As a potential optic for the new TT for the in-vac POPX WFS in HAM1, we tested the transmission of what is supposed to be the old ZM2 mirror from O3 days as a function of AOI.
The results summarized below doesn't make sense because it's least transmissive at 0 deg AOI and it's not HR at 45 deg (3.3% transmission). It's supposed to be E1700103 according to the label but with a handwritten note saying "verify??? doesnt look the same" or something like that. Anyway, if it is indeed E1700103, it should be R>99.99% @ 1064nm for both P and S at 45 +- 5 deg AOI.
This mirror is probably usable for POPX in that the transmission is not disastrously big at the proposed AOI (~30deg or so?) but this is a mystery optic as far as I'm concerned. If the mirror in ZM1 is better, we'll use it.
| AOI (deg) | power in transmission (mW) | power transmission in % |
| 0 | 0.05 | 0.03 |
| 10 | 0.08 | 0.04 |
| 15 | 0.09 | 0.05 |
| 20 | 0.11 | 0.061 |
| 25 | 0.16 | 0.089 |
| 30 | 0.28 | 0.16 |
| 35 | 0.44 | 0.24 |
| 40 | 1.23 | 0.68 |
| 45 | 5.94 | 3.3 |
Other things to note:
We mounted the mirror in a class A siskiyou mirror holder on a dirty rotational stage with a clean sheet of foil inbetween so we can easily change the AOI in YAW.
The apparatus was NPRO - BS (to throw away some power) - HWP - PBS cube transmission (to select P-pol) - steering - ZM2 optic transmission - power meter.
The beam height between the steering mirror and the ZM2 optic was leveled, then ZM2 was adjusted so the beam retroreflects within +-2mm over 19 inches, and this became our AOI=0 reference point with uncertainty of ~+-2mm/19inches/2 rad ~ +-0.1deg. We used the indicator on the rotational stage to determine the AOI, and overall AOI error should have been smaller than 1 deg.
Before/after the measurement, the power impinging the HR side of the mirror was 180.3mW/176.1mW. Since the transmitted power only had 2-digits precision at best, I used 1.8e2 mW as the input power. The ambient light level was less than 10uW and is ignored here.
Another obvious candidate is ZM1 (again from O3 days). The mirror was not removed from TT after deinstallation though. We'll see if we can roughly determine the AOI while the mirror is still suspended, as it's a hassle to remove it from the suspension and there's a risk of chipping.
I found out that
old ZM2 (HTTS, HAM5) optic is E1000425and not E1700103 (which is for the old HTTS ZM1 – HAM6). For reference please see Stuart’s LLO alog – 64077.