On 08/23/2012, the ITMY ring heater was operated at 630 mA from 20:59:30 UTC to 00:31:00 UTC. During the heating process, the cavity resonances were monitored through frequency modulation of the ALS laser. This frequency modulation measurement is also referred to as a cavity scan; a document detailing the method and its results will follow shortly. The time evolution of the LG10 mode was presented in animation form. These measurements are taken from the HG10 modes, initially at 45.4020 kHz and 66.1400 kHz.

The frequency separation between the FSR and the HG10 modes, or modal spacing, is measured during the ring heater operation. The modal spacing is used to calculate the cavity g-factor: G = (cos( (modalspacing)/FSR * pi ))^2. The cavity g-factor is a function of the radius of curvature of the test mass: G = (1 - L/R_1)*(1-L/R_2).

The figure in changeingfactor.pdf shows that the g-factor increases with heating. The initial value is 0.5408, and the maximum value is 0.6213 at 11822 seconds of heating. The calculated radius of curvature shifts from 2305 m to 2164.5 m.

The time scale is consistent with the measurements made with the Hartmann sensor in the time regime studied, reaching a maximum at ~1.2e4 seconds. A follow-up test of six hours heating is needed to observe the decrease in deformation.

The error bars in the plots are +/- 3 frequency steps. The smaller error bars were taken from a measurement of 200 steps over 1 kHz, and the larger error bars were taken from a measurement of 2000 steps over 30-80 kHz. During the scan, the first-order resonances used to monitor the modal spacing moved out of the 1 kHz window originally chosen for the measurement. The period with fewer data points and larger error bars corresponds to the time period after the resonances moved out of range but before the ranges were adjusted.