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.

Summary:

As "the last test before installation" I compared the dark noise level for all 8 PDs. Unfortunately the first PD in our own convention (top left when seen from the back, see this picture for PD number convention in the lab though it's probably different in the chamber) showed much larger noise level than all the others. See the first attachment left. (In this plot, PD 5 and 6 look noisier too, but this was found to be the preamp channels themselves.)

I swapped the entire PD assembly module (D1300130) for the noisy PD with the unit pulled from an incomplete spare ISS array assy originally removed from LLO HAM2 (S1202966) and measured the noise again. I also connected PD5 and 6 to the preamp channels for PD7 and 8 to remeasure the noise. Now no PD shows extra noise, see the right panel of the first attachment.

Note: Even though the plot title says "dark noise", the measurement is limited by the preamp noise and SR785 input noise (black trace). But this at least tells us that no PD is extra noisy. FYI the shot noise level for 10mA current is ~5.7e-11A/sqrtHz.

I checked the grounding of new PD1 unit (after temporarily disconnecting the SMP cables) and no shortcircuit was found.

I roughly aligned the newly installed PD1 but haven't done finer adjustment yet.

After PD1 position is finely adjusted, we'll have to repeat the jitter coupling measurement. 

Measurement Details:

All 8PDs were originally connected to two obsolete 4-channel transimpedance amplifier chassis (D1300639-v1) because they were available while spares for the latest ones (D1600193) weren't found. In this alog the channels of the first unit (S1301390) CH1-CH4 and those of the second unit (S1301386) CH5-CH8.

The output of the transimpedance stage (TP2 in the 2nd screen shot) was connected to SR785, 2 channels at a time. (Just for comparison, the 3rd screen shot is the transimpedance stage for the latest one (D1600193) which is pretty similar to the obsolete one except for the opamp (0.9nV/sqrtHz AD797 in the obsolete one VS 2.2nV/sqrtHz@1k TLE2027).)   I didn't use the whitening output as some of the channels of D1300639 weren't working (the output was railing).

Before swapping PD1, to make absolutely sure that the problem is PD not the preamp/SR785, I swapped the SMP-SMA cables for PD1 with those for PD2 at the back of the PD modules (i.e. PD1 goes to CH2 and PD2 to CH1) and the noise followed the PD.

The 4th attachment shows the noise level of the measurement. Red and blue traces were obtained by disconnecting two SMP-SMC cables from the preamp of CH1 and CH5.

CH1, 2, 3, 4, 7 and 8 were quite similar to each other, and CH6 was similar to CH5. In the end I had to swap cables for PD5 and PD6 to use CH7 and CH8.

"Preamp noise model" comprises the Johnson noise of 1.62k transimpedance, input voltage noise and input current noise of AD797 combined. I used typical 1kHz numbers here for AD797. The zero and the pole in the first stage are much higher than the measurement band here. Johnson noise of 10 Ohm (R7 in the second screenshot) in series with the PD won't matter in this measurement as well as when the PD is connected assuming that PD is a current source.

Other details:

The preamps are clearly labeled as D1300639-V2 (5th attachment), but the e-traveler for these boards (S1301390 and S1301386) say they're V1, and the actual board pattern (e.g. the first channel TIA opamp is U4, the transimpedance itself if R2 and the output of TIA opamp is connected to TP2 via R17, see the 7th screen shot) agrees with V1 (2nd screen shot) but not with V2 (6th screenshot).

I put "This is V1 not V2" label on both of the board. I also put "CH1 and CH2 noisy" label on S1301386.

Closes FAMIS 27399. Last checked in alog 87406

Laser Status:
    NPRO output power is 1.856W
    AMP1 output power is 70.51W
    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 26 days, 4 hr 48 minutes
    Reflected power = 24.74W
    Transmitted power = 106.7W
    PowerSum = 131.4W

FSS:
    It has been locked for 0 days 0 hr and 55 min
    TPD[V] = 0.5245V

ISS:
    The diffracted power is around 3.4%
    Last saturation event was 0 days 1 hours and 5 minutes ago

Possible Issues:
    PMC reflected power is high

Jennie W, Keita, Rahul

On Friday, Keita and Rahul and I tried moving PDs 2 and 6 to align them better with the others. As can be seen from the scans we did of the DC voltage of the diodes as we moved the input alignemnt in horizontal translation and yaw from alog #87290, 2 and 6 have a range of alignment that is shifted relative to the other 6.

We also checked this with a IR sensitive camera with a zoom lens.

One person used the camera with a zoom lens to check the spot on the PDs as another person loosened the screws from behind the array and the third person held the barrel of the PD assembly to stop it moving or rotating in an undesired direction.

There is not a lot of space as 2 and 6 are in a column and are very close to diodes 1 and 5 on the right.

The horizontal scan we took after these moves showed we had made things worse, see this image.

Later that afternoon, Keita moved the PD 2 back and checked the alignment and it looks better.

The alignment as of yesterday (Monday) was 143mm in pitch (as read out by the allen key in the PZT mirror pitch actuator wheel) and 0.4145 inches in horizontal translation as read out by the translation stage the PZT mirror sits on.

Keita measured the coupling (after finding an error in my code from the previous coupling measurement I plotted last Thursday (alog #87400)).

The coupling in both vertical and horizontal is below 10, so this should be good enough for install if all else checks out.

Yesterday afternoon, Rahul and I did the vertical scan (slightly off from the horizontal reference position of 0.4145 inches that Keita had aligned to). The data in this graph was collected at a horizontal translation stage reading of 0.4162 inches.

We had to redo the horizontal scan today as I missed out some scan values yesterday. The data was collected with the pitch indicator at 143mm (the allen key on the pitch wheel actuator).

This is for FAMIS #27398.
Laser Status:
    NPRO output power is 1.857W
    AMP1 output power is 70.67W
    AMP2 output power is 140.3W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 16 days, 21 hr 4 minutes
    Reflected power = 24.26W
    Transmitted power = 106.6W
    PowerSum = 130.8W

FSS:
    It has been locked for 0 days 1 hr and 35 min
    TPD[V] = 0.538V

ISS:
    The diffracted power is around 3.9%
    Last saturation event was 0 days 3 hours and 40 minutes ago

Possible Issues:
    PMC reflected power is high

Keita, Jennie W, Rahul

Executive Summary: The coupling for PDs & and 8 is between 200 and 300 RIN per m. This is far too high. We might need to re-align to a different spot tomorrow and retake coupling measurements.

We went back into the lab yesterday afternoon (8th October) to find a spot where the PDs were all aligned well in DC voltage.

We found a spot (by changing PZT mirror translation horizontally across the input beam and by tilting the input mirror. The first we use to optimise the horizontal coupling to the PDs, the second we use to optimise the vertical coupling.

The spot we arrived at for the input pointing is one which doesn't seem to have particularly bad coupling in vertical or yaw for any of the PDs. This is made more problematic as PDs 2 and 6 are mis-aligned relative to the others in pitch and yaw (see graphs of PD DC alignment in LHO alog #87324) we think so there coupling is not minimised close to where the coupling of the other 5 diodes is minimised.

Then we moved the QPD to be centred on this new spot.

We took coupling measurements but will do the calibration tomorrow.

The alignment references for this position are pitch allen key = 14.7mm

Micrometer reading on translation stage = 0.4162 inches.

Today I calibrated the data using the calibration from Tuesday. Since we moved the QPD after that point we need to scale the calibration value.

Attached is Keita's working for this here and here.

The processed data is shown here and the DC values for each PD are here.

One can see that 7 and 8 have a very high coupling, but their DC values are ok. PDs 2 and 4 have low coupling but their DC values are not too low as was the case with one of the PDs on Tuesday (LHO alog #87373), so I trust these values.

Jennie W, Keita, Rahul

Monday:

Keita and I re-optimised the array input pointing using the tilt actuator on the PZT steering mirror and the translation stage.

After taking a vertical and horizontal coupling measurement, he realised that the DC values were very low when we optimised the pointing to improve the vertical coupling. Looking at the QPD the cursor was in the bottom half and so we cannot use the QPD y-readout  channel to work out the 'A' channel for either measurement (where the TF is B/A).

So for the A channel in the TF for the vertical coupling we had to use 
A = QPD_X/(cos(QPD_angle*pi/180))/sqrt(2) /Calib_X where A is the times series for thr TF, 'QPD_angle' is the angle between the horizontal dither axis and the QPD x-axis, Calib_X is the calibration of motion on the QPD in the x-axis in V/mm (LHO alog #85897).

And for the A channel in the TF for the horizontal coupling we had to use 
A = QPD_X/(cos(QPD_angle*pi/180))/Calib_X.

The data is plotted here.

Yesterday Keita and I double-shcked the beam size calculation I did on 26th June when we reset the alignment to the ISS array form the laser after it got bumped (we think). The beam size calculated was 0.23 mm beam radius on PD1 (the one with no transmissions through the mirrors) in x direction and 0.20 mm in y direction. The beam size calculated on the QPD was 0.20 mm in x direction and 0.19 mm in y direction. The waist should be close to this point (behind the plane of the array photodiodes) as the Rayleigh range is 9cm in x direction and 10cm in the y direction.

This check is because our beam calibration as reported in this entry, seems to be at least a factor of 2 off from Mayank and Shiva's measurements reported here (dcc LIGO-T2500077).

Since we already know the QPD was slightly off from our measurements on the 6th October, Keita and Rahul went in and retook the calibration measurements of volts on the QPD to mm on the QPD.

In the process Keita noticed that the ON-TRAK amplifier for the QPD had the H indicator lit and so was saturating. He turned the input pump current down from 130mA to120mA and the gain value on the amplifier from G3 (64k ohm) to G2 (16k ohm). The QPD was also recentred on the input pointing position where we had good vertical and horizontal coupling as we had left it in the position we found on Monday where it was off in yaw. We had to do several iterations of alignment switching between vertical and horizontal dither and still could only find a place where the coupling of PDs 1-4 were optimised. PDs 5-8 have bad coupling at this point. At this position we also took calibration measurments where we scanned the beam and noted down the voltage on the QPD X, Y and SUM channels.

Keita notes that for the QPD to be linear the voltages need to be below +/- 7V.

I will attach the final set of measurements in a comment below.

We left the alignment in this state with respect to the bullseye QPD readout.

Rahul, Jennie W, Keita

Just catching up on historical alogs

We increased the dither amplitude to 1Vpp to give us better coherence in our horizontal input dither -> PD array RIN measurement compared to our previous alog (#87140).

We got pretty good coherences on PDs 2,3 5 -8. All of these measured between about 0.1 per m and 30 per m RIN.

After showing the results to Keita he got us to do two more measurements where we changed the input alignment yaw either side of the nominal to see if this had the expected results on the magnitude and phase of the transfer function.

The results are shown in the attached graphs, PD number is on the x axis and Magnitude, phase and coherence of each measurement are on the 3 y-axis. The measurements with the input aligned are shown in blue.

To get the two other measurements I looked at the two leeft-most diodes on the array (I think these are 4 on the top and 8 on the bottom) with the beam viwer as Rahul moved the PZT steering mirror in yaw.

For these three measuremenrts Keita pointed out that the discrepancy between the diodes phases didn't make much sense.

Jennie W, Keita,

Since we don't have an easy way of scanning the input beam in the vertical direction, Keita used the pitch of the PZT steering mirror to do the scan and we read out the DC voltages for each PD.

The beam position can be inferred from the pictures setup - see photo. As the pitch actuator on the steering mirror is rotated the allen key which is in the hole in the pitch actuator moves up and down relative to the ruler.

height on ruler above table = height of centre of actuator wheel above table + sqrt((allen key thickness/2)^2 + (allen key length)^2) *np.sin(ang - delta_theta)

where ang is the angle the actuator wheel is at and delta_theta is the angle from the centre line of the allen key to its corner which is used to point at the gradations on the ruler.

The first measurement from our alignment that Keita found yesterday that minimised the vertical dither coupling is shown. It shows voltage on each PD vs. height on the ruler.

From this and from the low DC voltages we saw on the QPD and some PDs yesterday Keita and realised we had gone too far to the edge of the QPD and some PDs.

So in the afternoon Keita realigned onto all the of PDs.

Today as we were doing measurements on it Keita realised we still had the small aperture piece in place on the array so we moved that for our second set of measurements.

The plot of voltage with ruler position and voltage with pitch wheel angle are attached.

Yesterday I went into the optics lab and re-measured the coupling between input beam motion and PD array. While taking measurements I noticed that the injection could not be seen on the AC readouts of the PDs (example) so I tuned the temperature of the laser via changing the resistance of the controller, I went from ~10kOhms up to 13 kOHms and down to 8kOhms and while I found places where the noise reduced see example of noisy trace here, I couldn't find anywhere with the controller where the trace renamed stably in the non-noisy state. I then decided to tune the pump current down from 130mA to ~100mA and eventually found a somewhat stable place. I still had to wait through some periods of noise to trigger the measurement of the PDs.

I alos increased the modulation ampltitude to 80 mVpp. The counts on the QPD LCD readout were 10672, see image.

When the laser is in its quiet state the AC PD traces should comfortably fit on the screen of the osclloscopes with a 5mV scale, with the laser noisy this is more like 100mV, I also use 100mV scale for the QPD, I didn't change it when I reduced the noise on the laser.

The noisy state for the QPD outputs is here, the quiet state is here.

For each measurement I used a capture range of 400ms on the time axis of the scope and 125 000 samples selected on the 'ACQUIRE' menu.

The final measurements are:

PD 1 - 4 measured at AC: T0012ALL.CSV

PD 5 - 8 measured at AC: T0014ALL.CSV

QPD X, Y and SUM channels measured at AC: T0013ALL.CSV

The two DC measurements are going to be averaged so I didn't wait for a quiet time to measure them.

PD 1 - 4 measured at DC: T0011ALL.CSV 

PD 5 - 8 measured at DC: T0010ALL.CSV

To save you need to click on the menu button and change the resolution to be'Full', the format to be CSV and the channels captured to be 'ALL', the file number will roll over every time you save so you don't need to enter it manually.

Elenna, Camilla, Ryan. WP#12806 . IOT2L layout D1300357

Followup from the beam measurements taken last week 86962, while we still had the nominal ~115W through the PSL EOM. Elenna and I repeated these measurements today, now that the power through the EOM has been reduced to ~90W, see 86966, which appeared to improve the mode matching to the IMC. We see the beam has changed shape (now larger on IOT2L) since the power reduction.  

We took the PSL input power down to ~100mW, locked out the rotation stage and then used the nano scan to take some beam profiles in the IMC REFL path on IOT2L.

For positions B and C, we added a temporary steering mirror between IO_MCR_M7 and IO_MCR_L2. Distance between IO_MCR_BS1 and IO_MCR_M7 = 7"; Distance bewtween IO_MCR_M7 and temporary steering mirror = 1 1/2".