Cheryl, Rodica

Over the past days we worked on trying to improve thermal lensing in the Faraday isolator by swapping the 3 mm thick DKDP crystal that slightly undercompensated (and also has much poor surface quality) with a 4 mm thick crystal. With the 4 mm crystal we measured the beam profile and estimated a focal length f=-43 m, which determines >98% mode matching. However, the beam quality starts getting altered at powers above ~50 W, and we could assign this to higher oreder modes introduced by phase distortion after a thicker DKDP. The pictures attached show the beam profile and intensity map at ~140 W. For the estimation of the focal length we only used the data from the less distorted axis (y-profile).

We have available 3.5 mm thickness for DKDP which we are planing to measure this afternoon. Meantime, we are finishing the isolation measurements for the FI with the 4 mm thick DKDP crystal. We needed to redo the alignment for the isolation beam and redump ghost beams, which changed after modifying the alignment on the IO path, now with the EOM out of the beam.