Jon is doing some characterization of the AUX laser setup for which he wanted only the prompt retroreflection from the SRM on the AS table, so the PSL shutter is closed, and both ITMs and ETMs are misaligned. The prompt reflection from the SRM was getting clipped on something in vacuum - the ingoing beam looked pretty clean, but the reflection was totally clipped, as I think Johannes aligned the input beam with the SRM misaligned. So the input steering of the AUX laser beam into the vacuum, and also the steering onto AS110, were touched... Also, there were all manner of stray, undumped beams from the fiber on the AS table Jon will post photos.
Before we began this work, we found that c1susaux was dead so we rebooted it.
PSL shutter was re-opened at 6pm local time. IMC was locked. As of 10pm, the main volume pressure is already back down to the 8e-6 level.
This activity seems to have closed the PSL shutter (actually I'm not sure why that happened - the interlock should only trip if P1a exceeds 3 mtorr, and looking at the time series for the last 2 hours, it did not ever exceed this threshold). I saw no reason for it to remain closed so I re-opened it just now.
I vote for not remotely rebooting any of the vacuum / PSL subsystems. In the event of something going catastrophically wrong, someone should be on hand to take action in the lab.
The PSL shutter was closed from the vacuum interlock trip. Today, I did the following:
All looks good for now. I will probably get back to PRFPMI locking Monday.
Thu Aug 12 11:04:42 2021 Arrived to find the PSL shutter closed. Why? Who? When? How? No elog, no fun. I opened it, IMC is now locked, and the arms were restored and aligned.
What I was afraid of was the vacuum interlock. And indeed there was a pressure surge this morning. Is this real? Why didn't we receive the alert?
I did a bit more investigation on this.
- I checked P1~P4, PTP2/3, N2, TP2, TP3. But found only P1a and P2 were affected.
- Looking at the min/mean/max of P1a and P2 (Attachment 1), the signal had a large fluctuation. It is impossible to have P1a from 0.004 to 0 instantaneously.
- Looking at the raw data of P1a and P2 (Attachment 2), the value was not steadily large. Instead it looks like fluctuating noise.
So my conclusion is that because of an unknown reason, an unknown noise coupled only into P1a and P2 and tripped the PSL shutter. I still don't know the status of the mail alert.
I moved the axuiliary NPRO to the PSL table today and started setting up the optics.
The Faraday Isolator was showing a pretty unclean mode at the output so I took the polarizers off to take a look through them, and found that the front polarizer is either out of place or damaged (there is a straight edge visible right in the middle of the aperture, but the way the polarizer is packaged prevents me from inspecting it closer). I proceeded without it but left space so an FI can be added in the future. The same goes for the broadband EOM.
There are two spare AOMs (ISOMET and Intraaction, both resonant at 40MHz) available before we have to resort to the one currently installed in the PSL.
I installed the Intraaction AOM first and looked at the switching speed of its first order diffracted beam using both its commercial driver and a combination of minicircuits components. Both show similar behavior. The fall time of the initial step is ~110ns in both cases, but it doesn't decay rapidly no light but a slower exponential. Need to check the 0 order beam and also the other AOM.
I don't understand why the 1st order diffracted beam doesn't go to zero when you shut off the drive. My guess is that the standing acoustic wave in the AO crystal needs some time to decay: f = 40 MHz, tau = 1 usec... Q ~ 100. Perhaps, the crystal is damped by the PZT and ther output impedance of the mini-circuits switch is different from the AO driver.
In any case, if you need a faster shut off, or want something that more cleanly goes to zero, there is a large (~1 cm) aperture Pockels cell that Frank Siefert was using for making pulses to damage photo diodes. There is a DEI Pulser unit near the entrance to the QIL in Bridge which can drive it.
there is a large (~1 cm) aperture Pockels cell that Frank Siefert was using for making pulses to damage photo diodes. There is a DEI Pulser unit near the entrance to the QIL in Bridge which can drive it.
I'll look for it tomorrow, but I haven't given up on the AOMs yet. I swapped in the ISOMET modulator today and saw the same behavior, both in 0th and 1st order. The fall time is pretty much identical. Gautam saw no such thing in the PSL AOM using the same photodetector.
In the meantime I prepared the fiber mode-matching but realized in the process that I had mixed up some lenses. As a result the beam did not have a waist at the AOM location and thus didn't have the intended size, although I doubt that this would cause the slower decay. I'll fix it tomorrow, along with setting up the fiber injection, beat note with the PSL, and routing the fiber if possible.
I used Gautam's mode measurement of the auxiliary NPRO (w=127.3um, z=82mm) for the spacing of the optics on the PSL table for the fiber injection and light modulation. As mentioned in previous posts, for the time being there is no Faraday isolator and no broadband EOM installed, but they're accounted for in the mode propagation and they have space reserved if desired/required/available.
The coupler used for the injection is a Thorlabs F220APC-1064, which allegedly collimates the beam from the fiber type we use to 2.4mm diameter, which I used as the target for the mode calculations. I coupled the first order diffracted beam to a ~60m fiber, which is a tad long but the only fiber I could locate that was long enough. The coupling efficiency from free-space to fiber is 47.5%, and we can currently get up to 63 mW out of the fiber.
Tomorrow Steve and I are going to pull the fiber through protective tubing and bring it to the AS port. The next step is then characterizing the beam out of the collimator to match it into the interferometer.
As far as the switching itself is concerned: I confirmed that the exponential decay is still present when looking at the fiber output. I located the DEI Pulser unit in the QIL lab, and also found several more AOMs, including a 200MHz Crystal Technologies one, same brand that the PSL has, where the ringdown was not observed. According to past elogs, with good polarizers we can expect an extinction ratio of ~200 from the Pockels cell, which should be fine, but it's going to be tradeoff switching speed <-> extinction (if the alternate AOM doesn't show this ringdown behavior).
I brought the DEI Pulser unit and a suitable Pockels cell over from Bridge today (I also found an identical Pockels cell already at the 40m on the SP table, now that I knew what to look for).
I also brought the 200MHz AOM (Crystal Technology 3200-1113) along which can achieve rise times of 10 ns(!). Before I start setting up the Pockels cell I wanted to try this different AOM and look at its switching behavior. It asks for a much smaller beam (<65 um diam.) than what's currently in the path to the fiber (500 um diam.), although it's clear aperture is technically big enough (~1mm diam.). So I still tried, and the result was a somewhat elliptical deflected beam, and the slower decay was again visible after switching the RF input.
I was using the big Fluke function generator for the 200MHz seed signal, a Mini Circuits ZASWA-2-50 switch and a Mini Circuits ZHL-5W-1 amplifier. For the last two I moved two power supplies (+/-5V for the switch and +24V for the amplifier) into the PSL enclosure. I started at low seed power on the Fluke, routing the amplified signal into a 20dB attenuator before measuring it with an RF power meter. The AOM saturates at 2.5W (34 dBm), which I determined is achieved with a power setting on the Fluke of -4 dBm. As expected, this AOM performed faster (~80ns fall time) but I again observed the slower decay.
This struck me as weird and I started swapping components other than the AOM, which I probably should have done before. It turned out that it was the PD I was using (the same PDA10CF Gautam had used for his MC ringdown investigations). When I changed it to a PDA10A (Si diode, 150MHz bandwidth) the slow decay vanished! One last round of crappy screenshots:
Rather than proceeding with the Pockels cell, tomorrow I will make the beam in the AOM smaller and hope that that takes care of the ellipticity. If it does: the AOM can theoretically switch on ~10ns timescale, same for the switch (5-15ns typical), and the amplifier is non-resonant and works up to 500MHz, so it shouldn't be a limiting factor either. If this doesn't work out, we can still have ~100ns switching times with the other AOMs.
I changed the PSL table auxiliary laser setup to the 200 MHz AOM and put the light back in the fiber. Coupling efficiency is again ~50%, giving us up to about 75 mW of auxiliary laser light on the AS table. The 90% to 10% fall time of the light power out of the fiber when switched off is 16.5 ns with this AOM on the PDA10A, which will be sufficient for the ringdown measurements.
I cleaned up the scattered tools, optics, and mounts of the PSL table. I gathered those stuffs at the two coners.
At the end of the work I scanned the table with an IR viewer. (This is mandatory)
I put some beam block plates to kill weak stray beams.
One thing I like to call the attention is:
Particularly, there was no beam block at the forward rejection side of the first PBS where we dump the high power beam.
29 Thu BS chamber work: Move cable towers / green steering mirrors / (2 TTs with TT charactrization) / Put the heavy door by 5PM.
30 Fri Pumping down
31 Sat WFS work by Nancy
1 Sun - 5 Thu WFS work by Nancy
5 Thu PSL Table prep
6 Fri PSL Table prep / Likely to shut down the PSL
9 Mon PSL Table prep / shutting down of the PSL (optional)
10 Tue PSL box Frame lifting
12 Thu PSL table tapping
16 Mon - 17 Tue concrete pouring preparation
19 Thu - 23 Fri Tripod placement
24 Tue - 26 Thu concrete pouring
The PSL table height will be raised to the level of the AP table. This will be done using 6 TMC's Rigid Damped Tripod legs. Their planed positions shown below.
The legs will be grouted to the floor with concrete.
I assembled the telescope to couple PSL light into the fiber. The maximum coupling that I could obtain was 10mW out of 65mW (~15%).
I was expecting to achieve 80-90% coupling from my design estimates. It makes me wonder if the beam waist measurements made by Harry during summer were correct in the first place. I would like to go back and check the beam waist at the PSL table.
Also, we need a pair of 8m (~25 feet) long SMA cables to carry the RF signal from the beat PD on the PSL table to frequency counter module on the IOO rack.
Steve says that we had a spool of SMA cable and it was borrowed by someone a few months ago. Any updates on either who is holding it or if it has been used up already would help.
The X end slow computer was down this morning. So I used only the Y arm ALS to record the noise level for reference. DTT data for ALSY out of loop noise before opening PSL enclosure is saved in /users/manasa/data/141211/ALSYoutLoop.xml
The X end slow computer was down this morning. So I used only the Y arm ALS to record the noise level for reference. DTT data for ALSY out of loop noise before opening PSL enclosure is saved in /users/manasa/data/141211/ALSYoutLoop.xml
I missed to elog this earlier. I have temporarily removed the DC photodiode for GTRY to install the fiber holder on the PSL table. So GTRY will not be seeing anything right now.
After some confusion, I discovered this a few hours ago.
I have been commissioned to take pictures of the PSL table so that it can be diagrammed. I am starting now (1:42 pm, 10/5/09).
All done (for now). That wasn't so bad, was it?
The main motivation for this work is that I want +15VDC power available on the PSL table to hookup the Teledyne box that Koji made a week ago and do some noise measurements on my revised IR ALS signal chain. But I think this is a good opportunity to effect a number of changes I've been wanting to do for a while.
Tomorrow, Steve and I will do the following:
So in summary, we will need, at 1X1, (at least, including 1 spare for future work):
We completed this work today. Need to clean up a little (i.e. coil excess cable lengths, remove unused cables etc), which we will do tomorrow. All connections have been made at the DIN rail end, but the fuses have not been inserted yet, so there is no voltage reaching the PSL table on any of the newly laid out cables. We also need to establish two +15VDC connections at the DIN rail side. I may establish this later in the evening, as the main point of this work was to get the Teledyne signal path operational. Setting up these DIN connectors is actually a huge pain, we tried to setup a few extra ports for the voltages we used today so that in future, life is easier for whoever wants to pipe DC power to the PSL table. The rule is, however, to re-establish the same number of open ports for each voltage as was available when you started.
For the ZHL-3A, Teledyne, and AOM driver cables, we used 18AWG, 2 conductor, twisted wire, while for the PSL fan we used 20AWG. For the FSS box, we decided to use the 3 conductor 24AWG twisted wire. I believe that these wire gauge choices are appropriate given the expected current in each of these paths.
Pictures + further details tomorrow.
gautam @ 1030pm: there was some mistake with the +15V wiring we did in the evening (the PSL fan and Teledyne cables were plugged into the wrong DIN terminal blocks). I fixed this, and also routed +15VDC to the newly installed set of terminal blocks for this purpose (since we had run out of +15VDC ports at 1X1). After checking voltages at both 1X1 and on the PSL table, I hooked up
to their newly laid out power supplies. IMC locks so looks like the FSS box is doing fine . So we can recover one bench power supply from under the PSL table on the east side. I didn't hook up the AOM driver just now because of some accessibility issues, and I'd also like to do an ALS beat spectrum measurement if possible.
Jenne and Koji
Last week Jenne has put the accelerometers on and under the PSL table immediately after the plastic sheets were removed.
So I took the same measurement as I did on 9th Aug.
Here is the comparison of the vibrational performance of the table before and after the modification.
Basically the table is now stiffer and more damped than it was before.
We don't find any eminent structure below (at least) 70Hz.
This result is obtained despite elevating of the table.
1) Attachment 1
For the horizontal comparison (top), it is clearly seen that the large resonant peak at 20Hz was eliminated.
At least the new resonances went up to 70-90Hz region. Y is basically equivalent to X.
For the vertical comparison (bottom), it is clearly seen that the resonant peaks at around 50 & 70Hz were eliminated.
At least no new resonance is seen.
2) Attachment 2
All-in-one plot for the measurement --- spectra, coherences, transfer functions --- after the upgrade. I put the same plot for the one before the upgrade.
I've been working on the PSL table to put together a setup so that I can measure the reference cavity's response to a temperature step increase at the can surrounding it. My first step was to mode match the beam coming from the AP table to the cavity.
I implemented my mode matching solution. I ended up using a different one from the one I last elogged about. Here is the solution I used:
Two lenses: f = 1016.7.6 mm at -0.96 m and f = 687.5 mm at -0.658 m. (I set my origin at the polarizing beam splitter--the spot where I want my beam to match the beam coming from the PMC, so all waists are behind that point). Below is what it should look like.
What I did on the table:
Here's a picture of the PSL table with the lenses and mirror I added. The beam is redirected by a mirror and then a polarizing beam splitter. Past the beam splitter is another lens (f=286.5 mm), which was already in place from the mode matching of the beam from the PMC to the reference cavity.
Here is a block diagram of my intended experimental setup:
I am going to try to lock the laser to the cavity given my preliminary mode matching and then go back and improve it later. My next step is to find a frequency range for dithering the voltage sent to the PZT. To do this I will:
PSL temperature changed
The beat note of Xarm looked somehow strange before (elog). It should be the highest when the green transmission power is highest, in other words when the end green PDH locks with a TEM00 mode. But it was not like that. When the end PDH locked with other modes (GTRX: below 0.3), the beat note was higher than TEM00 mode (GTRX: around 0.5).
We guessed that end green laser was somewhere around the point where there were 2 stable TEM00 modes . In order to move away from this unstable region of the end laser, we changed PSL temperature to obtain beat note at a different green laser frequency where we do not have any of the weird modes oscillating.
We changed the PSL temperature from 31.63 degree to 31.33 degree. We measured the in-loop noise of ALS loop and I attached it. There is not big difference in Yarm, but the Xarm in-loop noise become better in high frequency region. We think before the xend green laser was in a not-so-good state and the laser had more frequency noise then.
After change PSL temperature, Xarm ALS is so stable. Actually Xarm is being locked right now and it is locked for more than 50 minutes!!
Although the Xarm ALS is so stable, Yarm ALS is not stable right now. It lost lock by ~5min. We don't know what is the reason, so we will try to fix it tomorrow.
I used some double-sided tape to attach a San Ace 60 9S0612H4011 to the Innolight controller (Attachment #1). This particular fan is rated to run with up to 13.8V, but I'm using a +15V Sorensen output - at best, this shortens the lifespan of the fan, but I don't have a better solution for now. Then I turned the laser on again (~1040 local time), using the same settings Rana configured earlier in this thread. PMC was locked, and the IMC also could be locked but I closed the shutter for now while the laser frequency/intensity stabilizes after startup. The purpose is to facilitate completion of the pre-vent alignment checklist in prep for the planned vent tomorrow. PMC Trans reports 0.63 after alignment was optimized, which is ~15% lower than in Oct 2016.
To test the hypothesis that the fan replacement had any effect on the NPRO shutoff phenomena, I turned the HEPA on the PSL table down to the nominal 30% setting at ~10am.
Tomorrow I will revert the laser crystal temperature to whatever the nominal value was. If the NPRO runs in that configuration (i.e. the only change from March 2019 are the diode TEC setpoints and the new fan on the back of the controller), then hurray.
As we have seen in the last few weeks, the laser turned itself off after a few hours of running. So bypassing the lab interlock system / reverting laser crystal temperature to the value from Innolight's test datasheet did not fix the problem.
I do not understand why the "Interlock" and "TGUARD" channels come revert to their values when the laser was lasing a few minutes after the shutoff. Is this just an artefact of the way the diagnostics is set up, or is this telling us something about what is causing the shutoff?
This time, it stayed on for ~24 hours. I am not going to turn it on again today as the crane inspection is tomorrow and we plan to keep the VEA a laser safe area for speedy crane inspection.
But what is the next step? If these diode temps maximize the power output of the NPRO, then it isn't a good idea to raise the TEC setpoint futher, so should I just turn it on again with the same settings?
I did not turn the HEPA down on the PSL enclosure. I also turned off the NPROs at EX and EY so now all the four 1064nm lasers in the VEA are turned OFF (for crane inspection).
locked PMC at 1900 PT; let's see how long it lasts.
My hunch is that the TECs are working too hard and can't offload the heat onto the heat sinks. As the diode's degrade, more of the electrical power is converted to heat in the diodes rather than 808 nm photons. So hopefully the increased airflow will help
I turned the 2W NPRO back on again at ~4pm local time, dialing the injection current up from 0-2A in ~2 mins. I noticed today that the lasing only started at 1A, whereas just last week, it started lasing at 0.5A. After ~5 minutes of it being on, I measured 950 mW after the 11/55 MHz EOM on the PSL table. The power here was 1.06 W in January, so ~💯 mW lower now. 😮
I found out today that the way the python FSS SLOW PID loop is scripted, if it runs into an EZCA error (due to the c1psl slow machine being dead), it doesn't handle this gracefully (it just gets stuck). I rebooted the crate for now and the MC autolcoker is running fine again.
NPRO turned off again at ~8pm local time after Anjali was done with her data taking. I measured the power again, it was still 950mW, so at least the output power isn't degrading over 4 hours by an appreciable amount...
Per instructions from Coherent, I made the some changes to the NPRO settings. The value we were operating at is in the column labelled "Operating value", while that in the Innolight test datasheet is in the rightmost column. I changed the Xtal temp and pump current to the values Innolight tested them at (but not the diode temps as they were close and they require a screwdriver to adjust), and turned the laser on again at ~1245pm local time. The acromag channels are recording the diagnostic information.
update 2:30pm - looking at the trend, I saw that D2 TGuard channel was reporting 0V. This wasn't the case before. Suspecting a loose contact, I tightened the DSub connectors at the controller and Acromag box ends. Now it too reports ~10V, which according to the manual signals normal operation. So if one sees an abrupt change in this channel in the long trend since 1245pm, that's me re-seating the connector. According to the manual, an error state would be signalled by a negative voltage at this pin, up to -12V. Also, the Innolight manual says pin 13 of the diagnostics connector is indicating the "Interlock" state, but doesn't say what the "expected" voltage should be. The newer manual Coherent sent me has pin13 listed as "Do not use".
My hunch is that the TECs are working too hard and can't offload the heat onto the heat sinks. As the diode's degrade, more of the electrical power is converted to heat in the diodes rather than 808 nm photons. So hopefully the increased airflow will help.
I tried to increase the DTEC setpoints, but that seems to detune them too far from the laser absorption band, so that's not very efficient for us. IN any case, if we end up changin the laser temperature, we'll have to adjust the ALS lasers to match, and that will be annoying.
The office area was very cold and the HVAC air flow stronger than usual. I changed the setpoint on the thermostat near Steve's desk from 71 to 73F at 1830 today.
Also, Kiwamu has modified the layout drawing to add the green PLL stuff. This has collapsed the reference cavity's wave function placing it close to its original position.
WE (maybe Valera and Steve) can now put the reference cavity back on the table.
- The PMC REFL PD was moved from the temporary location to the one called for by the PSL layout (picture attached). The leakage beams were dumped.
- The FSS reference cavity was aligned using temporary periscope and scanned using NPRO temperature sweep. The amplitude of the sweep (sine wave 0.03 Hz) was set such that the PMC control voltage was going about 100 V p-p with. With rough alignment the visibility was as high as 50% - it will be better when the cavity is locked and better aligned but not better than 80% expected from the mode astigmatism that Tara and I measured on Thursday. The astigmatism appear to come from the FSS AOM as it depends on the AOM drive. We reduced the drive control voltage from 5 V to 4V beyond that the diffraction efficiency went below 50%. The FSS REFL PD was set up for this measurement as shown in the attached picture. There is also a camera in transmission not shown in the picture.
Rana and I were poking around on the PSL table today, getting a few more items raised to the correct height.
I checked the polarization state of the new NPRO by using a HWP to minimize the transmission through a PBS cube, and then compared the power transmitted through the cube vs. reflected. When the NPRO current was 0.772 \pm 0.001 (as read on the LCD), the transmission through the cube was 1.44mW, while the reflected was 10.53mW. The reading of the Ophir power meter with no incident light was 0.03mW. This factor of 10 means that the NPRO beam is ~10% circularly polarized and ~90% linearly polarized. In order to improve the beam, we need a Quarter Wave Plate, which it turns out we don't have. We need a QWP!
After that, using the linearly polarized part of my beam (maximizing the transmission through the PBS by rotating my HWP by 45deg), I tried to tune the angle of the polarizers that Rana pulled out of the MOPA. I think I'm confused / too tired, because I can only get the polarizer to reflect a bunch of light, and I can't get it to pass any significant amount of light through, no matter where in its actuation range I put it (It's on a rotation stage with a few degrees of range). It should just be a Brewster's Angle thing, and since I already have P-pol coming through the BS cube, this shouldn't be so hard.....
In any case, it may not be useful to do the final fine tuning of these polarizers until they are in their final places. The hacky stack of mounts that I have has some slop in the position / alignment of the base of the polarizer, so no matter what we'll have to redo the tuning after the mounts are finalized.
To bypass the polarizer issue, I just used cubes. One I took from the FSS-Refcav path and the other from the power control part of the old MOPA, just downstream of the MOPA's periscope.
We'll swab these out with the thin-film polarizers after we get the mounts made.
With the cubes in, I also installed the Faraday + its 1/2-wave plate. The transmission looks good and we're getting into the PMC and its flashing a TEM00 mode sometimes. I set up a signal generator to drive the SLOW actuator by 1 FSR at 0.1 Hz.
I have set up a PMC transmission camera and transPD so that its easy to align. The flashing mode already allows us to align most of the rest of the table (except FSS).
Our next step should be to run the cables for locking the PMC:
On Tuesday, we need to make sure that all of our mounts' drawings are in the cue for the shop. I'll put the list of mounts onto the PSL upgrade wiki page.
We also have to come up with a plan for wiring some of the 2W NPRO's channels into the cross-connect so that we can have some laser channels recorded by EPICS.
I am feeling that it is ok to carefully make new holes and threads as far as the holes do not penetrate the plate.
The thickness of the plate can be measured by the four holes at the corners.
OK. Today we did the same type of measurement for the Y arm laser as was done for the X arm laser here: http://nodus.ligo.caltech.edu:8080/40m/3759
And attached here is a preliminary plot of the outcome - oddities with adding on the fitted equations, but they go as follows
(Red) T_yarm = 1.4435*T_PSL - 14.6222
(Blue) T_yarm = 1.4223*T_PSL - 10.9818
(Green) T_yarm = 1.3719*T_PSL - 6.3917
It's a bit of a messy plot - should tidy it up later...
It's a bit of a messy plot - should tidy it up later...
I'm going to take the easy question - What are the pink data points??
And I'm going to answer the easy question - they're additional beat frequency temperature pair positions which seem to correspond to additional lines of beat frequencies other than the three highlighted, but that we didn't feel we had enough data points to make it worthwhile fitting a curve.
It's still not entirely clear where the multiple lines come from though - we think they're due to the lasers starting to run multi-mode, but still need a bit of thought on that one to be sure...
The good news is that we seem to be running in a linear region of the PSL laser with a degree or so of range before the PSL Innolight laser starts to run multi-mode. On the attached graph we are currently running the PSL at 32.26degrees (measured) which puts us in the lower left corner of the plot. The blue data is the Lightwave set temperature (taken from the display on the laser controller) and the red data is the Lightwave laser crystal measured temperature (taken from the 10V/degC calibrated diagnostic output on the back of the laser controller - between pins 2 and 4).
The other good news is that we can see the transition between the PSL laser running in one mode and running in the next mode along. The transition region has no data points because the PMC has trouble locking on the multi-mode laser output - you can tell when this is happening because, as we approach the transition the PMC transmitted power starts to drop off and comes back up again once we're into the next mode region (top left portion of the plot).
The fitted lines for the region we're operating in are:
Y_arm_Temp_meas = 0.95152*T_PSL + 3.8672
Y_arm_Temp_set = 0.87326*T_PSL + 6.9825
X_arm and Y_arm vs PSL comparison.
Just a quick check of the performance of the X arm and Y arm lasers in comparison to the PSL. Plotting the data from the X arm vs PSL and Y arm vs PSL on the same plot shows that the X arm vs the PSL has no observable trending of mode-hopping in the laser, while the Y arm vs the PSL does. Suspect this is due to the fact that the X arm and PSL are both Innolight lasers with essentially identical geometry and crystals and they'll tend to mode-hop at roughly the same temperatures - note that the Xarm data is rough grained resolution so it's likely that any mode-hop transitions have been skipped over. The Lightwave on the other hand is a very different beast and has a different response, so won't hop modes at the same temperatures.
Given how close the PSL is to one of the mode-transition regions where it's currently operating (32.26 degC) it might be worth considering shifting the operating temperature down one degree or so to around 31 degC? Just to give a bit more headroom. Certainly worth bearing in mind if problems are noticed in the future.
This afternoon Q helped me put in some temporary PDs for checking for any mode hopping behavior in our 3 main lasers.
Q helped me install PDA55s on each of the lasers (I did the ends, he did the PSL) so that we could do the mode hop temperature check. For the Yend, I took the leakage transmission through the first Y1 steering mirror after the laser. This beam was dumped, so I replaced the dump with a PDA55. For the Xend, the equivalent mirrors are too close to the edge of the table, so I put in a spare Y1, and reflect most of the light to a beam dump. The leakage transmission then goes to a PDA55. Note that for both of these cases, no alignment of main laser path mirrors was touched, so we should just be able to remove them when we're through. For the PSL, I believe that Q took the rejected light from one of the PBSes before the PMC.
The end temporary PDs are using the TRX / TRY cables, so we will be looking at the C1:LSC-TR[x,y] channels for the power of the end lasers. The PSL's temporary PD is connected to the PMC REFL cable. For the end PDs, since I had filter banks available, I shuttered the end lasers and removed the dark offset. I then changed the gains to 1, so the values are in raw counts. The usual transmission normalization gains are noted in one of the control room notebooks.
I did a slow ezcastep and ramped the temperature of all 3 lasers over about an hour. Since we usually use the PSL around FSS slow slider value of zero, I swept that from -10 to +10. Since we usually use the Xend laser at around 10,000 counts, I swept that from 0 to 20,000. For the Yend laser, it is usually around -10,000 counts, so I swept it from -20,000 to 0. ezcastep -s 0.2 C1:ALS-X_SLOW_SERVO2_OFFSET +1,20000 C1:ALS-Y_SLOW_SERVO2_OFFSET +1,20000 C1:PSL-FSS_SLOWDC +0.001,20000
ezcastep -s 0.2 C1:ALS-X_SLOW_SERVO2_OFFSET +1,20000 C1:ALS-Y_SLOW_SERVO2_OFFSET +1,20000 C1:PSL-FSS_SLOWDC +0.001,20000
I was looking for something kind of similar to what Koji saw when he did this kind of sweep for the old MOPA (elog #2008), but didn't see any power jumps that looked suspicious.
Here is the PSL:
And the Yend:
[Jon, Gautam, Johannes]
Summary: In support of making a proof-of-concept RF measurement of the SRC Gouy phase, we've implemented a PLL of the aux. 700mW NPRO laser frequency to the PSL. The lock was demonstrated to hold for minutes time scales, at which point the slow (currently uncontrolled) thermal drift of the aux. laser appears to exceed the PZT dynamic range. New (temporary) hardware is set up on an analyzer cart beside the PSL launch table.
- Characterize PLL stability and noise performance (transfer functions).
- Align and mode-match aux. beam from the AS table into the interferometer.
- With the IFO locked in a signal-recycled Michelson configuration, inject broadband (swept) AM sidebands via the aux. laser AOM. Coherently measure the reflection of the driven AM from the SRC.
- Experiment with methods of creating higher-order modes (partially occluding the beam vs. misaligning into, e.g., the output Faraday isolator). The goal is identify a viable techinque that is also possible at the sites, where the squeezer laser serves as the aux. laser.
The full measurement idea is sketched in the attached PDF.
Some notes about the setup and work at the PSL table today, Jon can add to / correct me.
The reference cavity vacuum chamber temp is plotted starting Feb 22 of 2005
This plot suggest that the MINCO temp controller is not working properly.
Valera and I installed the the temp sensor and the interface box that Rana fixed. This may help with diagnosing the PSL drift.