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ID Date Author Type Category Subject
7865   Thu Dec 20 18:33:52 2012 JamieUpdateGeneralin-vac adapter cables for TTs

We need short cables that mirror the pins:

The male side will plug into the 25-pin female on the stack-top bracket.  The tip-tilt quadrapus cable will plug into the female side. This will match up pin 1 on the tip-tilt cable, which is connected to it's shield, to pin 13 on the bracket, which is the shield of the cable that runs to the stack.

They need to be vacuum compatible.  Shorter length is preferred, and there is no minimum length (something like an all-in-one gender changer would be ideal, but probably expensive to have made).




7868   Fri Dec 21 09:55:23 2012 SteveUpdateGeneralin-vac adapter cables for TTs

Accu-Glass is closed till Jan 2, 2013

Atm2 would be the ideal solution Gender Adaptor Special with male - female sides and vented D-sub. How many are we getting 2 or 6 ?

Attachment 1: extensioncable.pdf
Attachment 2: genderchanger.pdf
7885   Wed Jan 9 13:34:34 2013 KojiSummaryGeneralThe projector lamp ended its life?

[Koji, Manasa]

- A new projector lamp installed.

- The old lamp lasted 8751 "equivalent lamp hours".

- The old lamp was found being shattered inside. It contains mercury.
So next time you hear the explosion sound of the lamp, establish the ventilation of the room and escape for an hour.

7891   Fri Jan 11 11:07:04 2013 ManasaUpdateGeneralIFO status update - PMC problems

I came in this morning to see that the PMC was down. The PZT voltage had drifted to below 50V. I adjusted the FSS slow controls to 0V and PZT was back at 126V.

PMC and IMC could eventually be locked.

History of PZT voltage behaviour in dataviewer over the last 24 hours shows it has been drifting everytime after it has been fixed.

7892   Fri Jan 11 16:13:47 2013 JenneUpdateGeneralIFO status update - PMC fixed

 Quote: I came in this morning to see that the PMC was down. The PZT voltage had drifted to below 50V. I adjusted the FSS slow controls to 0V and PZT was back at 126V. PMC and IMC could eventually be locked. History of PZT voltage behaviour in dataviewer over the last 24 hours shows it has been drifting everytime after it has been fixed.

FSS was saturating.  Fixed.

7930   Wed Jan 23 18:16:11 2013 ManasaUpdateGeneralLaseroptik mirror - SN6

I repeated the transmittance measurements of LaserOptik SN6 @1064nm.

Transmittance for s-polarization

0 deg - 0.524
45 deg - 0.055

Transmittance for p-polarization

0 deg - 0.515
45 deg - 0.1047 0.01047

Raji's measurements are here.

Attachment 1: sn6_trans.png
7932   Wed Jan 23 20:24:05 2013 KojiUpdateGeneralLaseroptik mirror - SN6

Got confused (even after I talked with Manasa).

The plot shows the number ~0.01 or less at 45deg. But the number is the text does not match with the plot.

Please use the logarithmic scale for the vertical axis.
And more points between 35 to 50 deg please (like ~1deg spacing)

Don't we have the data sheet from the coater? Can we request it?

7935   Wed Jan 23 22:02:25 2013 ManasaUpdateGeneralLaseroptik mirror - SN6

 Quote: Got confused (even after I talked with Manasa). The plot shows the number ~0.01 or less at 45deg. But the number is the text does not match with the plot. Please use the logarithmic scale for the vertical axis. And more points between 35 to 50 deg please (like ~1deg spacing) Don't we have the data sheet from the coater? Can we request it?

I corrected the typo in the text...however, I agree the plot was lame...Will get the data sheet made tomorrow!

7940   Thu Jan 24 15:16:50 2013 ManasaUpdateGeneralLaseroptik mirror - SN6

I repeated the transmittance measurements of Laseroptik SN6 at 1064nm. The rotation stage could only resolve 2 deg rotation (We should consider buying a better rotation stage).

s-polarization

Percentage transmittance

0.177% 42 deg
0.806% 44 deg
0.57%   46 deg
54.8%    0 deg

p-polarization

Percentage transmittance

1.039% 42deg
1.155% 44 deg
1.159% 46 deg
65.6%   0 deg

7941   Thu Jan 24 16:23:24 2013 KojiUpdateGeneralLaseroptik mirror - SN6

The mirror T is completely out of spec. We should find or request the data sheet of the mirror.

> We should consider buying a better rotation stage

7943   Thu Jan 24 16:34:56 2013 ranaUpdateGeneralLaseroptik mirror - SN6

I have two questions:

1) Are we sure that the T measurement is not being compromised by some systematic? i.e. some leakage is making the apparent T appear too high.

2) IF the T is really so high, how should we decide whether or not to use this one rather than the G&H? Is the 532 nm property more important than the high recycling gain?

7944   Fri Jan 25 08:10:42 2013 SteveUpdateGeneralLaseroptik mirrors

Here are the German plots. Unfortunately they are not logarithmic.

Ed: Proprietary data removed. Use wiki (Koji)

Steve uploaded data to the 40m wiki  / Aux_Optics on 02-07-2013

7947   Mon Jan 28 19:07:45 2013 ManasaUpdateGeneralSN6 Laseroptik mirror - Tranmittance measurements

I repeated the measurements using NPRO instead of Crystalaser. I am attaching optical layouts for these measurements for future reference.

Lesson learnt : Do not use Crystalaser for transmission measurements and always separate the transmitted main beam from other beams that result from the wedged surface of the mirror.

Measurements match specs provided by Laseroptik

p-polarization

T percentage = 0.10% 42 deg
0.092% 44 deg
0.086% 46 deg
Minimum transmittance = 0.081% 52deg

s-polarization

T percentage = 0.048% 42 deg
0.047% 44 deg
0.047% 46 deg
Minimum transmittance = 0.047% 46 deg

7950   Mon Jan 28 21:36:44 2013 tall guyFrogsGeneralsmall people on notice

If I catch anyone putting small booties into the large bootie bin, I will make said person eat small booties.

7952   Tue Jan 29 10:59:37 2013 lazy personFrogsGeneralbetter plan

I propose we work around this problem with giant flip-flops.  These are in the vein of the take-off-your-shoes-and-put-on-Crocs, without the taking off your shoes part.  They're a little annoying on the sticky mats, but otherwise great.  They are also super easy to put on and take off without hands, so there's no excuse for wearing them around the control room.

I propose we buy many pairs of the smalls in green (since we already have one green small...they are big on me, so should be just right for most people), and a few mediums in, say, blue, and a few larges in black, and then maybe a few extra larges in green for people with extraordinarily large feet (they only have 3 colors).  Then we can keep a few pairs of each by each door to the lab, and have no more tracking dirty control room filth into the lab.

7953   Tue Jan 29 14:20:02 2013 KojiUpdateGeneralFiner rotation stage for optics characterization

A rotation stage has been ordered.

 Newport Rotation Stage, 360° Coarse, 5° Fine Rotation, Micrometer Newport 481-A Newport Solid Insert for RSP-1T Rotation Stage Newport RSA-1TI Newport Universal Mounting Plate, 2.56 in. x 2.56 in. x 0.5 in., 1/4-20 Thread Newport UP-1A

Specification: Newport 481-A

• Sensitivity: 15 arcsec
• Vernier: 5 arcmin
• Fine travel range: 5 deg
• With Micrometer
7955   Tue Jan 29 15:16:18 2013 ManasaFrogsGeneraltrial run

I would like to suggest a trial run on these....Ergomates and the cleanboot!

REPLY by JCD:  Are these going to trap dirt and be impossible to clean though?  The nice thing about Crocs and the giant flip flops is that they are solid and if they get dirty you can do a quick wipedown, and they're good as new.

7958   Tue Jan 29 20:28:11 2013 ericqUpdateGeneralEarly work on Mirror Mounts

[Q, Chloe]

Chloe has been to the lab twice to start up her investigations in acoustic noise coupling to mirrors. The general idea for the setup is a HeNe laser bouncing off a mirror and onto a QPD, whose signal provides a measure of beam displacement noise. The mirror will be mounted and excited in various ways to make quantitative conclusions about the quality of different mounting schemes.

We have set up the laser+mirror+QPD on the SP table, and collected data via SR560s->SR785, with the main aim of evaluating the suitability of this setup. The data we collected is not calibrated to any meaningful units (yet). For now, we are just using QPD volts.

Chloe collected data of vertical displacement noise for the following schemes: Terminated SR785 input, Terminated SR560 inputs, Laser centered directly onto the QPD, Laser shining on mirror centered on QPD, laser/mirror/qpd with some small desktop speakers producing white noise from http://www.simplynoise.com. Data shown below.

7960   Wed Jan 30 03:01:55 2013 KojiUpdateGeneralEarly work on Mirror Mounts

I can't believe that SR785 can have such a low input noise level (<1nV/rtHz). Review your calibration again.

It is also described in the manual that SR560 typically has the input noise level of 4nV/rtHz, although this number depends on which gain you use.

7967   Wed Jan 30 16:24:25 2013 ManasaFrogsGeneraltrial run

 Quote: REPLY by JCD:  Are these going to trap dirt and be impossible to clean though?  The nice thing about Crocs and the giant flip flops is that they are solid and if they get dirty you can do a quick wipedown, and they're good as new.

The Cleanboot is washable and reusable!

7989   Sun Feb 3 13:20:02 2013 KojiSummaryGeneralHypothesis

Rana mentioned the possibility that the PR2 curvature makes the impact on the mode stability. Entry 7988
Here is the extended discussion.

Hypothesis:

The small but non-negligible curvatures of the TT mirrors made the recycling cavity unstable or nearly unstable.

Conclusion:

If the RoC of the TT mirrors are -600 m (convex), the cavity would be barely stable.
If the RoC of the TT mirrors are less than -550m, the horizontal modes start to be unstable.
Assumption that all of the TT mirrors are concave should be confirmed.

Fact (I): Cavity stability

- The folded PRMI showed the mode stability issue. (L=6.78m from Jenne's entry 7973)
- The folded PRM-PR2-PR3-flat mirror cavity also showed the similar mode issue. (L=4.34m)
- The unfolded PRM-PR2 cavity demonstrated stable cavity modes. (L=1.91m)

Fact (II): Incident angle

- PRM 0deg
- PR2 1.5deg
- PR3 41deg

Fact (III): Mirror curvature

- RoC of PRM (PRMU02): +122.1m (measured, concave), or +115.6m (measured by the vendor)
- RoC of G&H mirrors: -600m ~ -700m (measured, I suppose the negative number means convex) (Jenne's entry 7851)
[Note that there is no measurement of the phase map for the PR2 mirror itself.]
- RoC of LaserOptik mirrors: -625m ~ -750m (measured, I suppose that the measurement shows the mirrors are convex.) (Jan's entry 7627 and 7638)

Let's assume that the TT mirrors are always convex and have a single number for the curvature radius, say RTT

Cavity mode calculation with Zach's arbcav

1) The unfolded PRM-PR2 cavity:

The cavity becomes unstable when 0 > RTT > -122m  (This is obvious from the g-factor calculation)
==> The measured RoC of the TT mirrors predicts the cavity is stable. (g=0.98, Transverse Mode Spacing 3.54MHz)

2) The folded PRM-PR2-PR3-flat mirror cavity:

The cavity becomes unstable when RTT < -550 m
==> The measured RoC of the TT mirrors (RTT ~ -600m) predicts the cavity is barely stable (g=0.997, TMS ~600kHz).

- The instability occurs much faster than the unfolded case.
- The horizontal mode hits unstable condition faster than the vertical mode.
- The astigmatism mainly comes from PR3.

3) The folded PRMI:

The cavity becomes unstable when RTT < -550 m
==> The measured RoC of the TT mirrors (RTT ~ -600m) predicts the cavity is barely stable. (g=0.995, TMS ~500kHz)

- The instability occurs with almost same condition as the case 2)

The calculation result for the PRMI with RTT of -600 m. The code was also attached.

Q&A:

Q. What is the difference between unfolded and folded?
A. For the unfolded case, the PR2 reflect the beam only once in a round-trip.
For the folded case, each TT mirror reflects the beam twice. Therefore the lens power by the mirror is doubled.

Q. Why the astigmatism mainly comes from PR3?
A. As the angle of incidence is much bigger than the others (41deg).

Q. Why the horizontal mode is more unstable than the vertical mode?
A. Off-axis reflection of a spherical mirror induces astigmatism. The effective curvature of the mirror in
the horizontal direction
is R / Cos(theta) (i.e. longer), while it is R Cos(theta) (i.e. shorter). Indeed, the vertical and horizontal ROCs are factor of 2 different
for the 45deg incidence.

Q. Why the stability criteria for the case 2) and 3) similar?
A. Probably, once the effective curvature of the PRM-PR2-PR3 becomes
negative when RTT < -550 m.

Q. You said the case 2 and 3 are barely stable. If the TMS is enough distant form the carrier, do we expect no problem?
A. Not really. As the cavity get close to the instability, the mode starts to be inflated and get highly astigmatic.
For the case 2), the waist radii are 5.0mm and 3.7mm for the horzontal and vertical, respectively.
For the case 3), they are 5.6mm and 4.1mm for the horzontal and vertical, respectively.
(Note: Nominally the waist radius is 3.1mm)

Q. What do you predict for the stability of the PRM-PR2-Flat_Mirror cavity?
A. It will be stable. The cavity is stable until
RTT becomes smaller than -240 m.

Q. If the TT mirrors are concave, will the cavity stable?
A. Yes. Particularly if PR3 is concave.

Q. Rana mentioned the possibility that the mirrors are deformed by too tight mounting of the mirror in a ring.
Does it impact the stability of the cavity?

A. Possible. If the curvature is marginal and the mounting emphasizes the curvature, it may meet the unstable condition.

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.

Attachment 1: mode_density_PRC.pdf
Attachment 2: mode_density_PRC.zip
7990   Mon Feb 4 10:45:51 2013 JamieSummaryGeneralrough analysis of aligned PRM-PR2 mode scan

Here's a sort of rough analysis of the aligned PRM-PR2 cavity mode scan.

On Friday we took some mode scan measurements of the PRM-PR2 cavity by pushing PRM (C1:SUS-PRM_LSC_EXT) with a 0.01 Hz, 300 count sine wave.  We looked at the transmitted power on the POP DC PD and the error signal on REFL11_I.

Below is a detail of the scan, chosen because the actuation was in its linear region and there were three relatively ok looking transmission peaks with nice PDH response curves:

The vertical green lines on the bottom plot indicate the rough averaged separation of the 11 MHz side-band resonances from the carrier, at +- 0.0275 s.  If we take this for our calibration, we get roughly 400 MHz / second.

The three peaks in top plot have an average FWHM of 0.00381 s.  Given the calibration above, the average FWHM = ~1.52 MHz.

If we assume a cavity length of 1.91 m, FSR = 78.5 MHz.

Putting this together we get a finesse = ~51.6.

Analysis of misaligned mode scans to follow.

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.

ELOG V3.1.3-