40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
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 Wed Apr 20 00:12:12 2022, Yehonathan, Update, WOPO, Still figuring out the readout electronics and fixing of some stuff Thu Apr 21 10:33:33 2022, shruti, Update, WOPO, Still figuring out the readout electronics and fixing of some stuff Mon Apr 25 11:08:35 2022, Yehonathan, Update, WOPO, Still figuring out the readout electronics and fixing of some stuff Thu Apr 28 14:12:20 2022, Yehonathan, Update, WOPO, Still figuring out the readout electronics and fixing of some stuff
Message ID: 2760     Entry time: Thu Apr 21 10:33:33 2022     In reply to: 2759     Reply to this: 2762
 Author: shruti Type: Update Category: WOPO Subject: Still figuring out the readout electronics and fixing of some stuff

[Yehonathan, Shruti]

First we turned on the relevant instruments for this experiment after the power shutdown:

- Main laser drivers and doubling cavity controller. We set the current to 2 A as we had it before.

- The waveguide TEC. We tried setting it to 60.99 C (for maximum efficiency) but the temperature ramps up much faster and over shoots the setpoint. So we had to do what we did earlier which was to adiabatically change the setpoint from room temperature and finally set it to something like 63 C so the actual measured temperature stabilizes at ~60.9 C. How do we change the PID parameters on this controller? The settings don't seem to allow for it.

- PD power supply, oscilloscopes, function generator, SR 560s lying nearby

Then we tried to probe further what was going on with the PDs (TL;DR not much made sense or was reproducible)

• Initially we were sending in 12 V from Ch1 of the Tenma power supply and $\pm$15 V to the mini-circuits RF amplifiers from Ch2 of the same Tenma. When we tried to observe the DC voltage levels (before amplification) and the noise (after amplification) but they did not make sense to us as described in the previous elog.
• Then we disconnected the RF amplifiers and switched the power supply for the PD transimpedance amps to Ch2 of the Tenma. Briefly we were able to see 2 V DC at each output (as expected for the ~1.3 mW of light incident  on each PD) when measured with the multimeter. On the scope we were seeing that one of the PDs was dominated by 60 Hz fluctuations with a much lower
• We tried to switch it back to Ch1 but even the DC levels seen by the multimeter were bogus (~1 V for one of the channels and 2 V for the other)
• When we switched the power supply to a HP one taken from CTN, the DC levels on both channels seemed ~1V without any light and the noise somehow seemed lower with some incident light

### Possible next steps

• Even though the AD 829 data sheet says it can be operated at up to 15 V, it is possible that we damaged both of them somehow when cycling the power. Elog 2324 also says that it was designed to be powered at $\pm$ 5 V. We could replace both op-amps and measure teh transimpedance TFs before and after the change
• Use different PDs. Maybe temporarily try with just the ThorLabs PDA20CS or similar with ~20 mW of LO power and measure the shot noise (possibly also squeezing).
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