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ID Date Author Typeup Category Subject
  4229   Mon Jan 31 07:03:59 2011 AidanSummaryGreen LockingDFD - noise spectra

Quote:

I've had a go at trying to estimate the frequency noise of the digital frequency discriminator (DFD). I input a 234.5Hz (0.5Vpp) signal from a 30MHz function generator into the ADC. The LP output of the DFD measured 234.5Hz. However, this signal is clearly modulated by roughly +/- 0.2Hz at harmonics of 234.5Hz (as you can see in the top plot in the dataviewer screenshot below). So the frequency noise can be estimated as rms of approximately 0.2Hz.

This is supported by taking the spectra of the LP output and looking at the RMS. Most of the power in the RMS frequency noise (above the minimum frequency) comes from the harmonics of the input signal and the RMS is approximately 0.2Hz.

I believe this stems from the rather basic LP filter (three or four poles around 10Hz?) that is used in the LP filter to remove the higher frequency components that exist after the mixing stage. (The currently loaded LPF filter is not the same as the saved one in Foton - and that one won't load at the moment, so I'm forced to remember the shape of the current filter).

 The attached screen capture from data viewer shows the LP_OUT hovering around 234.5Hz.

 Here is the spectrum of the input into the DFD (a 234.5Hz sine wave, 0.5 Vpp) and the spectrum and RMS of the LP output. The linewidth of the input signal is clearly much less than 0.1Hz, where as the RMS noise (above 2mHz) is approximately 0.2Hz and the main contributions are clearly the harmonics of the 234.5Hz signal.

Attachment 1: DFD-bandwidth_noise.pdf
DFD-bandwidth_noise.pdf
  4237   Wed Feb 2 03:27:20 2011 KojiSummaryGreen Locking85MHz Freq divider

The freq divider was built and installed in the beat detection path.

Attachment 1: Circuit diagram

  • Input stage:  Wideband RF amp with DC block at the input and the output. The gain is 10dB typ.
  • 2nd stage: Ultra fast comparator AD9696. Note: AD9696 is an obsolete IC and there are only a few extra at Wilson house.
    The output is TTL/CMOS compatible.
  • 3rd stage: 14bit binary ripple counter (fmax~100MHz.)

Note: I have added 7805/7905 regulators to the circuit as I could not find -5V supply on the 1X1/2 racks.

Attachment 2: Packaging

  • The box is german made Eurocard size box from Techno-Isel Linear Motion http://www.techno-isel.com/lmc/Products/EnclosureProfiles11055.htm
    The box is excellent but I didn't like the fixing bolts as they are self-tapping type. I tapped the thread and used #6-32 screws.
     
  • The prototyping board is BPS's (BusBoard Prototype System http://www.busboard.us/)  SP3UT. The card size is 160mm x 100mm.
    The other side is a ground plane and the small holes on the board are through holes to the ground plane.
    This particular card was not easy to use.
     
  • The input is SMA. Unfortunately, it is not isolated. The output is an isolated BNC.
     
  • The supply voltage of +/-15V is given by the 3pin D-connector. The supply voltages have been obtained from the cross connect of 1X1.

Attachment 3: Input specification

  • The input frequency is 10MHz~85MHz. At lower frequency chattering of the comparator against the multiple zero crossing of the (relatively) slow sinusoidal waves.
  • The input amplitude. There are no apparent degradation of the freq jitter when the input power was larger than -30dBm.

 

Attachment 1: freq_divider.pdf
freq_divider.pdf
Attachment 2: IMG_3816.JPG
IMG_3816.JPG
Attachment 3: IMG_3818.JPG
IMG_3818.JPG
  4238   Wed Feb 2 09:56:55 2011 KojiSummaryGreen LockingInstalled the freq divider and Rana's PFD

- The freq divider and Rana's PFD were hooked up to the ADCs. (Attachment 1)
(I leave the analog PFD not explained in this entry.)
For this purpose, the VCO feedback signal has been disconnected and the beat signal was moved from the VCO loop to the analog PFD.

The output level of the splitter was +12dBm and was too high for the freq divider.
So, I had to stupidly add an attenuator of 10dB before the box.

- Gain of the digital PFD LPF

The LPF of the digital PFD had the gain of -4096 to let the output signal indicate the direct frequency reading.

The gain has been changed to -67.108864
such that the output shows the direct reading of the beat freq in the unit of MHz

-4096*2^14/10^6 = -67.108864

 

- Attachment 2 shows the acquired beat note through the freq divider.
The blue is the beat note between "green locked" and "IR locked only to MC" (i.e. MC vs XARM)
The red is the beat note with the both beam locked to the arm

The freq divider is a bit flaky in some freq region as the divided output sometimes shows freq jumps or the captured at a freq.
I still don't know why it happens. We have to check why this happens.

Attachment 1: freq_divider_installation.pdf
freq_divider_installation.pdf
Attachment 2: 110201_freq_divider_output.pdf
110201_freq_divider_output.pdf
  4239   Wed Feb 2 10:44:26 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

The freq fluctuation of the beat note has been measured with the following condition

  • The IR beam only locked to the MC. The green beam locked to the arm
  • Both of the IR and green locked to the x-arm

Calibration
- The output of the freq divider is already calibrated to have the unit of MHz.

- The transfer function between the analog PFD channel and the digital PFD output was measured to be -23dB = 0.7.
  The gain of the XARM-FINE channel was changed to 0.7 such that the output is calibrated in MHz.

Results

- I have not checked the analog noise level of the analog PFD path. We may need more whitening gain (by icreasing the gain of SR560).

- The analog PFD is always better than the digital PFD above 20Hz.

- Both the digital and analog PFD showed good agreement below 20Hz.
  Note the measurement was not simultaneous.

- When the arm is locked with the ETMX being actuated , the fluctuation of the arm length must be stabilized by a huge factor
(~10^5 according to Kiwamu's entry) However, we only could see the stabilization factor of 30.

As this residual is the difference of the freq noise felt by the IR and the green,
this is a real issue to be tackled.

- The RMS fluctuations of the arm with and without the IR beam being locked are 2MHz and 0.1MHz,
which correcponds to the arm length motion of 250nm and 13nm, respectively.
Ed: I had to use 532nm in stead of 1064nm. The correct numbers are 130nm and 7nm.

- Without the IR locked, The typical peak-to-peak fluctuation of the beat freq was 10MHz.

Attachment 1: 110201_green_freq_fluctuation.pdf
110201_green_freq_fluctuation.pdf
  4240   Wed Feb 2 12:55:34 2011 KojiSummaryGreen LockingFreq fluctuation measured by the freq divider and Rana's analog PFD

I found that some flakiness of the beat signals comes from the RF components for the beat detection.
They are touching the racks in an indefinite way. If we move the components the output of the analog PFD
goes crazy.

Once Kiwamu is back I will ask him to clean up all of the green setting in an appropriate way.

 

  4254   Sat Feb 5 23:03:04 2011 rana, kojiSummaryElectronicsAnalog Frequency Discriminator: splitter + mixer + long cable

This diagram shows the setup of the analog Mixer-Frequency Discriminator (MFD).

The idea is similar to the one of the Schnupp Asymmetry for our Michelson interferometers. The signal from the PD (or any signal source for which you want to know the frequency) is split into two legs; one leg is much longer than the other. The two legs are recombined at a mixer/demodulator. The demodulator output varies sinusoidally with the phase difference of two legs, the same as when we try to measure the phase noise of an oscillator, for example. This is the same concept as the digital frequency discriminator that Aidan and Joe put into the GFD FE system recently.

With a ~1m cable length asymmetry, we get 180 deg of phase shift for a ~100 MHz signal (recall that the speed of light in most of our cables is ~2 x 10^8 m/s). The mixer gives a linear output at 50 MHz (and 150 MHz, 250 MHz, etc.).

This single mixer based setup is fine for most everything we do. In order to get even more resolution, one can just use 2 mixers by splitting the signal with a 4-way instead of 2-way mixer. One setup can have a 0.5-1 m asymmetry to have a large range. The other can have a ~10-30m asymmetry to get a comb of linear readouts.

Typically, we will have some kind of weak signal at the photodiode and will use a 20 or 40 dB gain RF amp to get the signal into the mixer. In this case, the mixer output noise will be at the level of tens of nV/rHz. Any usual low noise audio amplifier (SR560 variety) will be enough to read out the signal.

Why the 50 Ohm terminator? If you look at the specs of the BLP-1.9 filter from Mini-Circuits (its the same for almost all of their LP filters) you see that there's ~90 dB of attenuation above ~30 MHz (where our signals 2*f product will show up). If we use an RF input signal of ~0 dBm, this means that we get a high frequency product of -95 dBm (~10 uVrms) which is OK. But the return loss is 0 dB above 5 MHz - this means that all of the high frequency content is reflected back into the mixer! The 50 Ohm terminator is there to absorb the RF signals coming out of the mixer so as to prevent them from going back into the mixer and mixing with the RF/LO signals. The 50 Ohm terminator does attenuate the DC/audio frequency signals we get out of the mixer by a factor of two, but that's OK since we are not limited by the mixer's thermal noise.


Noise Measurement:

To checkout the noise, we used a 6m RG-58 cable in one leg. We used the DS345 signal generator for the source. We adjusted the frequency to (~21 MHz) give a ~zero mean signal at the demod output. The 6m cable makes the demod output's peak-peak swing correspond to ~16 MHz. We then used an SR560, DC coupled, G=1000, low-noise, 2pole low pass at 1 kHz, to get the signal into the ADC.

 fsm.png

The attached plot shows the noise. We have caibrated the digital gain in the channel to make the output into units of Hz. The high frequency noise floor is ~0.3 Hz/rHz and the 1/f knee is at 10 Hz. This setup is already good enough for all of the green locking work at the 40m. In order to make this useful for the reference cavity work or the gyro, we will have to use a longer cable and a lower noise audio amplifier.

As can be seen from the plot, the ADC noise is below the measured noise. The noise of the SR560 with the input terminated is shown in grey - the measured noise of the MFD is very close to this. In order to improve the performance, the next step should be to use a longer cable. There's clearly going to be some trade-off between the temperature dependent effects which come with long cables (dphi/dT gets bigger) and trying to use a high gain ~1 nV/rHz amplfier at the mixer output.


Temperature Drift of the long cable:

Untitled.png

This 24-hour minute-trend shows the frequency wander as well as the room temperature. This is not proof of a temperature dependence, but if it is then we get ~3 kHz/deg for the sensitivity. If this is actually the cable and not the amplifier, then we'll have to hunt for a lower tempco cable and put it in a box to isolate it.

Attachment 1: mixer.pdf
mixer.pdf
  4259   Tue Feb 8 10:23:02 2011 AidanSummaryGreen LockingDigital Frequency Discriminator - reference

 

Here's the reference for the self-reference frequency detection idea. See Figure 2.

http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/mixers.pdf

  4260   Tue Feb 8 13:26:11 2011 AidanSummaryGreen LockingTemperature dependence of phase change of green on reflection

 I did a quick back of the envelope calculation of the expected green phase change on reflection from the aLIGO ITM.

The phase change per nm, K1 = delta phi/delta Lambda, around 532nm is ~1.5 degrees/nm (from the LMA data) [this number is approximately 100x smaller at 1064nm]

I assumed that very small changes in the thickness of the coating appear equivalent to shifting the spectra for reflection/transmission/phase-change-on-reflection up or down by delta lambda, where

delta Lambda/Lambda = delta h/h

where h is the total thickness of the coating and delta h is the change in the thickness of the coating.

Assume that delta h/h = alpha deltaT, where alpha is the coefficient of thermal expansion and delta T is the change in temperature. (approximately 1K)

Then delta phi = K1* Lambda * alpha * delta T = 1.5 degrees/nm * 532nm * 10^-5 K^-1 * 1.0 K =  8 * 10^-3 degrees.

Assume that 360 degree phase change corresponds to one FSR.

Therefore, the frequency shift due to temperature change in the coating = 8*10^-3/360 * FSR = 2.2 *10^-5 * FSR.

Therefore, the expected frequency shift per degree temperature change = 2.2*10^-5 * FSR [Hz/K]

  4293   Mon Feb 14 23:29:04 2011 ranaSummarySUSETMX Fitlers moved around

All of the SUS used to have only 1 filter module for SIDE. They now have 3 filter modules for SIDE just like the other DOFs.

Today I moved the filters around so that the sensor filters are in SDSEN, the servo filters are in SUSSIDE, and the dewhitening for the coil is in SDCOIL.

I noticed along the way that the bounce/roll mode notches for all of the suspensions are still set for the frequencies of the previous suspensions. Suresh has 'volunteered' to find the new frequencies and make the new bandstop filters by looking up the seminal work on this by Dan Busby / Sam Waldman.

  4294   Tue Feb 15 02:13:16 2011 kiwamuSummaryASCa daytime task : small signals on ETMX OL

Rana and I found that the QPD for the optical lever at X end are showing small signals.

At this moment each of the segments exhibits approximately 200 counts when the oplev beam is centered.

These small numbers may be due to the coating of ETMX, but we are not sure.

Probably we have to increase the gain of the QPD depending on situations.

 

So a set of the tomorrow's daytime task is:

   1. check the trend data of the QPD outputs to see how much signals were there in the past.

   2. check the whitening filters to make sure if it's on or off.

   3. If it's necessary, increase the gain of the QPD to have reasonable readouts.

I am going to ask somebody to do this task.

  4299   Tue Feb 15 11:53:02 2011 kiwamuSummaryGeneraltoday's missions

I think this week is going to be an "alignment week".

The goal is to get a good alignment on X arm for both the green and the IR beam in order to reduce a2l couplings.

 

Today's missions are :

 - fixing the oplev channel names (see here)

 - fixing the oplev gain issue (see here)

 - engage the oplev servos

 - f2p adjustment

 - make a realtime lockin model for the f2p measurement and the dithering technique

 - alignment of the MC incident beam  (because we installed a new PMC this morning)

 - manual alignment of the IR beam by steering PZT1 and PZT2 (this procedure will be replaced by an automatic way soon)

 - bounce roll filters (see here)

 

  4310   Thu Feb 17 00:43:13 2011 kiwamuSummaryGeneralto do list for tomorrow

Let's share our tasks !

 

==== daytime ===

 . mode matching for MC  (Jenne/Koji)

 . mode matching for doubling crystal on PSL table (Suresh/Koji)

 . f2p adjustment (Kiwamu)

 . fix daq and CDS issues (Joe)

 . increase oplev gain (low priority)

 . make ITMY camera nicer (Steve)

 . c1ass simlink model (Valera/Joe)

 . Bounce Roll notches (Suresh)

 

==== nighttime (after 7pm) ====

 . align everything   (at first green beam, then X arm cavity and finally IR beam)

 . update the noise spectrum of the green locking

 . estimate the noise from angle to length coupling

  4317   Thu Feb 17 22:51:04 2011 josephb, valeraSummary dither alignment model

We made a model for the dither angular stabilization system c1ass.mdl. The attached file shows the diagram.

The idea is to dither a combination of 6 optics (ETMs, ITMs, PZTs) at different frequencies and demodulate three PDs (TRX, TRY, REFL11I). Then form the DOFs from demodulted signals, filter, and send each DOF to a combination of optics.

This is enough to get started with arm cavities alignment (we may need to add the BS for the Y arm). More optics and PD can be added as they become available and/or needed.

The DAC for the fast PZT  are not connected and have to be commissioned.

Attachment 1: ass-model.png
ass-model.png
  4322   Fri Feb 18 00:35:21 2011 kiwamuSummaryGeneralto do list for Feb. 18th

DAYTIME

  -  more precise F2P measurement and modify lockin simlink model (Kiwamu)

  -  run  C1ASS to check it (Valera)

  -  take care of CDS (Joe)

  -  MC mode matching (Jenne/Koji)

   -  RF stuff  (Suresh)

  -  mode matching for doubling crystal at PSL table (low priority)

  -  OPLEV (low priority)

NIGHITTIME

 -  update the noise spectra of green locking

 -  make noise budgets

  4326   Fri Feb 18 18:46:08 2011 kiwamuSummarySUSf2p done on ETMX and ITMX

The f2p measurements are done on ETMX and ITMX with the real time lockin systems.

I don't explain what is the f2p measurement in this entry, but people who are interested in it can find some details on an old elog entry here or somewhere on DCC.

So far the resultant filters looked reasonable compared with the previous SRM f2p filters.

 

- backgrounds -

  Some times ago I found that the coils on ETMX had not  been nicely balanced, and it made a POS to angle coupling when I tried green locking (see here).

In addition to that, accuracy of A2L kind of measurement including the dithering techniques depend on how well the coils are balanced.  Therefore we need to balance the coils basically at all the suspended optics.

There used to be a script for this particular purpose, called f2praio.sh. This script does measure the imbalances and then balance the coils.

However this time I used the realtime lockin system to measure the imbalances instead of using the old f2p script.

One of the reasons using the real time system is that,  some of the ezca and tds commands for the old script don't work for some reasons.

Therefore we decided to move on to the real time system like Yuta did for the A2L measurement a couple of months ago.

The f2p measurement finally gives us parameters to generate a proper set of filters for POS and also the coil gains. We apply those filters and the gains in order to eliminate the POS to angle coupling and to balance the coils.

 

- results -

The followers are the resultant filters and coil gains.

The plots below show new f2p filters according to the measurement.

f2p_ITMX.png       f2p_ETMX.png

 

ITMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)

ULPOS  fz = 1.009612   Qz = 1.009612 

URPOS fz = 1.125965   Qz = 1.125965  

LLPOS  fz = 0.873725   Qz = 0.873725    

LRPOS  fz = 0.974418   Qz = 0.974418  

C1:SUS-ITMY_ULCOIL_GAIN      -1.103044

C1:SUS-ITMY_URCOIL_GAIN      0.884970

C1:SUS-ITMY_LLCOIL_GAIN      0.950650

C1:SUS-ITMY_LRCOIL_GAIN      -1.060326

 

 

ETMX (assuming pendulum POS has f0 = 1 Hz and Q = 1)

ULPOS  fz = 1.055445   Qz = 1.055445   

URPOS  fz = 1.052735   Qz = 1.052735   

LLPOS  fz = 0.944023   Qz = 0.944023   

LRPOS  fz = 0.941600   Qz = 0.941600   

C1:SUS-ETMX_ULCOIL_GAIN      -0.887550

C1:SUS-ETMX_URCOIL_GAIN      1.106585

C1:SUS-ETMX_LLCOIL_GAIN = 1.07233

C1:SUS-ETMX_LRCOIL_GAIN      -0.931013

  

The precision of the coil gains looked something like 1% because every time I ran the measurement script, the measured imbalances fluctuated at this level.

The precision of the filter gain at DC (0.01 Hz) could be worse, because the integration cycles for the measurement are fewer than that of the coil gains done at high frequency (8.5 Hz).

Of course we can make the precisions by increasing the integration cycles and the excitation amplitudes, if we want to.

  4327   Fri Feb 18 20:06:59 2011 kiwamuSummarySUScheck f2p function on ETMX

 The plot below shows how the f2p filters work.

At -2 min I turned on the f2p filters.

 f2p_ETMX.png

  4328   Fri Feb 18 20:17:07 2011 JoonhoSummaryElectronicsIsolation of Voltage regulator

Today I was working on RF distribution box.

So far I almost finished to electronically isolate voltage regulators from the box wall by inserting mica sheet, sleeve, and washers.

 

The problem I found is the resistance between wall and the voltage regulator is order of M ohms

I checked my isolation (mica sheet and sleeve and washer) but there is no problem there.

But I found that the power switch is not completely isolated from the wall.( around 800 kohm)

and that the resistance between the regulator and the wall is smaller for the regulator closer to the power switch

and greater for the regulator less closer to it.

So I think we need to put washer or sleeve to isolate the powersitch electronically from the box wall.

Suresh or I will fix this problem

[ To Suresh, I can finish the isolation when I come tomorrow. Or you can proceed to finish isolation.]

  4329   Sat Feb 19 01:58:20 2011 ranaSummaryElectronicsLow Noise BJT Pre-Amp

Frank put his low noise preamp info here.

I suggest that we build these (using Altium) but replace the cheapo transistors with the high class MAT03 matched BJT pair from Analog Devices.

This will allow us to have a pre-amp better matched to the noise of the mixers down to low frequency.

  4333   Mon Feb 21 17:29:57 2011 ranaSummaryIOOMyterious data loss: FB needs investigation

Looks like there was a mysterious loss of data overnight; since there's nothing in the elog I assume that its some kind of terrorism. I'm going to call Rolf to see if he can come in and work all night to help diagnose the issue.

Untitled.png

  4334   Mon Feb 21 23:00:06 2011 ZachSummaryelogrestarted

 again

  4343   Wed Feb 23 10:37:02 2011 josephbSummaryIOOMyterious data loss: FB needs investigation

Friday: 

In addition to the other fixes, Alex rebuilt the daqd process. I failed to elog this. When he rebuilt it, he needed change the symmerticom gps offset in the daqdrc file (located in /opt/rtcds/caltech/c1/target/fb). 

On Friday night, Kiwamu contacted me and let me know the frame builder had core dumped after a seg fault.  I had him temporarily disable the c1ass process (the only thing we changed that day), and then replaced Alex's rebuilt daqd code with the original daqd code and restarted it.  However, I did not change the symmetricom offset at this point.  Finally, I restarted the NDS process.  At that point testpoints and  trends seemed to be working.

Sunday:

The daqd process was restarted sometime on Sunday night (by Valera i believe).  Apparently this restart finally had the symmetricom gps offset kick in (perhaps because it was the first restart after the NDS was restarted?).  So data was being written to a future gps time.

Monday:

Kiwamu had problems with testpoints and trends and contacted me.  I tracked down the gps offset and fixed it, but the original daqd process only started once successfully, after that is was segfault, core dump non-stop. I tried Alex's rebuilt daqd (along with putting the gps offset to the correct value for it), and it worked.  Test points, trends, excitations were checked at the point and found working.

I still do not understand the underlying causes of all these segmentation faults with both the old and new daqd codes.  Alex has suggested some new open mx drivers be installed today.

Quote:

Looks like there was a mysterious loss of data overnight; since there's nothing in the elog I assume that its some kind of terrorism. I'm going to call Rolf to see if he can come in and work all night to help diagnose the issue.


 

  4357   Fri Feb 25 13:28:14 2011 kiwamuSummaryGeneralto do list
 Because it maybe useful to share this kind of information among us, I just put a to-do-list which has been continuously noted in my laptop.
 I guess those items can be applied for the coming two months (i.e. March and April). Anything else ?

-- Alignment

     - C1ASS

           * finalize the model and make user friendly scripts and medm screens
           * adjustment of phase rotations
           * cavity auto alignment for green

     - MC WFS 

          * put sensing matrices
          * whitening ?

    - OPLEVs

        * binary output for OPLEV whitening
        * calibration of OPLEVs  [rad/count]
        * characterization of OPLEV servos
        * bigger trans impedance gains to have reasonable readouts


-- Optimization of Suspended Optics

  - diagonalizations

         * input matrices
         * f2p with higher precision

  - damping control

        * fix ETMY damping
         * Bounce Roll notches
         * Q adjustment for damping

  - upgrading of electronics

        * bigger trans impedance gain for OSEMs
        * widen the voltage range of AA filter boards
   

   - weekly check

       * a routine script for measuring free swinging spectra


-- Input Optics

   - PMC

         * mode matching
         * epics LO HI values

   - FSS and ISS

        * recover FSS
        * make ISS working

   - EOM

       * AM minimization
       * triple resonant box

   - doubling and RFPD for green

        * mode matching to doubling crystal
        * connect RFPD_DC_MON to ADC
        * string +/-150 V and +/-15power cables from 1X1 rack to RFPDs
        * visibility check and loss investigations for the beat RFPD
        * rearrange RF amplifiers (ZLN series) for the RFPD
        * realgin Jenne's DCPD

 

-- Length Sensing and Control

   - digital system and electronics

       * characterization of RFPDs ==> SUresh/UG
       * installation of RF generation box and distribution box ==> Suresh/U
       * new LSC model and start making useful scripts (csh ? perl ? python ?)
       * binary outputs for PD whitening
       * make item lists for ordering (?)
       * draw cool diagrams for RF cable distribution and map of LSC rack.


-- Green Locking

    - X end station

           * eliminate undesired multiple spots on RFPD
           *  connect REFLPD_DCMON to ADC
           *  remote local boost
           * demodulation phase adjustment
           *  look for a high voltage amp. (bipoler)
           * installation of a mechanical shutter
           *  ETMX_TRANS CCD camera
           * analog low pass filter for temperature control

    - Y arm green locking ==> Suresh/Bryan

        * item lists
        * preparation of base mounts
        * mode matching estimation
        * mode measurement of input beam from Lightwave
        * temeperature scanning for beat location finding with IR beam
        * Installation
       * modification of PDH box

    - digital control systems

           * user friendly medm screens
           * apply proper filters for AC-DC whitened signal blending
           * add MC2 feedback path

      - noise budget

          * in-loop and out-of-loop evaluation
          * shot noise  
          * RFPD noise modeling
          * how intensity noise couples through MFD
          * electrical noise
          * frequency noise contribution from end laser and PSL
          * calibration of arm PDH signal

   - cavity scan and handing off

         * optimization of open loop transfer function for ALS
         * auto scripts   

-- misc.

   - CCD camera
        * color filters to separate IR and green (?)
   - lab laptops
        * a laptop for each end station (?)
    - dichroic TT (?)
        * large wegded and AR coated for 532nm (?)
    - epics for RS232C      
        * RS232C for doubling oven temperature

 

  4359   Fri Feb 25 14:50:16 2011 KojiSummaryGeneralto do list

- Put priority on the list

- Put names on the items

- Where is the CDS TO DO ==> Joe

-

- Remote disconnection of the greeen PDH 

- What is the situation of the PD DC for the LSC PDs?

- SUS Satelite box Resister replacement ==> Jamie

- IMC mode matching ==> Jamie/Larisa 

- Mechanical shutters everywhere

- SRM OPLEV Connection

- MC OAF

- Better LSC whitening boards

- DAFI 

Quote:
 Anything else ?

  4364   Mon Feb 28 11:22:40 2011 josephbSummaryGeneralto do list
Quote:

- Where is the CDS TO DO ==> Joe

CDS To Do:

1) Get ETMY working - figure out why signals are not getting past the AI board (D000186) to the coils.

2) Get TDS and command line AWG stuff working

3) Get c1ass and new c1lsc (with Koji) fully integrated with the rest of the system.

4) Get CDS software instructions up to date and well organized.

5) Redo cabling  and generally make it a permanent installation instead of hack job:

   a) Measure cable lengths, check connectors, wire with good routes and ensure strain relief.  Ensure proper labeling

   b) Get correct length fiber for c1sus RFM and timing.

   c) Fix up final BO adapter box and DAC boxes.

   d) Make boxes for the AA filter adapters which are currently just hanging.

   e) Get two "faceplates" for the cards in the back of the ETMY IO chassis so they can screwed down properly.

   f) Remove and properly store old, unused cables, boards, and anything else.

6) Create new documentation detailing the current 40m setup, both DCC documents and interactive wiki.

7)  Setup an Ubuntu work station using Keith's wiki instructions

 

Simulated Plant To Do:

1)Create simulated plant to interface with current end mass controls (say scx).

2) Create proper filters for pendulum and noise generation, test suspension.

3) Propagate to all other suspensions.

4) Working on simulated IFO plant to connect to LSC.  Create filters for near locked (assume initial green control perhaps) state.

5) Test LSC controls on simulated IFO.

6) Fix c code so there's seamless switching between simulated and real controls.

CDS Status:

MC damp dataviewer diaggui AWG c1lsc c1ioo c1sus c1iscex c1iscey RFM The Dolphins Sim.Plant Frame builder TDS Cabling
                             
  4371   Wed Mar 2 22:57:57 2011 sureshSummaryGeneralStuff from LLO

Here is a partial list of stuff which is being packed at LLO to be shipped to CIT.  The electronics ckt boards are yet to be added to this list.  Will do that tomorrow.

 

 

Attachment 1: eLIGO_items_from_LLO_for_Caltech.xls
  4375   Thu Mar 3 20:30:03 2011 ranaSummaryPSLPMC Sweeps @ different input power levels to measure the Finesse

Its been well noted in the past that sweeping the PMC at high power leads to a distortion of the transmitted power curve. The explanation for this was coating absorption and thermo-elastic deformation of the front face of the mirrors.

Today, I did several sweeps of the PMC. I turned off its servo and tuned its PZT so that it was nearly resonating. Then I drove the NPRO via the HV driver (gain=15) with 0-150 V (its 1.1 MHz/V) to measure the PMC transmitted light. I adjusted the NPRO pump diode current from 2A on down to see if the curves have a power dependent width.

In the picasa web slideshow:

There are 3 significant differences between this measurement and the one by John linked above: its a new PMC (Rick says its the cleanest one around), the sweep is faster - since I'm using a scope instead of the ADC I feel free to drive the thing by ~70 MHz in one cycle. In principle, we could go faster, but I don't want to get into the region where we excite the PZT resonance. Doing ~100 MHz in ~30 ms should be OK. I think it may be that going this fast avoids some of the thermal distortion problems that John and others have seen in the past. On the next iteration, we should increase the modulation index for the 35.5 MHz sidebands so as to get a higher precision calibration of the sweep's range.

By eye I find that the FWHM from image #4 is 11 ms long. That corresponds to 300 mV on the input to the HV box and 15 V on the PZT and ~16.5 MHz of frequency shift. I think we expect a number more like 4-5 MHz; measurement suspicious.

  4381   Mon Mar 7 17:58:14 2011 sureshSummaryGeneralStuff from LLO

Here is the updated list. These lists were used as packing lists and therefore are organised by Box #.
Attachment 1: eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf
eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf eLIGO_items_from_LLO_for_Caltech_Sheet1.pdf
  4382   Mon Mar 7 18:20:01 2011 kiwamuSummaryGreen Lockingplans
This week's goal is to investigate the source of the differential noise and to lower it.
 
Plans for tonight
 - realign GREEN_TRANS PD at the PSL table
 - update the noise budget
 - take spectrum of the differential noise
 - investigate a noise coupling to the differential noise especially from the intensity noise
 - update the noise budget again
 
Plans for this week :
 - Auto alignment scripts for green (Kiwamu)
 - connect the end REFL_DC  to an ADC (Kiwamu)
 - make an active phase rotation circuit for the end PDH (undergrads)
 - bounce-roll notches (Suresh)
 - optimization of the suspensions including the input matrices and the Q-values (Jenne)
 - optimization of MFSS (Koji/Rana/Larisa)
 - rewire the mechanical shutter on the 1X9 binary outputs (Steve)

 

  4387   Tue Mar 8 15:33:09 2011 kiwamuSummaryGreen Lockingplan on Mar.8th
Today's goal is to measure the contribution from the intensity noise to the beatnote.
 
Plans for today
  - check the ADC for the DCPD that Jenne installed yesterday
  - adjust RF power on the AOM
  - take spectrum of the differential noise and measure the coupling from the intensity noise
  - update the noise budget

Quote: from #4382
This week's goal is to investigate the source of the differential noise and to lower it.

 

  4391   Wed Mar 9 17:29:11 2011 steveSummaryVACsingle O-ring protection

We have one single O-ring on the 40m vacuum envelope. It is on the OOC west side, facing the AP table. This O-ring has to be protected from the force of this

door. There should be 3 shims  ~120 degrees apart to carry the full load, so it is not the O-ring that is getting squashed.

This morning I found only one of these shims in place.

Attachment 1: so1.jpg
so1.jpg
Attachment 2: P1070458.JPG
P1070458.JPG
  4394   Thu Mar 10 01:28:47 2011 joe, jamie, rana, chrisSummaryCDSSimSuspension !

Today was a banner day for Simulated Plants.

Joe and Jamie have been working to get it all happening and this afternoon we started stuffing filters into the plant to make it act like the:

40mETMY.png

We put in the following features so far:

  1. Anti-Imaging filters (these are hacked to be approximate since the real ones are 7570 Hz LP filters and the SimAI only can have filters up to 8192 Hz).
  2. Dewhitening filters (copied from the SimDW in the SUS-ETMY screens)
  3. Coil Driver transimpedance (1 / 200 Ohms)
  4. Magnet-coil force constant (0.016 N/A)
  5. Conversion from Coil to DOF Basis
  6. All DOFs of the mechanical model are represented as simple harmonic oscillators with Q~100 and f ~ measured free swinging peaks.
  7. Signals/Noise can be injected either as force noise on the test mass or as displacement noise at the suspension point.
  8. Conversion from DOF to Shadow Sensor basis.
  9. Optical Levers (with whitening)
  10. Shadow Sensors have 2V/mm readout gain and whitening filters before being digitized by the SimADC.

We have also changed the switching logic for the SUS and SimETMs for the shadow sensor whitening. It used to be that either the hardware OR the software whitening was on. Now we have made it like all of the other whitening/antiwhitening in LIGO and the whitening/antiwhitening come on together. Joe and Jamie are going to propagate this to the other SUS. The hardware filter is a 30,100:3 (poles:zeros) whitening filter. The digital filter used to also be 30,100:3 with a DC gain = 1. I've changed the FM1 filter in the XXSEN filter banks into a 3:30 for the ETMY so that it now comes on and just compensates the hardware filter. This change should be propagated to all other SUS and the MEDM screens updated to show the new situation.

After this change, we decided to calibrate the {UL,UR,LL,LR,SD}SEN channels into units of microns. To do this we have made an FM6 filter called 'cts2um' that accounts for the OSEM gain and the ADC conversion factors. These channels are now in units of microns without applying any calibration in the DTT or Dataviewer. The plot below shows the OSEM shadow sensor time series with all damping loops ON and a very rough version of seismic noise being injected in all 6 DOFs (note that the y-axis is microns and the x-axis is seconds).

dvsim.png

Next, Jamie is adding the angular calibrations (so that SUSPIT and SUSYAW are in rads) and Chris is making vectift quality seismic noise injectors.

We also need to add coating thermal noise, suspension thermal noise, substrate thermal noise, ADC/DAC noise and a lot of MEDM screen indicators of what state we're in. I myself can't tell from the OSEM time series if its real or Sim.

redpill_bluepill.jpg

  4412   Fri Mar 18 14:18:00 2011 kiwamuSummaryGeneralnew laser pointers

Just for a record. We got 4 new laser pointers (2 greens, 1 blue, and 1 green and red combination). Don't lose them.

They reside in a bucket on the SP table, where IR viewers and sensor cards also reside.

DSC_2883_ss.jpg

  4419   Mon Mar 21 16:49:11 2011 kiwamuSummaryGreen Lockingplan for this week

- Plan for this week

  * Intensity stabilization for the end green laser (Matt / Kiwamu)

  * Hand off the servo from Green to Red (Matt / Kiwamu)

  * Y end green locking (Suresh / Bryan) (rough schedule)

  * Reconnect the X end mechanical shutter to 1X9 (Kiwamu)

  * Connect the end DCPD signal to a DAC (done)

  * Make a LPF in a Pomona box for the temperature (Larisa)

  * Clean up and finalize the X end setup (Kiwamu)

  * Make a item lists for electronics. Order the electronics. (Aidan / Kiwamu)

  4421   Tue Mar 22 00:01:25 2011 kiwamuSummaryGreen Lockingplan for daytime tasks

Some tasks for the daytime tomorrow.

  * Beam profile measurements of the Y end laser  (Suresh / Bryan)

  * Taking care of CDS and the simulated plant (Jamie / Joe)

  * Reconnect the X end mechanical shutter to 1X9 (Kiwamu)

  * LPF for the X end temperature feedback (Larisa)

  4433   Wed Mar 23 14:19:35 2011 KojiSummaryGeneralGrand Plan

This is the grand plan we talked about in the beginning of the meeting.

  • (Kiwamu) X-end Green cleaning up / Prep for DRMI
  • (Bryan) Y-end Green
  • (Suresh) Help Bryan / RF (w. Kevin)
  • (Jenne) MC WFS / Y-arm IR alignment / MC adaptive feedforward (incl. CDS)
  • (Koji) LSC
  • (Joe) CDS cleaning up
  • (Jamie) Help Joe / Noise Budget
  • (Larisa) PMC scan / PSL photo&diagram
  • (Barbarela) ASS
  4435   Wed Mar 23 19:16:17 2011 AidanSummaryGreen LockingY-END green equipment is all available

With the exception of a 2" mirror mount, I've confirmed that we have everything for the Y-end green production and mode-matching.

We need to calculate a mode-matching solution for the Lightwave laser so that it gives the correct beam size in the doubling crystal.

Additionally, Rana has suggested that we change the pedestals from the normal 1" diameter pedestal+fork combo  to the 3/4" diameter posts and wider bases that are used on the PSL table (as shown in the attached image).

Attachment 1: three-quarter_inch_pedestal.jpg
three-quarter_inch_pedestal.jpg
  4436   Thu Mar 24 01:16:19 2011 SureshSummaryGreen LockingY-END green equipment is all available
There was a 2" mirror mount among the spares on the PSL table.  It has a window LW-3-2050 UV mounted in it.  I
have moved it to the Y-end table.  We seem to have run out of 2" mirror mounts ...
  4471   Wed Mar 30 21:43:31 2011 Aidan, KiwamuSummaryGreen LockingCalculation of the green contrast on the RF PD

Skip to final thought ...

Kiwamu and I have set about measuring the contrast of the signal on the RF PD. We can only do this when the end green laser is locked to the cavity. This is because the green transmission through the cavity, when unlocked, is too low. Unfortunately, once we lock the green beam to the cavity, we can't keep the beatnote on the RF PD stable to within a few hundred Hz of DC (remember that the cavity is swinging around by a couple of FSRs). So we also lock the PSL to cavity.

At this point we're stuck because we can't get both of these beams resonant within the cavity AND have the frequency difference between them be less 1kHz - when the lasers are locked to the cavity, their frequencies are separated by an integer number of FSRs + a fixed frequency offset, f_offset, that is set by the phase difference on reflection from the coating between the two wavelengths (532nm and 1064nm). We can never get the frequency difference between the lasers to be less than this offset frequency AND still have them both locked to the cavity.

 

So our contrast measuring method will have to use the RF signal.

 

So this is our method. We know the incident power from each beam on the RF PD (see Kiwamu's elog entry here), but to recap,

P_green_PSL = 72 uW (as measured today)

P_green_XARM = 560 uW (as measured by Kiwamu last week).

The trans-impedance of the RF PD is 240 Ohms. We'll assume a responsitivity of 0.25 A/W. So, if the XARM transmission and PSL green beams are perfectly matched then the maximum value of the RF beat note should be:

RF_amplitude_max = 2* SQRT(P_green_PSL*P_green_XARM) * responsivity * transimpedance = 240*0.25*2*(72E-6*560E-6)^(1/2) (volts)

= 24 mV = -19.5 dBm (or 27.5dBm after the +47 dB from the two  ZFL-1000LN+ amplifiers - with +15V in - that protrude from the top of the PD)

The maximum RF strength of the beat-note that we measure is around -75 dBm (at the RF output of the PD). This means the contrast is down nearly 600x from optimal. Or it means something is broken.

Final thought: at the end of this procedure we found that the RF beat note amplitude would jump to a different and much higher amplitude state. This renders a lot of the above useless until we discover the cause.

  4479   Thu Mar 31 20:37:10 2011 AidanSummaryGreen LockingRF amplitude source

 I gutted one of the $2 red laser pointers to build a laser source whose amplitude we could modulate at RF frequencies. Basically, I cut off the bulk of the housing from the pointer and soldered a BNC connection into the two terminals that the 2x 1.5V batteries were connected to. When I applied 3V across this BNC connector the diode still worked. So far so good.

Next I added a bias tee to the input. I put 3V across the DC input of the bias tee and added a -3dBm signal into the RF port of the tee. The laser beam was incident on a PDA100A (bandwidth of 1.7MHz) and, sure enough, Kiwamu and I could see a flat response in the amplitude at a given drive frequency out to around 1.7MHz.

We should check the response on a faster PD to see how fast the laser diode is, but we should be able to use this now to check the RF response of the green beat note PD. 

TO DO:

1. Add some capacitors across the DC input of the bias tee.

2. Do something about the switch on the laser diode.

3. Attach some labels to the laser that specify what is the required DC voltage and the maximum acceptable RF modulation amplitude.

Attachment 1: P1000543.jpg
P1000543.jpg
Attachment 2: P1000544.jpg
P1000544.jpg
Attachment 3: P1000545.jpg
P1000545.jpg
  4480   Thu Mar 31 20:46:11 2011 AidanSummaryGreen LockingGreen beat note PD DC response

I measured the DC response of the Green PD


Power into PD at DC (green laser pointer) = 285 uW
Voltage out of PD = 552mV/(100x SR560gain) = 5.52mV
Photocurrent = 5.52mV/(241 Ohms)*3 = 68.7uA
Responsivity = 68.7/285 = 0.24 A/W

Therefore, since the responsivity is in the correct range for a Silicon PD at 532nm, the DC output is giving us sensible response to an input signal.


But, there is a 2.12MHz, 328mV oscillation on the DC output irrespective of the incident power.
 

  4483   Fri Apr 1 23:49:24 2011 kiwamuSummaryGreen Lockingtwo states in green beat-note

According to the measurement done by Aidan and me, there are two beat-note state.

One gave us a small beat signal and the other gave us a bigger signal by approximately 20 dB.

 

 A possible reason for this phenomenon is that the end laser is operating at a special temperature that somehow drives the laser with two different modes at the same time.

So that it permits the laser sometimes locked with one of the two modes and sometimes with the other mode.

For the first step we will change the temperature such that the laser can run with a single stable mode.

Then for investigating it we will put a scanning cavity on the X end table to see if it really exhibits a two modes or not.

Quote from #4472

The attached table shows the amplitude of the green beat note when the end laser was in various states. We can increase the beat note amplitude dramatically by switching to a different states.

  4487   Tue Apr 5 17:04:36 2011 steveSummarySAFETYcranes inspected and load tested

Mike Caton of Konecranes inspected and loadtested all 3  of the 40m cranes at max reach trolley positions with 1 ton.

Attachment 1: P1070522.JPG
P1070522.JPG
Attachment 2: P1070532.JPG
P1070532.JPG
  4488   Tue Apr 5 17:31:59 2011 steveSummaryGeneralnew laser pointers

Quote:

Just for a record. We got 4 new laser pointers (2 greens, 1 blue, and 1 green and red combination). Don't lose them.

They reside in a bucket on the SP table, where IR viewers and sensor cards also reside.

DSC_2883_ss.jpg

 Low power green-red laser pointers are in. High power green, red and blue pointers are confiscated.

Attachment 1: P1070530.JPG
P1070530.JPG
  4489   Tue Apr 5 19:54:39 2011 KojiSummaryGreen LockingHamamatsu S3399 test

Since last Friday I have been testing the broadband RF photodetector in order to figure out the capability of S3399 with the similar circuit as Matt's BBPD
We also like to figure out if it has sufficient performance for the 40m green locking.

The circuit diagram is shown in the first attachment. The RF amplifier is attached at the diode while the reverse bias voltage is applied at the other side of the diode. The amplifier's input impedance is used as the transimpedance resister. Note that the bandwidth of this configuration is limited by the RC filter that consists of the junction capacitance of the diode, the series resistance of the diode, and the transimpedance resister. This cut off freq is in general lower than that cut off obtained with the usual transimpedance amplifier which has the readout resister at the feedback path of the opamp.

The transfer function of the PD is measured using Jenne's laser. At the reverse bias voltage of 30V, the -3dB bandwidth of 178MHz was obtained. This is quite high bandwidth for the most of the applications at the 40m.

Because of the low transimpedance the low-noise level of the RF amplifier is very crucial. Recently we can obtain an ultra low noise RF amplifier like Teledyne Cougar AC688 which has the NF of 0.9dB with the bandwidth between 10MHz - 600MHz. Next step will be to obtain this kind of amplifier to test the noise performance.

 

 

Attachment 1: S3399_test_110405.png
S3399_test_110405.png
Attachment 2: S3399_test_110405.pdf
S3399_test_110405.pdf
  4490   Tue Apr 5 21:20:11 2011 KojiSummaryGreen LockingX-arm cavity locked with LB1005 servo box

Last Thursday, I tested Newport Servo Controller LB1005 with the X_arm green PDH servo.

The setup and the settings I could lock the arm is depicted in the attached figure.
To lock the cavity, follow the steps below

1) Toggle the switch to the "lower" position. This disengages the servo and reset the integrator.

2) Toggle the switch to the "middle" position. The zero freq is set to the "PI corner" freq. At the low freq the gain is limited
at the value of "LF Gain Limit". This gives us a single pole at the low freq.

3) Once the lock is acquired, toggle the switch to the "upper" position. This moves the pole freq to DC, resulting in the complete integration of the signal at the low frequency.

I measured the openloop transfer function (attachment 2). The amp is quite fast and exhibits almost no phase delay upto 100kHz.
The UGF was 10kHz with the phase mergin of ~45deg. I had to tune the input offset carefully to stay at the center of the resonance.

Attachment 1: servo.png
servo.png
Attachment 2: OLTF.pdf
OLTF.pdf
  4494   Wed Apr 6 19:36:32 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I moved the Hartmut Green PD to the Jenne laser bench to try to determine if the response at RF was reasonable or somehow very much smaller than it should be. It was set up as shown in the attached diagram. The first pass at this was by comparing the ratio of the RF photocurrent of the green PD to the RF photocurrent of the New Focus 1611 InGaAs PD. That ratio (at a sufficiently low frequency) should be the same as the ratio the DC photocurrents of the two PDs.

Using the network analyzer I measured the ratio of the voltages of the two RF signals (and then scaled each of these by the respective transimpedances of the PDs: 700 Ohms for the 1611 and 240 Ohms for the Harmut PD). The resulting ratio is shown in the attached plot.

I measured the DC voltages from each PD and scaled those by the transimpedances to get the photocurrent (10 kOhm for the 1611 and 80 Ohm effective for the Harmut PD). The ratio of the DC photocurrents was 0.37. This is roughly 3x the ratio of the RF photocurrents at 500kHz (=0.14). This discrepancy is uncomfortably large.

 The full set of measurements is given in the table below:

Measurement Value
DC voltage from Hartmut PD 6.5mV (checked by turning laser on and off and measuring the difference)
DC voltage from 1611 InGaAs PD 2.20V
Transimpedance of Harmut PD at DC 80 Ohm (effective)
Transimpedance of Harmut PD at RF 240 Ohm
Transimpedance of 1611 InGaAs at DC 10 KOhm
Transimpedance of 1611 InGaAs at RF 700 Ohm
Incident Power on Hartmut PD (100% on PD area) 0.28mW (measured by Ophir power meter)
Incident Power on 1611 InGaAs (<100% on PD area) 0.64mW
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W
   

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

Attachment 1: PD_measurement.png
PD_measurement.png
Attachment 2: plot_PD_RF_ratios.pdf
plot_PD_RF_ratios.pdf
  4497   Thu Apr 7 11:51:13 2011 steveSummarySAFETYnew crane operator inaugurated

Quote:

Mike Caton of Konecranes inspected and loadtested all 3  of the 40m cranes at max reach trolley positions with 1 ton.

 Konecrane representative gave crane operator training in the 40m. Koji has become a qualified, trained crane operator of the 40m lab.

Attachment 1: P1070535.JPG
P1070535.JPG
  4500   Thu Apr 7 16:09:17 2011 AidanSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

I think I had underestimated the responsivity of the Silicon PD at 1064nm. The previous value was based on a rough search online for the responsivity of Silicon (I couldn't find the product number of the actual PD we are using). For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm. 

If we calculate the responsivity of the Hartmut PD from the measurements I made today (input power = 0.300mW, output voltage = 5.56mV, effective transimpedance = 80 Ohms), then the responsivity at 1064nm is 0.23 A/W which is not an unreasonable number given the response of the Thorlabs detector.

Quote:

Measurement Value
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W
   

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

 

  4501   Thu Apr 7 19:28:02 2011 KojiSummaryGreen Locking(In)sanity check of Green PD - some inconsistencies

Responsivity of SGD-444A

Quote:

For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm.

 

Attachment 1: SGD-444A.png
SGD-444A.png
  4502   Thu Apr 7 21:58:57 2011 AidanSummaryGreen LockingBeat note amplitude

Having convinced myself that the green Hartmut PD is giving an acceptable response at RF frequencies I decided to double-check the beatnote at IR (fiber transmission from the X-end beating with the PSL). This took a while because I had to realign the beam into the fiber at the X-end (I had a PD monitoring the output from the fiber on the PSL table and 40m of BNC cable giving me the signal from it at the X-end).

Eventually, I managed to get a beatnote on the PD. At first there was no signal at the temperature calculated using Koji and Suresh's calibration, but it turned out that the mode-overlap wasn't good enough on the PD. Now I can clearly see beats between a couple of modes, one of which is much stronger than the other. I think we should use a frequency discriminator on the output from the IR PD to servo the end laser and keep the strong beat note within <100MHz of DC.

 

ELOG V3.1.3-