Development of a Passively Q-switched Microchip Laser Operating at 914 nm for Automotive Lidar Applications

Abstract

Since most solid-state lasers have emission wavelengths above one micrometer, they cannot be used for contemporary lidar systems in combination with inexpensive and widely established silicon-based detector technology. Therefore, the aim of this work is to investigate and realize a passively Q-switched Nd3+:YVO4 laser at a wavelength of 914 nm for the application in an automotive lidar sensor. To investigate the laser parameters relevant for the lidar application, a total of three experimental resonator configurations is used. Thereby, the configurations are chosen in such a way that the laser parameters can be analyzed as decoupled as possible from the overall system. Experimental investigations demonstrate that the quasi-continuously pumped Nd3+:YVO4 laser can achieve pulse durations in the single digit nanosecond range and pulse energies of almost 40 µJ. Moreover, for a possible lidar application, the repetition rate can be scaled up to about 60 kHz via the applied pump power without significantly affecting the other parameters. Theoretical comparison via a rate equation model provides close agreement with the experiments and enables an assessment of the future potential for possible applications of the laser. Across all studies, a very good beam quality was observed, which suggests an excellent resolution capability in lidar applications. In addition to the consideration of various system relationships using the experimental configurations, a passively Q-switched monolithic resonator approach is presented operating in a single-pulse regime at a repetition rate of 200 Hz. The system is pumped by a 808 nm single broad area laser diode, which offers a more compact overall system and a narrower linewidth compared to a fiber-coupled diode laser module Consequently, the entire laser system can be operated without active temperature control in a temperature range of 20-50 °C merely by adjusting the pump laser current. Besides short pulse durations, the short resonator of the monolithic laser crystal allows operation on a single longitudinal mode and consequently a spectral emission bandwidth of a few picometers only. This results in excellent stability of the spectral properties, the pulse energy, and the pulse duration for long-term measurements over 60 minutes