The SALT gang decided to get together for a group photo out in the snow today... Yes, it really was COLD out there!
Then back in the clean room, it was time to put in the small CGH to check that the M3 alignment survived the removal of the big CGH. A few quick puffs of air to blow off any dust...
Then the SAC was tilted over to 37 degrees & the whole CGH assembly was inserted into the hole in M3.
With the tube in place, all the actuators were connected & the cables secured so that they don't pull on the CGH.
Seen from above, through the hole in M5, one can see the cross hair strung across the CGH.
After using the alignment telescope to set the CGH up on the new invar coat hanger, the CGH & interferometer were adjusted to null the fringes.
Hardly any tip & tilt adjustment of the CGH was necessary - even when the SAC was tilted over & when the temperature was lowered to 10 C. This is great news as it means that M3 needs no further adjustment!
Here's our final fantastic wavefront measurement: peak-to-valley = 0.82 & RMS = 0.17 waves :)