Mode transition of plasma expansion for laser induced breakdown in Air

Abstract

High-speed shadowgraph visualization experiments conducted using a 10 J pulse transversely excited atmospheric (TEA) CO2 laser in ambient air provided a state transition from overdriven to Chapman–Jouguet in the laser-supported detonation regime. At the state transition, the propagation velocity of the laser-supported detonation wave and the threshold laser intensity were 10 km/s and 1011 W/m2, respectively. State transition information, such as the photoionization caused by plasma UV radiation, of the avalanche ionization ahead of the ionization wave front can be elucidated from examination of the source seed electrons.