[Matt, Lisa, Chris, Kiwamu, Alexa]

(This alog pertains to work done last night).

Last night we went to EY and adjusted several settings in both the PLL and PDH loops.

PLL LOOP:

We changed the settings on CMB_FIBR to increase the UGF of the loop. In particular, we turned off the output gain and decreased the input gain to -6dB. In addition, we turned the generic filter on. The settings are now as follows:

Common Compensation: ON

Boost one:  ON

Fast Option: ON

Generfic filter (in common path): ON

Input gain: -6dB

With these settings, the UGF is now 29kHz (up from 20kHz). We also measured the error signal spectrum and saw a peak at 28kHz.

PDH LOOP:

We also made changes on CMB_REFL. In particular we increased the input gain to 12dB. The settings are now as follows:

Common Compensation: ON

Boost one: ON

Input gain: 12dB

Output gain: 0dB

In addition, we altered the temperature control to reduce oscillations of the signal; on the PLL autolocker we reduced the slow frequency servo UGF to 0.01 from 0.035. We also tried using a 4dB attenuator on the RF modulator to see if that would reduce the oscillations; however, this did not seem to help.

With these settings, the UGF is now around 3kHz (down from 9kHz). Again, we measured the error signal spectrum and saw a peak at 28kHz. Clearly, we were seeing the features of the PLL loop in the PDH loop.

Additionaly, we saw that H1:ALS-Y_REFL_A_DC_POWER was oscillating vary rapidly from 50 counts to zero counts. As we misaligned the PD, the oscillation continued but reduced to 20 counts. If we completely blocked the beam, the signal dropped down to zero counts and remained so. As of last night, we left the PD slightly misaligned to reduce the oscillations in the PDH loop.

Attachments:

The attached pictures are as follows:

1) PLL transfer function

2) PLL error signal spectrum

3) PDH transfer function

4) PDH error signal spectrum

5) CMB_FIBR (as of this morning)

6) CMB_REFL (as of this morning)