It is ~1mm from the zero of the micrometer readings. See attached photos from the 1st OMC build.

In the end, we'll use the FSR measurement to finely adjust the cavity length, but let's try to make them as symmetric as possible.
i.e. if you need 0.4mm shrink of the cavity roundtrip length, move CM1 and CM2 by 0.1mm each.

7/21/23

Fringes were observed at the optic-breadboard interface. This was eliminated by cleaning the interface with IPA while making sure the coated surfaces are untouched.  

What's the nominal position of the screws for the curved mirror?

Beam spots centered on curved mirror 1 and 2 and we're trying to merge spots resulting from multiple beam circulation through the cavity, this will result in resonance. 

Nice measurement. This result suggests that the fiber mode is supposed to be matched to the OMC cavity by 99.8% at z0=0.358 m. Note that the OMCmode has a waist radius of 0.4896 mm and 0.4905 mm for the horizontal and vertical modes, respectively.

In reality, the fiber mode contains higher-order HG modes. Therefore the actual mode matching will be limited to ~98%.

Below are the gluesheets for the first four PZT subassembly bonding.

[Camille, Thejas, Stephen]

Effort was made to coarsely align the laser beam into the caivty

FM1: #17 (wedge angle: 0.4788 deg, deviaiton from perp: 5.7 arcsec acute)

FM2: #11 (wedge angle: 0.4856 deg, deviation from perp.: 6.3 arcsec obtuse)

CM1: #30 

CM2: #14

Beam profile of the input beam was measured at it's beam waist, this is to ensure the input beam waist matches the cavity beam waist (mode-matching) - ref attachement 2

w_0x: 456.47032902662903 +/- 1.4466927709703827 um
z_0x: 0.35828846919253937 +/- 0.008323313108283267 m

w_0y: 495.1490367020396 +/- 1.917471337851956 um
z_0y: 0.3568228323785801 +/- 0.01418698585815903 m

The larger y wasit size is realized to be due to a pitch angle of the beam. But the relevance if this exercise is to determine the position of the beam waist so that the transport fixture can be positioned such that there is good matching. 

The error in beam profiler measuremetns is between 4-6 um for the data points.

The modematching lens breadboard was translated along the direction of the beam to make available enough room for the transport fixture's placement such that the input beam waist falls at the center of the cavity. 

We aligned the bonding template onto the glass braedboard. This was done with the help of a vernier caliper and adjusting teh peek screws at the edge of the templates to make sure that the gap between the breadboard and template edges are equal for each pair of opposite sides.

Pens like Sharpie are not recommended to be used for CLASS B parts.

[Camille, Thejas]

The A+ OMC transport fixture and optic breadboard was transported to the OMC lab. They were cleaned thouroughly using high grade IPA red wipes after using a nitrogen gun to blow away contaminants (carefully away from rest of the optics on the bench). The breadboard was examined under halogen light for contaminants from the lens tissue as it can shed fibres that's hard to see under normal lighting. 

Results for PZT reliability test:
Batch 3: SN31, SN32, SN35, SN40, SN45

This reliability test was performed using the procedure described in https://nodus.ligo.caltech.edu:8081/OMC_Lab/?mode=full&reverse=0&reverse=1&npp=50&Subject=Summary+of+PZT+reliability+test+procedure

*Note: The drive function used here was a triangle function (not sine function).

[Camille, Thejas]

Post sub-assembly bonding of CM : Madeline will post a separate update on the Oven temperature profile.

The subassemblies were taken out of the oven. The bonding fixture plates were carefully taken apart, sub-assembly #1 involving curved mirror #30 required a large amount of force with a tweezer to pull the fixture plates apart from the subassembly.  

All the other subassemblies were easy to separate from the bonding fixtrue. 

Excess bond was cleaned off of the mounting prism surface carefully.

The subassemblies were then packed carefully to be transported to the OMC lab west bridge sub basement.

The transport 

[Camille, Thejas, Stephen]

Results for PZT reliability tests:

Batch 1: SN37, SN38, SN39, SN44
Batch 2: SN41, SN42, SN43, SN46, SN47, SN48

The reliability tests were performed using the procedure described in https://nodus.ligo.caltech.edu:8081/OMC_Lab/?mode=full&reverse=0&reverse=1&npp=50&Subject=Summary+of+PZT+reliability+test+procedure

[2023.07.13 - Stephen, Camille, Thejas, Maria]

We bonded Curved Mirror assemblies today. Some notes about this log entry:

• Thejas will post a log discussing matching.
• This log hosts a subset of the photos posted to the A+ OMC photo dump.
• The results of the bonding activities (including photos of complete assemblies, comments on bonding fixture take-apart, and assesment of bonding) will be discussed in an upcoming log

The bonding procedure E1300201-v1 section 6.2 was followed, with the following additions:

• PZT surfaces and leads were wiped with IPA. (Attachment 1)
• Tombstone surfaces were sprayed with Top Gun and then wiped with IPA. (Attachment 2)
• Curved mirror optical surfaces S1 and S2 were sprayed with Top Gun.
• Curved mirror barrel was sprayed with Top Gun and then wiped with IPA.
  • This should have been with acetone per E1100439-v7 "Diagnostic Optics, In Vacuum, without ground glass, superpolished" but we did not find lens tissue and made a compromise.
• Two styles of transparent measurement template were constructed, and the intended optic fiducial location was marked on the PEEK bonding ficture plate. (Attachment 3)
• A small dot of First Contact had been added to the S1 surface of each curved mirror during characterization. This dot had to be removed by gentle scraping with the plastic surface of a cleanroom swab. (Attachment 4)
• The least count of the scale we were using was 0.5g (when I started, I didn't notice, and thought it was 0.1g). As a result, we measured *just a bit more than* 7.5 g of epoxy and *just a bit less than* 8.0 g of epoxy + spheres. Not ideal. Calibration with 300g is shown. (Attachment 5)

The remaining images and comments simply present an abbreviated log of the bonding activities.

• Epoxy was not expired! (Attachment 6)
• The curing test went well - the epoxy cracked very dramatically. (Attachment 7)
• Bonding of the first PZT and Curved Mirror seemed to go pretty well. (Attachment 8-10)
• Some new recruits got their hands dirty! (Attachment 11)
• Four assemblies were prepared (Attachment 12) and loaded into the oven (transported there with foil) (Attachment 13).
• The run was started (Attachment 14), the soak started on time (Attachment 15), and the soak ended on time (Attachment 16).
  • In-person check-in on ABO A controller software at ~3 hours after run start and ~5.5 hours after run start.

[2023.07.13]

The attached table includes the characterization values used to inform the matches for the first four units, Curved Mirror Assy Batch 1.

Thejas prioritized the matches using these insights. Some notes:

• Only PZTs which were listed in the "DC Response after burn-in" column were available for selection.
• The "Corrected Length to Angle" column includes the after burn-in DC Response.
• The script-generated value in the "Length to Angle" column is using the before burn-in DC Response.

I'm planning to update this log eventually with the script and with the report plots showing the raw data and calculations.

We had missing digital caliper from the clean room. As it is an essential component, I have ordered a replacement.

Belated entry: OMC(004) TMS measurement with the PZT voltages scanned (Jun 12/15, 2023)

Belated entry: OMC(004) PZT Slow scan / freq response measurements (May 10/11/17, 2023)

PZT DC scan measurement showed that CM1 had a significantly larger response than the usual PZT responses, and CM2 has the one significantly less. The measurements were repeated and the same result was confirmed.

 Curiously enough, the AC response didn't show a significant difference between the two PZT responses.
Further investigation showed that CM2 shows a similar response to CM1 at low voltage, but has a reduction of the response at high V (like >100V).

So there is something strange with CM2.

Meanwhile, CM1 actuation shows much larger angular coupling and also increased cavity loss.
Therefore, CM1 should be used for the shutter function, and CM2 for the OMC servo.

Belated entry: OMC(004) Spot positions (Jun 15, 2023)

Photographs of the spot positions on the cavity mirrors and the DCPDs/QPDs as well as the reflected beams towards the beamdumps.

Belated entry: OMC(004) FSR / Finesse measurement (Jun 13th, 2023)

RFAM Injection (Attachment 1)

FSR: 264.7939 +/- 0.0004 [MHz]
Cavity roundtrip length: 1.132173 +/- 0.000002 [m]
Finesse: 381.3 +/- 0.4

Note that the finesse still looks lower than expected from the transmission.

Belated entry: OMC(004) FSR / Finesse measurement (May 3rd, 2023)

1) FSR measurement with offset locking (Attachment 1)
FSR: 264.8003 +/- 0.0007 [MHz]
Cavity roundtrip length: 1.132146 +/- 0.000003 [m]

2) RFAM Injection (Attachment 2)

• Placed a PBS before the OMC
• Placed an HWP before the above PBS
• HWP before the EOM was rotated

FSR: 264.794 +/- 0.001 [MHz]
Cavity roundtrip length: 1.132174 +/- 0.000005 [m]
Finesse: 369 +/- 1

Note that the finesse looks lower than expected from the transmission.

[Camille, Thejas]

The optics table in OMC lab was cleaned up, cameras and photodiodes used to measure the reflected and transmitted beam were unmounted to make space for the new cavity. The input beam for the new cavity is injected from the short side (unlike the long side previously) of the breadboard. A 45deg mirror was mounted to redirect the beam. Next step: Cavity assembly 

[Camille, Thejas, Stephen]

To test the reliability of the PZTs, they were driven for 10^7 cycles. (At 100Hz, this is ~28 hours.) The drive function was a 100Hz sine wave with peak-to-peak amplitude of ~100V. The drive function was monitored using an oscilloscope and recorded at the start of the test. A thermal imaging camera was used to record the temperature of each PZT at the start of the drive and at ~10 minute intervals during the first hour of the drive. The temperatures of the PZTs are expected to rise slightly (1 or 2 degC above ambient) and then level off during the first hour or so.
At the end of the drive (10^7 cycles), the temperature of each PZT is recorded again and the drive function on the oscilloscope is also recorded to verify that the peak-to-peak amplitude did not change.

[Camille, Thejas, Stephen]

The DC response of the PZT was measured using the following setup (pictures attached):
The output from a HeNe laser was transmitted through two lenses forming a beam reducer, giving us a beam size of 0.34mm. The PZT was placed on a labjack and a 62g washer was placed on top of the PZT. The HeNe beam grazes the top of the washer and the beam is monitored by a photodiode. The labjack height is adjusted so that the PZT stack clips half of the beam signal. 
In order to avoid scatter as the beam grazes the top surface of the washer, an extra layer of kapton tape was placed on one side of the bottom of the washer, giving it a slight tilt so that the beam is clipped by the washer at the front surface of the washer (surface closest to beam source).
The PZT was driven from 0 to 150V at 0.5Hz using a triangle function. The drive function and the photodiode response was recorded using a spectrum analyzer.
The DC resposne was measured twice for each PZT: before the reliability test and again after the reliability test.

Calibration of the DC response measurement:
The setup was calibrated using a height gauge with a dial indicator to monitor the labjack height. (A PZT was not needed for the calibration; only the labjack and the washer.) The labjack was adjusted so that its height is such that the entire beam just passes over the top and the photodiode response was recorded.
The labjack height was increased in 10um increments, with the photodiode response recorded at each increment. The height values were plotted against the photodiode response values. The slope of this line was used to convert the photodiode response from mV to um.

OMC (004) + the transport fixture was transported to Downs 227 with the boxes for OMC cabling hardware and DCPD/QPD connector parts.

Optical assembly/testing of OMC (004) completed
- OMC (004) with the transport fixture was wrapped and moved to Downs 227 together with the boxes for OMC cabling hardware and DCPD/QPD connector parts.
- The table was cleared for building the O5 OMCs.

QPD#              QPD1       QPD2
Housing#          #008       #009
Diode#            #62        #70
Shim              2.50mm 05  0.75mm 08   (see D1201467)
-------------------------------------
Power Incident     76.5 uW   71.5 uW
Sum Out            49.0 mV   50.2 mV
Vertical Out      -16.0 mV    8.2 mV
Horizontal Out    - 2.4 mV   -3.6 mV
SEG1              - 8.2 mV  -16.2 mV
SEG2              - 8.0 mV  -13.0 mV
SEG3              -15.1 mV  - 9.5 mV
SEG4              -17.4 mV  -11.5 mV
-------------------------------------
Spot position X   + 8   um  +33   um  (positive = more power on SEG1 and SEG4)
Spot position Y   +81   um  -52   um  (positive = more power on SEG3 and SEG4)
-------------------------------------
Responsivity[A/W] 0.64      0.70
Q.E.              0.75      0.82
-------------------------------------

Arrangement of the segments
View from the beam
/ 2 | 1 X
|---+---|
\ 3 | 4 /

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

I(w,x,y) = Exp[-2 (x^2 + y^2)/w^2]/(Pi w^2/2)

(SEG_A+SEG_B-SEG_C-SEG_D)/(SEG_A+SEG_B+SEG_C+SEG_D) = Erf[sqrt(2) d/w]

d: distance of the spot from the center
w: beam width

Work log for June 14, 2023

• Selected QPDs from the stock: QPD#62 for QPD1 and QPD#70 for QPD2 were selected from the QPD stock T1200063.
• The legs of the QPDs were trimmed so that the cable could completely flush with the mount.
• A test PD (Excelitas) was mounted on a DCPD housing.
• They are ready for installation and testing.

A+ OMC Build efforts ongoing or completed in the last two weeks:

•  PZT lead onboard strain relief (D2000172)
  • Some more discussion in A+ SUS calls - PEEK material callout is to be updated in v2, Don is handling this.
  • Looking forward to timeline update in coming week
• Rework of Helicoil holes
  • Don's C&B Ticket is being processed by Maty, will go for bake next week - request/1835
• PZT characterization (ref. T1500060-v2 - PZT Testing Section 2.3.2)
  • DC Response measurement - no new data collection.
    • 5 articles need to be recharacterized (after soldering rework).
    • Code for quantitative results is 90% complete, still debugging (WIP).
  • Lab move to Downs 320 - updated setup logged in OMC_Lab/545.
    • DC Response setup has not been rebuilt yet, but will need to be for more testing after solder repairs and/or reliability testing.
    • Oplev setup for Length to Angle measurement is operational.
  • Length to Angle measurement - lots of setup, refinement, and growing pains toward data collection.
    • 11 PZTs measured, just like DC Response (5 articles requiring solder rework)
• Component matching for Curved Mirror Subassembly
  • Matching calculations first draft (implemented manually) was supplied by Thejas.
  • EP30-2 batch (2x 50mL syringes) arrived, plenty for all curved mirror subassembly bonding and first OMC unit bonding, at least.

We have the following plans for the week ahead:

• Complete PZT DC Response and Length to Angle data analysis. (WIP)
  • We have been making manual comparisons / data quality checks throughout data collection.
  • Comparisons with past results from aLIGO build have suggested that our results are reasonable.
• Finish solder rework of PZT leads. (had been planned, solder hasn't arrived yet)
• Set up shadow sensor in new lab for future DC Response measurements.
• Set up PZT reliability testing (burn-in test). (ref. T1500060-v2 - PZT Testing Section 2.3.4)
• Resume transport fixture build effort at 40m Bake Lab.
  • Summer student Maria will be heavily involved.
• Insert helicoils in Class A plasma-sprayed DCPD housings

We have the following near future plans:

• Bond first batch of Curved Mirror Subassemblies.
• Conduct walkthrough of OMC lab with build in mind.
  • Transport Class A components that are ready for build to OMC cleanroom.
• Follow updates of top level assy D2000172, and send finalized assy for 3D printing of mockup unit.
  • Make sure that strain relief components are all on order and we know the timeline.

The op-lev setup was modified slightly (picture attached). The He-Ne laser was replaced with one with a lower divergence angle. The stage that the PZT/mirror stack sits on was replaced with a setup that allows for tip/tilt adjustements. The PZTs were driven from 0 to ~92V at 0.5Hz. The total path length from the PZT stack to the QPD is ~1.6m.
The following PZTs have been measured in the current oplev setup: 37, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48.

Oplev setup was built: arm length about 2 m 

As the PZT 44 was actuated with a drive voltage 0-150 V signal was observed on the Spectrum Analyser.

The signal on the top and bottom are X and Y signals from the QPD. This will analyzed and other PZTs will undergo similar measurement. 

A+ OMC Build efforts ongoing or completed this week:

•  PZT lead onboard strain relief (D2000172)
  • Brief discussion in A+ SUS call - PEEK material callout is to be updated in v2, Don is handling this.
  • v1 drawings posted and UK team out for production, with Angus already communicating PEEK grade requirement to vendor during procurement process.
  • DCN is WIP per Russell.
• Rework of Helicoil holes
  • D1201278 and D1300498 were already Class A, but we recognized that the hole callouts were not consistent with current LIGO notation, and we decided to make sure that these holes were in a good state.
  • Don and I chased the holes with taps (gloves on, but in a dirty area)
  • Don created a C&B Ticket request/1835
• PZT characterization (ref. T1500060-v2 - PZT Testing Section 2.3.2)
  • DC Response measurement - see OMC_Lab/542 for initial findings.
    • 11 units appear to be good, 2 units appear to be damaged, 5 units need to be recharacterized (after soldering rework).
    • Quantitative results WIP.
  • Lab move to Downs 320 - this work needs to be logged.
    • DC Response setup updated, beam focusing was changed.
    • Oplev setup for Length to Angle measurement constructed for the first time.
• Component matching for Curved Mirror Subassembly
  • Continued work on algorithm-based matching code
  • Discussion with Gari and Calum - we will move toward manual matching to expedite

We have the following plans for the week ahead:

• Complete PZT DC Response data analysis.
• Finish solder rework of PZT leads.
• Start PZT Length to Angle measurement.
• Manually match Curved Mirror Subassembly components, enough to bond first 4 assemblies.
  • (this will be pending full characterization of PZTs)
• Make sure clean and bake ticket gets processed for reworked parts mentioned above.

We have the following near future plans:

• Start PZT reliability testing (burn-in test) (ref. T1500060-v2 - PZT Testing Section 2.3.4),
  • Focused on units that will be used to bond first 4
• Bond first batch of Curved Mirror Subassemblies.
  • Make sure we have enough EP30-2 for subsequent batches (some used by HoQi effort)..
• Resume transport fixture build effort at 40m Bake Lab.
• Conduct walkthrough of OMC lab with build in mind.
• Follow updates of top level assy D2000172, and send finalized assy for 3D printing of mockup unit.

12 May 2023, Downs 227

Stephen, Camille, Thejas

We completed a first batch of PZT DC response measurements, and we are working on the processing of quantitative results.

For now, presented below are some general observations and remarks, as well as qualitative results for the full set of 18 PZTs.

General observations

• The following improvements have helped us graduate to observing and measuring DC response:
  • Improving our drive electronics (better function generator, direct monitoring of function generator output and PZT drive amplifier input)
  • Improving our experimental design (focusing and collimating of input beam allowed greater sensitivity to same PZT motion)
  • Improving our signal chain (PD to SR785 Spectrum Analyzer allowed better resolution and reduced systematic noise)
• It seems that Qty 2 of the PZTs that we handled a lot during our test setup may have degraded due to some inattention or accidental mistakes.
• Qty 5 PZTs had solder preventing uniform contact with the end face, which seemed to effect our ability to observe well-resolved DC response.
  • Resoldering next for these articles!
  • We had not clearly specified that there was a restriction to the extent of the solder joint - something to add to the DCC entry for the PZT. We'd also like to recommend that specific soldering steps for the leads be documented here!
• The remaining articles were characterized using a 0.5 Hz triangle wave of range 0-150 Hz, sampled for 8 seconds (128 Hz sample rate) on a SRS785 Spectrum Analyzer.

Qualitative DC Response Results

11 PZTs are Good (DC Response measured)
36 - labeled "?" due to a fair amount of initial handling
37 - good
38 - good
39 - somewhat high intrinsic noise
41 - good
42 - good
43 - good 
44 - good
46 - good
47 - good
48 - good

5 PZTs are WIP (Still need to measure DC Response)
31 - Solder extends past end face
32 - Lead Desoldered
35 - Solder extends past end face
40 - Solder extends (maybe) past end face
45 - Solder blob on ID of end face

2 PZTs are Bad (Inadequate DC response)
33 - 150 V applied in reverse due to lead polarity mistake; still buzzes, but now DC response is unreliable
34 - Low DC response, maybe because we were using it in tests?

Next Steps

We need to remeasure the 5 PZTs that had soldering issues. We'll call this Batch 2.

Soon we will finish analyzing the quantitative response, with an output of PZT Displacement per Drive Voltage.

Then we will decide whether we are happy to move forward without additional PZT spares to replace the faulty articles, or if we want to order additional units.

We also will continue characterizing the PZT Length-to-Angle Coupling and Reliability, per OMC Testing Procedure ref. T1500060-v2 PZT Testing Sections Section 2.3.2 and 2.3.4

• FSR measurement (dip) - done May 3, 2023
• FSR measurement (RFAM injection) - done May 3, 2023
• TMS measurement with PZT1/2 swept from 0V~200V
• Mirror cleaning / Power budget - done [OMC ELOG 530]
• PZT response DC / AC done May 11, 2023 [OMC ELOG 537]
• DCPD shim height adjustment
• QPD alignment / shim height adjustment
• Alignment: beam spot photos

The OMC PZT ac response was resorded was not as expected and a remeasurement will be attempted this week. Data: https://www.dropbox.com/s/7pf0k6awoa4wg0z/230503.zip?dl=0 

Koji's mirror measurement result attached herewith for comparison. 

Herewith attached are the results of curved mirror radius of curvature characterization. 

The ThorLabs MDT694B piezo driver was returned to the OMC lab.

[Thejas, Camille, Koji]

We aligned the laser beam to the cavity and drove the OMC cavity PZTs (0 to 5 V from signal generator with 15x amp from the piezo driver) with a ramp signal and logged the transmission mode spectrum. The drive PZT voltage changes from 3.4 V to 7 V for one fringe shift or half wavelength change in cavity length. The voltage gain of the PZT driver is 15 V/V so that's a difference of 54 V for half weavelngth of driving or 532 nm/54V or 9.85 nm/V. 

[Thejas, Camille, Stephen]

In Downs 227 on 05 May 2023

We took the following actions:

• Reconfigure our data acquisition with a SR785 instead of the oscilloscope.
  • The scope had been limited to ~10 mV precision, and the SR785 has better than mV precision.
• Contract the beam using some lenses borrowed from Gabriele.
  • Increases sensitivity, following some feedback from Koji which Gabriele had also mentioned
  • We measured the spot size on our flag to be .44 mm (had been about 1 mm).
• Moved all electronics, especially AC function generator, off of optical table.
  • Feedback from Koji.

We recalibrated the photodiode using the razorblade flag. We continued to be plagued by slow variations but we had much better data quality (less fuzziness and fewer spikes in the time series). It seemed like the razorblade was not stiff enough and was sensitive to airflow.

We may readjust and recalibrate to see if our data is better, but in the meantime, below are images of the calibration and setup. Data is at T2300050 Optical Component Testing Measurements, sheet "PiezoDCResponse".

Revisiting the measurement requirements and applying the sensitivity of the new setup:

• The NAC2124 PZT nominally extends 3.3 microns with a 200 V drive, +/- 15%.
  • Our 150 V drive should extend the PZT by 2.5 microns nominally.
  • Our shadow sensor would ideally be able to observe with accuracy better by order of magnitude (.25 microns).
• Our stage-driven, dial-indicator-observed PD calibration reveals a sensitivity of -6.704 V PD output per mm of displacement.
  • This corresponds with 149 microns of displacement per V PD output.
  • Across these 11 stage calibration measurements, the error terms were:
    • Standard Deviation: max. 0.00182 V, min. 0.00008 V, avg. 0.00069 V (no, I'm not going to report the standard deviation of the standard deviations.)
    • Range, V (max. value - min. value): max. 0.00563V, min. {C} 0. 00042 V, avg. 0. 00232 V
• If we want to measure with accuracy of .25 microns, that corresponds with a PD output of .0017 V
  • Looks like some of our measurements had low enough error for this accuracy, but there were some measurements which did not.
  • Hopefully we can improve by reducing the impact of vibration and airflow.

• FSR measurement (dip) - done May 3, 2023
• FSR measurement (RFAM injection) - done May 3, 2023
• TMS measurement with PZT1/2 swept from 0V~200V - 1st session Jun 12, 2023 / 2nd session Jun 15
• Mirror cleaning / Power budget - done [OMC ELOG 530]
• PZT response DC / AC - done May 17, 2023
• DCPD shim height adjustment
• QPD alignment / shim height adjustment
• Alignment: beam spot photos

Efforts from Tuesday through Thursday Wednesday, 02 through 04 May, are described below.

The main outcomes were:

• We are able to see some response in the frequency domain (which confirms the response that we hear at acoustic drive frequencies) on a few PZTs Wednesday and Thursday.
• We then improved our drive input and monitoring, so we now see the full waveform delivered to the PZT.
• Now, we are able to reliably see some length response, though typically the reponse seems to be somewhat less than the expected 3.3 micron / 200 V from the spec sheet.
• We are also still subject to low SNR, though at least now the DC response is visible to the eye.
  • We also recalibrated the PD using the stage in the current setup.
• We met this morning to talk about data collection, and we realized it would be best to try to improve the setup.
  • Koji provided some good suggestions, some of which reflected feedback collected from Gabriele, Dean, and Luis.
  • Our setup was sensitive enough to observe the response (yay) but not sensitive enough to make a good measurement.

The next log will reflect the updated setup.

I hope to come back to edit this log to fill out more detail, but the detail reflects intermediate steps with the old setup.

[Stephen, Camille, Thejas]

A running log of our efforts from Monday 1 May. Data continues to be placed in T2300050 at sheet "PiezoDCResponse":

• Continuing with the DCPD and 3-axis piezo driver for our "final" setup
  • PD Thorlabs
  • Driver Thorlabs MDT694B
  • Function Generator in line
• "Averaging" mode of the oscilloscope only reported 3 significant figures, so there was no benefit from switching away from "Sampling" mode
• Acoustic buzzing test of PZT 36 and PZT 31 yielded consistent results
  • Audible buzzing tone with 1 kHz, 10 Vpp input
  • Reverse polarity also buzzes
• We attempted on/off testing, and also AC drive testing, for PZTs 31, 32, and 36
  • PZT 36 was used in the initial setup effort, and since there was inadequate insulation of the PZT from the setup, there was charge buildup and static discharge during that early effort. This PZT was chosen because it has the greatest wedge. We should be skeptical of it now that we have used it in these setup efforts.
  • PZT 31 was used next, also during setup but only after adequate insulation of the PZT had been implemented. It probably has been treated well! Except during today's efforts, one of the solder joints debonded. (Need to follow up with Dean to confirm that LIGO soldering practice follows recommendations of vendor - pads should be clean, solder should include Ag; see D1102070 and other sources)
  • PZT 32 was used afterwards, and was measured.
• We were not really satisfied with the "feel" of the measurement
  • The oscilloscope output didn't seem to change on time scales that we were expecting, when we manipulated the frequency of the drive
  • We attempted to directly measure the PZT extension using the dial indicator, but did not succeed
• We tried to make a list of items that we didn't understand fully, and came up with these:
  • We aren't really that familiar with the driver/amplifier and how it interacts with the input from the function generator:
    • Thorlabs documentation was reviewed - driver manual
      • https://www.thorlabs.com/drawings/d90d63f542e805de-80E05D38-00C3-80BB-4CF17F9FDBF42AB6/MDT693B-Manual.pdf
    • V_out = V_manual + 15 * V_external
      • We applied a 2 V peak-to-peak external voltage, so we were not driving through the full range of the output voltage
      • We may benefit from a low frequency, triangular wave drive so that we can better monitor the output voltage
  • Maybe the time constant of the capacitive charging is too long?
    • Thorlabs documentation was reviewed - Piezo Bandwidth section of Piezo Tutorial
      • https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5030
    • Slew rate (rate of capacitive charging, V/s) is more complicated for a sinusoidal wave than a triangular wave, but the maximum is characterized by the Maximum Driver Current / System Capacitance.
      • Max Driver Current I_max = .06 A, System Capacitance C_sys = C_PZT + C_driver = 5.1 E-7 F + 1 E-9 F
      • Slew rate = 1.18 E5 V/s, or a charging time of 1.28 E-3 s to reach 150 V (note that this is not a true value as the input waveform was sinusoidal)
    • More helpfully, the system bandwidth for a sinusoidal wave is f_max = I_max / (pi * V_pp * C_sys); a triangular wave with a minimum of 0 V is f_max = I_max / (V_pp * C_sys)
      • Our system, if driven sinusoidally from 0 to 150 V, would have a bandwidth of 249 Hz
      • Our system, if driven triangularly from 0 to 150 V, would have a bandwidth of 783 Hz
• We should try to get a low frequency triangular wave drive output from 0 to 150 V with a frequency of 100 Hz, and see if that generates any meaningful signal.

The measurement "results" for PZT 32 (note that these results seem to be dominated by a slow drift in the measurement, and this measurement was not reproducible):

• PD signal with PZT 32 on (150 V) : 3.242934 V, standard deviation 0.013894 V
• PD signal with PZT 32 off (0 V): 3.315395 V, standard deviation 0.014658 V
• sensitivity: -13.65102 V per mm PZT displacement
  • (from PD Calibration, removing factor of 10 from oscilloscope during that measurement)
• displacement of PZT = 5.308 microns
  • the standard deviation of the On measurement was 1.018 microns, and the standard deviation of the Off measurement was 1.074 microns.
• Conclusion: this measurement has a rather large error bar, and was not very repeatable / could not be directly observed by another means (see above comments in log) we were not really satisfied with the "feel" of the measurement
  • The oscilloscope output didn't seem to change on time scales associated with low frequency AC drive; Since high frequency AC drive does cause motion (witnessed by buzzing) maybe we need to find other ways to measure the motion that are more sensitive?

[Stephen, Camille, Thejas, with support from Luis]

Calibration reattempted with the PD borrowed from Koji, equivalent to the last PZT measurment (OMC_Lab/336). There were a couple of differences in contrast to the last measurement:

• We navigated to the central 1 mm of the range (the interval we found to be sensitive in the QPD calibration, dictated by the beam size) and we stepped through in .05 mm intervals.
• We had the oscilloscope on 10x Voltage probe mode. See setup in Attachment 1.

Data collected in table at T2300050 Optical Component Testing Measurements, sheet "PiezoDCResponse" (Day 2 section).

In the linear range from stage position [3.450, 3.550] the least squares linear fit is:

QPD_Sum = m * Stage_Position + b

• QPD_Sum is the dependent variable of QPD signal voltage, derived from the Channel 1 (sum) average, unit V.
• m = -136.45 V / mm is the response of the QPD to change in stage position.
• Stage_Position is the independent variable of stage height, observed via dial indicator readout, unit mm.
• b = 501.91 V is the best fit y-intercept - not a physical quantity.

So, does this setup allow us to measure the DC response of the PZT?

• Over the linear range, the "m" sensitivity parameter would correspond with a signal of .13645 V / micron
• We expect a stroke of 3 or 4 microns, yielding a signal of .40 V to .55 V.
  • (Noliac NAC2124 nominal free stroke is 3.3 microns +/- 15% for a maximum operating voltage of 200 V)
• The standard deviation was not consistent for each measurement; at this linear range, the standard deviation was between .10 V and .15 V.
  • This would be a large error bar in comparison to the signal level

So, is this DCPD setup better than the QPD?

• Comparing sensitivity against standard deviation, there is not much difference.
  • Standard deviation is the same for each measurement in the QPD case, while the PD has some variation (as the signal increases, the standard deviation also increases, but not with uniform scaling; at lower signal levels, the standard deviation is smaller for the PD than the QPD).
  • The ratio between Channel 1 Average and Standard Deviation is similar for the two setups, so neither setup reduces the error significantly.

We will probably just keep the PD in place, since there is not a great motivation to revert to the QPD, and the QPD could then be used for the OpLev independently. We will look at using the oscilloscope "Averaging" mode to reduce the noise in our measurement.

[Thejas, Camille, Stephen] 

Here are some notes on how I plan to approach matching of the PZTs, mounting prisms and curved optics. 

Step 1: Match the prisms and the PZTs such that resulitng 18 combiations will have minimum vertical wedging.

- I will be usign scipy.optimize.minimize to implement this.

Step 2: Arrange the curved mirror wedge angles ascending order. This prioritizes matching of low wedge angled mirorrs first. The high wedge angled ones have a much larger range of vertical component of wedge angle due to freedom of rotation of the mirrors. Attention should also be given to error in the wedge angle due to phase spread of the various clocking data. The more the wedge angle, the more it is sensitive to this error.

- This will be implemented using standard loops. 

[Camille, Koji, Thejas]

Yesterday, we cleaned the cavity optics with first contact, aligned the input laser beam to the cavity and measured the power at different terminals on the cavity breadboard. 

The measured OMC losses were:
SET1 0.042 +/- 0.003
SET2 0.035 +/- 0.002
SET3 0.030 +/- 0.0014
-> 0.033 +/- 0.001

The measured OMC mode-matching efficiencies were:
SET1 0.9795 +/- 0.00016
SET2 0.9797 +/- 0.00005
SET3 0.9794 +/- 0.00035

Attached herewith is the scrrenshot of the notes of with input power parameters.

Borrowed for PZT DC Response Shadow Sensor Setup (see Attachment 1):

• Thorlabs PDA100A Photodiode (and power supply)
• Thorlabs MDT694B Piezo Driver

Current Location: Downs 227

[Stephen, Camille, Thejas, with support from Marie, Dean, Luis]

We setup a shadow sensor! (Attachment 1)

• QPD (Thorlabs PDQ80A) and HeNe laser (< 4 mW @ 633 nm, Thorlabs HNLS008R, 12V / .7A) borrowed from Marie.
  • QPD supplied by 5V from DC power supply.
• Razor blade flag used to eliminate effect of pitch misalignment, atop a 62.5 gram mass.
• Lab jack used to provide height adjustment.
• Dial indicator (Mitutoyo Absolute +/- .001 mm, p/n S112TXB) mounted to height gauge, used to monitor stage height.

The calibration measurement proceeded as follows:

• Manually lowered the stage until the flag was not occluding any light on the QPD
• Raised the stage in 0.5 mm increments and recorded raw data (using the oscilloscope "Sampling" mode), until the flag occluded all of the light previously on the QPD.
• Identified the central 0.5 mm increment, and stepped through that range in .05 mm increments

Data collected in table at T2300050 Optical Component Testing Measurements, sheet "PiezoDCResponse"

In the linear range from stage position [3.450, 3.550] the least squares linear fit is:

QPD_Sum = m * Stage_Position + b

• QPD_Sum is the dependent variable of QPD signal voltage, derived from the Channel 1 (sum) average, unit V.
• m = -9.685 V / mm is the response of the QPD to change in stage position.
• Stage_Position is the independent variable of stage height, observed via dial indicator readout, unit mm.
• b = 35.6111 V is the best fit y-intercept - not a physical quantity.

So, does this setup allow us to measure the DC response of the PZT?

• Over the linear range, the "m" sensitivity parameter would correspond with a signal of .009685 V / micron
• We expect a stroke of 3 or 4 microns, yielding a signal of .03 to .04 V.
  • (Noliac NAC2124 nominal free stroke is 3.3 microns +/- 15% for a maximum operating voltage of 200 V)
• The typical standard deviation of each measurement is .009 to .011 V.
  • This would be a large error bar in comparison to the signal level.
• We will try again using a different photodiode.

Summary of Zygo setups

Initial Zygo Setup:
Our initial Zygo setup consisted of a flat transmission sphere with the 0.5" curved mirror mounted against a 1" flat mirror.
Mounting procedure:
The bottom part of the gluing fixture was attached to a mounting plate using two screws. The 1" reference flat was placed on the gluing fixture. The reference flat was inspected with a green flashlight to ensure that there was no dust on the mirror surface. Any dust was removed using top gun. If any dust remained after using top gun, it was removed with a swab.
The back surface of the curved mirror was inspected and cleaned using the same method (flashlight inspection, followed by top gun if necessary, followed by swab if necessary).

After ensuring that both surfaces are clean, the back surface of the curved mirror was placed on the front surface of the reference flat. The fiducial of the curved mirror was positioned at 12:00. (12:00 is defined as the top of assembly.) The two mirrors were held in place using a mounting plate with a 0.4" aperture. The mounting plate was fixed to the bottom part of the gluing fixture using two screws and a spring for each screw (see attached picture).

The mounting plate holding this assembly was then attached to a optical mount with tip/tilt adjustments (see attached picture).
This assembly was placed facing the Zygo transmission flat (see attached picture) and the mount was pitched/yawed until the fringes on the 1" reference flat were nulled. After nulling the fringes, the data was then recorded.

The mounting plate was then removed from the tip/tilt mount and dissassembled so that the curved mirror could be rotated so that the fiducial is in the 3:00 position. The procedure is then repeated and the data recorded.
This was repeated again with the fiducial in the 6:00, 9:00 and 12:00 (again) positions.

Review of this data shows that the positions of the curvature minimums was not reproducible with sufficient precision. A teflon mounting plate was added to clamp the 1" reference flat more securely to the gluing fixture (See attached pictures). Data was collected in the same manner (twice with the fiducial at 12:00 and once with fiducial at each of the positions 3:00, 6:00, and 9:00).
Additional data collected still failed to produce reproducible results and the removing/remounting process of the curved mirror was time-consuming, so we attempted a new setup for the Zygo measurments.

Final Zygo Setup:
The new setup used a fold mirror mounted at 45degrees to direct the Zygo beam downwards into the plane of the table. A 3" flat was used as our reference flat. The reference flat was placed on some lens tissue parallel to the plane of the table. The same inspection and cleaning method was used to ensure that there was no dust on the reference flat (flashlight inspection, followed by top gun if necessary, followed by swabbing if necessary).
The back of the curved optic was inspected and cleaned using the same method. The curved mirror was placed on the 3" reference flat with the fiducial at the 12:00 position. (12:00 here is defined as the direction ponting towards the Zygo instrument.) (See attached picture of this setup.)
The fold mirror was pitched/yawed so that the fringes on the 3" reference flat were nulled. (An additional advantage of this setup is that more surface of the reference flat was viewable.) After nulling the fringes, the curved mirror was picked up and replaced a few times to verify that the fringe pattern on the curved mirror appeared reproducible. The data was collected with the fiducial at the 12:00 position. This process was repeated with the fiducial at 3:00, 6:00, 9:00, and again at 12:00.
Results from this setup were reproducible and this setup was used to measure the surface profile of all the curved mirrors.

Restimation of the parameters

Camille and I went back to the lab to re-measure the beam profile follwoing the beam expanding lenses. I was observed after turning on the laser that the beam spot on  the turning mirror had displaced off to the mirror edge. We had to re-align the beam.

We have the following parameters from the fitting now, see attached.

w_0x: 1.44 mm +/- 0.0016 mm 
z_0x: 0.575 m +/- 0.046 m
w_0y: 1.50 mm +/- 0.0014 mm
z_0y: 0.004 m +/- 0.029 m

For the p - plane:

Beam waist occurs at 1.249 m +/- 0.002 m from the curved optic of f = 1.25 m 

For the s plane:

Beam waist occurs at 1.269 m +/- 0.001 m from the curved optic of f = 1.25 m 

And the angle of incidence on th ecurved optic was astimated to be 2.66 deg. This imparts a very negligible astigmatism in the reflected beam. But after collecting more data points of the beam profile we see that there is significant astigmatism in the input beam which translates to a decent amount of astigmatism in the reflected beam. 

w_0x: 1.429 mm +/- 0.006 mm
z_0x: 0.421 m +/- 0.131 m

w_0y: 1.526 mm +/- 0.023 mm
z_0y: 0.352 m +/- 0.597 m

This is a test bake conducted in Air Bake Oven A (ABO-A) held in the 40m Clean and Bake facility. The overall objective is to sucessfully cure the Curved Mirror Subassemblies with the appropriate temperature profile. In this test run, we wanted to ensure that the temperature profile dictated via the Platinum software is stable and repeatable.

Specific curing instructions can be found in LIGO-E1300201-v1, section 6.2.4 (https://dcc.ligo.org/E1300201-v1). This test air bake load contained several stainless steel masses and a stainless steel tray that will be utilized in the production curing run. Note that the thermacouple has been placed between two stainless steel masses.

Temperature profile results from 4/14/23 test cure can be seen in attachments below.

PZT dimension analyzed and characterized. The blue dot in the images represents the position of the cathode. The length of the arrows indicates the amount of wedging.