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ID Date Author Type Category Subject
16051   Mon Apr 19 19:40:54 2021 YehonathanUpdateGeneralGlue Freezer completely frozen

{Paco, Yehonathan}

We broke the last chunk of ice and cleaned the fridge. We move the fridge back inside and plugged it into the wall. The glues were moved back from the main fridge.

The batteries that were found soaking wet are now somewhat dry and were left on the cabinet drawers for future recycling.

 Quote: {Anchal, Paco, Yehonathan} We took the glue fridge outside.

3958   Fri Nov 19 18:20:59 2010 SureshUpdateSUSGlue dynamics!

I examined the magnet-dumbbell joints under the microscope to see whether the glue that I applied yesterday was sufficient or in excess.

I think the pictures below speak for themselves !

During the gluing process the Al dumbbell stays below and the magnet with a drop of glue on the lower face is placed on it and held in the teflon fixture.  As seen in the pics the glue seems to have run up the surface of the magnet and has not collected in the narrow part of the dumbell.  So it has climbed up along the narrow gaps between the magnet and the teflon fixture by capillary action. The glue stops where the teflon fixture ends, a little before reaching the free end of the magnet, which further indicates the capillary action.

Attachment 2: Too_much_glue_2.jpg
2618   Fri Feb 19 15:29:14 2010 kiwamuUpdateCOCGluing dumbbells and magnets

Jenne and kiwamu

We have glued the dumbbells to the magnets that will be used for the ITMs

We made two sets of glued pair of the dumbbell and the magnet ( one set means 6 pairs of the dumbbell and the magnet. Therefore in total we got 12 pairs. )

You can see the detailed procedure we did on the LIGO document E990196.

Actually we performed one different thing from the documented procedure;

we made scratch lines on the surface of the both dumbbells and magnets by a razor blade.

According to Steve and Bod, these scratch make the strength of the glues stronger.

Now the dumbbell-magnet pairs are on the flow bench in the clean room, and supported by a fixture Betsy sent us.

- -  notes

On the bench the left set is composed by magnets of 244 +/- 3 Gauss and the right set is 255 +/- 3 Gauss.

12305   Fri Jul 15 16:23:51 2016 ericq UpdateGeneralGluing setbacks

[ericq, Lydia]

Here is a picture of the ETMX guide rod post-gluing. There is unfortunately a fair amount of excess. The "tab" is the result from the epoxy travelling along the finger of the fixture arm that held the guide rod.

We set out to glue the previously remove ETMX side magnet, and set up the fixture to do so. For ETMX we needed 3 mm of shimming on the thick side, and 6mm on the thin side.

However, while cleaning the magnet+dumbbell base of epoxy residue, I broke the dumbbell off of the magnet

We then fetched the spare side magnet that Steve had been holding onto. While cleaning it, it was dropped and dissapeared from this plane of existence

So, instead of gluing a side magnet today, we are gluing the existing magnet and dumbbell back together:

Sadly, this used up the last of our EP30.

Though Koji had the foresight to order more(), it will not arrive until Monday/Tuesday, so no side magnet gluing until then.

5850   Wed Nov 9 16:03:21 2011 kiwamuSummaryGeneralGoal this week

Goal of this week :  ALS on the Y arm

Minimum success : Detection of the green beatnote between the freq-doubled PSL and the Y arm transmitted light

5885   Mon Nov 14 11:32:02 2011 kiwamuSummaryGeneralGoal this week

Goal of this week : Noise budgeting on the Y arm ALS

Minimum success : bring the Y arm to the resonance by using ALS  NOISE BUDGETING!!!

=> as a preparation the incident beam pointing needs to be fixed by steering the MC suspensions.

 Quote from #5850http://nodus.ligo.caltech.edu:8080/40m/5850 Goal of this week :  ALS on the Y arm (DONE)

3651   Tue Oct 5 14:11:09 2010 josephb, alexUpdateCDSGoing to from rtlinux to Gentoo requires front end code clean out

Apparently when updating front end codes from rtlinux to the patched Gentoo, certain files don't get deleted when running make clean, such as the sysfe.rtl files in the advLigoRTS/src/fe/sys directories.  This fouls the start up scripts by making it think it should be configured for rtlinux rather than the Gentoo kernel module.

13304   Fri Sep 8 12:08:32 2017 GabrieleSummaryLSCGood reconstruction of PRMI degrees of freedom with deep learning

Introduction

This is an update of my previous reports on applications of deep learning to the reconstruction of PRMI degrees of freedom (MICH/PRCL) from real free swinging data. The results shown here are improved with respect to elog 13274 and 13294. The training is performed in two steps, the first one using simulated data, and the second one fine tuning the parameters on real data.

First step: training with simulation

This step is exactly the same already described in the previous entries and in my talks at the CSWG and LVC. For details on the DNN architecture please refer to G1701455 or G1701589. Or if you really want all the details you can look at the code. I used the following signals as input to the DNN: POPDC, POP22_Q, ASDC, REFL11_I/Q, REFL55_I/Q, AS55_I/Q. The network is trained using linear trajectories in the PRCL/MICH space, and signals obtained from a model that simulates the PRMI behavior in the plane wave approximation. A total of 150000 trajectories are used. The model includes uncertainties in all the optical parameters of the 40m PRMI configuration, so that the optical signals for each trajectory are actually computed using random optical parameteres, drwn from gaussian distributions with proper mean and width. Also, white random gaussian sensing noise is added to all signals with levels comparable to the measured sensing noise.

The typical performance on real data of a network pre-trained in this way was already described in elog 13274, and although being reasoble, it was not too good.

Second step: training with real data

Real free swinging data is used in this step. I fine tuned the demodulation phases of the real signals. Please note that due to an old mistake, my convention for phases is 90 degrees off, so for example REFL11 is tuned such that PRCL is maximized in Q instead of I. Regardless of this convention confusion, here's how I tuned the phases:

• REFL11: PRCL is all in Q when crossing the carrier resonance
• REFL55: PRCL is all in Q when crossing the carrier resonance
• AS55: MICH is all in Q when crossing the PRCL carrier resonance
• POP22: signal peaking in Q when crossing carrier or sideband resonances. Carrier resonance crossing gives positive sign

Then I built the following training architecture. The neural network takes the real signals and produces estimates of PRCL and MICH for each time sample. Those estimates are used as the input for the PRMI model, to produce the corresponding simulated optical signals. My cost function is the squared difference of the simulated versus real signals. The training data is generated from the real signals, by selection 100000 random 0.25s long chunks: the history of real signal over the whole 0.25s is used as input, and only the last sample is used for the cost function computation. The weights and biases of the neural network, as well as the model parameters are allowed to change during the learning process. The model parameters are regularized to suppress large deviations from the nominal values.

One side note here. At first sight it might seems weird that I'm actually fedding as input the last sample and at the same time using it as the reference for the loss function. However, you have to remember that there is no "direct" path from input to output: instead all goes through the estimated MICH/PRCL degrees of freedom, and the optical model. So this actually forces the network to tune the reconstruction to the model. This approach is very similar to the auto-encoder architectures used in unsupervised feature learning in image recognition.

Results

After trainng the network with the two previous steps, I can produce time domain plots like the one below, which show MICH and PRCL signals behaving reasonably well:

To get a feeling of how good the reconstruction is, I produced the 2d maps shown below. I divided the MICH/PRCL plane in 51x51 bins, and averaged the real optical signals with binning determined by the reconstructed MICH and PRCL degrees of freedom. For comparison the expected simulation results are shown. I would say that reconstructed and simulated results match quite well. It looks like MICH reconstruction is still a bit "compressed", but this should not be a big issue, since it should still work for lock acquisition.

Next steps

There a few things that can be done to futher tune the network. Those are mostly details, and I don't expect significant improvements. However, I think the results are good enough to move on to the next step, which is the on-line implementation of the neural network in the real time system.

14044   Sun Jul 8 12:20:12 2018 JonSummaryAUXGouy Phase Measurements from AUX-Laser Scans

This note reports analysis of cavity scans made by directly sweeping the AUX laser carrier frequency (no sidebands). The measurement is made by sweeping the RF offset of the AUX-PSL phase-locked loop and demodulating the cavity reflection/transmission signal at the offset frequency.

Y-Arm Scan

Due to the simplicity of its expected response, the Y-arm cavity was scanned first as a test of the AUX hardware and the sensitivity of the technique. Attachment 1 shows the measured cavity transmission with respect to RF drive signal.

The AUX laser launch setup is capable of injecting up to 9.3 mW into the AS port. This high-power measurement is shown by the black trace. The same measurement is repeated for a realistic SQZ injection power, 70 uW, indicated by the red curve. At low power, the technique still clearly resolves the FSR and six HOM resonances. From the identified mode resonance frequencies the following cavity parameters are directly extracted.

YARM Gautam's Finesse Model Actual
FSR 3.966 MHz 3.967 MHz
Gouy phase 54.2 deg 52.0 deg

PRC Scan

An analogous scan was performed for the PRC, with the IFO locked on PSL carrier in PRMI. Attachment 2 shows the measurement of PRC transmission with respect to drive signal.

The scan resolves HOM resonances to at least ~13th order, whose frequencies yield the following cavity parameters.

PRC Gautam's Finesse Model Actual
FSR 22.30 MHz 22.20 MHz
Gouy phase 13.4 deg 15.4 deg

SRC Scan

Ideally (and at the sites) the SRC mode resonances will be measured in SRMI configuration. Because every other cavity is misaligned, this configuration provides an easily-interpretable spectrum whose resonances can all be attributed to the SRC.

Due to time constraints at the 40m, the IFO could not be restored to lockability in SRMI. It has been more than two years since this configuration was last run. For this reason the scan was made instead with the IFO locked in DRMI, as shown in Attachment 3. The quantity measured is the AUX reflection with respect to drive signal.

This result requires far more interpretation because resonances of both the SRC and PRC are superposed. However, the resonances of the PRC are known a priori from the independent PRMI scan. The SRC mode resonances identified below do not conincide with any of the first five PRC mode resonances.

Based on the identified mode resonance frequencies, the SRC parameters are measured as follows.

SRC Gautam's Finesse Model Actual
FSR 27.65 MHz 27.97 MHz
Gouy phase 10.9 deg 8.8 deg

Lessons Learned

From experience with the 40m, the main challenges to repeating this measurement at the sites will be the following.

• Pointing jitter of the input AUX beam. This causes the PSL-AUX beam overlap to vary at transmission (or reflection), causing variation in the amplitude of the AUX-PSL beat note. As far as we can tell, the frequency of the resonances (the only object of this measurement) is not changing in time, only the relative amplitudes of the diferent mode peaks. I believe the SQZ alignment loops will mitigate this problem at the sites.
• Stabilization of the network analyzer time base. We found the intrinsic frequency stability of the network analyzer (Agilent 4395A) to be unacceptably large. We solved this problem by phase-locking the Agilent to an external reference, a 10-MHz signal provided by an atomic clock.
Attachment 1: yarm_aux_carrier_trans.pdf
Attachment 2: prmi_aux_carrier_trans.pdf
Attachment 3: drmi_aux_carrier_trans.pdf
Draft   Wed Jul 11 18:13:19 2018 keerthanaSummaryAUXGouy Phase Measurements from AUX-Laser Scans

From the Measurement Jon made, FSR is 3.967 MHz and the Gouy phase is 52 degrees. From this, the length of the Y-arm cavity seems to be 37.78 m and the radius of curvature of the mirror seems to be 60.85 m.

$Guoy Phase = \cos^{-1} \sqrt{g1.g2}$

$\\ g = 1- \frac{L}{R}$

$L = \frac {c} {2*FSR}$

FSR = Free spectral Range

L = Lenth of the arm

R = Radius of curvature of the mirror (R1 =$\infty$  , R2= unknown)

Quote:

This note reports analysis of cavity scans made by directly sweeping the AUX laser carrier frequency (no sidebands). The measurement is made by sweeping the RF offset of the AUX-PSL phase-locked loop and demodulating the cavity reflection/transmission signal at the offset frequency.

Y-Arm Scan

Due to the simplicity of its expected response, the Y-arm cavity was scanned first as a test of the AUX hardware and the sensitivity of the technique. Attachment 1 shows the measured cavity transmission with respect to RF drive signal.

The AUX laser launch setup is capable of injecting up to 9.3 mW into the AS port. This high-power measurement is shown by the black trace. The same measurement is repeated for a realistic SQZ injection power, 70 uW, indicated by the red curve. At low power, the technique still clearly resolves the FSR and six HOM resonances. From the identified mode resonance frequencies the following cavity parameters are directly extracted.

YARM Gautam V. Finesse Model Actual
FSR 3.966 MHz 3.967 MHz
Gouy phase 54.2 deg 52.0 deg

14822   Thu Aug 1 13:55:34 2019 DuoBureaucracyEquipment loanGpib module taken to QIL lab

vanna --> QIL.

gautam 20190804: The GPIB module + power supply were returned to me by Duo ~5pm today at the 40m.

4433   Wed Mar 23 14:19:35 2011 KojiSummaryGeneralGrand Plan

This is the grand plan we talked about in the beginning of the meeting.

• (Kiwamu) X-end Green cleaning up / Prep for DRMI
• (Bryan) Y-end Green
• (Suresh) Help Bryan / RF (w. Kevin)
• (Jenne) MC WFS / Y-arm IR alignment / MC adaptive feedforward (incl. CDS)
• (Koji) LSC
• (Joe) CDS cleaning up
• (Jamie) Help Joe / Noise Budget
• (Larisa) PMC scan / PSL photo&diagram
• (Barbarela) ASS
3018   Sun May 30 22:18:49 2010 ranaUpdatePEMGranite slab w/ lead balls is so far a flop

The seismometers showed an increased noise in the Y-direction when put on top of the granite slab. By tapping the slab, you can tell that its really a mechanical resonance of the lead balls + granite system at ~15-20 Hz.

I tried new balls, flipping the slab upside down, and sitting on the slab for awhile. None of this changed the qualitative behavior, although each of the actions changed the resonance frequencies by several Hz.

I have removed the granite/balls and put the seismometers back on the linoleum floor. The excess noise is gone. I have put the new big box back on top of them and we'll see how the data looks overnight.

I expect that we should remove the linoleum in a wider area and put the seismometers directly on the floor.

3022   Mon May 31 22:52:57 2010 ranaUpdatePEMGranite slab w/ lead balls is so far a flop

This plot shows the noise with the box on, but no granite. We're still pretty far off from the Guralp data sheet.

I implemented software rotation in the huddle subtraction as Valera suggested and it works much better. The two plots below show the before and after. So far this is just 2 deg. of rotation around the z-axis. I'm assuming that aligning the seismometers vertically via bubble level is good enough for the z-axis, but I haven't calibrated the bubble yet.

The residual slope is now suspiciously smooth. I somehow suspect that our readout electronics can still be responsible. We need to hook up a 9V battery to the input terminals to check it out. Its a little steeper than 1/f and I thought that we had exonerated the Guralp breakout box in the past, but now I'm not so sure. I'll let Jenne comment on that.

I also noticed that we have not yet divided by sqrt(2) to account for the fact that we are subtracting 2 seismometers. In principle, an unbiased estimate of the single seismometer noise will be lower by sqrt(2) than the green curve.

8414   Thu Apr 4 13:39:12 2013 Max HortonUpdateSummary PagesGraph Limits

Graph Limits: The limits on graphs have been problematic.  They often reflect too large of a range of values, usually because of dropouts in data collection.  Thus, they do not provide useful information because the important information is washed out by the large limits on the graph.  For example, the graph below shows data over an unnecessarily large range, because of the dropout in the 300-1000Hz pressure values.

The limits on the graphs can be modified using the config file found in /40m-summary/share/c1_summary_page.ini.  At the entry for the appropriate graph, change the amplitude-lim=y1,y2 line by setting y1 to the desired lower limit and y2 to the desired upper limit.  For example, I changed the amplitude limits on the above graph to amplitude-lim=.001,1, and achieved the following graph.

The limits could be tightened further to improve clarity - this is easily done by modifying the config file.  I modified the config file for all the 2D plots to improve the bounds.  However, on some plots, I wasn't sure what bounds were appropriate or what range of values we were interested in, so I will have to ask someone to find out.

Next:  I now want to fix all the funny little problems with the site, such as scroll bars appearing where they should not appear, and graphs only plotting until 6PM.  In order to do this most effectively, I need to restructure the code and factor it into several files.  Otherwise, the code will not only be much harder to edit, but will become more and more confusing as I add on to it, compounding the problems that we currently have (i.e. that this code isn't very well documented and nobody knows how it works).  We need lots of specific documentation on what exactly is happening before too many changes are made.  Take the config files, for example.  Someone put a lot of work into them, but we need a README specifying which options are supported for which types of graphs, etc.  So we are slowed down because I have to figure out what is going on before I make small changes.

To fix this, I will divide the code into three main sectors.  The division of labor will be:
- Sector 1: Figure out what the user wants (i.e. read config files, create a ConfigParser, etc...)
- Sector 2: Process the data and generate the plots based on what the user wants
- Sector 3: Generate the HTML

3418   Fri Aug 13 01:53:12 2010 GopalUpdateOptic StacksGravity Implementation Confirmed

Time Domain Analysis on a Driven, Damped Simple Pendulum has produced a method for implementing gravity.

• Previous Frequency Domain testing lead to unwanted oscillations of all loads.
• Prescribed accelerations at first seemed to create a constant gravity, but instead incorrectly constrained net acceleration to the inputted amount

Methodology:

1) An (approximately) impulse displacement was applied in the horizontal direction. The pendulum bob's displacement was observed for varying pendulum lengths.

2) The drive and response displacements vs. time were FFT'd to produce transfer functions.

3) The fundamental frequencies were inverted, squared, and plotted against frequency.

4) Since the graph is linear with an R^2 of over 0.99, it is reasonable to assume that gravity is properly acting as a restoration force.

Attachment 1: Pendulum_Length.png
Attachment 2: Pendulum_Length.png
15062   Tue Dec 3 00:03:57 2019 gautamUpdateLSCGreen ALS also shows elevated noise with high arm buildup

Summary:

1. While noisier, I was able to control the arm lengths to ~30pm RMS(!) using the green ALS beats as error signals (cf. ~10 pm RMS with the IR ALS system).
2. The PRMI could be locked with a CARM offset applied.
3. When lowering the CARM offset, I saw an increase in the in-loop ALS error signal, just as I had with the IR beat.
4. IR TRX / TRY unsurprisingly did not stabilize in any meaningful way.
5. The noise increase seems to have some periodicity along the frequency axis - need to think about what this means.
6. Since there is no apparent benefit to using the green ALS beats, I restored the IR system. The green PDs should still retain somewhat good alignment if one wishes to do a comparison measurement.
7. While the shadow sensors of the ITMs report elevated noise, it is unlikely to be responsible for the cavity moving by the amount suggested by the elevated ALS error signals because of the digital low-pass filtering and 1/f^2 of the pendulum.
8. I confirmed that the ITM shadow sensors do not report elevated noise when the PRMI is locked such that the carrier is resonant. In this config, there is comparable circulating power in the PRC as to when the CARM offset is reduced to ~0.
9. The fact that the IR and green beats both show similar increase in noise suggestes that the cavity length / laser frequency is in fact being modulated, but I still don't know what the exact mechanism is.

was worth a shot i guess.

Trawling through some elogs, I see that this kind of feature showing up in the ALS CARM is not a new problem, see for example here. But I can't find out what the resolution was.

Attachment 1: ALSnoiseIncrease_greenBeat.pdf
15058   Mon Dec 2 00:27:20 2019 gautamUpdateALSGreen ALS resurrection

Attachment #1 - comparison of phase tracker servo angle fluctuations for the green beat vs IR beat.

• To convert to Hz, I used the PT servo calibration detailed here.
• This is only a function of the delay line length and not the signal strength, so shouldn't be affected by the difference in signal strength between the IR and green beats.
• For the green beat - I divided the measured spectra by 2 to convert the green beat frequency fluctuations into equivalent IR frequency fluctuations.
• There is no whitening before digitization. I believe the measured spectra are dominated by ADC noise above ~50 Hz. See this elog for the frequency discriminant as a funtion of signal strength, so 5uV/rtHz ADC noise would be ~2 Hz/rtHz for a -5dBm signal, which is what I expect for the Y beat, and ~0.5 Hz/rtHz for a +5dBm signal, which is what I expect for the X beat. Hence the brown (Green beat, XARM) being lower than the green trace (IR beat, XARM) isn't real, it is just because of my division of 2. So I guess that calibration factor I applied is misleading.
• I did not yet check the noise in the other configuration - arm lengths controlled using ALS, and POX/POY as the OOL sensors. To be tried tonight.

Attachment #2 - RIN of the DCPDs.

• I noticed that over 10s of seconds, the GTRY level was fluctuating by ~5%.
• This was much more than any drift seen in the GTRX level.
• Measuring the RIN on the DCPDs (Thorlabs PDA36A) supports this observation (spectra were divided by DC value to convert into RIN units).
• There is ~120uW (1.6 VDC, compatible with 30dB gain setting) incident on the GTRX PD, and ~6uW (170 mVDC, compatible with 40dB gain setting) incident on the GTRY PD.
• Not sure what is driving this drift - I don't see any coherence with the IR TRY signal, so doesn't seem like it's the cavity.

Characterization of the green beat setup [past numbers]:

• With some patient alignment effort (usual near-field/far-field matching), I was able to recover the green beat signals.
• Overall, the numbers I measured today are consistent with what was seen in the past when we had the ability to lock using green ALS.
• The mode-matching between the PSL and AUX green beams are still pretty abysmal, ~40-50%. The mode shapes are clearly different, but for now, I don't worry about this.
• I saw some strong AM of the beat signal (for both EX and EY beats) while I was looking at it on a scope, see Attachment #3. This AM is not visible in the IR beat, not sure what to make of it. The frequency of the AM is ~1 MHz, but it's hard to nail this down because the scope doesn't have a very long buffer, and I didn't look at the frequency content on the Agilent (yet).

o BBPD DC output (mV), all measured with Fluke DMM

             XARM   YARM
 V_DARK:     +1.0    +2.0  V_PSL:      +8.0    +13.0  V_ARM:      +157.0  +8.0

o BBPD DC photocurrent (uA)
I_DC = V_DC / R_DC ... R_DC: DC transimpedance (2kOhm)  I_PSL:       3.5    5.5  I_ARM:      78.0    3.0

o Expected beat note amplitude I_beat_full = I1 + I2 + 2 sqrt(e I1 I2) cos(w t) ... e: mode overlap (in power) I_beat_RF = 2 sqrt(e I1 I2) V_RF = 2 R sqrt(e I1 I2) ... R: RF transimpedance (2kOhm) P_RF = V_RF^2/2/50 [Watt]      = 10 log10(V_RF^2/2/50*1000) [dBm]
     = 10 log10(e I1 I2) + 82.0412 [dBm]
     = 10 log10(e) +10 log10(I1 I2) + 82.0412 [dBm]

for e=1, the expected RF power at the PDs [dBm]  P_RF:      -13.6  -25.8

o Measured beat note power (measured with oscilloscope, 50 ohm input impedance)        P_RF:      -17.95dBm (80 mVpp)  -28.4dBm (24mVpp)   (40MHz and 42MHz)       e:        37%                    55  [%]                                             

I also measured the various green powers with the Ophir power meter (filter off):

o Green light power (uW) [measured just before PD, does not consider reflection off the PD]
 P_PSL:       18    24  P_ARM:       400     13

The IR beat is not being made at the moment because I blocked the PSL beam entering the fiber.

Attachment 1: ALSnoiseComparison.pdf
Attachment 2: ALS_TR_RIN.pdf
Attachment 3: GreemAM.pdf
9406   Tue Nov 19 00:18:30 2013 JenneUpdateLSCGreen ALS wishlist

EricQ said that he's going to start hanging out at the 40m a bit, and I was thinking about what I can have him help me with.  This lead to me writing up a wishlist for things that have to do with the ALS system and green lasers.  Some of these are very small tasks, while others are pretty big.  They are certainly not all high priority.  But, they're on my wishlist.

Calibrations

• How many counts of SLOW_SERVO2_OFFSET is one green FSR (for each arm)?
• Calibrate ALS OFFSETTER#_OFFSET counts to nm or Hz offset between the end lasers and the PSL.

Automation / script writing

• Automate finding the beatnotes (requires freq counters)
• Automate locking the ALS

Digital Acquisition

• All 3 laser temperatures
• Frequency counting of beatnotes

Hardware

• Install flipper mirrors on the PSL table to switch between trans DCPDs and far-field views of beam overlap for each arm.
• IR beatnote project - send pickoff of end lasers to PSL via fiber, set up beat detection for each arm, create PLLs.
• Yarm PZT installation and autoalignment.
16845   Wed May 11 15:49:42 2022 JCUpdateOPLEV TablesGreen Beam OPLEV Alignment

[Paco, JC]

Paco and I began aligning the Green Beam in the BS Oplev Table. while aligning the GRN-TRX, the initial beam was entering the table a bit low. To fix this, Paco went into the chamber and correcting the pitch with the steering mirror. The GRN-TRX is now set up, both the PD and Camera. Paco is continuing to work on the GRN-TRY and will update later on today.

In the morning, I will update this post with photos of the new arrangement of the BS OPLEV Table.

Update Wed May 11 16:54:49 2022

[Paco]

GRY is now better mode matched to the YARM and is on the edge of locking, but it more work is needed to improve the alignment. The key difference this time with respect to previous attempts was to scan the two lenses on translation stages along the green injection path. This improved the GTRY level by a factor of 2.5, and I know it can be further improved. Anyways, the locked HOMs are nicely centered on the GTRY PD, so we are likely done with the in-vac GTRY GTRX alignment.

Update Wed May 12 10:59:22 2022

[JC]

The GTRX PD is now set up and connected. The camera have been set to an angle because the cable to connect it is too thick for the camera to maintain its original position along the side.

Attachment 1: IMG_0770.jpeg
2907   Mon May 10 20:03:22 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.

The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.

Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to

b + a*erf(sqrt(2)*(x-x0)/w) with the following results:

scan down: w = (0.908 ± 0.030)mm  chi^2 = 3.8

scan up:      w = (0.853 ± 0.025)mm   chi^2 = 2.9

giving a weighted value of w = (0.876 ± 0.019)mm at this distance.

The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.

 distance (cm) vertical w (µm) horizontal w (µm) 3.2 ± 0.1 1231 ± 8 1186 ± 7 4.7 ± 0.1 1400 ± 4 1363 ± 6 7.4 ± 0.1 1656 ± 5 1625 ± 9 9.6 ± 0.1 1910 ± 10 1863 ± 9 12.5 ± 0.1 2197 ± 8 2176 ± 8 14.6 ± 0.1 2450 ± 12 2416 ± 10 17.5 ± 0.1 2717 ± 12 2694 ± 14 20.0 ± 0.1 2973 ± 16 2959 ± 8 22.4 ± 0.1 3234 ± 12 3193 ± 14

This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:

For the vertical beam profile:

reduced chi^2 = 3.29

x0 = (-87   ± 1)    mm

w0 = (16.30 ± 0.14) µm

For the horizontal beam profile:

reduced chi^2 = 2.01

x0 = (-82   ± 1)    mm

w0 = (16.12 ± 0.10) µm

Note: These fits were done with the beam diameter instead of the beam radius. The correct fits to the beam radius are here: http://nodus.ligo.caltech.edu:8080/40m/2912

Attachment 1: vbp.jpg
Attachment 2: vbp_residuals.jpg
Attachment 3: hbp.jpg
Attachment 4: hbp_residuals.jpg
2909   Mon May 10 22:25:03 2010 KojiUpdateGreen LockingGreen Laser Beam Profile

Hey, what a quick work!

But, wait...

1) The radius of the beam was measured by the razor blade.

2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1)

3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it?

So the fitting must be recalculated with correct radius.
Make sure that you always use radius and write with a explicit word "radius" in the record.

Quote:

Kiwamu and Kevin measured the beam profile of the green laser by the south arm ETM.

The following measurements were made with 1.984A injection current and 39.65°C laser crystal temperature.

Two vertical scans (one up and one down) were taken with a razor blocking light entering a photodiode with the razor 7.2cm from the center of the lens. This data was fit to

b + a*erf(sqrt(2)*(x-x0)/w) with the following results:

scan down: w = (0.908 ± 0.030)mm  chi^2 = 3.8

scan up:      w = (0.853 ± 0.025)mm   chi^2 = 2.9

giving a weighted value of w = (0.876 ± 0.019)mm at this distance.

The beam widths for the profile fits were measured with the beam scanner. The widths are measured as the full width at 13.5% of the maximum. Each measurement was averaged over 100 samples. The distance is measured from the back of the lens mount to the front face of the beam scanner.

 distance (cm) vertical w (µm) horizontal w (µm) 3.2 ± 0.1 1231 ± 8 1186 ± 7 4.7 ± 0.1 1400 ± 4 1363 ± 6 7.4 ± 0.1 1656 ± 5 1625 ± 9 9.6 ± 0.1 1910 ± 10 1863 ± 9 12.5 ± 0.1 2197 ± 8 2176 ± 8 14.6 ± 0.1 2450 ± 12 2416 ± 10 17.5 ± 0.1 2717 ± 12 2694 ± 14 20.0 ± 0.1 2973 ± 16 2959 ± 8 22.4 ± 0.1 3234 ± 12 3193 ± 14

This data was fit to w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2) with lambda = 532nm with the following results:

For the vertical beam profile:

reduced chi^2 = 3.29

x0 = (-87 ± 1)mm

w0 = (16.30 ± 0.14)µm

For the horizontal beam profile:

reduced chi^2 = 2.01

x0 = (-82 ± 1)mm

w0 = (16.12 ± 0.10)µm

2910   Tue May 11 14:39:17 2010 AidanUpdateGreen LockingGreen Laser Beam Profile

Here's a photo of the set-up used. The beam profile is measured relative to the f=-100mm lens.

Attachment 1: P5110057_beams.jpg
2912   Tue May 11 17:02:43 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

 Quote: Hey, what a quick work! But, wait... 1) The radius of the beam was measured by the razor blade. 2) The diameter of the beam (13.5% full-width) at each point was measured by Beam Scan. The one at z=~7cm was consistent with 1) 3) The data 2) was fitted by a function w = sqrt(w0^2+lambda^2*(x-x0)^2/(pi*w0)^2). This is defined for the radius, isn't it? So the fitting must be recalculated with correct radius. Make sure that you always use radius and write with a explicit word "radius" in the record.
I recalculated the fits using the radius of the beam instead of the diameter of the beam at 13.5% full-width with the following results:

For the vertical beam profile:

reduced chi^2 = 3.25

x0 = (-86 ± 1)mm

w0 = (46.01 ± 0.38)µm

For the horizontal beam profile:

reduced chi^2 = 2.05

x0 = (-81 ± 1)mm

w0 = (45.50 ± 0.28)µm

Attachment 1: vbp.jpg
Attachment 2: vbp_residuals.jpg
Attachment 3: hbp.jpg
Attachment 4: hbp_residuals.jpg
2916   Wed May 12 03:42:38 2010 KojiUpdateGreen LockingGreen Laser Beam Profile

Strange. I thought the new result became twice of the first result. i.e. w0=32um or so.

Can you explain why the waist raidus is estimated to be three times of the last one?
Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time,
but is 0.6mm?

The measurements have been done at the outside of the Rayleigh range.
This means that the waist size is derived from the divergence angle

theta = lambda / (pi w0)

At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0.
So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.

 Quote: I recalculated the fits using the radius of the beam instead of the diameter of the beam at 13.5% full-width with the following results: For the vertical beam profile: reduced chi^2 = 3.25 x0 = (-86 ± 1)mm w0 = (46.01 ± 0.38)µm For the horizontal beam profile: reduced chi^2 = 2.05 x0 = (-81 ± 1)mm w0 = (45.50 ± 0.28)µm

2933   Fri May 14 16:14:37 2010 KevinUpdateGreen LockingGreen Laser Beam Profile

 Quote: Strange. I thought the new result became twice of the first result. i.e. w0=32um or so. Can you explain why the waist raidus is estimated to be three times of the last one? Can you explain why the measured radius @~70mm is not 0.8mm, which you told us last time, but is 0.6mm? The measurements have been done at the outside of the Rayleigh range. This means that the waist size is derived from the divergence angle theta = lambda / (pi w0) At the beginning you used diameter instead of radius. This means you used twice larger theta to determine w0. So if that mistake is corrected, the result for w0 should be just twice of the previous wrong fit.
I was off by a factor of sqrt(2). The correct fit parameters are

for the vertical beam profile:

reduced chi^2 = 3.28

x0 = (-87 ± 1) mm

w0 = (32.59 ± 27) µm

for the horizontal beam profile

reduced chi^2 = 2.02

x0 = (-82 ± 1) mm

w0 = (32.23 ± 20) µm

In the following plots * denotes vertical data points and + denotes horizontal data points. The blue curve is the fit to the vertical data and the purple curve is the fit to the horizontal data.

Attachment 1: profile.png
Attachment 2: residuals.png
9442   Wed Dec 4 21:41:09 2013 ericqUpdateGreen LockingGreen PDH Characterization

My job right now is to characterize the green PDH loops on each arm. Today, Jenne took me around and pointed at the optics and electronics involved. She then showed me how to lock the green beams to the arms (i.e. opening the shutters until you hit a TM00 shape on the transmitted beam camera). Before lunch, the y arm was easiest to lock, and the transmitted power registered at around 0.75.

After lunch, I took a laptop and SR785 down to the y end station. I unhooked the PDH electronics and took a TF of the servo (without its boost engaged, which is how it is currently running) and noise spectrum with the servo input terminated.

I then set up things a la ELOG 8817 to try and measure the OLTF. However, at this point, getting the beam to lock on a TM00 (or something that looked like it) was kind of tough. Also, the transmitted power was quite a bit less than earlier (~0.35ish), and some higher order modes were higher than that (~0.5). Then, when I would turn on the SR785 excitation, lock would be lost shortly into the measurement, and the data that was collected looked like nonsense. Later, Koji noted that intermittent model timeouts were moving the suspensions, thus breaking the lock.

We then tried to lock the x arm green, to little success. Koji came to the conclusion that the green input pointing was not very good, as the TM00 would flash much less brightly than some of the much higher order modes.

Tomorrow, I will measure the x arm OLTF, as it doesn't face the same timeout issue that is affecting the y arm.

9447   Fri Dec 6 12:45:51 2013 ericqUpdateGreen LockingGreen PDH Characterization

Yesterday, made a slew of measurements on the X-arm when locked on green. By tweaking the temperature loop offset and the green input PZT pointing, I was able to get the transmitted green to around 1.0. The PDH board gain was set to 4.0. I had trouble making swept sine measurements of the OLTF; changing the excitation amplitude for different frequency ranges would result in discontinuities in the measured TF, and there was only a pretty narrow band around the UGF that seemed to have reasonable coherence.

So, I used the SR785 as a broadband noise generator and measured the TF via dividing the spectra in regions of coherence. Specifically, I used the "pink noise" option of the SR785. I also used a SR560 as a low pass to get enough noise injected into the lower frequency range to be coherent, while not injecting so much into the higher frequencies that the mode hopped while measuring.

The servo board TF was easily fitted to a 4th order zpk model via VFIT, but I'm having trouble fitting the OLTF. (There is a feature in the servo TF that I didn't fit. This is a feature that Zach saw [ELOG 9537], and attributed to op amp instability) Plots follow. Also, while these need to be calibrated to show the real noise spectrum of the cavity motion, I'm attaching the voltage noise spectra of the error and control signals as a check that electronics/PD noise isn't dominating either signal.

10446   Wed Sep 3 18:42:43 2014 JenneUpdateLSCGreen PDH box boosts

From EricQ's simulations reported in elog 10390, we want to transition from ALS comm to DC transmission signals around 500 pm.  However, around 100 pm, the DC transmission signals have a sign flip, so we don't want to have the ALS swing that close to the CARM resonance.  So.  We want to be at about 500 pm, and not touch 100 pm.  So, we don't want our peak ALS motion to go beyond ~400 pm.  Which means that we need to have less than about 40 pm in-loop RMS, to avoid hitting 400 pm.  This is an ALS requirement, but since the analog PDH box is what forces the end laser to follow the arm cavity, and thus give us information about the arm length fluctuations, the PDH residual noise is part of our sensor noise for the full ALS.  So, we need to have the PDH in-loop RMS be less than 40 pm, integrated from a few kHz down to at least 30 mHz. Recall that above the ALS UGF (of about 200 Hz), the sensor noise will be suppressed by 1/f, so we should take that into account when we are looking at the PDH error signal, before we calculate the RMS motion.

Q also measured the in-loop error signal with the current Yend PDH box in elog 10430, and it looks like most of the RMS is coming from a few hundred Hz.  I designed a hack to the PDH board boost that has a zero at about 2kHz, and a gain of 30 at DC, so that we will win by squishing all that RMS.  Also, it shouldn't be too aggressive, so we should be able to leave it on all the time, and still acquire lock of the green laser to the arm, without having to do triggering.

The board schematic is at DCC D1400294.  The boost is also called the "integrator stage", although it will no longer be a simple integrator.

EDIT, JCD:  This cartoon is not correct for the non-boosted state, doesn't include effect of R16.

10448   Thu Sep 4 00:56:44 2014 JenneUpdateLSCGreen PDH box boosts

Okay, went back to the drawing board with Rana and Koji on PDH box stuff.

Currently (at least for the Yend), in the boost OFF state, we have an overall gain of about 50.  This is crazy big.  Also, the zero in the "transfer function stage" is around 1kHz, however our green cavity pole is (calculated) to be around 20 kHz.  Since these are supposed to cancel but they're not, we have a wide weird flat region in our loop TF.

So.  I calculated the changes to the TF stage that I'll need so that I have an increase of about 20 in DC gain, kept the pole at the same ~20Hz, but moved the zero way out to 18kHz.  I also calculated the changes needed for the integrator stage to make it effective at much higher frequency than it was designed for.  Now the pole is at 75 Hz, and the zero will be at 1.6kHz, and the high frequency gain will stay pretty close to the same with and without the boost.

Planned new TF stage:

Planned boost stage (with and without boost activated):

New boost stage only, so you can see the phase:

The schematic, modified to show my planned changes (which I will put in the DCC after I make the changes):

10450   Thu Sep 4 03:12:55 2014 ericqUpdateLSCGreen PDH box boosts

Jenne made her board modifications, and the measured TF agreed with the design. Alas, the green would not lock to the arm in this state.

I think that the reason is that the new TF does not have nearly as much low frequency gain as the old one, for a given UGF. Thus, for example, the 1Hz noise due to the pendulum resonance, has 30dB less loop gain suppressing it.

NEED MORE

10452   Thu Sep 4 16:45:10 2014 JenneUpdateLSCGreen PDH box boosts

As EricQ mentioned in last night's elog, the modifications were made to the Yend (SN 17) uPDH board.

R31 became 49.9 Ohms, R30 became 45.3kOhm, R24 became 1.02k, R16 became 1k, a new flying resistor is tombstoned up against R24 and connected by purple wire to C6 and it is 20k.  C28 is 183nF and C6 is 100nF.  These numbers were used in Q's simulation last night.

10458   Fri Sep 5 05:32:57 2014 JenneUpdateLSCGreen PDH box boosts

[Rana, Jenne, EricQ]

* Too much gain overall on Yend box, needed attenuator on output to get lock.  Rethought gain allocation.  Resoldered board, installed, Ygreen locks nicely.  Error point and control point spectra, box TF and open loop TF data collected, to be plotted.

* Q replaced the Xend box, with a matching TF.

* Locked both arms individually, Yend has lots of low freq fluctuation, Xend has some.  Can't do out of loop measurement since we're going well beyond the range of the PDH signals (Yarm RIN is between 1/2 and 1.) Plot TRX and TRY spectra with ALS lock vs. IR lock to get an idea of what frequencies we have a problem with.

* Tried comm/diff locking anyway.  Works.  Used cm_up script to get CARM to sqrtInvTrans.  Went to powers of about 0.5 (hard to say really, because of fluctuations), put sine at 611.1 Hz, 200 cts onto ETMs (-1*x, +1*y), looked at TF between ALS diff and AS55Q.  Put that amount into the static power normalization spot for AS55.  In steps of 0.1, reduced ALSdiff input matrix elements and increased AS55->DARM element.  2 (3?) times was able to get to AS55Q for DARM.  Lost lock once unknown reason, while reducing CARM offset.  Lost lock once trying to turn on FM4 LSC boost for DARM.

TRX/TRY spectra:

12097   Thu Apr 28 15:23:11 2016 ericqUpdateLSCGreen PDH demod lowpass

The 2F product out of the mixer is a natural concern when demodulating. However, I think this isn't so big of a deal in our green PDH servos; 420kHz isn't so high of a frequency that the servo amplifiers are bandwidth or slew-rate limited. Furthermore, the amplitude of this line is supressed by the loop somewhat, since it arises from the same field product that the loop is acting on. Measuring the Y end mixer output with a high impedance probe and the AG4395 shows it to be something like -50dBm.

In fact, the main thing that the pomona LPFs are accomplishing right now is filtering the 1F content of the mixer output that arises from the second order sideband creating a signal at 2F, and beating with the LO at (2F-1F)=1F. This line is something like -30dBm (5mVrms) at the mixer output; I can reproduce this amplitude with a back-of-the envelope calculation using a modulation depth of 0.3, 8V out of the PD at DC when unlocked, the mixer datasheet, and the nominal cavity parameters.

The nice thing about this is that we don't need to filter this after the mixer, we can use a [bandpass/lowpass/notch] filter before the mixer (as is done in the LSC demod boards) to filter out the 2F (420kHz) content of the PD signal, which will only introduce some small amount of linear time delay to the PDH loop, instead of the wicked phase loss from the current post-mixer LPF. We can then replace that 70kHz filter with something of lower order or higher corner frequency to win a good deal of phase in the PDH loop.

12098   Thu Apr 28 18:53:05 2016 ranaUpdateLSCGreen PDH demod lowpass

OK - but give us a circuit diagram and the expected before/after loop plots. Got to make sure we keep the right impedance from PD to mixer. Some of the Thorlabs PDs have a 50 Ohm instead of 0 Ohm source impedance. Maybe you can try it out now since the green arm is ready.

12101   Fri Apr 29 16:13:36 2016 ericqUpdateLSCGreen PDH demod lowpass

We can get as much, if not more, attenuation of the 1F line in the mixer output that we get from the post-mixer LPF from using the following passive filter between the PD and mixer RF input:

There should still be some kind of LPF after the mixer, but I haven't yet determined what it should be; this will determine how much phase the PDH loop wins. At most, this should win around 25 degrees at 10kHz.

The filter was designed by referencing the "Handbook of Filter Synthesis" by Zverev, looking for an elliptic filter for matched source and load impedences, 40dB min attenuation in the stopband, a stopband frequency that starts at twice the corner frequency, and minimizing the VSWR between the PD and filter in the passband.

In terms of the tables in the book, this means: n=5, rho=2%, theta=30deg, K**2 = 1.0. The dimensionless component values were scaled by the corner frequency of 200kHz, and reference impedence of 50 Ohm. (The corner is a little lower than the real modulation frequency, since the nonzero resistance of the inductors pushes the frequency up a bit)

The ideal capactior values do not correspond to things we have in hand, so I checked our stock and chose the closest value to each one.Unsurprisingly, due to these component substitutions, and the fact that the coilcraft inductors have a resistance of about 7 Ohms, the predicted TF of the realizable filter does not match the design filter exactly. However, the predicition still looks like it will meet the requirement of 40dB of supression of the 2F line in the PD signal. (Since we have tunable inductors, I've used the ideal inductor values in generating the TF. In practice I'll inspect the TF while I tune them)

 Desired Realizable C1 8.28 nF 10 nF C2 1.39 nF 1.5 nF C3 19.6 nF 22 nF C4 4.22 nF 4.7 nF C5 6.08 nF 6.8 nF L2 43.1 nH 32-48 nH + 7 Ohm L4 34.4 nH 32-48 nH + 7 Ohm

[In this TF plot, I've multiplied the real response by 2 to account for the voltage division that occurs with ideal 50 Ohm impedance matching, to make 0dB the reference for proper matching]

The filter's phase delay at the modulation frequency is just about 180, which as a time delay of 5usec works out to 9 degrees of phase loss at 10kHz in the PDH loop. According to some old measurements, the current LPF costs something like 35 degrees at 10k, so this wins at most around 25 degrees, depedent on what LPF we put after the mixer.

LISO source both traces is attached!

Attachment 3: elp_liso.zip
12110   Fri May 6 16:42:12 2016 ericqUpdateLSCGreen PDH demod lowpass

I've build the filter, and it seems to have the desired TF shape.

I also re-purposed the 70k lowass to a ~120k lowpass by changing the 68nF caps to 22nF caps, since we still want some post-mixer rolloff.

However, putting the ELPF in the chain caused some weird shapes in the OLG. I still need to get to the bottom of it. However, just with the post-mixer LPF modification, here's what the OLG looks like:

As Rana surmises, we definitely still add a boost and maintain a 10k UGF. I still need to look into the state of the remote boost....

12111   Fri May 6 19:08:52 2016 ranaUpdateLSCGreen PDH demod lowpass

Seems weird to design a PD lowpass with a corner at the modulation frequency. Recall what our strategy is with the other photodetectors we use for PDH servos: bandpass, not low-pass, and the band has to be wide enough to not effect the phase of the servo.

12112   Sat May 7 09:40:40 2016 ericqUpdateLSCGreen PDH demod lowpass

As I was looking at filter designs, it seemed difficult to get 40dB of supression at 2F with a bandpass without going to a pretty high order, which would mean a fair number of lossy inductors.

I'll keep working on it. Maybe we don't need 40dB...

12113   Sun May 8 08:39:21 2016 ranaUpdateLSCGreen PDH demod lowpass

Indeed. This is why the LSC PDs have a 2f notch in addition to the 1f resonance. In recent versions, we also put a 2f notch in the feedback of the preamp which comes after the diode but before the mixer. The overall 1f to 2f ratio that we get is in the 50-60 dB region. I don't think we have to go that far with this thing; having a double LC already seems like it should be pretty good, or we could have a single LC bandpass with a 2f notch all in one Pomona box.

10462   Fri Sep 5 21:13:57 2014 JenneUpdateLSCGreen PDH out of loop

I locked the arms with IR, and measured the beatnote spectra to get the out of loop noise for the PDH boxes.

Unfortunately, we don't have a reference saved (that I can find), so we're going to have to compare to an elog of Koji's from a month ago.  I have created an out of loop ALS reference .xml file in the Templates/ALS folder.

As we can see from Koji's elog 10302, the Xarm seems to have stayed the same, but the Yarm seems to have increased by about an order of magnitude below 100 Hz.  :(

10296   Wed Jul 30 10:16:54 2014 AndresUpdate40m Xend Table upgradeGreen Steering Mirror Upgrade completed

Green Steering Mirror Update

Yesterday, Nick and I completed the green steering mirrors upgrade. I attached the file that contained the procedure that we plan before we did the upgrade. We placed an iris at the input of the OL and we place another iris before the harmonic separator. We did not use the beam scanner because someone was using it, so what we did was to assume that the cavity is well align and place the iris so that we can recover the alignment. We used the measuring tape to approximate as close as we could the position where the lenses were supposed to go. I did a measurement of the derivative of the waist size in terms of the position of the lens and the derivative of the waist Position in terms of the lenses position at the optimum solution that a la mode give us. Because of this plot, we decide to mount lens 3 and lens 5 into translational stages. After mounting each lenses and mirrors we worked on the alignment of the beam into the cavity. We were able to align the green into the cavity and we were able to locked the cavity to the TEM00 mode. We started to work on the optimization of the mode matching. However, the maximum mode matching that we got was around 0.6, which we need to work a little bit more on the tuning of the mode matching. We leave the iris mounted on the table. I took a picture of the table, and I attached below. For the OL, we just make sure that the output where somehow hitting the QPD, but we didn't really I aligned it. We need to work a little bit more on the alignment of the OL and the tuning of the mirror to maximize the green mode matching.

Attachment 2: dWaistSize_dlensVsdWaistPosition_dlens.png
Attachment 3: XarmNewOpticalSetup.PNG
4267   Thu Feb 10 00:23:25 2011 JenneUpdateGreen LockingGreen TRX DC PD installed on PSL

Using a stray beam that is generated as the transmitted green beam from the Xarm goes through the viewport to the PSL table, I installed a fast lens (because I was constrained for space) and a Thorlabs PDA36 photodiode on the PSL table.

The BNC cable runs along the edge of the PSL table, up the corner hole with the huge bundle of cables, and over to IOO_ADC_0. It's channel 3 on the simulink model, which means that it is plugged into connector #4.

With the green resonating TEM00, I have ~1.4V output from the photodiode, as seen on a voltmeter. This corresponds to ~1500 counts on the MEDM screen.

Note to self:  Switch to a ~1cm diode with a boatload of gain (either from the 40m or Bridge), and use transmission through a steering mirror of the actual beat note path, not the jittery viewport pickoff.  Want RIN noise level to be about 1e-5, only care about below ~100Hz so don't need broadband.

6855   Fri Jun 22 17:51:04 2012 JenneUpdateCamerasGreen Trans camera repositioning attempt

[Yuta, Jenne]

We tried to find a different place, not in the main green transmitted beam path, to place the trans camera for the green beams.  There is a little bit of leakage through the 3 high reflector mirrors which steer the beams from the direction when they first come out of the chamber over to the main green beat setup.  2 of these mirrors have virtually no space behind them for a camera (the first one the green beams encounters is right next to the EOM mount, and the 2nd one is pretty close to the Input Pointing QPDs.  We can potentially use the beam leaking through the 3rd steering mirror, if the camera is very close to the edge of the table (so that the camera isn't blocking the IR input pointing beams), but the X beam is so dim as to be nearly impossible to see, even when TEM00.  This precludes the point of the camera, which is to see the modes when we're aligning the beams.  (X power on the PSL table is pretty high - 330uW measured today, but those mirrors must transmit the Y beam's polarization more than the X beam's.)

Our other thought was to use one of the secondary beams coming out of the chambers.  This is kind of Mickey Mouse, but we thought that since this is just a camera to see the modes, as opposed to a PD, maybe it's okay.  This is a moot point however, since the secondary and tertiary beams (due to the wedge of the window) are clipped for the Y green.  We closed the PSL shutter then removed the beam pipe between the PSL table and the chamber so I could look inside.

It looks to me like the main green transmitted beams are exiting through the window several inches from any edge, so they're definitely not clipping.  But the reflection from the window back into the chamber is hitting some optic.  The X green is hitting the face of the optic, while the Y green is hitting the edge of the optic and part of the mount.  The reflections from this mount then go back toward the chamber window and out toward the PSL table.  This isn't a big deal for the camera situation - we'll just use the leakage from one of the steering mirrors somehow, but it does mean that there is some green light reflected back onto an IR mirror, and potentially causing grief.  I didn't look to see if the mirror it's hitting is the 1st in-vac IR steering mirror (I don't think so) or something in the OMC / AS path (I think it's something here), but either way, we could be making trouble for ourselves.  We should try to dump the reflection from the window when we vent.  Jamie has put it on the List.

We replaced the beam pipe between the PSL table and the chamber before opening the shutter on the laser.  We are currently sticking with the plan of putting the camera in the main green trans path for initial alignment, then removing it for the rest of the work.

16844   Tue May 10 18:25:43 2022 PacoUpdateBHDGreen Transmission path

[Yuta, Paco]

We installed GRX_SM1, GRX_SM2, and finished aligning the GRY_SM1, and GRY_SM2 steering mirrors in the BS and IMC Chambers. GRY_SM1 was slightly misplaced (by ~ 2 inches), so we had to move it slightly. Luckily this didn't grossly misaligned the IMC, and we could recover quickly by touching MC1 & MC3 pitch, and MC1 slight yaw.

Then, Yuta installed GRX_SM1, and GRX_SM2 by repurposing two 45 AOI P-Pol GR transmission mirrors on the flowbench. Because one of the weights on the BSC was in the way of GRX_SM2, it was shifted it before installation. This probably shifted the balancing of the whole table. The GRY beam is still not lock-able to the YARM, so as a proxy for GRY transmission beam we used the slight GRX reflection from the BS, and noted slight clipping through PR3 (in transmission). This should probably be checked with GTRY.

We believe this is the last installation operation of this vent.

We made sure the WFS feedback loop is working, and realigned the arm cavities to be flashing.

12090   Tue Apr 26 23:19:42 2016 gautamUpdateendtable upgradeGreen aligned to arm - high order mode flashes seen

Attachment #1

Layout as of today. Most of the green path is done. The Green REFL PD + PZT mirrors have not been hooked up to their respective power sources yet (I wonder if it's okay to start laying cables through the feedthroughs on either end of the table already, or if we want to put whatever it is that makes it airtight eventually in first?). A rough power budget has been included (with no harmonic separator just before the window), though some optimization can be done once the table is completely repopulated.

Attachment #2

A zoomed-in version of the REFL path.

Some general notes:

1. I've tried to use the custom 3/4" O.D. posts + baseplate arrangement wherever possible (only 1 steering mirror is on a 1" post clamped with a fork to the table because of space constraints). Where the baseplates could not be bolted onto the table directly, I've used Newport SS Dogs to do the job.
2. I checked for continuity between the PZT outer case and the table top with a multimeter, and found none. So I chose to leave the Thorlabs baseplates in place. For the REFL PD, I've used an insulating baseplate given to me by Steve.
3. I've used some custom length 3/4" O.D. posts to get the beam up to the right height (~4.75") just before sending the green beam in. The beam height is 4" elsewhere.
4. I was playing around with positioning the harmonic separator immediately before the vacuum chamber window - I found that there is a substantial amount of green light that is reflected, though there doesn't seem to be any IR leaking through. The mirror was labelled Y1-1037-45P, which is a code for CVI mirrors, though I believe it is a LaserOptik product and that we have a couple of other such mirrors in the optics cabinet - though they are all 1". This document suggests that from the back side, there should be <0.1% reflection of green while on the front side it should be < 3%. I will have to hunt a little more for the specs, and measure the powers to see if they match the previously quoted numbers. In any case, I'll have to think of how to separate the (unwanted) reflected green and the transmitted IR from the cavity in the IR transmon path.
5. There are some minor changes to the planned layout posted here - I will update these in due course once the Transmon path and Oplev have been set up.

I am closing the PSL shutter and the EX laser shutters for the night as I have applied a layer of first contact to the window for cleaning purposes, and we don't want any laser light incident on it. It may be that the window is so dirty that we may need multiple F.C. cleaning rounds, we will see how the window looks tomorrow...

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7347   Thu Sep 6 02:51:47 2012 KojiUpdateGeneralGreen beam roughtly aligned (Re: Yarm aligned to IR incident beam)

The Y-End green beam was roughly aligned by the steering mirrors for the green beam.

I couldn't understand the Y-End green setup as the PD was turned off and the sign of the servo was flipped. Once they are fixed, I could lock the cavity with the green beams.

After a long alignment session, TEM00 was found. The alignment of the green beam has not been optimized.

Looking at the spot position at ETMY OSEM holders (not by the ccd image), it seems that the cavity mode is not at the center of the mirrors.

 Quote: [EricQ, Jenne, brains of other people] Get green spots co-located with IR spots on ETMs, ITMs, check path of leakage through the arms, make sure both greens get out to PSL table

Attachment 1: green_y.png
11887   Wed Dec 16 18:34:40 2015 gautamUpdateGreen LockingGreen beat channels temporarily set up as IR beat channels

Since there are a few hours to go before the locking efforts tonight, I've temporarily borrowed the channels used to read out the green beat frequency, and have hooked them up to the broadband IR PDs in the FOL box on the PSL table. I've used the network analyzer in the control room to roughly position the two beatnotes. I've also turned the green beat PDs back on (since the PSL shutter has to be open for the IR beat, and there is some green light falling on these PDs, but I've terminated the outputs).

So this needs to be switched back before locking efforts tonight...

11888   Wed Dec 16 23:15:28 2015 ericqUpdateGreen LockingGreen beat channels temporarily set up as IR beat channels

With the IR beats going to the nominal ALS channels as Gautam left them, we're able to measure the free running frequency noise of the end AUX lasers.

Specifically, the end shutters are closed, leaving the AUX lasers free running. The IR beats then consist of this free running light beating with the PSL light, and the ALS phase trackers give a calibrated frequency noise spectrum. I've stabilized the PSL light by locking the laser to the Y arm via MC2 acutation, so the free running AUX laser noise should dominate by a lot above the suspension resonances. This also has the benefit of giving me the use of the CAL'd Y arm displacement as a sanity check.

At this point in time, it looks like the X laser is close to 10x noisier than the Y laser, though it does seem to be at the rule-of-thumb "10kHz/rtHz at 100Hz" level.

Attachment 1: 2015-12-16_AUXfreerunning.pdf
4480   Thu Mar 31 20:46:11 2011 AidanSummaryGreen LockingGreen beat note PD DC response

I measured the DC response of the Green PD

Power into PD at DC (green laser pointer) = 285 uW
Voltage out of PD = 552mV/(100x SR560gain) = 5.52mV
Photocurrent = 5.52mV/(241 Ohms)*3 = 68.7uA
Responsivity = 68.7/285 = 0.24 A/W

Therefore, since the responsivity is in the correct range for a Silicon PD at 532nm, the DC output is giving us sensible response to an input signal.

But, there is a 2.12MHz, 328mV oscillation on the DC output irrespective of the incident power.

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