I made some further alignment adjustments of the modulators and some changes to the polarization inputs and outputs. A lambda/2 wave plate was installed directly after the AEOM (for now) so that the PBS could be manually tuned to the 50% transmission point for s- polarisation into the AEOM. For now we will ignore the circular polarization generated by the AEOM and the small amount introduced by the previous EOM.
After checking the field after first EOM I determined that the residual polarization was 108 uW out of 83.4 mW or 0.13 %. Without the EOM installed the extinction was down to ~10 uW. For now this level of circular polarization should be tolerable. It is something we can optimize later.
I also realigned (again) the AEOM and 2nd EOM using Antonio's methods. This gave a satisfactory looking Gaussian beam. The profile was again remeasured. Its fitted values are:
Horz. beam waist = 259.6243 um
Horz. beam waist position = 1436.9167 mm
Vert. beam waist = 215.7146 um
Vert. beam waist position = 1319.3657 mm
Data and plots attached below.
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