The SHG servo threshold setting is broken and outputs zero volts. This makes the SHG incapable of good green output, since it will just lock to zero volts output. Obviously no green means no squeezing so this needs to be fixed.

Turning the knob makes the signal jump a little with the polarity depending on the direction of adjustment. But then it goes back to zero.

Also the knob itself is broken and seems detached from the circuit assembly. 

I guess the potentiometer connection is broken, but turning the knob maybe applies a little pressure on the circuit that is then released when I stop adjusting. Initially I thought the circuit was preferring to go through some capacitor but looking at the schematic it seems not likely.

I turned on all of the remaining filter cavity systems in the center and end room. Also Koach filter and air conditioning in ATC.

I reloaded the DDS. I didn't check everything yet, but the RF signal levels I did look at were the same as before.

Homodyne PSU: +19 V 64 mA, -19 V 60 mA ok

OPO Temp Act: 7.116 ok
SHG Temp Act: 3.191 ok

Clock 1: -10 dBm
Clock 2: -13 dBm
Clock 3: -11 dBm
Clock 4: -9.9 dBm

SHG EOM: -9.9 dBm (same as before, goes to +14 dB amplifier)
SHG demod: 4.5 dBm (same as before)

SHG mode matching: 1840 mV + (200, 140) -> 84.4% (same as before)
SHG demod phase: 110 -> 65
SHG error: 576 mVpp
SHG threshold: 5 V -> 9 V - had trouble locking to TEM00 at 5 V but at 9 V it was fine. As before, SHG threshold is 10x higher than the TRANSMISS OUT reading would suggest.
SHG green level: 330 mW (same as before)

GRMC was quite misaligned so I realigned.

GRMC mode matching: 1460 mV + (50, 50, 32, 24) -> 90.3%
GRMC demod phase: 135 -> 195
GRMC error: 1.68 V - the error signal is quite fuzzy. This is to be expected since the modulated sidebands from the ML EOM have to pass through three dichroics. But the error signal PD is very sensitive so the signal is large. I didn't see any of the strange behaviour of GRMC changing optimal demodulation phase at random, and I think it might have been me making an error in aligning the GRMZ assembly at one time. Maybe I forgot to turn on GRPS or MZ PZT while aligning it.

When I was just about to check the GRMC lock point, I lost the transmission, and the cause was another issue...

Measuring polarizer at 45 deg. 

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\GTPC Polarizer\45 deg\Mon, Nov 11, 2024 8-22-25 PM.txt

the results (birefringence and diattenuation) for both points are attached. 

Fig 1 , 2 - point where laser is at center

Fig 3, 4 - point where laser is on one side (not center)

I restarted wifi and ethernet, all hepa filters, old DGS and control pcs

The function generator used for timing is making a strange sound and should be monitored and probably replaced.

It seems I was supposed to put some voltage values. I didn't put any. Perhaps shouldn't have turned on. FYI I only turned on the power switch on the voltage extension board, which was outside for the FC one, and inside for the PCI one.

Workstation in on now.

1. Everything on bigfoot table

2. Server rack near pci

3. server rack near FC clean room

But, there is no internet(both wifi and ethernet) in tama right now. I don't see the ethernet on the pc. I don't know where to turn it on from.

I wish to compare the effect of polcam setting on uncertainity (for future measurements), so I generated polarization states with different settings.

Polarization states are measured without BS

1. pol cam with full wave plate rotat 2048 pt fft, scan speed 60Hz

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241106\Wed, Nov 6, 2024 8-32-38 PM.txt

2. pol cam with dual full rotation and 2048 pt fft, scan speed 60Hz

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241106\Thu, Nov 7, 2024 8-05-47 AM.txt

3. full wave plate rotation by 1048pts, scane speed 60Hz (all the previous analysis were done using this setting)

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Polarization states\20241106\Fri, Nov 8, 2024 1-44-00 PM.txt

4. Polarizer was installed and measured using generated states

C:\Users\atama\Dropbox\LC-Experiment\Measurement Data\Birefringence Measurements\GTPC Polarizer\Fri, Nov 8, 2024 3-25-19 PM.txt

Fig 1 shows the orientation of the polarizer.

In preparation for NAOJ blackout I completely shutdown all equipment in the ATC ISO Class 1 booth

Air conditioner, lightwave PSU, coherent PSU, SHG temperature controller, OPO temperature controller, homodyne PSU, PZT driver, Anritsu function generator, OPO translation driver, topgun

Then I disconnected all wall plugs for cleanroom equipment

Koach was already off

In preparation for NAOJ blackout, I completely shutdown all filter cavity related electronics.

All cleanroom equipment - lasers, NIM racks, photodetector power supplies, measurement instruments, computer, homodyne PSU, AOM RF amplifier PSU, rack RF amplifier PSU, filter fan. Then I switched off the power at the cluster behind PR/IMC_IN, which is the cleanroom main power.

External equipment - all oplev lasers, PD/QPD, coil drivers and pico controllers (PR, BS, IN, END), SR560, NIM racks, ADC, camera adapters, workstation, monitor, air conditioning main control

More detail later

I tried to find the source of the small squeezing instability, about 1 dB noise floor glitch every second or so. Initially I thought it was from ppol to OPO - I could see weird flashing that was quite frequent. When I was aligning ppol to the OPO I could also see higher order modes appear/disappear at about the glitch frequency. Also, I thought it would be related to ppol because the CC PLL and green controls seemed stable enough, and the homodyne spectrum shows no glitches when only IRMC is locked. 

Actually, the ppol transmission spectrum flickering disappears when the SHG is unlocked. I also now notice the same behaviour of the glitchy transmission spectrum when observing OPO transmission of only CC and only main laser. So it's maybe some stray green problem.

I tried to look in squeezing again and somehow the squeezing spectrum didn't show the glitch issue anymore, however, depending on the spectrum analyzer span, there were a lot of noise peaks. So we still have some unclear noise issues. 

Then it was time for electrical shutdown so I didn't have time to narrow down the problem further.

I have added an option to make a newfile inside the vi irrespective of it running..so we don't have to start everytime we want to create a new file. It was very tedious if we wanted to make a new file between measurements as we had to stop the entire VI. This took time as there is a certain warm up time for all instruments after shutting down, espcially camera and LC temperature controller.

see the part circled in red in the image

I recovered 5-6 dB squeezing and the major nonstationary coherent control/green phase glitch noise is gone!

There is still another lesser glitch source coming from somewhere. It has some relation to the ppol to OPO path, since it is present when all green is blocked and LO shot noise is measured with OPO locked. LO shot noise with OPO unlocked is fine.

BAB nonlinear gain

I optimized the OPO temperature, PLL settings and green alignment to maximize the amplification and deamplification of BAB. Method is to lock OPO using ppol, while transmitting BAB to the stick power meter. Green is unlocked. The phase of green is constantly being modulated sinusoidally so the transmitted BAB level is amplified/deamplified according to the green phase. The optimum OPO temperature is 7.116 kOhm (down from 7.118 kOhm before) and the optimal ppol frequency is 195 MHz (same as before). The green alignment was not too bad, only about 10% off of maximum. This gives a maximum transmitted power measured on the power meter as 1.484 mW, about a factor of 4 increase compared to the transmitted power without green.

LO/sqz overlap

The LO/sqz overlap is optimized by sending both, one at a time, to the alignment mode cleaner (a reference target). LO to AMC mode matching was improved to 99.89% and BAB (sqz) to AMC mode matching was improved to 98.39%. I checked homodyne balance afterwards and it is still zeroed so ok.

CC loop lock

I fixed the stability of the CC PLL loop a while ago, so now it's time to check if the squeezing controls are stable. I locked everything and checked the CC error signals. when turning on the servo scan I can see a modulation that indicates that there is nonlinear gain. Then, I locked. It works! And I could see squeezing. The CC PLL loop remains stable and there is no crazy destabilization of squeezing from before! (characterized by a huge rise in the squeezing noise floor and wacky green phase shifter PZT oscillation to the maximum of 140V).

Squeezing spectrum

There is still some minor glitch noise to be fixed before we can get fast data for Hsien Yi and the Taiwan people. The squeezing spectrum is experiencing a roughly 2 Hz pulse that kind of interrupts the measurement and raises the noise floor by about 1 dB. However, it doesn't raise the noise floor by 10-20 dB so it's nowhere near as bad as before. I can still see the "squeezing level" (about -6 dB). During BAB and ppol alignment I noticed that the infrared transmission through the OPO is experiencing these glitches. Perhaps the ppol PLL could also be fixed a bit. But I'm not entirely sure if it's coming from ppol PLL. It could also be the ppol laser since I noticed weird flashing while aligning it.

I had thought to just go home and brainstorm it later, but I wondered if it was a ppol laser mode hop. I checked and for some reason the ppol laser current and temperature were set to the CC laser values. However, replacing the correct settings didn't fix the new glitch issue.

Misc

GRMZ control loop is quite temperamental. The optimal demodulation phase seems to go between whatever value it wants every now and then. I optimize and then suddenly the PDH signal goes to a bad shape and the optimal demod phase has gone to some other value. The loop sometimes has trouble stabilizing the GR to OPO power level at the proper amount (for reference, GRMC transmission monitor reads 312 mV for 25 mW green injection to OPO) but it seems to get better by switching INV to NON INV or vice versa. It tends to unlock after about 5-10 minutes. Anyway it seems to be a problem primarily with the GRMC error signal but maybe also the MZ loopology.

I left lasers open and both PLLs locked to see if they stay locked over the long weekend.

Nishino,

2024.10.31

I characterized the GR locking loop. UGF is 580 Hz with the phase margin of ~40 degrees.

Figures:

1) Open loop transfer function (G)

6) Filters of SR560 and Moku PID controller (F)

2) G/F=AH, A: PZT actuator efficiency, H: optical gain

3-5) Settings of SR560, Moku fast, and, slow controller 

Nishino,

2024.10.31 (see mainOLTF_retake/OLTF_retake.ipynb)

I characterized the GR locking loop. UGF is 7.0 kHz with the phase margin of ~30 degrees.

Figures:

1) Open loop transfer function (G)

2) Filters of SR560 and Moku PID controller (F)

3) G/F=AH, A: PZT actuator efficiency, H: optical gain

4-7) Settings of Moku low pass, fast, slow controller and SR560

Nishino

2024.10.30 (see GROLTF_sub/OLTF.ipynb)

I characterized the GR locking loop. UGF is 1.4 kHz with the phase margin of ~80 degrees.

Figures:

1) Open loop transfer function (G)

2) Filters of SR560, Moku PID controller,  and PZT driver (F)

3) G/F=AH, A: PZT actuator efficiency, H: optical gain

4) Settings of SR560

5) Settings of Moku PID controller.

I recovered bright alignment beam and local oscillator alignment to the homodyne detector. The homodyne detector shot noise is ok (-132 dBVrms/rtHz at 2.2 mW LO injection) but has some 50 Hz line presence so power cables should be checked.

BAB and ppol to OPO

I  realigned BAB and ppol to OPO to about 87% mode matching. ppol is aligned from OPO TRANSMISS IN on the servo, BAB from the "stick" power meter in transmission of the OPO set to HI BW and range 8.8 mW. Then I optimized the ppol frequency and OPO temperature by locking OPO for ppol and maximizing the transmission of BAB with the power meter still in place. The optimal settings without green are 7.120 kOhm OPO temperature (from 7.118 kOhm before) and 245-250 MHz ppol PLL frequency (same as before, OPO generally is not hugely sensitive to this parameter). The transmitted BAB power through the OPO is 346 µW (79.2 mV on oscilloscope when power meter is set to 8.8 mW range).

Homodyne balance

I balanced the homodyne using the usual method - lock IRMC, block IR transmission through OPO. Tweak the lens near to IRMC to maximize HOM SUB DC on oscilloscope and tweak the lens further from IRMC to minimize HOM SUB DC. These steps are just to prevent clipping of the beam on the homodyne aperture. Then, adjust the input beam splitter in yaw to balance the homodyne (average level 0 V).

Homodyne noise

I checked the homodyne shot noise. At 2.2 mW IRMC transmission (LO power) I see -132 dBVrms/rtHz which is basically the nominal level. In full span (102.4 kHz) it looks flat, but at 6 kHz span there is a lot of 50 Hz peaks. Checking homodyne shot noise with all of the lights off gives not a huge amount of difference for LO shot noise so it is probably a power supply issue. I should check the plugs (next time).

Homodyne dark noise floor is about -155 dBVrms/rtHz, so more than 20 dB clearance below shot noise, but has a lot of 50 Hz peaks as well. The spectrum analyzer noise (put 50 Ohm terminator in the measurement channel) is about -164 dBm.

Misc

ppol PLL lock still bounces a lot - it will unlock then quickly relock. I noticed that it's less "bouncy" if you place the peak (by ppol laser temperature adjustment) about 15-20 MHz above the target frequency. I guess this has something to do with the "gain/bandwidth" (technically charge pump and timeout counter) of the PLL phase frequency detector.

Nishino,

2024.10.29 (TF3)

Estimated loss is 240 ppm this time. I guess it's because the PCC length was detuned from the opimal case.