how about calibrate the DC channels so that you can just get the acutal power levels from the trend data?
I keep adding traces to this plot, here is the most complete one I have now. Looks like the input noise to the D040179 (measured at "Q out" SMA jack of D990511 with RFPD input terminated) is ~10nV/rtHz. This supports the hypothesis that something is wonky on the daughter board, because the purple trace should only be the quad sum of the orange and green traces. I will pull it out and have a look.
Some other follow-ups on the questions raised at the meeting:
I measured the output voltage noise of the Q output of the AS55 Demod Board with the PSL shutter closed, using the SR785 (see Attachment #1). The measured noise is consistent with the expected number of ~120nV/rtHz around 100Hz. I had measured the gain of this board from RFPD input to Q output to be ~5.1: so if the PD dark noise is 16nV/rtHz, this would be amplified to ~80nV/rtHz. Still a discrepancy of ~50%. I didn't measure the noise with the PD input terminated. Added the noise of the demod board output with the RFPD input terminated. The level of ~100nV/rtHz seems consistent with the actual PD dark noise being ~80nV/rtHz, as their quadrature sum is around 130nV/rtHz. Need to dig up the schematics for the demod board + daughter board, and check against LISO, to see if this is consistent with what is expected.
Also - I think I was using the wrong value of the DC power on the AS55 photodiode for shot noise calculations - 13mW was for REFL55, not AS55. I did a crude measurement of the power by sticking the Ophir power meter (filter removed) in front of the AS55 PD with the Michelson flashing around, and noticed the maximum value registered was ~1.2mW. So in the DRMI lock, there would be ~2.4mW, which is 10x lower than the value I was assuming. I've made the correction in the NB code, for the next time the plot is generated. A more rigorous measurement would involve sticking the Ophir in front of the AS110 PD during a DRMI lock. The light from the AS port is split by a 50-50 BS to the AS55 and AS110 PDs (so measuring at AS110 is a reasonable proxy for power at AS55), and the AS110 signals are not used for triggering in the DRMI lock, so this is feasible.
I tried replacing the AD797s on the daughter board with OP27s, and saw no significant improvement in the electronics noise of the demod board. Note that according to LISO, in this configuration, the voltage noise of the Op27 is expected to dominate the total noise of the daughter board. Measurement condition was that the RFPD input was terminated, but the LO input was still being driven (SR785 input range is -50dBVpk for all traces, and the input ranging was set to "UpOnly"). Need to do a more systematic investigation to figure out where this excess noise is coming from. I will upload photos of the board later.
This supports the hypothesis that something is wonky on the daughter board, because the purple trace should only be the quad sum of the orange and green traces. I will pull it out and have a look.
I worked on the daughter board a little more in the evening. I have somehow managed to make the dark noise ~25% worse [Attachment #1].
After making all these changes, I re-installed the card in the eurocrate and repeated the measurement. The Q channel noise was close to the expected value (~50nV/rtHz), but the I channel is twice as noisy. I will continue this investigation tomorrow.
Here is the marked up schematic with the board as it is stuffed. Annoyingly, there is a capacitor (C1) which according to the schematic is supposed to be open, but is stuffed in our board. I can't find any elog about this, and its a pain to measure the value of this capacitance. I will upload all of this + LISO + noise model/measurements to a 40m AS55 daughter board DCC page.
Attachment #1 - Measured / modelled noises for AS55 demod board. I've plotted quadrature sum of the LISO trace with the SR785 noise floor with input terminated to ground via 50ohm. Note that these measurements were made after all the changes in the marked up schematic in the previous elog were implemented.
Both channels should be identical - I don't understand why the I channels are noisier than their Q counterparts. This is almost certainly a problem on the daughter board, as the orange traces are pretty much identical for both channels.
The dark red curves were measured by shorting the inputs to D040179 to ground via 50ohms using some Pomona minigrabbers - I wanted to avoid ripping the daughter board out, but this probably explains the excess noise compared to the green trace at low frequencies. All other measurements were made with the board installed in the LSC rack eurocrate, with the LO input driven at the nominal level (I didn't measure this yesterday but a measurement from ~6months ago says that this level is 1.5dBm).
Koji suggested looking at the output of the AS55 demod board on a fast oscilloscope to look for differences in the two channel outputs (if there is some high-frequency oscillations, for example, we could miss this information in the SR785 spectra). Besides, I was only looking at spectra out to a few kHz on the SR785. I grabbed this data with a 300MHz BW Tektronix oscilloscope (battery mode) today. Input impedance of both channels were set to 1Mohm, and the measurement was made with the RFPD input terminated, output of the daughter board is what is measured. The vertical scaling of the channels was set to the minimum allowed, 1mV/div.
Attachment #1 shows that there is indeed a visible difference between the two channels - the (noisier) I channel has a much larger DC offset of ~5mV compared to the Q channel (I tried switching channels on the O'scope and the larger DC offset remained on the I channel, so seems real). There is also some kind of oscillation going on in the I channel, although the frequency is pretty low, with the peaks spaced ~50us apart. Indeed, in the ASD of the acquired data, the excess power in the I channel at 20kHz and higher harmonics are evident (see Attachment #2). Anyway all of this points to something being anomalous on the daughter board I channel signal path - I will pull it out and monitor the outputs at various points along the signal path with the fast scope to see if I can narrow down what's going on where.
We took a closer look at the AS55 demod board today. The procedure was to just be as thorough as possible, and check the behaviour of the circuit (both Transfer Function and Noise) stage by stage. Checking the transfer function was the key.
During this process, we found that the reason why the Q channels had lower noise than the I channels was because of the gain of the AD829 stage of the circuit was 0dB rather than 4dB (which is what it should be according to the component values used). Specifically, resistor R12, which is supposed to be 1.30kohm, was measured to be 1.03kohm. Replacing this resistor, the transfer functions (see Attachment #1) and noise levels (see Attachment #2) match the expectations from LISO. Some notes:
Assming the whitened ADC noise level is much below this (should only be ~10nV/rtHz), and given the measured sensing element of 6.2e8 V/m, this means that the dark noise sets a maximum achievable sensitivity of 2e-16m/rtHz.
To figure out what (if anything) is to be done next, we need to first figure out what is the goal. In the end, we care about DARM and not MICH. The optical gain for the former is ~300x the latter, so the dark noise contribution gets scaled by this factor (giving us a number of 7e-19 m/rtHz). There are certainly many noises above that level which have to be handled first. Indeed, looking at the DARM spectrum from DRFPMI lock back in March 2016, it looks like the current 1f DRMI (with coils de-whitened) Michelson sensitivity is within a factor of 2 of DARM in the full lock (albeit with vertex DoFs on 3f signals, and no coil de-whitening). Koji pointed out that we need to consider the photodiode resonant circuit itself too.
TODO: Upload all this onto the DCC
The gain of whitening filters on AS55 was decreased from 21 dB to 0 dB for the Y arm locking.
- - (Background)- -
Since the modulation depths became bigger from the past (#5462), the PDH signal from Y arm was saturated in the path of AS55.
Due to the saturation the lock of the Y arm became quite difficult so I decreased the gain of of the whitening filter from 21 dB to 0 dB.
In this condition, a required gain in C1:LSC-YARM_GAIN is about -0.3, which is 10 times bigger from the default number.
For the MICH locking tonight, it may need to be back to a big gain.
I temporarily replaced AS55 PD with PD labeled "POP55(POY55)".
I think POP55 is working because I could lock MI with this PD using AS55_Q_ERR as an error signal. I rotated I/Q phase (C1:LSC-AS55_PHASE_R) to 70 deg by minimizing ASDC during MI lock.
POP55 PD was freely sitting on the ITMX table.
I will leave AS55 PD at free space of the AP table. Someone, please look into it.
A new 90 deg splitter, PSCQ-2-51W, has been installed on another demod board called AS55.
It shows a reasonably close 90 degree separation between the I and Q signals at 55 MHz with various LO and RF power.
So far we have ordered only three PSCQ-2-51Ws for test. Now we will order some more for the other demodulators.
Some plots will be posted later.
I measured the transfer function, shot noise, and dark spectrum of AS55.
From the shot noise measurement, the RF transimpedance is (556.3 +- 0.8) Ohms and the dark current is (2.39 +- 0.01) mA. The dark noise agrees with the approximate value calculated from the circuit components.
There are no anomalous oscillations when there is no light on the photodiode. I am working on fitting the transfer function in LISO but the other plots are on the wiki at http://blue.ligo-wa.caltech.edu:8000/40m/Electronics/AS55
I finally did carry out a measurement on the network analyzer. This proves that the previous system will work properly. Just the optical splitter problem is to be taken care of.
For this, after Elog 10102, I did not touch any of the tables or photodiodes. Only turned on the laser at 1Y1 and took readings from the NA located nearby. I switched off the laser after measurements. The power to REF PD remains on.
I plotted transimpedence plots in the usual way and got ridiculous values of 15 ohms at 55MHz. Obviously there is the problem of varying amount of power illuminating the REF PD and AS55.
So, I just plotted the bode plots of transfer function got from the NA to check if the characteristics of AS55 looks as it was supposed to be and Yes! I got a nice peak at 55MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
1) Frequency sweep range: 1MHz to 100 MHz.
2) Number of Points sampled in the range: 801
3) Type of sweep: Linear
The experimental values obtained were:
The experimental values obtained were:
DC output voltage of REF PD: 7.48V
DC output voltage of AS55: 53.7mV
Power incident on REF PD and AS55 respectively: 2.4mW and 1.6mW
Taking the DC transimpedence of AS55 as 66.2 ohms (from schematic given at D1300586-v1) and for REF PD as 1E04 ohms
Hence, Responsivity for REF PD and AS55 respectively are: 0.312 A/W and 0.51 A/W
The data and code used are in the zip file.
AS4 is set to go through a free swinging test at 10 pm tonight. We have used this script (Git/40m/scripts/SUS/InMatCalc/freeSwing.py) reliably in the past so we expect no issues, it has a error catching block to restore all changes at the end of the test or if something goes wrong.
To access the test, on allegra, type:
Then you can kill the script if required by Ctrl-C, it will restore all changes while exiting.
Came this morning, the gluing of the magnets was 100% successful. Side blocks, counterweights were assembled. We suspend AS4 and adjust the roll balance and the magnet height (attachments 1,2). OpLev was slightly realigned.
The pitch was balanced. We had to compensate for the pitch shift due to the locking of the counterweights. Once we got good pitch balance, the motion spectrum was taken (attachment 3). Major peaks are at 755mHz, 953mHz, 1040mHz.
Previous peaks were 755mHz, 964mHz, and 1.062Hz so not much has changed. We pushed back the OSEMs, adjusted OSEM plate and locked it tightly. We lock the EQ stops and transfer AS4 to the vacuum chamber in foil. We open the foil inside the chamber. No magnets were broken. Everything seems to be intact. We connect the OSEMs to CDS.
AS4 was succesfully suspended and trasported to ITMY chamber (40m/16589). We placed it near the door to make it easy to tune the OSEMs. We connected the OSEMs and found that the LL OSEM is not responding. Even though the the OSEMs are completely out right now, there was no signal on this OSEM. This could be an issue in either at the LED driver circuit or the PD circuit in AS4 Sat Amp box, or it could be the OSEM that is bad. We'll investigate further next day. For now, we recorded the full brightness reading for the OSEMs:
Another thing to note is that UL value above is not changing at all. I checked the CDS screen and the the ADC input is overflowing in complete bright position of the OSEM.
AS4 satellite amplifier D1002818 / D080276 troubleshoot
I dug into the circuit to see what/where things were wrong.
- UL saturation issue: The open light voltage at the TIA output (I-V out) was 10.4V. It seemed that the photocurrent of 86uA was simply a little too much for the transimpedance gain of 121kOhm. So the R18 was replaced to 100kOhm. This made the I-V out to be 8.6V and the ADC input count to be 28200 (Attachment 1). This modification was done on the unit S2100742 CH1 (LEFT CH1)
- Non responding LL issue: Now moved on to LL (LEFT CH2). The basic circuit test didn't reveal any problem. So the DSUB25 cables were swapped at the vacuum feedthru flange. The result is shown in Attachment 2. LL OSEM issue was moved to the 2nd ch of the right channel of the sat amp (CH6). This is means that the problem is somewhere in the vacuum chamber (including the vacuum feedthru). We need to check the in-vacuum cable and the OSEM. We can test the OSEM by swapping the position of the OSEM connector between LL and UL (for example).
Turns out, the shifting was likely due to the table level. Because I didn't take care the first time to "zero" the level of the table as I tuned the OSEMs, the installation was b o g u s. So today I took time to,
a) Shift AS4 close to the center of the table.
b) Use the clean level tool to pick a plane of reference. To do this, I iteratively placed two counterweights (from the ETMX flow bench) in two locations in the breadboard such that I nominally balanced the table under this configuration to zome reference plane z0. The counterweight placement is of course temporary, and as soon as we make further changes such as final placement of AS4 SOS, or installation of AS1, their positions will need to change to recover z=z0.
c) Install OSEMs until I was happy with the damping. ** Here, I noticed the new suspension screens had been misconfigured (probably c1sus2 rebooted and we don't have any BURT), so quickly restored the input and output matrices.
SUSPENSION STATUS UPDATED HERE
[Paco, Tega, Anchal]
Today, we started work on AS4 SOS by checking the OSEM and cable. Swapping the connection preserved the failure (no counts) so we swapped the long OSEM for a short one that we knew was working instead, and this solved the issue. We proceeded to swap in a "yellow label", long OSEM in place and then noticed the top plate had issues with the OSEM threads. We took out the bolt and inspected its thread, and even borrowed the screw from PR2 plate but saw the same effect. Even using a silver plated setscrew such as the SD OSEM one resulted in trouble... Then, we decided to not keep trying weird things, and took our sweet time to remove the UL, UR OSEMs, top earthquake stops, and top plate carefully in-situ. Then, we continued the surgery by installing a new top plate which we borrowed from the clean room (the only difference is the OSEM aperture barrels are teflon (?) rather than stainless. The operation was a success, and we moved on to OSEM installation.
After reaching a good place with the OSEM installation, where most sensors were at 50% brightness level and we were happy with the damping action (!!), we fixed all EQ stops and proceeded to push the SOS to its nominal placement. Then upong releasing the EQ stops, we found out that the sensor readings were shifted.
After the debacle with AS1 (40m/16580), we decided the put the PEEK earthquake stop by first removing the lower OSEM plate and then doing it. So I unfastened AS4 from its position with the earthquake stops in place and moved the suspension to the center of the table. Then I carefully removed the bottom OSEM plate. But I found out that the LR magnet is broken and lying on the floor of the suspension . Given my past on the same day, it could be me breaking it again during the moving of the suspension of taking off the OSEM plate or there is a small chance that this break happened before. Regardless of fault, this meant we have to resuspend AS4 again as well. So we transported AS4 back to the clean room and the work on it's re-suspension has begun.
The free swinging test was successful. I ran the input matrix diagonalization code (/opt/rtcds/caltech/c1/Git/40m/scripts/SUS/InMAtCalc/sus_diagonalization.py) on the AS4 free-swinging data collected last night. The logfile and results are stored in /opt/rtcds/caltech/c1/Git/40m/scripts/SUS/InMAtCalc/AS4 directory. Attachment 1 shows the power spectral density of the DOF basis data (POS, PIT, YAW, SIDE) before and after the diagonalization. Attachment 2 shows the fitted peaks.
The new matrix was loaded on AS4 input matrix and this resulted in no control loop oscillations at least. I'll compare the performance of the loops in future soon.
I think our suspension input matrix diagonalization is not so robust usually because we only choose a inverting matrix which gives the best separation for a single suspension alignment.
i.e. we have seen in the past that adjusting the bias for the alignment makes the matrix inversion not work well. Sometime people turn OFF the alignment bias before making the ringdown and that makes the whole measurement invalid.
This is because the sensitivity of the OSEMs to longitudinal and/or transverse motion is significantly different for different alignment.
I wonder if there's a way we can choose a better matrix by putting in random gain errors on the shadow sensor signals and then finding the matrix which gives the best diag under an ensemble of gain errors.
I agree. That's an interesting idea. But does that mean that there is an always working inverse matrix solution or that any solution will be vulnerable to the alignment biases.
I think we can also calculate the matrix rotation required as a function of dc biases and do that rotation in the simulimk model.
[Jenne / Kiwamu]
We have installed a broad band PD in the AS path in order to monitor the 110 MHz signal associated with the SRC.
The PD is currently connected to the POP110 demodulation board and it seems working fine.
I know this is confusing but right now the signal appears as "POP110" in the LSC front end model.
I worked on AS_11 today. Its ready for its noise / optical gain calibrations. I have left it on Suresh's desk.
This was one of the 24.5 MHz Black Box (Ben Abbott) style RFPDs rescued from LLO. The tunable inductor that was installed was too small to get the frequency down to 11 MHz and so I swapped in one of the shielded, ferrite core ones from our '7mm' CoilCraft kit. It had a range of 1.2 - 1.8 uH according to the datasheet.
I wasn't able to simulataneously get the peak at 11.06 MHz and the notch at 59.3 MHz and so I took Koji's advice and tuned the peak best. The plot above shows how the notch is slightly off. I think its not a problem; to get it better we would have to change out the inductor for the "2-omega" notch, but I was too lazy. The thinking is that its more important to have the gain be symmetric around the signal readout frequency so as to not imbalance the audio sidebands.
Since this one is going to be AS_11, we think that the 22 MHz signal will be tiny: the transmission of the 11 MHz sidebands to the dark port is small. If we later want to put in a 22 MHz notch anyway, there is space to do this via the 'active notch' pads around the MAX4107.
For the above plot, I used the Jenne laser. The DC output of the PD was ~30 mV (~0.6 mA). The RF drive to the laser was -10 dBm: no saturations. I have calibrated out the cable responses, but not using the 1811 setup, so the absolute calibration has yet to be done.
Also, it needs some new stickers. It would be handy if someone can figure out how to get some sheets of stickers that we can put into the printer. Then we can laser printer all of the data onto the stickers and stick them to the RFPD box.
AS1, PR2 and PR3 are set to o go through a free swinging test at 3 am. We have used this script (Git/40m/scripts/SUS/InMatCalc/freeSwing.py) reliably in the past so we expect no issues, it has a error catching block to restore all changes at the end of the test or if something goes wrong.
Today I suspended AS1. Anchal helped me with the initial hanging of the optics. Attachments 1,2 show the roll balance and side magnet height. Attachment 3 shows the motion spectra.
The major peaks are at 668mHz, 821mHz, 985mHz.
For some reason, I was not able to balance the pitch with 2 counterweights as I did with the rest of the thin optics (and AS1 before). Inserting the weights all the way was not enough to bring the reflection up to the iris aperture that was used for preliminary balancing. I was able to do so with a single counterweight (attachment 4). I'm afraid something is wrong here but couldn't find anything obvious. It is also worth noting that the yaw resonance 668mHz is different from the 755mHz we got in all the other optics. Maybe one or more of the wires are not clamped correctly on the side blocks?
The OSEMs were pushed into the OSEM plate and the plates were adjusted such that the magnets are at the center of the face OSEMs. The wires were clamped and cut from the winches. The SOS is ready for installation.
Also, I added a link to the OSEM assignments spreadsheet to the suspension wiki.
I uploaded some pictures of the PEEK EQ stops, both on the thick and thin optics, to the Google Photos account.
I was wondering whether I should take AS1 down to redo the wire clamping on the side blocks. I decided to take the OpLev spectrum again to be more certain. Attachments 1,2,3 show 3 spectra taken at different times.
They all show the same peaks 744mHz, 810mHz, 1Hz. So I think something went wrong with yesterday's measurement. I will not take AS1 down for now. We still need to apply some glue to the counterweight.
The LO phase lock that was achieved lasts for a short time because as soon as a considerable POS offset is required on AS1, the POS to PIT coupling causes the AS-LO overlap to go away. To fix this, we need to balance the coil outputs of AS1 atleast and add the f2a filters too. To follow similar method as used for IMC optics, we need a sensor for true PIT and YAW motion of AS1. Today, we looked into the possiblity of installing a QPD at BHD output path to use it for AS1, AS4, LO1, LO2, SR2, PR2 and PR3 coil strength tuning. We found a QPD which is mentioned in this elog. We found QPD interface boards setup for old MCT and MC Refl QPDs (dating before 2008). We also found the old IP-POS QPD cable between 1Y2 and BS Oplev table. We took out this cable from BS oplev end upto ITMY opleve table, put on a new DB25 connector on the ribbon cable, and connected it to the QPD on ITMY table. There is still following work to be done:
Tega and Paco reported that the UR OSEM of AS1 lost the response.
- I have checked the LED MON (left) of the satellite amp for AS1. CH1/2/3 had 5V -> This indicates that the OSEM LEDs are (most likely) functioning.
- Then I went to the ITMY flange and connected the OSEM emulator instead of the Dsub25 cable. The attachment shows that the UR OSEM LED/PD worked fine with the OSEM emulator. WIth the vacuum flange connected it lost the response.
This indicates that the AS1 UR OSEM problem is localized in the chamber. Please check if the DSUB pins are touching the table or something else.
[JC, Tega, Ian, Paco]
We found that the UR cable was clamped to the table by one of the ITMY OPLEV steering mirror mounts that was recently installed. After freeing the cable, the UR signal is now active again.
AS1 Sat Amp (S2100741) has a critical PCB issue on it's Ch5-8 board S2100548. This board is supposed to just feed through the coil driver signal from the front DB9 connector to the back DB25 connector but it has a short between pins 2 and 7 at the "Coil Input" end (connector J1). The short persists even after I disconnect the sat amp to the flange connector on the back of this board, which definitely means the short is present in the passive channeling through the PCB or at the soldering points of the two DB connectors. I just flipped the board and found that the soldering connections are clean and separate. I think we'll have to use one of the spare sat amp boxes for AS1 for now, while we either declare this one manufacture defected or fix the issue.
I actually found the short on the PCB trace by just looking carefully at it. Attachment 1 shows the photo of it. Maybe we can fix this by simply cutting the tumor between the two traces (why are these traces so close together in such a large board anyways!!!), but I'm not sure if that is a reliable way of fixing this issue. I'll wait for Koji's comments on what to do with this. We'll recommence OSEM tuning for AS1 tomorrow with fixed electronics.
I fixed the issue in AS1 Sat Amp (S2100741) by using a razor blade. I cut the short between the two places, cleaned up the area and covered it with electrical tape. However, later feedback from Rana was to not use electrical tape as it dries up and becomes brittle and lfaky in long run. So after the AS1 OSEM tuning is over, I'll open this box again and use something else to insulate the exposed area. See attached pictures for current status.
We found that there was a small offset (~300 mV) at TP6 and TP8, in PD2 circuit (CH2 of the board). I replaced U3 AD822ARZ but did not see any affect. I disconnected the adaptor board in the back and saw that the offset went away. This might mean that the cable had some flaky short to a power supply pin. However, when I just reinserted the adaptor board back again, there was no offset. We could not find any issue with the board after that to fix, so we left it as it is. If this board gives offset issues in the future, most probably the ribbon cable would be the suspect.
Now all ADC channels are showing no offset or overflows in C1SU2 chassis.
[Anchal (vacuum work), Paco (outside)]
After the AS1 Sat Amp fix (40m/16579), we today were able to tune all OSEMs to the mid-bright level. But when we were about to call it, we were told that the new PEEK earthquake stop screw and bolts need to go on the thin suspended optics. Against better judgment, we decided to install the new back earthquake stop in-situ since we had tuned all OSEMs already. I installed the new stop but after that found that in the process I have broken off the side magnet and LR magnet from the optic adaptor and they are inside the OSEM coils now. This means we'll have to redo the AS1 suspension almost from scratch again . We have transported AS1 to the cleanroom where the work on re-suspension has begun.
These don't show anything too interesting, but we're including them to show where the beams are right now on the cameras, so we can compare on Monday.
To get the camera shot of AS, Y1 mirror on the path was replaced by a 99% BS and transmitted beam was directed to the camera via a 50-50 BS (ND filters were distorting the image on the camera introducing fringes).
IPANG / IPPOS trends:
c.f. screen caps from Friday:
I slightly changed the orientation of a few mirrors on AS table that are used to make the AS light get into PDs, in order to confirm that the strange behavior of ASDC (I will report later) is not caused by clipping related to these mirrors or miscentering on PDs.
Then output level of ASDC, AS55, and AS165 could have changed.
So take care of this possible change when you do something related to them. But the relative change of them would be at most several %, I think.
[Jenne, Jamie, Manasa, Ayaka]
Flipped mount of OM2, moved OM2 behind POY pickoff so we're out of the way of POY. Adjusted and recovered rest of AS path.
We found that IPANG was not on its photodiode, but determined that it was centered on all of the in-vac mirrors, and that it was just a little bit of steering on the ETMY end out-of-vac table that needed to be done.
Got green flashes in Yarm, moved down periscope to the north by ~1 inch in order to get y green out to PSL table. This also involved moving the steering mirror on the IOO table immediately after the down periscope to match. We measured the MC spot positions before and after touching the periscope, and there was no significant change.
Aligned X green to X arm (centered on ITMX, ETMX, although no flashes since we didn't move ETMX's biases around), then made sure it was centered on all of its steering mirrors, and came out of the vacuum.
Manasa took photos of all test mass chambers and the BS chamber, so we can keep up-to-date CAD drawings.
Oplevs and IPPOS/IPANG are being centered as I type. Manasa and Ayaka are moving the lens in front of IPANG such that we have a slightly larger beam on the QPD.
In the morning, Jamie is going to put apertures back on 2 of the suspended mirrors for one last check that moving things on the IOO table didn't do anything bad, but since the AS and REFL beams on those cameras didn't move significantly, we think things are fine.
Heavy doors go on in the morning, and access connector at ~1pm, if not before lunch. Then Steve will start pumping early Monday morning! Hooray!
PS, for reference,
Here is a set of mode scans of the AS port, using the OMC as a mode scanner. The plot overlays various configurations of the IFO.
To remove PZT nonlinearity, each scan was individually flattened in fsr-space by polynomial (3rd order) fitting to some known peak locations (the carrier and RF sidebands).
Status of the AS-port auxiliary laser injection
Using Gautam's Finesse file and the cad files for the 40m optical setup I propagated the arm mode out of the AS port. For the location of the 3.04 mm waist I used the average distance to the ITMs, which is 11.321 m from the beam spot on the 2 inch mirror on the AS table close to the viewport. The 2inch lens focuses the IFO mode to a 82.6 μm waist at a distance of 81 cm, which is what we have to match the aux laser fiber output to.
I profiled the fiber output and obtained a waist of 289.4 μm at a distance of 93.3 cm from the front edge of the base of the fiber mount. Next step is to figure out the lens placement and how to merge the beam paths. We could use a simple mirror if we don't need AS110 and AS55, we could use a polarizing BS and work with s polarization, or we find a Faraday Isolator.
While doing a beam scan with the razor blade method I noticed that the aux laser has significant intensity noise. This is seen on the New Focus 1611 that is used for the beat signal between PSL and aux laser, as well as on the fiber output PD. There is a strong oscillation around 210 kHz. The oscillation frequency decreases when the output power is turned down, the noise eater has no effect. Koji suggested it could be light scattering back into the laser because I couldn't find a usable Faraday Isolator back when I installed the aux laser in the PSL enclosure. I'll have to investigate this a little further, look at the spectrum, etc. This intensity noise will appear as amplitude noise of the beat note, which worries me a little.
For the arm cavity ringdowns, I guess we don't need AS55/AS110 (although I think the camera will still be useful for alignment). But for something like RC Gouy phase characterization, I'd imagine we need the AS detectors to lock various cavities. So I think we should go for a solution that doesn't disturb the AS PD beams.
It's hard to tell from the plot in the manual (pg 52) what exactly the relaxation oscillation frequency is, but I think it's closer to 600 kHz (is this characteristic of NdYAG NPROs)?? Is the high RIN on the light straight out of the NPRO?
We could use a simple mirror if we don't need AS110 and AS55, we could use a polarizing BS and work with s polarization, or we find a Faraday Isolator.
There is a strong oscillation around 210 kHz. The oscillation frequency decreases when the output power is turned down, the noise eater has no effect.
Instead of trying to couple the fiber output into the interferometer, I'm doing the reverse and maximize the amount of interferometer light going into the fiber. I set up the mode-matching solution shown in attachment #1 and started tweaking the lens positions. Attachment #2 shows the setup on the AS table. After the initial placement I kept moving the lenses in the green arrow directions and got more and more light into the fiber.
When I stopped this work yesterday I measured 86% of the AS port light coming out the other fiber end, and I have not yet reached a turning point with moving the lenses, so it's possible I can tickle out a little more than that.
It occured to me though that I may have been a little hasty with the placement of the mirror that in attachment #2 redirects the beam which would ordinarily go to AS55. For my arm ringdown measurements this doesn't matter, I could actually place it even before the 50/50 beamsplitter that sends light onto AS110 and double the amount of light going into the IFO. What signals are needed for the Guoy phase measurement? Is AS 110 sufficient, or do we need AS55?
I think we need AS55 for locking the configuration Jon suggested - AS55 I and Q were used to lock the SRMI previously, and so I'd like to start from those settings but perhaps there is a way to do this with AS110 I and Q as well.
What signals are needed for the Guoy phase measurement? Is AS 110 sufficient, or do we need AS55?
I was planning to set up the additions to the AS table that are outlined in Attachment #1. Unfortunately the beam is too large for the 2mm clear aperture Faraday rotators that we have available at that position. I checked the 40m and QIL and found 5 Faraday isolators/rotators for 1064 nm total, but none have large enough aperture for the current setup. Some options for buying a larger aperture isolator are:
I wanted to leave the rest of the setup undisturbed at first, but I think a much easier solution would be to move the 2" focusing lens up by about 12", which moves the beam focus away from AS55 to where the Faraday will be placed, but we can re-focus it with another lens. I may have to change the mode-matching for the aux laser fiber slightly to accomodate this change, but if there are no other concerns I would like to start this work tomorrow (Wednesday).
[Tega, Yehonathan, Koji, Yuta]
We tried to align AS path this afternoon.
IMC is not aligned now after the work today
Green mirrors/perisocope in IMC chamber were removed since some of them was clipping the AS beam, and this changed the balance of the IMC stack and thus MC1 and MC3 alignment.
Summary of changes:
- Rotated AS2 in roll by 90 deg to have more aperture for the transmission (photo)
- IR beams are now centered on AS1, AS2, AS3 and AS4 (photo, photo)
- Moved ASL towards -X direction for about 1/4 inch
- Installed GRY_SM2 at the nominal position (re-used GR_SM3 from IMC chamber)
- Removed green optics GR_SM4, GR_SM3, GR_PERI2L (GR_PERI2L is now stored at Xend)
- Removed IFI camera mirrors FIV1, FIV2 (they are now stored at Xend) (photo, photo)
- GR_SM4 mount is now reused as GRY_SM1 (Y2-2037-0 is now mounted instead of previously mounted Y2-LW1-2050-UV-45P/AR), and GRY_SM1 is installed at the nominal position (photo)
- Moved weights to balance the stack
OMC chamber (we don't have OMC in this chamber...)
- We swapped AS5 and AS6 so that the nobs comes in -X direction to have more spacing between AS beam and IMC REFL beam (photo)
- Moved weights to balance the stack
What we did:
1. Misaligned ITMX and use ITMY reflected beam to align AS path
2. Centered the IR beam on AS1 using SR2
3. Centered the IR beam on AS2 and ASL using AS1. AS2 was rotated in roll by 90 deg to have more aperture for the transmisson.
4. Centered the IR beam on AS3 using AS2 nobs, centered the IR beam on AS4 by rotating AS3 in yaw.
5. "AS beam" (it turned out that what we are looking was actually not the AS beam!! Some stray light) was in +X direction by 1 inch or so at AS5. Moving AS5 to center the beam would clip IMC REFL beam. So we swapped AS5 and AS6 so that the nobs comes in -X direction to have more spacing between AS beam and IMC REFL beam.
6. Balanced OMC chamber stack again using IMC REFL beam as a referece (bring the IMC REFL beam to the reference red circle on the monitor).
7. Tweaked the alignment of TT1 and TT2 to have Yarm flashing to ~0.9 in TRY.
8. Moved AS5 towards +X by an inch or so to center the "AS beam."
9. Moved ASL towards -X direction for about 1/4 inch and re-centered the beam by AS1 to see if the "AS beam" gets far from IMC REFL at OMC chamber, but the "AS beam" didn't move much.
10. By blocking the beam from ITMY, we found that "AS beam" was not the actual one.
11. Opened IMC chamber and found that AS beam is blocked by the past optics.
12. Removed old green optics and IFI camera mirrors. GR_SM4 mount and GR_SM3 were reused as mentioned above.
13. Tried to balance IMC chamber stack to recover IMC alignment. We used IMC REFL beam as a reference, but it was hard to completely bring the IMC REFL beam to the reference red circle on the monitor. It is now off by a beam diameter or so. No IMC flashing now.
Theoretically, balancing IMC chamber stack would recover all the IFO alignment, but maybe tough. It is maybe easier to align MC1 and MC3 to have IMC locked. Assuming input pointing to IMC is not drifted too much, we should be able to recover Yarm flashing by tweaking TT1 alignment only. However, MC3 SD OSEM is at the edge of the range. We might have to balance the stack more or tweak SD OSEM position.
We finally managed to steer the AS beam from ITMY chamber, through BS and IMC chambers, to the in-air AP table.
We moved the AS5 mirror north to its nominal position and we also moved the ASL lens on BS chamber back to its nominal position. Attached photos are taken after today's alignment work.