[Aidan, Camilla]
This morning we retro-reflected the HWS beam from AFTER the PBS to check whether that was causing any issues. The return beam from there was nice and Gaussian (slightly ellipitcal but free of high spatial frequency noise). The return beam from the ETM was still mottled. (Images of both return beams are attached to this alog). We tweaked the alignment to steer the ITM reflection out of the FOV of the HWS.
We also switched out the collimating lens in front of the fiber laser output from 50mm focal length to 75mm focal length. We confirmed that the beam converged from this laser+lens combo about 1.3m away on the HWS Lens L3.
We tweaked the position of the HWS camera itself to try to get it closer to the nominal image plane. We didn't see evidence of a sharp aperture from the baffle behind the ETM. Also the apparent aperture diameter is smaller than I had expected - it should be around 9mm diameter on the HWS.
We also ran the HWS last night (post 2" optics insertion) and today (post 50mm to 75mm collimating lens change). The noise of the spherical power time series (H1:TCS-ETMX_HWS_PROBE_SPHERICAL_POWER) was very high on those two measurements (Around +/-30-50uD when judged by eye). The other day, when we ran our RH test, the noise was +/-4uD when judged by eye (close to the expected shot noise limit for the HWS). [Caveat: the IFO has been locked for the last two days during these measurements - did we totally eliminate ITM return beam or is some still getting onto the HWS?]
So we undid major clipping on the HWS optics but have not made the HWS measurement better.
I'm concerned that the Transmon optics have point defects on them that MAY be interfering with our measurements. We have seen evidence of these point defects before.
To bring the imaging path closer to nominal we shortened the path by 2" by flipping the camera around. Photo attached.
Brief timeline of events this week:
- 05/03 (am) alog 62953
- Changed camera frame rate so pixels not saturating, took RH test.
- 05/03 (pm) alog62963
- Changed L2, L3, CCD positions to closer match design after taking beam profile measurements
- 05/04 alog62984
- Cleaned all HWS in-air optics.
- Left SLED off overnight to see if any coupling to IFO 1064nm beam: none seen.
- 05/05 alog63009
- Swapped M1, M1B, M1A 1" optics to 2" optics. This made outgoing beam good. BUT now spherical power very noisy.
- 05/06 alog63019
- Shortened imagining path 2"
- Changed collimating lens from 50mm to 75mm.
Strangely our spherical power is now noisier than during our 05/03 RH test. See attached plot. We are still thinking about why our spherical power is drifting so much. The IFO is locked at 2W but this drifting isn't related to our ETMX, TMSX or ITMX alignment. Plot attached. Also the total pixel power seen on the HWS isn't changing much: plot here.
Keita notes that the deflects seen on the TMS coating Aidan links to are on TMSY which is expected to be the worse TMS as was made first and with optics of a different run. We can expect TMSX to have similar defects due to the nature of these silver coatings.
The estimate of ~9mm diameter for the expected aperture on the HWS comes from the 190mm diameter baffle behind the ETM divided by a nominal magnification of 20.5x.
Below is my recollection about TransMon telescope optics.
TMSY is a prototype, everything else is a production unit. Some TransMon telescope optics are different between these, notably the primary mirror and the F1 folding mirror.
All are metal coated by various vendors. All except the newer F1 mirrors show numerous pinholes, hazes and scratches. The prototype F1 was the worst in terms of #pinholes/area. I thought that the prototype primary was worse than production units, but sadly most of the pictures were lost when resourcespace was shut down.
I'm not 100% certain about the coating coater info for the primary.
|
LHO TMSY (Prototype) |
Everything else (Production) |
References | |
| Primary |
Coated (and recoated?) by the substrate vendor. Pinholes, scratches, haze. Size up to the original spec. |
Coated by a local (SoCal) coater (?). Pinholes, scratches, haze. Thinner. |
ECR E1300611 describing the Primary mirror thickness change. alog 1164 (Lisa's inspection of the optics for the prototype). alog 7196 (Prototype vs Production F1). G1300643 (Various mirrors before we purchased production F1). alog 2542 (pinholes in the TMSY primary using flashlight). alog 10920 picture showing pinholes in the TMSY primary with the ALSY laser.
|
| F1 |
Edmund off-the-shelf. Pinholes, scratches, haze. Size up to the original spec. |
Newport off-the-shelf "PinholeFree (TM)". Good. Thinner. |
|
| F2 | Coated by a local (SoCal) coating vendor. OK. | Coated by a local (SoCal) coating vendor. OK. | |
| Secondary | Recoated by a local (SoCal) coater. OK. | Recoated by a local (SoCal) coater. OK. |
