Amplitude and frequency stabilisation of a Tm–Ho:YAG laser for coherent lidar applications at 2.1μm

Abstract We developed a low-noise, single-frequency Tm–Ho:YAG laser tunable in the wavelength interval between 2087 and 2099 nm. To suppress both amplitude and frequency fluctuations the laser has been stabilised by two different control loops. Intensity noise has been effectively reduced using a feedback loop acting on the pump diode current, based on a biquadratic bandpass filter, which provides up to 17 dB suppression at the relaxation oscillation peak. Absolute frequency stabilisation has been achieved by locking the oscillator to the P(12) absorption line of the HBr molecule at 2097.2 nm using the fringe side locking technique, obtaining a long-term frequency stability better than 32 kHz over an observation time of 60 min. This stabilised source is aimed to injection seeding of a coherent lidar system for high precision measurements of wind velocity.