Triple-pulsed single-frequency laser at 1645 nm and 822 nm simultaneously for CH₄ and H₂O differential absorption lidar

We proposed a novel, to the best of our knowledge, triple-pulse dual-wavelength 1645 nm and 822 nm laser for differential absorption lidar (DIAL) to measure methane and water vapor simultaneously. The laser is developed with a 1064 nm triple-pulse high-energy fiber-slab hybrid laser amplifier as the pump source. Seeder-injected optical parametric oscillator (OPO) is designed to generate narrow linewidth and single-frequency 1645 nm pulses, while optical parametric amplification (OPA) and second-harmonic generation (SHG) are utilized to amplify the signal pulses and generate 822 nm pulses. Operating at a repetition rate of 25 Hz with a three-pulse interval of 200 <b><i><i>μ</i></i></b>s, a single pulse energy of 98.6 mJ at 1064 nm pump wavelength is achieved, resulting in 18.8 mJ at 1645 nm after OPA. After the SHG, a pulse energy of 7.5 mJ at 822 nm is generated with an efficiency of 39.98%. Both the 1645 nm and 822 nm pulses obtain low-frequency fluctuation and good beam quality. The frequency stabilities are 9.07 MHz and 4.89 MHz, and the beam qualities are less than 2.2 and 3.9, respectively.