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ID Date Author Type Category Subjectup
  204   Wed Jul 29 16:39:00 2009 Aidan, ConnorLaserFiberInterference signal setup for FS

Aidan and I are acquiring a beat signal from the interference of a reference beam and a frequency-modulated beam. The demodulated output can be seen on THIS ENTRY.

I have attached a photograph of our setup below. The reference beam is a pickoff from the 1W NPRO, and the zeroth order AOM beam is blocked by an iris.

Aidan will shortly post a schematic of the electronics, and we hope to start actuating on the laser frequency later today.

Attachment 1: Single_Pass_Noise_Measurement_Setup.jpg
Single_Pass_Noise_Measurement_Setup.jpg
  2178   Mon Sep 18 19:29:24 2017 awadeComputingGeneralInternet access down

I have rebooted the network.  All internal IP addresses seem to be pingable but cdsrana wifi is returning garbage self assigned IP address.  There is also no connection to the outside internet.

I plugged my laptop directly into the LIGO network port and DHCP failed, my computer is assigning itself and IP and so nothing is accessable to the outside world.  I also tried pinging the static IP address accociated with out lab, no response from our router.  

I've emailed Larry Wallace to see what is up.  This is not something I can resolve if something is wrong with the LIGO network.

 

  2179   Mon Sep 18 20:46:43 2017 awadeComputingGeneralInternet access down

Larry Wallace was still on campus and came around.  Apparently he wants to replace the switch in the entrance to the ATF anyway with something that isn't 20 years old. 

It turns out the issue was a combination of a poor connector from the LIGO network switch to the wall socket (wobbly patch) AND a bad cable from the wall socket to our gateway router 10.0.1.1. The LIGO switch patch is now pushed firmly in and the offending wall-to-our-router cable is in the bin. Fault was a broken clip on the cable.  Essential network links should be firmly clipped in.

There were also some config changes to both the 10.0.1.1 gateway and 10.0.1.2 wireless bridge router.  I have screen shot the new configuration and put it on the ATF wiki page.  It seems like the previous configuration was to feed the network connection through regular connection ports (rather that "internet" input) on the gateway router (10.0.1.1).

Internet is now accessible through the local ATF network and into the PSL lab computers

Quote:

I have rebooted the network.  All internal IP addresses seem to be pingable but cdsrana wifi is returning garbage self assigned IP address.  There is also no connection to the outside internet.

I plugged my laptop directly into the LIGO network port and DHCP failed, my computer is assigning itself and IP and so nothing is accessable to the outside world.  I also tried pinging the static IP address accociated with out lab, no response from our router.  

I've emailed Larry Wallace to see what is up.  This is not something I can resolve if something is wrong with the LIGO network.

 

 

  945   Wed Aug 18 11:52:00 2010 AlastairLab InfrastructureGeneralInternet in lab was down again

I power cycled the Linksys router but that didn't do anything.  Then I power cycled the 3com switch, and it came back on again.

  364   Wed Oct 7 00:05:17 2009 AidanMiscFiberIntraaction 70 MHz AOM - photos

Here are some photos of the inside of the 70MHz Intraaction AOM that we're using temporarily in the FS experiment. I'm not sure what the crazy red glue is all about.

Attachment 1: aom1.jpg
aom1.jpg
Attachment 2: aom2.jpg
aom2.jpg
Attachment 3: aom3.jpg
aom3.jpg
Attachment 4: aom4.jpg
aom4.jpg
Attachment 5: aom5.jpg
aom5.jpg
  1959   Mon Jul 6 13:27:48 2015 ranaMiscSeismometerInverted Pendulum links

Inverted Pendulum links:

  1. http://dx.doi.org/10.1063/1.1149783
  2. http://dx.doi.org/10.1016/j.nima.2007.08.161
  3. https://en.wikipedia.org/wiki/Inverted_pendulum
  1967   Thu Jul 9 14:35:30 2015 AlessandraMiscSeismometerInverted pendolum

I estimated what the inverted pendulum leg's spring constant (K) should be using some realistic/desired parameters.

Me and Kate assumed the inverted pendolum made of a cylindrical steel leg of radius 0.5 cm and lenght 0.42 m, and a point mass of 1 kg. With a resonant frequency of 40 mHz we obtain:

K\simeq {4.1 \frac{N}{m}}

  1998   Sat Aug 8 19:05:38 2015 KojiMiscGeneralInverted pendulum 10mm rod holder

LIGO-D1500236

Attachment 1: 10mm_Rod_Holder.pdf
10mm_Rod_Holder.pdf
  1925   Wed May 27 22:51:11 2015 KateMiscSeismometerInverted pendulum design

I talked with Steve Penn at GWADW, and he made a suggestion for an inverted pendulum design based on something he built some time ago to measure the thermal noise of fused silica fibers. His sketch is attached and I've labeled key parts. The sketch on the left provides a side view and the sketch on the right is a top-down view. The thick rod-like ends of a pulled fiber are welded to glass disks which can be easily clamped to a metal structure. The clamps are not depicted below, but would take the form of an 'L', sandwiching the glass disk against the metal plate. The clamps themselves would be screwed to the plate. The top plate is attached to support arms which are fixed rigidly to a table (or, in our case, to the rhomboid). The structure beneath the glass fiber has three legs that extend up and beyond the support arms. At the top of these legs is a disk and on top of the disk is a vertical rod with a mass that can slide up and down. The height of the mass is adjusted to set the resonance frequency.

This seems like a design that is quite compatible with what we need. The moveable mass would need to be designed such that we can fix a mirror for the Michelson on top of it. Steve also suggested that if we want to limit the number of degrees of freedom, we could pull a glass ribbon instead of using multiple fibers.

Attachment 1: SCAN7432_000.pdf
SCAN7432_000.pdf
  1573   Mon Nov 28 19:12:05 2011 EricLaserIodineIodine frequency stabilization layout

I have included below my proposal for the design of the Iodine-stabilized laser system. It is a slight variation on the standard implementation of the FM spectroscopic approach to frequency stabilization, and is sort of a hybrid between the two designs investigated by Leonhardt and Camp (article).

Brief overview of my implementation of laser frequency stabilization by FM spectroscopy:

1. Nd:YAG laser outputs ~700mW infrared (1064nm) light, which is passed through a Faraday isolator and the frequency doubling oven (stabilized by Zach's precision temperature controller)

2. Dichroic mirror transmits second harmonic, reflects the infrared light for optical heterodyne detection with IR output from second identical laser system (each system locked to a difference resonance)

3. The 532nm light is split into pump and probe beams, whose relative intensity can be adjusted to optimize the SNR (minimize power broadening, maximize signal strength)

4. Probe beam is RF phase modulated by the EOM, adding a pair of weak FM sidebands to the 532nm carrier signal. 

5. Probe is then passed through Iodine vapor cell, overlapping temporarily with the saturating pump beam. The partial depletion of the Iodine ground state by the pump beam causes each frequency component of the probe beam to experience different levels of absorption and dispersion.

6. Probe impinges on a square-law photodetector, which converts the time-varying field amplitude of the probe beam into a beat signal at the RF modulation frequency. This RF heterodyne beat signal contains the imprint of both the absorption and dispersion profiles of the spectral feature of interest.

7. The beat signal is then fed into a double-balanced mixer (DBM) along with the local RF oscillator which drove the EOM. Assuming the beat signal has been appropriately phase-matched with the oscillator, the output from the DBM should be the dispersion profile of this given spectral feature at DC, which is an ideal error signal for frequency locking.

8. The error signal is then fed back into the laser head controller where the fast and slow internal frequency actuators work to lock the laser.

Any questions and/or feedback regarding this layout would be appreciated. This overview was very rough, and clarification can be provided as needed. More details will follow as soon as I begin rounding up the necessary components in lab tomorrow.

 

Hybrid_FMS_Schematic_DBM.png

 

  1615   Thu Feb 9 01:02:47 2012 EricMiscIodineIodine localized in cold fingers

As Zach observed in a previous post (elog #1560), the BIPM Iodine cells he shipped from Goddard arrived with globs of Iodine scattered randomly throughout the cell. Before we could put them to use, we needed to find some way to localize the globs of Iodine into the cold fingers. The general idea was to use some heating element to gently melt the solid chunks of Iodine and carefully direct the liquid into the cold finger. 

Well, I gave this a try today with the heat gun Zach left in the lab for me, and it was a bit more difficult than I imagined it would be. The heat gun reached its maximum temperature rather quickly and has no temperature control settings beside "hot" and "cold", so I altered the cell temperature by placing the heat gun on its flat back mount and varied the cell height above it. With the heat gun at max temperature, I observed the following:

  • Iodine globs quickly vaporized within 5-10cm of the heat gun
  • Iodine liquified for about 2-5 seconds between 10cm and 20cm before vaporizing
  • Iodine globs began to "slide" around the cell above 30cm, retaining their form for > 5 seconds

Iodine vapor and liquid are supposed to have distinct colors, but when present in such miniscule amounts I couldn't see either of them. The best way I found to move the globs into the cell finger was to hold the cell more than 30cm away from the heat gun and try to slide them into the finger. It took a bit of practice, but I think as a first (and very rough) attempt, it was pretty successful.

Below is a picture of the first of two BIPM cells I modified today. The picture was taken when the cell had been cooling down for ~5 minutes, so you can distinctly see both the solid and liquid phases of Iodine at the bottom of the finger. Those dark colored specs used to be scattered randomly throughout the cell and after my manipulations today I couldn't find any of them outside the finger. I've also heard the color of liquid Iodine described as "orange-brown", so I assume the ring above the solid Iodine specs is condensed Iodine vapor still cooling down. Unfortunately, I had to leave shortly after making these manipulations, but I look forward to seeing how they look after completely cooling down to room temperature. As a final touch, once all the Iodine present in the finger has solidified, I will slightly heat it while holding the cell with the cold finger pointing downward in an attempt to make all the scattered globs merge into a single clump of Iodine.

Photo_Feb_08_4_48_10_PM.jpg

 

 

  436   Fri Nov 13 14:37:11 2009 MottElectronicsFiberIsomet and Marconi Phase noise Datasets

I am attaching the datasets for the phase and frequency noise plots for the Isomet and the Marconi.  The structs also include the noise measurements taken from the spectrometer and the input amp in both phase and frequency space.  As soon as I get the NEOS measurement working, I will upload some plots for that and the data sets as well.

Attachment 1: MarconiData.mat
Attachment 2: IsometData.mat
  668   Fri Mar 12 17:27:22 2010 AlastairLaserGYROIsomet shmisomet

 Here is the fft of the output of the Isomet oscillator (10mW output power, with a 50ohm attenuator on the frequency modulation input).  The input of the spectrum analyser had the input attenuator set to 20dB.

I centered the measurement around the oscillator frequency (approx 30MHz).  We see large peaks every 132kHz and smaller sidebands on each of these.

Attachment 1: isomet_oscillator.jpg
isomet_oscillator.jpg
  670   Sat Mar 13 07:32:20 2010 ranaElectronicsGYROIsomet shmisomet

Although this is bad, I'm not sure that this is the issue. We'll have to diagnose it on the bench, but I think it just may be the way you guys were powering it.

Those lines are probably from the switching power supply; the type of RF amplifier that's in there probably has no power supply rejection at all. We'd be

much better off powering this thing from a real, regulated DC power source and then make sure to put the bypass capacitors (one big, one small) right on the power pins of the AOM driver.

  671   Sat Mar 13 11:45:20 2010 AlastairElectronicsGYROIsomet shmisomet

Quote:

Although this is bad, I'm not sure that this is the issue. We'll have to diagnose it on the bench, but I think it just may be the way you guys were powering it.

Those lines are probably from the switching power supply; the type of RF amplifier that's in there probably has no power supply rejection at all. We'd be

much better off powering this thing from a real, regulated DC power source and then make sure to put the bypass capacitors (one big, one small) right on the power pins of the AOM driver.

Agreed we didn't have the capacitors right up against the AOM driver.  They were on the power supply, and the large ones could be bigger.

However we did try it with a second totally different style of power supply, and the frequency of the lines was exactly the same.  It will be interesting to see whether a regulated supply gets rid of them.

  469   Fri Dec 4 16:15:12 2009 DmassLab InfrastructureGeneralIsopropyl

We have large glass jugs of methanol and acetone - we need one of isopropyl too. I'm not sure how to go about this.

  2057   Mon Aug 1 15:33:25 2016 AidanMiscANTS!It's summer. The ants are back. I have laid down some ant bait

One in the TCS Lab. One by the ATF door. I have more ant bait available in the TCS Lab.

  2488   Thu Feb 27 14:26:52 2020 KojiSummaryLab MonitoringItem lending: Particle Counter from OMC Lab to QIL

Item lending as per Ian's request: Particle Counter from OMC Lab to QIL

The current particle class of the room was measured to be 800.

The particle counter went back to the OMC lab on Aug 10, 2020.

Attachment 1: P_20200227_134755_vHDR_On.jpg
P_20200227_134755_vHDR_On.jpg
  2489   Fri Feb 28 13:36:32 2020 Ian MacMillanSummaryLab MonitoringItem lending: Particle Counter from OMC Lab to QIL

Still trying to figure out how to set up the particle counter remotely. The current particle count is 576.

Particle counts over time
Feb. 28 at 12:30pm 576
Feb. 28 at 5:00pm 594
Mar. 2 at 8:30am 393
Mar. 2 at 11:30am 650

Note: the particle count is the number of particles detected over 0.3um size.

  1   Sun Oct 21 23:06:49 2007 ranaLab InfrastructureHVACIts too cold again
Friday evening it was a pleasant 70 deg F in the lab.

Tonight (Sunday evening) its back down to 61 deg F.

This happened ~a week ago; emailed Jeanne and Jo Ann and it got fixed. Will
try again and post results here.
  2516   Mon Nov 9 15:49:58 2020 AidanUpdate2um PhotodiodesJPL PD resurrection (cont.)

Okay - all the steps in the procedure of eLOG 2476 have been verified as working - with the exception of the RTDs in the chamber.

 With regards to taking dark noise spectra at different biases and temperatures, looks like Raymond took spectra with biases of [50, 100, 200, 400, 600, 1000]mV. If no objections, I’ll stick to that number of measurements. 

I’m a bit pushed for time with other stuff. I wonder if the shield RTD is sufficient to run tests on the system? I’ll go back through the data and see how reproducible the relationship between shield temperature and PD temperature is. If it is reliable then in the interests of time, I’m going to forgo re-installing the extra RTDs in the chamber just now.

 

  2517   Tue Nov 10 12:46:34 2020 AidanUpdate2um PhotodiodesJPL PD resurrection (cont.)

Looks like the temperature difference between the PD and the shield is relatively small. Even the transients when the heater is applied are order 5K. 

This means that, for quick purposes, the shield RTD is a good proxy for the PD temperature. 

The attached data is the difference between PD and shield RTD from circa 5th-6th February 2020.

Quote:

Okay - all the steps in the procedure of eLOG 2476 have been verified as working - with the exception of the RTDs in the chamber.

 With regards to taking dark noise spectra at different biases and temperatures, looks like Raymond took spectra with biases of [50, 100, 200, 400, 600, 1000]mV. If no objections, I’ll stick to that number of measurements. 

I’m a bit pushed for time with other stuff. I wonder if the shield RTD is sufficient to run tests on the system? I’ll go back through the data and see how reproducible the relationship between shield temperature and PD temperature is. If it is reliable then in the interests of time, I’m going to forgo re-installing the extra RTDs in the chamber just now.

 

 

Attachment 1: temperature_diff_shield_v_PD.png
temperature_diff_shield_v_PD.png
  2535   Thu Mar 4 16:12:26 2021 AidanHowto2um PhotodiodesJPL PD set up tutorial video

I recorded a 15 minute overview that describes the JPL PD set up and how to operate it. I'm in the process of embellishing the operation procedure (previous version can be found here: eLOG 2476).

 

  2613   Wed Jul 21 14:53:28 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light borrowed -> QIL

See https://nodus.ligo.caltech.edu:8081/40m/16250

  2616   Fri Jul 23 20:53:40 2021 KojiSummaryGeneralJul 17, 2021: Canon camera / small silver tripod / macro zoom lens / LED ring light returned / ELectronics borrowed

[Returned] Brought one HAM-A coil driver (D1100687 / S2100619) and one Satellite Amplifier (D1002818 / S2100741) from the 40m

Also brought some power cables.

Brought ~1m of 0.0017" (~43um) misical wire. This will make the tension stress be 341MPa. The safety factor will be ~7.

 

Attachment 1: P_20210723_212158.jpg
P_20210723_212158.jpg
  745   Wed Apr 28 19:57:19 2010 DmassLaserPSLKEYS TO 35W MISSING

The keys to the 35W (as well as the gyro laser) have been removed. There is no elog entry saying who did this, where they are, or when it happened.

[Edit: We found it in one of the drawers of the console tables!]

 

  1105   Wed Oct 6 17:06:45 2010 FrankMiscPulserKeithley 2635A i-v curve config files

 - for personal use only -

pd_darkcurrent_100mV_-20V_range1uA_limit1uA.prj

  2572   Thu May 20 16:57:32 2021 KojiElectronicsGeneralKeithley Source Meter returned to Downs

I've returned the Keithley Source Meter unit
- The unit (Keithley 2450?2460?)
- A power cable
- A pair of banana clips
- the transistor test fixture & triax cable/connectors
 

Attachment 1: P_20210520_154439.jpg
P_20210520_154439.jpg
Attachment 2: P_20210520_154505.jpg
P_20210520_154505.jpg
Attachment 3: P_20210520_154523.jpg
P_20210520_154523.jpg
  2566   Mon May 10 15:38:36 2021 ranaSummary2um PhotodiodesKeithley connections

Note that the back panel connectors are Triax, not the usual Coax.

  777   Tue May 18 09:43:55 2010 AidanComputingDAQKilled the DAQD process. It restarted automatically.

I added some EPICS channels to the Hartmann sensor softIoc and then added these to be recorded in the frames.

I then killed the daqd process on fb1 so it would start afresh.

  • /cvs/cds/caltech/target/softIoc/HWS.db      - the file with the HWS EPICS channels
  • /cvs/cds/caltech/chans/daq/C4TCS.ini            - the .ini file telling the frame builder what channels to record.
  860   Tue Jul 20 18:12:02 2010 AidanComputingDAQKilled the DAQD process. It restarted automatically.

I killed and restarted the daqd process because I wanted to add some 16Hz TCS channels to the frame builder. These are from the Athena DAQ box.

I edited the following files:

  • on fb1: /cvs/cds/caltech/chans/daq/C4TCS.ini    -the .ini file telling the frame builder what channels to record
  • on tcs_daq: /target/TCS_westbridge.db  - added the names for the ADC inputs and DAC outputs for the Athena box

 

Quote:

I added some EPICS channels to the Hartmann sensor softIoc and then added these to be recorded in the frames.

I then killed the daqd process on fb1 so it would start afresh.

  • /cvs/cds/caltech/target/softIoc/HWS.db      - the file with the HWS EPICS channels
  • /cvs/cds/caltech/chans/daq/C4TCS.ini            - the .ini file telling the frame builder what channels to record.

 

  861   Wed Jul 21 13:59:29 2010 DmassComputingDAQKilled the DAQD process. It restarted automatically.

We are continuing the naming scheme with CX? I thought we were planning on making C2 the whole subbasement...

Like

C2ATF

C2PSL

C2TCS...

  862   Wed Jul 21 14:20:54 2010 JenneComputingDAQKilled the DAQD process. It restarted automatically.

Quote:

We are continuing the naming scheme with CX? I thought we were planning on making C2 the whole subbasement...

Like

C2ATF

C2PSL

C2TCS...

 Nope.  Each lab has its own number.  I think PSL is C3, TCS is C4, ATF gets C2....Frank has the full listing of these things.  Or at least that's the latest I heard a few months ago after several elogs back and forth.

  864   Wed Jul 21 20:08:53 2010 DmassComputingDAQKilled the DAQD process. It restarted automatically.

Right - I am questioning the scalability and sense of this scheme, and inquiring if this is aesthetic.... i.e. is there a reason it cannot be C2SYS for all of bridge, (possibly front end naming limitations)?

  1431   Tue May 31 19:54:14 2011 ZachElectronicsGYROLAST CALL for PDH2 comments

 I have run the design rule check on the new PCB and there are no violations. I am going to do one last run of checking dimensions (hole placement, BNC mount clearance, etc.) and then generate files. Once I have them, provided there are no more comments, I will take them to Steve or someone to purchase.

PDH2.pdf

  1528   Tue Aug 23 00:56:07 2011 ZachElectronicsGYROLC homodyne discriminator

I thought of a primitive device that could be used as a frequency discriminator in our (and similar) readouts. It is sort of like the "cable" method championed earlier this year, only instead of using an asymmetric michelson style setup for the phase shift, one uses a high-Q LC filter tuned to the carrier in one path, as below:

LC_homodyne_diagram.png

As the signal from the PD changes frequency, the phase shift from the LC filter changes, providing a linear output from the mixer proportional to the frequency shift. Using high-enough-quality components (DCR ~ 50 mOhm), we can get discriminants approaching 1 mrad/Hz, which would require hundreds of km of cable in the other case.

Feeding to the LO with the LC leg ensures that AM from the filter---which is already higher than first-order---is removed.

There are two probable issues:

  • Range: Choosing high Q for a large discriminant means a small linear range (~1-10 kHz), which means that, in the gyro case, the diurnal fluctuation in cavity length must be kept below around 10 um. We are already considering locking the cavity length to a stable reference, so this may not be an issue in the end.
  • Thermal drift: Thermal expansion of the capacitor will likely cause ugly drift in the LC resonance frequency. As far as I can tell, this is the reason something like this hasn't been suggested in the past (or at least why it's not in common use). For this, I thought of a tricky solution. Expansion causes the capacitor's plates to separate, lowering the C. Since the inductor's L is dependent on the depth of a ferrite core into the coil, it should be possible to mount the core to some substance whose dimensions and CTE are cleverly selected so that the overall effect of a temperature swing is drastically reduced. That is, as the temperature goes up, the capacitor expands and C goes down, but the cleverly chosen substance also expands, pushing the core further into the inductor, increasing L proportionally and minimizing the change in the resonance frequency. This may not even be necessary for our application, but in the event that thermal drift is measured to be several times worse than what we need, we may consider it.

I talked to Frank before thinking about this much further, and he didn't think there was anything obviously wrong with the idea. To the contrary, he thought it might be worth looking at because it could be useful for other experiments. I don't think we have good enough components to try this yet. We may have some good capacitors somewhere, and Frank mentioned that we might have a DIY inductor kit, so that's promising. Otherwise, I think we might want to order some good high-Q components and try this out.

 

  1529   Wed Aug 24 05:26:03 2011 ranaElectronicsGYROLC homodyne discriminator

The reason I went for cable length instead of LC, is that the LC is basically a version of a VCO with a PLL, except that the VCO is made of macroscopic L & C. I think the only way to be

sure about the performance is just to build it and see. But basically, you can be sure that you have to ovenize the LC and pack it with putty. Might as well get yourself warmed up for some

ovenizing one way or another: gyro, table, EOM, LC, etc.

  1530   Wed Aug 24 10:47:58 2011 ZachElectronicsGYROLC homodyne discriminator

Yes, I can see that. I also figured it was because the intended purpose of the cable method was to measure much larger frequency shifts, not mHz-level. So they shouldn't really be compared directly.

I'm building a simple LC to see how it performs. If it does even close to well then maybe I'll order some nicer parts.

Quote:

The reason I went for cable length instead of LC, is that the LC is basically a version of a VCO with a PLL, except that the VCO is made of macroscopic L & C. I think the only way to be

sure about the performance is just to build it and see. But basically, you can be sure that you have to ovenize the LC and pack it with putty. Might as well get yourself warmed up for some

ovenizing one way or another: gyro, table, EOM, LC, etc.

 

  1395   Thu Apr 21 02:45:28 2011 ZachLaserGYROLF noise hunting

[Alastair, Zach]

Over the past couple days (in between overhauling malfunctioning PDs), we have been trying to hunt down the excess low-frequency noise. Last week, with Koji's help, we essentially ruled out the possibility of scattered light noise from the transmitted end of the gyro by intentionally reflecting varying amounts of light back into the cavity and observing NO DIFFERENCE in the low-frequency spectrum.

AM from the EOM still seems to be the most likely suspect, and we continue to find ways in which it could couple. Yesterday, we think we traced the crazy AM level modulation that I mentioned in my last post to the iris we are using to isolate the proper beam out of the AOM setup. The double-1st order (desired) and single-1st order (undesired) beams are extremely difficult to isolate from one another, so we had to use a very small aperture that we think was coupling EOM jitter into AM quite strongly. We moved the iris down the beam path closer to the waist(s) and were able to get better isolation with a larger aperture. The drift in AM level now seems absent.

While the AM levels in the CCW and CW beams (as measured on the RF analyzer) are not simultaneously minimized at the same pre-EOM HWP angle, there is no longer a large-angle discrepancy; the difference is <1 degree and the noise in both beams can now be kept fairly low at some compromise angle. I have set up a PDA255 in each path immediately before the cavity to monitor them both simultaneously. By adjusting the HWP before the EOM and fine-tuning the EOM orientation, I was able to get the AM peaks in both beams to be <10 ppm relative to the carrier.

After re-locking the gyro, I saw NO IMPROVEMENT in the low-frequency noise yet again. I replaced the PDA255s and tried looking at the LF noise directly after demodulation. I saw some excess noise above the broadband floor below about 1 Hz, which is roughly where the excess gyro noise begins. Upon deliberately de-tuning the HWP so that the RF peaks were >20x higher, however, I saw NO NOTICEABLE CHANGE in the audio spectrum. Looking at the peaks in the RF spectrum more closely, I discovered that the linewidths are below 1 Hz, suggesting that this may not be the source after all.

I suggest that we vent the chamber and obstruct the cavity so that we can run the same tests with the REFL PDs themselves. Then, we can use the noise we measure in the error signal to easily and accurately estimate the contribution to the NB.

  1556   Thu Oct 20 00:47:21 2011 ZachLaserGYROLF noise still there

The low frequency noise is still present in the TRANS signal, seemingly discounting the beam jitter theory. I think I am too sad to ask Rana for the $5, though.

TRANS_with_PMC_10_19_11.pdf

  1536   Fri Sep 9 19:14:07 2011 ZachLaserGeneralLF_WTF?

I am still absolutely stumped about the LF noise. Today I revisited and reconfirmed the fact that the gyro noise is strongly correlated with the noise in the DC_TRANS level at low frequencies:

gyro_noise_vs_dc_trans_9_9_11.pdf

What this means remains a mystery to me. I also re-verified that the laser power fluctuations do not have the right shape to explain this noise (nor is there an obvious coupling from laser intensity noise to gyro noise in this case). The fact that we have ruled out traditional RAM as the source makes it anyone's guess as to what's happening here. Increasing the LF common-mode gain by ~50 has zero effect on either the gyro noise or the DC_TRANS noise.

I am pointing out the DC_TRANS correlation again because I think it is a potential smoking gun. If you or someone you know has any information regarding this matter please call 1-800-GYRO-WTF.

 

  1890   Wed Dec 3 19:37:09 2014 ZachElectronicsM2 ISSLT1128 current noise

Quote:
  • My best guess is that we got a bum batch of LT1128s that I used for the whitening stages, and to check that I'll replace one with another if I can find one.

 I replaced the LT1128 in the whitening filter for channel B with one from Downs, to see if it exhibited better low-frequency current noise. It did, but only very marginally:

M2_noise_vs_LT1128_batch_12_3_14.pngM2_input_noise_vs_LT1128_batch_12_3_14.png

The Downs part is about a factor of sqrt(2) better, but even it is not appreciably below the "max" estimate from LISO. However, the fact that the noise improves slightly here (and nowhere else) when that one LT1128 is replaced only strengthens my suspicion that this is indeed just bad current noise performance from the LT1128.

In fact, if you look at the performance of the aLIGO in-vacuum DCPD preamps, which have essentially same LT1128 whitening stages as I used in the M2 (actually 2 in series), you see a similar amount of excess low-frequency noise. Here is a measurement of one DCPD I made while at LLO, compared with LISO estimates using the "typical" and "maximum" noise specs for the LT1128:

excess_LT1128_inoise_in_aLIGO_DCPD_12_3_14.png 

As you can see, the data match the "max" curve very well. So, either a.) Linear is pulling a fast one on us and under-reporting the typical current noise or b.) we are doing something silly with the circuit, and this is somehow perfectly mimicking a "max" current noise part.

 

  1884   Mon Aug 4 10:27:45 2014 EvanElectronicsFSSLTSpice simulation of AD829 inverters

For a while now I've wondered how LTSpice thinks the the AD829 should perform around 1 MHz. To that end, I ran simulations of an AD829 inverter for a few different gain/compensation settings.

This is also of potential interest to the 40m and cryo, both of whom may want to construct detailed phase budgets in the region from 100 kHz to a few megahertz.

As a reminder, this is how Analog Devices thinks we should stuff the AD829:

ad829_components.png

What I simulated was slightly different:

  1. G = −1 V/V: R1 = 1 kΩ, R2 = 1 kΩ, R3 = 500 Ω, Ccomp = 25 pF.
  2. G = −10 V/V: R1 = 220 Ω, R2 = 2.2 kΩ, R3 = 200 Ω, Ccomp = 3 pF.
  3. G = −100 V/V: R1 = 220 Ω, R2 = 22 kΩ, R3 = 220 Ω, Ccomp = 0 pF.

Here R3 means I've added a resistor from the (+) pin to gnd, in order to cancel some of the bias current.

For each gain, I ran the simulation with both a 50 Ω load and a 1 MΩ load. In the attached zip file you can find screenshots of the Spice model for each gain setting.

Attachment 1: ad829_invert.pdf
ad829_invert.pdf
Attachment 2: ad829inv.zip
  1356   Thu Mar 17 15:09:18 2011 AidanMiscstuff happensLVC Lab Tour

Visitors to the lab ...

Attachment 1: P1000411.JPG
P1000411.JPG
Attachment 2: P1000412.JPG
P1000412.JPG
Attachment 3: P1000413.JPG
P1000413.JPG
  12   Wed Dec 12 16:10:19 2007 tobinLab InfrastructureHVACLab Temperature
The lab temperature at 2pm was a comfortable 69 degrees.
  13   Wed Dec 12 16:19:00 2007 tobinLab InfrastructureHVACLab Temperature
I connected the particle counter to the Dell computer for PEM data logging (temperature, humidity, and particle count). The data shows that while the temperature is comfortable right now, it was quite warm in here yesterday (78 degrees). A plot is attached.

For this I made a serial cable using two DB9-to-RJ45 converters and a length of Cat5 ethernet cable. The computer end of the cable has a female connector; the particle counter end of the cable has a male connector. Only three conductors are connected: transmit (pin 2), receive (pin 3), and ground (pin 7 on the particle connector, pin 5 on the computer). I used the USB-to-serial dongle, which shows up in Linux as /dev/ttyUSB0.

Someone later can write a script to automatically poll the particle counter for new data. For now, I just emptied its internal buffer, which stores the last 200 measurements. The secret to communicating with the particle counter, which I learned by examining the c1psl statecode at the 40m, is to first transmit the letter "U". After this, the particle counter will listen to you and do what you say. In particular, sending a capital letter "A" will cause the counter to emit the next measurement from its buffer, until there are none left, at which time it will just respond with "#". To read the data I just ran a "cat /dev/ttyUSB0" command in one terminal, while in another terminal I ran a loop "while 1; echo -n A > /dev/ttyUSB0; sleep 1; end". I set the serial port parameters (9600BPS, 8N1) using Minicom.

Also, there's a Matlab script to parse and plot the output, in ~controls/tobin.
Attachment 1: temperature.pdf
temperature.pdf
  14   Thu Dec 13 18:47:02 2007 tobinLab InfrastructureHVACLab Temperature
Extech: 66.8F, 25%RH. Met One: 68F, 20%RH.

Here is the datalogger's contents:
A  121307 161942 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000130 LOC 000000 C/S 000E54
A  121307 164641 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000130 LOC 000000 C/S 000E53
A  121307 171340 0100 0.3 000000 0.5 000000 TMP 000685 R/H 000130 LOC 000000 C/S 000E52
A  121307 174039 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000200 LOC 000000 C/S 000E53
A  121307 180738 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000210 LOC 000000 C/S 000E57
A  121307 183437 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000210 LOC 000000 C/S 000E56
A  121307 190136 0100 0.3 000000 0.5 000000 TMP 000680 R/H 000195 LOC 000000 C/S 000E5C
A  121307 192835 0100 0.3 000000 0.5 000000 TMP 000685 R/H 000195 LOC 000000 C/S 000E69
I'm not sure why it only starts at 12:13pm today. Also, looks like its clock is 50 minutes fast.
  15   Tue Dec 18 13:49:50 2007 tobinLab InfrastructureHVACLab Temperature
Extech: 68.6F, 57%RH. Met One: 68F, 53%RH. Drizzling outside.

Particle counter log shows stable temperature 67.5-69.5F over the last four days.
Attachment 1: temperature-20071218.pdf
temperature-20071218.pdf
  16   Fri Dec 21 21:27:12 2007 tobinLab InfrastructureHVACLab Temperature
Extech: 67.9F, 26%RH. Met One: 68F, 20%RH. Clear & cold outside.

Particle counter log looks stable.
  18   Wed Jan 2 15:10:24 2008 tobinLab InfrastructureHVACLab Temperature
The lab temperature appears to have been stable over the holiday, always between 68.5 and 70.0 degrees F. (There is no data from Dec 28-29 due to a computer reboot.)
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