[Aidan, Marie, Dan, Keita, Alexei, TJ]
Yesterday we started the process of installing the new green LED source for the ETM HWS, per T1800229.
We started by making sure the ALS beam was aligned to the TMS and there was a return beam getting to the ALS photodiode. We inserted two irises, one immediately after ALS-M11 and another about half way up the periscope. These were aligned to the existing ALS beam to secure the axis. Unfortunately, subsequent analysis at the end of the day showed that one of the PZT mirrors railed at some point during or after this process of aligning the irises. We're not currently sure if they really represent the ALS axis. We will investigate this further this morning.
We inserted all the optics per T1800229 (the fiber LED source, 4 steering mirrors, a polarizer, a 50/50 beam splitter). Also, we added the polarizing beam splitter which transmits the P-polarized (horizontally polarized) HWS light and reflects the S-polarized ALS beam. This PBS has not yet been aligned to get the ALS beam back to centered on the irises.
The new HWS beam was aligned to the centers of the existing optics. We have yet to align it to the PBS or the irises.
A couple more notes:
- when designing the system, I forgot that HWS-M3 and HWS-M4 were not HR mirrors for 532nm. These are uncoated optics to attenuate the return beam getting to the Hartmann sensor. We had to replace both of these optics with HR mirrors for 532nm.
- We found, much to our delight, that the 20 uW HWS beam coming out of the fiber-optic launcher is visible through the laser safety goggles (because of the 30nm linewidth). This makes aligning it much easier. However, the polarizing beam splitter strips off much of the blue portion of the light and the remaining green portion is much more difficult to see through the goggles. So alignment is easy up to the PBS.
Some photos from installation are attached.
- Photo of fiber launcher [IMG_3829]
- HWS probe beam from fiber launcher on card between first mirror and second mirror [IMG_3828]
- HWS fiber launcher and injection optics installed [IMG_3827]
- Fiber launcher [IMG_3826]
- 2" diameter uncoated beam sampler that was replaced with 2" diameter max R mirror - the former ALS-M11 [IMG_3825]
- 1" diameter uncoated beam sampler [IMG_3824]
- HWS PBS and iris [IMG_3823]
