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ID Date Authorup Type Category Subject
  194   Mon May 9 11:25:05 2011 Mingyuan, taraDailyProgressCreakShim/mirrors replaced

  We switched the current metal shim with the thicker Aluminium shim. Now both mirrors are also the same. We tested and showed that the shim is not too hard to be pushed by pzt.

First, the thicker Al shims have bigger bending stiffness and more difficult to bend under the surrounding perturbation. Therefore, the signal we got has less noise from the surrounding perturbation.

By using the PZT we have, we can still drive the shim well. With the driving, we observed intensity oscillates from ~50 mV to ~200 mV. 

We also observed a low frequency (~80 mHz) oscillation of the signal. I didn't find the source of this oscillation. The sensitivity of response to driving is lower while the intensity is near the minimum and Maximum and higher while intensity is at the middle.

 

pdout.png

 
  148   Fri Feb 12 11:33:04 2010 MottMiscSUSState of the Shaker

The Shaker project is coming along nicely.  I am currently looking into using the built-in ability to download a waveform to the front end to do the sweeps, but we are running into memory problems, and I get the sense from Tony that it was not really designed to do this.  Currently we are able to download a waveform to the frontend, run the generator according to it, and make a measurement over a full run of the waveform.  If we can crack the limited time constraint and figure out the averaging, this is going to be the most straightforward solution.

I am working, in parallel, with Gert (who is out of the office at the moment) on using pure script to do this, although I am worried about starting and stopping the generator so frequently.  Apart from anything else, there is a slight hang in the frontend when the generator start method is called; it is not noticeable when the button is pushed in the app, but I think it adds quite a bit of latency to the program.  I am still waiting to hear from Gert about how to acquire a time series; hopefully we can figure that out by early next week, since it is critical.  I am also not entirely sure how we force the program to do all the analysis on the time series after it is acquired.  Ideally we would want the analysis to run in parallel and update the frontend continuously, but I am not sure this is possible with VBA (I don't think you can do multithreaded programming) and I am not sure I would know how to do so even if it is!

 

 

  149   Fri Feb 12 11:35:19 2010 MottMiscSUSPiezos

Engineering was very helpful showing me how to make the leads we need for the piezos; I will go crimp some more at the beginning of next week. 

The new structures should be coming in soon, so we will have a dedicated structure for the piezo damping, at which point we can really get cracking.

  150   Thu Feb 18 17:43:15 2010 MottMiscSUSPiezos

 

I finished crimping all the connectors we will need for the piezos.  We are now just waiting for the new structures to arrive so we can start gluing the piezos on.

  1835   Wed Dec 4 19:00:37 2019 Noisemon board modifiedDailyProgress Noisemon board modifications

According to previous post 1834, we think the noisemon problem is very likely caused by C2 charging. Hence we did the following modifications on a noisemon board:

1. Split R2 into two 400 Ohm resistors, with grounding between them.

2. Split C2 into two 3.3uF capacitors, with grounding between them.

We hope these modifications will provide a path for the bias current to go to ground, instead of charging up C2.

  1836   Thu Dec 5 12:37:58 2019 Noisemon board modifiedDailyProgress Noisemon board modifications

The modification is successful. The attachment shows the result after the board runs for 12 hours. We modified channel 1 and 2 so we see FM0 and FM1 channels are still decent. We only split C2 but not R2 for channel 3 and 4 so FM2 and FM3 are bad.

Quote:

According to previous post 1834, we think the noisemon problem is very likely caused by C2 charging. Hence we did the following modifications on a noisemon board:

1. Split R2 into two 400 Ohm resistors, with grounding between them.

2. Split C2 into two 3.3uF capacitors, with grounding between them.

We hope these modifications will provide a path for the bias current to go to ground, instead of charging up C2.

 

Attachment 1: ModificationComparison.pdf
ModificationComparison.pdf
  106   Mon Nov 26 16:05:43 2007 Norna RobertsonMiscSUSMass of OMC silca bench (measured 16 Nov 2007)
For the record here is a note sent round OMC-SUS colleagues on 16th November.

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

A team of Chris, Chub, Helena and me ably led by Sam (who did the scary lifting) got the OMC bench dismounted from its suspension and weighed today. It is now sitting on its custom plate with dark side down (minus the preamp boxes) in the centre of the optics table in room 56. It will remain there for the forseeable future. The metal parts of the suspension will be disassembled by Chris with Ken Mailand's help starting Monday.

Results of weighing

1) Optical bench including preamps and the wire bundle to the heater, pzt etc = 6.514 kg
2)Preamp cable (mock-up) = 24.4 g (without the connectors to the preamp)
3) The two leaning towers of counterweights (which were situated close to the far corners of the mass - NOT above the holes where they need to be for fixing in place) = 200.2 g and 187.7 g

I remind you all that there are 2 more tombstones ( fused silica 8 mm thick x 30 mm tall x 32? mm wide with 18 mm diam hole- size to be checked from CAD drawing) and two pieces of black glass 1 inch by 1 inch by 3 mm ( I noted at our telecon that these weigh 8.5 gm total) to be added to the bench - situated close to the DC photodiodes which sit on bright side under the preamps.
  119   Wed Jan 23 22:52:21 2008 Norna RobertsonMiscSUSOMC SUS assembly adjustments made and lessons learnt
Calum and I have been working in the 40 m annex re-assembling and testing the OMC SUS after the parts have been cleaned and baked and various parts modified. We have had several problems which needed to be addressed and made several observations of items which need attention for the next OMC. Also we note several points which need to be followed when the OMC is being prepared at LLO for input into the vacuum chamber. The following are in no particular order.

1) Problem with one of the blades
When we got the double pendulum hanging today we noticed that one of the lower blades was interfering with part of the top mass - hitting a block which holds one of the screws for adjusting the position of the clamp for the upper wire ( for adjusting pitch). The blade was 13S - one of those which had an angled clamp of 3.5 degrees (the larger of the angles - the blades at the other end of the bench have 3 degree angles). These large angles are being used to counteract the fact that the bench weighs more than these blades were designed for. The blades thus have a convex curvature (looking from above) and the crown of the bend was where the interference was occuring. The puzzling bit is why only one blade showed this, and not its partner. We tried another 3.5 degree clamp ( in case it was a fault with the clamp) but saw the same effect. We then tried reducing to 3 degrees for that blade - still almost touching. We then reduced the angle for that blade to 2.5 degrees. This worked Ok - and when the masses were hanging again all the blade tips appeared to be at approximately the same height (measured using a steel rule). So the dynamics should be OK. Puzzle remains why only one blade showed this behaviour. Note that for the LHO OMC we will be getting new blades designed for the mass they will be taking, and so we should not need to use angled clamps as large as for the LLO suspension Hence this interference problem should not arise again.
Lesson for the future - need to characterise all blades with the full range of angled clamps to be used. (We did not have time to do this for this suspension).

2) Test of new method of hanging silica bench (using metal bench)
Yesterday with Ken Mailand's help we tried out the new way of suspending the bench using Ken's bench holder with one of the metal benches and the two lab jacks. We learnt that to get the right range of height adjustment to lift the bench to put the discs on the lower wire clamps and then lower the bench again the mating pieces on the lab jacks had to mate with the central portion of the handles at each end rather than the top part of the handles. Also it looks like the lower EQ stop holder (which sits under the bench) should be put in place before the bench is brought in - otherwise difficult to get into place. Finally we note that this job is a three person job - need one on each end to raise and lower the lab jacks and one to fit the discs and then guide the discs and clamps into the holes and check they are seated correctly as the bench is lowered.

3) Height of bench.
We measured the height of the lower surface of the metal bench above the optics table to be (160.5 - 38.75) = 121.75 mm. Requirement is 101.6 + 20 = 121.6 (+/- 2mm) so we are OK. This was without any extra mass added to the top mass. We note that the tabelcloth is close to lower end of its range, but should be OK. However the final alignment needs to be done when the OSEMs are in place.

3) EQ stops and parts which should be removed before putting into vacuum chamber.
For sending the OMC to LLO we put on double nuts on all the EQ stops. This limits the range of the stops and in particular the ones under the bench were not long enough to reach the bench when double nuts are used. So we had to improvise the position of the EQ holder by putting ~ 1/2 inch "shims" to raise the holder ( the shims were three of the masses made for attaching to the metal bench to increase its mass). We also removed all "loose" parts - the adjustment mechanisms for the top blade yaw positions, the magnets and flags, the set screws for locking the larger vertical stops used to hold the top mass, and the screws used to alter the pitch adjustment clamp positions.
When the OMC is reassembled at LLO and made ready for installation, all the second nuts on the EQ stops should be removed. Also once the pitch adjustment using the moveable clamps is set correctly, the screws for doing those adjustments should be removed again. Basically all loose screws should be removed.

4) Parts needing modifications
i) EQ cross pieces holding the plate which goes over the bench need to be reduced in length to fit between the structure legs.
ii) Blind holes in EQ corner brackets.

5) Point to note for next OMC.
i) The slots in the structure which take the dowel pins for alignment need to be lengthened to allow the tableloth the full range of movement which the slots for the attachment screws would allow.
ii) The targets for aligning OSEMS need a hole in the centre for the flag.

More to follow tomorrow
Also we took lots of pictures today. will put relevant ones into installation document.

OMC is due to be crated tomorrow for pick-up on Friday am.
  566   Tue Aug 28 16:16:00 2012 Norna RobertsonMiscSUSProposed quad pendulm with 143 kg silicon test mass for LIGO-III

Our high school summer student Madeleine Waller has produced a set of slides describing work she has been doing over the summer working with Calum and  Norna.

She has been using Solidworks to look at how a proposed quad suspension with 143kg silicon mass might fit into an existing BSC chamber with a  BSC-ISI, a Transmon and an arm cavity baffle.

See G1200828 on the DCC at https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=95782

Screen_shot_2012-09-12_at_1.51.57_PM.png

  1852   Wed Oct 28 17:29:14 2020 PacoSummaryGeneralLab organization

I entered Crackle lab circa ~11:15. I started some basic lab inventory and started cleaning/organizing stuff. We will use the first optical table (as you enter the lab) because it's the easiest to clear (see below before and after clearing). Some of the cleared items on the table include:

- UHV foil (moved to top left cabinet above the work bench)
- OSEM components for Crackle (?) (moved to top left cabinet above the work bench)
- Various metallic parts/components (moved some in a plastic container to the second drawer from the bottom of the second red tool storage, and others to the second optical table)
- Various screw/screwdriver kits (moved some to work bench right by the electronic storage area and others to the second optical table)
- Power supply and laser diode driver (moved to control/acquisition rack)

I then moved the 1064nm pump Innolight Mephisto 800NE to the clear table, clamped it down, and cleaned/organized the lab a little, which involved:

- Shelve orphan/incomplete PCBs and electronic components from the work bench up to the cabinets.
- Organized some cables by the fume hood.
- Organized other random hardware on the work benches. 

I found the Emergency STOP (OMRON STI #A22EM02B) button buried on the fume hood, so I gave it a quick test, and after confirming it worked I wired it to the interlock on the back of the laser controller. Then tested it along with the interlock and verified it's working, but I have yet to solder it nicely (I didn't commit to the wire lengths yet).

Left at ~ 14:45. Noted that we had more cockroaches in the floor at the beginning of the day than 2 um laser sources. Now we are tied.

Attachment 1: IMG-20201028-WA0011.jpeg
IMG-20201028-WA0011.jpeg
Attachment 2: IMG_20201028_144653.jpg
IMG_20201028_144653.jpg
  1853   Mon Nov 2 18:23:46 2020 PacoDailyProgressGeneral 

Today; entered lab at ~09:08. I verified the orientations of the aspheric lenses and blaze gratings relative to the flextures, packaged and then dropped the parts for epoxying to Koji in 40m ~ 11:00. Spent some time between 12:00 and 12:45 finishing the ECDL connections. Everything looked good so I hooked it up to the TED200C controller. After a bit of research, I found out the Steinhart constants for the 10k thermistor;

a=1.129241e-3

b=2.341077e-4

c=8.775468e-8

Plugging these into the Steinhart equation give the actual temperatures from the Tact output on the TED200C (otherwise read as kOhm). According to the spec sheet, the TEC was tested at 250 mA (0.40 V), so not knowing a bunch more, set I_TEC on the TED200C to this limit and inspect the actual TEC current by scanning the Tset (setpoint) and recording the current in the ~ 15 - 25 deg C (attached plot, horizontal line marks room temperature). The diode current driver is hooked up, and everything is on the table as is. Left Crackle ~ 18:30.

Attachment 1: 2020_11_02_ted200c_test.png
2020_11_02_ted200c_test.png
  1855   Fri Nov 6 10:47:49 2020 PacoDailyProgressGeneralConnecting SAF1900S

Here is a summary for how to connect the SAF1900S gain chip to TED200C temperature controller and LDC220C diode current driver. The chip itself lacked substantial documentation, so this comes after requesting tech support from the manufacturer. The SAF1900S pinout is

1 - TEC+ 

6 - TEC-

2 - Thermistor

3 - Thremistor

4 - Anode

5 - Cathode

The TED200C has a DSub15 output, but the cable provides a DSUB9 adapter. Then, only the following pins are connected to the SAF1900S

2: Thermistor

3: Thermistor

4: TEC+

5: TEC-

The LDC220C has a DSUB9 output, and its bipolar nature allows it to drive either anode-grounded or cathode-grounded diodes, so the question was wether the SAF1900S is AG/CG? In a first attempt, I assumed the diode was meant to be driven with a floating source (and that the LDC220C could do that), but the driver remained in "LD OPEN" state. Then, I revised the documentation for TLK1900 (an old, discontinued laser kit using the same gain chips). There, the bottom line seemed to suggest CG, but to be sure I asked a technician in thorlabs. They say most of their 14 pin butterfly chips are AG, but the 6pin ones seem to be CG. Anyways, the relevant pins (for either connection) are:

3: Ground (for AG/CG)

7: LD Cathode (for floating / AG)

8: LD Anode (for floating / CG)

After some communication with ANU's Disha, I found the diode pins are floating from the case (personally confirmed this), and an additional connection between pins 1 and 5 of the LDC220C needs to be established to override the interlock. The suggested connections are three: shortcut, resistance < 430 Ohm, or LED || 1 kOhm resistor (to match the Laser ON status in the front panel). I opted for this last one, made the connections and was able to correctly feed the SAF gain chip.

Attachment 1: saf1900s_conn.png
saf1900s_conn.png
Attachment 2: saf1900_conn2.png
saf1900_conn2.png
  1857   Mon Nov 9 17:38:18 2020 PacoDailyProgressGeneralSAF gain chip first light

Entered Crackle ~ 8:47 AM.

Briefly fixed the LDC220C connection to the SAF1900 as described previously, and then installed the aspheric flexture and shoulder to the assembly (pictures below). Then, I used the thermal power meter head borrowed from OMC to check for emission as a function of laser diode current at a fixed temperature of 25 C (to match testing conditions). The result is below, where I seem to be getting slightly better amplified spontaneous emission (ASE) power than the attached test sheet. It may as well be that I am not measuring the ASE power alone, but I cannot presently determine this.

I added the grating and moved the power meter to the correct output aperture, but failed to detect any power. This suggests a wrong grating orientation, although I will try to verify this more carefully.

Attachment 1: 2020_11_09_ldc200c_test.png
2020_11_09_ldc200c_test.png
Attachment 2: 20201109_aspheric.jpg
20201109_aspheric.jpg
Attachment 3: 20201109_firstlight.jpg
20201109_firstlight.jpg
Attachment 4: 20201109_grating.jpg
20201109_grating.jpg
  1859   Tue Nov 10 10:32:57 2020 PacoDailyProgressGeneralSAF gain chip first light

Set grating in front of 1064 nm beam (current set to 1.058 A for a beam visible on the IR card). After testing both orientations, it becomes clear the grating is misoriented. The difference is very clear, there is only specular reflection in the current configuration, whereas the m=0, and +- 1 orders are visible in the 180 deg flipped configuration. 

Quote:

Very exciting to see the gain chip curve!

Grating orientation: Whaaat... If you already have the 1um laser SOP approved, you can use that laser to check the grating orientation.

 

 

  1860   Wed Nov 11 12:28:33 2020 PacoDailyProgressGeneralEP30 softening

Attempted two methods to soften EP30-2, the results are summarized below.

(a) Heat -- Used the heat gun set to 200 F (~ 93 C) and held it near the back of the part so that the grating surface was never in direct exposure. The airflow was kept constant for a period of ~ 10 min, while I periodically checked to see if there were any signs of bond softening. After no signs of softening, I stopped and moved to method (b).

(b) Solvent -- After brief investigation and referring to T1400711, I got some acetone from CTN, and set up a ~ 50 ml bath. The part was not completely submerged and was arranged such that the grating face was always exposed to air, which I left for ~14 hours. The drawback of this method is that some of the acetone evaporated and at some point the EP30 bond stopped being in contact with the solvent. A picture for reference is attached, with the light blue line indicating the highest acetone level, and the red line indicating the EP30 bond level at the beginning of the bath.

Attachment 1: acetone_bath.jpg
acetone_bath.jpg
  1861   Wed Nov 11 12:55:18 2020 PacoLab InfrastructureGeneral1064 pump power curve

Log of the output power vs current in the 1064 nm (Innolight) pump laser. The crystal temperature was set to 45.5 C, and the current limit is set to 2.1 A

Attachment 1: 2020_11_10_mephisto_test.png
2020_11_10_mephisto_test.png
  1864   Wed Nov 18 17:49:05 2020 PacoDailyProgressOpticsbeam profiles

Used BeamR and WinCamD to profile the two light sources (ECDL and OPO pump) 

(1) ECDL; profile 19** nm beam after the aspheric lens. I guess we want this beam to be nominally collimated for optimal feedback with the Littrow-configured grating, so I recorded the 1/e^2 waists (x, y) as a function of longitudinal displacement. The result is attached below. Linear fits provide rough estimates for the beam divergences, giving 2.0 mrad along x (parallel to the table) and 1.2 mrad along y (normal to the table) suggesting some astigmatism which is common in high NA aspheric lenses. I inspected the distance from the aspheric lens to the SAF gain chip and measured ~ 2.0 mm (compared to the 1.99 mm working distance specified for this lens with NA=0.71). The SAF1900S specifies a beam divergence angle of 35 deg  (corresponding to NA=0.57), so there is room for improvement by tweaking the aspheric flexure alignment.

(2) NPRO; profile 1064 nm beam at low power (~10 mW) right after the head output. Having 10x more power made things way easier for this as compared to the ECDL, but the method was the same (record 1/e^2 waists as a function of longitudinal displacement). The result is attached below. Linear fits provide rough estimates for the beam divergences, giving 2.1 mrad along x, and 2.1 mrad along y. Here I grabbed the specified divergence of 2.3 mrad from a relatively old manual, and even drew the displaced waist profile (w0 = 160 um) which seemingly fit the profile, but the actual values may be different.

Attachment 1: 2020_11_18_ecdlprofile.png
2020_11_18_ecdlprofile.png
Attachment 2: 2020_11_18_mephistoprofile.png
2020_11_18_mephistoprofile.png
  1866   Mon Nov 23 11:43:26 2020 PacoMiscEquipmentLoanbeam profiler

Shruti took back the beam profilers today AM to Cryo.

 


Shruti: returned to Gabriele's office

Quote:

I placed the two beam profilers with the two laptops and chargers right inside the Crackle lab, as requested by Paco.

 

  1867   Mon Nov 23 11:44:13 2020 PacoMiscGeneralMDT694B python controller

Today entered lab ~ 09:00. Over the weekend I coded a PySerial wrapper for the thorlabs MDT694B single channel piezo controller. I spent some time testing and debugging the code but it now works fine (tested on Linux, python=3.8.6 and PySerial=3.4-4). The wrapper refers to the manual available here. The code is available in the labutils repo

  1869   Tue Nov 24 16:30:59 2020 PacoMiscEquipmentLoanbroadband EOM

Borrowed 1 (new focus) broadband EOM from CTN for temporary use in Crackle (2 um OPO exp)

  1870   Tue Dec 1 18:37:09 2020 PacoDailyProgressOpticsOPO pump steering

Enter lab ~09:20. Today I spent a while looking at the broadband EOM drivers used in CTN (presently optimized for 37 MHz) and installed the preceding steering and power control (half waveplate + pbs) optics. The beam path for the OPO pump beam is now set to 3 inches (note the NPRO head is nominally 4 inch above the table).

  1872   Wed Dec 9 17:47:12 2020 PacoMiscElectronicsquick test of 14.75 MHz RFPD

On Monday, tested a 1998 (Rev. 0) RFPD originally found in Crackle (serial #010). Looks like it was first resonant at 24.493 MHz, but was later tuned for 14.75 MHz. I used the AG4395A network analyzer in CTN following the procedure in the previous ELOG post, splitting R output into the test input of the RFPD. Driving at up to -10dBm, couldn't see any resonant feature in the TF below 150 MHz. Tuning the inductor L1 made no difference. The regulator (U3 and U4 near bottom right in picture below) outputs were nominal.

I borrowed a flat response (DC to 125 MHz) PD from CTN lab (New Focus 1811) along with its power supply for short term use.

Below are some photos of the aformentioned RFPD. I added some kapton to keep dust off the PD.

Attachment 1: rfpd_2.jpg
rfpd_2.jpg
Attachment 2: rfpd_1.jpg
rfpd_1.jpg
Attachment 3: rfpd_0.jpg
rfpd_0.jpg
  1873   Wed Dec 9 18:03:31 2020 PacoDailyProgressGeneralLab organization

In the process of adding a PC/controls, and other related instruments, reorganized items in the lab. Threw out some boxes and stored cabling and unused power dock. Moved the sticky mat and put out large trash bin. Organized electronics rack to which a Sorensen (DCS33-33) power supply was attached. For this, took a 14 AWG wire (should be fine up to 15 A at 115 VAC) and cut plug end. Then connect neutral and live as indicated by the rear of the panel and add chassis ground. Tested DC output voltage of 3 V and it works ok.

There are now two workstations in the lab attached to the same monitor (VGA and DVI ports), and it is ok to ssh from one to the other. They both now have fresh debian 10 installs.

  1874   Fri Dec 11 16:04:36 2020 PacoLab InfrastructureOpticsPPKTP crystals

Two crystals from Raicol arrived. Picked them up from Downs today and inspected them (see photos below). The lengths are nominal (20 mm), they are serialized as 123 and 124, and the ends look like they have the specified (AR) coating. I reached out for Covesion two days ago to track the ovens so we can mount these guys, but have yet to hear back from them.

Attachment 1: raicol_124.jpg
raicol_124.jpg
Attachment 2: raicol_123.jpg
raicol_123.jpg
  1875   Fri Dec 11 17:53:07 2020 PacoDailyProgressElectronicsUPDH box alternative power supply

Today, after struggling to find a 4-pin circular power supply cable for the UPDH box (still interested btw) punched a hole for connec power connector in the back panel and found an appropriate cable. See attached photo. Intended for +- 15 VDC.

Attachment 1: connec_pdhsupply.jpg
connec_pdhsupply.jpg
  1879   Thu Dec 17 11:59:14 2020 PacoMiscEquipmentLoanbeam profiler

Borrow both beam profilers and laptops from WB 264A.

  1880   Thu Dec 17 12:01:54 2020 PacoLab InfrastructureOpticscrystal ovens, clips and controllers

Covesion order arrived, containing 2x

  • Crystal oven (20 mm long) (below)
  • Clips (for mounting crystals) (below)
  • Blank crystal (to press on the ppktp crystal) (below)
  • OC2 oven controller
  • Controller cable and power cable
Attachment 1: covesion_oven_clip_blank.jpg
covesion_oven_clip_blank.jpg
  1883   Wed Dec 23 15:43:01 2020 PacoDailyProgress OPO cavity assembly

Laseroptik optics (4x pairs of cavity mirrors) arrived earlier this week, so I began assembling the input mirror with Noliac (NAC2124) PZT. The (15 mm OD) pzt will sit between a 1" post spacer and the mirror. I applied a thin layer of BT-120-50 (bondatherm) adhesive, which I found in EE shop. From what I gather this adhesive doesn't have softeners (almost doesn't smell) and is a good electrical insulator. The PZT + spacer is sitting below a metallic weight block on the left corner of the table (by the electronics test bench corner), and should finish hardening in a little over 24 hours at room temperature. The PZT was labeled 520 nF (spec. 510 nF).

  1885   Wed Dec 30 09:57:56 2020 PacoDailyProgressOpticsDOPO crystal oven

Assembled first DOPO oven with the crystal. The components (shown below) are:

  • Oven clip
  • Oven
  • ITO crystal spacer
  • PPKTP crystal

The NL crystal sits in the (brass?) clip directly, with the ITO (dummy) crystal pressing it uniformly down. There are no placement references to align the crystal with the oven axis, so this was done very carefully by hand. Once this is roughly straight, the copper arms are fastened in place tight enough to hold everything in place but without excess strain on the NL crystal. The assembly (shown below) is then mounted enclosed in the oven. I put some kapton in place to shield from dust until operation.

Attachment 1: ppktp2.jpg
ppktp2.jpg
Attachment 2: ppktp1.jpg
ppktp1.jpg
  1888   Thu Jan 7 09:44:52 2021 PacoDailyProgressOpticsShaping the OPO cavity mode

Summary of solution number 2 (from previous post). 

After installing the lenses, mirrors and some minor alignment, took the beam profile around the expected minimum waist position (~102" from laser head). The beam profile is astigmatic as can be seen from the plot below (red / blue = x / y), so the mode matching will be suboptimal from the start. 

Taking the geometric mean of the waists (w = sqrt(wx * wy)) we represent our nominal mode and find a min waist of 36.8 um (shaded region in the plot).

The OPO cavity model targets a min waist of 35.5 um (for an optimal Boyd--Klein parameter of ~2.7), but solutions exist with slightly shorter cavities and slightly larger waists which would only compromise the optimal Boyd--Klein parameter to ~2.55 for the sake of better mode matching. I think this is a good place to move out of calculation-land and see how well we can make the cavity work in reality.

Attachment 1: profile_20210106.jpg
profile_20210106.jpg
  1892   Wed Jan 13 17:52:35 2021 PacoDailyProgressOpticsOPO cavity resonance

Observed first resonant transmitted (& reflected) light from the DOPO cavity; the PZT scan was centered at 31 V, at 2 Hz, with an amp. of 1.5 Vpp. To get there, revisited the path's alignment upstream to the last mirror (before the last lens), removing, inspecting, and reinstalling each component. After this, I used the camera at the end of the optical path as a "pinhole" (beam center placeholder) and after inserting each element (mirrors / crystal) checked carefully that the beam was landing straight. Then, patiently scanned various knobs (mirror mounts X/Y/XY, crystal manually) until HOM started resonating. After a bit of further alignment managed to see transmission dips in the FI pickoff. Below are two photos illustrating the current state (way more optimization is needed), as well as the setup viewed from one side (for the scope picture, purple is the ramp, yellow is cavity reflection, green is cavity transmission). Will keep optimizing in the couple next days, all at low power first, and then start cranking the power up to factor in any thermal effects into the optimized cavity.

Attachment 1: dopo_first_resonance.jpg
dopo_first_resonance.jpg
Attachment 2: dopo_sideview.jpg
dopo_sideview.jpg
  1893   Fri Jan 15 10:57:39 2021 PacoLab InfrastructureEquipmentLoanBorrow AG4395A and EOM Driver TF re-tune

See equipment borrowing note here.

Attempting TF measurement for resonant EOM driver, but not having luck reproducing the measurements done recently (Dec-03), so I started debugging the circuit. Both power supply connections (+- 18 VDC) seem nominal. The MAX2470 buffer regulated input is nominal at 5VDC. Looking at MMBT5551 HF transistor, base-emitter voltage is -0.60 VDC (nominal wrt -0.66 V). Using a scope, I feed a single tone (36 MHz, 190 mVpp) and look at the RFmon output and it looks ok (gain ~ 1). I changed the RFmon SMA cable and that seemed to do the trick... Bad cable (now in trash) stole my morning.

Tune EOM driver resonance to 35.993 MHz (shown below for reference).

Attachment 1: EOMDriver_TF_Inp_to_RFMon_CloseUp_15-01-2021_160402.pdf
EOMDriver_TF_Inp_to_RFMon_CloseUp_15-01-2021_160402.pdf
Attachment 2: EOMDriver_TF_Inp_to_RFMon_Wide_15-01-2021_151039.pdf
EOMDriver_TF_Inp_to_RFMon_Wide_15-01-2021_151039.pdf
  1894   Fri Jan 15 17:21:53 2021 PacoDailyProgressElectronicsRFPD TF

Record TF for RFPD SN09, resonant at 36 MHz, using the exact procedure as with EOM Resonant Driver.

Attachment 1: RFPD009_TF_Inp_to_RFMon_Wide_15-01-2021_172008.pdf
RFPD009_TF_Inp_to_RFMon_Wide_15-01-2021_172008.pdf
  1897   Tue Jan 26 11:47:12 2021 PacoDailyProgressGenerallow quality PDH error signal

After getting what looked like a decent cavity reflection signal, installed RFPD yesterday. For this, removed the lens that was right before the PD because the RFPD area is large enough, but keep ND filter in place. Powered with +- 18 VDC and monitor DC out on the scope, and RF out is sent to the IF of the mixer in the PDH box. For the LO, split the Marconi RF output and connected the demodulated signal into Ch2 of the scope in hopes that there was an error signal.

A hint of the error signal is present (blue trace below), although deeply buried in line noise (and harmonics up to ~180 Hz) so there really are two things to optimize now -->

  1. Line noise (hunting for ground loops or equipment, e.g. power supplies, analyze LO spectrum before/after splitters, mixers, etc...)
  2. Mode matching (this was the first reaction, as improving the cav refl SNR by means of mode matching makes a better pdh err signal)

Other things attempted so far -->

  • Switched mixers, splitter, and RF cables
  • Bypass the phase shifter completely
  • Scan LO phase
  • Floated RFPD power supply
  • Floated PDH box power supply (really only affecting the phase shifter if anything, though unlikely to matter at this point)
Attachment 1: poor_PDH_err.jpg
poor_PDH_err.jpg
  1899   Tue Feb 2 17:39:52 2021 PacoDailyProgressOpticsre: Figuring out how much astigmatism is hurting us

Motivated in part by the conclusions below, improved estimated mode matching efficiency from a poor 13% at the beginning of day to 48% (estimated using the reflection signal levels from the rfpd). What helped was walking the beam with the last two mirrors, and then scanning the cavity output coupler around to center the resonant mode which at this point seems optimal. This process was tedious, but effective apparently.

The distance between the two mirrors is ~ 45 mm which slightly undershoots the planned 47.5 mm which could limit the achievable 100% in simulation-land, but I'm moving on for now, hoping the lock will bump it up enough for the OPO threshold to be within our pump power range.

Quote:
  • Astigmatism should not be hurting us significantly.
  • The mode matching in principle can be improved in the experiment
  1900   Thu Feb 4 16:46:06 2021 PacoDailyProgressOpticsOPO cavity lock

Demodulation stage

Update on demod. for OPO cavity lock. Last related elog entry described prevalence of <= -77 dBm of odd line noise harmonics (60, 180...) Hz, along with poor SNR PDH error signal. First attachment is a drawing of the current RF connections. Upon completing list of suggested actions from this post, the difference was mostly made by looking at RFPD RF out power before mixer < -40 dBm. This was no good, so after realizing that the OD = 3 nd filter before RFPD was only allowing 80 uW of a nominally reflected ~25 mW, swapped the ND filter with HWP + PBS for adjustable power splitting. Then, a healthier  -10dBm made it into the mixer and SNR improved considerably (see second attachment). Upon closer examination of err signal, low freq. sinusoidal modulation sat on top of it suggesting slightly off-resonant demodulation so finely adjusted the (Marconi) LO frequency from 36.000 MHz --> 35.999828 MHz until the error signal had a good enough shape (see third attachment below).

Lock

First attempt at cavity lock was done with ~46% mode matching efficiency and max. modulation depth (estimated ~0.21) on the EOM. The loop is achieved using UPDH box (v3) which I stole from CTN lab. Upon connecting all the inputs, scanning the phase shifter without making much of a difference, and enabling the lock, saw a stabler higher order mode on the cavity transmission which is nice. The natural follow up of scanning the PZT driver (i.e. as an offset) and re-engaging the lock resulted in what I can only describe as a "visit to the dentist", where the cavity PZT (on the output coupler) was resonating quite loudly (!!). After looking at the output monitor of UPDH box with engaged lock on SR785 an ~ 8 kHz peak explains the noise as an audible mechanical resonance. Adjusting the servo gain finely tunes it out a bit, and adding an SR560 in line before the PZT driver unit greatly helps, but changes the overall loop gain and the lock becomes unstable...  Current efforts are therefore geared towards improving the pdh loop, for which an option is to bypass the thorlabs MDT694 HV piezo driver and directly connect the UPDH output to PZT (which it may be meant to directly drive) and use slow temp. control on pump laser to approach the lock point. Another option, involving way more time, would be to *not* use UPDH box at all and implement a digital feedback loop + filter with the Red Pitaya. Perhaps the pragmatic action is to get the analog solution working and develop digital solution on the side.

Attachment 1: rf_diagram.png
rf_diagram.png
Attachment 2: offresonantpdherr.jpg
offresonantpdherr.jpg
Attachment 3: pdherrorsig.png
pdherrorsig.png
  1902   Wed Feb 17 11:56:48 2021 PacoLab InfrastructureElectronicsUPDH box zero model and SR560 "lock"

UPDHv3 box (serial 17142) is bogus. While retrieving values of some of the components to plug into working zero model, saw the VGA stage is bypassed by a previously unnoticed hack. Verified this by taking TF and not seeing any changes with respect to the gain knob (shown below are zero's model TFs suggesting a tunable UGF from ~ 10 Hz to 1 kHz), so this box is not good for a standalone servo.

As suggested a few meetings ago, made a quick and dirty lock using a single SR560 and took measurement of something* CLTF (SR560 gain = 10) below. New goal is to find a decent replacement, for which decided to use RedPitaya's python API "pyRPL". Just using the GUI out of the box can also lock the cavity relatively quickly but neither method results in longer than 1 minute lock... so took one step back to polish the pdh error signal.

* Something = Use SR785 TF measurement with source on Ch1, and to B input in SR560. The SR560 in (A-B) mode, and demodulated signal connected to A. The loop was closed with the SR560 output driving the PZT, and Ch2 of SR785. Wouldn't call this CLTF...

Attachment 1: updhv3_VGA_gain.pdf
updhv3_VGA_gain.pdf
Attachment 2: SR560_OLTFSR785_17-02-2021_164500.pdf
SR560_OLTFSR785_17-02-2021_164500.pdf
  1903   Thu Feb 18 09:39:01 2021 PacoDailyProgressElectronicsPDH error signal misbehaving

Error signal

Upon closer inspection the error signal seems to vary quite significantly on the scope (scanning @ 2 Hz), sometimes completely flipping its sign even though it always triggers on the same side of the ramp (see attachment for video, along with some neck excersise).

This might be the same behaviour from before, whereby the demodulated signal might still be "riding" a low-freq componen which can't be compensated with the LO (Marconi's carrier resolution = 1 Hz). Using the 10 MHz external Rb reference doesn't change anything. It seems that even with the coupler, reflections may be entering the mixer... 

Adding a LP filter (BLP-1.9+) right at the mixer output solves this for good. Even using 36 MHz LO vs anything else doesn't make a difference so this explains the previous issue. Moving back to lock using stable err signal.

For reference, the LO carrier is set to 36.000 MHz, +7 dBm (so the EOM is driven with an estimated +30 dBm well below the saturation or damage threshold +40 dBm).

DOPO locked

Achieved a good lock for pretty much all of the afternoon today. The laser ran at 937 mA current, the optimal gain on SR560 was found to be 50, with a LP cutoff at 300 Hz (12 dB/oct rolldown). The 300 Hz cutoff supresses most of the nasty 8 kHz noise (and harmonics) which I can hear with enough gain. Source still to be determined.

Attachment 1: misbehaving_pdh.mp4
  1904   Wed Feb 24 17:42:49 2021 PacoDailyProgressGeneralDOPO locking and SHG

Locking update

The plan during these past few days has been to have fast control loop of the cavity (locked to laser using PZT, which succeeded using SR560s), and slow control loop where the laser temp. actuator is fed back the integrated PZT input to follow the long term cavity drift. For that, have been messing around with the high-level (GUI) API of PyRPL, with basically no success. In fact currently the RedPitaya cannot even replace the SR560 fast controls, which probably has to do with the +- 1 Volt limits on the RP input/output.

Another issue is that any loop gain depends on the REFL power, which will be at some point slowly ramped up to cross the OPO operating threshold, and while there is a (PBS + HWP) knob on how much light is hitting the RFPD, the lock is not yet good enough to keep up with the slow human action.

First light from nonlinear conversion

WIth the cavity locked, and under ~ 220 mW of pump (right before the cavity, i.e. 1.3 Amps of current on the driver), noticed a tiny green dot coming from within the crystal oven. This is pretty great news in terms of phase matching, but not necessarily so in terms of the right parametric conversion process (understanding is that SHG is easier to attain even with single pass). See tiny green spot as caught using phone camera in the attachment.

Attachment 1: shg.jpg
shg.jpg
  1905   Thu Feb 25 10:28:07 2021 PacoDailyProgressOpticsDOPO lock endurance

Test long term stability of the DOPO cavity lock; The cavity remained resonant overnight (start ~ 8 PM yesterday) and lost around 11 AM today. It might be good enough to approach lock point manually using laser temp. control and then engage the fast loop. In any case, today will set up an acromag channel for this. Configured "XT1541-2um-SlowDAC" to 10.0.1.47

  1906   Tue Mar 9 19:21:38 2021 PacoMiscOpticsDOPO cavity pole

- Noticed that the cavity transmission peaks @ 1064 nm were much wider than originally estimated by the dopo cavity design notebook suggesting a lower Finesse. So using the PDH error signal, and knowing the EOM sidebands are at 36 MHz estimated the current DOPO cavity linewidth to be 19.5 MHz, well in excess of the target 10.4 MHz.

- Updated the crystal AR coating specs from Raicol (R < 0.3% @ 1064/2128), but more importantly, I included the absorption coefficient of KTP, alpha=0.005/cm (often quoted as < 0.01 / cm) into the roundtrip loss and the design now gives 17.97 MHz. So, given the uncertainty in the absorption coefficient of the NL crystal, and all the coatings in the experiment, this adjustment might be enough to explain this observation.

  1907   Tue Mar 30 15:18:06 2021 PacoLab InfrastructureEquipmentLoan2um CCD borrowed

With Aidan's assistance, I borrowed

  • WiDy SWIR camera (Pembroke WiDy SWIR 640U-A) from the QIL (Attachment 1)
  • Heimann thermopile sensor (HTPA80x64d) with microUSB-A and ethernet cables from the Adaptive optics lab (Attachment 2)

for ~ 2 um imaging in the Crackle lab.

Attachment 1: IMG_20210330_151046.jpg
IMG_20210330_151046.jpg
Attachment 2: IMG_20210330_150958.jpg
IMG_20210330_150958.jpg
  1908   Wed Apr 14 16:49:30 2021 PacoMiscOptomechanicsDOPO mount v2

Drew some new mounting scheme for the DOPO cavity; main revisions with respect to the current mount are -->

  • Side mounts for both mirrors (instead of vertical)
  • Both mirror mounts are the same (3-axis polaris K1) so both mirrors need to be attached properly
  • Improved access to align crystal using newport 9031 (6 axis displacement mount), which is crucial to make the DOPO fields co-resonant

Attachment 1 illustrates the design; shows three views of the same assembly.

Concerns: mechanical noise from side mounted mirrors ... for this, there could be a solid piece which makes a rigid connection between the two mirrors (that's why they are upside down) and perhaps between the two tall posts (so S-shaped as viewed from the top)? Still working on this.

Attachment 1: dopo_mount_v2.pdf
dopo_mount_v2.pdf dopo_mount_v2.pdf dopo_mount_v2.pdf
  1909   Tue May 18 10:28:50 2021 PacoLab InfrastructureEquipmentLoanheimann sensor update

Heimann (HTPA80x64d) thermopile array;

- First test to grab frames was done in my personal Win10 machine, with no success. Either I was unable to configure the server correctly, or the software "ArraySoft" is not supported in Win10. Upon contacting Heimann, I received instructions to update to a newer version but was warned that it's just a new GUI, nothing really changed from v1 --> v2. So didn't even bother.

- Instead, wrote a simple python-socket UDP server to catch the video stream. Most trouble happened when using temperature mode (command "K"). The client streams a bunch of zeros... My guess is that this unit does not have an internal temperature calibration, and one could in principle be uploaded but we probably don't care. Streaming in raw voltage mode (command "t") works well, as shown by the sample frame shown in Attachment 1.

- After recovering the CTN Win7 laptop from Radhika, I gave "ArraySoft" another change just to know the frames I was getting in python were not bogus. For this I pointed a 532 nm laser pointer straight to the sensor and got an image shown in Attachment 2. The key difference is the processing of the video stream. Attachment 1 is a single frame, while Attachment 2 is the average of 30 frames with no offsets present. 

- Another issue present during this task was a faulty USB connection. Sometimes moving the sensor around would interrupt the stream (power lost). I carefully removed the case and exposed the TO-39 package and surrounding electronics to inspect and search possible failures but after seeing none, I swaped the USB power cable with my portable battery charger and had a more robust operation... So I dumped the old USB cable, and will get a new one.

- Since this one was borrowed from TCS lab, I placed an order for another one which will be set up permanently in the lab. Hopefully this will be enough for the OSA.

Attachment 1: no_light.png
no_light.png
Attachment 2: light.png
light.png
  1910   Wed May 19 09:25:34 2021 PacoNoise HuntingDOPO316 Hz noise

[Paco]

- Have been investigating 316 Hz noise in the control signal for the DOPO lock. Here is a list of some things that have been ruled out, mostly electrical:

  - EOM power supply --> noise still present in DOPO transmission
  - RFPD DC out --> no funky ground loops with scope (also looking at demod signal in different channel), noise still visible in transmission
  - RFPD power supply --> noise still visible in transmission...
  - Pump laser intensity (upstream pickoff) --> not a great test because pickoff optics are also on the optical table..
  - 2 x SR560s --> No effect after bypassing
  - Marconi --> same result as with anything in the loop after RFPD demod

- Things left to rule out:
  
  - Fume hood exhaust fan ** highly suspected, my phone's own cheap-o microphone power spectrum shows peaks at 316.5 Hz (!) when near the exhaust fan
  - NPRO temp controller fan --> phone audio spectrum shows line noise (60 Hz) mostly, and also 188 Hz... need to test further independently of the fume hood...

In ruling out the 6-axis translation mount on the DOPO cavity, I removed the PPKTP crystal + oven temporarily but still saw the noise. Since the resonator was no longer stable without the crystal, I needed to bring the mirrors closer and realign the output coupler from scratch. 

Restored DOPO cavity with crystal, alignment. MM efficiency ~ 35%... still optimizable.

  1912   Wed Jun 2 18:37:09 2021 PacoSummaryCrackleVent crackle experiment

[Paco, Anchal, Ian, Yehonathan]

Today, in preparation for the optical table to come, we vented the big crackle jar using the vent valve near the gauge. We detached the roughing pump and covered the bellows and pump connections with clean aluminum foil. We then proceeded to move several instruments, including some other pumps, a compressor, a couple of power supplies, power cords, the HeNe laser, misc. material blocks, and boxes with bearings and springs into the cage. The next operation required for us to displace the table is to lift the jar from the top and carefully dismantle the Crackle experiment and store it away somewhere.

Questions: where to store mostly?

  1913   Thu Jun 10 09:59:52 2021 PacoLab InfrastructureDOPODisassembly for new optical table

Today the DOPO v0 got disassembled to make way for the optical table swap. Most components have been stored in the white cabinet's bottom panel.

Attachment 1: IMG_20210610_092713.jpg
IMG_20210610_092713.jpg
  1914   Wed Jul 7 13:05:07 2021 PacoDailyProgress1418 nm AUX ECDLNew aspheric flexures

[Radhika, Paco]

Today we fired up the 1418 nm ECDL and attempted initial adjustment of the aspheric lens. The design follows D2100115 which is a copy of the 2 um ECDL so we just changed the diode, the grating flexure angle, and the aspheric + flexure assembly and we are good to go. Radhika removed the 1900 nm aspheric flexure and we mounted the new collimating assembly which uses a f=3.1 mm (NA = 0.69) lens. At the beginning we had to feed over 300 mA of current to be able to see a beam (which was still diverging) so we had to free the flexure completely and align by hand to find the nominal positioning for a collimated beam. We lost a 2-56 screw in the process, but the final assembly is still in progress. The plan to follow is:

  • Finalize flexure alignment
  • Insert grating
  • Characterize ECDL emission
  1915   Fri Jul 9 11:40:42 2021 PacoDailyProgress1418 nm AUX ECDLNew aspheric flexures

[Radhika, Paco]

We tweaked the flexure alignment until we had a nominally collimated beam (~2 mW @ 250 mA of diode current) through the output aperture in the ECDL housing. We noted that the collimated beam is off-centered on that circular aperture along the horizontal (yaw) angle. After this, Radhika installed the ECDL grating and we hooked up the fiber output onto a InGaAs PD to monitor the power output. We tweaked the alignment of the grating (mostly yaw) to try and see a change in the power output to indicate optical gain in the diode, but saw no changes. We observed a change in the PD photocurrent as a function of the diode current in the absence of the grating (no optical feedback) which is indicative of ASE. We measured this level to be ~ 140 mV at 200 mA of current; with no observed threshold. In conclusion, we still need to refine our grating alignment to provide gain on the diode and observe lasing at the nominal 1450 nm wavelength.

Attachment 1: IMG_1773.jpeg
IMG_1773.jpeg
  1916   Wed Jul 14 12:21:08 2021 PacoDailyProgress1418 nm AUX ECDLECDL lases... and MZ locked mid-fringe

[Paco]

Worked for a few hours to get the aspheric properly aligned. The procedure is quite finnicky, as the four 2-56 flexure screws have too much game and the fine thread setscrew that adds tension is too constrained. Anyways, it generally goes like this:

  1. With the grating out of the way, and the 2-56 screws slightly loose, move the aspheric flexure until a collimated beam (as round as possible) exits the centered round aperture in front of the SAF chip.
  2. Very carefully tighten the fine threaded setscrew in place to register the aspheric alignment.
  3. Check that the desired beam hasn't changed
  4. Insert grating careful not to touch the aspheric flexure (again, the mechanical registration is not great!)
  5. Manually rotate the grating while monitoring the power at the fiber output until non-ASE light appears. This is quite sensitive to alignment/angle and the better the mode is matched back into the fiber, the easier it is to find the right position.
  6. Fix the grating flexure.
  7. Slightly tweak the grating mirror knobs by hand to maximize said power (careful to avoid saturating PD)

After this, I installed a second amplified InGaAs detector, hooked up the unbalanced MZ beamsplitter output into the two PDs, adjusted the gains to equalize the output voltages and then hooked the two signals to the A and B inputs of an SR560 in "A-B" mode. The output (gain 1) was good enough to feed back in the HV PZT amplifier input modulation which allowed the MZ to lock mid-fringe. The lock is rough, as the balanced homodyne signal retains a tiny offset due to imperfect balancing... Attachment 1 shows the setup, including a typical scope trace after coarse current tuning (Ch1 and Ch2 in yellow and blue represent the photocurrents in the two MZ ports in the absence of feedback).

Indeed, scanning the nominal PZT voltage broke the lock, potentially after crossing a mode hopping region.

Tasks to be done:

  • Power characterization, including RIN, emission vs current.
  • Emission spectrum characterization; using the homemade spectrograph (grating + lens + camera) as the PZT is scanned
  • MZ feedback loop characterization, including optimizing the balancing stage
  • Self-homodyne phase noise spectrum

Next, as was suggested during yesterday's group meeting, we will transition into a self-heterodyne setup (with an AOM which I have yet to check out in the QIL).

Attachment 1: selfhomodyne_1418.jpg
selfhomodyne_1418.jpg
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