J. Kissel, S. Dwyer (others) We're ~2 hours after achieving stable lock at 60W (see LHO:70648), and we were interested to see how our power recycling gain is doing vs. 75W earlier today, and 60W back in March / April 2023. Attached is screenshot of two trends of three channels -- the power recycling gain (PRG. dimensionless W/W), the power on the LSC POP diode in HAM1 (in [uW]) and the arm cavity powers (in [kW]). The left shot shows how things were in March / April, and the right shot shows the past ~10 hours. The PRG looks to be successfully restored to ~50-51 after thermalization, similar to the best of times in March / April 2023 at 60W. Where at 75W, we had been running with a PRG of ~47 after thermalization.
Comparing today's lock to yesterday, we have 80.4% of the input power, 86% of the circulating power, and the optical gain is 1.04% of yesterday's.
The power on the DCPDs is alpha x^2, with x the DARM offset and alpha should be proportional to the square root of power on the beamsplitter. Since we have kept the power on the DCPDs at 40mA, we would expect the DARM offset to be increased by the ratio of circulating powers to the 1/4th power, so we should expect a 4% increase in DARM offset. The optical gain should scale as alpha* darm offset, so we would expect it to scale as the power ratio ^(1/4). This means that we should have expected the optical gain to be 96% of what it was at 430kW circulating power, so we have 8% more optical gain than would be expected if only the circulating power were changing.