This afternoon I went into the LVEA (HAM2 clean room area) and canned & stored the old unit of the ISS PD - s/n S1202971. This unit was uninstalled on May 13th, 2026 and replaced with a new unit (S1202965) - see LHO alog 90237 for details.

I have moved this old unit (s/n S1202971) to the vacuum prep area of the optics lab (OSB) and stored it in the blue cabinet. 

Please see pictures attached below for reference.

Good news is that we're done with the alignment of the ISS path. Pictures and details are to follow.

Then I reinstalled the last IFO REFL baffle right in front of the HAM2-HAM1 septum window. (The baffle was removed after marking the exact position using three temporary dog clamps on the ISI on day 1 because it was in the way, I was supposed to record that in alog 90158 but forgot. I'm absolutely sure that the position of the baffle was restored within 0.1mm of the original position.)

Bad news is the IFO REFL was clipped on that baffle. 00 mode flash isn't clipped that much but horizontal modes certainly are. That was not THAT surprising because the IMC alignment was/is not great (see my comment 90224). This looks to me that the uncontrolled degree of freedom of the IMC is wrong regardless of the reason why a huge alignment change had to be made to center the MC2 TRANS QPD.

Good news is the ISS path alignment is not impacted by that, at least greatly, because we made sure that the beam hit the right location of IM4 TRANS as well as ISS array QPD before we did anything in the ISS path. Note that the baffle clipping the beam is not in the ISS path.

In other words,

• the beam position on MC3 might have been poor but we used IM3 and IM2 to steer the beam INTO the ISS path such that the alignment there is reasonably close to in-vac alignment,
• when the beam coming out of MC3 is brought back to the good position/angle, we can bring the beam back onto IM4 trans using IM3 and IM2,
• if the beam is not found on the ISS QPD at that point, we can scan IM3 (and IM2 if necessary) further to find the beam,
• and use the first pico for the ISS array path to keep the beam on the array QPD while slowly bringing IM3 (and IM2 if that's touched) back to the good angle.

However, since we don't want to revisit HAM2 once we close it, I'd like to understand what's going on for the IMC/IFO alignment. 

This is for FAMIS #39758.
Laser Status:
    NPRO output power is 1.841W
    AMP1 output power is 70.55W
    AMP2 output power is 138.4W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 27 days, 19 hr 55 minutes
    Reflected power = 27.29W
    Transmitted power = 103.6W
    PowerSum = 130.9W

FSS:
    It has been locked for 0 days 2 hr and 22 min
    TPD[V] = 0.484V

ISS:
    The diffracted power is around 4.3%
    Last saturation event was 0 days 21 hours and 25 minutes ago
Possible Issues:
    PMC reflected power is high

F. Clara, J. Kissel, S. Koehlenbeck, J. Oberling, M. Pirello
D2400110

Today we picked up where we left off with the install of SPI into H1. 
Where we last left things, we'd installed a new SPI pick-off of ALS/SQZ beam in Apr 2025 (see ECR E2400083 and results in LHO aLOGs 83989, 83996, 83978). Back then, we had ended the work with the input to the fiber collimator within the PSL dumped.

With Jason and Sina in the PSL, we confirmed that the SPI path was still blocked. 

However, we also realized/remembered/confirmed that the entire ALS/SQZ/SPI path had 25% less power -- We've been running the PSL at lower power allocation downstream of the PMC since Sep 2025 to prevent issues we'd found with the currently installed EOM after a power outage triggered a dust monitor to spew out dust into the PSL (see that saga in e.g. LHO:87109 LHO:86966). They found the power at the SPI pick-off was 140 [mW] instead of the 188 [mW] we left in Apr 2025 (see LHO:83996).

(Using labels in the half-up-to-date drawing D1300348)
Jason and Sina rotated ALS-HWP2 upstream of ALSPBS01 to restore the nominal 50 [mW] into the ALS/SQZ pick-off and ~200 [mW] (190 [mW] measured). This means there's ~50 [mW] less out to ALS / ISCT1 than before today.

Then with the SPI pickoff still dumped, we installed a 30 [m] patch cord*** from the PSL optical table, out the mouse hole between the +X wall of the PSL enclosure and HAM1, then up running along the upper racks to waterfall down at SUS-H2. The fiber sits within the typical orange tubing. Per D2400110, this is SPI_PSL_001, and it's labeled as such on both ends.

After install, I connected the SUS-R2 end to a Thorlabs S121C power meter with S120-APC2 fiber adapter. 
With this installed (making the system laser safe at SUS-R2 end), Jason/Sina unblocked the SPI pickoff input. 
With 190 [mW] in, we measure 187 [mW] out on the other end. 98% transmission, pretty excellent. Almost unbelievably excellent but we weren't rigorous with our uncertainty and systematics.

Happy with this result, we then blocked the SPI path again, and re-capped the SUS-R2 end for final dressing in the racks.
We'll unblock again when we're read to connect it to the Laser Prep Chassis.

***Patch cord details:
Manufacturer DIAMOND
DIAMOND Part Number: ENS/1094388
Customer Part Number: 9711228
Patchcord SM L=30 PM
2xFC 2mm APC (i.e. 2mm narrow key FC/APC on both ends)
tran 6,6/125/245 PAND 980nm



 

J. Kissel, R. Short, J. Oberling

This is the first installment of aLOGs documenting the setup of a new stand-alone 1064 nm NPRO laser system whose current "end game" intent is to provide ~100 [mW] of fiber-coupled p-pol light to the SPI laser prep chassis.

Step 1: Gathering materials, find what optics / mounts we had vs. what would be need, and physically layout the plan.

Jason lets Ryan and I know that there are three NPROs in the optics lab, two of which are PSL spares that cannot be used. 
The remaining laser is S/N 1661, the laser used in the PSL during O3 which is *functional* but was briefly installed during O4 circa Fall/Winter 2024 then removed from use in the PSL because of reported glitching / incompatibility with the frequency stabilization servo (FSS) issues -- see the bottom of LHO:81391 for a nice summary, and LHO:81409 for record of its removal.

Inspired by the setup at Stanford Sina shared with us, we're looking to build up the following system to accomplish the goal:
    - NPRO (presumed to be elliptically polarized with Is / Ip = 5:1)
    - QWP (to linearize the polarization)
    - HWP1 (to rotate the polarization into horizontal)
    - FI (accepts horizontal linear polarization, to ensure back-reflections from down-stream components don't seed the NPRO causing glitches/mode hopes/frequency noise)
    - HWP2 (to rotate the FI output polarization into the desired amount of vertical polarization -- aka the desired amount p-polarization)
    - PBS (to filter out and dump the unneeded horizontal / s-pol light, and transmit the desired power of p-pol)
    - SM1 (one of two steering mirrors to align the beam into the fiber collimator)
    - L1 (the single-lens mode-matching solution to convert the NPRO beam into what the fiber collimator needs)
    - SM2 (two of two steering mirrors for alignment into the fiber collimator)
    - 50:50 PWR BS (45 [deg] AOI, optimized for p-pol; to provide a pick-off port for live power measurement)
    - Fiber Collimator

Ryan started with a 24" by 12" breadboard that was lying around in the optics lab. He build up a makeshift stand from three posts and dogs in the lower left corner such that the S/N 1661 NPRO projects the beam at 4" height. The 0.5" thick breadboard has a 1 inch hole pattern offset by 0.5" from the edges. I'll refer to this grid as having axes "m" and "n" where the m-axis are the "row" holes running from 0 to 23, and the "column" n-axis holes run from 0 to 11. I chose (m,n) breadboard coordinates so as to not confuse them with traditional beam profile coordinates of (z [propagation distance], x (transverse horizontal), y (transverse vertical)). 

Thus, the NPRO being in the "lower left" means it projects the beam along the m = 3 row, and the front face of the NPRO is sitting at n = 8. We'll call this beam position z = 0.

We then proceeded to gather as much as we could of optical components from the optics lab drawers, and ended up with this pictured preliminary version of the setup.

Step 2. Power up the NPRO.
Here's were we ran into our first snag. Normally, NPROs are paired/tuned with specific controller boxes. However, when Ryan turned on the S/N 1661 laser with the S/N 1661 control box, the crystal temperature readback reported the temperature was quickly, linearly rising well beyond the desired temperature of 24.7 [deg C]. At ~42 [deg C], (but still below the internal automatic watchdog threshold of 50 [deg C]), Ryan knew something was wrong and turned it all off. He repeated the turn on just in case, and it did the same.

After conversing with Jason, we figure it's good enough to run with one of the other controllers for now, and in the mean time figure out how what's wrong and repair the S/N 1661 controller.

So, we're running with the S/N 7974, and things seem fine. 
    Laser Diode Temp Setup:
        Diode 1 33.7 [deg C]
        Diode 2: 33.1 [deg C]
        Laser diode injection current readback 2.08 [A] (for both diodes)
    Crystal Temp setting is 24.7 [deg C]

We measured the output power*** with no optical elements at all as 1.820 +/- 0.005 W (not noisey, but a slow drift around).
Good enough! Onward and upward!

*** Power measured by ThorLabs power meter
	Model S302C
	SN 111149
	Sensing factor of 316.25 [mV/W]
	(last calibrated Feb 3 2012).

We replaced the failed +/-12V Kepco supplies in VDD-C6 U34 which power the PSL dome cameras
U34_LHS: +12V supply S1201947 removed due to failed fan, replaced with upgraded supply S1202017
U34_RHS: -12V supply S1201992 removed due to failed fan, replaced with upgraded supply S1300289

F. Clara, M. Pirello

This is for FAMIS #39750.

Laser Status:
    NPRO output power is 1.841W
    AMP1 output power is 70.43W
    AMP2 output power is 139.4W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 0 days, 21 hr 23 minutes
    Reflected power = 27.19W
    Transmitted power = 103.9W
    PowerSum = 131.1W

FSS:
    It has been locked for 0 days 18 hr and 54 min
    TPD[V] = 0.4791V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 0 days 0 hours and 0 minutes ago

Possible Issues:
    PMC reflected power is high

Jennie W, Jason O, Masayuki N, Keita K, Jim W,

Summary: To check the function of the new EOM in chamber we made a measurement of the modulation indexes by locking the IMC and aligning the beam to AS_C with SR2. We couldn't get a good measurement of the sideband heights but this is probably due to the RF power being down by a factor of 100 from nominal. Will check with EE/Daniel on Monday.

First order of business was checking for stray beams at 100mW input power. Jason moved the BD we already placed for JM2 as we had moced this mirror position yesterday. We also put a new beam dump right after unused JAC port (output side there is tranismission through the curced mirror).

After this we turned the power up to 1W.

Lastly we found a stray beam exiting the table in the -Y direction, this was traced to the JAC REFL path. The REFL beam was hitting the side of a beam dump (near the -X side/PSL of the table) which is meant to cath a beam reflecting off the SEPTUM plate. This beam reflected off the beam dump causing a stray beam. We re-aligned the REFL path so the beam does not do this and instead bounces off the three REFL path steering mirrors and heads into a previously placed beam dump for this purpose on the -Y side of the table. This path will have to be re-aligned in order for the beam to get onto the IOT1 table.

No further stray beams were found so Jason de-energised the waveplate.

Photos to come.

After realising that the beam did not reach the AS_C,A and B QPDs yet we came to the control room to re-align to the output port. This is with the ITMY, PRM and SRM mirrors mis-aligned to allow us to mode scan the OMC in the 'single bounce' IFO configuration.

After Jim re-isolated HAM4,5 and 6 and BSC2 for us we were able to use SR2 to bring back the alignment to AS_C and then turn on the DC centering loops for AS_A and AS_B.

The OMC ASC did not work at first as the suspensions were railed. I cleared the ASC history, this did not help. We cleared the locking filter banks for OM1-3 and this unrailed the outputs and allowed us to turn on the OMC ASC.

We took an OMC scan at 1W input power, shown here. Roughly calibrated into MHz with the known FSR.

We cannot identify the 45MHz or 9MHz peaks, but after checking we realied that these RF driver powers were lowered 15 days ago. See image.

We will come back to this Monday.

Jason put back the rotation stage, locked it out and closed the light pipe.

[Jason, Jennie, Masayuki]

• We swapped and installed three new lenses—IO_MB_L1 (Rc = 250 mm), L2 (Rc = −150 mm), and L3 (Rc = 750 mm)—replacing the existing lenses with the same notation. The former two are 1″ diameter lenses, and the latter is a 2″ lens. All lenses were mounted in Newport lens mounts, with posts and post holders installed on Thorlabs BA2 bases.
• Set the power stage to 2 W with 100 W of PMC output. The power along the path where the new lenses were installed was then reduced as much as possible using IO_MB_HWP1.
• Before swapping the lenses, two irises were placed to provide alignment references. The final reference is the set of irises in HAM1; however, the in-PSL iris allowed alignment without external communication and made the process easier. These irises were placed downstream of the existing IO_MB_L2.
• After removing the old lenses, the new IO_MB_L1 was installed such that the distance from IO_MB_M2 to L1 was 0.22 m. The beam was centered on the iris by adjusting the lens position. Subsequently, L2 was installed 6 cm downstream of L1 using the same procedure.
• After alignment, we verified that the beam path around the beam adjustment stage was not clipped by any optics. All beam positions appeared nearly identical to those before the work began.
• The third lens was then installed between IO_MB_M4 and M5 (the bottom mirror of the periscope) with a separation of 9 cm. To ensure the lens was centered on the beam, we centered the iris on the beam reflected from IO_AB_BS1 before and after installation. To observe the transmitted beam from M4, higher power was required; therefore, IO_MB_HWP1 was rotated to increase the EOM output power to 4–5 W.
• The first and second pictures document the original lens positions, in case recovery of the mode matching directly to the IMC is required.
• After completing the work, all power levels were restored. During this period, the new lenses were inspected with an IR viewer to confirm the absence of unusual stray light or unintended beam exposure.
• Remaining work: alignment of the photodiodes monitoring the EOM output and PSL output. Since the overall beam profile has changed, it may be necessary to reposition the lenses to properly focus the beam onto the PDs.
• During the work we found the beam is almost clipped on the beam dump capturing the mispolarized beam difracted by the EOM. So, we move the beam dump. The third picture shows this beam dump.

TITLE: 12/26 Day Shift: 1530-0030 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 25mph Gusts, 16mph 3min avg
    Primary useism: 0.05 μm/s
    Secondary useism: 0.90 μm/s 
QUICK SUMMARY:
Cameras:
Everything looks fine currently.  
Lights were left on in the Woodshop & OSB 163, ifsomeone is heading to site. 


SEI: Looks as I'd expect it to look. HAM7 is red because it's had people in and out of it since before the break. I imagine leaving that watchdog tripped is fine.
SUS: Seems to be looking reasonable as well considering the OPO and Jack work that was being done before break.

PSL Status: 

Laser Status:
    NPRO output power is 1.84W
    AMP1 output power is 70.51W
    AMP2 output power is 139.4W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 16 days, 17 hr 48 minutes
    Reflected power = 25.41W
    Transmitted power = 106.2W
    PowerSum = 131.6W

FSS:
    It has been locked for 2 days 23 hr and 15 min
    TPD[V] = 0.5254V

ISS:
    The diffracted power is around 3.7%
    Last saturation event was 2 days 22 hours and 25 minutes ago

Possible Issues:
        PMC reflected power is high
 

VEA Temps:

LVEA looks good for the last day.

The HAM Shaq looks good.

Arm VEAs

Betsy, Rahul

We found that SUS JM1 had a faulty quadrupus cable, which we replaced it today. Next, I took OLC for both JM1 and JM3 in HAM1 chamber. I applied the offsets, gains and then centered the BOSEMs - and they look good. Next, I will start checking the health of the electronics chain and the suspension itself (i.e. by taking the transfer function measurements).

The offsets and gain for JM1 is recorded in this screenshot - accepted in the SDF (safe).

The offsets and gain for JM3 is recorded in this screenshot - accepted in the SDF (safe).

For the upcoming ISS array swap, we plan to bypass the IMC, which is known to be a pain, but we need a stable beam for the array alignment.

Once the corner volume is vent, we use the QPD on the old array and IMC-IM4_TRANS as the initial reference for bypassing the IMC. Once IMC is bypassed, we will center REFL WFS BEFORE removing the old array and record the RM1/RM2 PIT and YAW. This way, even if we somehow suspect e.g. the pointing of the beam going to the IM4 moved after removing the old array, we can still restore the pointing by looking at the REFL WFSs in addition to IM4.

We measured the beam positions on these QPDs today even though we'll repeat this later.

IFO configuration:

• IMC was locked with 2W.
• REFL beam diverter was closed so no light comes out. (POP bdv was also closed just because.) 
• The cover on the REFL septum window was removed.
• PRM, all IMs and RMs are aligned. (Watchdog of RMs were reset.) ITMs are misaligned.

Arrow ("->") means before and after the REFL centering servo (DC1 and DC2) was turned ON:

Septum cover is left OFF but the PSL light pipe was closed after this. REFL centering was turned off but I didn't bother to offload the ASC output to RM sliders.

REFL WFS nubmers as of now are not super meaningful as we'll still have to lock HAM2 down, which potentially change the relative alignment between HAM1 and HAM2. (But it's good that the beam is still hitting REFL WFSs after HAM1 was locked down even though Jim noted that the ISI position of HAM1 is not good. )

I'll open the light pipe tomorrow and quickly repeat the measurement after Jim locks down HAM2 HEPI.

Betsy, Fil, Rahul

Today we kicked started the installation activities in HAM1 chamber for the Jitter Attenuation Cavity (JAC). Given below are the things we placed on the ISI table - they are all roughly positioned and dog clamped. 

1. Tip Tilt JM1 - now connected to electronics chain, having some issues with the bosem adc counts etc, will continue looking into it.

2. Tip Tilt JM3 - now connected to the electronics chain, bosem centered, will proceed for health checks once the chassis and electronics chain looks okay.

3. The two periscopes for the JAC, Type 121 and 132 - assembly report posted by Jennie - 88574.

4. Some optics on Siskiyou mount were also added to the table.

I am attaching pictures which shows the above mentioned things added to the table - and for comparison a picture showing before any addition was (here) made.

Fil also performed group loop checks on JM1 and JM3 and did not find any issues with them.

[Jason, Betsy, Masayuki]

Two arises are installed into HAM1 chamber. They will be used as the alignment reference for new PSL modematching lens installation.

• Assembled a Thorlabs ID12 iris mounted on a 0.5-inch post with a post holder and BA2 base.
• The assembled iris was temporarily placed inside the chamber and secured with a dog clamp.
• Transitioned to laser hazard.
• Performed rough alignment using a sensor card, followed by fine alignment with an IR viewer, to center the beam through the iris.
• The beam path is offset by ~+5 mm in the +y direction from the ISI design center; this is not considered a significant issue.
• The iris location is marked with a blue circle in the attached figure.

Next step: move to the PSL and install the new mode-matching lens, likely tomorrow. This will break the IMC mode matching; IMC relocking will not be possible until the JAC installation is completed.

Closes FAMIS 27622, last checked in alog 88380

Laser Status:
    NPRO output power is 1.86W
    AMP1 output power is 70.35W
    AMP2 output power is 139.5W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 6 days, 14 hr 45 minutes
    Reflected power = 24.87W
    Transmitted power = 105.8W
    PowerSum = 130.7W

FSS:
    It has been locked for 0 days 16 hr and 45 min
    TPD[V] = 0.5086V

ISS:
    The diffracted power is around 4.5%
    Last saturation event was 0 days 18 hours and 22 minutes ago

Possible Issues:
    PMC reflected power is high

[Joan-Rene Merou, Alicia Calafat, Sheila Dwyer, Anamaria Effler, Robert Schofield]

This is a continuation of the work performed to mitigate the set of near-30 Hz and near-100 Hz combs as described is Detchar issue 340 and lho-mallorcan-fellowship/-/issues/3. As well as the work in alogs 88089, 87889 and 87414.

In this search, we have been moving around two magnetometers provided to us by Robert. Given our previous analyses, we thought the possible source of the combs would be around either the electronics room or the LVEA close to input optics. We have moved around these two magnetometers to have a total of more than 70 positions. In each position, we left the magnetometers alone and still for at least 2 minutes, enough to produce ASDs using 60 seconds of data and recording the Z direction (parallel to the cylinder). For each one of the positions, we recorded the data shown in the following plot

  

That is, we compute the ASD using 60s FT and check the amplitude of the ASD at the frequency of the first harmonic of the largest of the near-30 Hz combs, the fundamental at 29.9695 Hz. Then, we compute the median of the +- 5 surrounding Hz and save the ASD value at 29.9695 Hz "peak amplitude" and the ratio of the peak against the median to have a sort of "SNR" or "Peak to Noise ratio".

Note that we also check the permanent magnetometer channels. However, in order to compare them to the rest, we multiplied the ASD of the magnetometers that Robert gave us times a hundred so that all of them had units of Tesla.

After saving the data for all the positions, we have produced the following two plots. The first one shows the peak to noise ratio of all positions we have checked around the LVEA and the electronics room:

  

Where the X and Y axis are simply the image pixels. The color scale indicates the peak to noise ratio of the magnetometer in each position. The background LVEA has been taken from LIGO-D1002704.
Note that some points slightly overlap with other ones, this is because in some cases we have check different directions or positions in the same rack.

It can be seen how from this SNR plot the source of the comb appears to be around the PSL/ISC Racks. Things become more clear if we also look at the peak amplitude (not ratio) as shown in the following figure:

  

Note that in this figure, the color scale is logarithmic. It can be seen how, looking at the peak amplitudes, there is one particular position in the H1-PSL-R2 rack whose amplitude is around 2 orders of magnitude larger than the other positions. Note that this position also had the largest peak to noise ratio. 

This position, that we have tagged as "Coil", is putting the magnetometer into a coil of white cables behind the H1-PSL-R2 rack, as shown in this image:

  

The reason that led us to put the magnetometer there is that we also found the peak amplitude to be around 1 order of magnitude larger than on any other magnetometer on top of one set of white cables that go from inside the room towards the rack and up towards we are not sure where:

  

This image shows the magnetometer on top of the cables on the ground behind the H1-PSL-R2 rack, the white ones on the top of the image appear to show the peak at its highest. It could be that the peak is louder in the coil because there being so many cables in a coil distribution will generate a stronger magnetic field.

This is the actual status of the hunt. These white cables might indicate that the source of these combs is the different interlocking system in L1 and H1, which has a chassis in the H1-PSL-R2 rack. However, we still need to track down exactly these white cables and try turning things on and off based on what we find in order to see if the combs dissapear.

Closes FAMIS 27538, last checked in alog 87902

Laser Status:
    NPRO output power is 1.85W
    AMP1 output power is 70.63W
    AMP2 output power is 139.9W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 9 days, 23 hr 29 minutes
    Reflected power = 24.68W
    Transmitted power = 106.3W
    PowerSum = 131.0W

FSS:
    It has been locked for 0 days 8 hr and 51 min
    TPD[V] = 0.5364V

ISS:
    The diffracted power is around 4.2%
    Last saturation event was 0 days 8 hours and 53 minutes ago

Possible Issues:
    PMC reflected power is high

Related: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=87729

We disconnected everything from the ISS array installation spare unit S1202965 and stored it in the ISS array cabinet in the vac prep area next to the OSB optics lab. See the first 8 pictures.

The  incomplete spare ISS array assy originally removed from LLO HAM2 (S1202966) was moved to a shelf under the work table right next to the clean loom in the optics lab (see the 9th picture). Note that one PD was pulled from that and was transplanted to our installation spare S1202965.

Metadata for both 2965 and 2966 were updated.

ISS second array parts inventory https://dcc.ligo.org/E2500191 is being updated.

Summary:

We aligned everything such that none of 8 PDs was excellent but all were OK (we were also able to set up such that 4 pds were excellent but a few were terrible but decided not to take that), we were preparing for putting the array in storage until the installation, only to find that something is wrong with the design of the asymmetric QPD clamp D1300963-V2. It's unusable as is.

QPD clamp doesn't constrain the position of the QPD laterally, and there's a gross mismatch between the position of properly aligned QPD and that of the center hole of the QPD clamp. Because of that, when QPD is properly positioned, one of the QPD pins will touch the QPD clamp and be grounded unless the QPD connector is fixed such a way to pull the QPD pins sideways. Fortunately but sadly, the old non-tilt QPD clamp D1300963-V1 works better, so we'll use that.

Another minor issue, is that there seems to be a confusion as to the direction of the QPD tilt in terms of the word "pitch" and "yaw". The way the QPD is tilted in D1101059-v5 (this is how things are set up in the lab as of now) doesn't seem to follow the design intent of ECR E1400231 though it follows the word of it. After confirming that this is the case with systems, we'll change the QPD tilt direction (or not). This means that we're not ready to put everything in storage quite yet.  

None of these affect the PD array alignment we've done, this is just a problem of the QPD.

Pin grounding issue due to the QPD clamp design.

I loosened the screws for the QPD connector clamps (circled in blue in the first attachment) and the output of the QPD preamp got crazy with super large 60Hz noise and large DC SUM even though there was no laser light.

I disconnected the QPD connector, removed the connector clamps too, and found that one pin of the QPD was short circuited to the ground via the QPD clamp (not to be confused with the QPC connector clamps, see 2nd attachment).

Turns out, the offending pin was isolated during our adjustments all the time because the QPD connector clamps were putting enough lateral pressure as well as down such that the pins were slightly bent from the offending side. I was able to reattach the connector, push it laterally while tightening the clamp screws, and confirm that the QPD functioned fine. But this is not really where we wanted to be.

I rotated the QPD clamp 180 degrees (which turns out to make more sense judging from the drawings in the first attachment), which moved the QPD. Since the beam radius is about 0.2mm, if the QPD moves by 0.2mm it's not useful as a reference of the in-lab beam position. I turned the laser on, repositioned the QPD back to where it should be, but the pin on the opposite side started touching. (Sorry no picture.)

I put the old non-tilt version clamp and it was much, much better (attachment 3). It's annoying because the screw holes don't have an angled recess. The screw head is tilted relative to the mating surface on the clamp, contacting at a single point, and tightening/loosening the screw tend to move the QPD. But it's possible to carefully tighten one screw a bit, then the other one a bit, repeat that dozen times or so until nothing moves even when pushed firmly by finger. After that, you can still move the QPD by tiny amounts by tapping the QPD assy by bigger Allen key. Then tighten again.

What's going on here?

In the 4th attachment, you can see that the "center" hole of the QPD clamp is offset by 0.55" (1.4mm) in the direction orthogonal to A-A, and about 0.07" (even though this number is not specified anywhere in the drawing) or 1.8mm in A-A direction. So the total lateral offset is sqrt(1.4^2+1.8^2)~2.3mm. OTOH, the QPD assy is only 0.5" thick, so the lateral shift arising from the 1.41deg tilt at the back of the QPD assy is just 1.41/180*pi*0.5=0.0123" or 0.3mm.

Given that the beam position relative to the array structure is determined by the array itself and not by how the QPD is mounted, 2.3mm lateral shift is impossibly large, something must be wrong in the design. The 5th attachment is a visual aid for you.

Anyway, we'll use the old clamp, it's not worth designing and manufacturing new ones at this point.

QPD tilt direction.

If you go back to the first attachment, the QPD is tilted in a direction indicated by a red "tilt" arrow in the lab as we just followed the drawing.

The ECR E1400231 says "We have to tilt the QPD 1 deg in tip (pitch) and 1 deg in tilt (yaw)" and it sounds as if it colloborates with the drawing.

However, I suspect that "pitch" and "yaw" in the above sentence might have been misused. In the right figure of the 6th attachment (screeshot of ECR unedited), it seems that the QPD reflection hits the elevator (the red 45 degree thing in the figure) at around 6 O'clock position around the eliptic exit hole, which means that the QPD is tilted in its optical PIT. If it's really tilted 1 degree in optical PIT and 1 degree in optical YAW, the reflection will hit something like 7:30 position instead of 6:00.

That makes sense as the design intent of the ECR is to make sure that the QPD reflection will not go back into the exit hole. The 7th attachment is a side view I made, red lines represent the IR beams, yellow lines the internal hole(s) in the elevator, and green lines the aperture of the two eliptical exit holes. Nothing is to scale, but hopefully you agree that, in order to steer the QPD reflection outside of the exit hole aperture, PIT UP requires the largest tilt and PIT DOWN requires the least tilt. We have a fixed tilt of QPD, so it's best to PIT DOWN, that's what I read from the ECR. If you don't know which angle is bigger or smaller, see attachment 8.

Anyway, I'll ask Callum if my interpretation is correct, and will act accordingly.