Abstract

Laser induced breakdown (LIB) in air has been explained by different ways along pulse width τ. Cascade ionization (CI) is considered as the mechanism for long pulse widths of over 1 ns. On the other hand, laser filamentation is alternative mechanism of air-breakdown for fs pulses, because CI processes based on collision cannot play a role in fs pulses. However, for intermediate ps pulse region, the mechanism is unclear because of ambiguity of contribution of multi-photon ionization (MPI) to air-breakdown. Since we cannot have access to a pulse width gap between one nanosecond to a few tens picosecond for a long time [1], there is a lack of knowledge about air-breakdown based on CI in sub-ns region. Wang et al. reported that breakdown threshold of fluence F_th has ~τ scaling for a long pulse width of over than ~1 ns [2]. On the other hand, Van Stryland et al. reported that F_th is almost constant in 30-140 ps region [3,4]. Nevertheless, there are still open questions about the cause of the scaling and the degree of contribution of MPI because of lack of data between the pulse width gap.

© 2017 IEEE