| Quote: |
| Quote: | | The 64k is the series resistor after the PA85, not the modeled resistance of the PZT itself. |
Yes. What I meant was that because the measured voltage across the PZT was a half of the open voltage of the HV amp, the DC impedance of the PZT is expected to be similar to the output impedance of the HV amp. Of course, I don't think the DC impedance of a normal PZT should be such low.
I'm puzzled by the discrepancy between this expected DC impedance and the directly measured impedance by the Fluke DVM (1.5M Ohm).
One possibility is that the PZT leaks current only when a high voltage is applied. |
|
703
|
Sat Jul 19 19:41:56 2008 |
Yoichi | AoG | PSL | The author of the entry 702 is Yoichi not Rob |
| I made a mistake. |
|
711
|
Tue Jul 22 03:03:22 2008 |
John, Rob | Update | PSL | FSS open loop transfer function |
With the common gain slider maxed out the unity gain frequency is 58kHz.
The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.
Tomorrow I'll take a closer look at the board. |
|
712
|
Tue Jul 22 09:24:17 2008 |
steve | Update | PSL | laser power |
| Laser power reality of 120 days |
| Attachment 1: power120d.jpg
|
|
|
713
|
Tue Jul 22 11:55:22 2008 |
rana | Update | PSL | Note from R. Abbott re: the PMC |
an email from Rich:Your PZT is broken.
R |
|
714
|
Tue Jul 22 13:15:14 2008 |
rob | Update | PSL | Note from R. Abbott re: the PMC |
| Quote: | an email from Rich:Your PZT is broken.
R |
Quelle surprise
 |
|
715
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Tue Jul 22 13:16:09 2008 |
John, Rob | Update | PSL | FSS open loop transfer function |
| Quote: | With the common gain slider maxed out the unity gain frequency is 58kHz.
The reference cavity refl diode appears to be okay. RF OUT/ TEST IN transfer function was normal.
There is a ~220mV offset in the RF out. We removed this using a coupler - no change. We also checked the
diode->FSS cable.
Tomorrow I'll take a closer look at the board. |
Should note that the UGF of 58kHz was measured with the test cable (from RFPD to board), so the demod phase was presumably sub-optimal. |
|
719
|
Wed Jul 23 01:42:26 2008 |
rana | Configuration | PSL | FSS RFPD: Examined, "repaired", and re-installed |
Rob said that there might be something wrong with the FSS RFPD since the loop gain is so low.
Next time we should just use the Jenne laser on it in-situ and compare with our reference.
We had a 24.5 MHz LSC PD which Rob got from Sam. Sam got it from Rai. I gave it to Rai in Livingston
because it seemed suspicious. Seems fine now. This black box PD had a lower overall response than
the goldbox one we already had. The 2001-2005 era diodes which we got from the Canadian Perkin-Elmer
all had high capacitance and so that's not a surprise.
So the goldbox one was not broken totally.
I found that the offset came from a cracked capacitor. C25 was a yellow thru-hole ceramic 0.1 uF.
Its a surface mount board...don't know why this was like this but there's also no reason it should
have cracked unless it was soldered on with too much heat. I replaced it with a 0.47 uF ceramic
surface mount. Also R24 was a 20 Ohm resistor and L3 was not stuffed?? Removed R24 and put a 1 uH
inductor into L3. This is there so that the input to the MAX4107 is AC coupled.
However, the DC signal that Rob saw was actually because of the cracked C25. It had shorted and was
making a 25 mV signal at the input to the MAX4107 which has a gain of 10. This was producing ~165 mVdc
into a 50 Ohm load and so it could have saturated most mixers. The FSS board, however, has an overly
monstrous level 21 (I think) mixer and so this should not have been an issue. Maybe.
I was able to lock with the 24.5 MHz black box PD but it was not too hard to repair the gold box one
so I did. I tuned it so that the notch is truly at 43 MHz (2x the FSS 21.5 MHz modulation) but because
someone has done this using a hacky cap in parallel with the main PD, I am unable to get the resonant
peak to line up at 21.5 MHz. Its at 23 MHz instead. This loses us ~2 dB in signal. Since the frequency
is so low, we can increase the gain in the MAX4107 by another factor of 3 or so in the future.
So the PD is not our problem. Still worth verifying that the cable is good -- its around 10 miles long!!
And loops around in there with a bunch of other cables. We have an electronic phase shifter so this seems
totally misguided.
The other bad problem is that the mode matching is pretty horrible. Something like 1/3 of the carrier
power doesn't go into the cavity.
FSS TODO:
1) Check cable between RFPD and FSS box for quality. Replace with a good short cable.
2) Using a directional coupler, look at the RFPD output in lock on a scope with 50 Ohm term.
I suspect its a lot of harmonics because we're overmodulating to compensate for the bad
mode matching.
3) Purchase translation stages for the FSS mode matching lenses. Same model as the PMC lenses.
Fix the mode matching.
4) Get the shop to build us up some more bases for the RFPDs on the PSL such as we have for the LSC.
Right now they're on some cheesy Delrin pedestals. Too soft...
5) Dump the beam reflected off the FSS RFPD with a little piece of black glass or a razor dump.
Anodized aluminum is no good and wiggles too much.
The attached PDF shows photos of the old and new style PDs. One page 3 there's a wire that I soldered on
as a handle so that we can remove the RF can (occasionally people claim that soldering to the lid screws
up the magnetic shielding magic of the lid. use this as a litmus test of their electronics know-how; its
a tin can - not an orgone box). Pages 4 & 5 are the circuit before I soldered, page 6 the cap after I
tried to remove it, page 7 is the circuit after I put in the new cap, and page 8 is the schematic with
the mark up of the changes. |
| Attachment 1: Untitled.pdf
|
|
|
726
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Wed Jul 23 18:42:18 2008 |
Jenne | Update | PSL | Alignment of AOM |
[Rana, Yoichi, Jenne]
Short Version: We are selecting the wrong diffracted beam on the 2nd pass through the AOM (we use the 2nd order rather than the first). This will be fixed tomorrow.
Long Version of AOM activities:
We checked the amount of power going to the AOM, through the AOM on the first pass, and then through the AOM on the second pass, and saw that we get about 50% through on the first pass, but only about 10% on the 2nd pass. Before the AOM=60mW, after the first pass=38mW, after the 2nd pass=4mW. Clearly the alignment through the AOM is really sketchy.
We translated the AOM so the beam goes through the center of the crystal while we align things. We see that we only get the first order beam, which is good. We twiddled the 4 adjust screws on the side of the AOM to maximize the power at the curved mirror for the 1st order of the first pass, which was 49.6mW. We then looked at the DC output of the Reference Cavity's Refl. PD, and saw 150mV on the 'scope. The power measured after the polarizing beam splitter and the next wave plate was still 4mW. Adjusting the curved mirror, we got up to 246mV on the 'scope for the Refl. PD, and 5.16mW after the PBS+Waveplate. We adjusted the 4 side screws of the AOM again, and the tip/tilt of the PBS, and got up to 288mV on the 'scope.
Then we looked at the beam that we keep after the 2nd pass through the AOM, and send to the reference cavity, and we find that we are keeping the SECOND order beam after the second pass. This is bad news. Yoichi and I will fix this in the morning. We checked that we were seeing a higher order beam by modulating the Offset of the MC servo board with a triangle wave, and watching the beam move on the camera. If we were chosing the correct beam, there would be no movement because of the symmetry of 2 passes through the AOM.
I took some sweet video of the beam spot moving, which I'll upload later, if I can figure out how to get the movies off my cell phone. |
|
735
|
Thu Jul 24 19:29:26 2008 |
Yoichi | Configuration | PSL | C1:PSL-STAT_FSS_NOM_C_GAIN is changed from 30 to -0.7 |
Koji, Yoichi
Since the light power going to the ref. cavity is now significantly increased (see Janne's elog later), C1:PSL-STAT_FSS_NOM_C_GAIN is changed from 30 to -0.7.
Otherwise, the MC did not lock. |
|
736
|
Thu Jul 24 21:04:58 2008 |
rana | Update | PSL | FSS |
Since Jenne and Yoichi are going to finish up their refcav/FSS work in the morning I decided to
look at the trends. I set the RF modulation level from 10.0 back down to 7.5 so that we would
have the same RF modulation depth as before. I also set the FSS common gain and its nominal to
1.0 dB since it seemed more stable this way.
With 7.5, the transmission of the refcav is ~6.9 V. It was around 0.7 V before so there's already
been a factor of 10 improvement in the power since the work started. In addition to the mode matching
work which is about to commence, we should attenuate the RC TRANS with a real mirror (not ND) so that
the camera and PD don't saturate. We should also do the same for the REFL PD and camera and make sure
to put in a steering mirror for the REFL PD and orient REFL so that it faces West (so that we can
look at its face with a viewer) and dumps its reflection.
Since the common gain is so low now, I expect that we will want less light in total. We can achieve
this by turning down the RF drive to the VCO.
I also fixed the MC down script which was putting the FSS common gain to the unstable +10 dB level
during the MC locking process. |
|
741
|
Fri Jul 25 19:57:18 2008 |
Jenne | Update | PSL | Ref Cav & PMC |
"PMC is in, but is still being worked on. Leave it alone." ---Rana
Ref. Cavity is locked again. Still a work in progress. I think we're ready to mode match on Monday. ---Jenne |
|
745
|
Sun Jul 27 23:06:17 2008 |
rana | Update | PSL | PMC, MZ, MC-MMT, etc. |
With the new PMC now in I aligned the MZ to the new beam (there is sadly no steering
between the PMC and the MZ).
I also removed the pickoff that we had put before the MZ just in case we wanted to
move the FSS pickoff to there - its been 2 years now so I guess its not going to happen.
The new PMC's cavity axis seems to be a few hundred microns higher than the old one. So I
tried to move the MZ EOMs to compensate but ended up also steering all of the MZ's mirrors
to get the contrast good, the beam onto the ISS PDs, centered (sort of) onto the MMT lenses
and onto the periscope.
Along the way I also removed some of the vestigial squeezer stuff around the power control
PBS. The output of the PBS now goes directly into the high power dump with no steering. This
eliminated around a dozen clamps, bases, etc. and a couple of mirrors.
The MC is locked on the low power beam we have running through everything. I restored the
PSL launch beam just using the MC-WFS and it locked on a TEM00. So now we know that we
really don't need the PSL quads for this as long as the MC1 angle is stable.
The good news is that the PMC PZT voltage is now flat: the problem must have really been with
the PZT and not the cabling or notch box like I had wondered about.
Todo:
-----
1) Continue mode matching into the PMC. Its transmission now is around the same as the
old one.
2) Put a UHV foil covered lead brick onto the PMC to quiet it down.
3) Characterize the PMC loop and retune the body notch for the new body.
4) Tweak the MZ alignment to minimize the RFAM. We can use StochMon to do this as
long as we have the MC WFS turned off or we can put in a flipper to take the
beam before the MC and send it to the StochMon RFPD.
5) Re-align onto the ISS.
6) Install irises around the periscope for the beam. The old iris there is way off.
7) Fix PSL ANG and center both POS and ANG.
|
|
746
|
Mon Jul 28 11:20:13 2008 |
Jenne | Update | PSL | Work on the FSS and Reference Cavity |
[Yoichi, Jenne, Koji]
The Reference Cavity's saga continues....
Thursday, Yoichi and I worked to change the beam that we chose from the 2nd pass through the AOM, to the first order beam rather than the 2nd order beam (see elog #726). After choosing the correct beam, we get 29mW incident on the reference cavity (compared with 4mW before any work began). We adjusted the angle of the AOM in the plane of the table, and got up to 30.6mW. We adjusted the tip/tilt of the AOM and got to 30.7mW (the tip/tilt adjustment made a more significant difference in the work described in elog #726, but after that work, it was probably already pretty close to optimized). We noticed that for the above measurements, we had 2 beams through the Polarizing Beam Splitter and Waveplate (one very dim), so after excluding that beam, the power meter read 30.4mW. We adjusted the curved mirror a little, and got 30.8mW incident on the reference cavity.
We then put a triangle wave into the offset of the MC Servo Board using the "trianglewave <channel> <center> <amplitude> <period> <runtime>" command in a terminal screen. This changes the voltage to the VCO, and thus the frequency response of the AOM. We watch the diffracted spots from the second pass through the AOM, and confirm that the beam we have chosen is not moving, and all the others are. By symmetry, if we chose the first order beam after the first pass through the AOM, and then again chose the first order beam after the second pass, the resulting beam will not move with the frequency change of the AOM.
We saw 1.50V (Refl. PD, unlocked) on the 'scope after aligning the optics to make the newly chosen beam hit the input mirror of the reference cavity. Order of operations for this alignment:
- Recenter the beam on the 2 lenses that are just after the PBS and the waveplate
- Adjust pitch and yaw of the two steering mirrors until the beam reflected off the input mirror of the reference cavity is parallel to the incident beam
- Use a sensor card to check the alignment of the incident and reflected beams, and adjust the steering mirrors to get the alignment close
- Note the amplitude of the DC output of the Refl. PD with the iris completely open. Close the iris until the signal decreases by ~50%, then adjust the steering mirrors until the original amplitude is regained. Repeat until the iris can be almost completely closed but the Refl. PD signal doesn't change
- Watch the DC output of the Refl. PD, and maximize the signal on a 'scope
- Sweep the PZT of the laser using a function generator into the RAMP input on the FSS board (~10Vpp at ~1Hz), OR sweep the temperature of the laser using the trianglewave function on the SLOW FSS channel (amplitude~0.5, period~50)
- Watch the modes that resonate in the cavity, and adjust pitch and yaw of the steering mirrors to get closer to the TEM00 mode
- When the TEM00 mode appears in the sweep, stop the sweep, and lock the cavity
- Watch the DC output of the Transmitted PD, and maximize the signal on a 'scope
- Celebrate!
After all of this adjusting,
Refl. PD (unlocked) = 1.48V
Refl. PD (locked) = 680mV
Trans. PD (locked) = 6.28V
Power reflected (unlocked) = 26.28mW
Power transmitted (locked) = 13.89mW
Thus, 53% transmission
Next: check the amount of power transmitted by reducing the amplitude of the RF modulator. This reduces the amount of power used by the sidebands, and so should increase the transmission.
Power incident = 27mW
Power transmitted = 17.2mW
Thus, 64% transmission
We then put the RF modulator back where it was originally.
We then replaced the lens mounts for the f=802 and f=687 lenses between the AOM and the reference cavity, to the new mounts that Yoichi bought. Koji helped me realign into the reference cavity, and we got:
Refl. PD (unlocked) = 1.48V
Refl. PD (locked) = 880mV
Trans PD (locked) = 4.64V
Power incident = 26.97mW
Power transmitted = 10.39mW
39% transmission
Since more mode matching etc. is in the works, we left this for the night.
On Friday, we changed the setup of the cameras and PDs for both reflection and transmission, to avoid saturating the PDs and cameras.
On the Refl. side of the reference cavity, we put a W2-PW-1025-UV-1064-45P pickoff between the last mirror and lens before the camera and PD. We moved the camera to the pickoff side of the new optic. We then replaced teh 45UNP beam splitter that split the beam between the PD and the camera with a Y1-1037-45P highly reflective mirror, and put the PD in the old camera location.
On the Trans. side of the ref. cavity, we replaced the BSI-1064-50-1025-45S with a W2 pickoff, and replaced the Y1-1037-45-P highly reflective mirror with the 50/50 beam splitter that was replaced by the W2.
Now we have:
Refl. PD (unlocked) = 1.68V
Refl. PD (locked) = 640mV
Trans PD (locked) = 4.24V
Power incident = 25mW
Power transmitted = 14.48mW
58% transmission
Koji pointed out that when remounting, I had put the f=802 lens ~2cm away from its original position (along the z-axis), so I moved the lens back to where it should be, and realigned into the reference cavity. Since Rana was working on the PMC at the same time, the laser was turned down by about a factor of 100, so my starting measurements were:
Refl. PD (unlocked) = 23.6mV
Refl. PD (locked) = 10.2mV
Trans PD (locked) = 56mV
Power incident = 0.35mW
Power transmitted = 0.16mW
46% transmission
Since it was late on Friday by the time everything was realigned into the ref. cavity (I'm still working on my optics aligning skills), I forgot to measure the transmission after all of my work. I'll do that today (Monday) as soon as Sharon/Koji are done working with the IFO this morning. Also, I'll put up before/after pictures as soon as I find the camera...it seems to have walked off.
UPDATE:
Ref. Cav. measurements after Friday's alignment (and after turning the laser power back up to normal):
Refl. PD (unlocked) = 1.58V
Refl. PD (locked) = 304mV
Trans PD (locked) = 3.68V
Power incident = 24.96mW
Power transmitted = 16.45mW
66% transmission
To do: Start the actual mode-matching into the reference cavity. |
|
749
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Mon Jul 28 17:44:07 2008 |
rana | Update | PSL | PMC PZT v. temperature |
This plot shows that the PMC PZT has ~20 Vpp fluctuations on a 24 hour timescale
which is correlated to the 24 hour temperature fluctuations. By contrast, the MZ
has ~75 Vpp. |
| Attachment 1: Untitled.pdf
|
|
|
751
|
Mon Jul 28 23:41:07 2008 |
rob | Configuration | PSL | FSS/MC gains twiddled |
I found the FSS and MC gain settings in a weird state. The FSS was showing excess PC drive and the MC wouldn't lock--even when it did, the boost stage would pull it off resonance. I adjusted the nominal FSS gains and edited the mcup and mcdown scripts. The FSS common gain goes to 30dB, Fast gain to 22dB, and MCL gain goes to 1 (which puts the crossover back around ~85 degrees where phase rises above 40 degrees). |
|
758
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Tue Jul 29 19:41:38 2008 |
Yoichi | Update | PSL | FSS loop transfer functions |
Last night I measured a bunch of transfer functions on the FSS loop.
All the loop gains were measured with the common gain = 30db and the fast gain = 18dB.
(1) The first attachment is the overall open loop transfer function of the FSS loop. I put a signal from the Test IN2 and observed signals from IN1 and IN2.
The UGF is about 180kHz.
By increasing the RF amplitude going to the EOM (i.e. increasing the sideband power), I can further increase the gain of the servo.
However, it made the PC drive immediately crazy. Probably it was some oscillation.
(2) Then I locked the ref. cav. with only the PZT actuator. I did so by simply unplugging the cable going to the PC.
Surprisingly, the cavity locked with the *same* gain setting as before. The second attachment shows the open loop transfer function measured in this configuration. It seems wrong, I mean, it should be unstable. But the cavity locked. A mystery.
(3) The third plot is the measured TF from the Test IN1 of the FSS board to the fast out (output to the PZT).
(4) By dividing the TF measured in (2) with the TF of (3), I got the response of the PZT times the cavity response. This is shown in the attachment 4.
(5) We can guess the open loop TF of the PC path by subtracting the TF in (2) from (1). It is shown in the attachment 5.
(6) The filter shape of the PC path is measured by injecting signal from the Test IN1 of the FSS board and observing it at the PC output. Since it is a high voltage output, I reduced the common gain to -8.5dB during the measurement. The attachment 6 is the measured filter shape. The gain is corrected to show what it should look like when the common gain = 30dB.
(7) By dividing (5) with (6), I plotted the response of the PC times the cavity response in the attachment 7. Since the 1/f cavity pole and the response of the PC, which is proportional to f, should cancel out, we expect a flat response above the cavity pole frequency (38kHz). You could say it is a sort of flat, if you have obscured eyes.
The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.
The plot (4) is also strange becaues it does not show the low pass feature expected from the cavity pole. |
| Attachment 1: OverallOPLTF.eps
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| Attachment 2: OpltfPZTOnly.eps
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| Attachment 3: PZTFilter.eps
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| Attachment 4: PZTxCavityPole.eps
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| Attachment 5: OpltfPCOnly.eps
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| Attachment 6: PCFilter.eps
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| Attachment 7: PCxCavityPole.eps
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|
761
|
Tue Jul 29 23:04:34 2008 |
Yoichi | Update | PSL | FSS loop transfer functions |
| Quote: |
The measurement of the PZT open loop TF is very suspicious. According to this, the PC path has a very large gain even at very low frequencies (there is no cross over above 1kHz). This cannot be true. Maybe the cavity's optical gain was low when it was locked with only the PZT. I will re-measure it.
|
I measured it again and found that the loop was oscillating at 13.5kHz. I think this oscillation prevented the ref. cavity from building up the power and consequently lowered the optical gain making it marginally stable. So the PZT path open loop TF posted in the previous entry is wrong.
I was able to stop the oscillation by lowering the gain down to CG=-7.6dB and FG=-8.78dB.
The first attachment shows the measured open loop transfer function.
Since the gain setting is different from when the over all open loop TF was measured, I scaled the gain (attachment 2).
However, this plot seems to have too much gain. Scaling it down by 20dB makes it overlap with the over all open loop TF.
Maybe the gain reading on the EPICS screen is wrong. I will measure the actual gain tomorrow. |
| Attachment 1: OpltfPZTOnlyRaw.eps
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| Attachment 2: OpltfPZTOnly.eps
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767
|
Wed Jul 30 13:09:40 2008 |
josephb, Eric | Configuration | PSL | PMC scan experiment |
We turned the PSL power down by a factor of 4, blocked one half of the Mach Zehnder and scanned the PMC by applying a ramp signal to PMC PZT. Eric will adding plots later today of those results.
We returned the power to close to original level and removed the block on the Mach Zehnder, and then relocked the PMC. |
|
772
|
Wed Jul 30 16:35:56 2008 |
Eric | Update | PSL | PMC Scan Graphs |
Graphs of the PMC scan data that I got earlier today.
PMCLongScanWide.tiff shows the transmission intensity and PZT voltage plotted against time for a longer scan of the PMC (~120 seconds for one sweep).
PMCLongScanPeak.tiff is the same scan zoomed in on the primary peak. This scan was done with the laser power at around 1/3 its original value. However, scans done at around 1/6 the original value have peaks that are just as messy.
PMCShortScanWide.tiff shows the intensity and voltage for a more rapid scan (~30 second for one sweep). The black lines show how the peak positions are at very different PZT voltages (a difference of ~10 volts in both cases).
PMCShortScanPeak.tiff is zoomed in on the primary peak. The peak is much cleaner than for the long scan (less time for the laser's heat to expand the mirror?), though it is likely still too messy to reliably fit to a lorentzian. |
| Attachment 1: PMCLongScanPeak.tiff
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| Attachment 2: PMCLongScanWide.tiff
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| Attachment 3: PMCShortScanPeak.tiff
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| Attachment 4: PMCShortScanWide.tiff
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|
775
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Thu Jul 31 10:27:17 2008 |
rana | Update | PSL | PMC Scan Graphs |
| Quote: | Graphs of the PMC scan data that I got earlier today.
|
On the UNIX computers, one can use 'convert' to change these to PNG. A DC offset should be added to the transmitted
light so that the scan can be plotted with a log y-scale. And, of course, Acrobat can be used to make it into a
single PDF file.
The PMC scan always has this distortion and so the input power has to be decreased to a few mW to reduce the
thermal expansion effect; the expansion coefficient for SiO2 is ~5 x 10^-7 / K and we're worried about nm level
expansions. |
|
778
|
Fri Aug 1 01:13:32 2008 |
rana | Configuration | PSL | PSL Quad change and new script |
Koji and I changed a few optics so that now ~60% of the beam that went to the PSL POS QPD
now goes to the west side of the table for the aux. laser locking PLL. The beam is sort of
on the QPD again but needs a centering.
After this work I wrote a script SUS/freeswing-all.csh which puts a 30000 count offset into
the UL coil of each suspension and then disables it. This is just good enough to kick it up
so that the eigenfrequency can be measured. I ran it and it worked -- it finished running at
Fri Aug 1 00:44:30 PDT 2008 |
|
781
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Fri Aug 1 16:33:52 2008 |
rana | Configuration | PSL | PSL Quad change and new script |
| Here's the sensor ringdown trend from the kick. |
| Attachment 1: Untitled.png
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791
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Mon Aug 4 13:43:02 2008 |
Yoichi | Summary | PSL | FSS loop calibration |
As a part of the effort to repair the FSS loop bandwidth, I tried to calibrate the FSS loop.
First, I scanned the MOPA frequency by injecting a triangular wave into the ramp-in of the FSS box, which goes to the PZT of the NPRO.
The first attachment shows the transmitted light curve (pink one) along with the PDH signal (light blue).
The sweep was very slow (0.1Hz for 2Vp-p). From this measurement, the FWHM was 6.8e-3V. Then fpol = FWHM/2=3.4e-3V, where fpol is the cavity pole frequency.
So the PZT's DC response is 294*fpol/V. If we use the canonical fpol=38kHz, it is 11.172MHz/V.
Then I tried to measure the cavity pole. First I tried the cavity ring down measurement, by blocking the beam abruptly. Unfortunately, my hand was not fast enough.
The ring down shape was not an exponential decay.
I then locked the reference cavity only using the PZT with very narrow bandwidth (UGF=2kHz). I injected signal into the external modulation input of the 80MHz VCO
for the AOM. The second attachment shows the transfer function from this input to the IN2 (mixer output monitor port) of the FSS servo box.
To plot this, I corrected the measurement for the open loop TF (i.e. multiplying the measured TF with (1+G)), and other filters in the path (8MHz LPF after the ext. mod.
input of the 80MHz VCO, and an RCL network after the mixter). The gain looks like a cavity pole, but the phase decreases very rapidly.
If you look at the third attachment showing a wider band transfer function, there are notches at 1.8MHz and above. I couldn't find this kind of filter in the schematic.
Maybe this is the RFPD's bandpass filter. I will check this later. From these plots, it is difficult to tell the cavity pole frequency. From the -3dB point, fpol is around 83kHz,
but from the phase=-45deg point, fpol is around 40kHz.
Finally, I calibrated the cavity's optical gain by locking the Ref. Cavity with only PZT, and injecting a signal into the loop.
The signal was injected from Test-In2 of the FSS servo box and the transfer function from the PZT output signal (TP10) to IN1 (mixer output) was measured.
The transfer function was corrected for a 10Hz LPF after TP10.
The attachment4 shows a nice flat response up to 30kHz. Above 30kHz, the measurement is too noisy. The optical gain at DC is about 22dB from the PZT drive to the error signal (IN1).
Using fpol=38kHz, it means 887kHz/V calibration factor for the signal at IN1. There is a mixer output monitor DAQ channel in the FSS but it seems to be not working at the
moment. I will look into this later. There is a gain of 10dB between IN1 and the mixer monitor channel.
By looking at the phase response of the attachement4, there is a cavity pole like behavior around 30kHz. If we assume the PZT response is flat up to this frequency, it is
roughly consistent with fpol=38kHz.
I was not able to take a sensible spectrum of IN1 using the network analyzer. When the FSS servo was engaged, the signal was too small.
I will try to use an AF spectrum analyzer later to get a calibrated spectrum. |
| Attachment 1: P7310048.JPG
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| Attachment 2: cavity-response.pdf
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| Attachment 3: cavity-response2.pdf
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| Attachment 4: cavity-gain.pdf
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873
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Sat Aug 23 09:39:51 2008 |
rana, jenne | Update | PSL | PMC Survey |
Jenne, Rana
We scoped out the PMC situation yesterday.
Summary: Not broke. UGF ~ 500 Hz. Needs some electronics work (notches, boosts, LPFs)
Ever since we swapped out the PMC because of the broken PZT of the previous one, the UGF has been
limited to a low value. This is because the notches no longer match the mechanical resonant
frequencies of the body. The old one had a resonance at 31.3 kHz which we were notching using
the LC notch on the board as well as a dangling Pomona box in the HV line to the PZT. The one
has a resonance at ~14.5 kHz which we don't yet have a notch for. Jenne has all the real numbers and
will update this entry with them.
Todo:
- Implement the 4th order Grote low pass after the mixer.
- Replace the AD797 with an OP27.
- Change servo filter to have a boost (need DC gain)
- Make a 14.5 kHz notch for the bode mode.
- Put a 20 lb. gold-foil wrapped lead brick on the PMC.
Here's the link about the modified PMC board which we installed at LHO:
LHO PMC elog 2006 |
|
874
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Mon Aug 25 10:07:35 2008 |
Jenne | Update | PSL | Numbers for the PMC servo board (Re: entry # 873) |
Jenne, Rana
These are the numbers that go along with Rana's entry #873:
The existing notch in the PMC servo is at 31.41kHz.
The power spectrum of the PMC has a peak at 14.683kHz when it is just sitting on the PSL table (no extra mass). When we put a pile of steel and aluminum (~20lbs) on top of the PMC, the body resonance moves to 14.622kHz, but is decreased by about 40 dB!
Rana has ordered a lead brick + foil that should arrive sometime this week. To complete the mechanical part of this installation, we need to extend the earthquake mounts around the PMC so that the lead brick can't fall off of the PMC onto the rest of the table. |
|
876
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Mon Aug 25 10:51:06 2008 |
steve | Update | PSL | psl headtemp is coming down |
The laser water cooler was overflowing this morning.
I removed 500 cc water from the chiller.
The 4 days plot shows clearly:
that the capacity of the chiller is depending on the water level.
Overflowing water is a heat load for the chiller, so laser head temp goes up. |
| Attachment 1: ht4dw.jpg
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878
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Mon Aug 25 12:13:49 2008 |
Jenne | Update | PSL | Broken PMC Servo Board |
I broke the PMC servo board (on accident).
I was trying to measure the resistance of the extra resistor that someone put between the board and the HV OUT connector, since this is part of an RC filter (where C is the capacitance of the PZT on the PMC) that I need to know the values of as part of my mission to make a 14.6kHz notch for the PMC body mode. The resistance is 63.6k. I had to pull the board to get in to measure this resistance.
This resistor between the board and the center pin of the panel-mount HV OUT connector made a rigid connection between the board and the panel. When I was putting the board back in, I must have strained this connection enough that it broke. We don't have any of the same kind of resistor here at the 40m, so I'm waiting until after lunch to go to Wilson house and see if they've got any. The IFO is down until I get this sorted out. |
|
879
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Mon Aug 25 14:18:36 2008 |
Jenne | Update | PSL | PMC servo board is fixed |
| The PMC servo board is back in place, all fixed up with a shiny new resistor. The PMC locks, and the MC locks (I'm not saying anything either way about how long the MC will stay locked, but it is locked for now). The resistor is connected to the connector using a short piece of wire, so this problem won't happen again, at least with this connector on this board. |
|
884
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Tue Aug 26 09:04:59 2008 |
rana | Configuration | PSL | PMC Servo Board: Out for Repairs |
| I've started modifying our PMC board to bring it up to the 21st century - leave the screen alone or else you might zap something. |
|
892
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Wed Aug 27 13:55:43 2008 |
rana,jenne | Update | PSL | PMC Servo Board |
Board is back in. PMC is locked.
Nominal gain is now 15 dB with brick. We need to do more studies:
- Find out why there is still 35 MHz signal at the error point. Order some low pass filters to cut off above 35 MHz.
- Explore brick + no-brick loop shapes and error spectra.
- Measure and set the OLG.
We've left the copper-wrapped lead brick installed to let it slowly conform to the glass better. |
|
893
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Thu Aug 28 18:56:14 2008 |
rana | Configuration | PSL | beam block distorted |
There was a beam block after the Mach Zender. Who or what put this there?
The going to the MC now looks distorted as if someone has left something funny in the beam or maybe the new PMC has started to degrade??
Use the ELOG people...its good for you. |
|
895
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Fri Aug 29 02:40:43 2008 |
rana,jenne | Update | PSL | PMC Servo Board |
| Quote: | Board is back in. PMC is locked.
|
This entry has details about the low pass filter after the PMC mixer. This filter has a few purposes:
1] Remove the beat signal (at 2*f_mod) between the PD RF signal at f_mod and the LO signal at f_mod.
2] Remove the beat signal (at f_mod) between the PD RF signal at 2*f_mod (which comes from the
beating of the upper and lower RF sidebands) and the LO signal at f_mod.
3] Remove other RF signals from non-ideal behavior of the LO drive signal and distortion in the RF PD pre-amp.
So its important to have a very good rejection at 35 MHz and higher. I used the Hartmut LC network design which is
installed on H1, H2, & L1. Since there is a high gain in the audio amps right after the mixer we have to get rid of
the RF or else we'll get slew rate limited or otherwise rectified downconversion of the RF signal into our audio band.
Of course, what everyone immediately realizes from the above 3 points, is that this filter can't protect the PMC
noise performance from homodyne mixing (e.g. 2*f_mod in the LO and 2*f_mod in the RF PD). To get around that, we're
ordering some filters from Mini-Circuits to remove the 2f from those signals by ~30 dB. As long as we install
the same filters on the RF and LO legs, there should be no significant phase shift in the demodulated signal.
The attached 2 page PDF shows the calculated before and after TFs of this filter. The 2 attached .m files
calculate the TF's and have ascii art which shows how the filter works.
Here's a comparison of the attenuation (in dB) of 2 candidate Mini-circuits filters:
|
f(MHz) | SLP-30 | SLP-50
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31 | 0.5 | 0.4
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35 | 1.3 | 0.4
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38 | 6.1 | 0.4
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40 | 10.8 | 0.42
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61 | 46.3 | 14.8
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71 | 60 | 29
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91 | 76.9 | 48
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107 | 80 | 60
|
We don't have tabulated data at the same frequencies for both filters so I just made up some of the points by eye-balling the
plots from the catalog - but you get the idea: we can get away with using the SLP-30 at 35 MHz since it only attenuates the
signals by ~1.5 dB. So if someone can find 4 of these then Steve doesn't have to order any from Mini-Circuits. |
| Attachment 1: pmclp-07.pdf
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| Attachment 2: pmclp_40m_080824.m
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% PMCLP is a TF of the IF filter after the PMC mixer
%
% Mixer_Voltage -- Rs -- L1 --- L2 ---------Vout
% | | |
% C1 C2 Rl
% | | |
% GND GND GND
%
... 58 more lines ...
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| Attachment 3: pmclp.m
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% PMCLP is a TF of the IF filter after the PMC mixer
%
% Mixer_Voltage -- Rs -- L1 --- L2 ---------Vout
% | | |
% C1 C2 Rl
% | | |
% GND GND GND
%
... 57 more lines ...
|
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896
|
Fri Aug 29 10:20:32 2008 |
Yoichi | Configuration | PSL | beam block distorted |
| Quote: | There was a beam block after the Mach Zender. Who or what put this there?
The going to the MC now looks distorted as if someone has left something funny in the beam or maybe the new PMC has started to degrade??
Use the ELOG people...its good for you. |
I put the block. I was frequently reaching to the FSS box to change the test point probes. I put the block to protect my hands/clothes from being burnt accidentally. |
|
901
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Fri Aug 29 15:01:45 2008 |
steve | Update | PSL | MOPA_HTEMP in increasing |
The laser chiller temp is 21.9C ( it should be 20.0C )
Control room temp 73F ok, no obvious block
Ops, there is a piece of paper blocking the intake of the chiller
This is a four day plot. The paper was blocking the air flow all day. |
| Attachment 1: htcl.jpg
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902
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Fri Aug 29 16:35:18 2008 |
Yoichi | Configuration | PSL | beam block distorted |
| Quote: | There was a beam block after the Mach Zender. Who or what put this there?
The going to the MC now looks distorted as if someone has left something funny in the beam or maybe the new PMC has started to degrade??
Use the ELOG people...its good for you. |
The apparent distortion of the MC refl. was caused by mis-alignment of the MC mirrors.
Because the MC1 was mis-aligned, the reflected light was clipped by a steering mirror.
I restored the MC angle bias values from the conlog history and now the MC locks.
According to conlog, the MC alignment was changed at around 18:30 on Thursday PDT.
It could have been caused by the computer reboots. |
|
903
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Fri Aug 29 17:39:25 2008 |
rana | Configuration | PSL | PMC: ADC Channels |
The attached PNG shows the PMC error and controls signals with no calibration.
There are 3 states:
DARK - RF input disabled & output blanked. This should be a measure of the ADC noise
(-10 dB) - This is with the gain slider down at 5 dB instead of the nominal 15 dB.
Looks like the Generic DAQ board whitening is good enough for these signal levels above ~1 Hz.
From the low and high gain spectra it also looks like the UGF is ~500 Hz with the gain at 15 dB. |
| Attachment 1: mcf.png
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904
|
Fri Aug 29 18:24:48 2008 |
rana | HowTo | PSL | PMC: PZT Calibration |
I calibrated the PMC PZT at DC by using 'trianglewave' to drive the DC offset slider
and reading back PMC_PZT and PMC_TRANSPD_F (both are DC coupled DAQ channels).
The attached PDF illustrates the method: look at the voltage required to span 1 FSR and then divide.
PMC_cal (m/V) = (1064 nm)/2 / V_FSR The calibration for our PZT is therefore 10.4 nm/V.
The full scale (0-300 V) range is 3.1 microns.
From Jenne's elog entry we know that the series resistor to the PZT is 63.6 kOhms. The PZT is labeled as
having a capacitance of 279 nF. So the PMC drive's pole frequency is 1/2/pi/63.6e3/279e-9 = 9 Hz +/- 0.5 Hz.
The cable capacitance is ~20 pF/foot so its not significant for this.
The template file is Templates/PMC-PZTcal.xml.
Using the above calibrations, also plot the calibrated PMC ERR and PZT spectra. |
| Attachment 1: pmc-pzt-cal.pdf
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| Attachment 2: mcf.png
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