Fransicso, Dhruva, Camilla, Austin, Sheila
Last week we set up to measure the throughput and mode out of our new diamond feedthrough for 1064 and the new collimator.
We connected the feedthrough to the oz optics IR laser, after Marc made a connector for us to be able to power it from the interlock in the optics lab. The feedthrough we are using has serial number 2138800V002. First we made a rough check of the feedthrough throughout by measuring the poewr out of the laser on a power meter (12.4mW) and the power out of the feedthrough once they were connected (10mW). This is 80% throughput, I think that we expected better although this is similar to the performance we've had from others. We can remeasure this with the collimated beam at the output when we disconnect.
We set up the collimator (I dont see a serial number for the collimator) in a class A lens mount, and Camilla and Austin used the nanoscan to measure the output mode.
%fit data taken by Camilla and Austin
zScan = [210, 337, 464, 591, 718, 845, 972, 1099]*1e-3; %distance from collimator in meters
hWidth = [573.8, 476.4, 632.5, 981.8, 1355.2, 1708.5, 2097.9, 2535.1]*1e-6/2; %horizontal beam radius (note factor of 1/2)
vWidth = [554.2, 457.4, 633.1, 1006.3, 1375, 1751.1, 2157.6, 2573.1]*1e-6/2; %vertical beam radius
The design for the VIP mode matching of the CLF is in figure 23 of T1900649, and suggests that M2 of the OPO as designed would be 317 mm, the path as built is 307 mm as described in 57960. In the attached png, the black beam is what we are aiming for, (the beam we need coming out of the collimator, propagating through +150 ROC lens in it's current location and well matched to the OPO waist), while the red and blue data and fits show what we currently have.
The main message is that we need the beam to be more collimated, which in this case should mean moving the lens closer to the fiber tip.
This morning Dhruva and I went back and adjusted the collimator.
As we disconnected the oz optics laser, we measured the power throughput again, this time we got 86% (measuring after the collimator, the first measurement was without the collimator attached).
Based on the info in the above alog, to get perfect mode matching without moving the lens we would like a beam out of the collimator with a 402um radius waist 232mm in front of the collimator. Dhruva iteratively adjusted the lens position while we measured the beam diameter in one location (about 740mm from the collimator.) The resutling beam has a horizontal waist of 501um 228mm in front of the collimator, and a vertical waist of 503um 180 mm in front of the collimator. This gives us 95% overlap with the target beam, so if this goes as planned we will actually end up improving our CLF mode matching with the feedthrough swap. Attached png shows the new beam, and the updated script is also attached.
%new data after adjusting collimator
zScan2 = [0, 4, 8, 12, 16]*25.4e-3 +0.210;
hWidth2 = [1002, 1009, 1029, 1076, 1131]*1e-6/2;
vWidth2 = [1011, 1017, 1053, 1104, 1166]*1e-6/2;
