Shock and thermal wave study of laser-induced plasmas in air by the probe beam deflection technique

Abstract

A plasma induced by focusing a 7 ns Nd:YAG laser at 1.06 µm in air at atmospheric pressure was studied by the probe beam deflection method. The evolution of the shock wave and the thermal expansion of the hot air in the core of the decaying plasma were monitored by using this technique. The shapes of the shock and thermal waves were mapped and the velocities were determined as being as high as 528 and 40 m s −1 at 1 µs. In addition, it was also possible to measure the relaxation time required to bring the hot air to room temperature: it was measured to be 5 ms. This technique is versatile, economic, and simple to implement, giving essential information from processes that occur from the microsecond to the millisecond timescale.

Laser Extinguishment of CH4-N2/Air Counterflow Diffusion Flame

“…However, the spatial range of influence of the hot gas core may be limited in the expanded radius of the hot gas core. For the laser energy of 200 mJ/pulse in the present study, a hot gas core expands by a radius of about 5∼6 mm normal to the laser axis over several hundreds microseconds (3), (4) , and disappears after about 5 milliseconds (5) . If we take transferring the hot gas core by flow convection during its disappearance into account, the effective z r range of the hot gas and turbulence may be limited to about 6 mm.…”

“…After propagation of the blast wave in a laser-induced breakdown, the disappearing process of the hot gas core, which the plasma core turns into owing to a decrease in its temperature, is observed (3) - (5) . In the early stage of the process, the hot gas core expands and its temperature decreases with time.…”

“…In the early stage of the process, the hot gas core expands and its temperature decreases with time. At the same time, a vortex is generated and the shape of the hot gas core is deformed (3) - (5) . Then, the hot gas core expands more toward the normal direction to the laser axis (3) - (5) while taking the surrounding gas into it.…”

“…Then, the hot gas core expands more toward the normal direction to the laser axis (3) - (5) while taking the surrounding gas into it. Consequently, turbulent mixing of the hot gas and the surrounding gas occurs (9) , the hot gas disappears, and the initial condition is recovered (5) . Based on this process, the hot gas and the turbulence may affect the determination of X f .…”

Optodynamic Characterization of Laser-Induced Bubbles

“…These beam deflections can be detected with a position-sensing photodetector such as a quadrant photodiode. Such a method can be used in various applications, such as cavitation-bubble measurements [9], plasma characterization [10], or monitoring of the laser drilling of through-holes in glass [11].…”