The IMC has not been behaving well since this morning and totally not happy when Q was finishing his measurements. The WFS servo had large offsets in pitch. Looking back at the trend and using ezcaservo to restore the suspensions did not help.
I realigned the IMC and brought TRANS SUM to ~18000 and MCREFL to < 0.5. The spot positions are not very good; nearly 2 mm off in pitch on MC1 and MC3. But after the alignment of MC, the WFS servo offsets were below +/-20.
The MC has been locked stably with WFS servo ON for the last few hours.
P.S. I did not touch the WFS pointing or reset the WFS offsets.
MC remained locked with WFS enabled all through last night and this morning. Koji dropped by and looked at the MC. The MC WFS servo, though stable, was at the edge of becoming unstable. This was because I did not touch the WFS pointing on the QPDs yesterday after realigning. So I recentered the WFS, reset the WFS filterbank offsets and reenabled the servo.
I measured the spot positions on MC mirrors for reference.
Spot positions in mm (MC1,2,3 pit MC1,2,3 yaw): [1.405767579680834, 0.79369009503571208, 1.3220430681427462, -1.2937873599406551, -1.1704264340968924, -1.2518046122798692]
ALS common locked by actuating on MC2 and ALS Differential locked by actuating on ETMX and ETMY (Stable lock acquired for over an hour).
Common and Differential offsets were swept to obtain IR resonance in both the arms (arms stayed on resonance for over 15 minutes).
1. Configured LSC settings to allow locking using ALS error signals.
2. Locked common and differential using ALS error signals
XARM 1 -1
YARM 1 1
X arm servo settings:
FIlters: FM1, FM5, FM6, FM7, FM9
Gain = -8.0
Y arm servo settings:
Filters: FM1, FM5, FM6, FM7, FM9
Gain = +8.0
ETMX 1 0
ETMY 0 1
3. Transitioned CARM control output to actuate on MC2 instead of ETMX
SUS-MC2_LSC servo gain = 1.0
The transition was done in very small steps : actuating on MC2 in -0.01 steps at the outmatrix upto -1.0 while reducing the ETMX actuation to 0 simultaneously.
DARM still stayed locked only with actuation on ETMY.
4. Transitioned DARM control to ETMX and ETMY.
Used ezcastep to step up DARM control (Y arm output) actuation on ETMX and step down the actuation on ETMY.
Final output matrix
ETMX 0 -0.5
ETMY 0 0.5
MC2 -1.0 0
Noise plot in attachment.
5. Finding arm resonance
Used ezcastep to gradually build up offsets in CARM (LSC-XARM_OFS) to find IR resoance in one arm (Y arm).
Introducing a small (order of 0.5) DARM offset (LSC-YARM_OFS) shifted the Y arm off-resonance.
Used CARM offset to get back the Y arm to resonance.
Changing CARM and DARM offsets alternately while tracking the Y arm resonance got us to a point where we had both the arms resonating for IR.
6. At this point the MC decided to give up and we lost lock.
1. We found that the WFS2 YAW output filterbank had the output switched OFF (probably accidentally by one of us). This was reenabled. Please be careful while manually turning ON and OFF the MC WFS servos.
Nic, Jenne, EricQ, and Koji should describe the demonstartion of CESAR achieved tonight.
Q and I have started to use the ALS slow servo for the end aux lasers while locking the arms using ALS. The servo prevents us from hitting the limits of the PZT range for the end lasers and a better PDH locking.
But keeping the servo ON causes the slow output to drift away making it hard to find the beat note everytime the arm loses lock. The extensive beat note search following the unlock can be avoided by clearing history of the slow servo.
I have modified the IFOconfigure scripts and the corresponding .req files for the X arm and Y arm in burt. I have also added configure scripts to save and restore LSC settings for locking the arms using ALS error signals.
The settings are yet to be saved and the scripts should also be checked if they are working as required.
Off again. Restarted ntp on fb.
I tried to repeat Koji's PRMI lock using REFL165I/Q. I was not able to lock PRMI stably. All I could get was momentary PRMI sb locks (few seconds) using AS55Q for MICH and REFL165Q for PRMI. I tried to transition MICH locks from AS55Q to REFL165I/Q and this did not work well; I lost even the momentary locks.
The demod phases for both AS55 and REFL165 were also very different.
AS55 WHTN: 21dB demod phase -78.7deg
REFL165 WHTN: 45dB demod phase -80.7deg
AS55Q x1.00 MICH
MICH POP110I 100up/10down / FM Trig FM2/3/6/7/9 35up 2down 5sec delay
PRCL POP110I 100up/10down / FM Trig FM2/3/6/9 35up 2down 0.5sec delay
MICH OFS 0.0 / Gain -10 / Limiter ON
PRCL OFS 0 / Gain -0.023 / Limiter ON
MICH ITMX -1.0 / ITMY +1.0
PRCL PRM 1.0
I've also turned on the MC2 TRANS path to gather some data over the weekend on how well or bad it works. Please turn it off on Monday.
MC2_TRANS path in WFS servo turned OFF.
While I'm looking at the PRM ASC servo model, I tried to use the current servo filters for the ASC
as Manasa aligned the POP PDs and QPD yesterday. (BTW, I don't find any elog about it)
The POP PD was showing only ~200 counts which was very low compared to what we recollect from earlier PRMI locks (~400 counts). Also, the POP ASC QPD was also not well-aligned.
While holding PRMI lock on REFL55, I aligned POP path to its PD (maximize POP DC counts) and QPD (centered in pitch and yaw).
X and Y green
The X green totally lost its pointing because of the misaligned PZTs from last week's power failure. This was recovered.
Y arm green alignment was also recovered.
I have included Yarm CESAR to the LSC model. It was just a copy paste of the Xarm CESAR. Since we are now meditating about implementing CCESAR and DCESAR, I did not run or install the model as yet.
Since we don't have an arm length precision measurement (i.e. better than centimeters), why not just do as Koji suggests and use the ALS to get the frequency spacing between a few red FSR and then we have the measurement solid ?
Arm lengths measured using ALS. Both the arms were estimated to have the same length (to the order of a centimeter) 37.51 m
I used ALS error signal to lock the arms and scanned the arm to find 4 consecutive IR resonances. From the beat note frequencies measured using the spectrum analyser during IR resonance, the FSR, and hence the length of the arms were calculated.
The estimated lengths are not very precise down to a mm given the resolution of the spectrum analyser. We have brought out the rubidium clock to use as reference for the spectrum analyser to challenge the measurements.
The MC had not been stable lately with WFS drifting constantly. I checked the servo and found that the MC_TRANS path was still running. It turned out that the autolocker script enables the TRANS path in the locking process. I have turned the MC_TRANS path servo inputs OFF and now it is no more a part of the WFS servo.
P.S. Jenne fixed the PMC alignment mostly in pitch to bring it up to 0.81 from 0.77. But the temperature fluctuations have still not got us to the sweet spot for optimum PMC trans.
Arm lengths were measured using ALS
X arm length = 37.79 +/- 0.05 m
Y arm length = 37.81 +/- 0.01 m
Whats and whys
We want to measure the arm length with an accuracy of say a mm.
This would mean a measurement precision of 1e-3/40=25ppm. (1mm in 40m)
So the required measurement resolution on the spectrum analyser is 25ppm*4MHz=100Hz (assuming the cavity FSR is roughly 4MHz).
Although the spectrum analyser does not limit the measurement precision, we are limited by the noise in ALS at 1000Hz rms. So we can use ALS only to measure arm length precise to the order of a few mm.
RXA: Not that we really need to right now, but even with an ALS noise of 1000 Hz, we can can do better just by averaging at each resonance point. And fitting a line as you have already done gets even better:
The Spectrum analyser was reference locked to the rubidium clock @10MHz for these measurements.
The FSRs of the arms
X arm = 3.9671e+06 +/- 4.8535e+03 Hz
Y arm = 3.9648e+06 +/- 1.1064e+03 Hz
1&2. Plots representing the arm scans showing the beat frequency for which IR resonates in the arm vs the ALS offset (position of the ETM).
3. Data and code (zip file)
P.S. We had trouble scanning the arms using ALS. This was because the slow servo was not enabled. Hence ALS was losing its PDH lock everytime we scanned past a couple of FSRs.
Last night, as well as tonight, the ALS seems not quite as robust as it was earlier in the week.
I have just taken noise spectra, and ALS is definitely more noisy than usual.
These plots are with the arms held in CARM and DARM mode, with servo gains of 8. I was seeing the beginnings of gain peaking at a gain of 10, so I turned it back to 8. Our ALS in-loop RMS is usually something like a few hundred Hz, but I'm seeing over 1kHz, so I have a factor of 4 or 5 too much noise. Why?!?!?
I have noticed that ALS noise has been at 1KHz rms since LSC arm lock servos have been used to lock arms using ALS error signals. May be this has not been given much attention.
But looking more closely at the ALS noise (better dtt resolution for noise power spectrum) , there seems to be too much noise suppression at <1Hz and not much happening at around 10Hz.
Attachment 1 (data files at /users/manasa/data/140421/)
So I made a bunch of transfer function measurements for ALS and phase tracker servo. Koji will be using these and redesigning the servo filters so that we can get more suppression at 10Hz.
Other than this I also found that the Y arm showed more high frequency noise as compared to the X arm. (Edit by manasa: Thinking back now, this could be related to the onset of 60Hz noise at the Y end elog 9838. But still has to be looked at after fixing TRY)
Tip: Once the arms are ALS locked, enabling the SLOW_SERVO helps hold the lock stably.
P.S. I realigned the Y green to the arm and brought GTRY to 0.93
Find out what makes Y arm in-loop noise at high frequency higher than X arm.
This evening, I was not able to successfully transition CARM from ALS to 1/sqrt(trans) signals. The TRY time series looked odd, so I took a spectra, and we have huge 60Hz noise in TRY.
Manasa, can you please take a look, and see if you can figure out what is going on? We need TRY so that we can transition to 1/sqrt(trans) signals for CARM. Thanks!!
I went to the Y end to look at the TRY 60Hz noise situation this morning. While looking at TRY noise on dtt, I found that just lifting the cable away from the cable bunch that runs out of the table suppressed the noise drastically.
I removed the unwanted bnc connector in the path of the already long TRY cable running from the PD to the 1Y4 rack and isolated it from the bunch. TRY became less noisy.
But the noise was back again earlier in the evening and it looks like the noise is very much related to the TRY cable. TRY cable might have moved from its sweet spot while I was around checking cable connections yesterday.
I couldn't find a spare to replace it right away today (We need a BNC to 4 pin lemo).
To find noise source
1. Swapped the power cable of the PD and checked that it is connected to the right power source.
2. Changed the aluminium base of the post holding the diode so that the diode is floating
3. Grounded the table and the rack
4. Routed the cable on the other side of the beam tube to isolate it from other cables.
After all the above, we still found that shaking the cable was making TRY noisy.
I pulled out the PD whitening board to replace the 4 pin lemo connector with a bnc connector so that we can swap the cable with a new one. So there is no TRY right now.
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.
We turned on the MC2_TRANS paths for both PIT/YAW tonight.
I turned off the BLP200 and turned on the RLP7 (RLP always are better than BLP). G_PIT = -0.111, G_YAW = 0.111. On Monday, let's let Steve look at the trends and determine if this centering servo is bad or good.
The MC was showing slow but periodic alignment drifts and eventually unlocked around noon. I looked up the alignment trend (Attach: 2 day trend)
MC_TRANS_PIT_ERR and MC_TRANS_Y_ERR show that the MC_TRANS servo slowly drifted the IMC alignment causing it to lose lock from time to time (mostly in yaw).
To confirm that the drift was NOT due to off-centering in the MC2_TRANS QPD, I turned off the WFS servo, moved MC2 to recenter the trans beam on the QPD, and re-enabled WFS servo.
MC_TRANS path in WFS is still left enabled.
The Y arm locks stably for IR PDH now.
The reason for ETMY getting kicked during lock acquisition was finally found to be related to the limiter value set in the Y arm servo. We reduced the limiter value unintentionally and found that the lock acquisition stayed smooth. The limiter value was stepped in 1000s from 7000 and eventually found that the ETMY suspension was kicked when we try to acquire lock with the limiter value was set at 11000.
The limiter for X arm at 11000 is not causing any trouble at the moment.
In the process, we did a bunch of things through the evening to troubleshoot IR locking of the Y arm.
Earlier today running the IFO configure script did not restore the arms to lock and both the ETMs needed to be aligned to lock the arms. The arms stayed locked for 15 minutes and the Y arm lost lock eventually leaving the ETMY in a misaligned state.
The state of the Y arm was similar to what Jenne has explained in ELOG where the ETMY was kicked during lock acquisition and would move to a misaligned state.
To trouble shoot, there were several things that were done. A few of them might not have any direct correlation to the locking issue but could just be a coincidence.
1. The trigger time for the filters in the arm filter modules were set such that they switch on after the SUS violin filters. Arm FM trigger time = 3 s (previously set at 0.1s) and SUS violin trigger time = 1s. This reduced the number of lock loss events.
2. There was some drop in transmission when the bounce filter of Y arm (FM6) turned ON. This was fixed by changing its ramp time (initially set at 1s). The filter has been modified to turn on immediately upon arm lock acquisition before the other triggered filters in the filter module turn on.
3. The QPD and SUS signal cables running to the rack were checked to be intact. Koji found some of them to be loose. But this had no evident correlation with the arm locking problem.
4.The oplev and PD alignment was checked at the Y end. The high gain trans PD for Y arm was checked for good alignment by looking at TRY. It was found that the EXIT light at the Y end is injecting some noise to the transmission PD.
5. The ETMY was given offsets in PIT, YAW and POS and the OSEM sensor values were checked to see if the suspension is behaving well. It was behaving well.
c1sus and c1isey were not talking to fb. The usual mxstream restart did not help.
>>telnet fb 8087
All lights on the FE status screen are green now.
Note that Steve did an mxstreamrestart earlier today because the same machines c1sus and c1isey were not talking to fb.
I. The Y arm stayed stable through last night and I have saved the arm lock settings to IFOconfigure.
II. ALS X arm noise measurements
I looked at the before and after noise of ALSX.
Phase tracker gain = 85
Xarm servo gain = -17
The rms in loop noise has dropped from 3KHz to 500 Hz.
Attachment 1: Phase tracker OLTF
Attachment 2: Free running noise and in loop noise
Attachment 3: Out of loop noise (measured with arms locked using PDH for IR)
Attachment 4: ALS arm servo OLTF
xml data files can be found in /users/manasa/data/140430/
I found MC unlocked this morning. I looked at the 2 day trend of the MC suspensions and found MC2 suspensions have been misaligned.
I used Rana's ezcaservo trick to recover MC lock. This brought the MC_REFL down to 0.7 counts. I did the rest of the alignment by moving the MC2 suspension sliders only. MC_REFL is down to 0.45-0.5 counts and TRANS_SUM is at ~16300.
Also, I found the WFS servo was left turned OFF. I re-enabled them as well.
9. Arm cavity alignment. Significant DC effect.
* When the alignment of one of the arm cavity mirrors is changed, the DC value of the beatnote signal changes.
* ITMX moved in yaw, we see a 7kHz/15urad DC shift in the BEATX_FINE_PHASE_OUT_HZ time series.
* ETMX moved in yaw, we see an 8kHz/5.5urad DC shift in the time series. We aren't sure why this is about a factor of 3 times larger effect (same shift for smaller misalignment) than the ITM.
* We want to do a Yuta-style analysis to see what the angle to length coupling looks like, so that we can measure the angular motion of our cavity mirrors and put the expected noise into our ALS noise budget. Perhaps this will help us understand the low frequency difference between our in-loop beatnote error signal and our in-loop PDH error signals (red vs. maroon on the ALS noise budget posted above Pianosa).
* I've asked Manasa to take some transfer functions in the morning, so that we can start to have an idea of what is going on with this.
Attached is the measurement of the transfer function from ITMX oplev error in yaw to the ALSX error signal.
The arm was locked to the IR using POX and the green beat frequency (between X arm trans in green and PSL green) in this case was 27MHz.
The transfer function looks mostly flat between 1Hz - 30Hz at 700-800 Hz/urad. The DC shift that Jenne measured from the time series is ~500 Hz/urad.
So far I have not been able to measure the TF below 1Hz without the arm losing its lock. Updates will follow.
Data xml file can be found in /users/manasa/data/140521/
Below are the transfer functions measured between the angular (pit, yaw) motion of X arm mirrors and the ALSX error signal. The measurements were again made for 1Hz-30Hz.
The transfer functions are mostly flat.
ITMX P - 200-300 Hz/urad (beat freq = 45 MHz)
ITMX Y - 700-800 Hz/urad (beat freq = 27MHz)
ETMX P - 500-600 Hz/urad (beat freq = 56 MHz)
ETMX Y - 1000-2000 Hz/urad (beat freq = 62.5MHz)
Data xml files can be found in /users/manasa/data/140521/
The Y arm green transmission had come down to 0.3 and the green steering mirrors on the Y end table required some minor alignment adjustments to bring back transmission to around 0.75 counts.
MC wouldn't relock, it looked misaligned in pitch and yaw on MC camera.
I've touched the alignment, and gotten the reflection below 0.5, but it unlocks periodically, spot positions aren't great, and turning on WFS throws it out of alignment. ughhhhh
I realigned the MC mirrors and brought down MC_REFL to 0.42 and MC_TRANS_SUM came up to ~ 17400 counts.
I measured the spot positions after alignment. MC1 and MC3 are slightly off in pitch :
spot positions in mm (MC1,2,3 pit MC1,2,3 yaw):
[2.0535418031770249, 0.84870716159663184, 1.9759940800847962, -1.6706240175650202, 0.089441353070240759, -1.0339963871771678]
I reset the WFS filterbank offsets and engaged the MCWFS servo. Atleast now the MC is not being thrown out of lock with WFS enabled. I have NOT touched the alignment to the WFS PDs.
Grr. I am very frustrated. After lunch I redid alignment for both X and Y green systems (Yarm both at the end and on the PSL table, Xarm just on the PSL table). After that realignment work, I cannot find a beatnote for the Xarm!!!
At this point, I still hadn't touched anything on the X path (except the PZT input steering mirrors, remotely from the control room). The beatnote was about the same size as it was on Friday, around -27dBm. I went onto the PSL table and did the same alignment procedure that I had just done for the Yarm: Remove the green trans PD and the accompanying lens so that I get far-field spots on the wall, and then steer the PSL green and the X green spots until they are nicely overlapped at both the camera (near-field) and on the wall. I looked at the DC output of the beat PD, and centered the beam on the diode. I put back the thorlabs DC transmission PD and the lens, and centered the beam on that. However, after this work, I cannot find a beatnote for the X arm! I still see the nice big Ygreen beatnote, and I have the PSL and Xend temperatures where they usually are ( abs(FSS Slow) < 0.1, and X end Slow around 10,090. ) I scanned -10,000 counts, and +5,000 counts from there, and still don't find a beatnote!
I went back inside, and I don't see an RF signal coming into the beatbox from the Xarm. It's not the cable's fault though, since I then hooked the RF output of the beat PD to a 'scope, and still didn't see any beatnote. The DC path of the PD is definitely seeing things, because when I switch the 'scope over to the DC output of the Xbeat PD, and I block/unblock the beam, I see the voltage step up and down as expected.
I have not pulled out the Xgreen broadband PD, but unless someone else has a good idea of what to check, that might be one of the next things to do.
Ideas of things I could try:
* Put the X broadband PD on the Y beatnote path to see if I see the same Y beatnote (use the port where the Y green trans PD is, since it has the coaligned beams, and a lens).
* Open the PD and see if anything on the RF path is fried.
* Move the Y PD over to the X path, to see if it sees the beatnote.
I made my attempts trying to figure out what was wrong.
Checking if we are at the right X end laser temperature:
I aligned the arms and found the Y beatnote.I blocked the light falling on the X beat PD so that the RF analyser was only looking at the output from the Y beat PD. AT the RF analyser, I found the strong Y-PSL beatnote, the X-Y beat note and a weak X-PSL beatnote. This confirmed that we have the X end laser at the right temperature to be able to detect the beatnote. Unblocking the light on the X beat PD did not bring in any additional peaks.
Checking the RF cabling from the X beat PD to the beat box:
I swapped the RF cables such that the signal from the Y beat PD output was going to the X input on the beatbox. I could still see the beatnote on the RF analyser. This confirmed that there aren't any broken RF cables along the X path.
Checking X green PSL alignment:
I replaced the X beat PD with the Y beat PD to check if the alignment of X&PSL green are alright. I could find the X beat note this way without any alignment tweaking.
I suspect we probably have some RF component burnt in the X beat PD. Do we have any spares lying around? There is a Koji's box with a PD having the same serial number.
IFO status report for anyone who is looking to do some locking tonight :
The Y beat PD is back along the Y path and I have confirmed the presence of Y-PSL beat note after replacing the PD.
The X beat PD has been removed and now rests on the electronics bench for checking.
While aligning the arms today, I noticed that enabling LSC would cause misalignment of the ETMY suspension. I haven't tried to find out what has been causing this. Could be something similar to what was noticed with the ETMX suspension a couple of weeks ago elog9969.
Ant season has set in. I spotted and killed a few ants around the optics and the enclosure of the PSL table yesterday. TIme for our pest control crew to get busy!
A recap of the ringdown measurements made at the 40m in mid 2012, the hardware that was installed for the same and results from the measurements.
A trans PD was installed (elog 7122).
This PD does not exist in the trans path anymore.
The polarity in the MC servo was flipped with the MC WFS disabled and the PD trans signal was used to look at the cavity ringdown.
Ringdown time = 13 us
Cavity finesse from the measurement = 453 (inconsistent with actual finesse).
Attachment: Ringdown measurement and fits
The AOM was installed before the PMC. The AOM was driven by the driver installed on the PSL table. (RF power ~1.5W @ 80MHz @1.0V modulation input). An RF switch was installed to control the AOM driver input. ZASWA-2-50DR+ was installed.
Note: The AOM was used by the ISS crew after this. So the RF switch has been removed and the AOM is no more a part of the ringdown setup.
No measurements were made as we could not obtain relevant TTL signals to control the switch remotely.
MC autolocker and Ottavia
I assume that the MC was left with a fully functioning autolocker enabled and running on ottavia last night.
But as of this morning, the MC autolocker is NOT running alright. The MC was in an unlocked state and the autolocker has been doing nothing to the servo sliders. I think this was the state of MC since last night as seen on the stripchart.
Since the autolocker has been left to run on ottavia, I tried to look at the cronlogs to see if it running the autolocker script at all. I looked at the list on ottavia and it has the MCautlocker on it cronjobs list and yet doing nothing.
Later, I did a softreboot on ottavia when I could not ssh into it from rossa or pianosa. ssh to ottavia now works just fine.
I am leaving Ottavia at this and returning to the more important job of fixing the MC. I locked the MC manually and am now working on the alignment.
Also, the CDS FE status screen had red lights blinking as if it required an 'mxstream restart'. I did the same and it did not fix the problem. So I tried to restart fb using the usual 'telnet fb 8087'; but could not restart fb that way.
Attached: FE status screen
The IMC stayed locked last night, but with a high REFL ~3.0. I found the WFS servo OFF; so went ahead and enabled it. (Did somebody disable it for reasons not elog'd?)
MC returned to a happy state. But the WFS offsets are quite large. So I tweaked the alignment and got MC REFL down to ~0.45 and MC TRANS SUM to ~16500 counts. MC WFS offsets also dropped significantly after this without any need to touch the alignment to the WFS PDs.
All suspension damping restored. There had to be an earth quake.
PMC was relocked.
MC did not need any fixing to its alignment. I had to lock it manually and autolocker is set running now. So that should take care of things
The arms were aligned and ASS'd for IR PDH.
Green light PDH locks to the arms alright.
I moved stuff on the PSL table to accommodate the PMC ringdown setup.
I used the beam that leaks from the steering mirror at the PMC transmission that was dumped to a razor blade dump. I installed a Y1 to steer the beam to the ringdown PD. Power in the beam 75mW.
Results are in here elog
The RF cables have been routed incorrectly. The cables run to the module from the front of the rack. We cannot close the doors to the racks if they are to remain this way.
I have asked Nichin to reroute the cables properly.
I used the beam that leaks from the steering mirror at the PMC transmission that was dumped to a razor blade dump. I installed a Y1 to steer the beam to the ringdown PD. Power in the beam 75mW.
I am guessing that 75 mW will burn / destroy any Thorlabs PD. I hope that mW is supposed to be uW.
It was ~7.5mW and measured ~2V at the PD output (given its range 0-5V ) on the oscilloscope . So PD is safe !
After the fits, here are the numbers!
* We have a huge difference to the AOM switching time that was measured. The spec sheet mentions acoustic velocity in the material to be 4.2 mm/us and the well matched diameter in the AOM to be 1100 um. This would give a switching time ~ 200 ns. We could probably be having a much smaller beam size in the AOM for the measured switching time.
* The PMC parameters that I had been referring to from the wiki were actually wrong and which was the reason for the mismatch that I was finding. I modified the wiki according to the found references to the actual measurement here: PMC parameters The measured values now and then match pretty well.
* Since the AOM does not change the power of the output beam by very much, what we see is actually a step response. Also, we have a lot of noise in the data obtained at the PD.
RXA: some more comments...
I think we should revisit the AOM alignment because the last time it was aligned, PMC trans dropped from 0.84 to 0.15 (a little more than 80%) for 0-1V modulation input to the AOM driver [elog]. The drop in power right now is ~10-15% only.
I could not find any elogs of AOM alignment touchups after Oct 2012.
But can the ISS team throw some light on the status of AOM when they were installing the ISS servo before we decide on touching the AOM alignment? [elog]
I am going to tweak the alignment of the beam into the AOM (before the PMC) tomorrow morning. If anybody has any objections to this, please raise a red flag.
Proposed alignment procedure:
1. Reduce PSL power to say 10%
2. Since the AOM is not on any sort of a mechanical stage, I will have to just play around carefully until I see a maximum power rejection into first order.
I am assuming that moving the AOM is not going to affect the input pointing because all these activities are happening before the PMC. So as long as I have the output beam from the AOM aligned to the PMC at the end, everyone should be happy.
AOM removed from the beampath and PMC relocked.
1. Measured the initial power after PMC as 1.30W and reduced it down to 130mW.
2. Checked the power in the AOM zero order transmission before touching it. For 0-1V modulation input, the power dropped from 125uW to 98.3uW.
3. Steered the mirror right before the AOM to increase AOM zero order transmission and then carefully moved the AOM around to obtain maximum power attenuation. I repeated this a few times and the maximum attenuation that I could obtain was 125uW to 89.2uW (~30% attenuation).
Although this is not the right way to align the AOM, we do not have much options with the current setup as there is not enough separation between the zero order and first order beams and the AOM is on a fixed rigid mount.
4. I tried to dump the first order beam from the AOM and it wasn't satisfactory as well. There is barely any separation between the zero order and first order beams.
1. SInce the alignment to the PMC was disturbed by moving the AOM and the steering mirror in front of it, the PMC alignment was lost.
2. I could not relock the PMC at low power or high power. Rana had to come to rescue and fixed the alignment so that we could see flashes of PMC on the trans camera (This was done by aligning refl beam to the PMC REFL PD while giving a triangular ramp to the PMC PZT voltage).
Also I should not have tried to lock the PMC at high power as I could have been steering the beam at high power to the edges of the PMC mirrors that way and burning stuff easily.
3. Before fine tuning the alignment, I decided to remove the AOM from the beam path as there needs some work done on it to make it useful.
4. I removed the AOM from the beam path and relocked the PMC.
5. PMC is relocked with 0.79 counts in TRANS and I measured the power after PMC 1.30W
Attachment: picture showing AOM removed from the beampath.
FYI: in that rack, the +15V pulls ~0.5 A more than -15V usually. I think this is due to some RF amplifiers which are powered by this (e.g. the AOM that Manasa set up). The Sorensen's can source ~30A in principle, so we should make sure to set the current limit appropriately so as to not overheat them when there is a short.
Was this power supply not fused for all of its connections? I remember that this was connected to at least one un-fused connection in the past year.
+15V supply powers the following (from what I see):
1. PMC and MC boards on the rack.
2. RF amplifiers on the rack for the beat signals from the green beat PDs.
3. Beatbox itself.
The beatbox was the one that had an un-fused connection last year. I re-did it properly to go through a fuse quite sometime ago.
I dont see any other un-fused connections now from the +15V supply right now.
P.S. AOM driver takes a 0 to +28V power supply and not connected to the +15V
I looked at the CAD layout and it seems like we will clearly be clipping POY if we move SRM by 7.5cm. Since POY is not visible at low power, we cannot be sure about the clipping.
We should have a plan B before we move everything. I suggest we move a combination of SRM and SR2 to get the desired SRC length.
Moving SR2 will require extra effort to walk the beam unclipped through all the 6 output steering mirrors that follow; but there will be little room for error if we use irides to propagate the beam through the first 4 mirrors that are in the BS and ITMY chamber.
We had a unexpected power shutdown for 5 sec at ~ 9:15 AM.
Chiara had to be powered up and am in the process of getting everything else back up again.
Steve checked the vacuum and everything looks fine with the vacuum system.
The last time we had a power failure IFO recovery elog
After Q brought back the IR, I went to check the green situation.
1. The end lasers had to be turned ON.
2. The heaters for the doubler crystals had to be enabled. The heaters are at the set values.
3. The X arm PZTs for the steering mirrors had to be powered up (Set voltage 100V and current 6.7mA)
4. I aligned the green to the already IR-aligned arms.
Green PSL alignment has to be done after Q finishes his work on the MC WFS.
Chiara doesn't seem to be responding and I guess something happened 7 hrs ago.
I tried to hook up chiara to a monitor to reboot or atleast look for error messages; but it is not even detecting the external monitor (Tried changing monitors and vga cables; still see nothing).
I tried to ssh into it and only received errors :
NFS lookup failed for server XXX.XXX.XXX.XXX : error 5 (RPC: Timed out)
ssh: chiara: host/servname not known
Steve had the vacuum checked and everything seems fine with the status of the vacuum system atleast.
Post 30-40min unexpected power outage this morning, Steve checked the status of the vacuum and I powered up Chiara.
I brought back the FE machines and keyed all the crates to bring back the slow machines but for the vac computers.
c1vac1 is not responding as of now. All other computers have come back and are alive.
The He-Ne laser oplev setup was swapped with a fiber-coupled diode laser from W Bridge. The laser module and its power supply are sitting on a bench in the east side of the SP table.
This is our first time touching tables for Frequency Offset Locking.
The goal was to couple the 1064nm that leaks after the SHG crystal and couple it into the fiber before we run it along the length of the arm.
The fiber has been mounted at the end but there is no light coupled into the fiber as yet.
In the process, the following were done:
1. ETMY oplev servo disabled. This was enabled after the work.
2. NPRO laser power was reduced so that nothing gets burnt accidently while putting things on the table. This was also reset after the work.
The arms could be locked to green and IR after the work. So I am hoping today's work will not affect locking.
The Y end aux laser light leaking after the doubling crystal has been coupled into the 70m long PM fiber.
Input power = 250mW; Output after 70m = 20mW
The poor efficiency is partially due to the ellipticity of the beam itself and partially due to the compromise I had to make using a single lens to couple the light into the fiber (given the limitations in space). But 20mW should be more than sufficient for a beat note setup.
Light propagates as follows after the doubling crystal:
Doubler ---> Harmonic Separator (45deg) ---> Lens (f=12.5cm) --> Steering mirror (Y1) --> Fiber collimator ( Thor labs CFC-2X-C) --> FIber end
I will update photos of the setup shortly.
I have left the 70m fiber in its spool sitting at the Y end and blocked the light before the last Y1 steering mirror in the above setup. So it should be safe.
Through the course of the work, I disabled the ETMY oplev and enabled it before closing the enclosure. I also reduced the AUX laser power and brought it back up after the work.
I did a check to see if the arms are locking in both IR and green and they did.
Since I obtained a poor coupling efficiency from the earlier setup, I went back to calculate the coupling efficiency of the current setup.
For the current setup, I took the average of the x and y waist of the input beam and calculated the distance at which the input beam diameter would match the (fiber +collimator) beam diameter.
Average waist = 40.2um @-3.3mm from face of doubling crystal
(Fiber PM980 + Collimator f=2.0mm) beam waist = 205um
Distance(z) at which the input beam waist is 205um = 11.9cm
The closest available lens was f = 12.5cm. So I used it to couple the input beam by placing it at z ~12.5cm on a micrometer stage.
Since this gave only 10% coupling, I went back to calculate (using 'a la mode') the best possible coupling that can be obtained taking into consideration the ellipticity of the beam.
The maximum obtainable coupling (mode overlap) is 14.5% which is still poor.
Taking into account the ellipticity of the input beam, the available lenses and the space restrictions (lens can be placed only between z= 8 to 28cm), I calculated the best possible coupling efficiency (using 'a la mode').
The maximum possible mode overlap that can be obtained is 58.6% (matlab code and plot attached)
modematching = 0.58632
Optimized Path Component List:
label z (m) type parameters
----- ----- ---- ----------
L1 0.0923 lens focalLength: 0.0750
I looked at what are the situations that make ETMX lose alignment.
This is not occur all that often this morning; less than 10 times in may be the last 4 hours of poking the X arm. I found that the bad behavior of ETMX also exists in certain other cases apart from the case when we enable LSC.
(I) Even the MISALIGN and RESTORE scripts for the suspensions make the suspension behave bad. The RESTORE script while in the process of bringing back the suspension to the place where it was, kicks it to some place else sometimes (even with LSC disabled)
(II) The suspension also gets kicked while realigning ETMX manually using sliders at 10^-3 (pace of 2-3 steps at a time).
I am suspecting something wrong right at the coil inputs and gains of the suspension.
Also, I recollect that we haven't done a check on the X arm LSC limiters and filters ramping times like it was done for the Y arm ( Elog 9877 ). We should do this check to be sure that we are not seeing a mixed puddle of problems from 2 sources.