I unlocked the PMC and swept over C1:PSL-PMC_RAMP's full range a couple of times this morning. The PMC should now be relocked and returned
Your PZT is broken.
1) Check cable between RFPD and FSS box for quality. Replace with a good short cable.
2) Using a directional coupler, look at the RFPD output in lock on a scope with 50 Ohm term.
I suspect its a lot of harmonics because we're overmodulating to compensate for the bad
3) Purchase translation stages for the FSS mode matching lenses. Same model as the PMC lenses.
Fix the mode matching.
4) Get the shop to build us up some more bases for the RFPDs on the PSL such as we have for the LSC.
Right now they're on some cheesy Delrin pedestals. Too soft...
5) Dump the beam reflected off the FSS RFPD with a little piece of black glass or a razor dump.
Anodized aluminum is no good and wiggles too much.
1) Continue mode matching into the PMC. Its transmission now is around the same as the
2) Put a UHV foil covered lead brick onto the PMC to quiet it down.
3) Characterize the PMC loop and retune the body notch for the new body.
4) Tweak the MZ alignment to minimize the RFAM. We can use StochMon to do this as
long as we have the MC WFS turned off or we can put in a flipper to take the
beam before the MC and send it to the StochMon RFPD.
5) Re-align onto the ISS.
6) Install irises around the periscope for the beam. The old iris there is way off.
7) Fix PSL ANG and center both POS and ANG.
% PMCLP is a TF of the IF filter after the PMC mixer
% Mixer_Voltage -- Rs -- L1 --- L2 ---------Vout
% | | |
% C1 C2 Rl
% | | |
% GND GND GND
PMC_cal (m/V) = (1064 nm)/2 / V_FSR
I've been measuring a bunch of transfer functions of the FSS related stuffs.
There are a lot to be analyzed yet, but here I put one mystery I'm having now.
Maybe I'm missing something stupid, so your suggestions are welcome.
Here is a conceptual diagram of the FSS control board
RF PD -->--[Mixer]-----[Sum Amp]------>--[Common Gain]--->----[Fast Gain]----[Filter]--> NPRO PZT
^ | ^ | |
| V | V |
LO ---->------- TP1 IN TP2 -->---[Filter]--[High Volt. Amp.] --> Phase Corrector
What I did was first to measure a "normal" openloop transfer function of the FSS servo.
The FSS was operated in the normal gain settings, and a signal was injected from "IN" port.
The open loop gain was measured by TP1/TP2.
Now, I disconnected the BNC cable going to the phase corrector to disable the PC path and locked the ref. cav.
only using the PZT. This was done by reducing the "Common Gain" and "Fast Gain" by some 80dB.
Then I measured the open loop gain of this configuration. The UGF in this case was about 10kHz.
I also measured the gain difference between the "normal" and "PZT only" configurations by injecting
a signal from "IN" and measuring TP3/TP2 and TP4/TP3 with both configurations (The signal from the Mixer was
disconnected in this measurement).
The first attachment shows the normal open loop gain (purple) and the PZT only open loop gain scaled by the
gain difference (about 80dB). The scaled PZT open loop gain should represent the open loop gain of the PZT
path in the normal configuration. So I expected that, at low frequencies, the scaled PZT loop TF overlaps the normal
open loop TF.
However, it is actually much larger than the normal open loop gain.
When I scale the PZT only TF by -30dB, it looks like the attachment #2.
The PZT loop gain and the total open loop gain match nicely between 20kHz and 70kHz.
Closer look will show you that small structures (e.g. around 30kHz and 200kHz) of the two
TFs also overlap very well. I repeated measurements many times and those small structures are always there (the phase is
also consistently the same). So these are not random noise.
I don't know where this 30dB discrepancy comes from. Is it the PC path eating the PZT gain ?
I have measured many other TFs. I'm analyzing these.
Here is the TO DO list:
* Cavity response plot from AOM excitation measurements.
* Cavity optical gain plot.
* Reconstruct the open loop gain from the electric gain measurements and the optical gain above.
* Using a mixer and SR560(s), make a separate feedback circuit for the PZT lock. Then use the PC path
to measure the PC path response.
* See the response of the FSS board to large impulse/step inputs to find the cause of the PC path craziness.