A propagation model of a laser-absorption wave was proposed and validated using the measured propagation velocity. The model describes the propagation mechanism in terms of avalanche ionization through an inverse Bremsstrahlung process and photoionization by UV radiation from bulk plasma behind the wave. Using plasma spectroscopy, the electron temperature and density at the head of laser-absorption wave were estimated as 2 eV and (1.5-2.6) × 10 24 m −3 , respectively, at 10.6-µm laser wavelength and 5 eV and (2.6-3.3) × 10 24 m −3 at 1.05 µm when the laser intensity was near the laser-supported detonation threshold in the air and argon atmosphere. Using the measured plasma properties, we estimated UV photon flux radiated by the Bremsstrahlung, which contributes the photoionization ahead of the laser-absorption wave. The resulting propagation velocity of the laser-absorption wave was 10 3 m/s, which showed good agreement with the velocity measured using a high-speed camera.Index Terms-Laser-induced plasma, laser propulsion, plasma measurement, shock wave.
Termination conditions of a laser-supported detonation (LSD) wave were investigated using control volume analysis with a Shimada–Hugoniot curve and a Rayleigh line. Because the geometric configurations strongly affect the termination condition, a rectangular tube was used to create the quasi-one-dimensional configuration. The LSD wave propagation velocity and the pressure behind LSD were measured. Results reveal that the detonation states during detonation and at the propagation limit are overdriven detonation and Chapman–Jouguet detonation, respectively. The termination condition is the minimum velocity criterion for the possible detonation solution. Results were verified using pressure measurements of the stagnation pressure behind the LSD wave.
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.
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