[Dan, Tanaka, Ushiba]

Abstract:

We performed fine alignment of GRY with POS picomotors.
Now, normalized GRY transmission is over 1 and seems good enough.

Detail:

After the ADS phasing and confirming that ADS works well, we performed fine alignment of GRY by using POS picomotors.
Basically what we need to do is just tweeking two pico mirrors and find the good alignment for maximizing GRY transmission.
However, it is a little hard to do so seeing only GRY transmission power because GRY transmission fluctuates a lot due to large suspension motion, especially ETMY.
So, this time, I also used ADS error signals for the alignment.
Followings are the procedure.

1. Lock GRY with YARM guardian (request ALS_LOCKED state).
2. Add dither signals to SR3 (500 and 300 cnts at K1:ADS-{PIT,YAW}_SR3_OSC_CLKGAIN, respectively)
3. Move POS 1 PITCH or YAW until reducing GRY transmission slightly.
4. Move POS 2 PITCH and YAW so that error signals of SR3 ADS becomes 0 (K1:ADS-{PIT,YAW}_SR3_DEMOD_I_OUT16)
5. Iterate 3 and 4 to maximize GRY transmission.

Figure 1 shows the GRY transmission before and after the alignment (left: before, right: after).
Figure 2 and 3 show the PICO motor medm before starting and after finishing the alignment, respectively.