40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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ID Date Author Type Category Subjectdown
  17013   Mon Jul 18 16:49:57 2022 YehonathanUpdateBHDadd Laser RIN to MICH budget

I measured the RIN by taking the spectrum of C1:MC_TRANS_SUMFILT_OUT and dividing it by the mean count on that channel (~13800 cts). Attachment 1 shows the result.

I updated the MICH AS55 noise budget but got a very low contribution (gold trace in attachment 2).

It seems too low I think. What could've gone wrong? Finesse calculates that the transfer function from laser amplitude modulation to AS55 is ~ 1.5e-9 at DC. If I turn off HOMs I get 1e-11 at DC, so this coupling is a result of some contrast defect. Should I include some RMS imbalances in the optics to account for this? Should I include it as a second-order effect due to MICH RMS deviation from zero crossing?

Quote:

the main laser noise coupling for a Michelson is because of the RIN, not the frequency noise. You can measure the RIN, in MC trans or at the AS port by getting a single bounce beam from a single ITM.

 

  17015   Mon Jul 18 18:33:38 2022 KojiUpdateBHDadd Laser RIN to MICH budget

You should measure the coupling by noise injection. Noise budgeting does not need any modeling:

1) Measure the power spectrum density of the target signal (i.e. DARM) and the source noise (i.e. RIN this case)

2) Calibrate both using a calibration peak to convert 1) into the physical units (m/rtHz, 1/rtHz, etc)

3) Measure the transfer function from source to target using the noise injection. (i.e. RIN injection this case and look at the injection to RIN and injection to DARM)

4) Measure open-loop transfer functions if necessary. (i.e. DARM control open-loop transfer function to convert the error signal into the free running noise level)

Primarily, these are measured noise levels and noise couplings there is no room to involve a model there.
Once the noise budget was done, you can compare it with the model and say "the coupling is big/small/comparable".
 

Also, why don't you use C1:MC_TRANS_SUMFILT_IN1_DQ instead? Your _OUT signal seems affected by the bunch of comb notch filters to artificially remove the 60Hz harmonics. It's not a fair RIN measurement.

  15882   Mon Mar 8 20:11:51 2021 ranaFrogsComputer Scripts / Programsactivate_matlab out of control on Megatron

there were a zillion processes trying to activate (this is the initial activation after the initial installation) matlab 2015b on megatron, so I killed them all. Was someone logged in to megatron and trying to run matlab sometime in 2020? If so, speak now, or I will send the out-of-control process brute squad after you!

  5143   Mon Aug 8 19:45:27 2011 jamieUpdateCDSactivateDQ script run; SUS channels being acquired again

> Also the BS is missing its DAQ channels again (JAMIE !) so we can't diagnose it with the free swinging method.

I'm not sure why the BS channels were not being acquired.  I reran the activateDQ script, which seemed to fix everything.  The BS DQ channels are now there.

I also noticed that for some reason there were SUS-BS-ASC{PIT,YAW}_IN1_DQ channels, even though they had their acquire flags set to 0.  This means that they were showing up like test point channels, but not being written to frames by the frame builder.  This is pretty unusual, so I'm not sure why they were there.  I removed them.

  4241   Wed Feb 2 15:07:20 2011 josephbUpdateCDSactivateDAQ.py now includes PEM channels

[Joe, Jenne]

We modified the activateDAQ.py script to handle the C1PEM.ini file (defining the PEM channels being recorded by the frame builder) in addition to all the optics channels.  Jenne will be modifying it further so as to rename more channels.

  8261   Fri Mar 8 16:05:56 2013 yutaBureaucracyGeneralaction items for PRMI / ALS-FPMI

We should focus our work both on PRMI and ALS-FPMI (elog #8250).

CDS:

    - Check out ASS and A2L working -JENNE (ALS done, ASS on going elog #8229)
    - Are all whitening filters for PDs toggling correctly? -JENNE, JAMIE (POX11 was OK, elog #8246)

PRMI locking:
    - Adjust I/Q rotation angles for error signals -JENNE, YUTA (coarsely done elog #8212)
    - Adjust filters -JENNE, YUTA (coarsely done elog #8212)
    - Coil balancing for BS (and ITMs/ETMs) -YUTA (done elog #8182)
    - Calculate sensing matrix for PRMI and convert them into physical units -JENNE, JAMIE
    - Measure sensing matrix for PRMI -JENNE, MANASA
    - Measure 55 MHz modulation depth -KOJI

PRC characterization in PRMI:

    - Measure PR2 loss from flipping -MANASA (on going elog #8063)
    - Measure mode matching ratio -JENNE, YUTA
    - Measure finesse, PR gain -JENNE, YUTA (done elog #8212)
    - Calibrate PRM and/or ITM oplevs -MANASA, YUTA (done elog #8221)
    - Measure g-factor by tilting PRM or ITMs -JAMIE, YUTA (coarsely done elog #8235, use other methods to check)
    - Simulate intra-cavity power dependance on PRM tilt -JAMIE (see elog #8235)
    - Calculate expected finesse, PR gain -JENNE
    - Mode match and align aux laser from POY -ANNALISA (on going elog #8257)

ALS:
    - Prepare for installation of new end tables on next vent -MANASA
    - Install green DC PDs and cameras on PSL table -JENNE, MANASA
    - Make ALS handing off to DARM/CARM LSC script -JENNE, YUTA
    - Demonstrate FPMI using ALS -JENNE, YUTA
    - Phase tracker characterization -YUTA, KOJI (bad whitening elog #8214)
    - better beatbox with whitening filters -JAMIE, KOJI

Others:
    - Update optical layout CAD after PR2 flipping -MANASA
    - IMC REFL demod phase rotation -EVAN, ANNALISA (done elog #8185)
    - Look into PMC drift -JENNE, MANASA
    - Measure RFAM contribution to error signals -YUTA
    - Look into TT2 drift -JENNE, MANASA

  8103   Tue Feb 19 02:23:40 2013 yutaBureaucracyGeneralaction items for PRFPMI

These are things need to be done for demonstrating PRFPMI using ALS.
All of these should be done before March 8!

CDS:
    - Fix c1iscex -JAMIE (done Feb 19: elog #8109)
    - Is ASS and A2L working? -JENNE
    - Are all whitening filters for PDs toggling correctly? -JENNE, JAMIE

PRMI locking:
    - Adjust I/Q rotation angles for error signals -JENNE, YUTA
    - Adjust filters -JENNE, YUTA
    - Coil balancing for BS (and ITMs/ETMs) -YUTA

PRC characterization in PRMI:

    - Measure PR2 loss from flipping -MANASA
    - Measure mode matching ratio -JENNE, YUTA
    - Measure finesse, PR gain -JENNE, YUTA
    - Calibrate PRM and/or ITM oplevs -MANASA, YUTA
    - Measure g-factor by tilting PRM or ITMs -JAMIE, YUTA
    - Calculate expected mode matching ratio and g-factor -JAMIE
    - Calculate expected finesse, PR gain -JENNE
    - Align aux laser into AS port? -ANNALISA?

ALS:
    - What's the end green situation? Optical layout changed? Laser temperature in CDS? -MANASA
    - What's the PSL green situation? Green trans cameras/PD? -JENNE, MANASA
    - Make ALS handing off to DARM/CARM LSC script -JENNE, YUTA
    - Demonstrate FPMI using ALS -JENNE, YUTA
    - Phase tracker characterization -YUTA, KOJI

PRFPMI:
    - Measure mode matching between PRC and arms -JENNE, YUTA
    - Measure PR gain -JENNE, YUTA
    - Calculate expected finesse, PR gain -JENNE

Others:
    - Update optical layout CAD after PR2 flipping -JAMIE, MANASA
    - AS55 situation? -YUTA
    - Look into PMC drift -JENNE, MANASA
    - Measure RFAM contribution to error signals -YUTA

 


Please fix, add or update if you notice anything.

  8163   Mon Feb 25 22:30:40 2013 JenneBureaucracyGeneralaction items for PRFPMI

 

 CDS:
    - Check out ASS and A2L working -JENNE
    - Are all whitening filters for PDs toggling correctly? -JENNE, JAMIE

PRMI locking:
    - Adjust I/Q rotation angles for error signals -JENNE, YUTA
    - Adjust filters -JENNE, YUTA
    - Coil balancing for BS (and ITMs/ETMs) -YUTA

PRC characterization in PRMI:

    - Measure PR2 loss from flipping -MANASA
    - Measure mode matching ratio -JENNE, YUTA
    - Measure finesse, PR gain -JENNE, YUTA
    - Calibrate PRM and/or ITM oplevs -MANASA, YUTA
    - Measure g-factor by tilting PRM or ITMs -JAMIE, YUTA
    - Calculate expected mode matching ratio and g-factor -JAMIE
    - Calculate expected finesse, PR gain -JENNE
    - Mode match and align aux laser into AS port -EVAN

ALS:
    - What's the end green situation? Optical layout changed? Laser temperature in CDS? -MANASA
    - What's the PSL green situation? Green trans cameras/PD? Design better layout -ANNALISA
    - Make ALS handing off to DARM/CARM LSC script -JENNE, YUTA
    - Demonstrate FPMI using ALS -JENNE, YUTA
    - Phase tracker characterization -YUTA, KOJI

PRFPMI:
    - Measure mode matching between PRC and arms -JENNE, YUTA
    - Measure PR gain -JENNE, YUTA
    - Calculate expected finesse, PR gain -JENNE

Others:
    - Update optical layout CAD after PR2 flipping -MANASA
    - IMC REFL demod phase rotation -EVAN, ANNALISA
    - Look into PMC drift -JENNE, MANASA
    - Measure RFAM contribution to error signals -YUTA

  12604   Mon Nov 7 19:49:44 2016 JohannesUpdateCDSacromag chassis hooked up to PSL

[Lydia, Johannes]

We're waiting on the last couple electrical components to arrive that are needed to complete the acromag chassis, but it is essentially operational. Right now it is connected to the PSL Mephisto's diagnostics port, for which only a single XT1221 A/D unit is needed. We assigned the IP address 192.168.113.121 to it. For the time being I'm running a tmux session on megatron (named "acromag") that grabs and broadcasts the epics channels, with Lydia's original channel definitions. Since the chassis is 4U tall, there's not really any place in the rack for it, so we might want to move it to the X-end before we start shuffling rack components around. Once we finalize its location we can proceed with adding the channels to the frames.

For the eventual gradual replacement of the slow machines, we need to put some thought into the connectors we want in the chassis. If we want to replicate the VME crate connectors we probably need to make our own PCB boards for them, as there don't seem to be panel-mount screw terminal blocks readily available for DIN 41612 connectors. Furthermore, if we want to add whitening/AA filters, the chassis may actually be large enough to accomodate them, and arranging things on the inside is quite flexible. There are a few things to be considered when moving forward, for example how many XT units we can practically fit in the chassis (space availability, heat generation, and power requirements) and thus how many channels/connectors we can support with each.

Steve: 1X3 has plenty of room

  12607   Tue Nov 8 17:51:09 2016 LydiaUpdateCDSacromag chassis hooked up to PSL

We set up the chassis in 1X7 today. Steve is ordering a longer 25 pin cable to reach. Until then the PSL diagnostic channels will not be usable.

  12632   Mon Nov 21 19:54:13 2016 JohannesUpdateCDSacromag chassis hooked up to PSL

[Lydia, Johannes]

We connected and powered up the Acromag chassis today. It lives in 1X4 and is powered by the Sorensen +20V power supply in 1X5 via the fuse rail on the side of 1X4. For this we had to branch off the 20V path to the dewhitening and anti-image filter crate of the c1:susaux driven SOS optics. After confirming that none of the daughter modules in the crate draw from the 20V line, we added a wire leading to a new fuse we added for this unit and ran a power cable from there.

The diagnostic connector of the PSL laser is now connected to the unit and a tmux session was created on megatron that interfaces with the chassis and broadcasts the EPICS channels. We need to watch out in the coming days for epics freezes/outages, as in the past these seemed to occur around the same times we were toying with the Acromags.

Quote:

We set up the chassis in 1X7 today. Steve is ordering a longer 25 pin cable to reach. Until then the PSL diagnostic channels will not be usable.

 

  13530   Thu Jan 11 09:57:17 2018 SteveUpdateDAQacromag at ETMX

Good going Johannes!

Quote:

This evening I transitioned the slow controls to c1auxex2.

  1. Disconnected satellite box
  2. Turned off c1auxex
  3. Disconnected DIN cables from backplace connectors
  4. Attached purple adapter boards
  5. Labeled DSub cables for use
  6. Connected DSub cables to adapter boards and chassis
  7. Initiated modbus IOC on c1auxex2

Gautam and I then proceeded to test basic functionality

  1. Pitch bias sliders move pitch, yaw moves yawyes.
  2. Coil enable and monitoring channels work yes
  3. Watchdog seems to work. yes We set the treshold for tripping low, excited the optic, watchdog didn't disappoint and triggered.
  4. All channels Initialize with "0" upon machine/server script restart. This means the watchdog happens to be OFF, which is good yes. It would be great if we could also initialize PIT and YAW to retain their value from before to avoid kicking the optic. This is not straightforward with EPICS records but there must be a way.
  5. We got the local damping going yes.
  6. There is some problem with the routing of the fast BIO channels through the new chassis - so the ANALOG de-whitening filter seems to be always engaged, despite our toggling the software BIO bits no. Something must be wrongly wired, as we confirmed by returning only the FAST BIO wiring to the pre-acromag state (but everything else is now controlled by acromag) and didn't have the problem anymore. Or some electrical connection is not made (I had to use gender changers on these connectors due to lack of proper cabling)
  7. The switches for the QPD gain stages did not work. no I suspect a wiring problem, since the switching of the coil enables did work.

Arms are locked, have been for ~1hour with no hickups. We will leave it like this overnight to observe, and debug further tomorrow.

 

  7659   Thu Nov 1 20:20:33 2012 Den, AyakaUpdateWienerFilteringacoustic noise in PMC

We've subtracted acoustic noise from PMC using 1 EM 172 microphone. We applied a 10 Hz high-pass filter to PMC length signal and 100,200,300:30,30 to whiten the signal.We used ~10 minutes of data at 2048 Hz as we did not see much coherence at higher frequencies.

We were able to subtract acoustic noise from PMC length in the frequency range 10-700 Hz. In the range 30-50 Hz error signal is less by a factor of 10 then target signal.

psd.pngcoh.png

  445   Thu Apr 24 23:27:48 2008 ranaUpdatePEMacoustic noise in MC_F
I looked at the coherence between the Microphone in the PSL (PEM-AS_MIC) and the MC_F channel.

We want to use a microphone to do Wiener/Adaptive noise cancellation on the MC and so we need to
have a coherence of more than ~0.1 in order for that to have any useful effect.

The attached plot shows the spectrum and coherence with and without the HEPA turned up. As you can
see, the HEPA noise is just barely noticeable in this microphone. Mad

We will need to get something with at least 20 dB more sensitivity.:P
  6671   Thu May 24 02:55:36 2012 DenUpdatePEMacoustic noise in MCL

Mic in the PSL showed that fluctuations in the MCL in the frequency range 10 - 100 Hz are due to acoustic noise. I've measured MCL, MCL / PSL mic coherence 2 times with interval 300 seconds.

Surprisingly, acoustic noise level did not change but MC sometimes is more sensitive to acoustic noise, sometimes less.

audio_noise.png

  6565   Wed Apr 25 00:20:01 2012 DenUpdatePEMacoustic noise at 40m

 Blue Bird Mic is suspended close to PMC now and outputs ~10 counts when pre-amp gain is 8 dB. This means that the mic outputs ~2.42 mV. Its sensitivity is 27 mV/Pa => acoustic noise is ~0.1 Pa or ~75 dB SPL.

If we buy Panasonic WM61A with their sensitivity -35 dB => they will output ~1.7 mV. We can amplify this signal without adding significant noise. For WM61A S/N ratio is given to be 62 dB. This is for some standard signal that is not specified. For Blue Bird mic it is specified according to IEC 651. So I assume SPL of the standard signal = 94 dB => noise level of WM61A is 32 dB (pretty bad compared to 7 dB-A of Blue Bird). But in our case for PSL S/N ratio is ~43 dB that is not too bad. PSL is noisy due to HEPA, acoustic noise level close to MC2 stack will be less. So we may want to consider Primo EM172/173 where the noise level is claimed to be 18 dB less. I think we should buy several WM61A and EM172.

  7650   Wed Oct 31 22:56:41 2012 DenUpdatePEMacoustic noise

Microphone preamp box had a low-pass filter at 2kHz, Ayaka changed it to 20 kHz by replacing 100pF capacitor with a 10pF.

We've measured frequency response of the box. Signal from the microphone was split into two. One path went to the box, while another was amplified by the gain 20 (and bandpass filter 1Hz - 300kHz) and sent to spectrum analyzer. Coherence and frequency response were measured using box output and amplified input. Low-pass filter in the box does not limit our sensitivity.

Acoustic noise significantly decreases at frequencies higher then 2kHz. So we need to modify the circuit by adding whitening filter.

pre_after_mic.png  freq_resp.png

I've plugged in PMC length channel into PEM board CH15 through and amplifier (gain=200) that is AC coupled to avoid ~2.5 DC V coming from PMC servo.  I measured coherence with microphone that was located ~30 cm higher. Measurements show contribution of acoustic noise to PMC length in the frequency range 20-50 Hz. In this range PMC length / MC length coherence is ~0.5.

Acoustic noise couples to PMC length in a non-stationary way. 5 minutes after the first measurement I already see much higher contribution. This was already discussed here. I've made C1:X02-MADC3_TP_CH15 a DQ channel at 64kHz. This a fast PMC length channel.

Next step will be to use several microphones located around PMC for acoustic noise cancellation.

DSC_4792.JPG    DSC_4793.JPG

  13186   Thu Aug 10 15:45:34 2017 SteveUpdateVACaccidental vent to 17 Torr

Finally we got the cold cathode gauge working. IFO pressure 7e-6 Torr-it, vacuum normal valve configuration with all 4 ion pump gate valves closed at ~ 9e-6 Torr.  The cryo pump was also pumped yesterday to remove the accumulated outgassing build up.

The accidental vent was my mistake; made when I was replacing the battery pack of the UPS. The installed pack measured 51 V without any load. The "replace battery" warning light did not go out after the batteries were replaced. 

I then mistakenly and repeatedly pushed the "test" button to reset this, but I did not wait long enough for the batterries to get fully charged. The test put the full load on the new batteries and their charging condition got worse. I made the mistake when trying to put the load from the battery to online and pushed "O" so the power was cut and the computer rebooted to the all off condition. On top of this, I disconnected the wrong V1 cable to close V1.  As the computer rebooted it's interlock closed V1 at 17 Torr.

Never hit O on the Vacuum UPS !

Note: the " all off " configuration should be all valves closed ! This should be fixed now.

In case of  emergency  you can close V1 with disconnecting it's actuating power as shown on Atm3 if you have peumatic pressure 60 PSI 

  10473   Mon Sep 8 16:23:25 2014 LarryHowToComputer Scripts / Programsaccessing 40m data remotely with python

 

Attached is an example script showing how to access 40m data remotely. The only two nonstandard python modules you need are the nds2 client module and astropy (used for time conversion). For mac users, both of these are available via macports (nds2-client and, e.g. py27-astropy). Otherwise, check out their websites:

https://www.lsc-group.phys.uwm.edu/daswg/projects/nds-client.html

https://github.com/astropy/astropy

 

Have fun!

 

 

  7407   Wed Sep 19 09:24:01 2012 SteveOmnistructureIOOaccess connector at athmoshere

Quote:

Quote:

We really need something better to replace the access connector when we're at air.  This tin foil tunnel crap is dumb.  We can't do any locking in the evening after we've put on the light doors.  We need something that we can put in place of the access connector that allows us access to the OMC and IOO tables, while still allowing IMC locking, and can be left in place at night.

 It is in the shop. It will be ready for the next vent. Koji's dream comes through.

 24" diameter clear acetate access connector is in place. The 0.01" thick plastic is wrapped around twice to insure air and bug tight barrier for the MC to lock overnight. The acetate transmission for 1064 nm is 90 % This was measured at 150 mW   2.5 mm beam size.

 

  7518   Wed Oct 10 10:55:56 2012 SteveOmnistructureIOOaccess connector at athmoshere

Quote:

Quote:

Quote:

We really need something better to replace the access connector when we're at air.  This tin foil tunnel crap is dumb.  We can't do any locking in the evening after we've put on the light doors.  We need something that we can put in place of the access connector that allows us access to the OMC and IOO tables, while still allowing IMC locking, and can be left in place at night.

 It is in the shop. It will be ready for the next vent. Koji's dream comes through.

 24" diameter clear acetate access connector is in place. The 0.01" thick plastic is wrapped around twice to insure air and bug tight barrier for the MC to lock overnight. The acetate transmission for 1064 nm is 90 % This was measured at 150 mW   2.5 mm beam size.

 

 Aluminum sheet as shown will replace the acetate. Side entries for your arms and "window" on the top will be covered with acetate using double- sided removable-no residue tape 3M 9425

  747   Mon Jul 28 12:02:32 2008 SharonUpdate accelerometers settings
Jenne, Sharon


We looked again at the channels of the accelerometers and there are some updates. Last time when we reported, we crossed the ADAP channels and the accelerometer. Now that there is a new MEDM screen, with which you can control which channels goes to which adaptive channels, this has no meaning...
Therefore, the channels that go with the noise source channels are:

PEM 15 MC1_X
PEM 16 MC1_Y
PEM 17 MC1_Z
PEM 18 MC2_X
PEM 19 MC2_Y
PEM 20 MC2_Z
PEM 21 SEIS

disregard the last post regarding these channels by Jenne, since I am changing the ADAP channels all the time...
  1613   Wed May 20 10:43:17 2009 steveOmnistructureEnvironmentaccelerometers sensitivity

Quote:

2009 May 18 03:39:36 UTC

Earthquake Details

Magnitude 5.0
Date-Time
  • Monday, May 18, 2009 at 03:39:36 UTC
  • Sunday, May 17, 2009 at 08:39:36 PM at epicenter
Location 33.940°N, 118.338°W
Depth 13.5 km (8.4 miles)
Region GREATER LOS ANGELES AREA, CALIFORNIA
Distances
  • 2 km (1 miles) E (91°) from Lennox, CA
  • 2 km (1 miles) SSE (159°) from Inglewood, CA
  • 3 km (2 miles) NNE (22°) from Hawthorne, CA
  • 7 km (4 miles) ENE (72°) from El Segundo, CA
  • 15 km (10 miles) SSW (213°) from Los Angeles Civic Center, CA
Location Uncertainty horizontal +/- 0.4 km (0.2 miles); depth +/- 0.9 km (0.6 miles)
Parameters Nph=139, Dmin=7 km, Rmss=0.42 sec, Gp= 40°,
M-type=local magnitude (ML), Version=C
Source
Event ID ci10410337

 Wilcoxon 731A seismic accelerometers and Guralp CMG-40T-old seismometer at magnitude 5 and 4 erthquakes

  11950   Tue Jan 26 15:07:47 2016 SteveUpdatePEMaccelerometers moved to ETMX

Objective:  measure the noise floor on the optical table and the floor so we can decide if the table needs better anchoring before swapping in

                   the larger optical table

The accelerometrs labeled as MC1 ( just north east  of IOO chamber floor ) and MC2 ( north east leg of MC2 table floor ) were moved:

MC1 to the floor at the north west leg of optical table.

MC2 is in the north east corner of the optical table

Atm2 was taken after table leg bolts were tighed at 40 ft/lb

The spectrum looks similar to ETMY     (Guralp for below 3 Hz )  except  the Z direction 

ETMY  .

  2119   Mon Oct 19 17:12:54 2009 jenneUpdatePEMaccelerometers and seismomters are all good.

Quote:

Some of these channels are not like the others.

 All of the PEM channels seem to be okay right now.  The accelerometers didn't turn out to have any differences in the traces when we put both XYZ triplets right next to each other, so we put them back where they belong.  Gur2 seismometer was showing a few problems, especially with Gur2_X, as Rana posted in elog 2079.  This was solved by tightening the cable screws which hold the Dsub end of the Guralp cable to the front panel of the Guralp box.  All is now well.

  7562   Tue Oct 16 21:57:47 2012 DenUpdatePEMaccelerometers

All accelerometers are now at the table behind 1X4, cables are near readout box.

  1696   Wed Jun 24 12:04:00 2009 ClaraUpdatePEMaccelerometer clarification

When I said "MC1/MC2 accelerometers," I meant the entire three-axis accelerometer set at each point.

  3551   Thu Sep 9 11:31:54 2010 steveUpdatePEMaccelerometer cable connection

I turned off/on the power to the accelerometers in order to re rout their connections. I found cable connector body-nut  #3 loose to Accelerometer 2X This connector should be checked for solid performance.

  940   Wed Sep 10 19:53:53 2008 AlbertoUpdateGeneralabs length experiment
Update of the last days work on the experiment to measure the absolute length of the cavities.

I'm trying to repeat the same measurement that Koji did on the Y arm, before switching to the X arm.

I switched to the PHD universal box for the PLL control between the main laser and the secondary laser. I found a good gain value for the servo and now I can set the frequency of the beat to any value as long as I do it slowly turning the LO frequency from the knob on the Marconi.

I laid down a 50m BNC cable from the Y end to near the BS chamber, where all the abs length equipment is. I matched the two laser beams changing the alignment of the injection steering mirror at the the dark port on the AP table. I then locked the Y arm cavity. When I first tried to do that, the locking script didn't work because the beam was off of the 'sweet spot' where Rob had set it on Monday. It turned out that aborting the script during one of its previous run, had changed the alignment of the PZT steering mirrors. So with Rob I brought them back near the positions as in the snapshot and then saved a new one with the latest values.

Eventually I could set the beat frequency to the FSR of the arm cavity and saw it in transmission at the ETMY.

Now I'm working on the LabView interface for the GPIB data acquisition board.
  656   Thu Jul 10 19:12:07 2008 AlbertoUpdateGeneralabs cavity length measurement experiment
Yesterday morning, when I started, I found the IFO beam on a different position and the beam spot at the AS port looked very deformed. The overlapping with the secondary beam was not good enough to observe the beats anymore. Restoring the alignments of the interferometers did not work because, as John found out later, some of the photodiodes had offsets and gain which made the restore script ineffective. After resetting the parameters, we had to align every mirror of the interferometers and save the configuration twice. The second times was because on the first time the alignment had been done with the illuminators on. To avoid that in the future, John wrote an alarm to warn about the status of the lights.

After that we fixed the IFO beam, I had to realign the optics in the table to match the secondary beam to the IFO beam. I got the two beam overlapping and, even though the NPRO spot looked distorted, I could observe again some signal of the beat. To do that it was also necessary to have all the interferometer mirrors aligned so that we had more power from the ifo beam although it also made the spot flash. Ideally, to avoid the flashing (which we would also impede the PLL to work) we should work with the interferometer locked. Since that doesn't seem actually possible, we should just keep one of the ITM aligned and improve the beam matching so that we can observe the beats even with less power.

Today I spent the day trying to improve the alignement of the optics to observe the beats with only the ITM aligned, resetting the alignment of both beams with the ireses, with the Farady and all the rest. It was a rather long and tiring process but I think I'm close to the target and maybe tomorrow.
  668   Mon Jul 14 19:15:43 2008 AlbertoUpdateGeneralabs cavity length measurement experiment
Lately I've been dealing with the alignment of the interferometer to have a good beam spot at the AS port. Today the alignment script kept failing because of computer problems (failure of the frame builder) and also because the IFO was probably too far from the range where the automatic alignment works.

An other problem I keep having with the alignment of the optics on the AP table is with multiple reflection beams of the NPRO beam at the Farady.
Although I believe that now the two beams are quite well aligned, I don't see any reflection of the secondary beam from the IFO anymore.

It's like the more I try to improve the alignment, the worse I get from the beam matching. I'll keep working on this.
  669   Mon Jul 14 21:34:10 2008 AlbertoUpdateGeneralabs cavity length measurement experiment

Quote:
Lately I've been dealing with the alignment of the interferometer to have a good beam spot at the AS port. Today the alignment script kept failing because of computer problems (failure of the frame builder) and also because the IFO was probably too far from the range where the automatic alignment works.

An other problem I keep having with the alignment of the optics on the AP table is with multiple reflection beams of the NPRO beam at the Farady.
Although I believe that now the two beams are quite well aligned, I don't see any reflection of the secondary beam from the IFO anymore.

It's like the more I try to improve the alignment, the worse I get from the beam matching. I'll keep working on this.


Realigning the OSA I also had to move a little bit the mirror that reflects the IFO beam of at the AS port in order to raise the beam height. This had the effect of changing the position of the AS spot on the camera and on the monitors.

Tonight with John, we made sure that the AS beam was still aligned to the PD.
  943   Thu Sep 11 23:28:35 2008 albertoUpdateGeneralabs cavity length experiment
The MC lost lock for some reason not related to either the FSS or the PMC I'm done with my measurement for tonight. I've shut the NPRO beam before leaving.
  944   Fri Sep 12 11:09:20 2008 AlbertoUpdateGeneralabs cavity length experiment
I'm leaving the lab for a couple of hours. I shut the NPRO. The interferometer is available to anyone.
  945   Sat Sep 13 23:13:01 2008 AlbertoUpdateGeneralabs cavity length experiment
The Y arm was locked all time today but, suddenly, this afternoon it lost lock and since then I've been unable to restore it. I tried unsuccessfully the Restore and the Align scripts several times, although the position of PZT steering mirrors were good (as in the snapshot). I tried things like unlocking/locking the MC, the FSS reference cavity, the PMC but it didn't work. Then I decided to switch to the X arm. Locking it was a piece of cake compare to Y. I'm going to start measuring the FSR of the X arm.
  5670   Sat Oct 15 16:01:26 2011 kiwamuUpdateIOOabout LOCKIN module

Quote from #5669

To make things faster, I think we can just make a LOCKIN which has 3 inputs: it would have one oscillator, but 6 mixers. Should be simple to make.

 I think the idea of having multiple inputs in a LOCKIN module is also good for the LSC sensing matrix measurement.

Because right now I am measuring the responses of multiple sensors one by one while exciting a particular DOF by one oscillator.

Moreover in the LSC case the number of sensors, which we have to measure, is enormous (e.g. REFL11I/Q, REFL33I/Q, REFL55I/Q, ... POY11I/Q,...) and indeed it has been a long-time measurement.

  9786   Mon Apr 7 15:26:32 2014 jamie, ericqUpdateCDSaborted attempt to update c1sus machine with second CPU

This morning we attempted to replace the c1sus front end machine with a spare that had been given a second CPU, and therefore 6 additional cores (for a total of 12).  The idea was to give c1sus more cores so that we could split up c1rfm into two separate models that would not be running on the hairy edge of their cycle time allocation.  Well, after struggling to get it working we eventually aborted and put the old machine back in.

The problem was that the c1sus model was running erratically, frequently jumping up to 100 usec of a 60 usec clock allocation.  We eventually tracked the problem down to the fact that the CPUs in the new machine are of an inferior and slower model, than what's in the old c1sus machine.  The CPU were running about 30% slower, which was enough to bump c1sus, which nominally runs at ~51 usec, over it's limit.

This is of course stupid, and I take the blame.  I skimped on the CPUs when I bought the spare machines in an attempt to keep the cost down, and didn't forgot that I had done that when we started discussing using one of the spares as a c1sus replacement.

I think we can salvage things, though, by just purchasing a better CPU, one that matches what's currently in c1sus.  I'll get Steve on it:

c1sus CPU: Intel(R) Xeon(R) CPU X5680 3.33GHz

In any event, the old c1sus is back in place, and everything is back as it was.

  7189   Wed Aug 15 10:40:16 2012 DenUpdateCDSaa filters

The lack of AA filter for MCL signal is RFM model strongly disturbed entering to OAF signal

aa.png

  15613   Mon Oct 5 14:01:41 2020 gautamUpdateElectronicsaLIGO demod boards stuffed and delivered

We received 20pcs of stuffed demodulator boards from Screaming Circuits today. Some caveats:

  1. The AP1053 amplifiers weren't stuffed. Note that this part is no longer in standard production, and lead time for a custom run is ~half a year. I recommend stuffing R2 and using a minicircuits amplifier upstream of this board. We have 6 pcs of AP1053 in hand so we can use those for the first AS WFS, but a second WFS will require some workaround.
  2. AD8306ARZ weren't sent to Screaming Circuits. This part is used for the LO and RF signal level detection/monitoring stage, and so aren't crucial to the demodulation operation. @Chub, did we order the correct part now? They are rather pricey so maybe we can just adapt the footprint using some adaptor board?
  3. DQS-10-100 hybrid 90 degree splitters were delivered to us after the lot was sent to Screaming Circuits. We have the pieces in hand, so we can just stuff them as necessary.

I removed 1 from the group to stuff some components that weren't sent to Screaming Circuits and test the functionality on the benchtop, the remaining have been stored in a plastic box for now as shown in Attachment #1. The box has been delivered to Chub who will stuff the remaining 19 boards once I've tested the one piece.

  11438   Thu Jul 23 03:09:05 2015 ericqUpdateLSCaLIGO demod board lives!

I'm a little mystified. Peeking inside the aLIGO demod board, I saw that the reason that two of the channels weren't working was that their power connectors weren't plugged in, so no real mystery there. 

I hooked up the board at the electronics bench, and found the noise to be completely well behaved, in contrast to the measurements I made when it was in the LSC rack. I've taken it back out to the LSC rack, and given it the X beatnote, and it seems to be performing pretty well. 


I switched between the aLIGO demod board and beatbox during the same lock / beat. The LSC board performs margnially better from 3-100 Hz. The high frequency noise comes from the green PDH loop (coherence is near one above a few hundred Hz), so we don't expect any difference there. 

To me, the beatbox noise looks like there is a broad feature that is roughly the same level as the real cavity motion in the 10-100 Hz range. So, I think we should use the aLIGO board afterall, presuming the noise doesn't shoot back up when I remount it in the rack...


The ALS noise is getting low enough where our normal approach of measuring ALS sensing noise by simply taking the PSD of the signal when the arm is PDH locked is not quite valid anymore, as it is sensing the real cavity fluctuations. Doing a frequency domain coherent subtration of the PSDs suggests a sensing noise RMS of ~150Hz for ALSX. 

When the X arm is locked on ALS, POX sees about 250Hz RMS out of loop noise, which isn't the greatest; however, I used to be happy with 500Hz. By eye, sweeping through IR resonance is smoother. The real test is to get the Y arm ALS running, and swing it through PRFPMI resonance...


Fair warning, the LSC rack area is not so tidy right now, the demod board is resting on a stool (but not in the way of walking down the arm). I'll clean this up tomorrow. 

  11468   Thu Jul 30 14:42:03 2015 ericqUpdateLSCaLIGO demod board lives!

ALS is not currently limited by the demod board or whitening electronics.

The noise budget in the green locking paper shows the main noise sources to be these two, plus the residual fluctuations of the green PDH loop. 

So, one next step is AUX PDH noise budget. 

However, I wonder how much of the low frequency noise can be explained by instability of the beat alignement on the PSL table, and how this might be quantified. 


Yesterday, I put together a few measurements to asses whether the new demod board has moved us in the right direction. Specifically I measured the output of the phase tracker in the following states, adjusting the phase tracker gain to maintain a ~2kHz UGH (but no boost on):

  • Whitening chassis inputs terminated. BEAT_I input channels were given a 3000 count offset to give the phase tracker something to work with. This is a typical beatnote amplitude with the new RF amplifiers. 
  • aLIGO LSC demod board driven with an SRS SD345 at 30MHz. (First with +3dBm into the splitter, which is about what it sees with the green beatnotes, then with +13dBm into the splitter, to give the board the +10dBm LO it expects)
  • Arms locked with POX, POY. AUX laser temperature servos on. Green beatnotes in the 20-40MHz range. 

Results: The beat frequency spectrum is above the measured demod board and whitening chassis/ADC noise at all frequencies. It's a little close at 10Hz. 

One nice feature is that the beat spectra are far more similar to each other than they used to be. RMS noise is in the 300-400Hz range, which isn't mindblowing, but not terrible. On the order of 50 pm for each arm. Most of this comes from below 10Hz. 

Another thing to note is that, when we switch in the 50m cables, we should win a fair bit of Hz/V gain and push down these noises futher. (We're currently using 30m cables.)


By looking at some coherences, we can attribute some of the noise when IR locked to both colors of PDH loops. 

Specifically, the coherence with the Green PDH error implicates the residual frequency noise of the AUX laser above a few hundred Hz, whereas the feature from 20-50Hz is probably real cavity motion, not ALS sensing noise. Some of the 1-3Hz noise is from real suspension/stack resonances too. 


If it turns out that we do want to push the demod board noise down further, we could think about increasing the RF amplification. Driving the board harder translates directly to better noise performance. The 60Hz harmonics aren't so exciting, but not the end of the world.


Data files are attached, if you're in to that sort of thing. 

  15817   Thu Feb 18 15:33:21 2021 gautamUpdateSUSaLIGO Sat Amp installed, powered and commissioned

The WFS servo was recommissioned. The matrix can be tuned a bit more, but for now, I've recovered the old performance and the alignment doesn't seem to be running away, so I defer further tuning for later. The old Satellite box was handed over to Yehonathan for his characterization of the "spare" OSEMs.

This finishes the recovery of the MC1 suspension, I am now satisfied that the local damping loops are performing satisfactorily, that the WFS servo is also stable, and that POX/POY locking is recovered. On MC1, we even have 4 actuatable face OSEMs and the PIT(YAW) bias adjust slider even moves the optic in PIT(YAW), what a luxury. 

I've SDFed all the changes, and have backup of the old realtime model and C1SUSAUX_MC1 database files if we want to go back for whatever reason. The changes required to make this suspension work are different from what will eventually be required for the BHD suspensions (because of the hybrid iLIGO/aLIGO electronics situation), so I will not burden the readers with the tedious details.

  15809   Tue Feb 16 14:56:44 2021 gautamUpdateSUSaLIGO Sat Amp installed, powered

[jordan, gautam]

  • Ran 60ft long cables from 1X4 to MC1/MC3 chamber flange, via overhead cable tray, and top of PSL enclosure for the last ~20ft. Note that it may be that the overhead cable trays cannot support the weight of the cables for 15 SOSs (total 30 shielded cables with 37 wires as twisted pairs) when we eventually add the optics for the BHD upgrade.
  • Installed aLIGO satellite amplifer in 1X4.
  • Tapped +/-20 V (which is the available voltage closest to the required +/-18V). For this, the Sorensens were powered down, and the actual taps were made from the fusable blocks powering the Trillium interface box. We made sure to leave an extra slot so that this kind of additional headache is not required for the next person doing such work.
  • Once installed, I plugged in the dummy suspension box and verified that the unit performs as expected. 
  • Some photos of the installation are here.

After this work, the IMC locked fine, the AS camera has the Michelson fringing, the fast CDS indicators are all green, and the seismometer BLRMS all look good - therefore, I claim no lasting damage was done as a direct result of today's work at 1X4. I will connect up the actual suspension at my leisure later today. Note that the MC1 glitches seem to have gone away, without me doing anything about it. Nevertheless, I think it's about time that we start testing the new hardware. 


Unrelated to this work: while I was testing some characteristics of the MC1 suspension (before we did any work in the VEA, you can see the timestamp in the ndscope), I noticed that the MC1 UL coil channel cannot actually be used to actuate on the optic. The coil driver Vmon channel demonstrates the appropriate response, which means that the problem is either with the Satellite box (it is just a feedthrough, so PCB trace damaged?) or with the OSEM itself (more likely IMO, will know more once I connect the new Satellite Amplifier up). I only show comparison for UL vs UR, but I checked that the other coils seem to be able to actuate the optic. This means we have been running for an indeterminate amount of time with only 3 face actuators on MC1, probably related to me having to do this work


Also unrelated to this work - while poking around at 1X5 rear, I noticed that the power connections to the existing Satellite Boxes are (understatedly) flaky, see connections to T1-T4 in Attachment #2..

  15814   Wed Feb 17 16:11:53 2021 gautamUpdateSUSaLIGO Sat Amp installed, powered

There is some non-trivial sign flipping in the sensors/coils in this new setup because it is a hybrid one with the old interfacing electronics (D000210, D010001) and the new Satellite Amplifier (D080276). So I haven't yet gotten the damping working. I am leaving the PSL shutter closed and will keep working on this today/tomorrow. I have made various changes to the c1mcs realtime model and the c1susaux database record where MC1 is concerned. I have backups of the old ones so we can always go back to that if we so desire.

In the meantime, the PSL shutter is closed and there is no light to the IFO.


Update 1700: I've implemented some basic damping and now the IMC is now locked. The WFS loop runs away when I enable it, probably some kind of weird interaction with the (as of now untuned) MC1 local damping loops. I will write up a more detailed report later.


Update 2300: Did the following:

  1. Re-calibrated the cts2um filter in all SENSOR filter banks to account for the increased transimpedance and LED drive current. I judged the overall scaling to be x0.25 but this can be calibrated against the bounce peak height for example (it lines up pretty well).
  2. Re-measured the input matrix - it was very different from what was loaded. I am measuring this again overnight for some consistency.
  3. Re-tuned the damping gains. Now the optic damps well, and the loops seem file to me, both via broadband noise injection TF and by step response metrics.
  4. Yet, the WFS servo cannot be enabled. The WFS signal is summed in before the output matrix so I don't know why this would have a different behavior compared to the local damping, or indeed, why this has to be changed. Will need some (WFS) sensing/actuation matrix measurements to know more.

Dropping this for tonight, I'll continue tomorrow. Meanwhile, the OSEM input matrix measurement is being repeated overnight. PSL shutter is closed.

  15818   Thu Feb 18 18:05:04 2021 gautamUpdateSUSaLIGO Sat Amp characterization

Before installation, I performed a bunch of tests on the aLIGO sat amp. All the measurements were made with the dummy suspension box substituting for an actual suspension. Here are the results.

Attachment #1: Transimpedance amplifier noises.

  • Measurement setup: J7 of the Satellite Amp goes to J9 on D1900068 front end (even though the connector is actually labelled "J3" on the box we have - maybe a versioning problem?). The outputs then go to a G=100 SR560 in AC coupled mode (the main purpose here was to block the large DC from the SR785, but I tacked on G=100 while I was at it).  
  • Top panel shows the raw measured voltages.
  • The bottom panel does a bunch of transformations:
    • Undoes the z:p = 3:30 Hz whitening on board the sat amp.
    • Undoes the G=100 gain of the SR560, and the AC coupling poles/zeros of SR560 and SR785.
    • Converts from voltage to current by dividing by the transimpedance gain, 242 kohms. 
  • Some model curves are shown for comparing to the measured spectra. It may be possible that we don't need to modify the nominal z:p = 0.4:10 Hz - I don't think the nominal seismic level will saturate the output even with the 0.4:10 Hz whitening, and it gives us even more clearance to the ADC noise (although we don't need it, we are gain limited at those frequencies, this is mostly a suggestion to reduce the workload).
  • The neon green curve is measured with the actual MC1 suspension plugged in, local damping enabled. It doesn't line up with the nosie floor of the bench tests, probably because the cts/um conversion factor could be off by some factor? Around 1 kHz, you can also see some broad peaks that are reminiscent of those seen in the MC_F spectrum after the c1psl Acromag upgrade. I hypothesize this is due to some poor grounding. Hopefully, once we get rid of the single-ended sending/receiving components in the suspension electronics chain, these will no longer be an issue.

Attachment #2: LED drive current source noises. I mainly wanted to check a claim by Rich in a meeting some time ago that the LED intensity fluctuations are dominated by inherent LED RIN, and not by RIN on the drive current. 

  • Measurement setup: a pair of pomona mini-grabbers was used to clip onto TP3. I found the voltage noise to be sufficiently high that no preamplification was required, and the DC level was <1V, so I just used the SR785 in AC coupled mode. 
  • The dummy suspension box was being driven while the measurement was being made (so the current source is loaded).
  • One channel (CH6) shows anomalously high nosie. I confirmed this was present even after the box was plugged in for ~1 day, so can't be due to any thermal / equilibriating transients.
  • I didn't check for consistency at the monitor testpoint, but that is exposed even with the MC1 suspension plugged in, so we can readily check. Anyways, from the corresponding photodiode curve in Attachment #1, it would seem that this excess RIN in the drive current has no measurable effect on the intensity fluctuations of the LED (the DC value of the paired PD is consistent with the others, ~6V DC). I must say I am surprised by this conclusion. I also checked for coherence between TP3 and the PD output using the SR785, and found none. 🤔 
  • Nevertheless, for the remaining channels, it is clear that the drive current is not shot noise limited for <1kHz. This isn't great. One possible reason is that the collector voltage to Q1 is unregulated (my modeling suggests only ~10dB rejection of collector voltage fluctuations at the output). I believe the current source designed by Luis for A+ makes some of these improvements and so maybe Rich was referring to that design, and not the aLIGO Satellite Amplifier flavor we are using. Anyways, this is just academic I think, the performance is the unit is fine for our purposes.

I will update with the MC1 suspension characterization (loop TFs, step responses etc) later.

  15819   Thu Feb 18 20:20:25 2021 KojiUpdateSUSaLIGO Sat Amp characterization

Yeah, it's really inconsistent. You had 35mA LED drive and the current noise of the noisy channel was 5e-7 A/rtHz at 1Hz. The RIN is 1.4e-5 /rtHz. The approx. received photocurrent is 30uA as we discussed today and this should make the noise around 4e-10 A/rtHz at 1Hz. However, the readout noise level is better than this level. (well below 1e-10 A/rtHz)

BTW, the IMC seemed continuously locked for 5 hours. Good sign.

  9089   Fri Aug 30 01:01:28 2013 rana, nicSummaryComputer Scripts / ProgramsaLIGO Noise Budget code installed and running

Chris Wipf has been developing a new Noise Budget code that allows us to use our existing Simulink models to handle all of the noise transfer functions. This is mainly by being clever about avoiding the numerical pitfalls that we encounter when doing linearization of Simulink models (e.g. linmod or linmod2).

Screen_Shot_2013-08-30_at_1.00.02_AM.png

In this model, the optical plant is done with analytic TFs using the formulae from the Sigg Frequency Response doc. The big Orange block has just the DAC and some simple pendulum TFs. The upper section contains the simulated digital system: input matrix, digital filter TFs, and output matrix. The digital filters are just based on my memory of iLIGO. The CARM path is made to be fast to approximate the high gain of the Common Mode servo. Without this high gain the PRC optical plant is unstable due to the right half plane zeros. This simple model is used just so that we could see the NB work on a multi-loop system. For the next steps of getting it to work for the 40m, we will use the Optickle TFs instead of analytic functions and also load the digital filters directly from the FOTON files. For the LLO DRMI, we'll add some simplified version of the SUS Simulink models for triples and quads.

 

Yesterday, Nic and I took my old iLIGO IFOmodel.mdl Simulink model and added the new NB hooks that allowed us to use the new code. The screenshot below is from a run of this code:

1) Figure 1 shows the DARM Noise budget. So far we have included shot noise in DARM, CARM, MICH, & PRC. Radiation pressure noise on the ITMs and ETMs. Coating thermal noise on all mirrors.

2) Figure 2 shows the breakdown of how each of the shot noises at each port couple to the DARM readout. The RED trace is the AS port DC readout shot noise. The GREEN trace is the MICH shot noise feeding through the MICH loop and being mostly cancelled by the scalar MICHdamp feedforward path.

3) Figure 3 shows that we've set the coating thermal noise to be equal on all 4 TMs.

4) Figure 78754 is a set of Bode plots of the open loop gains of the 4 LSC loops (inferred from the closed loop TF). Also plotted is the residual MICH2DARM TF (with the MICHdamp cancellation path ON).

5) Figure 9911123 are the step responses of the LSC loops: step inserted at the error point and response measured just after the excitation point.

The editor window on the left shows how simple the NB code is to use once the Simulink model has had all the hooks added to it.

  13720   Fri Mar 30 03:23:50 2018 KojiUpdateGeneralaLIGO EOM work

I have been working on the aux beat setup on the PSL table between 9PM-3AM.

This work involved:

- Turning off the main marconi
- Turning off the freq generation unit (incl IMC modulation)
- Closing the PSL shutter

After the work, these were reverted and the IMC and both arms have been locked.

  13650   Thu Feb 22 16:11:14 2018 KojiUpdateGeneralaLIGO EOM crystal replacement

aLIGO EOM crystal replacement

  • The entire operation has been performed at the south flow bench @40m.
  • We knew that the original crystal in the aLIGO EOM we are testing has some problem. This was replaced with a spare RTP crystal.
  • Once the housing was removed, it was obvious that the crystal has a crack (Attachment 1).
    It seemed that it was produced by either a mechanical stress or a thermally induced stress (e.g. soldering).
  • I wanted to make sure the new crystal is properly aligned interms of the crystal axis.
    The original crystal has the pencil marking at the top saying "Z" "12". The new (spare) crystal has "Z" and "11".
    So the new crystal was aligned in the same way as the original one. (Attachment 2)
  • I took an opportunity to measure the distribution of the electrode lengths (Attachment 3). The lengths are 14, 5, and 14mm, respectively.
  4649   Fri May 6 01:27:12 2011 KojiSummaryGeneralaLIGO BBPD / Green PD investigation

Minicircuits ERA-5SM was used for the RF amp of the BBPD. This amp is promising as a replacement of Teledyne Cougar AP389
as ERA-5SM gave us the best performance so far among the BBPDs I have ever tested for the aLIGO BBPD/Green.

The -3dB bandwidth of ~200MHz and the noise floor at the shotnoise level of 0.7mA DC current were obtained.


1. Introduction

The aLIGO BBPD candidate (LIGO Document D1002969-v7) employs Teledyne Cougar AP389 as an RF amplifier.
This PD design utilizes the 50Ohm termination of the RF amp as a transimpedance resistance at RF freq.

However, it turned out that the bandwidth of the transimpedance gets rather low when we use AP389, as seen in the attachment2.
The amplifier itself is broadband upto 250MHz (the transfer function was confirmed with 50Ohm source).
The reason is not understood but AP389 seems dislike current source. Rich suggested use of S-parameter measurement
to construct better model of the curcuit.

On the other hand, the RF amplifiers from Minicircuits (coaxial type like ZFL-1000LN+), in general, exhibit better compatibility with PDs.
If you open the amplifier case, you find ERA or MAR type monolithic amplifiers are used.

So the question is if we can replace AP389 by any of ERA or MAR.

2. Requirement for the RF amp

- The large gain of the RF amp is preffered as far as the output does not get saturated.

- The amplifier should be low noise so that we can detect shot noise (~1mA).

- The freq range of the useful signal is from 9MHz to 160MHz.

The advanced LIGO BBPD is supposed to be able to receive 50mW of IR or 15mW of 532nm. This approximately corresponds to
5mA of DC photocurrent if we assume FFD-100 for the photodiode. At the best (or worst) case, this 5mA has 100% intensity modulation.
If this current is converted to the votage through the 50Ohm input termination of the RF amp, we receive -2dBm of RF signal at maximum.

This gives us a dilemma. if the amp is low noise but the maximum output power is small, we can not put large amount of light
on the PD. If the amp has a high max output power (and a high gain), but the amp is not low noise, the PD has narrow power range
where we can observe the shotnoise above the electronics noise.

What we need is powerful, high gain, and low noise RF amplifier!

Teledyne Cougar AP389 was almost an ideal candidate before it shows unideal behavior with the PD.
Among Minicircuits ERA and MAR series, ERA-5 (or ERA-5SM) is the most compatible amplifier.


AP389 ERA-5
Freq Range 10-250MHz DC-4GHz
Gain >24.5dB 20dBtyp
Output power (1dB compression)
23dBm 18.4dBm
IP3 36dBm 33dBm
Noise Figure <3.3dB 3.5dB

Considering the difference of the gain, they are quite similar for our purpose. Both can handle upto -2dBm,
which is just the right amount for the possible maximum power we get from the 5mA of photocurrent.

3. Test circuit with ERA-5SM

A test circuit has been built (p.1 attachment #1) on a single sided prototype board. 

First, the transfer function was measured with FFD-100. With the bias 100V (max) the -3dB bandwidth of ~200MHz was observed.
This decreases down to 75MHz if the bias is 25V, which is the voltage supplied by the aLIGO BBPD circuit. The transimpedance
at the plateau was ~400Ohm.

Next, S3399 was tested with the circuit. With the bias 25V and 30V (max) the -3dB bandwidth of ~200MHz was obtained although
the responsivity of S3399 (i.e. A/W) at 1064nm is about factor of 2 smaller than that of FFD-100.

The noise levels were measured. There are many sprious peaks (possibly by unideal hand made board and insufficient power supply bypassing?).
Othewise, the floor level shows 0.7mA shotnoise level.

ELOG V3.1.3-