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ID Date Author Type Category Subjectup
  791   Sat Jan 21 01:20:28 2012 FrankDailyProgressRefCavrefcav work

re-did the RF wiring for both cavities:

  • Power splitters are now located on the table below the TTFSS box. This keeps all cables from/to the PDs and EOMs very short
  • Power level at res. EOM is ~20dBm, LO is ~7dBm (TTFSS has an internal amplifier) - Master LO is still a SR345 with 23dBm.
  • Removed all old cables which we don't need anymore and moved the ones used from the table to the framing structure to get less seismic coupling to the floating table from them.
  • Finished phase adjustment for the TTFSS and locked the cavity using all three actuators.
  • Temp feedback to the laser is now done by the TTFSS unit. There is NO computer control for any of the FSS stuff anymore - only for the PMC. cable to laser unit is temporary as we don't have the right cable length available.
  • Power is adjusted to 1mW (total)
  • We still don't have enough gain. Common gain is at max, fast at 782, (offset 500).
  • Measured in-loop ep noise floor - will add plot later. Noise floor measured at OUT1 of TTFSS box (common path, mixer output) is ~10nV/rtHz
  • Error signals are still pretty tiny (230 mVpp)
  • re-wired beat setup. Need to add a coupler to hook up the frequency counter in parallel. Will use that for characterization of radiative heater and temp feedback to it for beat note stabilization.

Next steps:

  • Full characterization of 14.75MHz res. PD from TNI
  • build a second PD for 14.75MHz.
  • add some channels to DAQ - there are currently no FSS channels at all
  • measure beat note by Tue
  • finish in-vac wiring
  • open vacuum can and install rad shields+heater
  • while in air measure TF from table to top stack with small accelerometer and compare with model
  793   Mon Jan 23 09:16:43 2012 ranaDailyProgressRefCavrefcav work

 

 The PD seems certainly good enough - no need for new pre-amp. With such a high Q resonance, you might be limited by the 1 pA/rHz of the preamp, but if so that's OK.

Error signal size seems too small: for 1 mW and 6 kOhm from the RFPD...

  794   Mon Jan 23 11:36:18 2012 FrankDailyProgressRefCavrefcav work

Right, it's certainly good enough for now and the next months. However there are better opamps available which might give us a better SNR at lower power levels which i would like to try (and replacing opamps is only a few minutes). This would give us the chance to operate at lower power levels with better SNR, which might be useful later.

The error signal size mentioned has been measured with an un-characterized PD from the TNI, where i already mentioned that they are too small but i don't know what's inside the PD. We will check today what we get from the new PD and then either fix/modify the TNI PD or a second PD from LLO (where i have to replace the diode which has a big burn spot)

Quote:

 

 The PD seems certainly good enough - no need for new pre-amp. With such a high Q resonance, you might be limited by the 1 pA/rHz of the preamp, but if so that's OK.

Error signal size seems too small: for 1 mW and 6 kOhm from the RFPD...

 

  112   Sun May 2 19:18:36 2010 FrankMiscRefCavreference cavity moved to new chamber

i finally moved the reference cavity to the new chamber and pump it since Friday. The legs are now insulated and it comes with a removable, thick insulation using the good CertiFoam25 insulation.The sensors for stabilization are now glued to small pieces of Kapton tap which is sticks directly to the chamber surface. I'm still using the four AD590 sensors as we have all the electronics available and ready to use. I modified the temperature sensor readout box a little bit to gain a little more SNR. The gain in the first stage (TIA) is now 29.4k (~9.2V output). The individual outputs are now connected to the DAQ. In addition the sum of all four is subtracted from a reference voltage (AD586 reference) so that the output is 0 at 35C with a range of +-5K (we need at least 4.5K for tuning one FSR, so to not be stuck at either ends i made it a bit larger ). This signal is also connected to the DAQ. An additional sensor (PT1000)  is now connected to the top plate of the stack, right below the reference cavity. Readout electronics is in preparation, as well as for the other platinum sensors we can put on the outside of the chamber (not done yet). I'm also planning on replacing the noisy power supplies by low-noise current sources to drive the heaters. The required heating power could be reduced a lot to ~10W total now, measured with a not fully sealed insulation and missing parts. So i expect even less when we are done with that.

  298   Thu Aug 19 19:17:44 2010 FrankSummaryDAQremoved connecting blocks J21 & J22

removed both 9-pin D-SUB blocks (blocks J21 & J22) which were used for the RF photodiodes (PMC, RCAV) before (only to power them).
As we hooked them up to individual power supplies a long time ago they are free to use for the temp readout of the cavities.

  420   Mon Dec 6 22:09:59 2010 frank, taraDailyProgressBEATreplacing PMC, adding EAOM

Today we 1)replaced out PMC with DMASS' PMC and get better transmission efficiency, 2) added EAOM to modulate the laser intensity

3) measured TF to see how RIN couples into laser frequency shift, it is small and not the current limiting source for now.

 

Our PMC is not very clean and get the transmission only ~60-70%. The PMC we got from DMASS is much better, now the transmission is up to ~80-90%, we have not

align it carefully yet.  After replacing the PMC, the beat noise did not change.

 

The Faraday isolator was re-installed and optimized, I used the wrong side before and dumped the beam inside the isolator, instead of outside.

A PBS and a 1/2 wave plate were installed after the PMC to adjust the power without changing the power input of the PMC, the beat noise gets higher

a bit.  I mounted the beam splitter for beat signal on a more rigid post, and aligned the two beams, then measure the beat noise.

See plot.

 Intensity modulation set was installed. The set consists of a 1/2 WP, an EAOM, a PBS. Then we amplitude modulated by sending a sine wave to

the EAOM, and measured the TF between (The excitation is sent to the EAOM)

 

1) intensity modulation and ACAV_trans_PD

2)intenisity and RCAV_trans_PD

3) intensity and beat noise

4) ACAV_trans_PD and VCO feed back to AOM

extra: we measure the TF between PMC_trans_PD and ACAV/RCAV_trans_PD, since the line width of PMC is much larger than that of RCAV/ACAV,

we can measure the TF of their poles.

 [The plot will be posted soon]

  946   Fri Apr 27 22:37:54 2012 taraDailyProgressBEATreplacing one mirror mount in beat path

One of the mirror mount in beat path was not properly mounted on the board because of the limited space. I changed that mirror mount with a block mount (similar to the one we use for the beam recombining beam splitter). The acoustic coupling is getting better.

 

IMG_0842.jpg

fig1: the mirror with the mount similar to that of the BS, see psl:818.

beat_2012_04_27.png

fig2: beat signal, comparison between before and after the mount replacement.

I'm not sure why the beat signal at 2kHz and above does not match. It might be that I did not align the beat well enough, or the alignment in front of the cavities changed. However, there is a significant improvement in beat signal, except the new mechanical peak around 1.2kHz, it might be from the new mirror mount.

 

Note: I turned off the air compressor switch after I measured the beat before the mount replacement to make sure that the seismic isolation for both measurements will be similar.

 

 

  956   Wed May 9 19:59:44 2012 taraNotesSeismicreplacing table legs

I'm replacing our table legs with the ones from Jan's lab.  Those should be a little newer than the one we are using. However, the regulators we have are not compatible with those new legs.

 The pressure regulator for the old legs (which we are using) need a plate with a slot for holding it lever (in red square). However, the legs I took from Jan's lab do not have such the structure because it has different regulator style (in green square) and there is only one.  Basically, we don't have enough regulators for the new legs (need 3, have 1). I'll look around, check the 40m if they have some unused regulator.

IMG_0893.jpgIMG_0894_1.jpg

Above, left) the structure for the regulator for the current legs. Right) the regulator for the new leg.

 

 

 

 

 

  958   Thu May 10 16:04:24 2012 taraNotesPurchasesreplacing table legs

There are no spare leveling valve at 40m, I'll buy a set of new one from Newport. It costs ~ $ 800. I asked Eric and he said to go ahead and buy it.

leveling valve set of 3 

It should be able to mount on the leg with an adapter piece easily.

This is how it looks like when it is mounted on the leg

http://search.newport.com/?q=*&x2=sku&q2=S-2000A-819.5

Quote:

I'm replacing our table legs with the ones from Jan's lab.  Those should be a little newer than the one we are using. However, the regulators we have are not compatible with those new legs.

 The pressure regulator for the old legs (which we are using) need a plate with a slot for holding it lever (in red square). However, the legs I took from Jan's lab do not have such the structure because it has different regulator style (in green square) and there is only one.  Basically, we don't have enough regulators for the new legs (need 3, have 1). I'll look around, check the 40m if they have some unused regulator.

IMG_0893.jpgIMG_0894_1.jpg

Above, left) the structure for the regulator for the current legs. Right) the regulator for the new leg.

 

 

 

 

 

 

  959   Fri May 11 01:00:42 2012 taraNotesPurchasesreplacing table legs

Frank told me to get the leveling pressure from Cryo table. Now I have enough for the table (a set of three), so I don't need to buy the new set. All CTN table legs are replaced. I'll connect the pressure tube to the legs tomorrow.

Quote:

There are no spare leveling valve at 40m, I'll buy a set of new one from Newport. It costs ~ $ 800. I asked Eric and he said to go ahead and buy it.

leveling valve set of 3 

It should be able to mount on the leg with an adapter piece easily.

This is how it looks like when it is mounted on the leg

http://search.newport.com/?q=*&x2=sku&q2=S-2000A-819.5

 

 

 

  962   Tue May 15 21:57:49 2012 frank, taraDailyProgressSeismicreplacing table legs

The leveling valve for table legs are installed. With the new legs, the beam can maintain its alignment better than before (from 30 minutes observation period).

      Three leveling valves are installed, all of them have T connectors for linking two legs together, so we use a short tube, filled with epoxy to blind the unused side of the T for two legs. The compressor works every 30 mins. Although the period is shorter than before (~1 hr), but  it takes only ~ 2 minutes to compress the air, and the beam alignment is stable before and during the air compression, see fig 2. 

IMG_0930.JPG

fig1: new legs with new leveling valve.

IMG_0931.jpg

fig2: RCAV_RFPD_DC, over 100 seconds while the compressor is working. Generally, the reflected power on the RFPD increases if the alignment changes. The stable DC level indicates good stability. For this setup, the DC level is 1.7V. when the beam is off resonance. The previous setup had bad stability, it drifted from ~ 100mV to ~400mV.

We will use soap water to check for any possible leak tomorrow to make sure that there is no obvious leak in the setup.

  963   Wed May 16 22:25:06 2012 frank, taraDailyProgressSeismicreplacing table legs

We check the leak. There are no obvious leak on the hose or connectors. It appears that the current leveling valves are more sensitive than the previous sets. That explains why the compressor is activated every 30 minutes while the beam alignment is still quite good.

  2   Sun Nov 8 14:35:25 2009 FrankLaserRefCavresonance frequencies

i checked the resonant frequency of both cavities in order to see if we can lock both using the existing frequency actuator (AOM) for the first one. Used the slow frequency actuator of the NPRO (temp) to scan the frequency.

refcav1 is resonant @ 0.7578V

refcav2 is resonant @ 0.5068V

assuming about 1GHz/V the resonances are about 250MHz different. So we have to use the thermal actuator on one of the cavities in order to tune it. I started a calibration scan for the heater on friday in order to set the correct heating power as the time constant is more than an hour and trial and error method would take too long...

  4   Mon Nov 9 02:19:45 2009 ranaLaserRefCavresonance frequencies

I don't know if its worth the trouble, but we do have a ~200 MHz AOM. Sam Waldman had us buy one of these for doing the OMC g-factor measurements.

 

  5   Mon Nov 9 18:49:15 2009 FrankLaserRefCavresonance frequencies

Quote:

I don't know if its worth the trouble, but we do have a ~200 MHz AOM. Sam Waldman had us buy one of these for doing the OMC g-factor measurements.

 

 i think the problem is that we don't have the VCO for the FSS for 200MHz. so i think it"s easier to heat one of the cavities. the temperature required to match them should be only a couple of Kelvin difference. and by heating one of those cavities the frequency noise due to ambient temperature fluctuations might be uncorrelated as well.

i had a problem taking the data from one of the photodiodes over the weekend. We had a loose connection for the cavity1 transmitted light PD. i only checked on a scope and assumed that the (already) connected cable to the DAQ is OK as i saw some fluctuations while scanning. so i have no data from that long scan over the weekend. we repaired this today and also made the FSS for the first cavity work. now everything is working and i started a new measurement...

sweep frequency is 50uHz which is almost 3h for the full ramp from min to max

C:PSL-FSS_RMTEMP is used for the heating voltage set point (not the heater voltage!). calibration is [-273-(voltage*100)] (is still calibrated for temperature sensors)

  • cavity1 is on resonance if C:PSL-FSS_RCTRANSPD is ~1.8V
  • cavity2 is on resonance if C:PSL-PMC_TRANSPD is ~780mV

we will add the temp sensors on the cavity tank tomorrow...

  1296   Tue Aug 13 12:39:36 2013 EricaDailyProgressfiber opticrewrote calculations for converting from voltage noise to frequency noise
The equation for voltage is derived here: 1241
  712   Mon Oct 24 21:20:26 2011 frank, taraDailyProgressFSSrf summing box

 We check modulation depth of the PDH signal to see if we have enough modulation depth or not. The result will be analyzed later.

==motivation==

Based on the design of the RF summing box we got from Peter ,

IMG_2176.JPG

the TF from 35.5 MHz input to EOM does not have a resonant frequency at 35.5 MHz. Rather, the resonance is ~ 10MHz. We are not sure if we need to have the resonance at 35.5 Mhz or not. So we decide to check if the modulation index is already large enough for the current design, and compare it with that of the modified one. If the modulation depth is already large enough, we can keep it as it is. Basically we just need a high pass for 35.5MHz input to EOM.

By changing the inductance L from 1uH to 80 nH, the peak can be moved to ~ 35.5 MHz.

==Setup & Measurement==

 We want to check the slope of the error signal when the RF power changes, so there's a small change in the setup, see fig1.

setup.png

The input power is 2mW.

Then the slope of the error signal was record, the pk-pk of the sideband and carriers were also record between the input power of 10dBm and 13dBm to the EOM.

Then the RF summing box was modified (changing L), and the measurement was repeated.

==results==

coil       |  input pwr (dBm) |  Carrier slope ( MHz/V) |   pk-pk value (mV) (carrier/side band)          

 80nH   |     10                   |     1.43                          ||   28/18

            |             13           |      1.11                          ||  38.8/22.6

1 uH    |       10                 |      0.91                          ||   49.2/27.6

            |             13          |       0.74                         ||    68.4/37.2

 

From the result, the best setup is 1uH coil with maximum side band power which provides the best slope ( maximum gain at frequency discriminator). Note that 1uH coil is the original value for the schematic, so modification to 80nH does not help.

-> Modulation depth

  651   Thu Aug 4 22:45:10 2011 RaphaelDailyProgressElectronics Equipmentrfpd progress

I measured the shot noise again because the data I got yesterday was kind of garbage. I tried to get an error estimate by taking average of at least 10 measurements for each dc output. However, Frank said that the error wasn't so important. I was happy to know that I could just let the spectrum analyzer do 100 averages and not worry about getting a standard deviation. The data that I got looks pretty decent now. I'll post the graphs after I analyze the data.

  717   Thu Oct 27 20:45:58 2011 frank, taraNotesSeismicring down measurement for rubber spring

We did ring down measurement of the rubber cone used for supporting the seismic isolation stacks. The resonant frequency and Q of the spring will be used for better TF of the stack later. The measured values are f =46.7 Hz, Q = 14.67. (mass will be added later)

[details about the measurement will be added later]

These are the results from the data Frank gave me.

There is a problem in the result. The frequency of the ring down response can vary from 42 Hz to 47 Hz. So when I fit it I cannot really get the "best" frequency fit from the whole train of data.

From figure (1)

  • At point A) The data and fit seem to be well matched.
  • At B) The phase of the fit curve advances the measurement ( the fit frequency is too large)
  • At C) The phase of the fit curve lags the measurement (The fit frequency is too small)
  • At D) The frequency totally changes causing the fit and the measurement to be almost out of phase

 fit4.png

fig1: showing fit with the data. Non-linearity behavior of the spring can be seen clearly.

 

There are 5 sets of measurement. I notice that the nonlinear behavior was very small in the first data set which has its initial amplitude smaller than 0.4 V

fit1.png

fig2 Fit from data TEK00000. The initial amplitude is less than 0.4 V.

 

For other data sets, where their initial amplitude exceed 0.4, it does not matter where I analyze the data, fitted frequency still varies a lot. I take the data set #4, and  fit the data at high amplitude and low amplitude (when it is less than .15V). The frequency still varies. See fig3 below.

comparefit.png

fig3: fit from data TEK00003. Even when I use data at smaller amplitude, frequency still varies from the fit, similar to what happens in fig(1).

 

The problem is, the fitted frequency from fig(2) is ~ 46 Hz, while the fitted frequency (at low amplitude) from fig(3) is ~ 43 Hz. The difference is too large. So we decided to sample the frequency by averaging the frequency over 3 adjacent cycles of the ring down data, ignoring the first few peaks. Then histogram the samples.

hist.png

Most of the counts are around 46.5 Hz, which is contributed mostly from the first data set where the variance is very small. I think it is ok to pick the value from that data set

f =46.7Hz, Q = 14.67.

  721   Thu Nov 3 01:55:03 2011 FrankNotesSeismicring down measurement for rubber spring

The total mass of the load including the accelerometer was 397g. Will recalculate the spring constant an damping of the RTV later.

 

  479   Tue Feb 8 00:26:44 2011 frank, taraDailyProgressRefCavrunning thermal PID perl script

We installed ezca library on PLS's Sun machine. Now, we can run perl script for Refcav thermalPID control.

The PID gain is being optimized. Channels for SLOWDC's PID thermal control are also created (C3:PSL-FSS_SLOWPID....)

and saved in fss_pid.db file. 

 

We copied a command package from op440m to the sun machine here, and it can run perl script (RCthermalPID.pl)used at 40m.

The current gain setup is

KP = -0.6

KI = -0.007

KD = 0

The plot below shows a response from a step change of temperature (set to 34.86 C). The cavity temperature does not hang around the set temperature. Instead, it hovers just below the set temp point, see fig1. The time span is 110 mins.

I think it reaches equilibrium quite fast.

 

 

  484   Wed Feb 9 15:41:45 2011 frank, taraDailyProgressRefCavrunning thermal PID perl script

The thermal control perl script is added for ACAV. The file is saved in SUN machine, all channels are renamed for ACAV and the limit for hardstop is changed to 4.9 V.

an medm screen for ACAV RCPID control, C3PSL-ACAV_RCPID.adl, is also created.

Now we are tuning the gain for ACAV Temperature control.

Quote:

We installed ezca library on PLS's Sun machine. Now, we can run perl script for Refcav thermalPID control.

The PID gain is being optimized. Channels for SLOWDC's PID thermal control are also created (C3:PSL-FSS_SLOWPID....)

and saved in fss_pid.db file. 

 

We copied a command package from op440m to the sun machine here, and it can run perl script (RCthermalPID.pl)used at 40m.

The current gain setup is

KP = -0.6

KI = -0.007

KD = 0

The plot below shows a response from a step change of temperature (set to 34.86 C). The cavity temperature does not hang around the set temperature. Instead, it hovers just below the set temp point, see fig1. The time span is 110 mins.

I think it reaches equilibrium quite fast.

 

 

 

  153   Tue Jun 8 20:16:21 2010 taracLaserLaserscanning ACav

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

  154   Wed Jun 9 03:55:40 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  156   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  155   Wed Jun 9 03:55:41 2010 FrankLaserLaserscanning ACav

There is no attenuator connected to the AOM. The device on the AOM (the white attenuator looking like thing) is a DC-blocker which protects the AOM. The high-power attenuators which have to be used to attenuate the high RF power in order to measure it are the black, radial heatsinked parts.

Quote:

Now I'm working on aligning the beam into ACav. I got the reflected light on the PD, and I'll scan the cavity soon.

My plan on connecting the servo:

I'll use a power splitter to split 35.5 MHz signal from "LO to SERVO" channel on the crystal frequency reference card, which is driving the 35.5 MHz EOM, to beat with the PD's signal.

If the power is too low, I might use a Marconi to beat the signal for ACav, with appropriate power level.

I also need to check which power splitters and mixers are suitable for our power output. 

The demodulated signal will be filtered by a 50 Ohms low pass filter before sent to "Servo Input" channel of the Universal PDH Servo box (D0901351.)

 

The box has two knobs that allow us to change gain and LO phase manually.

From the PDH box, the "Piezo Drive Out" will be connected to the VCO's External Modulator channel.

 

 

About AOM:

     I try to adjust the voltage of the VCO that maximize the 1st order beam from AOM. I use 5 V which is maximum on the medm control screen, but I'm not sure if it's the best or not because,

the power in the 1st order still goes up even though I reach 5V (see the attached plot.) There is an attenuator on the AOM which Frank left for me. I'll check the power that goes into the AOM and check the manual again how much power it can take. If it can take more power, I'll remove the attenuator and see if I can get more efficiency. But I'll do that after aligning ACav.

 

 

  157   Thu Jun 10 00:21:15 2010 taracLaserLaserscanning ACav

I'm scanning the laser to align ACav. It's a long day of adjusting 4 knobs and 1 lens (and one periscope for a while.) 

I see higher order TEM modes at the back of the cavity, but still cannot see TEM 00 yet.

Thu Jun 10 00:20:39 2010

 

I saw TEM 00 and trying to minimize the reflected power on the PD.

I just realize that the beam path is very close to the edge of the hole (see attached.) Part of the beam might be clipped.

I'll check that with IR viewer tomorrow.

The value for Voltage Calibrator is 6.17 V.

Thu Jun 10 00:58:56 2010

 

  158   Fri Jun 11 01:04:42 2010 taracLaserLaserscanning Acav2

From yesterday, after getting TEM 00 out of the cavity, I checked the beam if it's clipped on the edge of the hole or not. There is small light on as seen by an IR viewer. Since it seems to be very small, I'll leave it as it is for now.

There was one problem. The beam was almost on the edge of the periscope's top mirror, I decided to change the height and move the periscope , and other optics in the row, side way, since the beam was really close to the edge of the opening ( I set the beam path to the center of the hole before, so it's bit off ( 5mm, 0.2") from the cavity's natural axis), and made sure that the beam is on the center of every mirror. Then, it's 4 knob adjustment which takes me a whole day again

As of now, I got TEM00, out of the cavity. I still have to adjust the lens' position to minimize the reflected beam. Before doing so, I'll prepare a mixer, a power splitter for locking the cavity.

 

One thing about the AOM, the beam after double pass is quite elliptic. I'm not sure how to correct it, and whether it's going to be a problem or not. I'll find something to read about this.

Fri Jun 11 01:00:17 2010

  899   Fri Apr 6 00:34:28 2012 ranaHowToNoiseBudgetscattered light hunting

How to find parasitic scatterers by the GEO600 gang.

  374   Wed Oct 27 13:12:12 2010 taraNotesEnvironmentschedule for pipes installation

 At 8:30 am, tomorrow, a workman will come in and install two pipes in the lab.

The pipes will be brazed, so no smoke or dust. 

The working area will only above the fume hood near the entrance.

I'll be in the lab during the installing process.

  375   Thu Oct 28 10:49:53 2010 taraNotesEnvironmentschedule for pipes installation

The pipes are installed. The insulation for the pipes will be installed on Nov 2, Tuesday 8:30am.

The work area will be the same, they just wrap insulation around the pipe, there should not be a lot of dust.

Quote:

 At 8:30 am, tomorrow, a workman will come in and install two pipes in the lab.

The pipes will be brazed, so no smoke or dust. 

The working area will only above the fume hood near the entrance.

I'll be in the lab during the installing process.

 

  377   Tue Nov 2 17:50:33 2010 taraNotesEnvironmentschedule for pipes installation

The insulation work is done. 

Quote:

The pipes are installed. The insulation for the pipes will be installed on Nov 2, Tuesday 8:30am.

The work area will be the same, they just wrap insulation around the pipe, there should not be a lot of dust.

Quote:

 At 8:30 am, tomorrow, a workman will come in and install two pipes in the lab.

The pipes will be brazed, so no smoke or dust. 

The working area will only above the fume hood near the entrance.

I'll be in the lab during the installing process.

 

 

  212   Tue Jul 13 14:46:23 2010 taraNotesFSSschematic for FSS servo

The current FSS servo we are using is labeled D980536 Rev. C on the PCB, but the schematic that matches the PCB more is D980536-D (there are minor corrections).

The schematic is posted below.

I'm checking If the board will match the schematic or not. Then its transfer function (TF) will be calculated by simulink, and compared with the result from measurement. 

The correction will be added soon.

 

  859   Sat Mar 3 14:52:40 2012 FrankNotesTempCtrlscript crashed - restarted

the temp control script crashed with an epics exception some time ago - the reason why it took forever to heat the chamber. Restarted the perl script and also changed the hard stop for the heater from 1.7 to 2.0 in the code to get more umpf

  1274   Thu Aug 1 21:19:57 2013 taraDailyProgressBEATsearching for beat

I locked both cavities and trying to search for the beat signal, I have not succeeded yet.

I used lenses that could get the two transmitted beam to be close and small enough for the beat PD (new focus 1811) (we ordered  what we need but they are not here  yet).

I locked ACAV at a fixed SLOW DC level (1.207 V), and varied RCAV's SLOW DC level from 1.199V, 0.33V, -0.554V, -1.477V (1FSR ~ 4GHz is about 1 V). The slider for RCAV slow is set to +/- 2V so I have not tried other values yet. It can be changed to -2V to 9 V, but I have to restart the crate which will disturb the temperature servo, so I'll try to adjust RCAV slow value using a voltage calibrator instead.

I talked to Evan about the beat measurement in GYRO lab, the SLOW DC for both lasers can be different up to 6 V (for ~100MHz beat). see gyro1832

I varied RCAV's SLOW DC first because this path does not have a PMC, so I don't have to worry about locking the PMC.

From PSl:1124 ,the beat frequency should be ~60-100 MHz, without the heater on any cavity.  I'll try the same method to check the beat frequency between the two cavities one more time. If it is still ~ 100 MHz, I'll increase the range of SLOWDC, and see if the beat will show up of not.  The setpoint was not changed that much (31.2 to 31.25), So I expect the beat frequency should still be close.

If the beat still not show up, I'll try to realign the beam.

 

Current setup

Vac chamber Setpoint = 31.25

Vheat for RCAV =  0

Vheat for ACAV = 0

 

 

  1275   Fri Aug 2 12:18:16 2013 taraDailyProgressBEATsearching for beat

Found the beat @ 116 MHz. RCAV SLOW =5.762V, ACAV SLOW = 1.209 V.

beat_2012_08_02.JPG

 

beat 1kHz input range, calibration  = 718 Hz/V

nb_short_cav.png

above, beat signal with 1kHz input range on Marconi.

Plenty of things that I need to optimize and add:

input optics (ACAV/RCAV):

  • beam alignment
  • optimizing quarter wave plates in front of the cavities.
  • block all the reflected beams properly
  • fixing the back reflection from vac window for ACAV.
  • measure error point noise from both servos and compare them with beat
  • optimizing TTFSS servo gain

Beat setup:

  •  mode matching lens
  • power on beat PD
  • optimizing PLL servo
  • implementing ISS

Seismic isolation

  • new table legs ( I have not ordered the new set yet). The current set is broken
  •  
  702   Mon Oct 10 21:30:45 2011 Tara, FrankSummarySeismicsecond leg replaced

we have replaced the second leg which was leaking. It could be that the legs are simply to old and the rubber got brittle. As far as i know the table has never been operated floating as it had the suspended reference cavity on it since the beginning. We operate at around 85 PSI, maximum operational pressure is specified at 100PSI so that should be OK. The second leg started leaking after one day of floating operation. We disassembled one today to have a close look but we can't really tell where the leak is. We will check with some pressure to see what's broken within the next few days. Let's see what the other legs do in the near future. We still have plenty of "spares", as Aidan bought two new sets (taller ones) for the old tables in the TCS lab. So we have 8 short ones which are currently not used (and seem to be newer than the ones we currently have). And they still work as passive legs.

  703   Wed Oct 12 00:53:40 2011 Tara, FrankSummarySeismicsecond leg replaced

As the table was floated, we measured the noise from error point again.

 

     We tried to determine if the noise bump we saw were from the window, so we place an extra window in front of a mirror [add fig] and compare to the noise when there was no window. The results are not different that much.

     From a quick look, by adjusting the input power, from 1mW to 10mW. The shape of the noise from error point changes substantially. This could be come from RFAM or scattering.  I'll measure the noise vs input power after I optimize everything first. RFAM, beam splitter, back reflection have to be optimized.

 

 

  705   Thu Oct 13 02:36:58 2011 Tara, FrankSummarySeismicsecond leg replaced

After optimized everything, I repeated the measurement that was done in this entry (noise at detection point). There is some improvement, the result is shown below.

 

==What have been done==

By "optimize everything", I meant:

  1. The Faraday Isolator was installed back in the setup, and optimized for maximum isolation. [add pic]
  2. Beam splitter and quarter wave plate sets (for double passed AOM and cavities) were optimized for minimum back reflection.
  3. EOM with half wave plate were adjusted for minimum RFAM (reduced by ~ 20 dB)
  4. Beam alignment to the cavities: visibility are up to 93% for both cavities now.

 Measurement Recap:  We want to check the noise from scattering noise or RFAM at the detection point, so we measure the noise at error point when the beam reflected off the cavity, or a mirror in front of the chamber (cf entry:700). We also want to see the dependent on power input, so we chose 10mW, 5mW and 1mW input power.

    Below are measurements from error point (Mixer out) which are calibrated to absolute frequency noise through the slope of error signal from each setup (power input of 10mW, 5mW and 1mW)

plot_2011_10_12.png

==Comments for the results==

  1.    The noise level when the beam reflected off the cavity goes down when we float the table and optimize everything ( red, green, blue are lower than pale pink (result from 2011_10_07).
  2.    The noise level when the beam reflected off the cavity do not change much with input power ( red, green, blue are about the same)
  3.    At 1mW the noise at high frequency (above 50Hz)  raises up for both cases (reflected off cavity / mirror) I'm not sure what happens. The calibration seems to be ok since the noise level at low frequency matches the results from 5mW and 10mW setup.
  4.    Seismic stack's resonant frequency at 6.7 Hz shows up more clearly after RFAM/ back reflection are minimized.

 

To Do: We will check the beat signal tomorrow. There should be improvement, since optics are optimized and the table is floated.

  734   Wed Nov 16 19:11:38 2011 taraNotesNoiseBudgetseimic coupling to beat noise

Seismic noise is currently a limiting source for our setup, here is a list for what we have to do for figuring out the coupling from seismic to beat. Once we know exactly what's going on we can fix it correctly.

  1. TF measurement between seismic and feedback to NPRO (RCAV)
  2. TF measurement between seismic and feedback to VCO    (ACAV)
  3. TF measurement between seismic and beat             (psl:)

[more details soon]

  687   Tue Sep 20 00:12:46 2011 ranaDailyProgressBEATseismic noise coupling

By taking the passive transfer function between a vertical seismometer on the table and the individual cavity signals, we should be able to see which direction to move the cavity supports so as to minimize the seismic coupling.

Our first iteration probably will have a sign error, but by making a few iterations we ought to be able to home in on a better support. Also, we should compare the theoretical estimate with the measured coupling in units of strain/(m/s^2).

  688   Tue Sep 20 01:49:44 2011 FrankDailyProgressBEATseismic noise coupling

Tara showed me a quick plot which showed the spectrum taken with the new (current) setup and the one taken when we removed the springs from the wire suspension. They look pretty identical between 10Hz and 100Hz or so. So it is likely that we see a lot of vertical seismic. I've measured a little bit at low frequencies to see where we are and we are better than before now, i would guess an order of magnitude or so, without any optimized stabilization, alignment and loops. Tara will take a nice set of measurements tomorrow and make a nice plot. The peak at 6.7Hz or so is actually the horizontal motion of the two top stack plates (not only the top plate). I used our pzt-shaker to shake the table and even with a small signal i could increase it until i got scatter noise bumps around 100Hz. So we have to damp this somehow. Is there an easy way to get some more vertical isolation? what about putting the top plate on a few springs instead of rubber? How much do you typically get when floating the table? I don't have realistic numbers for that...

We also don't have a seismometer. Jenne took her's back and Jan shipped the others back to where they came from i think. i think we should get one which we can share between labs in bridge which we can keep for longer. We needed one quite often in the past couple of months and i guess once we start with the cryo cavity we will even more frequently. Any idea where to get a cheap one? We don't need an STS-2 or so... Seismic sucks anyway in bridge...

The problem with moving supports is that the spacer has pretty wide groves. But we have to think about a clever support anyways. Currently it's sitting on viton in the groves of the spacer, which, according to comsol, is very close to the optimum position but who knows in reality.

Quote:

By taking the passive transfer function between a vertical seismometer on the table and the individual cavity signals, we should be able to see which direction to move the cavity supports so as to minimize the seismic coupling.

Our first iteration probably will have a sign error, but by making a few iterations we ought to be able to home in on a better support. Also, we should compare the theoretical estimate with the measured coupling in units of strain/(m/s^2).

 

  690   Wed Sep 21 01:39:11 2011 taraDailyProgressBEATseismic noise coupling

The beat signal I measured today(orange) has noise level close to what we had before (blue,purple), so I'll try to check it again tomorrow. Meanwhile, this is the plot with beat signal when we modified the suspension (removed the spring), and the cavities were in two separate chambers (blue). The noise level around 20-100 Hz is very similar to what we have right now. Since the spring filters mostly vertical seismic, these peaks should be mostly vertical seismic coupling into the system.

beat_2011_09_20_m.png

Quote:

Tara showed me a quick plot which showed the spectrum taken with the new (current) setup and the one taken when we removed the springs from the wire suspension. They look pretty identical between 10Hz and 100Hz or so. So it is likely that we see a lot of vertical seismic. I've measured a little bit at low frequencies to see where we are and we are better than before now, i would guess an order of magnitude or so, without any optimized stabilization, alignment and loops. Tara will take a nice set of measurements tomorrow and make a nice plot. The peak at 6.7Hz or so is actually the horizontal motion of the two top stack plates (not only the top plate). I used our pzt-shaker to shake the table and even with a small signal i could increase it until i got scatter noise bumps around 100Hz. So we have to damp this somehow. Is there an easy way to get some more vertical isolation? what about putting the top plate on a few springs instead of rubber? How much do you typically get when floating the table? I don't have realistic numbers for that...

We also don't have a seismometer. Jenne took her's back and Jan shipped the others back to where they came from i think. i think we should get one which we can share between labs in bridge which we can keep for longer. We needed one quite often in the past couple of months and i guess once we start with the cryo cavity we will even more frequently. Any idea where to get a cheap one? We don't need an STS-2 or so... Seismic sucks anyway in bridge...

The problem with moving supports is that the spacer has pretty wide groves. But we have to think about a clever support anyways. Currently it's sitting on viton in the groves of the spacer, which, according to comsol, is very close to the optimum position but who knows in reality.

Quote:

By taking the passive transfer function between a vertical seismometer on the table and the individual cavity signals, we should be able to see which direction to move the cavity supports so as to minimize the seismic coupling.

Our first iteration probably will have a sign error, but by making a few iterations we ought to be able to home in on a better support. Also, we should compare the theoretical estimate with the measured coupling in units of strain/(m/s^2).

 

 

  432   Thu Dec 16 12:38:57 2010 Frank, JanDailyProgressEnvironmentseismometer installed on PSL table

Jan and I installed one of his seismometers on the PSL table to get some seismic data for the noise projection.
We ran three cables (x,y,z) to his lab trough the door connecting both labs. Jan is taking some data.
Once the device is in equilibrium (thermally) we can also perform some correlation measurements.

  550   Wed Mar 23 23:22:28 2011 taraDailyProgressElectronics Equipmentsensing noise checking

OK, so what I did

1) Compare the sensing noise between ACAV and RcAV loop.

    Measure sensing noise from RCAV loop. it is about 30e-9 [V/rt Hz] flat which is much lower than ACAV sensing noise (1e-6 [V/rtHz].)

    I checked RCAV noise at error point(loop closed). It is ~ 50e-9 [V/rt Hz] which is higher than the sensing noise.

    I haven't measure the input referred noise for RCAV servo yet.

2) so I switch the RFPDs to check if ACAV's RFPD is broken or not, and measure the sensing noise again.

    It got the same result ~ 1e-6 [V/rtHz] flat, so both RFPDs give the same noise level.

3) I realize that we have an amplifier for ACAV's RFPD before the mixer, so I remove the amp and measure the sensing noise, the noise level

   is ~ 30 e-9 [V/rt Hz] flat. So this shows that the high sensing noise comes from the amplifer

enoise.png

 

4) I check the beat measurement again, now the gain for ACAV loop is set to 7.2 (instead of 1.5), where the noise at the error point is smallest.

It starts to get higher around 7.5. The beat noise does not change between having the amp or not. The data is valid upto a few kHz.

beat_10kHz.png

 

5) The Noise at error point for ACAV loop after removing the amplifier, with sensing noise and input referred noise is still weird. RFPD noise

is still higher than the error noise, I'll think about this.

TFacav72.png

first, the TF of the PDH box, gain 7.2.

acav_noise.png

then, the ,sensing noise, input referred noise and noise at error point.

 

  551   Thu Mar 24 00:02:57 2011 FrankDailyProgressElectronics Equipmentsensing noise checking

Be very careful comparing the plain numbers! You have different error signal slopes so the corresponding frequency noise level for the sensing might be totally different !
Anyway it is good to compare individual parts which should be equal, e.g. the RFPDs at RF frequencies (or mixed down using the same(!) LO power (or better: mixing/conversion gain)

So what you say in the first sentence is right, but don't forget the gain of the amplifier! You can't compare those without taking that into account.

The increase from 30nV/rt Hz to 1uV/rt Hz is a bit higher as i would expect it but still makes sense. The minimum gain for the ZFL-500LN amplifier is 24dB, the difference between those numbers is ~30dB.
We should measure the mixer output with the amplifier but without the photodiode (input terminated) to see where the noise floor of the amplifier is. Then you know how far that is below the RFPD noise.(and can calculate the RFPD noise level from that i\f you want)

You say that the noise at the mixer output is the same for both loops, but the setup is completely different (different mixer, different LO power (23dBm and 7dBm or so). So be careful. It shouldn't make a big difference but you have to measure the RF noise around 35.5MHz or use the same mixer setup, e.g. plug in the ACAV RFPD in the RCAV mixer and compare then. Then you have real good numbers for comparison of the PDs.

 

 

  554   Thu Mar 24 23:46:13 2011 taraDailyProgressElectronics Equipmentsensing noise checking

Here is the noise plot for ACAV electronic noise. It is basically the same as yesterday plot,

except new data from the sensing noise which is lower by a factor of 2 because of the terminated input.

This is the plot for no amplifier setup. It was removed during the whole measurement. Gain is 7.2, error signal is 18.9 mV pkpk. When I measure the sensing noise, and error signal

the mixer out was connected to the PDH box with a T for measurement, so it's 50ohms terminated.

This gives the slope to be 108 kHz/18.8 mV = 5.7 MHz/V. However the sensing noise projected on the noise budget is still

higher than the measurement result.   

 

acav_enoise.png

 

 

beat_10kHz_sensing.png

 

note: I compare ACAV and RCAV's RFPD by measuring the sensing noise from the same setup (RCAV servo) and changing the RFPDs.

ACAV's RFPD noise is slightly higher.

RFPDcompare.png

 

Note2: I terminated the amplifier and measure the noise from the mixer ( LO --->(X)<----amp--terminated)

to see the amp noise. Much lower than the noise level with RFPD connected (~ 1uV)

mixernoise.png

 

Quote:

Be very careful comparing the plain numbers! You have different error signal slopes so the corresponding frequency noise level for the sensing might be totally different !
Anyway it is good to compare individual parts which should be equal, e.g. the RFPDs at RF frequencies (or mixed down using the same(!) LO power (or better: mixing/conversion gain)

So what you say in the first sentence is right, but don't forget the gain of the amplifier! You can't compare those without taking that into account.

The increase from 30nV/rt Hz to 1uV/rt Hz is a bit higher as i would expect it but still makes sense. The minimum gain for the ZFL-500LN amplifier is 24dB, the difference between those numbers is ~30dB.
We should measure the mixer output with the amplifier but without the photodiode (input terminated) to see where the noise floor of the amplifier is. Then you know how far that is below the RFPD noise.(and can calculate the RFPD noise level from that i\f you want)

You say that the noise at the mixer output is the same for both loops, but the setup is completely different (different mixer, different LO power (23dBm and 7dBm or so). So be careful. It shouldn't make a big difference but you have to measure the RF noise around 35.5MHz or use the same mixer setup, e.g. plug in the ACAV RFPD in the RCAV mixer and compare then. Then you have real good numbers for comparison of the PDs.

 
 

 

 

  1449   Tue Jul 15 18:26:20 2014 taraDailyProgressopticsetting up scattered light measurement

I'm setting up a scattered light measurement for AlGaAs samples. The methods are summarized below.

 

I discussed with Manasa about the setup and how to do the measurement. The goal is to measure  scattered losses from AlGaAs samples from a normal incident beam. The setup is shown below.

 

==setup==

The setup is in the ATF lab, on the unused optical table. It is too crowded on CTN table. So I will need a to borrow a 1064 laser from somewhere. 

The incident beam will have to be slightly angle from the normal angle in order to dump the beam properly. 

The arm holds the camera, it can rotate to change the angle to cover the measurement from around 10 degrees to ~70 degrees.

 photo.JPG

==calibration method==

  • We can take a picture from a diffuser plate, make sure it is not saturated. 
  • Then use a power meter, measure the power fall on the camera.
  • compare the output of the camera and the measured power
  • I have to think about how to make sure the solid angle of the camera aperture and the power meter are the same.

==measurement and data analysis==

  • For each position, take one picture without the beam on the mirror and one with the beam on the mirror. The first one will be used for subtracting the ambient noise from a picture when the beam is on the mirror. 
  • Make sure that no pixel is saturated
  • For each pair of picture, we will use Matlab to count the output, then use the calibration to convert to power.
  • integrate over half the sphere. I have to think about this to make sure I get it right.

 

  1452   Thu Jul 17 18:57:54 2014 taraDailyProgressopticsetting up scattered light measurement

I'm testing the setup and a code for extracting scattered light from the images. 

 

I used a red laser pointer to test the scattered light setup. Then took a picture with no light (fig1) and a picture with the incident light (fig2). The scattered light can be extracted by subtract fig1(background) from fig2.

The snapshots saved by SampleViewer are in .bmp file. When it is read by MATLAB, the file will contain 480x752x3 matrix element, Each are varied between 0 and 255. The values are proportional to the brightness (how many photons hit the cell). 480x752 is the resolution of the image, x3 are for R G B color. In our case, the image is greyscale and the values are identical. The code can be found in the attached file.  

 dark1.png

fig1: The test mirror without incident beam taken as a background image. The image is enhanced by a factor of 5 (by matlab).

 

light.png

fig2: The test mirror with a red incident beam around the center. The image is enhanced by a factor of 5.

 

residual.png

fig3: the image is created by subtracting data of fig1 (background) from fig2 (scattered light) and enhanced by a factor of 100. The scattered light on both surfaces can be seen clearly around the center.

 ==To do next==

  • From fig 3, the background can be seen even after subtraction, so some black curtains and beam dumps should be added behind the mirror.
  •  A room light filter should be installed in front of the camera.
  • I'll see if we can find a sample with known scattering loss, so that we can compare how accurate the measurement is.
  1455   Wed Jul 23 00:28:14 2014 taraDailyProgressopticsetting up scattered light measurement

I'm checking the linearity of power and exposure on the camera. The ccd counts are quite linear with the exposure setup, but I have to check the power again.

 

==ccd count vs exposure setup==

  The exposure time on the camera can be set to adjust the brightness of the image. Since we might have to adjust it to make sure that the images won't be saturated, it is necessary to check if the ccd count response linearly to the exposure setup or not.

I used a silver mirror as a test sample. The incident power is constant, and the camera position is fixed. Then adjust the exposure from 5k to 30k. I'm not sure if it is in nano second or microsecond unit. [Edit, 20140725: according to page 18 of the manual for the Prosilica GC750, the available exposure options are 30 µs to 60 s, in 1 µs increments. —Evan] But from fig1, the ccd count is quite linearly proportional to the exposure value.

exp_vs_light.png

It turns out that when I try to calibrate a sample, the incident power on the sample has to be more (so the power meter can measure some scattered power) and the camera can be saturated. The exposure value has to be around 1000, and I have not checked the response at this level. I might have to remeasure it.

 

==ccd count vs power== 

 This measurement is similar to the above. But this time the incident power (to the sample) is varied. The result is not linear. I check the images and see that the bright spot moves. The camera might move during the measurement. I'll repeat this again. It will be complicated for the calibration if the ccd count is not linear with the power.

power.png

== To do==

  • check the ccd count for exposure value down to lowest setting.
  • check the ccd count for different power incident.
  • check the ccd count with different ND filter in front of the camera.

 

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