laser power is still drifting with the ISS turned on, but much less. Primary suspects are
- sensing PD: is a Silicon PD and so the change in Responsivity caused by thermal fluctuations could be the reason. Sensitivity is typically 1.5%/K @1064nm for Si.
- Input offset of SR560
Replaced the PD with a InGaAs diode and re-started a measurement. Will also add sampling of the laser power in the VI. I can't easily switch to the lock-in amplifier as it does not have a GPIB interface to read it. |