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ID Date Authorup Type Category Subject
  7209   Thu Aug 16 20:04:46 2012 YaakovUpdatePEMTransfer functions of seismic stacks, differential motion of test mass


 I made the plots a little nicer and added new sensor noises (from Brian Lantz's scripts and measurements). Click to enlarge.



The last plot shows that these other sensors' noises are lower than the differential ground motion below 1 Hz.  Though 3 seismometers per STACIS is impractical, this shows that such seismometers could be used as feedforward sensors and provide isolation against differential ground motion. At these noise levels, the noise of the high voltage amplifier circuit in the STACIS would probably be the limiting factor.

  7210   Thu Aug 16 20:18:39 2012 YaakovUpdateSTACISInput for feedforward/feedback in the STACIS

Below is the bottom view of the geophone preamplifier and controller for the STACIS. It slides into the upper part of the STACIS, under the blue platform. The geophone signal goes in the bottom left, gets amplified, filtered, and otherwise pampered, and goes out from the bottom right. From there it goes on to the high voltage amplifier, and finally to the PZT stacks. Below right is a closer view of the output port for the preamplifier, top and bottom.


I suggest de-soldering and bending up the pins that carry the geophone signal (so the signals don't go directly to the high voltage amplifier), and adding the circuit below between the preamp and amplifier. The preamp connector is still attached to the high voltage amplifier connector in this setup, only the geophone signal pins are disconnected.


More on the circuit and its placement:

The first op-amp is a summing junction, and the second is just a unity gain inverter so that signal doesn't go into the high voltage amplifier inverted. I tested this with the breadboard, and it seems to work fine (amplitudes of two signals add, no obvious distortion). The switches allow you to choose local feedback, external feedforward, or both.

The geo input will be wires from the preamp (soldered to where the pins used to go), and the external input will be BNC cables, with the source probably a DAC. The output will go to the bent up pins that used to be connected to the preamp (they go into the high voltage amplifier). This circuit can sit outside of the STACIS- there is a place to feed wires in and out right near where the preamplifier sits. For power, it can use the STACIS preamp supply, which is +/- 15V. The resistors I used in the breadboard test were 10 kOhm, and the op-amp I used was LT1012 (whose noise should be less than either input, see eLog 7190).

This is visually represented below, with the preamp pin diagram corresponding to the soldering points with the preamp upside down (top right picture):



  7231   Sun Aug 19 19:56:20 2012 YaakovUpdateSTACISSTACIS signal box made

I made the signal box as described in eLog 7210. It adds the geophone signal and an external signal.

It has six switches, for x, y, and z signals from both an external and local (geophone) source. The x signals add if both x switches are flipped down (and the same for the other directions). For example, if you want to feed in only an external signal in the x direction, flip down the external x direction switch (it's labeled on the box), leaving all others flipped up.

The x, y, and z outputs are wired to the pins from the preamplifier that go to the high voltage board. These I disconnected from the preamplifier by cutting at their base (there are spare connectors if this wants to be undone, or, a wire can just be soldered from the pin to its old spot on the board). The power (plus/minus) and ground are wired to the respective pins from the geophone preamplifier (naturally, the STACIS must be turned on for the box to work since the box shares its power source). Below, the front (switches and geophone/external inputs) and back (power, ground, outputs) of the box are shown:


The preamplifier can plug into its regular connectors- the x,y,and z signals will all be redirected to the signal box with these modifications. The box sits outside the STACIS, there is room to feed the wires out from underneath the STACIS platform.


NOTE: The geophone z switch is a little different than the others, just make sure it's flipped all the way down if you want that signal to be seen in the z output.


  7262   Thu Aug 23 21:53:18 2012 YaakovUpdatePEMAccelerometer location

The MC1 accelerometer cube (3 accelerometers arranged in x,y,z) is under the PSL table, as I found it at the beginning of the summer.

The MC2 accelerometer cube is on the table where I worked on the STACIS, right when you walk into the lab from the main entrance. Their cables are dangling near the end of the mode cleaner, so the accelerometers are ready to be placed there if wanted.

All accelerometers are also plugged into their ADC channels.

  6882   Wed Jun 27 14:18:30 2012 Yaakov SummarySTACISFirst week summary

The beginning of my first week was spent at various orientations and safety meetings, some for general SURF and some more specific to LIGO and the lab. In between these I started  work.

Jenne and I took out the spare STACIS and took it apart, taking out the circuit boards. I've spent some time looking through the boards and sketching various parts of the board in trying to understand the exact function without any useful technical diagrams (STACIS supplied us only with a picture of the board without components, not all that helpful). I think I now at least understand the basic block diagram of the circuitry: the STACIS geophone signal goes through a preamplifier and filters (the semi-circular board), and converts it into a signal for the PZT stacks. This signal then goes through a high voltage amplifer, and then goes to the five PZTs (3 in the z, one each in the x and y direction). The unit I am looking at has an extension board, which allows us to tap into the signal going into the preamp and the one leaving it. This should allow us to input our own signal instead of the geophone signal, and thereby drive the PZTs ourselves.

My next step, once I get a resistor to replace a burnt one on the high voltage amplifier, is to take a transfer function of the STACIS and see if it is possible to drive the PZT stacks with the cables from the extension board. If that does not work, I'll have to keep tracing the circuit to determine where to input our own signal.

  14568   Wed Apr 24 17:39:15 2019 YehonathanSummaryLoss MeasurementBasic analysis of loss measurement


  • Getting myself familiar with Python.
  • Characterize statistical errors in the loss measurement.


​The precision of the measurement is excellent. We should move on to look for systematic errors. 

In Detail

According to Johannes and Gautam (see T1700117_ReflectionLoss .pdf in Attachment 1), the loss in the cavity mirror is obtained by measuring the light reflected from the cavity when it is locked and when it is misaligned. From these two measurements and by using the known transmissions of the cavity mirrors, the roundtrip loss is extracted.

I write a Python notebook (AnalyzeLossData.ipynb in Attachment 1) extracting the raw data from the measurement file (data20190216.hdf5 in Attachment 1) analyzing the statistics of the measurement and its PSD.

Attachment 2 shows the raw data. 

Attachment 3 shows the histogram of the measurement. It can be seen that the distribution is very close to being Gaussian.

The loss in the cavity pre roundtrip is measured to be 73.7+/-0.2 parts per million. The error is only due to the deviation in the PD measurement. Considering the uncertainty of the transmissions of the cavity mirrors should give a much bigger error.

Attachment 4 shows noise PSD of the PD readings. It can be seen that the noise spectrum is quite constant and there would be no big improvement by chopping the signal.

The situation might be different when the measurement is taken from the cavity lock PD where the signal is much weaker.

Attachment 1: LossMeasurementAnalysis.zip
Attachment 2: LossMeasurement_RawData.pdf
Attachment 3: LossMeasurement_Hist.pdf
Attachment 4: LossMeasurement_PSD.pdf
  15005   Sat Nov 2 16:36:55 2019 YehonathanUpdatePSLUp to date sketch of the 1x1 and 1x2 Eurocrates

I reproduced Gautam's sketch of the 1x1 and 1x2 Eurocrates into a pdf image that contains links to the appropriate DCCs in the legend (see attachement).

Attachment 1: 1x1_1X2_Eurocrates_with_links.pdf
  15006   Sat Nov 2 17:08:34 2019 YehonathanUpdatePSLUp to date sketch of the 1x1 and 1x2 Eurocrates

Thanks. Please update this wiki page too.


  15008   Mon Nov 4 13:26:04 2019 YehonathanUpdatePSLUp to date sketch of the 1x1 and 1x2 Eurocrates



Thanks. Please update this wiki page too.


  15011   Mon Nov 4 19:02:25 2019 YehonathanUpdatePSLMapping the PSL electronics

I created a spreadsheet (Attached) by taking Koji's c1psl sheet from slow_channel_list and filtering out the channels that do not need an Acromag. I added in the QPD channels that are relevant to the PSL from the c1iool0 sheet.

I began mapping the PSL related Eurocrates connectors to their respective VME channels starting with the PMC electronics.

I am confused about the TTFSS interface (D040423): While it is a Eurocrate card, in the schematics it seems to have 50 pin connectors.

I found old wiring schematics that might help with identifying the channels once the connector issue is clarified.



Attachment 1: PSL_Wirings_-_Sheet1_(1).pdf
  15039   Wed Nov 20 17:20:24 2019 YehonathanUpdateLSCQPD Investigation

{Gautam, Yehonathan}

In search of the source of discrepancy between the QPD readings in the X and Y arms, we look into the schematics of the QPD amplifier - DCC #D990272.

We find that there are 4 gain switches with the following gain characteristics (The 40m QPD whitening board has an additional gain of 4.5):

S4 S3 S2 S1 V/A
0 0 0 0 2e4
0 0 0 1 2e5
0 0 1 0 4e4
0 0 1 1 4e5
0 1 0 0 1e5
0 1 0 1 1e6
0 1 1 0 2e5
0 1 1 1 2e6
1     0 5e2
1     1 5e3

Switch 4 bypasses the amps controlled by switch 2 and 3 when it is set to 1 so they don't matter in this state.

Note that according to elog-13965 the switches are controlled through the QPD whitening board by a XT1111a Acromag whose normal state is 1.

Also, according to the QPD amplifier schematics, the resistor on the transimpedance, controlled by switch 1, is 25kOhm. However, according to the EPICS it is actually 5kOhm. We verify this by shining the QPD with uniform light from a flashlight and switching switch1 on and off while measuring the voltages of the different segments. The schematics should be updated on the DCC.

Surprisingly, QPDX switches where 0,0,0,0 while QPDY switches where 1,0,0,1. This explains the difference in their responses.

We check by shining a laser pointer with a known power on the different segments of QPDX that we get the expected number of counts on the ADC and that the response of the different segments is equal.

gautam edits:

  1. Lest there be confusion, the states of the switches in the (S1, S2, S3, S4) order are (0,0,0,0) for QPDX and (0,1,0,1) for QPDY.
  2. The Acromag XT1111 is a sinking BIO unit - so when the EPICS channel is zero, the output impedance is low and the DUT (i.e. MAX333) is shorted to ground. So, the state of the MAX333 shown on the schematics corresponds to EPICS logic level 1, and the switched state corresponds to logic level 0.
  3. For the laser pointer test, we used a red laser pointer. Using a power meter, we measured ~100uW of 632nm power. However, we think this particular laser pointer had failing batteries or something because the spot looked sometimes brighter/dimmer to the eye. Anyways, we saw ~10,000 ADC counts when illuminating a single segment (with the QPD gain switches at the 0,0,0,0 setting, before we changed anything). We expect 100uW * 0.4 A/W * 500 V/A * 10 * 40 * 4.5 * 3267.8 cts/V = ~12000 cts. So everything seems to check out. We changed the gain to the 5kohm setting and bypassed the subsequent gain stages, and saw the expected response too. The segments were only balanced to ~10%, but presumably this can be adjusted by tweaking digital gains.
  15048   Tue Nov 26 13:33:33 2019 YehonathanUpdateCamerasMC2 Camera rotated by 90 degrees

MC2 analog camera was rotated by 90 degrees. Orientation correctness was verified by exciting the MC2 Yaw degree of freedom.

Attached before and after photos of the camera setup.

Attachment 1: MC2AnalogCameraAfter.jpg
Attachment 2: MC2AnalogCameraBefore.jpg
  15070   Wed Dec 4 08:54:07 2019 YehonathanUpdateIMCMirror analog shaking

{Yehonathan, Gavin}

Yesterday we tried to shake ITMX with a function generator in order to observe the 28.8kHz drum mode.

We laid a long BNC cable that runs from the YARM to the XARM. This cable either needs to be collected back to the BNC big plastic cable box under the IMC or be labeled so that it could be found easily in the future.

First, we tried to shake it at a lower frequency (100's of Hz) where the shaking should be easily observed in the POSX channel. We try driving the POS channel on the ITMX servo but nothing happens. Most likely it is disconnected.

While setting up for shaking the individual OSEM channels 4 CDSs crashed (c1lsc, c1ass, c1oaf, c1cal).


  15071   Wed Dec 4 09:11:42 2019 YehonathanUpdateCDSReboot script

After the CDSs crashed we run the rebootC1LSC.sh script.

The script is a bit annoying in that it requires entering the CDSs' passwords multiple times over the time it runs which is long.

The resulting CDS screen is a bit different than what was reported before (attached). Also, not all watchdogs were restored.

We restore the remaining watchdogs and do XARM locking. Everything seems to be fine.

Attachment 1: medmScreen11.ps
  15086   Mon Dec 9 13:08:24 2019 YehonathanSummaryPEMJump test of seismometers: EX needs recentering

I check the seismometers in the last 14 hours (Attached). Seems like the coherenece is restored in the x direction.



Attachment 1: seis_191208.pdf
  15087   Mon Dec 9 19:19:04 2019 YehonathanUpdatePSLAOM first order beam alignment

{Yehonathan, Rana}

In order to setup a ringdown measurement with perfect extinction we need to align the first order beam from the AOM to the PMC instead of the zeroth order.

We connected a signal generator to the AOM driver and applied some offset voltage. We spot the first order mode and align it to the PMC. The achieved transmitted power is roughly as it was before this procedure.

Along the way few changes has been made in the PSL table:

1. Some dangling BNCs were removed.

2. Laser on the south east side of the PSL table was turned off.

3. DC power supplies were removed (Attachment 1 & 2). The rubber legs on the first one are sticky and leave black residue.

4. The beam block that orginally blocked the AOM high order modes was raised to block the zeroth order mode (Attachment 3).

5. The unterminated BNC T junction (Attachment 4 - before picture). from the PMC mixer to the PMC servo was removed.

However, we are currently unable to lock the PMC on high gain. When the gain is too high the PZT voltage goes straight to max and the lock is lost.

Attachment 1: 20191209_193112.jpg
Attachment 2: 20191209_193203_HDR.jpg
Attachment 3: imageedit_2_7551928142.gif
Attachment 4: imageedit_3_5863650538.gif
  15089   Tue Dec 10 01:24:17 2019 YehonathanUpdatePSLAOM first order beam alignment


However, we are currently unable to lock the PMC on high gain. When the gain is too high the PZT voltage goes straight to max and the lock is lost.

Just realized that the diffracted beam is frequency shifted by 80MHz. It would shift the PZT position in the PMC lock acquisition, wouldn't it?

  15090   Tue Dec 10 13:26:46 2019 YehonathanUpdatePSLAOM first order beam alignment

nvm the PZT can scan over many GHz.



However, we are currently unable to lock the PMC on high gain. When the gain is too high the PZT voltage goes straight to max and the lock is lost.

Just realized that the diffracted beam is frequency shifted by 80MHz. It would shift the PZT position in the PMC lock acquisition, wouldn't it?


  15091   Tue Dec 10 15:17:17 2019 YehonathanUpdatePSLPMC is locked

{Jon, Yehonathan}

We burt-restored the PSL and the PMC locked immediately.

The PMC is now locked on the AOM first order mode.

  15092   Tue Dec 10 18:27:22 2019 YehonathanUpdatePSLPMC is locked

{Yehonathan, Jon}

We are able to lock the PMC on the TEM00 mode of the deflected beam.

However when we turn off the driving voltage to the AOM and back on the lock is not restored. It get stuck on some higher order mode.

There are plethora of modes present when the PZT is scanned, which makes us believe the cavity is misaligned.


To lock again on the TEM00 mode again we disconnect the loop (FP Test point 1), find a TEM00 mode using the DC output adjust and close the loop again.


  15094   Wed Dec 11 15:29:17 2019 YehonathanUpdatePSLPMC is locked

Make sure to measure the power drop of the beam downstream of the AOM but before the PMC. Need to plot both together to make sure the chop time is much shorter than the 1/e time.

  15096   Thu Dec 12 19:20:43 2019 YehonathanUpdatePSLPMC cavity ringdown measurement

{Yehonathan, Rana, Jon}

To check whether we laser is being shut fast enough for the ringdown measurement we put a PD55 in the path that leads to the beat note setup. The beam is picked off from the back steering mirror after AOM and before the PMC.

@Shruti the PD is now blocking the beam to your setup.

As before, we drive the AOM to deflect the beam. The deflected beam is coupled to the PMC cavity. We lock the PMC and then shut the beam by turning off the output of the function generator that provides voltage to the AOM driver.

We measure the transmitted light of the PMC together with the light that is picked off before the PMC. In Attachment 1, the purple trace is the PMC transmission, the green trace is the peaked-off beam and the yellow trace is the function generator signal.

Rana was pointing out that the PDs, the function generator and the scope were not carefully impedance matched, which could lead to erroneous measurements. He also mentioned that the backscattered beam was too bright which might indicate that the PMC is oscillating. To remedy this we lowered the gain of the PMC lock to ~8.

We repeat the measurement after setting all the components to 50ohm (attachment 2). We then realize that the BNC T junction connected on the function generator is splitting the signal between the 50ohm AOM driver and 1Mohm oscilloscope channel which causes distortions as can be seen. We remove the T junction and get a much cleaner measurement (see next elog).


It seems like either the shutting speed or the PDs are only slightly faster than the PMC. I also check the AOM driver RF output fall time doing the same kind of measurement (attachment 3).

We suspect the PDs' bandwidth is to blame (although they are quoted to have 10MHz bandwidth).

In any case, this is fast enough for the IMC and arm cavities whose lifetime should be much longer than the PMC.

I will post an elog with some numbers tomorrow.

Attachment 1: IMG_0105.jpeg
Attachment 2: TEK00001.PNG
Attachment 3: 20191212_151642.jpg
  15097   Fri Dec 13 12:28:43 2019 YehonathanUpdatePSLPMC cavity ringdown measurement

I grab the data we recorded yesterday from the scope and plot it in normalized units (remove noise level and divide by maximum). See attachment.

It can be seen that the measured ringdown time is ~ 17us while the shut-off time is ~12us.

I plan to model the PD+AOM as a lowpass filter with an RC time constant of 12us and undo its filtering action on the PMC trans ringdown measurement to get the actual ringdown time.

Is this acceptable?


Attachment 1: Ringdown_InitialProcess.pdf
  15099   Tue Dec 17 00:23:28 2019 YehonathanUpdatePSLMapping the PSL electronics

I added to the PSL wiring list the ioo channels and the laser shutter (See attached pdf for an updated list).

The total channel numbers for now:

ai 57
ao 13
bi 1
bo 36

I counted each mbbo as 1 bo but I am not sure that's correct.

Still need to allocate Acromags.

Attachment 1: PSL_Wirings_-_Sheet1_(2).pdf
PSL_Wirings_-_Sheet1_(2).pdf PSL_Wirings_-_Sheet1_(2).pdf
  15100   Tue Dec 17 18:05:06 2019 YehonathanUpdatePSLMapping the PSL electronics

Updated the channel list (Attached):

1. Removed the MC steering mirror PZT channels

2. Added Sourcing/Sinking column

3. Recounted the mbbos correctly

4. Allocated Acromags:

Model Purpose No. Spare channels
XT1221 ai 7 11
XT1541 ao + src bo 2 9 ao
XT1121 src bo 2 4
XT1121 sink bo 1 4

I think we can start wiring.

Attachment 1: PSL_Wirings_-_Sheet1_(3).pdf
PSL_Wirings_-_Sheet1_(3).pdf PSL_Wirings_-_Sheet1_(3).pdf
  15103   Fri Dec 20 18:33:21 2019 YehonathanUpdatePSLMapping the PSL electronics

Final (hopefully) PSL channel list is attached with allocated Acromag channels. Wiring spreadsheet coming soon.

Current Acromag count:

AI 8
AO 2
Number of channels 8*8+2*8+4*16=144
Number of wires 144*2=288


Attachment 1: PSL_Wirings_-_Channel_List.pdf
PSL_Wirings_-_Channel_List.pdf PSL_Wirings_-_Channel_List.pdf PSL_Wirings_-_Channel_List.pdf PSL_Wirings_-_Channel_List.pdf PSL_Wirings_-_Channel_List.pdf
  15104   Mon Dec 23 19:30:20 2019 YehonathanUpdatePSLMapping the PSL electronics

PSL wiring spreadsheet is ready. (But the link was stripped. Koji)

Link to a wiki page  with the link to the wiring spreadsheet (Yehonathan)

  15105   Fri Dec 27 15:01:02 2019 YehonathanUpdatePSLPMC cavity ringdown measurement

I measured PMC ringdowns for several input powers. I change the input power by changing the DC voltage to the AOM.

First, I raise the DC voltage to the AOM from 0V and observe the signal on the picked off PD. I see that at around 0.6V the signal stops rising. The signal on the PD is around 4V at that point so it is not saturated.

Up until now, we provided 1.5V to the AOM, which means it was saturated.

I measured ringdowns at AOM voltages of 0.05, 0.1, 0.3, 0.5, 1 volt by shutting off the DC voltage to the AOM and measuring the signal at the PMC transmission PD and the picked off PD simultaneously for reference.

Attachment 1 shows the reference measurement for different AOM voltages. For low AOM DC voltages, the response of the AOM+PD is slower.

Attachment 2 shows the PMC transmission PD measurements which barely change as a function of AOM voltage but shows the same trend. I believe that if the AOM+PD response was much faster there would be no observable difference between those measurements.

Attachment 3 shows PMC transmissions and references for AOM voltages 0.05V and 1V. It seems like for low AOM voltages we are barely fast enough to measure the PMC ringdown.

I fitted the 0.3V ringdown and reference to a sum of two exponentials (Attachment 4).

The fitting function is explicitly a * nm.exp(-x/b) +c* nm.exp(-x/d) +e

For the PMC transmission I get:

a = 0.21
b = 3.64 (us)
c = 0.69, 
d = 39.62 (us)
e = 2.0e-04

For the reference measurement:

a = 0.34
b = 4.97 (us)
c = 0.58
d= 31.22 (us)
e = 1.11e-03

I am still not able to do deconvolution of the ref from the measurement reliably. I think we should do a network analyzer measurement.

Shruti, the PD is again in your beam path.

Attachment 1: PDAOMResponse.pdf
Attachment 2: PMCTransmission.pdf
Attachment 3: RingdownsAndRefs.pdf
Attachment 4: TwoExponentialFitAOM0.3V.pdf
  15106   Fri Dec 27 16:26:11 2019 YehonathanUpdatePSLPMC Linewidth measurement

I try to measure the linewidth of the PMC by ramping the PMC PZT. 

I do it by connecting a triangular shape signal to FP Test 1 on the PMC servo front panel (I know, it is probably better to connect it to DC EXT. next time.) and turn the servo gain to a minimum.

Attachment 1 shows the PMC transmission PD as the PZT is swept with the EOM connected and when it is disconnected. It shows the PMC over more than 1 free spectral range.

For some reason, I cannot seem to be able to find the 35MHz sidebands which I want to use to calibrate the PZT scan. I made sure that the EOM is driven by a 35MHz signal using the scope. I also made sure that the PMC cannot to lock without the EOM connected.

I am probably doing something silly.

Attachment 1: PMCTransmissionSpectra.pdf
  15109   Wed Jan 1 14:14:00 2020 YehonathanUpdatePSLPMC Linewidth measurement

Turns out the 35MHz sidebands are way too weak to resolve from the resonance when doing a PZT scan.

I connect the IFR2023B function generator on the PSL table to the EOM instead of the FSS box and set it to generate 150MHz at 13dbm.

To observe the resulting weak sideband I place a PDA55 at the peak-off path from the transmission of the PMC where there is much more light than the transmission of the PMC head mirror. Whoever is using this path there is a PD blocking it right now.

I do a PZT scan by connecting a triangular signal to the EXT DC on the PMC servo with and without the EOM (Attachment 1). A weak sideband can clearly be spotted now.

Using the above 150MHz sideband calibration I can find the roundtrip time to be 1.55ns.

I take a high-resolution scan of a resonance peak and fit it to a Lorentzian (Attachment 2) and find a roundtrip loss of 1.3%.

Using the above results the cavity decay time is 119ns.

We should investigate what's going on with the ringdown measurements.

Attachment 1: 150MHzSideBandCreation.pdf
Attachment 2: LinewidthMeasurment.pdf
  15110   Wed Jan 1 16:04:37 2020 YehonathanUpdatePSLMapping the PSL electronics



For the IMC servo board, it'd be easiest to copy the wiring scheme for the BIO bits as is configured for the CM board (i.e. copy the grouping of the BIO bits on the individual Acromag units). This will enable us to use the latch code with minimal modifications (it was a pain to debug this the first time around). I don't see any major constraint in the wiring assignment that'd make this difficult.


PSL wiring spreadsheet is ready. (But the link was stripped. Koji)

Link to a wiki page  with the link to the wiring spreadsheet (Yehonathan)


  15115   Fri Jan 10 14:21:19 2020 YehonathanUpdatePSLc1psl reboot

PSL controls on the sitemap went blank. Rebooted c1psl. PSL screens seem normal again.

  15119   Mon Jan 13 23:30:53 2020 YehonathanSummaryPSLChanges made since Gautam left

As per Gautam's request, I list the changes that were made since he left:

1. The AOM driver was connected to a signal generator.

2. The first order beam from the AOM was coupled into the PMC while the zero-order beam is blocked. We might want to keep this configuration if the pointing stability is adequate.

3. c1psl got Burt restored to Dec 1st.

4. Megatron got updated.

Currently, c1susaux seems unresponsive and needs to be rebooted.

  15131   Fri Jan 17 21:56:22 2020 YehonathanUpdatePSLAOM first order beam alignment

Today I noticed that the beam reflected from the PMC into the RFPD has a ghost (attachment) due to reflection from the back of the high transmission beam splitter that stirs the beam into the RFPD.

The two beams are focused into the RFPD.

In the past, the ghost beam was probably blocked by the BS mirror mount.

I put an iris to block the ghost beam.

Attachment 1: 20200117_174841.jpg
  15132   Fri Jan 17 22:11:19 2020 YehonathanUpdatePSLRingdown measurements

I prepare for the ringdown measurement of the PMC according to Gautam's previous experiments.

1. I assembled the needed PDs and power supplies, lenses, beamsplitters and optomechanics needed for the measurement.

2. I surveyed the laser power with an Ophir power meter in the different parts of the experiment. All the measurements were done with the AOM driver excited with 1V DC.

For the PMC reflection, we chose to split off the beam that goes into the reflection camera. The power in that beam is ~ 0.11mW when the PMC is locked and 2.1mW otherwise.

For the PMC transmission, we chose to split the beam that is transmitted through the second steering mirror after the PMC. The power in that beam is 2mW.

For the peak off before the PMC, we chose to split the beam that goes into the fiber coupler. That path contains also the other AOM diffraction orders: 2.26mW in the 0th order beam, 6.5mW in the 1st order beam, 0.14mW in the 2nd order beam.

3. I placed a 10% beam splitter in the peak-off path such that 90% still goes into the fiber coupler (Attachment 1). I place a lens and PDA255 to measure the peak-off (Attachment 2).

It's getting late, I'll continue with the PD placements on Tuesday.

Attachment 1: 20200117_192455.jpg
Attachment 2: 20200117_192448.jpg
  15154   Sat Jan 25 11:54:42 2020 YehonathanUpdatePSLRingdown measurements

Zero order beam PMC ringdown

On Wednesday I installed 3 PDs (see attached photos) measuring: 

1. The input light to the PMC. Flip-mirror was installed (sorry Shruti) on the beam path to the fiber coupler.

2. Reflected light from the PMC.

3. PMC transmitted light.

I connected the three PDs to the oscilloscope and the AOM driver to a function generator. I drive the AOM with a square wave going from 1V to 0V.

I slowly increased the square wave frequency. The PMC servo doesn't seem to care. I reach 100KHz - it seems excessive but still works. In any case, I get the same results doing a single shut-down from a DC level.

I download the traces. I normalize the traces but I don't rescale them (Attachment 4) so that the small extinction can be investigated.

I notice now that the PDs show the same extinction. It probably means I should have taken dark currents data for the PDs.

Also, I forgot to take the reflected data when the PMC is out of resonance with the laser which could have helped us determine the PMC transmission.

Again, the shutdown is not as sharp as I want. There is a noticeable smoothening in the transition around t = 0 which makes the fit to an exponential difficult. I suspect that the function generator is the limiting device now. I hooked up the function generator to the oscilloscope which showed similar distortion (didn't save the trace)

I try to fit the transmission PD trace to a double exponential and to Zucker model (Attachment 5).

The two exponentials model, being much less restrictive, gives a better fit but the best fit gives two identical time constants of 92ns.

The Zucker model gives a time constant of 88ns. Both of these results are consistent with more or less with the linewidth measurement but this measurement is still ridden with systematics which hopefully will become minimized IMC ringdowns.

Attachment 1: Input_beam_path.jpg
Attachment 2: Reflected_Beam_Path.jpg
Attachment 3: Transmitted_Beam_Path.jpg
Attachment 4: PMCRingdownNormalizedRawdata.pdf
Attachment 5: TransPDFits.pdf
  15170   Tue Jan 28 20:51:37 2020 YehonathanUpdateIOOIMC WFS servos stable again

I resume my IMC ringdown activities now that the IMC is aligned again.

To avoid any accidental misalignments Gautam turned off all the inputs to the WFS servo.

I set up a PD and a lens as in attachment 1 (following Gautam's setup).

I connect the REFL, TRANS and INPut PDs to the oscilloscope.

I connect a Siglent function generator to the AOM driver. I try to shut off the light to the IMC using 1V DC waveform and pressing the output button manually. However, it produced heavily distorted step function in the PMC trans PD.

I use a square wave with a frequency of 20mHz instead with an amplitude of 0.5V offset of 0.25V and dutycycle of 1% so there will be minimal wasted time in the off state. I get nice ringdowns (attachment 2) - forgot to take pictures. The autolocker slightly misaligns the M2 every time it is acting, so I manually align it everytime the IMC gets unlocked.

Data analysis will come later.

I remove the PD and lens and reenable the WFS servo inputs. The IMC locks easily. The WFS outputs are very different than 0 now though.

  15175   Wed Jan 29 12:40:24 2020 YehonathanUpdateIOOIMC Ringdowns preliminary data analysis

I analyze the IMC ringdown data from last night. 

Attachment 1 shows the normalized raw data. Oscillations come in much later than in Gautam's measurement. Probably because the IMC stays locked.

Attachment 2 shows fits of the transmitted PD to unconstrained double exponential and the Zucker model.

Zucker model gives time constant of 21.6us

Unconstrained exponentials give time constants of 23.99us and 46.7us which is nice because it converges close to the Zucker model.

Attachment 1: IMCRingdownNormalizedRawdata.pdf
Attachment 2: IMCTransPDFits.pdf
  15183   Mon Feb 3 13:54:10 2020 YehonathanUpdateIOOIMC Ringdowns extended data analysis

I extended the ringdown data analysis to the reflected beam following Isogai et al.

The idea is that measuring the cavity's reflected light one can use known relationships to extract the transmission of the cavity mirrors and not only the finesse.

The finesse calculated from the transmission ringdown shown in the previous elog is 1520 according to the Zucker model, 1680 according to the first exponential and 1728 according to the second exponential.

Attachment 1 shows the measured reflected light during an IMC ringdown in and out of resonance and the values that are read off it to compute the transmission.

The equations for m1 and m3 are the same as in Isogai's paper because they describe a steady-state that doesn't care about the extinction ratio of the light.

The equation for m2, however, is modified due to the finite extinction present in our zeroth-order ringdown.

Modelling the IMC as a critically coupled 2 mirror cavity one can verify that:

m_2=P_0KR\left[T-\alpha\left(1-R\right)\right]^2+\alpha^2 P_1

Where P_0 is the coupled light power 

P_1 is the power rejected from the cavity (higher-order modes, sidebands)

K=\left(\mathcal{F} /\pi \right )^2 is the cavity gain.

R and T are the power reflectivity and transmissivity per mirror, respectively.

\alpha^2 is the power attenuation factor. For perfect extinction, this is 0.

Solving the equations (m1 and m3 + modified m2), using Zucker model's finesse, gives the following information:

Loss per mirror = 84.99 ppm
Transmission per mirror = 1980.77 ppm
Coupling efficiency (to TEM00) = 97.94%
Attachment 1: IMCTransReflAnalysis_anotated.pdf
  15186   Tue Feb 4 18:13:01 2020 YehonathanUpdatePSLBench testing of PSL ai channels

{Yehonathan, Jon, Jordan}

I tested the ai channels of the new PSL Acromag by looping an already-tested ao channel (C2:PSL-FSS-INOFFSET) back to the different ai channels.

I use Jon's IFOTest with /users/jon/ifotest/PSL.yaml.

I created a spreadsheet for the testing based on the current wiring spreadsheet. I added two columns for the high and low readings for each ai channel (attached pdf).

I marked in red the failed channels. Some of them are probably calibration issues, but the ones that show the same voltage for high and low are probably disconnected wires.

I redid the test on the channel that seemed disconnected to confirm.

I created a yaml file with all the failed channels for retesting called /users/jon/ifotest/PSL_failed_channels.yaml.

Attachment 1: c1psl_wire_testing_-_By_Connector.pdf
c1psl_wire_testing_-_By_Connector.pdf c1psl_wire_testing_-_By_Connector.pdf c1psl_wire_testing_-_By_Connector.pdf c1psl_wire_testing_-_By_Connector.pdf
  15187   Wed Feb 5 08:57:11 2020 YehonathanUpdatePSLBench testing of PSL ai channels

I checked the failed channels against the EPICS database definitions and the yaml file inputted to IFOTest. The channels where the readings are something other than +10/0 V, but the high/low values do change, I think can be attributed to one of two things:

  • An incorrect gain and/or offset conversion parameter in the yaml file
  • The EPICS SMOO parameter (smoothing) is set to some long value

I fixed the channel gains/offsets in the master yaml file (PSL.yaml). I also disabled smoothing in the EPICS defintions of the new PSL channels for the purpose of testing. We can uncomment those lines after installing the new chassis if noise is a problem. Please go ahead and re-test the channels again.


I marked in red the failed channels. Some of them are probably calibration issues, but the ones that show the same voltage for high and low are probably disconnected wires.

  15189   Wed Feb 5 21:04:10 2020 YehonathanUpdatePSLBench testing of PSL ai channels

{Yehonathan, Jon}

We retested the failed ai channels. Most of them got fixed by applying the inverse calibration in the yaml file.

We still find some anomalous channels, mostly in the DB25 connector. Turns out, their limits were ill-defined in the EPICS database. Specifying the right limit fixed the issue.

We find one miswired channel (BNC4). We connected the BNC to the right channel on the Acromag unit which fixed the issue.

Overall all the ai channels were successfully bench-tested.


I checked the failed channels against the EPICS database definitions and the yaml file inputted to IFOTest. The channels where the readings are something other than +10/0 V, but the high/low values do change, I think can be attributed to one of two things:

  • An incorrect gain and/or offset conversion parameter in the yaml file
  • The EPICS SMOO parameter (smoothing) is set to some long value

I fixed the channel gains/offsets in the master yaml file (PSL.yaml). I also disabled smoothing in the EPICS defintions of the new PSL channels for the purpose of testing. We can uncomment those lines after installing the new chassis if noise is a problem. Please go ahead and re-test the channels again.


I marked in red the failed channels. Some of them are probably calibration issues, but the ones that show the same voltage for high and low are probably disconnected wires.

  15190   Wed Feb 5 21:13:17 2020 YehonathanUpdateIOOIMC Ringdowns extended data analysis

I translate the results obtained in the previous elog to the IMC 3 mirror cavity. I assume the loss in each mirror in the IMC is equal and that M2 has a negligible transmission.

I find that to a very good approximation the loss per IMC mirror is 2/3 the loss per mirror in the 2 mirror cavity model. That is the loss per mirror in the IMC is 56 ppm. The transmission per mirror in the IMC is the same as in the 2 mirror model, which is 1980 ppm.

The total transmission is the same as in the 2 mirror model and is given by:

\frac{P_0}{P_0+P1}KT^2\approx 90\%

where \frac{P_0}{P_0+P1} is the coupling efficiency to the TEM00 mode.

  15198   Fri Feb 7 12:58:25 2020 YehonathanUpdateGeneralMetal PMC parts

I took the metal PMC box and examined its content and find the following items:

Name Quantity Picture (Attachment #)
Metal PMC body (PMC1) 1 1-3
Metal PMC body with two mounted 41 deg mirrors (PMC2) 1 4-6
"Baked PZT Caps" 3 7
PZT Caps 2 8
Flat mirror mounts 2 9
Bar clamps 4 10
Clamp studs 8 10
PZTs 4 11
ORings INF 12
Ball bearings INF 13
6.8 deg AoI curved mirrors (r=-1000mm) 6 14
41 deg AoI flat mirrors, R=99% @ 1064nm (1 Damaged) 11 15

There seem to be enough parts to build 2 PMCs + spares.

I find several problems in the metal PMCs:

PMC1 has a broken screw in one of its flat mirror mounts (Attachment 16). We need to get it out in the machine shop.

PMC2 one of the flat mirrors has a scratch on the AR coating and its ORing is failing (Attachment 17). Mirror and ORing need to be replaced.

I measure the physical dimensions of the PMC with the help of https://dcc.ligo.org/LIGO-E1400332. The roundtrip is found to be 24cm which gives an FSR of 1.25GHz.

I use Evan Hall's Python script for calculating the mode spectrum as a function of the cavity length of the metal PMC and overlay the RF sidebands (Green dashed lines) on it (Attachment 18) to check for any HOM coincidence. The width of the lines is the mode splitting due to the cavity astigmatism.

It seems like the only issue might come from a 10th order modes (green ribbon) which are hopefully small enough in reality.

Attachment 1: PMC1Side.jpg
Attachment 2: PMC1Front.jpg
Attachment 3: PMC1Back.jpg
Attachment 4: PMC2Side.jpg
Attachment 5: PMC2Back.jpg
Attachment 6: PMC2Front.jpg
Attachment 7: 20200207_123118.jpg
Attachment 8: 20200207_123055.jpg
Attachment 9: 20200207_122448.jpg
Attachment 10: 20200207_122400.jpg
Attachment 11: 20200207_122040.jpg
Attachment 12: 20200207_122227.jpg
Attachment 13: 20200207_122149.jpg
Attachment 14: 20200207_123328.jpg
Attachment 15: 20200207_123405_HDR.jpg
Attachment 16: PMC1Screw.jpg
Attachment 17: PMC2BadMirror.jpg
Attachment 18: homVersusLength.pdf
  15215   Sat Feb 15 12:56:24 2020 YehonathanUpdateIOOIMC Transfer function measurement

{Yehonathan, Meenakshi}

We measure the IMC transfer function using SR785.

We hook up the AOM driver to the SOURCE OUT, Input PD to CHANNEL ONE and the IMC transmission PD to CHANNEL TWO.

We use the frequency response measurement feature in the SR785. A swept sine from 100KHz to 100Hz is excited with an amplitude of 10mV.

Attachment 1 shows the data with a fit to a low pass filter frequency response.

IMC pole frequency is measured to be 3.795KHz, while the ringdowns predict a pole frequency 3.638KHz, a 4% difference.

The closeness of the results discourages me from calibrating the PDs' transfer functions.

I tend to believe the pole frequency measurement a bit more since it coincides with a linewidth measurement done awhile ago Gautam was telling me about.


I think of trying to try another zero-order ringdown but with much smaller excitation than what used before (500mV) and than move on to the first-order beam.

Also, it seems like the reflection signal in zero-order ringdown (Attachment 2,  green trace) has only one time constant similar to the full extinction ringdown. The reason is that due to the fact the IMC is critically coupled there is no DC term in the electric field even when the extinction of light is partial. The intensity of light, therefore, has only one time constant.

Fitting this curve (Attachment 3) gives a time constant of 18us, a bit too small (gives a pole of 4.3KHz). I think a smaller extinction ringdown will give a cleaner result.

Attachment 1: IMCFrequencyResponse.pdf
Attachment 2: IMCRingdownNormalizedRawdata.pdf
Attachment 3: IMCREFLPDFits.pdf
  15225   Wed Feb 26 17:17:17 2020 YehonathanUpdate Arms DC loss measurements

{Yehonathan, Gautam}

In order to measure the loss in the arm cavities in reflection, we use the DC method described in T1700117.

It was not trivial to find free channels on the LSC rack. The least intrusive way we found was to disconnect the ALS signals DSUB9 (Attachment 1) and connect a DSUB breakout board instead (Attachment 2).

The names of the channels are ALS_BEATY_FINE_I_IN1_DQ for AS reflection and ALS_BEATY_FINE_Q_IN1_DQ for MC transmission. Actually, the script that downloads the data uses these channels exactly...

We misalign the Y arm (both ITM ad ETM) and start a 30 rep measurement of the X arm loss cavity using /scripts/lossmap_scripts/armLoss/measureArmLoss.py and download the data using dlData.py.

We analyze the data. Raw data is shown in attachment 3. There is some drift in the measurement, probably due to drift of the spot on the mirror. We take the data starting from t=400s when the data seems stable (green vertical line). Attachment 5 shows the histogram of the measurement

X Arm cavity RT loss calculated to be 69.4ppm.

We repeat the same procedure for the Y Arm cavity the day after. Raw data is shown in attachment 5, the histogram in attachment 6.

Y Arm cavity RT loss calculated to be 44.8ppm. The previous measurement of Y Arm was ~ 100ppm...

Loss map measurement is in order.

Attachment 1: 20200226_171155.jpg
Attachment 2: 20200226_171539.jpg
Attachment 3: XArmLossMeasurement_RawData.pdf
Attachment 4: XArmLossMeasurement_Hist.pdf
Attachment 5: YArmLossMeasurement_RawData.pdf
Attachment 6: YArmLossMeasurement_Hist.pdf
  15243   Tue Mar 3 17:59:33 2020 YehonathanUpdateElectronicsPSL Shutter and PMC TRANSPD working

I used existing BNC cables running from the PSL table to the PSL rack and reassigned them to the PSL Shutter and PMC transmission PD channels.

The PSL shutter turned out to be a sinking channel. Jordan reconnected the PSL shutter wires to a sinking BIO Acromag. Channel list is updated.

Both channels have been tested to be working as expected.

gautam add on about EPICS:

  • the PSL shutter channels were previously hosted on c1aux.
  • I didn't comment out the original database entries on c1aux because we changed the prefix for all these channels - i.e. C1:AUX-PSL_Shutter --> C1:PSL-PSL_Shutter.
  • Modified the LSC offset script to close/open the PSL shutter by writing to the correct channel now.
  • there is some EPICS logic that checks the main volume pressure and prevents the opening of the PSL shutter if the main volume pressure is between 0.003 torr and 500 torr. I preserved this capability (so there are some associated soft channels in the database as well).

P.S - there is a problem we noticed - if the modbus process is started with the local subnet not having a fixed IP address, then all the EPICS channels will not be responsive. The way to fix this is to run the following sequence of commands:

sudo systemctl stop modbusIOC.service
sudo ifdown enp4s0
sudo ifup enp4s1
sudo ssytemctl start modbusIOC.service
  15246   Wed Mar 4 11:10:47 2020 YehonathanUpdateComputersAllegra revival

Allegra had no network cable and no mouse. We found Allegra'snetwork cable (black) and connected it.

I found a dirty old school mouse and connected it.

I wiped Allegra and now I'm currently installing debian 10 on allegra following Jon's elog.

04/01 update: I forgot to mention that I tried installing cds software by following Jamie's instruction: I added the line in /etc/apt/sources.list.d/lscsoft.list: "deb http://software.ligo.org/lscsoft/debian/ stretch contrib". But this the only thing I managed to do. The next command in the instructions failed.

  15255   Thu Mar 5 15:03:48 2020 YehonathanUpdateElectronicsPSL Shutter and PMC TRANSPD working

[Jon, Yehonathan]


With the Acromag chassis now permanently installed, we tested the C1PSL channels going over the channel list one by one, excluding the IMC channels which Gautam is taking responsibility for (the servo board itself is also in question).

The strategy is to check the response of input channels to specific output channels for expected behaviour whenever is possible.

We marked on the channel list spreadsheet the status of the channels that were tested.

In more detail


Channels under test What was done
C1:PSL-FSS_SW1 Switched C1:PSL-FSS_SW1 and observed the IMC unlock
C1:PSL-FSS_SW2, C1:PSL-FSS_MIXERM Connected a signal to Test2 on FSS box and observed a proportional change on C1:PSL-FSS_MIXERM
C1:PSL-FSS_INOFFSET Disconnected feedback by switching C1:PSL-FSS_SW1. Tweaked C1:PSL-FSS_INOFFSET and observed a proportional response in C1:PSL-FSS_MIXERM
C1:PSL-FSS_MGAIN, C1:PSL-FSS_PCDRIVE Disconnected feedback, turned on some offset using C1:PSL-FSS_INOFFSET. Tweaked C1:PSL-FSS_MGAIN and observed a response in C1:PSL-FSS_PCDRIVE
C1:PSL-FSS_SLOWDC, C1:PSL-FSS_SLOWM Disconnected feedback. Tweaked C1:PSL-FSS_SLOWDC and obsereved a proportional response in C1:PSL-FSS_SLOWM
C1:PSL-FSS_FASTGAIN, C1:PSL-FSS_FAST Disconnected feedback, turned on some offset using C1:PSL-FSS_INOFFSET. Tweaked C1:PSL-FSS_FASTGAIN and obsereved a response in  C1:PSL-FSS_FAST


Frequency Ref

Channels under test What was done
C1:PSL-PMC_PHCON Observed the PMC unlocks when a big change in C1: PSL-PMC_PHCON is made
C1:PSL-PMC_RFADJ, C1:PSL-PMC_MODET Tweaked C1:PSL-PMC_RFADJ and obsereved a proportional response in C1:PSL-PMC_MODET
C1:PSL-PMC_PHFLIP Observed the PMC unlock when C1:PSL-PMC_PHFLIP is switched


PMC Servo Card

Channels under test What was done
C1:PSL-PMC_SW1, C1:PSL-PMC_PMCERR, C1:PSL-PMC_INOFFSET, C1:PSL-PMC_PZT Unlocked the PMC by switching C1:PSL-PMC_SW1. Tweaked C1:PSL-PMC_INOFFSET and observed a proportional change in C1:PSL-PMC_PMCERR and C1:PSL-PMC_PZT
C1:PSL-PMC_BLANK Observed the PMC unlock with when C1:PSL-PMC_BLANK is switched
C1:PSL-PMC_GAIN Unlocked the PMC by switching C1:PSL-PMC_SW1. Turned on some offset using  C1:PSL-PMC_INOFFSET. Tweaked C1:PSL-PMC_GAIN and observed response in C1:PSL-PMC_PZT
C1:PSL-PMC_SW2 Unlocked the PMC by switching C1:PSL-PMC_SW1. Connected a signal to TP2 on the PMC card and observed a proportional change in C1:PSL-PMC_PZT.

Unlocked the PMC by switching C1:PSL-PMC_SW1. Tweaked C1:PSL-PMC_RAMP and observed a change in C1:PSL-PMC_PZT.

C1:PSL-PMC_RFPDDC Observed a high value 0.5V when PMC is unlocked and a low value 0.03V when it is locked



Channels under test What was done

We misaligned MC1 to get a measurable signal in WFS channels. NDScoped the corresponding C1:IOO-WFS*_SEG*_I&Q channels and observed a change in those channels in response to switching the attenuation on and off.

C1:IOO-WFS*_LO_LOCK_MON Disconnected the LO cable from the WFS boards and observed C1:IOO-WFS*_LO_LOCK_MON go to zero.
C1:IOO-WFS*_SEG*_I&Q Connected a short SMA cable to the 29.5MHz frequency distribution board. Attenuated the signal by 20db and connected it to the different SEG channels one at a time and observed a response in C1:IOO-WFS*_SEG*_I&Q channels.
C1:IOO-WFS*_SEG*_DC We shined a laser pointer to the different quadrants and observed saturation in the corresponding C1:IOO-WFS*_SEG*_DC with no cross talks.

MC Servo

Channels under test What was done
C1:IOO-MC_SW1, C1:IOO-MC_OPTIONA, C1:IOO-MC_POL, C1:IOO-MC_OPTIONB,C1:IOO-MC_FASTSW These switches unlocked the IMC when flipped.
C1:IOO-MC_SW2, C1:IOO-MC_SUM_MON, C1:IOO-MC_SLOW_MON, C1:IOO-MC_FAST_MON A sine wave signal was injected in IN2 on the servo board. C1:IOO-MC_SW2 was switched on and the value of C1:IOO-MC_SUM_MON, C1:IOO-MC_SLOW_MON and C1:IOO-MC_FAST_MON changed accordingly.
C1:IOO-MC_SW3 Connected a scope to OUT2 on the servo board. Switched C1:IOO-MC_SW3 on and observed a signal on the scope.
C1:IOO-MC_EXCA_EN Unlocked the IMC by switching C1:IOO-MC_SW1 off. Connected a signal to EXC A and a scope to TP2A on the servo board and observed the signal on the scope when C1:IOO-MC_EXCA_EN was switched on.
C1:IOO-MC_EXCB_EN Unlocked the IMC by switching C1:IOO-MC_SW1 off. Connected a signal to EXC B and a scope to TP2B on the servo board and observed the signal on the scope when C1:IOO-MC_EXCB_EN was switched on.
C1:IOO-MC_REFL_OFFSET Unlocked the IMC by switching off. Tweaked C1:IOO-MC_REFL_OFFSET and observed a proportional change in C1:IOO-MC_SUM_MON.
C1:IOO-MC_LATCH_EN Tweaked the VCO gain slider and observed the latch switch off and on.
C1:IOO-MC_LIMIT Unlocked the IMC by switching C1:IOO-MC_SW1 off. Connected a sine wave signal to EXC B and enabled C1:IOO-MC_EXCB_EN. Ramped up the VCO gain. Raised the sine wave amplitude until C1:IOO-MC_LIMIT turned on.
C1:IOO-MC_LIMITER We ramped the VCO such that C1:IOO-MC_LIMIT was switched on. We switched C1:IOO-MC_LIMITER on and observed C1:PSL-FSS_MIXERM high value go down.

NPRO Diagnostics

Channels under test What was done

The signals were compared to previous values for consistency. Then they were unplugged from the Acromag chassis to confirm their values went to 0 and returned to the same values after being reconnected.

  15264   Tue Mar 10 19:59:09 2020 YehonathanUpdateLoss MeasurementArm transfer function measurement

I want to measure the transfer function of the arm cavities to extract the pole frequencies and get more insight into what is going on with the DC loss measurements.

The idea is to modulate the light using the PSL AOM. Measure the light transmitted from the arm cavities and use the light transferred from the IMC as a reference.

I tried to start measuring the X arm but the transmission PD is connected to the QPD whitening filter board with a 4 pin Lemo for which I couldn't find an adapter.

  • I switch to the Y arm where the transmission PD - Thorlabs PDA520 (250KHz Bandwidth) - is BNC all the way.
  • I lay an 82ft BNC cable from the Y Arm 1Y4 to 1Y1 where the BNC from the IMC Trans PD and an SR785 are found. 
  • I lock the Arm cavities.
  • I connect the AOM cable to the source, the TRY PD (Teed off from the QPD whitening filter) to CH1 and IMC_TRANS to CH2 and measure the transfer function using a swept sine with an offset of 300mV and amplitude of 100mV.
  • I fit it to a low pass filter function - see attachment 1 - but it seems like the fit rails off at 10KHz. 

Could this be because of the PDA520 limited BWs? I tried playing with the PD gain/bandwidth switch but it seems like it was already set to high bandwidth/low gain.

In any case, the extracted pole frequency ~ 2.9kHz implies a finesse > 600 (assuming FSR = 3.9MHz) which is way above the maximal finesse (~ 450) for the arm cavities.

I disconnected the source from the AOM. But left the other two BNCs connected to the SR785. Also, TRY PD is still teed off. Long BNC cable is still on the ground.

Attachment 1: YArmFrequencyResponse.pdf
ELOG V3.1.3-