[Radhika, Paco, Anchal]
I placed a lens in the B-beam path to focus the beam spot onto the RFPD [Attachment 1]. To align the beam spot onto the RFPD, Anchal misaligned both ETMs and ITMY so that the AS and LO beams would not interfere, and the PD output would remain at some DC level (not fringing). The RFPD response was then maximized by scanning over pitch and yaw of the final mirror in the beam path (attached to the RFPD).
Later Anchal noticed that there was no RFPD output (C1:LSC-BH55_I_ERR, C1:LSC-BH55_Q_ERR). I took out the RFPD and opened it up, and the RF OUT SMA to PCB connection wire was broken [Attachment 2]. I re-soldered the wire and closed up the box [Attachment 3]. After placing the RFPD back, we noticed spikes in C1:LSC-BH55_I_ERR and C1:LSC-BH55_Q_ERR channels on ndscope. We suspect there is still a loose connection, so I will revisit the RFPD circuit on Monday.
A design flaw in these initial LIGO RFPDs is that the SMA connector is not strain releieved by mounting to the case. Since it is only mounted to the tin can, when we attach/remove cables, it bends the connector, causing stress on the joint.
To get around this, for this gold box RFPD, connect the SMA connector to the PCB using a S shaped squiggly wire. Don't use multi-strand: this is usually good, since its more flexible, but in this case it affects the TF too much. Really, it would be best to use a coax cable, but a few-turns cork-screw, or pig-tail of single-core wire should be fine to reduce the stress on the solder joint.
I further updated LSC model today with following changes:
The model built and installed with no issues.
Further, the slow epics channels for BH55 anti-aliasing switch and whitening switch were added in /cvs/cds/caltech/target/c1iscaux/C1_ISC-AUX_LSCPDs.db
The IPC issue that we were facing earlier is resolved now. The BH55_I and BH55_Q signal after phase rotation is successfully reaching c1hpc model where it can be used to lock LO phase. To resolve this issue, I had to restart all the models. I also power cycled the LSC I/O chassis during this restart as Tega suspected that such a power cycle is required while adding new dolphin channels. But there is no way to find out if that was required or not. Good news is that with the new cds upgrade, restarting rtcds models will be much easier and modular.
Since ETMY does not use HV coil driver anymore, the watchdog on ETMY needs to be similar to other new optics. We made these updated today. Now ETMY watchdog while slowly ramps down the alignment offsets when it is tripped.
We followed rana's suggestion for stress relief on the SMA joint in the BH55 RFPD that Radhika resoldered. We used a single core, pigtailed wire segment after cleaning up the solder joint on J7 (RF Out) and also soldered the SMA shield to the RF cage (see Attachment #1). This had a really good effect on the rigidity of the connection, so we moved back to the ITMY table.
We measured the TEST in to RF Out transfer function using the Agilent network analyzer, just to see the qualitative features (resonant gain at around 55 MHz and second harmonic suppression at around 110 MHz) shown in Attachment #2. We used 10kOhm series resistance in test input path to calibrate the measured transimpedance in V/A. The RFPD has been installed in the ITMY table and connected to the PD interface box and IQ demod boards in the LSC rack as before.
Locked LO phase to ITMX single bounce beam at the AS port, using the DCPD (A-B) error point and actuating on LO1 POS. For this the gain was tuned from 0.6 to 4.0. A rough Michelson fringe calibration gives a counts to meters conversion of ~0.212 nm/count, and the OLTF looks qualitatively like the one in a previous measurement (~ 20 dB at 1 Hz, UGF = 30 Hz). The displacement was then converted to phase using lambda=1e-6; I'm not sure what the requirement is on the LO phase (G1802014 says 1e-4 rad/rtHz at 1 Hz, but our requirement doc says 1 to 20 nrad/rtHz (rms?)... anyways wit this rough calibration we are still off in either case.
The balancing gain is obvious at DC in the individual DCPD spectra, and the common mode rejection in the (A-B) signal is also appreciable. I'll keep working on refining this, and implementing a different control scheme.
Update; the high frequency ( > 100 Hz) drop is of course not real and comes from a 4th order LP filter in the HPC demod I filter which I haven't accounted for. Furthermore, we have gone through the calibration factors and corrected a factor of 2 in the optical gain. Then, I also added the CLTF to show in loop and out of loop error respectively. The updated plot, though not final, is in Attachment #1.
I don't know what was wrong with the past setup but the 950nm laser (QPHOTONICS QFLD-950-3S) just worked fine up to ~300MHz with basically the same setup.
A 20dB coupler picks up a small amount of the driving signal from the source signal of the network analyzer. This was fed to CHR. The fiber-coupled NewFocus PD RF output was connected to CHA.
The calibration of the response was done with the thru response (connect the source signal to the CHA via all the long cables).
Attachment 1 shows the response CHA/CHR. The output is somewhat flat up to 20MHz and goes down towards 100MHz, but still active up to 500MHz as long as the normalization with the New Focus PD works.
The structure around 200MHz~300MHz changes with how the wires of the clips are arranged. I have twisted and coiled them as shown and the notch disappeared. For the permanent setup we should keep the lines as short as possible and take care of the stray capacitance and the inductance.
Attachment 2 shows the setup at the network analyzer side. Nothing special.
Attachment 3 shows the setup at the laser side. The DB9 connector on the Jenne's laser has the negative output of the LD driver connected to the coax core and the positive output connected to the shield of the coax. Therefore the coax core (red clip) has to be connected to Pin 9 and the coax shield (black clip) to PIn 5.
Repeated the LO phase noise measurement, this time with the LO - ITMY single bounce, and a couple of fixes Koji hinted at including:
This time, after alignment the fringe amplitude was 500 counts. Attachment #1 shows the updated plot with the calibrated noise spectra for the individual DCPD signals A and B as well as their rms values. Attachment #2 shows the error point, in loop and the estimated out of loop spectra with their rms as well. The peak at ~ 240 Hz is quite noticeable in the error point time series, and dominates the high frequency rms noise. The estimated rms out of loop noise is ~ 9.2 rad, down to 100 mHz.
[Jamie, Christopher, JC]
This morning we decided to label the the fiber optic cables. While doing this, we noticed that the ends had different label, 'Host' and 'Target'. Come to find out, the fiber optic cables are directional. Four out of Six of the cables were reversed. Luckily, 1 cable for the 1Y3 IO Chassis has a spare already laid (The cable we are currently using). Chris, Jamie, and I have begun reversing these cable to there correct position.
We laid 4 out of 6 fiber cables today. The remaining 2 cables are for the I/O chassis on the vertex so we would test the cables the lay it tomorrow. We were also able to identify the problems with the 2 supposedly faulty cable, which are not faulty. One of them had a small bend in the connector that I was able to straighten out with a small plier and the other was a loose connection in the switch part. So there was no faulty cable, which is great! Chris wrote a matlab script that does the migration of all the model files. I am going through them, i.e. looking at the CDS parameter block to check that all is well. Next task is to build and install the updated models. Also need to update the '/opt/rtcds' and '/opt/rtapps' directory to the latest in the 40m chiara system.
I updated c1ass model today to use PR2 PR3 instead of TT1 TT2 for YARM ASS. This required changes in c1su2 too. I have split c1su2 into c1su2 (LO1., LO2, AS1, AS4) and c1su3 (SR2, PR2, PR3). Now the two models are using 31 and 21 CPU out of 60 which was earlier 55/60. All changed compiled correctly and have been uploaded. Models have been restared and medm screens have been updated.
We took lo phase noise spectra actuating on the for different optics-- LO1, LO2, AS1, and AS4. The servo was not changed during this time with a gain of 0.2, and we also took a noise spectrum without any light on the DCPDs. The plot is shown in Attachment #1, calibrated in rad/rtHz, and shown along with the rms values for the different suspension actuation points. The best one appears to be AS1 from this measurement, and all the optics seem to show the same 270 Hz (actually 268 Hz) resonant peak.
Koji suspected the observed noise peak belongs to some servo oscillation, perhaps of mechanical origin so we first monitored the amplitude in an exponentially averaging spectrum. The noise didn't really seem to change too much, so we decided to try adding a bandstop filter around 268 Hz. After the filter was added in FM6, we turned it on and monitored the peak height as it began to fall slowly. We measured the half-decay time to be 264 seconds, which implies an oscillation with Q = 4.53 * f0 * tau ~ 3.2e5. This may or may not be mechanical, further investigation might be needed, but if it is mechanical it might explain why the peak persisted in Attachment #1 even when we change the actuation point; anyways we saw the peak drop ~ 20 dB after more than half an hour... After a while, we noticed the 536 Hz peak, its second harmonic, was persisting, even the third harmonic was visible.
So this may be LO1 violin mode & friends -
We should try and repeat this measurement after the oscillation has stopped, maybe looking at the spectra before we close the LO_PHASE control loop, then closing it carefully with our violin output filter on, and move on to other optics to see if they also show this noise.
I turned on WFS on IMC at:
PDT: 2022-10-01 13:09:18.378404 PDT
UTC: 2022-10-01 20:09:18.378404 UTC
The following channels are being saved in frames at 1024 Hz rate:
We can keep it running over the weekend as we will not use the interferometer. I'll keep an eye on it with occasional log in. We'll post the time when we switch it off again.