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ID Date Author Type Category Subject
7991   Mon Feb 4 11:10:59 2013 KojiSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

The expected finesse is 100ish. How much can we beleive the measured number of 50?
From the number we need to assume PR2 has ~93% reflectivity.
This does not agree with my feeling that the cavity is overcoupled.
Another way is to reduce the reflectivity of the PRM but that is also unlikely from the data sheet.

The scan passed the peak in 4ms according to the fitting.
How do the analog and digital antialiasing filters affect this number?

7992   Mon Feb 4 15:06:56 2013 KojiSummaryGeneralHypothesis

 Quote: Q. How can we avoid this instability issue? A. 1. Use flatter mirrors or at least concave mirrors. 2. Smaller incident angle to avoid emphasis of the RoC in the horizontal direction 3. Use weaker squishing force for mounting of the mirrors 4. Flip the PR3 mirror in the mounting ring by accepting the compromise that the AR surface is in the cavity.

Another possibility is to use a ring heater to correct the curvature. I talked a bit with Aidan about this.

7994   Mon Feb 4 19:33:19 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

[Jenne, Yuta]

We redid PRM-PR2 cavity scan because last one (elog #7990) was taken with the sampling frequency of 2 KHz. We have also done TMS measurement.

Method:
1. Align input TTs and PRM to align PRM-PR2 cavity.
2. Sweep cavity length using C1:SUS-PRM_LSC_EXC.
3. Get data using Jamie's getdata and fitted peaks using /users/jrollins/modescan/prc-pr2_aligned/run.py
4. Calculated cavity parameters

Results:
Below is the figure containing peaks used to do the calculation.

From 11 MHz sidebands, calibration factor is 462 +/- 22 MHz/sec (supposing linear scan around peaks)
FWHM is 1.45 +/- 0.03 MHz.
TMS is 2.64 +/- 0.05 MHz.
Error bars are statistical errors of the average over 3 TEM00 peaks.

If we believe cavity length L to be 1.91 m, FSR is 78.5 MHz.
So, Finesse will be 54 +/- 1 and cavity g-factor will be 0.9944 +/- 0.0002. 0.9889 +/- 0.0004   (Edited by YM; see elog #8056)
If we believe RoC of PRM is exactly +122.1 m, measured g-factor insists RoC of PR2 to be -187 +/- 4.
If we believe RoC of PR2 is exactly -600 m, measured g-factor insists RoC of PRM to be 218 +/- 6.

Discussion:
1. Finesse is too small (expected to be ~100). This time, data was taken 16 KHz. Cut-off frequency of the digital antialiasing filter is ~ 5 kHz (see /opt/rtcds/rtscore/release/src/fe/controller.c). FWHM is about 0.003 sec, so it should not effect much according to my simulation.

2. I don't know why FWHM measurement from the last one is similar to this one. The last one was taken 2 KHz, this means anti-aliasing filter of 600 Hz. This should double FWHM.

3. Oscilloscope measurement may clear anti-aliasing suspicion.

7995   Mon Feb 4 19:48:32 2013 JamieSummaryGeneralarbcav recalc of PRC with correct ITM transmission

I noticed that Koji used a high reflector for the ITMs for his full PRC arbcav calculation. I just redo it here with the correct ITM transmission and RoC for completeness.

In this case the finesse is 95, instead of 121.

7996   Mon Feb 4 22:46:03 2013 JamieSummaryGeneralarbcav for SRC with curved TTs

I ran Zach's arbcav on our SRC with curved TTs and the situation looks much worse than the PRC.

I used the following parameters

SRM: RoC = 142 m, T = 10%
ITM: RoC = 83.1e3 m, T = 1.4%
SRC length: 5.37 m

In this case, with TT RoC of -600, the combined cavity g-factor = 0.9986, and astigmatism from SR3 makes the cavity patently not stable.  You have to go up to an RoC of -710 before the cavity is just over the edge.

7997   Tue Feb 5 02:04:44 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

I redid PRM-PR2 cavity scan using oscilloscope to avoid anti-aliasing effect.
Measured Finesse was 104 +/- 1.

Method:
1. Splitted POP DC output into three and plugged two into oscilloscope TDS 3034B. Ch1 and Ch2 was set to 1 V/div and 20 mV/div respectively to take the whole signal and higer resolution one at the same time (Koji's suggestion). Sampling frequency was 50 kHz. Sweeping time through FWHM was about 0.001 sec, which is slow enough.
2. Took mode scan data from the oscilloscope via network.

Preliminary results:
Below is the plot of the data for one TEM00 peak.

The data was taken twice.
Measured FWHM was 0.764 MHz and 0.751 MHz. By taking the average, FWHM = 0.757 +/- 0.005 MHz.
This gives you Finesse = 104 +/- 1, which is OK compared with the expectation.

What I need:
I need better oscilloscope so that we can take longer data (~1 sec) with higher resolution (~0.004 V/count, ~50kHz).
TDS 3034B can take data only for 10 ksamples, one channel by one!  I prefer Yokogawa DL750 or later.

7998   Tue Feb 5 03:16:51 2013 KojiSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

0.764 and 0.751 do not give us the stdev of 0.005.

I have never seen any Yokogawa in vicinity.

 Quote: Measured FWHM was 0.764 MHz and 0.751 MHz. By taking the average, FWHM = 0.757 +/- 0.005 MHz.  This gives you Finesse = 104 +/- 1, which is OK compared with the expectation. What I need  I need better oscilloscope so that we can take longer data (~1 sec) with higher resolution (~0.004 V/count, ~50kHz).  TDS 3034B can take data only for 10 ksamples, one channel by one!  I prefer Yokogawa DL750 or later.

8000   Tue Feb 5 10:09:08 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

stdev of [0.764, 0.751] is 0.007, but what we need is the error of the averaged number. Statistical error of the averaged number is stdev/sqrt(n).

 Quote: 0.764 and 0.751 do not give us the stdev of 0.005.

8002   Tue Feb 5 11:30:19 2013 KojiSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

Makes sense. I mixed up n and n-1

Probability function: X = (x1 + x2 + ... + xn)/n, where xi = xavg +/- dx

Xavg = xavg*n/n = xavg

dXavg^2 = n*dx^2/n^2
=> dXavg = dx/sqrt(n)

Xavg +/- dXavg = xavg +/- dx/sqrt(n)

8004   Tue Feb 5 15:31:03 2013 SteveUpdateGeneralclean assembly room benches cleaned up

Manasa, Jamie and Steve,

Tip-Tilts and parts moved into the most north " 40m "  cabinet  in the assembly room.

Green-black glass and related components were moved to the 40m E0 cabinet in plastic boxes.

The north flow bench has a few items that belong to us: HE/Ne laser, qpd on translation stages, an iris and one red mirror.  These were moved to the north edge of this bench.

However this leveled table is still full with other people's stuff

Attachment 1: IMG_0057.JPG
Attachment 2: IMG_0061.JPG
8005   Tue Feb 5 19:16:22 2013 JamieSummaryGeneralarbcav of PRC with +600 RoC PR2/3

This is just a simple rerun of arbcav from #7995 but with the PR2/3 RoCs set to 600, instead of -600.  Overall g-factor = 0.922, and the modes are well separated:

This doesn't take into account the effect of traveling through the substrates (still working on it).  It assumes the PR2/3 have been moved such that the cavity fold lengths remain the same.

This is something that we need to keep in mind: we will need to adjust the position of the PR2/3 to keep the fold lengths the same.

8006   Tue Feb 5 19:32:47 2013 yutaSummaryGeneralPR2/PR3 flipping and PRC stability

We are considering of flipping PR2 and/or PR3 to make PRMI stable because PR2/PR3 seems to be convex.
I calculated dependency of the PRC stability on the PR2/PR3 curvature when PR2/PR3 flipped and not flipped.
Flipping looks OK, from the stability point of view.

Assumption:
 PRM-PR2 distance = 1.91 m  PR2-PR3 distance = 2.33 m  PR3-ITM distance = 2.54 m  PRM RoC = +122.1 m  ITM RoC = Inf
 theta_inc PRM = 0 deg  theta_inc PR2 = 1.5 deg  theta_inc PR3 = 41 deg           (all numbers from elog #7989)

Here, RoC means RoC measured from HR side. RoC measured from AR side will be -n_sub*RoC, assuming flat AR surface.
I also assumed mirror thickness to be negligible.

Method:
1. I used Zach's arbcav and modified it so that it only tells you your cavity is stable or not.
(It lives in /users/yuta/scripts/mode_density_PRC/stableornot.m)

2. Swept PR2/PR3 RoC (1/RoC from -0.005 to 0.005 1/m) to see the stability condition.

Results:
1. Stability condition of the PRMI when PR2 and PR3 is not flipped is depicted in the graph below. Black region is the unstable region. We all know that current PRMI is unstable, so we are in the black region.

2. Stability conditions of PRMI with one of the PR2/PR3 flipped are depicted in the graphs below. If we flip one of them, PRMI will likely to be stable, but if the flipped one is close to flat and the RoC of the other one is  >~ -250 m (more convex than -250 m), PRMI will remain unstable.

3. Stability condition of PRMI with both PR2 and PR3 flipped is depicted in the graph below. If we flip both, PRMI will be stable.

Discussion:
1. Flipping one of PR2/PR3 seems OK, but I cannot guarantee. TMS measurement insists RoC of PR2 to be ~ -190 m, if we believe PRM RoC = +122.1 m (elog #7997). We need more precise measurement if we need to be sure before flipping. I prefer PR2 flipping because PR3 flipping gives us longer path in the substrate and larger astigmatism. Also, PR3 RoC is phase-map-measured to be ~ -600 m and PR2 RoC seems to be more convex than -600 m from the TMS measurement.

2. Flipping both is good from stability point of view. We need calculation of the loss in the PRC (and mode-mismatch to the arms). Are there any requirements?

3. If we are going to flip PR3, are there any possibilities of clipping the beam at PR3? We need to check.

4. I need to calculate whether mirror thickness and AR surface curvature are negligible or not.

Conclusion:
I want to flip only PR2 and lock PRMI.

By the way:
I don't like matlab plots.

8012   Wed Feb 6 15:20:55 2013 yutaSummaryGeneralFWHM was wrong

I have to blame Jamie for putting extra 2 randomly.
Measured PRM-PR2 cavity finesse was actually 108 +/- 3 (even if you use digital system to get data).

Lorentzian fit:
Lorentzian function is;

f(x;x0,gamma,A) = A * gamma**2/((x-x0)**2+gamma**2)

where x0 is the location of the peak, gamma is HWHM, and A is the peak height.
Lorentzian fitting function in my original code (/users/yuta/scripts/modescanresults/analyzemodescan.py) was

fitFunc = lambda p,x,m: (m-p[2])*p[0]**4/(4*(x-p[1])**2+p[0]**4)+p[2]

In this function, p[0] is sqrt(FWHM), not sqrt(HWHM). I doubled gamma to make it FWHM and squared it because they should be positive.
During Jamie's modification of my code, he doubled p[0]**2 to get FWHM, which is wrong (/users/jrollins/modescan/modescan.py).

I should have commented that p[0] is sqrt(FWHM).

Redoing the analysis:
1. I pulled 2 out, and modified Jamie's modescan.py so that you can name each peak with peakdistinguish=True option. I also modified fitpeak function so that it throws away "peaks" which don't look like a peak.

2. If you run /users/yuta/PRCmodescan/run.py and name each peak, you will get peaks.csv which includes peak position, FWHM, and the type of the peak;

0.065017,0.001458,l
0.070446,0.001463,3
0.075940,0.001509,2
0.081552,0.001526,1
0.087273,0.001565,0
0.112027,0.001911,u
0.278660,0.002211,u
0.306486,0.001658,0
0.312480,0.001576,1
0.313626,2.507910,
0.318486,0.001626,2
0.319730,2.633097,
0.324801,0.001739,3
0.331848,0.001922,l
0.527509,0.001603,l
0.533231,0.001445,3
0.538648,0.001488,2
0.544081,0.001455,1
0.549517,0.001498,0
0.551725,2.422759,
0.570972,0.001346,u

3. /users/yuta/PRCmodescan/calcmodescanresults.py reads peaks.csv and tells you the results;

Time between TEM00 and sideband  0.0239435  pm  0.00115999887452  sec
Calibration factor is  462.167602898  pm  22.3907907867  MHz/sec
FSR is  78.4797010471  MHz
FWHM is  0.729828720682  pm  0.0174145743828  MHz
TMS is  2.64718671684  pm  0.0538858477824  MHz
Finesse is  107.53166986  pm  2.5658325169
Cavity g-factor is  0.994390582331  pm  0.000228155661075
Cavity g-factor is  0.988812630228  pm  0.000453751681357   (Edited by YM; see elog #8056)
RoC of PR2 is  -187.384503001  pm  4.26100999578  m (assuming PRM RoC= 122.1  m)
RoC of PRM is  217.915890722  pm  5.65451518991  m (assuming PR2 RoC= -600  m)

8019   Wed Feb 6 22:39:23 2013 JamieUpdateGeneralPRC/arm mode matching with flipped PR2/PR3: coming soon

I intended to post a long analysis of the PRC/arm mode matching for the various TT situations using Nic's a la mode mode matching program, but I seem to have encountered what I think might be a bug.  I'll talk to Nic about it first thing in the AM.  Once the issue is resolved I should be able to post the full analysis fairly quickly.  Sorry about the delay.

8020   Thu Feb 7 09:03:54 2013 ManasaUpdateGeneralStore optics in respective cabinets

@Yuta

The ITMX table has been left open since yesterday. I am disconnecting your oscilloscope and closing the table.

To whomsoever it may concern...

I found about half a dozen new cvi optics (beam splitters, waveplates and lenses) lying around on the SP table.

Please store optics back in their respective cabinets if you are not using them immediately. Somebody might be looking around to use them.

8021   Thu Feb 7 10:35:35 2013 yutaUpdateGeneralStore optics in respective cabinets

I'm not the one who opened the ITMX table yesterday, but thanks for reminding me.
I put POP DC oscilloscope and its cables back.

Also, I relocked PMC and MC. It was unlocked since last night.

8022   Thu Feb 7 12:56:18 2013 JamieSummaryGeneralPRC/arm mode matching calculations

NOTE: There was a small bug in my initial calculation.  The plots and numbers have been updated with the fixed values.  The conclusion remains the same.

Using Nic's a la mode mode matching program, I've calculated the PRC mode and g-parameter for various PR2/3 scenarios.  I then looked at the overlap of the resultant PRC eigenmodes with the ARM eigenmode.  Here are the results:

NOTE: each optical element below (PR2, ITM, etc.) is represented by a compound M matrix.  The z axis in these plots is actually just the free space propagation between the elements, not the overall optical path length.

## ARM

This is the ARM mode I used for all comparisons:

 tangential sagittal gouy shift, one-way 55.63 55.63 g (from gouy) 0.303 0.303 g (product of individual mirror g) 0.303 0.303

## PRC, nominal design (flat PR2/3)

This is the nominal "as designed" PRC, with flat PR2/3 folding mirrors.

 tangential sagittal gouy shift, one-way 14.05 14.05 g (from gouy) 0.941 0.941 g (product of individual mirror g) 0.942 0.942

## PRC, both PR2/3 flipped

This assumes both PR2 and PR3 have a RoC of -600 when not flipped, and includes the affect of propagation through the substrates.

 tangential sagittal gouy shift, one-way 19.76 18.45 g (from gouy) 0.886 0.900 g (product of individual mirror g) 0.888 0.902

## PRC, only PR2 flipped

In this case we only flip PR2 and leave PR3 with it's bad -600 RoC:

 tangential sagittal gouy shift, one-way 18.37 18.31 g (from gouy) 0.901 0.901 g (product of individual mirror g) 0.903 0.903

# Discussion

I left out the current situation (PR2/3 with -600 RoC) and the case where only PR3 is flipped, since those are both unstable according to a la mode.

### I guess the main take away is that we get slightly better PRC stability and mode matching to the arms by only flipping PR2.

8025   Thu Feb 7 17:10:11 2013 KojiSummaryGeneralPRC/arm mode matching calculations

 Quote: I left out the current situation (PR2/3 with -600 RoC) and the case where only PR3 is flipped, since those are both unstable according to a la mode.

This surprises me. I am curious to know the reason why we can't make the cavity stable by flipping the PR3 as PR3 was supposed to have more lensing effect than PR2 according to my statement.

8029   Fri Feb 8 00:23:33 2013 ranaSummaryGeneralPRC/arm mode matching calculations

I would guess that either flipping PR2 or PR3 would give nearly the same effect (g = 0.9) and that flipping both makes it even more stable (smaller g). But what we really need is to see the cavity scan / HOM resonance plot to compare the cases.

The difference of 0.5% in mode-matching is not a strong motivation to make a choice, but sensitivity to accidental HOM resonance of either the carrier or f1 or f2 sidebands would be. Should also check for 2*f2 and 2*f1 resonances since our modulation depth may be as high as 0.3. Accidental 2f resonance may disturb the 3f error signals.

8033   Fri Feb 8 11:07:07 2013 JamieSummaryGeneralPRC/arm mode matching calculations

 Quote: I would guess that either flipping PR2 or PR3 would give nearly the same effect (g = 0.9) and that flipping both makes it even more stable (smaller g). But what we really need is to see the cavity scan / HOM resonance plot to compare the cases. The difference of 0.5% in mode-matching is not a strong motivation to make a choice, but sensitivity to accidental HOM resonance of either the carrier or f1 or f2 sidebands would be. Should also check for 2*f2 and 2*f1 resonances since our modulation depth may be as high as 0.3. Accidental 2f resonance may disturb the 3f error signals.

You would guess, and I would have guessed too, but the calculations tell the story.   Flipping both does not increase the stability.  The main issue is that flipping PR3 induces considerable astigmatism.  This is why flipping PR3 alone does not make the cavity stable.  I will do some simple calculations today that will demonstrate this effect.

But again, we should only change one thing at a time and understand that before moving on.  Given that the calculations show that flipping only PR2 should alone have a positive affect, we should do just that first, and verify that we understand what's going on, before we move on to making more changes.

I will try to make some more arbcav runs as well, for just the flipped PR2.

8035   Fri Feb 8 12:42:45 2013 nicolasSummaryGeneralPRC/arm mode matching calculations

 Quote: The main issue is that flipping PR3 induces considerable astigmatism.

Yes, at 45degrees PR3 will only have a curvature of about 850m for the vertical mode of the beam, apparently not enough to stabilize the cavity.

8040   Fri Feb 8 18:23:32 2013 JamieSummaryGeneralarbcav of half PRC with flipped PR2

Arbcav with half PRC (flat temporary mirror in front of BS), PR2 RoC = 600m, PR3 RoC = -600m:

NOTE: this does NOT include the affect of the PR2 substrate in the cavity.  Arbcav does not handle that.  It would have to be modified to accept arbitrary ABCD matrices.

NOTE: I added to the mode plot the frequency separation of the first HOMs from the carrier (\omega_{10/01}), in units of carrier FSR.

8041   Fri Feb 8 19:29:44 2013 yutaSummaryGeneralarbcav of half PRC with flipped PR2

We need expected finesse and g-factor to compare with mode-scan measurement. Can you give us the g-factor of the half-PRC and what losses did you assumed to calculate the finesse?

Also, flipped PR2 should have RoC of - R_HR * n_sub (minus measured RoC of HR surface multiplied by the substrate refractive index) because of the flipping.
According to Jenne dictionary, HR curvature measured from HR side is;

PRM: -122.1 m
PR2: -706 m
PR3: - 700 m
TM in front of BS: -581 m

Please use these values to calculate expected g-factor so that we don't get confused.

 Quote: Arbcav with half PRC (flat temporary mirror in front of BS), PR2 RoC = 600m, PR3 RoC = -600m:

8059   Mon Feb 11 17:17:30 2013 JamieSummaryGeneralmore analysis of half PRC with flipped PR2

 Quote: We need expected finesse and g-factor to compare with mode-scan measurement. Can you give us the g-factor of the half-PRC and what losses did you assumed to calculate the finesse?

This is exactly why I added the higher order mode spacing, so you could calculate the g parameter.  For TEM order N = n + m with spacing f_N, the overall cavity g parameter should be:

g = (cos( (f_N/f_FSR) * (\pi/N) ))^2

The label on the previous plat should really be f_N/FSR, not \omega_{10,01}

BUT, arbcav does not currently handle arbitrary ABCD matrices for the mirrors, so it's going to be slightly less accurate for our more complex flipped mirrors.  The affect would be bigger for a flipped PR3 than for a flipped PR2, because of the larger incidence angle, so arbcav will be a little more correct for our flipped PR2 only case (see below).

 Quote: Also, flipped PR2 should have RoC of - R_HR * n_sub (minus measured RoC of HR surface multiplied by the substrate refractive index) because of the flipping.

This is not correct.  Multiplying the RoC by -N would be a very large change.  For an arbitrary ABCD matrix:

R_eff = -2 / C


When the incident angle in non-zero:

tangential: R_eff = R_eff / cos(\theta)
sagittal:   R_eff = R_eff * cos(\theta)


For flipped PR2, with small 1.5 degree incident angle and RoC of -706 at HR:

M_t = M_s = [1.0000, 0.0131; -0.0028, 1.0000]
R_eff = 705.9


For flipped PR3, with large 41 degree incident angle and RoC of -700 at HR:

M_t = [1.0000, 0; 0.0038, 1.0000]
M_s = [1.0000, 0; 0.0022, 1.0000]
R_eff = 592.4


The affect of the substrate is negligible for flipped PR2 but significant for flipped PR3.

# The current half-PRC setup

OK, I have now completely reconciled my alamode and arbcav calculations.  I found a small bug in how I was calculating the ABCD matrix for non-flipped TTs that made a small difference.  I now get the exact same g parameter values with both with identical input parameters.

 Quote: According to Jenne dictionary, HR curvature measured from HR side is; PRM: -122.1 m PR2: -706 m PR3: - 700 m TM in front of BS: -581 m

Sooooo, I have redone my alamode and arbcav calculations with these updated values.  Here are the resulting g parameters

 arbcav a la mode measurement g tangential 0.9754 0.9753 0.986 +/- 0.001 g sagital 0.9686 0.9685 0.968 +/- 0.001

So the sagittal values all agree pretty well, but the tangential measurement does not.  Maybe there is an actual astigmatism in one of the optics, not due to angle of incidence?

arbcav HOM plot:

8061   Mon Feb 11 18:39:10 2013 ChloeUpdateGeneralPictures of Circuitry in Photodiode

I am going to be making measurements to find the optical mounts with the least noise. I am using a quadrature photodiode to record intensity of laser light. These are pictures of the circuitry inside (both sides). I will be designing/making some circuitry on a breadboard in the next few days in order to add and subtract the signals to have pitch and yaw outputs.

Attachment 1: IMG_0327.JPG
Attachment 2: IMG_0329.JPG
8068   Tue Feb 12 18:25:43 2013 JamieSummaryGeneralhalf PRC with astigmatic PR2/3

Quote:
 arbcav a la mode measurement g tangential 0.9754 0.9753 0.986 +/- 0.001 g sagital 0.9686 0.9685 0.968 +/- 0.001

Given that we're measuring different g parameters in the tangential and sagittal planes, I went back to alamode to see what astigmatism I could put into PR2 and/or PR3 to match what we're measuring.  I looked at three cases: only PR2 is astigmatic, only PR3 is, or where we split the difference.  Since the sagittal measurement matches, I left all the sagittal curvatures the same in

### case 1: PR3 only

 PR2 RoC (m) PR3 RoC (m) g (half PRC) tangential 706 -420 0.986 sagittal 706 -700 0.969

### case 2: PR3 only

 PR2 RoC (m) PR3 RoC (m) g (half PRC) tangential 5000 -700 0.986 sagittal 706 -700 0.969

### case 3: PR2 and PR3

 PR2 RoC (m) PR3 RoC (m) g parameter tangential 2000 -600 0.986 sagittal 706 -700 0.969

From Koji's post about the scans of the G&H mirrors, it looks entirely reasonable that we could have these levels of astigmatism in the optics.

## What this means for full PRC

These all make the same full PRC situation:

g (tangential):  0.966

g (sagittal):  0.939

ARM mode matching:  0.988

8074   Wed Feb 13 01:26:08 2013 yutaSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

Koji was correct.

When you estimate the variance of the population, you have to use unbiased variance (not sample variance). So, the estimate to dx in the equations Koji wrote is

dx = sqrt(sum(xi-xavg)/(n-1))
= stdev*sqrt(n/(n-1))

It is interesting because when n=2, statistical error of the averaged value will be the same as the standard deviation.

dXavg = dx/sqrt(n) = stdev/sqrt(n-1)

In most cases, I think you don't need 10 % precision for statistical error estimation (you should better do correlation analysis if you want to go further). You can simply use dx = stdev if n is sufficiently large (n > 6 from plot below).

 Quote: Makes sense. I mixed up n and n-1 Probability function: X = (x1 + x2 + ... + xn)/n, where xi = xavg +/- dx Xavg = xavg*n/n = xavg dXavg^2 = n*dx^2/n^2 => dXavg = dx/sqrt(n) Xavg +/- dXavg = xavg +/- dx/sqrt(n)

8078   Wed Feb 13 19:09:32 2013 yutaSummaryGeneralpossible explanations to oval REFL beam

[Jenne, Manasa, Jamie, Yuta]

The shape of the REFL beam reflected from PRM is oval after the Faraday.
We tried to fix it by MC spot position centering and by tweaking input TT1/TT2/PRM. But REFL still looks bad (below).

What has changed since:
REFL looks OK in mid-Dec 2012. Possibly related things changed are;

1. New active input TTs with new mirrors installed
2. Leveling of IMC stack changed a little (although leveling was done after installing TTs)

Possible explanations to oval REFL:
A. Angled input beam:
Input beam is angled compared with the Faraday apertures. So, beam coming back from PRM is angled, and clipped by the Faraday aperture at the rejection port.

B. Mode mis-match to PRM:
New input TTs have different curvatures compared with before. Input mode matching to PRM is not good and beam reflected from PRM is expanding. So, there's clipping at the Faraday.

C. Not clipping, but astigmatism:
New input TTs are not flat. Incident angle to TT2 is ~ 45 deg. So, it is natural to have different tangential/sagittal waist sizes at REFL.

How to check:
A. Angled input beam:
Look beam position at the Faraday apertures. If it doesn't look centered, the incident beam may be angled.
(But MC centering didn't help much......)

B. Mode mis-match to PRM:
Calculate how much the beam size will be at the Faraday when the beam is reflected back from PRM. Put some real numbers to curvatures of input TTs for calculation.

C. Not clipping, but astigmatism:
Same calculation as B. Let's see if REFL is with in our expectation or not by calculating the ratio of tangential/sagittal waist sizes at REFL.

8079   Wed Feb 13 19:30:45 2013 KojiSummaryGeneralpossible explanations to oval REFL beam

>> "What has changed since:"

Recently the REFL path has been rearranged after I touched it just before Thanksgiving.
(This entry)

If the lenses on the optical table is way too much tilted, this astigmatism happens.
This is frequently observed as you can find it on the POP path right now.

Also the beam could be off-centered on the lens.

I am not sure the astigmatism is added on the in-air table, but just in case
you should check the table before you put much effort to the in-vacuum work.

8080   Wed Feb 13 19:41:07 2013 yutaSummaryGeneralpossible explanations to oval REFL beam

We checked that REFL beam is already oval in the vacuum. We also centered in-air optics, including lens, in the REFL path, but REFL still looks bad.

By using IR card in vacuum, PRM reflected beam looks OK at MMTs and at the back face of the Faraday. But the beam looks bad after the output aperture of the Faraday.

8087   Fri Feb 15 09:58:49 2013 SteveUpdateGeneralbeam traps ready to be installed

Black-green glass traps are ready for light in vacuum. I can assemble more if needed. These three sizes are available.

Attachment 1: IMG_0083.JPG
Attachment 2: IMG_0084.JPG
8089   Fri Feb 15 16:09:19 2013 KojiUpdateGeneralbeam traps ready to be installed

For the hexagonal one, insert one of the glass plate only half. Use a 1"x.5" piece if exists.

For the diamond one, you don't need the forth glass piece.

Attachment 1: HexBeamDump.pdf
Attachment 2: DiamondBeamDump2in.pdf
8103   Tue Feb 19 02:23:40 2013 yutaBureaucracyGeneralaction items for PRFPMI

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

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

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

PRC characterization in PRMI:

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

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

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

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

Please fix, add or update if you notice anything.

8156   Mon Feb 25 13:01:39 2013 KojiSummaryGeneralQuick, compact, and independent tasks

- IMC PDH demodulation phase adjustment

- Permanent setup for green transmission DC PDs  on the PSL table

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

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

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

PRC characterization in PRMI:

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

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

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

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

8222   Mon Mar 4 17:32:26 2013 yutaBureaucracyGeneralflowchart for PRMI g-factor measurement

I made a very useful flowchart for the week. Our goal for the week is to measure g-factor of PRC in PRMI.

8224   Mon Mar 4 19:38:21 2013 CharlesUpdateGeneralIntensity Stabilization and Control Systems

I have been studying Jamies master's thesis concerning intensity stabilization of a solid-state laser (the 1064 nm specifically) to the ~10^-9 level, as well as relevant supporting material. I have also been reading about general control systems, photodiodes and acousto-optic modulators to help facilitate work on the ISS.

Now that Altium has been properly installed, I have also begun familiarizing myself with the program and general libraries of boards and devices that have already been modeled with the program.

8225   Mon Mar 4 19:52:03 2013 Jamie, YutaUpdateGeneralinput pointing mirror (TT1/TT2) control improved

We improved the active tip-tilt (TT) controllers such that they now have filter banks at the PIT/YAW inputs, and at the coil outputs:

This allowed us to do a couple of things:

• normalize the matrix to unity, and move overall gains into the filters (we moved x100 gain into PIT/YAW)
• slider control is now PIT/YAW OFFSET
• potentially do coil balancing
• allow for input excitiations
• automatically record EPICS values

These are all big improvements.  The TT MEDM screens were appropriately updated.

We had to rebuild/restart c1ass, which reset the TT pointing.  We recorded all the values before hand and were able to recover the pointing easily.  Interestingly, there did appear to be hysteresis in pitch, which is maybe not entirely unexpected, but still worth nothing.

8243   Wed Mar 6 18:27:24 2013 JamieUpdateGeneralnow recording input TT channels to frames, but why no autoburt?

I spent some time trying to figure out how to get a record of the pointing of the input pointing tip-tilt (TT) channels.

## Frames

Currently the TT pointing is done via the offset in the PIT/YAW filter banks, ie. C1:IOO-TT1_PIT_OFFSET, which is an EPICS record.  I added these channels to the C0EDCU.ini, which (I'm pretty sure) specifies which EPICS channels are recorded to frames.

controls@pianosa:~ 0$grep C1:IOO-TT /opt/rtcds/caltech/c1/chans/daq/C0EDCU.ini [C1:IOO-TT1_PIT_OFFSET] [C1:IOO-TT1_YAW_OFFSET] [C1:IOO-TT2_PIT_OFFSET] [C1:IOO-TT2_YAW_OFFSET] controls@pianosa:~ 0$


I then confirmed that the data is being recorded:

controls@pianosa:~ 0$FrChannels /frames/full/10466/C-R-1046657424-16.gwf | grep TT C1:IOO-TT1_PIT_OFFSET 16 C1:IOO-TT1_YAW_OFFSET 16 C1:IOO-TT2_PIT_OFFSET 16 C1:IOO-TT2_YAW_OFFSET 16 controls@pianosa:~ 0$


## BURT

The EPICS records for these channels *should* be recorded by autoburt, but Yuta noticed they were not:

controls@pianosa:~ 0$grep -R C1:IOO-TT1_PIT_OFFSET /opt/rtcds/caltech/c1/burt/autoburt/snapshots/2013/Mar/6/ controls@pianosa:~ 1$


The autoburt log seems to indicate some sort of connection problem:

controls@pianosa:! 130$grep C1:IOO-TT1_PIT_OFFSET /opt/rtcds/caltech/c1/burt/autoburt/logs/c1assepics.log pv >C1:IOO-TT1_PIT_OFFSET< nreq=-1 pv >C1:IOO-TT1_PIT_OFFSET.HSV< nreq=-1 pv >C1:IOO-TT1_PIT_OFFSET.LSV< nreq=-1 pv >C1:IOO-TT1_PIT_OFFSET.HIGH< nreq=-1 pv >C1:IOO-TT1_PIT_OFFSET.LOW< nreq=-1 C1:IOO-TT1_PIT_OFFSET ... ca_search_and_connect() ... OK C1:IOO-TT1_PIT_OFFSET.HSV ... ca_search_and_connect() ... OK C1:IOO-TT1_PIT_OFFSET.LSV ... ca_search_and_connect() ... OK C1:IOO-TT1_PIT_OFFSET.HIGH ... ca_search_and_connect() ... OK C1:IOO-TT1_PIT_OFFSET.LOW ... ca_search_and_connect() ... OK C1:IOO-TT1_PIT_OFFSET ... not connected so no ca_array_get_callback() C1:IOO-TT1_PIT_OFFSET.HSV ... not connected so no ca_array_get_callback() C1:IOO-TT1_PIT_OFFSET.LSV ... not connected so no ca_array_get_callback() C1:IOO-TT1_PIT_OFFSET.HIGH ... not connected so no ca_array_get_callback() C1:IOO-TT1_PIT_OFFSET.LOW ... not connected so no ca_array_get_callback() controls@pianosa:~ 0$


This is in contrast to successfully recorded channels:

controls@pianosa:~ 0$grep C1:LSC-DARM_OFFSET /opt/rtcds/caltech/c1/burt/autoburt/logs/c1lscepics.log pv >C1:LSC-DARM_OFFSET< nreq=-1 pv >C1:LSC-DARM_OFFSET.HSV< nreq=-1 pv >C1:LSC-DARM_OFFSET.LSV< nreq=-1 pv >C1:LSC-DARM_OFFSET.HIGH< nreq=-1 pv >C1:LSC-DARM_OFFSET.LOW< nreq=-1 C1:LSC-DARM_OFFSET ... ca_search_and_connect() ... OK C1:LSC-DARM_OFFSET.HSV ... ca_search_and_connect() ... OK C1:LSC-DARM_OFFSET.LSV ... ca_search_and_connect() ... OK C1:LSC-DARM_OFFSET.HIGH ... ca_search_and_connect() ... OK C1:LSC-DARM_OFFSET.LOW ... ca_search_and_connect() ... OK C1:LSC-DARM_OFFSET ... ca_array_get_callback() nreq 1 ... OK C1:LSC-DARM_OFFSET.HSV ... ca_array_get_callback() nreq 1 ... OK C1:LSC-DARM_OFFSET.LSV ... ca_array_get_callback() nreq 1 ... OK C1:LSC-DARM_OFFSET.HIGH ... ca_array_get_callback() nreq 1 ... OK C1:LSC-DARM_OFFSET.LOW ... ca_array_get_callback() nreq 1 ... OK controls@pianosa:~ 0$


In fact all the records in the c1assepics log are showing the same "not connected so no ca_array_get_callback()" error.  I don't know what the issue is.  I have no problem reading the values from the command line, with e.g. ezcaread.  So I'm perplexed.

If anyone has any idea why the c1ass EPICS records would fail to autoburt, let me know.

8245   Wed Mar 6 20:21:34 2013 JamieUpdateGeneralBeatbox pulled from rack

I pulled the beatbox from the 1X2 rack so that I could try to hack in some output whitening filters.  These are shamefully absent because of my mis-manufacturing of the power on the board.

Right now we're just using the MON output.  The MON output buffer (U10) is the only chip in the output section that's stuffed:

The power problem is that all the AD829s were drawn with their power lines reversed.  We fixed this by flipping the +15 and -15 power planes and not stuffing the differential output drivers (AD8672).

It's possible to hack in some resistors/capacitors around U10 to get us some filtering there.  It's also possible to just stuff U9, which is where the whitening is supposed to be, then just jump it's output over to the MON output jack.  That might be the cleanest solution, with the least amount of hacking on the board.

In any event, we really need to make a v2 of these boards ASAP.  Before we do that, though, we need to figure out what we're going to do with the "disco comparator" stage back near the RF input.  (There are also a bunch of other improvements that will be incorporated into v2).

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

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

CDS:

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

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

PRC characterization in PRMI:

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

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

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

8292   Thu Mar 14 11:51:14 2013 JamieUpdateGeneralBeatbox upgraded with output whitening, reinstalled

 Quote: I pulled the beatbox from the 1X2 rack so that I could try to hack in some output whitening filters.  These are shamefully absent because of my mis-manufacturing of the power on the board. Right now we're just using the MON output.  The MON output buffer (U10) is the only chip in the output section that's stuffed: The power problem is that all the AD829s were drawn with their power lines reversed.  We fixed this by flipping the +15 and -15 power planes and not stuffing the differential output drivers (AD8672). It's possible to hack in some resistors/capacitors around U10 to get us some filtering there.  It's also possible to just stuff U9, which is where the whitening is supposed to be, then just jump it's output over to the MON output jack.  That might be the cleanest solution, with the least amount of hacking on the board.

I modified the beatbox according to this plan.  I stuffed the whitening filter stage (U9) as indicated in the schematic (I left out the C26 compensation cap which, according to the AD829 datasheet, is not actually needed for our application).  I also didn't have any 301 ohm resistors so I stuffed R18 with 332 ohm, which I think should be fine.

Instead of messing with the working monitor output that we have in place, I stuffed the J5 SMA connector and wired U9 output to it in a single-ended fashion (ie. I grounded the shield pins of J5 to the board since we're not driving it differentially).  I then connected J5 to the I/Q MON outputs on the front panel.  If there's a problem we can just rewire those back to the J4 MON outputs and recover exactly where we were last week.

It all checks out: 0 dB of gain at DC, 1 Hz zero, 10 Hz pole, with 20 dB of gain at high frequencies.

I installed it back in the rack, and reconnected X/Y ARM ALS beatnote inputs and the delay lines.  The I/Q outputs are now connected directly to the DAQ without going through any SR560s (so we recover four SR560s).

8350   Tue Mar 26 08:50:02 2013 SteveUpdateGeneraljanitor day

Keven, our janitor accidentally pushed the main entry door laser emergency stop switch.

The laser was turned back on. The MC and the arms were  started  flashing happily as they were before.

8420   Sun Apr 7 20:49:19 2013 ZachUpdateGeneralRestarted elog

with the script, as it was down.

8428   Tue Apr 9 01:46:40 2013 ZachUpdateGeneralRestarted elog

Again.

 Quote: with the script, as it was down.

8440   Thu Apr 11 03:23:12 2013 DenUpdateGeneralMCL threshold

MC down script is too slow to block MC_L when the cavity goes out of lock. As a result the loop strongly kicks MC2. We decided to make a threshold inside MCS model on MC TRANS that will block MC_L during lock loss. This is a lower threshold. Upper threshold can be slow and is implemented inside MC up script.

Fast threshold can be set inside MC2 POS. I did not correct MC2 top level medm screen as it is the same for all core optics.

Note: Fast trigger will also block ALS signal if MC loose lock.

8559   Thu May 9 15:07:51 2013 JenneUpdateGeneralDistances from CAD drawing

Since I keep asking Manasa to "measure" distances off of the CAD drawing for me, I thought I might just write them all down, and quit asking.

So, these are only valid until our next vent, but they're what we have right now.  All distances are in meters, angles in degrees.

8579   Wed May 15 15:33:49 2013 SteveUpdateGeneralOn-Track QPD

I tested On-Track (from LLO) OT 301  amp with PSM2-10 qpd. It was responding. Jenne will calibrate it.  The 12V DC ps input is unipolar.

The one AC to DC adapter that Jenne tried was broken.

8605   Tue May 21 16:23:06 2013 ManasaUpdateGeneral40MARS wireless network problem RETURNS

 Quote: Here's an example of the total horribleness of what's happening right now: controls@rossa:~ 0$ping 192.168.113.222 PING 192.168.113.222 (192.168.113.222) 56(84) bytes of data. From 192.168.113.215 icmp_seq=2 Destination Host Unreachable From 192.168.113.215 icmp_seq=3 Destination Host Unreachable From 192.168.113.215 icmp_seq=4 Destination Host Unreachable From 192.168.113.215 icmp_seq=5 Destination Host Unreachable From 192.168.113.215 icmp_seq=6 Destination Host Unreachable From 192.168.113.215 icmp_seq=7 Destination Host Unreachable From 192.168.113.215 icmp_seq=9 Destination Host Unreachable From 192.168.113.215 icmp_seq=10 Destination Host Unreachable From 192.168.113.215 icmp_seq=11 Destination Host Unreachable 64 bytes from 192.168.113.222: icmp_seq=12 ttl=64 time=10341 ms 64 bytes from 192.168.113.222: icmp_seq=13 ttl=64 time=10335 ms ^C --- 192.168.113.222 ping statistics --- 35 packets transmitted, 2 received, +9 errors, 94% packet loss, time 34021ms rtt min/avg/max/mdev = 10335.309/10338.322/10341.336/4.406 ms, pipe 11 controls@rossa:~ 0$  Note that 10 SECOND round trip time and 94% packet loss.  That's just beyond stupid.  I have no idea what's going on.

## This has not been fixed!

Temporary solution: I ssh'd to nodus from the 40m wifi network and was able to connect to the FE machines.This works but the bandwidth is limited this way as expected.

40m MARS network needs to be fixed.

8643   Fri May 24 14:44:34 2013 JenneUpdateGeneralRossa freezes all the time

I am getting tired of having to restart Rossa all the time.  She freezes almost once per day now.  Jamie has looked at it with me in the past, and we (a) don't know why exactly it's happening and (b) have determined that we can't un-freeze it by ssh-ing from another machine.

I wonder if it's because I start to have too many different windows open?  Even if that's the cause, that's stupid, and we shouldn't have to deal with it.

\end{vent}

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