Investigation of laser induced air breakdown thresholds at 1064, 532, 355, 266 and 248nm

摘要

Laboratory air is one most popular transparent medium for high power laser beam propagation. Its threshold of laser induced breakdown is one of the key characters for the high power laser system. The thresholds of laser induced air breakdown under laboratory condition were measured using 1064, 532, 355, 266 and 248nm short pulse laser. The focal spot varies from 50μ m to 150μ m which achieved using a lens with 117mm focal length. The measured breakdown thresholds range from 3.2×10~(10)W/cm~2 to 5.1×10~(11)W/cm~2, depending on the wavelength. It is confirmed that the KrF laser induced air breakdown threshold should be 3.2×10~(10)W/cm~2, which is almost 1 order of magnitude higher than the reported value of 2.7×10~9W/cm~2. The measurements indicate multi-photon ionization is the dominant mechanism since the air breakdown thresholds at 1064, 532, 355, 266 and 248nm seemed well-agreed with the scale law of λ~2.