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ID Date Author Type Category Subject
2696   Mon Mar 22 22:11:26 2010 MottUpdateABSLPLL reconstructed

It looks like the PLL drifted alot over the weekend, and we couldn't get it back to 9 dBm.  We switched back to the new focus wideband PD to make it easier to find the beat signal.  I replaced all the electronics with the newly fixed UPDH box (#17) and we aligned it to the biggest beat frequency we could get, which ended up being -27 dBm with a -6.3V DC signal from the PD.

Locking was still elusive, so we calculated the loop gain and found the UGF is about 45 kHz, which is too high.  We added a 20 dB attenuator to the RF input to suppress the gain and we think we may have locked at 0 gain.  I am going to add another attenuator (~6 dB) so that we can tune the gain using the gain knob on the UPDH box.

Finally, attached is a picture of the cable that served as the smb - BNC adaptor for the DC output of the PD.  The signal was dependent on the angle of the cable into the scope or multimeter.  It has been destroyed so that it can never harm another innocent experiment again!

2697   Mon Mar 22 23:37:32 2010 MottUpdateABSLPLL reconstructed

We have managed to lock the PLL to reasonable stability. The RF input is attenuated by 26 dBm and the beat signal locks very close to the carrier of the marconi (the steps on the markers of the spectrum analyzer are coarse).  We can use the marconi and the local boost of the pdh box to catch the lock at 0 gain.  Once the lock is on, the gain can be increased to stabilize the lock.  The locked signals are shown in the first photo (the yellow is the output of the mixer and the blue is the output to the fast input of the laser.  If the gain is increased too high, the error signal enters an oscillatory regime, which probably indicates we are overloading the piezo.  This is shown in the second photo, the gain is being increased in time and we enter the non-constant regime around mid-way through.

Tomorrow I will use this locked system to measure the PZT response (finally!).

2703   Tue Mar 23 18:44:46 2010 MottUpdateABSLPLL reconstructed

After realigning and getting the lock today, I tried to add in the SR785 to measure the transfer function.  As soon as I turn on the piezo input on the PDH box, however, the lock breaks and I cannot reacquire it.  We are using an SR650 to add in the signal from the network analyzer and that has worked. We also swapped the 20 dB attenuator for a box which mimics the boost functionality (-20 dB above 100 Hz, 0 dB below 6Hz).  I took some spectra with the SR750, and will get some more with the network analyzer once Alberto has finished with it.

The SR750 spectra is posted below.  The SR750 only goes up to 100 kHz, so I will have to use the network analyzer to get the full range.

2714   Thu Mar 25 17:29:48 2010 kiwamu, mottUpdateGreen LockingPLL two NPROs

In this afternoon, Mott and I tried to find a beat note between two NPROs which are going to be set onto each end table for green locking.

At first time we could not find any beats. However Koji found that the current of innolight NPRO was set to half of the nominal.

Then we increased the current to the nominal of 2A, finally we succeeded in finding a beat note.

Now we are trying to lock the PLL.

P.S. we also succeeded in acquiring the lock

 innolight lightwave T [deg] 39.75 37.27 current [A] 2 2 laser power [mW] 950 700

3920   Mon Nov 15 11:52:22 2010 kiwamuUpdateGreen LockingPLL with real green signal

Stabilizing the beat note frequency using Yuta's temperature servo (see this entry)

I was able to acquire the PLL of 80MHz VCO to the real green signal.

Some more details will be posted later.

3927   Mon Nov 15 17:10:59 2010 kiwamuUpdateGreen LockingPLL with real green signal

I checked the slow servo and the PLL of 80MHz VCO using the real green beat note signal.

The end laser is not locked to the cavity, so basically the beat signal represents just the frequency fluctuation of the two freely running lasers.

The PLL was happily locked to the green beat note although I haven't fedback the VCO signal to ETMX (or the temperature of the end laser).

It looks like we still need some more efforts for the frequency counter's slow servo because it increases the frequency fluctuation around 20-30mHz.

(slow servo using frequency counter)

As Yuta did before (see his entry), I plugged the output of the frequency counter to an ADC and fedback the signal to the end laser temperature via ezcaservo.

The peak height of the beat note is bigger than before due to the improvement of the PMC mode matching.

The peak height shown on the spectrum analyzer 8591E is now about -39dBm which is 9dB improvement.

The figure below is a spectra of the frequency counter's readout taken by the spectrum analyzer SR785.

When the slow temperature servo is locked, the noise around 20-30 mHz increased.

I think this is true, because I was able to see the peak slowly wobbling for a timescale of ~ 1min. when it's locked.

But this servo is still useful because it drifts by ~5MHz in ~10-20min without the servo.

Next time we will work on this slow servo using Aidan's PID control (see this entry) in order to optimize the performance.

In addition to that, I will take the same spectra by using the phase locked VCO, which provides cleaner signal.

(acquisition of the PLL)

In order to extract a frequency information more precisely than the frequency counter, we are going to employ 80MHz VCO box.

While the beat note was locked at ~ 79MHz by the slow servo, I successfully acquired the PLL to the beat signal.

However at the beginning, the PLL was easily broken by a sudden frequency step of about 5MHz/s (!!).

I turned off the low noise amplifier which currently drives the NPRO via a high-voltage amplifier, then the sudden frequency steps disappeared.

After this modification the PLL was able to keep tracking the beat signal for more than 5min.

(I was not patient enough, so I couldn't stand watching the signal more than 5min... I will hook this to an ADC)

 Quote: #3920 Some more details will be posted later.

10180   Thu Jul 10 19:37:54 2014 ManasaUpdateGeneralPM980 fiber tested OK

[Harry, Manasa]

This is the update from yesterday that Harry missed to elog.

We pulled out the first spool of the PM980 fiber yesterday and checked it using the illuminator at the SP table. Harry will be using this for all his tests and characterisation of the fiber.

1666   Wed Jun 10 09:28:14 2009 steveUpdatePSLPMC

The PMC alarm was on this morning. It was relocked at lower HV

The FSS_RMTEMP jumped 0.5 C so The PZT was compensating for it.

6604   Sat May 5 01:24:07 2012 DenUpdatePSLPMC

I was interested what whitening filter do we have between MC servo and ADC. The shape is in the figure below, SR provided 1 V white noise. Before the whitening filter MC_F is measured in Volts with SR and ADC (for ADC the shape is calculated using the whitening filter form):

I also wondered if FSS or PZT servo can add noise to the mode cleaner length signal and what is their gain. It should be big, as the laser's calibration is ~1 MHz/V => to account for seismic noise of 10^-6 m at 1 Hz, the voltage given to the laser should be ~ 1 V. And it is indeed the case. The gain is ~1000. I measured the coherence between MC_F and the laser fast input. It is 1 in the range measured (0.05 - 100 Hz). FSS and PZT do not add significant noise.

Unfortunately, after the measurement when I unplugged BNS connector from the laser, I misaligned PMC. For several hours I adjusted the mirrors but could not significantly improve transmitted signal. I'll return to this issue tomorrow.

6605   Sat May 5 09:13:02 2012 KojiUpdatePSLPMC

I suspect that it was just unlocked when you had disconnected the cable.

There is not reflection now. It seems that it is now misaligned after the alignment work.

So what you need is "align while scanning PZT -> lock -> align".

 Quote: Unfortunately, after the measurement when I unplugged BNS connector from the laser, I misaligned PMC. For several hours I adjusted the mirrors but could not significantly improve transmitted signal. I'll return to this issue tomorrow.

6606   Sat May 5 10:20:21 2012 DenUpdatePSLPMC

Quote:

I suspect that it was just unlocked when you had disconnected the cable.

There is not reflection now. It seems that it is now misaligned after the alignment work.

So what you need is "align while scanning PZT -> lock -> align".

 Quote: Unfortunately, after the measurement when I unplugged BNS connector from the laser, I misaligned PMC. For several hours I adjusted the mirrors but could not significantly improve transmitted signal. I'll return to this issue tomorrow.

No, no, it was unlocked after I connected the cable back. The beam was even not on the PMC. I'll try PZT -> lock -> align.

6607   Sat May 5 12:23:38 2012 KojiUpdatePSLPMC

No matter how you connect/disconnect, touching the laser may cause the PMC unlocked.

At least, I don't see the PMC reflection on the PD.
This means that the beam towards the PMC is largely misaligned.

If you are not sure what is misaligned, stop touching the table.
Close the shutter of the laser on the laser housing and leave the optics as they are.

6608   Sat May 5 20:42:59 2012 DenUpdatePSLPMC

[Koji, Den]

Koji was right that I misaligned everything during the alignment work. I assumed that PMC should autolock and when I saw that it did not, I thought the laser is misaligned.

What we did:

1. Aligned mirrors to get the beam on the PD PMC REFL and PMCR camera. The PSL-PMC_RFPDDC was ~800 mV.

2. We disabled PMC servo, switching it to test position and changed "DC output adjust" by 0.01 in a loop

while true do     ezcawrite "C1:PSL-PMC_RAMP" -4.50     ezcastep "C1:PSL-PMC_RAMP" "+0.01,450" -s "0.1"     ezcawrite "C1:PSL-PMC_RAMP" 0.0     ezcastep -s "0.1" -- "C1:PSL-PMC_RAMP" "-0.01,450" done

3. While the script was running we adjusted the position of the beam on the far PMC mirror looking at an IR viewer. The goal is to align two steering mirrors to catch some resonances. We monitored them on the oscilloscope and on the PMCT camera.

4. We locked PMC and aligned steering mirrors.

11756   Thu Nov 12 09:41:02 2015 SteveUpdatePSLPMC

The PMC is not happy and the ITMX UL OSEM is moving too much

6236   Mon Jan 30 08:17:06 2012 steveUpdateIOOPMC

 Quote: I have realigned the beam pointing to PMC. The transmitted light increased from 0.74 to 0.83. The misalignment was mainly in pitch.

The PMC pointing has changed, so MC is resonating in high order modes.

9190   Thu Oct 3 01:24:31 2013 Jenne, RanaUpdateIOOPMC

The PMC transmission was around 0.78 all day, rather than the usual 0.83ish.  Rana went out to the PSL table and fixed up the PMC alignment.  This should not need to be done very often, so things to check before touching the alignment are FSS / PMC settings (digital stuff).  Make sure that the PC RMS (on the FSS screen) is low (at least below 2, preferably below 1), and that the FSS Fast monitor is near 5ish (not near 0 or 10).

This is a capture of PMC REFL's camera after Rana was finished. If it doesn't look this good when you finish then you are not done. Never do PMC alignment without looking at the PMC REFL camera.

The attached trend shows 80 days of PMC REFL and TRANS. The bad alignment stuff started on Sep 21-24 time period. You know who you are.

12214   Sun Jun 26 15:27:28 2016 ranaFrogsIOOPMC /MC lopced

Found PMC unlocked for many hours so I relocked it. IMC relocked by itself, but the input switch seems to be flickering to fast. Also the Keep Alive bit is not flashing.

12911   Mon Mar 27 20:41:21 2017 rana, gautamUpdatePSLPMC DAQ assay for feed-forward integration

We are thinking to use the PMC signals to help us in figuring out the feedback / feedforward stuff and making it better.

Today we scoped out the PMC DAQ channels (which were never re-hooked up after the Joe/Jamie CDS upgrade 6 years ago).

There is a 4-pin LEMO connector on the front panel which gives

1. the error signal (after the 4th order, post-mixer lowpass and a OP27 buffer with a 17 kHz low pass)
2. the feedback voltage to the PZT, after a resistive divide by 50

Both of these signals are buffered by the AD620 inst amp configured with a gain of 1. In the green scope trace, you can see that there's a ~110 MHz signal strongly evident there. In the spectrum analyzer screen shot there is a instrument noise trace and then a PMC error point trace. You can see that all the peaks are ony there when I connect to the servo board instead of a Terminator. This RF noise is mainly the higher harmonics of the 35.5 MHz modulation getting there. It seems to be in both the error and control DAQ outputs, and a question is whether or not it is also in the servo electronics.

I also attach a close up of the servo board in the region of the post-mixer LC low pass filtering. I think its supposed to be 4th order cutoff at 1 MHz, but maybe the caps are busted or there's a way for the RF from the mixer to bypass the filters and get into the main servo path?

In the medium term, we probably want to use the new PDH servo that Rich is making. Need to buy/make a HV driver to use, but that should be easy.

12916   Wed Mar 29 11:41:19 2017 gautamUpdatePSLPMC DAQ assay for feed-forward integration

The C1IOO frontend machine that resides in 1X1/1X2 has 2 ADCs, ADC0 and ADC1. The latter has 28 out of 32 channels unused at the moment, so I decided to use this for setting up fast channels for the PMC DAQ. On the RTCDS side of things, the PSL namespace block lives in the C1ALS model. I made the following modifications to it:

1. Added channels for the PMC DAQ
2. Added CDS filters for both the newly added PMC DAQ channels and the existing FSS DAQ channels, so that we can calibrate these into physical units
3. Changed the names of the existing FSS channels from FSS_MIXER and FSS_NPRO to FSS_ERR and FSS_CTRL. The latter is still a bit ambiguous, but I felt that FSS_CM_BOARD_CTRL was too long.
4. Added DQ channels for the new PMC channels. These are recording at 16K at the moment, but since we have the fast testpoints courtesy of the CDS filter modules for diagnostics, perhaps the DQ channels need only be recorded at 2K?

The PSL namespace block in C1ALS looks like this now:

I then tried hooking up the DAQ signals from the PMC servo board to the ADC via the 1U generic ADC interface chassis in 1X2 - this has 4pin LEMO inputs corresponding to 2 differential input channels. I used J6 (corresponding to ADC channels 10 and 11) for the PMC_ERR and PMC_CTRL respectively. I was a little confused about the status of the 4 pin LEMO output on the front panel of the PMC servo board. According to the DCC page for the modified 40m servo board, the DAQ outputs are wired to the backplane connector instead of the 4 pin LEMO. But looking at photographs on the same DCC page, there are wires soldered on the rear-side of the PCB from the 4-pin LEMO to the backplane connector. Also, I believe the measurements made by Rana in the preceeding elog were made via the front panel LEMO. In any case, I decided to use the single pin LEMO monitor points on the front panel as a preliminary test. The uncalibrated spectra with ADC terminated, IMC unlocked and IMC locked look like:

So it looks like at the very least, we want to add some gain to the AD620 instrumentation amplifiers to better match the input range of the ADC. We also want to make the PZT voltage monitor path AC coupled. My plan then is the following:

1. Figure out what is going on with the 4-pin LEMO connector on the front panel - is it connected to the DAQ monitor points or not?
2. Ground pin 5 of U15 (this has already been done by Koji for U14 according to the DCC page)
3. Add a resistor between pins 1 and 8 of U14 and U15 to get some gain. According to the datasheet, a 1k resistor will give a gain of 50, which for U15 will mean that we undo the existing 1/50 attenuation. Of course we need to AC couple this path first by adding a capacitor in series with R14.
4. Figure out where the RF harmonics are coming from and what is the best way to attenuate them.

I will update with a circuit diagram with proposed changes shortly.

Proposed changes:

1. Cut PCB trace between R14 and R13, install capacitor - what is is correct type of capacitor to use here? I figured installing a series capacitor after the resistive divider, to the input of the instrumentation amplifier avoids the need for a HV capacitor, so we can use a 1uF WIMA capacitor.
2. Add gains to U14 and U15 (error and control signal monitors respectively). Based on the uncalibrated spectra attached, I think we should go for a gain of ~50 for U15 (1kohm between pins 1 and 8), and a gain of ~200 for U14 (250ohms between pins 1 and 8).

The PCB layout is such that I think using components with leads is easier rather than SMD components.

If this sounds like a reasonable plan, I will pull out the servo card from the eurocrate and implement these changes today evening...

12920   Thu Mar 30 18:11:01 2017 ranaUpdatePSLPMC DAQ assay for feed-forward integration

What you have drawn looks good to me: the cut should be between TP3 and pin3 of the AD620. This should maintain the DC coupled respons for the single-pin LEMO and backplane EPICS monitors.

We want to use the PMC signal down to low frequencies, so the filter on the input of the AD620 should have a low frequency cutoff, but we should take care not to spoil the noise of the AD620 with a high impedance resistor.

It has a noise of 100 nV/rHz and 1 pA/rHz at 1 Hz. If you use 47 uF and 10 kOhm, you'll get fc = 1/2/pi/R/C ~ 0.3 Hz so that would be OK.

12926   Mon Apr 3 23:07:09 2017 gautamUpdatePSLPMC DAQ assay for feed-forward integration

I made some changes to the DAQ path on the PMC servo board, as per the plan posted earlier in this thread. Summary of changes:

1. AC coupling PMC control signal path using 2 x 47uF metal film capacitors (in parallel)
2. Grounding pin 5 of U15
3. Adding gain to U14 (gain of ~500) and U15 (gain of ~50)

Details + photos + calibration of DAQ channels to follow. The PMC and IMC both seem to remain stably locked after this work.

11900   Wed Dec 23 15:43:02 2015 ranaSummaryPSLPMC FSS IMC RF summing box

The EOM upstream of the PMC is used as the phase corrector for the FSS/IMC servo. It is also used to apply the 35.5 MHz PDH RF sidebands for the PMC locking. There is a Pomona box which is used to merge the two signals onto a single cable for the EOM.

Does this circuit make sense to anyone?

1471   Fri Apr 10 19:09:48 2009 JenneUpdatePSLPMC LO Calibration
I measured the RF LO output level from the PMC's LO board which goes directly into the LO input on the PMC Servo board. This goes hand-in-hand with Rana's thoughts
that we might be giving the PMC mixer a too-low LO value, and we might need to switch out the mixer. Steve ordered some new mixers today to try out.

The RF Output Adjust slider (on the C1:PSL_PMC_PS screen) goes from 0-10V; The nominal value (or at least the value I found it at today) is 2.014V.

To measure the RF level: I unlocked the Mode Cleaner and turned off the ISS servo per Yoichi's suggestion. I then unplugged the input to the PMC servo board's LO input,
and put that cable into a 300MHz 'scope, with 12dB attenuation. The 'scope was AC coupled, with the input set to 50Ohms.

I then changed the RF Output Adjust slider in increments of 0.5, and measured the peak-to-peak values on the scope. In the table and on the plots, I've taken into account
the 12dB attenuation. i.e I actually measured 964mV, so 964mV*10^.6 = 3838mV.

 RF Output Adjust Output measured on scope Oscillator Output Monitor [V] [Vpp] [no units given on MEDM screen] All \pm 0.0159 all of this column is NEGATIVE 0.0000 3.838 0.007 0.5000 3.854 0.007 1.0000 3.838 0.006 1.5000 3.838 0.007 2.0000 3.838 0.006 2.5000 3.838 0.007 3.0000 3.838 0.007 3.5000 3.838 0.007 4.0000 3.838 0.007 4.5000 3.822 0.007 5.0000 3.822 0.012 5.5000 3.790 0.076 6.0000 3.758 0.257 6.5000 3.694 0.555 7.0000 3.615 0.931 7.5000 3.535 1.277 8.0000 3.456 1.532 8.5000 3.392 1.709 9.0000 3.344 1.829 9.5000 3.312 1.908 10.0000 3.296 1.966

I think it's kind of funky that it's so flat for ~half the slider. Also, the third column includes the Oscillator Output Monitor value from the MEDM screen at various RF Adjust slider values. All of these should be negative (i.e. -0.007), but the TABLE function doesn't like "-" signs. I don't know if this information is degenerate with the 'scope measurements, or if it's an indicator of what (might be) wrong.

After finishing, I plugged the cable back into the PMC servo board as it was, turned back on the ISS and relocked the PMC and the MC.
1473   Sat Apr 11 00:45:41 2009 YoichiUpdatePSLPMC LO Calibration

 Quote: I then changed the RF Output Adjust slider in increments of 0.5, and measured the peak-to-peak values on the scope. In the table and on the plots, I've taken into account the 12dB attenuation. i.e I actually measured 964mV, so 964mV*10^.6 = 3838mV.

The mixer for the PMC demodulator is level 23. So 16dBm is insufficient.
What is the level of the new mixer Steve ordered ? 13 ?
1475   Sun Apr 12 19:27:20 2009 ranaUpdatePSLPMC LO Calibration

 Quote: 3.8Vpp is about 16dBm. The mixer for the PMC demodulator is level 23. So 16dBm is insufficient. What is the level of the new mixer Steve ordered ? 13 ?

Since Steve and Jenne were on it, I'm sure they ordered the optimum values...

From the table, it looks like the drive level adjuster is busted. Its not supposed to just give a
1-2 dB change over the full range. We'll have to think about what exactly to do, but we should
probably install the level 13 mixer and put in the right attenuation to make the LO be ~13.5 dBm
including the filter. Also need to calibrate the LO readback on the board like what Peter did for
the FSS.
1478   Mon Apr 13 17:55:37 2009 JenneUpdatePSLPMC LO Mon Calibration

I have calibrated the PMC LO Mon (C1:PSL-PMC_LODET) on the PMC's EPICS screen, by inputting different RF LO levels into the LO input of the PMC servo board.

Since the RF output adjust slider on the PMC's Phase Shifter screen doesn't do a whole lot (see elog 1471), I used a combination of attenuators and the slider to achieve different LO levels. I measured the level of the attenuated RF out of the LO board using the 4395A in spectrum analyzer mode, with the units in dBm, with 50dB attenuation to make it stop complaining about being overloaded.  For each row in the table I measured the RF level using the 4395, then plugged the cable back into the PMC servo board to get the EPICS screen's reading.

The last 2 columns of the table below are the 'settings' I used to get the given RF LO level.

 RF LO Input to PMC Servo Board [dBm] LO Mon on EPICS Screen [no units] RF Output Adjust Slider [V] Attenuators used [dB] 16.004 +- 0.008 0.1200 +- 0.0003 0 0 15.001 +- 0.004 0.0708 +- 0.0008 0 1 14.079 +- 0.008 0.0318 +- 0.0001 8 1 13.002 +- 0.006 0.0126 +- 0.0004 0 3 11.992 +- 0.010 0.0024 +- 0.0008 0 4 10.994 +- 0.010 -0.0024 +- 0.0003 0 4+1=5 9.993 +- 0.008 -0.0047 +- 0.0007 0 3+3=6

When the new mixers that Steve ordered come in (tomorrow hopefully), I'll put in a Level 13 mixer in place of the current Level 23 mixer that we have.  Also, Rana suggested increasing the gain on the op-amp which is read out as the LO Mon so that 13dBm looks like 1V.  To do this, it looks like I'll need to increase the gain by ~80.

11763   Fri Nov 13 22:32:54 2015 KojiSummaryPSLPMC LO degraded, usual ERA-5 replacement, LO recovered

[Yutaro, Koji]

We found that the PMC LO level was fluctuating in a strage way (it was not stable but had many clitches like an exponential decay), we suspected the infamous PMC LO level decay. In fact, in June 2014 when Rana recalibrated the LO level,  the number on the medm screen (C1:PSL-PMC_LO_CALC) was about 11dBm. However, today it was about 6dBm. So we decided to jump in to the 1X1 rack.

The LO and PC outputs of the PMC Crystal module (D980353) were measured to be 6.2dBm and 13.3dBm. Rana reported in ELOG 10160 that it was measured to be 11.5dBm. So apparently the LO level decayed. Unfortunately, there was no record of the PC output level. In any case, we decided to pull the module for the replacement of ERA-5 chips.

Once we opened the box we found that the board was covered by some greasy material. The ERA-5 chip on the LO chain seemed unreasonably brittle. It was destryed during desoldering. We also replaced the ERA-5 chip in the PC chain, just in case. The board was cleaned by the defluxing liquids.

Taking an advatage of this chance, the SMA  cables around the PMC were checked. By removing some of the heat shrinks, suspicious broken shields of the connectors were found. We provided additional solder to repair them.

After the repair, the LO and PC output levels became icreased to 17.0dBm(!) and 13.8dBm, respectively. (Victory)
This LO level is way too much compared to Rana's value. The MEDM LO power adj has little effect and the adj range was 16dBm~17dBm. Therefore we moved the slider to 10, which yields 16dBm out, and added a 5dB attenuator. The measured LO level after the attenuator was measured to be 11.2dBm.

Locking of the PMC was tried and immediately acquired the lock. However, we noticed that the nomoinal gain of 10dB cause the oscillation of the servo. As we already adjusted the LO level to recover the nominal value, we suspeced that the modulation depth could be larger than before. We left the gain at 0dB that doesn't cause the oscillation. It should be noted that the demodulation phase and the openloop gain were optimized. This should be done in the day time as soon as possible.

When the PMC LO repair was completed, the transmission of the PMC got decreased to 0.700V. The input alignment has been adjusted and the transmission level of 0.739V has been recovered.

The IMC lock stretch is not stable as before yet. Therefore, there would still be the issue somewhere else.

11765   Sun Nov 15 22:43:48 2015 KojiSummaryPSLPMC LO degraded, usual ERA-5 replacement, LO recovered

I think the IMC locking was somewhat improved. Still it is not solid as long time before.

Before the PMC fix (attachment 1)
After the PMC fix (attachment 2)

To do
- PMC loop inspection / phase check / spectral measurements
- PMC / IMC interaction
- IMC loop check

11560   Wed Sep 2 23:50:00 2015 ranaUpdatePSLPMC LO dying

Let's order a pair of 35.5 MHz Wenzel for this guy and package like Rich has done for the WB low noise oscillators.

WE're only sending 6 dBm into it now and its using a 13 dBm mixer. Bad for PMC stability.

Also, if anyone has pix of the servo card, please add them to the DCC page for the PMC.

9381   Thu Nov 14 00:33:37 2013 ranaConfigurationPSLPMC LO is dying...

Back in 2009, Jenne replaced the PMC board mixer with a Level 13 one. Today I noticed that the LO level on the PMC screen was showing a LO level of ~5-10 dBm and fluctuating a lot. I think that it is related to the well known failure of the Mini-Circuits ERA-5SM amplifier which is on the D000419-A schematic (PMC Frequency Reference Card). The Hanford one was dying for 12 years and we found it in late 2008. If we don't have any in the blue bin, we should ask Steve to order 10 of them.

The attached trend shows 2000 days of hour trend of the PMC LODET channel. The big break in 2009 is when Jenne changed the mixer and then attenuated the input by 3 dB. The slow decay since then is the dying amplifier I guess.

Since the LOCALC channel was not in the trend, I added it to the C0EDCU file tonight and restarted the FB DAQD process. Its now in the dataviewer list.

I went out and took out the 3 dB attenuator between the LO card and the PMC Mixer. The LO monitor now reads 14.9 dBm (??!!). The SRA-3MH mixer data sheet claims that the mixer works fine with an LO between 10 and 16 dBm, so I'll leave it as is. After we get the ERA-5, lets fix the LODET monitor by upping its gain and recalibrating the channel.

10167   Wed Jul 9 19:53:34 2014 ranaUpdatePSLPMC LO monitor trend (5 years)

The first step is

The second uptick (In Nov 14, 2013) is when I removed a 3 dB attenuator from the LO line. Don't know why the decay accelerates after that.

15106   Fri Dec 27 16:26:11 2019 YehonathanUpdatePSLPMC Linewidth measurement

I try to measure the linewidth of the PMC by ramping the PMC PZT.

I do it by connecting a triangular shape signal to FP Test 1 on the PMC servo front panel (I know, it is probably better to connect it to DC EXT. next time.) and turn the servo gain to a minimum.

Attachment 1 shows the PMC transmission PD as the PZT is swept with the EOM connected and when it is disconnected. It shows the PMC over more than 1 free spectral range.

For some reason, I cannot seem to be able to find the 35MHz sidebands which I want to use to calibrate the PZT scan. I made sure that the EOM is driven by a 35MHz signal using the scope. I also made sure that the PMC cannot to lock without the EOM connected.

I am probably doing something silly.

15109   Wed Jan 1 14:14:00 2020 YehonathanUpdatePSLPMC Linewidth measurement

Turns out the 35MHz sidebands are way too weak to resolve from the resonance when doing a PZT scan.

I connect the IFR2023B function generator on the PSL table to the EOM instead of the FSS box and set it to generate 150MHz at 13dbm.

To observe the resulting weak sideband I place a PDA55 at the peak-off path from the transmission of the PMC where there is much more light than the transmission of the PMC head mirror. Whoever is using this path there is a PD blocking it right now.

I do a PZT scan by connecting a triangular signal to the EXT DC on the PMC servo with and without the EOM (Attachment 1). A weak sideband can clearly be spotted now.

Using the above 150MHz sideband calibration I can find the roundtrip time to be 1.55ns.

I take a high-resolution scan of a resonance peak and fit it to a Lorentzian (Attachment 2) and find a roundtrip loss of 1.3%.

Using the above results the cavity decay time is 119ns.

We should investigate what's going on with the ringdown measurements.

15126   Wed Jan 15 15:04:31 2020 gautamUpdatePSLPMC Linewidth measurement

For the ringdowns, I suggest you replicate the setup I had - infrastructurally, this was quite robust, and the main problem I had was that I couldn't extinguish the beam completely. Now that we have the 1st order beam, it should be easy.

13488   Mon Dec 18 20:37:18 2017 gautamUpdatePSLPMC MEDM cleanup

There are fewer lies on this screen now. For reference, the details of the electronics modifications made are in this elog.

1. Error and control signals are now in units of nm, the appropriate filter switches have been SDF'ed.
2. I think it's useful to see the control voltage to the PZT in volts as well, so I've made two readbacks available at the control point, one in V and one in nm.
3. Indicated that the on-board LO mon readback, which reads "nan", is no longer meaningful, as the mixer is off the demod board.
 Quote: I think many of the readbacks on the PMC MEDM screen are now bogus and misleading since the PMC RF upgrade that Gautam did awhile ago. We ought to fix the screen and clearly label which readbacks and actuators are no longer valid.

1837   Wed Aug 5 15:57:05 2009 AlbertoConfigurationComputersPMC MEDM screen changed

I added a clock to the PMC medm screen.

I made a backup of the original file in the same directory and named it *.bk20090805

497   Sun May 25 20:30:25 2008 ranaSummaryPSLPMC Mode Matching
I checked the PMC mode matching by ramping the gain down to -10 dB (from +20 dB) and
moving the DC offset around until it caught lock on the different HOMs. Then I recorded
the output power (PMCTRANSPD). The DC offset on this EPICS channel was -0.013 V, so I
used its AOFF field to zero this out. Here is a list of the power in the largest modes:
Mode    Power (V)
----    ---------
00        2.7
10        0.2
04        0.04
02        0.02
BE        0.36      **Bull's Eye mode is TEM02 + TEM20. This can be fixed by lens adjustment.

N.B. To make a PNG file with DTT, just make an EPS file -- then use the eps2png perl script.
1883   Mon Aug 10 20:49:13 2009 Alberto, RanaUpdatePSLPMC Mode Matching Lenses Tuning

Rana, Alberto

This afternoon we tried to improve the mode matching of the beam to the PMC. To do that we tuned the positions of the two lenses on the PSL table that come before the PMC.

We moved the first lens back an forth the without noticing any improvement on the PMC transmitted and reflected power. Then we moved the first backwards by about one cm (the order is set according to how the beam propagates). That made the things worse so we moved also the second lens in the same direction so that the distance in between the two didn't change significantly. After that, and some more adjustments on the steering mirrors all we could gain was about 0.2V on the PMC transmission.

We suspect that after the problems with the laser chiller of two months ago, the beam size changed and so the mode matching optics is not adequate anymore.

We have to replace the mode matching lenses with other ones.

12944   Tue Apr 18 01:01:03 2017 gautamUpdatePSLPMC OLTF measured, DAQ channels calibrated

Quick entry, details to follow in the AM tomorrow.

• I calibrated the PMC DAQ channels into physical units - there now exists in the filter modules  cts2m and cts2Hz filter modules, though of course only one must be used at a time
• Finally measured the PMC OLTF, after moving the PMC PDH error signal demodulation off the servo board - I used the same procedure as Koji when he made the modifications to the PMC servo board, I will put up the algebra here tomorrow. Turns out the previously nominal servo gain of +10dB on the MEDM sliders was a little low, the new nominal gain is +20dB, and has been updated on the MEDM screen.

ToDo:

• Put up the modified schematic on the 40m DCC tree Done April 18 10pm
• Check calibration by comparing inferred PMC cavity displacement from error point and control point spectra, using the measured OLTF
• Finish up looking at multicoherence with MCL and various witness channel combinations

12945   Tue Apr 18 16:10:00 2017 gautamUpdatePSLPMC OLTF measured, DAQ channels calibrated

Here are the details:

1. PMC OLTF:
• the procedure used was identical to what Koji describes in this entry.
• I used the SR785 to take the measurement.
• MEDM gain slider was at +20dB
• I used the two single pin LEMO front panel monitor points to make the measurement.
• Mix_out_mon was CH2A, HV_out_mon was CH1A on the SR785
• A = CH2A/CH1A with the SR785 excitation applied to the EXT_DC single pin LEMO input on the front panel. I used an excitation amplitude of 15mV
• B = CH2A/CH1A without any excitation
• Couple of lines of loop algebra tells us that the OLTF is given by the ratio A/B. The plot below lines up fairly well with what Koji measured here, UGF is ~3.3kHz with a phase margin of ~60degrees, and comparable gain margin at ~28kHz. As noted by Koji, the feature at ~8kHz prevents further increase of the servo gain. I've updated the nominal gain on the PMC MEDM screen accordingly... I couldn't figure out how to easily extract Koji's modelled OLTF so I didn't overlay that here... Overlaid is the model OLTF. No great care was taken in analyzing the goodness of the agreement with the model and measurement by looking at residuals etc, except that the feature that was previously at 28.8kHz now seems to have migrated to about 33.5 kHz. I'm not sure what to make of that.
2. PMC DAQ calibration:
• The calibration was done using the swept cavity, the procedure is basically the same as described by Koji in this elog.
• The procedure was slightly complicated by the fact that I added gain to the AD620 buffers that provide the DAQ signals. So simply sweeping the cavity saturates the AD620 very quickly.
• To workaround this, I first hooked up the un-amplified single pin LEMO front panel monitor points to the DAQ channels using some of the available BNC-LEMO patch cables.
• I then did the swept cavity measurement, and recorded the error and control signals fron the single pin LEMO front panel monitor points. Sweep signal was applied to EXT_DC input on front panel.
• In the nominal DAQ setup however, we have the amplification on the AD620. I measured this amplification factor by hooking up the single pin LEMO monitor point, along with its corresponding AD620 amplified counterpart, to an SR785 and measuring the transfer function. For the PMC_ERR channel, the AD620 gain is ~53.7dB (i.e. approx 484x). For the PMC_CTRL channel, the AD620 gain is ~33.6dB (i.e. approx 48x). These numbers match up well with what I would expect given the resistors I installed on the PMC board between pins 1 and 8 of the AD620. These gains are digitally undone in the corresponding filter modules, FM1.
• To calibrate the time axis into frequency, I located the zero crossings of the sidebands and equated the interval to 2 x fmod. For the PMC servo, fmod = 35.5MHz. I used ~1Hz triangle wave, 2Vpp to do the sweep. The resulting slope was 1.7026 GHz/s.
• The linear part of the PDH error signal for the carrier resonance was fitted with a line. It had a slope of 1.5*10^6 cts/s.
• The round trip length of the PMC cavity was assumed to be 0.4095m as per Koji's previous entry. This allows us to calibrate the swept cavity motion from Hz to m. The number is 1.4534 * 10^-15 m/Hz. I guess we could confirm this by sweeping the cavity with the DC bias slider through the full range of 0-250V, but we only have a slow readback of the PMC reflection (and no readback of the PMC transmission).
• Putting the last three numbers together, I get the PMC_ERR signal calibration as 1.6496 pm/ct. This is the number in the "cts2m" filter module (FM10).
• An analogous procedure was done to calibrate the control signal slope: from the sweep, I got 4617 cts/s, which corresponds to 2.7117*10^-6 cts/Hz. Using the FSR to convert into cts/m, I get for PMC_CTRL, 535.96 pm/ct. This is the number in the "cts2m" filter module (FM10).
• For convenience, I also added "cts2Hz" calibration filters in FM9 in the corresponding filter modules.

The updated schematic with changes made, along with some pictures, have been uploaded to the DCC page...

 Quote: Quick entry, details to follow in the AM tomorrow.​

12946   Tue Apr 18 23:37:15 2017 ranaUpdatePSLPMC OLTF measured, DAQ channels calibrated

What's the reasoning behind setting the the gain to this new value? i.e. why do these 'margins' determine what the gain should be?

1049   Wed Oct 15 17:40:50 2008 ranaUpdatePSLPMC Offset adjusted
I set the PMC servo input offset: closed the MOPA shutter, zeroed the mixer output with the offset slider,
relocked everything, and set the nominal to the new value of -6 V.
924   Thu Sep 4 14:43:58 2008 JenneUpdatePSLPMC Open Loop Gain
I have measured the PMC's open loop gain. UGF is 629.7Hz, with a phase margin of 53 degrees.

I injected into FP2 on the front panel, and measured MixOut/Source from 100Hz to 100kHz using the SR785. I did this both when the loop was open, and when the loop was closed (open the loop by enabling FP1, which breaks the loop).

We have 2 transfer functions involved: The actual open loop gain of the PMC servo loop (G1), and the gain between FP2 and the MixerOut monitor point (G2). This gives us:

TF(closed loop) = G2*(1+G1)
TF(broken loop) = G2

G1 = TF(closed)/TF(broken) - 1

This G1 is the final open loop gain, and it is plotted below.
11781   Wed Nov 18 16:53:17 2015 KojiSummaryPSLPMC PZT capacitance

The PMC PZT capacitance was measured.
- Turn off the HV supplies. Disconnect HV OUT cable.
- Make sure the cable is discharged.
- Measure the capacity at the cable end with an impedance meter.
=> The PMC PZT capacitance at the cable end was measured to be 222nF
Combined with the output impedance of 63.3kOhm, the LPF pole is at 11.3Hz

699   Fri Jul 18 19:41:09 2008 YoichiUpdatePSLPMC PZT investigation
I measured the HV coming to the PMC PZT by plugging it off from the PZT and hooking it up to a DVM.
The reading of DVM is pretty much consistent with the reading on EPICS. I got 287V on the DVM when the EPICS says 290V.

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

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

 Quote: I measured the HV coming to the PMC PZT by plugging it off from the PZT and hooking it up to a DVM. The reading of DVM is pretty much consistent with the reading on EPICS. I got 287V on the DVM when the EPICS says 290V. Then I used a T to monitor the same voltage while it is connected to the PZT. I attached a plot of the actual voltage measured by the DVM vs the EPICS reading. It shows a hysteresis. Also the actual voltage drops by more than a half when the PZT is connected. The output impedance of the HV amp is 64k (according to the schematic). If I believe this number, the impedance of the PZT should also be 64k. The current flowing the PZT is 1.6mA at 200V EPICS reading. The impedance of the PZT directly measured by the DVM is 1.5M ohm, which is significantly different from the value expected above. I will check the actual output impedance of the HV amp later. The capacitance of the PZT measured by the DVM is 300nF. I don't know if I can believe the DVM's ability to measure C. I noticed that when a high voltage is applied, the actual voltage across the PZT shows a decay. The second plot shows the step response of the actual voltage. The voltage coming to the PZT was T-ed and reduced by a factor of 30 using a high impedance voltage divider to be recorded by an ADC. The PMCTRANSPD channel is temporarily used to monitor this signal. After the voltage applied to the PZT was increased abruptly (to ~230V), the actual voltage starts to exponentially decrease. When the HV was reduced to ~30V, the actual voltage goes up. This behavior explains the weird exponential motion of the PZT feedback signal when the PMC is locked. The cause of the actual voltage drop is not understood yet. From the above measurements, we can almost certainly conclude that the problem of the PMC is in the PZT, not in the HV amp nor the read back.

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

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

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

Quote:

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

Yes. What I meant was that because the measured voltage across the PZT was a half of the open voltage of the HV amp, the DC impedance of the PZT is expected to be similar to the output impedance of the HV amp. Of course, I don't think the DC impedance of a normal PZT should be such low.
I'm puzzled by the discrepancy between this expected DC impedance and the directly measured impedance by the Fluke DVM (1.5M Ohm).
One possibility is that the PZT leaks current only when a high voltage is applied.
749   Mon Jul 28 17:44:07 2008 ranaUpdatePSLPMC 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
.
15138   Wed Jan 22 11:00:21 2020 gautamUpdatePSLPMC REFL ghost beam

I looked into this a little more today.

1. The steering optic used to route PMC REFL to the RFPD is in fact a window (labelled W1-PW-1025-UV-1064-45P), not a High-T beamsplitter.
2. With the PMC unlocked, I measured ~10.70 mW in the stronger of the two beams, 5.39 mW in the weaker one.
• The window spec is Tp > 97%. Since we have ~1.3 W incident on the PMC, the primary reflection corresponds to T=99.2%, which is consistent with the spec.
• There is no spec given for the coating on the back side of this window. But from the measured values, it seems to be R = 100* 5.39e-3 / (1.3*T^2) ~ 0.4%. Seems reasonable.

Currently, the iris is set up such that the stronger beam makes it to the PMC RFPD, while the weaker one is blocked by the iris. As usual, this isn't a new issue - was noted last in 2014, but who knows whether the new window was intalled...

 Quote: Today I noticed that the beam reflected from the PMC into the RFPD has a ghost (attachment) due to reflection from the back of the high transmission beam splitter that stirs the beam into the RFPD.
15147   Thu Jan 23 18:52:31 2020 gautamUpdatePSLPMC RFPD characterization

Summary:

The RF transimpedance of the PMC PDH RFPD was measured, and found to be 1.03 kV/A

Details:

With the new fiber coupled PDFR system, it was very easy to measure the response of this PD in-situ 🎉 . The usual transfer function measurement scheme was used, with the AG4395 RF out modulating the pump current of the diode laser, and the measured transfer function being the ratio of the response of the test PD to the reference PD.

I assume that the amount of light incident on the reference NF1611 photodiode and the test photodiode were equal - I don't know what the DC transimpedance of the PMC REFL photodiode is (can't find a schematic), but the DC voltage at the DC monitor point was 16.4 mV (c.f. -2.04 V for the NF1611). The assumption shouldn't be too crazy because assuming the reference PD has an RF transimpedance of 700 V/A (flat in the frequency range scanned), we get a reasonable shape for the PMC REFL photodiode's transimpedance.

The fitted parameters are overlaid in Attachment #1. The 2f notch is slightly mistuned it would appear, the ratio of transimpedance at f1/2*f1 is only ~10. The source files have been uploaded to the wiki.

Knowing this, the measured PDH discriminant of 0.064 GV/m is quite reasonable:

• expected optical gain from modulation depth assuming a critically coupled cavity is 0.089 GW/m.
• Assume 0.7 A/W responsivity for InGaAs.
• Account for the fact that only 0.8 % of the reflected light reaches the PMC photodiode because of the pickoff window.
• Account for a conversion loss of 4.5 dB in the mixer.
• Account for the voltage division by a factor of 2 at the output of the BLP-1.9 filter due to the parallel 50 ohm termination.
• Then, the expected PDH discriminant is 0.089e9 W/m * 0.7 A/W * 0.8e-2 * 1.03kV/A * 10^(-4.5/20) * 0.5 ~ 0.15 GV/m. This is now within a factor of ~2 of the measured value, and I assume the total errors in all the above assumed parameters (plus the cable transmission loss from the photodiode to the 1X1 rack) can easily add up to this.

So why is this value so different from what Koji measured in 2015? Because the monitor point is different. I am monitoring the discriminant immediately after the mixer, whereas Koji was using the front panel monitor. The latter already amplifies the signal by a factor of x101 (see U2 in schematic).

Conclusion:

I still haven't found anything that is obviously wrong in this system (apart from the slight nonlinearity in the VGA stage gain steps), which would explain why the PMC servo gain has to be lower now than 2018 in order to realize the same loop UGF.

 So the next step is to characterize the RF transimpedance of the PMC RFPD.
ELOG V3.1.3-