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ID Date Author Type Categoryup Subject
  2229   Tue Nov 10 19:19:57 2009 AlbertoUpdateABSLRotated polarizer on the PSL table, along the MC input pick off beam

Aligning the beam for the PLL of the AbsL Experiement I rotated the polarizer along the path of the MC Input pick off beam (= the pick off coming from the MC periscope).

  2230   Tue Nov 10 19:21:53 2009 AlbertoUpdateABSLPLL Alignment

I've been trying to lock the PLL for the AbsL Experiment but I can't see the beat (between the auxiliary NPRO and the PSL).

I believe the alignment of the PLL is not good. The Farady Isolator is definitely not perfectly aligned (you can see it from the beam spot after it) but still it should be enough to see something at the PLL PD.

it's probably just that the two beams don't overlap well enough on the photodiode. I'll work on that later on.

I'm leaving the lab now. I left the auxiliary NPRO on but I closed its shutter.

All the flipping mirrors are down.

  2238   Wed Nov 11 15:04:52 2009 AlbertoUpdateABSLWorking on the AP table

I've opened the AP table and I'm working on it.

  2239   Wed Nov 11 16:18:57 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

I've opened the AP table and I'm working on it.

I re-aligned the Faraday on the AP table. I also aligned the beam to the periscope on the PSL and all the other optics along the beam path.  Now I have a nice NPRO beam at the PLL which overlaps with the PSL beam. The alignment has to be further improved because I see no beat yet.

I wonder if the all the tinkering on the PSL laser done recently to revive the power has changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat. So maybe the misalignment is the casue.

Not feeling very well right now. I need to go home for a while.

AP table closed at the moment.

NPRO shutter closed

  2240   Wed Nov 11 17:10:51 2009 JenneUpdateABSLWorking on the AP table

Quote:

Quote:

I've opened the AP table and I'm working on it.

I re-aligned the Faraday on the AP table. I also aligned the beam to the periscope on the PSL and all the other optics along the beam path.  Now I have a nice NPRO beam at the PLL which overlaps with the PSL beam. The alignment has to be further improved becasue I see no beat yet.

I wonder if the all the tinkering on the PSL laser done recently to revive the power have changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat. So maybe the misalignment is the casue.

Not feeling very well right now. I need to go home for a while.

AP table closed at the moment.

NPRO shutter closed

 We definitely changed the PSL NPRO temp while fiddling around, trying to increase the laser power.  I think it's noted in the elog both times that it's happened in the last few months (once when Rana, Koji and I worked on it, and then again when it was just Koji), but we opened up the side of the MOPA box so that we could get at (and change) the potentiometer which adjusts the NPRO temp.  So you may have to search around for a while.

  2241   Wed Nov 11 17:33:54 2009 KojiUpdateABSLWorking on the AP table

Yes it did.

For long time, the crystal temperature C1:PSL-126MOPA_LTMP was 43~46deg. Now it is 34deg. Try ~10deg lower temperature.

Quote:

I wonder if the all the tinkering on the PSL laser done recently to revive the power have changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat.

 

  2250   Thu Nov 12 10:45:36 2009 AlbertoUpdateABSLWorking on the AP table

I've opened the AP table and I'm working on it.

Also auxiliary NPRO turned on and mechanical shutter opened.

  2252   Thu Nov 12 11:34:38 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

Yes it did.

For long time, the crystal temperature C1:PSL-126MOPA_LTMP was 43~46deg. Now it is 34deg. Try ~10deg lower temperature.

Quote:

I wonder if the all the tinkering on the PSL laser done recently to revive the power have changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat.

 

 Beat found at 30MHz with auxiliary NPRO temperature of 37.19 degrees, vs. ~48 deg as it used to be.

The beat is small (-70dBm). PLL alignment has to be improved.

  2254   Thu Nov 12 12:51:45 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

I've opened the AP table and I'm working on it.

Also auxiliary NPRO turned on and mechanical shutter opened.

AP table and aux NPRO shutter just closed.

  2257   Thu Nov 12 16:53:59 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

Quote:

Yes it did.

For long time, the crystal temperature C1:PSL-126MOPA_LTMP was 43~46deg. Now it is 34deg. Try ~10deg lower temperature.

Quote:

I wonder if the all the tinkering on the PSL laser done recently to revive the power have changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat.

 

 Beat found at 30MHz with auxiliary NPRO temperature of 37.19 degrees, vs. ~48 deg as it used to be.

The beat is small (-70dBm). PLL alignment has to be improved.

 PLL alignment improved. Beat amplitude = -10dBm. Good enough.

DC readouts at the PLL photodiode:

V_NPRO = -4.44V

V_PSL = -3.76V

The NPRO beam is attenuated by a N.D.=1 attenuator just before going to the photodiode.

Something strange happened at the last. Right before -10dBm, the amplitude of the beat was about -33dBm. Then I was checking the two interfering beams with the IR card and saw that they overlapped quite well. I then turned my head back to the spectrum analyzer and suddenly the beat was at -10dBm. Not only, but a bunch of new peaks had appeared on the spectrum. Either I inadvertently hit the PD moving it to a better position or something else happened.

Like if someone was making some other modulation on the beam or the modulation depth of the PSL's sidebands had gone up.

  2261   Thu Nov 12 18:10:27 2009 AlbertoUpdateABSLPLL Locked

I locked the PLL and made some first measuremtns of the spectrum of the error signal. I'll post them later.

I closed the shutter of the NPRO.

  2321   Tue Nov 24 14:33:22 2009 AlbertoUpdateABSLworking on the AP table

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

  2324   Tue Nov 24 19:16:02 2009 AlbertoUpdateABSLworking on the AP table

Quote:

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

 Closing the AP table and the NPRO shutter now.

  2326   Wed Nov 25 08:43:08 2009 AlbertoUpdateABSLWorking on the AP table

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

  2328   Wed Nov 25 10:20:47 2009 AlbertoUpdateABSLAbsL PLL not able to lock

Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.

The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.

Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.

Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.

It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.

Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.

I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.

  2329   Wed Nov 25 11:02:54 2009 AlbertoUpdateABSLAbsL PLL not able to lock

Quote:

Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.

The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.

Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.

Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.

It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.

Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.

I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.

 I confirm what I said earlier. The amplitude of the beat is -10 dBm at 300MHz. It goes down at lower frequencies. In particular it gets to-60 dBm below 20 MHz. For some strange reason that I couldn't explain the beating efficiency has become poorer at low frequencies.

  2334   Wed Nov 25 15:42:27 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.

 NPRO shutter closed

  2337   Wed Nov 25 20:14:58 2009 AlbertoUpdateABSLAbsL PLL not able to lock: problem fixed

Quote:

Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.

The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.

Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.

Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.

It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.

Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.

I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.

 

Problem found. Inspecting with Koji we found that there was a broken SMA-to-BNC connector in the BNC cable from the photodiode.

  2338   Wed Nov 25 20:24:49 2009 AlbertoUpdateABSLPLL Open Loop Gain Measured

I measured the open loop gain of the PLL in the AbsL experiment.

I repeated the measurement twice: one with gain knob on the universal PDH box g=3.0; the second measurement with g=6.0

The UGF were 60 KHz and 100 KHz, respectively.

That means that one turn of the knob equals to about +10 dB.

Attachment 1: 2009-09-25_OLgain_g3png.png
2009-09-25_OLgain_g3png.png
Attachment 2: 2009-09-25_OLgain_g6png.png
2009-09-25_OLgain_g6png.png
  2339   Wed Nov 25 20:28:17 2009 AlbertoUpdateABSLStopped working on the AbsL

I closed the shutter of the NPRO for the night.

  2342   Fri Nov 27 02:25:26 2009 ranaUpdateABSLPLL Open Loop Gain Measured

Quote:

I measured the open loop gain of the PLL in the AbsL experiment.

 Plots don't really make sense. The second one is inherently unstable - and what's g?

  2420   Tue Dec 15 21:39:34 2009 AlbertoUpdateABSLbrief summary of this afternoon's measurements
I took measurements of the open loop gain of the AbsL PLL with the old Universal PDH Box.
I Also measured the filter shape of both the new and the old PDH box.
I'm going to plot the results in a nice form tomorrow morning.
For who's interested, the PLL UGF was at 10KHz.
 
I can't lock the PLL with the new PDH box. Measuring its filter's shape, as suggested by Koji, I found out that it differs from the old one. That despite the fact that the two boxes should share the same circuit schematic. O,r at least, that is what it looks like from the schematics in the DCC.
I need to understand whether that is intentional and, if that was the case, what kind of use  Rich Abbott designed it for.
 
Tomorrow I'm going to post in the elog the filter's transfer functions too.
 
Before leaving the lab I closed the auxiliary laser's mechanical shutter.
  2421   Wed Dec 16 11:21:20 2009 AlbertoUpdateABSLUniversal PDH Box Servo Filters
Yesterday I measured the shape of the servo filter of both the old and the new Universal PDH boxes.
Here they are compared.

NewandOlfFilterTF.png

The way the filter's transfer function has been measured is by a swept sine between the "SERVO INPUT" and the "PIEZO DRIVE OUTPUT" connection on the box front panel. The spectrum analyzer used for the measurement is the SR785 and the source amplitude is set at 0.1V.

The two transfer functions are clearly different. In particular the old one looks like a simple integrator, whereas the new one already includes some sort of boost.

That probably explains why the new one is unable to lock the PLL. Indeed what the PLL needs, at least to acquire lock, is an 1/f filter.

I thought the two boxes were almost identical, at least in the filter shapes. Also the two schematics available in the DCC coincide.

Attachment 1: NewandOlfFilterTF.png
NewandOlfFilterTF.png
  2422   Wed Dec 16 11:46:25 2009 AlbertoUpdateABSLAbsl PLL Open Loop Gain

Yesterday I measured the Open Loop Gain of the PLL in the absolute length experiment. The servo I used was that of the old Universal PDH box.

The OLG looks like this:

OldBoxOLTF.png

The UGF is at 10 KHz.

  2423   Wed Dec 16 11:55:47 2009 ranaUpdateABSLUniversal PDH Box Servo Filters

 

 To me, they both look stable. I guess that the phase has to go to -180 deg to be unstable.

Why does the magnitude go flat at high frequencies? That doesn't seem like 1/f.

How about a diagram of what inputs and outputs are being measured and what the gain knob and boost switch settings are?

  2460   Mon Dec 28 15:34:14 2009 AlbertoUpdateABSLWorking on the AP table

I opened the auxiliary laser's shutter.

I'm currently working on the AP table.

  2461   Mon Dec 28 18:35:27 2009 AlbertoUpdateABSLWorking on the AP table

Quote:

I opened the auxiliary laser's shutter.

I'm currently working on the AP table.

 I finished working on the table.

I closed the AUX NPRO's shutter.

  2493   Sat Jan 9 15:02:01 2010 AlbertoUpdateABSLPRC scanning
I scanned the PRC in the frequency range of 30-60 MHz, untill the PLL lost lock. But everything is working fine.
The PRC remained lock for all time, with SPOB at ~1000.
I'm leaving the lab now, planning to come back tomorrow.
I turned the flipping mirrors down and closed the mechanical shutter of the auxiliary NPRO.
  2502   Mon Jan 11 11:06:53 2010 AlbertoUpdateABSLMeasurement running

Quote:

I'm working on the AbsL experiment. A measurement which involved the PRC locked is running at the moment.

Please make sure of not interfering with the interferometer until it is done. Thank you.

 I'm done for the moement.

I realized that I need to take into account somehow the DC power from the photodiode. By now the measurement of the transmitted beat's power is affected by the total power circulating inside of the PRC and thus it depends on the cavity alignment.

I closed the laser shutter and turned down the flipping mirrors.

I'm planning to restart measuring by 2.30pm today. Till then the interferometer is available.

  2504   Mon Jan 11 16:59:14 2010 AlbertoUpdateABSLInterferometer Busy

I'm currently running a measurement on the PRC.

Please don't interfere with the IFO until it is done. Talk with Alberto if you've been intending to work inside the lab.

Thank you.

  2505   Mon Jan 11 19:36:13 2010 AlbertoUpdateABSLMeasurement running

Leaving for dinner. Back in ~1hr.

I left a measurement running. Please don't interfere with it till I'm back. Thanks.

  2506   Mon Jan 11 21:49:17 2010 JenneUpdateABSLMeasurement running

Quote:

Leaving for dinner. Back in ~1hr.

I left a measurement running. Please don't interfere with it till I'm back. Thanks.

 Per Alberto's instructions, I have closed the shutter on his laser so that the Adaptive Team can play with the Mode Cleaner.

  2508   Tue Jan 12 09:37:05 2010 AlbertoUpdateABSLIFO available

I finished measuring the AbsL for this morning. The IFO is again available.

Please don't mess up with the interferometer though. I'll be back in a couple of ours

  2513   Wed Jan 13 12:03:00 2010 AlbertoUpdateABSLMeasurement now running. Please be careful

At the moment I'm running a measurement on the PRC and I'm planning to leave it going for the time we'll be at the 40m meeting.

Please be careful in the lab. Thank you.

  2521   Mon Jan 18 18:34:01 2010 AlbertoUpdateABSLMeasurement in progress

I started a long measurement of the PRC's transmissivity. I'm leaving the lab and I'm going to be back at about 8 tonight. Please do not disturb the interferometer. it is important that the MC and the PRC stay locked all the time.

  2522   Mon Jan 18 20:58:40 2010 AlbertoUpdateABSLMeasurement in progress

Quote:

I started a long measurement of the PRC's transmissivity. I'm leaving the lab and I'm going to be back at about 8 tonight. Please do not disturb the interferometer. it is important that the MC and the PRC stay locked all the time.

 That measurement is finished. I'm now going to start another one that will take another hour or so. I'm leaving it running for the night. If you want to work on the IFO, it should be definitely done by 11pm.

  2531   Tue Jan 19 12:54:39 2010 AlbertoUpdateABSLMeasurement in progress

A measurement will be running for the next hour. Please be careful.

  2532   Tue Jan 19 16:21:18 2010 AlbertoUpdateABSLWatchdogs not working and then fixed

This afternoon the watchdogs stopped working: they didn't trip when the suspension positions crossed the threshold values.

I rebooted c1susaux (aka c1dscl1epics0 in the 1Y5 rack), which is the computer that runs the watchdog processes.

The reboot fixed the problem.

  2534   Wed Jan 20 20:11:56 2010 AlbertoUpdateABSLSome preliminary results from measuring PRC's transmissivity for an amplitude modulated beam
Here I'm posting a plot showing a set of measurements that I made in the past few days to determine the absolute length of the PRC cavity.
As in my other AbsL measurements, I inject an auxiliary laser beam into the cavity and look at the transmission. In the PRC case, the beam is injected through the dark port and I look at a pick-off of the REFL beam. The aux laser is phase locked to the PSL beam and I control the differential frequency between the two. The PSL and the aux beam interfere and beat at their differential frequency.
 
The attached plot shows the transmitted power as a function of the beat frequency.
 
Fitting the data with the model would let me determine the cavity length. 
By now I can estimate the length of the PRC at about 2.257m, but it's still a rather approximate value.
I can't provide accurate error bars yet. I need to optimize the measurements to get a more precise value.
 
I will go more through the details of the measurement technique and of the fitting function as soon as I have more definitive results.
 
The data points shown here were taken at different times and not always in optimal alignment condition of the PRC. 
To get a good fit of the data I should have fewer frequency segments, taken in a shorter period of time, and in which the power circulating inside of the cavity (ie SPOB) fluctuates as little as possible.
 
For what regards the time needed for a measurements, I already significantly sped up the measurements (i.e. optimizing the scanning and acquisition GPIB scripts, and fixing a couple of problems with the PDH box used in the PLL), and finally now I can scan several tens of MHz in few minutes.
About the frequency segments, so far they have been determined by two factors
1) Tthe frequency generator in the PLL: the Marconi works as a continuous wave generator only in limited ranges. Switching from one to another brakes the wave in a way that causes the PLL to lose lock.
2) Getting below 18 MHz a series of other beats appear on the PLL photodiode and make the PLL lose lock.
 
For the first problem, I'm thinking of using two Marconis and to mix their signals. I would keep one at 300MHz and I would scan the other from 300MHz to 500MHz. In fat, in that frequency range the Marconi has not discontinuity.
 
To try to avoid the other beats at low frequency, I'm not entirely sure about what to do yet. 
 
To be continued...
Attachment 1: 2010-01-19_PRCtransmissivityVsModel.png
2010-01-19_PRCtransmissivityVsModel.png
  2536   Thu Jan 21 10:31:13 2010 KojiUpdateABSLSome preliminary results from measuring PRC's transmissivity for an amplitude modulated beam

Nice and interesting plot.

I suppose slight decrease of the Schnupp asymmetry (in your model) adjusts the discrepancy in the high freq region.
At the same time, it will make the resonance narrower. So you need to put some loss at the recombination (=on the BS)?

...of course these depends on the flatness of the calibration.

  2541   Fri Jan 22 02:54:06 2010 AlbertoUpdateABSLOvernight measurement

I'm leaving a measurement running overnight. It should be done in about one hour.

Tomorrow morning, If you need to use the interferometer, and you don't want to have the auxiliary beam going onto the dark port, you can turn down the flipping mirror and close the NPRO's mechanical shutter.

  2543   Fri Jan 22 14:40:49 2010 AlbertoUpdateABSLOvernight measurement

Quote:

I'm leaving a measurement running overnight. It should be done in about one hour.

Tomorrow morning, If you need to use the interferometer, and you don't want to have the auxiliary beam going onto the dark port, you can turn down the flipping mirror and close the NPRO's mechanical shutter.

 This is what I measured last night:

2010-01-21_PRCtransmissivityVsModel.png

 This is not a fit. It's just a comparison of the model with the data.

  2545   Mon Jan 25 16:30:37 2010 AlbertoUpdateABSL166 MHz sideband turned off

I turned off the modulation at 166MHZ becasue I don't need it if I'm only locking the PRC.

It was introducing extra amplitude modulations of the beam which interfered with the AbsL's PLL photodiode.

I'm going to turn it back on later on.

  2546   Mon Jan 25 16:46:33 2010 AlbertoUpdateABSL166 MHz sideband turned off

Quote:

I turned off the modulation at 166MHZ becasue I don't need it if I'm only locking the PRC.

It was introducing extra amplitude modulations of the beam which interfered with the AbsL's PLL photodiode.

I'm going to turn it back on later on.

 I turned back on the 166MHz modulation just a bit. I set the slider at 4.156.

When it was totally off the MZ seemd quite unhappy.

  2547   Tue Jan 26 03:28:56 2010 ranaUpdateABSL166 MHz sideband turned off

 

 You can turn the 166 off if you want. MZ is unhappy after its turned off, but that's just the thermal transient from removing the RF heat. After a several minutes, the heat goes away and the MZ can be relocked.

One of these days we should evaluate the beam distortion we get in EOMs because of the RF heat induced dn/dT. Beam steering, beam size, etc.

  2550   Wed Jan 27 11:02:30 2010 AlbertoUpdateABSLPRC Cavity Length
 I fitted the data from scanning the PRC by changing the beat frequency of the auxiliary laser beam with the PSL beam.
The data points that I've taken so far over the entire frequency range (0-300 MHz) are not continuous. For several reasons the PLL was unable to maintain lock for such a large range and I had to break it into smaller segments. The measurements to acquire them stretched over a too long period of time during which the status of the PRC changed.
 
Because of that, before I get a continuous set of data points (perhaps normalized by the circulating power inside of the cavity), I restricted the fit to a 55MHz range around 100MHz. I obtained the following numbers for the fit parameters:
Length PRC = 2.169 +/- 0.007 m
Schnupp Asymmetry: 0.471+/- 0.006 m
 
The fit is shown in the attached plot:
2010-01-21_PRCtransmissivityVsFit.png
When I fit over the entire set of data I get this:
 
2010-01-21_PRCtransmissivity_EntireFreqRange_VsFit.png
 
Length PRC = 2.224 +/- 0.005 m
Schnupp Asymmetry: 0.457+/- 0.005 m
 
The results are different. Evidently I have to improve the measurement. I'm working on it.
 
For posterity:
The function I used to fit the transmitted beat power vs. frequency is the following:
 
E_trans = - t_prm * r_itm * exp(1i*2*wb*l_prc/c) .* sin(wb*l_/c) ./ ( 1 + r_prm * r_itm * exp(1i*2*wb*l_prc/c) .* cos(wb*l_/c)
 
Where wb is the angular frequency of the beat, l_prc and l_ are the length of the PRC and the Schnupp asymmetry, respectively; r_itm, t_itm, r_prm, t_prm are reflectances and transmittances of PRM and ITM; c is the speed of light.
 
  2553   Fri Jan 29 12:06:58 2010 AlbertoUpdateABSLMeasurement running today at lunch time

I just started a measuremtn that will be running for the next hour or so. Please be careful with the interferometer.

  2554   Fri Jan 29 13:14:49 2010 AlbertoUpdateABSLMeasurement running today at lunch time

Quote:

I just started a measuremtn that will be running for the next hour or so. Please be careful with the interferometer.

Done. IFO available

  2576   Mon Feb 8 14:13:03 2010 AlbertoUpdateABSLPLL Characterization

Lately I've been trying to improve the PLL for the AbsL experiment so that it could handle larger frequency steps and thus speed up the cavity scan.

The maximum frequency step that the PLL could handle withouth losing lock is given by the DC gain of the PLL. This is the product of the mixer's gain factor K [rad/V ], of the laser's calibration C [Hz/V] and of the PLL filter DC gain F(0).

I measured these quantities: K=0.226 V/rad; C=8.3e6 Hz/V and F(0)=28.7dB=21.5. The max frequency step should be Delta_f_max = 6.4MHz.

Although in reality the PLL can't handle more than a 10 KHz step. There's probably some other effect that I'm not.

I'm attaching here plots of the PLL Open Loop Gain, of the PLL filter and of a spectra of the error point measured in different circumstances.

I don't have much time to explain here how I took all those measurements. After I fix the problem, I'm going to go go through those details in an elog entry.

Does anyone have any suggestion about what, in principle, might be limiting the frequency step?

I already made sure that both cables going to the mixer (the cable with the beat signal coming from the photodiode and the cable with the LO signal coming from the Marconi) had the same length. Although ideally, for phase locking, I would still need 90 degrees of phase shift between the mixing signals, over the entire frequency range for which I do the cavity scan. By now the 90 degrees are not guaranteed.

Also, I have a boost that adds another 20 dB at DC to the PLL's filter. Although it doesn't change anything. In fact, as said above calculating the frequency step, the PLL should be able to handle 100KHz steps, as I would want the PLL to do.

Attachment 1: 2010-02-08_Old_PDH_Box_Filter_TF_gain_knob_0_Boost_OFF.png
2010-02-08_Old_PDH_Box_Filter_TF_gain_knob_0_Boost_OFF.png
Attachment 2: 2010-02-08_PLL_OLG_gain_knob_0_Boost_OFF.png
2010-02-08_PLL_OLG_gain_knob_0_Boost_OFF.png
Attachment 3: 2010-02-08_PLL_Noise_Budget.png
2010-02-08_PLL_Noise_Budget.png
  2577   Mon Feb 8 14:56:17 2010 AlbertoUpdateABSLSuddenly a much better alignment of PRC

I just aligned PRM and locked PRC and I noticed that SPOB is much higehr than it used to be. It's now about 1800, vs 1200 than it used to be last week.

Isn't anyone related to that? If so, may I please know how he/she did it?

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