Aaron removed the plastic wrap and began powering and reconnecting all electronics.
I drilled three holes into the plastic box that covers the cavity, reconnected the south laser diode and TEC to the ITC 502 combi controller and set the laser temperature to 9.888 kOhms and current to 126 mA (until the beam was visible).
Continued with alignment of the cavity.
[aaron, shruti, raj]
We added the acrylic framing that supports the HEPA FFU, as well as two of the 3 panels covering the top of the enclosure. Raj and Shruti also unwrapped and added handles to the orange acrylic doors.
However, the last acrylic panel for the roof of the enclosure is too small. Though the part is cut as specified at 23" on the short side, the counterbore holes on the long side of the panel do not span the distance between the two rails where the panel mounts. The counterbore holes are 0.75" from the edge of the panel, which means the two lines of holes are 21.5" apart. However, the distance between the center of the rails is specified at 22.5". The distance between the rails is appropriate for the size of the HEPA FFU, and the 0.75" gap along the edge of the panel is standard across the other roof panels. Therefore, I suspect the overal width of the panel was just specified 1" too short.
I'll alert F&L and have them send another panel ASAP
[aaron, shruti, chris, raj, radhika]
On Tuesday, Shruti and I did fit checks of all connectors for the enclosure. We received the remaining parts according to the parts list from F&L, so should have everything we need. We requested clarification on where to use a few connectors, though haven't yet received a reply (our contact at F&L was unavailable).
With some adjustments, we completed steps 1-5. The frame of the enclosure is around the table. Tomorrow we'll try to complete the rest of the build, which includes adding the roof and panel doors to the enclosure.
Backups were restarted for the cryo lab computers gaston, spirou, and cominaux. A 4TB USB drive was connected to cominaux, mounted under /backup, and rsnapshot was configured to run on a nightly basis. It does not back up the full disk, but only those directories where user-generated files are kept (/home, /etc, /usr/local, /opt, /ligo). rsnapshot's configuration files are: /etc/rsnapshot.conf and /etc/cron.d/rsnapshot.
For the cymac, configuration and minute trend files are backed up by rsnapshot to a 1TB disk, mounted as /backup on cymac1.
[shruti, aaron, raj, chris, ian]
I've asked F&L for a parts list so we can do a proper inventory before starting assembly. Also requested a quote on purple panels, update on shipment for the cross bars, and imperial threaded feet.
Shruti and I transferred the materials for our new enclosure from receiving to the subbasement hallway. I noticed that the acrylic panels we received are amber, not purple as we specified... unfortunately it looks like the error was already present in the quote, which listed acrylic #2422 (in my emails with their rep, we'd both confirmed acrylic #2424). Because it was in the quote, I'm not sure there's anything we can do, but I'll ask.
Ian, Raj, Shruti, Chris, Aaron, and possibly other grads will meet at 10 tomorrow for assembly.
We returned CFC-2X-C into the same cabinet it was borrowed from. Thanks CRYO!
I've borrowed 2 collimating lenses (for fiber input) for use with the free-space AOM in the DOPO lab.
Today I began to see a forest of peaks in the transmission (transmission through the cantilever optic) while aligning meaning that the cavity is around resonance. I then adjusted the Watec camera to the transmission of the curved mirror and began to see some flashes. I took a video showing this which can be found here.
I tried activating the feedback loop with the settings we had on earlier but while it did seem to increase the peak powers of the peaks it did not seem to lock. The steering mirror to the refl photodiode (Newfocus 1811) and the corresponding lens needs to be re-adjusted.
Similar to elog 2767, before changing out the mirror from a rigid mounted one to the cantilever, I measured the loop transfer functions and noise spectra since we had not done so since we moved the table.
The only change between the current and previous version was that I tried to make the low frequency phase offset zero.
Attachment 1 shows different estimated open loop transfer functions corresponding to ratios of specified closed loop transfer functions (as mentioned in the labels). The UGF was lower than what was previously acheived.
Attachment 2 shows the fit of the slope of the open loop transfer function as done previously in elog 2776.
Unfortunately, I did not notice the issue with binning when I measured the noise spectra which resulted in a discontinuous spectra corresponding to the different regions I measured separately on the Moku. The data for this and everything else mentioned in this post is in Attachment 3.
In short: Between Friday and today, I de-bonded the mirror from the broken cantilever, picked two cantilevers and bonded both the mirrors to them with the AR surface being the one on the bond side, clamped and mounted on a post one of these cantilevers, and placed it in the cavity replacing one of the flat mirrors (M3).
For this, I used methanol and soaked it for around 30 min similar to the procedure here. Since this bond was weaker, it took lesser time.
I picked one cantilever from the previous collection and another from the dish shown in Attachment 1. This second cantilever did not seem to have the back surface passivated with SiNx and looked like it was just oxidized silicon.
I used the GE cryo-varnish at four points around the mirror placed on the etched edge of the cantilever for both and let it dry for a few hours (Attachment 2). The bonding was performed such that the AR surface was on the side of the cantilever.
Using the alignment jig on the table, I picked the cantilever without the SiNx passivation on both sides (identifiable as with one non-glossy side) to mount to the clamp. I tightened it not too strongly and then used a 3/4" post of suitable height to get the center of the mirror to a height 4" from the table.
I placed it roughly where I thought it should be on the table replacing the flat mirror M3 from the previous setup. I got the beams from two round-trips to overlap visually and added a PDA10CS to look at the transmission from the cantilever.
The aim now is to do as we did earlier - sinusoidally change the temperature by driving the TEMP TUNE input with a function generator and slowly tweak the alignment of the steering mirrors to find the cavity resonance.
I also measured the transmission of the cantilever as roughly 0.1% using the power meter.
I broke the cantilever while fastening the fork clamp. Afterwards, I used methanol to remove the varnish and separate the mirror from the cantilever shard. I then used a cotton-tipped swab soaked in methanol to clean the varnish from the sides of the mirror. I drag wiped the HR and AR surfaces of the mirror with methanol followed by isopropyl alcohol. Finally, I bonding the mirror to a different cantilever (this one with somewhat more pitting than the previous) -- again bonding with cryo varnish at four points on the sides of the mirror, but on recommendation from Chris this time with the mirror AR surface touching the cantilever.
This morning, I clamped the cantilever-with-mirror that we bonded yesterday.
I first used a broken cantilever to practice the clamping. I clamped the test piece first in the nominal position, then with slight alignment errors in the available degrees of freedom to see what those errors would look like. If the cantilever is misaligned such that it does not rest in the clamping groove, the clamping block will show a larger than usual gap on at least one side (attachments 1, 2). If the cantilever is not entirely 'in' the clamp, the thicker part of the cantilever will be visible above the clamp (attachment 3). Attachment 4 and 5 show the test cantilever in good alignment.
Next, I clamped the cantilever-with-mirror by
The Q may improve with more clamping force, but I'd like to do a more controlled test of how much torque can safely be applied to the clamping screws. We don't want to break any usable cantilevers.
[Shruti, Koji, Aaron]
Today Koji guided us to (1) remove the mirror I had contacted to the cantilever that later broke, and (2) clean and contact the second flat (1550 nm wavelength coated) mirror to another cantilever using cryo varnish.
After my failed attempts at using methanol and acetone along the edges followed by soaking the contacted-to-silicon optic in isopropanol, today we were finally able to de-bond the mirror by soaking in methanol. We used two washers to raise the optic from the aluminum surface and folded foil pieces to keep everything in place. The setup shown in Attachment 1 was covered with another aluminum foil dish and let sit. It took at least an hour of soaking to completely de-bond.
Koji then drag wiped the optic with pure isopropanol to clean any remaining residue and cryo-varnish hairs.
First we tested drag wiping the broken silicon cantilever with methanol and isopropanol. Then we selected a reasonably looking cantilever that was not chipped at the edges, though it had an uneven surface, and drag-wiped both surfaces with isopropanol.
We drag-wiped the HR surface of the optic a few times and then placed it on the portion of the cantilever that had the square etched-out region. While Koji held the mirror in place I applied cryo-varnish to four points around the mirror. This is now set to dry.
Update: Photos are available on the ligo.wbridge google drive. I uploaded everything, but could pare down to save drive space.
I borrowed this free-space AOM (1550 nm) for use in the DOPO lab.
The cantilever clamp with a cantilever on it to be used on an optical post. This will replace the non-transmitting flat mirror in the PSOMA cavity. There are two screw holes to mount the optical post, but it would only be possible to use one, therefore this will be initially mounted asymmetrically.
Cantilever with the two flat mirrors from Zach's setup. Without having it properly mounted, I could only very crudely measure its reflectivity as R>81% using a power meter.
The one on the left is shown with (what I believe, by comparing to the curved optic in our present setup, is) its HR surface facing up and the one on the right with its AR coated surface shown.
I attempted to bond the mirror to the cantilever with cryo-varnish after testing that it bonded two pieces of silicon. The HR surface which would be facing the interior of the cavity was the side I decided to put the varnish on because the pictures from Zach's thesis depicted the cantilevers that way. I coated the edge of the square-shaped hole on the cantilever head with the varnish and placed the mirror on it. I placed a lens wipe on top of the mirror and then another flat optic over it. While applying pressure on it with a tweezer the cantilever broke (possibly because the aluminium foil below it was very crinkly which I didn't think too much about beforehand).
While the mirror seems to have bonded after a couple of minutes of holding it down, I probably have to remove the varnish (with IPA/acetone I think ?) and re-bond to a different cantilever.
What about showing the E/W beat noise for several different operating points on the W laser? Temperature and current.
Between 0.5 and 50 Hz, there are a couple of regions where the Rio W laser noise dominates the three corner hat measurement. And, below 0.3 Hz, the Teraxion laser noise dominates the measurement. Today I'm going to try to quiet these two lasers a bit to make a slightly improved three corner hat estimate.
I'll be looking at the output of the delay line frequency discriminator (DFD) on the moku spectrum analyzer, so I've swapped in the 1.9 MHz lowpass filter for the one Rana was using to check the noise out at MHz.
I saved the following traces on an SR785, but with a nonfunctioning GPIB so ended up storing them on a floppy drive.
I saw minor improvements to the Rio W x Teraxion beat note spectrum, and took 20 minutes of data for each beat note. Dropbox upload failed several times, so I sent it to my laptop via ipad file storage and airdrop. After swapping fiber connectors and covering with foam, the system took ~15-30 minutes to equilibrate each time (though perhaps longer would have been prudent, since I still saw low frequency drift up to 4 MHz during the 20 min measurement time). No improvement to the estimate on Teraxion laser, and if anything the West laser was even more noisy relative to Rio E and Teraxion, across a wider frequency band (almost the entire band from 30 mHz - 90 Hz). The foam and turning off the HEPA FFU did reduce the noise below 1 Hz, especially for the Rio E x Teraxion beat note. Figure 1 uses maximal averaging for every 2-fold frequency increase, on 20 minutes of data taken today (attachment 2 reproduces the relevant figure from last week's data, without the Marconi reference for better viewing).
Attachment 3 is the updated Teraxion noise estimate.
Update: attachment 4 is a comparison of the frequency noise (uncalibrated) for three different configurations: after taping down the fibers, after adding foam, and after turning off the HEPA blowers. I'm not sure why turning off the HEPA blowers increased the noise, maybe should have let the system settle longer? Despite the overall higher noise floor with HEPA blowers off, several peaks between 10 and 100 Hz were reduced.
We found a heavily pitted cantilever from Zach's early fab runs, and mounted it in his clamp using the alignment jig and pins. We tried optically contacting one of the mirrors to the cantilever, but some combination of surface oxidation and roughness (or just inexperience) prevented us from making a bond. The surface of the cantilever had obvious defects, so we weren't very hopeful. We're seeing what Koji suggests for glue.
We're starting to make new cantilevers this week. Here is our process, largely drawn from Zach's thesis, based on the process from the Chao group (D1200849) and the standard techniques of hard mask etching.
Zach started with a 100 mm (4") undoped <100> Si wafer with 500 um thickness. He reports achieving similar mechanical Qs of the final cantilevers when starting with either SSP or DSP polished wafers, though we may want to investigate this further. To avoid spoiling too many large wafers, I'd like to start by processing our 2" x 280 um wafers that are leftover from the cryo Q experiment, and will inventory our larger wafers to determine what we should order. We also have some 3" wafers we can use to fabricate full-length (7 cm) cantilevers in smaller batches than had we used 4" wafer.
Zach's procedure calls for thinning the central region of the cantilever, which softens the suspension and improves isolation. I expect we'll want to evaluate our cantilevers before thinning, since the procedure to thin the central region is a bit tricky. When we do thin the cantilevers, we will not terminate the process at step 6 but instead continue with the following:
Materials we need to acquire are in bold
Our training status on the equipment is green for 'full user,' orange for 'supervised user,' or red for 'need initial training.
rather than the perfect solution to PSD estimates, how about using the code you already have and just change the binning a little more often than once per decade? i.e. stich together as you already did, but get more averaging in the noisy spots. Should be a very easy modification to the code.
I modified Aaron's DFD box: I replaced the SLP-1.9 (1.9 MHz low pass filter) with a 44 MHz low pass that we conveniently had in the lab.
The purpose of this is to measure the high frequency noise of some of our lasers to figure out if there's any difference between the RIO Planex and Teraxion NLL.
I did the hookup and everything looks good so far. So far I have measured the RIO E/W beat and the RIO E vs Terax beat.
Need to do some more data processing to get plots.
Some notes along the way:
Attaching beat note noise spectra showing the noise of the DFD (with no pre-amp, so probably Moku input noise), the RIO Planex (E & W lasers from the Cryocav table), and the Teraxion NLL. Looks like they're similar in HF noise.
Yesterday (August 25), I measured another 10 min at 488 Hz of Moku phasemeter data for the three pairs of beat notes. All three lasers had been on overnight, so there was no longer low frequency drift of the Teraxion laser. Rather than amplifying then picking off the beat note, I sent the RF output of the 1611 directly to the Moku's phasemeter input.
Today, I've been figuring out how to get more averages out of our data. One approach (the one used above) is a modification of Welch's method:
The above procedure sacrifices some frequency resolution at the higher frequencies in exchange for additional averaging. The tradeoff with resolution is necessary, because the window size determines not only the smallest resolvable frequency, but also the spacing of frequencies in the spectrum. For the spectra from the previous elog in this thread where N=10, the total measurement time is 10 minutes, and the sampling rate 488 Hz, there is evidently more noise higher in the frequency decade (7-9e^n) than lower (1-3e^n). More consistent averaging can be achieved by setting N=2, but at the expense of most of the high frequency resolution (only 33 frequency bins survive the procedure).
One workaround is to modify the procedure so the frequency binning is mostly set at the beginning, by the 'highest resolution' available. Then, perform Welch's method with as small a window as possible while still resolving the frequency bins. Care must be taken at high frequency: eventually, the 'FSR' of our Welch's method cannot resolve an f_0 difference in frequency into an integer change in the number of samples per segment. The spectrum can either be cut off at that frequency, or the procedure can continue while accepting nonstandard bin widths at high frequency.
Other workarounds are perhaps less desirable. One could accept nonuniform frequency binning, and simply compute Welch's method for every available choice of nperseg. This would maximize the number of averages in each bin, but especially at low frequency, there will be substantial correlation between adjacent frequency bins. Another workaround is to save the entire spectrum wherever evaluated, then combine the data later. One must again worry about correlations between the measurements: at high frequency, we would be combining coarse data with many averages with fine data with fewer averages.
Another approach entirely is to do something smarter than Welch's method. In our meeting today, Chris suggested I look into multitapering. Spectral estimates can reduce bias due to leakage by introducing a tapered window, at the cost of increased measurement variance. Welch's method heals the variance relative to standard tapering by overlapping the windowed segments, at the cost of some frequency resolution. Multitapering instead minimizes loss of information by increasing the number of degrees of freedom of the estimates. The Here are a few resources on the topic:
While checking out Percival and Walden, I stumbled across parametric methods for spectral estimation -- those where an early spectral estimate is used to refine the procedure and spectral estimate iteratively. Perhaps up the alley of some recent discussions at our group meeting.
Simply applying Gaussian error propagation is not quite right, because the PSD is exponential distributed (the ASD is Rayleigh distributed, see Evan's note T1500300). Each ASD is Rayleigh distributed with
For a large number of averages, the central limit theorem lets us estimate the mean of each PSD, , with normal distributed uncertainty and variance . Our three corner hat estimates of the ASD are based on the scaled, root mean-squared sum of three such PSD estimates, so for each frequency bin we can estimate the variance of the laser's ASD by
I'll use the final equation above, along with the number of averages, to estimate the uncertainty in each frequency bin of the final frequency noise ASD of the individual lasers. In particular, the filled region is .
[OK, I'm having a lot of trouble uploading pdfs to the elog this week, even with rasterizing. I've dropped these figures along with one set for the case of 'Welch's with no averaging' onto gaston under /home/controls/cryo_lab/Figures/3CH ]
I think these results warrant a more careful measurement, especially in the decade around 1 Hz. Also, the error bars are obviously way underestimated.
We uploaded the data from moku to dropbox, and pulled it to spirou via the web interface. Should give the workstations dropbox.
Later, I realized we could probably have done better by sending the output of the 1611 directly to the moku. Instead, we were amplifying +16 dB then using an RF coupler to pick off 1% for the moku.
After plugging back in all the cables, I was struggling to get the cavity locked again or seeing the transmitted beam on the monitor.
Today, following Aaron's suggestion, I removed the connection from the PDH mixer IF port to the oscilloscope and also the power splitter I had added earlier (now sending the IF output directly to the LB input only with the 10 dB attenuator). The cavity didn't lock right away but changing the gain to 6 and re-adjusting the input and output offset got the cavity locked again.
When we tried to get it on the monitor, we saw that the mode it locked to was a higher order mode misaligned in the vertical direction. We first aligned the beam vertically until we started seeing lower order modes and finally the TEM00 mode.
I adjusted the lenses a little to tweak the mode-matching after aligning the beam into the cavity for maximum transmission when locked. Calculating the mode-matching using the reflected beam when locked and unlocked shows that it is only 60% though.
The noise I was seeing last week on the ADC did not show up when driving the same channels directly with a function generator, only when buffering the function through the SR560. Wrapping the BNC several times around a ferrite toroid between the SR560 and ADC reduces the noise to close to the level of the ADC noise floor (there is a < 5 count pkpk sine wave cross-coupled into the adjacent channels for a ~2000 count pkpk sine wave on the channel of interest, but the signal carrying channel itself looks clean).
The SR560 that was overloading on battery last week is now also overloading on line power. I've swapped it with one of our functioning SR560.
Afterwards, I looked at the spectrum for the Rio E x Rio W laser beat note. Looked OK... there's some kind of filtering happening in my delay line though. If I watch the spectrum of the RF coupler's pickoff (1% between the amplifier and delay line box), the implied peak power entering the delay line box is ~ 5 dBm near any of the nulls (so ~113 MHz or 176 MHz), but over 15 dBm between the nulls. I hadn't noticed this behavior before (with the busted mixer and RF coupler before the amplifier).
I'm driving the input of the delay line box with 10 dBm from Marconi's RF output.
Ack!! stay out of the "Fix the SR560s" game Do not repair, do not send back.
Let's get a trustworthy measurement of the frequency noise ASAP.
I've borrowed one SR560 from CTN to get us by for now, but am wondering if I should order parts to make repairs, or simply send the units to SRS?
I replaced the mixer from my delay line box with a functioning ZFM-2-S+. I also replaced the lossy pink SMA cable (122 cm) with a slightly longer (150 cm) cable that I made from a spool of LCOM coax. I also replaced the shorter cables with solder soaked ones. The final build is in attachment 1.
I drove the delay line frequency discriminator with a swept sine from the Marconi, and observed a symmetric response in the IF output. Sweeping from 5 MHz to 80 MHz is in attachment 2, showing that the response is symmetric about zero from -107 to 108 mA.
I'll return later this afternoon for a more careful calibration and to take some data.
I'm calibrating the delay line discriminator by running a swept sine from the Marconi, and this time reading back on an acromag channel.
Attachment 3 is the first run (y axis in Volts), where the Marconi is ramping from 1 MHz to 240 Mhz, stepping by 10 kHz every 100 ms. There are some surprises. The output is linear until about 70 MHz, possibly because the mixer is only good down to 5 MHz. The upper half fringe is not symmetric to the lower half fringe, even comparing the curve only above 10 MHz.
I'm repeating the measurement with different sweep parameters: 1 MHz to 250 MHz, stepping 1 kHz every 50 ms. The steps will be somewhat faster than the Acromag's sampling rate, but those units dither so it should smooth out. I'll post some plots with the time axis converted to frequency when the data come in.
I'm taking this data today, here are the issues I've hit
We have 7x SR560 in need of repair in the cryo lab. Most of these (at least 5) are constantly overloading, which indicates the front end transistor and op amp need replacing. From SRS, these parts are $50 each, but I found I think the same parts on digikey (the FET transistor is LSK389B; the amp is OP37A) for about $10 each. There are at least 2 that need a new battery.
Rana noticed that my delay line is asymmetrical -- sweeping the frequency through a full cycle of the interferometer should reverse the sign of the output, but instead the output was biased negative.
Indeed, when I drive the mixer RF with 0.5 Vpp at 25 MHz from a function generator while supplying the LO with 7 dBm at 150 MHz from the Marconi (see attachment 1), my ZFM-3-S+ has an asymmetric waveform despite at most a few mV difference in the LO and RF DC levels (see the video in attachment 2). The same test with a different mixer (ZFM-1-S+) gives the balanced waveform in attachment 3.
I'll replace the mixer, and make a few modifications to the cables of my delay line box.
I'm repeating this measurement, but moving the photodiode and electronics to the cryo cavs table, so we don't send anything over a long, floppy fiber across the room. See attachment 1 for diagram.
I set up the measurement, but didn't take any data. What's the right way to find the IP address for these GPIB controllers? I ended up scanning with nmap, but suppose I should mess with prologix' netfinder tools to assign our controllers static IP addresses and just label them.
could the pumpdown plot be made so that the units are visible? Maybe use dataviewer or python?
We repeated steps 1-4 in elog 2789 and, with two people, managed to get the o-ring to stay in place while lowering.
During the vacuum testing, I'm continuing some lab maintenance, mostly cleaning up and labeling cables on the electronics racks.
The cantilevers cryostat has only reached 7 utorr (the reading on the gauge matches epics) after pumping overnight. I'm going to try manually actuating the gas ballast valve in case our roughing pump is manual-only.
After closing the gas ballast valve, the pressure drops below 7 utorr in under 30 minutes and is approaching 1 utorr. That's not the best I've seen from this pump, but should be good enough to continue diagnosing the cryostat.
To that end, I'm installing a new 2-270 Viton o-ring on the cantilever cryostat (needs name).
Facilities came to move out the cryo Q (central, rigid legs) optics table, and left us the legs. They also took the two desks from the lab. Lastly, they moved the PSOMA table to the center of the room and rotated it 90 degrees so its long axis runs EW. Afterwards, Shruti and I moved the PSOMA rack to the E end of the PSOMA table, directly across from the other two racks .
Attachment 1 is a screenshot of the temperature and particle count trends over the last 4 weeks. I need to figure out how to add axis labels on ndscope... the units for both temprature channels are F, relative humidity is %, and all particle count channels are log(counts). There is a factor of 10-1000 excess particle counts around the time of our lab rearrangement, mostly affecting the larger particle sizes. Humidity also experienced a mild increase. The AD590 temperature channel drops off because I turned off its power supply to accommodate our rearrangement, and haven't yet turned it on again. The daily and weekly particle count fluctuations are interesting, presumably dictated by lab access.
Today we are testing the pumping station while pumping on just some blanked off Ts and the vacuum gauge. Last time, we pumped on the vacuum hose leading to the closed Key valve at the cryostat, and observed the pressure level off near mtorr, before eventually reaching only several utorr. The turbo should really have no trouble getting to utorr pumping on just hose sections, so we'll try to observe some better pumping action today.
I continued preparing the PSOMA table and cryo lab for moving out the central optics table and 2 desks tomorrow:
The SR560 on the PSOMA rack are still plugged in to a power strip connected to the wall, but that is the only remaining cable running from the PSOMA rack or table. I'll return tomorrow morning to finish securing and wrapping the PSOMA table. Other than that, should be ready to move.
I did a rough calibration of the South laser diode's temperature-to-frequency response near 9.02 kOhm and 140 mA by
Since the temperature control loop is slow, the deviation in the current control signal upon stepping the TEC knob, along with our known Hz/mA calibration, tells us the frequency deviation of the laser in response to the temperature step. When the system equilibrates at a new temperature tuning, the difference of the old and new temperature tuning tells us by how much we stepped the control knob.
I observed about 1000 counts (0.3 V, assuming 10 V / 2^15 counts) deviation in the current control channel, corresponding to 890 MHz (assuming 148 MHz/mA as measured earlier, and 20 mA / V_modIn according to ITC 502 data sheet). The average temperature tuning changed by about -0.26 V, corresponding to -0.05 kOhm (the coefficient of the temperature tuning input on ITC 502 is 0.2 kOhm/V). This implies the South laser diode (SN 104987) -1.7 GHz/kOhm. Because the temperature was set near 9 kOhm, the resistance-to-temperature curve for the diode's temperature monitor tells us the temperature-to-frequency coefficient is about 630 MHz / K.
I made a page in the ATF Wiki for Delay Line Frequency Discriminators. There is some prior work on these things, but these links are maybe a good starting point to see what the state-of-the-art is and whether our thing is better or not.
I started moving our fiber components to the rack-mounted box. I inspected and cleaned the tip of the fibers for the 50-50 fiber beamsplitter. Will work on some photos through the viewer of the analog microscope.
We need an uncoated APC to uncoated PC fiber patch cable to send a beam to our FC 1611. We have a coated patch cable, but should only use that for launching to free space.
I also searched for an appropriate replacement o-ring for the cantilever cryostat. I found the drawings and manual from IR labs, but they don't mention the size of the o-ring, and I didn't find something suitable in our supply. I'll order a new one, along with the patch cables and some panel mount DB9 adapters.
We cleared out the desk drawers and the middle optics table today. This involved
We still need to clear the following heavier equipment from the desks. To move this equipment, we'll first need to sort through the miscellaneous objects on the workbench so we have somewhere to put everything. It will require at least two people to move the reference cavity safely.
Other than that, we're ready for facilities to move out the desks and optics table. We should place an order for the new desks by tomorrow so they will arrive without too much awkward waiting.
Shruti and I opened up the cantilevers cryostat. Vacuum wasn't fully vented despite the valve being fully open, due to the foil covering the open valve sealing against the flange while venting. The cryostat popped rather than lifted open. The damage is at least:
Overall pretty disastrous. We'll have to investigate the full extent of the damage this afternoon, and first order of business will be cleaning out the broken Si fragments and evaluating the vacuum pressure.
We removed the silicon cantilever from the bottom of the cryostat with teflon-tipped foreceps, and stored them in a wafer casette. We also cleaned and regreased the o-ring with Krytox lubricant (we couldn't find the cryo lab's Apiezon N grease, must have been lent).
We pumped down the cryostat, but the roughing pump wasn't able to reach a low enough pressure to switch on the turbo. We also valved off the cryostat from the rest of the system, and pumped down on the hose + gauge + up-to-air valve (closed). The turbo was able to spin up to 90 krpm, but the pressure leveled out a several 100 uTorr. Pumpdown curves are in attachment 2.
The second pumpdown curve (pumping on just the hose and pressure gauge) suggests the pumping station needs some maintenance. I've seen this behavior before from a faulty KF flange connection, or when some condensation had built up in the roughing pump line. There is a procedure in the HiCube manual for flushing this line, I'll dig it up from my old elogs. However, the pumpdown on the cryostat suggests an even more severe leak in the cryostat itself, since the turbo wasn't even able to spin up and the curve appears leak-limited well above 1 torr. This is consistent with the visible damage to the mating surface in attachment 1. I suspect we need to send the cryostat to be reground and polished.
Attached is the most recent month of temperature trends for the lab, as measured by the particle counter. The lab temperature has been steady at 78 F for a couple weeks. I added a config file for this plot to our scripts repo under ndscope, so we can easily reproduce this plot.
While the particle counter has been logging, the AD590 temperature mon is again not logging. Possibly relatedly, when I try to apt-get install emacs on cominaux, it's complaining that the ligo repos 'couldn't be verified because the public key is not available.' I noticed that it was looking for the buster distribution in http://apt.ligo-wa.caltech.edu/debian, but the code currently lives in */debian/pool. Adding /pool/ (and commenting out the lines referring to stretch, which we are no longer using) let me upgrade cds-workstation and install emacs.
apt-get install emacs
I did find some apparent bugs in the modbusIOC database file (CRYOXT.db), but none restored these ai channels. Haven't quite finished yet.
Update: I identified that only the slow ADC channel 15 was not logging by observing a 1 Hz sine from a function generator on the other channels. Unfortunately we use channel 15 for the AD590 temperature sensor. There was just an extra character in the epics record for that channel, removing it fixed the problem and the AD590 is again logging. I've updated with a new temperature trend that includes both sensors and the particle counts in attachment 2. I used dataviewer because ndscope doesn't support log axes, but also defined some new calc channels to record the log of particle counts... and upvoted the log-axis feature request for ndscope.
We've been using T-junctions to pick off PDH control and error signals, but sometimes we should have a high impedance, floating buffer between our current control loop and noisy or grounded devices like the ADC or oscilloscopes. I've added an SR560 between the PDH error signal and control signal pickoff points, and also used the 'aux out' connector on the back of the LB servo box as the control signal monitor point. I terminated aux out into 50 Ohm, with a T to the SR560 high impedance input.
Changes to the previous configuration are highlighted in attachment 1.
We should note that the LB box driving into 50 Ohm is current limited at its output (assuming we don't narrow the voltage window using the trim pots on the back panel). It can supply up to +- 20 mA, so if we see control voltages approaching 1 V we are nearing saturation of the servo controller.
I also added a 50 ohm terminator in parallel to the 20 dB attenuator at the analog input modulation port of the ITC 502 current driver. This is to ensure a more or less accurate 20 dB attenuation of the control signal since the ITC 502 input has an impedance of 10 kOhm.
Following our discussion earlier when we realized that the AC electronics of the 1811 may be saturating, since our RF power (at the mod freq of 33.59 MHz) is near or over 55 microW, I added an additional 10dB attenuator before the EOM. The total attenuation is now 40 dB. To compensate for this I removed the 10 dB attenuator at the input of the LB1005.
Everything seemed to lock once again when the gain on the LB1005 was increased from 5 to 6.
I'm trying to make sense of these noise curves in relation to the free running noise I measured earlier with the three corner hat (3CH). The free running frequency noise of the S laser as measured by the three corner hat (attachment 6 from elog 2740) should be the same as the estimate off the free running noise using the PDH error signal and normalizing out the loop suppression ('open loop estimate' in attachment 2 of elog 2775). Here's what I'm noticing:
We should certainly try to resolve these discrepancies... perhaps we are seeing extra noise due to the electronics used for locking (the PDH measurement includes the LB box, analog RF electronics, a long DB9 cable to ADC that was observed to inject noise around 100 kHz only partially attenuated by our ferrite toroid, etc). There might also simply be a bug in the noise budget script, I'll check it out.
I agree that the more-than-1/f dependence in the transfer function from attachment 1 above seems fishy. It's above 10 kHz, so it can't be due to the influence of the temperature control loop.
I've moved Shruti's NoiseSpectra.ipynb script to the cryo_lab scripts repository, and pushed the version she uploaded earlier. I also added the data to cryo_lab/data/PDH/Noise with git lfs.
I found a couple bugs in the script, and made some modifications
Following these modifications, the noise at 10 kHz - 100 kHz is closer to that measured by 3CH. The updated open loop transfer function and noise curves are attached. I'm not chasing after the remaining discrepancy yet, since we expect that the PDH error signal was saturating during the attached measurement (see Shruti's elog from today for what we're doing about that).
[chris, aaron, shruti]
We (Aaron, Shruti) re-measured the PDH error signal slope for calibration since the previous measurements were for the settings before the mode-matching was optimized.
The cavity pole has changed but the peak-peak voltage of the PDH error signal seems roughly the same as measured on Thursday before optimizing the mode-matching. It seems like the different temperature setting we are now at has changed the polarization of light entering the cavity; there is no half-wave plate in the path between the fiber launch and input coupler.
I used the above estimate of the cavity pole and response along with the data measured on Friday to obtain a calibrated noise spectrum (red curve in Attachment 2), then for data above 100 Hz I used the linear estimate of the open loop gain and roll-off shown in Attachment 1 to obtain the blue curve in Attachment 2.
All data and the jupyter notebooks are in Attachment 3