Evan G, Darkhan T
Today we wanted to know the power impinging on the ETM per volt of drive requested to the OFS in the x-arm Pcal. To measure this, we used the 3001.3 Hz calibration line and made a point transfer function from H1:CAL-PCALX_TX_PD_VOLTS_OUT to H1:CAL-PCALX_OFS_PD_OUT_DQ. The OFS PD voltage is equal and opposite sign to the requested excitation, so it is a good measure of the magnitude of the excitation that is requested in counts.
Taking the transfer function between these channels at 3001.3 Hz, we find the transfer coefficient to be 0.4605 V/V
Then we can use the TX_PD_VOLTS calibration to convert this value to watts on the ETM, accounting for the optical loss. NOTE: the x-arm Pcal is currently suffering from apparent clipping, on the reciever side. So we use value of the TXPD calibration from May/Aug 2015 (LIGO-T1500252 v6, weighted mean value). At this point, we do not quantify the uncertainty due to the optical efficiency. This calibration value is 1.322e-9 N/V. Using the force-to-power conversion c/(2*cos(8.75o)) = 1.5166e8 W/N and the calibration value, we find the OFS volts-to-ETM watts transfer coefficient to be 0.0923 W/V.
This value can be used for quantifying the Pcal to length transfer function, aka the Pcal actuation function (which I will finish tomorrow!).