40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log, Page 322 of 337  Not logged in ELOG logo
ID Date Author Type Category Subject
  762   Wed Jul 30 00:42:04 2008 ranaUpdateSUSTrends and file formats
I propose that we do not use .eps format but .pdf instead. For images like the plots Sharon
has below we should use only .png and for pictures like what Steve posted, use JPG or PNG.

PDF is a standard and light weight. PNG is very good for plots/lines and is lossless. JPG does
a good job with regular camera pictures because we don't really care about the compression
loss on those.

Here's a trend of the UL sensors for all the optics - conversion is 32768 cts / mm. You can see
that the quake was just before 19:00 UTC (noon our time). The events an hour after are when
Rob, Jenne, and I start exciting the optics to shake them loose - wanging the pit/yaw sliders
around is not violent enough and so I injected a 130000 count sine wave at 0.5 Hz so as to
create a high force square wave. This seems to have worked for ETMY but no such luck yet with
the others.
Attachment 1: Untitled.png
Untitled.png
  761   Tue Jul 29 23:04:34 2008 YoichiUpdatePSLFSS loop transfer functions

Quote:

The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.


I measured it again and found that the loop was oscillating at 13.5kHz. I think this oscillation prevented the ref. cavity from building up the power and consequently lowered the optical gain making it marginally stable. So the PZT path open loop TF posted in the previous entry is wrong.

I was able to stop the oscillation by lowering the gain down to CG=-7.6dB and FG=-8.78dB.
The first attachment shows the measured open loop transfer function.
Since the gain setting is different from when the over all open loop TF was measured, I scaled the gain (attachment 2).
However, this plot seems to have too much gain. Scaling it down by 20dB makes it overlap with the over all open loop TF.
Maybe the gain reading on the EPICS screen is wrong. I will measure the actual gain tomorrow.
Attachment 1: OpltfPZTOnlyRaw.eps
OpltfPZTOnlyRaw.eps
Attachment 2: OpltfPZTOnly.eps
OpltfPZTOnly.eps
  760   Tue Jul 29 21:04:55 2008 SharonUpdate OSEM's Power Spectrum
From 16:30 this afternoon
Attachment 1: ITMY2.JPEG
ITMY2.JPEG
Attachment 2: ITMY.JPEG
ITMY.JPEG
Attachment 3: ITMX2.JPEG
ITMX2.JPEG
Attachment 4: ITMX.JPEG
ITMX.JPEG
Attachment 5: ETMY2.JPEG
ETMY2.JPEG
Attachment 6: ETMY.JPEG
ETMY.JPEG
Attachment 7: ETMX2.JPEG
ETMX2.JPEG
Attachment 8: ETMX.JPEG
ETMX.JPEG
  759   Tue Jul 29 19:53:19 2008 KojiUpdateSUSPRM photos from the south window
Steve and Koji

We took some photos of PRM from the south window.
You can see one of the side magnets, a wire stand-off, and the wire itself from the round hole.
So, the wire looks OK.

For the coils, we could see only one coil. The magnet is apparently too high.
Attachment 1: PRM_from_South_Window1.jpg
PRM_from_South_Window1.jpg
Attachment 2: PRM_from_South_Window2.jpg
PRM_from_South_Window2.jpg
  758   Tue Jul 29 19:41:38 2008 YoichiUpdatePSLFSS loop transfer functions
Last night I measured a bunch of transfer functions on the FSS loop.
All the loop gains were measured with the common gain = 30db and the fast gain = 18dB.

(1) The first attachment is the overall open loop transfer function of the FSS loop. I put a signal from the Test IN2 and observed signals from IN1 and IN2.
The UGF is about 180kHz.
By increasing the RF amplitude going to the EOM (i.e. increasing the sideband power), I can further increase the gain of the servo.
However, it made the PC drive immediately crazy. Probably it was some oscillation.

(2) Then I locked the ref. cav. with only the PZT actuator. I did so by simply unplugging the cable going to the PC.
Surprisingly, the cavity locked with the *same* gain setting as before. The second attachment shows the open loop transfer function measured in this configuration. It seems wrong, I mean, it should be unstable. But the cavity locked. A mystery.

(3) The third plot is the measured TF from the Test IN1 of the FSS board to the fast out (output to the PZT).

(4) By dividing the TF measured in (2) with the TF of (3), I got the response of the PZT times the cavity response. This is shown in the attachment 4.

(5) We can guess the open loop TF of the PC path by subtracting the TF in (2) from (1). It is shown in the attachment 5.

(6) The filter shape of the PC path is measured by injecting signal from the Test IN1 of the FSS board and observing it at the PC output. Since it is a high voltage output, I reduced the common gain to -8.5dB during the measurement. The attachment 6 is the measured filter shape. The gain is corrected to show what it should look like when the common gain = 30dB.

(7) By dividing (5) with (6), I plotted the response of the PC times the cavity response in the attachment 7. Since the 1/f cavity pole and the response of the PC, which is proportional to f, should cancel out, we expect a flat response above the cavity pole frequency (38kHz). You could say it is a sort of flat, if you have obscured eyes.

The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.
The plot (4) is also strange becaues it does not show the low pass feature expected from the cavity pole.
Attachment 1: OverallOPLTF.eps
OverallOPLTF.eps
Attachment 2: OpltfPZTOnly.eps
OpltfPZTOnly.eps
Attachment 3: PZTFilter.eps
PZTFilter.eps
Attachment 4: PZTxCavityPole.eps
PZTxCavityPole.eps
Attachment 5: OpltfPCOnly.eps
OpltfPCOnly.eps
Attachment 6: PCFilter.eps
PCFilter.eps
Attachment 7: PCxCavityPole.eps
PCxCavityPole.eps
  757   Tue Jul 29 18:15:36 2008 robUpdateIOOMC locked

I used the SUS DRIFT MON screen to return the MC suspensions to near their pre-quake values. This required fairly large steps in the angle biases. Once I returned to the printed values on the DRIFT screen (from 3/08), I could see HOM flashes in the MC. It was then pretty easy to get back to a good alignment and get the MC locked.
  756   Tue Jul 29 14:38:02 2008 robUpdateSUSETMY and PRM have EQ related problems

Quote:
The attached trend shows that ETMY and PRM both had large steps in their sensors
around the time of the EQ and didn't return afterwards. The calibration of the
OSEM sensors is ~0.5 mm/V. The PRM sensors respond when we give it huge biases
but there is very little change in the ETMY. Almost certainly true that the
optics have shifted in their wire slings and that we will have to vent to
examine and repair at least ETMY.

Jenne is looking at the spectra of the other suspensions to see if there is
other more subtle issues.


Some additional notes/update:

ETMY, PRM, & MC2 had OSEM signals at a rail (indicating stuck optics). Driving the optics with full scale DAC output freed ETMY and MC2, so while these may have shifted in their slings it may be possible to avoid a repair vent. PRM is still stuck. One OSEM appears to respond with full range to large drives, but the other three face OSEMS remain disturbingly near the rail (HIGH, which is what would happen if a magnet fell off).
  755   Tue Jul 29 13:54:08 2008 ranaUpdateSUSETMY and PRM have EQ related problems
The attached trend shows that ETMY and PRM both had large steps in their sensors
around the time of the EQ and didn't return afterwards. The calibration of the
OSEM sensors is ~0.5 mm/V. The PRM sensors respond when we give it huge biases
but there is very little change in the ETMY. Almost certainly true that the
optics have shifted in their wire slings and that we will have to vent to
examine and repair at least ETMY.

Jenne is looking at the spectra of the other suspensions to see if there is
other more subtle issues.
Attachment 1: Untitled.png
Untitled.png
  754   Tue Jul 29 11:50:01 2008 JenneUpdateEnvironment5.6 Earthquake
Earthquake Details
Magnitude 5.6
Date-Time

* Tuesday, July 29, 2008 at 18:42:15 UTC
* Tuesday, July 29, 2008 at 11:42:15 AM at epicenter

Location 33.959N, 117.752W
Depth 12.3 km (7.6 miles)
Region GREATER LOS ANGELES AREA, CALIFORNIA
Distances

* 3 km (2 miles) SW (235) from Chino Hills, CA
* 8 km (5 miles) SE (127) from Diamond Bar, CA
* 9 km (5 miles) NNE (23) from Yorba Linda, CA
* 11 km (7 miles) S (178) from Pomona, CA
* 47 km (29 miles) ESE (103) from Los Angeles Civic Center, CA

Location Uncertainty horizontal +/- 0.3 km (0.2 miles); depth +/- 1.3 km (0.8 miles)
Parameters Nph=144, Dmin=8 km, Rmss=0.42 sec, Gp= 18,
M-type=local magnitude (ML), Version=1
Source

* California Integrated Seismic Net:
* USGS Caltech CGS UCB UCSD UNR

Event ID ci14383980

All the watchdogs tripped. I'll put them back after lunch, after the optics have had time to settle down.
  753   Tue Jul 29 09:12:43 2008 KojiConfigurationIOOMC length measurement
I found that the prev modulation freq had been determined with a same kind of measurement by Osamu, which also looked accurate.
http://www.ldas-sw.ligo.caltech.edu/ilog/pub/ilog.cgi?group=40m&task=view&date_to_view=09/12/2002&anchor_to_scroll_to=2002:09:12:17:10:30-ajw

(There is also a document by Dennis to note about this measurement
http://www.ligo.caltech.edu/docs/T/T020147-00.pdf )

So, it means that the round trip length of the MC shortened by 1mm in the 6 years.
New              OLD
--------------------------
27.0924          27.0934    [m]

Quote:
rob, yoichi

We measured the length of the mode cleaner tonight, using a variant of the Sigg-Frolov method.
....
The new f2 frequency is:
New              OLD
--------------------------
165983145        165977195
  752   Tue Jul 29 01:03:17 2008 robConfigurationIOOMC length measurement
rob, yoichi

We measured the length of the mode cleaner tonight, using a variant of the Sigg-Frolov method. We used c1omc DAC outputs to inject a signal (at 2023Hz) into the AO path of the mode cleaner and another at DC into the EXT MOD input of the 166MHz IFR2023A. We then moved an offset slider to change the 166MHz modulation frequency until we could not see the 2023Hz excitation in a single-bounce REFL166. This technique could actually be taken a step further if we were really cool--we could actually demodulate the signal at 2023Hz and look for a zero crossing rather than just a powerspec minimum. In any case, we set the frequency on the Marconi by looking at the frequency counter when the Marconi setting+EXT MOD input were correct, then changed the Marconi frequency to be within a couple of Hz of that reading after removing the EXT MOD input. We then did some arithmetic to set the other Marconis.

The new f2 frequency is:

New              OLD
--------------------------
165983145        165977195

  751   Mon Jul 28 23:41:07 2008 robConfigurationPSLFSS/MC gains twiddled

I found the FSS and MC gain settings in a weird state. The FSS was showing excess PC drive and the MC wouldn't lock--even when it did, the boost stage would pull it off resonance. I adjusted the nominal FSS gains and edited the mcup and mcdown scripts. The FSS common gain goes to 30dB, Fast gain to 22dB, and MCL gain goes to 1 (which puts the crossover back around ~85 degrees where phase rises above 40 degrees).
  750   Mon Jul 28 17:58:05 2008 SharonUpdate TOP screen changes
I wanted to test the adaptive code with a downsampling rate of 32 instead of 16. To do this I entered a 32 Hz ((2048/32)/2 - match Nyquist Freq.) low pass filter on the ERROR EMPH, MC1 and the relevant PEM channels.
  749   Mon Jul 28 17:44:07 2008 ranaUpdatePSLPMC PZT v. temperature
This plot shows that the PMC PZT has ~20 Vpp fluctuations on a 24 hour timescale
which is correlated to the 24 hour temperature fluctuations. By contrast, the MZ
has ~75 Vpp
.
Attachment 1: Untitled.pdf
Untitled.pdf
  748   Mon Jul 28 15:54:04 2008 KojiUpdateGeneralAbs. Len. Meas. ~ More on the beat / the PLL setup
Alberto and Koji,

Last Friday evening, Koji found that the power adj setting (indicated by ADJ) of the NPRO was somehow set to be 
ADJ=-45 and yielded the output power of about 200mW instead of 700mW. This is not good because too small pump power 
varies thermal conditions of the crystal such as thermal lensing, thermal gradient, and os on. The ADJ setting and the 
crystal temperature had been restored to ADJ=0 and LT=~48deg (nominal of the controller), respectively.

Today we tried the quest of the beating again and the above power setting helped a lot! The beating was immediately 
found at LT=48.55deg that is very close to the laser's nominal temp. Also the beating got significantly bigger. 
After the alignment adjustment 50%-intenisity modulated signal was obtained. From the power calculation it was 
estimated that the power coupling of the injected beam is to be 12%~13%. This not so good yet, but something which we 
can work.

This time the modulation structure of the PSL beam was clearly observed. I could obtain the beating of the injection 
beam with the carrier, the upper/lower sidebands of the 33MHz and 166MHz modulations, and the 2nd order of the 
33MHz. They were beautiful as if working with an OSA. Very nice.

In reality, those additional intenisty modulations as well as the residual 33MHz signal from the main IFO are 
disturbing for the PLL to be locked at the proper frequency. So, now Alberto is working on a passive LPF with 
notch at 33MHz. The design was already done. This allows us to work up to 20MHz and at the same time, provides 
60dB attenuation at 33MHz (in principle). Very cool.

Koji, on the other hand, continued to work with the PLL servo with some ready-made passive filters. Owing to the 
fillters, the error signal was cleaner and the PLL was locked at the proper frequency. The PLL setup is as attatched. 
Sideband rejection filter will be replaced to Alberto's one. The photo is the display of the RF spectrum analyzer with 
beat locked at 8MHz.

So the next step, we try to find the resonances of the arm cavity with the injection beam once the IFO comes back.

At the last of the experiment "Last autoalignment" was restored, the flipper for the 
inj beam was down, and the shutter for the NPRO was closed.
Attachment 1: PLL_setup.png
PLL_setup.png
Attachment 2: beat_at_8MHz.jpg
beat_at_8MHz.jpg
  747   Mon Jul 28 12:02:32 2008 SharonUpdate accelerometers settings
Jenne, Sharon


We looked again at the channels of the accelerometers and there are some updates. Last time when we reported, we crossed the ADAP channels and the accelerometer. Now that there is a new MEDM screen, with which you can control which channels goes to which adaptive channels, this has no meaning...
Therefore, the channels that go with the noise source channels are:

PEM 15 MC1_X
PEM 16 MC1_Y
PEM 17 MC1_Z
PEM 18 MC2_X
PEM 19 MC2_Y
PEM 20 MC2_Z
PEM 21 SEIS

disregard the last post regarding these channels by Jenne, since I am changing the ADAP channels all the time...
  746   Mon Jul 28 11:20:13 2008 JenneUpdatePSLWork on the FSS and Reference Cavity
[Yoichi, Jenne, Koji]

The Reference Cavity's saga continues....

Thursday, Yoichi and I worked to change the beam that we chose from the 2nd pass through the AOM, to the first order beam rather than the 2nd order beam (see elog #726). After choosing the correct beam, we get 29mW incident on the reference cavity (compared with 4mW before any work began). We adjusted the angle of the AOM in the plane of the table, and got up to 30.6mW. We adjusted the tip/tilt of the AOM and got to 30.7mW (the tip/tilt adjustment made a more significant difference in the work described in elog #726, but after that work, it was probably already pretty close to optimized). We noticed that for the above measurements, we had 2 beams through the Polarizing Beam Splitter and Waveplate (one very dim), so after excluding that beam, the power meter read 30.4mW. We adjusted the curved mirror a little, and got 30.8mW incident on the reference cavity.

We then put a triangle wave into the offset of the MC Servo Board using the "trianglewave <channel> <center> <amplitude> <period> <runtime>" command in a terminal screen. This changes the voltage to the VCO, and thus the frequency response of the AOM. We watch the diffracted spots from the second pass through the AOM, and confirm that the beam we have chosen is not moving, and all the others are. By symmetry, if we chose the first order beam after the first pass through the AOM, and then again chose the first order beam after the second pass, the resulting beam will not move with the frequency change of the AOM.

We saw 1.50V (Refl. PD, unlocked) on the 'scope after aligning the optics to make the newly chosen beam hit the input mirror of the reference cavity. Order of operations for this alignment:
  • Recenter the beam on the 2 lenses that are just after the PBS and the waveplate
  • Adjust pitch and yaw of the two steering mirrors until the beam reflected off the input mirror of the reference cavity is parallel to the incident beam
    • Use a sensor card to check the alignment of the incident and reflected beams, and adjust the steering mirrors to get the alignment close
      • Note the amplitude of the DC output of the Refl. PD with the iris completely open. Close the iris until the signal decreases by ~50%, then adjust the steering mirrors until the original amplitude is regained. Repeat until the iris can be almost completely closed but the Refl. PD signal doesn't change
    • Watch the DC output of the Refl. PD, and maximize the signal on a 'scope
    • Sweep the PZT of the laser using a function generator into the RAMP input on the FSS board (~10Vpp at ~1Hz), OR sweep the temperature of the laser using the trianglewave function on the SLOW FSS channel (amplitude~0.5, period~50)
    • Watch the modes that resonate in the cavity, and adjust pitch and yaw of the steering mirrors to get closer to the TEM00 mode
    • When the TEM00 mode appears in the sweep, stop the sweep, and lock the cavity
    • Watch the DC output of the Transmitted PD, and maximize the signal on a 'scope
  • Celebrate!

After all of this adjusting,
Refl. PD (unlocked) = 1.48V
Refl. PD (locked) = 680mV
Trans. PD (locked) = 6.28V
Power reflected (unlocked) = 26.28mW
Power transmitted (locked) = 13.89mW
Thus, 53% transmission

Next: check the amount of power transmitted by reducing the amplitude of the RF modulator. This reduces the amount of power used by the sidebands, and so should increase the transmission.
Power incident = 27mW
Power transmitted = 17.2mW
Thus, 64% transmission
We then put the RF modulator back where it was originally.

We then replaced the lens mounts for the f=802 and f=687 lenses between the AOM and the reference cavity, to the new mounts that Yoichi bought. Koji helped me realign into the reference cavity, and we got:
Refl. PD (unlocked) = 1.48V
Refl. PD (locked) = 880mV
Trans PD (locked) = 4.64V
Power incident = 26.97mW
Power transmitted = 10.39mW
39% transmission
Since more mode matching etc. is in the works, we left this for the night.

On Friday, we changed the setup of the cameras and PDs for both reflection and transmission, to avoid saturating the PDs and cameras.

On the Refl. side of the reference cavity, we put a W2-PW-1025-UV-1064-45P pickoff between the last mirror and lens before the camera and PD. We moved the camera to the pickoff side of the new optic. We then replaced teh 45UNP beam splitter that split the beam between the PD and the camera with a Y1-1037-45P highly reflective mirror, and put the PD in the old camera location.

On the Trans. side of the ref. cavity, we replaced the BSI-1064-50-1025-45S with a W2 pickoff, and replaced the Y1-1037-45-P highly reflective mirror with the 50/50 beam splitter that was replaced by the W2.

Now we have:
Refl. PD (unlocked) = 1.68V
Refl. PD (locked) = 640mV
Trans PD (locked) = 4.24V
Power incident = 25mW
Power transmitted = 14.48mW
58% transmission

Koji pointed out that when remounting, I had put the f=802 lens ~2cm away from its original position (along the z-axis), so I moved the lens back to where it should be, and realigned into the reference cavity. Since Rana was working on the PMC at the same time, the laser was turned down by about a factor of 100, so my starting measurements were:
Refl. PD (unlocked) = 23.6mV
Refl. PD (locked) = 10.2mV
Trans PD (locked) = 56mV
Power incident = 0.35mW
Power transmitted = 0.16mW
46% transmission

Since it was late on Friday by the time everything was realigned into the ref. cavity (I'm still working on my optics aligning skills), I forgot to measure the transmission after all of my work. I'll do that today (Monday) as soon as Sharon/Koji are done working with the IFO this morning. Also, I'll put up before/after pictures as soon as I find the camera...it seems to have walked off.

UPDATE:
Ref. Cav. measurements after Friday's alignment (and after turning the laser power back up to normal):
Refl. PD (unlocked) = 1.58V
Refl. PD (locked) = 304mV
Trans PD (locked) = 3.68V
Power incident = 24.96mW
Power transmitted = 16.45mW
66% transmission


To do: Start the actual mode-matching into the reference cavity.
  745   Sun Jul 27 23:06:17 2008 ranaUpdatePSLPMC, MZ, MC-MMT, etc.
With the new PMC now in I aligned the MZ to the new beam (there is sadly no steering
between the PMC and the MZ).

I also removed the pickoff that we had put before the MZ just in case we wanted to
move the FSS pickoff to there - its been 2 years now so I guess its not going to happen.


The new PMC's cavity axis seems to be a few hundred microns higher than the old one. So I
tried to move the MZ EOMs to compensate but ended up also steering all of the MZ's mirrors
to get the contrast good, the beam onto the ISS PDs, centered (sort of) onto the MMT lenses
and onto the periscope.

Along the way I also removed some of the vestigial squeezer stuff around the power control
PBS. The output of the PBS now goes directly into the high power dump with no steering. This
eliminated around a dozen clamps, bases, etc. and a couple of mirrors.


The MC is locked on the low power beam we have running through everything. I restored the
PSL launch beam just using the MC-WFS and it locked on a TEM00. So now we know that we
really don't need the PSL quads for this as long as the MC1 angle is stable.

The good news is that the PMC PZT voltage is now flat: the problem must have really been with
the PZT
and not the cabling or notch box like I had wondered about.

Todo:
-----
1) Continue mode matching into the PMC. Its transmission now is around the same as the
   old one.

2) Put a UHV foil covered lead brick onto the PMC to quiet it down.

3) Characterize the PMC loop and retune the body notch for the new body.

4) Tweak the MZ alignment to minimize the RFAM. We can use StochMon to do this as
   long as we have the MC WFS turned off or we can put in a flipper to take the
   beam before the MC and send it to the StochMon RFPD.

5) Re-align onto the ISS.

6) Install irises around the periscope for the beam. The old iris there is way off.

7) Fix PSL ANG and center both POS and ANG.
  744   Sun Jul 27 20:49:21 2008 ranaConfigurationComputersNTP
After Aidan did whatever he did on op440m, I had to restart ntpd. I noticed it didn't actually do
anything so I restarted it by hand with the '-l' option to make a logfile. Essentially, the
problem is that NTPD is not allowed access to the outside world's NTP servers by our NAT router;
this should be fixed.

So for now I set all of the .conf files to point to rana and nodus' IP addresses. According to the
log files, that is successful. Rosalba and Mafalda, however, seem to have correct time but are
looking at rhel.ntp.pool.org and time.nist.gov, respectively. Maybe these have special rules?

For reference, the linux machines' conf files are /etc/ntp.conf
and the solaris machines' conf files are /etc/inet/ntp.conf

I also logged into dcuepics (aka scipe25) and did as instructed.
  743   Sun Jul 27 20:25:49 2008 ranaConfigurationEnvironmentOffice Temperature increased to 75 F
Since we have the chiller for the PSL chiller now, I've just increased the office area
temperature set point by 2 F
to 75 F to see if the laser will still behave.
  742   Sat Jul 26 15:09:57 2008 AidanUpdateComputersReboot of op440m

I was reviewing the PSL Overview screen this afternoon and op440m completely froze when I center-clicked on the REF CAVITY TRANSMISSION indicator. It was unresponsive to any keyboard or mouse control. The moon button had no effect to shut the machine down.

Called Alberto in and we logged into op440m from rosalba. From there we logged in as 'root' and run a shutdown script '/usr/sbin/shutdown -i S -g 1'. The medm screens started disappearing from the op440m display and we were eventually asked to enter System Maintenance Mode. From here we selected RUN LEVEL 5: "state 5: Shut the machine down so that it is safe to remove the power". Following this the machine turned itself off.

We powered it back on, logged back in as controls and restarted the medm screens. Everything seems to be running fine now.
Aidan.
  741   Fri Jul 25 19:57:18 2008 JenneUpdatePSLRef Cav & PMC
"PMC is in, but is still being worked on. Leave it alone." ---Rana

Ref. Cavity is locked again. Still a work in progress. I think we're ready to mode match on Monday. ---Jenne
  740   Fri Jul 25 17:32:46 2008 SharonUpdate ASS computer
So, it seems a bit too complicated getting the coefficients the way I wanted it to happen (simulink-.ini...).
I returned everything to the way it was and it's all working. The new plan is to choose the specific channel I want to find its instantanous coefficients, let the adaptive code run for a while, setting mu and tau to zero (freezing the coefficients), and exciting the noise signal channel taking the transfer function. This way I can find the filter I want to simulate with an IIR filter.
Once I have the mode cleaner to myself, I'll start posting results.
  739   Fri Jul 25 13:30:53 2008 SharonUpdate Changes in ASS computer
I editted the simulink diagram of the ASS computer so it now has 2 more channels reading 2 sets of the FIR coefficients to match Alex's changes in the C code.
The new simulink has already been compiled and can be found in /cvs/cds/caltech/users/alex/cds/advLigo/src/epics/simLink/ass.mdl
I backed up the old file and it's also in that folder under ass_BAK_24_jul.mdl

There is also a backup of the old ASS.ini file in caltech/chans/daq/C1ASS_BAK_24_jul.ini

Will update once it's all set and running
  738   Fri Jul 25 10:48:13 2008 KojiUpdateGeneralAbs. Len. Meas. ~ Realignment / beating / PLL trial
Alberto and Koji

o We worked for the abs length measurement setup on Thursday night.
o At the last of the work Koji left the 40m lab at 2AM. "Last autoalignment" was restored. The flipper for the 
inj beam was down. The shutter for the NPRO was closed.

----
o The alignment of the injection beam (NPRO) was re-adjusted.
o The laser crystal temp (LT) of the NPRO was scanned.
o After a long struggle the beat was found at about LT=61deg(!). I think this is almost at the maximum temp 
for the NPRO. Note that this is not the diode temp, and therefore it will not damage the laser as far as the 
TEC for the crystal works.

o Only the X arm was aligned.
o The alignment of the injection beam was adjusted such that the beating amplitude got maximum.
o At the faraday of the NPRO, we had 2.4V_DC and 1.8V_DC with and without the inj beam, respectively. The 
beating amplitude was 200mVpp (at around 2.4V).
o With a simple calculation, the mode overlapping of tghe injection beam is only 0.0023. Ahhh. It is too weak. 
In the modematching or something must be wrong. 
o The position of the mode matching lens was tweaked a little. It did not help to increase the beat ampitude. 
Even worse. (The lens was restored and the values above was obatined with the latest setting.) 

o Then tried to build a PLL. It locks easily. 
  - Put the beat signal into the mixer RF input.
  - Connect 10dBm @1MHz-10MHz from the marconi oscillator to the LO input. The supposed nominal LO level was 
not checked so far. Just used 10dBm.
  - The IF output was connected to an SR560 with 10Hz LPF (6dB/oct) with G=500 or so.We don't need to care 
about the sign.
  - The output of the SR560 was connected to FAST PZT input of the NPRO.
o The problem was that there was strong intermodulations because of 33MHz. No LPFwas used before the mixer. 
Because of this spourious modulations, the PLL servo locks at the local zero crossings. These will be solved 
next time. 

o Eventually left the 40m lab at 2AM. "Last autoalignment" was restored. The flipper for the inj beam was 
down. The shutter for the NPRO was closed.
  737   Thu Jul 24 21:53:00 2008 ranaSummaryTreasureHigh School Tour group and the PMC
There was a tour today of 40 high school kids. I warned them that the lasers could burn out their
eyes
, that the vacuum could suck them through the viewports like tubes of spaghetti and that the
high voltage amps would fry their hair off.

One of them was taking a picture of the SOS in the flow bench and another one was whispering what
a dumb idea it was to leave a sensitive clean optic out where people might breathe on it. I told
one them to cover his mouth. The other one asked what was the glass block behind the SOS.

It was a spare PMC! s/n 00-2677 with a 279 nF capacitance PZT. I guess that this is the one that
Go brought from MIT and then left here. So we don't have to take the one away from Bridge in the
35 W laser lab.

We can swap this one in in the morning while the FSS people work on the reference cavity
alignment. Please email me if you object to this operation.
  736   Thu Jul 24 21:04:58 2008 ranaUpdatePSLFSS
Since Jenne and Yoichi are going to finish up their refcav/FSS work in the morning I decided to
look at the trends. I set the RF modulation level from 10.0 back down to 7.5 so that we would
have the same RF modulation depth as before. I also set the FSS common gain and its nominal to
1.0 dB since it seemed more stable this way.

With 7.5, the transmission of the refcav is ~6.9 V. It was around 0.7 V before so there's already
been a factor of 10 improvement in the power since the work started. In addition to the mode matching
work which is about to commence, we should attenuate the RC TRANS with a real mirror (not ND) so that
the camera and PD don't saturate. We should also do the same for the REFL PD and camera and make sure
to put in a steering mirror for the REFL PD and orient REFL so that it faces West (so that we can
look at its face with a viewer) and dumps its reflection.

Since the common gain is so low now, I expect that we will want less light in total. We can achieve
this by turning down the RF drive to the VCO.

I also fixed the MC down script which was putting the FSS common gain to the unstable +10 dB level
during the MC locking process.
  735   Thu Jul 24 19:29:26 2008 YoichiConfigurationPSLC1:PSL-STAT_FSS_NOM_C_GAIN is changed from 30 to -0.7
Koji, Yoichi

Since the light power going to the ref. cavity is now significantly increased (see Janne's elog later),
C1:PSL-STAT_FSS_NOM_C_GAIN
is changed from 30 to -0.7.
Otherwise, the MC did not lock.
  734   Thu Jul 24 11:49:07 2008 MashaSummaryAuxiliary lockingbelated weekly summary
I designed a high pass filter to whiten the spectrum from the Mach Zehnder to optimize the
input into the ADC. The swept sine response measurement and the effect of the filter on the
spectrum are attached. If I start using the digital system (it is currently down in Bridge),
I will decide if the filter needs to be improved/better matched to the ADC there.

I moved from the 40m to Rana's lab in bridge. I am making a new and improved Mach Zehnder
setup with a 50m fiber in one arm; currently the transmission through the fiber is 44%. I
am working out how to mode match the laser to the fiber to improve this number.
Attachment 1: filter_tr_function.pdf
filter_tr_function.pdf
Attachment 2: filtered_spectr0724.pdf
filtered_spectr0724.pdf
  733   Thu Jul 24 08:09:26 2008 YoichiUpdateLSCArm cavity g-factor measurement

Quote:

A-ha! Do you always expect the 30Hz signal, don't you?
Because this is the PDH technique.


Yes you are right. I realized this when I was thinking about it in the bed Smile
The 30Hz signal should always be present because the carrier is phase shifted at 30Hz by the cavity length change.
I think the change in the signal ratio between I and Q happened because as the 166MHz sidebands get phase change when they move around the MC transmission peak due to the cavity pole of the MC. It changes the optimal demodulation phase for the 166MHz PDH signal at the AS port.


Quote:

We should be able to see 166MHz sideband resonances using the double demodulated photodetectors. With these, the 33MHz sidebands will be acting as LO when the 166MHz sideband (or mode) resonates. Some modeling may be necessary to determine if the SNR will be good enough to make this worthwhile, however.


I will try, but at 100kHz away from the MC FSR (the number predicted by John's calculation), the transmission of the 166MHz sidebands is very weak. I did not see any signal when I swept it +/- 500kHz. Unfortunately, the Marconi's output level is almost at its maximum. So we don't have much room for increasing the sideband power.
  732   Thu Jul 24 03:08:20 2008 robUpdateLocking+f2 DRMI+2ARMS

rob, john, yoichi

Tonight we tried to move the 166MHz (f2) sideband frequency by changing the settings on the Marconi. Reducing the frequency by 4kHz reduced the amplitude of the 166MHz sidebands, but we were still able to lock the DRMI with the +-f2 sidebands by electronically compensating for the gain decrease, and also to lock the DRMI+2ARMs while resonating the -f2 sideband. No luck with the +f2.

Then we larkily tried increasing the frequency by 4kHz, which ~doubled the f2 sideband transmission through the MC. This means our frequencies/MC length have been mismatched for months. Apparently I explained the level of the f2 sidebands by just imagining that I'd (or someone) had set the modulation depth at that level some time in the past.

It's a miracle any locking worked at all in this state. Once this was done and we worked out a few kinks in the script, adjusting some gains to compensate, we managed to get the DRMI+2ARMS to lock a couple of times while resonating the +f2 sideband. It takes a while, but at least it happens. Tomorrow we'll measure the length of the mode cleaner properly and then try again. No need to vent just yet.
  731   Thu Jul 24 02:57:26 2008 robUpdateLSCArm cavity g-factor measurement

Quote:

So, now I feel that the method for the TEM01 quest should be reconsidered.

If we have any unbalanced resonance for the phase modulation sidebands, the offset of the error signal is to be observed even with the carrier exactly at the resonance. We don't need to shake or move the cavity mirrors.

Presence of the MC makes the things more complicated. Changing the frequency of the modulation that should go throgh the MC is a bit tricky as the detuning produces FM-AM conversion. i.e. The beam incident on the arm cavity may be not only phase modulated but also amplitude modulated. This makes the measurement of the offset described above difficult.

The setup of the abs length measurement (FSR measurement) will be easily used for the measurement of the transverse mode spacings. But it needs some more time to be realized.


We should be able to see 166MHz sideband resonances using the double demodulated photodetectors. With these, the 33MHz sidebands will be acting as LO when the 166MHz sideband (or mode) resonates. Some modeling may be necessary to determine if the SNR will be good enough to make this worthwhile, however.
  730   Thu Jul 24 01:27:00 2008 KojiUpdateLSCArm cavity g-factor measurement

Quote:
I locked the Y-arm and mis-aligned the end mirror in Yaw until the transmission power gets half.
Then I injected a 30Hz sinusoid into the error point of the Y-arm servo to shake the ETMY.
I observed AS166_I and AS166_Q as I changed the 166MHz frequency.


A-ha! Do you always expect the 30Hz signal, don't you?
Because this is the PDH technique.

---------------
Recipe:
You have a carrier and phase modulation sidebands at 166MHz this time.
Inject them into a cavity. Detect the reflection by a photo detector.
Demodulate the photocurrent at 166MHz.

This is the PDH technique.

A 30Hz sinusoid was injected to the error point of the cavity lock.
This means that the cavity length was fluctuated at 30Hz.

We should see the 30Hz signal at the error signal of the 166MHz demodulation, regardless of the tuning of the modulation frequency!
In other words, the 30Hz signal in the demod signal at the 166MHz is also understandable as the beating between the 30Hz sidebands and the 166MHz sidebands.

---------------

So, now I feel that the method for the TEM01 quest should be reconsidered.

If we have any unbalanced resonance for the phase modulation sidebands, the offset of the error signal is to be observed even with the carrier exactly at the resonance. We don't need to shake or move the cavity mirrors.

Presence of the MC makes the things more complicated. Changing the frequency of the modulation that should go throgh the MC is a bit tricky as the detuning produces FM-AM conversion. i.e. The beam incident on the arm cavity may be not only phase modulated but also amplitude modulated. This makes the measurement of the offset described above difficult.

The setup of the abs length measurement (FSR measurement) will be easily used for the measurement of the transverse mode spacings. But it needs some more time to be realized.
  729   Thu Jul 24 01:04:01 2008 robConfigurationLSCIFR2023A (aka MARCONI) settings

Quote:


P.S.: We made a test by changing the frequency of the local oscillator by a little bit and then coming back to the original value. We observed that the phase of the signal can change, so every time this frequency is moved the 3f demod phase need to be retuned.



We discovered this little tidbit in March, and remembered it tonight. Basically we found that whenever you change the frequency on one of these signal generators (and maybe any other setting as well), the phase of the signal can change (it's probably just the sign, but still...), meaning that you when you return settings to their intial value, not everything is exactly as it once was. For most applications, this doesn't matter. For us, where we use one Marconi to demodulate the product of two other Marconis, it means we can easily cause a great deal of grief for ourselves, as the demod phase for the double demod signals can appear to change.

Programmatically, what this means is that every time you touch a Marconi you must elog it. Especially if you change a setting and then put it back.
  728   Wed Jul 23 22:34:07 2008 YoichiUpdateLSCArm cavity g-factor measurement
I tried the same thing as the X-arm to the Y-arm.
I'm puzzled. I found exactly the same behavior as the X-arm in the AS166 demodulated signals, whereas I expected different resonance frequency because of the arm length difference.

Here is more detailed account of the measurement today.

I locked the Y-arm and mis-aligned the end mirror in Yaw until the transmission power gets half.
Then I injected a 30Hz sinusoid into the error point of the Y-arm servo to shake the ETMY.
I observed AS166_I and AS166_Q as I changed the 166MHz frequency.

At 165.977MHz, both AS166_I and AS166_Q showed the 30Hz signal (15cnt p-p).
At 165.981MHz, Only I phase showed the 30Hz signal (40cnt p-p). No signal in Q.
At 165.984MHz, I and Q became the same amplitude again (20cnt p-p).
At 165.987MHz, Only Q phase showed the 30Hz signal (40cnt p-p). No signal in I.

Outside the above range, the signal decreases as the frequency go away. I think this is (at least partly) because the 166MHz sidebands no longer go through the MC at those frequencies.

I then locked the X-arm to the TEM01 mode. I saw exactly the same behavior as described above. This could be the resonance of TEM02 mode. I was expecting to see the resonance of TEM00 mode at the opposite side, but nothing there.

I unlocked the arm cavities and tried the same frequency scan of the 166MHz with one of the end mirrors shaken at 30Hz. I saw no signal at the AS166 port.
I also tried locking Y-arm and shaking the ETMX. No signal.
So it has to be something to do with the cavity resonance.

Since the MC transmission curve for 166MHz is folded in the measurement, it makes the interpretation of the results harder.
  727   Wed Jul 23 21:48:30 2008 robConfigurationGeneralrestore IFO when you're done with it

when you are done with the IFO, please click "Restore last auto-alignment" on the yellow IFO portion of the C1IFO_CONFIGURE.adl screen. Failure to comply will be interpreted as antagonism toward the lock acquisition effort and will be met with excoriation.
  726   Wed Jul 23 18:42:18 2008 JenneUpdatePSLAlignment of AOM
[Rana, Yoichi, Jenne]

Short Version: We are selecting the wrong diffracted beam on the 2nd pass through the AOM (we use the 2nd order rather than the first). This will be fixed tomorrow.

Long Version of AOM activities:

We checked the amount of power going to the AOM, through the AOM on the first pass, and then through the AOM on the second pass, and saw that we get about 50% through on the first pass, but only about 10% on the 2nd pass. Before the AOM=60mW, after the first pass=38mW, after the 2nd pass=4mW. Clearly the alignment through the AOM is really sketchy.

We translated the AOM so the beam goes through the center of the crystal while we align things. We see that we only get the first order beam, which is good. We twiddled the 4 adjust screws on the side of the AOM to maximize the power at the curved mirror for the 1st order of the first pass, which was 49.6mW. We then looked at the DC output of the Reference Cavity's Refl. PD, and saw 150mV on the 'scope. The power measured after the polarizing beam splitter and the next wave plate was still 4mW. Adjusting the curved mirror, we got up to 246mV on the 'scope for the Refl. PD, and 5.16mW after the PBS+Waveplate. We adjusted the 4 side screws of the AOM again, and the tip/tilt of the PBS, and got up to 288mV on the 'scope.

Then we looked at the beam that we keep after the 2nd pass through the AOM, and send to the reference cavity, and we find that we are keeping the SECOND order beam after the second pass. This is bad news. Yoichi and I will fix this in the morning. We checked that we were seeing a higher order beam by modulating the Offset of the MC servo board with a triangle wave, and watching the beam move on the camera. If we were chosing the correct beam, there would be no movement because of the symmetry of 2 passes through the AOM.

I took some sweet video of the beam spot moving, which I'll upload later, if I can figure out how to get the movies off my cell phone.
  725   Wed Jul 23 17:19:48 2008 AlbertoConfigurationComputersMegatron connected
We changed the IP address. Ther new one is 131.215.113.95.

Joe, Alberto


Quote:
Joe, Rana, Alberto,

we found out the password for Megatron so we could log in and set a new one so that now it's the same as that for controls.
The IP address is 131.215.113.59.

We had to switch to another LAN ports to actually connect it.
  724   Wed Jul 23 16:31:02 2008 AlbertoConfigurationComputersMegatron connected
Joe, Rana, Alberto,

we found out the password for Megatron so we could log in and set a new one so that now it's the same as that for controls.
The IP address is 131.215.113.59.

We had to switch to another LAN ports to actually connect it.
  723   Wed Jul 23 13:52:26 2008 SharonUpdate MEDM changes
There is a new MEDM screen now when you go from c1ass>top>pem.
Instead of having 12 "mini filters" screens go to 8 outputs (with the wrong correlation impression from the table), we have a 24X8 matrix.
This matrix is there so you could choose which noise signals you want to send to the adaptive code. When you indicate the number of noise channels you are going to use
on the nAUX option on the screen top, you are choosing the channels 1 to nAUX. Channels 15-22 are the seismic and accelerometers we are now using. (you can see the order in Jenne's post 673).
Hope this will make things clearer.
Attachment 1: matrix
  722   Wed Jul 23 12:42:23 2008 EricSummaryCamerasWeekly Summary
I finally got the ezcaPut command working. The camera code can now talk directly to the EPICS channels. However, after repeated calls of the ezcaPut function, the function begins claim to time out, even though it continues to write values to the channel successfully (EPICS is successfully getting the new value for the channel, but failing to reply back to the program in time, I think). It has seg-faulted once as well, so the stability cannot yet be trusted for running long term. For now, however, it works well enough to test a servo in the short term. The current approach simply uses a terminal running ezcaservo with the pitch and yaw offset channels of the ETMX, as well as the channels that the camera code output to. This hasn't actually been tested since we haven't had enough time with the x-arm locked.

Tested various fixed zoom lens on the camera, since the one we were previously using was too heavy for its mount and likely more expensive than necessary. The 16mm lens gets a good picture of the beam and the optic together, though the beam is a little too small in the picture to reliably fit a gaussian to. The 24mm lens zooms too much to see the whole optic, but the beam profile itself is much clearer. The 24mm lens is currently on the camera.

Scanned the PZT voltage of the PMC across its full offset range to gain a plot of voltage vs intensity. I used DTT's triggered time series response system to measure the outputs of the slow PZT voltage and transmission intensity channels, and used the script triangle wave to drive the PZT ramp channel slowly over its full range (I couldn't get DTT to output to the channel). Clear resonances did appear (PMCScanWide.tif), but the number of data points per peak was far too small reliably fit a lorentzian to (PMCScanSinglePeak.tif). When I decreased the scanning range and increased the time in order to collect a large number of points on a few peaks, the resulting data was too messy to fit to a lorentzian (PMCSlowSinglePeak.tif).
Attachment 1: PMCScanSinglePeak.tif
PMCScanSinglePeak.tif
Attachment 2: PMCScanWide.tif
PMCScanWide.tif
Attachment 3: PMCSlowSinglePeak.tif
PMCSlowSinglePeak.tif
  721   Wed Jul 23 10:49:37 2008 MaxUpdateComputer Scripts / ProgramsWeekly Progress Report
This week I installed the magnetometer. The channels seem to be reading correctly. I'm back to working on noise budget and have added the MICH and will soon add the PRC source. The various source-specific scripts still need to be adjusted and the transfer functions remeasured since they do not match in any reasonable manner the SRD Rana put out in the e-log yesterday.
  720   Wed Jul 23 10:47:05 2008 SharonUpdate Weekly update
This week I spent some time with Alex who updated the adaptive code to save the filter's coeffs all the time, stop when I open the loop, and reload the latest coeffs. when I start it again.
The point was to minimize the adaptation rate. Unfortunately, seems it is making some filters go wild, so it is not in use yet.
After taking some more measurements with the adaptive filter running, I have noticed a new peak in the signal around 22-23 Hz. My first assumption was that this is caused due to internal resonance of MC1 (which is driven when the adaptive code is running, and not when it's not). Therefore, I drove MC1 without the adaptive filter looking for the same peak... which wasn't there.
This sent me back to the adaptive code... Seems there is a matrix in the simulink file of the adaptive filter which doesn't have an MEDM screen. I am now working on making this screen. Once I am done with that, and make sure there is correlation between simulink and MEDM, I'll keep on chasing the peak in the code.
  719   Wed Jul 23 01:42:26 2008 ranaConfigurationPSLFSS RFPD: Examined, "repaired", and re-installed
Rob said that there might be something wrong with the FSS RFPD since the loop gain is so low.
Next time we should just use the Jenne laser on it in-situ and compare with our reference.

We had a 24.5 MHz LSC PD which Rob got from Sam. Sam got it from Rai. I gave it to Rai in Livingston
because it seemed suspicious. Seems fine now. This black box PD had a lower overall response than
the goldbox one we already had. The 2001-2005 era diodes which we got from the Canadian Perkin-Elmer
all had high capacitance and so that's not a surprise.

So the goldbox one was not broken totally.

I found that the offset came from a cracked capacitor. C25 was a yellow thru-hole ceramic 0.1 uF.
Its a surface mount board...don't know why this was like this but there's also no reason it should
have cracked unless it was soldered on with too much heat. I replaced it with a 0.47 uF ceramic
surface mount. Also R24 was a 20 Ohm resistor and L3 was not stuffed?? Removed R24 and put a 1 uH
inductor into L3. This is there so that the input to the MAX4107 is AC coupled.

However, the DC signal that Rob saw was actually because of the cracked C25. It had shorted and was
making a 25 mV signal at the input to the MAX4107 which has a gain of 10. This was producing ~165 mVdc
into a 50 Ohm load and so it could have saturated most mixers. The FSS board, however, has an overly
monstrous level 21 (I think) mixer and so this should not have been an issue. Maybe.

I was able to lock with the 24.5 MHz black box PD but it was not too hard to repair the gold box one
so I did. I tuned it so that the notch is truly at 43 MHz (2x the FSS 21.5 MHz modulation) but because
someone has done this using a hacky cap in parallel with the main PD, I am unable to get the resonant
peak to line up at 21.5 MHz. Its at 23 MHz instead. This loses us ~2 dB in signal. Since the frequency
is so low, we can increase the gain in the MAX4107 by another factor of 3 or so in the future.


So the PD is not our problem. Still worth verifying that the cable is good -- its around 10 miles long!!
And loops around in there with a bunch of other cables. We have an electronic phase shifter so this seems
totally misguided.

The other bad problem is that the mode matching is pretty horrible. Something like 1/3 of the carrier
power doesn't go into the cavity.
FSS TODO:
1) Check cable between RFPD and FSS box for quality. Replace with a good short cable.

2) Using a directional coupler, look at the RFPD output in lock on a scope with 50 Ohm term.
   I suspect its a lot of harmonics because we're overmodulating to compensate for the bad
   mode matching.

3) Purchase translation stages for the FSS mode matching lenses. Same model as the PMC lenses.
   Fix the mode matching.

4) Get the shop to build us up some more bases for the RFPDs on the PSL such as we have for the LSC.
   Right now they're on some cheesy Delrin pedestals. Too soft...

5) Dump the beam reflected off the FSS RFPD with a little piece of black glass or a razor dump.
   Anodized aluminum is no good and wiggles too much.

The attached PDF shows photos of the old and new style PDs. One page 3 there's a wire that I soldered on
as a handle so that we can remove the RF can (occasionally people claim that soldering to the lid screws
up the magnetic shielding magic of the lid. use this as a litmus test of their electronics know-how; its
a tin can - not an orgone box). Pages 4 & 5 are the circuit before I soldered, page 6 the cap after I
tried to remove it, page 7 is the circuit after I put in the new cap, and page 8 is the schematic with
the mark up of the changes.
Attachment 1: Untitled.pdf
Untitled.pdf Untitled.pdf Untitled.pdf Untitled.pdf Untitled.pdf Untitled.pdf Untitled.pdf Untitled.pdf
  718   Tue Jul 22 22:25:31 2008 ranaUpdateLSCLooptickle for existing 40m
John and I have adapted the Stefan-Looptickle model of the 40m upgrade to have the parameters of the old one.
(old one = what we have had for the last 4 years).

Its in the /cvs/cds/caltech/iscmodeling directory on the CDS computers but you can also check it out from the
MIT CVS repo; its part of the whole shebang.

It makes the attached theoretical NB. Feel free to modify it.
Attachment 1: nb.png
nb.png
  717   Tue Jul 22 22:11:58 2008 YoichiUpdateLSCX-arm g factor measurement
Alberto, Yoichi

We measured the g factor of the X-arm by slightly shifting the 166MHz sideband frequency:

We first locked the X-arm to TEM00 mode. Then misaligned the ETMX in yaw a little bit until the transmitted power is a half of the normal value.
In this way, we can expect that TEM01 mode will be resonated in the arm if a sideband with a suitable frequency is introduced.
To add such a sideband, we used the 166MHz EOM. According to John's calculation (ELog entry 690), the TEM01 mode of the 166MHz upper sideband is only about 100kHz away from the resonance. So by changing the 166MHz modulation frequency, we should be able to see the 166MHz upper sideband resonating in the X-arm.
We used the 166MHz PD at the AS to find the resonance.
When we modulated the 166MHz RF frequency by +/- 100kHz, we could see spikes in the AS166_I signal.
Then we fine tuned the RF frequency slowly by hand to find the exact resonant frequency. At that time, the X-arm PDH servo was oscillating at ~480Hz.
So the resonance was determined by maximizing this signal in the AS166_I.
The 166MHz signal was originally at 165.977195 MHz. I found the resonance around 165.985MHz. It is surprisingly close to the original modulation frequency (only 7.3kHz away). This number yields the g factor of 0.626 and the transverse mode interval of 0.285*FSR. I used the arm length of 38.5750m in this calculation. Because of the 480Hz oscillation, it was difficult to precisely determine the resonant frequency. We will try this again tomorrow after mitigating the oscillation.
Although the resonance of the 166MHz upper sideband is located at a lower frequency in John's prediction, we found a resonance at a higher frequency.
This can be interpreted as the discrepancy between the actual g-factor and the designed g-factor.

To confirm what we saw was really an arm cavity resonance, we will try to do the same thing with the arm cavities all mis-aligned.
(We expect no signal in this configuration.)

Appendix: the expected signal from AS166 port when the 166MHz upper sideband passes by a resonance of the arm cavity.
Since the carrier is resonating in the cavity and kept there by the PDH feedback using 33MHz sideband, its phase is virtually fixed at the AS166 port. The lower sideband's phase also does not change much because it is off resonance. The upper sideband get a large phase change when approaching to the resonance. This effectively rotates the modulation angle of the 166MHz sidebands, which was orthogonal to the carrier when off resonance (i.e. phase modulation), to create 166MHz amplitude modulation. Because the sideband axis is rotated, the signal should appear both in I and Q phases.
  716   Tue Jul 22 16:50:09 2008 steveMetaphysicsEnvironmentprofessorial clean up of work bench
Atm1: is showing the spiritual satisfaction after work bench clean up by the professor himself.

Atm2: some items are still waiting to be placed back to their location
Attachment 1: ranaclup.png
ranaclup.png
Attachment 2: cleanup2.png
cleanup2.png
  715   Tue Jul 22 13:16:09 2008 John, RobUpdatePSLFSS open loop transfer function

Quote:
With the common gain slider maxed out the unity gain frequency is 58kHz.

The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.

Tomorrow I'll take a closer look at the board.


Should note that the UGF of 58kHz was measured with the test cable (from RFPD to board), so the demod phase was presumably sub-optimal.
  714   Tue Jul 22 13:15:14 2008 robUpdatePSLNote from R. Abbott re: the PMC

Quote:
an email from Rich:
Your PZT is broken.

R


Quelle surprise

Frown
  713   Tue Jul 22 11:55:22 2008 ranaUpdatePSLNote from R. Abbott re: the PMC
an email from Rich:
Your PZT is broken.

R
ELOG V3.1.3-