Measurement of absolute optical length of Fabry-Perot cavity using frequency measurement

(Second report : Improvement of the signal to noise ratio for FSR measurement)

Abstract

In this research, we propose a novel method to measure the absolute optical length of a Fabry-Perot Cavity (FPC) using single-frequency modulation (FM) with one Electro- Optic Modulator (EOM) and the null method. In the first report, we demonstrated the principle of the optical resonator length measurement, in which, the null method combined with interference of FM side bands so carrier frequency is slightly detuned from the resonance of the FPC. In this paper, the improvement of signal to noise ratio by using high modulation index and high power laser is presented.