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  734   Fri Apr 23 17:20:34 2010 ZachElectronicsGYRORFPD circuit

 I finished stuffing our first RFPD board with everything we want (for now) this afternoon. This one will be used for one of the transmission PDs, so I tuned it to 95 MHz. The transfer function looked a little funny (it was oscillating at ~130 MHz), but Rich thinks this will go away once the diode is installed.

On Monday, I'll install the diode, do some more stuff with the test input, and then we can try some optical demod funny business.

  1216   Wed Dec 15 15:41:45 2010 Alastair & ZachElectronicsGeneralRFPD design

Here is our layout for the RFPD in Altium. We are working on routing the board now.

Attachment 1: RFPD_1.pdf
RFPD_1.pdf
  1219   Wed Dec 15 22:29:27 2010 FrankElectronicsGeneralRFPD design

you don't wanna have 4 power supplies to power the detector, way too complicated. I would change it to power the entire thing by +/-24V and regulate that to +/-15V. Then use the already regulated +/-15V to regulate it down to something else in addition.

 

 Here is our layout for the RFPD in Altium.  We are working on routing the board now.

 

  1220   Wed Dec 15 22:36:05 2010 AlastairElectronicsGeneralRFPD design

You mean we don't want two +/- connectors run from two separate supplies?  I only put them on there because we are planning on running it from the NIM crate.  You're right though that we should make it just one +/- supply because it is meant to be a general design.  I'll alter it so the 5v regulators are powered from the 15v ones.  Thanks.

I do have a question for someone about how we make up the board.  At the moment we're modifying the aLIGO design, and it has all the power planes inside the board.  My question is this - do we want to add in two extra planes to take the +/-15v to the other opamps?  The number of layers is starting to look like a lot.

Quote:

you don't wanna have 4 power supplies to power the detector, way too complicated. I would change it to power the entire thing by +/-24V and regulate that to +/-15V. Then use the already regulated +/-15V to regulate it down to something else in addition.

 

 Here is our layout for the RFPD in Altium.  We are working on routing the board now.

 

 

  1221   Thu Dec 16 03:50:33 2010 ranaElectronicsGeneralRFPD design: comments
  1. Add pads around all the voltage regulators for diodes to prevent transient spikes (e.g. preventing the 7815 output from spiking higher than its input).
  2. Add pads to allow more capacitors around the voltage regulators; the large caps ought to be bypasses by little ceramic caps.
  3. May want to add an L between the +15V and the power supply pin on the RF amp. This is sometimes done for RF amps to keep the RF out of the supply for the other guys who need +15V.
  4. The 4107 can develop DC offsets. Should AC couple the output going in to the RF amp.
  5. Add a series L-C in parallel with the R8. Sometimes we like to put a notch in the feedback of the 4107 to get extra notch action.
  6. Put a note on the schematic (almost obvious) that all resistors must be metal film. If any resistors require more than a 1/8W power rating, it should be indicated on the schematic.
  7. Since the 4107 is nearly obsolete, you ought to also scope out another amp and list it in the schematic notes as a good replacement choice.
  8. Put a note on there about what the hell a AP1053 is.

Otherwise, looks pretty good to me. Make sure to calculate the input-referred noise of the AD620 with the gain setting that's there to make sure you're happy with the circuit's RIN sensitivity.

  1224   Thu Dec 16 15:27:12 2010 AlastairElectronicsGeneralRFPD design: comments

The 4107 replacement that Rich suggests using is the LMH6624MA.  It's pin for pin compatible with the 4107, which is why I hadn't changed the part on the board - I'll do that now though just to avoid confusion.

The AP1053 is a teledyne-cougar RF amp.  Highlights are:

  • Gain doesn't roll off till above 1GHz
  • 50 ohm input and output
  • Power output of 26dBm.  
  • This is the 10dB gain model, but it is pin for pin compatible with a whole load of others in the range so we can swap in whatever gain we want.
  • Rich tells us the input will be internally AC coupled, so we don't need to do this on the board.  Looking at the website and the datasheet this isn't explicitly mentioned though.

 

Quote:
  1. Add pads around all the voltage regulators for diodes to prevent transient spikes (e.g. preventing the 7815 output from spiking higher than its input).
  2. Add pads to allow more capacitors around the voltage regulators; the large caps ought to be bypasses by little ceramic caps.
  3. May want to add an L between the +15V and the power supply pin on the RF amp. This is sometimes done for RF amps to keep the RF out of the supply for the other guys who need +15V.
  4. The 4107 can develop DC offsets. Should AC couple the output going in to the RF amp.
  5. Add a series L-C in parallel with the R8. Sometimes we like to put a notch in the feedback of the 4107 to get extra notch action.
  6. Put a note on the schematic (almost obvious) that all resistors must be metal film. If any resistors require more than a 1/8W power rating, it should be indicated on the schematic.
  7. Since the 4107 is nearly obsolete, you ought to also scope out another amp and list it in the schematic notes as a good replacement choice.
  8. Put a note on there about what the hell a AP1053 is.

Otherwise, looks pretty good to me. Make sure to calculate the input-referred noise of the AD620 with the gain setting that's there to make sure you're happy with the circuit's RIN sensitivity.

 

  1228   Fri Dec 17 22:07:00 2010 AlastairElectronicsGeneralRFPD design: comments

Do we need to add extra caps to both the input and output sides of the regulators, or just the output side?

RA: Both. There are multiple schools of thought on what gives the best performance, so its best to have both possibilities. The large electrolytic caps give good filtering of the low frequency stuff but also have a big inrush current when the supply is first activated. Even so, it would be good to have a pad available so that we can have a large-ish cap on the input and output with a 35V or higher rating. Its not necessary that it be surface mount - could also use tantalum. There's no need to make it larger than 100 uF.

  2786   Tue Jun 21 10:35:15 2022 Clare NelleDailyProgressEmissivity estimationRTD Calibration

RTD Calibration Plan Developed on 16-06-2022:

  1. Prepare an ice bath and liquid nitrogen bath to calibrate the RTD.

    1. Ice bath: fill cup (?) with ice. Fill with water until 2 inches below the top of the ice. Let sit for 2 minutes before calibration. 

  2. We will use a DMM to measure the resistance across the leads. Right now, we are thinking that we will connect the leads to the resistor using alligator clips or solder them together.

  3. Use linear fit to calibrate the RTD value as a function of resistance using these two reference values. 

  4. Repeat for all three RTDs

-----------------------------------

  1. Q: What is the tolerance of the resistor?

    1. 100 ohm +/- .06%. Means that our calculation if done correctly will be between 99.4 → 100.6 ohms in the ice bath. Our RTD is class A, which has tolerance +/- .15 degrees. Pt-100 SHOULD be 100 ohms at 0C – the temp changes linearly.

  2791   Wed Jun 29 09:39:01 2022 Clare NelleDailyProgressEmissivity testingRTD Calibration Day 2

[Radhika, Hiya, and Clare]

We debonded the RTDs from the chamber using isopropanol and acetone, then soaked the RTDs in isopropanol for about 15 minutes to remove residue. We then took resistance measurements in ice water detailed below:

Ice Water Calibration Measurements (completed 28-06-2022):

1) Prepared ice water bath by filling beaker with crushed ice and then water to one half inch below the ice surface. Let the ice bath sit for about 1 minute. 

2) All six RTDs were measured (labeled A-F). For each RTD, the resistance in the ice water bath was measured by swirling the RTD held by the DMM leads in the water until the DMM readout stabilized. 

3) These measurements were repeated in the reverse direction (Started with RTD F).

*Note: in the process of ice bath calibration, RTD D broke. 

RTD Trial 1 (\Omega) Trial 2 (\Omega)
A 100.2 100.15
B 100.15 100.3
C 100.1 100.1
D X X
E 100.1 100.1
F 100.1 100.1

Liquid Nitrogen Calibration Measurements (completed 30-06-2022):

Procedure: We clipped the DMM leads to the RTDs and taped the two clips together. This is very secure - good method for the future. We dipped the taped clips with the RTD into the LN2, and swirled under the liquid surface until the DMM readout stabilized. We only took one set of measurements because we are very confident of the boiling point of N2. 

*Note: RTD A broke. This is because we spread the RTD wires out to put into the aligator clips, making them very prone to snapping when we move them. This means that we do not have an RTD on the cold head.

Results (ohms):

A: X

B: 19.8

C:18.2

E:18.5

F:19.8

Attachment 1: ice_bath_calibration.xlsx
  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.

 

  797   Thu Jun 3 03:24:41 2010 DmassLab InfrastructureFuglyRack terrible-ness

The rack has been moved away from the wall, and the 300V power supply to the PZT is half perched on/in the blue ADC box, whose top is partially hanging into the box itself. This was very much not the state it was last seen in.

Attachment 1: 00001.jpg
00001.jpg
  31   Sat Feb 16 15:33:25 2008 DmassLaserPSLRadial Beam Profile
The following were taken with the beam scanner (having gone through a number of optical elements).

After leaving the main laser housing, the beam hits:
polarizer -> PBS -> low reflectivity pickoff mirror -> 1m lens -> 0.5m lens -> 45-P HR mirror -> 45 P HR mirror -> beamscan.

In taking my initial waist measurements, I had the beamscan after the LR pickoff, and the beam looked similar.
Attachment 1: 2_16_0835w.bmp
  2276   Fri Dec 7 16:08:45 2018 RahulDailyProgressCryo vacuum chamberRadiation shields

The cold plate and radiations shields (100K, 50K and bottom 100K shields) are at 40m for cleaning and baking. The outer shields will be cleaned and then sent for gold plating. The inner shield and cold plate be baked after cleaning. 

Attachment 1: shields_1.jpg
shields_1.jpg
Attachment 2: shield_2.jpg
shield_2.jpg
Attachment 3: shields_bottom.jpg
shields_bottom.jpg
  2429   Thu Oct 10 17:28:33 2019 Raymond, ChrisDailyProgressCryo vacuum chamberRadiation shields unpacked

Today we unpacked the radiation shields and started to puzzle out how to assemble them. Attached are photos of the parts as we guessed they are intended to stack up. We didn't see how the outer shield would be supported and isolated from the cold plate, so we are contacting Rahul to clarify.

One detail not shown in these photos is the rather poor weld quality on the interior of the outer shield.

 

Attachment 1: IMG_20191010_150645.jpg
IMG_20191010_150645.jpg
Attachment 2: IMG_20191010_150700.jpg
IMG_20191010_150700.jpg
Attachment 3: IMG_20191010_150711.jpg
IMG_20191010_150711.jpg
Attachment 4: IMG_20191010_150757.jpg
IMG_20191010_150757.jpg
Attachment 5: IMG_20191010_150817.jpg
IMG_20191010_150817.jpg
Attachment 6: IMG_20191010_150826.jpg
IMG_20191010_150826.jpg
  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
  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.

  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
  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.
  2705   Wed Dec 31 15:59:59 1969 StephenDailyProgressCryo vacuum chamberRadiative Cooling of Si Mass, with worse inner shield inner surface emissivity - retry run was successful

This post will host plots and trends from this radiative cooling run (QIL/2704).

Preliminarily, it looks like the reconfiguration to remove a hardware mistake or two led to a healthier run. The comparison below clarifies the two runs:

  • QIL/2702 - conductive link between inner shield and outer shield (twisted pair from an RTD lead accidentally clamped); possibly another conductive link between outer shield and baseplate (outer shield more wobbly than usual on spacers)
    • this data set should only be used to study the impact of a known conductive link between inner and outer shields.
    • this run demonstrates that there will be more effective, faster cooling if the outer shield is conductively cooled!
  • QIL/2704 - resolved above mistakes!
    • this data set may be used to gain understanding of the impact of emissivity changes to the inner surface of the inner shield.
    • may be compared to QIL/2695, a run that is equivalent except with a higher emissivity inner surface of the inner shield

Run ended with cryocooler shutdown at 12:27 pm (actual duration just under 92 hours). System will warm up with pumps on for the rest of the break, unless I am inspired to come in and run one of the next intended runs discussed in QIL/2704. I did not run any heat input test for this data set, as I am not planning to come in frequently enough to monitor the heating safely.

Data:

Attachment 1 compares QIL/2704 (solid) to QIL/2702 (dashed). As expected, the outer shield temperature from the latter run stays warm since the conductive short was resolved. Due to the reduction of the inner shield's thermal load, the inner shield is able to cool faster and plateau at a colder temperature. As Stephen pointed out, however, the test mass is not cooled as efficiently compared to when the outer shield was conductively cooled.

Fitting Results:

Attachment 2 is a current model diagram of the various components being considered, and their thermal couplings. Attachment 3 plots the fitted model (dashed) over the temperature data (solid). The fit parameters were the following emissivities: aluminum foil, rough aluminum, and aquadag. Notes from the fit:

1. With the conductive shorting of the outer shield resolved, the model (which considers only radiative cooling of the OS) is well fit to the OS temperature data

2. The inner shield model is missing some key term(s) affecting its time constant and steady state temperature.

3. The above error propagates to the test mass model (I believe). 

Given these caveats, the fit results are as follows: aquadag e = 0.92, Al foil e = 0.04, rough Al e = 0.19. These all initially seem reasonable, and I'm happy to see that the aquadag emissivity is higher than previously estimated.

Next steps:

1. Separate the cold plate from the inner shield, and model their conductive and radiative link. Also model the radiative link between the cold plate and the test mass.

2. Cover the test mass in foil (to best of our ability) to refine the radiative link between the test mass and inner shield. Doing so will mean both elements have the same emissivity, so there is only one unknown parameter.

Attachment 1: cooldown_12-21_vs_12-10.pdf
cooldown_12-21_vs_12-10.pdf
Attachment 2: Megastat_Heat_Load_Sketch.png
Megastat_Heat_Load_Sketch.png
Attachment 3: 12_21_cooldown_fit.png
12_21_cooldown_fit.png
  2078   Fri Dec 16 12:41:50 2016 awadeLab InfrastructureGeneralRain, lab checkup

It has rained (something on the order of 50 mm) in the last two days.  I checked the ATF lab, no water inside.

  2060   Mon Aug 8 17:05:28 2016 ranaMiscGeneralRaspberry Pi beam profiles: possible student project

http://hackaday.com/2015/12/21/raspberry-pi-laser-beam-profiler/

UCLA project. Should we try to make one of these?

  2063   Tue Aug 16 16:01:21 2016 awadeMiscGeneralRaspberry Pi beam profiles: possible student project

Looks kind of cool. Could probably skip the LCD interface and have it screen forward to any laptop or maybe python imbedded in a self hosted html webpage or iPad app?

Many CCDs seem to have some pretty low saturation points which makes them a pain for profiling some beamsI remember an undergrad experiment I did with a setup where we had a razor blade on a stepper motor. If accuracy of step precision was good enough (and repeatable enough) with a reasonable PD could make a beam profiler with a much bigger dynamic range on power. The only problem was that there was some strange relaxation in razor blade position.

It would be cool if we could fit it on something like a linear stage or an old scanner bed stepper to get a full automatic profile of a beam. 

 

 

Quote:

http://hackaday.com/2015/12/21/raspberry-pi-laser-beam-profiler/

UCLA project. Should we try to make one of these?

 

  177   Thu Jul 16 04:59:38 2009 DmassLaserPSLRazor Blades!

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

Attachment 1: Photo_1.jpg
Photo_1.jpg
Attachment 2: Photo_3.jpg
Photo_3.jpg
  178   Thu Jul 16 15:01:48 2009 Koji & Connor LaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

  179   Thu Jul 16 17:43:59 2009 DmassLaserPSLRazor Blades!

Quote:

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 

Actually, it would be nicer if we have a calibrated micrometer screw for the thread.
Connor and I tried to make another set of the razor blade arrangement with a micrometer.
We put it on the PSL optical table. Please use it.

 

I got about a .002" error using a micrometer with my other setup, I expect this will suffice. If the errors in position end up too large I will use the new setup.

  182   Fri Jul 17 15:39:31 2009 DmassLaserPSLRazor Blades!

Quote:

Since the beamscan is in a questionable state of scanny goodness, Koji advised that I do some razor blade occlusion power measurements of the beam and then fit an erf to it to find the waist. I took data with the tinker toys pictured below.

I will compare these results with some beamscans results to verify (hopefully) that the beamscan is outputting useful results, not lies.

 Using the setups in the quoted post, I took manual beamscans 23" in front of the PSL enclosure, before the first steering mirror, and fit P = A erf(B*x + C)

 I measured the relative position of my razorblade with a micrometer and calculated the error from an estimated uncertainty of it's angle. This seemed to agree with repeatability of measurements for a given experimental state. Uncertainty < .002"

I watched the Power meter for ~ 60 seconds for each measurement, it fluctuated around some point and seemed to not be drifting @ DC, so the upper and lower error bars of each point included are the bounds of the fluctuation of the power meter. These were less than +/- 5mW about my points, so a fractional uncertainty of about 2% at my maximum power.

 

I got waists of:

Vertical: 799 +/- 4.5 microns

Horizontol 827 +/- 1.2 microns

Attached plot includes data w/ error and functional form of fit

 

As expected, my Chi^2 is "bad" since I am fitting the input beam to the PMC with a 00 mode description of the waist, which ignores all higher order modal content.

Attachment 1: RazorScans.pdf
RazorScans.pdf
  184   Mon Jul 20 23:19:49 2009 ranaLaserPSLRazor Blades!
Yeah, real micrometer with a reading is > plain screw.
  188   Tue Jul 21 20:41:56 2009 DmassLaserPSLRazor Blades!

Quote:
Yeah, real micrometer with a reading is > plain screw.


Converting from flemish ells was hard. I'll just use a mic next time.
  1286   Fri Feb 4 16:58:39 2011 AlastairLaserGYRORb Clock data

 Here is the data from our Rb clock frequency noise measurement that was on the 40m elog here.

Attachment 1: RbMeasurements.txt.zip
  1780   Sat Nov 3 13:20:27 2012 AidanComputingComputingRe-compiled Real Time Model with TCS channels

 I saved the existing ATF model as atf.mdl.ctrl and built a modified version for some temporary TCS real-time work for aLIGO. The new ATF model is saved as atf.mdl.tcs (and currently as atf.mdl).

The new model compiled and was installed. It still runs all the GYRO stuff (which was all unaltered) but I replaced the defunct CTRL block from the doubling experiment with a new TCS block.

- should the old model need to be replaced, this can be done by copying aft.mdl.ctrl to atf.mdl and compiling with fb0:/cvs/cds/advLigo$ make atf install-atf

 

Attachment 1: Screen_Shot_2012-11-02_at_11.51.42_AM.png
Screen_Shot_2012-11-02_at_11.51.42_AM.png
  2019   Tue Feb 16 23:51:31 2016 KojiNMiscPD QERe-measurement of the PD efficiencies for P-pol. and S-pol.

We aligned the single mode fiber again and We obtained the linear polarization without QWP as shown in Fig. 1.

P-pol. and S-pol. are able to be obtined at 34.8 deg and 81.0 deg in angle of HWP #3, respectively.

Then, We checked the PD read-out circuit and the circuit diagram is shown in Fig. 2.

Important resistanve values are as follows:

R4 = 20.2 Ohm, R5 = open, R11 = 1.000 kOhm, R16 = 9.82 kOhm, R7 = 50.2 Ohm.

In this circuit, the current generated by PD (I_PD) can be calibrated from the DC output voltage (V_out) using the following equation:

I_{\rm PD} = \frac{R_{11}}{R_4(R_{11}+R_{16})}V_{\rm out} = 4.57\times10^{-3} \left( \frac{V_{\rm out}}{1 {\rm V}}\right)

(In other words, the trans-impedance of the readout circuit is 219 Ohm.)

After that, we measured the DC output voltage at every 10 deg in the incident angle with the window glass as shown in Fig. 3.

The PD position is 5 cm after the beam waist and, at this position, the beam sizes in x-direction and y-direction are 215 um and 210 um, respectively.

The incident angle is determined with +/- 0.5 deg error by following way:

step1 (in this step, PD is alomost perpendicular to the beam) seeing reflected light from the PD, we centerd the beam to the PD using the steering mirror. 

step2 We miscenterd the beam to the border of the PD, and checked the incident angle seeing the reflected light. The incident angle was 0.5 deg (-0.5 deg in the opposite side.) Then the beam was re-centerd to the PD by the steering mirror.

step3 The PD is tilted by the rotational stage (the angle of the stage is called "alpha"), and, if the beam is miscenterd, we centerd the beam to the PD using steering mirror (the angle caused by the steering mirror is called "beta"). Thus the incident angle is "alpha + beta"

step4 Without touching the steering mirror, the PD is rotated to be perpendicular to the beam (i.e. "alpha" became 0 deg).

step5 We checked whether the beam is still on the PD or not (in today's measurement, the beam is on the PD in this step). If the beam is on the PD, the incident angle at step3 is estimated as follows,

alpha - 0.5 < alpha + beta (incident angle) < alpha + 0.5 (degree)

Therefore, the incident angle is determined with +/- 0.5 deg error.

We are going to measure again the reflectivity tomorrow with this method.

Fig. 1 Current setup.
Fig. 2 Readout circuit diagram.
Fig. 3 Measured DC output and EQE.

D980454-00(QE).pdf

Attachment 3: D980454-00(QE).pdf
D980454-00(QE).pdf D980454-00(QE).pdf
Attachment 4: D980454-00(QE)_2.pdf
D980454-00(QE)_2.pdf
Attachment 5: D980454-00(QE).pdf
D980454-00(QE).pdf D980454-00(QE).pdf
  2031   Tue Feb 23 00:22:01 2016 KojiNMiscPD QERe-measurement of the QE of the PD without window glass

The QEs were measured again at every 10 deg incident angle.

The power meter to measure the incident angle was S401C (Thorlabs).

Output voltage was read by the degital multimeter 77 IV (Fluke).

The results are shown in Figs. 1--3.

(About the reflectivities, the data measured in elog2024 are used for now. Those data are obtained with S130C (Thorlabs. error is +/- 7%.))

In Fig. 3, the ratio of the enhanced QE and the not-enhanced QE is shown.

In these figures, the error of the S401C (3%), 77 IV (about 0.4% (depends on the measure value)), and resistances of the readout circuit (assumed to be 1%) are taken into consideration and they are assumed to be independent.

These results are consistent to the data we have measured by last week in the error.

Current errors of the EQEs in Figs. 1 and 2 about +/- 4% and they are mainly determined by the systematic error of the power meter.

Figure 3 claims that the QEs are improved with +/- 0.6% error using our new method.

Fig. 1 Measured QEs.
Fig. 2 Zoomed version of Fig. 1.
Fig. 3 Improvement ratio of the QE.

 

Attachment 1: QE.pdf
QE.pdf
Attachment 2: QE2.pdf
QE2.pdf
Attachment 3: QE3.pdf
QE3.pdf
Attachment 4: QE_enh.txt
angle inc(mW,P) error DC(V,P) error enh(V,P) error inc(mW,S) error DC(V,S) error enh(V,S) error
-10 11.45 0.3 1.914 0.007 2.000 0.007 11.48 0.3 1.915 0.007 2.003 0.007
-15 11.50 0.3 1.936 0.007 2.013 0.007 11.53 0.3 1.922 0.007 2.007 0.007
-20 11.56 0.3 1.950 0.007 2.010 0.007 11.62 0.3 1.939 0.007 2.012 0.007
-30 11.53 0.3 1.984 0.007 2.026 0.007 11.65 0.3 1.954 0.007 2.023 0.007
-40 11.55 0.3 2.001 0.007 2.029 0.007 11.58 0.3 1.968 0.007 2.029 0.007
-50 11.66 0.3 1.996 0.007 2.031 0.007 11.60 0.3 1.953 0.007 2.028 0.007
-60 11.67 0.4 1.938 0.007 2.030 0.007 11.68 0.4 1.888 0.007 2.026 0.007
-70 11.69 0.4 1.768 0.006 2.003 0.007 11.68 0.4 1.680 0.006 1.974 0.007
Attachment 5: Ref_QE_wow.txt
angle Ref(mW,P) error DC(V,P) error Ref(mW,S) error DC(V,S) error
-10 0.480 0.001 2.02 0.02 0.504 0.001 2.02 0.02
-15 0.434 0.001 2.02 0.02 0.487 0.001 2.02 0.02
-20 0.367 0.001 2.04 0.02 0.454 0.001 2.04 0.02
-30 0.217 0.001 2.06 0.02 0.363 0.001 2.06 0.02
-40 0.136 0.001 2.06 0.02 0.313 0.002 2.04 0.02
-50 0.197 0.002 2.06 0.02 0.408 0.002 2.02 0.02
-60 0.532 0.002 1.98 0.02 .806 0.005 1.94 0.02
-70 1.54 0.01 1.80 0.02 2.04 0.02 1.72 0.02
Attachment 6: QE_enh_cal_NK.m
% 
filename='QE_enh.txt';
delimiterIn = ' ';
headerlinesIn = 1;
A = importdata(filename,delimiterIn,headerlinesIn);

filename='Ref_QE_wow.txt';
B = importdata(filename,delimiterIn,headerlinesIn);

phiP=A.data(:,2);
... 74 more lines ...
  2020   Thu Feb 18 08:12:53 2016 KojiNMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

The reflecrivities and the EQEs of the PD (C30665GH, with the glass window) for S-pol and P-pol were measured at every 10 deg in incident angle as shown in Fig. 1 and Fig. 2.

In this measurement, for alignmnet the steering mirror was used and it was confirmed that the beam was not clipped.

The EQE is obtained from the DC output voltage which was read from the oscilloscope using the following equation (see also elog2019):

{\rm EQE} = \frac{I_{\rm PD}hc}{\phi ne\lambda} = 5.32 \times 10^{-3} \left( \frac{V_{\rm out}}{1 {\rm V}} \right) \left( \frac{1{\rm W}}{\phi} \right),

where I_PD is the photocurrent, V_out is the DC output voltage, h is Planck's constant, c is the speed of light, phi is the incident power, n is the index of refraction of air, e is the elementary electronic charge, and lambda is the wavelength of the laser.

Fig. 1 Measured reflectivities for P-pol and S-pol.
Fig. 2 Determined EQEs for P-pol and S-pol.

 

Attachment 1: QE3.pdf
QE3.pdf
Attachment 2: QE_ll.pdf
QE_ll.pdf
  2021   Thu Feb 18 13:39:33 2016 KojiMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

Can you calculate the IQE from EQE and reflectivity (by ignoring scatter loss)?

Can you measure the EQE/IQE/reflectivity at the angle where the EQE goes maximum for the P pol?

Can you use larger fonts in the plots?

  2022   Fri Feb 19 00:01:36 2016 KojiNMiscPD QERe-measurement of the reflectivities and the EQEs of the PD for S-pol and P-pol

I calculated IQEs using the measured EQEs and reflectivities and the following formula:

{\rm IQE} = \frac{{\rm EQE}}{1-R-T},

where R is the reflectivity of the PD, and T is the transmittance of the PD.

Here T is assumed to be zero and the scattering loss is ignored as you said.

The obtained IQEs are shown in Fig. 1.

 

Also the EQE, IQE, and reflectivity at a few angles near the angle where the EQE goes maximum for the P pol were measured as shown in Fig. 2 and Fig. 3.

The angle where the EQE goes maximum for the P pol is -51 deg.

So far, in these plots, the systematic errors because of the power meter are not considered.

 

And I replaced the figures with the figures having larger fonts.

Fig. 1 Measured EQEs and IQEs.
Fig. 2 Measured reflectivities around -51 deg.
Fig. 3 Measured EQEs and IQEs around -51 deg.

QE_Ref_P.txt QE_Ref_S.txt

AroundPeak.txt

Attachment 1: IQE.pdf
IQE.pdf
Attachment 2: Ref.pdf
Ref.pdf
Attachment 3: QE_Ref_P.txt
# angle(deg) 3beams(mW) error DCout(V) error
# incident power is 11.7 +/- 0.2 mW
-80.    4.6     0.1     0.14    0.02
-75.    3.52    0.02    1.02    0.02
-70.    1.24    0.02    1.58    0.02
-60.    0.627   0.002   2.04    0.02
-50.    0.244   0.002   2.12    0.02
-40.    0.410   0.002   2.10    0.02
-30.    0.512   0.002   2.04    0.02
-20.    0.851   0.002   1.98    0.02
... 13 more lines ...
Attachment 4: QE_Ref_S.txt
# angle(deg) 3beams(mW) error DCout(V) error
# incident power is 11.7 +/- 0.2 mW
-80.   6.61     0.03    0.04    0.02
-75.   6.17     0.03    0.52    0.02
-70.   5.29     0.02    0.98    0.02
-60.   3.40     0.02    1.42    0.02
-50.   1.85     0.02    1.70    0.02
-40.   1.78     0.02    1.84    0.02
-30.   1.372    0.004   1.90    0.02
-20.   1.293    0.004   1.92    0.02
... 13 more lines ...
Attachment 5: AroundPeak.txt
angle(deg) inc.pow.(mW,P) error Ref(mW,P) error DCout(V,P) error inc.pow.(mW,S) error Ref(mW,S) error DCout(V,S) error
-47 11.64 0.03 0.173 0.003 2.02 0.01 11.54 0.03 1.92 0.03 1.70 0.01
-49 11.46 0.02 0.375 0.004 1.99 0.01 11.60 0.03 2.12 0.04 1.66 0.01
-51 11.67 0.03 0.282 0.003 2.04 0.01 11.61 0.03 2.36 0.03 1.64 0.01
-53 11.56 0.02 0.325 0.003 2.00 0.01 11.35 0.03 2.59 0.04 1.56 0.01
-55 11.62 0.02 0.518 0.003 1.97 0.01 11.53 0.02 2.86 0.04 1.51 0.02
Attachment 6: QE2.pdf
QE2.pdf
  753   Fri May 7 07:42:09 2010 AidanLab InfrastructureHVACRe-sealing and laser keys

The guys are back this morning to reseal the vents. There are some green marks around the place but also what looks like new red ones over the top of the silicon they laid down two weeks ago.

I shutdown the 35W laser using the 'System Off' option on the touch-screen and then turned off the NPRO and removed the key. That key is now in the second drawer down in the first desk. The key for the Gyro NPRO was not in the laser.

  754   Fri May 7 10:16:24 2010 ZachLab InfrastructureHVACRe-sealing and laser keys

Gyro key is in the top drawer of the center workstation.

Quote:

The guys are back this morning to reseal the vents. There are some green marks around the place but also what looks like new red ones over the top of the silicon they laid down two weeks ago.

I shutdown the 35W laser using the 'System Off' option on the touch-screen and then turned off the NPRO and removed the key. That key is now in the second drawer down in the first desk. The key for the Gyro NPRO was not in the laser.

 

  755   Fri May 7 11:10:17 2010 AlastairLab InfrastructureHVACRe-sealing and laser keys

Sealing is done.  They left the air on this time while doing it so they could get as many small leaks as possible.  Anyway, that means that the air is still on in the lab and they have finished for good now.

Quote:

Gyro key is in the top drawer of the center workstation.

Quote:

The guys are back this morning to reseal the vents. There are some green marks around the place but also what looks like new red ones over the top of the silicon they laid down two weeks ago.

I shutdown the 35W laser using the 'System Off' option on the touch-screen and then turned off the NPRO and removed the key. That key is now in the second drawer down in the first desk. The key for the Gyro NPRO was not in the laser.

 

 

  210   Fri Jul 31 01:12:41 2009 DmassLaserPSLReReReLocking the PMC aaaaaand stuck.

I spent some time tonight realigning and relocking (attempting to relock) the PMC.

 

I got to a point where I did not understand the behavior of my error signal. I did the standard things...

  • Changed cable length by pi/2
  • Eventually realized that I had done this all before and looked at my old elog to not do the same dumb things again
  • Same setup as this elog entry
  • Change the offsets muchly
  • Change the gain
  • Change the sign of the gain
  • Make sure just a single pole @ 1Hz is toggled on

I get a behavior where my transmitted beam would oscillate in power, seemingly about the center, and my error signal looked as below

 

When I say error signal I mean "Thing that should be my error signal but for some reason is not" this is the raw signal I am inputting into the DAQ - so this is what I pass to my filters then to teh PZTChange the offsets

Attachment 1: ErrSignal.png
ErrSignal.png
  212   Fri Jul 31 14:38:51 2009 DmassLaserPSLReReReLocking the PMC aaaaaand stuck.

Quote:

I spent some time tonight realigning and relocking (attempting to relock) the PMC.

I got to a point where I did not understand the behavior of my error signal. I did the standard things...

  • Changed cable length by pi/2
  • Eventually realized that I had done this all before and looked at my old elog to not do the same dumb things again
  • Same setup as this elog entry
  • Change the offsets muchly
  • Change the gain
  • Change the sign of the gain
  • Make sure just a single pole @ 1Hz is toggled on

I get a behavior where my transmitted beam would oscillate in power, seemingly about the center, and my error signal looked as below

 

When I say error signal I mean "Thing that should be my error signal but for some reason is not" this is the raw signal I am inputting into the DAQ - so this is what I pass to my filters then to teh PZTChange the offsets

 

I called upon Koji to assist me in my woes.

We got a lock by turning off the digital filter. We could not lock with it on at any gain we tried

I will take a transfer function with the 35670A and try to get at the real transfer function.

 

Sure would be nice to have AWG

  213   Fri Jul 31 14:58:14 2009 KojiLaserPSLReReReLocking the PMC aaaaaand stuck.

We inserted an SR560 with G=+100 as a preamplifier for the mixer output so that we can have a ~100mV error signal for a cavity swing.
The error signal of ~mV with the offset of ~mV (presumably coming from both the ADC and the mixer) is a totally wrong approach.

Ah, you don't need the 50Ohm termination at the ADC input any more as we are handling only AF signals there.
It just make the signal amplitude half.

Quote:

I called upon Koji to assist me in my woes.

We got a lock by turning off the digital filter. We could not lock with it on at any gain we tried

I will take a transfer function with the 35670A and try to get at the real transfer function. 

Sure would be nice to have AWG

 

  474   Wed Dec 9 00:45:31 2009 DmassLaserDoublingRealigned the MZ

I realigned the Mach Zehdner, so here are some numbers to quantify the "I can't have good contrast @ both wavelengths simultaneously" statement. Each value is followed by what I think is limiting it

  • Best Contrast @ 1064 = 88% (mode matching/alignment)
  • Best contrast @ 532 = 63% (power imbalance)

Balanced Contrast (rough simultaneous optimization)

  • 1064 = 40% (dispersion in the beamsplitter)
  • 532 = 40% (dispersion in the beamsplitter)

I will also post a picture of the scope trace I took while sweeping vertical angular alignment

  677   Wed Mar 17 16:18:32 2010 DmassLaserPSLRealignment

Koji and I realigned the steering into the PSL amplifier, and increased the output power from 15W to 25W.

The beam quality was so low that the previous nights best transmission through the PMC went up by a factor of 5.

We investigated the AOM driver and alignment. The alignment verdict is "all degrees of freedom explored to some degree, maximum seems found for drive strength"

  • We checked the output of the NEOS driver, and found that it was only putting out 1W (20 Vpp = 7 Vrms into 50 Ohms = 1 W).
  • We turned up the power supply to the NEOS to 27.5V. (They say no more than 28 V).
  • We got an output of 24 Vpp = 8.4 Vrms = 1.4 W nominally. We have a 20% range in the AOM now.
  • There is a terrible terrible feature of the SR function generator. 0-1 V DC offset on 50 Ohm output mode does not produce the same AOM change as 0.5 Vpp + 0.5 Vpp*sin(wt). When we increased the AC signal portion from the function generator, we recovered the proper range. This would have affected previous calubration attempts, but my old 12% number WAS from checking with DC offsets.
  680   Wed Mar 17 20:17:27 2010 DmassLaserPSLRealignment

PMC loop changed. Old UGF: 1 kHz with 30 degrees of phase margin.

New UGF - 600 Hz with 45 degrees.

Testpoints broken

DTT in horrible state of disrepair

Frontend generally brokeded

No transfer functions via DTT for a bit methinx.

 

Attachment 1: PMCOLTFanalog.png
PMCOLTFanalog.png
  682   Thu Mar 18 16:26:06 2010 DmassLaserPSLRealignment

Quote:

PMC loop changed. Old UGF: 1 kHz with 30 degrees of phase margin.

New UGF - 600 Hz with 45 degrees.

Testpoints broken

DTT in horrible state of disrepair

Frontend generally brokeded

No transfer functions via DTT for a bit methinx.

 

 

Adjusted the loop gain to compensate for the change in optical gain. Same ugf (hypothetically).

Gain = oldgain * 25/29.5 where 25W is old power, and 29.5 W is new power.

  124   Tue May 5 16:36:40 2009 AidanComputingCDSRealtime code generation (RCG) troubleshooting

Useful things to try when making Simulink models with RCG


1. When making a new model foo.mdl use the following text
make uninstall-daq-foo
make clean-foo foo install-foo
make install-daq-foo
make install-screens-foo


2. start the MEDM screen C2FOO_GDS_TP.adl

2. A. kill whatever is running:
e.g. on oms > killoms
       > killatf

2. B.  find the .ini (C2FOO.ini) and edit it so that at least one channel is acquiring - do this whenever an install or reinstall are run.
2. C. manually edit the master file in fb0 to point to C2FOO.ini
  /cvs/cds/caltech/target/fb/master
2. D. start foo on oms > startfoo

see if things start to light up on the MEDM screen C2FOO_GDS_TP.adl

check if the front end is running
      /sbin/lsmod
  - should see 'foofe' and 'gm' running

look at the log file in /cvs/cds/caltech/target/c2foo
 - log.txt - will either be a couple of lines with an error message or a lot of stuff that looks like things are working:


3. go to /etc/rc.local and add foo to file. file is read-only so use 'sudo vi rc.local'
e.g. /etc/setup_shmem.rtl ipc sas test oms atf afb afc foo&

update shared library index (see Tobin's entry)
   > /sbin/ldconfig


4. try a restart of oms
   > sudo reboot

try 'startfoo' again - hopefully at this stage parts of the MEDM screen should start lighting up


5. if still problems (parts of GDS MEDM screen are still white), try to reboot fb0
   > telnet fb0 8087
      > shutdown

 
try to start again
   > killfoo
   > startfoo


6. check last line of log file /cvs/cds/caltech/target/c2foo/log.txt -
might require BURT restore

go to C2FOO_GDS_TP.adl MEDM screen and set BURT restore value to 1

should be okay now ...
 

  2187   Wed Jan 3 20:20:07 2018 awadeDailyProgressWOPOReboot WOPO

Laser restarted + 1064 for Shotnoise + SQZ measurment

I've restarted the Diabolo and am checking the alignment into fibers. The current configuration coming out of the WOPO breadboard is a fiber 50:50 beam splitter followed by two matched F240APC-1064 nm fiber collimators.  There is a HT532HR1064 dichroic mirrors in each of the split arms remove any remaining residual green.  The plan is to use a single NF1811 in one arm to see if we can see SQZ out at RF.  It will be lossy and susceptible to RIN, but we will be measuring at very high frequency.

Power of 1064 nm after the power-control PBS is 3.12 mW, at the other end of the fiber I am seeing 300 uW.  At the output of the HD fiber colimators there is an even split of about 148 uW: about what we should expect. I will try to check the alignment tomorrow and see if I can identify shot noise on the NF1811 above the dark noise. I haven't don the calculations, will check these number tonight.

---

Temperature control WOPO

I also tracked down the Newport 3040 temperature controller (found in the PSL lab).  I've reattached this to the WOPO butterfly mount and am able to get a temperature readout from the 10kΩ thermistor with a 10 µA test current (this should deliver 0.1V to the NP3040 ADC). There is an option for 100 µA excitation of the sensor (have used this in the past), but I figured less current means less self heating. Not sure what the situation is with S/N inside the box, its an expensive mystery.

Settings on the Newport 3040 are basically the same as before, see ATF:2124,  for good measure here are the full settings list:

Newport 3040 settings WOPO
Setting Value [units]
Sense type 10 [µA]
Mode Const T
Gain 2 Slow
Limit Ite 0.65 [A]
Tol time 1.0 [s]
Tol Temp 0.1 [C]
Limit Tl 18.00 [C]
Limit Th 70 [C]
C1 1.0445e-3
C2 2.5075e-4
C3 0
Ts (set point) 61.93 [C]

 

 

 

 

 

 

 

 

 

 

 

The NP3040 does give you explicit gain levels for P and I terms in the feedback loop real values. It just has mystery numbers 0.2, 0.6, 1, 2, 3, 5, 6, 10...300 with either "fast" or "slow". I used 2 Fast, and then gain 10 Fast.  Integration doesn't seem to be aggressive enough as its not reaching the set point.  Any more proportional gain and it overshoots and hits the shutdown rail on loop startup. A current of 0.4 A is needed to reach a set point of 61.93 C, so there is plenty of actuation headroom.  Its not an ideal PID loop but I'll leave this for now, it is enough to just move the set point a little higher.  

---

LO phase scanning

There is a 1064 nm mirror mounted on a PZT just before coupling into the fiber. Wires have been soldered to a BNC and solidly mounted to a L-bracket on the table. I have obtained a thorlabs HV driver that can do upto 150 V from 10 V .  There is an adjustable range with a switch on the back (75V, 100V or 150V), I need to check the voltage range allowable for this PZT before powering up.  The plan is to scan 1064 nm phase over a few wavelengths to scan the detected SQZ phase. About 100V will do it.

Something to check is the impact of banana shapped motion of the mirror+PZT, in the past this changed power through modecleaners by misaligning with the voltage scan. However, that was on very long PZT stacks. Might expect a similar effect coupling into fiber, its just something to calibrate out in the baseline shotnoise curve as a function of scan voltage.

---

I haven't checked the 532 nm coupling efficiency or made a shot noise measurement.  I have a  NF1811 + power supply and will try to look at this tomorrow with a spectrum analyzer.

  2174   Wed Aug 30 21:22:20 2017 awadeLab InfrastructureCDSReboot fb1

I rebooted the fb1 frame builder computer in the ATF lab. It took a few hours to go through disk checks but landed on the command line eventually. Not sure when it was last used but it might be useful to the PSL lab for a framebuilder. Also the higher sample rate channels would be SUPER useful if we can get those back up. I might need a hand getting up to speed on how to configure this. 

  2324   Wed Apr 10 13:10:45 2019 awadeDailyProgressWOPORebuild of WOPO homodyne detectors using AD829

[awade]

This post details the rebuild I made of the transimpedance amplifiers (TIA) for the homodyne detectors.  My previous iteration of this design failed to take into account the output swing limitations and current draw limitations at the output of the op amp.  It turns out that the OP27 was not the best choice here.  On the face of it its GBP and input referred noise were fine for a ~ 1 MHz detection.  However, operating the chip with 5V output voltage (to get 10 dB shot noise clearance from thermal noise) and with output impedance on order of 150 Ω meant that the frequency response was not as expected (see ATF:2316). 

A better choice is something like AD829 which is designed for driving signals directly into 50Ω terminated outputs.  The updated design is illustrated below.

Here the transimpedance gain has been lowered to 2 kΩ to lower the relative input referred noise contributed by the AD829's slightly higher current noise.  Here the optical power can be increased to give the same effective output signal.  In this case increase optical power and lowering gain keeps the thermal noise clearance below shot noise constant but improves the clearance of the AD829 input current noise.

 

Scaling of thermal noise relative to shot noise given DC output voltage

For reference the thermal noise of the TIA is given by the Johnson noise

\delta n_\mathrm{thR} = \sqrt{\frac{4k_BT}{R_\textrm{fb}}}

where k_B is the  Boltzmann's constant, T is the temperature (300K) and Rfb is the feedback resistor value.  Also here the shot noise is

\delta n_\mathrm{SN} = \sqrt{2 e^- \mathcal{R}P_\textrm{PD}}

Where e is the charge on an electron (1.602e-19 C), R is the photodiode responsivity (~0.8 A/W), and P_PD is the power on the photodetectors (0.5-5 mW).  Keeping in mind that there is a maximum voltage swing (V_max) on the output of the op amp, this comes from its current driving capability into a given load, then the feedback resistance (TIA gain) is limited to 

R_\textrm{fb} = \frac{V_\textrm{Max}}{\mathcal{R} P_\textrm{PD}}

The noise clearance, given a maximum output voltage, is then given by the ratio

NR = \frac{\delta n_\mathrm{SN}}{\delta n_\mathrm{thR}} = \sqrt{\frac{e^-V_\textrm{Max}}{2kT}}

Power on the photodiode and responsivity cancel out for the noise clearance.  Assuming we are not optical power limited then the thermal noise ratio (clearance below shot noise) is wholly determined by V_Max and the physical constants e, k_B and T.  For room temperature (300 K) this reduces to the rule of thumb 

NR \sim 4.4 \sqrt{V_\textrm{Max}}

Keeping the V_max to within 3 V means that we will get a thermal noise clearance factor of 7.6 below shot noise (8.8 dB). V_max of 5.2 volts will give 10 dB clearance. Ok I guess. 

Choosing AD829

Koji suggested the AD829 as a replacement to OP27.  AD829 has applications in driving 50 Ω/75 Ω loads in video applications and has some nice noise characteristics.  The bottom line is that it has 1.7 nV/√Hz input voltage noise, 1.5 pA/√Hz input current noise, can do a ±3 V voltage swing into 150 Ω load (DC coupled), and is fast (600 MHz uncompensated, with 230 V/µs slew).  There are some quirks.  AD829 seems have have a weird 80 MHz feature that causes oscillations if not compensated properly.  I did a bit of modeling in LISO and then just decided to build it once I found that ~2 kΩ gain was about right for ensuring that the dark noise wasn't dominated by the op amp current noise.

Because I was building on proto-board I wanted to ensure that there was as little parasitic capacitance as possible.  I built the whole amplifier + PD onto a single SOIC-14 to 0.1 pitch adaptor (Adafruit SMT Breakout PCB for SOIC-14, Part No. 1210), pictured below.  The small footprint and short trace lengths between critical pins means that there is a lower chance of parasitic impedance causing instability or impact on bandwidth.  

Top view of Unit B TIA with PD mount soldered directly to inverting pin and positive bias
TIA at earlier stage of construction for both unit A and unit B
shows feedback resistor and capacitor soldered on reverse side (these passive
components are stacked on top of each other).

The feedback resistor (2 kΩ) and feedback compensating capacitor (15 pF ceramic + 3 pF nominal pin parasitic) were soldered directly to the reverse side where the TSSOP-14 pins were connected through vias to the top side.  This minimized the path length of this electrical signal.  I scratched off pads that were unused in case they shorted or were a source of crosstalk.  The photodiode mount pin was soldered directly to the edge of the board to minimize distance.  The power bypassing capacitors were SMT 100 nF ceramics (5%) that were soldered directly to the SMT breakout with the shortest path to ground on that board (see pictured).  The other photodiode pin was soldered to +5 V (-5V) supply pin in unit A (unit B).  The opposite biasing makes subtracting the signals using a summing circuit easier but may affect the overall TF response. There is no power regulation, I'm planning to use batteries to power these circuits.

In my initial tests I had no compensating capacitor attached to pin 5.  I inserted a 40 pF ceramic capacitor in place of the photodiode and looked at the AD829 output pin with a high impedance probe on an oscilloscope.  I immediately saw 80 MHz oscillations.  I don't really need a super high bandwidth so I went strait to the maximum recommended choice for pin5 compensating capacitor of 68 pF.  This makes AD829 unity gain stable with 66 MHz bandwidth (slew 16V/µs) but is more than enough for my needs.  This killed the high frequency RF ringing junk. Maybe less capacitance here would have worked, but this performance is enough for my needs and gives some certainty about the op amps stability (ignoring input capacitance compensation).

At the output I added 100 Ω of series resistance to limit the loading on the op amp and current draw when 50 Ω terminated.  With 50 Ω terminating impedance this makes a 150 Ω to ground.  Providing the output DC swing is kept within 3V the op amp should behave as expected.

The whole thing fits together very nicely on a single SMT breakout board. Making it compact will hopefully avoid any issues with stray capacitance messing up the performance.  I have then mounted this on a larger proto board for ease of installing in the experiment. Paths to the output SMA output are thin wire and not routed through the underlying board. Only power and ground is routed through the board, all other pins to the op amp disconnected. 

 

Transfer function PD

I measured the signal transfer function of the above TIA units using the Jenne rig at the 40 m.  It took me a number of tries: I made the mistake of loading the DC port of the NF 1611 detector with 50 ohms (which resulted in too much current draw and affected the LF response of the witness detector); there were also some issues with the polarization/positioning onto the beam splitter there that made it not 50:50 (it was 69:33 ), I moved the fiber launch a bit to get the splitting right and retook measurements after that; also I initially had the current set too high on the laser current driver which I think was saturating its response.  I'll skip over the details and just present the final measurement. I've included a zip in the attachments with the data that logs some more of the details of my failed attempts.

I used the same calibration as used in PSL:2247.  Here the laser diode current was set to 25.0 mA, which is 1.51 mW of 1064 nm, and the AC excitation into the laser was set to -21 dBm (19.9 mV rms).  Power on the witness detector was measured to be 0.79 mW and that on the PD under test was 0.75 mW (as measured with a power meter).  Units of measurement were linear magnitude and phase in degrees. DC voltages were measured with 1 MΩ impedance.

Unit A: using 25 mA current into laser and -21 dBm sweep I get DC on PD of 1.20 V (into 1 MΩ) and a DC voltage of NF1611 detector of -2.13 V (into 1 MΩ).

Unit B: using 25 mA current into laser and -21 dBm sweep I get DC on PD of 1.07 V (into 1 MΩ) and a DC voltage of NF1611 detector of -2.12 V (into 1 MΩ). 

The calibrated TIA current to voltage gain is plotted below:

A notebook detailing all the attempts is attached below.

 

 

Quote:

This set of measurments turned out to be bad. The OP27 (±15V supplies) with 50 Ω series at the output + 50 Ω load impedance seemed to be saturated.

Attachment 1: BasicSchematic_TranImpPD_AD829.pdf
BasicSchematic_TranImpPD_AD829.pdf
Attachment 4: WOPO_HDPD_AD829_2kohmTranImpGain_UnitAandBandLISO.pdf
WOPO_HDPD_AD829_2kohmTranImpGain_UnitAandBandLISO.pdf
Attachment 5: 20190405_TFHDPDs_AD829Design_LargeBoard.zip
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