Logan, Michael

We proceeded with trying to get the mode matching to the OPO. We have, as last time, a mode matching telescope consisting of f = 40mm and f = 75mm lenses which are mounted on millimeter rails. We saw that the height of the center of these lenses was 75mm and 77 mm. 

When we tried to do the mode matching previously we set the beam profiler at the nominal OPO waist position and then iteratively adjusted the lenses around their design positions in the same manner as the steering mirror beam walking alignment method. However, the beam profile was quite asymmetric at times. Somehow, last time we did this OPO test, we managed to get a quite good beam profile coming out of this mode matching telescope design (25.5 vs 26 um), despite the beam coming from the preset beam path (Lightwave Laser + lenses) being quite astigmatic (135 vs 160 um). However, in that case we had one steering mirror between the lenses at 45 degree incidence. We saw that the beam, which we had previously set to travel "approximately" along a set of screw holes at about 73mm height, was entering the first lens low and to the right, causing a large deflection to hit the second lens up and to the left. This might cause some difference in horizontal versus vertical focusing and also deflects the beam going into the beam profiler, making adjustment a bit annoying.

We decided to more precisely center the beam going to the mode matching telescope. Before, we set up this beam path by diverting the s-pol beam going to the Korean Faraday isolator. We replaced that mirror with a BSW11 50:50 beamsplitter then set up two steering mirrors at 45 degree incidence to more accurately set the beam path along a set of screw holes, this time at 75mm height. The beam was aligned iteratively along the path using the two steering mirrors and close/far targets. We also took a proper spacer to make the second lens at 75mm height. So now we have an adjustable beam going to our OPO MMT, as well as incidenct s-pol light on the Korean FI.

We took a steering mirror from the Taiwan SHG p-pol path. Since I will change the input coupler to one with a 1.53 mm diameter input beam (vs 4.5 mm clear aperture to meet the CA = 2.7D -> 1 ppm diffraction requirement), we are going to mess up this path either way. We were running out of mirrors so I took two Optosigma TVFM-25C05-1064 steering mirrors from the KFC box.

We also labelled some unlabelled optics on the table.