We tried to see the Yarm length change using Yarm green beat note. The beat note is still puny, so we put an extra amplifier. We saw something, but still can't control the arm length with ALS.
What we did:
1. Aligned Y arm and PSL green optics as usual.
2. By changing the temperature of the PSL laser with C1:PSL-FSS_SLOWDC, we find small beat note when
PSL laser temperature on display: 30.59 deg C (PSL HEPA 100%)
C1:PSL-FSS_SLOWDC = 5.2100
Y end laser "T+": 34.049 deg C
Y end laser "ADJ": 0
Y end laser measured temperature: 34.68 deg C (*)
C1:GCY-SLOW_SERVO2_OFFSET = 29425
(*) Measured using diagnostic output on the back of the laser controller(Lightwave 125/6-OPN-PS) - between pins 2(GND) and 4. Calbration factor is 10 degC/V.
3. The peak height right after the amplifier on the Y green beat PD was ~ -48dBm, so we put another amplifier (and attenuator) because the beat note which goes into the frequency divier should be -30 dBm to +7 dBm. After we put the amplifier, the peak height was ~ -23 dBm.
4. We could see the C1:ALS-BEATY_COARSE_I_ERR ringing down, when opening and closing the control room door, which may introduce Y arm length change(screenshot of dataviewer below). But we are still not sure if we are actually getting the Y arm length signal because closing and opening Y end green shutter doesn't make difference on C1:ALS-BEATY_COARSE_I_ERR. The ring down was seen when we turned on the unWhiten filters in C1:ALS-BEATY_COARSE filter modules.
5. Tried to hold Y arm length with ALS, but couldn't.
Red ones are the ones we added or changed.
Dataviewer is so slow and flakey now.