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ID Date Author Type Category Subject
370   Mon Jul 1 12:49:42 2019 KojiOpticsCharacterizationScattering measurement of A and C mirrors

Liyuan's scattering measurement for the A and C mirrors.

Attachment 1: omc_cm_tis_062419.pdf
Attachment 2: omc_prism_tis_062419.pdf
371   Thu Aug 22 12:35:53 2019 StephenOpticsCharacterizationWedging of the debonded PZTs 2019 August

Wedge and thickness measurements of PZTs 12 and 13 took place after debonding and cleaning - results are shown in the first image (handwritten post-it format).

These thickness measurements seem to have come back thinner than previous measurements. It is possible that I have removed some PZT material while mechanically removing glue. It is also possible that there is systematic error between the two sets of measurements. I did not run any calculations of wedge ange or orientation on these data.

Note that cleaning of debonded PZTs involved mechanically separating glue from the planar faces of PZTs. The second image shows the razer blade used to scrape the glue away.

There were thick rings of glue where there had been excess squeezed out of the bond region, and there was also a difficult-to-remove bond layer that was thinner. I observed the presence of the thin layer by its reflectivity. The thick glue came off in patches, while the thin glue came off with a bit of a powdery appearance. It was hard to be certain that all of the thin bond layer came off, but I made many passes on each of the faces of the 2 PZTs that had been in the bonded CM assemblies. I found it was easiest to remove the glue in the bonded

I was anticipating that the expected 75-90 micron bond layer would affect the micrometer thickness measurements if it was still present, but I did not notice any irregularities (and certainly not at the 10 micron level), indicating that the glue was removed successfully (at least to the ~1 micron level).

 Quote: Yesterday I measured the thickness of the PZTs in order to get an idea how much the PZTs are wedged. For each PZT, the thickness at six points along the ring was measured with a micrometer gauge. The orientation of the PZT was recognized by the wire direction and a black marking to indicate the polarity. A least square fitting of these six points determines the most likely PZT plane. Note that the measured numbers are assumed to be the thickness at the inner rim of the ring as the micrometer can only measure the maximum thickness of a region and the inner rim has the largest effect on the wedge angle. The inner diameter of the ring is 9mm.   The measurements show all PZTs have thickness variation of 3um maximum.  The estimated wedge angles are distributed from 8 to 26 arcsec. The directions of the wedges seem to be random (i.e. not associated with the wires)   As wedging of 30 arcsec causes at most ~0.3mm spot shift of the cavity (easy to remember), the wedging of the PZTs is not critical by itself. Also, this number can be reduced by choosing the PZT orientations based on the estimated wedge directions --- as long as we can believe the measurements.   Next step is to locate the minima of each curved mirror. Do you have any idea how to measure them?

Attachment 1: IMG_4775.JPG
Attachment 2: IMG_4770.JPG
372   Fri Aug 23 11:11:44 2019 shrutiOpticsCharacterizationFinding the curvature bottom

I attempted to fit the data taken by Koji of the beam spot precession at the CCD in order to find the location of the curvature bottom in terms of its distance (d) and angle ($\phi$) from the centre of the mirror. This was done using the method described in a previous similar measurement  and Section 2.1.3 of T1500060.

Initially, I attempted doing a circle_fit on python as seen in Attachment 1, and even though more points seem to coincide with the circle, Koji pointed out that the more appropriate way of doing it would be to fit the following function:

$f(i, \theta, r, \phi) = \delta_{i,0} [r \cos(\theta+\phi) + x_c] + \delta_{i,1} [r \sin(\theta+\phi) +y_c]$

since that would allow us to measure the angle $\phi$ more accurately; $\phi$ is the anti-clockwise measured angle that the curvature bottom makes with the positive x direction.

As seen on the face of the CCD, x is positive up and y is positive right, thus, plotting it as the reflection (ref. Attachment 2) would make sure that $\phi$ is measured anti-clockwise from the positive x direction.

The distance from the curvature bottom is calculated as

$d = \frac{rR}{2L}$

r: radius of precession on CCD screen (value obtained from fit parameters, uncertainty in this taken from the std dev provided by fit function)

R: radius of curvature of the mirror

L: Distance between mirror and CCD

R = 2.575 $\pm$ 0.005 m (taken from testing procedure doc referenced earlier) and L = 0.644 $\pm$ 0.005 m (value taken from testing doc, uncertainty from Koji)

d (mm) $\phi$ (deg)
C7 0.554 $\pm$ 0.004 -80.028 $\pm$ 0.005
C10 0.257 $\pm$ 0.002 -135.55 $\pm$ 0.02
C13 0.161 $\pm$ 0.001 -79.31 $\pm$ 0.06

Attachment 1: CircleFit.pdf
Attachment 2: SineFit.pdf
373   Thu Aug 29 11:51:49 2019 shrutiOpticsCharacterizationWedging of the debonded PZTs - Calculation

Using the measurements of PZTs 12,13 taken by Stephen, I estimated the wedging angle and orientation following Section 2.3.1 of T1500060. The results can be found in Attachment1 and is summarised as follows.

For PZT 12, PZT 13 respectively:

Avg. height = 2.0063 mm, 2.0035 mm

Wedge direction (from the same direction as in the doc: positive right) = 120 deg, 120 deg

Wedge angles = 45.8 arcsec, 30.6 arcsec

This was done assuming that the measurements were taken uniformly at intervals of 60deg along the inner rim of the PZT. The diameter (2r) of the inner rim, according to T1500060, is 9mm. The measured heights were fitted with the function

$h = h_0 + \tan(\Omega)\text{ }r(1-\cos(\theta - \alpha))$

as depicted in Attachment2 to find wedging angle $(\Omega)$ and orientation $(\alpha)$.

Quote:

Wedge and thickness measurements of PZTs 12 and 13 took place after debonding and cleaning - results are shown in the first image (handwritten post-it format).

These thickness measurements seem to have come back thinner than previous measurements. It is possible that I have removed some PZT material while mechanically removing glue. It is also possible that there is systematic error between the two sets of measurements. I did not run any calculations of wedge ange or orientation on these data.

Note that cleaning of debonded PZTs involved mechanically separating glue from the planar faces of PZTs. The second image shows the razer blade used to scrape the glue away.

There were thick rings of glue where there had been excess squeezed out of the bond region, and there was also a difficult-to-remove bond layer that was thinner. I observed the presence of the thin layer by its reflectivity. The thick glue came off in patches, while the thin glue came off with a bit of a powdery appearance. It was hard to be certain that all of the thin bond layer came off, but I made many passes on each of the faces of the 2 PZTs that had been in the bonded CM assemblies. I found it was easiest to remove the glue in the bonded

I was anticipating that the expected 75-90 micron bond layer would affect the micrometer thickness measurements if it was still present, but I did not notice any irregularities (and certainly not at the 10 micron level), indicating that the glue was removed successfully (at least to the ~1 micron level).

 Quote: Yesterday I measured the thickness of the PZTs in order to get an idea how much the PZTs are wedged. For each PZT, the thickness at six points along the ring was measured with a micrometer gauge. The orientation of the PZT was recognized by the wire direction and a black marking to indicate the polarity. A least square fitting of these six points determines the most likely PZT plane. Note that the measured numbers are assumed to be the thickness at the inner rim of the ring as the micrometer can only measure the maximum thickness of a region and the inner rim has the largest effect on the wedge angle. The inner diameter of the ring is 9mm.   The measurements show all PZTs have thickness variation of 3um maximum.  The estimated wedge angles are distributed from 8 to 26 arcsec. The directions of the wedges seem to be random (i.e. not associated with the wires)   As wedging of 30 arcsec causes at most ~0.3mm spot shift of the cavity (easy to remember), the wedging of the PZTs is not critical by itself. Also, this number can be reduced by choosing the PZT orientations based on the estimated wedge directions --- as long as we can believe the measurements.   Next step is to locate the minima of each curved mirror. Do you have any idea how to measure them?

Attachment 1: PZT_Wedging_Results.pdf
Attachment 2: PZT_Wedging_Calc.pdf
395   Thu Oct 8 19:55:22 2020 KojiGeneralCharacterizationPower Measurement of Mephisto 800NE 1166A

The output of Mephisto 800NE (former TNI laser) was measured.
The output power was measured with Thorlabs sensors (S401C and S144C). The reference output record on the chassis says the output was 837mW at 2.1A injection.
They all showed some discrepancy. Thus we say that the max output of this laser is 1.03W at 2.1A injection based on the largest number I saw.

Attachment 1: Mephisto800NE_1166A.pdf
402   Sat Nov 21 13:58:30 2020 KojiElectronicsCharacterizationDark Current Measurement for InGaAs QPDs

Dark current measurement for InGaAs QPDs (OSI FCI-InGaAs-Q3000) has been done using Keithley 2450 and Frank's diode test kit. Frank's setup uses various custom instruments which are no longer exist, therefore the kit was used only for switching between the segments.

The diodes were serialized as 81, 82, 83, 84, continuing the numbering for the OMC QPDs. The numbers are engraved at the side and the back of the diode cans.

Overall, the QPDs nominally indicated the usual dark current level of <10nA.
SEG1 of #82 showed a lower voltage of reverse breakdown but this is not a critical level.
#83 showed variations between the segments compared to the uniform characteristics of #81 and #84.

Attachment 1: Q3000_dark_current.pdf
403   Sun Nov 22 13:49:12 2020 KojiElectronicsCharacterizationImpedance Measurement for InGaAs QPDs

To know any anomaly to the junction capacitance of the QPD segments, the RF impedances were tested with a hand-made impedance measurement.
All segments look almost identical in terms of capacitance.

Measurement setup:
The impedance of a device can be measured, for example, from the complex reflection coefficient (S11). To measure the reflection, a bidirectional coupler was brought from the 40m. Attachments 1 and 2 shows the connection. The quantity A/R shows S11. The network analyzer can convert a raw transfer function to an impedance in Ohm.

Calibration and Measurement limit:
The network analyzer was calibrated with 1) a piece of wire to short the clips 2) 50ohm resistor 3) open clips. Then the setup was tested with these three conditions (again). Attachment 3 shows the result. Because of the impedance variation of the system (mainly from the Pomona clip, I guess), there looks the systematic measurement error of ~1pF or ~25nH. Above 100MHz, the effect of the stray impedance is large such that the measurement is not reliable.

The setup was tested with a 10pF ceramic capacitor and this indicated it is accurate at this level. The setup is sufficient for measuring the diode junction capacitance of 300~500pF.

Impedance of the QPD segments:

Then the impedances of the QPD segments were measured (Attachment 4). The segments showed the identical capacitance of 300~400pF level, except for the variation of the stray inductance at high freq, which we can ignore. Note that there is no bias voltage applied and the nominal capacitance in the datasheet is 225pF at 5V reverse bias. So I can conclude that the QPDs are quite nominal in terms of the junction capacitance.

(Ed: 11/23/2020 The RF components were returned to the 40m)

Attachment 1: impedance_measurement.pdf
Attachment 2: P_20201121_183830.jpg
Attachment 3: impedance_test.pdf
Attachment 4: Q3000_impedance_test.pdf
404   Mon Nov 23 23:17:19 2020 KojiElectronicsCharacterizationThe dark noise of the Q3000 QPDs

The dark noise levels of the four Q3000 QPDs were measured with FEMTO DLPCA200 low noise transimpedance amp.

The measurement has been done in the audio frequency band. The amp gain was 10^7 V/A. The reverse bias was set to be 5V and the DC output of the amplifier was ~40mV which corresponds to the dark current of 4nA. It is consistent with the dark current measurement.

The measured floor level of the dark current was below the shot noise level for the DC current of 0.1mA (i.e. 6pA/rtHz).
No anomalous behavior was found with the QPDs.

Note that there is a difference in the level of the power line noise between the QPDs. The large part of the line noises was due to the noise coupling from a soldering iron right next to the measurement setup, although the switch of the iron was off. I've noticed this noise during the measurement sets for QPD #83. Then the iron was disconnected from the AC tap.

Attachment 1: Q3000_dark_noise_81.pdf
Attachment 2: Q3000_dark_noise_82.pdf
Attachment 3: Q3000_dark_noise_83.pdf
Attachment 4: Q3000_dark_noise_84.pdf
405   Tue Nov 24 10:45:07 2020 gautamElectronicsCharacterizationThe dark noise of the Q3000 QPDs

I see that these measurements are done out to 100 kHz - I guess there is no reason to suspect anything at 55 MHz which is where this QPD will be reading out photocurrent given the low frequency behavior looks fine? The broad feature at ~80 kHz is the usual SR785 feature I guess, IIRC it's got to do with the display scanning rate.

 Quote: The measured floor level of the dark current was below the shot noise level for the DC current of 0.1mA (i.e. 6pA/rtHz).
406   Tue Nov 24 12:27:18 2020 KojiElectronicsCharacterizationThe dark noise of the Q3000 QPDs

The amplifier BW was 400kHz at the gain of 1e7 V/A. And the max BW is 500kHz even at a lower gain. I have to setup something special to see the RF band dark noise.
With this situation, I stated "the RF dark noise should be characterized by the actual WFS head circuit." in the 40m ELOG.

454   Mon Nov 14 08:34:45 2022 CamilleOpticsCharacterizationtransmission measurements through OMC #1 (before cleaning)

[Camille, Koji]

Friday, Nov 11th, 2022

Setting up OMC #1 for transmission measurements:

The laser beam was aligned to the OMC cavity. The OMC cavity was locked and the transmission measurements were recorded.

Attachment 1: PXL_20221111_200942943.jpg
Attachment 2: PXL_20221111_200957951.jpg
455   Mon Nov 14 09:27:13 2022 KojiOpticsCharacterizationtransmission measurements through OMC #1 (before cleaning)

The measured total optical loss of the OMC was

1st:   0.015 +/- 0.003
2nd: 0.085  +/- 0.005
3rd:  0.0585+/- 0.0008
4th:  0.047  +/- 0.002

In avegrage the estimated loss is
Loss = 0.055 +/- 0.014

This is unchanged from the measurement at LLO after the FC cleaning
Loss = 0.053 +/- 0.010

Attachment 1: OMC_Powerbudget.xlsx
460   Thu Nov 17 19:50:00 2022 KojiOpticsCharacterizationConclusion on the cleaning of OMC #001

Conclusion on the cleaning of OMC #001

- After a couple of first contact cleaning trials and deep cleaning, the total loss was measured to be 0.045+/-0.004.
This indicated a slight improvement from the loss measured at LLO before any cleaning (0.064+/-0.004).
However, the number did not improve to the level we marked in 2013 (0.028+/-0.004).

- This loss level of 4.5% is comparable to the loss level of OMC #3, which is currently used at LHO.
Therefore, this OMC #1 is still a useful spare for the site use.

- Some notes / to-do regarding this unit:
1) The beam dump with melted black glass was removed. A new beam dump needs to be bonded on the base.
2) The connector bracket still needs to be replaced with the PEEK version.
3) The PZT of CM1 has been defunct since 2013. Combining LV and HV drivers is necessary upon use at the site. (LLO used to do it).

Attachment 1: OMC_loss.pdf
464   Fri Dec 2 11:42:03 2022 KojiOpticsCharacterizationOMC #1 cleaning for water soluble contaminants
[Camille, Koji] Log of the work on Nov 30, 2022

The following is the notes from GariLynn

Cleaning for water-soluble contaminants:
It uses deionized water instead of acetone.
Note:
• The first contact must go on the mirror before the water can dry,  so you will need a bigger brush. We have some that are 1cm, I think they are in the back wall cabinet of B119.
• For the bigger brush, you will need a beaker and perhaps a bigger bottle of First Contact.  There is one in the mini-fridge in the back corner of B110
• You use an alpha swab instead of a cotton bud
• For this effort, I encourage you to get a bottle of DI water from stores.
• I also encourage you to rehearse the motions beforehand - timing is critical, and your mirrors are in a tight spacing

(Attachment 1)
We obtained Regent grade DI water. It was poured into a smaller cup.
FC liquid was also poured into a small beaker.
Wash the mirror with a swab. We should have used a smaller swab that GariLynn has in her lab.

As soon as the mirror was wiped with the water, the FC was applied with a large brush. Don't let the water away!
Then more layer of the FC was added as usual.

The quick painting of FC made a mess around the mirrors due to excess liquid (Attachment 2). So, we decided to remove the FC remnants (on non-optic surfaces) with cotton swabs and then applied FC as usual.

This made the mess removed, however, we found the OMC loss was increased to >10%(!) (Attachment 3). We decided to continue tomorrow (Thu) with more weapons loaded consulting with GariLynn.

Attachment 1: PXL_20221130_234101575.jpg
Attachment 2: PXL_20221130_234013958.jpg
Attachment 3: PXL_20221201_021727724.jpg
Attachment 4: Screen_Shot_2022-12-02_at_12.43.02.png
465   Fri Dec 2 12:38:15 2022 KojiOpticsCharacterizationOMC #1 cleaning for water soluble contaminants

Another set of FC cleaning was applied to FM1/FM2/CM1/CM2 and SM2. Some FC strings are visible on SM2. So I decided to clean SM2 as well as the cavity mirrors close to SM2 (i.e. FM2 and CM2)

As a result, the bright scattering spot on CM1 is now very dim. And the loss was reduced to 4.0%. This is 0.4% better than the value before the water cleaning.

It'd be interesting to repeat the water cleaning, at least on FM1. FM1 is the closest cavity mirror to the beam dump damaged by the high-power laser pulse.
Maybe we should also clean the AR side of FM1 and BS1, as they were right next to the damaged beam dump. It is not for the loss but for reducing the scattering.

Attachment 1: PXL_20221202_034932211.jpg
Attachment 2: OMC_loss.pdf
466   Fri Dec 2 23:58:33 2022 KojiOpticsCharacterizationOMC #1 cleaning for water soluble contaminants

The second trial of the water scrub

A bright scatter is visible on FM1, so I tried water scrub on FM1. This time, both surfaces of FM1 and both surfaces of BS1 were cleaned.

Smaller Vectra swabs were used for the scrub. Then the water was purged by IPA splashed from a syringe. Right after that FC was applied.
This was a bit messy process as the mixture of water/IPA/FC was splattered on the breadboard.
Nevertheless, all the mess was cleaned by FC in the end.

The transmission measurements are shown in Attachment 1, and the analyzed result is shown together with the past results.

The 2nd water scrub didn't improve the transmission and it is equivalent to the one after the two times of deep cleaning.
I concluded that the water scrub didn't change the transmission much (or at all). We reached the cleaning limit.

Attachment 1: PXL_20221203_063327268.jpg
Attachment 2: OMC_loss.pdf
468   Fri Dec 9 13:13:13 2022 KojiOpticsCharacterizationFSR/TMS/Spot Positions/Transmission

[Camille Koji]

We quickly measured the basic parameters of the OMC as is.

=== FSR ===
Used the technique to find a dip in the transmission transfer function (TF) with offset locking + phase modulation. The FSR was 264.79003MHz = The cavity length of 1.13219 [m] (requirement 1.132+/-0.005 [m])

=== TMS ===

Used the technique to find the peaks in the trans TF with phase modulation + input misalignment + trans PD clipping.
TMS_V: 58.0727 / TMS_H: 58.3070 => TMS/FSR V:0.219316 H:0.220201

This makes the 9th-order modes nicely avoided (Attachment 1). A slightly longer FSR may makes the numbers close to the nominal.

=== Spot positions ===

The image/video capture board turned out not functional with the new Apple silicon mac. We decided to use a small CCD monitor and took a photo of the display.

All the spots are within the acceptable range. The scattering on CM2 was particularly bright on the CCD image and also in the image with the IR viewr.

The spot on FM1/2 are right at the expected location. The spot on CM1 is 0.5mm low and 0.7mm inside (left). The spot on CM2 is ~0.25mm too high and 0.3mm outside.
(Attachment 2, a small grid is 1 mm/div)

== Transmission ==

We made a quick simplified measurement (Attachment 3).

Assuming the reflectivity of the matched beam to be ~0, the mode matching is M=1-(59.2e-3-(-6.5e-3))/(3.074-(-6.5e-3))=0.979
==> The power of the coupled mode is M x 21.28mW = 20.83 mW
The measued transmission was 19.88 mW

==> The OMC transmission (total) was 0.954 (4.5% loss)

This number is not too bad. But the spot on CM2 has too bright scattering. Next week, we want to check if swapping CM2 may improve the situation or not.

Attachment 1: HOM_plot_PZT.pdf
Attachment 2: OMC4_spot.png
Attachment 3: PXL_20221208_233706115.jpg
469   Mon Dec 12 19:04:40 2022 KojiOpticsCharacterizationFSR/TMS/Spot Positions/Transmission 2nd trial

[Camille Koji]

We replaced CM2 with a PZT mirror subassembly serialized by PZT "13" (Attachment 1).
This made the transmission increase to 96.x%. Therefore the quick measurement of FSR and TSM were done. Also more careful measurement of the transmission was done.

Next time

== Alignment ==

• CM2 was replaced from PZT "12" to PZT "13".
• The resulting position of the cavity spot were all over 1mm too "+" (convention T1500060 Appendix C).
• So we decided to rotate CM2 by 1mrad in CW. This was done with (-) micrometer of CM2 "pushed" by 20um (2 rotational div).
• The resulting spot positions were checked with CCD. (Attachment 2). The spot positions seemed to be within +/-1mm from the center as far as we can see from the images. (good)
• CM2 spot looks much darker. CM1 spot is almost invisible with a CCD and also an IR viewer. FM1/2 spots were nominal bright level. (Looks OK)

== Quick measurement of the transmission ==

Transmission: 20.30 mW
Reflection Voltage (locked): 65.0 mV
Reflection Voltage (unlocked): 3.094 V
Reflection Voltage (dark): -6.5 mV
Incident Power: 21.64 mW

---> Mode matching 1-0.023 / Pcoupled = 21.14 / OMC Transmission 0.96

96% transmission is not the best but OK level. We decided to proceed with this mirror combination.

== Quick measurement of FSR/TMS ==

FSR: 264.7837MHz
TMS_V = 58.2105MHz
TMS_H = 58.1080MHz

The HOM structure (with PZT Vs = 0) is shown in Attachment 3. 9th order modes look just fine. The excplicit coincidence is 19th order 45MHz lower sideband. (Looks good)

== Transmission measurement ==

The raw measurements are shown in Attachment 4. The processed result is shown in Attachment 5.
We found that data set 2 has exceptionally low transmission. So we decided to run the 4th measurement excluding the set 2.

Over all OMC loss
Set1: 0.029 +/- 0.014
Set3: 0.041 +/- 0.0014
Set4: 0.038 +/- 0.001

--> 0.036 +/- 0.004
(0.964 Transmission)

Attachment 1: PXL_20221212_235351320.jpg
Attachment 2: OMC4_spot.png
Attachment 3: HOM_plot_PZT.pdf
Attachment 4: PXL_20221213_000406843.jpg
Attachment 5: Screen_Shot_2022-12-12_at_19.36.10.png
470   Mon Dec 19 18:51:50 2022 KojiOpticsCharacterizationTMS measurement with the PZT voltages altered

[Camille, Koji] Log of the work on Dec 15, 2023

The vertical and horizontal TMSs for OMC #4 were measured with the PZT voltages scanned from 0V to 200V.

We concluded that this alignment nicely avoids the higher-order mode structure up to ~19th order. We are ready for the cavity mirror bonding.

The RF transfer functions to the trans RF PD from the modulation on the BB EOM were taken with the presence of the vertical misalignment of the incident beam and the vertical clipping of the beam on the RFPD.

The typical measurement results and the fitting results are shown in Attachments 1/2.

The TFs were taken with the voltage 0, 50, 100, 150, and 200V applied to PZT1 while PZT2 were left open. The measurement was repeated with the role of PZT1 and PZT2 swapped.

The ratio between the TMS and FSR was evaluated for each PZT voltage setting. (Attachment 3)

When the PZTs are open, the first coincident resonance is the 19th-order mode of the 45MHz lower sideband. (Attachment 4)

When the PZT2 voltage is scanned with PZT1 kept at ~0V, no low-order sidebands come into the resonance (Attachment 5) until the PZT1 voltage is above 100V.

We found that the high voltage on PZT1 misaligns the cavity in yaw and the spot (presumably) moves to an undesirable area regarding the cavity loss.
This does not happen to PZT2. Therefore the recommendation here is that the PZT2 is used as the high voltage PTZ, while PZT1 is for the low voltage actuation.

Attachment 1: Cav_scan_response_PZT1_0_Pitch.pdf
Attachment 2: Cav_scan_response_PZT1_0_Yaw.pdf
Attachment 3: OMC_20221215.pdf
Attachment 4: HOM_plot_PZT0_0.pdf
Attachment 5: HOM_PZTV_PZT1_0V.pdf
489   Wed Feb 8 16:10:52 2023 StephenOpticsCharacterizationA+ OMC, Parallelism of HR Prisms

[Camille, Thejas, Stephen]

We set up the white light autocollimator in the Downs B119 cleanroom. (Nippon Kogaku, from Mike Smith).

After some initial effort to refine the fixturing and alignment, we located the S1 crosshair reflection and aligned to the autocollimator reticle using the pitch and yaw adjustments in the prism mount.

We subsequently used the rotation stage adjustment to locate the S2 crosshair reflection and measure the vertical and horizontal wedges.

Faint horizontal crosshair from the S2 reflection can be seen in the image below.

This is aligned with the reticle using rotation mount on which the prism mount is clamped.

Initial readiing of the rotation mount screw: 9.2

Here we see that the crosshair from S2 reflected light is offset in the vertical axis by approx. 2 div. From hte image below this should

correspond to 2 arcmin vertical wedge angle.The horizontal wedge angle is yet to be caluclated.

Attachment 3: IMG_3C6388ECD50E-1.jpeg
490   Thu Feb 9 15:54:41 2023 Thejas OpticsCharacterizationA+ OMC, Parallelism of HR Prisms

[Camille, Thejas, Stephen]

Continuing yesterday's efforts to measure the wedge angle of the back surface of the prisms. We completed measurement for all the 18 prisms.

The images below accompanying the readings represent the S2 crosshair image on top of the reticle, alighned for yaw.

But note that the vertical misalignement with the reticle does not give an accurate measurement for vertical wedge angle. This is because, as it's notecable in the images,

the S1 reflected crosshair's horizontal axis goes out of coincidence from the horizontal axis of the reticle as the stage is rotated. Our thoughts: MAy be the horizontal

plane of the mount is not the same as the horizontal plane of the autocollimator.

Each unit of the readings corresponds to 0.1 deg., the resolution of the rotational stage is 0.2 deg. The requirement is 0.5 deg of wedge angle. And this angle is related to the horizontal wedge angle by:

Prism 02

Initial reading of the screw on the rotation (yaw) stage (ini): 7.6

Final reading of the screw (fin): 0.2

Prism 04

ini: + 5.1

fin: - 8.0

Prism 05

ini: + 1.8

fin: - 5.5

Prism 06

ini: + 5.8

fin: - 8.5

Prism 07

ini: 8.2

fin: 1.0

Prism 09

ini: +1.0

fin: - 4.2

Prism 10

ini: +9.1

final: +2.2

Prism 11

ini: 9.1

fin: 2.0

Prism 12

ini: 9.0

fin: 2.2

Prism 13

ini: 9.0

fin: 2.2

Prism 14

ini: 9.0

fin: 2.1

Prism 15

ini: 9.0

fin: 2.0

Prism 16

ini: 9.0

fin: 2.2

Prism 17

ini: 9.0

fin: 2.0

Prism 22

ini: 9.0

fin: 2.1

Prism 24

ini: 9.1

fin: 2.1

Prism 26

ini: 9.0

fin: 2.3

This totals 18 prisms including yesterdays.

Attachment 18: Raw_data.pdf
491   Tue Feb 14 10:45:00 2023 Thejas OpticsCharacterizationA+ OMC Prism perpendicularity

[Camille, Stephen, Thejas]

Following the wedge angle measurements of the prisms, perpendicularoty of their bottom surface with respect to their HR surface was measured usign the autocollimator. More info. about the procedure can be found in the OMC testing document. We want to set the requiremetns for perpendicularity to better than 30 arcsec (or 0.-0083 deg).

Images of the setup

Prism 1:

View through teh autocollimator (AC) while hte prism is unclamped:

Two horizontal crosshair lines can be seen, with a common vertical crosshair. These corresspond to the two separate reflections of the AC beam fom the retroflector (RR) surfaces formed by the prism and the flat Al mirror (see image below). When the RR formed is 90 deg the two horizontal lines overlap. The separation between the lines, when calibrated, represents 4 x the deviation of the prism from perpendicularity. Note that, since this prism is unclamped the crosshairs don't indicate a true reading. Note that since the autocollimator images are in far field, the splitting of the horizontal lines shouldn't depend on the pitch angle of the coupling mirror, this can also be checked by the adjusting the pitch screws.

Clamped:

Multiple images below to check reproducibility:

1 div. of the reticle in the above images corresponds to 1 arc min. By measuring the separation of the horizontal shifting gives angle of deviation from perpendicularity.

From the above images it can be inferred that the surfaces form a 90 deg RR.

Prism 2

As it can be seen in the top images there's a splitting of hte horizontal lines indicating deviation from perpendicularity. The direction of the deviation can be inferred by softly tocuhing/pressing on the front orn the back en of the flat Al mirror surface as shown in the images below.

Prism 4

Prism 5

Prism 6

Prism 7

Prism 9

Prism 10

Prism 11

Prism 12

Prism 13

Prism 14

Attachment 10: IMG_379CF9F79CCB-1.jpeg
Attachment 12: IMG_146D1BDD8AC5-1.jpeg
Attachment 17: IMG_5783285B694E-1.jpeg
Attachment 23: IMG_FC0EC9B1CA92-1.jpeg
Attachment 25: OMC_2_(dragged).pdf
Attachment 26: OMC_2_(dragged)_(dragged).pdf
492   Tue Feb 14 22:52:35 2023 Thejas OpticsCharacterizationA+ OMC Prism perpendicularity of HR Prisms and BS

[Camille, Stephen, Thejas]

Continuing with the efforts to measure the perpndicularity.

Prism 15

Prism 16

Prism 17

Prism 22

Prism 24

Prism 26

Perpendicularity measurement for Beam Splitters

BS 25

BS 29

BS 28

BS 36

BS 33

BS 34

BS 35

BS 37

BS 38

BS 39

Attachment 17: OMC.pdf
Attachment 18: OMC_annex.pdf
494   Wed Feb 15 17:40:21 2023 Thejas OpticsCharacterizationA+ OMC perpendicularity of hole prisms

[Camille, Stephen, Thejas]

Contnuing the efforts to measure and check perpendicularity: tombstone prisms with holes/ hole prisms (HP).

Note: Veritcal crosshair splitting can be seen in the some of the image. This is probably because the horizontal of the Al flat mirror is not parallel to that of the coupling mirror. This was confirmed by touching the so that the setup roll a bit so as to reduce the vertical splitting. In some cases the position of the prism on the flat mirror was changes to reduce this effect, in some other cases this was not very helpful and measurement was done anyway. We expect that teh vertical splitting and horizontal splitting don't couple into each other. We think the clamping mechanism for this kind of measurement can be improved to avoid these artefacts.

HP40

HP41

HP42

HP43

HP44

HP45

HP46

HP47

HP48

HP49

HP50

HP51

HP 52

HP 53

HP 54

HP 55

HP 56

HP 57

Attachment 19: OMC_2_(dragged)_2.pdf
Attachment 20: OMC_2_(dragged)_3.pdf
495   Fri Feb 17 17:11:28 2023 Thejas OpticsCharacterizationA+ OMC beam-splitter prisms wedge angle measurement

[Camille, Stephen, Thejas]

Yesterday we measured wedge angle of the beamsplitter (BS) prisms. I reckon these measurements are not as important as the BSs will be used outside the cavity and the angle of incidence is significant.

Measurement procedure and setup used are the same as that for the prism mirrors wedge angle measurements.

BS25

BS28

ini: 9.0

fin: 2.0

BS29

ini: 9.0

fin: 1.9

BS33

ini: 9.0

fin: 2.0

BS34

ini: 9.0

fin: 1.7

BS35

ini: 9.0

fin: 2.0

BS36

ini: 9.0

fin: 2.3

BS37

ini: 9.0

fin: 2.3

BS38

ini: 9.0

fin: 2.2

BS39

ini: 9.0

fin: 2.4

Attachment 11: OMC_5_(dragged)_2.pdf
496   Fri Feb 17 17:25:39 2023 Thejas OpticsCharacterizationA+ OMC Breadboard measuerements

Yesterday we also measured weight and dimensions of breadboard. Error for the following measurements is same as the least count of the instruments used.

26

6149 g

450.56 mm x 41.45 mm x 150.39 mm

23

6127 g

450.37 mm x 41.25 mm x 150.17mm

25

6155 g

450.83 mm x 41.44 mm x 150.15 mm

24

6158 g

450.30 mm x 150.42 mm x 41.42 mm

20

6147 g

450.06 mm x 150.18 mm x 41.42 mm

22:

6149 g

450.01 mm x 150.57 mm x 41.43 mm

21:

6143 g

450.01 mm x 150.06 mm x 41.44 mm

Attachment 1: IMG_3753BB8D72D5-1.jpeg
Attachment 3: OMC_5_(dragged).pdf
497   Fri Feb 17 17:41:57 2023 Thejas ElectronicsCharacterizationA+ OMC Piezos wedge angle

[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.

Attachment 1: OMC_6_(dragged).pdf
498   Mon Feb 27 17:40:27 2023 Thejas OpticsCharacterizationA+ OMC curved mirror 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.

499   Wed Mar 1 10:23:10 2023 Thejas OpticsCharacterizationA+ OMC curved mirror characterization

[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.

502   Tue Mar 7 10:20:55 2023 Thejas OpticsCharacterizationA+ OMC Curved mirror radius of curvature

[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.

Attachment 1: image.jpeg
Attachment 3: image.jpeg
503   Tue Mar 7 23:00:16 2023 Thejas OpticsCharacterizationOMC Lab clean up

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.

504   Wed Mar 8 17:27:51 2023 Thejas OpticsCharacterizationA+ OMC Curvature minimum of curved optics

[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.

Attachment 1: image.jpeg
505   Fri Mar 10 10:23:08 2023 ThejasOpticsCharacterizationA+ OMC curved mirror radius of curvature

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.

Attachment 4: OMC_8_(dragged).pdf
506   Fri Mar 10 11:12:57 2023 Thejas OpticsCharacterizationA+ OMC Curvature minimum of curved optics

[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.

507   Tue Mar 14 10:41:06 2023 Thejas OpticsCharacterizationA+ OMC curved mirror characterization

[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.

Attachment 1: image.jpeg
508   Tue Mar 14 12:12:41 2023 Koji OpticsCharacterizationA+ OMC curved mirror characterization

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.

509   Tue Mar 14 18:24:03 2023 Thejas OpticsCharacterizationA+ OMC Curved mirror radius of curvature

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

510   Tue Mar 14 20:06:03 2023 Koji OpticsCharacterizationA+ OMC Curved mirror radius of curvature

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.

511   Wed Mar 15 15:28:24 2023 Thejas OpticsCharacterizationA+ OMC Curved mirror radius of curvature

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.

 Quote: 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.

512   Wed Mar 15 17:07:35 2023 Koji OpticsCharacterizationA+ OMC Curved mirror radius of curvature

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.

513   Fri Mar 17 15:01:21 2023 Koji OpticsCharacterizationA+ OMC Curved mirror radius of curvature

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

 Quote: 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.

4   Wed Jun 20 20:37:45 2012 ZachOpticsConfigurationTopology / parameter selection

EDIT (ZK): All the plots here were generated using my MATLAB cavity modeling tool, ArbCav. The utility description is below. The higher-order mode resonance plots are direct outputs of the function. The overlap plots were made by modifying the function to output a list of all HOM resonant frequencies, and then plotting the closest one as a function of cavity length. This was done for various values of highest mode order to consider, as described in the original entry.

Description:

This function calculates information about an arbitrary optical cavity. It can plot the cavity geometry, calculate the transmission/reflection spectrum, and generate the higher-order mode spectrum for the carrier and up to 2 sets of sidebands.

The code accepts any number of mirrors with any radius of curvature and transmission, and includes any astigmatic effects in its output.

As opposed to the previous version, which converted a limited number of cavity shapes into linear cavities before performing the calculation, this version explicitly propagates the gouy phase of the beam around each leg of the cavity, and is therefore truly able to handle an arbitrary geometry.

----------------Original Post----------------

I expressed concern that arbitrarily choosing some maximum HOM order above which not to consider makes us vulnerable to sitting directly on a slightly-higher-order mode. At first, I figured the best way around this is to apply an appropriate weighting function to the computed HOM frequency spacing. Since this will also have some arbitrariness to it, I have decided to do it in a more straightforward way. Namely, look at the spacing for different values of the maximum mode number, nmax, and then use this extra information to better select the length.

Assumptions:

• The curved mirror RoC is the design value of 2.50±0.025 m
• The ±9 MHz sidebands will have ~1% the power of the other fields at the dark port. Accordingly, as in Sam's note, their calculated spacing is artificially increased by 10 linewidths.
• The opening angle of 4º is FIXED, and the total length is scaled accordingly

Below are the spacing plots for the bowtie (flat-flat-curved-curved) and non-bowtie (flat-curved-flat-curved) configurations. Points on each line should be read out as "there are are no modes of order N or lower within [Y value] linewidths of the carrier TEM00 transmission", where N is the nmax appropriate for that trace. Intuitively, as more orders are included, the maxima go down, because more orders are added to the calculation.

*All calculations are done using my cavity simulation function, ArbCav. The mode spacing is calculated for each particular geometry by explicitly propagating the gouy phase through each leg of the cavity, rather than by finding an equivalent linear cavity*

Since achievable HOM rejection is only one of the criteria that should be used to choose between the two topologies, the idea is to pick one length solution for EACH topology. Basically, one maximum should be chosen for each plot, based on how how high an order we care about.

Bowtie

For the bowtie, the nmax = 20 maximum at L = 1.145 m is attractive, because there are no n < 20 modes within 5 linewidths, and no n < 25 modes within ~4.5 linewidths. However, this means that there are also n < 10 modes within 5 linewidths, while they could be pushed (BLUE line) to ~8.5 linewidths at the expense of proximity to n > 15 modes.

Therefore, it's probably best to pick something between the red and green maxima: 1.145 m < L < 1.152 m.

By manually inspecting the HOM spectrum for nmax = 20, it seems that L = 1.150 m is the best choice. In the HOM zoom plot below and the one to follow, the legend is as follows

• BLUE: Carrier
• GREEN: +9 MHz
• RED: -9 MHz
• CYAN: +45 MHz
• BLACK: -45 MHz

Non-bowtie

Following the same logic as above, the most obvious choice for the non-bowtie is somewhere between the red maximum at 1.241 m and the magenta maximum at 1.248 m. This still allows for reasonable suppression of the n < 10 modes without sacrificing the n < 15 mode suppression completely.

Upon inspection, I suggest L = 1.246 m

I reiterate that these calculations are taking into account modes of up to n ~ 20. If there is a reason we really only care about a lower order than this, then we can do better. Otherwise, this is a nice compromise between full low-order mode isolation and not sitting directly on slightly higher modes.

RoC dependence

One complication that arises is that all of these are highly dependent on the actual RoC of the mirrors. Unfortunately, even the quoted tolerance of ±1% makes a difference. Below is a rendering of the RED traces (nmax = 20) in the first two plots, but for R varying by ±2% (i.e., for R = 2.45 m, 2.50 m, 2.55 m).

The case for the non-bowtie only superficially seems better; the important spacing is the large one between the three highest peaks centered around 1.24 m.

Also unfortunately, this strong dependence is also true for the lowest-order modes. Below is the same two plots, but for the BLUE (nmax = 10) lines in the first plots.

Therefore, it is prudent not to pick a specific length until the precise RoC of the mirrors is measured.

Conclusion

Assuming the validity of looking at modes between 10 < n < 20, and that the curved mirror RoC is the design value of 2.50 m, the recommended lengths for each case are:

• Bowtie: LRT = 1.150 m
• Non-bowtie: LRT = 1.246 m

HOWEVER, variation within the design tolerance of the mirror RoC will change these numbers appreciably, and so the RoC should be measured before a length is firmly chosen.

5   Thu Jun 21 03:07:27 2012 ZachOpticsConfigurationParameter selection / mode definition

EDIT 2 (ZK): As with the previous post, all plots and calculations here are done with my MATLAB cavity modeling utility, ArbCav.

EDIT (ZK): Added input q parameters for OMMT

found the nice result that the variation in the optimal length vs. variation in the mirror RoC is roughly linear within the ±1% RoC tolerance. So, we can choose two baseline mode definitions (one for each mirror topology) and then adjust as necessary following our RoC measurements.

Bowtie

For R = 2.5 m, the optimal length (see previous post) is LRT = 1.150 m, and the variation in this is dLRT/dR ~ +0.44 m/m.

Here is an illustration of the geometry:

The input q parameters, defined at the point over the edge of the OMC slab where the beam first crosses---(40mm, 150mm) on the OptoCad drawing---are, in meters:

• qix = - 0.2276 + 0.6955 i
• qiy = - 0.2276 + 0.6980 i

Non-bowtie

For R = 2.5 m, the optimal length is LRT = 1.246 m, and the variation in this is also dLRT/dR ~ +0.44 m/m.

Geometry:

q parameters, defined as above:

• qix = - 0.0830 + 0.8245 i
• qiy = - 0.0830 + 0.8268 i
36   Thu Nov 8 19:47:55 2012 KojiElectronicsConfigurationSolder for PZTs

Rich saids:

I have ordered a small roll of solder for the OMC piezos.
The alloy is: Sn96.5 Ag3.0 Cu0.5

38   Thu Nov 8 20:12:10 2012 KojiOpticsConfigurationHow many glass components we need for a plate

Optical prisms 50pcs (A14+B12+C6+E18)
Curved Mirrors 25pcs (C13+D12)

 Qty Prisms Curved No BS OMC Wedge tested Coating A: IO coupler 14 0 2 prisms 5/5 Coating B: BS 45deg 12 0 2 prisms 0/5 Coating C: HR 6 13 2 curved Coating D: Asym. output coupler 0 12 - Coating E: HR 45deg 18 0 4 prism (1 trans + 3 refl) 0/3 D1102209 Wire Mount Bracket 25 4 D1102211 PD Mount Bracket 30 8

55   Fri Jan 18 13:25:17 2013 KojiOpticsConfigurationAutocollimator calibration

An autocollimator (AC) should show (0,0) if a retroreflector is placed in front of the AC.
However, the AC may have an offset. Also the retroreflector may not reflect the beam back with an exact parallelism.

To calibrate these two errors, the autocollimator is calibrated. The retroreflector was rotated by 0, 90, 180, 270 deg
while the reticle position are monitored. The images of the autocollimator were taken by my digital camera looking at the eyepiece of the AC.

Note that 1 div of the AC image corresponds to 1arcmin.

Basically the rotation of the retroreflector changed the vertical and horizontal positions of the reticle pattern by 0.6mdeg and 0.1mdeg
(2 and 0.4 arcsec). Therefore the parallelism of the retrorefrector is determined to be less than an arcsec. This is negligibly good for our purpose.

The offset changes by ~1div in a slanted direction if the knob of the AC, whose function is unknown, is touched.
So the knob should be locked, and the offset should be recorded before we start the actual work every time.

Attachment 1: autocollimator_calibration.pdf
63   Thu Feb 21 18:44:18 2013 KojiOpticsConfigurationPerpendicularity test

Perpendicularity test of the mounting prisms:

The perpendicularity of the prism pieces were measured with an autocollimator.

Two orthogonally jointed surfaces forms a part of a corner cube.
The deviation of the reflected image from retroreflection is the quantity measured by the device.

When the image is retroreflected, only one horizontal line is observed in the view.
If there is any deviation from the retroreflection, this horizontal line splits into two
as the upper and lower halves have the angled wavefront by 4x\theta. (see attached figure)

The actual reading of the autocollimator is half of the wavefront angle (as it assumes the optical lever).
Therefore the reading of the AC times 30 gives us the deviation from 90deg in the unit of arcsec.

SN / measured / spec

SN10: 12.0 arcsec (29 arcsec)

SN11: 6.6 arcsec (16 arcsec)

SN16: 5.7 arcsec (5 arcsec)

SN20: -17.7 arcsec (5 arcsec)

SN21: - 71.3 arcsec (15 arcsec)

Attachment 1: perpendicularity_test.pdf
Attachment 2: P2203206.JPG
64   Wed Feb 27 18:18:48 2013 KojiOpticsConfigurationMore perpendicularity test

Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec. 10   0.3989    11.97   29    good 11   0.2202     6.60   16    good 16   0.1907     5.72    5    good 20  -0.591    -17.73    5    good 21  -2.378    -71.34   15 21  -1.7      -51.     15 01  -0.5      -15.     52 02  -2.5      -75.     48 06  -1.0      -30.     15    good 07   1.7       51.     59 12  -2.2      -66.     40 13  -0.3      - 9.     12    good 14  -2.8      -84.     27 15  -2.5      -75.     50 17   0.7       21.     48 22   2.9       87.     63

Mirror A:
A1  -0.5      -15.     NA    good A3   0.5       15.     NA    good A4   0.9       27.     NA    good A5   0.4       12.     NA    good A6   0.1        3.     NA    good A7   0.0        0.     NA    good A8   0.0        0.     NA    good A9   0.0        0.     NA    good A10  1.0       30.     NA    good A11  0.3        9.     NA    good A12  0.1        3.     NA    good A13  0.0        0.     NA    good A14  0.6       18.     NA    good

Mirror B: B1  -0.9      -27.     NA    good B2  -0.6      -18.     NA    good B3  -0.9      -27.     NA    good B4   0.7       21.     NA    good B5  -1.1      -33.     NA B6  -0.6      -18.     NA    good B7  -1.8      -54.     NA B8  -1.1       -33.     NA  B9   1.8       54.     NA B10  1.2       36.     NA    B11 -1.7       -51.     NA B12  1.1       33.     NA 

65   Fri Mar 1 23:06:15 2013 KojiOpticsConfigurationMore perpendicularity test final

Perpendicularity of the "E" mirror was measured.

Mounting Prisms:
(criteria: 30arcsec = 145urad => 0.36mm spot shift)
SN  Meas.(div) ArcSec Spec. 10   0.3989    11.97   29    good 11   0.2202     6.60   16    good 16   0.1907     5.72    5    good 20  -0.591    -17.73    5    good 21  -2.378    -71.34   15 21  -1.7      -51.     15 01  -0.5      -15.     52 02  -2.5      -75.     48 06  -1.0      -30.     15    good 07   1.7       51.     59 12  -2.2      -66.     40 13  -0.3      - 9.     12    good 14  -2.8      -84.     27 15  -2.5      -75.     50 17   0.7       21.     48 22   2.9       87.     63

Mirror A:
A1  -0.5      -15.     NA    good A3   0.5       15.     NA    good A4   0.9       27.     NA    good A5   0.4       12.     NA    good A6   0.1        3.     NA    good A7   0.0        0.     NA    good A8   0.0        0.     NA    good A9   0.0        0.     NA    good A10  1.0       30.     NA    good A11  0.3        9.     NA    good A12  0.1        3.     NA    good A13  0.0        0.     NA    good A14  0.6       18.     NA    good

Mirror B: B1  -0.9      -27.     NA    good B2  -0.6      -18.     NA    good B3  -0.9      -27.     NA    good B4   0.7       21.     NA    good B5  -1.1      -33.     NA B6  -0.6      -18.     NA    good B7  -1.8      -54.     NA B8  -1.1       -33.     NA  B9   1.8       54.     NA B10  1.2       36.     NA    B11 -1.7       -51.     NA B12  1.1       33.     NA

Mirror E: E1  -0.8      -24.     NA    good E2  -0.8      -24.      NA    good E3  -0.25     - 7.5     NA    good E4  -0.5      -15.     NA    good
 E5   0.8       24.     NA    good E6  -1.0      -30.     NA    good E7  -0.2      - 6.     NA    good E8  -0.8      -24.     NA    good E9  -1.0      -30.     NA    good E10  0.0        0.     NA    good E11 -1.0      -30.     NA    good E12 -0.3      - 9.     NA    good E13 -0.8      -24.     NA    good
E14 -1.0      -30.     NA    good E15 -1.2      -36.     NA E16 -0.7      -21.     NA    good E17 -0.8      -24.     NA    good E18 -1.0      -30.     NA    good 

86   Thu Mar 28 03:37:07 2013 ZachOpticsConfigurationTest setup input optics progress

[Lisa, Zach]

Last night (Tuesday), I finished setting up and aligning most of the input optics for the OMC characterization setup. See the diagram below, but the setup consists of:

• HWP+PBS for power splitting into two paths:
• EOM path
• Resonant EOM for PDH sideband generation
• Broadband EOM for frequency scanning
• AOM path
• Double-passed ~200-MHz Isomet AOM for subcarrier generation. NOTE: in this case, I have chosen the m = -1 diffraction order due to the space constraints on the table.
• Recombination of paths on a 50/50 beam splitter---half of the power is lost through the unused port into a black glass dump
• Coupler for launching dual-field beam into a fiber (to OMC)

Today, we placed some lenses into the setup, in two places:

1. In the roundabout section of the AOM path that leads to the recombination, to re-match the AOM-path beam to that of the EOM path
2. After the recombination beam splitter, to match the combined beam mode into the fiber

We (Koji, Lisa, and myself) had significant trouble getting more than ~0.1% coupling through the fiber, and after a while we decided to go to the 40m to get the red-light fiber illuminator to help with the alignment.

Using the illuminator, we realigned the input to the coupler and eventually got much better---but still bad---coupling of ~1.2% (0.12 mW out / 10 mW in). Due to the multi-mode nature of the illuminator beam, the output cannot be used to judge the collimation of the IR beam; it can only be used to verify the alignment of the beam.

With 0.12 mW emerging from the other end of the fiber, we could see the output quite clearly on a card (see photo below). This can tell us about the required input mode. From the looks of it, our beam is actually focused too strongly. We should probably replace the 75mm lens again with a slightly longer one.

Lisa and I concurred that it felt like we had converged to the optimum alignment and polarization, which would mean that the lack of coupling is all from mode mismatch. Since the input mode is well collimated, it seems unlikely that we could be off enough to only get ~1% coupling. One possibility is that the collimator is not well attached to the fiber itself. Since the Rayleigh range within it is very small, any looseness here can be critical.

I think there are several people around here who have worked pretty extensively with fibers. So, I propose that we ask them to take a look at what we have done and see if we're doing something totally wrong. There is no reason to reinvent the wheel.

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