[Vicky, Regina, Dorotea, Sheila]

The attached plot shows the ratio of green light transmitted vs reflected through the OPO over the past year to see how green OPO cavity losses have changed.

We last moved the OPO crystal in Nov. 2022 (see relevant alog). Shortly after moving the crystal, the ratio was around 5% and degraded to around 4% within the first week; it has since settled between 2-3% for most of the past year.

We think the discontinuity around 23/04/16 was due to rejecting power away from the refl PD, which was done around that time because the PD was being saturated. If we look at the refl power alone we can see clear saturation occurring on the PD in the time before the power was lowered. We think the loss curve would be fairly continuous if not for the saturation, but can't exactly compensate since we don't know how much power is being lost. The plot shows only times from when the detector was "stable", but stability was calculated fairly naively, leading to some outlier points remaining from when the detector wasn't actually locked; however, the general trend seems pretty consistent.