Laser spark ignition: experimental determination of laser-induced breakdown thresholds of combustion gases

This short paper reports preliminary results on experimental measurements of breakdown threshold laser intensities of air, O-2,O- N-2, H-2, and CH4 using a Q-switched Nd-Yag laser operating at 532 nm and 1064 nm and 5.5 ns pulse. The breakdown threshold intensities were measured for the range of pressure from 150 to about 3040 Torr. The results showed that the pressure dependence of breakdown threshold is I-thr proportional to p(-n) which is in agreement with the inverse bremsstrahlung absorption process creating breakdown, The degree by which I-thr depends on pressure was found to be stronger at 532 nm than at 1064 nm indicating the important effect of diffusion loss. Published by Elsevier Science B.V.