Daniel, Nutsinee

Last week we went out to SQZT6 with a halogen light bulb and measured shotnoise of the OPO refl PD (aLIGO broadband PD). An input of 0.5mA (0.7V/1400 Ohms transimpedance) gives ~200nVrms/sqrt(Hz). Using a responsivity of 0.3 A/W I calculated what shotnoise would be like for a green input power of 7mW (right below threshold power of 7.4-8mW, see alog41150 for details) and 3.5 mW (~half the threshold power, possible operating point according to Sheila). At 7mW input to the OPO, 6.02 mW is expected to hit the PD (14% loss between fiber and SQZT6, see alog41623)  we expect about 40% coming back when we're locked (alog41045)  and we are about 2 orders of magnitude about a factor of 2 above dark noise at this operating power. At half power we are just a factor of 1.2 above the dark noise. The shotnoise limited power is about 1mW.

Note: OPO locking signal comes from this PD.

We also measured shotnoise of the homodyne. More alog to come.