A Dual Locking Scheme for Measurement of Long-Term Stability of a Triangular Ring Resonator

The triangular ring resonator is an optical cavity that filters the higher order Hermite-Gaussian modes of a laser beam. Once locked to the fundamental mode, the resonator behaves as a Fabry-Perot interferometer. We analyze the sensitivity of the triangular ring resonator using a dual-locking scheme based on the Pound-Drever-Hall (PDH) method. The resonator is locked to the fundamental mode of a 1064-nm Nd:YAG Laser using the PDH error signal to drive the piezo-mounted curved mirror of the resonator. The laser is then locked to the transition line of a stable atomic reference (Iodine vapor cell). Once the frequency of the laser is stabilized, the PDH error signal pertains only to the intrinsic noise of the resonator. The proposed scheme is intended for measurement of long-term stability of the ring resonator and its limiting noise performance at very low frequencies.