Laser-induced ignition by optical breakdown

This paper is an experimental work of the applied methodical character in which as an attempt to optimize a laser ignition system a systematic study of the best incoupling geometry for the employed Nd:YAG laser was performed. The incoupling geometry comprises the pump fiber and an aspheric collimating lens. In this context, the distance between pump fiber and collimating lens was made continuously variable. The distance between fiber and lens primarily influences the diameter of the pump beam. In this way, it is possible to control the pulse energy as well as the number of pulses generated within a pump cycle. Furthermore, investigations to analyze the focal size dependence of plasma generation were carried out. As a result, it was found that it is possible to reduce optical losses caused by plasma transmission by choosing an optimum focal volume. This experiment was carried out for different pressures and focal volumes.