Frequency locking of a Nd:YAG laser using the laser itself as the optical phase modulator

Abstract

We report frequency locking of a Nd:YAG tunable laser to a 2000 finesse 87-cm-long Fabry–Pérot cavity in air using the Pound–Drever technique. The novelty is that the necessary phase modulation of the beam is obtained using the laser directly instead of an external phase modulator (Pockels cell). The spurious relative amplitude modulation using this method was ∼3×10−5 with a modulation index β∼1 and the spectral density of the frequency difference between the laser and the cavity is below 1 mHz/√Hz in the region 1–500 Hz.