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ID Date Author Type Categorydown Subject
  1995   Wed Sep 23 19:36:41 2009 ranaUpdatePSLRC temperature performance

This first plot shows the RC temperature channels' performance from 40 days ago, before we disabled the MINCO PID controller. Although RCTEMP is supposed to be the out of loop sensor, what we really care about is the cavity length and so I've plotted the SLOW. To get the SLOW on the same scale, I've multiplied the channel by 10 and then adjusted the offset to get it on the same scale.

 The second plot shows a period after that where there is no temperature control of the can at all. Same gain scaling has been applied to SLOW as above, so that instead of the usual 1 GHz/V this plot shows it in 0.1 GHz/V.

The third plot shows it after the new PID was setup.

Summary: Even though the PID loop has more gain, the true limit to the daily fluctuations in the cavity temperature and the laser frequency are due to the in-loop sensors measuring the wrong thing. i.e. the out-of-loop temperature is too different from the in-loop sensor. This can possibly be cured with better foam and better placement of the temperature sensors. Its possible that we're now just limited by the temperature gradients on the can.

Attachment 1: Untitled.png
Untitled.png
Attachment 2: Untitled.png
Untitled.png
Attachment 3: e.png
e.png
  2008   Sun Sep 27 14:45:45 2009 KojiUpdatePSLSLOWscan result

I ran (script dir)/PSL/FSS/SLOWscan on op440m from 11:30 to 12:30 on 27th. Although Rana and later I myself set "timed bombs" for the scan, they did not work as they have probably been ran on Linux. After the scan I relocked PMC, FSS, and MZ . MC locked automatically.

Observation:

1. To keep away from the mode hop, FSS_SLOWDC is to be at around 0. The values -5 ~ -6 is the place for the power, which is my preference for now. BTW, the mode hop only appears to the PSL output (=AMPMON) is this normal?

2. The PSL output looks dependent on the NPRO wavelength. The NPRO output and the PSL output tends to be high when the FSS_SLOWDC is low (= LTMP: Laser Crystal Temp is low). Also there is a step at the LTMP where we think the mode hop is present. This may cause the daily PSL output variation which induced by the daily change of the reference cavity length.

My naive speculation is that the NPRO wavelength is too long (= hot side) for the MOPA absorption as the MOPA heads are cooled to 19deg.

3. Scanning of -10 to +10 changes the LTMP from 42-49deg. This is almost 1/10 of the NPRO capability. The manual told us that we should be able to scan the crystal temperature +/-16deg (about 30deg to 60deg).

What I like to try:
a) Change the NPRO temp to more cold side.
b) Change the MOPA head temp to a bit hot side.
c) Tweak the MOPA current (is it difficult?)

Attachment 1: SLOWscan_090927.png
SLOWscan_090927.png
Attachment 2: Pages_from_miser_126_manual.png
Pages_from_miser_126_manual.png
  2009   Sun Sep 27 15:25:58 2009 KojiUpdatePSLSLOWscan result
Oh, AMPMON dependence could be an artifact of the ND filter???
For my case, it should be real dependence on the NPRO wavelength,
as the other PDs like the PMC reflection (PMC_RFPDDC) and the RC reflection (FSS_RFPDDC) show the same dependence.
Attachment 1: power_dependence.png
power_dependence.png
  2010   Sun Sep 27 23:21:14 2009 ranaUpdatePSLSLOWscan result

Quote:

What I like to try:
a) Change the NPRO temp to more cold side.
b) Change the MOPA head temp to a bit hot side.
c) Tweak the MOPA current (is it difficult?)

 I think that the AMPMON ND problem was just that the responsivity changes with angle. So when I aligned it a little we got some few% improvement in the signal which is not a real power increase.

I don't think we can adjust any of the MOPA parameters because the controller is broken, but we can try the NPRO crystal temperature.

  2013   Mon Sep 28 17:39:34 2009 robUpdatePSLproblems

The PSL/IOO combo has not been behaving responsibly recently. 

The first attachment is a 15 day trend of the MZ REFL, ISS INMON, and MC REFL power.  These show two separate problems--recurring MZ flakiness, which may actually be a loose cable somewhere which makes the servo disengage.  Such disengagement is not as obvious with the MZ as it is with other systems, because the MZ is relatively stable on its own.  The second problem is more recent, just starting in the last few days.  The MC is drifting off the fringe, either in alignment, length, or both.  This is unacceptable.

The second attachment is a two-day trend of the MC REFL power.  Last night I carefully put the beam on the center of the MC-WFS quads.  This appears to have lessened the problem, but it has not eliminated it. 

It's probably worth trying to re-measure the MCWFS system to make sure the control matrix is not degenerate. 

Attachment 1: problems.png
problems.png
Attachment 2: problems2.png
problems2.png
  2033   Thu Oct 1 10:23:00 2009 steveUpdatePSLMC2 damping restored again

 The EQ did not change the input beam pointing. All back to normal, except MC2 wachdogs tripped again.

Attachment 1: mc2again.jpg
mc2again.jpg
  2049   Mon Oct 5 09:31:05 2009 AlbertoFrogsPSLPSL laser accidentally turned off

Alberto, Steve,

While I was moving a cart near by the PSL table I pushed the red emergency button that turns off the PSL laser. We had to unlock the button and then power cycle the laser driver to turn the laser back on.

I relocked MZ, FSS, PMC and I'm now waiting for the power to finish ramping up back to the previous value.

  2050   Mon Oct 5 10:41:31 2009 KojiUpdatePSLPSL laser accidentally turned off

The PSL output looks smaller than the incident. Try to FSS Slow actuator adj of -5.6 (nominal), instead of -3.5.

Quote:

Alberto, Steve,

While I was moving a cart near by the PSL table I pushed the red emergency button that turns off the PSL laser. We had to unlock the button and then power cycle the laser driver to turn the laser back on.

I relocked MZ, FSS, PMC and I'm now waiting for the power to finish ramping up back to the previous value.

 

  2051   Mon Oct 5 13:43:37 2009 ZachUpdatePSLPSL table photos

I have been commissioned to take pictures of the PSL table so that it can be diagrammed. I am starting now (1:42 pm, 10/5/09).

  2052   Mon Oct 5 14:18:41 2009 ZachUpdatePSLPSL table photos

Quote:

I have been commissioned to take pictures of the PSL table so that it can be diagrammed. I am starting now (1:42 pm, 10/5/09).

All done (for now). That wasn't so bad, was it?

  2055   Mon Oct 5 19:39:26 2009 KojiUpdatePSLPSL laser accidentally turned off

I set the FSS slow actuator adj to -5.6 at the lunch time. It gave a little help at that time. Now max of the MC Trans is comming back somehow. I hope the MC Trans level is as good as before, if the HEPA is slowed down.

Quote:

The PSL output looks smaller than the incident. Try to FSS Slow actuator adj of -5.6 (nominal), instead of -3.5.

Quote:

Alberto, Steve,

While I was moving a cart near by the PSL table I pushed the red emergency button that turns off the PSL laser. We had to unlock the button and then power cycle the laser driver to turn the laser back on.

I relocked MZ, FSS, PMC and I'm now waiting for the power to finish ramping up back to the previous value.

 

 

  2057   Tue Oct 6 10:09:55 2009 ZachUpdatePSLMore pictures

I'm back to terrorize the PSL table again. The pictures I took yesterday were rubbish--today I'm using a clamp that Steve was nice enough to loan me. I'm starting now, at 10:09 am.

  2083   Mon Oct 12 18:37:55 2009 ZachUpdatePSLInventory

--Apologies for the late post--

I was at the PSL table taking an inventory of the components for a while after Koji, Steve, and Kiwamu were there. I set the HEPAs back to 20% when I left (assuming that they were turned up when the compartment was opened).

  2088   Mon Oct 12 22:15:15 2009 ranaConfigurationPSLStray beam blocking

You can remove the RFAM measuring setup. Once we upgrade, we will no longer have a MZ or the related problems.

  2089   Tue Oct 13 10:31:11 2009 ZachUpdatePSLone more time

I am at the PSL table taking what is hopefully the last set of pictures for the diagram. Woohoo.

  2090   Tue Oct 13 10:50:58 2009 ZachUpdatePSLone more time

Quote:

I am at the PSL table taking what is hopefully the last set of pictures for the diagram. Woohoo.

 I'm out, HEPAs are back at 20%.

  2098   Thu Oct 15 12:35:09 2009 ZachUpdatePSLinventory

I'm at the PSL table taking inventory of the elements I don't have down yet.

  2099   Thu Oct 15 12:57:23 2009 ZachUpdatePSLinventory

Quote:

I'm at the PSL table taking inventory of the elements I don't have down yet.

 OK, I'm out--hopefully for good. HEPAs back at 20%.

  2142   Mon Oct 26 15:40:01 2009 steveUpdatePSLlaser power is down

The laser power is down 5-6%

Attachment 1: laserpowerdown.jpg
laserpowerdown.jpg
  2147   Mon Oct 26 23:14:08 2009 KojiUpdatePSLlaser power is down

I adjusted the steerings to the PMC and gained 7%. Now the MC_TRANS 7.0 has been recovered.

Actually I need another 7% to get MC_TRANS 7.5.
But I couldn't find how I can recover 126MOPA-AMPMON to 2.8ish.

Quote:

The laser power is down 5-6%

 

Attachment 1: PSL091026.png
PSL091026.png
  2151   Tue Oct 27 18:01:49 2009 robUpdatePSLhmmm

A 30-day trend of the PCDRIVE from the FSS.

Attachment 1: pcdrive_trend.png
pcdrive_trend.png
  2155   Wed Oct 28 09:12:18 2009 steveUpdatePSLPMC power on the rise?

The PMC power is seems to be on the rise, ( MOPA_AMPMON is dropping ?) but I do not think it is real. We have Santa Anna wind condition, when the relative humidity drops and  ......

There is an other funky think. The room temp became rock solid. The PSL HEPAs running at 20% and IFO-room ACs are also in normal operational mode.

Attachment 1: pmcprising.jpg
pmcprising.jpg
  2158   Thu Oct 29 13:48:32 2009 KojiUpdatePSLNPRO LTMP lowered 9.5deg

13:00 Found MC TRANS less than 7.
13:50 Go into the PSL table.
14:20 Work done. Now I am running SLOWscan script.
15:10 SLOWscan finished. It was not satisfactory. I go into the table again.
15:15 Running SLOWscan again.
16:00 SLOWscan done. Lock PMC. Adjust NPRO current so as to maximize PMC TRANS.
16:10 Lock RC, PMC, MZ, MC. Align PMC / MZ on the table. Align MC WFS beams on the QPDs.
16:30 Work done.

New FSS-SLOWDC nominal is -4.0

Now MC TRANS is 7.9. This is +12% increase. ENJOY!
HEPA is on at 90%. Light is off.

---------

NPRO TEMP trimmer adjustment
o PSL NPRO TEMP trimmer at the back of the laser head was turned 6.5 times in CW.
o It reduced NPRO crystal temp by 9.5deg. (43.5deg -> 34.0deg for FSS_SLOWDC -5.5)

To revert the previous setting, refer to the former measurement
c.f. http://nodus.ligo.caltech.edu:8080/40m/2008

NPRO Thermal scan
o 2 scans are performed.
o I selected the colder side of the second scan. i.e. SLOWDC=-4.0

NPRO Current adjustment
o Tweaked C1:PSL-126MOPA_126CURADJ while looking at PMC TRANS.
o CURADJ was changed from -2.25 to -1.9. This corresponds to change of C1:PSL-126MOPA_CURMON from 2.503A to 2.547A.

Attachment 1: 091028_PSL.png
091028_PSL.png
  2161   Thu Oct 29 20:21:14 2009 KojiUpdatePSLNPRO LTMP lowered 9.5deg

Here is the plots for the powers. MC TRANS is still rising.

What I noticed was that C1:PSL-FSS_PCDRIVE nolonger hit the yellow alert.
The mean reduced from 0.4 to 0.3. This is good, at least for now.

Attachment 1: PSL_MC.png
PSL_MC.png
  2165   Fri Oct 30 10:52:56 2009 JenneUpdatePSLHEPAs

Zach found the HEPA switch on the PSL table OFF.  He turned them on.

  2169   Mon Nov 2 13:34:36 2009 kiwamuConfigurationPSLremoved multiply resonant EOM

I removed the multiply resonant EOM that has been set by a SURF student from PSL table.

I will use it for checking the resonant circuit.

  2236   Wed Nov 11 12:29:44 2009 AlbertoFrogsPSLMC Locked on the wrong mode?

This morning, after Steve pointed out that the readout RFAMPD_DC was zero, I thought of realigning the beam on the photodiode. Maybe I touched the lens or the beam splitter that send the beam on the diode when I installed an other beam splitter to make the measurement of the calibration between two ThorLabs PDA255 photodiodes.

After aligning the beam on the RFAMPD, the voltage of the DC readout was lower than it used to be (C1:IOO-RFAMPD_DC ~ 0.4 now vs. 4 as it was on November 4th).

I maximized the DC readout but the problem seems to be that the beam spot is not a round TEM00. In particular the spot looks like that of a TEM10 mode.

Since we're looking at the MC transmitted beam, is it possible that the MC is locked on the wrong mode?

Check out the attached picture.

Attachment 1: PB110184-1.JPG
PB110184-1.JPG
  2249   Thu Nov 12 10:45:02 2009 AlbertoUpdatePSLAbandoned Frequency Generator

This morning I found a frequency generator connected to something on the PSL table sitting on the blue step next to the sliding doors.

Is anyone using it? Has it been forgotten there? If that's the case, can the interested person please take care of removing it?

  2251   Thu Nov 12 11:19:10 2009 KojiUpdatePSLAbandoned Frequency Generator

Last night there was an activity for a calibratuon work, which I helped. I can take care of the FG.

Quote:

This morning I found a frequency generator connected to something on the PSL table sitting on the blue step next to the sliding doors.

Is anyone using it? Has it been forgotten there? If that's the case, can the interested person please take care of removing it?

 

  2256   Thu Nov 12 16:13:05 2009 AlbertoUpdatePSLMC Trans Offset

On Rana's suggestion I checked the MC transmission QPD (C1:IOO-MC_TRANS_SUM). I found that the readout is almost zero when the MC is unlocked.

I unlocked the Mode Cleaner turning off the LSC control and disabling the autolocker. The QPD reads 0.014. It seems that there is no offset.

I also checked with the IR card around the photodetector and I didn't see any stray beam.

  2258   Thu Nov 12 17:15:43 2009 KojiUpdatePSLMC Trans Offset

OK. I have been keeping my eyes on the MC transmission. In deed, the MC trans has been well kept at around 7.7 since the last PSL work.
Even it was over the 8 today!

Quote:

On Rana's suggestion I checked the MC transmission QPD (C1:IOO-MC_TRANS_SUM). I found that the readout is almost zero when the MC is unlocked.

I unlocked the Mode Cleaner turning off the LSC control and disabling the autolocker. The QPD reads 0.014. It seems that there is no offset.

I also checked with the IR card around the photodetector and I didn't see any stray beam.

 

Attachment 1: MC_TRANS.png
MC_TRANS.png
  2260   Thu Nov 12 17:42:04 2009 KojiUpdatePSLMC Trans Offset

PC_DRIVE is also improving after the last PSL work!

Quote:

OK. I have been keeping my eyes on the MC transmission. In deed, the MC trans has been well kept at around 7.7 since the last PSL work.
Even it was over the 8 today!

 

Attachment 1: PC_DRV.png
PC_DRV.png
  2311   Mon Nov 23 00:46:09 2009 rana, robUpdatePSLISS RIN: Its too high by 10x

This plot shows the RIN as measured by the ISS. Its ~2 x 10^-7, whereas its supposed to be more like 3 x 10^-8.

The ISS has DC coupled RIN channels (with a _F suffix) and AC coupled RIN channels (with a _FW suffix). By using a swept sine, Rob determined that the AC coupled channels have an AC coupling pole at ~80 Hz. The attached plot uses this and then has the overall gain adjusted to match with the _F channels below 10 Hz.

The _F channels can be converted directly into RIN by just dividing the spectra by the mean value of the time series. The dark offset of these channels is small and so this only introduces a ~5-10% calibration error.

Question #1: Why is the RIN so bad? According to the MEDM screen, the photocurrent on the MON/SENS PDs is 1.9/1.3 mA. That's sort of low, but should still allow us to get 5x10^-8 in RIN.

Question #2: Does it make an effect on the current DC Readout work? IF so, should we try to fix up the ISS in a temporary way? Since the in-loop and out-of-loop detectors are completely coherent, all of the noise is likely just unsuppressed noise from the laser. We are unable to increase the gain because of the high frequency noise from the NPRO.

 

Let's remember to replace this ISS with a new one that can drive an AOM. Need a volunteer to get us a new ISS.

 

Attachment 1: Untitled.png
Untitled.png
  2335   Wed Nov 25 16:13:27 2009 ranaUpdatePSLMeasured MC length--FSS trend

but the increase in both the RCtrans and the RCrefl is consistent with my theory that the power going to the RC has increased ; its not just an increase in the visibility.

We should scan the AOM/VCO to make sure the frequency is matched to the resonance to within 0.5 dB.

  2336   Wed Nov 25 16:44:52 2009 KojiUpdatePSLMeasured MC length--FSS trend

I checked C1:PSL-FSS_VCODETPWR. The attached is the 4 months trend of the FSS RCTRANS / RFPDDC(=FSS REFL) / VCODETPWR / VCOMODLEVEL.

Although VCO modulation level setting was mostly constnt, VCODETPWR, which presumably represents the RF level, changes time by time.
It coincides with the recent reduction of the RCTRANS/RFPDDC. Actually, my touch restored the VCO to the previous more stable state.
One can see that this is not only a single occation, but it happened before too. (In the middle of Aug.)

This could be explained by the bad contact of some cable or connector.

Nevertheless we need more careful investigation:

1. Understand what VCODETPWR is exactly.
2. Investigate relationship between VCOMODLEVEL / VCODETPWR / AOM deflection efficiency / RCTRANSPD
3. Confirm the frequency matching between the VCO and AOM.

Quote:

but the increase in both the RCtrans and the RCrefl is consistent with my theory that the power going to the RC has increased ; its not just an increase in the visibility.

We should scan the AOM/VCO to make sure the frequency is matched to the resonance to within 0.5 dB.

 

Attachment 1: 091125_FSS.png
091125_FSS.png
  2343   Sat Nov 28 20:27:12 2009 KojiUpdatePSLFSS oscillation: Total gain reduced

I stopped by the 40m for some reason and found that the MC trans was 7.5.
This was caused by an oscillation of FSS, which seemed to be started by itself.

The oscillation stopped by reducing the FSS total gain to +9dB (from +11dB).
This is not a permanent fix (i.e. autolocker will restore the gain).
If it seems necessary to reduce the FSS gain always, we change the MC autolocker script.

Attachment 1: 091128_PSL.png
091128_PSL.png
  2379   Thu Dec 10 09:51:06 2009 robUpdatePSLRCPID settings not saved

Koji, Jenne, Rob

 

We found that the RCPID servo "setpoint" was not in the relevant saverestore.req file, and so when c1psl got rebooted earlier this week, this setting was left at zero.  Thus, the RC got a bit chilly over the last few days.  This channel has been added. 

 

Also, RCPID channels have been added (manually) to conlog_channels. 

  2381   Thu Dec 10 09:56:32 2009 KojiUpdatePSLRCPID settings not saved

Note: The set point C1:PSL-FSS_RCPID_SETPOINT is 37.0 on C1PSL_FSS_RCPID.adl.

Now the temp is recovering with its full speed. At some point we have to restore the value of the FSS SLOW DC as the temp change drag it up.

Quote:

Koji, Jenne, Rob

We found that the RCPID servo "setpoint" was not in the relevant saverestore.req file, and so when c1psl got rebooted earlier this week, this setting was left at zero.  Thus, the RC got a bit chilly over the last few days.  This channel has been added. 

Also, RCPID channels have been added (manually) to conlog_channels. 

 

Attachment 1: RC_TEMP.png
RC_TEMP.png
  2466   Wed Dec 30 09:57:53 2009 steveUpdatePSLthirsty water chiller

I added 600 cc of Arrowhead Distilled Water to the chiller.

60 days plot shows that about every ~ 10 days I have to add some.

Please check the water level yourself.

Attachment 1: htemp60d.png
htemp60d.png
  2563   Tue Feb 2 22:39:12 2010 JenneUpdatePSLIFO isn't playing nice tonight

[Jenne, Kiwamu]

It's been an iffy last few hours here at the 40m.  Kiwamu, Koji and I were all sitting at our desks, and the computers / RFM network decided to crash.  We brought all of the computers back, but now the RefCav and PMC don't want to lock.  I'm a wee bit confused by this.  Both Kiwamu and I have given it a shot, and we can each get the ref cav to sit and flash, but we can't catch it.  Also, when I bring the PMC slider rail to rail, we see no change in the PMC refl camera.  Since c1psl had been finicky coming back the first time, I tried soft rebooting, and then keying the crate again, but the symptoms remained the same.  Also, I tried burt restoring to several different times in the last few days, to see if that helped.  It didn't.  I did notice that MC2 was unhappy, which was a result of the burtrestores setting the MCL filters as if the cavity were locked, so I manually ran mcdown.  Also, the MC autolocker script had died, so Kiwamu brought it back to life.

Since we've spent an hour on trying to relock the PSL cavities (the descriptive word I'm going to suggest for us is persistent, not losers), we're giving up in favor of waiting for expert advice in the morning.  I suppose there's something obvious that we're missing, but we haven't found it yet......

  2564   Wed Feb 3 01:17:19 2010 KojiUpdatePSLIFO isn't playing nice tonight

I checked the situation from my home and the problem was solved.

The main problem was undefined state of the autolocker and the strange undefined switch states, being associated with the bootfest and burtrestore.

- MC UP/DOWN status shows it was up and down. So I ran scripts/MC/mcup and scripts/MC/mcdown. These cleared the MC autolocker status.

- I had a problem handling the FSS. After mcup/mcdown above, I randomly pushed the "enable/disable" buttons and others, and with some reason, it recovered the handling. Actually it acquired the lock autonomously. Kiwamu may have also been working on it at the same time???

- Then, I checked the PSL loop. I disconnected the loop by pushing the "test" button. The DC slider changes the PZT voltage only 0~+24V. This is totally strange and I started pushing the buttons randomly. As soon as I pushed the  "BLANK"/"NORMAL" button, the PZT output got back under the control.

- Then I locked the PMC, MZ, and MC as usual.

Alberto: You must be careful as the modulations were restored.

Quote:

[Jenne, Kiwamu]

It's been an iffy last few hours here at the 40m.  Kiwamu, Koji and I were all sitting at our desks, and the computers / RFM network decided to crash.  We brought all of the computers back, but now the RefCav and PMC don't want to lock.  I'm a wee bit confused by this.  Both Kiwamu and I have given it a shot, and we can each get the ref cav to sit and flash, but we can't catch it.  Also, when I bring the PMC slider rail to rail, we see no change in the PMC refl camera.  Since c1psl had been finicky coming back the first time, I tried soft rebooting, and then keying the crate again, but the symptoms remained the same.  Also, I tried burt restoring to several different times in the last few days, to see if that helped.  It didn't.  I did notice that MC2 was unhappy, which was a result of the burtrestores setting the MCL filters as if the cavity were locked, so I manually ran mcdown.  Also, the MC autolocker script had died, so Kiwamu brought it back to life.

Since we've spent an hour on trying to relock the PSL cavities (the descriptive word I'm going to suggest for us is persistent, not losers), we're giving up in favor of waiting for expert advice in the morning.  I suppose there's something obvious that we're missing, but we haven't found it yet......

 

  2565   Wed Feb 3 07:57:01 2010 steveUpdatePSLPMC transmission is low

The low PMC transmission alarm was on this morning. The PMC alignment needs a touch up.

Attachment 1: pmct40d.jpg
pmct40d.jpg
  2650   Tue Mar 2 12:20:54 2010 kiwamuUpdatePSLstray beam

In order to block stray beams, I have put some beam dumps and razor blades on the PSL  table.

There were three undesired spots in total. I found two spots on the south side door of the PSL room, close to Mach-Zehnder.

Another spots was on the middle of the north door. Now they all are blocked successfully.

  2690   Sun Mar 21 20:08:20 2010 kiwamu, ranaUpdatePSLEOM wasit size

We are going to set the waist size to 0.1 mm for the beam going through the triple resonant EOM on a new PSL setup.

When we were drawing a new PSL diagram, we just needed to know the waist size at the EOM in order to think about mode matching.

waist.png

This figure shows the relation between the waist size and the spot size at the aperture of the EOM.

The x-axis is the waist size, the y-axis is the spot size. It is clear that there is a big clearance at 0.1 mm waist size. This is good.

Also it is good because the waist size is much above the damage threshold of the EO crystal (assuming 1W input).

The attached file is the python code for making this plot.

Attachment 2: waist.py.zip
  2691   Sun Mar 21 21:02:39 2010 KojiUpdatePSLEOM waist size
You don't need a lengthy code for this. It is obvious that the spot size at the distance L is minimum when L =
zR, where zR is the Rayleigh range. That's all.

Then compare the spot size and the aperture size whether it is enough or not.

It is not your case, but if the damage is the matter, just escape to the large zR side. If that is not possible
because of the aperture size, your EOM is not adequate for your purpose.
  2720   Sun Mar 28 20:05:33 2010 ranaSummaryPSLFSS Work from Sunday: AOM/VCO level set wrong

Just before working on the FSS today, I noticed that the VCO RF output level was set incorrectly.

This should ALWAYS be set so as to give the maximum power in the first order diffracted sideband. One should set this by maximizing the out of lock FSS RFPD DC level to max.

The value was at 2.8 on the VCOMODLEVEL slider. In the attached plot (taken with the FSS input disabled) you can see that this puts us in the regime where the output power to the FSS is first order sensitive to the amplitude noise on the electrical signal to the AOM. This is an untenable situation.

For adjusting the power level to the FSS, we must always use the lamba/2 plate between the AOM and the RC steering mirrors. This dumps power out to the side via a PBS just before the periscope.

Attachment 1: Untitled.png
Untitled.png
  2721   Sun Mar 28 20:51:31 2010 ranaSummaryPSLFSS Work from Sunday: Cavity Suspension is Ridiculously Undamped!

What is the Transfer Function of the suspension of the reference cavity? What were the design requirements? What is the Q and how well does the eddy current damping work? What did Wolfowitz know about the WMD and when? Who cooked the RTV in there and why didn't we use Viton??

To get to the bottom of these questions, today I shook the cavity and measured the response. To read out the pitch and yaw modes separately, I aligned the input beam to be misaligned to the cavity. If the beam is mis-aligned in yaw, for example, the transmitted light power becomes first order sensitive to the yaw motion of the cavity.

In the attached image (10 minute second-trend), you can see the second trends for the transmitted and relfected power. The first ringdown comes from the pitch or vertical mode. The second (shorter) one comes from the yaw misalignment and the yaw shake.

To achieve the up/down shake, I leaned onto the table and pumped it at its eigenfrequency. For the yaw shake, I put two fingers on the RC can's sweater and pushed with several pounds of force at the yaw eigenfrequency (2.6 Hz). For the vertical, I jumped up and down at half the vertical eigenfrequency (4 Hz).

I also made sure that the .SCAN field on these EPICS records were set to 9 so that there is no serious effect from a beating between the eigenfrequency and the EPICS sample rate.

Punchline:

f_vert   = 4 Hz

tau_vert = 90 seconds

Q_vert   = 1000            (yes, that number over there has 3 zeros)

 

f_hor    = 2.6 Hz

tau_hor  = 30 seconds

Q_hor    = 250

 

This is an absurd and probably makes us very sensitive to seismic noise - let's make sure to open up the can and put some real rubber in there to damp it. My guess is that these high Q modes

are just the modes of the last-stage steel spring / pendulum.

Attachment 1: Untitled.png
Untitled.png
  2722   Sun Mar 28 23:17:46 2010 ranaSummaryPSLFSS Work from Sunday: noise spec

This is the error point spectrum - it is filled with huge multiples of ~75 kHz as Yoichi noticed a couple years ago.

I tried to use the netgpib.py package to read out the Agilent 4395, but the SVN had been corrupted by someone saving over the netgpib.py package. To get it to work on rosalba I reverted to the previous version, but whoever is busy hacking on netgpib.py needs to checkin the original package and work on some test code instead.

I also noticed that the default output format for the AG4395.py file is in units of Watts. This is kind of dumb - we need someone to develop this package a little as Yoichi did for the SRS785.

Attachment 1: in2.png
in2.png
  2723   Sun Mar 28 23:47:47 2010 ranaSummaryPSLFSS Work from Sunday: Open Loop Gain

I measured the open loop gain of the FSS (as usual, I have multiplied the whole OLG by 10dB to account for the forward loop gain in the box). I used a source level of -20 dBm and made sure this was not saturating by changing the level.

Its clear that the BW is limited by the resonance at ~1.7 MHz. Does anyone know what that is?

Attachment 1: fssloop.png
fssloop.png
Attachment 2: sweep2.png
sweep2.png
  2724   Mon Mar 29 01:11:33 2010 ranaSummaryPSLFSS Work from Sunday: RF Out Spectrum

I measured the RF spectrum coming out the FSS RFPD to look for saturations - its close to the hairy edge. This is with the 8x power increase from my AOM drive increase. I will increase the FSS's modulation frequency which will lower the Q and gain of the PD to compensate somewhat. The lower Q will also gain us phase margin in the FSS loooop.

 

I put in a bi-directional 20 dB coupler (its only rated down to 30 MHz, but its only off by ~0.3 dB at 21 MHz) between the RFPD and the FSS box. I looked at the time series on the 300 MHz scope and measured the power spectrum.

The peak signal on the scope was 40 mV; that translates to 400 mV at the RFPD output. Depending on whether the series resistor in the box is 20 or 50 Ohms, it means the MAX4107 is close to saturating.

As you can see from the spectrum, its mostly likely to hit its slew rate limit (500 V/us) first. Actually its not going to hit the limit: but even getting within a factor of 10 is bad news in terms of distortion.

Besides the multiples of the modulation frequency, you can see that most of the RMS comes from the strange large peaks at 137.9 and 181.1 MHz. Anyone know what these are from?

TEK00000.PNGTEK00001.PNGTEK00002.PNG

On the middle plot above, I have enabled the 20 MHz BW limit so you can see how much the amplitude goes down when only the 21.5 MHz SB is included. You can also see from the leftmost plot that once in awhile there is some 400mV/10ns slewing. Its within a factor of 10 of the slew rate limit.

Attachment 1: rfout.png
rfout.png
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