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

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.