We have discovered that the MCL loop squishes the length fluctuations that result from the MC spot measurement angular dither. This is good, in that the MCL is doing what it ought to do. However, we need to turn it off before doing a spot measurement.
This is totally non-sensical statement, of course.
We might also say that the DARM loop totally squishes the GW signal and so its better not to have any feedback in the interferometer.
The aLIGO-style summary webpages are now running on 40m data! They are running on megatron so can be viewed from within the martian network at:
At the moment I have configured the 5 seismic BLRMS bands, and a random set of PSL channels taken from a strip tool.
Since there are no segments or triggers for C1, the only data sources are GWF frames. These are mounted from the framebuilder under /frames on megatron. There is a python script that takes in a pair of GPS times and a frame type that will locate the frames for you. This is how you use it to find T type frames (second trends) for May 25 2012:
python /home/controls/public_html/summary/bin/framecache.py --ifo C1 --gps-start-time 1021939215 --gps-end-time 1022025615 --type T -o framecache.lcf
If you don't have GPS times, you can use the tconvert tool to generate them
$ tconvert May 25
$ tconvert May 25
The available frame types, as far as I'm aware are R (raw), T (seconds trends), and M (minute trends).
The code is designed to be fairly easy to use, with most of the options set in the ini file. The code has three modes - day, month, or GPS start-stop pair. The month mode is a little sketchy so don't expect too much from it. To run in day mode:
python /home/controls/public_html/summary/bin/summary_page.py --ifo C1 --config-file /home/controls/public_html/summary/share/c1_summary_page.ini --output-dir . --verbose --data-cache framecache.lcf -SRQDUTAZBVCXH --day 20120525
Please forgive the large apparently arbitrary collection of letters, since the 40m doesn't use segments or triggers, these options disable processing of these elements, and there are quite a few of them. They correspond to --skip-something options in long form. To see all the options, run
python /home/controls/public_html/summary/bin/summary_page.py --help
There is also a convenient shell script that will run over today's data in day mode, doing everything for you. This will run framecache.py to find the frames, then run summary_page.py to generate the results in the correct output directory. To use this, run
Different data tabs are disabled via command link --skip-this-tab style options, but the content of tabs is controlled via the ini file. I'll try to give an overview of how to use these. The only configuration required for the Seismic BLRMS 0.1-0.3 Hz tab is the following section:
[data-Seismic 0.1-0.3 Hz]
channels = C1:PEM-RMS_STS1X_0p1_0p3,C1:PEM-RMS_STS1Y_0p1_0p3,C1:PEM-RMS_STS1Z_0p1_0p3
labels = STS1X,STS1Y,STS1Z
frame-type = R
amplitude-log = True
amplitude-lim = 1,500
amplitude-label = BLRMS motion ($\mu$m/s)
The entries can be explained as follows:
Other compatible options not used in this example are:
At the moment a package version issue means the spectrogram doesn't work, but the spectrum should. At the time of writing, to use the spectrum simple add 'plot-dataplot2'.
You can view the configuration file within the webpage via the 'About' link off any page.
Please e-mail any suggestions/complaints/praise to email@example.com.
There is now a job in the crontab that will run the shell wrapper every hour, so the pages _should_ take care of themselves. If you make adjustments to the configuration file they will get picked up on the hour, or you can just run the script by hand at any time.
$ crontab -l
# m h dom mon dow command
0 */1 * * * bash /home/controls/public_html/summary/bin/c1_summary_page.sh > /dev/null 2>&1
vanna --> QIL.
gautam 20190804: The GPIB module + power supply were returned to me by Duo ~5pm today at the 40m.
Today tried to take our first cavity scan. We unplugged the 55MHz sideband input from the RF combiner on the PSL table, and connected a network analyser instead. Using the network analyzer we injected a 12dBm signal (swept from 32MHz to 45MHz) through the RF combiner into the EOM to create our swept sidebands. We measured the MC cavity response by looking at the signal comming out of the RF photodiode on the MC2 table. I replaced the BNC cable connected to the RF PD with a longer BNC cable that could reach our network analyzer next to the PSL table. Riju will post a diagram of our setup.
We didn't see the expected carrier resonances when we performed a cavity scan. The light incident on the RF PD is around 0.7micro Watts and we are still thinking about whether this is strong enough to see our signal above the noise. We also want to work out what the strength of our swept sidebands is. We will attempt to do a 'real' cavity scan tomorrow.
Koji, Riju, Elli
This morning Koji discovered that the 55MHz input into the RF combiner that I disconnected yesterday wasn't terminated properly, so it was reflecting power back into the amplifier in the signal generation unit. We turned off the signal generation unit and checked that the amplifier was still working properly- it was. A 50 ohm terminator was attached to the end of the 55MHz cable so that it is now terminated properly.
When we tried to turn the signal generator box back on we discovered the switch is broken (the box will only stay on while you hold down the on switch) and will need to be replaced. In order to create the 29.5MHz sidebands to lock the mode cleaner, we bypassed the signal generation unit which won't stay on (unplugging '29.5 MHZ out' cable from the frequency generation unit), and instead sent a 0.39V 29.5MHz signal from a function generatior into 'RF input' on the 'RF AM Stabiliser' board.
We also increased the power coming exiting the PSL table and going into the cavity from 11 microwatts to 20 microwatts by adjusting the polariser at the end of the table slightly. The power has been set to 20 microwatts using the polariser a few days ago but had drifted down since then.
Today we prepared our experimental setup to take a cavity scan of the input mode cleaner, which we want to measure in the next day or so. Attached is a diagram of our setup.
What we want to do is to inject a set of sidebands into the PSL and sweep their frequency from 32-45 MHz (a range just over one fsr of the mode cleaner- vfsr=11MHz). We will measure the power transmitted out of the MC using a photo-diode and demodulate this signal with our input signal from the Marconi. From this we should be able to see the resonant frequencies of the carrier and the higher order modes.
One aspect we spent some time thinking about; whether we would be able to inject a signal into an EOM given the EOM and the Marconi are not perfectly impedance matched. Based on Kiwamu’s previous e-log entries designing the EOM, we decided that injecting a signal in 32-45 MHz region at 15dBm is similar to injecting the 29.5MHz sideband (at the same power level with very similar input impedance.) Fingers crossed we don’t blow anything up first week on the job.
I took back he VCO driver that Reetika brought over to the 40m from the PSL lab.
I unlocked the PMC and swept over C1:PSL-PMC_RAMP's full range a couple of times this morning. The PMC should now be relocked and returned
I tracked the tendency for ezcaPut to fail and sometimes seg-fault in the camera code to a conflict between the camera API and ezca, either on the
network level or the thread level. Since neither are sophisticated enough to provide controls over how they handle these two things, I instead
separated the call to ezcaPut out into a small, separate script (a stripped down ezcawrite), which the camera code calls at the system level. This is a
bit hacky of a solution, but its the only thing that seems to work.
I've developed a transformation based on Euler angles that should be able to take the 4 OSEMs in a picture of the end mirror and use their relative
positions to determine the angle of the camera to the optic. This would allow the position data determined by the fitting software to be converted
from pixels to meaningful lengths, and should aid any servo-ing done on the beams position. I've yet to actually test if the equations work, though.
The servo code needs to have slew rate limiters and maximums/minimums to protect the mirrors written in to it before it can be tested again, but I
have no idea what reasonable values for these limits are.
Joe and I recently scanned the PMC by driving C1:PSL-PMC_RAMP with the trianglewave script over a range of -3.5 to -1.25 (around 50 to 150 volts
to the PZT) and read out C1:PSL-ISS_INMONPD to measure the transmission intensity. This included slightly under 2 FSRs. For slow scans (covering
the range in 150 to 300 s), the peaks were very messy (even with the laser power at 1/6 its normal value), and it was difficult to place where the
actual peak center occurred. For faster sans (covering the range in 30 seconds or so), the peaks were very clean and nearly symmetric, but were
not placed logically (the same peak showed up at two very different values for the PZT voltage in two separate runs). I don't have time to put
together graphs of the scans at the moment; I'll have that up sometime this afternoon.
I started work familiarizing myself with the ELOG and some of the control systems at the 40m. I spent a fair bit of time gaining some general knowledge of the interferometer, control systems, calibration, null instruments, etc. On Friday, June 22 Yaakov and I spent the afternoon pulling cables for the beatbox that Jamie had finished up. We were able to get the cables from the rack containing the beatbox routed to the control room.
Then I started work on calibrating the beatbox. I set up the function generator to send a sine wave into the beatbox, then sent the signal from the beatbox to the oscilloscope. I compared both the input sine wave and the output from the beatbox at many frequencies, taking peak to peak measurements. I'm working on using the data to calibrate the beatbox now.
Here's what I accomplished since my last elog:
I continued working on the beatbox calibration. Instead of using the function generator for an input signal,
I used the network analyzer because it can generate higher frequencies that are of more interest to us. I ran
the network analyzer output into the RF in port, and took voltage measurements from the Q port using the
oscilloscope. The frequency range I focused on was 100 - 200 MHz, and I also took more closely spaced measurements
from 180 - 200 MHz. The data is recorded on the computer now, and I will analyze it more fully in the future.
I also edited the Calibration page on the LIGO 40 m wiki. Rana showed me the page on calibration, but there was
limited information there, so he recommended that I post my work there as well. Right now I haven't posted much,
but I will likely add some information on the Simulink model I'm working on and results of measurements to be
taken as the project progresses.
The majority of my work has been on developing a Simulink model in Matlab of the differential arm length sensing
and control loop. I am using Figure 6-1 from Rana's thesis as a guide on important components to include in the
model. Some of the details on the transfer functions of components need to be worked out, but a basic framework has
been established. Right now the transfer function of the arm cavity is being approximated as a single pole, but
we may integrate the calibration model I'm working on with Sasha's work on the arm cavity. I have also begun to
implement the length response function in the model. I believe it is giving correct results at frequencies up to
100 Hz, but is off at higher frequencies. This might be fixed after I continue to fill in the transfer functions
of the digital components; they are currently set to 1 until I find more information on them.
Most of my work has been on continuing to develop the Simulink model of the differential arm length control loop.
I have filled in transfer functions for the digital components after looking up the configuration of filters and
gains on the control screens. Filters that were active at the time included 1:50 and 1000:10 on C1LSC_YARM and
C1LSC_POY11 with a gain of 0.1. Jamie also introduced me to foton so that I could obtain the transfer functions
for the necessary filters. I have also continued to work on obtaining the open loop gain and length response
function from the model. The majority of the work now is to refine what I've accomplished so far. Adding details
to the arm cavity and the optics is one potential area for improvement.
I have also spent some time looking at real-time calibration methods from GEO and a proposal for a similar system
on LIGO in P040057-x0 from the DCC. While the work for this project may follow a different path for a real-time
calibration, having a sense for what's been accomplished so far should be helpful in working on a new system.
I am continuing work on simulating the DARM control loop. There is now a block for the length response
function that allows one to recover the h(t) GW input to the model. However, in order to add this
block I had to add some artificial poles to the length response function beacuse Simulink gave me errors
when the transfer function had more zeros than poles. The artificial poles are at 10^6 Hz and higher, so
that they should not affect the response function at the lower frequencies of interest. This approach
appears a bit computationally unstable though because without changing any parameters and re-running
the simulation, a different magnitude for h(t) would be calculated sometimes. A different method may be
necessary to get this working more accurately.
By looking through the C1LSC Simulink model and the C1LSC control screens, Jenne helped me determine
which digital filters are active while the interferometer is locked. To do this, open the C1LSC control
screen, then open the trigger matrix. Inside the trigger matrix window there is a button titled Filter
Module Triggers which opens another window that indicates which filters are triggered for a given channel,
and what values trigger them. For the y arm servo filters FM2, 3, 6, 7, 8 are triggered while in lock and
FM4 and 5 are controlled manually; I am including all of these in the model now.
I have changed the way I manipulate the output from the model for analysis, using Rana's advice. I also
improved the plotting code, now using a custom Bode plot instead.
Attached is a screenshot of the Simulink model as it currently stands, and an older implementation of the
open loop gain. I am in the process of updating the servo filters now, and what is shown in the plot does
not include all the filter modules for the servo filter.
Since my last update I have modified the DARM control loop model to the extent that it resembles the
measured open loop transfer function much more closely. The phase especially is much more accurate, with
a phase margin of about 35 degrees at the unity gain frequency of 156 Hz. Right now I'm normalizing to
the unity gain frequency still to adjust the gain properly. Using the length response function from the
model, I can calibrate the error signal as well to find the simulated h(t) output. There were a number of
computational problems in calculating the length response function, but I eventually found a work-around.
Attached is an updated plot of the open loop transfer function and the length response function of the model.
This week Jamie showed me around the real-time Simulink models as well. The one specific to my project
is c1cal.mdl. It takes the output in the form of the error and control signals from c1lsc.mdl as its
input and produces the calibrated signal as output. In order to produce the calibrated signal we need the actuation
function and the inverse of the sensing function for the model as it stands now. We also built, installed,
and restarted the c1cal model because no data was showing up in data viewer, but the problem remained
after this attempt.
Jamie and I also started on calibrating the interferometer in the traditional way. Jamie aligned the beam
splitter and the input test masses so we could take free-swinging Michelson measurements. However, taking
the data with the nds system appears to be giving different results than what is showing up in data viewer.
The goal of this measurement is to get a value for the peak to peak amplitude of the Michelson error signal.
To take the free swinging Michelson measurements for the interferometer calibration Jamie aligned the beam splitter with ITMX and ITMY. I recorded the GPS time (1027827100 and for several hundred seconds later) when the Michelson was aligned in order to look at the correct data. I then copied the python script nds-test.py from Jamie, and modified it to take and plot data from C1:LSC-AS55_Q_ERR_DQ offline. I used dataviewer to verify that C1:LSC-AS55_Q_ERR_DQ and C1:LSC-AS55_Q_ERR were recording the same signal, and to check that I was taking the correct data with NDS. Taking data online worked as well, but it was easier to use a time when the Michelson was known to be free-swinging and take data offline. Attached is some sample data while free-swinging, with time in GPS time.
This week I spent most of my time learning about how the interferometer is calibrated and working on the calibration itself. I also looked more into the Pound-Drever-Hall technique.
Continuing work on the free-swinging Michelson measurements, I changed the signal that I was using to C1:LSC-ASDC_OUT_DQ. This is a proper power signal so that the peak-to-peak amplitude of this error signal can be directly read off the graph. The motivation to measure this amplitude is that it must be known in order to calibrate the actuation of the input and end test masses.
Next I looked into using DTT to make some measurements. I ran the Michelson restore script in the IFO Configure screen to adjust the optics to be near alignment. Then I tweaked the precise settings in the IFO Align screen of pitch and yaw for the ITMX, ITMY, and BS. The goal with this was to minimize the magnitude of the C1:LSC-ASDC_OUT_DQ signal. After it was well-aligned, back in DTT I sent in a sine wave excitation and used a Triggered Time Response measurement to see the output. As a first test I put the excitation signal in the ASDC channel and I was able to plot the resulting OUT signal in DTT. The amplitude was different than I input due to gains between the excitation and the point of measurement, but this can easily be accounted for by adjusting the amplitude in DTT accordingly.
The next step is to work on measurements of a single arm cavity, introducing excitations there and measuring the response.
Today I spent time locking the YARM in order to calibrate the arm cavity. Here's what I did:
1. Misalign all optics other than the beam splitter, ITMY, ETMY and PZT2
2. Restore BS, ITMY, ETMY, and PZT2
3. Open Dataviewer and run /users/Templates/JenneLockingDataviewer/Yarm.xml from the Restore Settings. This opens the signals C1:LSC-POY11_I_ERR (the Pound-Drever-Hall error signal for this measurement) and C1:LSC-TRY_OUT (the light transmitted through ETMY) in the plot window.
4. Adjust ITMY and ETMY pitch and yaw using the video screens looking at AS and ETMYT as a first, rough guide. It can be helpful at first to increase the gain on the YARM servo filter module in the C1LSC control screen to about 0.3 and decrease it back down to 0.1 as the beam becomes better aligned. You know when to decrease this gain when fuzzy, small oscillations appear on the C1:LSC-TRY_OUT signal. If the mode cleaner is locked you should see a bright spot on the AS camera.
5. Tinker with pitch and yaw while looking at the AS screen until you see a reasonably good circular spot without other fringes extending from a bright center.
6. The overall goal is to maximize C1:LSC-TRY_OUT because the power transmitted through EMTY is proportional to the power within the cavity. A decent target value is 0.85 and today I was able to get it to just over 0.80 at best. At first there will probably be small spikes in C1:LSC-TRY_OUT. You want to adjust pitch and yaw until the deviation in the signal from zero is no longer just a spike, but a sustained, flat signal above zero. By this time there should be light showing up on the ETMYT camera as well.
7. Once that happens, continue to successively adjust ITMY and ETMY doing the pitch adjustments on both first, and then the yaw adjustments, or vice versa. You can also tweak the PZT2 pitch and yaw. Once you've got C1:LSC-TRY_OUT as large as possible, you've locked the cavity.
I saved the pitch and yaw settings I ended up with for ITMY, ETMY, BS and PZT2 in the IFO_ALIGN screen. Before the end of the day I think Jenne restored the rest of the previously misaligned optics because they were restored when I got back from dinner.
I also worked on calibrating the YARM. I opened up DTT using C1:LSC-POY11_I_ERR as the measurement channel and C1:SUS-ITMY_LSC_EXC as the excitation channel. I ran a logarithmic swept sine response measurement with 100 points and an amplitude of 25. The mode cleaner kept losing its lock all day, and if this happened while making this measurement I tried to pause the sweep as quickly as possible. I analyzed the the transfer function and the coherence function that the sweep produced, and thought that some of the odd behavior was due to losing the lock and getting back to a slightly different locked state when resuming the measurement. The measured transfer function and coherence plots are attached below. Both the transfer function and the coherence look good above roughly 30 Hz, but do not look correct at low frequencies. There's also a roll-off in the measured transfer function around 200 Hz, while in the model the magnitude of the transfer function drops only after the corner frequency of the cavity, around several kHz. I have attached a plot of the roughly analogous transfer function from the DARM control loop model (the gains are very large due to the large arm cavity gain and the ADC conversion factor of 2^16/(20 V) ). The measured and the modeled transfer functions are slightly different in that the model does not include the individual mirrors, while the excitation was imposed on ITMY for the measurement.
The next steps are to figure out what's happening in DTT with the transfer function and coherence at low frequencies, and to understand the differences between the model and the measurement.
Once you've got C1:LSC-TRY_OUT as large as possible, you've locked the cavity.
Both the transfer function and the coherence look good above roughly 30 Hz, but do not look correct at low frequencies. There's also a roll-off in the measured transfer function around 200 Hz, while in the model the magnitude of the transfer function drops only after the corner frequency of the cavity, around several kHz. I have attached a plot of the roughly analogous transfer function from the DARM control loop model (the gains are very large due to the large arm cavity gain and the ADC conversion factor of 2^16/(20 V) ). The measured and the modeled transfer functions are slightly different in that the model does not include the individual mirrors, while the excitation was imposed on ITMY for the measurement.
The cavity is actually "locked" as soon as the feedback loop is successfully closed. One easy-to-spot symptom of this is that, as you mentioned elsewhere in your post, TRY is a ~constant non-zero, rather than spikey (or just zero). Once you've maximized TRY, you've got the cavity locked, and the alignment optimized.
We didn't get to this part of "The Talk" about the birds, the bees, and the DTTs, but we'll probably need to look into increasing the amplitude of the excitation by a little bit at low frequency. DTT has this capability, if you know where to look for it.
It would be great to see the model and your measurement overlayed on the same plot - they're easier to compare that way. You can export the data from DTT to a text file pretty easily, then import it into Matlab and plot away. Can you check and maybe repost your measured plots? I think they might have gotten attached as text files rather than images. At least I can't open them.
Here's the same plots in pdf format now. I originally posted them as jpg because I couldn't open the resulting pdf from DTT on rosalba, but I could open the jpg. I'll look into overlaying the measured and modeled curves as well.
I forgot to post this last night, but I locked the YARM again yesterday and misaligned the other optics. I took measurements on ITMY and ETMY with DTT again as well. At the end of the day I aligned the rest of the optics before I left.
I'm working on locking the Michelson now in order to put an excitation on one of the input test masses and measure the resulting error signal at the anti-symmetric port. I aligned the beams from ITMX and ITMY by looking at the AS camera with the video screens, but the fringes were not destructively interfering. Jenne advised that I look at the gain on the MICH servo filter modules in the LSC screen. We flipped the sign on the gain (it was 0.120 and it is now -0.120) and the fringes destructively interfered as desired after this change.
For purposes of documentation, I locked the YARM earlier in the morning before moving on to the Michelson. The purpose of this was to put another excitation on C1:SUS-ETMY_LSC_EXC and then measure the error signal on C1:LSC-POY11_I_ERR.
Today I worked on locking the Michelson. Here's what I did:
Open Data Viewer and Restore Settings /users/Templates/JenneLockingDataviewer/MICH.xml. This opens the C1:LSC-ASDC_OUT and C1:LSC-AS55_Q_ERR plots.
Check the LSC screen to verify that the path between the Servo Filter Modules and the SUS Ctrls are outlined in green. If not turn on the OUT button within the Filter Servo Modules, enable LSC mode, and turn on the SUS Ctrls for the BS.
Misalign all optics other than BS and one of ITMX and ITMY. The ITMY was already well-aligned from my work on locking the YARM, so I actually chose to misalign ITMY at first.
Restore BS and ITMX. Use the AS camera on the video screen as your guide when aligning ITMX.
Adjust pitch and yaw of ITMX until a bright, circular spot appears near the middle of the AS camera.
Now restore ITMY and adjust pitch and yaw until a second circular spot appears on the AS camera.
Adjust both ITMX and ITMY until both bright spots occupy the same location. If the spots remain bright when they are in the same location you are locking onto a bright fringe actually, and need to flip the sign of the gain on the MICH servo filter modules. I had to do this today in fact, as discussed in ELOG 7145.
If the sign is correct, the two beams should interfere destructively and the formerly bright spots will form a comparatively dark spot. The shape of the spot will likely be two bright lobes separated by a dark middle.
C1:LSC-ASDC_OUT should be a roughly flat signal, and the goal now is to minimize the magnitude of this signal. The smaller this signal, the darker the AS camera should look. Decent target values for C1:LSC-ASDC_OUT are around 0.10 to 0.05.
Once I did this, I made measurements by exciting C1:SUS-ITMY_LSC_EXC and measuring with C1:LSC-AS55_Q_ERR. I ran a logarithmic swept sine response from 1 to 1000 Hz again, with an envelope amplitude dependence. Again I looked at the measured transfer function and coherence. I was able to get good coherence, but it was somewhat erratic in that it dipped low at high frequency multiple times.
I modified my Simulink model of the YARM to match the new filter modules Rana installed on YARM. I also scaled the open loop transfer function of the model to fit the measured open loop transfer function at the unity gain frequency, as shown in the figure below. From this I produced the length response function correctly scaled, also shown below. Then I applied the calibration factor to the YARM data measured in /users/Templates/Y-Arm_120815.xml. Both the uncalibrated and calibrated spectra are included below.
Summary: Routing Fibers on AP table for Photo Diode Frequency Response Measurement System
Objective: We are to set-up one simultaneous transfer-function measurement system for all the RF-PDs present in 40m lab. A diode laser output is to be divided by 1x16 fiber splitter and to be sent to all the PDs through single-mode fiber. The transfer function of the PDs will be measured using network analyzer. The output of the PDs will be fed to network analyzer via one RF-switch.
Work Done So Far: We routed the fibers on AP table. Fibers from RF PDS - namely MC REFL PD, AS55, REFL11, REFL33, REFL55, REFL165, have been connected to the 1x16 fiber splitter. All the cables are lying on the table now, so they are not blocking any beam.
We will soon upload the schematic diagram of the set up.
Missing Component: Digital Fiber Power Meter, Thorlab PM20C
This week I took more data for the calibration of YARM. The summary of measurements taken is:
1. Peak-to-peak on Michelson
2. Michelson open loop
3. Excite ITMY and measure on AS55_Q_ERR
4. Excite ITMY and measure on POY11_I_ERR
5. Excite ETMY and measure on POY11_I_ERR
6. YARM open loop
Then I worked on comparing these measurements to the Simulink model of the interferometer control loop. The measured open loop transfer function of the YARM matched well with the model above about 20 Hz, after the gain was scaled properly to fit the data. Next is to fit the length response function of the model and the measurements, and then use DTT to calibrate the arm cavity's power spectrum.
Jenne, Mike and I installed all of the post holders we could today including: REFL11, REFL33, REFL55, AS55, MCRef, POX11 and POP55. We did not install AS110, POY or REFL165 because there are interferences that will require moving stuff around. We also did not mount POP22 because it is a peely wally ThorLabs PD that will be replaced by a strong, straight and right thinking LIGO PD in the fullness of time. We did move it out of the way however which is no more than it deserves. Next step this afternoon Mike and I will install all of the telescopes and launching hardware. Then with the help of Steve we will begin routing the fibers. The splitter module will be here by next Monday, the laser by the following Friday and then we will light up the fibers.
Mike and I installed all of the telescopes and launching hardware for REFL11, REFL33, REFL55, AS55, MCRef, POX11 and POP55. On Monday afternoon Steve will work with us on the fiber routing. Steve is buying some protective covers for the fibers.
1064 nm Semiconductor Laser Fiber Distribution System and Mirror Tomography
Below threshold these Semiconductor Fabry-Perot lasers have an axial mode structure with a spacing of about a THz. As you turn up the current to above threshold the first mode to oscillate saturates the gain down on all the modes and only it oscillates. The laser I have here in my office (a backup for the one you have at the 40 meter) has a wavelength of 1064.9 nm at 70 Degrees C. We should be able to temperature tune it down to 1064.3 nm although this could be a bit tedious the first time we do it. The specifications claim a "spectrum width" of 1.097 nm which I believe is the temperature tuning range. I don’t know what the line width is but it will be single frequency and we shouldn’t have mode hoping problems. So we should be able to use it in the “Mirror Tomography” experiment. You might want to use some sort of polarization diversity to avoid the problems of fiber polarization drift.
There have been 2 student projects on using the fiber distributed PD frequency response at1064 nm laser.
“Automated Photodiode Frequency Response Measurement System,” Alexander Cole - T1300618
“Final Report: Automated Photodiode Frequency Response Measurement System for Caltech 40m lab,” Nichin Sreekantaswamy - P140021
I’ll look up a few more references and add include them in the next elog.
And (2) P140021 “Final Report: Automated Photodiode Frequency Response Measurement System for 40m Lab” by Nichin Sreekantaswamy and also as part of Nichin’s report by there is an archive of data at https://wiki-40m.ligo.caltech.edu/Electronics/PDFR%20system
I made a visual inspection of the system and saw that the following fibers collimators are still mounted in alignment mounts and the fiber is attached and pointed at a photodetector but possibly not aligned.
Photodetector Label Fiber Label
REFL11 REFL55 Fiber on mount
REFL33 REFL33 Fiber on mount
REFL55 REFL11 Fiber on mount
REFL165 No Fiber
AS55 AS55 Fiber on mount
MCREFPD MCREFPD Fiber on mount
No PD Loose unlabeled Fiber No mount
ITMX Optics Table
POX11 POX11 on mount
Unlabeled PD POP22/POP110 on mount
NO PD POP55 loose fiber No mount
The RF switch seems to be hooked up and there is a fiber running from the Diode Laser module to the fiber splitter module. So REFL 11 and REFL545 seem to be illuminated by the wrong fiber. I’ll try and run the software on Monday and check to see if I need to move the fibers or just relabel them.
A schematic of the overall subsystem diagran in attachment.
RF and Optical Connections
Starting at the top left corner is the diode laser module. This laser has an input which allows it to be amplitude modulated. The output of the laser is coupled into an optical fiber which is connectorized with an FC/APC connector and is connected to the input port of a 1 by 16 Optical Fiber Splitter. The Splitter produces 16 optical fiber outputs dividing the input laser power into 16 roughly equal optical optical fiber outputs. These optical fibers are routed to the Photodiode Receivers (PD) which are the devices under test. All of the PDs are illuminated simultaneously with amplitude modulated light. The Optical Fiber outputs each have a collimating fiber telescope which is used to focus the light onto the PDs. Optical Fiber CH1 is routed to a broadband flat response reference photodiode which is used to provide a reference to the HP-4395A Network Analyzer. The other Channel outputs are connected to an RF switch which can be programmed to select one of 16 inputs as the output. The selected outputs can then be sent into channel A of the RF Network Analyzer.
The RF switch consists of two 8 by 1 Multiplexers (National Instruments PXI-254x) slotted into a PXI Chassis (National Instruments PXI-1033). The Multiplexers have 8 RF inputs and one RF output and can be programmed through the PXI Chassis to select one and only one of the 8 inputs to be routed to the RF output.) The first 8 Channels are connected to the first 8 inputs of the first Multiplexer. The first Multiplexer’s output is then connected to the Channel 1 input of the second Multiplexer. The remaining PD outputs are connected to the remaining inputs of the second Multiplexer. The output of the second Multiplexer is connected to the A channel of the RF Network Analyzer. Thus it is possible to select any one of the PD RF outputs for analysis.
Something on this tomorrow.
We conducted a beam scan on the AP table of the AS beam. We used a lens to focus the beam onto a power meter, and slowly moved a razor blade across the beam using a micrometer, vertically and horizontally both in front of and behind the beam. We also had to block the beam next to the AS beam in order to do this, but is unblocked now. Mike will begin curve fitting the data to try and see if there is a different spot size given by the x-axis vs. the y-axis, and if the lens has any effect.
Joe and I have taken control of the EPICS channels C1:PEM-Stacis_EEEX_geo and C1:PEM-Stacis_EEEY_geo since we heard that they are no longer in use. We are currently
using them to test the ability for the Snap camera code to read and write from EPICS channels. Thus, the information being written to these channels is completely unrelated
to their names or previous use. This is only temporary; we'll create our own channels for the camera code shortly (probably within the next couple of days).
Tonight we made an attempt at getting the PRM + ITMY aligned with correct input pointing. We steered the good PZT so that the input beam makes it through the aperture in front of ETMY. We then aligned the PRM so that the retroreflection of the input beam makes it back into the Faraday. After that we tried dithering the alignment of ITMY and the beamsplitter to see if we could see a spot flash across the AS port, but we saw nothing.
For the PRM alignment we set up a camera looking into the window at the Faraday in the IOO chamber; it's called FI_BACK. We stole a 50mm lens from the ETMY face camera.
We also tried looking for beam on IP_POS and IP_ANG. When the input beam is aligned to pass through the ETMY aperture, we can see beam on the steering mirrors preceding IP_POS, but it hits a mirror mount. When the input beam is aligned as it was on Monday, it clips on the ETMY aperture but makes it further along the IP_POS optical path. In both cases, we weren't able to see any beam coming out for IP ANG.
Adjusted focus on ETMYF camera so that the IR beam is in focus.
Tonight we made a non-folded cavity between the PRM and PR2 as follows. I put down two dog clamps to constrain the original position of the PR2 mount. I then loosened the dog clamps holding the mount to the table and nudged the mount until we saw a few reasonably well-aligned bounces in the cavity. I then dogged down the mount.
We played with the PRM and TT2 steering until we saw flashes of TEM00. However, the resonance is not clean so we couldn't lock.
Since we changed the PRM alignment, we had to redo the last bit of steering for the PRM oplev into the photodiode. We also put a few ND filters on the POP camera.
Manasa and I are trying to get the AS beam onto the AS camera with a focusing lens. Currently, the mirror immediately preceding the camera has been removed and the camera and lens are sitting directly behind the BS.
I took out a short (~12 cm) SMA cable from the "LO input" path into the MC demod board in an attempt to maximize the power in Q and minimize the power in I. The path might benefit from being shortened a little more, but it's hard to tell since I is noisy. (In the attached plots, channel 1 is Q and channel 2 is I.)
Should you find it necessary to restore the original path length, the cable I took out is in the "SMA ONLY" tupperware and has a printed label with "5" on it.
I goofed on the transfer function requirement by not giving you the plant transfer function, which looks to be about 0.014 V/V, independent of frequency (PSL:1278). This needs to be compensated for in the electronic transfer function.
Comsol 4.3b is now installed under /cvs/cds/caltech/apps/linux64/COMSOL43b. I've left the existing Comsol 4.2 installation alone; according to the Comsol installation guide [PDF], it is unaffected by the new install. On megatron I've made a symlink so that you can call comsol in bash to start Comsol 4.3b.
The first time I ran comsol server, it asked me to choose a username/password combo, so I made it the same as the combo used to log on to megatron.
Edit: I've also added a ~/.screenrc on megatron (based on this Stackoverflow answer) so that I don't constantly go nuts trying to figure out if I'm already inside a screen session.