Shadowgraph of Pulse CO₂ Laser Induced Breakdown in Different Pressure Air

Abstract

The expansion property of an infrared CO2 laser produced air plasma is characterized using a high-speed imaging shadowgraph technique. The shadowgraphs were taken by a time-gated intensified charge-coupled device at various delay times after single pulses induced gas breakdown. We examined five incident laser energy of 180, 240, 345, 420 and 600 mJ induced air breakdown at the pressure of atmospheric and 104 Pa. A shock wave produced by laser induced breakdown was also observed and its speed was measured as a function delay time between the breakdown and the shadow imaging under different air pressure. The experimental results indicated that the radial and axial shock wave front evolutions showed similar behavior, which increased fast with delay time at early stage and slowly at later stage. The propagation speed of the wavefront was about 2 cm/μs at the initial stage of breakdown, and then decreased very quickly. The propagation speed under low air pressure was higher than that of gases under high pressure and the spark sustained less time at lower pressure. The size of laser induced air spark increased with incident laser energy but not simple linear relationships.

Some experimental studies on the UV spark pin-array pre-ionization in TEA CO2 laser

“…so far to characterize the spatial-temporal properties of the output pulses of the pulsed CO 2 lasers according to their structural and operational conditions. The transversely excited atmospheric (TEA) CO 2 lasers are the most studied type of the CO 2 lasers owing to relatively simple structure, easy implementation, stable performance, desired output characteristics and wide spread applications as well [38][39][40][41][42]. However, the issue of the designing and characterizing of TEA CO 2 lasers cannot be yet considered completely solved.…”