After Alberto and Dan re-aligned the ALS beam to the periscope, Dan installed a retro-reflector and we aligned the pick-off beam into the HWS path. There was ~120uW of power getting into this path. The concave lens that Dan substituted in last week is AR coated for 1064nm, so there is a 10% reflection off the surface of that which is hitting the inner wall of the enclosure.

There is a second wedged uncoated 2" optic (uncoated on front surface, AR coated on the back surface) in the HWS beam path that is used to further attenuate the beam. There is a 10% reflection off the front surface and a 1% reflection off the back surface. (The 10% beam was significantly saturating the HWS camera, so we settled on using the 1% AR beam).

We aligned the rest of the optics to get the 532nm beam onto the HWS. The incident power was ~1.2uW. With two OD 0.5 filters in front of the HWS, it was only just saturating with an exposure time of 9ms (and dead time of ~8.5ms between exposures).

We removed one of the OD0.5 filters and set the exposure time to 1ms, (with dead time of 16.5ms)  to only just saturate the camera (although this produced streaking in the image that is characteristic of long dead times). From this I estimate that we'll want roughly 50x attenuation to get the camera to run at 57Hz with no significant dead time between exposures.

I installed the TCS SVN on the HWS computer (called h2hwsey) and recorded some of the images from the camera to the SVN.

Here is the first aLIGO HWS image ever ....