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ID Date Author Typeup Category Subject
  471   Fri Feb 4 13:59:48 2011 FrankDailyProgressBEATtrend of the setup

 This setup has too much gain (i.e. not enough range). Please reduce the arm length asymmetry by a factor of 10 so that we can monitor over 24 hours.

Also the temperature channels ought to be calibrated (via the EPICS .db) so that the readout is in degC instead of ARB.

Attachment 1: Untitled.png
Untitled.png
  472   Fri Feb 4 19:26:50 2011 FrankDailyProgressBEATchanged to shorter cable

exchanged the 500ft spool by a shorter cable to get more range (but less resolution).
Due to the lower losses of the cable i also removed the 2W amplifier.
Right now both cavities can't be locked at the same time, they are slightly out of range.

RCAV is resonant at 0.1958 for the slow actuator, ACAV is resonant at 0.1930

max range for VCO is reached at 0.1948

i've changed the RCAV settemp a little bit and will keep an eye on that and we will hopefully be back online tonight

  473   Sun Feb 6 02:38:07 2011 FrankDailyProgressRefCavboth cavities locked again

locked both cavities. Current slowdc value is 0.1925. VCOmon is -2.2V. Changed RCtemp to 35.00.

Data is valid since 11/2/6 10:10:00 UTC

  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.

 

 

Attachment 1: 2011_02_07_RCPID.png
2011_02_07_RCPID.png
  481   Tue Feb 8 12:02:06 2011 taraDailyProgressRefCavTemperature response

The perl script is working fine on RCAV. It has faster response than the other control system (see ACAV's temp)

Attachment 1: Screenshot.png
Screenshot.png
  483   Wed Feb 9 02:07:25 2011 Frank,TaraDailyProgressBEATlong-term frequency drift/noise - once more

Changed the setup to be used with two different cables at the same time, but only using one right now.

mixer signal calibration with PD signal ~4.7dBm:  5V = 157.295MHz  -5.09V=150.725MHz    dfpkpk=6.57MHz

channel names:

  • C3:PSL-GEN_DAQ15 : SR560, DC-coupled signal, gain somewhere between 100 and 200, LP30KHz
  • C3:PSL-GEN_DAQ16 : SR560, AC-coupled signal, gain 1000, LP30kHz

data valid from 11/02/09 6:20:00 UTC

will post schematic later...

 

  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.

 

 

 

  497   Tue Feb 15 01:02:31 2011 FrankDailyProgressBEATcalibration problems?

looks like a fu**** up the data aquisition with the short cable, but i don't know how.

When trying to calibrate the data taken i realized that something was totally wrong as i got some khz/rHz but i couldn't find the mistake.
So i thought the gain setting if the preamps must be different than i wrote down but they are not.
So i checked the calibration again, this time in 1MHz steps all the way through the system but everything was/is OK.
Got almost exactly the same mixer response vs frequency tuning and also the dc-coupled signal was what i measured before.

Here the problem:

The VCO feedback signal gives us a rough idea what frequency we have, which i checked over and over again and matches the frequency counters we have.
The problem is that the DC signal (already amplified) for pi in phase change goes from something like 2.3V to -2.4V.
The same signal from end to end of the VCO goes from -1.7V to 1.4V, see
here.
I measured this several times, last week and today and this is fact whatever equipment i use (scope, multimeter, DAQ).

So now the funny part:

The DC signal and the VCO monitor signal look almost identical (shape, uncalibrated).
As i checked  the calibrated (fitted) VCO monitor signal reflects the beat signal within 100kHz or so, but 1MHz for 100% sure.
Now, taking the recorded DC-signal from the mixer from 35h of data and using the calibration (which i did several times) the beat frequency is out of range of the VCO, totally different !
The recorded signal does not match the VCO signal at all! Using the same coefficient to calibrate the spectrum recorded with the AC-coupled amplifier the noise is way to high, higher than everything we had before.
So i took the VCO monitor signal, assuming it is right and showing me the absolute beat frequency and calculated the right coefficient for the mixer signal, which is something like 5MHZ/V instead of 170MHz/V.

Done that, comparing both time series looks fine.
Taking this coefficient to calibrate the spectrum then gives, at least for a the features around a couple of Hz the right level we measured several times before.
The lower frequencies are dominated by the noise of the preamp, so no comparison possible.

So i don;t know what's wrong because i can't reproduce what we recorded. Everything looks the same as last week, checked over and over again. But the DAQ shows something different.

RESULT:

As we can't trust whatever we recorded we redo the measurement. After bringing back the 4-way splitter to 40m i'm using 2-way splitters now instead, increased the signals where possible and the gain of the preamp. re-calibrated everything and triple checked, taking another measurement over night. We will see tomorrow....

 

Plots, 32h data stretches.
noise plot shows spectrum of data taken with and without 30mHz high pass correction

frequency_drift.png

 

fnoise.png

  498   Tue Feb 15 23:19:54 2011 FrankDailyProgressBEATsome (minor) calibration problem found

Found at least two (minor) problems:

  1. So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
    For calibration i used the slope of the sine near the zero-crossing.
    As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
    Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
    full_error_signal.png
  2.  

    it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!

  3. the channel which contains the calibrated VCO monitor signal uses a wrong sign.
    The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
    However, the frequency tuning curve i measured with the old (wrong) cable.
    I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
    This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
    Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
    frequency_drift.png
    so i think once the EPICS channel is fixed we can trust that channel
  499   Tue Feb 15 23:33:51 2011 taraDailyProgressBEATsome (minor) calibration problem found

So, from the first plot, is the calibration factor for cable delay technique ~ 8MHz/Volt?

Quote:

Found at least two (minor) problems:

  1. So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
    For calibration i used the slope of the sine near the zero-crossing.
    As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
    Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
    full_error_signal.png
  2.  

    it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!

  3. the channel which contains the calibrated VCO monitor signal uses a wrong sign.
    The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
    However, the frequency tuning curve i measured with the old (wrong) cable.
    I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
    This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
    Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
    frequency_drift.png
    so i think once the EPICS channel is fixed we can trust that channel

 

  500   Wed Feb 16 00:02:51 2011 FrankDailyProgressElectronics Equipmentnoise of SR560

to have real data for comparison i measured the noise of the SR560 for different (high) gain settings.
Will add lower gain settings and line powered measurements later.

test setup: SR560, AC-coupled, low-noise setting, battery powered measured with SR785

SR560_noise_02_15_2011.png

datafiles contain raw output noise values, so for input referred noise plz divide by gain given in filename. first col = frequency, second col = noise spectral density

SR560_gain1k_AC-coupled.dat

SR560_gain2k_AC-coupled.dat

SR560_gain5k_AC-coupled.dat

SR560_gain10k_AC-coupled.dat

SR560_gain20k_AC-coupled.dat

SR560_gain50k_AC-coupled.dat

  501   Wed Feb 16 09:14:14 2011 FrankDailyProgressBEATsome (minor) calibration problem found

yes, for yesterdays measurements 7.435 MHz/V.

But that number changes from measurement to measurement as i'm changing the setup every time to improve SNR (or bring back stuff i've stolen from 40m)

Quote:

So, from the first plot, is the calibration factor for cable delay technique ~ 8MHz/Volt?

Quote:

Found at least two (minor) problems:

  1. So far i measured the zero-crossing of the mixer signal and both peak values and modeled the signal using a sine.
    For calibration i used the slope of the sine near the zero-crossing.
    As the frequency range for pi in shift is about 60MHz the function is almost linear for the range we measure over 24h (~2MHz).
    Today i measured the mixer signal in small steps and compared both techniques. The result surprised me a little bit:
    full_error_signal.png
  2.  

    it is not a lot of difference in slope but it is surprisingly linear over a range of 40MHz!

  3. the channel which contains the calibrated VCO monitor signal uses a wrong sign.
    The fit is right, but i remembered that i exchanged the BNC to 2-pole LEMO connector some time ago because it had the wrong sign.
    However, the frequency tuning curve i measured with the old (wrong) cable.
    I used the right sign on my computer but implemented the wrong one in EPICS, so that data was/is wrong. Will change that tomorrow.
    This can't explain the problems i had last week as i used Matlab to convert the monitor signal into frequency, not that channel.
    Anyway, this is how the data i took last night (19h) looks like using the right slope (see item 1):
    frequency_drift.png
    so i think once the EPICS channel is fixed we can trust that channel

 

 

  503   Thu Feb 17 23:50:55 2011 taraDailyProgressVCOPDH box irregular gain behavior

I measured the input referred noise of the VCO's PDH box at different gain setting.

The input refer noise varies with gain setup. The result is plotted below

 

When both cavities are in lock, the VCO receives the feedback signal from the PDH box to control the laser frequency.

The PSD of the feedback signal to VCO varies with gain setup on the PDH box significantly, so it needs to be checked.

To decide the gain setup range for test, the gain is adjusted while the beat noise is observed. The minimum gain and maximum gain

where the beat noise still looks nice are chosen, which are 4 and 7 as read on the knob dial.

 

Then the noise of the PDH box is measured at different gain setups (4,5,6,7.) When

1) the PDH input is shorted (for PDH intrinsic noise alone ), and

2) the beam on the RFPD is blocked (for whole set of RFPD, mixer and PDH box)

 (data from gain 4 with RFPD has to be remeasured )

 

Then the open loop TF is measured. The measured noise divided by the TF is the input referred noise of our system.

The TF in the measured region can be approximated with 1/f slope.

 The input referred goes down alot from gain 4 to 5, and not much from 5 to 7;

 

The input referred noise doesn't seem correct. I'll double check it later.

 

 

Attachment 1: PDH_input_refernoise.png
PDH_input_refernoise.png
Attachment 2: ACAVTF.png
ACAVTF.png
Attachment 3: noise.png
noise.png
  504   Fri Feb 18 23:52:42 2011 taraDailyProgressVCOPDH box irregular gain behavior

The input referred noise for the PDH box is measured and corrected.  The input referred noise (IRN) of the PDH box

is getting lower from gain 4 to 5 and increase at gain 6 and does not change until gain 10(max).

The IRN (from PDH + RFPD setup)is converted to laser frequency noise and put on the noise budget.

It seems to be a limiting source at high frequency.

 

 

Frank pointed out that I made a mistake my measuring the whole OLGTF of ACAV instead of the PDH' TF only.

So I remeasure the PDH's TF at different gain. For the range of interest, the TF has a pole at 48 Hz. The TF's DC gain for each gain settings are

gain   DC gain [dB]
4        55
5        60
6        65
7        70
8        75
9        80
10       85

The TF for each gains and the fit are plot below, they are offset for comparison. (The name should be PDH TF file.)

 

The input referred noise is then calculated, and plotted below (fig2)

For PDH alone (Line plots), the input referred noise (PDH alone) at gain 5 is smallest. gain 4 is a bit higher, gain 6 to 10 are about the same. 

For PDH + RFPD setup (dot lines), the input referred noise at gain 4 and 5 are about the same,

and getting higher at gain 6  and remains  the same to gain 10.

 

The IRN (PDH + RFPD set) from gain 5 and 7 are chosen for the noise budget plot as our gain is always set around this.

(I will interpolate it to lower frequency with 1/f slope, the actual data will be measured)

 

 To convert it to frequency noise, the IRN is multiplied by the slope of the error signal, 4.67 MHz/V. (See below for detail.)

and plot it together on the noise budget.

 

This time, the beat signal (green)is measured with smaller input range (10kHz),

so the signal is not limited by LO phase noise and goes below the noise budget .

However, the IRN (from PDH+ RFPD) noise at gain 7 is higher than the beat noise, by a factor of 2, but the IRN at gain 5 

matches the signal. The peaks from IRN and beat b/w 100 to 1kHz matches quite well

Note that LO phase noise from 10kHz input range is l~ 30-40 mHz at this BW which is lower than the measured beat noise.

(I'll find the data for LO phase noise and plot it together

).

 

 

%%%%%%

error signal slope msmt

%%%%%

I scanned the laser by injecting a sinusoidal signal via fast channel. (Unlock laser from RCAV.)

Set  SLOWDC so the frequency is close to ACAV resonance, and measure the signal from the mixer output.

The pk - pk is 22.8 mV. The frequency between pk-pk is FWHM of the cavity = 2x ACAV's pole = 108 kHz,

so the slope is 108 kHz/ 22.8 mV = 4.74 [MHz/V]

 

Quote:

I measured the input referred noise of the VCO's PDH box at different gain setting.

The input refer noise varies with gain setup. The result is plotted below

 

When both cavities are in lock, the VCO receives the feedback signal from the PDH box to control the laser frequency.

The PSD of the feedback signal to VCO varies with gain setup on the PDH box significantly, so it needs to be checked.

To decide the gain setup range for test, the gain is adjusted while the beat noise is observed. The minimum gain and maximum gain

where the beat noise still looks nice are chosen, which are 4 and 7 as read on the knob dial.

 

Then the noise of the PDH box is measured at different gain setups (4,5,6,7.) When

1) the PDH input is shorted (for PDH intrinsic noise alone ), and

2) the beam on the RFPD is blocked (for whole set of RFPD, mixer and PDH box)

 (data from gain 4 with RFPD has to be remeasured )

 

Then the open loop TF is measured. The measured noise divided by the TF is the input referred noise of our system.

The TF in the measured region can be approximated with 1/f slope.

 The input referred goes down alot from gain 4 to 5, and not much from 5 to 7;

 

The input referred noise doesn't seem correct. I'll double check it later.

 

 

 

Attachment 1: VCOTF.png
VCOTF.png
Attachment 2: refernoise.png
refernoise.png
Attachment 3: beat_2011_02_18.png
beat_2011_02_18.png
  506   Mon Feb 21 20:15:14 2011 frank, taraDailyProgressBEATbeat measurement b/w cable delay and PLL

Today we compared beat noise measured from phase lock loop(PLL) and cable delay technique (CD.)

The results do not agree well. Eventhough we can get the calibration factor correctly, CD is not working yet.

 

We want to use CD instead of PLL because CD has no phase noise added to the signal which is the limiting

source for PLL at high frequency.

One drawback is that to get the calibration factor for CD. It has to be done every time with each measurement

as the calibration factor varies with the carrier frequency of the beat, cables used for the measurement, but it's not that hard.

 

We use CD to measure the phase noise of IFR2023b used for PLL, its phase noise was measured and added in the noise budget.

The result at 100kHz input range from CD agrees well with the previous measurement, we can see the feature of the phase noise nicely.

 phasenoise_by_CD.png

 This ensures that we got the CD calibration [Hz/V] correctly.

 

Then we switch to a 500 ft cable for better resolution and measure the phase noise of the LO again.

The results from 100 kHz input range are similar.

However, for phase noise at 10kHz input range (with lower phase noise,) CD cannot measure it properly by either short or long cables.

there is no phase noise's feature at high frequency like the previous result measured by SR785, note that

CD's noise floor is still lower than LO phase noise.

500ftCD.png

With that in mind, we measured beat noise by PLL(10kHz input range) and CD (500ft +2w amplifier).

We also injected a 1.092 kHz peak, generated by a func generator through a speaker on the table, to compare for the calibration.

1)If we use our regular calibrations for PLL and CD, the noise looks like this

beat_CD_PLL.png

 

 

2)If we match the 1.092 kHz peaks in both plot (I use a regular calibration for PLL). The result looks like this

matchpeak.png

And the coherence between PLL and CD is quite low (we have to think about it if the two signal should be coherence or not)

 

coherence.png

We will figure out what happen with the cable delay tech.

 

To sum up, we

1) make sure that we get the calibration factor correct for 500 ft cable setup with 2W amplifier,

by measuring ifr2023B phase noise at 100kHz range and compare it to the previous result.

 

2) are not certain why the LO phase noise and beat results are not similar at 10 kHz range

 

3) trust signal from PLL more than CD, since the beat noise from CD changed

(while PLL gave the similar result)when we adjusted the equipment, and we could not find out why.

Attachment 1: phasenoise_by_CD.png
phasenoise_by_CD.png
  507   Tue Feb 22 21:57:02 2011 frank, taraDailyProgressBEATbeat

Today, we found out that at high frequency, the limiting noise source is probably electronics noise might be from the Universal PDH box.

 

We tweaking the setup parameters, FSS gain, UPDH gain, sideband power, laser power to see what will change the beat noise.

We learned that

 

1) The current setup is not FSS gain limit, because we adjust the gain, but the beat noise remains the same,

and the range of the gain we can adjust is quite high, between 5 - 30 dB.

 

2) By adjusting side band power, the noise level changes.

However, when we added gain to compensate for the lower side band power, the noise does not go back to original level.

This is weird. We adjusted decrease 35.5 MHz sideband power, and noise level goes up. Increasing gain in FSS and ACAV loop does not change it back.

 

3) The peaks around acoustic frequency (mechanical peaks)can be suppressed by increasing PDH gain, but the flat level changes.

The noise level calculated from input referred noise sitll does not match with the beat noise, but they are close.

beat_2011_02_22.png

Now the beat noise is not limited by LO phase noise.From the flat shape of the noise, we think that it might be the electronic noise

from the PDH box.

 

To do next: increase the error signal slope for ACAV path. Now it is very small ~23 mV.

  509   Wed Feb 23 01:47:15 2011 frankDailyProgressBEATbeat

you have to be a bit more precisely fro points 2 and 3, e.g. no one knows what you mean as "PDH" gain as you have two loops using the PDH technique.

Some comments:

  • For Point 1: What does it mean "and the range of the gain we can adjust is quite high, between 5 - 30 dB" ? From you description it could be that the gain adjustment is limited by loosing lock below gain of 5dB or lower, but you can actually change it from -20 to 30dB without loosing lock. Forgot to mention that the noise does not stay the same if you change the gain below that value. If you lower it below a threshold you see that you don't have enough gain to suppress the laser noise. Only for gains above ~5dB or so you have enough gain and so for the setting we typically use we are not gain limited.
  • For point 2: You forgot to describe what happens when you change the optical power . Reducing the sideband power causing a higher noise floor and not be able to bring it back by increasing the gain is not surprising, e.g. the power is so low that the shot noise level limits you. Then you can't win with more gain. You have to calculate that level and compatre it before you can make a statement.
     
  • For point  3: Describe a bit more detailed what you changed, no one understands it. Which noise projection did you use, PDH box terminated or with photodetector? That's a huge difference. The noise of the box can be well below and you are still limited by electronic noise from the detection! You should work on that block diagram with all the parts and individual noise sources to get a better picture of what's going on and which noise couples in which way.

 

  510   Thu Feb 24 01:40:00 2011 FrankDailyProgressBEATinfluence of power fluctuations

I had a closer look into effects caused by power fluctuations. To summarize : It is easy to measure TFs from power fluctuations to any other point in the system. SNR is good to very good.

I mainly focused on the effect of changes in shape of the TF from power fluctuations into changes of the beat frequency when changing the power levels anywhere in the system, especially in the cavity paths.
After playing a couple of hours and getting a feeling for what's going on i finally realized that only if changing the power in the ACAV-path strange things happen. This includes changing the total power going to both cavities as well. As taking TF's is taking too long at low frequencies i decided to switch from swept sine measurements to a simple digital modulation of the laser power with 100ms period. This is slow enough to see thermal effects in the cavity and other strange things which i will show below.

For the first set of measurements i reduced the power to the REFCAV path to about 460uW. The total modulation is very large, about 15.6%. The max power to ACAV was about 5.76mW, which i reduced later.
The following graphs shows the response of the beat signal to the digital modulation, beat signal calibrated to Hz, modulation signal a.u.., but the amplitude didn't change between measurements.

 powermod_ACAV.jpg

 on the left graph (measured at very low power) one can see that the power modulation causes a sudden changes in frequency of the beat signal.
This can be caused by everything producing an offset in the EP which depends on power, e.g. RF-AM, higher-order modes in reflection etc. Nothing unusual so far.
 If the optical power going to the ACAV is increased one can find a point where the change in frequency is almost gone, showed in the center graph.
When the power in increased further the sign of the frequency shift changes! Now some thermal effect becomes dominant, most likely the cavity as the period is 10s and after 5s equilibrium isn't reached.

Now this explains everything i saw before: When measuring the TF from power fluctuations to frequency shift and varying the power the shape of the TF changed because we have two different effects which can even cancel at the right power level send to the cavity!

 

As we know already that the size of the error signals is too tiny this effect will probably be almost gone once we fixed the demodulation for ACAV. I tried to reduce it a little bit by re-aligning the cavity but no luck - it's already aligned very well. I didn't try the EOM asthis changes the alignment to the other cavity as well and i was to lazy to re-align everything

  529   Wed Mar 2 23:20:49 2011 FrankDailyProgressSeismicpiezo shaker updated - TF measurement started

Koji and i updated the shaker today. We replaced the short multilayer piezoelectric actuator (10mm) by a longer one (20mm) from the NEC TOKIN’s we have. (datasheet)
The pzt is glued to a brass disk, about 2" diameter and clamped between the side of the table and the steel frame around it using a aluminum base on the other side. (will add photo later).

We use a modified PMC servo card as a HV piezo driver. The modified schematic can be found below.
We added a 1kOhm resistor in the output which forms a ~100Hz low-pass with the 1.5uF capacitance of the PZT.

We get a good SNR ratio for TF measurements even when using white noise as the source. doing some low-frequency TF measurement over night.
WiIl also try a swept-sine measurement if required, but takes too long at low frequencies.

We also tried to build a simple loop using two stanford preamps to suppress the horizontal seismic motion of the table but couldn't see any improvement. Will wait for the measured TF to design the right loop.

 

HV amplifier schematic (modified PMC servo):

HV-amp_modified_D980352-A.pdf

  531   Thu Mar 3 22:37:51 2011 frank, taraDailyProgressRefCavQ measurement for refcav's suspension (RCAV)

Today we measured one of RCAV's suspension modes, The mode @ 3.73 Hz, Q = 190+/- 10 is probably tilt.

This can be excited by shaking the curtain frame above the table.

 

Yesterday we measure several eigenmodes of the suspension on a model. So now

we measure the real suspension used in the experiment.

1) First we tried to use shadow sensing technique on the copper plate for eddy current damping.

I used the lower edge instead of the side edge because I expect to see large signal from vertical mode.

000_0008.jpg

The 3.73 Hz mode can be excited by shaking the metal frame above the table.

Q from this measurement varies alot, depending on where we start counting.

It can be ~ 70 just after the excitation or upto 180 when the motion damped down for awhile.

q18.png

q17.png

2) we used reflected beam from the mirror. The reflected beam is then used

for shadow sensing technique, this can be used for determining tilt/yaw and longtitudinal motion.

Note: there might be dust on the mirror, we can see it with HeNe laser.

 000_0010.jpg

We use a PZT set for pushing the table for seismic feedback control. With 3.73 Hz

signal, we can drive the tilt motion of the cavity (the reflected beam clearly move up and down)

Result for ringdown measurement. Q is 200. f0 = 3.73 Hz.

q20.png

 

We can excite 2 modes, one is 3.73 Hz (tilt), another is 4.5 Hz (yaw). From the motion

of the reflected beam, we can roughly identify what mode we excite. We will try to excite another modes

and see the actual motion of the cavity.

peak_beat.png

SO if I replace f0 and Q in the noise budget, and remove the horizontal seismic for now( I'm not sure how it couple into frequency change)

The peak seems close to the measurement data

nb.png

 

  536   Fri Mar 4 22:28:39 2011 frank, taraDailyProgressRefCavQ measurement for refcav's suspension (RCAV/ACAV)

Today we measured Q for several modes of RCAV and ACAV's suspension the numbers are summarized below.

 We removed the insulation  foams on both cavities for Q measurement.

We bounce the beam on reference cavity's mirror and used the motion of the reflected beam to

observe the motion of the cavity. For RCAV, we used two PDs for shadow sensing on 2 directions (vertical and horizontal motions)

For ACAV, we use a QPD to observe the beam motion.  PSD from 4 signals are taken to identify the peaks

and compared with the beat signal.

rcav_motion.png

fig1,PSD from RCAV H,V motion

 

acav_motion.png

fig2, PSD from ACAV, H,V motion

 

compare.png

Fig3, beat measurement compared with PSD of ACAV and RCAV motion observed by reflected beams

on the mirrors' surfaces. The PSD is offset for comparison. We still have unknown peaks in the beat to investigate.

Most of the peaks we can excite by white noise on the table do not match with the beat signal

 

We used PZT attached on the table to excite each mode at its frequency and measured Q.

Beam movement can be observed by eyes for rough identification which suspension mode we excite

 RCAV

f                  Q              movement

3.15 Hz     150 -300        N/A

3.73           190           Vertical

4.3 Hz      220           Vertical

4.55 Hz     140          Horizontal

5.1            150                V

7               100               V

ACAV

f              Q        movement

4.3 Hz     120     V

3.4        N/A       H(?)*

 

For 3.4 Hz horizontal mode, it dies too fast even though we drove at the right frequency,

so Q cannot be measured properly. Its motion is also uncertain. We cannot see by eyes

but the signal on QPD shows that the motion is mostly horizontal at 3.4 Hz.

 

We will try to get the beat signal and excite each mode we found to check what modes

from which cavities have significant effects on beat signal. Then we will fix the motion of

that cavity. All insulation are back to normal (I misaligned the mirror behind RCAV when I

slide the back panel back, some alignment have to be done later.)

I'll check the temperature and make sure that we can

get both cavities locked for Monday.

 

Attachment 4: q21.png
q21.png
Attachment 5: q24.png
q24.png
Attachment 6: q27.png
q27.png
Attachment 7: q29.png
q29.png
Attachment 8: q31.png
q31.png
Attachment 9: q34.png
q34.png
  540   Mon Mar 7 23:14:09 2011 koji, frank, taraDailyProgressRefCavchanging RCAV suspension

We opened RCAV's chamber, removed the springs from the suspension and use wire with viton damping on the suspension points instead.

The cavity is put back into the chamber. More details are coming soon

 

  541   Wed Mar 9 02:21:06 2011 Tara, FrankDailyProgressRefCavcavity back in vacuum

cavity is back in chamber and started pumping. Had some trouble with one of the windows. More details and photos later...

  542   Thu Mar 10 01:58:11 2011 Tara, FrankDailyProgressRefCavcavity back in vacuum

Front and back Periscope for RCAV are back on the table. The input beam is aligned.

The transmitted beam is coarsely aligned.

 

Note that the coupling efficiency for RCAV is down to ~ 85%, probably from the change of cavity's position.

I used the periscope to adjust only beam's position and angle. I haven't tried to reposition the lenses yet.

The input beam has multiple reflections from the periscope's top mirror, but beam is quite center on the mirror, not sure what causes this.

 Instead of a single beam, I get one bright center beam and top and bottom faint beams ??

The cavities' insulation is back on both cavity. However, the outer box front panel is left open for the vacuum pumping.

We should be able to measure the beat by tomorrow.

Quote:

cavity is back in chamber and started pumping. Had some trouble with one of the windows. More details and photos later...

 

  543   Thu Mar 10 23:10:27 2011 Tara, FrankDailyProgressRefCavcavity back in vacuum

We measured beat noise. With new suspension, the signal is getting worse from ,probably, seismic  .

The peak at 3.73 Hz is suppressed, but other mechanical peaks appear.

 

RCAV is aligned, the efficiency is ~98%

The plot below shows the beat and seismic measurements (x, y, z directions) in arbitrary unit.

The seismometer is placed on the optical table

 

beat_seismic.png

 

These peaks have not been seen before, so it seems that our new suspension is not working well, especially

on vertical (z) direction.

We will investigate what cause those peaks, and see if we can fix them.

 

beat_2011_03_10.png

Quote:

Front and back Periscope for RCAV are back on the table. The input beam is aligned.

The transmitted beam is coarsely aligned.

 

Note that the coupling efficiency for RCAV is down to ~ 85%, probably from the change of cavity's position.

I used the periscope to adjust only beam's position and angle. I haven't tried to reposition the lenses yet.

The input beam has multiple reflections from the periscope's top mirror, but beam is quite center on the mirror, not sure what causes this.

 Instead of a single beam, I get one bright center beam and top and bottom faint beams ??

The cavities' insulation is back on both cavity. However, the outer box front panel is left open for the vacuum pumping.

We should be able to measure the beat by tomorrow.

Quote:

cavity is back in chamber and started pumping. Had some trouble with one of the windows. More details and photos later...

 

 

  544   Tue Mar 22 00:38:11 2011 taraDailyProgressBEATcurrent beat measurement

Today I measured beat noise again to see where we are after adjusting many parameters.

The beat measurements are plotted below for 100 kHz and 10 kHz input range.

For 100kHz input range (grey), we are limited by LO phase noise. The shape of the phase noise has changed

from previous data in pink.

For 10 kHz input range (red), something else is the limiting source. I'm checking if we are limited by RFPD noise or not, but

the result is not conclusive yet.

 

 

 

beat_2011_03_21_full.png

 

I also measured the noise at the error point for ACAV loop (loop closed) in green, then projected it on the nb

by multiplying by the slope of the error signal (0.252 MHz/V = cavity's FWHM / error signal pkpk value = 108 kHz / 428 mVpk-pk.)

The level of the noise match the beat around 30Hz to 1kHz, but diverges at higher frequency.

Not quite sure if it makes sense or not (PLL loop is valid upto ~  3kHz.)

 

The input referred noise of RFPD and the PDH box is measured, by blocking the beam on the RFPD

and measuring the singal on PDH out.  The data is divided by the TF of the PDH box ( I measured this while the loop is closed,)

and multiplied by the error signal's slope, then plotted in blue.

The result is not quite right. It's higher than the beat. I'll have to check this.

 

*ACAV gain is set to 1.5 for all measurements.

RCAV common gain is set to 22.0 dB

power to each cavity = 1 mW

 

 

 

 

  545   Tue Mar 22 15:59:49 2011 frank, taraDailyProgressRefCavQ measurement for RCAV new suspension

Today we tried to measure Q factor from RCAV's suspension.  By measuring the FWHM of the peak and the ring down signal,

however, the results are no good, we cannot excite the mode to see clear ring down patterns, and the FWHM for the excited peaks are too narrow.

So we present here the motion of the top stack(vertical translation combined with pitch) and the cavity's motion 

 

After we changed RCAV's suspension, beat becomes worse between 10 - 100Hz from many mechanical peaks.

Since we changed only the spring of the suspension, we expect that the peaks should originate from vertical motion.\

 

We used optical lever to observe the front mirror's pitch motion. The PZT is placed under the chamber's flange  to excite the modes.

Only f = 19.88 and 25.69 Hz can be excited, but still very small, other modes show no ring up during the excitation at all.

Then we measured the stack's top motion, by shadow sensing technique. From the setup it will sense both vertical translation and pitch

motions of the cavity. Most of the peaks from the stack match with the cavity's motion, except a broad peak around 65 Hz which we don't

see on the cavity (from shadow sensing and oplev)

seis_v.png

 

We know the calibration factor from oplev, so the motion of the cavity in rad/ rt Hz measured by oplev is plotted.

- calibration on QPD 46.1 V/m  (10mV over 200 micron)

- lever length  1.8 m  ->  46.1 V/m *1.8 m = 83 V/rad

- divide the signal by 83 V/rad to get rad/ rt Hz

pitch.png

 

 

 

 

  546   Tue Mar 22 21:59:21 2011 taraDailyProgressElectronics Equipmentinput refered noise for UPDH and sensing noise (RFPD) in ACAV

We remeasured the input referred noise(IRN) of the UPDH box, and sensing noise (RFPD + mixer +LO) for ACAV loop.

Sensing noise is ~2 order of magnitude higher than UPDH's  IRN.

 

 We do this because we want to check if electronic noise in ACAV loop is limiting our beat signal or not.

Data from yesterday is not good because I did not cover the whole frequency for PSD measurement,

and got the wrong TF for UPDH, and wrong sensing noise. So I redo the measurement and plot the noise

in Vrms/rt Hz instead of converting it to frequency noise for debugging purpose.

 

To measure sensing noise (RFPD+mixer+LO)

1) block the beam on the RFPD and measure the signal after the mixer (after the low pass filter too, of course.)

 the noise is flat and roughly around 1 uV/rtHz.

 

To measure UPDH's IRN

2) terminate the UPDH with 50 ohm (it is self terminated, so just unplug the input) and measure the output of the PDH,

  boost off, gain 1.5 on the knob.

3) measure the TF of the UPDH

 PDHTF.png

 

Both measurements are not limited by SR785's noise floor which is ~ 5 nV/rtHz flat at 100 Hz and above.

noise_raw.png

 

3) divide the UPDH signal from (2) by TF from (3) to get IRN.

errnoise.png

 The IRN (cyan) looks good. At 100k where the gain is 40 dB and at 10k where the gain is 20 dB,

the IRN is lower than the raw data by  2 and 1 order of magnitude respectively, and the crossing happens at UGF (1kHz),

so everything looks ok so far.

 

However, the noise from the error point (purple) (same point for sensing noise) when the systems is locked does not match the noise we have now

(data from yesterday.) I'll redo the measurement to see if it's the same or not.

 

I also notice that the sensing noise alone is already higher than the beat. The slope of the error signal is

cavity's FWHM / Vpk-pk =  108 kHz / 428 mV = 0.25 MHz/V.

beat_sensing.png

 So either the measurement for RFPD is wrong, or the slope of the error signal I got is wrong. This will be investigated next.

Just for fun, I match the 120Hz peaks on the RFPD noise and the beat, the calibration factor is 3.78e4 Hz/V. Although I did not take the contribution from other electronics into account, the RFPD noise sits a bit below the current beat. If this were true, we will have to fix the RFPD next.

peak_match.png

 

 

  547   Tue Mar 22 23:38:02 2011 FrankDailyProgressElectronics Equipmentinput refered noise for UPDH and sensing noise (RFPD) in ACAV

nice, much better, i only have two little things at the moment:

  1. would be great to have the noise spectrum of the error point when locked for a larger frequency span. Do you have data?
  2. How did you measure the slope of the error signal? I think the error is there so plz explain in detail what you connected to where and how you measured it. I have a strong feeling that you missed at least a factor of two already there...

we should check the mixer signal, the noise level is too high. We should compare it with the other EP signal (of the other cavity). If there is a huge difference between both we should start searching there. We should also check the RF noise level of the RF-PD. Maybe something is broken there.

  548   Wed Mar 23 18:12:01 2011 taraDailyProgressElectronics Equipmentinput refered noise for UPDH and sensing noise (RFPD) in ACAV

I think the reason of the high mixer noise is the amplifier for the RFPD signal before the mixer. I remove it for now and the noise seems comparable with that from RCAV's RFPD. The beat measurement between with and without the amplifier is quite similar.

the result will be posted soon.

 

1)Here is the noise at the error point from ACAV loop during lock.

electronic_noise.png

The mixer signal is really high. The sensitivity range on SR785 was on -50dB. To check that there is no weird coupling

between the signal and the spectrum analyzer I tried changing the range up to - 20 dB, but the noise level is still the same ~ 1uV /rtHz.

2) slope of the error signal,

    a) connect the triangular signal from the function gen, 10Vpkpk, 2 Hz to piezo sweep ch on the PDH box, turn the switch on.

000_0002.jpg

    b) unplug the mixer signal from the PDH box, connect it on the scope, ch A. connect the triangular signal on ch B.

   c) pk-pk value is 424 mV.

000_0001.jpg

 

I also tried sweeping on the FAST channel. The triangular signal is sent to FAST on the laser, 10Vpkpk 20 Hz

and read out the mixer out signal again. I get the same pk-pk value, 424mV.

000_0003.jpg

 

Then the width of the linear region is approximately FWHM of the cavity108kHz, (cavity pole x 2), the slope is then

108kHz/424 mV   ~ 0.25 MHz/V

Quote:

nice, much better, i only have two little things at the moment:

  1. would be great to have the noise spectrum of the error point when locked for a larger frequency span. Do you have data?
  2. How did you measure the slope of the error signal? I think the error is there so plz explain in detail what you connected to where and how you measured it. I have a strong feeling that you missed at least a factor of two already there...

we should check the mixer signal, the noise level is too high. We should compare it with the other EP signal (of the other cavity). If there is a huge difference between both we should start searching there. We should also check the RF noise level of the RF-PD. Maybe something is broken there.

 

  549   Wed Mar 23 22:09:08 2011 FrankDailyProgressElectronics Equipmentinput refered noise for UPDH and sensing noise (RFPD) in ACAV

Ok, hmm,  still doesn't make sense. The first problem is that you don't have 50Ohm termination for the mixer signal when measuring with the scope, but if you connect it to the pdh box you have 50 Ohms. But that can't explain the plot alone.

Hmm, the amplifier might be a problem, it's a low-noise one but i didn't check the RF noise after installation. So remove the amplifier and redo the measurements. Be careful as the size of the error signal changes quite a lot and you have to turn the gain of the box back to 8 or so. So you have to re-measure everything.

 

 

  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.

 
 

 

 

  559   Thu Mar 31 20:47:32 2011 taraDailyProgressSeismicaccelerometer installed on the table

Today we installed two accelerometers on the table, for vertical and horizontal(beamline) positions.

The TF between the PZT's driving V and the signal from the accelerometer are plotted below.

 

I did some calculation on frequency noise due to beam/cavity mismatching in translational and pitch which causes the natural axis to change from the designed value. For example, if the beam translate away from the center by a little, same angle, the cavity length as seen by the beam will be shorter because of the curve mirrors.

It looks comparable to what we see on the beat signal.

nb_2011_03_31.png

Frank found me 2 of Breul & kjaer 8318 accelerometer. I installed them on the table for vertical and beamline horizontal directions.

I chose vertical direction because the spring was removed from the cavity suspension and become susceptible to vertical seismic.

For beamline horizontal direction, I chose it because it is the same direction the PZT pushes the table, so I expected to see some strong signal.

000_0004.jpg

 000_0006.jpg

The signal from 8318 is sent to SR560 preamp, ac couple(doesn't change between dc/ac), roll off at 1kHz, gain200.

The signal from SR560 is sent to response (B channel on SR785)

The source is sent to HV amplifier that drives the PZT and reference (A on SR785).

The integration cycle is 50, with 10 settle cycles. I tried 100 integration cycles (quickly cheking between 100Hz and 1kHz again), but there was no significant change.

No strong signal on the horizontal direction. The magnitude is even smaller than that of vertical one.

accTF.png

 I'm not sure how valid the TFs are. I tried changing gain on SR560 and looked at high frequency, 100 - 1kHz,TF the magnitude changes correspodingly

with the gain, the shape looks the same.

The next plan will be measuring the TF between cavity motion (shadow sensing technique)and acceleration on the table. I'll also compare with the seismometer on the table.

  567   Thu Apr 7 02:37:34 2011 taraDailyProgressBEATNoise hunting

I searched for the limiting noise source at high frequency of the beat measurement. I have not founded anything conclusive yet, but the key

seems to be the power on ACAV path.

 

From previous entries, the evidence suggested that I should look into the PLL readout technique for beat measurement, so I tried:

1) changing the beam spot size on the beat RFPD, to see if it was the result from scattering on the RFPD. the beat still looks the same even the beam is clipped.

2) adjusting + removed the 1/4, 1/2 wave plates that turn the circularly polarized beams from to cavities to linearly polarized beam,

3) using ND filters to reduce power from each of the beam, and both of them,

4) checkig the noise level of the RFPD and the mixer out, gain 10. They are lower than the beat.

 

So It is probably not the PLL problem. Then I revisited the idea of the noise in ACAV/ RCAV loop.

I used a 0.3 ND filter to reduce the power in RCAV path, after I adjusted the gain, the beat still remained the same.

However, when I used the filter to reduce the power into ACAV, beat was getting higher, and could not be brought down with the higher gain.

So I increased the power to ACAV from 1 mW to 2 mW, and maintained the power to RCAV at 1mW and measured the beat.

The flat high frequency noise goes down by about a factor of 2. This is surprising, I checked the error noise in ACAV loop and made sure that it was not the limiting part. I will think about it.

Note that peaks around 170 Hz are from the periscopes, and peaks around 600Hz are from the mirror mount on the periscopes.

I plan to replace them with better one after RCAV's chamber is fixed tomorrow.

 

 beat_2011_04_06.png

  569   Thu Apr 7 23:18:49 2011 koji, frank, taraDailyProgressSeismicprevious suspension for RCAV restored

Today we changed the suspension on RCAV back to the original one (spring + wire) and put the cavity back in the chamber.

The beam to RCAV is realigned, but the beam position changes a bit and might clipped on the insulation's opening.

The cavity is being pumped down now.

 

We decided to switch back to original suspension for RCAV for now before designing a new one.

However, a stronger eddy damping system (thicker metal plate, larger magnet) we added last time is still kept.

This thicker plate might add extra weight to the cavity and cause the spring to extend more, sothe cavity hangs ~5mm lower from the original setup.

I had to adjust the height of the input periscope, but there was no other problem.

The mode matching efficiency is more than 95%.

 

The exiting beam seems ok, see below figure.

 

000_0014.jpg

 

However, the incoming beam is off by almost 5mm and migh clip at the edge.

000_0018.jpg

 I'll fix the opening tomorrow, and check if the vacuum works or not.

I borrow a torque wrench from 40m and used it to tighten the screws on the flange.

There should be no problem this time.

 

 

 

 

  571   Sat Apr 9 07:11:20 2011 koji, frank, taraDailyProgressSeismicQ measurement

Q measurement from the cavity's suspension is measured. Vertical translational mode is 3.46 Hz, Q=52 (previous setup was ~200 .) Pitch mode is damped very fast and turns into vertical mode quickly. Q measurement for new periscope is measured and compared with one of the current periscopes (the one for exiting beam, RCAV). The new one is quite better.

 

The suspension of RCAV is restored, with better eddy current damping. We used shadow sensing technique to measured Q of vertical translational motion of the cavity.

f0 = 3.46 Hz, Q = 45.

cavity_v.png

However, pitch mode dies down very fast and turns into vertical mode. We could not really measure it properly. The data looks like this.

pitch.png

 

Next, we measured Q factors for the new periscope that will replace the current one. The current one is made by adding a few 2"-3" posts together, the mirror mounts

are also shaky. So before replacing it, we want to see how better the new one will be.

For the new periscope, there will be one mirror mounted on the post. The bottom mirror will be mounted on the table. So the setup is shown below.

HeNe beam reflects at the mirror on the mirror mount. The post is tapped on two directions, pitch and yaw. They are slightly different due to asymmetry introduced by the top mirror mount.

Then the beam falls on the PD, which is mounted on the table to reduce any extra resonant peaks.

The beam is clipped by a razor blade attached on the PD when the beam moves.

We also increased the sensitivity by focusing the beam to a smaller spot.

Qmsmt.jpg

First, we measured the PSD of the PD signal by tapping on each directions because we could not excite it with white noise, and we wanted to see the peak from each mode clearly.

Once we see the resonance peak, we can fit it to see the Q of each peak

 newperiscope.png

Mode    Resonant freq    Q

yaw          221                27

pitch        249.5               70

 Note: the peak at 108 Hz is the resonant frequency of the laser mount.

The result from ring down measurement is quite different, the pitch frequency is the same, but Q is 45.

The discrepancy might come from the fact that when we measured the ring down, we did not excite exactly one mode, so we see the result from the combination of pitch and yaw.  But the number is not outrageously different anyway.

newperi_ringdown.png

 

Then we tested the curernt periscope. The setup was quite similar except we removed the bottom mirror, so any peaks from bottom mirror will not be seen here

and its peaks' resonant frequencies might shift a bit due to the missing mirror' mass. The results are

 

Mode    Res freq[Hz]      Q

               131          120

              148           100

              526            40

              886            30

 

badperi.png

I could not identify which modes cause which frequencies. But those peaks do not appear in the new periscope test, so they are likely to be from the bad one.

I'm surprised that those measured peaks do not appear in the beat measurement.

 

 

  574   Mon Apr 11 18:20:02 2011 taraDailyProgressBEATbeat setup is back

The optics behind RCAV for beat measurement are re-installed, with the new periscope. I'm waiting for the temperature to settle.

 

The periscope behind RCAV was removed when we opened the chamber and took out the cavity. Now everything is back in place  

The new periscope is installed. The bottom mirror is still on the same mount we have used before(fig1), but the top part is removed, so it should be less sensitive to seismic compared to what it was before (fig2).

 

I removed the hose between the RCAV chamber and the turbo pump since the valve and the turbo were turned off. Then I closed the insulation box.

The yellow foam insulation on RCAV was fixed. I melted it a bit to make sure that no part of the beam is blocked by the insulation.

 

000_0019.jpg

fig1: new periscope setup

 000_0020.jpg

 fig2) previous periscope

  576   Tue Apr 12 18:42:59 2011 Dmass, taraDailyProgressTempCtrltime constant between can and cavity

Today we connected the PT1000 thermostat on RCAV's stack to C3:PSL-GEN_DAQ16. This will be used for time constant between chamber to cavity measurement.

 

We want to learn the time constant between the chamber's outside surface to the cavity, so we need to know the temperature of these two points.

The temperature on the outside surface of the chamber can be measured by 4 sensors that we already have. For the inside,

Frank left one PT1000 on the top seismic stack, just under the cavity inside the chamber. It's wired to the D-sub connector. We made a circuit, as shown below, to measure the change of the resistance( which is proportional to T) of the sensor.

insert fig

Slide1.png

R(T) at 30 C is about 1.2 k ohms.

SR560 is set to DC couple, gain x2. The output is connected to C3:PSL-GEN_DAQ16

This should give us the temperature of the stack inside the vacuum.

Now I'm waiting to see any change of the voltage.

 

 

  577   Tue Apr 12 19:49:39 2011 taraDailyProgressBEATBeat measurement is back

I realigned the beam on the beat path and measured the beat. With new eddy current damping, the peaks at 3.73 Hz now becomes smaller.

beat_2011_04_12.png

 

  578   Tue Apr 12 20:54:36 2011 DmassDailyProgressTempCtrltime constant between can and cavity

The 10V supply is an AD587 with a 22 uF foil capacitor connecting its "noise reduction" pin (8) to ground which I had sitting around from the doubling phase noise experiment.

The signal goes like:

10V x (1 - 9.1k / {9.1k + R(T) } ) =10 V x (1 - 9.1k/{9.1k + 1.2k + dR} ) =10 x (1 - 9.1k / 10.3k x 1 / {1 + dR/10.3k } )

which by taylor expansion is:

10 x  (1 - 9.1 / 10.3 x (1 - dR / 10300 ) = 10 - 10 x 9.1 / 10.3 - 10 x 9.1 / 10.3 x dR / 10300 = 1.165 V - 8.6e-4 x dR/Ohms V

for a 1 kOhm RTD, dR/dT is about 4 Ohms / K so we get a total signal temperature sensitivity that goes like (after the 560 x2 gain):

V(deltaT) = 2 x (1.165V - 8.6e-4 x dR/dT x deltaT /Ohms V)

V(deltaT) = ( 2.33 - 6.8 x 10^-3 x deltaT / K ) Volts.

 

We plugged this into an epics channel and confirmed that it was being recorded.

Tara regularly makes ~ 0.1K adjustments to the temperature of the can in the course of the refcav beat experiement. This will show up as a 700 uV change on the 2.3 V DC signal. I'm not positive that it's this is large enough for us to see, but we get it for free. If we can't see this, we can try a 1K step for a 7 mV change, and if that doesn't work I'll put something less crappy in to readout the PT1000 sensor.

The DC signal read as 2.6 V on a scope and 2.43 V with the existing calibration of the frontend. The 1.2K number I plugged in is wrong by a bit. I trust the systematic calibration (as recorded by the frontend) to ~10%

WHY AM I DOING THIS?

Me and Frank disagree about what the radiative time constant is between the cavity and the can, in the case of both the cryo cavity, and the as built cavity in the PSL. (see this elog).

  1. Envelope physics says it should be on the order of 41 hrs.
  2. The reference cavity + can + heater at the 40m has a time constant of 4 hours
  3. Frank has said "the radiative time constant from the can to the cavity is like 30 minutes," (though he may have since rescinded that statement)
  4. I looked through the PSL elog for some info about what these time constants actually are. I found:
    1. This elog where they do a step in the heater temp, but I can't glean anything clearly useful from it
    2. Another elog claiming a 7.5 hour time constant just for the heater where Rana made a few criticisms on the measurement
  5. The other salient point is that Frank has talked to some people (who exactly?) in both LISA and at UF, and seems to have been told "the only way to get long time constants is to have really good radiation shields with a bunch of layers." This doesn't seem to jive with the second point above, where envelope calculations give you a > 1 day time constant. It would be awesome if Frank could elaborate on exactly what is known here to help remove one person from the telephone chain.

My money is that the thermal time constant is totally dominated by the conductive pole through the stack, and that's what we see (in the PSL lab and at the 40m), so depending on what the time constant between the can heater and the stack thermometer is, we might be able to rule some things out.

Is there any model for the thermal conductivity of the stack + suspension?

  579   Wed Apr 13 09:18:50 2011 taraDailyProgressTempCtrltime constant between can and cavity

 

 This morning, I decided to adjust RCAV's temperature setpoint (C3:PSL-RCAV_RCPID_SETPOINT) up by 1 Kelvin. As I saw not much change in the readout of the PT1000 sensor overnight, I'm afraid that the signal might be too small for a 0.1 k change.

We might be able compare the readout from C3:PSL-GEN_DAQ16 to C3:PSL-FSS_SLOWDC level. SLOWDC controls the temperature of the NPRO crystal for adjusting laser frequency.

The calibration for SLOWDC is 4700 MHz/V*. The resolution of SLOWDC is 0.0001 V => 0.47 MHz. 

Use df/f = dL/L to compute the equivalent cavity's length change, dL ~ 3 e-10 m.

Compare this dL to the effect of thermal expansion of the cavity.

dL = alpha x L x dT =>

3 e-10 [m]= 0.51 e-6 [1/K/m]  x 0.203 [M] * dT [ K]

dT [K] = 3 milliKelvin is the resolution of the temperature we can measure, so we should be able to measure 1 K change on the cavity easily, and we can compare with what we see on the sensor.

From above equations, the cavity's temperature is related to SLOWDC by

dT  = dV_slowdc x 32.91 [K/V].

 For 1 kelvin change on the cavity, SLOWDC should change by 0.0304 [V]

 

 

Cavity's parameters

cavity's length, L = 0.2032 [m]

SiO2 expansion coeff, alpha = 0.51 e-6 [1/K/T]

 

channel list:

C3:PSL-RCAV_RCPID_SETPOINT    set temperature for PID cavity's thermal control

C3:PSL-RCAV_TEMAVG                   average temperature on the outside surface of the can

C3:PSL-FSS_SLOWDC                     thermal control on laser's PZT for adjusting frequency

C3:PSL-GEN_DAQ16                         readout from the temperature sensor on the top seismic stack 

* About the calibration, I used sidebands (35.5MHz x2 =71 MHz) to calibrate SLOWDC to frequency. I also used the cavity's free spectral range (737 MHz) for comparison as well. The results agree well.

  580   Wed Apr 13 11:25:13 2011 DmassDailyProgressTempCtrltime constant between can and cavity

 Tara, please post what the channel names are, physically.

  581   Wed Apr 13 11:29:50 2011 taraDailyProgressTempCtrltime constant between can and cavity
It's C3:PSL-FSS_SLOWDC. I'm not keeping the cavity locked in order to avoid any heat absorption from the beam. I only lock the cavity when I check the SLOWDC level every hour.

[DYM: What IS it in the real world, you shouldn't make someone search your elog to parse your channel names into physical signals]

Duly noted. I edited the entry accordingly.
SLOWDC is for thermal control on NPRO crystal. It is used for adjusting laser frequency.
  582   Thu Apr 14 10:02:11 2011 taraDailyProgressTempCtrltime constant between can and cavity

Result from a step function test.

          At ~1.5 h, I changed the temperature setpoint from 33.5 to 34.5 C, so the voltage supply to the heater rose up. It reached at 1.7 V and constant because the perl script limited the voltage at that value for preventing any mishap.  The can reached the equilibrium first, in ~ 5.5 hrs after the setpoint was changed. Then the cavity's temperature reached the equilibrium, ~ 3 hrs later. The stack temperature had not reached equilibrium yet.

         Heat transfer mechanism that heats up the cavity seems unlikely to be conduction from can-> stack -> suspension-> cavity. If that were the case, the stack would reach equilibrium before the cavity.

 

RCAV_timecon.png

 I'm repeating the experiment, but this time I turn off the thermal PID feedback of the can temperature, and make a step down in the heater voltage supply, and keep the laser locked to the cavity so that we can read the continuous value from SLOWDC.

 

*I'm sure I made this entry last night. Where did it go?

  583   Fri Apr 15 18:59:41 2011 taraDailyProgressFSSPreparing to install TTFSS

I'm preparing the cables for the new TTFSS. A cable for +/-220V is made.

 

I'm planning to install the new TTFSS.  I think the interface and the TTFSS can be fitted on the main PSL rack with power supplies below.

We need +/-17 V, +/-24V, and +/-200V. There is still at least one available KEPCO HV supply I can use.

The cable for +/-200V are almost ready. I went to Wilson house to get the appropriate cable and connector case.

I still need to find banana connectors for another end.

  584   Tue Apr 19 22:40:03 2011 taraDailyProgressFSSPreparing to install TTFSS

 

 All cables and power supplies for the new TTFSS are ready. I'll fire it up tomorrow.

 

 With Peter help, +/- 200V power supply is ready. I'll use the same power supply for the current FSS. I removed the cable for the current FSS, and installed the cable for the new TTFSS.

+/- 24V is already in used, I just added the connector for TTFSS on top of it.

+/-17V is prepared for temporary solution. I used two HP DC power supplies. There are two available KEPCO power supplies on the racks, but I could not turn them on for now. I have to find the manual and read it first.

  585   Wed Apr 20 17:54:52 2011 taraDailyProgressFSSPreparing to install TTFSS

TTFSS is not working properly yet. The signal from Fast out is distorted, but it still can lock the laser. All three actuators are being tested over night. Fine tuning has yet to be done. Once the temperature is settled, I'll measure the beat signal.

 

       I tried to lock the laser with the new TTFSS. There are three actuators, SLOW (thermal control), FAST (acts on PZT), and PC ( acts onEOM).  First, I locked the laser with FAST actuator only. PD input and LO input were removed from the old FSS card and connected to the TTFSS servo box.Then, I scanned the laser by modulating the laser frequency via laser's FAST input to check the error signal. The signal measured at mixer out, FAST MON, RAMP IN OUT2 (see fig 0, for where the outputs are) were good, see fig1 and fig2, but the signal from FAST OUT(tnc) is distorted, see fig3.

      Another problem was about the lemo output, it appeared that

     1)when I measured the signal from FAST OUT(lemo), I did not see any signal at all, and

     2)when I observed the distorted signal from FAST OUT(tnc) and plugged in a lemo connector to lemo FAST OUT, the signal from tnc also disappeared. The connector on the cable is the one we used for FSS, it should be working properly, but I will double check it. There might be shorted/ bad connections in the cable. It probably is the problem from the lemo connector on the board. When I did the test on the box 6 months ago, I used only FAST OUT(tnc).

  

fastout.png

fig0: a part of the schematic from TTFSS servo. FAST OUT has two output, tnc and lemo connectors. The full schematic can be found here.

I measured the signal from FASTM, RAMP IN OUT2, FAST OUT (tnc), and FAST OUT(lemo)

 

000_0025.jpg

 fig1: signal from mixer mon

 

000_0024.jpg

fig2 signal from fast out2 (similar to that from fast out mon (different in amplitude), so I post only this picture)

 

000_0023.jpg

fig3: signal from fast out (which is fed to the laser)

  587   Sat Apr 23 11:40:09 2011 taraDailyProgressFSSPreparing to install TTFSS

 koji, tara

 The mystery about the distortion FASTOUT is solved. It actually works propperly.

From previous entry, the distortion in the error signal from FAST OUT is due to the low pass filter at 10 Hz just before the output.

The signal from tnc FASTOUT disappears when we plug in the lemo FASTOUT because the lemo cable we used has its polarity switched.

So it grounds the signal from TNC output as well.

 

     For an easy reference, I draw a cartoon diagram for the TTFSS circuit.

The small circles are SMA inputs,

the large circles with shadow are manual knobs,

the middle size circles are bnc outputs,

the diamonds are TNC outputs, and the half circles are bnc outputs for monitor.

TTFSS_cartoon.pdf

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