PSL 70W Amplifier Installation Update #8

J. Oberling, E. Merilh

We began today by searching for a smaller micrometer to replace the rather large one on the 2nd mode matching lens mount.  We found one in the PSL enclosure and Ed installed it, see 1st picture.  We were then able to move the dog leg up by 1 row of holes, which cleared the interference with 70W amplifier output beam path.

We then mounted and installed 2 HR mirrors to re-direct the beam back online for the 70W amplifier.  We used a couple of mirror pedestals from the IOO cabinet and used spare HR mirrors from the PSL spare stock.  We then proceeded to align the beam.  We started with the mode matching lenses, as the 2nd lens needed to be removed to install the shorter micrometer.  We then realigned through the dog leg, using M08 and M34 to bring the beam up to the level for AMP_FI.  We used a beam target to to align the beam down the required row of holes and at the right height.  We then installed AMP_FI, AMP_WP02, and AMP_WP03 and checked that the beam was centered on them all.  Using the same alignment target, we then used our 2 new HR mirrors to align the beam down the required row of holes for AMP_M01 and the new FE DBB beam path.

At this point we placed the Thorlabs beam profiler and spent some time optimizing the lens positions.  The best waist we could get today was 365µm diameter horizontal and 344µm diameter vertical, likely due to the slightly increased optical path length due to AMP_FI, AMP_WP02, and AMP_WP03.  This is close enough for rough mode matching, so we moved on.  We roughly placed the 70W amp in its location so we could install AMP_M02 and mark its location for alignment purposes.  We then removed AMP_M02 and the 70W amplifier and installed AMP_M01.  Using the same alignment target, and the 2nd new HR mirror and AMP_M01, we aligned the beam down the row holes between AMP_M01 and AMP_M02.  This is a very rough starting alignment for the 70W amplifier, likely not close to the final alignment but at least somewhere to start.  We then installed AMP_M02 and AMP_M06, and placed beam dumps so all beams (leakage beams through AMP_M01 and AMP_M02 and the main beam reflected from AMP_M02) were blocked.  Finally, we installed the 4 beam dumps for AMP_FI.

I've attached a few pictures of the new layout.  The 1st shows the new, shorter micrometer.  The 2nd is an overview shot of the pre-70W amp beam path.  The 3rd shows the mode mathcing lenses, as well as WP02 and PBS02 in their new homes.  The 4th shows the re-located dog leg and AMP_WP02 at the entrance to AMP_FI.  The final picture shows AMP_WP03 at the exit of AMP_FI, the 2 new HR mirrors, AMP_M01, AMP_M02, and AMP_M06.  The 70W amplifier will sit in-between AMP_M01 and AMP_M02.

Next week, Peter will begin the process of aligning the 70W amplifier and optimizing the mode matching.

HAM6 squeezer work

Nutsinee Terry Daniel

OPO locking:

• With the ISI no longer locked the ~1kHz acoustic peak is a factor of a few lower and the OPO locking needs correspondingly less range. The lock also looks much better now.
• We copied the guardian from the SHG and updated it for the OPO. It seems to work.
• The power coupled through the fiber was increased by a few. We get just under 6mW onto the OPO REFL diode.
• OPO REFL Photodiode DC: Unlocked 5.8mW, Locked 2.2mW. The dip in reflection therefore is 62%

Fibers:

• We tried the waveplates in the green pump path and we are able to go as low as 0.7mW for the rejected light. The adjustment was somewhat cumbersome, since both waveplates needed to be rotated simultaneously to make further improvements towards the end.
• We also tried the manual waveplates in the seed path. We were able to get the rejected light up and down by about a factor of 4. It seems difficult to do better by hand.

Translation stage:

• We were able to move the lens translation stage using the PI controller.
• We didn't try the oven translation stage since we had no feedback, if it is moving.

Next:

• We need to realign the pick-off beam towards the homodyne detector,
• and find the red/green double resonance in the OPO.

Latest version of VerbalAlarms running on alarm0

The newest version of VerbalAlarms is now running on alarm0 (alarm handler computer). I've been running it on zotws8 all week and I think it is stable enough for control room use. If there are any issues with it, running the normal "VerbalAlarms -dc" will start the old one.

There will be a longer alog with details of this new version on another day.

Pcal alignment work at X-end, seems to have been successful

JimW, NikoL, JimW, ArijitS, RickS

This morning, we went into X-end to try to restore the alignment of the Pcal beams.

First, we tried tapping on the Pcal periscope flexures with the newly-acquired aluminum hammers.  That was not as successful as we had hoped.  The beams didn't move as we expected, which probably means that the tapping was not moving the periscope the same way it had shifted during the addition of the vibration absorbers and the "baffles and shields" hardware.

In the end, we used the adjustable mirror mounts on the periscope to restore pointing to the ETM target mounted on the suspension frame.

We also adjusted the centering on the 4th lower beam periscope mirror (M4)r.  We name the lower beam relay mirrors M1-M5 starting at the Tx module.  We adjusted M2 pitch to bring the beam up on M3, then adjusted the pitch of M3 to lower the beam on M4.  With a couple of iterations, we significantly improved the centering of the lower beam on M4.

We then adjusted the relay mirrors in the Receiver Module to center the beams on the aperture of the Rx integrating sphere.

We also adjusted the compression of the upper periscope flexures.  As found, the upper gaps were slightly more that 0.230".  We adjusted the flexure compression screws to reduce the gaps to slightly less than 0.210", increasing the pre-load forces constraining the periscope structure.

Photos of the beam positions on the ETM target and at the entrance to the Rx module integrating sphere are attached.

Ops Day Shift Summary

Shut down Y-end purge-air

Purge-air flow was brought to a halt once the BSC door was installed earlier this week -> Isolated purge-air from VE via closing vent/purge isolation valve.  Shut down purge-air supply.  We will restart as required to install the refurbished 2500 l/s ion pump, new gate valve, nipple and chevron baffle as soon as all items have arrived at LHO.  

modified instafoton to point to debian8 version of foton

launching foton from MEDM is having problems. As a temporary solution, I have modified instafoton.py to run /ligo/apps/debian8/gds-trunk/bin/foton

TCS glitches - 3 varieties identified

1. original glitch, shown in alog 40965, now showing both TCSY and TCSX
   •   this shows that where the TCSY laser temperature, chiller flow, and QPD B seg4 all glitched, nothing is seen on TCSX signals
   • all 3 signals from TCSY glitch independently of TCSX
2. new glitch
   • both TCSY and TCSX QPD B seg4's gltich, but no other signals do
   • TCSY and TCSX QPDs glitch at the same time
3. new glitch
   • both TCSY and TCSX QPD B seg4's gltich, and at the same time both laser temperatures start a slow rise in value, right before TCSX laser is turned on
   • this variety may have been due to preparations for turning the TCSX laser on, however, if that's true, it's significant that both TCSX and TCSY signals were effected
   • TCSY and TCSX QPDs and laser temperatures glitch at the same time

From these plots, I would say that it's very possible that there are multiple sources of glitching in the TCS system.

H1SUSOPO: HAM6 ISI Unlocked, Drive Templates Tailored, Model Updated, DC Scale Better Understood = Cleaner TFs, but Still Confusing.

J. Kissel

Hugh and Corey have unlocked, balanced, floated, and damped the HAM6 ISI LHO aLOG 41031, so I wanted to see if I could get new, more coherent TFs of the OPOS to better understand if the problems we're seeing are dynamics (rubbing, bad physical parameters, unmodelled but physical cross-coupling), electronics, basis issues, or something else.

The TFs are more coherent (I've also used the same drive filtering and amplitudes used to get the beautifully clean LLO aLOG 37508), but they're still confusing.

The encouraging news: now that I account for
    - The updated dynamical model, as discussed in LHO aLOG 41032
    - The change in transconductance between a v2 and v3 HAM-A driver (I had mistakenly used the -v3 transconductance, which was a factor 10 weaker)
    - The understood-but-not-yet-fixed, factor of 1e-6, unit flaw in the lever arm calculation in L1's OSEM2EUL and EUL2OSEM matrices
the DC scale of all DOFs in L1's TFs line up with the dynamical model exquisitely, and *at least one* of the DOFs of H1's data also line up. 

Also -- a lot of the (apparently incoherent) features in the H1 OPO's 2018-02-27 data that I was trying to explain with dynamics have gone away with the improved drive templates and the unlocking of the ISI.
Now, the response features and shape in L2L, V2V, P2P, and R2R (aside from scale factor issues) TFs look quite similar between L1 and H1.

Progress!

What remains as strange and/or a problem:
    - 5 of 6 H1 DOFs still don't match the DC scale factor of the dynamical model.
    - There remains a good deal of Yaw to Transverse coupling in T2T.
    - Also in T2T -- there's very little actual of the primary transverse model
    - The high-frequency asymptote in P2P seems to have drastically changed. It's unclear if this is dynamical interaction between the floating ISI and the floating OPOS, or if, for some strange reason the well-known electrical cross-coupling between drive and sensor has changed. Comparing pg 17 of 2018-03-16_1652_H1SUSOPO_M1_ALL_TFs.pdf and 2018-02-27_2209_H1SUSOPO_M1_ALL_TFs.pdf, one sees that the source of the change is mostly do to a change in V2's response.

However, now that we understand the DC gain of these transfer functions better, I'll take a look at the damping loops again and check if I can get somewhere by adjusting their gain to match the better understood plant.
    

TCS CO2 ITMX and ITMY laser servo transfer functions

To become more familiar with TCS, I've taken open loop transfer functions (OLTF) for the TCS lasers. These maintain the CO2 laser output powers at some reference level by feeding back to the laser PZT and the chiller temperature.

The UGF is 0.7 Hz and ITMY_CO2 and 0.4 Hz for ITMX_CO2, which is the same order of magnitude as presented in llo-alog-14338. I didn't wait to go down to mHz where the chiller servo takes over.

Transfer functions attached for reference, with the OLTF shown in red. Note that I took the TFs from TSC-ITMX_CO2_LSRPWR_ERR_SIGNAL_EXC, with 0.05 amplitude which gives ~4Vpk-pk to the laser PZT.

ZM1 Update: After Flag Replacement, TFs Look Different, But Still Abnormal

J. Kissel, T. Shaffer

I've remeasured transfer functions on H1 SUS ZM1 after TJ has improved the UL flag situation (see LHO aLOG 41001). I'm sad to say this has changed the problem, but not fixed it:
    - The primary P and L mode frequencies are still low with respect to the model and other suspensions in L2L and P2P
    - There is now Y cross coupling seen in L2L where there was not before (and is never expected to be there)
    - What was one extra mode below the primary Y resonance in Y2Y, is now two, and the lower of the two doesn't correspond to an L, P, or Y mode. (Maybe it's a T R or V mode?)

For this measurement, the ISI is now floating and damped.

Suggestions (in order from NONINVASIVE to DRASTIC): 
    - Investigate LL OSEM. 
        - Comparing EUL L and P drive to OSEM UL LL UR LR basis response plots -- pages 7 and 8 of 2018-03-16_1643_H1SUSZM1_M1_ALL_TFs.pdf against 2017-08-08_1520_H1SUSRM2_M1_ALL_TFs.pdf and 
2018-01-24_1909_H1SUSZM2_M1_ALL_TFs.pdf  -- one can see that ZM1's LL OSEM has less response than is typical (i.e. typically LL and LR show roughly the same response).
        - Also, In the L to UL LL UR LR plot, (pg 7) one can see some coupling to modes at 6.1 and 8.8 Hz in LL that's not in the other OSEMs. ZM2 shows some minor 8.8 Hz coupling, but it appears in all OSEMs.

    - Measure some of the fundamental parameters of the suspension
        - Do we have the right wire length? The right wire thickness?
        - The Y2Y TF worries me, and so does the reduced frequency of the L and P TFs. It makes me worried that there's some mechanical parameter of the suspension is wrong. 
        - The tip tilts, to-date, have had remarkably reproducible transfer functions, and H1 ZM1 is definitely an outlier -- see allhttss_2018-03-16_Phase3a_AllHTTS_ALL_ZOOMED_TFs.pdf. OK, OK, H1 OM1's pitch frequency is a little bit low, but all DOFs of H1 ZM1 look obviously different.

    - Back off all eddy current damping magnets, EQ stops and any other adjustable thing that might possible by rubbing. See what anything changes.

    - (Measure H1 OM2 before you do this, but) swap in-vacuum cables between OM2 and ZM1. In otherwords, use an entirely different, known-to-be-healthy (to be confirmed with the prior measurement) suspension's electronics chain, so as to completely rule out all electronics questions.

    - Completely replace the tip-tilt for a spare, and swapping the optic into another suspension.

It really is depressing how difficult these new single stage suspensions are to debug! HAM Single State Suspensions (HSSS) are supposed to be the easy ones...

SHG TEC

The SHG temperature controller has been upgraded to Lee's new TEC controller that was developed for the OPO.

New medm screens are linked form the the squeezer overview screen.

More testing and fine tuning is still needed.

10kW duct heater added to CP4 bake-out apparatus

Kyle R., Mark L., Mark D., Ken D., Richard M. and Jacob (MCE)

The initial 20kW duct heater used to supply heated air to the CP4 bake enclosure has proven insufficient to heat CP4, GV11 and GV12 to the desired 130C setpoint. As such, we shut down heating this morning to allow the installation of an additional 10kW duct heater.  The current setup uses an independent squirrel cage fan to circulate air within the insulated bake enclosure, the newly installed 10kW duct heater (on/off operation, shares AC source but not PLC controlled) and the initial 20kW duct heater (PID/PLC controlled).  Should the addition of this second duct heater still not be enough, we may choose to utilize the CP4's regeneration circuit as an alternative means to supply more Joules to the bake effort.  This setup vaporizes liquid nitrogen (stored in large tanks (dewars) outside of the building and nominally used for the cryogenic pumps) using ambient heat absorbed in a heat exchanger then further heats this gas to the desired temperature via electric heating element.  This heated GN2 then flows through the inner vessel (nominally filled with LN2) located within CP4 vacuum chamber before exiting to atmosphere via an exhaust line. 

We will allow the duct heaters to reach maximum output over the weekend before experimenting with the regeneration circuit.  

Turn Off End-Y VEA-2 Dust Monitor

   Now the cleanroom over BSC10 has been turned off, I've shutdown dust monitor EY VEA2. This monitor has been removed from the "check_dust_monitors_are_working" script. It will be physically removed from End-Y at the next opportunity. 

Understanding H1SUSOPO TFs with Modeling and Comparison with L1SUSOPO: Progress, but Not Enough

S. Aston, Á. Fernández-Galiana, J. Kissel, M. Pirello, T. Shaffer

We're still struggling for understanding as to why the H1SUSOPO suspension transfer functions looks like garbage in so many confusing ways. 

The message: we're getting closer, but it still doesn't make complete sense -- which means we still can't damp the suspension -- which means we can't just "close it up" 'cause it's "good enough."

Details below.

Attached are an annotated set of .pdfs that summarize the current state of knowledge.

ANNOTATION LEGEND

BLUE / RED: 
Stuff with which I’m happy, and I think we should just update the old model.
	- Increased the length of the wires from 146 mm to 155 mm. This was an honest mistake in not accounting for the distance between the bottom of the wire clamp and the actual suspension break off point:
         % See Wire Assembly D1500483-v3 and
         % Wire Pulling Jig Assembly D1500481-v1
         % [[D1500485-v2 (0.25in + 1.5in) + D1600451-v2 (3.983in) + D1600462-v1 2*(0.18in) = 6.093 in = 154.76 mm]]
         % (was 145.61, but forgot the extra thickness to the *actual* suspension point i.e. the 2*0.18in from D1600462)
		> This dead reckoned number then immediately better matched the L, T, and Y 
		  primary resonances without further tweaking needed.

	- Increased the blades’ Young’s modulus by only 11% to better match the primary V frequency.

	- (The mass remains at 36 kg).

	- Updated diagonal MoI’s, Ixx, Iyy, Izz (corresponding to R, P, and Y, respectively) 
	  to better match measured primary R, P and Y frequencies.
		> started with Álvaro’s updated Solidworks numbers, and only had to tweak the numbers ~5%.

	- Broke out the damping matrix into a value for each DOF (but still a diagonal matrix)
		> Used to be all 1.0. Now (L, T, V, R, P, Y) = (0.3, 0.3, 3, 0.03, 0.06, 0.1).
		> This nailed the Qs of the primary resonances, and therefore automatically got most of the cross-coupling right.

	- Added off-diagonal MoI’s to the parameter file and model. 
		> Essential to explaining the third resonance in the R and P transfer functions.
		> had to do a lot of playing here, but good enough for government work. 
		> Ixy = 30% lower, Ixz = factor of 10 higher, Iyz = factor of 100 higher.

GREEN: 
Unexpected, yet measured, cross-coupling + dubious modeling with which I’m guessing and would love insight.  The few physical mechanism I can imagine, but only guess how to model:
	- V to Y coupling, or a “corkscrewing”. This, I’d imagined was a sensor or actuator flaw, like the V OSEMs sensing/driving at some angle to the vertical axis. A little implausible, because they’d have to all be cocked in the same direction. I modeled this by adding a V to Y component to the stiffness matrix, but I have now idea how one should really do it.
	- T to Y coupling. Here, the mechanism I imagine is a little more plausible: a ~5 mm offset from the transverse actuation plane (TAP) and the horizontal CoM would create a yaw torque. I’m a little more confident in adding that term to the stiffness matrix, because it’s a similar effect to what Álvaro already has in the model to create the “standard” (Longitudinal to Pitch) and (Transverse to Roll) coupling. BUT — if that TAP offset exists, there’s no reason to think an LAP doesn’t exist. 

ORANGE / PURPLE: 
Stuff I still have no clue how to explain.


THINGS WE'VE RULED OUT IN HARDWARE

     - TJ promises that the H1SUSOPO is not rubbing, but continues to question whether he can really tell given the poor visibility and tight quarters in chamber. I've told him to hold off checking again until we can get the HAM6 ISI balanced, floating and damped. That might at least get rid of some of the incoherent noise.

     - TJ, Alvaro, and myself have all gone over the OSEM2EUL and EUL2OSEM basis transformation matrix math, and it all seems to check out. See the "other files" of G1701821.

     - After consulting with the analog CDS team project-wide, we identified that the OPOS is the last hold-out using -v2 of the HAM-A coil driver D1100117, which has lower output impedance, and thus increasing the transconductance from v3 by a factor of 10. Every other SUS that uses the HAM-A driver (HAUX and HTTS) have had their impedance increased, as per ECR E1201027. This explains some of the discrepancy between the model L1's measurement, but it doesn't explain why H1 is all over the map.

     - Hearing this, (and remembering the jumper issues with ZM2, LHO aLOG 40218, and ZM1 LHO aLOG 40241), I was suspicious we were driving one-third of the SUS with v2 and two thirds with v3. Even though the chassis were clearly labeled when we got to the racks, Marc was gracious enough to open up the OPOS HAM-A coil drivers so we could see with our own eyes that the output impedance on R33 and R11 were 100 Ohms as expected.

ANALYSIS DOCUMENTATION 
Also attached is the model ssmake_voposus.m and RED parameter set, oposopt_h1susopo_fit.m which produced to today's results, which will become obsolete after we merge the stuff we like with the BLUE parameter set oposopt_h1susopo.m, which we'll probably rename to something like oposopt_production once we're happy.

Just to record everything I've been using:
${SusSVN}/sus/trunk/Common/MatlabTools/SingleModel_Production/
    comparesingleparams.m    << comparison script

    ssmake_voposus.m         << dynamical model

    oposopt_h1susopo.m       << BLUE reference parameter
    oposopt_h1susopo_fit.m   << RED updated parameter set

${SusSVN}/sus/trunk/OPOS/L1/OPO/SAGM1/Results/2018-01-29_0900_L1SUSOPO_M1.mat
${SusSVN}/sus/trunk/OPOS/H1/OPO/SAGM1/Results/2018-02-27_2209_H1SUSOPO_M1.mat

*phew* this is exhausting.

WHAM6 ISI Unlocked and Balanced. Left unlocked & floating with C3 Covers pulled away--purge is pretty strong though

w/ unwavering support and patience from Corey, we got the table floated and balanced, finally.  Added a loooot of weight to get it.  Will detail things in an additional alog tomorrow.

PSL 70W Amplifier Installation Update #7

J. Oberling, C. Vorvick, E. Merilh, P. King, J. Bartlett

Mode matching, mode matching, and more mode matching.  We began Monday by installing the mode matching solution detailed in the previous alog, and then attempting to optimize it to get close to the desired waist for the 70W amp.  Unfortunately, as is the case with most 1st attempts at mode matching, this didn't get us where we needed to be; the smallest we could get the beam was ~450 µm in diameter, a bit off of the required 273 µm diameter.  At this point, Cheryl volunteered to lend us her experience in mode matching, which I accepted (thank you Cheryl!).  So on Tuesday morning, Cheryl and I went into the enclosure to tweak up the mode matching.  She took accurate measurements of the lens positions and we re-measured the waist; in addition we looked at the previous measurement Ed and I took of the FE beam to assess beam quality (done with the Wincam), and we took a new one with the Thorlabs beam profiler after the mode matching lenses (1st attachment).  As them beam looked like it had some lobes on it (which was not different than the older Wincam image), we then looked at the beam path from the NPRO to the MOPA inside the 35W FE to see if there was anything that could be causing it.  We found that the beam alignment through the extra AOM inside the FE was off, as well as some very slight clipping on the razor blade dump meant to block the 1st order diffraction from said AOM (if it was being utilized, which it is not).  We also took a look at the beam profile of the NPRO using the Thorlabs beam profiler (2nd attachment), and didn't see anything that looked amiss.  We decided to move on with optimizing the mode matching, so Cheryl took the lens position and waist measurements and plugged them into A La Mode (Matlab mode matching script), which told us how to move the mode matching lenses to optimize the output waist.  We went back and forth with this for a while, getting closer, but not quite getting there.  One problem we immediately noticed: the downward angle of the FE beam induced by the new pick-off was causing us problems with the lens alignment.  We did not have enough adjustment range on the Owis lens mounts to center the lenses on the beam, and since these mounts were originally installed on fixed-height pedestals, the small amount of adjustment range from the mount was all we had.  We decided to call it a day and continue on Wednesday morning.  That evening, Cheryl dug into A La Mode to work on a robust mode matching solution.  Her results were to use the same lenses (f1 = -50mm, f2 = 80mm), but move the position to +479.5mm for the 1st lens and +527.7mm for the 2nd lens (this assumes 0.0 mm is the outside edge of the 35W FE enclosure).

First things first on Wednesday, we had to decide what to do about the lens alignment problem.  In an ideal scenario (assuming we had all the time in the world), we would painstakingly align the beam out of the FE to correct for the downward beam angle.  Back in the real world however, we decided to ditch the fixed height pedestals for adjustable height.  Due to the odd mounting of the Newport SDS40 translation stages, we had to ditch these as well.  Eventually, we were able to come up with a workable solution that gave us the adjustments we needed to complete the mode matching; unfortunately, this took most of the day.  While I was building out the new mounts, Cheryl painstakingly measured the distances to position the lenses and made fiducial marks on the table.  Once the new mounts were assembled (3rd and 4th attachments), we test fit them on the table; the footprints are larger than the old fixed-height pedestals, but they fit where they need to and give us the adjustment we need.  We have since found (see below) that we probably need to swap out the huge micrometer on the 2nd lens mount with a smaller one, but for now this gave us a workable solution.

On Thursday, Ed and I began fixing the above noted clipping issues in the FE.  We removed the side panel and adjusted the AOM position so it was centered on the beam.  We then moved the beam dump just enough to clear the slight clipping.  Of course, upon turning the MOPA on, we had to slightly adjust the alignment into it to return to optimum operation.  We checked the beam alignment outside of the FE and everything looked to be in the same place, so we moved onto installing the mode matching lenses.  We started by installing and aligning the new lens mounts; we took care to ensure the mounts were even and aligned to the beam.  We then installed the lenses, aligning after each install.  After this, we set up the Thorlabs profiler and began adjusting the position of the 2nd lens.  Right off the bat we had a waist of ~344 µm in diameter (5th attachment).  Moving the 1st lens a small bit and readjusting the 2nd, I was unable to get the beam any smaller (moving both directions for the 1st lens produced the same results, a larger beam at our desired waist location).  Cheryl had joined us by this time, and we decided that this was close enough for a rough mode match (we'll optimize the mode matching once we have the 70W amplifier installed and aligned), so we started placing the other required optics in the beam path: WP02, PBS02, AMP_WP02, AMP_FI (and associated beam dumps), AMP_WP03, and AMP_M01. 

We immediately ran into a problem.  Due to an interference between M04 and M33 on the original PSL layout (that oddly enough was not present at LLO, per M. Heintze), the beam out of the LHO FE was not aligned along the row of holes as indicated in the layout; it was angled towards the FE slightly.  Because of this, the mount for WP02 (which assumes the beam is aligned along a row of holes), is clipping the beam.  At this point I had to leave to attend a meeting, so Cheryl and Ed finished up installing the table components.  The WP02 issue was resolved by changing the mount to a fixed height post and a baseplate.  They put the Faraday isolator (AMP_FI) on the table and noticed immediately that the beam was clipping (once again being bit by the downward launch angle imparted on the beam by the new FE pick-off).  They re-installed the dog leg after M33 so the beam height could be adjusted up and made level through AMP_FI.  The final attachment shows this setup; this is simply a mock up, as M09 and M10 are to be used in the FE DBB path, and they had to shift AMP_FI laterally, which blocks the beam from the 70W amplifier.  Unfortunately, given the huge micrometer on the 2nd lens mount, this is the only way to currently install this setup.  So first thing tomorrow we need to hunt down a smaller micrometer for the 2nd lens mount, so the dog leg can be shifted up the table to clear the interference between AMP_FI and the resulting 70W amplifier output beam.

While all this has been going on, Peter has been working on figuring out the wiring for the new external shutter so that is ready for when we have light through the 70W amplifier.  Jeff Bartlett has been working on the plumbing required to get the power meter in the new external shutter plumbed into the PSL cooling loops; this power meter will use the old HPO power meter circuit.  In addition to this, Peter and Jeff dried out the old HPO Laser Head and Laser Crystal water circuits; once the new external shutter power meter has been plumbed in, the HPO Power Meter water circuit will be dried out as well, thus completing the mothball of the HPO.

Scan PopAir B 90 Mhz for faults with VNA

Scanned the 90MHz patch cables and Heliax cable for faults with the Agilent Vector Network Analyzer (VNA) set to Distance to Fault (DTF) mode.  The scan originating at the CER was clean with one suspicions marker near the 20m mark.  The scan originating at the PSL did not record this marker, and was much noisier.  We suspect this final patch cable between the patch panel, and the I/Q Demod is damaged and needs to be replaced.

After further review, the Balun was causing problems with the VNA.  Upon removal of the Balun the plot started to look what it should look like.  There is still a suspicious blip at 18.4m from the CER patch panel, but the blip is less of a disturbance than a connector.

WP7419

FRS6599

 

PSL 70W Amplifier Installation Update

J. Oberling, E. Merilh

The last few days have been spent taking caustic measurements and searching for mode matching solutions so we can identify what lenses we need for mode matching prior to placing elements on the table; as a result there is not a whole lot of installation activity to report.  We left off Friday with a lovely LG01 mode in the Wincam.  On Monday morning Bubba very kindly shaved some mounts down for us (for WP02 and PBS02) to solve our clipping problem.  These were installed and the LG01 mode was still observed on the Wincam.  To see if we were seeing something real or just an issue with the Wincam, we borrowed a Thorlabs rotating slit beam profiler from the Pcal folks (who had lent it to the SQZ folks).  Setting this profiler up, we saw a nice Gaussian beam on the profiler.  Apparently something is up with that Wincam, so we will continue to use the Thorlabs profiler.

Using the same 300mm focal length lens, we took a measurement of the FE beam caustic, attached as LHO_FE_Caustic1.txt.  The first column is scale position in cm (corrected for the fact we had the wrong location of the sensor in the profiler when taking the measurement), and the last 2 columns are horizontal and vertical beam radii in µm, respectively.  This was imported into JamMT, the lens added, and the resulting FE waist given as 77.2 µm in radius, positioned ~15mm outside of the FE box.  This is uploaded as FE_caustic_after_distance_check.png (z=0 is the end of the scale used to take the caustic measurement, all distances are relative to that); we doubled checked all of our distance measurements this morning and made some small corrections, hence the filename.  While the location makes sense, the beam radius seems small as the LIGO FE lasers were all measured to be between 150µm and 250µm; although we have swapped the NPRO in the FE, which can have an effect on the waist size and location.  JamMT yielded only one mode matching solution with this initial waist that fits within the constraints of the beam path; this is uploaded as 70W_MM_solution1-FE_caustic_with_lens.png.  Unfortunately, I didn't think to take a picture of the measurement setup used; I'll take one tomorrow morning and upload it as a comment to this alog.

As a double check, we measured the caustic with no lens in place, and followed the same procedure as above.  The measurement is uploaded as LHO_FE_Caustic_no_lens.txt (same units as the previous .txt file, this time the position dimension is referenced to the FE box (since there was no lens installed)), and the resulting FE waist as FE_Caustic_no_lens.png.  As can be seen, something is not quite right with this measurement as it claims the waist is 2mm in diameter and located some 4.9 meters (yes, meters) behind the FE box (this is somewhere way past the NPRO and not in the FE box at all...), so this isn't the double check we thought it would be.  We tried installing a 400mm focal length lens in place of the 300mm, but this put the resulting focus off the edge of the table; a 200mm focal length lens gets the spot too small for the profiler to give accurate measurements.  We will do some more investigation of this in the morning (maybe try the 200mm lens anyway and see what we get), but at this point I think our best check is to set up the lenses from the given solution, put the Thorlabs profiler at the location the 70W amplifier expects the beam waist to be, and see what our beam diameter is.  If we're close, then onward we go; if not, then more investigation is needed.

Fiber Coupling

At the moment we have a mix of commercial fibre and the custom (Fabrice) fibre. The mix is due to some fiber being short and the necessity to get light into HAM6 and align the OPO asap.

For Green

We still have a Thorlabs patch fiber from the PAF-X-5-A coupler delivering 2.6mW to the patch panel with about 70% coupling efficienecy. A Thorlabs fiber (extension) delivers 1.4mW to Fiber SN11 (E1700235-V6). SN11 delivers 0.7mW to the vacuum feedthrough. A seperate measurement (alog40762) shows the vacuum feedthrough (SN8) and in-vacuum fibre (SN6) together are 88% efficient. 

For IR

SN10 temporarily goes from the  PAF-X-5-C coupler to the patch panel delivering 9.37 mW with 72% coupling efficiency. We use a communications fibre as an extension that delivers 8.9mW to SN12. We forgot to measure the output of SN12 and we only get 3.5 mW into the chamber at the output of SN7. 

Summary to date of Fabrice's fibres

SN8+SN6=88% (alog40762)

SN11=50%

SN10>72% (includes free-space to fibre coupling efficiency)

SN12+SN9+SN7=40% (unfortunately forgot to measure SN12 individually until after it was connected, and it's awkward, maybe revisit after close HAM6)

Still to install switch and fibres SN9, SN8 and SN7, revisit SN11 and SN12 when time allows.