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  637   Mon Jul 7 11:22:02 2008 AlbertoUpdateGeneralBeats of the two lasers in the absolute length measurement observed
I didn't post a screenshot from the RF SA because I had troubles with the interface with the computer (unfortunately the network SA cannot export the data either).

There is problem with the PLL circuit. The signal, beside the beat, also contains peaks at 33, 66 and 99 MHz, so we should think about filtering those out.


Quote:
Great! Conguraturation! I wish if I could see it! It's nice if you can put the photo or anything of the RF spectrum analyzer.

Next step:
o You can try to maximize the beat amplitude by the tuning of the Injection steering mirrors.

o At the south end of the SP table, I prepared a frequency mixer. You can put the beat signal into the RF input, and an oscillator (which you can bring from somewhere) to the LO input in order to obtain the error signal of the PLL. Put the IF output of the mixer in a SR560, and please try to lock it by a simple 6db/oct (1st order) LPF of the SR560. For the actuator you can use the fast-pzt input of the NPRO.


Quote:
Then I explored the range of temperature of the NPRO from 35deg (C) to 51.2807deg and at that point I could observe a peak corresponding to the beat at about 10MHz on the network analyzer.
  638   Mon Jul 7 13:06:38 2008 KojiUpdateGeneralBeats of the two lasers in the absolute length measurement observed
One may need an RF filter after the mixer. I expect the SR560 does work for this purpose.
If it does not, a passive LPF can be used.


Quote:
I didn't post a screenshot from the RF SA because I had troubles with the interface with the computer (unfortunately the network SA cannot export the data).

There's is problem with the PLL circuit. The signal, beside the beat, also contains peaks at 33, 66 and 99 MHz, so we should think about filtering those out, correct?
  643   Mon Jul 7 19:15:38 2008 AlbertoUpdateGeneralOptics alignement on the ABS length experiment
Today I started setting up the PLL instruments to lock the frequency of the NPRO beam to the IFO beam. with no need of a new alignment after the weekend I was able to see the beat again, although this time I found at a different temperature of the NPRO laser of about 54 degrees (vs 51 of the last time).
I've got the Marconi as local oscillator (LO), the mixer Koji suggetsed, the SR560 and a 5 MHz low pass filter to cut the 33, 66 and 99 MHz present in the output signal from the PD. The filter worked well and I was able to single out only the beat resonance from the power spectrum.
In the attempt to enhance the amplitude of the beat, as Koji suggested, I tried to work on the alignment of the steering mirrors. While I was doing that, for some reason the pre-modecleaner lost the alignment and I had to ask John to help me lock it again. during the process I lost the old alignment but at the end I got a new one, apparently (from the camera) even better than the other. Although after that the beats were gone. Actually after the lock-in of the PMC the IFO beam didn't look as good as before, so it might be also for that reason.

I'll try again tomorrow, after that probably tonight Rob is going to reset the alignments of the interferometers.
  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.
  653   Wed Jul 9 17:58:19 2008 JohnSummaryGeneralIlluminator alarms
This morning some time was wasted on alignment due to the illuminators.

I added the illuminators to the alarm handler. They will give a RED alarm whenever
they are turned on. You can find the alarms in 40M->Misc->Illuminators.

To do this I edited the Illuminators.db file and restarted c1aux by telneting and typing Ctl-X.
I then added the groups and channels to 40M.alhConfig.
  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.
  664   Sun Jul 13 22:39:16 2008 JohnSummaryGeneralEdited medm screens
I've edited the FSS and PMC screens so that red boxes are shown around the appropriate slider if a gain or offset is not within the limits defined in C1PSL_SETTINGS_SET.adl

With the current setting of 0 V the FSS input offset is red. According to the settings screen the nominal value is 0.3 +/- 0.050. Are there any objections to editing the nominal value?

I changed the LockMC screen so that red boxes are not shown when the up/down scripts are not running; when they are active you should see a green box.
  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.
  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.
  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.
  687   Thu Jul 17 00:59:18 2008 JenneSummaryGeneralFunny signal coming out of VCO
While working on calibrating the MC_F signal, Rana and I noticed a funny signal coming out of the VCO. We expect the output to be a nice sine wave at about 80MHz. What we see is the 80MHz signal plus higher harmonics. The reason behind the craziness is to be determined. For now, here's what the signal looks like, in both time and frequency domains.

The first plot is a regular screen capture of a 'scope. The second is the output of the SR spectrum analyzer, as seen on a 'scope screen. The leftmost tall peak is the 80MHz peak, and the others are the harmonics.
Attachment 1: VCOout_time.PNG
VCOout_time.PNG
Attachment 2: VCOout_freq.PNG
VCOout_freq.PNG
  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.
  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.
  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.
  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
  774   Thu Jul 31 10:24:32 2008 KojiUpdateGeneralIFO status
Last night I used the Y-arm for the abs length measurement. The Yarm was aligned by the script.
I left the ifo with the Yarm locked as it is the only meaningful configuration so far.
  776   Thu Jul 31 11:19:30 2008 KojiUpdateGeneralAbs. Len. Meas. ~ Resonance search trial
Last night, I tried to find the resonance of Yarm by sweeping the frequency of the injection beam.

A strong beat was present at LT_NPRO=48.7856[C_deg], the power coupling of the injection beam was estimated to be 35%. 
(Vmax_beat = 1.060[V], Vmin_beat = 0.460[V], Vno_inject = 0.664[V])

The Yarm was locked and the alignment script was executed. The PLL between the PSL beam and the injection beam was 
somehow locked.

I tried to scan the freq offset (f_PLL) at around 3.88MHz first, then at around 15.52MHz. They are supporsed to be the 
first and fourth FSR of the Yarm cavity. The Yarm transmitted power (DC) was observed to find the resonance of the 
injection beam. It would have been better to use the RF power, but so far I didnot have the RF PD prepared at the end 
transmission. I just used the DC power.

I think I saw the increase of the transmitted power by 10%, at f_PLL = 15.517 +/- 0.003 [MHz]. This corresponds to the 
arm cavity length of 38.640 +/- 0.007 [m]. The previous measurement was not so bad!

Y-arm length
e-log             length [m]
-----------------------
556(2008-Jun-24)  38.70    +/- 0.08    Cavity swinging measurement
556(2008-Jun-24)  38.67    +/- 0.03    tape & photo
This              38.640   +/- 0.007

However, I had difficulties to have more precise measurement mainly because of two reasons:
o The PLL servo is too naive, and the freqency stability of the inj beam is not enough.
  The injected beam should have the linewidth (=freq stability) narrower than the cavity linewidth.

o The PLL servo may experience change of the transfer function at around the resonance. The PLL works the other 
frequencies. However, close to the resonance, it starts to be unstable.

So the next stuffs we should do is 
o Build the PLL just using the incident beams to the ifo, not by the reflected beams.
o Build sophisticated servo to have better frequency stability.
o RF PD at the transmission.

Left the lab with Yarm locked, flipper down, shutter for the NPRO closed.
  782   Sat Aug 2 12:53:43 2008 KojiUpdateGeneralAbs. Len. Meas. ~ New PLL at the PSL table
Report of the work last night:
The new heterodyne interferometer on the PSL table was built.
The length of the Yarm cavity was measured with better precision.

-------------
Yarm is locked. The injection beam was aligned. The beat was there at around LT=48.9 [C_deg] of the NPRO.

The new PLL setup on the PSL table has been built. The two beams from the MC incident beam and the injection beam are
mode-matched with lenses. I measured the Rayleigh ranges of the beams by a sensor card and my eyes, and then placed
appropriate lenses so that they can have 5~6 [m] Rayleigh range. They looks a bit too thick but just ok for an inch
optics. The new PLL setup shows ~70% intensity modulation which is enormous. The servo is still SR560-based so far.

Now the PLL has no singular frequency within its range. I could sweep the 4th FSR of the cavity with 500Hz interval. I
was still observing at the transmitted DC.

At each freqency from 15.51MHz to 15.52MHz, a timeseries data of the Yarm transmitted was recorded at sampling of 32Hz for 10
seconds. The figure shows the averaged values of the transmitted DC with errors. An increase of the transmitted power by
3-4% was found. If we consider the resonance is at f_PLL = 15.515 +/- 0.0005 [MHz], this indicates the
arm cavity length of 38.6455 +/- 0.0012 [m].
Y-arm length
e-log    length [m]
-----------------------------
556      38.70   +/- 0.08   Cavity swinging measurement
556      38.67   +/- 0.03   tape & photo
776      38.640  +/- 0.007  Beam injection, poor PLL, Transmitted DC
this     38.6455 +/- 0.0012 Beam injection, independent PLL, Transmitted DC
-----------------------------

NEXT STEPS:
o RF detection at the transmitted
o Better PLL: PLL stability (in-loop / out-of-loop)
o Measurement for the 1st~3rd FSR
o Reproducibility of the measurement
o Higher order mode search
o Check the acuuracy and presicion of the Marconi
Attachment 1: yarm_dc.png
yarm_dc.png
  783   Sat Aug 2 13:07:23 2008 KojiConfigurationGeneralThe AP table cleaned
During the construction of the independent PLL I cleaned up some of the unused optics from the AP table. Essentially this should be harmless as they had already been isolated from any beam. They were related to Go's squeezing project and Osamu's MC Transmitted beam measurement.

Nevertherless, if you find any problem on the signals at the AP table (when the ifo returns), I am the person to be blamed.

I am going to update the table layout later next week.
  787   Mon Aug 4 00:37:58 2008 KojiUpdateGeneralAbs. Len. Meas. ~ RF PD at the Y end / Manual frequency scan
Work log on August 2nd

o Just remind you:
The idea of the absolute length measurement was to detect an RF beat between the injection beam and the PSL beam by resonating both of the beams to the cavity at the same time, but on different londitudinal modes. From the frequency separation between the two beams, we get the FSR of the cavity. In order to have an injection beam with stable frequency separation, a heterodne interferometer was built at the PSL table, and the PLL servo is used to control and stabilize the frequency of the inj. beam.

----------

o An RF PD (Tholab PDA255) and a steering mirror were placed at the Yarm END. Fortunately, I found that an unused BS was already in the optical path. There was a beam block which dump the reflection of the BS and some stray lights of the OPLEV. I moved the beam block to make the BS reflection available, as well as to block the OPLEV stray light still (Photo1). In order to have the RF signal from the PD, a long BNC cable was laid along the Yarm. I did't know any better idea than this. Don't blame me.

o To have an intuitive interpretation of the beat frequency, the injection beam was set to be at higher frequency than the PSL beam. How did I confirm this? When the crystal temp (LT) of the NPRO was tuned to be higher, the beat frequency got lower.

o Frequency of the PLL was manually swept at around 15.51MHz where the 4th FSR was expected to be found. I could see strong RF peak at that frequency! When I tuned the PLL frequency, the peak height changes dramatically! Too cool!

o The amplitude of the RF peak was measured by an RF spectrum analyzer. I did all of this scan by my hands and eyes. The center frequency of the 4th FSR was 15.5149MHz. From the eye I would say the error is +/-150Hz. It is OK so far although I am not sure statistically this is correct or not. This corresponds to the length of 38.64575 +/- 0.00037 [m].

o All of the past measurements are fairly consistent.
Y-arm length
e-log              length [m]           Measurement Conditions
----------------------------------------------------------------------------------------
 556(2008-Jun-24)  38.67    +/- 0.03    Cavity swinging measurement
 776(2008-Jul-31)  38.640   +/- 0.007   Beam injection, poor PLL, Transmitted DC
 782(2008-Aug-02)  38.6455  +/- 0.0012  Beam injection, independent PLL, Transmitted DC
this(2008-Aug-04)  38.64575 +/- 0.00037 Beam injection, independent PLL, Transmitted RF
----------------------------------------------------------------------------------------
Attachment 1: YEND_LAYOUT.png
YEND_LAYOUT.png
Attachment 2: 4th_FSR1.png
4th_FSR1.png
Attachment 3: 4th_FSR2.png
4th_FSR2.png
  788   Mon Aug 4 00:56:07 2008 KojiHowToGeneralAbs. Len. Meas. ~ Auto freq scanner with GPIB
Work log on August 3rd - Part1

o Yesterday I was too much tired of changing the RF frequency, reading peaks on the RF spectrum, and writing the values. Rana saw me and thought I was such poor that he gave me an USB-GPIB adapter.

o I dig into the internet for the manuals of the adapter, IFR2023A(Marconi), and HP8591E(RF spectrum analyzer) in order to learn how to use them.

o I had LabVIEW installed on my laptop. Finally I understand how to use that adapter (by Agilent) with LabVIEW. I made a small program to scan the frequency of IFR2023A, and read the peak values from HP8591E. It is unfortunate that there is no LabVIEW in the 40m lab. I think I can make an independent executable which does not need the LabVIEW itself. Give me some time to understand how to do it.
Attachment 1: freq_scan.png
freq_scan.png
  789   Mon Aug 4 05:23:57 2008 KojiUpdateGeneralAbs. Len. Meas. ~ Measurement for Y-arm completed
Finally, I have completed the abs length and g-factor measurements for Y-arm.
>>>GO FOR THE VENT<<<

I will report the results later.

Some notes on the status:
o Y-arm was aligned at the end of the experiment by the script. The values were saved.

o At the AP table, the injection beam and the flipper were left aligned so that the inj. beam can be used as a reference of the SRM and the ITMs. But the shutter of the NPRO was closed.

o The experiment setup was mostly left at the side of the AP table. I tried not to disturb the walk as much as possible.

o The long cable from the Y-end was wound and placed at the Y-end. The knife-edge was left on the Y-end bench. It is not disturbing any beam.
  793   Mon Aug 4 21:48:24 2008 KojiUpdateGeneralAbs. Len. Meas. ~ Scan for TEM00/01/10
Work log on August 3rd - Part2

o I tried to measure the frequency of the FSRs using TEM00 resonances. Also search of TEM01/TEM10 resonances were tried.

-----------
Measurement for TEM00

o The frequency of the injection beam was scanned from 2MHz to 20MHz using the LabVIEW panel with GPIB. The 1st figure attached below is the result of the scan. Equispaced peaks were found as expected. The interval of the peaks are about 3.89MHz. Each peaks were measured with freq intervals of down to 50Hz. I will analyze the center frequency of the peaks precisely later in order to have a final result.

Measurements for TEM01/TEM10

o The beam injection technique is thought to be useful for measureing the frequency of the higher-order resonances. In order to measure the higher-order resonances the modifications of the experimental setup were applied as below.

1) For TEM10 (the beam like "OO" shape), a razor blade which blocked the horizontal half of the transmitted beam was placed. We needed to disturb half of the beam because the beat between the PSL TEM00 and the injection TEM01 cancels if the PD receives all of the light.

2) The injection beam is slightly misaligned in the horizontal direction in order to enhance the coupling of the injection beam to the cavity TEM01 mode.

3) For TEM01 (the beam like "8" shape), a razor blade cutting the vertical half and the misalignment of the inj beam in the vertical direction are applied.

o The frequency of the injection beam was scaned from 1st FSR of TEM00 in the upward direction. The alignment of the arm cavity was left untouched during the measurement. As shown in the 2nd figure attached below, the resonances were found about 1.19MHz away from the TEM00, but they are separated by about 19kHz(!). This could be split of the degenerated modes which corresponds to the difference of the mirror curvature in two directions! This difference is something like 56 m and 57 m. Can you believe this?

(To be continued to the next entry)
Attachment 1: TEM00.png
TEM00.png
Attachment 2: TEM01.png
TEM01.png
Attachment 3: knife_edge.png
knife_edge.png
  794   Mon Aug 4 22:31:10 2008 KojiUpdateGeneralAbs. Len. Meas. ~ Simple Test for TEM01/10 split
Work log on August 3rd - Part3

Question:
o The TEM01 and TEM10 of the Yarm were found to split with 19kHz separation. Is this true?
o In which direction the eigenmodes are?

Thought:
o The separation of 19kHz is a kind of too big because the cavity bandwidth is several kHz.
o This means that "TEM01 and TEM10 can not resonate at the same time (by the PSL beam)".

Test:
o Imagine we are just using the PSL beam and playing with an arm cavity.
o Tilt the end mirror in pitch. Resonate the TEM01 mode (8-shaped).
o Then tilt the end mirror in yaw.
o a) If the resonances are degenerated within the bandwidth of the laser, it rotates freely.
o b) If the resonances splits, the tilt in yaw does not change the shape. Then suddenly jumps to TEM10 (by an accident).

Result:
o The shape does not change. Just jumps to the other mode. (The case above b.)
o The eigenmode looked like quite horizontal and vertical.

Conclusion: the mode really splits.
Attachment 1: TEM01_10.png
TEM01_10.png
  795   Tue Aug 5 00:05:57 2008 KojiUpdateGeneralAbs. Len. Meas. ~ IFR2023A calibration
Work log on August 4th

o IFR2023A (Marconi) was calibrated by the SR620 frequency counter which is locked to the GPS signal.
o The frequency of the IFR2023A was scanned from 1MHz to 20MHz with 1MHz interval. The readout of the frequency counter was recorded.
o The linear fit was taken.
f_freq_count = K0 + K1 * f_IFR [Hz]
K0 = 0.00        +/- 0.02
K1 = 0.999999470 +/- 0.000000001

o So, the IFR seems to have -0.5ppm systematic error.
  796   Tue Aug 5 02:39:55 2008 KojiConfigurationGeneralAbs. Len. Meas. ~ Optical Layout on the AP / PSL table 2008-Aug-05
Here are the PDF and the PNG of the AP and PSL table layouts.
After this photo, the squeezing setup at the AP table was removed.
Attachment 1: optical_layout_ap_table3.png
optical_layout_ap_table3.png
Attachment 2: optical_layout_ap_table3.pdf
optical_layout_ap_table3.pdf
Attachment 3: optical_layout_PSL_table1.png
optical_layout_PSL_table1.png
Attachment 4: optical_layout_PSL_table1.pdf
optical_layout_PSL_table1.pdf
  798   Tue Aug 5 10:56:05 2008 AlbertoConfigurationGeneralITMX chamber opened and mirror released
D-Mass, Steve, Rana, Koji, Yoichi, Alberto,
We opened the ITMX chamber to check the optics after last week earthquake. In particular, from the spectra, ITMX seemed to be stuck and had to be released again. When we inspected the mirror, we found that it wasnít necessary to touch it. It had become free again during the vent thanks to the change of conductivity in the air inside during the vent.
We checked the magnets and they seemed to be fine.
A couple of stop screws had lost the rubber on their tips, although we donít know if that was due to the earthquake.
We also took advantage of the opening to center the LR and the left OSEMs in the mirror to their zero.
Inspecting the table we found a couple of things not totally clear on the configuration of the optics in the table. In particular we found a beam dump located too close to the ifo beam. Eventually we found out that the dump was meant to block a ghost beam coming from the ITM. A better location should probably be figured out for that. We also found that the POXM1 mirror designed to have the maximum reflectivity for the P polarization of the beam at 45 degrees is mounted so that the incident beam is at 22 degrees. This cause the beam to be 90% transmitted and only 10 percent reflected to POX. The transmitted beam appears at ther BSC chamber.

The ifo beam passes so close to the POXM1 mirror so that it can be clipped by its large metal frame ring. The beam at that point is about 6mm large and the ring is about 1cm thick so that we could gain some distance with a different mount.
  800   Tue Aug 5 17:56:23 2008 AlbertoConfigurationGeneralSRM and PRM inspection
Yoichi, Koji, Rana, Steve, Alberto

Today we opened the BSC to inspect the optics, and in particular the SRM and PRM.
We found that one of the side magnets of the SRM was broken and a piece of it fell and got stuck to the LR magnet.
We removed the LR OSEM and took off the broken part with tweezers. Since we couldnít replace the magnet on the side,
we decided to just switch the OSEM to the other side were a second magnet was available. Then we centered the OSEMs.
Using the optical levers we aligned both the ITMX and the SRM so that now we have to center again the OSEMs on both.

The PRM was visibly tilted and it was out of the range of the OSEMs. To try to fix the tilt we lift it up a little
with the screws on the bottom and pushed it with the third screw on top. That had the effect of making the mirror
tilt to the opposite direction. We looked at the wires (see attached picture) and it seemed centered on the side
of the mirror.

Tomorrow we are going to reset the OSEMs on ITMX and SRM and then weíre going to try to fix the tilt on PRM.
Attachment 1: IMG_1434.JPG
IMG_1434.JPG
Attachment 2: IMG_1456.JPG
IMG_1456.JPG
  801   Wed Aug 6 11:10:34 2008 KojiUpdateGeneralAbs. Len. Meas. ~ analysis of the TEM00 scan
Analysis of the data on August 3th ~ Part 1

From the measurement of the 5 FSRs, the FSR frequency for the Yarm cavity was estimated as
f_FSR = 3878678 Hz +/- 30 Hz
and the Yarm length is
L_yarm = 38.6462 m +/- 0.0003 m
This is the precision of 8ppm. In my opinion, this is a satisfactory result for our purpose.
Y-arm length
e-log    length [m]
-----------------------------
 556(2008-Jun-24)  38.70    +/- 0.08    Cavity swinging measurement
 556(2008-Jun-24)  38.67    +/- 0.03    Tape & photo
 776(2008-Jul-31)  38.640   +/- 0.007   Beam injection, poor PLL, Transmitted DC
 782(2008-Aug-02)  38.6455  +/- 0.0012  Beam injection, independent PLL, Transmitted DC
 787(2008-Aug-04)  38.64575 +/- 0.00037 Beam injection, independent PLL, Transmitted RF
this(2008-Aug-04)  38.6462  +/- 0.0003  Beam injection, independent PLL, Transmitted RF, five FSRs, freq calibrated
-----------------------------
----------------
o According to the entry 795, all of the scan frequency was calibrated.
o The five peaks of the scanned data for TEM00 were fitted. Each peak was fitted by the following formula:

V(f) = A / Sqrt(1 - ((f-f0)/fc)^2)

Variable
f: scan frequency

Parameters
A: peak amplitude
f0: center frequency
fc: half bandwidth of the peak for -3dB

o The results are shown in the attached figure 1. They look very similar each other but they are different plot! The fittings were extremely good. The center frequencies estimated were as follows:
FSR1:  3879251.9 Hz +/-  8.8 Hz
FSR2:  7757968.1 Hz +/- 10.8 Hz
FSR3: 11636612.9 Hz +/- 10.2 Hz
FSR4: 15515308.1 Hz +/-  8.7 Hz
FSR5: 19393968.7 Hz +/-  8.4 Hz
o The FSR frequencies were fitted by a line. The fitting and the residuals are shown in the attached figure 2.
The fitting results were

f_FSR(n) = 586.4 + 3878678 * n

This means that:
o FSR frequency was 3878678 [Hz].
o The lock of the carrier had detuning of 586 [Hz].

The detuning of the carrier from the resonance can be explained by the alignment drift. In deed, at the end of the measurement, decrease of the transmitted power by -15% was found. Then, the frequency of the 1st FSR was measured before and after the alignment adjustment. This changed the frequency of the FSR1 by 350Hz. This change could not be explained by the cavity length change as this is too big (~3.5mm).

Actually, the spacing of the cavity length is more stable. The residual is rather scattered with in 20-30Hz. So, I took the error of 30Hz as the whole precision of the frequency measurement that includes the fluctuation of the alignment, the cavity length itself, and so on. This yields the FSR and the cavity length of
f_FSR = 3878678 Hz +/- 30 Hz
L_yarm = 38.6462 m +/- 0.0003 m .
Attachment 1: TEM00fit.png
TEM00fit.png
Attachment 2: TEM00FSRfit.png
TEM00FSRfit.png
  802   Wed Aug 6 11:43:52 2008 KojiUpdateGeneralAbs. Len. Meas. ~ analysis of the TEM01 scan
Analysis of the data on August 3th ~ Part 2

o I already have reported that the resonant freq of TEM10 and TEM01 split.

o Again, note that TEM10/01 were arranged almost in the horizontal/vertical by the observation of the video.

o The peaks of TEM10 and TEM01 were fitted with the same method as of TEM00.

o The peak freqs were:
f_TEM10: 5087040 Hz +/- 20 Hz
f_TEM01: 5068322 Hz +/- 15 Hz
The split is 18.7kHz.

o The additional parameter from the previous entry:
f_TEM00: 3879252 Hz +/- 9 Hz
L_yarm: 38.6462 m +/- 0.0003 m

o Radius of curvature
Rx = L /(1-Cos^2(Pi (f_TEM10 - f_TEM00) / (c/L/2) ))
Ry = L /(1-Cos^2(Pi (f_TEM01 - f_TEM00) / (c/L/2) ))

from these formula we get the value
Rx = 56.1620 +/- 0.0013 [m]
Ry = 57.3395 +/- 0.0011 [m]
Attachment 1: TEM01fit.png
TEM01fit.png
  805   Wed Aug 6 19:01:15 2008 AlbertoUpdateGeneralITMX and SRM OSEM post-earthquake diagnostic
Koji, Yoichi, Alberto

Today we reset the OSEMs on ITMX and SRM in order to be centered when the mirrors are aligned to the IFO beam. Since the PRM is still out of order, we used the beam from NPRO laser of the absolute length measurement experiment as it is injected through the AS port.
Thatís how we did it:

1) We aligned the SRM so that the reflected beam from the NPRO was at the camera after at the AS port.

2) We traded off the alignment of SRM in order for the reflected beam at the camera to have a nice shape, avoiding any clipping from the optics, and for the optical lever to be not too far from zero. The final alignment for SRM, as read on the sliders on the MDM screen, is: Pitch=1.1650, Yaw=1.4674.

3) We aligned ITMX checking out by an IR card that the incoming and the reflected main beam in between ITMX and the BS matched. The alignment of the two beams was improved checking the matching after the SRM. The final alignment for ITMX, as read on the sliders on the MDM screen, is: Pitch=-1.2937, Yaw=-0.9890.

4) After the alignment of SRM and ITMX these were the voltages at the OSEMs:

SRM
UL=0.957
UR=1.254
LR=0.768
LL=0.620
Side=0.958

ITMX
UL=1.144
UR=1.360
LR=0.591
LL=0.325
Side=-----

5) Finally we centered the OSEMs on both mirrors and we read these voltages:

SRM
UL=0.939
UR=0.994
LR=0.782
LL=0.938
Side=0.953

ITMX
UL=0.918
UR=0.891
LR=0.887
LL=0.875
Side=0.883
  838   Thu Aug 14 21:52:51 2008 KojiSummaryGeneralAbs. Len. Meas. ~ summary of my Summer
I have made the summary of the absolute length measurement.
It is attached here. The file is a bit big (~8.6MB).
Attachment 1: mode_spacing_measurement_080816_v2.pdf
mode_spacing_measurement_080816_v2.pdf
  875   Mon Aug 25 10:23:53 2008 steveHowToGeneralcable killer
Rack 1Y7 double violation:

BNC cables left to be jammed by door

and see destroyed BNCs

RED fibers should be rerouted.
I placed protective obstacle in position
so the door can not be closed.

Please do not do this!

DNA analysis is in progress on your finger prints.
Attachment 1: cablkill.png
cablkill.png
Attachment 2: cablkll2.png
cablkll2.png
  938   Wed Sep 10 08:57:03 2008 steveUpdateGeneraletmy illuminator turned off
The ETMY illuminator was left on yesterday.
I just turned it off.
  940   Wed Sep 10 19:53:53 2008 AlbertoUpdateGeneralabs length experiment
Update of the last days work on the experiment to measure the absolute length of the cavities.

I'm trying to repeat the same measurement that Koji did on the Y arm, before switching to the X arm.

I switched to the PHD universal box for the PLL control between the main laser and the secondary laser. I found a good gain value for the servo and now I can set the frequency of the beat to any value as long as I do it slowly turning the LO frequency from the knob on the Marconi.

I laid down a 50m BNC cable from the Y end to near the BS chamber, where all the abs length equipment is. I matched the two laser beams changing the alignment of the injection steering mirror at the the dark port on the AP table. I then locked the Y arm cavity. When I first tried to do that, the locking script didn't work because the beam was off of the 'sweet spot' where Rob had set it on Monday. It turned out that aborting the script during one of its previous run, had changed the alignment of the PZT steering mirrors. So with Rob I brought them back near the positions as in the snapshot and then saved a new one with the latest values.

Eventually I could set the beat frequency to the FSR of the arm cavity and saw it in transmission at the ETMY.

Now I'm working on the LabView interface for the GPIB data acquisition board.
  943   Thu Sep 11 23:28:35 2008 albertoUpdateGeneralabs cavity length experiment
The MC lost lock for some reason not related to either the FSS or the PMC I'm done with my measurement for tonight. I've shut the NPRO beam before leaving.
  944   Fri Sep 12 11:09:20 2008 AlbertoUpdateGeneralabs cavity length experiment
I'm leaving the lab for a couple of hours. I shut the NPRO. The interferometer is available to anyone.
  945   Sat Sep 13 23:13:01 2008 AlbertoUpdateGeneralabs cavity length experiment
The Y arm was locked all time today but, suddenly, this afternoon it lost lock and since then I've been unable to restore it. I tried unsuccessfully the Restore and the Align scripts several times, although the position of PZT steering mirrors were good (as in the snapshot). I tried things like unlocking/locking the MC, the FSS reference cavity, the PMC but it didn't work. Then I decided to switch to the X arm. Locking it was a piece of cake compare to Y. I'm going to start measuring the FSR of the X arm.
  946   Sun Sep 14 18:30:32 2008 AlbertoUpdateGeneralABSL: measured X arm
Today I measured the X arm FSR.
Hi moved the fast PD (Thor Labs PDA255) from the Y end table to the X end table. I had to use a beam splitter to pick out the transmitted beam from the cavity beam and send it to the PD. I did not want to interpose the BS before the TRANS X PD, so I had to move the ETMXT camera to an other place in the table to gain some room. Now the beam that used to go directly to the camera is 50% split and goes also to the PD. I had to put a lens to focus the beam on the PD. The transmitted beam is currently not aligned to the ETMXT camera, I need to fix the alignment of the BS before.
I'm now doing a rough scan of a frequency range 5 times as large as the FSR. I'll post the results soon.
  947   Sun Sep 14 19:29:07 2008 AlbertoUpdateGeneralABSL: measured X arm

Quote:
Today I measured the X arm FSR.
Hi moved the fast PD (Thor Labs PDA255) from the Y end table to the X end table. I had to use a beam splitter to pick out the transmitted beam from the cavity beam and send it to the PD. I did not want to interpose the BS before the TRANS X PD, so I had to move the ETMXT camera to an other place in the table to gain some room. Now the beam that used to go directly to the camera is 50% split and goes also to the PD. I had to put a lens to focus the beam on the PD. The transmitted beam is currently not aligned to the ETMXT camera, I need to fix the alignment of the BS before.
I'm now doing a rough scan of a frequency range 5 times as large as the FSR. I'll post the results soon.


I'm leaving a long measurement running. I should be back later on. If I won't, whoever wanted to use the interferometer has just to shut the NPRO laser in the AP table.
  956   Wed Sep 17 13:58:36 2008 AlbertoUpdateGeneralABSL: results from the X arm
Today I repeated the measurement of the FSR on the X arm cavity. The noise in the transmitted power that made the measures fluctuate was much reduced after last night Rob worked on the interferometer. The X arm cavity length is now: (38.4580+/-0.0003)m. I'm attaching a summary of the data I've taken.

I'm now preparing the setup to measure the transverse mode spacing.
Attachment 1: Sept17_XarmFSRmeasurement_report.ps
Sept17_XarmFSRmeasurement_report.ps
  960   Wed Sep 17 19:13:47 2008 AlbertoUpdateGeneralABSL: status
I installed the setup for measuring TEM01/10 on the X end table.
I'm leaving. I shut the laser, flipped down the flipper mirror, disconnected the pzt drive signal from the laser.
For Jenne. The power cable for the Guralps' board is now connected to the PDH box on my instruments cart but you can take it.
  962   Thu Sep 18 09:30:12 2008 steveUpdateGenerallow noise metal film resistors are in
Low noise metal film resistor and capacitor kits from www.garrettelec.com are in.

manufacturer: Dale, 289 values, 25ea, surface mount,1206, 0.1% from 100 to 100K, 1/8 or 1/4W
additional values below 100 ohm and above 100K were purchased from Mouser with the same Dale specification

Ceramic capacitor kit from AVX
67 values, 25ea, surface mount, 1206 from 1.0 pF up

atm2: our new storage cabinet pick and put together by Jenni
Attachment 1: mfr&cap.png
mfr&cap.png
Attachment 2: storcab.png
storcab.png
  979   Mon Sep 22 20:00:35 2008 AlbertoUpdateGeneralABSL: running measurement
I'm leaving the X arm locked on the TEm01 mode while a measurement is running. Just please wait for 40 minute if you need the interferometer tonight.
  987   Wed Sep 24 17:57:04 2008 AlbertoUpdateGeneralABSL: FSS Slow Actuator Control
Rana, Alberto

Today when I started working with the PLL that I use to control the secondary laser on the ABSL experiment, I found that the beat between the two lasers was at a much higher temperature of NPRO than usual (about one Celsius Degrees higher, 49.79 instead of 48.7). It turned out that the main beam frequency had changed, and so had its frequency, because of a too much high value of the slow actuator gain on the FSS. We looked at the trend for the gain and noticed it had changed from 0.3 to 3 at about noon today. We brought it back to the old value and also optimized the single gains in the FSS slow servo to obtain a faster and stabler response to step changes in the laser temperature.

It is very important for the ABSL experiment that the frequency and the NPRO temperature of the main laser do not change.

** update:
you asked for:   diff 2008/09/25,0:00 2008/09/25,8:50:19 utc 'FSS[-_]SLOW'
LIGO controls: differences, 2008 09/25 00:00:00 utc vs. 2008 09/25 08:50:19 utc
__Epics_Channel_Name______   __Description__________   __value1____     __value2____
C1:PSL-FSS_SLOWKD                                      0.000000         0.001000
C1:PSL-FSS_SLOWKI                                     -0.001000        -0.001700
C1:PSL-FSS_SLOWKP                                     -0.000300        -0.001000

It seemed later that it was not being cool with the derivative gain up at -0.001, so I set it to zero. We really need some documentation on this
loop (e.g. pseudo code and a PID tuning procedure). Note that the PID record as documented in the EPICS Reference Manual
has been deprecated and so we run a perl script that Tobin wrote.
  994   Thu Sep 25 17:14:31 2008 ranaConfigurationGeneralnew sitemap
Attachment 1: vegemite.png
vegemite.png
  1030   Tue Oct 7 10:49:29 2008 AlbertoUpdateGeneralDisplaced Photodiode
This morning I found that the photodidode of the PLL in the PSL table was not aligned to the beam anymore. The PD support was not tight to the pedestal so that the PD was rotated and completely off of the beam.

It is possible that the BNC cable connected to the PD was pulled very strongly, or the PD was hit so that the support got unscrewed by its pedestal. Anyways, it did not happen spontaneously.

I re-aligned the PD and observed again the beat between the two laser beams. Here are the values from the measurement of the signal from the PD:
I measured the DC values of the hitting power, alternatively occluding one of the two laser beams, and I measured the beat amplitude letting them interfere and reading the peak-to-peak amplitude of the oscillating signal:

main beam DC: 200mV
secondary beam DC: 490
beat: 990mV
beat at the spectrum analyzer (after the two-way splitter of the PLL): -8.40dBm on a noise floor of the photodiode of -75dBm

the frequency of the beast is 8.55MHz and the temperature of the NPRO of the secondary beam, as read from the laser driver display, is 48.7357C.


Alberto
  1062   Tue Oct 21 16:14:42 2008 steveUpdateGeneraldivergence of He Ne 1035P
The ITM oplevs laser diodes are noisy.
They will be replaced by JDS 1035P
SN T8093307 was measured with the beamscanner.
This will able us to calculate the right lenses to get a small beam on the qpd.

**
The first column is distance from the front face of the laser in cm.
The second column is beam diameter in the horizontal direction in microns.
The third column is the beam diameter in the vertical direction in microns.
(edit by Rana)
Attachment 1: 1035p_divergence.png
1035p_divergence.png
  1069   Wed Oct 22 17:48:58 2008 YoichiUpdateGeneralLenses for focusing the optical lever laser (Re:divergence of He Ne 1035P)
Steve had difficulty in finding lenses for focusing the HeNe laser for the ITM op-lev.
Following his measurement of the beam divergence, I did some calculation to find a suitable set of lenses and positions.

First, I fitted Steve's data to get the waist size and location of the new HeNe.
The first plot shows the fitting result.
The size of the waist is 0.3mm at -367mm from the laser output (i.e. inside the laser).
(I only used horizontal beam size data.)

Then using the obtained beam parameter, I calculated the propagation of the beam through two lenses.
After playing with the focal length and location of the lenses, I found that with parameters {f1=-0.125m, f2=0.2m, d1=0.2m, d2=0.1m} we get about 1mm beam at the QPD (about 4m away from the laser). f1 and f2 are the focal lengths of the lenses, d1 is the distance from the laser to the first lens and d2 is the distance between the two lenses.
The second plot shows the beam size as a function of the distance from the laser.

The Mathematica notebook used to plot the beam propagation is attached.
By running it on Mathematica 6, you can dynamically change the parameters (focal lengths and locations) by sliders, and the plot (like the one shown in the second attachment) updates in real time. It is cool. Please try it.



Quote:
The ITM oplevs laser diodes are noisy.
They will be replaced by JDS 1035P
SN T8093307 was measured with the beamscanner.
This will able us to calculate the right lenses to get a small beam on the qpd.

**
The first column is distance from the front face of the laser in cm.
The second column is beam diameter in the horizontal direction in microns.
The third column is the beam diameter in the vertical direction in microns.
(edit by Rana)
Attachment 1: BeamProfile.png
BeamProfile.png
Attachment 2: BeamPropagation.png
BeamPropagation.png
Attachment 3: BeamPropagation.zip
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