Jennie W, Masayuki N, Keita K, Betsy W
Today we worked on improving the mode matching of the HAM1 output beam to the IMC. We also noticed the beam was going through the EOM and clipping somewhere inside so had to move the EOM up and sideways by a small ampunt to fix this. We will need to redo the RF electrical testing and the modulation depth testing for the EOM.
We improved the mode-matching of the HAM 1 output beam to the IMC by moving the lens L2 further away from JM2. We did 3 moves of 1 inch each and regained the alignment into IMC each time by using JM3 and JM2 to regain the pointing. At the end of this process we had a mode-mis-match of 1.1 % into the IMC.
After this a clipping of the beam was spotted by Keita somewhere between JM2 and JM3. We traced this down to the beam clipping somewhere inside the EOM crystal. This was fixed by shimming up the EOM at three points, after this we checked the mode-mis-match and it was 0.7%.
Then we realised there was still some clipping in pitch and so moved the EOM towards the -Y side of the table slightly. After these moves the mode mismatch was still 0.63 %.
Then after some alignent checks Keita and Masayuki have realised we need to rotate the EOM relative to the beam. This will require a sawn-off allen key as one of the 3 bolts required to yaw the EOM on its base is too near the sma connector elbows.
Camilla informed me that the non-magnetic tools might have one clean sawn-off 1/4 " allen key so left these in a tote bagged up on the + Y side outside the clean room.
- We put two of 91080A026 MCMASTER OR EQ (parts#37 for EOM assembly) under the baseplate to sim up the EOM.
- The IMC scan for the mode mismatch estimation is shown in the attached plot fraction of the HOM in IMC scan is as follows:
[After JAC_L1 adjustment]
fraction mean ± sem (nseg=13)
TEM00: 0.946604 ± 0.00119 (n=13)
TEM10: 0.010114 ± 0.000345 (n=13)
TEM2nd: 0.0185568 ± 0.000474 (n=13)
TEM01: 0.0247254 ± 0.000723 (n=13)
[L2_pos2_MCalign] finesse (=2π/FWHM) mean ± sem over TEM00 peaks: 524.733 ± 15.6 (n=26)
[After_EOM_moved] fraction mean ± sem (nseg=32)
TEM00: 0.866311 ± 0.00153 (n=32)
TEM10: 0.113113 ± 0.00144 (n=32)
TEM2nd: 0.00915663 ± 0.000228 (n=32)
TEM01: 0.011419 ± 0.000204 (n=32)
[After_EOM_moved] finesse (=2π/FWHM) mean ± sem over TEM00 peaks: 519.284 ± 12.3 (n=64)
Note: Since we have >10% first order mode for the last measurement, the mode mismatch would be lower than 0.9%.