The PMC mode matching was initially done at low power ~150 mW. It was expected and found that at full power ~2 W (injection current 2.1 A) the mode matching got much worse:
the visibility degraded from 80% to 50% (1 - refl locked/refl unlocked) . The thermal lensing could be in the laser, EOM, or FI.
The first attached plot shows the scan of the beam after the EOM at low and full laser power. At full power the waist position is 10 mm after the turning mirror after the EOM and the waist size is 310 um.
The second plot shows the ABCD calculation for the mode matching solution.
I removed the MM lens PLCX-25.4-77.3-C and placed the PLCX-25.4-180.3-UV about 20 mm after the first PMC periscope mirror (the second mirror after the EOM).
The PMC visibility improved to 94% and the power through the PMC, as measured by the PMC transmission PD, went up by a factor of 2.