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ID Date Author Type Category Subjectup
  6466   Thu Mar 29 18:42:11 2012 keikoUpdateLSCPOP22/POP110 amplifires

Adding two amplifiers on POP22/110, I checked the signals going to the dmod board of 22 and 110.

The signal flows: Photodetector of POP --> Amp1 --> Amp2 --> RF splotter --> bandpass filter for 22MHz / 110MHz --> 22MHz / 110MHz demod board.

 

 

 

 Here is the picture of RF spectrum just after the bandpass filter of 22MHz going to the 22MHz demod board. The signal peak at 22MHz is about -40dBm. There is a structure slightly lower than 22MHz.

P3290004.JPG

The below is the RF spectrum for 110MHz branch. The peak at 110MHz is about -15dBm. The peak on the left of 110MHz is 66MHz peak.

P3290005.JPG

 

Quote:

Yesterday I and Kiwamu connected two amplifiers (mini-circuit, ZFL-1000LNB+) for POP22/110. Dataviewer can see some signals. I'll test the signal levels and freq components before the rack just in case. [Kiwamu, Keiko]

 

  4783   Fri Jun 3 14:27:32 2011 KojiUpdateElectronicsPOP55 test results

The full characterization of POP55 is found in the PDF.

Resonance at 54.49MHz
Q of 2.5, transimpedance 241Ohm
shotnoise intercept current = 4.2mA (i.e. current noise of 37pA/rtHz)

Notch at 11.23MHz
Q of 2.4, transimpedance 6.2 Ohm

Notch at 110.80MHz
Q of 53.8, transimpedance 13.03 Ohm

 

Attachment 1: POP55_test.pdf
POP55_test.pdf POP55_test.pdf POP55_test.pdf POP55_test.pdf
  15029   Fri Nov 15 12:08:04 2019 gautamUpdateLSCPOPDC whitening board

The DC port of the Bias-Tee is routed to (a modified version of) the iLIGO whitening board. This has the well-known problem of the protection diodes of the LT1125 quad-op-amp lowering the (ideally infinite) input impedance of the first gain stage (+24 dB). To be sure as to how much signal we can put into this port (in anticipation of trying some variable finesse PRFPMI locking but also for general book-keeping), I tested the usable input range by driving a triangle wave at ~3 Hz and changing the amplitude of the signal until we observed saturation. We found that we could drive a 10 Vpp signal at which point there was evidence of some clipping (it was asymmetric, the top end of the signal was getting clipped at +14,000 cts while the bottom end still looked like a triangle wave at -16,000 counts). Anyway we probably don't want to exceed +/- 10,000 counts on this channel. This is consistent with Hartmut's statement of having +/- 4V of usable range (although the counts he mentions are twice what I saw yesterday).

Other discussion points between Rana, Koji and Gautam:

  1. Conside putting an in-vacuum (Silicon ?) QPD for the PRC angular motion sensing
    • In-vacuum will yield lower acoustic noise coupling
    • Bring the photocurrent out and do the transimpedance amplification in air 
    • Use a large area QPD so as to be more tolerant to alignment drifts without having to introduce picomotors (but how much does the POP spot actually drift and is this feasible?)
  2. Is there some better telescope configuration for the existing in-air QPD?
    • What is the correct Gouy-phase for this to be able to best sense the PRC cavity axis motion?
  16817   Thu Apr 28 11:53:10 2022 AnchalSummaryBHDPOP_SM4 and POP_SM5 Assembly

POP_SM4

I tried out this stack today and found some change of plans.

  • The attachment in elog 40m/16640 says to use 1/4-20 silver coated non-vented screws for joining BA2V to PLS-T238, however PLS-T238's bottom hole is a blind hole and is not vented. So we actually required <1 in long silver plated vented 1/4-20 cap screw for this purpose. Jordan and I were only able to find the correct length silver plated screw but it is not vented. So we decided to make a venting hole on the post from the side.
  • I had to use a 0.14" spacer as washer between PLS-T238 and BA1V. The 1" post shim that Koji got for this purpose had too small a hole in the center to let the 8-32 screw pass (I know, weird). but I think we had 3 spare 0.14" ad we bought 10 when we required 7, so we should be good.
  • The attachment in elog 40m/16640 also says to use 8-32 silver coated vented setscrew for joining TR-1.5 to LMR1V mount. I found one vented silver coated set screw nearby in the clean room but it turned out to be too long. Worse, I overtightened the setscrew when trying this connection which damaged the inner threads of one of the LMR1V. So we need to buy one more LMR1V (maybe an additional spare too) for future installation of OMC1R1/OMC2R1.
    • Then Jordan and I searched for a smaller silver coated and vented 8-32 setscrew but didn't find any. Jordan also noted that LMR1V is an aluminium mount and we should not use silver coated setscrew with it. Since the TR-1.5 mount is ok to be sacrificed if a cold weld happens, we'll just use an uncoated SS 8-32 setscrew to join TR-1.5 and LMR1V. We could not such vented setscrews, but we have plenty of non-vented once. So Jordan is going to make a venthole in TR1.5 top end as well. LMR1V already has a vent hole on its side.

tl,dr; Jordan is preparing PLS-T238 and TR-1.5 with venting holes and C&B and they would be ready by tomorrow. I have collected all other parts for assembly, still looking for the mirror but I know other lab members know where it is, so no big issue there.


POP_SM5

The assemly of this mirror is complete. A slight change here as well, we were supposed to use the former POYM1 (Y1-2037-0) mirror for POP_SM5 but I could not find it. It was stored on the right most edge of the table (see 40m/16450), but it is not there anymore. I found another undocumented mirror on the flow bench on the left edge marked (2010 July: Y1-LW1-2037-UV-0-AR) which means this mirror has a wedge of 1 degree and an AR coating as well. We do not need or care about the wedge or AR coating, so we can use this mirror for POP_SM5. Please let me know if someone was saving this mirror for some other purpose.


I'll finish assembly of POP_SM4 tomorrow and install them in ITMX chamber and resurrect POP path.

Quote:

Here is more detail of the POP_SM4 mount assembly.

It's a combination of BA2V + PLS-T238 + BA1V + TR-1.5 + LMR1V + Mirror: CM254-750-E03
Between BA1V and PLS-T238, we have to do a washer action to fix the post (8-32) with a 1/4-20 slot. Maybe we can use a 1" post shim from thorlabs/newport.
Otherwise, we should be able to fasten the other joints with silver-plated screws we already have/ordered.

I think TR-1.5 (and a shim) has not been given to Jordan for C&B. I'll take a look at these.

 

  1963   Tue Sep 1 13:52:06 2009 steveConfigurationGeneralPOX rfpd is back & needs alignment

Quote:

I removed POX rfpd to see how it is mounted on its base. It is here on the work bench just in case someone wants to use it the IFO over the week end.

 I put POX back to it's place with markers. The pd was removed from it's base so it is for sure misaligned.

  1961   Fri Aug 28 15:30:15 2009 steveConfigurationGeneralPOX rfpd removed

I removed POX rfpd to see how it is mounted on its base. It is here on the work bench just in case someone wants to use it the IFO over the week end.

  1966   Thu Sep 3 23:41:32 2009 AlbertoConfigurationLSCPOX (PD3) aligned

Today I aligned the beam to PD3 (POX) since Steve had moved it.

The DC power read 1.3mV when the beam was on the PD.

  15049   Tue Nov 26 17:07:41 2019 gautamUpdateLSCPOX / POY calibration

Summary:

Since we are using the POX and POY photodiodes as out-of-loop sensors for measuring the ALS noise, I decided to double-check their calibrations. I determined the following numbers (for the single arm lock):

POX_I [with 30dB whitening gain]: (8 +/- 1)e-13 m/ct

POY_I [with 18dB whitening gain]: (0.9 +/- 0.1)e-13 m/ct

With this calibration, I measured the in-loop spectra of the XARM and YARM error-points when they are locked - they line up well, see Attachment #1. Note that these numbers are close to what we determined some time ago using the same method (I drove the ITMs then, but yesterday I drove the ETMs, so maybe the more accurate measure of uncertainty is the difference between the two measurements).

Attachment #2 shows the out-of-loop spectra sensed by these photodiodes with this calibration applied, when the arms are under control using ALS beat frequencies as the error signals, and controlled in the CARM/DARM basis. Need to think about why there is such a difference between the two signals.

Methodology:

The procedure used was the same as that outlined here.

  • I started by calibrating the AS55_Q output with the free-swinging Michelson.
  • Next, I lock the Michelson and calibrate the BS and ITM actuators using the newly calibrated AS55_Q.
  • Next, I calibrate the ETM actuator gains by measuring the ratio of response in POX/POY of driving the (unknown) ETMs and the (known) ITMs.
  • Finally, I calibrate the POX/POY photodiodes by driving the ETMs by a known amount of meters (at ~310 Hz where the loop gain is negligible because of the sensing matrix measurement notches).

Summary of DC actuator gains:

Optic Series resistance [ohms] x3 Analog gain? x3 Digital gain? DC gain [nm/ct]
BS 100 No Yes 9.48 +/- 0.01
ITMX 400 No Yes 2.42 +/- 0.01
ITMY 400 No Yes 2.41 +/- 0.01
ETMX 2.2k Yes No 1.23 +/- 0.02
ETMY 400 Yes No 6.62 +/- 0.12

The quoted values of the DC gain are for counts seen at the output of the LSC filter bank. I've attempted to show that once we account for the different series resistance and some extra gains between the output of the LSC filter bank and the actual coil, things are fairly consistent.

Some remarks:

  • I do not understand why we need an extra 12dB of whitening gain on the POX channel to get similar PDH fringe height as the POY channel. The light level on these photodiodes is the same, and the RF transimpedances at 11 MHz are also close according to the wiki (3kohm for POX, 2kohm for POY).
  • At night-time, the ALS noise did indeed get reduced compared to what I measured earlier in the evening.
  • Even assuming 50% error in the calibration factors, it's hard to explain the swing of TRX/TRY when the CARM offset is brought to zero.
  • The increase in (admittedly in-loop) CARM noise as the offset is reduced still seems to me to be correlated with the buildup of IR power in the arm cavities.
Attachment 1: POX_POY_sensorNoise.pdf
POX_POY_sensorNoise.pdf
Attachment 2: ALSnoise_20191125.pdf
ALSnoise_20191125.pdf
  15050   Tue Nov 26 18:16:08 2019 ranaUpdateLSCPOX / POY calibration

...maybe the opto-mechanical CARM plant is changing as a function of the CARM offset...

Quote:

Even assuming 50% error in the calibration factors, it's hard to explain the swing of TRX/TRY when the CARM offset is brought to zero.

  • The increase in (admittedly in-loop) CARM noise as the offset is reduced still seems to me to be correlated with the buildup of IR power in the arm cavities.
  15123   Wed Jan 15 10:04:19 2020 gautamSummaryGeneralPOX / POY locking restored

Single arm locking using POX and POY has been restored. After running the dither alignment servos, the TRX/TRY levels are ~0.7. This is consistent with the IMC transmission being ~11000 counts with the AOM 1st order diffracted beam (c.f. 15000 counts with the undiffracted beam).

Quote:

Tomorrow, I'll check the single-arm locking and the ALS system.

Attachment 1: singleArms.png
singleArms.png
  16799   Thu Apr 21 18:18:42 2022 yehonathanUpdateBHDPOX Alignment

{Yehonathan, Paco}

BS, ITMX and ETMX were aligned to get flashing in the X arm.

I aligned the POX beam on the ITMX table using a mixture of the old POP and POX optics. The beam was stirred to the POX11 RFPD. We measure the DC power using a scope but we see nothing. We went and saw that the POX11 cable was not connected to RF rack so we connected it along with some other RFPD cables.

We return but there is still no DC. We ndscope C1:LSC-POX11_I_ERR_DQ C1:LSC-POX11_Q_ERR_DQ and maximize the signal (attachment). The readout is very weak though. It should be as strong as POY which we already observed to have good SNR.

We also noticed that the one of the beam dumps for the POX RFPD is not glued and easily falls down.

Attachment 1: POX11_alignment.png
POX11_alignment.png
  16824   Mon May 2 17:51:30 2022 AnchalUpdateBHDPOX Beam aligned on RFPD, YARM locked

[Paco, Anchal]

We found that one of the Y1-1037-45P marked mirror that we used was actually curved. So we removed it and used a different Y1-1037-45P mirror, adjusted the position of the lens and got the beam to land on POX11 RFPD successfully.

Then in control room, we maximized the POX11_I_ERR PDH signal amplitude by changing C1:LSC-POX11_PHASE_R to 42.95 from -67.7. We kept the C1:LSC-POX11_PHASE_D same at 90. We were getting +/- 200 PDH signal on POX_I_ERR.

Then in our attempt to lock the XARM, when we ran the "Restore XARM (POX)" script, YARM locked!

We are not sure why the YARM locked, we might have gotten lucky today. So we ran ASS on YARM and got the transmission (TRY_OUT) stable at 1. The lock is very robust and retrievable.

Coming back to XARM, we realized that the transmission photodiode used for XARM was the low-gain QPD instead of the thorlabs high gain photodiode. The high-gain photodiode was outputing large negative counts for some reason. We went to the Xend to investigate and found that the high gain photodiode was disconnected for some reason. Does anyone know/remember why we disconnected this photodiode?

We connected the photodiode back and it seems to work normally. We changed the photodiode selection back to high gain photodiode for TRX and on 40 dB attenuation, we see flashing between 1.4 to 1.6. However, we were unable to lock the XARM. We tried changing the gain of the loop, played a little bit with the trigger levels etc but couldn't get it to lock. Next shift team, please try to lock XARM.

Quote:

[Paco, Anchal, Yuta]

We opened the BSC and ITMX chamber in the morning (Friday) to investigate POX11 beam clipping. We immediately found that the POX11 beam was clipping by the recently installed cable posts, so luckily no major realingment had to be done after reinstalling the cable post in a better location.


Because we had the BSC open, we decided to steer the AS1 mirror to align the AS path from ITMY all the way to the vertex chamber.  Relatively small AS1 offsets (of ~ 2000 counts each) were added on PIT / YAW to center the beam on ASL (there is slight clipping along PIT, potentially because of the AS2 aperture. We then opened the vertex chamber and located the AS beam with relative ease. We decided to work on this chamber, since major changes propagate heavily downstream (simply changing the IMC pointing).

Anchal removed old optics from the vertex chamber and we installed the steering pair of mirrors for AS path. This changed the balance of the vertex table by a lot. By using the MC REFL camera beam spot we managed to coarsely balance the counterweights and recover the nominal IMC injection pointing. Simply reenabling the IMC autolocker gave us high transmission (~ 970 counts out of the typical 1200 these days).

The final IMC alignment was done by Anchal with delicate PIT motion on the input injection IMC miror to maximize the transmission (to our satisfaction, Anchal's motion was fine enough to keep the IMC locked). The end result was quite satisfying, as we recovered ~ 1200 counts of MC transmission.

Finally, we looked at the arm cavity transmission to see if we were lucky enough to see flashing. After not seeing it, we adjusted TT1 / TT2 to correct for any MMTT1 pitch adjustment needed after the vertex table rebalancing. Suprisingly, we didn't take too long and recovered the nominal arm cavity pointing after a little adjustment. We stopped here, but now the vertex table layout is final, and AS beam still needs to be aligned to the vertex in-air table.

 

  16818   Thu Apr 28 17:45:53 2022 AnchalUpdateBHDPOX Beam issues

[Anchal, Paco]

We investigated the low power issue with POX11 photodiode.

  • We used a power meter to confirm that above 12 uW of power is reaching the ITMX oplev table.
  • But the power reaching the photodiode was only 3 uW, because the 2 steering mirrors used were discarding half of the light. These mirrors were taken from former POP setup and are probably BS or meant for different incidence angle/polarization.
  • We used flashlight to test that the photodiode gives a response, so it is not dead.
  • We also put in a db15 breakout board in line to the PD and confirmed that power input is correct, temperature is nominal, enable is ON, and DC out is responsive to flashlight.
  • So we decided to redo the path with Y1-45P 1inch mirrors. I found two such mirrors in the lab.
  • When setting up the path again, I realized that the beam shape is not even. I took a photo of the beam on the card (see attachment 1) and indeed the POX beam that is coming to the table is half clipped.
  • So tomorrow, we'll open the chamber and find out where this is happening. For now, I've setup a nominal path to the POX11 photodiode, but we'll tune it after we get a clear POX beam on the table.
Attachment 1: PXL_20220429_002703686.jpg
PXL_20220429_002703686.jpg
  16821   Sat Apr 30 13:29:33 2022 PacoUpdateBHDPOX Beam issues --- fixed, ASL alignment on vertex chamber

[Paco, Anchal, Yuta]

We opened the BSC and ITMX chamber in the morning (Friday) to investigate POX11 beam clipping. We immediately found that the POX11 beam was clipping by the recently installed cable posts, so luckily no major realingment had to be done after reinstalling the cable post in a better location.


Because we had the BSC open, we decided to steer the AS1 mirror to align the AS path from ITMY all the way to the vertex chamber.  Relatively small AS1 offsets (of ~ 2000 counts each) were added on PIT / YAW to center the beam on ASL (there is slight clipping along PIT, potentially because of the AS2 aperture. We then opened the vertex chamber and located the AS beam with relative ease. We decided to work on this chamber, since major changes propagate heavily downstream (simply changing the IMC pointing).

Anchal removed old optics from the vertex chamber and we installed the steering pair of mirrors for AS path. This changed the balance of the vertex table by a lot. By using the MC REFL camera beam spot we managed to coarsely balance the counterweights and recover the nominal IMC injection pointing. Simply reenabling the IMC autolocker gave us high transmission (~ 970 counts out of the typical 1200 these days).

The final IMC alignment was done by Anchal with delicate PIT motion on the input injection IMC miror to maximize the transmission (to our satisfaction, Anchal's motion was fine enough to keep the IMC locked). The end result was quite satisfying, as we recovered ~ 1200 counts of MC transmission.

Finally, we looked at the arm cavity transmission to see if we were lucky enough to see flashing. After not seeing it, we adjusted TT1 / TT2 to correct for any MMTT1 pitch adjustment needed after the vertex table rebalancing. Suprisingly, we didn't take too long and recovered the nominal arm cavity pointing after a little adjustment. We stopped here, but now the vertex table layout is final, and AS beam still needs to be aligned to the vertex in-air table.

  3971   Tue Nov 23 01:27:33 2010 KevinUpdateElectronicsPOX Characterizations

I measured the RF transimpedance of the POX photodiode by measuring the optical transfer function with the AM laser and by measuring the shot noise with a light bulb. The plots of these measurements are at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX.

I measured the noise of the photodiode at 11 MHz for different light intensities using an Agilent 4395a. The noise of a 50 ohm resistor as measured by this spectrum analyzer is 10.6 nV/rtHz. I fit this noise data to the shot noise formula to find the RF transimpedance at 11 MHz to be (2.42 ± 0.08) kΩ. The RF transimpedance at 11 MHz as measured by the transfer function is 6.4 kΩ.

  14915   Mon Sep 30 14:16:43 2019 gautamUpdateLSCPOX PD checkout - solved

I confirmed that there is light incident on the POX photodiode. So the problem must lie downstream in the demod / whitening / AA electronics. With the PRM aligned (i.e. PRFPMI config with all DoFs uncontrolled), I could see the flashing beam on an IR card. I could also see the spikes in DC power incident on the photodiode using the "DC Monitor" port on the photodiode head and an oscilloscope.

Update 245 pm: I confirmed that I could see a 11 MHz sine wave by connecting the POX11 RFPD output cable at the 1Y2 end to an oscilloscope. The amplitude of this signal was also changing, corresponding to the cavity fringing in and out of resonance. I couldn't, however, see any signal on the RFPDmon port, or the I/Q demodulated output ports. So as of now, the culprit seems to be something on the Demod board. Further investigations underway...

Update 315pm: I did the following checks:

  1. Checked the LO signal level into a 50ohm input scope - it was ~720 mVpp, which was compatible with the LO level into the POY Demod board, so the LO signal level couldn't be to blame.
  2. Connected an RF funcgen to the PD input of the demod board. Drove it at 11.066210 MHz, 50 mVpp, and saw a signal 400 cts-pp in the CDS system - so the demod + digitizaiton electronics also seemed fine.
  3. #2, coupled with the fact I could see no signal at the RF-mon port of the demod board (even though there was a signal visible at the cable coming to 1Y2) suggested that the cable routing the POX11 PD output from the Heliax-breakout in 1Y2 to the demod board was busted - indeed this was the case!
  4. Koji replaced the cable without changing its length, and now the XARM locks readily 👏 . I ran ASS and got TRX ~ 0.95. See Attachment #1
Quote:

Look for the POX beam with an IR viewer.

  4167   Wed Jan 19 04:25:54 2011 KevinUpdateElectronicsPOX Transfer Functions

I redid the optical POX transfer functions and updated the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX.

I measured each transfer function several times to calculate uncertainties for each measured point. There is one large transfer function from 1 MHz to 500 MHz showing a resonance peak at 11 MHz and notches at 22 MHz and 55 MHz. I also made more detailed measurements around each of these resonance peaks. These measurements were fit to a resonance curve to determine the resonant frequency, transimpedance at resonance, and Q for each peak. These measurements agree with the shot noise measurement for the transimpedance at 11 MHz taken earlier considering that this measurement was made at 11 MHz instead of at the resonant frequency of 11.14 MHz.

I measured these transfer functions with the Agilent 4395a using the netgpib.py script last week. I realized that when using this script to save multiple copies of the same measurement after setting up the instrument, the first and second measurements are saved but all measurements saved after are identical to the second measurement until the instrument is physically reset. This happens because the analyzer switches the trigger from continuous to hold after making a measurement using this script. Kiwamu said that the script can be modified to return the trigger to continuous after saving the data so that multiple measurements can be saved without being at the analyzer physically. I did not want to waste more time figuring out how to modify the script to do this so I used one of the netbooks and sat at the analyzer manually returning the trigger to continuous after each measurement.

  4169   Wed Jan 19 10:45:00 2011 KojiUpdateElectronicsPOX Transfer Functions

TF looks fine except for the large peak at around 200MHz which has been reported by Rana. The time series and the spectrum without the light are pathetic...

I still prefer to see the fit by LISO as the pole/zero fitting of LISO as the fit result is more physically understandable.
Anyone can ask me about the instruction how to use LISO

I guess Idc of 24mA would be just a mistake. It looks like ~0.2mA from the plot that sounds normal for the transimpedance of 2kOhm.

Question: What is the HWHM of the reesonance when you have f0 and Q.

 

  4170   Wed Jan 19 17:00:23 2011 KevinUpdateElectronicsPOX Transfer Functions

 The value of I_dc was a mistake. The value should be 240 µA.

The widths of the resonance peaks are listed below the fits to each peak on the wiki.

  4172   Thu Jan 20 01:50:30 2011 KevinUpdateElectronicsPOX Transfer Functions

[Koji, Kevin]

We fit the entire POX optical transfer function from 1 MHz to 500 MHz in LISO. The fit is on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POX. Using LISO's root fitting mode, we found that the transfer function has five poles and four zeros.

I will work on making plots of the residuals. This is difficult because by default, LISO does not calculate the fitting function at the frequencies of the data points themselves and I haven't figured out how to force it to do this yet.

  16850   Thu May 12 20:24:29 2022 yutaUpdateBHDPOX and POY investigation

[Anchal, Yuta]

We checked POX and POY RF signal chains for sanity check since Xarm cannot be locked in IR stably as opposed to Yarm.
POX beam seems to be healthy. This issue doesn't prevent us from closing the vacuum tank.

POY
 - RF PD has SPB-10.7+ and ZFL-500NL+ attached to the RF output.
 - At the demodulation electronics rack, SMA connectors are used everywhere.
 - With Yarm flashing at ~1, RF output has ~24 mVpp right after RF PD, ~580mVpp after SPB-10.7+ and ZFL-500NL+, and ~150mVpp at right before the demodulation box.
 - There is roughly a factor of 3 loss in the cabling from POY RF PD to the demodulation rack.
 - Laser power at POY RF PD was measured to be 16 uW

POX
 - RF PD doesn't have amplifiers attached.
 - At the demodulation electronics rack, N connector is used.
 - With Xarm flashing at ~1, RF output has ~30 mVpp right after RF PD, and ~20mVpp at right before the demodulation box.
 - Losses in the cabling from POX RF PD to the demodulation rack is small compared with that for POY.
 - Laser power at POX RF PD was measured to be 16 uW

Summary
 - POX and POY RF PDs are receiving almost the same mount of power
 - POY has larger error signal than POX because of RF amplifier, but the cable loss is high

Conclusion
 - There might be something in the electronics, but we can close the vacuum tanks

Attachment 1: POY.JPG
POY.JPG
  14704   Wed Jun 26 21:01:26 2019 gautamUpdateLSCPOX and POY locking

Now that the IMC is remaining locked for extended periods of time, the next problem to attack is the ASS dither alignment system. For a start, I decided to try and get the POX and POY locking working again, as we have not fully recovered the interferometer alignment after the most recent pumpdown. I spent a couple of hours tweaking the alignment of the arm cavity mirrors, BS, and TTs to try and recover the maximum possible TRX and TRY - however, my best efforts only yielded TRX~0.8, TRY~0.75. Moreover, the beam axis is such that the spot is significantly off in YAW on both ETMs, as evidenced by the camera views (also true but less obvious on the ITMs). However, trying to bring the beam back to the center of the optics yields TRY and TRX values lower than the above reported maxima. The EX green beam is currently unavailable to verify the arm cavity alignment because of my hijacking the EX NPROs PZT control for PLL investigations, but with the Y arm, I'm able to lock a TEM00 mode. Probably just needs more careful systematic alignment, but I'm not pursuing this tonight.

  14705   Thu Jun 27 14:28:12 2019 gautamUpdateLSCPOX and POY locking

After a more systematic alignment effort, I was able to get the spots better centered on the optics (judged by eye from the analog camera views). TRY ~0.7, TRX~1.15. The X-arm dither alignment system seems to work out-of-the-box with the existing settings, I was able to run it and maximize the X-arm transmission.

Other work: I also cleaned up the area around MC2 a litte - laptop from on top of the vacuum chamber was removed and a rogue ethernet cable was also removed. The resulted in some misalignment of the IMC, which I corrected by manual alignment. Now the IMC is locked again with nominal transmission levels.

On the PSL table, I re-routed the RF output from the BeatMouth to the regular IR-ALS electronics chain (it was hijacked for PLL investigations). At EX, I disconnected the cable running from the LB1005 to the EX NPRO laser PZT (again was being used for PLL locking), and re-connected the output from the Green uPDH box to allow for some ALS tests to be done. I could then lock the EX green beam to the X-arm, and achieved GTRY ~ 0.35 using the ASX system. More to follow on ALS tests later today.

  8249   Thu Mar 7 11:43:15 2013 JenneUpdateElectronicsPOX and POY whitening DC gain left low

Manasa and Jan were having trouble locking the Yarm, and asked me to take a look at it.  After a good long time of trying to figure out what was going on, it finally occurred to me that I did not turn the DC gain on POX and POY back to the nominal 36dB.  As soon as I did that, both arms acquired lock.  Ooops.

  5525   Thu Sep 22 22:55:01 2011 AnamariaUpdateLSCPOX channel = POY PD connected + Bad Rack

Keiko, Anamaria

We decided we needed a DC channel to sense the gain in the PRC, so we set to align POY55. It took a while because the beam was very weak, and it comes in upwards, so we used a couple of mirrors to bring to a reasonable flat level, and put it on the PD. Then we went to read the DC out and we got 1.3V stationary! Nonsense. We also realized there is no LO for this PD, or any other 55MHz PD, aside from REFL55. Oh well, we only wanted the DC for now. POY55 is aligned (decently).

Koji told me to try swapping the power cable, so I unplugged it at the rack and plugged it in another power card. And it worked! I then moved the DC out (back of rack) to follow the front, and it turns out POY55 diode is read on the POXDC channel. I plugged and unplugged it in disbelief, but it is what it is. At least we have a readout on the power level in PRC.

I attach a picture of the power cards for the LSC RFPDs, with the 3 I found to be bad, and showing current config. I had to move REFL11 and POY55 from their assigned spot.

The two on the lower left are bad in the sense that they put an offset on the PD and make the DC readout be 1.3V for no reason (when working, for example, POY55 read 60mV). The one on the lower right I had trouble with some time ago, it made the PD not read any voltage at all (when working it would read at least 100mV). Beyond that I have not investigated what is up, since I could find working plugins.

Attachment 1: RFPDpowerRack2.pdf
RFPDpowerRack2.pdf
  8513   Tue Apr 30 21:24:15 2013 JenneConfigurationRF SystemPOX fiber laying

Nice work.  That was a lot of effort, but having done it so nicely will definitely pay off, since it is now much harder to break the fibers.

2 small issues:  In your attachment 3, I see a coil of fiber just outside the POX table.  I thought Koji had asked that all spare coiled-up length of fiber always be at the splitter side.  Also, in securing the plastic tubing as it comes down near the PSL table, you have zip-tied the tubing to the PSL table.  Since that is a space that we need to access to align the Xgreen beatnote stuff, please disconnect that zip tie, and secure the tubing on the north side somewhere, underneath the AP table, rather than the PSL table (when you look closer, you may notice that no cables in that bundle are attached to the PSL side at the bottom, for this same reason). 

  14910   Sun Sep 29 15:58:19 2019 gautamUpdateLSCPOX locking attempt

Summary:

There is no visible PDH error signal on the POX11 channels. As a result, I am unable to lock the XARM length to the laser frequency. See Attachment #1 - the Y arm length is locked to the PSL frequency, and control is disabled for the XARM servo.

Details:

Now that several of the c1iscaux functionality tests have been completed, I wanted to push ahead with some locking. However, I was foiled at this early stage, for reasons as yet unknown. One possibility is that the

  • I am able to see TRX cavity flashes >0.8, which suggest to me that the cavity is well aligned.
  • Moreover, I am able to lock some (admittedly high TEM order) mode of the green laser, which further supports the above hypothesis.
  • However, there are no visible PDH-like features in the POX11_I or POX11_Q channels.
  • I checked that the cables from the output of the POX11 demod board are in fact going to the correct channels on WF1 (#5 and #6 respectively), and that the whitening gain for this channel is set to the nominal +30 dB.
  • Next, I went to the POX table and looked for the POX IR beam. I couldn't see anything, but this beam is expected to be weak (of the order of 1 W * T_PRM * R_AR_ITM ~ 30 uW), which is probably not so easily visible.

Next steps:

  • Look for the POX beam with an IR viewer.
  • Confirm that everything is order on the LSC Demod board for POX 11 - maybe the LO isn't connected (somehow)?
Attachment 1: POXlockAttempt.png
POXlockAttempt.png
  15718   Wed Dec 9 12:02:04 2020 gautamUpdateLSCPOX locking still unsatisfactory

Continuting the IFO recovery - I am unable to recover similar levels of TRX RIN as I had before. Attachment #1 shows that the TRX RIN is ~4x higher in RMS than TRY RIN (the latter is commensurate with what we had previously). The excess is dominated by some low frequency (~1 Hz) fluctuations. The coherence structure is confusing - why is TRY RIN coherent with IMC transmission at ~2 Hz but not TRX? But anyways, doesn't look like its intensity fluctuations on the incident light (unsurprisingly, since the TRY RIN was okay). I thought it may be because of insufficient low-frequency loop gain - but the loop shape is the same for TRX and TRY. I confirmed that the loop UGF is similar now (red trace in Attachment #2) as it was ~1 month ago (black trace in Attachment #2). Seismometers don't suggest excess motion at 1 Hz. I don't think the modulation depth at 11 MHz is to blame either. As I showed earlier, the spectrum of the error point is comparable now as it was previously.

What am I missing?

Attachment 1: armRIN.pdf
armRIN.pdf
Attachment 2: POX_OLTF.pdf
POX_OLTF.pdf
  7168   Tue Aug 14 00:42:40 2012 JenneUpdateLockingPOX signal sometimes looks very funny

I'm trying to lock / align the Xarm, and POX 11 I looks funny sometimes.

I attach 2 screenshots so you can see what I mean.  I'm leaving them uncropped so that you can see the only thing that has changed is the LSC enable / disable button. 

The situation:

PRM, SRM, ITMY, ETMY all misaligned.  BS, ITMX, ETMX aligned so that most of the time I can't lock better than 04, bad in yaw, but very occasionally I'll get lucky and catch a 00.  When the LSC enable switch is ON (2nd attachment), the POX signal (green trace in dataviewer in both attachments) looks almost square-ish, and definitely funny.  It doesn't seem to correspond directly to flashing in the cavity (red trace in dataviewer in both attachments).  However when I disable the LSC, POX goes back to looking normal - 1st attachment.  Right around -5 seconds in the 1st attachment, I disabled the LSC.

I don't really know what this means.

Attachment 1: POX_13Aug2012_LSCdisabled_pox_is_normalish.png
POX_13Aug2012_LSCdisabled_pox_is_normalish.png
Attachment 2: POX_13Aug2012_LSCenabled_pox_is_squareish_funny.png
POX_13Aug2012_LSCenabled_pox_is_squareish_funny.png
  7169   Tue Aug 14 04:32:49 2012 rana, yoichiUpdateLockingPOX signal sometimes looks very funny

 The alignment was way off. We moved the PZT, the BS, and the x arm to get it to lock. Along the way we noticed that giving the ETM and POS offsets makes it tilt a lot. The DC coil balancing is no good at all.

After locking, we tuned up the X arm filters in the LSC and activated the filter module triggers.  I would attach a screenshot of the trigger screen, but sadly it has no snapshot button on it.

WE changed the integrator into a double integrator with a complex zero pair. We also replaced the 1:50 boost with a 2nd order complex pole:zero pair. And added a 18 Hz RG. These were all set by looking at the error point spectra and minimizing the RMS. Hopefully, this kind of work will all be obsolete once we get the optimal feedback code. For now, the arm is very stable - we're leaving it locked overnight since the filter triggering seems to work well.

The loop kept oscillating, so we turned the xarm gain down from the 0.3 that we found it at down to 0.045. We measured the loop gain using our old xarm loopgain DTT template (which is in the Templates directory, not in /users/IAmAnAmateur/secret/secret/bozo/). It shows that we are missing ~20 deg of phase at the peak of the phase bubble compared to the old days. We guess that its because of the downsample/upsample digital AA filters which we now have in addition to the 7kHz hardware AA/AI which we still have from the pre-upgrade times). We (Jamie) have to think about how to rationalize this: we cannot survive with double AA/AI.

Another big hindrance in the lock acquisition is that the whitening filters were on. Because the WG is set to 45 dB, the ADCs are getting saturated when the flashes are large. We should have the whitening filters switch after acquiring lock.

Also, why are all the camera views of the ITMs and ETMs different? Steve, please go back and make them all the same (angles, aperture, lenses, etc.). Without them being the same, we cannot compare them.

ETMXF_1028975007.bmp

ETMXT_1028975105.bmpAS_1028975166.bmp

 I have found the video capture scripts in Yuta's personal directory. This is illegal, of course. All useful scripts (even when in development) go into the shared scripts directory. As a punishment, I have added some nasty typos to a couple of his other scripts and then backdated the timestamps so that he cannot find it easily.

 Also, I fixed the "mcup" script. After the ringdown people inserted the pickoff for MC2 trans, no one adjusted the thresholds in the MC autolocker. I've fixed mcup to trigger at 7000 cts. This should be changed back if the pickoff is removed someday. MC WFS now coming on.

Attachment 1: ITMX_1028974969.bmp
  8246   Wed Mar 6 21:58:39 2013 JenneUpdateElectronicsPOX whitening was fine all along

After my investigations this afternoon (with help from Sendhil and Shivaraj), I do not find any problems with the POX whitening switching.

Earlier this afternoon / evening I was misleading myself into thinking that either the switching component (ADG333ABR) was broken, or that the whitening op amps (LT1124CS8) were broken on the POX I&Q and POY I&Q channels.  I had not realized until Jamie mentioned the possibility, that some of the DC gain stages were on for POX and POY.  POX and POY (I&Q for both) all had +36dB of gain, so when I was injecting my 60Hz sine wave into those channels, the whitening opamps were already saturated, which is why it didn't look like I was getting any gain.  When I set them all to 0dB (which is what AS11 and REFL11, the other 2 PDs using that whitening board, were set to), all 8 channels behaved the same.

The shaped whitening (which is either bypassed or not, depending on the condition of the software "unwhite" switch) is 2 filters in series, each with a zero at 15Hz, and a pole at 150Hz, with DC gain of 0dB.  For a 60Hz sine wave, this gives a factor of ~4 from each stage.  After setting all of the whitening gains to 0dB, I was able to see on all 8 channels of the board an input sine wave, a larger (by 4-ish) sine wave, and then a larger (by 4ish again) sine.  When I looked at the output of the switch of all 8 channels, the signal was either the same as the input amplitude, or the same as after the 2nd whitening stage, depending on the "unwhite" filters.

Before looking at actual signals, Sendhil and I also had checked to see that indeed, the board was receiving the digital signal input to the switch chip, requesting switching based on the state of the "unwhite" filters.

I looked through the elogs, and the only "symptoms" I find are from an IFO check-up session that Koji, Den and I had back in May, where we declared in the elog that POX whitening may or may not be switching.  See elog 6595.  We didn't mention what the actual symptoms we saw were, so unless Koji or Den remember something that I don't, I cannot confirm that we are no longer seeing those symptoms.  However, based on the number of "?" after "POX whitening not toggling the analog whitening", I don't think that we were totally sure that something was wrong in the first place.

Anyhow, the whitening board in the LSC rack labeled "WF1", serving AS11, REFL11, POX11 and POY11 has had a thorough checkup, and I give it a clean bill of health.

  8247   Wed Mar 6 22:11:19 2013 KojiUpdateElectronicsPOX whitening was fine all along

At the time you, den and I worked together, we could not lock the X-arm on TEM00 with the FM1s of the POX11 on.
We could lock the arm only on the higher order mode but he gain was low. Once we turned off the FM1s, we immediately
locked the cavity on TEM00.

Don't you have the direct measurement of the TF with FM1 on and off?

  8253   Thu Mar 7 18:41:03 2013 JenneUpdateElectronicsPOX whitening was fine all along

Here are the transfer functions that we took back in 2011 (see elog 4915 and replies) for POX:

POX11I.png

POX11Q.png

The table of all whitening filter zpk values is on the wiki: https://wiki-40m.ligo.caltech.edu/Electronics/WhiteningFilters

  7427   Fri Sep 21 22:25:44 2012 Mike J.UpdateGeneralPOX, POY, PR2 pics

Unaltered PR2 images, with IR card, without card, and steering mirror:

PR2_card.jpgPR2_nocard.jpgPR2_Steering2.jpg

Unaltered POX and POY images:

out_25.jpgout_0.jpg

The POX images only needed a major brightness reduction and increased contrast to view:

out_25_brigcon.jpgout_29_brigcon.jpg

The POY images needed their intensity histograms shifted slightly right and made left-tailed:

out_0_brigcon.jpgout_13_brigcon.jpgout_43_brigcon.jpg

  17141   Thu Sep 15 16:19:33 2022 YehonathanUpdateLSCPOX-POY noise budget

Doing POX-POY noise measurement as a poor man's FPMI for diagnostic purposes. (Notebook in /opt/rtcds/caltech/c1/Git/40m/measurements/LSC/POX-POY/Noise_Budget.ipynb)

The arms were locked individually using POX11 and POY11. The optical gain was estimated to be by looking at the PDH signal of each arm: the slope was computed by taking the negative peak to positive peak counts and assuming that the arm length change between those peaks is lambda/(2*Finesse), where lambda = 1um and the arm finesse is taken to be 450.

Xarm peak-to-peak counts is ~ 850 while Yarm's is ~ 1100. This gives optical gains of 3.8e11 cts/m and 4.95e11 cts/m respectively.

Next, ETMX actuation TF is measured (attachments 1,2) by exciting C1:LSC-ETMX/Y_EXC and measuring at C1:LSC-X/YARM_IN1_DQ and calibrating with the optical gain.

Using these calibrations I plot the POX-POY (attachment 3) and POX+POY (attachment 4) total noise measurements using two methods:

1. Plotting the calibrated IN and OUT channels of XARM-YARM (blue and orange). Those two curves should cross at the UGF (200Hz in this case).

2. Plotting the calibrated XARM-YARM IN channels times 1-OLTF (black).

The UGF bump can be clearly seen above the true noise in those plots.

However, POX+POY OUT channel looks too high for some reason making the crossing frequency between IN and OUT channels to be ~ 300Hz. Not sure what was going on with this.

Next, I will budget this noise with the individual noise contributions.

Attachment 1: XARM_Actuation_Plot.pdf
XARM_Actuation_Plot.pdf
Attachment 2: YARM_Actuation_Plot.pdf
YARM_Actuation_Plot.pdf
Attachment 3: Sensitivity_Plot_1347315385.pdf
Sensitivity_Plot_1347315385.pdf
  14933   Thu Oct 3 19:40:18 2019 gautamUpdateLSCPOX/POY imbalance

Summary:

There is an imbalance between the POX and POY detector outputs reported in the CDS system. Possibilities are (i) the POX PD has a uncoated glass window whereas POY does not or (ii) there is some problem in the elctronics.

Details:

  1. Nominally, we run the POX/POY locking with +18dB whitening gain on POY and +30 dB on POX. This is a factor of 4 difference.
  2. The DC levels reported in C1:LSC-POXDC_OUT and C1:LSC-POYDC_OUT differ by a factor of 10 (24 cts for POY vs 2.4 cts for POX with 0dB whitening gain). These channels come from the P2 connector on the back of the PD Interface board into the fast CDS system.
  3. The levels reported by the Acromag system (which come out of the P1 connector) are 60mV for POY  vs 15 mV for POX.
  4. I confirmed that this imbalance is not due to clipping on the POX photodiode - I tweaked the steering mirror and observed the plateau (I did not, however, look at the beam on the PD active area with an IR viewew which would be a more conclusive test).
  5. I measured the power incident on either PD (using Ophir power meter, filter OFF). They were both ~10uW, as expected since the beam extraction for POY and POX are identical - a single HR mirror and the vacuum viewport.

Update 820pm: 

  1. I checked that there is no glass window on the PD.
  2. It is hard to see the beam on a viewer - but with the PRM aligned, I think I convinced myself that the beam is pretty well centered on the PD. 

So increasingly, it looks like the electronics are the source of the problem.

  5743   Wed Oct 26 20:30:47 2011 KatrinUpdateLSCPOX11 and POP55 installed

[Katrin,Jenne]

RF photo diodes POP55 and POX11 are installed. The beams are aligned to the photo diodes.

 

PD DC out dark DC out bright light power calculated DC output  
POX11 0.1mV 1.3mV 0.09mW 3mV
POP55 35mV 55mV 3 to 4 µW 25mV

I used 0.7 A/W for the response and 50V/A for POP55 according to elog page #4576.

 

To install the third RF photo diode we need to order a plano-convex lens with a focal length of 750 or

maybe even better 1000

  5801   Thu Nov 3 18:41:36 2011 kiwamuUpdateLSCPOX11 demod board : haven't been modified yet

I pulled out the POX11 demod board and found the power splitter on the board hadn't been modified yet.

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

Quote from #5753
The POX11 demodulation board is broken

  5802   Thu Nov 3 19:58:18 2011 kiwamuUpdateLSCPOX11 demod board : modification done

The modification on the POX11 demod board has been successfully done.

I followed the procedure which had been posted in a past entry (#4554).

The home-made splitter was replaced by PSCQ-2-51W, which has a relatively wide band of 5 - 50 MHz.

The usual orthogonality adjustment will be done in the daytime.

 

 The attached snapshot was taken when an sinusoidal RF signal with a slight frequency offset from LO was injected to the RF input.

It is clear that the I and Q output show healthy signals (i.e. almost the same amplitude and 90 deg phase difference.)

POX11demod.png

Quote from #5801

I am going to replace the splitter which had been made with a hand-wounded coil because it can work only at a specific tailored frequency.

  5753   Fri Oct 28 04:57:00 2011 kiwamuUpdateLSCPOX11 demod board broken
The POX11 demodulation board is broken. It needs to be fixed in the daytime tomorrow.
It only outputs the Q signal and nothing is coming out from the I output.


(Some stuff checked)
 [OK] ADCs
 [OK] Whitening filters looked fine. Their gains were controllable from EPICS.
 [OK] Connection between the POX11 RFPD and demodulator box
 [OK] The Q signal showed the PDH signal of the X arm with an amplitude of about 200 counts, which almost is the same as that of POY11.
 [NOT GOOD] The I signal from the demod board
 [OK] Outputs cables, which send the I and Q signals from the demod board to WFs are fine.
         
(Test on the POX11 demod board)
 As usual, a test signal whose frequency is shifted by a little bit from that of LO was injected to the RF input of the board to see if the circuit is working.
The I signal didn't show up and there were no signals even in the monitor LEMO output.
Something is wrong in the I signal demodulation path on the circuit board.

Here is an actual time series of the I and Q signals in dataviewer. The I signal outputs just junk while the Q showed a nice sine curve.
Screen_shot_2011-10-28_at_2.26.02.png

  11254   Sun Apr 26 14:17:40 2015 JenneUpdateLSCPOXDC, POYDC unplugged for now

I have unplugged POXDC and POYDC from their whitening inputs.  They have labels on them which whitening channel they belong to (POY=5, POX=6) on the DCPD whitening board.

TT3_LR's DAC output is Tee-ed, going to the POYDC input and also to an SR560 near the Marconi.

TT4_LR's DAC output is Tee-ed, going to the POXDC input and also to the CM board's ExcB input.

  4164   Mon Jan 17 20:13:38 2011 ranaUpdateElectronicsPOX_11 Optical TF

I used 50 mA to drive the laser diode. The light is split 50/50 between the DUT (Device Under Test) and the New Focus 1611 (1 GHz BW) diode used as the reference.

This measurement is the TF of DUT/(New Focus). The resonances are there, but clearly there's an issue with instability around 200 MHz. The setup is still powered up, so please be careful around the RFPD testing table (don't stomp around yank the cables out of the power supplies).

I looked at the RF Photodiode wiki that Alberto has started - most of the TF features are replicated there. Todo:

* Update the 'schematic' with a real schematic instead of the cartoon.
* Change the circuit to remove the resistor in the RF path.
* Add compensation to avoid the 200 MHz instability.
* Make sure to include opamp current noise in the noise model (it is the dominant noise source but has been left out in the noise estimation plot).
* Make the output into a true 50 Ohms.
Attachment 1: A.TIF
A.TIF
  4568   Tue Apr 26 01:20:02 2011 ranaUpdateElectronicsPOX_11 debugging

The performance plots for POX_11 in the wiki are horrendous and the schematic is missing.

I opened up the box and found all kinds of horrors. There were multiple tunable parts and a flurry of excess nonsense.

The top 2 worst offenders:

1) The main tunable inductor was busted. I removed it and found that the coil was open. Too much indelicate soldering in its vicinity had melted the wire. Someone had put extra inductors and capacitors around it to make it seem as if the PD was working fine, but the noise performance was off by a factor of ~100.

2) The MAX4107 had a 1.4k series resistor. This make the output go through a 1450/50 voltage division which is not nice for the SNR. I removed it.

I then struggled for awhile to get a sensible response. It turned out that the TEST IN input was not giving me a sensible TF. Jenne and I fired the Jenne laser at it and found that the 11 MHz main resonance is there. In the morning I'll finish this off and post more results. I think its going to end up being fine.

We are going to have to take a careful look at all the RFPDs if this one is any indication...

  4569   Tue Apr 26 22:03:49 2011 ranaUpdateElectronicsPOX_11 debugging

I used the Jenne AM laser to tune up the PD (used to be POX_11 but now is called REFL_11). In addition to the notch at 22 MHz, I have also put in a LC notch at 5*f = 55.3 MHz. The transfer function below shows the RF OUT of the PD v. the drive to the laser. I didn't divide out by the 1811 because its not on the EE bench.

MM7.png

 

  4210   Thu Jan 27 03:24:56 2011 KevinUpdateElectronicsPOY Optical Transfer Function

[Rana and Kevin]

I measured the optical transfer function of POY and fit the data using LISO. The fit can be found at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY. POY was missing the RF cage and back cover so I took those parts from AS55 in order to make these measurements.

POY does not have the unwanted oscillations at 225 MHz that POX has. Attachment 1 shows the transfer functions of POX and POY.

To measure the transfer functions, I used a 50/50 beam splitter to send half the light from an AM laser to POY and half the light to a New Focus 1611 reference photodiode. The transfer function for POY was measured as the transfer function of the signal from POY divided by the signal from the 1611. When I was measuring the transfer function for POX, I failed to ensure that the photodiodes were operating linearly. Before making the measurements for POY, I varied the RF power modulating the AM laser and recorded the magnitude of the transfer function at the 11 MHz peak. Attachment 2 shows these values. The measurements for POY were made in the linear region at an RF power of -10 dBm. The measurements for POX were made at 0 dBm and were most likely not in the linear region for POX.

Attachment 1: tf_pox_poy.png
tf_pox_poy.png
Attachment 2: linearity.png
linearity.png
  937   Mon Sep 8 15:38:57 2008 YoichiConfigurationPSLPOY RF amp is back to its original task
I temporarily fixed the busted ZHL-32A RF amplifier's power connector by simply soldering a cable to the internal circuit and pulling the cable out of the box through a hole for the power connector.
So I released the POY RF amplifier from the temporary duty of serving the FSS RF distribution and put it back to the original task,
so that Rob can finally re-start working on the lock acquisition.
Now the temporarily fixed ZHL-32A is sitting next to the IOO rack along with the power supply and a Stanford signal generator.
Please be careful not to topple over the setup when you work around there. They will be there until Peter's Wentzel RF box arrives.
  10490   Wed Sep 10 20:24:00 2014 JenneUpdateElectronicsPOY RF cable loose

Sitting down to work on the IFO, I couldn't lock the Yarm.  I looked at the error signal as well as the transmission on Dataviewer, as usual, and saw that the POY error signal was almost non-existant. 

Since there was work on the POY table today (Steve removed the oplev test setup, elog 10489 and Q centered the SRM oplev after doing SRMI alignment, no elog yet), I went out to have a look at the table. 

There was nothing occluding the POY beam, which I traced back to the edge of the table.  The beam looked nice and round, so I decided that wasn't it.  I jiggled the PD cables, and lo and behold, the POY RF out cable almost came off in my hand it was so loose.  My suspicion is that whomever was the last to put the POY RF out back didn't tighten the cable and then the work today jiggled the cable loose.  I tightened the cable, and by the time I was back to the control room the arm was locked and Koji was already running the alignment scripts.

  4370   Wed Mar 2 22:04:22 2011 KevinUpdateElectronicsPOY Shot Noise Measurement

The previous measurement for the shot noise of POY had the dark noise at ~100 nV/rtHz. I redid the measurement and got 26 nV/rtHz for the dark noise. I think that when I made the previous measurement, the spectrum analyzer had automatically added some attenuation to the input that I failed to remove. This added attenuation raised the noise floor of the measurement making the dark noise of POY appear larger than it is.

The updated measurement can be found on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

  4242   Thu Feb 3 01:46:54 2011 KevinUpdateElectronicsPOY Shot Noise and Dark Spectrum

[Koji and Kevin]

I measured the shot noise of POY and fit the data to determine the RF transimpedance at 11 MHz and the dark current. The transimpedance is (3.860 +- 0.006) kΩ. I realize that there are not many data points past the dark current but I did not want to take any further data because the light bulb was getting pretty bright. If this is a problem, I can try to redo the measurement using a lens to try to focus more of the light from the bulb onto the photodiode.

I also measured the spectrum and recorded a time series of the RF signal with the light to the photodiode blocked. These measurements do not show any large oscillations like the ones found for POX.

The plots of the measurements are on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

  4244   Thu Feb 3 11:13:52 2011 KojiUpdateElectronicsPOY Shot Noise and Dark Spectrum

I wonder why POY11 has the dark noise level of 90nV/rtHz that is 5 times larger than that of POX (18nV/rtHz)
even though the Q are the same (~15) and the transimpedance is better (3.9k instead of 2k).

What cause this high noise level?
What is the expected dark noise level?

Quote:

[Koji and Kevin]

I measured the shot noise of POY and fit the data to determine the RF transimpedance at 11 MHz and the dark current. The transimpedance is (3.860 +- 0.006) kΩ. I realize that there are not many data points past the dark current but I did not want to take any further data because the light bulb was getting pretty bright. If this is a problem, I can try to redo the measurement using a lens to try to focus more of the light from the bulb onto the photodiode.

I also measured the spectrum and recorded a time series of the RF signal with the light to the photodiode blocked. These measurements do not show any large oscillations like the ones found for POX.

The plots of the measurements are on the wiki at http://lhocds.ligo-wa.caltech.edu:8000/40m/Electronics/POY.

 

ELOG V3.1.3-