Abstract

Laser-induced ignition offers significant advantages over a conventional spark-ignition system, such as higher probability to ignite leaner mixtures, reduction of erosion effects, increases of engine efficiency, or shorter combustion time [1]. An end-pumped Nd:YAG laser, passively Q-switched by Cr^4+:YAG saturable absorber is the most suitable for engine ignition [2,3]. Recent research reported improved performances of a laser-ignited engine in comparison with ignition induced by a spark plug: The results were obtained using a Nd:YAG/Cr⁴⁺:YAG micro-laser with pulses of 2.7-mJ energy and 600-ps duration [3]. It was also argued that multi-point ignition increases the combustion pressure and shortens the combustion time compared to single-point ignition [4]. However, building of a passively Q-switched Nd:YAG/Cr⁴⁺:YAG micro-laser with multiple-beam output and with its size close to that of a spark plug is a difficult task. In this work we report design and realization, for the first time, of compact, passively Q-switched Nd:YAG/Cr⁴⁺:YAG micro-lasers with two- and three-beam output, each beam being able to induce air-breakdown in points of adjustable depth and distance.

© 2011 Optical Society of America