Its going to need some kind of way to locate the PMC on the top. In the previous design, we had the 3 balls to decouple the body from the base. That design was flawed due to the roughness of the holes in the PMC body.
Hmmm, so, this was just meant to be a riser that goes underneath the old PMC mount, to raise it from 3" beam height to 4" beam height. I will make another one that is a complete mount, designed for 4" beam height. Please hold........... .......... ....... ..... ... .
The PSL enclosure now have 4 windows on each side. The bottom rail guides on the east side will be replaced by one U-channel for smoother, more gentle sliding.
Door position indicator- interlock switches are not wired yet.
Valera and I installed the the temp sensor and the interface box that Rana fixed. This may help with diagnosing the PSL drift.
eeek. I've been running around all day, so this is an incomplete elog. I'll fill in more stuff in the next hour or so, but just to let people know what's going on:
Valera noticed that lots of things in and around the PSL table are drifting with temperature. This is why he and Steve installed a temp sensor on the table earlier today.
Since the alignment into the PMC, and also the alignment downstream of the PMC have been drifting in angle, we supposed that it might be the PMC itself which is changing somehow with temperature. We don't have a good idea of how exactly it is sensitive to temperature, but we're working on figuring it out.
Round 1 of testing: We put a foil hat over the PMC to shield it from the HEPA air blowing directly down on top of it. I made sure that the foil is also covering the PZT and the metal ring at the end of the PMC, because this could potentially be the problem (metal is usually more temperature sensitive than glass, or the PZT itself could be changing, either of which could make the end mirror twist, and change the alignment of the PMC). We'll see later if this did anything useful or not.
I have photos of the aluminum foil setup, which I will post later when I get back to the lab after teaching.
I was wrong. Rana did not fix the interface box. I removed the interface box and turned down the HEPA flow from 100 to 20% on the Variac.
The PMC exhibited the reduction of the transmission, so it was aligned.
The misalignment was not the angle of the beam but the translation of the beam in the vertical direction
as I had no improvement by moving the pitch of one mirror and had to move those two differentially.
This will give us the information what is moving by the temperature fluctuation or whatever.
I looked at the PSL temperature box. It started out as D980400-B-C. Then it was revised by Peter King as per the LHO mods E020247.
There are some more things to do to it to make it useful for us:
** Frank reminds me that we don't use the TIdal or VME external inputs anymore since we moved to the EPICS/Perl PID control. So all we have to do is make sure these inputs are hardware disabled/disconnected.
The attached plot shows 7 day trends of the MC and PMC power levels, PSL QPDs, and temperature. The MC stayed locked for ~40 hours over the weekend. The temperature swings were somewhat smaller over the past couple of days but one should remember to turn the PSL HEPA down after working on the table. Steve turned the HEPA flow from 100% down to 20% on Thursday and posted the reminder signs on the PSL enclosure.
First we changed all the C1:IOO-QPD_*_* channels to C1:PSL-QPD_*_* channels in the /cvs/cds/caltech/target/c1iool0/c1ioo.db file, as well as the /opt/rtcds/caltech/c1/chans/daq/C0EDCU.ini file. We then rebooted the frame builder via "telnet fb 8087" and then "shutdown".
This change breaks continuity for these channels prior to today.
The C1:PSL-QPD_POS_HOR and C1:PSL-QPD_POS_VERT channels were found to be backwards as well. So we modified the /cvs/cds/caltech/target/c1iool0/c1ioo.db file to switch them.
Lastly, we changed the ASLO and AOFF values for the C1:PSL-QPD_POS_SUM and the C1:PSL-QPD_ANG_SUM so as to provide positive numbers. This was done by flipping the sign for each entry.
ASLO went from 0.004883 to -0.004883, and AOFF when from -10 to 10 for both channels.
The C1:PSL-QPD_ANG_SUM channel had been saturated at -10V. Valera reduced the power on the QPD to drop it to about 4V by placing an ND attenuator in the ANG QPD path.
I re-installed the box (@ ~8:15) after reflowing some of the solder joints. I will observe it over night and then remove the 1K resistors. Attached is a 8 hour minute-trend.
I added calculation entries to the /cvs/cds/caltech/target/c1iool0/c1ioo.db file which are named C1:IOO-QPD_*_*, as the channels were originally named. These calculation channels have the identical data to the C1:PSL-QPD_*_* channels. I then added the channels to the C0EDCU.ini file, so as to once again have continuity for the channels, in addition to having the newer, better named channels.
The c1iool0 machine ("telnet c1iool0", "reboot") and the framebuilder process ("telnet fb 8087", "shutdown") were both restarted after these changes.
These channels were brought up in dataviewer and compared. The approriate channels were identical.
Valera and I placed F 572.7 mm lens ~15 cm away from the ang qpd (in the same mount with ND filter) so that two qpds see different combination of ang and pos motion - there was no lenses prior to this change. The beam diameter is reduced to ~half .
I compared this 24 hour trend with the one from this day exactly one year ago. Seems the same, so now I can make the resistor change.
The PSL temperature box has returned to service, with some circuit modifications. The 1k resistors on all the temp. sensor inputs (R3, R4, R7, R8, R12, R12) were changed to 0 Ohm. Also, the 10k resistors R26, R28, R29, and R30 were changed to 10.2k metal film. The DCC document will be updated shortly. There is now an offset in the MINCOMEAS channel compared to the others, which will be corrected in the morning after looking at the overnight trend.
The PMC is losing power.
Nulling the slow actuation offset fixed the issue. Now PMC is back to normal.
The reflected beam on the CCD was quite symmetric (it looked very TEM00 mode !) for some reasons, I somehow suspected the mode matching to PMC.
One possibility I thought of was the laser temperature because it could change the laser spatial mode.
So I looked at the slow actuation offset on the FSS screen and found it was at -4.0 which sounds somewhat big.
Then I zeroed the offset by the slider and relocked PMC.
Then the spatial pattern of the reflected beam became usual (i.e. junk light looking) and the transmitted light wet up to 0.83 which is normal.
The PMC trans power was a little low (0.77V or so). I tweaked up the input pointing and now we're getting about 0.875V transmitted.
Access to the north side of the PSL table is blocked by the 8" beam guard. This opens the beam pathways between them.
I found the PMC unlocked. Koji noticed that the FSS Slow Actuator Adjust was railed at the positive end of the slider. I set it close to zero, and relocked the PMC. The FSS slow loop servo is doing its thing, and the PMC and MC are now locked.
I put labels on the pair of beam steering mirrors which are at the output end of the PSL table. I had changed one of these mirrors (elog) and Jenne had changed the other (elog). This was at about 3PM today
I just learned from Kiwamu that this has messed up the MC alignment.
It was unlocked since ~4:30am. No idea why. It's relocked so I can try round N of measuring the PRC length.
I found the PSL table left open, and unattended again.
As far as I know, Jamie and Jenne (working on the LSC rack, so no lasers / optics work involved) have been the only ones in the IFO room for several hours now.
I'm going to start taking laser keys, or finding other suitable punishments. Like a day of lab cleanup chores or something. Seriously, don't leave the PSL table open if you're not actively working on it.
80 days: PMC is drifting
Kiwamu and I aligned the PMC transmitted beam the incident beam going to PMC today.
I learnt how to lock the PMC using the digital controls.
I found that the ref cav trans CCD view was blinking with 30-50 fringe amplitudes. This meant the laser freq was swinging ~50GHz.
I checked the ABSL laser and the SG out of a lock-in amplifier was connected to the slow input.
This was shaking the laser temp from 29degC to 46degC. This was the cause of the fringe swinging.
This big excitation changing the output power too as the temp was changed across it mode-hop region.
I have disconnected the excitation from the laser no matter how useful experiments were took place as there was no e-log entry about this.
I need the explanations
1. Why our precious laser is exposed to such a large swing of temperature?
2. Why the excitation is left like that without any attendance?
3. Why there was no elogging about this activity?
Hmm. Should have only been +/- 1 GHz. Some setting got changed apparently...
This is a part of the RefCav temperature measurement setup. You'll get an elog from Jenny very soon.
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:
Forgot to do this in May. Have just changed the values in the psl.db file now as well as updating them live via Probe.
To make the appropriate change, I took the measured offset (5.31 deg) and added 2x this to the EGUF and EGUL field for the MINCO_MEAS channel. (see instructions here)
Committed the .db file to the SVN.
attached plot shows 8 days of trend with 5.31 degC added to the black trace using the XMGRACE Data Set Transformations
I turned the RefCav heater and servo back on a couple days ago. At first it was stabilizing again at a low setpoint, but in reality the right temperature (~40 C). After fixing the in-loop signal offsets, the setpoint now correctly reflects the actual temperature.
Jenny is going to calibrate the sensors using some kind of dunking cannister next week.
I think you made a simple mistake in your diagram -- the mixer must be replaced by a summer circuit. Otherwise you cannot do the PDH lock.
I am using a PDA255 photodiode to measure the power outputted by the NPRO beam on the PSL table. (I'm going to then use a network analyzer to measure the amplitude response of the PZT to being driven at a range of frequencies. I'll detect the variation in in response to changing the driving frequency using this PDA255.)
The PDA255 has an active area of 0.8mm^2 and a maximum intensity for which the response is linear of 10mW/cm^2. This means that a beam I focus on the PD must have a power less than 0.08 mW (and even less if the spot size is smaller than the window size).
I used a power meter to measure the beam power and found it was 0.381 mW.
The second polarizing beam splitter in the setup transmits most of the beam power, but reflects 0.04 mW (according to the power meter). I'm going to place the photodiode there in the path of the reflected beam.
Today I placed the PDA255 photodiode on the PSL table to catch the small amount of beam power reflected by the second polarizing beam splitter in my setup. I plugged the PD output to the oscilloscope to measure the voltage output and positioned the PD such that the voltage output was maximized. At best I was able to achieve a 300 mV DC output voltage from the PD, (which seems a bit low, as the PD is specified to go from 0 to 5 V and the specifications say that the response becomes nonlinear after 10 mW/cm^2 and my beam has an intensity of approximately 5 mw/cm^2. I would therefore expect to get more beam power but after over an hour of maneuvering, 300 mV was the highest voltage output I could get).
I am planning, tomorrow afternoon, to take a measurement of the amplitude response of the PZT driving the NPRO laser. I moved the 4395 spectrum/network analyzer to near the PSL table and connected the RF output to an RF splitter. I fed one output of that into the PZT and the other output into the R port on the network analyzer. I fed the PD output into the A port. I plan to measure A/R as a function of driving frequency, sweeping from 10 Hz to 30 mHz.
I also worked to improve the mode matching of the NPRO beam coming from the AP table to the reference cavity. I drove the temperature of the NPRO at 0.100 Hz with an amplitude of 0.300 V, which Koji told me corresponds to a 1GHz change in the laser frequency. The transmission from the cavity is being monitored by a camera connected to a TV monitor, and also by a PD connected to an oscilloscope. I then repositioned the second lens in my mode matching setup in an attempt to increase the transmission peaks from the zeroth order spacial mode and decrease the transmission peaks from higher order modes. I may have improved the mode matching slightly but I was unable to improve it significantly.
The ABSL beam had been blocked so that it wouldn't enter the interferometer. I moved the block so that the beam I've been using is unblocked by the beam going to the interferometer is still blocked.
I positioned a fast lens (f=28.7mm) a little over an inch in front of the PDA255 in order to decrease the spot size incident on the PD. I adjusted the rotation angle of the half wave plate to maximize the transmitted power through the PBS to the cavity and minimize the power reflected to my PD. I then adjusted the lens potion to fix the beam on the PD. The voltage output of the PD is now 150mW, but I have the ability to increase the incident power by rotating the wave plate slightly.
Now all I need is to set up the network analyzer again to record the amplitude response to modulating the PZT from 10 Hz to 30 MHz, reduce the input voltage into the analyzer using a DC block.
I rolled the network analyzer over to the PSL table (on the south side). I'm borrowing the DC block from Kiwamu's green locking setup. I'm going to first measure the amplitude response of a low pass filter to made sure that the analyzer is outputting what I expect. Then I will measure the laser PZT amplitude response. I plan to finish the measurement and return the network analyzer to it's usual location tonight.
Using a PDA255 on the PSL table, I measured the amplitude response of the NPRO PZT, sweeping from 10kHz to 5 MHz.
I took a run with the laser beam blocked. I then took three runs with the beam unblocked, changing the temperature of the laser by 10 mK between the first two runs and by 100mK between the second and third runs.
At the end of the night I turned off the network analyzer and unplugged the inputs. I'm leaving it near the PSL table, because I'd like to take more measurements tomorrow, probing a narrow bandwidth where the amplitude response is low.
On the PSL table, I'm still monitoring the reflected light from the cavity and the transmitted light through the cavity on the oscilloscope. I'm no longer driving the NPRO temperature with the lock-in.
I closed the shutter on the NPRO laser at the end of the night.
I'll log more details on the data tomorrow morning.
The top plot shows a sweep from 10 kHz to 5 MHz of the ratio of the voltage output of the PD detecting power from the NPRO laser beam and the RF source voltage (the magnitude of the complex transfer function). The black trace was taken with the laser beam blocked. For runs 2 and 3 I changed the laser temperature set point by 10 mK and 100 mK respectively to see if there was a significant change in the AM response. The bottom plots shows runs 2 and 3 compared to run 1 plotted in dB (to be explicit, i'm plotting 10 times the base 10 log of the magnitude of the ratio of two complex transfer functions). Changing the temperature seems to have only a minor effect on the output except at around 450kHz, where the response has a large peak in run 1 and much smaller peaks in runs 2 and 3.
The traces in the top plot consist of 16 averages taken with a 300Hz IF bandwidth, 15 dBm source power (attenuated with a 6 dB attenuator) and with 20dB attenuation of the input power from the PD.
Next I'm going to probe a narrow band region where the response is low (2.0MHz or 2.4MHz perhaps) and choose a bandwidth for the dither frequency for the PDH locking.
I've finished using the network analyzer to characterize find a dither frequency for driving the PZT to use in my PDH locking. I found a region in which the amplitude response of the PZT is low: The dip is centered at 2.418 MHz. Changing the NPRO laser temperature by 100mK has no significant effect on the transfer function in that region. I will post plots tomorrow.
I'm finished with the network analyzer. It is unplugged, and the cart is still near the PSL table. (I'll roll it back tomorrow when it won't disturb interferometer locking).
I closed the shutter on the NPRO at the end of the night.
Tomorrow I plan to put together the fast locking setup. I'll drive the PZT at 2.418 MHz. More details to come tomorrow.
I ended up choosing a different dither frequency for driving the NPRO PZT: 230 kHz, because the phase modulation response in that region is higher according to other data taken on an NPRO laser (see this entry). At 230 there is a dip in the AM response of the PZT.
I am driving the PZT at 230 kHz and 13 dBm using a function generator. I am then monitoring the RF output of a PD that is detecting light reflected off the cavity. (The dither frequency was below the RF cutoff frequency of the PD, but it was appearing in the "DC output", so I am actually taking the "DC output" of the PD, which has my RF signal in it, blocking the real DC part of it with a DC block, and then mixing the signal with the 230kHz sine wave being sent to the PZT.
I am monitoring the mixer output on an oscilloscope, as well as the transmission through the cavity. I am sweeping the laser temperature using a lock in as a function generator sending out a sine wave at 0.2 V and 5 mHz. When there is a peak in the transmission, the error signal coming from the mixer passes through zero.
My next step is to find or build a low pass filter with a pole somewhere less than 100 kHz to cut out the unwanted higher frequency signal so that I have a demodulated error signal that I can use to lock the laser to the cavity.
DMass and I locked the NPRO laser (Model M126-1064-700, S/N 238) on the AP table to the reference cavity on the PSL table using the PDH locking setup shown in the block diagram below (the part with the blue background):
A Marconi IFR 2023A signal generator outputs a sine wave at 230 kHz and 13 dBm, which is split. One output of the splitter drives the laser PZT while the other is sent to a 7dBm mixer. Also sent to the mixer is the output of a photodiode that is detecting the reflected power from off the cavity. (A DC block is used so that only RF signal from the PD is sent to the mixer). The output of the mixer goes through an SR560 low-noise preamp, which is set to act as a low pass filter with a gain of 5 and a pole at 30 kHz. That error signal is then sent to the –B port of the LB1005 PDH servo, which has the following settings: PI corner at 10kHz, LF gain limit of 50 dB, and gain of 2.7 (1.74 corresponds to a decade, so the signal is multiplied by 35). The output signal from the LB1005 is added to the 230 kHz dither using another SR560 preamp, and the sum of the signals drive the PZT.
I am monitoring the transmission through the cavity on a digital oscilloscope (not shown in the diagram) and with a camera connected to a TV monitor. I sweep the NPRO laser temperature set point manually until the 0,0 mode of the carrier frequency resonates in the cavity and is visible on the monitor. Then I close the loop and turn on the integrator on the LB1005.
The laser locks to the cavity both when the error signal is sent into the A port and when it is sent into the –B port of the PDH servo. I determined that –B is the right sign by comparing the transmission through the cavity on the oscilloscope for both ways.
When using the A port, the transmission when it was locked swept from ~50 to ~200 mV (over ~10 second intervals) but had large high frequency fluctuations of around +/- 50 mV. Looking at the error signal on the oscilloscope as well, the RMS fluctuations of the error signal were at best ~40 mV peak to peak, which was at a gain of 2.9 on the LB1005.
Using the –B port yielded a transmission that swept from 50 to 250 mV but had smaller high frequency fluctuations of around +/- 20 mV. The error signal RMS was at best 10mV peak to peak, which was at a gain of 2.7. (Although over the course of 10 minutes the gain for which the error signal RMS was smallest would drift up or down by ~0.1).
The open loop error signal peak-to-peak voltage was 180 mV, which is more than an order of magnitude larger than the RMS error signal fluctuations when the loop is closed, indicating that it is staying in the range in which the response is linear.
In the above plot the transmission signal is offset by 0.1 V for clarity.
Below is the closed loop error signal. The inset plot shows the signal viewed over a 1.6 ms time period. You can see ~60 microsecond fluctuations in the signal (~17 kHz)
The system remained locked for ~45 minutes, and may have stayed locked for much longer, but I stopped it by opening the loop and turning off the function generator. Below is a picture of the transmitted light showing up on a monitor, the electronics I'm using, and a semi-ridiculous mess of wires.
I determined that it’s not dangerous to leave the system locked and leave for a while. The maximum voltage that the SR560 will output to the PZT is 10Vpp. This means that it will not drive the PZT at more than +/-5 V DC. At low modulation rates, the PZT can take a voltage on the order of 30 Vpp, according to the Lightwave Series 125-126 user’s manual, so the control signal will not push the PZT too hard such that it’s harmful to the laser.
To aid Jenny's valiant attempt to finish her SURF project, I did some things with the front end system over the last couple days, largely tricking Jamie into doing things for me lest I ruin the 40m RCG system. Several tribulations have been omitted.
We stole a channel in the frontend, in the proccess:
Below are some plots from dataviewer of temperature-step data taken over the past 32 hours. (They show minute trends). I am looking at the thermal coupling from the can surrounding the reference cavity on the PSL table to the cavity itself, and trying to measure the cavity temperature response via the control signal sent to heat the NPRO laser, which is locked to the cavity.
I stepped the temperature set point from 35 to 36 deg. C for the can at 12:30am last night. Then I waited to see the cavity temperature change and the slow actuator (laser heater: TMP_OUTPUT) follow that change.
I was a bit worried about the oscillations that were occuring in the TMP_OUTPUT signal even long after this temperature step was made, but I figured that they were simply room-temperature changes propagating into the cavity, since they seemed to have a similar pattern to the room-temperature variations, and since it is clear that the out-of-loop temperature sensor on the can (RCTEMP) experiences variations, even when the in-loop sensors are recording no variation.
At 8:46pm tonight I stepped the temperature down 2 degrees to 34 deg. C. The step had a clear effect on TMP_OUTPUT. The voltage to the heater dropped and eventually railed at its lowest output. I'm worried that the loop is unstable, although I haven't ruled out other possibilities, such as that a 2 deg. C temperature step is too large for the loop. I will investigate further in the morning.
The lock was lost when I came in around noon today to check on it. The slow actuator was still railing.
1) I got lock back for a few minutes, by varying the laser temperature set point manually. TMP_OUTPUT was still reading -30000 cts (minimum allowed) and the transmission was not as high as it had been.
2) I toggled the second filter button off. The TMP_OUTPUT started rising up to ~2000 cts. I then toggled the second filter back on, and TMP_OUTPUT jumped the positive maximum number of counts allowed.
3) I lost the lock again. I turned off the digital output to the slow actuator.
4) I have so far failed at getting the lock back. My main problem is that when the BNC cable to the slow port is plugged in, even when I'm not sending anything to that port, it makes it so that changing the temperature set point manually has almost no effect on the transmission (it looks as though changing the setpoint is not actually changing the temperature, because the monitor shows the same higher order mode even when with +-degree temperature setpoint changes).
I am trying again to measure a temperature step response on the reference cavity on the PSL table.
I have been working to relock the NPRO to the cavity. I unblocked the laser beam, reassembled the setup described in my previous elog entry: 5202. I then did the following:
1) Monitored error signal (from LB1005 PDH servo), transmitted signal, and control signal sent to drive PZT on oscilloscope.
2) With loop open, swept through 0,0-mode resonance, saw a peak in the transmission, saw an accompanying error signal similar to the signal shown in 5202.
3) Tried to lock. Swept the gain on the LB1005 and could not find a gain that would make it lock. Tried changing the PI-corner freq. from 10 kHz to 30 kHz and back and still could not lock.
4) Noticed that the open loop error signal displayed on the scope was DC-offset from zero. Changed the offset to zero the error signal.
5) Tried to lock again and succeeded.
6) Noticed that upon closing the loop, the error signal became offset from zero again. Turning on the integrator on the LB1005 increased DC-offset.
7) Reduced the gain on the SR560 being used as a low pass filter from 5 to 1. Readjusted the open loop error signal offset on the LB1005.
8) Closed the loop and locked. Closing the loop then caused a much smaller DC change in the signal than I had seen with the larger gain (now around 3mV). RMS fluctuations in error signal are now 1 mV (well within the linear region of the error signal).
9) Noticed transmission has a strange distorted harmonic oscillation in it a 1MHz. (Modulation freq is 230kHz, so it's not that). Checked reflected signal and also saw a strange oscillation--in a sawtooth-like pattern.
I intend to
1) Post oscilloscope traces here showing transmitted and reflected signal when locked.
2) Look upstream to see if the sawtooth-like oscillation is in the laser beam before it enters the cavity:
3) At some point, try to close the slow digital loop, perhaps readjusting the gain.
4) Try to measure a temperature step response.
I decided to go forward and try to close the digital loop in spite of the unexplained oscillations in the transmission.
1) Plugged the 20dB attenuator into the slow port on the laser drive. This pushed the laser out of lock and, for some reason, made the laser temperature stop responding to sweeping the set point manually with the knob.
2) Plugged the output from the digital system into the slow port (with the attenuator still in place).
3) Displayed the beam seen by the camera on a monitor in the control room
4) Stepped the laser temperature using MEDM until finding the 0,1 mode. Locked to that mode.
5) Closed the digital loop (input to slow laser drive attenuated 20dB attenuator). Gain 0.010
6) Loop appeared stable for 30 minutes, then temperature began shooting off. I opened the loop, cleared history, reduced the gain to 0.008, and started it again. Loop appears stable after 15 minutes of watching. I'm going to leave it for a few hours, then come back to check on it and, if it's stable, step the can temperature.
After finishing my last elog entry, I monitored the digital loop's error signal (the control signal for the fast loop) and the output to the laser heater remotely, (from West Bridge), using dataviewer. The ref cav surrounding can temperature was set to 36 degrees C.
With the loop closed and a gain of 0.008, after seeing the output voltage to the laser heater (TMP_OUTPUT) remain fairly constant and the error signal (TMP_INMON) stay close to zero for ~3 hours, I tried to step the temperature. (This was at 2am last night). I was working remotely from West Bridge. To step the temperature I used the following command:
ezcawrite C1:PSL-FSS_RCPID_SETPOINT 35.5
Rather than change the can temperature to 35.5 C, it outputted:
It had set the setpoint to 0 degrees C, which was essentially turning the heater off. I tried resetting it back to 36 and had no luck. I tried changing the syntax slightly.: ezcawrite C1:PSL-FSS_RCPID_SETPOINT=36 and ezcawrite C1:PSL-FSS_RCPID_SETPOINT (36). No success.
I ran over to the 40m and changed the temperature back to 36 manually. The in-loop temp sensor had decreased to 31.5 degrees C before I was able to step the setpoint back up. The system seems to have recovered from this large impulse though, and the laser has remained locked.
(5 hours of minute-trend data)
From left to right:
Top: Out-of-loop can temp sensor; Voltage sent to heat can
Middle: signal sent to heat the laser (TMP_OUTPUT); room temp
Bottom: Error signal for slow loop (sampled control signal from fast loop); In-loop can temp sensor
At 9:30 this morning (7 and a half hours after accidentally setting the setpoint to zero), I came in to the 40m. TMP_OUTPUT was still decreasing but was slowing somewhat, so I decided to step the can temperature up half a decree to 36.5 C.
TMP_OUTPUT responded to the step, but it is also oscillating slowly with room-temperature changes, and these oscillations are on the same order as the step response. The oscillations look like the room-temp oscilations, but inverted. (TMP_OUTPUT reaches maxima when RMTEMP reaches minima). Oddly, there does not appear to be much of a time delay between the room temperature and TMP_OUTPUT signals. I would expect a time delay since there's a time constant for a room-temperature change to propagate into the cavity. Perhaps the laser itself is susceptible to room-temperature changes and those propagate into the laser cavity on a much faster time scale. I don't know the thermal coupling of ambient temperature changes into the laser.
(24-hours of second-trend data)
--If the system can handle it, do a larger temperature step (3 degrees, say), so that I can more clearly distinguish the oscillations with room temp from the step response.
--Insulate the cavity with foam (will in principle make the temperature over the can surrounding the ref cav more uniform and less affected by room temperature changes).
--Insulate the laser? Is this possible?
--Leave the system as is and, as a first approximation, fit the room-temp data to a sine wave and subtract it off somehow from my data to just see the step response.
--Don't bother with steps and just try to get the transfer function from out-of-loop temperature (RCTEMP, which is affected by temperature noise from the room) to TMP_OUTPUT via taking the Fourier transforms of both signals.
I'm flying out tomorrow morning, so I'll either need to figure out how to step the temperature set point of the can remotely, successfully, or I'll need someone to manually enter in the temperature steps for me in the control room.
c1psl has got frozen during our ezcaread/write business.
After the target was rebooted and we lost the previous setting as there was no burt snapshot for the slow targets since Dec 13, 2010.
It seems that burtrestore is essential for the bootstrapping of the MC servo, as the auto locker script refers the locking parameters
from the PSL setting values (C1PSL_SETTINGS_SET.adl).
Jenne is working on the recovery of the snap-shotting for the slow targets.
[Kiwamu Suresh Koji]
Some main parameters of the PSL has been recovered using Dataviewer and some screen snapshots, as seen in the screenshots below.
Relocked the PMC. MC came back immediately.
In the previous measurement, the PDA 255 had most probably saturated at DC, since the maximum ouput voltage of PDA255 is 5V when it is driving a 50 Ohm load. It has a bandwidth of 0 to 50MHz and so can be reliably used to measure only the 11 MHz AM peak. In this band it has a conversion efficiency of 7000 V per Watt (optical power at 1064nm). [Conversion efficiency: From the data sheet we get 0.7 A/W of photo-current at 1064nm and 10^4 V/A of transimpedance] The transimpedance at 55 MHz is not given in the data sheet. Even if PDA255 is driving a high impedance load, at high incident power levels the bandwidth will be reduced due to finite gain x bandwidth product of the opamps involved, so the conversion efficiency at 11 MHz would not be equal to that at DC.
So Koji repeated the measurement with a lower incident light level:
V_DC = 1.07 V with 50 Ohm termination on the multimeter.
Peak height at 11 MHz on the spectrum analyzer (50 Ohm input termination) = -48.54 dBm
a) RF_Power at 11 MHz : -48.45 dBm = 1.4 x 10^(-8) W
b) RF_Power = [(V_rms)^2] / 50_ohm ==> V_rms = 8.4 x 10^(-4) V
c) Optical Power at 11 MHz: [V_rms / 7000] = 1.2 x 10^(-7) W
d) Optical Power at DC = [V_DC / 7000] = 1.46 x 10^(-4) W
e) Intensity ratio: I_AM / I_c = 7.9 x 10^(-4) . AM:Carrier amplitude ratio is half of the intensity ratio = 4.0 x 10^(-4)
f) PM amplitude ratio from Mirko's measurement is 0.2
g) The PM to AM amplitude ratio is 506
As the AM peak is highly dependent upon the drifting EOM position in yaw, it is quite likely that a higher PM/AM ratio could occur. But this measurement shows how small it could get if the current situation is allowed to continue.
[Mirko / Kiwamu]
We have reviewed the AM issue and confirmed the ratio of AM vs. PM had been about 6 x103.
The ratio sounds reasonably big, but in reality we still have some amount of offsets in the LSC demod signals.
Next week, Mirko will estimate the effect from a mismatch in the MC absolute length and the modulation frequency.
Please correct us if something is wrong in the calculations.
According to the measurement done by Keiko (#5502):
DC = 5.2 V
AM @ 11 and 55 MHz = - 56 dBm = 0.35 mV (in 50 Ohm system)
Therefore the intensity modulation is 0.35 mV / 5.2 V = 6.7 x 10-5
Since the AM index is half of the intensity modulation index, our AM index is now about 3.4 x 10-5
According to Mirko's OSA measurement, the PM index have been about 0.2.
As a result, PM/AM = 6 x 103
* DC power = 5.2V which is assumed to be 0.74mW according to the PDA255 manual.
*AM_f1 and AM_f2 power = -55.9 dBm = 2.5 * 10^(-9) W.
Correction: Koji noted that Mirko actually reports a PM modulation index of 0.17 for the 11 MHz sideband (elog: http://nodus.ligo.caltech.edu:8080/40m/5462. This means
f) the amplitude ratio of the PM side-band to carrier is half of that = 0.084
g) the PM to AM amplitude ratio as 0.084 / [4.0 x 10^(-4)] = 209.