Summary

We improved the IMC mode matching by repositioning JM2 and JM3 based on the calculation from yesterday. The mode mismatch was reduced from about 10% to ~2% after iterative alignment and mirror position optimization. Further improvement is expected with additional calculations and tuning, which will be continued tomorrow.

Details

We worked on improving the IMC mode matching following the calculation from yesterday. As a first step, JM2 was moved by approximately 3 inches; the new position is shown in the attached photos. The alignment to the IMC was performed using the newly placed iris in front of JAC_L2 and the iris after the output periscope, as described in the previous alog. By centering these two irises, the alignment could be brought to the level where IMC flashes were visible. From that point, adjusting JM3 allowed us to easily reach an alignment where the TEM10 content was at the ~10% level.

After achieving a reasonable alignment using a scratched mirror, we replaced it with a newly cleaned narrow-angle mirror for JM2. The scratched mirror was moved to JACR_M1. As a note, the scratch was oriented on the +y side; by keeping the beam closer to the −y side, the impact of the scratch was minimized.

With this configuration, the mode mismatch improved from about 10% to approximately 4%. Since the calculation suggested that further improvement should be possible, we continued tuning by adjusting the JM3 position. Based on the previous calculation indicating an offset in JM3, we first moved JM3 by about 1/2 inch in the −x direction (increasing the L1–L2 distance). This resulted in a degradation of the mode mismatch to about 6%. We then moved JM3 in the +x direction by a total of 1.5 inches (i.e., 1 inch further from the original position), effectively shortening the L1–L2 distance. With this adjustment, the mode mismatch recovered to approximately 2%.

We stopped the work at this point and plan to perform updated calculations tomorrow to guide the next iteration of tuning.