Alignment into HAM2

Locked JAC with RF at 1W. IMC WFS was centered in IOT2L and IMC started working. As we steered JM3 MC2 TRANS responded as expected (i.e. JM3 PIT -> MC2 YAW and vice versa though there's a significant cross coupling). Sheila had to recenter the WFS once again at some point as the WFS started to get off-centered as we turned JM3, but as far as the WFSs were centered, things worked.

In the end, MC2 TRANS was centered reasonably well (right before the cursor in the attached), JM3 DAC output was O(1e7) while a 28 bit DAC's range is +-134e6.

Apparently we made the last step of JM3 PIT adjustment in the wrong direction at the time (we didn't notice because the WFS is very slow) and overshot. I steered it back later, now H1:SUS-JM3_M1_OPTICALIGN_P_OFFSET is -39 instead of -19 (second screen shot).

Anyway, this means that the alignment into HAM2 is good with more than a comfortable range left for JM3. No need to further refine.

One caveat is that the IM4 trans is totally off in PIT. But that's a downstream problem which we'll have to deal with later in HAM2. That should not prevent us from moving forward to close down the chamber.

The tasks listed below are described in different alogs.

JAC TRANS PD calibration

Last beam dump (alog 89249)

ALS beam path check

We installed JM1, balanced it and aligned it. A beam dump was placed behind it though we could not see the transmission with 1W input.

After this, JAC locked with RF without any problem though the input was wobbly when the purge was up.

We searched for unexpected ghost beams (also with 1W input) and didn't find any.

We uninstalled many (but not all) temporary dog clamps and irises.

We revisited the IMC alignment because it's been off in PIT since Thursday or Friday. We locked JAC using dither (because we wanted to turn down the purge air). We enabled the IMC WFS just for MC optics and steered JM3, but weren't able to center the MC2 trans. Steering JM3 just made the IMC transmission worse while making not much impact on the desired degree of freedon (JM3 PIT -> MC2 trans YAW, JAM3 YAW -> MC2 trans PIT).

Tomorrow, we'll revisit the IMC alignment. We'll also measure the power coming into JAC TRANS PD as well as the actual transmission of JAC while locking it with RF so we can use JAC trans PD as the measure of the power into HAM1.

Jennie W, Keita K, Rahul K, Ryan S,

This morning Keita turned the power up to 1 W and the purge air down in order to scan the OMC and measure the modulation index.

We had some work to do to lock the JAC, the cavity wouldn't scan properly when managed by the guardian code.

Ryan and I have looked back at it and think there may be something wrong with the feedback to the PZT. It can't be the PZT itself though, because Keita and I were able to lock on the TRANS PD signal with the dither locking done manually by tuning the PZT offset to find the resonance and then turning on the feedback.

I have enclosed a picture to aid problem solving next week.

We then had problems keeping the IMC locked so Keita had to change the threshold used to check if the cavity is locked down to 2. This was changed at line 133 in ISC_library.py at userapps/h1/isc/guardian/.

trans_pd_lock_threshold = 2

We then managed to do three scans,

one with 45 MHz off, one with both on, and one with 9 MHz off. Detailed analysis in progress.

After turning the power back down Keita and Rahul swapped the mirror we currently have in front of the TRANS PD, with the uncoated laser window that is meant to be there (JACT_BS1).

They had to top gun and swab it to remove two dust particles first.

This replacement means the power to the PD is lower and so we needed to power up to 1W to check this alignment.

I have left the mirror we took out on the table on the -Y side labelled as 'HR mirror taken out of JACT-BS1'. Need to check which exact mirror this is with Masayuki on Monday.

Keita locked the cavity manually with the REFL PD and optimised the amount of light falling onto the TRANS PD.

I powered down to 100mW and de-energised the rotation stage and closed the light pipe at the end of the day. We also had the rotation stage de-energised and locked out when we were working in chamber.

Modulation index measurement for 45M and 9M, they're healthy.

1W into JAC, no WFS for IMC, ITMY single bounce. Scanned OMC with both 45MHz minimal power (~4dBm) and 9MHz full (~27dBm), then both in full power, then only 45MHz in full (see screen shot).

Jennie will post the modulation index later, but the peaks look healthy to me.

The alignment into IMC was rather off in PIT and the guardian had a hard time locking IMC (I changed the lock threshold in the guardian). We didn't move MC, didn't bother to do any thorough investigation, but either JAC or MC mirrors moved. Maybe we have to lock IMC, use WFS for MC, and steer JM3 and see if the MC mirrors will be driven far from where they are. If they are we might have to touch up in-chamber alignment again.

JAC TRANS BS was swapped with the real one (laser window with AR only on one surface).

We replaced the JAC TRANS BS (which was a temporary high reflector until today) with the real one that is just a bare glass (the reflectivity is 7% or so depending on AOI). 

We locked JAC with RF, was able to see the beam coming to the TRANS PD but wasn't able to see the reflection of PD, so we raised the power to 1W.

Initially the beam was missing the PD because the new optic is thinner than the temporary one. We realigned the optic to steer the beam back to PD. Since we could not directly see the PD surface, we just steered the beam up and down, left and right until the PD output starts to drop, and put the beam roughly in the middle.

We were able to see the PD reflection using an IR card and an IR viewer. There were two reflection blobs (which was the case before, too),  and I moved the JAC TRANS BD in +X direction by 1/4~3/8" to catch both.

Beam dump for HAM1-HAM2 septum window AR reflection.

This was installed. 

Beam dump for the -Y door viewport reflection.

Jason and Betsy installed it. There seems to be a discussion as to whether or not something else needs to be done.

EOM and JAC power budget again.

We measured the power at various places. While Jason held the power meter head still, I ran the statistics function of the power meter for a few seconds. I only list the mean and the standard deviation.

Wrong pol is king of large, ~0.2% of the main beam power coming out of EOM. That's 200mW when 100W goes through the EOM. 

JAC throughput of 92% is not great, but Jason says the alignment and the matching are not really optimised.

I added this shutter (shutter H1:SYS-MOTION_C_SHUTTER_M) to the main shutters screen at sitemap->LSC->Shutters. I also added a menu button that takes you to the control screen to the sitemap->IOO->JAC Overview screen, see pic.

We locked JAC with 1W input to find ghost beams. Details will come after we're done with the septum window reflection, but anyway here is the list:

1. EOM AR reflection. Properly dumped today.
2. L1 reflections (front and back surface) are reflected by JAC output coupler and go through L1. Properly dumped today.
3. L2 reflections (front and back). Properly dumped today.
4. L3 reflections (front and back). Properly dumped today.
5. EOM wrong pol forward going beam. Changed the beam dump position today. This was brighter than I thought, we will measure the power again.
6. JM2 transmission. Already dumped, confirmed it's still there.
7. JM3 transmission. Already dumped, confirmed it's still there.
8. Septum window reflection. This was coming back horizontally in -Y direction, was about half inch off from the main beam at the top periscope mirror, and hitting the metal part at the top edge of the bottom peri mirror. Not dumped yet. 
   • We'll have to improvise something so the beam is dumped at the top periscope position before entering into the periscope structure. Something like a variation of the beam dump behind the top mirror of the  JAC input periscope. 

None of the new beam dumps are interfering with the main beam and JAC refl/trans.

Jennie W, Ryan S

Summary: Ryan and I updated the JAC and IMC ASC models. We installed JM3 yesterday and so now the IMC cannot use the PSL PZT mirror as an alignment actuator. I have committed the changes to the svn but erik and dave will do some checks tomorrow before they commit to the revision locked version of the model and restart the DAQ. So changes are not 'live' yet.

The edits were made to h1ascimc.mdl which has top level blocks for IMC and JAC.

The JAC top level model sends signals directly to the PSL PZT mirror and these degrees of freedom are swapped as the PSL PZT basis P and Y are switched before input to the JAC due to the HAM1 input periscope.

I took out the feedback paths for PZT_P and PZT_Y that come out of the IMC block. The picture shows the old config and I have highlighted what I removed.

At the top level, IMC no longer sends signals to the PZT but instead to JM3. On the top level diagram, the signal JM3_P is sent via PCI cards to the channel "H1ASC-JM3_YAW_SUSHTTS" as pitch in the JAC basis is yaw in the IMC basis due to the HAM1 output periscope. The picture shows the old config and I have highlighted what I swapped.

The signal JM3_Y is sent via PCI cards to the channel "H1ASC-JM3_PIT_SUSHTTS" as yaw in the JAC basis is pitch in the IMC basis due to the HAM1 output periscope.

Within the IMC top names block I removed the output channels for the PZT from the WFS feedback path, we already had paths to feedback to JM3 within this path. The picture shows the new config.

I removed the PZT locking path from the LCKIN block and replaced it with one for JM3. The picture shows the new config. I am not sure we ever use this path (which is for dither asc control of the IMC) in the first place so maybe this was unneccessary.

I also removed the channels H1:IMC-PZT_YAW_OUT and H1:IMC-PZT_PIT_OUT from the DAQ channel list for the IMC model.

We refined the alignment from JAC to IMC by iterating small amount between JM2 and JM3. It was hard due to purge air and the suspended JM3, instead of relying on the IMC scan and minimize 1st order modes, we locked IMC and minimized the IMC REFL DC on average. After that the beam was still centered on JM3 well.

We closed the chamber and turned down the purge all the way and the alignment was indeed good. There was almost no 01 (PIT) mode power, 10 (YAW) mode power was less than 1% of 00 mode power, and the 20/02 mode power was 0.23 to 0.24%. See MM.png.

(To identify which mode is what, I intentionally misaligned JM3 in YAW (that causes PIT misalignment for IMC. See  mode_identification.png.)

Or, rather, a better JM3 integration and PSL unintegration.

I made a temporary IMC_WFS_MASTER and IMC_WFS_OUTMATRIX_kk screen such that it's easy to route IMC WFS signal to JM3, not the PSL PZT, because I wanted something that works now.

However, right after I made what looks to be an OK screen, I realized that this doesn't work. PIT signal should be routed to JM3 YAW and vice versa. No fully-working IMC WFS until the next model update.

In addition, earlier today Daniel suggested to nuke PSL PZT from the IMC ASC (good idea).

If you want to revert back to the old medm, copy the backup

/opt/rtcds/userapps/trunk/asc/common/medm/imc/IMC_WFS_MASTER_BAK_20260218.adl 

to

/opt/rtcds/userapps/trunk/asc/common/medm/imc/IMC_WFS_MASTER.adl 

This morning we have pushed the JAC EOM by about 0.6mm (using ~25 thou thick washers) in -Y direction, following the finding of last Friday (alog 89158). 

After that the beam was good on the input side plate (the beam is offset in +Y direction by 0.1mm) and was OK on the output side plate (0.5mm offset in -Y direction).

The beam position on the crystal itself should be ~0.13mm in +Y direction on the input face and ~0.36mm in +Y direction on the output face. The angle between the nominal path and the actual path outside of the crystal is about 0.6 degrees. See pictures and cartoon.

Calculation depends on the refractive index, I assumed n~1+deflection/wedge=1+2.35/2.85~1.85, but using 1.85+-0.5 instead won't change anything in a meaningful manner.

This is acceptable, the beam is more than 1.5mm away from the side face of the crystal, cannot remember the beam radius but it should be smaller than 600um if FDR is still valid, so it might be 2.5 beam radius or maybe more.

Jennie W, Ryan S, Keita K

Summary: MC suspensions back to good time from 10th of Feb, we should only lock the IMC length loop manually during this installation period to avoid the WFS engaging.

Today Ryan and I had the task of figuring out why the IMC suspensions seemed to be badly aligned on Friday.

We found a good reference time 16:48:29 UTC on Tuesday 10th Feb at the end of the period where Olli, Jenne and I set the IMC axis back to its nominal state before the vent using ASC loops for DOF 1 and 2 of the IMC plus manual moves of the JM3 mirror in chamber as this cannot be moved by an ASC loop as it is not a tip-tilt currently. See photo of the WFS and MC mirror top mass OSEMS here. Note it is important to choose a time when IMC is in the locked state as the MC2 mirror gets mis-aligned when the IMC guardian is offline.

We figured out that the alignment was changed about 19:33:17 UTC on 13th Feb probably by the IMC guardian as Elenna used it to lock the IMC for phase check measurements. See photo, where the vertical cursors are set at the good reference time and today.

After some investigation of the guardian we reminded ourselves that DOFs 3-5 are turned off in the IMC WFS MASTER filter banks. DOF4 and 5 are normally off and DOF3 is intentionally left off because of the replacement of PSL PZT actuator by JM3.

When the IMC guardian is used to lock it automatically triggers the WFS through some logic from the simulink model, and so when Elenna used the guardian to lock it turned on the feedback to DOFs 1 and 2.

Until we install the JM3 tip-tilt and are finsihed most commissioning of the HAM1 hardware we should only lock the IMC manually by engaging the MC-L servo using the common mode servo board controls.

Keita and I zeroed the M1 LOCK fiters for all 3 MC mirrors and I changed the alignment sliders so the M1 osems were back to their values from the reference time on the 10th. See photo of ndscope.

Jennie W, Jason O, Keita K, Betsy W, Camilla C

Summary: EOM alignment and position captured, moved to opics lab for crystal replacment, JAC-REFL path alignment in progress.

This morning Jason, Keita and I checked the centering of the HAM1 irises after the JM3 alignment Olli and I did on Tuesday. We didn't move the irises right after JM3 as this seemed centred. We did reposition the iris right before the HAM2 septum plate in x and y.

This, along with the alignment of the IMC Olli, Jenne and I did on Tuesday, captures where the beam was with the current EOM installed.

Keita marked the EOM base position with a dog clamp and removed it to the optics lab for crystal replacement. The shims for the EOM and the screws that hold it to the table are in a foil packet on the +Y - X HEPI pier.

Betsy, Camilla and I rechecked the REFL path and spent some time moving JACR-M2 to centre it on the incoming and outgoing beams. Then we pitched down this mirror so the outgoing beam hit the upper periscope mirror. After this Betsy had some concerns that we were too close to where the JM3 tip-tilt will sit (we are  currently using a siskiyou mount for this mirror). So we yawed the JACR-M2 mirror so the beam hits the viewport slighly more to the right (as viewed from -Y side). Looking at the placement on the viewport simulator, the beam is low and right on the viewport, whereas it comes to the table, high and right in the bellows hole. This table it almost at the top of its adjustment range, so Jason and I plan to go in this afternoon and see it we can move up the table feet so the beam can move up in the viewport a bit. Betsy and I measured the tilt of the beaM from JACR_M2 off the table. The heigh is 103 mm at the table hole 8 inches from the -X edge and 8 inches from the +Y edge. It tilts up to 113mm at the last hole in this row on the -Y side.

Betsy and I also checked the pitch of the beam entering and leaving JAC after the EOM was removed. The input beam to the JAC was 102 mm above the table, the output beam before the L1 lens was the same height, and the beam height just before JAC_M3 was also 102mm. There is not a large distance between the JAC and JAC_M3 steering mirror so it is hard to get a good measurement of any small pitch in the beam. Pictures for this alog are coming.

Following alog 89115, we found that the old batch crystal from that alog (S/N10252003) had a big chip at one corner. It is pretty bad we don't want to use that.

Betsy found another old batch (S/N10252007, "inspected 12/21/11" and UF tag dated 4/21/09), so we A-B-ed that one with the spare new batch (S/N B1913108).

The beam path was made as level as possible at 3" height using a beam leveling tool (a black metal thing with a tiny aperture at each inch of height).

We put the crystal on a platform that is roughly 2" 29/32 (which is about 2.4mm lower than 3"). The crystal is 4x4x40mm so that's about the right height.

We spent some time to make YAW alignment as good as we can for each of the crystals.

We scanned the beam in PIT from top to bottom (or bottom to top), each extreme is where the beam is almost clipped (but not actually clipped) by the top or the bottom face of the crystal.

Look at the attached, the new batch (left column) clearly shows multiple beams even though the focus is not as sharp as the old batch photos. As we misalign in PIT, the dark place moves relative to the main beam and the contrast changes too, but multiple ghost never went away. At the extrema (very close to the top or bottom edge) it looked as if the beam is better but I'm not sure it actually was.

The old batch (right) didn't show such a behavior. The beam shows something like a diffraction pattern but no separate ghost beams. Everything moved with the main beam.  Not sure if the diffraction pattern came from the aluminum surface or EOM, but clearly this is MUCH better than the new batch.

Note, due to the apparatus (the steering mirror is 20" upstream of the EOM), we haven't searched in a huge PIT angle space, it's actually roughly +-4mrad or so, the angle is not negligible but it's more parallel displacement scan than an angle scan.

Also note, when the crystal was put in place it seems that there's some vertical deflection which was different for the old and the new. On the top two pictures, there's no change in the input alignment into the crystal. 

Based on this observation, I'd say using the old batch makes sense. LHO people (Jennie, Rahul, Betsy and myself) had a brief conversation with Masayuki and MichaelL and we all agreed that that's the way to go.

It took much longer than expected but we set up the beam path for the RTP test in the OSB optics lab.

Since more power makes it easier to see the ghost beams, I removed the beam dump that used to receive most of the red power (~530mW) and directed the beam to the front of the table (red path in the attached). I stole the steering mirror that used to be used for the low power P-pol path (circled in red). The low power p-pol path is now simply blocked. No other change was made to low power S-pol path (orange) as well as green path (green), but the beams are blocked by beam dumps. If you want to use these, simply unblock.

The beam radius will be 300~400 um or so at the location we plan to put the RTP (represented by a green rectangle in the second attachment). Elenna will post the plot of the beam size measurement.

The third picture shows the containers for different RTP. Left is the one for the crystal in HAM1. The middle seems to be from the same batch. Right looks different, on the bottom of the container there's a label saying "I/O something something 2017" so this is likely the old one.

We didn't have time to actually test the crystals, wait for tomorrow's udpate.

Jennie W, Jason O, Keita K.

As reported in this alog (#89073) from Masayuki and Keita, after we turned the power in HAM1 up to 1W we found a series of vertically spread ghost beams aroubnd the main beam after the EOM and before JM3.

These could not be removed by translating, yawing or pitching the EOM position relative to the beam. It was decided in a larger meeting with EOM design personnel that we would first check if the crystal was cracked or damaged anywhere in case this is the cause.

First photo shows the EOM from above, using a green torch to illuminate the beam path. I can't see any scatter from defects or cracks in the crystal.

Second photo shows possibly a chip at the corner, but this should not affect the beam as its right at the edge.

Third and fourth show side view with illumination from the top at an angle.

In summary we did not see any 'smoking gun' to cause these ghost beams.

Summary of investigation into the vertically split beam from the EOM

• First, we confirmed that the vertical beam splitting observed yesterday originates from the EOM itself. To check the possibility of multiple reflections from lenses, we inspected the back-reflection port of the JAC output mirror. Two reflected beams were observed, most likely originating from the planar and curved surfaces of the lens, and they were mainly separated in yaw. Since the space between the EOM and the lens was blocked during this test, these reflections were conclusively identified as lens reflections. No vertically split beams were observed from this source.

• A knife-edge–like test was performed by slowly lowering a metal ruler from the top at both the EOM input and output. At the EOM input, the entire beam disappeared simultaneously, whereas at the output the beam disappeared gradually from the top. This behavior confirmed that the vertical splitting is generated inside the EOM.

• To accurately determine the beam positions at the EOM input and output, beam positions were measured from photographs. Taking refraction and geometry into account, it was found that the beam is slightly displaced in the horizontal direction. Details of this analysis will be documented in Keita’s alog.

• Based on this result, the EOM was rotated in yaw. Dog clamps were placed at the ±y projection points of the EOM input and output, in contact with the base plate. One 0.5-mm shim was inserted between the base plate and each dog clamp to rotate the EOM counterclockwise. However, the beam pattern did not change. Additional shims were tested, but no significant change was observed. The EOM was fixed with one 0.5-mm shim at each position.

• Next, pitch adjustments were explored. The original shim configuration (two shims on the +y side and one on the −y side) was changed by moving shims to the +x side (one location at center) and the −x side (two locations, upper and lower). Each location initially had two shims, and by adding or removing shims, it was observed that the vertical positions of the split beams changed. When the +x (downstream) side was raised, the vertically split beams appeared in the upper part of the beam profile (approximately 5–7 beams; Keita will upload photos). Conversely, when shims were added to raise the −x side, the split beams moved toward the lower part of the beam. With the downstream side lowered by approximately 0.25 mm, about two beams were observed in the upper part and one in the lower part.

• 1W input power shows 6 or more beams, but 2-3 beams can be observed even with 100mW.

• With the last configuration, we proceeded the IMC scan measurement after alignment. The 2nd order mode peak was the same level as we observed when we sim up the EOM first time.

• In summary, the EOM shows highly questionable and nontrivial behavior. Possible causes include diffraction due to crystal defects or multiple reflections at the AR-coated surfaces. However, identifying the exact mechanism is challenging at this stage.

Following on from this log (alog #89046), we have already checked that the MC mirrors are restored to their previous positions from before the power cut in December. We know the seismic state now should be as close as we can manage to this time 2025-12-03 11:28:44 UTC when the mode cleaner was locked at 2W input power and before any HEPIs were locked for the vent.:

Summary of seismic state now:

HAM ISI locked. HAM 2, 3, 4, 5, 6 ISI isolated.

HAM1,2 and  BSC2 HEPI locked. HAM 3,4,5,6 HEPI isolated - ie. as per nominal operation.

I trended the IM osems and the MC2 and IM4 QPDs in HAM2 while the mode cleaner was locked for mode scans yesterday (reference time is 2026-02-05 18:44:36 UTC).

It seem as though the MC2 and IM4 trans powers we have are lower now, but also the IM mirrors have changed.

As Sheila did yesterday I will try and summarise these changes in a table and compare whether this makes sense with the greater HAM1 loss we have because of the JAC (~40 %).

Just posting an updated version of Sheila's table to compare this new time (3rd December).

So after this Sheila and I are going to try turning on the IMC ASC and working out if we can tune the alignment onto IM4-TRANS using the IMs.

While Keita will report the detail about the heater wiring trouble shooting, here is the quick report for the JAC heater functionality.
The attatched plot shows the two thermistor signals (top/bottom) and the heater input (middle). The temperature is reasonably changing with the heater driver input.