Design of an eye-safe passively Q-switched microchip laser for laser range-finding

Microchip lasers emitting at 1535nm are a valued tool for pulsed laser range-finding, due to their compactness, eye safety, and ability to generate nanosecond laser pulse durations. The generation of small pulse durations is substantially aided by the possibility to bond the laser material and the saturable absorber, which decreases internal losses and shortens the resonator length and therefore the resonator round-trip time. The optical pumping is done via a longitudinal diode-pumping scheme, focusing the pump radiation into a small spot size inside the laser material. Due to the flat resonator mirrors and the pumping scheme, the beam guiding inside the laser resonator is dominated by thermal and gain guiding effects due to the absorption of pump radiation, with its transversally varying intensity profile. In designing the laser, the laser materials length and doping concentrations are chosen to ensure a high absorption and energy conversion efficiency. The saturable absorber initial transmission and output coupler mirror reflectivity are determined, which optimize the laser pulse energy and pulse duration for a given pump level, when implemented in the laser setup.