1.645 µm Er:YAG single-mode dual-wavelength emitter for CH₄ differential absorption lidar

We present a hybrid fiber/bulk laser source at 1.645 µm designed for methane (CH₄) monitoring using differential absorption lidar (DIAL) measurements in the atmosphere. The emitter is also suited for coherent wind Doppler lidar. It relies on a Q-switched Er:YAG ring cavity pumped by erbium fiber lasers at 1532 nm. The pulsed laser is sequentially seeded by two fiber-coupled CW distributed feedback (DFB) laser diodes in the center of the CH₄ line multiplet at 1645.55 nm (ON wavelength) and out of at 1645.30 nm (OFF wavelength). Despite a gain difference in the crystal between the ON and OFF wavelengths, pulses with equal energies and durations (9 mJ/300 ns) are obtained at a rate of 1 kHz. The spectral stability and purity properties in the dual-wavelength operating regime are presented.