NAOJ GW Elog Logbook 3.2
Displaying report 1-1 of 1.
MarcEisenmann - 20:09, Tuesday 07 August 2018 (936)
CC and P-Pol beam recombination
Today we work on the recombination of the 2 auxiliary laser beams.
- We put the rail after the EOM so that the lens before the EOM is on an usual post. The purpose of this change was to be able to match the CC and P-Pol beam sizes. After trying a lot of lenses before the EOM, we couldn't see any drastic changes on the beam shape so we guessed this EOM doesn't affect the beam shape as much as the green one. We now have 85% transmission of the EOM. The missing few % can come from dust inside the EOM making the alignment a bit more tricky.
- We put 2 steering mirrors before the lens in order to save some space on the bench.
- The second lens is set such as the beam is collimated with diameters 2150 and 2050 um close to the CC beam size (2100 um)
- we put the lambda/2 on the rail in order to save place
- We put a 2' PBS cube and checked that the 2 beams are superposed. It is still the case after the last steering mirror.
Today the 2 beams seem to be overlapped.
One issue is that we have some power loss on the p-pol beam (EOM path) :
| before EOM | After EOM | After 1st steering mirror | before lambda/2 | After | PBS transmission | PBS reflection |
| 13.5 mW | 11.5 mW | 10.1 mW | 9.5 mW | 9.36 mW | 8.07 mW | 1.12 mW |
This might be linked with some polarization troubles. We will look this hypothesis tomorrow.
The new optical path is attached to this entry and the optical scheme will soon be updated.
After some rough simulations, it seems that one f = 125mm lens 5 holes before the OPO can provide a beam waist of 40 um. This is close to the nominal 36 um.
Anyway, we will use this lens tomorrow to make sure the 2 beam parameters are similar.
Images attached to this report
