Passively Q-switched 914 nm microchip laser for lidar systems

Abstract

Passively Q-switched microchip lasers enable great potential for sophisticated lidar systems due to their compact overall system design, excellent beam quality, and scalable pulse energies. However, many near-infrared solid-state lasers operate at >1000 nm which are not compatible with state-of-the-art silicon detectors. Here we demonstrate a passively Q-switched microchip laser operating at 914 nm. The microchip laser consists of a 3 mm long Nd3+:YVO4 crystal as a gain medium while Cr4+:YAG with an initial transmission of 98% is used as a saturable absorber. Quasi-continuous pumping enables single pulse operation and low duty cycles ensure low overall heat generation and power consumption. Thus, thermally induced instabilities are minimized and operation without active cooling is possible while ambient temperature changes are compensated by adjustment of the pump laser current only. Single-emitter diode pumping at 808 nm leads to a compact overall system design and robust setup. Utilization of a microchip cavity approach ensures single-longitudinal mode operation with spectral bandwidths in the picometer regime and results in short laser pulses with pulse durations below 10 ns. Furthermore, beam quality measurements show that the laser beam is nearly diffraction-limited. A 7% output coupler transmittivity is used to generate pulses with energies in the microjoule regime and peak powers of more than 600 W. Long-term pulse duration, pulse energy, and spectral wavelength measurements emphasize excellent system stability and facilitate the utilization of this laser in the context of a lidar system.

Compound Cavity Passively Q-Switched Single-Longitudinal-Mode Diode-Pumped Laser

“…From a practical standpoint, lasers which operate with a SLM must have an effective means of eliminating the spikes created by the beat frequency of adjoining longitudinal modes; this is because these spikes are the most common source of damage to laser system components [12][13][14]. A number of methods have been used to produce SLM output from solid-state lasers include twisted-mode cavities (TMC) [15], ring cavities [16], the application of etalons or gratings [17][18][19], microchip lasers [15,16], and seed injection lasers [20,21]. However, it should be noted that many of these approaches yield laser outputs with quite low SLM ratio (herein defined as the ratio of the number of single longitudinal mode pulses to the total number of pulses in a certain time).…”

“…The prior literature shows that the primary approaches to generating SLM output are based on threshold regulation and mode competition enhancement [18][19][20][21][22][23][24]. In comparison to ring cavities, it is commonly shown that standing wave cavities can generate higher energy pulses with narrower pulse width and with minor beam distortion.…”