RESUMO
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.
RESUMO
We present a broadly tunable highly efficient frequency conversion scheme, based on a low-threshold harmonic cavity optical parametric oscillator (OPO) followed by an idler-seeded power amplifier. By choosing the cavity length of the OPO equal to the 10th harmonic of its 41 MHz Yb:KGW solid-state pump laser, a very compact optical setup is achieved. A singly-resonant cavity without output coupler results in a low oscillation threshold of only 28-100 mW in the entire signal tuning range of 1.37-1.8 µm. The 2.4-4.15 µm idler radiation is coupled out at the 41 MHz pump frequency and employed to seed a post amplifier with nearly Watt-level output power. In addition, the seeder plus power amplifier concept results in clean signal and idler pulses at the fundamental repetition rate of 41 MHz with a time-bandwidth product below 0.4 and a relative intensity noise 10 dB lower compared to the solid-state pump laser.
