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ID Date Author Type Category Subject
7975   Thu Jan 31 15:20:46 2013 ZachUpdateLockingMode spacing calc

I should mention that I just found a bug in how it treats odd-mirror-number cavities. For such cavities, HG modes with odd horizontal indices should receive an extra roundtrip phase of pi/2 (due to the rotation by the cavity). Because of a numbering convention issue, arbcav actually used to apply this phase shift to even-order modes. Essentially, the only difference is that the fundamental mode was shifted to anti-resonance. Everywhere else, there are modes at both corresponding locations in frequency space, and so it does not back a big difference in terms of cavity design.

Thanks to this IMC modeling we are doing at the workshop, I caught it! It has been fixed in the SVN.

 Quote: I have calculated (using Zach's sweet software) the expected mode content for the various possible PRCs that we can make.  Also, Zach was right about the factor of 2.  I see now that I was calculating the mode spacing between a plane wave and a HOM, so the guoy phase had a factor of (n+m+1).  The right thing to do is to get the spacing between the 00 mode and HOMs, so the guoy phase just has (n+m).  Switching from n+m+1=2 to n+m=1, that fixes the factor of 2 problem.  I attach my results as a pdf, since I'm listing out 5 configurations.  Each config has a cartoon, with a small (hard to read) HOM plot, and then at the end, each HOM plot is shown again, but larger.  Also, "TM" is the "test mirror", the flat G&H that we're using as the cavity end mirror.

7976   Thu Jan 31 15:34:22 2013 RijuUpdateRF SystemPhotodiode transimpedance

Quote:

 Quote: Today I collected the data for shot noise intercept current for MC REFL PD. I didn't get many data points at higher DC voltage of the photodiode, cause the incandescent bulbs get burnt at that level; two bulbs I have burnt today. I will process the data and report.

This work was done in-situ, so no optics on the AS table were moved.  The PSL shutter was blocked since the IR beam was not necessary, and would scatter off the bulb Riju put in front of the PD.

Thanks Jenne.

7977   Thu Jan 31 15:56:38 2013 RijuUpdate Photodiode transimpedance

Summary: Measurement and plot of shot-noise-intercept-current for PDA10CF.

Motivation:It is to measure the shot noise intercept current for PDA10CF.

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.21mA

Discussion:

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946

In the present case dark-noise is 4.3e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 8.6pA/sqrt(Hz)

Therefore the approximate shot noise intercept current ~ (8.6/18)^2=0.22mA

This value matches well with the fitted data.

From PDA10CF manual, NEP=1.2e-11W/sqrt(Hz) and responsivity~0.9A/W. Therefore the noise current level will be ~10pA.

Attachment 1: shotnoiseinterceptpda10cf.pdf
7978   Thu Jan 31 20:06:22 2013 EvanUpdateLockingPRM/PR2 cavity

[Jenne, Evan]

Tonight we made a non-folded cavity between the PRM and PR2 as follows. I put down two dog clamps to constrain the original position of the PR2 mount. I then loosened the dog clamps holding the mount to the table and nudged the mount until we saw a few reasonably well-aligned bounces in the cavity. I then dogged down the mount.

We played with the PRM and TT2 steering until we saw flashes of TEM00. However, the resonance is not clean so we couldn't lock.

Since we changed the PRM alignment, we had to redo the last bit of steering for the PRM oplev into the photodiode. We also put a few ND filters on the POP camera.

7980   Thu Jan 31 23:48:45 2013 KojiUpdateLockingPRM/PR2 cavity

Wow! What's happened?

As the video showed good quality of resonances, I stopped by at the 40m on the way back home.

I looked at the error signals and found that they indicate high finesse and clear resonance of the sidebands.
The lock was immediate once the gain is set to be -0.004 (previous 0.05ish). This implies the optical gain is ~10 times larger than the previous configration.
The alignment was not easy as POPDC was saturated at ~27000I leave this as a daytime job.

As I misaligned the PRM, I could see that the lock hopped into the next higher order. i.e .from TEM00 to TEM01, from TEM01 to TEM02, etc
This means that the modes are closely located each other, but sufficiently separated to sustain each mode.

I definitely certify that cavity scans will give us meaningful information about the cavity.

7981   Fri Feb 1 09:33:11 2013 JamieUpdateLockingPRM/PR2 cavity

I replaced the BS1 between the POPDC PD and the camera with a 98 reflector, and moved the 50 up before the BS to dump half the light.  Still saturating POPDC, but hopefully the ratio between POPDC and the camera should be better.  We just need to dump more of the power before we get there.  I'll come back to this after C&D if no one else has already gotten to it.

I don't know why I didn't pay more attention last night, but things look way WAY better.  The beams are much cleaner and the power level is much much higher.

7983   Fri Feb 1 12:34:55 2013 JenneUpdatePSLToo much power injected into vacuum

I noticed (while relocking the MC after Jamie and I zeroed the LSC offsets) that the MC refl power was 4.8 V.  Usually we should be ~4.2, so I closed the PSL shutter and went in to measure the power.  We were injecting ~125mW or a little more.  I had adjusted the power the other day, and through yesterday, it looked fine, but overnight it looks like it drifted up.

7984   Fri Feb 1 14:47:17 2013 RijuUpdate Photodiode transimpedance

Summary: Measurement and plot of shot-noise-intercept-current for MC REFL PD.

Motivation:It is to measure the shot noise intercept current for MC REFL PD.

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 0.041mA

Discussion:

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region as described in manual of PDA255 (i.e. 5e3 when it is not in High-impedance region).

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946

In the present case minimum noise value is 2.03e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance = 4.06pA/sqrt(Hz)

Therefore the approximate shot noise intercept current value is (4/18)^2 ~ 0.049mA, which is close to the fitted value.

... hard to believe these numbers. Wrong DC transimpedance? (KA)

Attachment 1: shotnoiseinterceptmcreflpd.pdf
7985   Fri Feb 1 15:12:53 2013 JenneUpdateLockingPRM/PR2 cavity

After Jamie did all the work this morning on the POP table, I was able to get the cavity to lock.  It's not very stable until I engage the boost filters in the PRCL loop.  After locking, I tuned up the alignment a bit more.  Now we're taking mode scan data.  Look for results hopefully shortly after Journal Club!

7986   Fri Feb 1 19:55:33 2013 JenneUpdateLockingPRM/PR2 cavity

[Jamie, Koji, Jenne]

We are looking at the mode scan data, and have some preliminary results!  We have data from when the cavity was aligned, when it was slightly misaligned in pitch, and slightly misaligned in yaw.

Inverting the equation for transverse mode spacing, we infer (for pitch misalignment) a cavity g-factor of 0.99, and from there (assuming the G&H mirror is flat and so has a g-factor of 1), we infer a PRM radius of curvature of 168 meters which is ~50% longer than we expected.

More results to come over the weekend from Jamie.

7987   Fri Feb 1 23:12:42 2013 KojiUpdateLockingPRM/PR2 cavity

During the scanning we were riddled by the fact the PDH error and the transmission peaks do not happen simultaneously.

After a little investigation, it was found that "LP100^2" filter is left on in the POPDC filter.

Moreover, it was also found that the whitening filter switches for the POPDC does not switch the analog counterpart.

These were the culprit why we never saw accidental hitting of the max transmission by the peaks when the cavity was not locked.

I know that the most of the whitening filter in the RF paths were checked before (by Keiko?), but the similar failure still exists in the POX path.
We should check for the whitening filters in the DC path as well and fix everything at once. I can offer assistance on the fixing part.

7988   Fri Feb 1 23:52:59 2013 ranaUpdateLockingPRM/PR2 cavity

Very exciting result, if true. I suppose we should try to reconfirm this result by doing another phase map of PRM03.

Is it possible that PR2 is not flat? How would we test to see if the tip-tilt frame screw gives it a curvature? Perhaps we can check with COMSOL.

7993   Mon Feb 4 15:26:10 2013 JamieUpdateComputer Scripts / ProgramsNew "getdata" program to pull NDS channel data, including test points

I've added a new program called getdata (to scripts/general/getdata) that will conveniently pull arbitrary data from an NDS server, either DQ or online (ie. testpoints).

Start times and durations may be specified.  If past data is requested, you must of course be requesting DQ channels.  If no start time is specified, data will be pulled "online", in which case you can specify testpoints.

If an output directory is specified, the retrieved data will be stored in that directory in files named after the channels.  If an output directory is not specified, no output will be

Help usage:

controls@pianosa:~ 0$/opt/rtcds/caltech/c1/scripts/general/getdata --help usage: getdata [-h] [-s START] [-d DURATION] [-o OUTDIR] channel [channel ...] Pull online or DQ data from an NDS server. Use NDSSERVER environment variable to specify host:port. positional arguments: channel Acquisition channel. Multiple channels may be specified acquired at once. optional arguments: -h, --help show this help message and exit -s START, --start START GPS start time. If omitted, online data will be fetched. When specified must also specify duration. -d DURATION, --duration DURATION Length of data to acquire. -o OUTDIR, --outdir OUTDIR Output directory. Data from each channel stored as '.txt'. Any existing data files will be automatically overwritten. controls@pianosa:~ 0$


7999   Tue Feb 5 09:08:11 2013 SteveUpdatePEM exterier doors to be painted

 Quote: The wood exteier walls, gutters and doors were painted at CES-Annex building #69

The east and south end of the 40m emergency exit doors are sealed- tapped off temporarily.  They will be painted on the out side only.  This job will be done by tomorrow noon

Do not open chamber if you smell the paint !

Attachment 1: IMG_0055.JPG
8001   Tue Feb 5 10:18:54 2013 SteveUpdatePEMhigh particle count ALART

Quote:

 Quote: The BS camber is open only. We should close ASAP Outside air quality is 1.7- 2.2  million particles  / cf min of 0.5 micron

Air is still bad and the chambers are closed. Before lunch  Jamie repointed the PRM oplev. Manasa and I reset oplevs: BS and ITMX.

ETMX and ETMY are fine.

SRM and ITMY oplevs needs more work.

The bad outside air quality is pushing up the inside counts.

The outside air is 5 million counts / cf min for 0.3 micron and 2 million counts / cf min for 0.5 micron particles

Do not open chamber over 10,000 counts / cf min of 0.5 micron

Attachment 2: 100d_airq.png
8003   Tue Feb 5 12:08:43 2013 Max HortonUpdateSummary PagesUpdating summary pages

Getting started:  Worked on understanding the functionality of summary_page.py.  The problem with the code is that it was written in one 8000 line python script, with sparse documentation.  This makes it difficult to understand and tedious to edit, because it's hard to tell what the precise order of execution is without tracing through the code line by line.  In other words, it's difficult to get an overview of what the code generally does, without literally reading all of it.  I commented several functions / added docstrings to improve clarity and start fixing this problem.

Crontab:  I believe I may have discovered the cause of the 6PM stop on data processing.  I am told that the script that runs the summary_pages.py is called every 6 hours.  I believe that at midnight, the script is processing the next day's data (which is essentially empty) and thus not updating the data from 6PM to midnight for any of the days.

Git:  Finally, created git repository called public_html/__max_40m-summary_testing to use for testing the functionality of my changes to the code (without risking crashing the summary_pages).

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
8007   Wed Feb 6 11:59:12 2013 JenneUpdateLockingPRC cavity gains

EDIT:  These numbers are for a perfect, non-lossy arm cavity.  So, a half real, half imaginary world.

Carrier uses arm cavity reflectivity for perfectly resonant case.

PRC carrier gain, flipped PR2, PR3 = 61

PRC carrier gain, regular PR2, PR3 = 68  (same value, within errors, for no folding at all).

Carrier gain loss = (68-61)/68 = 10%

SB uses arm cavity reflectivity for perfectly anti-resonant case.

PRC SB gain, flipped PR2, PR3 = 21

PRC SB gain, regular PR2, PR3 = 22 (same value, within errors, for no folding at all). <--- yes, this this "regular PR2, PR3 = 22..."

SB % gain loss = (22-21)/22 = 4.5%

I claim that we will be fine, recycling gain-wise, if we flip the folding mirrors.  If we do as Yuta suggests and flip only one folding mirror, we'll fall somewhere in the middle.

8008   Wed Feb 6 14:51:25 2013 JenneUpdateElectronics1 power supply replaced!

 Quote: Currently, DC power for amplifiers ZHL-1000LN+ is supplied by Aligent E3620A. I tried to use power supply from the side of 1X1 rack, but fuse plug(Phoenix Contact ST-SI-UK-4) showed red LED, so I couldn't use it.

Yuta, Jenne

We fixed things so that we are now using regular fused rack power for these amplifiers.  The fuse no longer had a red LED, but it measured open when we checked the resistance.  Although, somehow (magic?) 13.73V were getting to the other side of the fuse.

Anyhow, replacing the fuse with a new one fixed the problem right up.

8009   Wed Feb 6 15:05:18 2013 SteveUpdateSAFETYcameras must be anchord

Cameras must be immediately anchord to avoid a possible collusion with the view port !

Attachment 1: IMG_0070_1.JPG
Attachment 2: IMG_0069_1.JPG
8010   Wed Feb 6 15:10:22 2013 SteveUpdatePEMnew safety signs on exterier doors

Quote:

 Quote: The wood exteier walls, gutters and doors were painted at CES-Annex building #69

The east and south end of the 40m emergency exit doors are sealed- tapped off temporarily.  They will be painted on the out side only.  This job will be done by tomorrow noon

Do not open chamber if you smell the paint !

The east and south end of the 40m emergency exit doors received new safety signs.

Attachment 1: IMG_0068.JPG
8011   Wed Feb 6 15:11:21 2013 JenneUpdateElectronics"Temporary" power supply situation

[Jenne, Yuta, Rana, Steve, Manasa]

We have taken stock of the lab "temporary" power supply situation, and things look much better.

This morning, I removed 2 unused power supplies and a function generator from the PSL table - these had been used for MC ringdown things.

I also removed the non-connected cables that had been used for the RAMMON setup, and the EOM temperature controller circuit.

This afternoon, Yuta removed the 2 HV power supplies that were used to keep PZT2 working near the end of its life.  Since we now have the active TTs, these have been turned off for a while, and just needed to be removed.

Manasa removed the power supply under the POP/POX table that was powering the amplifier for POP22.  If we are going to continue using a Thorlabs PD for POP22, then we need to make a twisted pair of wires (~20 feet) to get power from 1X1.  If we are going to (finally) install a gold RF PD, then that will not be necessary.

I removed the power supply sitting near the bottom of the LSC rack, for another amplifier for POP22 (with minicircuits filters attached).  Again, if we get a gold RF PD, we can remove the filters and amplifier.  If not, we can use the existing twisted pair of wires, and plug them into the rack rather than a power supply.

The power supply under the NE corner of the PSL table was no longer in use.  It was most recently used for amplifiers for the green beat PDs, as Yuta mentioned in elog 6862, those were moved over to 1X2.  In elog 8008 I mentioned that Yuta and I moved those amplifiers over to rack power.

The HV supply, the function generator and the OSA controllers that were on top of the short OMC rack next to the AS table have all been removed.  We need to come up with a better place for the OSAs, since we need to re-install them.  The power supply and the function generator (which was used just for a voltage offset) were formerly used for the output steering PZTs, but lately we have just been using those mirrors as fixed mirrors, since we don't need to steer into the OMC.  Some day, we will replace those mirrors with the output steering active tip tilts, and re-commission the OMC....someday.

The power supply for the amplifier set (that goes with the set of minicircuits filters) for the RAMMON PD (which took light from the IPPOS path) has been removed.  If we determine that we need RAMMON back, we will have to make a twisted pair to power those amplifiers.

SUMMARY:

* If we don't install a gold RF PD for POP22, we need a 20ft twisted pair for +15/GND.

* Also, if we don't install a gold RF PD for POP22, we need to plug the amplifier at the LSC rack into the rack power (twisted pair already exists).

* If we need RAMMON back, we will need a twisted pair to power those amplifiers.

* All other power supplies have been removed, and put away.  We currently have 0 "temporary" power supplies in use in the lab!

8013   Wed Feb 6 15:39:19 2013 SteveUpdateElectronicsDC power supplies in cabinets

East arm cabinet E9 and E10

Attachment 1: IMG_0066_1.JPG
8014   Wed Feb 6 18:39:08 2013 JenneUpdateLockingPRC cavity gains

[Yuta, Jenne]

We have both calculated, and agree on the numbers for, the PRC gain for carrier and sideband.

We are using the measured arm cavity (power) loss of 150ppm....see elog 5359.

We get a PRC gain for the CARRIER (non-flipped folding) of 21, and PRC gain (flipped folding) of 20This is a 4.7% loss of carrier buildup.

We get a PRC gain for the SIDEBANDS (non-flipped folding) of 69, and PRC gain (flipped folding) of 62This is an 8.8% loss of sideband buildup.

The only difference between the "flipped" and "non-flipped" cases are the L_PR# values - for "non-flipped", I assume no loss of PR2 or PR3, but for the "flipped" case, I assume 1500ppm, as in Rana's email.  Also, all of these cases assume perfect mode matching.  We should see what the effect of poor mode matching is, once Jamie finishes up his calculation.

Why, one might ask, are we getting cavity buildup of ~20, when Kiwamu always quoted ~40?  Good question!  The answer seems, as far as Yuta and I can tell, to be that Kiwamu was always using the reflectivity of the ITM, not the reflectivity of the arm cavity.  The other alternative that makes the math work out is that he's assuming a loss of 25ppm, which we have never measured our arms to be so good.

For those interested in making sure we haven't done anything dumb:

ppm = 1e-6; % ||      |      |        ||            || % PRM    PR2    PR3      ITM           ETM T_PRM = 0.05637; t_PRM = sqrt(T_PRM); L_PRM = 0 *ppm; R_PRM = 1 - T_PRM - L_PRM; r_PRM = sqrt(R_PRM); T_PR2 = 20 *ppm; t_PR2 = sqrt(T_PR2); L_PR2 = 1500 *ppm; R_PR2 = 1 - T_PR2 - L_PR2; r_PR2 = sqrt(R_PR2); T_PR3 = 47 *ppm; t_PR3 = sqrt(T_PR3); L_PR3 = 1500 *ppm; R_PR3 = 1 - T_PR3 - L_PR3; r_PR3 = sqrt(R_PR3); T_ITM = 0.01384; t_ITM = sqrt(T_ITM); L_ITM = 0;%100 *ppm; R_ITM = 1 - T_ITM - L_ITM; r_ITM = sqrt(R_ITM); T_ETM = 15 *ppm; t_ETM = sqrt(T_ETM); L_ETM = 0 *ppm; R_ETM = 1 - T_ETM - L_ETM; r_ETM = sqrt(R_ETM); rtl = 150*ppm;  % measured POWER round trip loss of arm cavities. rtl = rtl/2;     %    because we need the sqrt of the exp() for ampl loss....see Siegman pg414. eIkx_r = exp(-1i*2*pi); r_cav_res = -r_ITM + (t_ITM^2 * r_ETM * eIkx_r * exp(-rtl)) / (1 - r_ITM*r_ETM * eIkx_r * exp(-rtl) ); eIkx_ar = exp(-1i*pi); r_cav_antires = -r_ITM + (t_ITM^2 * r_ETM * eIkx_ar * exp(-rtl)) / (1 - r_ITM*r_ETM * eIkx_ar * exp(-rtl) ); %% PRC buildup gain g_antires = t_PRM*eIkx_ar / (1-r_PRM*r_PR2*r_PR3*r_cav_antires*eIkx_ar); G_ar = g_antires^2; G_ar = abs(G_ar)  % Just to get rid of the imag part that matlab is keeping around. g_res = t_PRM*eIkx_r / (1-r_PRM*r_PR2*r_PR3*r_cav_res*eIkx_r); G_r = g_res^2; G_r = abs(G_r) 

8015   Wed Feb 6 19:59:35 2013 ranaUpdateLockingPRC cavity gains

Getting closer, but need to use the real measured AR reflectivity values, not the 1500 ppm guess. These should be measured at the correct angles and pol, using an NPRO.

8016   Wed Feb 6 20:00:06 2013 ManasaUpdateElectronicsBNC cables piled up at every corner

[Yuta, Steve, Manasa]

There are cables piled up around the access connector area which have been victims of stampedes all the time. I have heard these cables were somehow Den's responsibility.

Now that he is not around here:

I found piled up bnc's open at one end and with no labels lying on the floor near the access connector and PSL area. Yuta, Steve and I tried to trace them and found them connected to data channels. We could not totally get rid of the pile even after almost an hour of struggle, but we tied them together and put them away on the other side of the arm where we rarely walk.

There are more piles around the access connector...we should have a next cleanup session and get rid of these orphaned cables or atleast move them to where they will not be walked on.

8017   Wed Feb 6 20:03:50 2013 ManasaUpdateLockingPRC cavity gains

 Quote: Getting closer, but need to use the real measured AR reflectivity values, not the 1500 ppm guess. These should be measured at the correct angles and pol, using an NPRO.

I'm still on that!

8018   Wed Feb 6 20:19:52 2013 ManasaUpdateOpticsG&H and LaserOptik mirrors

[Koji, Manasa]

We measured the wedge angle of the G&H and LaserOptik mirrors at the OMC lab using an autocollimator and rotation stage.

The wedge angles:

G&H : 18 arc seconds (rough measurement)

LaserOptik : 1.887 deg

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.

8023   Thu Feb 7 14:10:25 2013 ManasaUpdateOpticsLaserOptik - AR Reflectivity - Bad data

Reflectivity of AR surface of LaserOptik (SN6)

The first step measurements of R for AR surface. I am not convinced with the data....because the power meter is a lame detector for this measurement.

I'm repeating the measurements again with PDs. But below is the log R plot for AR surface.

R percentage

6000ppm @ 42 deg
3560ppm @ 44 deg
7880ppm @ 46 deg
4690ppm @ 48 deg

8024   Thu Feb 7 15:46:42 2013 JenneUpdateLockingPR2 flipped

More correctly, a different G&H mirror (which we have a phase map for) was put into the PR2 TT, backwards.

Order of operations:

* Retrieve flat test G&H from BS chamber.  Put 4th dog clamp back on BS optic's base.

* Remove flat G&H from the DLC mount, put the original BS that was in that mount back.  Notes:  That BS had been stored in the G&H's clean optic box.  The DLC mount is engraved with the info for that BS, so it makes sense to put it back.  The DLC mount with BS is now back in a clean storage box.

* Remove PR2 TT from ITMX chamber.

* Remove suspension mounting block from TT frame, lay out flat, magnets up, on lint-free cloth on top of foil.

* Remove former PR2 G&H optic.

* Put what was the flat G&H test optic into the PR2 optic holder, with AR surface at the front.

* Put PR2 suspension block back onto TT frame.

* Put PR2 assembly back in the chamber, solidly against the placement reference blocks that Evan put in last Thursday.

* Close up, clean up, put labels on all the boxes so we know what optic is where.

Why the switcho-changeo?  We have a phase map for the G&H that is the new PR2, and a measured RoC of -706m, surface rms of 8.7nm.  Now, we can measure the former PR2 and see how it compares to our estimate of the RoC from the cavity measurements we've taken recently.

8026   Thu Feb 7 17:24:13 2013 SteveUpdateSAFETYfire extinguishers checked

The fire department weighted and pressure checked our units today. Surprisingly they found one powder filled can. We can only use HALON  gas in the lab.

8027   Thu Feb 7 19:24:57 2013 RijuUpdate Photodiode transimpedance

Summary: Measurement and plot of shot-noise-intercept-current for MC REFL PD.

Motivation:It is to measure the shot noise intercept current for MC REFL PD.

Result: The final plot is attached here. The plot suggests that the value of shot-noise-intercept current is 1.9mA

Discussion:

The plot is for the measured data of Noise voltage (V/sqrt(Hz)) vs DCcurrent(A). The fitted plot to this measured data follows the noise equation

Vnoise = gdet* sqrt[ 2e (iDC+idet)] ,  where gdet= transimpedance of the PD in RF region ~600

To get an approximate idea of the shot noise intercept current, we may follow the same procedure described in 7946

In the present case minimum noise value is 1.46e-08 V/sqrt(Hz)

Therefore dark current(in2) ~dark noise voltage/RF transimpedance ~25pA/sqrt(Hz)

Therefore the approximate shot noise intercept current value is (25/18)^2 ~ 1.92mA, which matches well to the fitted value.

Attachment 1: reflshotnoise.pdf
8028   Thu Feb 7 19:25:22 2013 yutaUpdateCDSC1ALS filters reloaded

Filters for C1ALS were all gone. So, I copied /opt/rtcds/caltech/c1/chans/C1GCV.txt and renamed it as C1ALS.txt.

I'm not sure what happened to C1SC{X,Y} screens.

 Quote: I decided to rename the c1gcv model to be c1als.  This is in an ongoing effort to rename all the ALS stuff as ALS, and get rid of the various GC{V,X,Y} named stuff. (...snip...) The above has been done.  Still todo: FIX SCRIPTS!  There are almost certainly scripts that point to GC{V,X,Y} channels.  Those will have to be fixed as we come across them. Fix the c1sc{x,y}/master/C1SC{X,Y}_GC{X,Y}_SLOW.adl screens.  I need to figure out a more consistent place for those screens. Fix the C1ALS_COMPACT screen ???

8030   Fri Feb 8 02:12:14 2013 JenneUpdateLockingPRMI work

[Jenne, Yuta]

Lots of work, no solid conclusions yet.  In-vac, we aligned MICH and the PRM.  Out of vac, we got beam on AS and REFL paths.  We can lock MICH, but we're not as happy with PRCL.

In-vac alignment:

To get the beam centered on TT2 in yaw, Koji helped us out and moved TT1 with the sliders a little bit. Then to get the beam centered on PRM and PR2, Koji moved the TT2 sliders a little bit.

Yuta and I then moved PR2 forward a few mm, to keep the optical path length of the PRC approximately (within ~1mm, hopefully) the same as always.  After my PR2 optic swapping earlier, the pitch alignment was no longer good.  I loosened the screws holding the wire clamp to the optic holder, and tapped it back and forth until the alignment was good.  Of course, the screw-tightening / pitch-checking is a stochastic process, but eventually we got it.  A small amount of yaw adjustment by twisting the PR2 TT was also done, but not much was needed.

Beam was a little off in pitch at ITMY, so Yuta poked the top of PR3, and that one single poke was perfect, and the beam was very nicely centered on the ITMY target.  Beam was getting through BS target just fine.  We checked at ITMX, and the beam looked pretty centered, although we didn't put in a target.  We didn't do anything to BS while we were in-vac, since it was already good.

We aligned the ITMs so that their beams were retroreflecting back to the BS.  After this, we saw nice MICH fringes.

We aligned the PRM so that its beam was retroreflecting.

We checked that we were getting REFL and AS beams out of the vacuum, which we were (a small amount of adjustment was done to AS path steering mirrors).

AS table alignment:

We did a bit of tweaking of the REFL path, and lots of small stuff to the AS path.

The AS beam was coming out of vac at a slightly different place in yaw, so we moved the first out of vac AS steering mirror so the beam hit the center, rather than ~1/3 of the way to the edge.  We then aligned the beam through the lens, to the camera, and to AS55.  Most significantly, we removed the BS that was just before AS55.  This was sending beam to a dump, but it is in place to send beam over to AS110, once we get back to real locking.  We measured ~30 microwatts of power going to the AS55 PD, while MICH fringes were fringing.

The REFL path didn't need much, although we had never been going through the center of the HWP and PBS that are used to reduce the power before going to the PDs, so we translated them a millimeter or two.

We see signal on dataviewer for all of the channels that we're interested in....AS55 I&Q, ASDC, REFL11 I&Q, REFLDC (which comes from REFL55).

Locking:

Locking MICH was very easy, after we rotated the phase of AS55 to get all the good MICH signal in the Q phase.  Part of the criteria for this was that the AS55_Q_ERR signal should cross zero when ASDC went to 0.  This was done very coarsely, so we need to do it properly, but it was enough to get us locked.  We changed the phase from 24.5 to 90 deg.

PRCL has been more of a challenge, although we're still working on it.

On the back face of the Faraday, we see the michelson fringes, but they are not getting through the Faraday's aperture.  This implies that we have a poorly aligned michelson, in that the interference between the returning beams from the ITMs is happening at a different place than the original beam splitting.  Yuta is working on getting a better MICH right now.  EDIT, 10 minutes later....   This seems to be fixed, and the MICH fringes enter the back aperture of the FI, but there is still the PRM refl problem (next paragraph).

Also, when we get the most bright REFL beam, we see that there is some very obvious clipping in the back of the Faraday aperture, and this is matched by a clipped-looking REFL beam on the AS table.  We must understand what we have done wrong, such that when the beam is actually going through the Faraday, we see a much dimmer beam.  It's possible that there is some clipping happening at that time with the in-vac REFL path....we need to check this.  It's not a clipping problem on the AS table - I checked, and the beams are still reasonably  well centered on all of the mirrors.

We think that the MICH / REFL beam problems may be that the input pointing is close, but not perfect.  We have not confirmed today that the beam is centered on ETMY.  We should do this as part of our final alignment procedure before putting on doors.

Plans for tomorrow:

Get POP aligned, especially the camera, so we can see what our intracavity mode really looks like in the PRC.  This is probably (in part, at least) due to our having moved PR2 around, so the transmitted beams aren't in exactly the same place.

We think that it's more useful in the short term to check out the PRC, and since the clipping problem with the REFL beam is likely an imperfect input pointing, we want to use the other measured G&H mirror, and do another half-PRC test, with the test mirror in front of the BS.  This requires much less perfection in the input pointing, so it should be very quick to set up.

Confirm that PRM oplev is still aligned (turn laser back on first).

Plans for next week:

Perfect the input pointing, by checking the beam position at ETMY.  Recheck all corner alignment.

Try again locking PRMI in air.  First, confirm ITM and BS oplevs are all aligned.

8031   Fri Feb 8 02:38:04 2013 KojiUpdateLockingPRMI work

I feel it's too hasty to use the PRMI.
I support the idea of the half-PRC test, to make an apple-to-apple comparison.

Make haste slowly.

8032   Fri Feb 8 11:01:18 2013 JamieUpdateLockingPRMI work

I completely agree with Koji.  We definitely should have locked the half PRC first.  We were all set up for that.  Why go through all this work to align MICH when we haven't confirmed with the half PRC that the flipping is helping us?  The first rule of debugging is to only make one change at a time.  We have measurements from the half PRC, so we could have made a direct comparison with those to see how things have changed.  If we jump the gun we're going to end up wasting more time when we have to back-track.

Also, we never talked about moving PR2 to adjust optical path length, although I can understand why we would think that should be done.  My calculations were all done assuming the free-space separation between PRM/PR2 and PR2/PR3 were unchanged.  It's possible changing the position is better, but again, it's more work and it changes multiple things at one.  I can redo my calculations for this new scenario, but we need to update our drawings with this new configuration.  Please note precisely where PR2 has moved to.

We should have just flipped PR2 and that's it.  Then we could have run the exact same measurements we had previously.  Only then, once we understood this new simple cavity, should we have done further adjustments.

8034   Fri Feb 8 12:39:32 2013 yutaUpdateLockingPRMI work

Half-PRC at this time already have two changes from the previous half-PRC; PR2 replaced/flipped and different TM before BS.
PRMI has only one change from the previous PRMI; PR2 replaced/flipped.
This is why I wanted to try PRMI first. But we now recognized that MI alignment (including REFL and AS alignment) is tough without using the arms, I agree that we should try half-PRC first.

I don't exactly know what the situation in the Jamie's calculation, but to make the optical path length the same before and after flipping, PR2 holder have to move about n*t, where n is the substrate refractive index and t is the thickness of the mirror, towards PRM/PR3.

 Quote: The first rule of debugging is to only make one change at a time. Also, we never talked about moving PR2 to adjust optical path length,

8036   Fri Feb 8 12:43:26 2013 yutaUpdateComputersvideocapture.py now supports movie capturing

I updated /opt/rtcds/caltech/c1/scripts/general/videoscripts.py so that it supports movie capturing. It saves captured images (bmp) and movies (mp4) in /users/sensoray/SensorayCaptures/ directory.
I also updated /opt/rtcds/caltech/c1/scripts/pylibs/pyndslib.py because /usr/bin/lalapps_tconvert is not working and now /usr/bin/tconvert works.
However, tconvert doesn't run on ottavia, so I need Jamie to fix it.

videocapture.py -h:
Usage:     videocapture.py [cameraname] [options] Example usage:     videocapture.py MC2F -s 320x240 -t off        (Camptures image of MC2F with the size of 320x240, without timestamp on the image. MUST RUN ON PIANOSA!)     videocapture.py AS -m 10        (Camptures 10 sec movie of AS with the size of 720x480. MUST RUN ON PIANOSA!) Options:   -h, --help          show this help message and exit   -s SIZE             specify image size [default: 720x480]   -t TIMESTAMP_ONOFF  timestamp on or off [default: on]   -m MOVLENGTH        specity movie length (in sec; takes movie if specified) [default: 0]

8037   Fri Feb 8 15:53:48 2013 JenneUpdateLockingPRMI work

 Quote: I completely agree with Koji.  We definitely should have locked the half PRC first.  We were all set up for that.

I reminded Jamie this morning that we were not, in fact, set up yesterday for a half PRC.  I had extracted what was the flat test mirror, to put in as PR2.  The test mirror was the better of the 2 G&Hs that we had measurements for, so I had used it as the flat test mirror, but then also wanted it to be the more permanent PR2.  After doing the PR2 flip, the IFO was naturally all aligned for PRMI, which is part of why we just did that.

Anyhow, Jamie used his tallness to put the other measured G&H mirror into the mount, and put that in front of the BS.  He aligned things such that he saw fringes in the half PRC.

I then aligned POP onto the camera, and onto the PD.  Yuta is confirming that we're maximally on the REFL PDs.

We're starting locking in 5 min.

8038   Fri Feb 8 17:15:56 2013 JenneUpdateRF SystemMC REFL Photodiode transimpedance

This measurement was done already about a week ago, in elog 7984.  Can you please describe why the numbers for the last measurement were not believable, and what was done differently this time?

8039   Fri Feb 8 17:41:34 2013 JenneUpdateLockingPRMI work

[Yuta, Jenne]

After much tweaking of the alignment using TT1, TT2 and PRM sliders, we were able to get a TEM00 mode locked with the half PRC!

PRCL gain is -0.010

FM4, 5 are always on.  FM2,3,6 (boosts and stack res-gains) are triggered to come on after the cavity is locked.

We see a little clipping of POPDC, even though there are 2 BSs in the beam path, to dump 50% and then 67% of the beam.  But it's not so much that we can't align.

REFLDC goes from 28.5 to 24.5, so we don't have great visibility.

Please watch our awesome video of the cavity, where we demonstrate that the half cavity is stable:

The cavity is flashing for the 1st 15 sec, then locks.  Upper right is REFL, Lower right is POP, Upper left is back of the Faraday, Lower left is MC2F.   Note that we definitely see some not so beautiful modes flashing, but most of that is due to the half cavity length and thus greater degeneracy of modes.  Jamie is posting a HOM plot presently.

BEAM MOTION:

The beam is moving way more than it should be.  Right now the PRM oplev is not coming out of the vacuum, since the flat test mirror mount is obstructing it.  However, as we saw with other half-cavity tests, turning on the PRM oplev helps, but does not completely eliminate the beam motion.  We should consider putting oplevs on one of the passive TTs, at least temporarily, so we know what kind of motion is coming from where.

8042   Fri Feb 8 19:39:02 2013 KojiUpdateLockingPRMI work

It seems that the cavity trans looks much better than before. Cool.

At least the optical gain is ~x5 of the previous value. This means what we did was something good.

Looking forward to seeing the further analysis of the caivty...

8043   Fri Feb 8 20:05:15 2013 JenneUpdateLockingPRMI work

I fixed up the POP path so that there is no clipping, so that Yuta can take a cavity mode scan.

8044   Fri Feb 8 20:27:56 2013 KojiUpdateRF SystemMC REFL Photodiode transimpedance

The comment itself was added by me.
The difference between the previous and new measurements should be described by Riju.

In the entry 7984, the description has several PDs mixed up. The measurement was done with the MCREFL PD.
But the DC transimpedance of the thorlabs PD (5e3) was used, according to the text.
I first wonder if this is only a mistake not in the calculation but only in the elog due to a sloppy copy-and-paste.
But the resulting shot-noise-intercept current was 50uA, which is way too small
compared with a realistic value of 0.1~1mA. I have never seen such a good value with
C30642 at the resonant freq ~30MHz. That's why I said "hard to believe". I guessed this wrong
DC transimpedance was actually used for the calculation.

You may wonder why this 50uA is unreasonable number.
Basically this is just my feeling and probably is same as Rana's feeling.
But "my feeling" can't be a scientific explanation. Here is some estimation.

Looking at my note in 2010:
https://wiki-40m.ligo.caltech.edu/40m_Library (Comparisons of the PD circuits by KA)

The expected shot noise intercept current (idc) is

idc = 2 kB T / (e Rres),

where Rres is the impedance of the resonant circuit at the resonant freq.

This Rres is expressed as

Rres = 1/(4 pi^2 fres^2 Cd^2 Rs),

where Cd and Rs are the capacitance and series resistance of the diode.

If we input realistic numbers,

Cd = 100pF
Rs = 10 Ohm
fres = 30MHz

We obtain, Rres ~ 300Ohm, and idc = 0.2mA

In other words, Rs needs to be 2~3Ohm in order to have idc = 50uA.
This is too small from the previous measurements.
Test Results for C30642 LSC Diode Elements by Rich Abbott

8045   Fri Feb 8 21:14:52 2013 ManasaUpdateOpticsG&H - AR Reflectivity

Hours of struggle and still no data

I tried to measure the AR reflectivity and the loss due to flipping of G&H mirrors

With almost no wedge angle, separating the AR reflected beam from the HR reflected beam seems to need more tricks.

The separation between the 2 reflected rays is expected 0.8mm. After using a lens along the incident beam, this distance was still not enough to be separable by an iris.

The first trick: I could find a prism and tried to refract the beams at the edge of the prism...but the edges weren't that sharp to separate the beams (Infact I thought an axicon would do the job better..but I think we don't have any of those).

Next from the bag of tricks: I installed a camera to see if the spots can actually be resolved.

The camera image shows the 2 sets of focal spots; bright set to the left corresponding to HR reflected beam and the other from the AR surface. I expect the ghost images to arise from the 15 arcsec wedge of the mirror. I tried to mask one of the sets using a razor blade to see if I can separate them and get some data using a PD. But, it so turns out that even the blade edge is not sharp enough to separate them.

If there are any more intelligent ideas...go ahead and suggest!

8046   Fri Feb 8 22:49:31 2013 KojiUpdateOpticsG&H - AR Reflectivity

How about to measure the AR reflectivity at larger (but small) angles the extrapolate the function to smaller angle,
or estimate an upper limit?

The spot separation is

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) * n)

D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) / n)         (<== correction by Manasa's entry)

\theta is the angle of incidence. For a small \theta, D is propotional to \theta.

So If you double the incident angle, the beam separation will be doubled,
while the reflectivity is an even function of the incident angle (i.e. the lowest order is quadratic).

I am not sure until how much larger angle you can use the quadratic function rather than a quartic function.
But thinking about the difficulty you have, it might be worth to try.

8047   Fri Feb 8 23:04:40 2013 ManasaUpdateOpticsG&H - AR Reflectivity

 Quote: D = 2 d Tan(\phi) Cos(\theta), where \phi = ArcSin(Sin(\theta) * n) \theta is the angle of incidence. For a small \theta, D is propotional to \theta.

n1Sin(\theta1) = n2 Sin(\theta2)

So it should be

\phi = ArcSin(Sin(\theta) / n

I did check the reflected images for larger angles of incidence, about 20 deg and visibly (on the IR card) I did not see much change in the separation. But I will check it with the camera again to confirm on that.

ELOG V3.1.3-