Shadowgraphy and interferometry using a CW laser and a CCD of a laser-induced plasma in atmospheric air

We present a new application of a charged coupled device (CCD), where a continuous-wave (CW) laser is used as a probe beam in shadowgraphy and interferometric diagnosis of transparent media where the refractive index varies in time. The time resolution is obtained by gating the CCD. This configuration has the advantage that the temporal resolution of both techniques can be changed according to the evolution of the process under study and no stability setup is required, as usual, in CW interferometric techniques. We applied this method to the diagnosis of a laser induced plasma (LIP) in air measuring the evolution of plasma, shock wave, electron density, and hot core air expansion from the ns to the ms time scale.