Keita Kawabe, Jennie Wright, Masayuki Nakano, Khanh Vu

Below is a summary of how we closed the JAC ASC loops, including our measurements of the sensing and input matrices, the open-loop gain measurements, our work on the IOT1 table, and the final closing of the loops.

We attempted to measure the sensing matrix three times. During the first attempt, we observed strong cross-coupling between the pitch and yaw channels. However, we did not account for this coupling correctly because we inverted the full 4x4 sensing matrix, including the pitch-yaw cross terms, and then extracted the relevant values from the inverted matrix.

The second attempt was more successful. We removed the cross terms and reduced the 4x4 matrix, which would require 16 inputs, into two separate 2x2 matrices for pitch and yaw, requiring only eight inputs in total. We then inverted the two smaller matrices separately. There was also some confusion about the matrix labeling, but Masayuki noticed that the input and output ordering changes when the sensing matrix is inverted, so the rows and columns needed to be labeled accordingly. This proved to be correct. However, the newly calculated matrices were still not good enough because the PZT and JM1 responses in yaw were too similar. This was problematic because we wanted their signals on the two wavefront sensors to be well separated.

Therefore, we went to the IOT1 table to check the alignment. Masayuki made an important observation that the beam was being clipped at the shutter, with approximately half of the beam blocked on the left side. This explained why we were having more trouble with yaw than pitch, since the clipping affected yaw much more strongly.

After aligning the shutter, we measured the sensing matrix for a third time. The result was much better: the PZT and JM1 yaw response vectors were separated by approximately 45 degrees in the WFS basis, while the pitch response vectors were separated by approximately 124 degrees. Although these values are not at the ideal 90-degree separation, we determined that they were good enough and entered the new input matrices.

We then performed open-loop gain measurements and confirmed that all of the loops were behaving properly. Finally, we closed the loops and slowly increased the WFS gains from 0.1 to 1. All four loops closed successfully and worked well.