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ID Date Author Type Category Subject
14094   Sat Jul 21 01:06:49 2018 gautamSummaryThermal CompensationY arm locking

I implemented this today. For now, the LSC output matrix is set to actuate on MC2 for Y arm locking. As expected, the transmission was much more stable, and the PLL control signal RMS was also reduced by factor of ~3. MC2 control signal does pick up a large (~2000 cts) DC component over a few hours, so we need to relieve this periodically.

Now that we have a workable ASS for the Y arm as well, we should be able to have more confidence in returning to the same beam spot position on the ETM and staying there during a scan using this technique.

The main improvement to be trialled next in the scanning is to improve the speed of scanning. As things stand, my script takes ~2.5 seconds per datapoint. If we can cut this in half, that'd be huge. On Wednesday night, we were extraordinarily lucky to avoid MC3 glitching, EPICS/slow machine failures, and GPIB freezes. Today, the latter reared its head. Fortunately, since I'm dumping data to file for each datapoint, this means we at least have data till the GPIB freeze.

 Quote: For future measurements, we should consider locking the IMC length to the arm cavity - this would eliminate such alignment drifts, and maybe also make the PLL control signal RMS smaller.

Not related to this work: Terra, Sandrine, Keerthana and I cleaned up the lab a bit today, and made better cable labels. Aaron and I have to clean up the OMC area a bit. Huge thanks to Steve for taking care of our mess elsewhere in the lab!

14096   Sat Jul 21 14:03:19 2018 KojiSummaryThermal CompensationY arm locking

Ah. With MC2 feedback, we have about 3 times smaller "optical gain" for the ASS A2L. We have same dither, same actuator, but we need only 1/3 actuation of the MC2 compared to the ETMY case.
We had to reduce the ASS spot servo from 1 to 0.3 to make is stable, so this means that the ASS is really merginally stable.

14904   Fri Sep 20 18:28:34 2019 gautamUpdateLSCY arm locking attempt

I tried to lock the Y arm cavity length to the PSL frequency using POY11_I as an error signal. Even though I think the cavity alignment is good (I see TRY flashes ~0.8), I am unable to achieve a lock. I checked the signal conditioning, and as far as I can tell, all the settings are correct, but there may be some settings that have not been re-assigned correct values. The other possibility is that something is not quite right with the new c1iscaux. The PDH error signal and arm cavity flashes all seem good though (see Attachment #1), so I'm not sure what obvious thing I'm missing.

To be continued...

5392   Tue Sep 13 03:18:14 2011 kiwamuUpdateLSCY arm locking prep

(Preparation of Y arm locking)

(A) The f2a filters were newly designed and applied to ETMY (see the attachment)

(B) Once the Y arm is aligned such that the TEM00 mode flashes, the transmitted light is visible on the ETMYT CCD camera.

(C) With the newly installed resonant EOM circuit the PDH signal from AS55 looks healthy.

(some notes)

(A) To design the f2a filters there is a handy python script called "F2A_LOCKIN.py" in /scripts/SUS.

The script measures the coil imbalance at high frequency and low frequency using a LOCKIN module and then gives us the information about the imbalance.

The script hasn't yet been completed, so it doesn't return the intuitive answers but returns something non-intuitive. I will modify it.

(B)  To see the transmitted light from the Y arm I was going to align the CCD camera on the Y end table.

However I found that once the green light is blocked, the transmitted light can be visible on the camera without any re-alignment.

Therefore I haven't rearranged anything on the Y end table, but I just blocked the green light.

Perhaps we still need to align the photo diodes for the transmitted light.

(C) While Suresh was working on MC, I looked at the signal from AS55 with all the optics misaligned except for ITMY, ETMY and BS.

The signal from the Y arm looked very PDH signal, and the demodulation phase seemed to be about 45 deg to maximize the I signal.

I tried locking it by feeding the signal back to ETMY but failed due to a too much POS to angle coupling in the ETMY actuators.

I was momentarily able to capture a higher order mode with a negative gain in LSC-YARM_GAIN, but it was quite difficult to keep it locked.

This was because once I increased the gain to make it stable, the angle instability became more significant and lost the lock immediately.

This was the reason why I had to do the f2a filter redesign. Tomorrow we can try locking the Y arm.

5398   Tue Sep 13 19:31:09 2011 kiwamuUpdateLSCY arm locking prep

The Y arm has been locked with AS55.

A next thing is to check the spot positions on the ETMY and ITMY mirrors so that we can evaluate the recent beam pointing.

- - - parameter settings - - -

C1:LSC-YARM_GAIN = -0.03

AS55 demod phase = 0.2

WF gains = 21 dB

C1:LSC-TRY_OUT = 0.57 (maximized by steering PZT2)

 Quote from #5392 This was the reason why I had to do the f2a filter redesign. Tomorrow we can try locking the Y arm.

5410   Wed Sep 14 21:18:45 2011 kiwamuUpdateLSCY arm locking prep

Although we did some of the Input Matrix diagonalization, we have not yet actually used this knowledge. As a result all of the optics are shaking all over the place.

### Sunshine Task: Set the input matrices to their calculated values and then adjust the OSEM damping gains for all optics so as to get a Q ~ 5.

14450   Tue Feb 12 22:59:17 2019 gautamSummaryLoss MeasurementY arm loss

Summary:

There are still several data quality issues that can be improved. I think there is little point in reading too much into this until some of the problems outlined below are fixed and we get a better measurement.

Details:

1. Mainly, we are plagued by the inability of the ASS system to get back to the good transmission levels - I haven't done a careful diagnosis of the servo, but the ITM PIT output always seems to run away. As a result, the later measurements are poor, as can be seen in Attachment #2.
2. For this reason, we can't easily sample different spot positions on the ETM.
3. Data processing:
• Take their ratio
• Downsample to 4 Hz by repeated application of scipy.signal.decimate by a factor of 8 each time, thrice, with the filtfilt option enabled
4. Attachment #1 and #2 are basically showing the same data - the former collects all locked (top left) and misaligned (top right) data segments and plots them with the corresponding TRY values in the bottom row. The second plot shows a pseudo-continuous time series (pseudo because the segments transitioning from locked to misaligned states have been excised).

As an interim fix, I'm going to try and use the Oplevs as a DC reference, and run the dither alignment from zero each time, as this prevents the runaway problem at least. Data run started at 11:20 pm.

14451   Wed Feb 13 02:28:58 2019 gautamSummaryLoss MeasurementY arm loss

Attachment #1 shows estimated systematic uncertainty contributions due to

1. ITM transmission by +/- 0.01 % about the nominal value of 1.384 %
2. ETM transmission of +/- 3 ppm about the nominal value of 13.7 ppm
3. Mode matching efficiency into the cavity by +/- 5% about the nominal value of 92%.

In all the measurements so far, the ratio seems to be < 1, so this would seem to set a lower bound on the loss of ~35 ppm. The dominant source of systematic uncertainty is the 5% assumed fudge in the mode-matching

To do:

1. Account for uncertainties on modulation depths
2. To estimate if the amount of fluctuation we are seeing in the reflected signal even after normalizing by the MC transmission, get an estimate of statistical uncertainty in the reflected power due to
• Pointing jitter - is there some spec for the damped angular displacement of the TT1/TT2?
• Cavity length in-loop residual

Bottom line: I think we need to have other measurements and simultaenously analyse the data to get a more precise estimate of the loss.

6126   Fri Dec 16 13:29:15 2011 kiwamuUpdateGreen LockingY arm noise budget : 60Hz line noise is killing us
Along with development of the automation script, my goals last night were :
(1) Take a noise budget when the standard ALS configuration is applied
(2) Take a beautiful time series to show how ALS brings the cavity to the resonance point

However I gave up goal (2) because the resultant time series were very fluctuating at 60 Hz and it wasn't so beautiful enough.
As shown in the noise budget below, the 60 Hz line noise currently dominates the arm displacement.

The spectra were taken when the arm length was kept at the resonance point using the ALS servo.
So the error signal was taken from the beat-note and was fed back to ETMY.
The servo UGF was at about 100 Hz and the fine frequency discriminator was used.
The red curve in the plot is the arm displacement observed by POY11, which is an out-of-loop sensor in this case.
From the plot it is apparent that the 60 Hz line noise raises the rms to few 100 pm level.

How to improve it ?

According to my quick calculation if we can exclude the 60 Hz line noise from the rms integration, the rms becomes about 70 pm, which is nice.
I somehow believe this line noise comes from the ALS servo and is injected to the coil-magnet actuator.
So I propose to lower the UGF and make it lower than 60 Hz such that
the servo doesn't react to the 60 Hz line noise and hence no 60 Hz noise injection to the arm displacement.
In any case lowering the UGF is better since our ALS sensor sees only noise above 40 Hz according to the previous noise measurement (#5970)
10808   Wed Dec 17 11:57:56 2014 manasaSummaryGeneralY arm optical layout

I was working around the PSL table and Y endtable today.

I modified the Y arm optical layout that couples the 1064nm light leaking from the SHG crystal into the fiber for frequency offset locking.

The ND filter that was used to attenuate the power coupled into the fiber has been replaced with a beam sampler (Thor labs BSF-10C). The reflected power after this optic is ~1.3mW and the trasmitted power has been dumped to a razor blade beam dump (~210mW).

Since we have a spare fiber running from the Y end  to the PSL table, I installed an FC/APC fiber connector on the PSL table to connect them and monitored the output power at the Y end itself. After setting up, I have ~620uW of Y arm light on the PSL table (~48% coupling).

During the course of the alignment, I lowered the power of the Y end NPRO and disengaged the ETMY oplev. These were reset after I closed the end table.

Attached is the out of loop noise measurement of the Y arm ALS error signal before (ref plots) and after.

4411   Fri Mar 18 12:22:04 2011 kiwamuUpdateGreen LockingY arm plan for today

Prior to the works on the Y end setup I propose to perform the temperature scan business like Koji and Suresh did before (see this entry).

This business will allow us to easily find a beatnote at 532nm after the installation on the Y end.

I guess the right persons for this work are Bryan and Suresh.

Bryan will have a safety guidance from Steve in this after noon. So after that they can start working on it.

/* - - - coarse plan - - - */

* remove Alberto's laser from the AS table

* setup Alberto's laser on the PSL table

* put some stuff such as lenses, mirrors and etc. (Use the IR beam picked off after the doubling crystal for the main laser source)

* mode matching

* measurement

Which laser are we going to use,  Alberto's laser or MOPA laser ?

288   Thu Jan 31 12:39:14 2008 JohnConfigurationGeneralY arm test mass cameras
I've adjusted the test mass cameras on the y arm to make the beam injected through ETMY more visible.
8821   Wed Jul 10 11:44:02 2013 AnnalisaUpdateGreen LockingY beat note found!

I found the beat note for the Y arm. Nothing was changed with respect to yesterday night, but the beat is back!

9640   Fri Feb 14 21:03:13 2014 KojiUpdateGeneralY end "BS"

As I didn't have the green laser PZT feedback for the laser temp control, I went to the yend to check out what's the situation.

I found horrible and disgusting "remnants".

WHAT ARE THESE BSs AT THE Y END?

- The table enclosure was left open

- A (hacky) DB25 cable with clips was blocking the corridor and I was about to trip with the cable.

- This DB25 cable went to the table without going through the air tight feedthrough that is designed for this purpose.

- An SR560 (presumably for the openloop TF measurement) was left inserted in the loop with entangled cables connected to the servo box.

- Of course the laser PZT out mon was left unplugged.

Even after cleaning these cables (a bit), the end setups (including the X end too) are too amature.
Everything is so hacky. We should not allow ourselves to construct this level of setup everytime
we work on any system. This just adds more and more mysteries and eventually we can't handle
the complexity.

12057   Thu Mar 31 09:38:41 2016 SteveUpdateendtable upgradeY end 4x3 existing layout

Beam colors: 1064 nm red, 514 nm green and 633 nm yellow.

There should be room for lens in front of the pd at red3 and a mirror for alignment in the new layout.

This picture may help you how to improve the new ETMX 4' x 3' optical layout.

5890   Mon Nov 14 22:56:31 2011 kiwamuUpdateGreen LockingY end PDH lock : UGF at 17 kHz

The open loop transfer function of the Y end PDH loop was remeasured : the UGF was found to be at 17 kHz.

The phase margin at the UGF was about 27 deg.

While the measurement we noticed that the modulation onto the laser PZT was too big

and it was creating a big AM on the reflected light with an amplitude of a few mV.

So we put a 20 dB attenuator to decrease the modulations and the reflected light became much quitter.

Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).

5893   Tue Nov 15 09:51:04 2011 ZachUpdateGreen LockingY end PDH lock : UGF at 17 kHz

 Also the servo shape formed by Newfocus LB1005 looks too simple : we should have a more sophisticated servo filter (i.e. PDH box!!).

As promised, I will get on this this week.

4481   Fri Apr 1 18:54:41 2011 BryanConfigurationGreen LockingY end doubling oven

The doubling oven is now ready to go for the Y arm. The PPKTP crystal is mounted in the oven:

Note - the crystal isn't as badly misaligned as it looks in this photo. It's just an odd perspective shot. I then closed it up and checked to make sure the IR beam on the Y bench passes through the crystal. It does. Just need to tweak the waist size/position a bit and then we can actually double some frequencies!

5929   Thu Nov 17 17:21:22 2011 kiwamuUpdateGreen LockingY end green PDH servo : it's okay

 Quote from #5914 So I have added an SR560 in the other input of the Newfocus servo box to make the filter shape 1/f^2. I will post the servo shape and diagram later.

The Y arm green PDH servo is working fine with a sufficient amount of suppression.

(Servo filters)

As reported on the previous elog entry (#5914) an SR560 was installed to provide one more pole-zero combination in the servo filter.
Here is a plot showing the transfer function of the latest servo filter.

And the servo configuration looks like this :

The demodulated signal is split into two path; one goes directly to the Newfocus servo box and the other goes through SR560.
With the SR560 the two way summing path makes a pole at 1 Hz and zero at 100 Hz with when the SR560 has a gain of 100.
The overall gain is adjustable from a knob on the Newfocus servo box.

(the Error signal)

One of the reasons we wanted to increase the servo gain was that :
the laser frequency has to be tightly locked to the Y arm motion because the laser frequency must represent the arm motion in our scheme.

Our requirement for allowing a successful ALS is : RMS < 10 pm (1/100 of the cavity linewidth)

I took a spectrum of the error signal when the laser was locked to the Y arm and found that it meets the requirement.

In the plot I also put a dark noise from the PD to make sure the in-loop noise is above the dark noise.
Right now the power lines at 60 Hz and 180 Hz are lifting the RMS up.
Note that the UGF was at 20-30 kHz.
5945   Fri Nov 18 11:28:39 2011 ranaUpdateGreen LockingY end green PDH servo : it's okay

Quote:

 Quote from #5914 So I have added an SR560 in the other input of the Newfocus servo box to make the filter shape 1/f^2. I will post the servo shape and diagram later.

Another way to make a 1:100 pole:zero boost is to use resistors and capacitors in a Pomona box

mixer -> LB box -> Pomona box -> PZT

Pomona Box =     R1 = 7.2 kOhm, C2 = 22 uF, R2 = 72 Ohms     (sr560 = $2400, pomona ~$50)

For the RMS calculation, it would be good to notch out the harmonics. They don't matter since our ALS feedback will have notches at those frequencies.

5946   Fri Nov 18 12:11:24 2011 ZachUpdateGreen LockingY end green PDH servo : it's okay

 Quote: Another way to make a 1:100 pole:zero boost is to use resistors and capacitors in a Pomona box  mixer -> LB box -> Pomona box -> PZT Pomona Box =     R1 = 7.2 kOhm, C2 = 22 uF, R2 = 72 Ohms     (sr560 = $2400, pomona ~$50)   For the RMS calculation, it would be good to notch out the harmonics. They don't matter since our ALS feedback will have notches at those frequencies.

11865   Tue Dec 8 23:24:08 2015 gautamUpdateGreen LockingY end laser (Lightwave) PZT calibration

Summary:

I measured the PZT actuator gain for the Lightwave NPRO at the Y-end to be 3.6 +/- 0.3 MHz/V. This is somewhat lower than the value of 5 MHz/V reported here, but I think is consistent with that measurement.

Details:

In order to calibrate the Y-axis of my Aux PDH loop noise budget plots, I wanted a measurement of the end laser actuator gain. I proceeded to measure this as follows:

1. Use a function generator to add a DC offset to the error point - I did this by taking the output of the RF mixer -> Input A of an SR560, output of the function generator -> input B of the SR560 (via a 20 Ohm attenuator, and with a 50ohm T-eed to the input for impedance matching), and setting the output to A-B, and feeding that to the "Servo Input" on the PDH box.
2. I then locked the arm to IR, ran the dither to maximize the green transmission, and set up a beat note at ~39 MHz with the help of the analyzer in the control room.
3. Set phase tracker UGF, clear phase history.
4. Vary the DC offset to the error point by using the offset on the function generator. I varied the offset until the green TEM00 lock was lost, in steps of 0.1 V. At each step, I averaged the output of the phase tracker for 15 seconds.
5. Convert the applied DC offset to the DC offset appearing at the servo output using the transfer function of the servo box (DC gain measured to be ~65 dB), taking into account the 20dB attenuator also.

The attached plot shows the measured data. The X-axis is shown after the conversion mentioned in the last bullet point. The error bars are the standard deviations of the averaging at each DC offset.

To do:

1. The value of the DC gain of the servo, 65 dB, is an approximate one based on a rough measurement I did earlier today. I'll take a TF measurement with an SR785 tomorrow, but I think this shouldn't change the number too much.
2. Upload the noise budget measurements for the Y-end PDH loop.
11877   Sun Dec 13 21:55:28 2015 gautamUpdateGreen LockingY end laser (Lightwave) PZT calibration

Summary:

After the discussions at the Wednesday meeting, I redid this measurement using a sinusoidal excitation summed at the error-point of the PDH servo as opposed to a DC offset. From the data I collected, I measured the actuator gain to be 2.43 +/- 0.04 MHz/V. This is almost half the value we expect, I'm not sure if I'm missing something obvious.

Details:

1. Attachment #1 is a sketch of the measurement setup and points at which signals are measured/calculated. Some important changes:
• I am now using the channel C1:ALS-Y_ERR_MON_OUT to directly measure the input signal to the servo. In order to get the calibration constant for this channel from counts to volts, I simply hooked up the input to the channel to an oscilloscope and noted the amplitude of the signal seen on the scope in volts. The number I have used is 52uV/count (note that the signal to the ADC is amplified by a factor of 10 by an SR560).
• I measured the transfer function from the input to the servo (marked "A" in the sketch) to the output of the Pomona box going to the laser PZT (marked "B" on the sketch) using an SR785 - see Attachment #2. This allowed me to convert the amplitude of excitation at A to an amplitude at B, which is what we need, as we want to measure C/B.
2. The measurement itself was done by locking the arms to IR, running ASS to maximize IR transmission, setting up a green beat note, and then measuring the two channels of interest with the excitation to the error-point on.
3. I was initially trying to use time-series plots to measure these amplitudes - Koji suggested I use the Fourier domain instead, and so I took FFTs of the two channels we are interested in (using a flat-top window with 0.1 Hz BW) and estimated the RMS values at the frequency at which I had injected an excitation. Data+code used is in Attachment #3. In particular, I was integrating the PSD over 1Hz centered at the excitation frequency in order to calculate the RMS power at the excitation frequency - it could be that for C1:ALS-BEATY_FINE_PHASE_OUT_HZ, the spectral leakage into neighbouring bins is more significant than for C1:ALS-Y_ERR_MON_OUT (see Attachment #4)?
4. With the amplitudes thus obtained, I took the ratio C/B (see sketch) to determine the MHz/V actuator gain. I had injected excitations at 5 frequencies (916Hz, 933Hz, 977Hz, 1030Hz and 1067Hz, choses in relatively "quiet" parts of the spectrum of C1:ALS-Y_ERR_MON_OUT with no excitations), and the result reported is the average from these five measurements, while the error is the standard deviation in the 5 measurements.
5. Unrelated to this meaurement - while I had the SR560 hooked up to the input of the PDH box, I inverted the mixer output to the servo input, as I thought I could use this method to estimate the modulation depth. I did so by locking the Y arm green to the sideband TEM00 mode, and comparing the green transmission in this state to that when the Y arm is locked to a carrier TEM00 mode. I averaged C1:ALS-TRY_OUT for 10 seconds in 3 cases: (i) Carrier TEM00, (ii)sideband TEM00, and (iii) shutter closed - from this measurement, I estimate the modulation depth to be 0.209 +/- 0.006 (errors used to calculate the total error were the standard deviations of the measured transmission).

Next steps:

1. Check that I have not missed out anything obvious in estimating the actuator gain - particularly the spectral leakage bit I mentioned above.
2. If this methodology and measurement is legitimate, repeat for the X end, and complete the noise budgeting for both AUX PDH loops.
11906   Mon Jan 4 16:09:54 2016 gautamUpdateGreen LockingY end laser (Lightwave) PZT calibration

Summary:

I redid this measurement and have now determined the actuator gain to be 4.61 +/- 0.10 MHz/V. This is now pretty consistent with the expected value of ~5MHz/V as reported here.

Details:

I made the following changes to the old methodology:

1. Instead of integrating around the excitation frequency, I am now just taking the ratio of peak heights (phase tracker output / error signal monitor) to determine the actuator gain.
2. I had wrongly assumed that the phase tracker output was calibrated to green Hz and not IR Hz, so I was dividing by two where this was not necessary. I think this explains why my previous measurement yielded an answer approximately half the expected value.

I also took spectra of the phase tracker output and error signal to make sure I was choosing my excitation frequencies in regions where there were no peaks already present (Attachment #1).

The scatter of measured actuator gains at various excitation frequencies is shown in Attachment #2.

5852   Wed Nov 9 16:49:17 2011 kiwamuUpdateGreen LockingY end laser temperature with slow input connected

Indeed it is strange. I took a quick look at it.

In order to recover the same condition (e.g. the same amount of the reflected DC light and the same temperature readout),

it needed to have +8.9V in the slow input from the DAC through EPICS.

Obviously applying an offset in the slow input to maintain the same condition is not good.

It needs another solution to maintain the sweet frequency where the frequency of the PSL and the Y end laser is close in a range of 200 MHz.

 Quote from #5797 Plugging in the thermal feedback BNC cable to the laser reduced the DC voltage of the green PDH photo diode from 3.12 V to 1.5V off resonance.

2791   Mon Apr 12 17:37:52 2010 josephbUpdateComputersY end simulated plant progress

Currently, the y end plant is yep.mdl.  In order to compile it properly (for the moment at least) requires running the normal makefile, then commenting out the line in the makefile which does the parsing of the mdl, and rerunning after modifying the /cds/advLigo/src/fe/yep/yep.c file.

The modifications to the yep.c file are to change the six lines that look like:

"plant_mux[0] = plant_gndx"  into lines that look like "plant_mux[0] = plant_delayx".  You also have to add initialization of the plant_delayx type variables to zero in the if(feInt) section, near where plant_gndx is set to zero.

This is necessary to get the position feedback within the plant model to work properly.

#NOTE by Koji

CAUTION:
This entry means that Makefile was modified not to parse the mdl file.
This affects making any of the models on megatron.

2798   Tue Apr 13 12:49:35 2010 josephbUpdateComputersY end simulated plant progress

 Quote: Currently, the y end plant is yep.mdl.  In order to compile it properly (for the moment at least) requires running the normal makefile, then commenting out the line in the makefile which does the parsing of the mdl, and rerunning after modifying the /cds/advLigo/src/fe/yep/yep.c file. The modifications to the yep.c file are to change the six lines that look like: "plant_mux[0] = plant_gndx"  into lines that look like "plant_mux[0] = plant_delayx".  You also have to add initialization of the plant_delayx type variables to zero in the if(feInt) section, near where plant_gndx is set to zero. This is necessary to get the position feedback within the plant model to work properly.   #NOTE by Koji CAUTION: This entry means that Makefile was modified not to parse the mdl file. This affects making any of the models on megatron.

To prevent this confusion in the future, at Koji's suggestion I've created a Makefile.no_parse_mdl in /home/controls/cds/advLIGO on megatron.  The normal makefile is the original one (with correct parsing now).  So the correct procedure is:

1) "make yep"

2) Modify yep.c code

3) "make -f Makefile.no_parse_mdl yep"

14205   Fri Sep 21 09:59:09 2018 yukiConfigurationASCY end table upgrade plan

[Yuki, Gautam]

Attachments #1 is the current setup of AUX Y Green locking and it has to be improved because:

• current efficiency of mode matching is about 50%
• current setup doesn't separate the degrees of freedom of TEM01 with PZT mirrors (the difference of gouy phase between PZT mirrors should be around 90 deg)
• we want to remotely control PZT mirrors for alignment
(Attachments #2 and #3)

One of the example for improvement is just adding a new lens (f=10cm) soon after the doubling crystal. That will make mode matching better (100%) and also make separation better (85 deg) (Attachments #4 and #5). I'm checking whether we have the lens and there is space to set it. And I will measure current power of transmitted main laser in order to confirm the improvement of alignment.

I am considering what component is needed.

Reference:

14212   Sun Sep 23 19:32:23 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Gautam ]

The setup I designed before has abrupt gouy phase shift between two steering mirrors which makes alignment much sensitive. So I designed a new one (Attached #1, #2 and #3). It improves the slope of gouy phase and the difference between steering mirrors is about 100 deg. To install this, we need new lenses: f=100mm, f=200mm, f=-250mm which have 532nm coating. If this setup is OK, I will order them.

There may be a problem: One lens should be put soon after dichroic mirror, but there is little room for fix it. (Attached #4, It will be put where the pedestal is.)  Tomorrow we will check this problem again.

And another problem; one steering mirror on the corner of the box is not easy to access. (Attached #5) I have to design a new seup with considering this problem.

 Quote: One of the example for improvement is just adding a new lens (f=10cm) soon after the doubling crystal. That will make mode matching better (100%) and also make separation better (85 deg) (Attachments #4 and #5). I'm checking whether we have the lens and there is space to set it. And I will measure current power of transmitted main laser in order to confirm the improvement of alignment.

14214   Mon Sep 24 11:09:05 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Steve ]

With Steve's help, we checked a new lens can be set soon after dichroic mirror.

 Quote: There may be a problem: One lens should be put soon after dichroic mirror, but there is little room for fix it. (Attached #4, It will be put where the pedestal is.)  Tomorrow we will check this problem again.
14216   Tue Sep 25 18:08:50 2018 yukiConfigurationASCY end table upgrade plan

[ Yuki, Gautam ]

We want to remotely control steeing PZT mirrors so its driver is needed. We already have a PZT driver board (D980323-C) and the output voltage is expected to be verified to be in the range 0-100 V DC for input voltages in the range -10 to 10 V DC.
Then I checked to make sure ir perform as we expected. The input signal was supplied using voltage calibrator and the output was monitored using a multimeter.
But it didn't perform well. Some tuning of voltage bias seemed to be needed. I will calculate its transfer function by simulation and check the performance again tommorow. And I found one solder was off so it needs fixing.

Reference:
diagram --> elog 8932

Plan of Action:

• Check PZT driver performs as we expected
• Also check cable, high voltage, PZT mirrors, anti-imaging board
• Obtain calibration factor of PZT mirrors using QPD
• Measure some status value before changing setup (such as tranmitted power of green laser)
• Revise setup after a new lens arrives
• Align the setup and check mode-matching
• Measure status value again and confirm it improves
• (write programming code of making alignment control automatically)
14226   Wed Oct 3 14:24:40 2018 yukiConfigurationASCY end table upgrade plan

Interim Procedure Report:

Purpose

The current setup of AUX Y-arm Green locking has to be improved because:

• current efficiency of mode matching is about 50%
• current setup doesn't separate the degrees of freedom of TEM01 with PZT mirrors (the difference of gouy phase between PZT mirrors should be around 90 deg)
• we want to remotely control PZT mirrors for alignment

What to do

• Design the new setup and order optices needed (finished!)
- As the new setup I designed, adding a new lens and slightly changing the position of optics are only needed. The new lens was arrived here.
• Check electronics (PZT, PZT driver, high voltage, cable, anti-imaging board) (finished!)

- All electronics were made sure performing well.
- The left thing to do is making a cable. (Today's tasks)
• Calibrate PZT mirror [mrad/V] (finished!)

- The result was posted here --> elog:40m/14224.
• Measure the status value of the current setup (power of transmitted light ...etc) (Tomorrow, --> finished!)
• Install them in the Y-end table and align the beam (Will start from Tomorrow) (The setup has a probrem I found on 10/04)
• Measure the status value of the new setup
- I want to finish above during my stay.
• Prepare the code of making alignment automaticaly
14257   Mon Oct 15 20:11:56 2018 yukiConfigurationASCY end table upgrade plan

Final Procedure Report for Green Locking in YARM:

Purpose

The current setup of AUX Y-arm Green locking has to be improved because:

• current efficiency of mode matching is about 50%
• current setup doesn't separate the degrees of freedom of TEM01 with PZT mirrors (the difference of gouy phase between PZT mirrors should be around 90 deg)
• we want to remotely control PZT mirrors for alignment

What to do

• Design the new setup and order optices needed (finished!)
- As the new setup I designed, adding a new lens and slightly changing the position of optics are only needed. The new lens was arrived here.
• Check electronics (PZT, PZT driver, high voltage, cable, anti-imaging board) (finished!)

- All electronics were made sure performing well.
- The left thing to do is making a cable. (Today's tasks)
• Calibrate PZT mirror [mrad/V] (finished!)

- The result was posted here --> elog:40m/14224.
• Measure the status value of the current setup (power of transmitted light ...etc) (finished!)
• Install them in the Y-end table and align the beam (Almost finished!) (GTRY signal is 0.3 which means Mode-Matching efficiency is about 30%. It should be improved.)
• Measure the status value of the new setup (finished!)
• Prepare the code of making alignment automaticaly
• see sitemap.adl>ASC>c1asy. I prepared medm. If you move PZT SLIDERS then you can see the green beam also moves.
• Preparing filters is needed. You can copy them from C1ASX.
• Note that now you cannot use C1ASX servo because filters are not applied.
14260   Wed Oct 17 20:46:24 2018 yukiConfigurationASCY end table upgrade plan

To do for Green Locking in YARM:

The auto-alignment servo should be completed. This servo requires many parameters to be optimized: demodulation frequency, demodulation phase, servo gain (for each M1/2 PIT/YAW), and matrix elements which can remove PIT-YAW coupling.

9844   Wed Apr 23 23:48:30 2014 manasaUpdateLSCY end whitening board

The MON outputs of the Y end QPD whitening board were hot earlier today while pulling it out of the crate. After swapping the 4 pin lemo connector with an isolated panel mount bnc connector, I stuck the board back into the crate and this immediately kicked the ETMY suspension. Jenne and I went to the Y end to look at what was going on. We removed the board from the crate after smelling something burning. The MON output ports of the whitening board were super hot this time. There is no sign of any components melting on the board (comparing the board with its pictures that were taken earlier) and a tester board stuck into the crate lights up just fine.

So the back panel is still ok. We need to troubleshoot or replace the whitening board.

Edit, JCD:  The attached photos are from right after I replaced the "Rgain" resistor, elog 9823.  What they show is that it looks like some of the melting / burning may have already been happening before I pulled the board, and I just never noticed :(  In particular, look at the resistors on the main board above the blue "G" sticker.  There isn't a difference that I can tell between this photo from last week, and today's situation.

9849   Thu Apr 24 14:23:09 2014 not manasaUpdateLSCY end whitening board

maybe the tantalum caps on the daughter board power supply lines are blown? If so, replace with 35V+ ceramic.

9852   Thu Apr 24 23:55:31 2014 KojiUpdateLSCY end whitening board

The main problem was a panel fixing bolt that caused the short circuits between power supply layers.
This burned the PCB and secondarily caused permanent short circuit between +15V/-15V/+5V layers.

Diagnosis

- The resistances between +15V, +5V, and -15V were low. The resistance between +15V and -15V is 13 Ohm.
The one between +5V and -15V is 7Ohm. And the one between +15 and +5 is 19Ohm. So the situation is

                o -15V                 | +15V o-(13 Ohm)-+-(9 Ohm)-o +5V

Even after removing all of the active components from the board, they remained the same.

- The tantalum caps were removed from the board and it was confirmed that they are not the cause of the issue.

- The panel was removed from the module for the component migration to a spare board (to be described in the other entry).
I found that the screw hole and the screw have burnt marks. The screw need an insulation tube to avoid short circuit.
The other screw was also bare. The spare board has the screws with the insulation tubes.

10444   Wed Sep 3 04:17:21 2014 JenneUpdateLSCY green ALS (not PDH) needs investigation

Q put the X PDH box back, so that I could try locking, and remember which end is up after a week away.

I am unable to hold ALS comm/diff for any length of time. Only once today did I hold it through the FM3 boost turn-on.  So, I looked at the individual arms.

Xarm, even though it's the one that Q is seeing this saturation problem with, seems fine.

Yarm however is having trouble holding lock for more than a few minutes at a time.  The green beam stays locked to the arm for ~infinity, so I'm not so worried about the PDH box right now.  If I look at the error and control points of the ALS digital servo, the Yarm is much more noisy above about 20 Hz.  Something that I might think of for this kind of mismatch at higher frequencies is poorly matched whitening / dewhitening, or none at all for the Yarm, however this doesn't look like that to me.  Based on the shape of the spectra, I don't think that we're running into ADC noise. For this plot, both arms are individually locked with ALS feeding back to the ETM, gain magnitude of 15 (Xarm gets a minus sign because of our temperature / beatnote moving direction convention), FMs 1,2,3,5,6 on.  Something that seems critical for getting the Yarm to have the FM3 boost without losing lock is having the SLOW temperature servos on for a little while so that the PZT output (as monitored on the temp servo screen) for the end lasers fluctuate around zero. Right now, both beatnotes are at about 62MHz, with an amplitude of about -31dBm.

I still need to do a somewhat more thorough investigation of what might be causing the Yarm locklosses.  Is the length-to-angle decoupling worse for ETMY than for ETMX?  Am I moving the arm length so far that the PZT can't follow within its actuation limits?  Does the Yend PDH box have a similar saturation to the Xend box, but somehow (a) worse, and (b) not as obvious so we didn't suspect it before?

I need to put this plot into calibrated units, and also include the low frequency monitor that we have of the PDH error point (all of which are _DQ channels).

Things to do:

* Figure out Xend PDH box saturation issue.  Is Yend seeing same saturation in the variable gain amplifier?  We have 3 spares of these chips in the Plateau Tournant Bleu, if we need them.

* Check Yarm ALS stability.  (NB:  The arms have been individually locked for the last 15 min or so while I've been writing, so maybe letting the slow servo settle is the key, and this is not something that needs work).

* Get CARM on DC Trans, DARM on AS55Q (after arm powers of about 1).  Can we see good REFL DC dip?  Should we try using just the transmission PD signal as the error signal for the CM board, if we aren't close enough to resonance to use REFL DC?

6775   Thu Jun 7 01:46:05 2012 yutaSummaryGreen LockingY green beat - found it!!

I found the big big Y green beat. Details will be posted later.

6777   Thu Jun 7 02:59:31 2012 yutaUpdateGreen LockingY green beat - found it!!

Summary:
I found the big green beat note for the Y arm. The alignment of the green optics on the PSL table was crappy.

What I did:
1. By adjusting PSL laser temperature, I found tiny beat note when

PSL laser temperature on display: 31.35 deg C (PSL HEPA 100%)
C1:PSL-FSS_SLOWDC = 1.75

and

PSL laser temperature on display: 33.21 deg C (PSL HEPA 100%)
C1:PSL-FSS_SLOWDC = -6.82

Y end laser temperature settings are fixed as follows during the measurement.

Y end laser "T+": 34.049 deg C
Y end laser measured temperature: 34.13 deg C (*)
C1:GCY-SLOW_SERVO2_OFFSET = 29845

Bryan's formula (swapped one; see elog #6746),  suggests the paring

(Yend laser temp, PSL laser temp) = (34.13 deg C, 31.09 deg C).

2. Checked that beat PD is working by swapping the beat PDs for Y arm and X arm.

3. Checked that the mode-matching of the two beams, one from Y arm and the other from PSL, is OK by moving mode-matching lens and measuring the beam spot size at near/far field are the same.

4. When checking the beam spot size at far field(~ 1 m from the BS), I noticed the relative beam tilt by ~ 1 mrad. We aligned them few days ago, but I think the green beam from the Y arm has shifted. Of course we align IR to the Y arm first, but we difinitely need dither servo or A2L for the arm, too.

5. As soon as aligning the PSL green optics near the BS, I found a large beat note. The measured amplitude was ~ -26 dBm, without any amplifiers after the PD.

Currently the measured green beam power onto the beat PD from Y end is 75 uW and from PSL is 92 uW. So the calculated beat amplitude will be ~ -10 dBm (see calculation in elog #6746). So there is about 84% loss. Anyway, I will go on to the mode scan.

6746   Sat Jun 2 03:19:37 2012 yutaUpdateGreen LockingY green beat note found? - too small

Summary:
I tried to find Y arm green beat in order to do the mode scan.
I found a beat peak(see attached picture), but the amplitude seems too small.
It is may be because the alignment/mode matching of the green beams at the PSL table is so bad. Or, the peak I found might be a beat from junk light.

What I did:
1. Aligned Y arm to the IR beam from MC.

2. Re-aligned Y end green beam to the Y arm using steering mirrors on the Y end table.

3. Re-aligned PSL green optics.

# C1:GCV-GREEN_TRY is temporary connected to the DC output of the Y green beat PD.

4. Temperature of the PSL laser was 31.48 deg C, so I set "T+" of the Y end laser to 34.47 deg C, according to Bryan's formula (elog #4439);

Y_arm_Temp_set = 0.87326*T_PSL + 6.9825

5. Scanned Y end laser temperature by C1:GCY-SLOW_SERVO2_OFFSET. Starting value was 29725 and I scanned from 27515 to 31805, by 10 or 100. Laser frequency changes ~ 6 MHz / 10 counts, so it means that I scanned ~ 2.5 GHz. During the scan, I toggled C1:AUX-GREEN_Y_Shutter to make sure the green beam resonates in TEM00 mode.

# I made a revolutionary python script for toggling channels(/opt/rtcds/caltech/c1/scripts/general/toggler.py). I made it executable.

6. Found a tiny beat note when C1:GCY-SLOW_SERVO2_OFFSET = 29815. I confirmed it is a beat signal by blocking each PSL and Y arm green beam into the beat PD. I left  C1:GCY-SLOW_SERVO2_OFFSET = 29815.

7. I found that Bryan's formula;

Y_arm_Temp_meas = 0.95152*T_PSL + 3.8672
Y_arm_Temp_set = 0.87326*T_PSL + 6.9825

was actually

Y_arm_Temp_set = 0.95152*T_PSL + 3.8672
Y_arm_Temp_meas = 0.87326*T_PSL + 6.9825

according to his graph(elog #4439). So, I set  "T+" of the Y end laser to 33.82 deg C.

8. This time, I scanned PSL laser temperature by C1:PSL-FSS_SLOWDC. I found a tiny beat note when C1:PSL-FSS_SLOWDC = 1.0995. C1:PSL-FSS_SLOWDC has 10 V range, so I scanned ~ 10 GHz, assuming the laser frequency changes 1 GHz/K and the temperature changes 1 K/V.

9. Re-aligned PSL green optics so that the beam hits optics at their center, and checked that the poralization of the two green beams are the same.

10. Checked that amplifier ZFL-100LN+ on the beat PD is working correctly. The power was supplied correctly (+15 V) and measured gain was ~ 25 dBm.

11. Exchanged BNC cable which connects the beat PD to the spectrum analyzer. Previous one we used was too long and it had -15 dB loss(measured). I exchanged to shorter one which has -2 dB loss.

Beat note amplitude estimation:
The amplitude of the beat note observed in the spectrum analyzer was ~ -54 dBm. According to the estimation below, it seems too small.

The measured power of the two green beams are

P_Y = 4 uW
P_PSL = 90 uW

So, the power of the beat signal should be

P_beat ~ 2 sqrt(P_Y * P_PSL) = 37 uW

Responsivity and transimpedance of the beat PD (Broadband PD, LIGO-T0900582) are 0.3 A/W and 2 kOhm. So, the power of the electrical signal is

W = (P_beat * 0.3 A/W * 2 kOhm / sqrt(2))^2 / 50 Ohm = 5 uW

5 uW is -23 dBm. We have +25 dB amplifier after the PD and the loss of the BNC cable is -2 dB. So, if the two beams interfere perfectly, the peak height of the beat signal should be ~ 0 dBm. The measured value -54 dBm seems too small. According to elog #5860, measured value by Kiwamu and Katrin was -36 dBm.

Current values:
PSL laser temperature: 31.48 deg C (PSL HEPA 100%)
Y end laser "T+": 33.821 deg C
C1:GCY-SLOW_SERVO2_OFFSET = 29815 (was 29725)

11464   Thu Jul 30 10:38:18 2015 SteveUpdatePEMY sesimostation is back on

Koji soldered new 50" long cable for the Y station.

11466   Thu Jul 30 13:34:52 2015 KojiUpdatePEMY sesimostation is back on

Please check the spectra. If something is wrong, please swap the cables between X and Y in order to see if the cable is still the issue. I believe the cable was nicely made as I carefully checked the connection twice or more during and after the soldering work.

11469   Thu Jul 30 15:24:54 2015 SteveUpdatePEMY sesimostation is back on

Atm1,  New short-50" long cable was installed at ETMY end ( Y-station ) between Guralp-B ( MIT ) and granite base.

Interface box input 2 was left connected to cable 1 and input 1 to cable 2. This plot shows no change.

Atm2, Than I swapped the two long cables at the interface box

Now the signal seems to be ok <2 Hz,

>2 Hz some problem exist.

 Channel Name Location Seismometer 40m long cable Interfacebox input 50" short cable C1:PEM-RMS_GUR2X_.... ETMX Guralp -A 2 2 Jenne's friend C1:PEM-RMS_GUR1X_.... ETMY Guralp-B 1 1 Koji

I will look for more bad soldering tomorrow. How many cables did she make?

5066   Sat Jul 30 05:11:45 2011 SureshUpdateGreen LockingY- end table clean-up

The optics on the Y-end table which required to be moved have been repositioned.  Please see the attached pic for details.

The green beam is not yet aligned to the cavity. That is my next task.

4520   Wed Apr 13 16:56:08 2011 BryanConfigurationGreen LockingY-ARM Green-Locked!

Locked!

The Y-arm can now be locked with green light using the universal PDH servo. Modulation frequency is now 277kHz - chosen because it seems to produce smaller offsets due to AM effects

To lock, turn on the servo, align the system to give nice circular-looking TEM_00 resonances, and wait for a good one. It'll lock on a decent mode for a few seconds and then you can turn on the local boost and watch it lock for minutes and minutes and minutes.

The suspensions are bouncing around a bit on the Y-arm and the spot is quite low on the ETMY and a little low on ITMY, but from this point it can be tweaked and optimised.

7187   Wed Aug 15 04:03:55 2012 ranaSummaryLSCY-Arm Locking

0) Did a bunch of alignment to get beams roughly centered on ETMY and ITMY and maximize power. Adjusted the aperture and focus on ETMY camera to get nice image. Camera needs to be screwed in tightly and cables given some real strain relief, Steve.

1) snapshots not working on many MEDM screens. Who's on top of this?

2) save/restore not working for PZT2 sliders

3) changed power and filter triggers on yarm to match xarm

4) yarm filters copied from xarm (need to handtune RGs)

5) DTT wasn't working on rossa. Used the Date/Time GUI to reset the system time to match fb and then it stopped giving 'Test Timed Out'. Jamie check rossa ntpd.

6) Removed the high 3.2 Hz RG filter. We don't have any sharp features like that in the spectrum.
---then added it back. The 3.2 Hz comes and goes depending on what Yoichi is doing over in the MC area. Leaving it in by default, but lowering the Q from 2 to 1.5.

7) Attached is the noise spectra, coherence, and loop gain model for this yarm condition. For the plant model, I assume a pendulum (f=1 Hz, Q = 9) and a cavity pole of 1600 Hz. Gain is scaled to set the UGF at 165 Hz (as guessed by looking at the servo gain peaking frequency). This cheezy model doesn't include any of the delays from DAC, AA, or AI. Eric and Sasha should have something more useful for us by Friday.

8) Change the DQ channels: need XARM and YARM IN1 at 16k. e.g. XARM_ERR, etc.

9) To get the DTT plots to make thumbnails in the elog, I print a .ps file and then use 'epstopdf' to make the PDF.

5937   Fri Nov 18 00:36:23 2011 ZachUpdateGreen LockingY-Arm PDH box modified

I modified the Y-Arm PDH box (S/N 17) to have the same TF as the one of the temporary setup described in Kiwamu's earlier entryNote that the TF below was taken with the gain knob set to 0, so that the proper DC gain is achieved with a setting of ~4. This is desirable because it gives us wiggle room.

The changes were:

• R14: 25 -> 50
• R29: 1k -> 10.5k
• R30: 1k -> 20k
• R28: 102 -> OMIT
• C20: 84nF -> OMIT
• R31: SHORT -> 475
• R16: 10k -> 48.7k
• R24: 10 -> 5

Below is the TF along with the LISO model. They are different at low frequencies because the box must have been railing internally (though the phase shows that the result is as expected), and there is a feature around 60 kHz that probably arises from some op amp instability. I will see if adding a small cap somewhere does the trick, and then take a new TF with a lower source voltage.

I'll try to lock the arm with the box tomorrow.

5956   Sat Nov 19 00:47:24 2011 ZachUpdateGreen LockingY-Arm locked with PDH Box #17

I installed the newly modified PDH box #17 and locked the Y-Arm.

I wasn't able to bring the REFL level down to the 30% that Kiwamu claimed to get, despite readjusting the alignment---I got ~40-45%. I attained a UGF of ~8 kHz, lower than the 20 kHz that Kiwamu said he got with the temporary setup, probably because the PDH box just isn't as fast. Despite that, it looks like the error suppression is actually better than before...

Here is an error spectrum:

I have to admit that this calibration is worthy of suspicion and should be done more rigorously. I simply used the measured UGF frequency and known servo TF and PZT actuator gain to estimate the optical response. I am pretty confident that it's accurate to within a factor of 3 or so.

12188   Thu Jun 16 11:25:00 2016 JohannesUpdateLSCY-Arm round-trip loss measurement with ALS

Using the ALS green beat and armlength feedback I mapped an IR resonance of the Y-Arm by stepping through a ramp of offset values.

First I optimized the IR alignment with the dither scripts while LSC kept the arm on resonance, and then transitioned the length control to ALS. The beat frequency I obtained between the Y-arm green and the PSL was about 25 MHz. Then I applied a controlled ramp signal (stepping through small offset increments applied to LSC-ALSY_OFFSET, while logging the readback from channels LSC-TRY_OUT16 and ALS-Y_FC_SERVO_INMON with an averaging time of 1s.

The plots show the acquired data with fits to  $T(x)=\frac{T_0}{1+\frac{(x-x_0)^2}{\mathrm{HWHM}^2}}+\mathrm{offset}$ and $f(x)=mx+b$, respectively.

The fits, weighted with inverse rms uncertainty of the data points as reported by the cds system, returned HWHM = 0.6663 ± 0.0013 [offset units] and m = -0.007666 ± 0.000023 [MHz/offset unit], which gives a combined FWHM = 10,215 ± 36 Hz. The error is based purely on the fit and does not reflect uncertainties in the calibration of the phase tracker.

This yields a finesse of 388.4 ± 1.4, corresponding to a total loss (including transmissivities) of 16178 ± 58 ppm. These uncertainties include the reported accuracies of FSR and phase tracker calibration from elog 9804 and elog 11761.

The resulting loss is a little lower than that of elog 11712, which was done before the phase tracker re-calibration. Need to check for consistency.

ELOG V3.1.3-