    • We removed the inner shield, the outer shield, and the old thermal linkage.
      • To access the cold head side of the linkage, we had to remove the lower conflat of the T.
    • We installed a 6" conflat flange, double faced with 4" bore (Lesker p/n DFF600X400), between the cryocooler and the T. This spacer raised the bottom face of the cold head to the correct height, so that the rigid copper bar runs approximately through the center of the shield apertures.
      • This required an order of new bolts with 3" length, to squeeze the three flanges (cryocooler, spacer, T) that are now stacked together.
    • We bolted the rigid copper bar to the coldhead, yawing the cryocooler to match the conflat bolt hole orientation while also pointing the copper bar down the axis of the arm.
      • This used new vented screws (UC Components p/n C-412-A) which are also silver plated, except in the location borrowed for the RTD stack as mentioned above [Attachment 7]. The RTD stack included a nut to adjust spring compression independently from screw threading.
      • Apiezon N thermal grease was applied on both surfaces to improve thermal conductivity across this joint.
      • We initially forgot to reinstall the mylar sheet radiation shielding that had been removed from the area around the cold head and around the linkage. This required that we reopen the bottom conflat to install the coldhead mitten, and that we pitch the aluminum shields away from the rigid bar to allow the mylar sheet to be inserted from the inside.
      • We found that the coldhead RTD had failed during intial mounting efforts, and a new RTD (actually one that had been desoldered from the setup previously, removed from the workpiece on 2021.08.07 but found to have no issue) was soldered and attached to the cold head, under the spring clamp.
    • Each shield was reinstalled, including:
      • The newly cut slots were used to pass shields over the rigid copper bar.
      • Electrical cabling was threaded through the usual apertures.
      • The outer shield was positioned on the G10 spacers.
      • Rough alignment was completed based on clearance from the rigid copper bar, and line of sight to optical window.
    • Final touchups were implemented:
      • Aluminum foil covered unused outer shield apertures.
      • A small aluminum foil panel was placed underneath the rigid copper bar, to cover the slot in the inner shield.
      • Final clamping of the inner shield and the heater (with indium gasket) were completed.
      • Thermal strap was used to link the cold baseplate to the rigid copper bar, with a bolted joint at the copper bar and a dog clamp joint at the baseplate. Apiezon N grease was applied to all contact faces.

The rest of the installation effort is captured in the next log post QIL/2695, to partition the items relevant to the radiative cooling of the silicon mass.

The photos here (and others) are posted to the QIL Cryo Vacuum Chamber photo album.

Attachment 1: IMG_0352.JPG
IMG_0352.JPG
Attachment 2: IMG_0353.JPG
IMG_0353.JPG
Attachment 3: IMG_0371.JPG
IMG_0371.JPG
Attachment 4: IMG_0370.JPG
IMG_0370.JPG
Attachment 5: IMG_0343.JPG
IMG_0343.JPG
Attachment 6: IMG_0351.JPG
IMG_0351.JPG
Attachment 7: IMG_0358.JPG
IMG_0358.JPG
Attachment 8: IMG_0346.JPG
IMG_0346.JPG
Attachment 9: IMG_2734.jpeg
IMG_2734.jpeg
Attachment 10: IMG_2740.jpeg
IMG_2740.jpeg
  2695   Fri Nov 12 14:31:38 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

In this phase, we are working toward improving our setup with a rigid copper bar, and obtaining a new data point for our radiative cooling thermal models for a suspended silicon mass. Since the past cooling runs of a silicon test mass did not yet incorporate aquadag-painted shields, we wanted to obtain a new data point in the model (in other words, we painted the shields in QIL/2645, but the next test was a PD measurement, so this is the first silicon test mass measurment after shields were painted). The improvement to the thermal linkage, now using a rigid copper bar with higher conductivity (ref. QIL/2666), is a second variable being changed simultaneously in the spirit of improving the cooldown time.

Refer to the prior post (QIL/2694) for the bulk of the blow-by-blow of configuring the chamber to use the rigid copper bar linkage. This post will describe the mounting of the Si mass, and the pump down and cool down.

  • The silicon mass with Aquadag barrel was dropped into the existing frame, with the previous wire arrangement and with no particular requirement on position or orientation (just best effort centering and leveling). Adjustments were done chamberside as access was easier.
  • The frame was lifted into the chamber, with the hanging mass supported by auxiliary fingers, and placed in an available area. Since conductive cooling was not a dominant mode of heat transfer in this setup (ref. QIL/2647), clamping to the baseplate was simply a single dog clamp on each foot of the frame.
  • The cigarette paper was cryovarnished to the surface in the bare central position. Once the cryovarnish was set, the RTD was cryovarnished to the cigarette paper pad. No  strain relief or thermal anchoring considerations were implemented. RTD continuity was verified.
  • Lids were bolted down and shields were finalized (avoiding shorting to copper bar, making sure foil drapes covering apertures were well positioned, etc.
  • Vacuum pumps on at ~3 pm, cryocooler on at 3:30 pm. At 4 pm, things are still looking good!

Closeout photos will be posted to the QIL Cryo Vacuum Chamber photo album.

Attachment 1: IMG_2738.jpeg
IMG_2738.jpeg
Attachment 2: IMG_2741.jpeg
IMG_2741.jpeg
Attachment 3: IMG_2742.jpeg
IMG_2742.jpeg
Attachment 4: IMG_2745.jpeg
IMG_2745.jpeg
Attachment 5: IMG_2747.jpeg
IMG_2747.jpeg
  2697   Fri Nov 19 14:01:40 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with better shield emissivity

[WIP]

11/16 was the first Megastat cooldown after exchanging the copper braid linkage for a copper bar. Attachment 1 compares the cooldown trends for the test mass, inner and outer shields, and cold head. The solid curves are the new cooldown trends (copper bar), and the faded dashed curves are the previous cooldown trends (copper braid).

Immediate observations:

    - The coldhead has a reduced heat load, and interestingly a second time constant governs cooldown from ~2-35 hours.

    - The inner shield time constant is reduced significantly, but the inner shield experiences a slightly greater heat load at steady state.

    - The test mass cooling is improved as expected, given inner shield cooldown.

    - The coupling between the outer shield and inner shield has increased, resulting in greater cooling of the outer shield. This could explain the added heat load to the inner shield. 

Attachment 1: comp_cooldown_728_cooldown_1116.pdf
comp_cooldown_728_cooldown_1116.pdf
  2702   Thu Dec 16 15:54:44 2021 Stephen, RadhikaDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - CTC100 temperature control success

This post will host plots and trends from this radiative cooling run. At a glance, the tuned CTC100 PI control was able to control the workpiece steady state temperature in this radiative cooling test within .005 K.

Run description: At 4 pm Wednesday, the workpiece temperature was at steady state from the QIL/2701 cooldown, a little less than 120 K. From 4pm Wednesday thru 5pm Thursday (25 hours) the CTC100 controller was actuating on the workpiece RTD temperature (cryovarnished to the suspended Si mass) using the resistive heater (dog clamped to baseplate with indium foil gasket). The conductive heating of the cold plate, and therefore the inner shield, led to radiative heating capacity (via ΔT)  that actuated on the temperature of the suspended test mass. As found in QIL/2643, the suspended Si mass is well isolated from conduction to the cold plate.

Before the run, the CTC100 PID controller was allowed to autotune using a long lag (600 s) and a moderate acutation step (10 W). After autotuning, the D term was still 0, which seemed fine.

Data: Attachment 1 plots cooldown curves for all RTDs during this run. Attachment 2 compares this run's test mass and inner shield temperature curves to those from the previous run (Aquadag on inner surface of inner shield). The expected result of this change (coating inner surface of inner shield with Al foil) is a weakened radiative coupling between the inner shield and test mass, leading to less effective cooling of the test mass. 

Initial observations from data:

1) The cold head temperature curve again suggests 2 time constants, and cooldown is identical.

2) The inner shield's cooldown is roughly unchanged.

3) The outer shield's temperature drops significantly more, indicating a stronger coupling to the inner shield. We will check for a conductive short the next time we open up.

4) The test mass's cooldown matches expectations (weaker radiative coupling).

[WIP - The data will be fitted and discussed]. More detailed analysis from fit to come, including from heater runs.

 

Attachment 1: cooldown_12-10_all.pdf
cooldown_12-10_all.pdf
Attachment 2: cooldown_12-10_vs_11-16.pdf
cooldown_12-10_vs_11-16.pdf
  2559   Wed Apr 21 09:42:35 2021 Stephen, ranaThings to BuyCryo vacuum chamberReimagining QIL Cryo Vacuum Chamber

WIP log entry - working on getting all of our ideas down on the page, then will sort and elaborate.


We met to discuss a range of topics relating to the path ahead for the Cryo Vacuum Chamber. This reconsideration of the current state of things is necessary as the chamber needs to become the workhorse for PD characterization efforts soon, in addition to a range of other tests (large suspension tests will be conducted in a different chamber, yet to be designed)

  1. Pumping station should be moved away from table, with long roughing lines perhaps coming down from above using some ceiling-mounted cable tray or similar.
  2. Primary pumping line to chamber is large and overkill in terms of conductance. Can move to a longer, more flexible, smaller diameter connection (may need to adapt using CF zero-length flange).
  3. Pumping of the external volume may be managed by valve arrangement and direct connection of both volumes to the turbo pump. Valve out the external volume once the pressure is low, and the pressure should hold well enough for conductive losses to be minimal.
  4. Viewports seem suitable, no issues throughout. I learned about common coating behavior, namely that reflectance is generally at half the wavelength of transmission, so if I see a green reflection it suggests transmission at IR. Neat!
  5. Cabling into chamber for temp sensors is pretty scary. Noticed the kink in the cable bundle caused by the flexible part of the cable extending longer than the grip of the connector's stiffening. Needs to be reassembled with the stiff cabling under the grip (could extend the grip, shorten the flexible leads, etc.) to avoid the kink.
  6. External volume feels like a misdirected design.
    1. For general case, consider mounting the cryocooler directly to chamber. Avoid losses related to thermal linkages from cold head of cryocooler to baseplate (diagram will be supplied, Rana was especially concerned that the V clamping arrangement didn't have adequate contact area in the line contacts)
    2. For vibration-sensitive experiments, would be good to have a flexible bellows reducing vibrational energy through the vacuum skin, and flexible strap reducing vibrational energy to the baseplate.
    3.  For contamination-sensitive experiments, would be necessary to implement a feedthrough as currently, but seems overkill for current slate of experiments.
    4. The intention seems to have been to devise a scaleable solution that would work for Mariner, but we are currently very far from realizing that (cryocooler needs to be Stirling cycle for vibration, no validation yet of adequate thermal conductivity through the external volume to the baseplate, etc.)
  7. Thermal straps with Mylar shielding is not the optimal implementation. Something like a rigid copper bar provides better conductivity, and can be shielded by G10 tubing with Aluminum metallization on the OD. If a flexible connection is required (for example, vibration isolation or positional uncertainty) a thermal strap may also be shielded in this sort of conduit.
  8. Need to replace the V-groove copper connections with something with much more surface area. V-grooves are nearly 1D contact lines, so they are probably the mian cooling rate limiter at the moment. Need to get some new parts fabbed ASAP to continue working on this cryostat.
  9. Vent valve should be a leak valve with a controlled, small conductance, perhaps backed by a filter. Want to allow slow, controlled venting.
  10. Skyhook Crane should be on its cart wheels for easy relocation away from the experiments.
  11. Skyhook should be replaced by a simple hoist mounted to ceiling of enclosure. Would require stiffening of some members of the enclosure's ceiling, but would permit easier access with fewer traffic jams.
  12. Yellow solvent cabinet should be removed. Solvents should be stored under fume hood.
  13. Would be great to get a stand (ie wire shelving, but heavy duty) which could hold the compressor, hold the pumping station, and provide a single location for any other items that need to be interfaced. All connections would be routed over the walkway via a run of cable rack.
  14. Moving the chamber to the center of the table width would be helpful to opening up access to more ports. Currently located in a corner, such that only half of ports are accessible. This is an extra reason that the Sky Hook should be remounted to its wheeled base.
  15. Should put all controllers on a rack, rather than consuming optical table space. All necessary serial comm cabling could then run to this singular location. We can use the rack next to the sink which has the NIM racks. The rack is completely unused right now. Need to get some rack parts to put some shelving in there.
  16. Documentation of ongoing thoughts, design efforts, modifications, etc. can be contained at the wiki!
  17. What is currently installed? Some insights from the wiki (ie gauges, pumps, viewports) should be elevated into a comprehensive diagram with a bill of materials or similar.
  18. In the diagram need to note all instruments so that Radhika can include it in her work to interface with the DAQ. i.e. no more photos and screenshots to record data.
  19. Where am I? A floorplan for this experiment (current and planned) would be worth some time, now that we are considering specific improvements.

Will sort the above into some sort of timeline (such as short term / long term).

Ruminations about the future chamber for suspension work:

  1. Stirling cryocooler for vibration isolation
  2. Straight-sided construction (i.e. rectangular prism) for more usable footprint inside
  3. If vertical (i.e. lid) use counterbalance and hinge for easy opening without hoist or crane; might need side ports large enough for hand access, since the height will be prohibitive to reach all the way down to the baseplate.
  4. Horizontal (i.e. door) might be preferred, especially with the volume in the form of a rectangular prism. This would allow access throughout the height of the chamber.
  5. Usual vacuum vendors should be able to help bring the design from a sketch to a quote, so start those conversations.
  1843   Tue Sep 17 14:19:40 2013 SteveLab InfrastructureGeneraluse clean cover to keep optics clean

Quote:

[Eric G, Tara, Evan]

We have covered both optical tables with drop cloth in preparation for tomorrow's sprinkler installation. The laser and all electronics on the tables have been switched off, with the exception of the rubidium standard. The gyro HV supply in the rack has also been switched off.

 CP STAT 100 is the right material to use on optical tables. You can borrow some from the 40m. You guys should have a roll in the basement. Buy a roll that is cleaned to class 100 and certified

at CALTEX Plastix Ins

 

  1914   Fri Apr 3 16:22:12 2015 SteveMiscSeismometerPZT buzzer

We did not find our PZT buzzer. Replacement actuator was ordered April 1

Quote:

Rubber handles give too much low pass action - use the plastic handle of a ball driver instead. For a more calibrated result, even better is to use the PZT buzzer w/ HV driver. Nic and/or Steve know where it is.

The SR785 data can be save by using "Output"-> "ASCII Dump".

Its also good to include a diagram of the frame with the location and direction of the accelerometer on it for future reference.

 

  1955   Tue Jun 30 15:43:49 2015 SteveMiscSeismometerpin vises

These may work better. Steel wire will degrade the chuck every time you tie it.

http://www.amazon.com/Gyros-45-01819-Adaptor-094-Inch-Capacity/dp/B0000DD2N4/ref=pd_sim_469_10?ie=UTF8&refRID=0CC17RH707ZEJ3W942WZ

http://www.amazon.com/Gyros-45-01801-Adaptor-039-Inch-Capacity/dp/B0000DD2N3/ref=pd_bxgy_469_text_y

Quote:

We spent the afternoon preparing the rhomboid to be suspended once more. This was done once already with two wires, but we had found the wire lengths were not equal enough to work out. This time we set up a device to carefully adjust the wire lengths. This required cutting new wires and re-clamping them in the pin vises. Unfortunately, one of the upper pin vises broke (see photo). This is one of the two that we had died so that we could screw bolts onto it. It broke at a location such that the mechanism for closing the collet around the wire no longer functions. In a spirit of pushing through to try to get the rhomboid suspended anyway, we mixed up some expoxy and glued the wire into the collet and the collet into the pin vise head. We decided we would adjust the other wire to match this particular wire's length. We prepared the other wire and slowly lowered the rhomboid. Upon letting the 2 wires fully take the weight, the second wire pulled out of its bottom pin vise. The wire didn't break, but the pin vise was simply not clamping it well enough. Upon inspection, it turns out this was the pin vise that had previously been damaged. The collet teeth don't fit together perfectly anymore, and there is indeed a gap between two of them which is most likely the cause of the malfunction. We taped the free end of the wire so it's not a hazard and are leaving the setup as is for now until we get a replacement pin vise. 

 

  2090   Fri Apr 21 15:37:36 2017 SteveLab InfrastructureRF10 MHz reference distribution system planning

We are planning to establish a central GPS signal support from West Brige room B250  to all our sub basement  labs.

Each lab would have an indipendent Heliax line that would run on the west wall and end in a junction box SMA for you to connect to.

Few questions regarding to this effort:

1, Are the horizontal running of heliax cables will be enclosed in conduits? or they can lay in the cable tray.

2, Junction box https://www.mcmaster.com/#75065k21/=17a8rct   Is this good enough? with N fitting in and  SMA out connections

3,          Location A of these junction boxes: roughly inline with existing tray so the heliax N can be connected straight into it. They would be placed at a break-or end-or beginning of the tray.

    OR,  Location B of junction boxes with 2" od horizontal conduit running under or above cable tray depending on the location of the wall through 2" openings.

4, What is your idea? or need?

   




 

Attachment 1: S_033W_B2_SPM_DWG_FPL_CAD_LAYER_REPORT.PDF
S_033W_B2_SPM_DWG_FPL_CAD_LAYER_REPORT.PDF
  2107   Tue May 23 10:15:31 2017 SteveLab InfrastructureRF10 MHz reference distribution system planning

I'm proposing the picture below:

1, G-10 insulating cover plate to avoid ground loops. The SMA adaptor will be mounted on it.

2, The Heliax cable will have  N right angle male connectors. This cable can be inside of  ~1/2" OD flex conduit. This is not really needed, it is just an option. * The  flex conduit or Heliax  will be clamped by metal cable ties to the tray and vertial U channel guide.

3, The sourse end of the Heliax will have the identical N right angle male connector. The location of this point is not specified yet in room B250 The connectors-cables will be purchased assembled.

* I'm backing out of the option of flex conduit.

 

 

Quote:

We are planning to establish a central GPS signal support from West Brige room B250  to all our sub basement  labs.

Each lab would have an indipendent Heliax line that would run on the west wall and end in a junction box SMA for you to connect to.

Few questions regarding to this effort:

1, Are the horizontal running of heliax cables will be enclosed in conduits? or they can lay in the cable tray.

2, Junction box https://www.mcmaster.com/#75065k21/=17a8rct   Is this good enough? with N fitting in and  SMA out connections

3,          Location A of these junction boxes: roughly inline with existing tray so the heliax N can be connected straight into it. They would be placed at a break-or end-or beginning of the tray.

    OR,  Location B of junction boxes with 2" od horizontal conduit running under or above cable tray depending on the location of the wall through 2" openings.

4, What is your idea? or need?

   




 

 

Attachment 1: WBrf.jpg
WBrf.jpg
  2109   Tue May 23 16:06:41 2017 SteveLab InfrastructureRF10 MHz reference distribution system planning

 

Quote:

This is pretty close, but for the section that runs down from the cable tray to the breakout box, it needs to be fully enclosed. Something like this:

http://www.alliedeg.us/galvanized-rigid-steel-conduit/

with steel U-clamps to hold it to the wall; clamps will have to be put into the wall with some anchoring. The elbow piece starts from the cable tray so that there is no exposed cabling between the cable tray and the box.

I thoughed this DIN rail would give enough protection. The closed tube conduit will not allow the purchase of connectors attached Heliax. 1.5"  ID conduit required to get the right angle N connector  through. The rail would leave more options open in the future.

Attachment 1: DIN_rail_pr.jpg
DIN_rail_pr.jpg
  2111   Thu May 25 11:26:45 2017 SteveLab InfrastructureRF10 MHz reference distribution system planning

I'm showing the installation plan here.The labs raceway to tray distance vary from 28 to 63" from lab to lab.

The 1.5" size conduit  will be ending about  a foot from the tray or pipe.

Let me know, if you have a specific location for this outlet in your lab.

Attachment 1: WBrf2.jpg
WBrf2.jpg
  5   Fri Oct 26 15:38:43 2007 Tobin FrickeLaserPSLPolarizer
On Tuesday we installed a λ/2 plate and a polarized beamsplitter after the laser aperture; attached to this entry is a measurement of transmitted power versus polarizer angle.
Attachment 1: polarizer.pdf
polarizer.pdf
Attachment 2: polarizer.m
% Polarizer calibration / Rana's lab
% Tobin Fricke 2007-10-26

% Experimental setup:
%                                [Dump]   
%                                  |
%  +-------+                       |
%  | Laser |-------|lambda/2|----|PBS|----[Power Meter]
%  +-------+ 
%  
... 53 more lines ...
  2207   Fri Jun 29 09:18:32 2018 Vinny W.DailyProgress2micronLasersPower Loss in Fiber Optic Cable

One of the factors we're taking into account when figuring out the optimal fiber cable length to use in the 2um laser characterization project is the power loss present as a function of such length. Andrew and I worked through some figures and came up with the following plots, sampling a few values of the attenuation coefficient alpha. The process was relatively straightfoward, we introduced some loss, e^{-\alpha L}, into a signal. Thus, at one of the outputs of the MZ, the signal we receive would be:

e^{-2\alpha L_1}+e^{-2\alpha L_2}+2e^{-\alpha (L_1+L_2)}\cos (2\pi \Delta Lf/c)

 

Next, since we ideally want our signal to be locked at mid-fringe, we take the derivative of the function with respect to frequency and observe the maxima. 

In order to best visualize the points at which the slope is of highest sensitivity, we take the derivative once more and observe the zero points.

Through ThorLabs data on the SM2000 fiber optic cable ( https://www.thorlabs.com/drawings/d7a7404567d69154-FBD8C6B1-0D0E-7F1A-14D2F3A96ED2FF2E/SM2000-SpecSheet.pdf ), we came to a good approximation that our attenuation coefficient is approximately 8.63*10^-3 dB/m. The orange line in the above graph is a close approximation to this value, but the sensitivity slope for the approximation we obtained is shown in the following graph:

When considering power loss in the fiber optic cable, the optimal fiber cable length is roughly 116.8 meters. If we are willing to sacrifice roughly 10% of the calculated sensitivity*, then we can drop the cable length to approximately 72 meters. 

 

*This was done by subtracting 10% of the maximum value of the derivative of the output power w.r.t frequency (using the actual attenuation coefficient from ThorLabs). Maximum was 8.776*10^-8 W/Hz , 90% of max = 7.893*10^-8, which falls around 72 meters.

 

**First elog, critiques are very much welcome!

Attachment 2: dp_df.png
dp_df.png
Attachment 3: dpdf_dl.png
dpdf_dl.png
Attachment 6: dpdf_dl_actual.png
dpdf_dl_actual.png
  2211   Wed Jul 11 16:30:40 2018 Vinny W.Summary2micronLasersAcoustic and Thermal Sensitivity

I found some relevant work done on the discussion of acoustic and thermal sensitivity within a optic fiber. For reference, it's important to have an idea of the geometrics of the fiber. The core, cladding, and coating are 11 +/- 1 um , 125 +/- 1 um, and 245 +/- 10um in diameter, respectively. Though the cladding is pure silica, the coating is Ge-doped. ( http://www.thorlabs.com/drawings/65f0b20de1051938-7503B425-91B4-7335-B52672A2FD1F6447/SM2000-SpecSheet.pdf ). Additionally, the fiber's sensitivity to some pressure depends on its characteristic elastic coefficients ( Young's Modulus, E, and Poisson's Ratio, \sigma) and Pockels coefficients, P_{12} and P_{44} [1]. The elastic coefficients for fused silica can be found online but are also referenced below. 

Acoustic Sensitivity:
To have an idea of the approximate sensitivity we could expect, we can consider some preform silica cylinder that is undergoing a uniform pressure. Many of the references I found measured that pressure from variations of the relative phase change between two interferometer arms- one static and the other undergoing a pressure difference relative to it. The optical phase retardation per unit of pressure (in dyne/cm^2) can be expressed as:

\frac{\Delta\phi}{\phi} = \frac{(1-2\sigma)}{E}[\frac{n^2}{2}(3P_{12}+2P_{44})-1]

This comes out to be approximately  -1.23*10^{-14}${dyn}/{cm^2}$ .

Obviously there's more to the picture than just that. We need to consider the differences in refractives indices and and elastic coefficients between the different materials present in our optic fiber, as well as account for the radial and axial displacements in the "cylinder" caused by some pressure. The approach in reference [2] consideres a two layer cylinder, and assumes that the center is of homogenous material much like the example above. We can place the optic fiber in a cylindrical coordinate system as shown below:

(Insert crudely made cylinder coordinate system here)

Following reference [2], we'll assume that the axial stress at the very ends of the fiber is zero. ( \sigma _{22} = 0 at z = \pm L, where 2L is the full length of the fiber). This is referred to as the radial model, a form of boundary condition. Since axial symmetry is also assumed, the stresses and strains will be functions of r and z. For a single material solid cylinder, the solutions for the differential equations for the axial/radial displacements are expressed as products the trigonometric and modified Bessel functions. When we consider a multilayered cylinder, the general solution will be the the series expansion of those products, and their coefficients are determined by the boundary conditions.

It was shown both experimentally and theoretically that a 2D model of the above scenario (i.e. a plane strain ) gives nearly identical results as the 3D model, and involves much less calculation power. The reference goes in-depth at how the following equation was is derived, but to keep this concise, the average induced fractional phase change can be expressed as:

\frac{\Delta \phi}{\phi}= e_z-\frac{1}{2}n^2[2e_r(p_{11}-p_{44})+e_z(p_{11}-2p_{44})]

where e_z,e_r are the axial and radial strain, respectively. When the strains are a function of position along the axis of the fiber, we would need to average of its length:

\frac{\Delta \phi}{\phi} = \frac{1}{2L}[\int_{-L}^{+L}e_zdz-\frac{n^2}{2}[2(p_{11}-p_{44})\int_{-L}^{+L}e_rdz+(p_{11}-2p_{44}\int_{-L}^{+L}e_zdz)]]

 

[Work in progress. -Vinny (7/19/18)]

  2213   Thu Jul 19 11:50:11 2018 Vinny W.DailyProgress2micronLasersThe case of the DET10D Photodiode, featuring TIA

Down in the machine shop we've been developing and modifying a transimpedance amplifier to be used in conjuction with the photodiode in the 2micron experiment, schematic and noise analysis(with PD shot noise as horizontal line!) are shown below. With a dual 9V battery supply, we ran the output through our signal analyzer but quickly noticed the signal's unstable nature- a consequence of the lack of phase margin between the open loop gain and feedback factor. To address this issue and improve the circuit's stability, we simply added a phase compensator(i.e. a capacitor) in parallel with the gain resistor. Its capacitance can be calculated through a straightforward relationship between,

1. the intercept frequency, f_i ,  of the open loop gain curve and the reciprocal of the feedback factor.

2. The pole corner frequency, f_F.

3.  The unity-gain bandwidth, f_{GBWP}.

The intercept frequency can be expressed as,

f_i = \frac{1}{2\pi R_FC_F}

Where R_f and C_f are the values of gain resistor and phase compensator capacitance respectivel. Additionally, it follow that the pole corner frequency is,

f_F = \frac{1}{2\pi R_F(C_F+C_i)}

Where C_i is the capacitance of the PD's junction capacitor in parallel with the input capacitance of the op-amp. They are brought together by the following expression:

f_i = \sqrt{f_f*f_{GBWP}}

Solving for the phase compensator capacitance, we reach,

C_F = \frac{1}{4\pi R_Ff_{GBWP}}(1+\sqrt{1+8\pi C_if_{GBWP}})

Inputting the values of our circuit's components, we reach a capaticance of 200pF. Fortunately, the TIA proved to be more stable after this modification. Finally, we implemented our TIA circuit into our PD in the 2micron experiment and achieved better readings, which I'll be sure to elaborate more upon tomorrow.

Attachment 1: TIAcircuit.JPG
TIAcircuit.JPG
Attachment 2: TIAnoiseanalysis.JPG
TIAnoiseanalysis.JPG
  2214   Sat Jul 21 01:45:00 2018 Vinny W.DailyProgress2micronLasersThe Gentle Sway of the EP2004

We ran some more measurements of our laser's output and noticed a certain ampltiude swaying of our signal (a video of this will be commented below tomorrow) caused most likely by power fluctuations(any advice to fix this would be super appreciated!). Combined with the fringes that cycle along with the swaying, it made the task of locking the signal to mid-fringe for analysis very difficult. We checked the integrity of the optic fibers in the experiment and didn't notice much issue besides a few mottled tips which were cleaned. We noticed the experiment was most sensitive at the actual MZ interferometer segment, so we made a few changes to increase the radius of curvature of the optic fiber loops. (Picture below). This made a slight difference, but the sway is still there.

This all proved to be a good opportunity to start setting up the encasement for the project. We rounded up a structure that was in the lab, along with some insulated wall-plates. It hasn't been fully built yet, but the casing fortunately fits around the work-space of the experiment. (casing dimensions: 117.5x25.5x60.5 cm. LxHxW)

I did a little bit of characterization for the laser diode's power output as a function of applied current. A plot of that is also shown below. Tomorrow Andrew and I are going to work on settling the question of the noise budget, as well as start building some thermal sensors (AD590) to be used within, outside, and around the encasing of experiment. Using this will allow us to get a sense of the environment temperature differences and adjust our experiment accordingly. Finally, we're on a way to developing a circuit for our thermocoolers to be used within the casing that Aidan built.

 

 

Attachment 1: p_aafo_i.png
p_aafo_i.png
Attachment 2: 20180720_181301.jpg
20180720_181301.jpg
Attachment 3: 20180720_174216.jpg
20180720_174216.jpg
  2221   Thu Jul 26 17:49:28 2018 Vinny W.DailyProgress2micronLasersPower Loss through different optic components

In our mission to characterize our 2micron laser, I calculated the changes of power at different points within the experiment- the points are shown in the schematic below. I kept the input current constant at 50.02 mA, and the temperature of the laser diode at 8.657k\Omega.

Power from different points
Location (from laser to...)  Power (mW) (error, +/- 0.002 mW) Frequency (Hz) (error, +/- 3Hz)
Directly from laser 1.339 796.68
Faraday Isolator 0.894 61.09
Beam Coupler #1, A 0.528 60.09
Beam Coupler #1, B 0.707 61.20
Beam Coupler #2, A 0.762 60.55
Beam Coupler #2, B 0.480 61.40
Longer arm of interferometer 1.291 62.30

 

The excess power loss, L, at either beam splitter can be expressed in dB as:

L = 10\log{\frac{P_{laser}}{P_{A}+P_{B}}}

Running this through gives us an excess loss of 0.351dB at Beam Splitter #1 and 0.327dB at Beam Splitter #2. 

 

We're finishing up the thermal sensor to be placed in the ATF! Schematics and pictures will be provided later on today.

Attachment 1: poweranalysis.JPG
poweranalysis.JPG
  2228   Mon Aug 6 03:45:37 2018 Vinny W.DailyProgress2micronLasersThermal Sensor Circuit Update

Below are the schematics of the two added sections to the passive temperature sensor circuit we're building. Since we're trying to measure temperature differences/fluctuations throughout the ATF, we'll need to incorporate a voltage reference in our circuit- which is necessary in this analog-to-digital purpose. The addition of a Sallen Key filter in conjunction with the voltage reference is to overcome precision limitations of the component. The large values of the two resistors were chosen to counteract the decline in performace due to the component's output resistance at high frequencies. To characterize the temperature sensor, we ran the circuit through the EE shop's spectrum analyzer at points before the SK and after. I'm not too versed in extracting data from it(I was given a crash course earlier this morning, so I'll try again tomorrow). For now it's good to note that observing a 50Hz bandwidth, the Vrms noise before the SK, measured at the output of the LT1021 7V reference was 17.24nVrms/rtHz at 10Hz, and after the SK turned out to be 16.7nVrms/rtHz at 10Hz (pictured below. Apologies in advance for the picture of data, it's just to have a visual of the noise bandwidth characteristics. I'll have actual plots once I get working with the whole spectrum analyzer data-over-wifi scheme). Additionally, I'd like to update this e-log tomorrow with the transfer functions at both of those stages!

Conceptually, the device has been completed(pictured below, and a special thanks to Andrew for helping me out with molex connections!). At this point further modifications would be to switch out the film resistors for surface mounts to see if there is any improvement. 

Attachment 1: scheme_voltageref.JPG
scheme_voltageref.JPG
Attachment 2: scheme_thermalsensor.JPG
scheme_thermalsensor.JPG
Attachment 3: 20180806_162441.jpg
20180806_162441.jpg
Attachment 4: 20180806_135423.jpg
20180806_135423.jpg
  Draft   Tue Aug 14 13:44:47 2018 Vinny W.DailyProgress2micronLasersNoise Analyses

With the two 15m optic fibers in, we can start building the thermally-actuated reference interferometer portion of the 2um experiment. To have a re

On the thermal sensor: With it powered up, this signal is from one of the output BNCs. 

On the TIA: With it powered up, this signal is from the BNC output (note: the input end was open)

On the TMTF: With the photodetector and TIA powered on, this signal is 

  2723   Tue Feb 22 07:53:06 2022 YehonathanUpdateWOPOWaking up WOPO

{Shruti, Yehonathan}

On Friday, we came down to QIL to poke around the WOPO setup. The first thing we noticed is that the setup on the wiki page is obsolete and in reality, the 532nm light is coming directly from the Diablo module.

There were no laser goggles for 532nm so we turned on the 1064nm (Mephisto) only. The pump diode current was ramped to 1A. We put a power meter in front of Mephisto and opened the shutter. Rotating the HWP we got 39mW. We dialed it back so that 5mW is coming out of the polarizer.

The beam block was removed. We disconnected the LO fiber end from the fiber BS - there is light coming out! we connected a power meter to the fiber end using an FC/PC Fiber Adapter Plate. The power read 0.7mW. By aligning the beam into the LO fiber we got up to 3.3mW.

We connected the BHD PDs to the scope on the table to observe the subtraction signal. Channel 2 was negative so we looked at the sum channel.

Time ran out. We ramped down the diode current and turned off Mephisto.

Next time we should figure out the dark current of the BHD and work toward observing the shot noise of the LO.

  2727   Wed Mar 2 14:38:55 2022 YehonathanUpdateWOPOWaking up WOPO - some more fiddling and a plan

{Shruti, Yehonathan}

We made some a list of some random questions and plans for the future. We then went down and found answers to some of those:

1. Why is there no Faraday isolator in the 1064nm beam path? (edit: turns out there is, but inside the laser, see pictures in this elog).

2. Do the fibers joined by butt-coupling have similar mode field diameter? If not it can explain many loss issues.

a. In the green path we find that according to the SPDC datasheet the 532nm fiber (coastalcon PM480) is 4um while the input thorlabs fiber (P3-488PM-FC2) coupled to it has an MFD of 3.3um. This mismatch gives maximum coupling efficiency of 96%. Ok not a big issue.

b. At the 1064nm output the SPDC fiber is PM980 with MFD of 6.6um while the BS fiber is 6.2um which is good.

3. What is the green fiber laser damage threshold? According to Thorlabs it is theoretically 1MW/cm^2 practically 250kW/cm^2 for glass air interface. With 3.3um MFD the theoretical damage threshold is ~ 80mW and practically  ~ 20mW. It doesn't sounds like a lot. More so given that we could only get 50% coupling efficiency. How much is needed for observable squeezing? There is the possibility to splice the fiber to an end cap to increase power handling capabilities if needed.

4. Is stimulated Brillouin back scattering relevant in our experiment? According to this rp photonics article not really.

5. How much green light is left after the dichroic mirrors? Is it below the shot noise level? Should check later.

In addition, we found that the green fiber input and the 1064nm fiber output from the SPDC were very dirty! We cleaned them with a Thorlabs universal fiber connector cleaner.

 

 

 

 

  2733   Wed Mar 16 12:22:44 2022 YehonathanUpdateWOPOWaking up WOPO - attempts at readout

{Shruti, Yehonathan}

Yesterday, we measured a bunch of noises.

We wanted to have as reference the Moku noise, the PDs noise, and measure the shot noise of the LO again.

Attachment 1 shows the Moku noise measured by just taking data with no signal coming in. We tried both the spectrum analyzer (SA) and the oscilloscope tools, with and without averaging, and the difference between the channels.

For some reason, the SA has a worse noise figure than the oscilloscope and the difference channel doesn't give us any special common-mode rejection. Also more averaging doesn't help much because we are already taking 1.2ms of data which is way longer than 1/RBW=0.2ms we are taking here.

From now on we use the oscilloscope as the spectrum analyzer and to its noise we refer as the Moku noise floor.

Moving on, we try to measure the PD dark noise. Given that the PD dark noise floor is ~ 6nV we don't expect to see it with the Moku without amplification. Attachment 2 shows that indeed we couldn't resolve the PD dark noise.

We then opened the LO shutter. We measured with a power meter 1mW and 1.15mW coming impinging on the PDs. The voltage readings after the preamp were 1.66V for the white fiber, and 1.93 V for the red fiber. These values suggest responsivities of 0.830 and 0.834 respectively.

The PDs were measured using the Moku scope and subtracted digitally with some small gain adjustment (0.93*ch1-1.07*ch2) between the channels. The result is shown in attachment 3 together with the expected shot noise level.

1. There is not enough clearance for detecting squeezing.

2. Expected shot noise level is still too high. Does the 2kohm preamp gain go all the way above 1MHz??

Attachment 1: Moku_Noise.pdf
Moku_Noise.pdf
Attachment 2: PD_Connected_no_light.pdf
PD_Connected_no_light.pdf
Attachment 3: Diff_Channel.pdf
Diff_Channel.pdf
  2758   Wed Apr 20 00:00:39 2022 YehonathanLab InfrastructureGeneralPreparing for planned power outage

{Yehonathan, Shruti}

We shut down the workstations and the FBs by doing sudo shutdown and unplugged them from the wall.

Electronic equipment on the FB rack was shut down and unplugged from the wall.

Diablo's current was ramped down and the control unit was shutdown. Optical table electronic equipment was shutdown and the table's powerstrip was switched off.

Equipment under the optical table was switched off and unplugged.

  2759   Wed Apr 20 00:12:12 2022 YehonathanUpdateWOPOStill figuring out the readout electronics and fixing of some stuff

{Yehonathan, Shruti}

1. Grabbed 30Hz-3GHz HP spectrum analyzer from the Cryolab. Installed it in the WOPO lab under the optical table. We figured out how to do a zero-span measurement around 10MHz. The SA has only one input so we try to combine the signals with an RF splitter. We test this capability by sourcing the RF splitter with 10MHz 4Vpp sine waves from a function generator and measuring the output with a scope. We measure with the scope 1.44Vpp for each channel. The combined channel was 2.73Vpp. We then realized that we still don't have a way to adjust the gains electronically, so we moved on to trying the RF amplifiers (ZFL500 LN).

We assemble two amps on the two sides of a metal heatsink. We solder their DC inputs such that they are powered with the same wire (Attachment 1). We attach the heatsink to the optical table with an L bracket (Attachment 2).

We powered the amps using a 15V DC power supply and tested them by feeding them with 10MHz 10mVpp sine waves from a function generator. We observe on a scope an amplification by a factor of ~ 22. Which makes a power amplification of ~ 26db consistent with the amplifiers' datasheet.

We couldn't find highpass filters with a cutoff around 1MHz, so we resumed using the DC blocks, we test them by feeding white noise into them with a function generator and observing the resulting spectrum. First, we try the DC blocks with a 50 Ohm resistor in parallel. That happened to just cut the power by half. We ditch the resistor and get almost unity transmission above 20kHz.

Moving on to observing LO shot noise, we open the laser shutter. We find there is only 0.7mW coming out of each port of the fiber BHD BS. We measure the power going into the BS to be 4mW. This means the coupling between the LO fiber and the BS fiber is bad. We inspect the fibers and find a big piece of junk on the BS fiber core. We also find a small particle on the LO fiber side. We cleaned both fibers and after butt coupling them we measure 1.6mW at each port. We raise this power to 2mW per port.

We connect the outputs of the PDs to the amps through the DC blocks. The outputs of the amps were connected to the Moku's inputs. The PDs were responding very badly and their noise was also bad. We bypass the amps to debug what is going on. We connect the PDs to a scope. We see they have 300mV (attachment 3) dark noise which is super bad and that they hardly respond to the light impinging on them (attachment 4). We shall investigate tomorrow.

Attachment 1: 20220419_153109.jpg
20220419_153109.jpg
Attachment 2: 20220419_164600.jpg
20220419_164600.jpg
Attachment 3: 20220419_184248.jpg
20220419_184248.jpg
Attachment 4: 20220419_184233.jpg
20220419_184233.jpg
ELOG V3.1.3-