enter Wed Jan 6 10:47:10 2021
I figured I'd initialize our realtime model for PSOMA. First, copied over x1cry.mdl (cryo cavities model) into x1oma.mdl. When I build this model, I get the following error
Linux source does not match currently running kernel.
The RCG expects the linux source to be at /usr/src/linux. For modern
distros this should be a symlink to the source installed as part of
the kernel header package for the running kernel. For this system:
/usr/src/linux -> /usr/src/linux-headers-3.2.88-rtcds
Please create/update this link, or set the RCG_IGNORE_KERNEL_RELEASE
environment variable to bypass this check
I haven't seen this before, do I need to update something? I haven't made recent changes to cymac, so I would be surprised if it's running a newer version of linux / rtcds than the existing source (and only one version of rtcds exists in /usr/src anyway). Indeed, when I ask for the currently running kernel (uname -r), it is '3.2.88-rtcds'; and the link at /usr/src/linux points to /usr/src/linux-headers-3.2.88-rtcds. I would expect that the source "linux-headers-3.2.88-rtcds" matches the kernel '3.2.88-rtcds'. I'm setting the ignore flag for now, but would like to know what this means.
Setting ignore to '1' or 'True' does not avoid the error message. I don't see mention of this message on the 40m or other elogs, so I'm a bit stuck. Since the realtime model isn't critical right now anyway, that's all for now.
exit Wed Jan 6 16:27:10 2021
Here is the 10 min trend for the past day. The temperature fluctuates by up to ~0.3 F over short times, and drifted by only ~0.5 F on average throughout the day. The lab is running consistently hot.
Entered Mon Jan 4 10:45:56 2021 .
Temperature in the lab is 89 F at the sensor by the electronics rack. I had been planning to put our AD590s on a board today, unnecessary equipment is already off but I also turned off cominaux and the Sorensen DC supplies. There is hot air coming from HVAC.
I spent some time gathering components and checking out AD's notes on the sensor. I'm using the same components as Andrew/Johannes' old circuit, and putting it on one of Anchal's "generic op amp / diff amp" boards (D1900129-v2). After checking out the old circuit, I realized we still have it in the cryo lab -- it's just missing the AD590. I put the AD590 on a breadboard, made a few connectors, and confirmed that I get a sensible reading (83 K near the center of the room, a couple degrees hotter in/by the electronics rack where the sensor is located).
I noticed that the AC connection on one of our Tenma power supplies is loose (wobbling the cable switches the supply off/on). It's a dual supply, but since I wouldn't want to use it elsewhere I'm powering the AD590 with it (doesn't need to move, out of the way above the rack).
Here's the temperature (second trend) over 20 min, will post the overnight minute trends tomorrow.
Picked up the mess, changed the dust mats, exit
Entered lab around Wed Dec 23 11:14:29 2020 to bring in optomechanics from Newport, step stool from McMaster, and a few other items for around the lab.
enter Thu Dec 17 10:24:44 2020
Just deskwork today.
exit Thu Dec 17 16:54:59 2020
Enter Mon Dec 14 10:32:49 2020
Met with Shruti and finalized the fiber components we want to order.
Alignment procedure has apertures on the E beam path, one before the mixing BS and one after.
W path laser is down to 25 uW at the PD. Also noticed that the y-alignment depends sensitively on the position of the final lens. The PD height is not the same as the height of the apertures, or the lens is off-center.
Exit Mon Dec 14 15:36:59 2020
enter Thu Dec 10 10:04:54 2020
Doesn't the phase meter just read out the noise even with no locking? I thought that was going to be the magic.
For locking, the mixer readout is in units of phase and the laser current modulation gives a proportional frequency modulation with no frequency wiggles until > 1 MHz. So it should phase lock with no integrator, but I'm not sure if the free running noise will drive it out of the phase lock or not. I wonder if its possible to use the phase meter as an error signal. It would be much easier to lock frequency instead of phase via a mixer.
Hm, hadn't tried the phasemeter application. I'll check it out now... if I understand your second comment, you're saying because
an error signal proportional to phase is already integrating the frequency error. Makes sense, but does 'easier to lock frequency instead of phase via a mixer' follow, or is that unrelated?
The Moku phasemeter does produce a nice power spectrum. Here it is up to 200 Hz, I'm working with Anchal's ctn-scripts and pymoku to get the higher frequencies.
Still odd that the beat amplitude is so small. Let's check:
Looks like neither beam is producing the expected photocurrent, but because the error is not the same factor for both beams I suspect alignment / beam size. I'm aligning with some apertures to avoid smearing the beam on lenses. Aligning each beam led to more power, but my procedure doesn't simultaneously align both beams.
exit Thu Dec 10 15:11:30 2020
Entered lab, then grabbed a spool of cable from EE, started elog Fri Dec 4 10:37:52 2020
thought about filters. The narrowest line I managed (yes really) is in the attached screenshot. I amplified +40 dB with Agilent 8447A before the splitter.
exit Fri Dec 4 16:14:19 2020
Definitely always use 50 Ohm for all inputs and output with RF frequencies. The Moku should be able to drive the current modulation input of the diode driver to directly phase lock based on the 1611 signal with no amplifiers. A 1 mW beat should give you ~1 Vpp, which is a few dBm.
Entered somewhat before Thu Dec 3 10:18:07 2020
finishing up the PLL. I still need to set an appropriate gain for the LO, but in the meantime I'll try to use the Moku's laser lock feature
This is pretty straightforward. Moku has an internal oscillator and lets you control the LP (corner frequency) and controller filter (proportional gain, integrator frequency, differentiator frequency, integrator saturation level, differentiator saturation level). I'm driving the E laser HF and LF inputs from the Moku outputs. Quickly acquire a lock and play around with filter settings for a while.
exit Thu Dec 3 12:30:47 2020
Enter Wed Dec 2 13:37:57 2020
I'd like to know whether the problem is in the W laser driver (S1500207) or the diode (104987). I swap the E laser drive over to the W laser diode, so am driving diode 104987 with driver S1600246. I still don't see the E laser driver oscillating, but the W diode power still reaches only 1.38 mW before falling off (ramping up current at T_set). Just in case, I also drive the W diode using the E driver but the cable from the original W driver (checking that the cable isn't the cause); no oscillation.
Entered EE to obtain grounding strap (Wed Dec 2 14:10:12 2020). On second thought, putting off diagnosing the W laser drive and just continuing with ITC 502. I did get a look inside, and don't actually see evidence that R33 was changed, just a added resistor from R30 to V_ref mentioned on the schematic.
Found this elog helpful for making sure the pinout for ITC 502 is compatible. Oddly, I can't set the laser diode current limit higher than 10mA, though the range of the device is +- 200 mA. I suspect the left 2 digits of the current display are just inoperable, because I can turn the adjustment pot in either direction until the digits stop moving. I set the current limit at 149 mA by counting by 10, and will double check the eventual current from the monitor. the diode definitely is nearing end of life, I'm only getting 1mW at nominal setpoint. I was squeezing a little extra out of the custom laser driver, but probably at the expense of the diode.
With the thorlabs driver, we're down to 1 peak at last!
Looking at the spectrum today, maybe the low frequency cutoff I noticed yesterday is just a frequency offset issue?
switching over to Moku... wow this is a user friendly device.
While choosing the gain for producing an LO from the 1611 output, I tried to measure the absolute power with the Moku. When I change the range from 1 Vpp to 10 Vpp, the overall peak height changes by almost 10 dB. I wondered if this were just a clipping issue, so I hooked up the Moku function generator output to the channel 2 input to see if the behavior is consistent. The beat note is 300 mVpp at the laser settings I'm currently using, which should be about 0 dBm dissipated into 1 MOhm. Sourcing 300 mVpp from the Moku into its channel 2 input gives the correct power reading, but the 300 mVpp from the 1611 reads -25 dBm with 10 Vpp range and -34 dBm with 1 Vpp range. What's going on?
I would have to string together eg 2x SR560 to get enough gain. I guess that's fine, because the noise floor of the SR560 is O(nV/rtHz)... but it gives me the feeling of doing something wrong, and I'm hungry so will pick it up tomorrow.
exit Wed Dec 2 18:42:15 2020
Entered Tue Dec 1 10:59:48 2020
Turning on the lasers in a more controlled way today, trying to reach datasheet nominal setpoint
I'm getting turned around, so I'll summarize the state of the drivers and lasers. Yellow highlight indicates this is a best guess based on things like dates on the DCC, but I haven't verified by eye (by opening the driver chassis or making a measurement).
Something seems wrong with the W laser path. At the nominal laser setpoint, the E path puts out a steady 5.33 mW; the W path puts out up to 1.9ish mW, but the power is fluctuating between 1 and 2 mW.
Spent some time changing the W/E mixing BS into a michelson BS for the W path (uneven arms). The AS beam from one leg was substantially brighter (by eye and ~10x on the PD) than the other. I confirmed that the mirror is HR for 1550. Probably just clipping, I had the plate BS kinematic mount in the wrong handedness to avoid remounting it; this was misguided anyway, I return it to original state. When I realigned the PLL path (identical to before this Michelson excursion), the forest of modes returned to the gaussian envelope state (not the bessel 2 looking envelope from yesterday). Could this be alignment / path length dependent? I returned the lasers to nominal T and I, and the gaussian envelope remains, so optical path is my best guess.
A little later, I lowered the TEC setpoint for W laser, and the Bessel envelope returned. However, whereas yesterday the 2nd sideband had a maximum now the 1st sideband is maximized.
Another feature that's been puzzling me -- when I sweep the temperature or current monotonically in a direction that moves the beat to 0Hz, the forest moves towards 0 until about 50 MHz. Below 50MHz, the modes are suppressed nearly to the noise floor; I think the carrier is just visible above the floor, but above 50Mhz the carrier is 50 dB above the floor. The cutoff is sharp, and if I continue sweeping temperature or current in the same direction the modes eventually reappear above 50 MHz moving up. My guess is it's another 'feature' of the analog spectrum analyzer that I haven't worked out (maybe secretly normalizing out the 1/f? but it's faster than 1/f rolloff), and that something cuts off low frequency sensitivity. Seeing as I'm well within 200MHz, I'm switching to the moku to check.
While the ipad charges, made this table of the modes I'm seeing at the nominal T_set of 23 C (10.940 kOhm) for W laser, 25 C (10.050 kOhm) for E laser. The marker tells me sideband spacing is 9.6 MHz; the W current drive HF mon has a line at 9.7 MHz, so it does seem these are related. I've attached the oscilloscope trace, where you can see that the W laser drive HF mon (chan 4) has RMS noise at least 100x the noise on E laser HF mon. The oscillation is dominated by the peak at 9.7 MHz, though there are a few others. Maybe the solution is just to swap in another laser driver -- this driver is a modified version an out of date revision of the circuit. Tomorrow I will swap in the combi controller for the W current driver and see if that helps.
exit Tue Dec 1 18:08:59 2020
Entered lab about Mon Nov 30 10:21:35 2020, after taking a COVID test through Caltech's new surveillance testing program.
I'll pick up where Shruti left off on the beat note. The comb of sidebands becomes a single line remains a comb when the PID is off; Koji suggests maybe the (PLL) PID is oscillating at 10Mhz.
exit Mon Nov 30 16:12:04 2020
Thanks, the photos are now on the shared drive.
For storing lab photos in W Bridge, you can use our shared google acct instead so that we all have access to it (see chat for secrets)
Isn't the PID oscilating at 10MHz?
Attachment 1: Video of spectrum analyzer with zoomed out beat after turning off the PID loop of west laser
Attachment 2: Another image of the zoomed in spectrum when the PID is on.
Anchal dropped off the Moku from CTN, along with its USBA->USBC cable, power cable, and ipad.
Entered lab around Tue Nov 24 13:24:57 2020 to finish photographing Zach's cantilevers.
some things about cameras, and in particular the FinePix F300 EXR
- Found a suitable power cable M-M for the New Focus 0901 power supply on the east table (I did not realize yesterday that these were the same cables). Then I checked the voltage on the pins and they were fine.
- Using the New Focus 1611 (1 GHz PD) powered by the New Focus 0901 +-15 V / 0.3 A max. power supply, I tried finding the beat note. I looked at the RF output on a HP 8560 E spectrum analyzer and the DC output on an oscilloscope.
The DC output ranged from 500 mV to over 1 V as I scanned the temperature of one or both lasers.
- When the east laser temperature read roughly 8.34 kOhm and west was 9.04 kOhm I saw a pattern as in Attachment 2.
Changing the temperature slightly did cause the peaks to shift about, and further when I changed the polarization of the east laser using the HWP the height of the peaks varied. They also disappeared when either of the beams were blocked.
The estimated peak power in the taller peaks is ~0.1 µW from the plot.
- I also tried scanning the temperature of both lasers again to possibly find a single peak. No luck yet.
Today, I didn't check the alignment very carefully and I probably have to tune it further after the changes that Aaron and I made over the past few days.
The next step is to do the phase-locking.
Entered lab Fri Nov 20 19:24:32 2020, usual sanitation.
[blue "Photodiode Power Supply] Looking for a DB9 to BNC adapter. I found this spider instead -- close enough. Use multimeter to measure 24V between pints 4 an 9... not promising. Confirm power is connected, no signal on the frontpanel BNCs either. Could remove this one and take a look on the benchtop, but above is...
[Newfocus +-15V current-limited power supply] Has 3 pole bananas and a power switch on the front. Found a power cable for the back. There's a bananas to 3-pin LEMO already there. Double check the voltage with a multimeter. Alas the connector doesn't fit the PD, but should be some cables in the EE shop or elsewhere...
Didn't find the right connector in EE. On the 'power cables' rack (NE corner Cryo), there was a M-F connector, but I need M-M. Could cannibalize the 12VDC supply? I think for now +-12V is working, so should look a bit more.
I moved the power cables for our preamps for better strain relief (attachment 2 is the before photo).
I also had left this ND filter sitting on the table (attachment 1). Yikes!
More photos here.
ExitFri Nov 20 20:39:43 2020
Entered lab Thu Nov 19 16:33:57 2020. Usual sanitation, personal reminder to report campus access with Caltech.
we want to coat some of Zach's cantilevers with a-Si so we can make a cold Q measurement. I've started to take some photos, but have become tired and will finish tomorrow. There are O(5) suitable cantilevers produced in January 2018, but I'll have to dig a bit more (or ask Zach) to determine what's what. We can measure the Q of the most promising few cantilevers to be sure they're acceptable.
I borrowed the digital camera from EE shop, but left its case (which is very dusty).
Sending W path beam to a Newfocus 1811 to measure free running laser intensity noise.
Following Shruti's recent diagram, I moved the Newfocus 1811 into position after OMTL1. I also moved PO1.1 back into the beam path, so I can use it to align into the 1811. Turn on the E laser and TEC, also had to move Ma for alignment. I still don't have a +-15V power supply, will ask around. Turn off the laser and TEC before exit at Thu Nov 19 20:41:22 2020
Attachment 1: An updated version of the diagram in elog 2577 where the path lengths to the beat beam-splitter are identical. The fiber launchers and some components have been moved around, but everything after PO1.1 along the beam has been retained as before.
Attachment 2: Retaining the same configuration to the beat BS, the cavity with Mach-Zehnder interferometer has been added. Also the path lengths to the MZ input BS along both laser beam paths have the same length. Except for the ring cavity, the Mach-Zehnder is also balanced.
Attachment 3: Updates pertaining to the current setup
This is the data using the Data Ray Beam'R2 profiler with the InGaAs window. Attachment 1 contains images of each of those profiles.
D: distance from fiber launcher in inches; The two values in each of the cells are [Clip 13.5%, 4 sigma] respectively, i.e., the method used to calculate the beam widths.
The previous measurement using a razor blade refers to 'sigma' which I believe explains why these values are 4 times larger.
These profiles were taken with temperature stabilized such that the powers were ~1 mW.
East laser set to 8.070 k Ohm, West laser set to 9.065 k Ohm. I don't understand why there is such a difference.
I had hooked up the ITC 502 combi controller to the west Rio laser and used only its temperature controller. (I believe both the thermistors that measure the diode temperatures are TH-20k Ohm.)
Both the PID controllers work satisfactorily: the TED 200 C with the east laser stabilizes to within few Ohms of the setpoint thermistor resistance within some seconds;
the ITC 502 stabilizes at a similar rate but at an offset of ~10 Ohms despite the integrator being set to maximum. I fiddled around with the P and I settings a little but realized that this configuration seemed optimal.
To measure these profiles at different distances I moved the fiber launcher head and then replaced it back to its original position, roughly.
I entered the lab somewhat before Tue Nov 17 14:56:22 2020. Exited Tue Nov 17 16:39:12 2020
Hand sanitizer on entry, also sanitized the bulky green laser goggles before and after my use (forgot contacts). Turned off the laser, sat at desk and considered turning on the laser. Took a break. On my walk I wrote this haiku
I've placed the following items outside the cryo lab:
1. Cryo liquid N2 dewar
4. Two pairs of cryo gloves
Optical layout: beam launch -> lambda/2 -> steering mirrors -> lens 1 -> ND 0.6 -> lens 2 -> PD 1611
There is only a 12 VDC power supply compatible with the 1611 power port, but the PD requires +- 15V. Surely there's one somewhere. Perhaps this is why I observe only -6 V on the DC mon with 1mW input power at 1550nm (checked against the Thorlabs S122C; I expected -10V). Maybe the beam is too large.
- Although when we talked about adjusting the MZ-phase, we decided that having the phase/path length control with fiber components might be better initially (Refer Attachment 2), for now I began doing everything in free-space.
- Attachment 1 shows the setup as it is now. Previously I'd placed polarizing beam splitters instead of 90/10 beam-splitters because I thought it would be easier to work with, but now changed my mind and decided to stick with what we planned.
(Once the beat is obtained on the spectrum analyzer)
- Measure the laser frequency noise
29 Oct 20:
I've added Attachment 3 -- which is the current free space version and some PLL electronics.
- It does not show the Mach-Zehnder part as that will be added only later
- This setup is asymmetric but in a future version we will change that
Today I modified the optical setup with the aim of obtaining the beat between the two diode lasers for phase-locking.
I added pick-off polarizing beamsplitters with HWPs in each path for now (to be able to adjust their power) and mixed them at a 50/50 non-polarizing beam-splitter to eventually reach a Newfocus 1811 low noise PD.
I will add pictures and more details later.
I was in the Cryo lab between 1215-1230 this afternoon. I removed two resonant RFPDs from what was Johannes' setup (encircled in Attachment #1). I also brought a SR554 preamplifier to the 40m.
I was wearing the usual PPE (gloves, face mask) while I was in the lab.
This is the spectrum coming off of the sample. there should be a peak at 1038Hz... but there isn't. And what is even weirder is that the spectrum analyzer that is built into Simulink shows a peak where I expect but when I do it here it doesn't show up.
Update: I think I have found why there is a discrepancy between the two versions of the power spectrum. The spectrum analyzer in the Simulink model requires non-continuous data so you have to use a block to make your data discrete. The sampling rate of that block affects where the peak of the mode is seen. So it seems that that the mode seen in the previous post was just caused by making the data non-continuous.
I got the script to run the simulation and added color to the diagram just to make it pretty :0
The next step is quantifying the error of the loop. My plan for this was to just calculate the Q from figure 3 of the moderinger paper. Then I can see if that value is consistent. Aaron suggested settling time and phase margin of the loop. So that is the next step (once I figure out how to do that)
Also I added the code to the Qryo github
Beautiful! Want to push this to the repo under git large file storage?
The step function represents the excitation of the sample. Ideally, it would excite to the setpoint and stay there but for some reason, it is jumping way past the point before returning. By messing with the gain and the frequency of the low pass filter I could get a variety of results the best is shown below at 50 gain and 40 rad/s.
The overshoot is interesting! To understand the loop shaping, I suggest checking out Gardner's Phaselock Techniques or Astrom and Murray's Feedback Systems. They both have sections on optimal PID controller design (at least Astrom and Murray do). You can make a pole-zero plot to help choose the location of poles and zeros in your loop shaping filter (the discrete zero-pole TF we added, after the gain).
Working with Aaron's suggestions (In the previous post) we got the mode ringer to converge. Previously the loop would continue to excite the sample to infinity but by fixing the following things we were able to get the step function to converge.
The power spectrum shown is taken from the spectrum analyzer shown in the loop. It shows what I would expect with a peak around our mode frequency of 1038 Hz.
Tue Sep 22 21:33:30 2020
I'm cleaning a bit, and gathering items not in use or in need of repair. They would make less mess in my office.
took an inventory of optics cleaning supplies, first aid kit, general cleaning supplies, wipes, etc. I found most were included in the first round inventory, but I took photos this time to convince my future self of object permanence. Will add to the wiki and update in a bit.
gloved up, shoe covers, went to QIL to check out the sprinklers and CTN to grab a GHz spectrum analyzer (HP8560E).
out: Wed Sep 23 00:20:03 2020
I suggest just using what's used for th QIL table.
Yesterday into today, I've been shopping for laminar flow HEPA fan filter modules for the PSOMA optical enclosure. I didn't find a lot of LIGO documentation listing specific filters, but here's what I've found online with some downselection on 'low vibration / high filter quality'. Please let me know If there's a company we often use, or if you can help direct this search at all.
Another consideration is flow rate relative to our volume. I can do this calculation, but what is the particle density (eg at 0.3 um) we want to achieve inside the enclosure? I realize that I never got the particle counter recording despite it being on my list, so I'll try to do that remotely today. We need to know the ambient particle count and the clean volume in the enclosure.
*all prices listed here are from publicly available pages
I updated the stage 1/2 optical layout to be more detailed after getting a sense of the sizes of things again last week. Even though this isn't how the table is currently set up, it might be good to accommodate future vacuum chambers in our earlier designs to minimize how much we need to move and realign optics.
I will update the PSOMA hardware inventory tomorrow to reflect the additional details in the new drawing. The updated diagram is available on git LFS, and the hardware inventory now reflects the diagram up through stage 1.
Notice of lab entry: 20 Sep 2020 evening
Fiber modulators on the table :
1. Intensity modulators (BW: up to 12 GHz) MXAN-LN-10
2. EOM phase modulators (BW: up to 150 MHz) MPX-LN-01
Dimensions of vacuum cans mentioned in attachments.
Here's the layout.
Some easy things that should be changed:
I measured the transmission of the Coastline 1m mirror at 180. ppm (S122C).
Alignment procedure while setting location of optics:
Alignment procedure subsequently:
Not sure how, but none of the drawers of the blue optomechanics cabinet are opening. I don't have a key. Here's what happened
Found someone who's had this problem before, might give it a try...
This worked, I used the metal meter stick to unlock the drawer.
--> note that link formatting breaks link for me, so here it is - https://www.practicalmachinist.com/vb/general/help-my-lista-locked-me-out-how-do-i-open-201606/
--> wrote up a similar experience with additional detail ENG_Labs/260
Can anyone tell me the specs / history of some of the custom optics in cryo? I'm mounting the 1m Coastline mirror and will start with that in the PSOMA cavity.
I took some photos of the existing layout. I'll just take apart the E beam path, and leave the W path unchanged for now as reference.
I moved the E fiber output coupler closer to the edge of the table, to make this path easier to reach.
Hopped around on the laser hysterisis curve for a minute. To optimize the temperature,
I started a cryo lab inventory that is separate from the PSOMA hardware inventory, and intended for stock items in the lab (optics, electronics, clamps, general safety and cleaning supplies, etc). It will be a work in progress. Both are accessible to anyone logged in to google drive with their ligo.org credentials.
Both are also linked on the PSOMA project wiki.
Did some mode matching, see the git.
Date of entry: 24 Aug 2020
The cameras were unfortunately lost in the mail, but we can use my laptop or other camera. Ended up leaving to do a couple comsol things that needed completing today.
Date of entry: 18 Aug 2020