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 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
• Mirror cleaning / Power budget - done [OMC ELOG 530]
• PZT response DC / AC
• 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. 

Attached here with are relevant plots.

[Camille, Thejas]

We repeated Zygo measurements (using the same setup and method as below) for curved mirrors sn07, sn11, sn12, sn18, sn19, sn25, sn26, and sn30.

sn11 and sn25 still show a large spread in angular measurements (see attached.) This is attributed to the low decentering values for these two mirrors (0.072mm and 0.158mm, respectively).

[Camille, Thejas, Stephen]

We modified the Zygo setup for measuring the sagitta of the curved mirrors. A mirror at 45deg was used to reflect the interferometer beam down towards the surface of the table (see picture). A fused silica flat was placed horizontally with the surface of the table and was used as our reference flat. The back surface of the curved mirror and the top surface of the reference flat were cleaned using top gun and/or swabs. Once it was verified that the surfaces were clean, the curved mirror could be easily placed on the surface of the reference flat.

Once the curved mirror was placed on the reference flat, the fringes of the reference flat were nulled using the 45deg mirror. After nulling the flat's fringes, the data was recorded. The curved mirror was then rotated 90deg clockwise. The measurment was repeated with the curved mirror's fiducial located at 12:00, 3:00, 6:00 and 9:00. The 12:00 position was measured twice to ensure repeatability. (A drop of first contact had been placed at the edge of the optic to indicate where the fiducial arrow is. This helped with clocking alignment.)

The already-characterized aLIGO C7 mirror was measured to verify the setup. After verifying agreement with the results in T1500060, this process was repeated with all the remaining curved mirrors.

The data was analyzed using Thejas's python script (separation distance between mirror center and curvature minimum, angular position of curvature minimum.) Those mirrors with a large spread in the measurements will be remeasured.

Curved mirror radius of curvature raw data can be found in the DCC document: T2300050

The input beam falling on the curved optic was characterized. The beam waist and it's position was found by curve fitting gaussian beam propagation formula in near field:

Fitting gives the following values for the initial beam waist (w_0) and waist position (z_0) (see pdf attached below).

Using these fitted parameters in JAMMT (beam propagation software) gives the following results for a 1.25 m focal length optic:

P-plane

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

Beam waist @ 3.063 +/- 0.005 m

f = 1.25 m optic @ 1.807 m

Thus beam focuses at 1.256 +/- 0.005 m for the p-plane.

S-plane

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

Beam waist @ 3.064 +/- 0.02 m 

f = 1.25 m optic @ 1.807 m 

Thus beam focuses at 1.257 +/- 0.02 m for the s-plane. 

Hence we can use the distance measured from the optic to the beam profiler as a suitable figure for focal length (hence radius of curvature). Also astigmatism in the input beam is calculated to have negligible influence in causing astigmatism in following the curved optic. Hence, any astigmatism measured at the focus following the curved optic is due to the curved optic (?). Also because the incident beam on the curved optic is at an arbitrary angle of incidence, this introduces further astigmatism in the reflected beam given by equation 12 in this paper: https://opg.optica.org/ao/fulltext.cfm?uri=ao-8-5-975&id=15813

Chub finished the HEPA enclosure extension project.

I handed Camille the C7 mirror for the cross-calibration of the ROC characterization techniques.

Data can be found in DCC document T2300050. 

On Friday. Camille and I measured the flatness of the flat mirror.  Tilt values (without subtracting tilt) were less than 100 nm and PV across the surface was about 50 nm. 

This checks that the flat mirror surface distortions are not contributing to the systematic deviations in our measurement of curvature minimum with varying the fiducial clocking angle. The deviations in the data show a far more disagreement between Y-Tilt of different clocking angles than the X-Tilt. 

[Camille, Stephen, Thejas]

Curved mirror sn02 was used to test the method for collecting Zygo measurements on the curved mirrors. The curved mirror was mounted with its back surface against a reference flat. The reference flat was pitched/yawed until its fringes were nulled. Then a measurement of the surface profile of the curved mirror + flat mirror together was taken.
The curved mirror was rotated in 90deg increments and the measurements were repeated. (5 measurements in total were taken, with the curved mirror's fiducial in the 12:00, 3:00, 6:00, 9:00 and 12:00 again positions.) The curvature minumum was seen to clock as expected with the rotation of the mirror.

The attached figures show the surface profile of the central 8.5 mm diameter of the mirror (central with respect to the coating edge). Also attached is a plot of the surface profile across the line drawn in the figure.

[Camille]
22 March 2023
Beam profile measurements were continued for more of the curved mirrors.
Mirror sn07 was repeated to verify that Camille and Thejas get the same focal length measurement (plot attached).

[Thejas, Camille]
21 March 2023

We made slight adjustments to the beam expander lenses in the ROC setup. The position of the second lens was moved slightly (a few mm) to improve the collimation of the beam.  The beam profiler was used to measure the beam size at various distances (measurements attached). This will be used to characterize the beam divergence.
This beam was reflected off the curved mirror and the beam profiler was used to measure the beam size at various positions near the focal point. This process was repeated for various curved mirrors (measurements attached). These values will be used to determine the ROC of each mirror. ROC=2*FL

Thanks Koji, the lenses available in the cabinet in the lab actually sufficed. 

I hope you can find useful lenses from the lens kit in the cabinet. If you need more lenses and mounts, talk to our students in WB and the 40m.

Thanks for teh comment Koji. Yes, I did see this effect by comparing the beam sizes with and without the curved mirror. But the observation did not conform with the expectation that the beam should focus at a distance of 1.25 m from the curved mirror (as seen in the software images). So, I plan to use some lenses to increase the beam waist and perform the measurement.

If the mirror has the RoC, it works as a lens. And you should be able to see the effect in the beam profile.

Just what you need to do is to compare the beam profile without the mirror (or with a flat mirror) and then with the curved mirror.

Today, I tried to measure the radius of curvature of the curved mirror using the input beam for the OMC test set-up. It was noticed that the half inch curved optic (ROC=2.5 m), when placed within the Rayleigh range of the beam waist, did not focus the beam. This is probably becasue the beam diameter is small for this optic's radius of curvature to produce any focussing. This can be illustrated even further using the JAMMT software by replacing a concave sperical mirror with a ocnvex lens of focal length of 1.25 m. 

Substrate: 1/2 inch optic with f= 0.25 m 

Substrate: 1/2 inch optic with f= 1.25 m

Substrate: 1/2 inch optic with f= 1.25 m

The only wasy to resolve this is by incresing the beam diameter to > 2 mm

RoC: 2.65m ! Interesting. I'll wait for the follow-up analysis/measurements. The RoC may be dependent on the area (diameter) for the fitting. You might want to run the fitting of your own. If so, let me know. I have some Matlab code that is compatible with the CSV file exported from MetroPro data.

[Camille, GarriLynn, Stephen, Thejas]

Folllowing the replacement of the spherical transmission / reference mirror with a flat mirror, on Friday we were able to observe fringes that facilitated characterization of the curvature minimum. 

\

By rotating the curved optic by 90 deg we couodn't reproduce consistent data. 

This is probably due to insufficient attention given to the orientation/centering of the curved mirror under the clamp. 

[GariLynn, Stephen, Thejas]

Yesterday, we placed an iris (borrowed from OMC Lab) infront of the spherical transmission sphere to limit the spot size, on the other end of the cavity, to only the curved optic. This produced a crisp boundary for the interference pattern. We obtained some data at different imaging focal planes. The transmission optic here is a spherical mirror. This was replaced with a plane reference and the curved optic was moved closer to this optic. Intereference fringes were nuled for the plane mirror upon which the curved optic sits. This ensures that the curved mirror is head on to the laser beam. The spherical fringes were obscured by some diffraction artifacts. Today, we will be makign an attempt to eliminate that and try to see fringes from the whole curved optic. 

OMC test set-up

Yesterday, laser beam output from the fibre follwoing teh mode-matching lenses was picked off and beam profile was characterized using beam profiler Thorlabs BP209-VIS. 

The gaussian fit beam diameter was measured to be about wx = 939 um wy = 996 um at the location of a distance of 0.4 m from the high reflector. The mode content of this beam is about 98% TEM00. We want to use this beam within the Rayleigh range (near field) to measure radium of curvature of the curved optics. 

The Rayleigh range is about 0.74 m. 

[Stephen, Thejas]

Today, a more rigorous effort was made to re-measure the position of the optics forming the Fizeau cavity and re-position the curved optic to get more contrasting fringes. Distance measurements were made using a Fluke laser displacement sensor. We obtained a contrasting fringe pattern but the phase profile measured was assymmeteric and un-satisfactory. Tomorrow an attempt will be made to place an iris infront of the curved optic to define the edge of the beam and limit it only to the curved optic surface. 

Today, Koji and I cleaned up the the lab space and made some space on the optical table for radius of curvature measurement of the A+ OMC curved mirrors. 

[Camille, Stephen, Thejas]

Stephen returned the curved mirror #6 to Liyuan for point transmission measurement. We are now using #5 for to setup/align the ZYGO Fizeau interferometer setup to characterize the curvature center of the mirrors. It was setup such that the focal point of the input reference sphere was coincident with the radius of curvature of the test mirror. 

The curved mirror was mounted on a flat reference mirror, with the help of the sub-assembly bonding fixture:

The fringe pattern seen was:

Efforts were made today to improve the contrast of the fringe pattern and take some measurements.

On Feb 16, Camille and I attampted at locking the OMC cavity. It was quick to re-align the beam to the cavity (by using only the fine adjustment of the output fibre couple). This was done by looking to minimize the power reflected from the cavity and observing the mode shapes on the CCD. After we achieved locking we placed the lid of the OMC back and turned off the laser. 

Chub, JC, and co worked on the HEPA enclosure improvement.

[Camille, Thejas, Stephen]

Yesterday, efforts were made to measure ROC of curved mirrors (#6) in the ZYGO lab using a Fizeau Interferometer. Peculiar observation: Stray fringes were seen that dominated the fringes that conformed with the expectation. The origin of these fringes is still not accounted for (see attached screenshot). moreover, once the right fringe pattern is achieved by moving the end mirror of the interferometer using a translation stage, the cavity length is measured using a metre stick. This makes the measurement limited by the accuracy using ruler stick for cavity length measurement, which is not expected to be any better than usign a beam profiler to find the focal point from the curved mirror. Today we will, move ahead to corved mirror surface profile characterization.

[Camille, Stephen, Thejas]

Today, before the ZYGO lab was cleaned and prepared for the cureved mirrors' radius of curvature (ROC) characterization, Mirror no. 6 was mounted into one of the half inch mirror holders. The cleanliness of the envoronment and handling was not satisfactory. Tomorrow efforts will be made to start doing the ROC measurements with class B cleanroom garbing.

[Camille, Stephen, Thejas]

PZT model: Noliac 2124

Qty: 18 (Sr. No. 30 - 48)

Today, PZT dimensions were measured. Inner radius of the ring and thickness at different points can be used to determine the wedge angle and direction of the PZTs. This is essential for evaluation of appropriate combination of subassembly (curved mirror + PZT + Hole prism) prior to bonding them.