Eric, Den
We noticed that PRMI RIN is high when the cavity is locked on RELF33 I&Q signals. We compared the level of power fluctuations when PRMI was locked using REFL11, REFL55 and REFL 33. Attached plot "prmi_rin" shows the spectra.
Then we excited PRM and measured length to RIN coupling when PRMI was locked on REFL33 I&Q. DC offset of PRCL is only 3%. But MICH offset seems to be ~nm. When we gave offset of -15 cnts to the servo, power fluctuations improved by a factor of few.
Then we looked at DRMI. It seems that SRC macroscopic length is off but we still could lock it stably. To account for macroscopic length detuning we had to rotate REFL55 phase from 25 degrees to 50 degrees. Power at AS port increased by factor of ~2 compared to PRMI configuration. SPOP18 is decreased only by 30%. Attached plot "drmi_power" shows POP18, POP90, POPDC and ASDC in PRMI and DRMI configurations.
Plot "src_ol" shows srcl OL transfer function. UGF is 70 Hz. We have also centered SRM OL and copied the servo filters from PRM, gains are set to keep UGF at ~0.1 Hz and 7 Hz
This is a more detailed procedure:
1. Phase: REFL11: 19 degree, REFL55: 50 degrees (25 degrees for PRMI configuration)
2. Input matrix:
| PRCL |
|
0.15 |
0 |
0 |
REFL11I |
| MICH |
= |
0 |
0.15 |
0 |
REFL55Q |
| SRCL |
|
-0.09 |
0 |
1 |
REFL55I |
3. Servo parameters:
PRCL: gain = -0.02, FM4,5 + trigger FM2,3,6,9
MICH: gain = 0.8, FM4,5 + trigger FM2
SRCL: gain = 0.25, FM4,5 + trigger FM2,3
4. Triggering:
signal is SPOP22 , levels 40:25 |