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ID Date Author Typeup Category Subject
  645   Tue Jul 8 08:16:56 2008 steveUpdatePSLPMC problem
The PMC is unhappy. PMC auto locker is not working.
DC output slider adjust has to be moved from rail to rail before it locks.

MZ is working great.
  646   Tue Jul 8 10:20:10 2008 steveUpdatePEMHEPA turned on
It is specially important to run the PSL-HEPA filters when inside counts is peaking at 30,000 counts

There is a small label at the hepa on/off switch:
enclosure open 100%,
low noise off,
normal 60% of Variac voltage setting on the top of the enclosure

Not running the HEPAs will lower the temp fluctuations from 1.5 to o.5 degree C
at the cost of particle counts from 0 to immidiate room counts.
  647   Tue Jul 8 10:26:30 2008 MashaUpdateAuxiliary lockingsetup updates
Yesterday I changed one of the beam splitters in the Mach Zehnder to one with a more stable mount as to reduce the system's coupling to environmental noise.

With help from John, I worked out how to get the signals from the two channels of the interferometer into the digital system. I put up BNC cables along part of the Y arm to connect the output of the detectors into the digital channels.
  650   Tue Jul 8 21:58:22 2008 albertoUpdateGeneralSecondaty beam aligned to the IFO beam again
Yesterday the alignment of the secondary beam to the IFO was completely lost and today I had to realign all the optics before I was able to match the two spots again. I had to reset the height of the irises and I had also to replace mirror M1 with one with a larger angular motion. Eventually I obtained the beat again. Working on the optics table I inadvertently misaligned the OSA but I didn't make in time to bring it back before the night shift people came. I'll work on that tomorrow morning.
  651   Wed Jul 9 12:42:14 2008 JohnUpdateLockingHand off to RF CARM
Rob, Yoichi, John

Last night we were able to reduce the CARM offset to around 80. This was achieved by increasing the DARM gain and
switching to AS_I when AS_Q went bad. This is probably a temporary solution, we will probably switch to DC readout
for DARM as we bring the arms on resonance.

Having reduced the arm offset enough to get us into the linear region of the RF_CARM signal (POX_I) we worked on
analogue conditioning of this signal to allow us to hand over. Lock was maintained for over 20 minutes as we did
this work.

We were able to partially switch over both the frequency and length paths to this new signal before losing lock.
  655   Thu Jul 10 14:59:01 2008 robUpdateLockingRF common mode at zero offset
rob, john, yoichi

Last night we succeeded in reducing the CARM offset to zero.

We handed off control of the common mode servo from PO-DC to POX-I.

We pushed the common mode servo bandwidth to ~19kHz. Without the boosts, it had ~80 degs of phase margin. Didn't measure it after engaging the boosts (Boost + 1 superboost). Trying to engage the second superboost stage broke the lock.

The process is fully scripted, and the script worked all the way through several times.

The DARM ugf was ~200Hz. The RSE peak could clearly be seen. No optical spring, as expected (we're locking in anti-spring mode).

Engaging test mass de-whitening filters did not work (broke the lock).

I'm attaching a lock control sequence diagram and a trend of the arm power during a scripted up-sequence. I think the script can be sped up significantly (especially the long ramp period).

Up next:

Calibrated DARM spectrum
Noise hunting (start with dewhites)
DC - Readout
Lock to the springy side.
  656   Thu Jul 10 19:12:07 2008 AlbertoUpdateGeneralabs cavity length measurement experiment
Yesterday morning, when I started, I found the IFO beam on a different position and the beam spot at the AS port looked very deformed. The overlapping with the secondary beam was not good enough to observe the beats anymore. Restoring the alignments of the interferometers did not work because, as John found out later, some of the photodiodes had offsets and gain which made the restore script ineffective. After resetting the parameters, we had to align every mirror of the interferometers and save the configuration twice. The second times was because on the first time the alignment had been done with the illuminators on. To avoid that in the future, John wrote an alarm to warn about the status of the lights.

After that we fixed the IFO beam, I had to realign the optics in the table to match the secondary beam to the IFO beam. I got the two beam overlapping and, even though the NPRO spot looked distorted, I could observe again some signal of the beat. To do that it was also necessary to have all the interferometer mirrors aligned so that we had more power from the ifo beam although it also made the spot flash. Ideally, to avoid the flashing (which we would also impede the PLL to work) we should work with the interferometer locked. Since that doesn't seem actually possible, we should just keep one of the ITM aligned and improve the beam matching so that we can observe the beats even with less power.

Today I spent the day trying to improve the alignement of the optics to observe the beats with only the ITM aligned, resetting the alignment of both beams with the ireses, with the Farady and all the rest. It was a rather long and tiring process but I think I'm close to the target and maybe tomorrow.
  659   Fri Jul 11 09:29:02 2008 steveUpdatePSLthe PMC still hangs up
Morning alarms:

PMC high voltage is railing, it's auto locker is frosen
I have to move DC Output Adjust slider by hand and it locks immediately

PSL_ISS is saturating. Saturation goes away when PMC is locked.

Laser chiller water is overflowing again: removed 450 cc water
  661   Fri Jul 11 23:55:25 2008 alanUpdateLockingRF common mode at zero offset

Quote:
rob, john, yoichi

Last night we succeeded in reducing the CARM offset to zero.



Congratulations! Well done! I look forward to hearing the details and further progress!
  662   Sat Jul 12 23:28:31 2008 ranaUpdatePSLPMC needs help
As everyone has noticed recently, the PMC seems to have a PZT problem. It often zooms
of to one of its rails after locking as if the PZT range has decreased dramatically.

WE should check this on Monday by disabling the FSS and applying a slow triangle wave to
the NPRO frequency. The PMC will track this frequency change and this will allow us to
diagnose its problems.

If it has real problems, I have a spare in W. Bridge which we can swap in temporarily.

The attached plot shows 3 years of trend; looks like it went bad in summer of last year.

This also seems to be the cause of our ISS saturation problems: lowering the gain of the PMC
even slightly increased the intensity noise enough to cause saturation. Increasing the gain
even slightly increased the intensity noise enough to cause saturation due to PMC servo oscillation.
  668   Mon Jul 14 19:15:43 2008 AlbertoUpdateGeneralabs cavity length measurement experiment
Lately I've been dealing with the alignment of the interferometer to have a good beam spot at the AS port. Today the alignment script kept failing because of computer problems (failure of the frame builder) and also because the IFO was probably too far from the range where the automatic alignment works.

An other problem I keep having with the alignment of the optics on the AP table is with multiple reflection beams of the NPRO beam at the Farady.
Although I believe that now the two beams are quite well aligned, I don't see any reflection of the secondary beam from the IFO anymore.

It's like the more I try to improve the alignment, the worse I get from the beam matching. I'll keep working on this.
  669   Mon Jul 14 21:34:10 2008 AlbertoUpdateGeneralabs cavity length measurement experiment

Quote:
Lately I've been dealing with the alignment of the interferometer to have a good beam spot at the AS port. Today the alignment script kept failing because of computer problems (failure of the frame builder) and also because the IFO was probably too far from the range where the automatic alignment works.

An other problem I keep having with the alignment of the optics on the AP table is with multiple reflection beams of the NPRO beam at the Farady.
Although I believe that now the two beams are quite well aligned, I don't see any reflection of the secondary beam from the IFO anymore.

It's like the more I try to improve the alignment, the worse I get from the beam matching. I'll keep working on this.


Realigning the OSA I also had to move a little bit the mirror that reflects the IFO beam of at the AS port in order to raise the beam height. This had the effect of changing the position of the AS spot on the camera and on the monitors.

Tonight with John, we made sure that the AS beam was still aligned to the PD.
  670   Tue Jul 15 09:47:09 2008 steveUpdatePEMlab temps and particles
All air condtion units were serviced last Friday.
AC filters are trying to control our particle counts but they have no capacity to match bad Pasadena conditions.
IFO room filters at CES were really clean.
Air make up filters inside and outside were dirty.
They showed the construction effect.
Control room and clean assembly units needed all filters replaced.

Note: the PSL-FSS_RCTEMP droped o.1C when enclouser HEPAs were turned back on
The RC temp controller should be better than that!
  672   Tue Jul 15 10:24:57 2008 steveUpdatePSLPMC temp & pzt voltage
The PMC pzt HV was happy with no HEPA temp stability.
Can we thermally insulate the pmc ?
  674   Tue Jul 15 12:23:22 2008 JenneUpdateGeneralMC2 Watchdog tripped
Alberto, Jenne

Mode Cleaner was unlocked. We checked, and found that MC2's watchdog was tripped. It didn't look like anything bad was going on, so we turned the optic back on, and tried to relock the MC. It looks like the Mode Cleaner is now locked, but the lock bit on the LockMC screen is still red. I don't know what's up.
  677   Wed Jul 16 09:27:17 2008 steveUpdateALARMPSL-FSS_RMTEMP alarm is false
Morning alarm sound is good for people who does not drink coffee.
Our 40m alarm is on every morning.
Those whom are not here in the morning thinks that this beeping sound is inspirational.
Would someone change this sound into less punishing form, like mockingbird chirp....

The C1PSL_SETTINGS.adl (40mm PSL Settings ) indicating that
C1:PSL-FSS_INOFFSET (Input Offset Adjust ) should be 0.3 +-0.05 V (red warning tag )

Alarm Handler: 40M pointing to yellow grade warning of PSL-FSS_RMTEM
This is a false alarm.

Two years trend of these channels are here:
  679   Wed Jul 16 11:00:15 2008 MashaUpdateAuxiliary lockingimproving ADC input for the mach zehnder setup and completely unrelated happenings
For most of last week, the SURFs + Jenne were helping Mike and Ken with "stray light control for
Enhanced LIGO", i.e. cleaning and baking many many baffles which will catch scattered light in the
interferometer.

Otherwise, the two channels of the Mach Zehnder which will be used to measure fibre noise were
balanced, which should reduce the effect of laser amplitude noise in phase noise detection. I have
set up two digital channels to collect time series data from the two photodiodes and took some
preliminary noise measurements. I will be using Matlab to combine the signals as to directly measure
the phase noise, and I wrote some Matlab code to speed up this process: loading the files,
manipulating time series data, and converting into frequency domain. Currently I am building a
filter that will attenuate the signal at frequencies below 1Hz and amplify at higher frequencies in
order to whiten the spectra and reduce ADC noise.
  680   Wed Jul 16 11:26:47 2008 Max JonesUpdate This Week
Baffles.

I got a battery for the magnetometer today which is slightly too large (~2 mm) in one dimension. Not sure what I'm going to do.

I'm attempting to calibrate the magnetometer but I'm having a hard time calibrating the axis that I cannot simply put through a coil parallel to the coils length. I have attempted to use the end fields of the solenoid but the measurements from the magnetometer are significantly different from the theoretical calculations.

I would appreciate suggestions. - Max.
  683   Wed Jul 16 16:59:07 2008 AlbertoUpdateGeneralAligment
I think the two beams are aligned again - they both pass the Faraday, they match at the irises and all along the optical path on the AP table. Although the NPRO beam does not show up at the AS port.
  685   Wed Jul 16 17:51:58 2008 MashaUpdateAuxiliary lockinglong measurement
I'm taking a measurement on the SR785 spectrum analyzer at low frequencies, so I'm going to leave it by the symmetric port table for a while. Please don't move it!
  686   Wed Jul 16 22:29:05 2008 MashaUpdateAuxiliary lockinglong measurement

Quote:
I'm taking a measurement on the SR785 spectrum analyzer at low frequencies, so I'm going to leave it by the symmetric port table for a while. Please don't move it!


all done thanks.
  688   Thu Jul 17 08:30:15 2008 steveUpdatePSLPMC relocked manually
The PMC pzt HV and the servo gain adj. are railing at max this morning

Why is it on the decreasing side of FSS_RTTEMP slope?
  689   Thu Jul 17 12:15:21 2008 EricUpdatePSLSwept PMC PZT voltage range
I unlocked the PMC and swept over C1:PSL-PMC_RAMP's full range a couple of times this morning.  The PMC should now be relocked and returned 
to normal.
  691   Thu Jul 17 16:39:58 2008 Max JonesUpdateDAQMagnetometer Installed
Today I installed the magnetometer near the beam splitter chamber. It is located on the BSC chamber at head height on the inner part of the interferometer (meaning I had to crawl under the arms to install it). I don't think I disturbed anything during installation but I think that's it's probably prudent to tell everyone that I was back there just in case. I plan to run 3 BNC cables (one for each axis) from the magnetometer to the DAQ input either tonight or tomorrow. Suggestions are appreciated. - Max.
  692   Thu Jul 17 20:13:34 2008 YoichiUpdatePSLPMC alignment/mode matching effort
I'm working to improve the mode matching of PMC.
Because I noticed that the beam was hitting the aperture of the EOM for PMC, I moved the EOM a little bit to maximize the transmission.
This did not change the alignment to the reference cavity but changed the alignment of the PMC a lot.
So I adjusted it back.
The alignment of the PMC can be easily optimized but the Hermite 02 mode still remains. This means the mode matching is bad.
Moving the lenses by a small amount (a few mm) did not change the height of 02 mode.
I'm planning to move the lenses by a large amount tomorrow. But it will destroy the alignment to the PMC.
So I installed two irises in the beam path after the lenses to remember the alignment roughly.
Right now the PMC transmission is slightly worse than before because the lens positions are not good.
  694   Fri Jul 18 16:57:37 2008 JenneUpdateIOOCalibrated MC_F
I have calibrated MC_F. The conversion factor is 137.49 MHz/count.

The calibration data taken is attached, along with a calibrated power spectrum.

On the data plot, the x axis is volts from the C1:IOO-MC_FAST_MON channel, with the calibration between FAST_MON and MC_F = -788.18 volts/count.
The linear term of the fit line = -0.085MHz/volt. Error bars are +/- 1 in the last digit of what the spectrum analyzer gave me for frequency (+/- 0.01MHz).

The net conversion factor is then (-788.18)*(-0.085)*(2) = 137.49 MHz/count. The factor of 2 is because the light passes through the AOM twice.

On the power spectrum,
REF0 and REF1 = MC unlocked, HEPAs on, MC Refl gain = 22
REF2 and REF3 = MC locked, HEPAs on, MC Refl gain = 22
REF4 and REF5 = MC locked, HEPAs on, MC Refl gain = 19
REF6 and REF7 = MC locked, HEPAs off, MC Refl gain = 19
  695   Fri Jul 18 17:06:20 2008 JenneUpdateComputersComputers down for most of the day, but back up now
[Sharon, Alex, Rob, Alberto, Jenne]

Sharon and I have been having trouble with the C1ASS computer the past couple of days. She has been corresponding with Alex, who has been rebooting the computers for us. At some point this afternoon, as a result of this work, or other stuff (I'm not totally sure which) about half of the computers' status lights on the MEDM screen were red. Alberto and Sharon spoke to Alex, who then fixed all of them except C1ASC. Alberto and I couldn't telnet into C1ASC to follow the restart procedures on the Wiki, so Rob helped us hook up a monitor and keyboard to the computer and restart it the old fashioned way.

It seems like C1ASC has some confusion as to what its IP address is, or some other computer is now using C1ASC's IP address.

As of now, all the computers are back up.
  696   Fri Jul 18 17:12:35 2008 JenneUpdateIOOChecking out the MC Servo Board
[Jenne, Max]

One of the things that Rana thinks that might be causing my MC_F calibration to be off is that the MC Servo Board's filters don't match those on the schematics. Max and I pulled the MC servo board today to check resistor and capacitor values. Alberto needed the Mode Cleaner, so we put the board back before finishing checking values. We will probably pull the board again next week to finish checking the values.

I haven't checked to ensure that the MC still locks, because Yoichi is doing stuff on the PSL table, but I didn't change anything on the board, and hooked all the cables back where they were, so hopefully it's all okay.
  697   Fri Jul 18 19:15:15 2008 JenneUpdateIOOChecking out the MC Servo Board

Quote:
[Jenne, Max]

I haven't checked to ensure that the MC still locks, because Yoichi is doing stuff on the PSL table, but I didn't change anything on the board, and hooked all the cables back where they were, so hopefully it's all okay.


I put the PMC back and the MC now locks.
  698   Fri Jul 18 19:30:20 2008 MashaUpdateAuxiliary lockingmoving from 40m
I will be working in the basement of Bridge probably starting next week; I moved the NPRO laser and some of the optics from my mach zehnder setup on the SP table to Bridge. Thanks for your help!
  699   Fri Jul 18 19:41:09 2008 YoichiUpdatePSLPMC PZT investigation
I measured the HV coming to the PMC PZT by plugging it off from the PZT and hooking it up to a DVM.
The reading of DVM is pretty much consistent with the reading on EPICS. I got 287V on the DVM when the EPICS says 290V.

Then I used a T to monitor the same voltage while it is connected to the PZT. I attached a plot of the actual voltage measured by the DVM vs the EPICS reading.
It shows a hysteresis.
Also the actual voltage drops by more than a half when the PZT is connected. The output impedance of the HV amp is 64k (according to the schematic). If I believe this number, the impedance of the PZT should also be 64k. The current flowing the PZT is 1.6mA at 200V EPICS reading.
The impedance of the PZT directly measured by the DVM is 1.5M ohm, which is significantly different from the value expected above. I will check the actual output impedance of the HV amp later.
The capacitance of the PZT measured by the DVM is 300nF. I don't know if I can believe the DVM's ability to measure C.

I noticed that when a high voltage is applied, the actual voltage across the PZT shows a decay.
The second plot shows the step response of the actual voltage.
The voltage coming to the PZT was T-ed and reduced by a factor of 30 using a high impedance voltage divider to be recorded by an ADC.
The PMCTRANSPD channel is temporarily used to monitor this signal.
After the voltage applied to the PZT was increased abruptly (to ~230V), the actual voltage starts to exponentially decrease.
When the HV was reduced to ~30V, the actual voltage goes up. This behavior explains the weird exponential motion of the PZT feedback signal when the PMC is locked.
The cause of the actual voltage drop is not understood yet.
From the above measurements, we can almost certainly conclude that the problem of the PMC is in the PZT, not in the HV amp nor the read back.
  701   Fri Jul 18 23:24:24 2008 robUpdatePSLPMC PZT investigation

Quote:
I measured the HV coming to the PMC PZT by plugging it off from the PZT and hooking it up to a DVM.
The reading of DVM is pretty much consistent with the reading on EPICS. I got 287V on the DVM when the EPICS says 290V.

Then I used a T to monitor the same voltage while it is connected to the PZT. I attached a plot of the actual voltage measured by the DVM vs the EPICS reading.
It shows a hysteresis.
Also the actual voltage drops by more than a half when the PZT is connected. The output impedance of the HV amp is 64k (according to the schematic). If I believe this number, the impedance of the PZT should also be 64k. The current flowing the PZT is 1.6mA at 200V EPICS reading.
The impedance of the PZT directly measured by the DVM is 1.5M ohm, which is significantly different from the value expected above. I will check the actual output impedance of the HV amp later.
The capacitance of the PZT measured by the DVM is 300nF. I don't know if I can believe the DVM's ability to measure C.

I noticed that when a high voltage is applied, the actual voltage across the PZT shows a decay.
The second plot shows the step response of the actual voltage.
The voltage coming to the PZT was T-ed and reduced by a factor of 30 using a high impedance voltage divider to be recorded by an ADC.
The PMCTRANSPD channel is temporarily used to monitor this signal.
After the voltage applied to the PZT was increased abruptly (to ~230V), the actual voltage starts to exponentially decrease.
When the HV was reduced to ~30V, the actual voltage goes up. This behavior explains the weird exponential motion of the PZT feedback signal when the PMC is locked.
The cause of the actual voltage drop is not understood yet.
From the above measurements, we can almost certainly conclude that the problem of the PMC is in the PZT, not in the HV amp nor the read back.


I'd believe the Fluke's measurement of capacitance. Here's some info from PK about the PZT:


Quote:

But the PMC ones were something like
0.750 in. thick x 0.287 in. thick. 2 microns per 200 V displacement,
resonant frequency greater than 65 kHz. Typical capacitance is around 0.66
uF.


If the PZT capacitance has dropped by a factor of two, that seems like a bad sign. I don't know what to expect for a resistance value of the PZT, but I wouldn't be surprised if it's non-Ohmic. The 64k is the series resistor after the PA85, not the modeled resistance of the PZT itself.
  702   Sat Jul 19 19:39:44 2008 robUpdatePSLPMC PZT investigation

Quote:

Quote:
The 64k is the series resistor after the PA85, not the modeled resistance of the PZT itself.

Yes. What I meant was that because the measured voltage across the PZT was a half of the open voltage of the HV amp, the DC impedance of the PZT is expected to be similar to the output impedance of the HV amp. Of course, I don't think the DC impedance of a normal PZT should be such low.
I'm puzzled by the discrepancy between this expected DC impedance and the directly measured impedance by the Fluke DVM (1.5M Ohm).
One possibility is that the PZT leaks current only when a high voltage is applied.
  704   Mon Jul 21 09:52:05 2008 SharonUpdate Adaptive code changes
Thanks to Alex, we now save the coefficients of the adaptive filter every cycle. When we choose ENABLE: OFF on the MEDM screen, suppressing the signal to the MC1, we stop and save the last coefficients. When enabling it again, it starts from the last coefficients saved. I will take some measurements today to check how this contributes to the adaptation rate. If you change the number of taps or the number of AUX channels, the coefficients are again set to zero.
  705   Mon Jul 21 10:00:42 2008 steveUpdatePEMifo room temp
Five years of temp trend with 5 C fluctuation. The campus chilled water supply was upgraded ~ 1 year ago.

I requested our thermostats to be calibrated.
  706   Mon Jul 21 11:54:00 2008 JenneUpdateGeneralMC Servo Board
I pulled the MC Servo Board again, to check the components that are on the board, and compare them with the schematics. The filters that I'm interested in on the Fast Path haven't been changed. The high pass filters on the Fast Path have been changed.
Component      Schematic      Actual
---------      ---------      ------
C140           10u            open
C144           10u            open
C149           open           a gray Cap.  value unknown
C141           10u            open
C145           10u            open
R97            1.58K          0
R99            open           1130
R103           open           1130
R100           open           0
R104           100            1130
R98            1.58K          open
R109           367            365

Board is back in, and MC locks.
  709   Mon Jul 21 19:48:57 2008 SharonUpdate how tp restart C1ASS
How to restart C1ASS:

1. reboot
2. as root: caltech/target/c1ass:> ./startass
3. no need for root: burtgooey

that's it...
  711   Tue Jul 22 03:03:22 2008 John, RobUpdatePSLFSS open loop transfer function
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.
  712   Tue Jul 22 09:24:17 2008 steveUpdatePSLlaser power
Laser power reality of 120 days
  713   Tue Jul 22 11:55:22 2008 ranaUpdatePSLNote from R. Abbott re: the PMC
an email from Rich:
Your PZT is broken.

R
  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
  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.
  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.
  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.
  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.
  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.
  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.
  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.
  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.
  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.
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