This morning we start with the IR alignment recovery .
Being SQB1 open, we look at the IR and GR beams overlapp between SQB1_M21, M22 and M23, where it is possible observe both the incoming beams and the FC_IM retroreflected beam, once we have the last. In particular it is easy to overlapp looking the retroreflected from dichroic SQB1_M23 toward the FI. The overlapp has been done by acting on the cited three mirrors, but expecially on SQB1_M22 and SQB1_M23. We checked that the retroreflected IR coming from the SQB1_FI to EQB1 was well centered in SQB1_FI2. This has been done moving SQB1_M21 both in the vertical and horizontal direction until the beam coming out from the SQB1_FI3 first polarizer on SQB1_M12 was cut for both the direction, in both versus: we left the beam at the center of these range.
The mirrors pico motors positions were:
SQB1_M21_V : -26712
SQB1_M22_H : -53655
SQB1_M23_H : -18400
- EQB1_FI_Pin=1.90+/- 0.02 mW
- EQB1_FI_Pout=1.90+/-0.02 mW
- SQB1_FI2_Pin=1.90 +/-0.02 mW
- SQB1_FI2_Pout=1.90 +/-0.02 mW
- SQB1_FI3_Pout_POL1=1.85 +/-0.03 mW (Power from FC to EQb1, but the power meter sensor was 'floating')
SC: 18.9 mW;
- AOM_Pin=22.40 +/- .02 mW
- EQB!_FIin= 14.5 +/- .02 mW
- EQB!_FIout= 13.33 +/- .02 mW
ALUGNMENT ON EQB1_HD CAMs and LO overlapp
After this, we align the retroreflected IR on the EQB1_HD. The beam has been centered on all the steering mirrors SQB1_M12, M13 and M14 and on EQB1_M6 and overlapped weith the LO. To do this we remove d the two holed absorbing scrren between
M13 and M14 and just at the end of SQB1 path. We check the beam height with a movable diaphragm, but on the last absorbing hoed screen in any case results a litle low: even the beam leaving SQB1 to go in EQB1 seemed not cut, we decide to leave the screen out (it is just clumped on the benchnear the original posiiton, as it can see in the attached SQB1 picture)
We obtain a HD visibility with BAB abd LO ~ 80%. at beginning, and the end of the shift ~85% (see attached pictures) This improvement after tring to better align the IR on the FC and keeping as other reference the beam on HD cams.
The BAB retroreflected beam appears very similar in dimension to the LO on both the HD_CAMs (see picture BABfromFC_comparison), while is not the case for the SC (see SC_LO_fromFC_)
To overlapp ad the best
ALIGNMENt ON FCEB
Once aligned, we have observed the FC trasmission on FCEB_IR_PD. To be sure that the observed peaks were the IR and not the green, we have turned off the GR shutter (see pictures). IWe observed both the BAB and the SC resonances, observing more o less the expected ration between the transmitted power, about a factor 10 (BAB ~1.95 mW and SC ~18.8 mW are the power measured on EQB1). The BAB resonance appears more 'clean' as expected by the fact that yesterday we was not able to improve the matching between the SC and OPO due to a problem in the alugnment of the fotodiode that measure the beat between SC refelected by the OPO and BAB.
We try to improve the alignment of the BAB on the FC, but the fact that we cannot for the moment apply to the AOM a ramp with a sutable amplthe that allow to observe more than half FSR.
We work unlocking for few time the FC on green to observe the resonance with the mirrors free running. In this way we have improved a little the alignment.
We will update the data relative to IR trasmission (BAB and SC).
The plan is to give a right offset to the AOM RF ina way to bring the cavity near the IR resonance and scan in that region while the alignment will be improved.