Following on from yesterday's FSS work and taking advantage of the earthquake, I carried out some
further FSS work.
All power measurements were done with the Ophir PD300-3W.
- ~29 mW at base of periscope
- ~1.5 mW incident on RF photodiode
Noticed that there was a bit of beam clipping on the 21.5 MHz EOM, with the beam hitting around 9 o'clock
looking at the input face. After correcting for this the power on the RF photodiode increased to ~2.8 mW.
Adjusted the quarter-waveplate at the base of the periscope to give 3 mW on the RF photodiode. The UGF is now
back up over 500 kHz. At this point the transmission monitor was saturated at 10.95 V. (C28F15.TIF, C28F15.TXT
for data). Measured the power before the turning mirror in front of the ALS fibre to be ~7 mW at this point
(see Before.jpg for quarter waveplate angle). I adjusted the quarter waveplate located after the reference cavity
and this increased the power at the ALS fibre and decreased the transmission signal (see After.jpg and Power.jpg).
The transmission signal at this point was ~2.1. The maximum power to the ALS fibre appears to be somewhere between
11-12 mW and the transmission signal drops as low as 1.5 V. Thus far I haven't thought too much about what all
the polarising optics do.
Data files attached to this entry:
TP3-1.txt mixer monitor signal when the FSS was locked
DARK.txt mixer monitor signal when light to the RF photodiode was blocked
LOCKED.txt mixer monitor signal when the FSS was locked (data memory was recorded)
OLTF.txt open loop transfer function taken just prior to my exiting the enclosure (a reality check)
CG28FG15.txt transfer function out to 5 MHz
Richard trended the ALS fibre monitor signal, there was a small increase noted.
RF photodiode signal level: unlocked 290 mV locked 58-59 mV
The astute reader will have noticed that with ~30mW input, there is ~6mW in reflection and 12mW or less available to the ALS fiber. The attached plot shows a 300 day trend of the PMC power, the reference cavity transmitted power and the power available to the ALS fiber. In general, the transmitted and ALS power are tracking until about 2 weeks ago, when the ALS power started dropping relative to the transmitted power. As of today, there is about a factor of 2 missing.
Attachment One: Peter's three FSS OLGs plotted together. Attachment Two: Full 30W Lock CARM, IMC, and FSS OLGs together. (FSS OLG not taken during full lock)