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ID Date Author Type Category Subject
6306   Wed Feb 22 19:45:33 2012 kiwamuUpdateLSChow much length offset do we need ?

I did a quick calculation to see if the offset of the arm length which I tried last night was reasonable or not.

The conclusion is that the 20 nm offset that i tried could be a bit too close to a resonance of the 55 MHz sidebands.

A reasonable offset can be more like 10 nm or so where the phases of all the laser fields don't get extra phases of more than ~ 5 deg.

The attached plot shows where the resonances are for each sideband as a function of the displacement from the carrier's resonance.

The red solid line represent the carrier, the other solid lines are for the upper sidebands and the dashed lines are for the lower sidebands.

The top plot shows the cavity power and the bottom plot shows how much phase shift the fields get by being reflected by the arm cavity.

Apparently the closest resonances to the the main carrier one are that of the 55 MHz sidebands, and they are at +/- 22 nm.

So if we displace the arm length by 22 nm, either of the 55 MHz sidebands will enter in the arm cavity and screw up the sensing matrix for the 55 MHz family.

 Quote from #6304 In all the configurations I displaced the Y arm by 20 nm from the resonance.

6305   Wed Feb 22 16:55:16 2012 JamieUpdateSUSwacky state of SUS input matrices

While Kiwamu and I were trying to investigate the the vertex glitches we were noticing excess noise in ITMX, which Kiwamu blamed on some sort of bad diagonalization.  Sure enough, the ITMX input matrix is in the default state [0], not a properly diagonalized state.  Looking through the rest of the suspensions, I found PRM also in the default state, not diagonalized.

### We should do another round of suspension diagonalization.

Kiwamu (or whoever is here last tonight): please run the free-swing/kick script (/opt/rtcds/caltech/c1/scripts/SUS/freeswing) before you leave, and I'll check the matrices and update the suspensions tomorrow morning.

[0]

 0.25 0.25 0.25 0.25 0 1.66 1.66 -1.66 1.66 0 1.66 -1.66 -1.66 1.66 0 0 0 0 0 1

6304   Wed Feb 22 13:28:22 2012 kiwamuUpdateLSCY arm + central part locking

Last night I tried the "Y arm + central part" locking again. Three different configuration were investigated :

•  Y arm + DRMI
•  Y arm + PRMI
•  Y arm + MICH

In all the configurations I displaced the Y arm by 20 nm from the resonance.

As for the DRMI and PRMI configurations I wasn't able to acquire the locks.

As for the MICH configuration, the MICH could be locked with AS55. But after bringing the Y arm to the resonance point the lock of MICH was destroyed.

6303   Wed Feb 22 01:53:57 2012 kiwamuUpdateLSCupdate on glitch table

I tried SRMI. The glitch rate wasn't as high as that of PRMI but it happened once per 10 sec or so.

 Yarm (POY11 --> ETMY) Xarm (POX11 --> ETMX) MICH (AS55-->BS) or (AS55 --> ITMs) Half PRMI (REFL11 --> PRM) or (REFL33 --> PRM) low finesse PRMI (ASDC --> ITMs) (REFL33 --> PRM) PRMI (carrier) (AS55 --> ITMs) (REFL33 --> PRM) PRMI (sideband) (AS55 --> ITMs) (REFL33 --> PRM) SRMI(NEW) (AS55-->ITMs) (REFL11I --> SRM) DRMI AS55 NO NO NO NO glitch (depends on finesse) glitch glitch glitch glitch REFL11 NO NO NO NO glitch (depends on finesse) glitch glitch glitch glitch REFL33 NO NO NO NO - glitch glitch glitch glitch REFL55 NO NO NO NO glitch(depends on finesse) glitch glitch glitch glitch REFL165 NO NO NO - - - - - - POX11 - NO NO NO - glitch glitch - glitch POY11 NO - NO NO - glitch glitch - glitch POP55 - - - - - - - -

 Quote from #6284 I updated the table which I posted some time ago (#6231). The latest table is shown below. It seems that the glitches show up only when multiple DOFs are locked.

6302   Tue Feb 21 22:06:18 2012 jamieUpdateLSCbeatbox DFD installed in 1X2 rack

I have installed a proto version of the ALS beatbox delay-line frequency discriminator (DFD, formally known as MFD), in the 1X2 rack in the empty space above the RF generation box.

That empty space above the RF generation box had been intentionally left empty to provide needed ventilation airflow for the RF box, since it tends to get pretty hot.  I left 1U of space between the RF box and the beatbox, and so far the situation seems ok, ie. the RF box is not cooking the beatbox.  This is only a temporary arrangement, though, and we should be able to clean up the rack considerably once the beatbox is fully working.

For power I connected the beatbox to the two unused +/- 18 V Sorensen supplies in the OMC power rack next to the SP table.  I disconnected the OMC cable that was connected to those supplies originally.  Again, this is probably just temporary.

Right now the beatbox isn't fully functioning, but it should be enough to use for lock acquisition studies.  The beatbox is intended to have two multi-channel DFDs, one for each arm, each with coarse and fine outputs.  What's installed only has one DFD, but with both coarse and fine outputs.  It is also intended to have differential DAQ outputs for the mixer IF outputs, which are not installed in this version.

The intended design was also supposed to use a comparator in the initial amplification stages before the delay outputs.  The comparator was removed, though, since it was too slow and was limiting the bandwidth in the coarse channel.  I'll post an updated schematic tomorrow.

I made some initial noise measurements:  with a 21 MHz input, which corrseponds to a zero crossing for a minimal delay, the I output is at ~200 nVrms/\sqrt{Hz} at 5 Hz, falling down to ~30 nVrms about 100 Hz, after which it's mostly flat.  I'll make calibrated plots for all channels tomorrow.

The actual needed delay lines are installed/hooked up either.  Either Kiwamu will hook something up tonight, or I'll do it tomorrow.

6301   Tue Feb 21 18:39:11 2012 kiwamuUpdateGreen LockingNew BBPDs installed

Two new BBPDs have been installed on the PSL table.

The first one was installed by Koji a few days ago, and I stalled the second one today.

They will serve as beat-note detectors for the green locking.

Next step : I have to lay down a long SMA cable which goes from the BBPD to the IOO rack.

6300   Tue Feb 21 16:10:29 2012 kiwamuUpdateIOOdegradation in input PZT1

PZT1, the one with Koji's custom mid-HV driver (#5447), is getting degraded.

The movable range in the pitch direction became narrower than what it used to be (maybe a factor of 3 estimated by looking at the beam spots).

I think we should raise the priority level of the active TTs for the next vent.

I have been having a feeling that the PZT1 response is getting smaller since the end of the last year, but now I am confident

because I could see the difference between the movable ranges of Yaw and Pitch, and they used to have approximately the same amount of the movable ranges.

Right now this is not a serious issue as the beam pointing determined by the MC alignment is so good that the Pitch range doesn't rail.

I won't be surprised if it becomes completely immovable in 3 month.

6299   Tue Feb 21 08:33:16 2012 steveUpdateGreen Lockingperiscope adapter plate

Two extender plates ready for cleaning. The existing optical table tops have 38" OD. Using two of these the OD will be 44"

Attachment 1: percplate.PDF
6298   Tue Feb 21 04:30:02 2012 kiwamuUpdateLSCY arm + PRMI

I tried the "Yarm + PRMI" configuration to see what happens.
The Y arm was locked at a resonance and held with the ALS technique.
On the other hand, the X arm was freely swinging.

I briefly tried severl demod signals to calm down the central part, but didn't succeed.
Now I feel I really want to have the X arm locked with the ALS technique too.
Give me the beat-box !

The attached screen shot shows the transmitted light of both arms as a function of time.
TRY is always above 1, since it was kept at a resonance.
Sometimes TRY went to 50 or so.

6297   Sat Feb 18 18:29:38 2012 DenUpdateAdaptive Filteringonline filtering

I tried to filter MC_F from seismic noise measured by GUR1 seismometer. I've used 8000 tap filter, downsample ratio=8, delay=1. In the Figure the output of the filter is presented with MC_F signal.

We can see that output is close to the MC_F, but the phase for some reason is not zero. It should not be at 1 Hz - 10 Hz due to the actuator. But below these frequencies I do not see any reasons for the output phase to differ from MC_F phase. But it is possible, the phase of the actuator is evaluated very rough and the adaptive filter can't match it.

6296   Sat Feb 18 17:01:26 2012 DenUpdateAdaptive Filteringstatic variables

In order to prevent different DOF from redetermining static variables in the adaptive code, I've created a separate code for each DOF with the name ADAPT_XFCODE_{DOF}.c I've provided the links for these files in the c1oaf.mdl, compiled and run it. Now there are no conflicts between DOFs. 6295 Sat Feb 18 16:58:59 2012 kiwamuUpdateIOOMC suspension realigned [ Den / Kiwamu] We have realigned the MC suspensions so that the WFS servos are smoothly engaged. Now it seems working fine. The beam pointing to the interferometer also looks okay. The WFSs control kept failing to engage the servos because of large misalignments in the MC suspensions. When the TEM00 was locked, the transmitted light was only about 1200 counts and the reflected light was about 2.8 counts. We tweaked MC1, MC2 and MC3.  Quote from #6294 When I came to the 40m this afternoon, the MC was unlocked. Here is the trend of MC_F for last 2 hours 6294 Sat Feb 18 12:23:09 2012 DenUpdateIOOMC When I came to the 40m this afternoon, the MC was unlocked. Here is the trend of MC_F for last 2 hours C1:PSL-PMC_PMCTRANSPD = 0.800 Should I just disable the auto locker or try to realign it? 6293 Fri Feb 17 04:45:48 2012 kiwamuUpdateLSCsensing matrix of PRMI I locked the PRMI with the AS55I and Q combination. It seems the glitche rate decreased, but I am not 100 % sure because the rest of the demod signals (i.e. REFL11 and etc) were showing relatively big signals (noise ?), which may cover the glitches. Also the optical gain of PRCL at AS55I doesn't agree with my expectation based on the obtained sensing matrix (#6283). It looks too low and lower than the measured sensing matrix by a factor of 50 or so. I will continue working on this configuration tomorrow and then move on to the SRMI locking as a part of the glitch hunting activity.  Quote from #6287 So why don't you use AS55I and Q for the control of PRMI??? 6292 Fri Feb 17 01:02:22 2012 kiwamuUpdateIOOMC is back to normal [Koji / Kiwamu] The MC is now back to normal. The beam pointing to the interferometer is good. There were two different issues : • A mechanical mount was in the MC WFS path. • There were some loose connections in the SUS rack Slid have we the position of the mechanical mount. Nicely the WFS beam go through now. And also I pushed all the connectors associated with the MC SUS OSEMs in the SUS rack. After pushing the connectors, the MC1 OSEM readouts dramatically changed, which actually more confused us. As shown in the 3 hours trend below, the OSEM readouts have changed a lot (shown in the middle of the plot with arrows). Some bumps after the steps correspond to our alignment efforts.  Quote from #6291 The MC became crazy again. 6291 Thu Feb 16 23:12:55 2012 kiwamuUpdateIOOMC unlocking frequently The MC became crazy again. It seems that there were corresponding steps in the OSEM signals. Look at the one-day trend posted below. 6290 Thu Feb 16 21:13:07 2012 SureshUpdateElectronicsREFL165 repair: PD replaced, DC response checked with a torch light [Koji, Suresh] Kiwamu mentioned that REFL165 is not responding and its DC out seems saturated at 9V. Koji and I checked to see if changing the power supply to the PD changed its behaviour. It did not. I then look a close look at the PD and found that the front window of the PD was not clear and transparent. There was a liquid condensation inside the window, indicating an over heating of the PD at some point. It could have arisen due to excessive incident power. The pic below shows this condensation: I also checked the current flowing through the reverse bias voltage line. There was a voltage drop of 3V across R22 (DCC D980454-01-C) indicating a 150mA of current through the PD. This is way too much above the operating current of about 20mA. The diode must have over heated. I pulled out the old PD out and installed a new one from stock. The pic below shows the clear window of a new PD. After changing the PD I checked the DC output voltage while shining a torch light on to the PD. It showed an output of about 30 to 40 mV. This seemed okay because the larger 2mm photodiodes showed ~100mA DC output with the same torch.Below is the current state of the ckt board. I will tune the PD to 165 MHz tomorrow and measure its transimpedance. 6289 Thu Feb 16 13:12:30 2012 ranaUpdateLSCsensing matrix of PRMI  Quote: I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts. Smells like something is very wrong. Those Radar plots are awesome. Even more awesome would be if they were in units of W/m (so that it can be directly compared with Optickle) and so that the numbers are useful even 1 year from now. Otherwise, we will lose the RF transimpedance information and thereby lose everything. Also, please post the provenance of the counts->V calibration. 6288 Thu Feb 16 09:59:16 2012 steveUpdateASCIP- ANG Initial pointing or IP-ANG is a pointing monitor of the MC. This beam is launched after the second pzt steering mirror. IP-ANG is missing the pick up mirror by a few inches at ETMYchamber 1000 days plot show last appearance in Feb 2010 Attachment 1: lastIPang.png 6287 Thu Feb 16 07:38:24 2012 KojiUpdateLSCsensing matrix of PRMI So why don't you use AS55I and Q for the control of PRMI??? 6286 Thu Feb 16 04:29:30 2012 kiwamuUpdateLSCupconversion noise from BS motion Sometimes ago I reported that there have been a kind of upconversion noise when PRM was excited (#6211). This time I found another one, which showed up when BS was excited. Assuming this is related to some kind of scattering process and also assuming this is from the same scattering body as that for the PRM driven case, we may be able to localize and perhaps identify the scattering body. (Measurement Condition) All the suspended optics are intentionally misaligned except for ITMY so that the laser directly goes through to the dark port without any interference. Then BS_POS is excited at 3 Hz with amplitude of 1000 counts by an oscillator in the realtime lockin system. I also excited PITCH and YAW of BS and found that driving the angular motions didn't produce any upconversion noise. I didn't excite ITMY to do the same test because I was too lazy. (Noise spectrum) The plot below shows the upconversion noise observed at AS55 and REFL11. The reference curves were obtained when no excitation were applied on BS_POS. It is obvious that the AS55 signal shows a typical upconversion behavior. 6285 Thu Feb 16 04:02:16 2012 kiwamuUpdateLSCinsane REFL165 DC output I found that the DC monitor of the REFL165 was showing 9 V regardless of how much laser power goes to the diode. I am worried about whether the RF output is also broken. It needs to be checked and I will leave this to Suresh as one of his morning tasks. 6284 Thu Feb 16 03:47:16 2012 kiwamuUpdateLSCglitch table I updated the table which I posted some time ago (#6231). The latest table is shown below. It seems that the glitches show up only when multiple DOFs are locked. Interesting thing is that when the low finesse PRMI is locked with a big MICH offset (corresponding to a very low finesse) it doesn't show the glitches. Qualitatively speaking, the glitch rate becomes higher as the finesse increases. I will try SRMI tomorrow as this is the last one which I haven't checked the presence of the glitches.  Yarm (POY11 --> ETMY) Xarm (POX11 --> ETMX) MICH (AS55-->BS) or (AS55 --> ITMs) Half PRMI (REFL11 --> PRM) or (REFL33 --> PRM) low finesse PRMI (ASDC --> ITMs) (REFL33 --> PRM) PRMI (carrier) (AS55 --> ITMs) (REFL33 --> PRM) PRMI (sideband) (AS55 --> ITMs) (REFL33 --> PRM) DRMI AS55 NO NO NO NO glitch (depends on finesse) glitch glitch glitch REFL11 NO NO NO NO glitch (depends on finesse) glitch glitch glitch REFL33 NO NO NO NO - glitch glitch glitch REFL55 NO NO NO NO glitch(depends on finesse) glitch glitch glitch REFL165 NO NO NO - - - - - POX11 - NO NO NO - glitch glitch glitch POY11 NO - NO NO - glitch glitch glitch POP55 - - - - - - - - 6283 Wed Feb 15 17:15:33 2012 kiwamuUpdateLSCsensing matrix of PRMI I think I have told a lie in the last meeting -- the measured sensing matrix doesn't look similar to what Optickle predicts. Smells like something is very wrong. Measured sensing matrix The measured matrix are shown in the diagram below. The lengths of arrows corresponds to the signal strength in unit of V/m. The radial axis in in log scale. The angle of arrows corresponds to their best demodulation phases. Some obvious things: • REFL11 : The separation angle between MICH and PRCL is narrow and it is far from the ideal 90 degree. This doesn't agree with the simulation. • REFL33: The MICH and PRCL signals are almost degenerated in their demodulation phase. • REFL55 : It shows non-90 degree separation. This doesn't agree with the simulation. • REFL165 : The separation is close to 90 degree, but the signals are small. And I am not sure if the MICH signal is real or just noise. • AS55 : Somehow it shows a nice 90 degree separation, but this result doesn't agree with the simulation. Expected sensing matrix from a simulation For a comparison here is a result from an Optickle simulation. This time the radial unit is W/m instead of V/m, but they are qualitatively the same unit. The radial axis is in log, so when it says 2, it means 10^2 [W/m]. Simulation setup: l_PRC = 6.760 (see #4064) l_asy = 0.0364 (see #4821) loss per optic = 50 ppm Measurement • Locked PRMI with the carrier anti-resonating in PRCL. • Adjusted the control gains for both the MICH and PRCL control to have UGFs at ~ 100 Hz. • Put a 30 dB notch filter in each control servo at 283.1 Hz where an excitation signal will be. • Excited PRCL and MICH at different time via the realtime lockng in the LSC front end. The amplitude is 1000 counts and the frequency is at 238.1 Hz. • For the MICH excitation, I have coherently and differentially excited ITMs • Used DTT to take a transfer function (transfer coefficients at 283.1 Hz) from the lockin oscillator to each LSC demodulated signal. • Including AS55I/Q, REFL11I/Q, REFL33I/Q, REFL55I/Q and REFL165I/Q. • Calibrated the obtained transfer functions from unit of counts/counts to V/m using the actuator response (#5637)  Quote from #6281 I have measured the sensing matrix of PRMI. It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control. The data is coming soon. 6282 Wed Feb 15 11:34:01 2012 steveUpdate under the shouth end optical table I added an U channel based bottom shelf at the south end today. Attachment 1: P1080535.JPG Attachment 2: P1080537.JPG 6281 Wed Feb 15 05:29:22 2012 kiwamuUpdateLSCsensing matrix of PRMI I have measured the sensing matrix of PRMI. It seems that the MICH signal in the 3f ports (REFL33 and REFL165) were quite tiny, and because of that it is very tough to use them for the actual MICH control. The data is coming soon. 6280 Tue Feb 14 17:09:05 2012 steveUpdateGeneralreflectivity of green welding glass Schott, Athermal green welding glass, shade #14 reflectivity was measured in 1.2W, ~1 mm diameter beam of MC reflected. The P polarization measurement was done with the help of half wave plate and PBC Attachment 1: gg#14ref.pdf Attachment 2: gg14refl1Wps.png 6279 Tue Feb 14 15:52:11 2012 JenneUpdateAuxiliary lockingYarm fiber returned to ATF [Frank, Jenne] We extracted the fiber that Suresh and Sonali laid over the summer, for the IR beat for the Ygreen laser, and Frank took it back to Bridge to be used in the new fiber distributed reference laser setup. 6278 Tue Feb 14 08:22:27 2012 steveUpdateSUSsus damping restored ITMX, PRM and BS watchdogs are tripped. They were restored. Stable MC was disabled so I can use MC_REFL 1 W beam to measure green glass . 6277 Mon Feb 13 12:02:17 2012 KojiUpdatePEMseismic BLRMS loud too I reported the procedure to add slow channels to the FB. I guess you already have done Step.1 http://nodus.ligo.caltech.edu:8080/40m/5991  Quote: Tragically, this is more tricksy than I would have thought. The channels we need are "cdsEpicsOutput"s in the model. They don't show up in Dataviewer (fast or slow channels) or the regular fast channel .ini file. Jamie and I don't remember where these channels live and how to get them saved to frames. I'm on top of it though. 6276 Mon Feb 13 11:30:51 2012 JenneUpdatePEMseismic BLRMS loud too Quote:  Quote: So, none of our PEM BLRMS channels are recorded as of right now. All we have for long-term record is the StripTool on the wall. The 0.1-0.3Hz and 0.3-1 Hz traces both show these weirdo things, but the 1Hz and up BLRMS don't have any unusual noise. Seems like a problem to solve on Monday so that we don't end up without trends like this again. Tragically, this is more tricksy than I would have thought. The channels we need are "cdsEpicsOutput"s in the model. They don't show up in Dataviewer (fast or slow channels) or the regular fast channel .ini file. Jamie and I don't remember where these channels live and how to get them saved to frames. I'm on top of it though. I did notice however, that the striptool for seismic trends is showing the wrong channels for 3-10 and 10-30 Hz. The other 3 channels are correctly the output after the sqrt is taken, but those two (orange and red on striptool) are before the sqrt, but after the bandpass and low pass. I'll fix that now... 6275 Fri Feb 10 23:58:30 2012 ranaUpdatePEMseismic BLRMS loud too  Quote: So, none of our PEM BLRMS channels are recorded as of right now. All we have for long-term record is the StripTool on the wall. The 0.1-0.3Hz and 0.3-1 Hz traces both show these weirdo things, but the 1Hz and up BLRMS don't have any unusual noise. Seems like a problem to solve on Monday so that we don't end up without trends like this again. 6274 Fri Feb 10 23:19:09 2012 kiwamuUpdateIOOcross talk causing fake seimometer signals [ Koji / Kiwamu ] The frequent unlock of the MC are most likely unrelated to ground motion. Although the reason why MC became unstable is still unclear. There are two facts which suggest that the ground motion and the MC unlock are unrelated : (1) It turned out that the seismometer signals (C1:PEM-SEIS-STS_AAA ) have a big cross talk with the MC locking signals. For example, when we intentionally unlocked the MC, the seismometer simultaneously showed a step-shaped signals, which looked quite similar to what we have observed. I guess there could be some kind of electrical cross talk happening between some MC locking signals and the seismometer channels. So we should not trust the signals from the STS seismometers. This needs a further investigation. (2) We looked at the OSEM and oplev signals of some other suspended optics, and didn't find any corresponding fluctuations. The suspensions we checked are ETMX, ETMY, ITMX and MC1. None of them showed an obvious sign of the active ground motions in the past 24 hours or so.  Quote from #6266 It seems that somehow the seismic noise became louder from about 1:00 AM. 6273 Fri Feb 10 15:54:27 2012 steveUpdatePEMAC turned back ON The air cond was off for 2 hrs. I just switched it back on at 15:51 6272 Fri Feb 10 15:52:35 2012 JenneUpdatePEMseismic BLRMS loud too  Quote: Kiwamu and Steve maybe don't know about how to trend seismic noise. If you just take the mean of the time series, you don't prove that the seismic noise got any higher. The STS has a nominally zero DC output, so the long period level shifts that you see tell you just that there was a DC offset. This is NOT an increase in seismic noise. To see a seismic trend you should plot the trend of the BLRMS channels that we made especially for this purpose. So, none of our PEM BLRMS channels are recorded as of right now. All we have for long-term record is the StripTool on the wall. The 0.1-0.3Hz and 0.3-1 Hz traces both show these weirdo things, but the 1Hz and up BLRMS don't have any unusual noise. 6271 Fri Feb 10 15:47:38 2012 ranaUpdatePEMseismic noise back to normal Kiwamu and Steve maybe don't know about how to trend seismic noise. If you just take the mean of the time series, you don't prove that the seismic noise got any higher. The STS has a nominally zero DC output, so the long period level shifts that you see tell you just that there was a DC offset. This is NOT an increase in seismic noise. To see a seismic trend you should plot the trend of the BLRMS channels that we made especially for this purpose. 6270 Fri Feb 10 15:46:59 2012 steveUpdateSUSruby wire standoff Finally I found a company who can do Koji's improved -hard to make- specification on ruby or sapphire wire standoff. NOT POLISHED excimer laser cut, wire groove radius R 0.0005" + - 0.0002"250 ea at 50 pieces of order

6269   Fri Feb 10 11:46:44 2012 steveUpdateIOOseismic noise back to normal

The shaking has stopped at 9:32am  The AC was turned back on at 11:30am  We still do not have any explanation

Attachment 1: seism4h.png
Attachment 2: seis60s.png
Attachment 3: oneday.png
6268   Fri Feb 10 11:01:31 2012 steveUpdateIOOcrazy ground motion

 Quote: I gave up tonight's locking activity because the MC can't stay locked. It seems that somehow the seismic noise became louder from about 1:00 AM. I walked around the outside of the 40-m building to see what's going on, but no one was jumping or partying. I am leaving the MC autolocker disabled so that the laser won't be driven crazy and the WFS won't kick the MC suspensions.   The attachment is a 3-hour trend of the seismometer outputs and the MC trans.

Something has started shaking last night.  Everybody is claiming to be innocent next door.

I turned off the 40m AC at 11:06

Attachment 1: seism1davg.png
6267   Fri Feb 10 02:43:37 2012 ZachUpdateSUSOSEM LED driver noise *reduced*

I worked on the OSEM box a little more today, with the hopes of reducing the measured output current noise. I succeeded, at least modestly. It turns out that most of the noise was indeed caused by the crappy resistors.

Below is the circuit for one of the 5 LEDs. The output of the op-amp structure directly after the LT1031 reference is split between 5 stages identical to the structure on the right. I have shown just one (UR) for clarity. The various measurement points are explained below.

I started from the beginning of the circuit, directly after the LT1031, to make sure that the excess noise seen the other day wasn't just from a noisy reference. Below is the measured output voltage noise along with the LISO estimate. Clearly, the LT1031 is performing to spec (as it should, since it's a new part that I just put in). Note that the apparent better-than-spec performance at low frequencies is just from the AC coupling, which I needed due to the high DC level.

Since the reference was in order, the next step was to switch out some of the crappy old resistors for nicer thin-film ones. In case anyone is interested, Frank has done some detailed investigation of excess 1/f current noise in resistors. I measured the voltage noise level at the point labeled "inter-stage measurement" above, first without any modifications and then after swapping the old 10k resistors (R1 & R2) out for nice Vishay thin-film ones. There is clearly a big improvement, and the modified circuit essentially agrees with LISO now down to 1 Hz. Below this, it looks like there could still be an issue.

I wanted to see what the improvement was in the overall output current noise of the system, so I went about measuring the current noise as I had the other day (by measuring the voltage noise across R55 and dividing by the resistance). The performance was already better than the old measurement, but not at the LISO level. So, I replaced the current-setting resistors (R54 & R55)---which were actually 3 parallel resistors on a single pad in each case---by nice Vishay ones, as well. I didn't have any that were close to the original resistance of ~287 ohms, so I put three 1k ones in parallel. This of course shifts the resistance up to 333 ohms, but that only causes a ~16% change in current. I was sure to convert voltage noise into current noise with this new resistance, though.

With this change, the total output current noise is now very close to the LISO estimate as well down to ~1 Hz.

Some notes:

• First, I apologize for the noise margin at higher frequencies. I redid the higher frequency measurements with an SR560 as a preamp, but I must have screwed up the calibration because the data don't match up quite right with the LF measurements. It was clear while I was taking them that they followed the LISO trace.
• There still seems some excess noise below 1 Hz. It could be that the noisy resistors in the parallel stages were somehow still contaminating the cleaned-up channel. I'll look into this more soon.
6266   Fri Feb 10 02:35:29 2012 kiwamuUpdateIOOcrazy ground motion

I gave up tonight's locking activity because the MC can't stay locked.

It seems that somehow the seismic noise became louder from about 1:00 AM.

I walked around the outside of the 40-m building to see what's going on, but no one was jumping or partying.

I am leaving the MC autolocker disabled so that the laser won't be driven crazy and the WFS won't kick the MC suspensions.

The attachment is a 3-hour trend of the seismometer outputs and the MC trans.

6265   Thu Feb 9 20:01:02 2012 ranaSummaryElectronicsUsing RF LP filters as dispersion units for the MFD

WE currently use long cables to give us the dispersion that we want for the MFD. A cable gives a long delay - both the phase delay and the group delay.

But we only need the dispersion (group delay). We can get this by just using a very sharp low pass filter and having the corner be above the frequency that we have the beat signal.

For example, the MiniCircuits SLP-200+ has got a corner frequency of 200 MHz and a group delay of ~10 ns (like a 3 m vacuum delay). So we would have to use 10 of these to get the delay we now get. The passband attenuation is only 0.5 dB, so we would lose 5 dB. The cost is \$35 ea. We have a few on the shelf.

OTOH, if we tune the beat frequency down to 30 MHz, we can use the SLP-30 which has a group delay of 30 ns around 30 MHz. That's like 9m at light speed. We could easily get a nice result by just using 4 or 5 SLP in series.

So why is Kiwamu using cables?? And how should we really choose the beat note frequency??

6264   Thu Feb 9 17:11:05 2012 steveUpdateSUSmore OSEM problems

These observations of the OSEMs  were taken while taking transfer functions of oplev YAW at excitation amplitude 0.1

Atm1,  C1:SUS-ETMX_SENSOR_SIDE cross coupling

Atm2,   C1:SUS-ITMX_SENSOR_LL   not excitable

Atm3-4,   BS and PRM  insensitive

Good OSEM list: ITMY, ETMY and SRM

Attachment 1: ETMXosemEXC0.1ampl.png
Attachment 2: IMTX-YAW0.1.png
Attachment 3: BSosemEXC.1ampl.png
Attachment 4: PRMosemEXC.1ampl.png
6263   Thu Feb 9 16:46:02 2012 steveUpdateSUS ALL oplev YAW transfer functions

 Quote: SUS- BS, ITMX, ITMY, PRM, SRM, ETMX & ETMY_OLPIT transfer funtion with sine wave excitation 0.1 amplitude:

OL_YAW transfer functions are here.

I had two PHDs helping me to overlap the EXML files in DTT. We failed. This job requires professorial help.

Attachment 1: BS-OLYAW.1ampl.png
Attachment 2: ITMX-OLYAW.1ampl.png
Attachment 3: ITMY-OLYAW.1ampl.png
Attachment 4: PRM_OLYAW.1.png
Attachment 5: SRM_OLYAW.1ampl.png
Attachment 6: ETMX-OLYAW.1ampl.png
Attachment 7: ETMY-OLYAW.1ampl.png
6262   Thu Feb 9 13:04:11 2012 KojiSummaryIOOPMC/IMC alignment

There has been no lock of input MC for more than 5days. WTF???

I have fixed a loose mirror of the PMC input and the alignment of the MC2 Yaw.

- The PSL mech-shutter was closed. It has been opened.

- Then, I checked the MC suspensions. Mainly MC2 Yaw has kept drifting. (Fig.1)
In fact, there was no WFS actions during this drift.

Anyway, now MC2 Yaw was aligned and the lock was restored.

- It was very unsatisfactory for me that the PMC alignment kept drifting.
The trend of the PMC REFL and PMC TRANS for a year suggests that:

• Occasional drifts exist since a year ago (or probably since we built this new PMC setup in 2010 Sep)
• The drift has got frequent for the recent four months, and got more for the recent one month.

I went into the PMC setup and tapped several optics in order to find any loose optic.
Immediately I found that the mirror before the AOM was loose. Basically any mild tapping was enough
to misalign the mirror such that the caivty loose the TEM00 mode.

I tightened the retainer set screw of the optic and aligned the PMC again. It looks OK now as I can not
misalign this optic by the tapping anymore. But if it still remains drifting, we need to replace the mount.

Attachment 1: Untitled.png
Attachment 2: Untitled2.png
6261   Thu Feb 9 12:38:15 2012 ZachUpdateSUSOSEM LED driver noise

Frank pointed out to me that I had dumbly forgotten to include the voltage reference's noise. The LT1031 has an output noise level of ~125 nV/rHz above 10 Hz or so, and this at least makes the estimate much closer. I had also not included an extra LT1125 stage between the reference and the other stages. I guess I was tired.

The estimate is now within a factor of a few of the measured level, and it has roughly the right shape. Around 1 Hz, it looks like the measured data begin to roll up away from the model, though it's tough to say due to the effect of the AC coupling on the analyzer less than a decade below. If there is indeed extra noise here, Frank thinks it could be due to resistor current noise.

I'll switch one or two out for nicer ones and see if things change.

6260   Wed Feb 8 16:37:02 2012 steveUpdateSUSITMX OSEM LL is sick

I'm driving C1:SUS-ITMX_OLYAW and PIT_EXC with amplitude 0,1-0.3 while taking transfer funtions of oplev.

The transfer functions are normal. However I noticed that the LL osem is not responding to this excitations

Healthy sensor respons should be like Atm3

Attachment 1: ITMXsensorLL.png
Attachment 2: ITMXsensorLLyaw.1.png
Attachment 3: ETMX.2amplPIT2.png
6259   Tue Feb 7 16:30:46 2012 steveUpdateSUS ALL oplev PIT transfer functions

SUS- BS, ITMX, ITMY, PRM, SRM, ETMX & ETMY_OLPIT transfer funtion with sine wave excitation 0.1 amplitude:

Attachment 1: BS_PIT.png
Attachment 2: ITMX_PIT.png
Attachment 3: itmy_pit.png
Attachment 4: PRM_PIT.png
Attachment 5: SRM_PIT.png
Attachment 6: ETMX_PIT.png
Attachment 7: ETMY_PIT2.png
6258   Tue Feb 7 03:05:08 2012 ZachUpdateSUSOSEM sat amp measurements

I did some more investigation on the OSEM box today.

Troubleshooting:

After removing some capacitors and still finding that the +15V rail was at over +20V, I decided to see if the TO-3 7815 that I removed behaved properly all by itself. It did. After some more poking around, I discovered that whoever assembled the board isolated the case of the regulator from the board. It is through the case that this package gets its grounding, so I removed the mica insulator, remounted the regulator, and all worked fine.

Since I had gotten a spare from Downs, I also replaced the LT1031 (precision 10-V reference), for fear that it had been damaged by the floating voltage regulator.

Noise measurements:

LED Driver

With the above out of the way, I was finally able to take some measurements. The first thing I did was to look at the LED drivers. I fixed the one stage that I mentioned in my last post by adding two 820-ohm resistors in parallel with the 1k, such that it was very close to all the others (which are 806 || 806 || 1k). With that, using a red LED, I measured a current of 34.5 mA (+/- 0.1) out of each of the 5 stages (UL, UR, LL, LR, S).

I then measured the current noise of each one by monitoring the voltage across the 287-ohm resistor in series with the LED. The driver works by putting the LED in the feedback path of an inverting amp. There is a 10-V input from the LT1031, and the values of the input and feedback resistors determine the current drawn through the LED. There is a buffer (LM6321) in the path to provide the necessary current.

The LISO model I made according to that description seems to make sense. I simply modeled the LED as a small resistor and asked LISO for the current through it. The transfer function shows the proper DC response of -49.15 dB(A/V) -->  34.8 mA @ 10 V, but, the estimated current noise doesn't add up with the measured levels:

I have to get to the bottom of this. Two possibilities are: 1) The buffer adds noise, and/or 2) I am modeling this invalidly.

PD Amp

I also began measuring the PD amplifier noise levels, though I only measured two of them for lack of time. I find it odd that there is a 100-ohm input series resistor on what I thought would be just a transimpedance amplifier. For that reason, I want to look into how the OSEMs are connected to this guy.

In any case, I measured the output noise of two of the PD amps by shorting the input side of the 100-ohm resistors to ground, and then I divided by their TF to get the input noise level. Here it is compared with the LISO estimate. I have plotted them in units of voltage noise at the input side of the resistors for lack of a way to infer the equivalent photocurrent noise level.

Above 2 Hz or so, the measured level agrees with the prediction. Below this, the measured noise level increases as 1/f, while it should go as the standard 1/sqrt(f) (the manufacturer-quoted 1/f corner is at 2 Hz). Another thing to get to the bottom of.

6257   Mon Feb 6 17:06:11 2012 steveUpdateSUSoplev transferfunction of PIT: ETMY & ETMX

Kiwamu showed me how to do transferfunction of oplev pitch

Attachment 1: ETMX_PIT.png
Attachment 2: ETMY_PIT.png
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