LASER-INDUCED PLASMAS OBSERVED WITH AN OPTICAL IMAGING SPECTROMETER

Laser-induced plasmas generated by a Q-switched Nd:YAG laser were observed with an optical imaging spectrometer which was assembled from a 0.32 m spectrometer and a cooled CCD (charge-coupled device) detector. The ambient atmosphere, the kind of gas used and its pressure, influenced the emission intensities for both atomic lines and the continuum, and the volume of emissive regions of plasmas. The power density of the laser also affected the plasma characteristics. Tight focusing of laser radiation did not directly bring about a plasma of high emission intensity, because of the absorption of laser energy by the plasma itself. The importance of prevention of a gas breakdown before sample vaporization was also indicated. These effects are discussed from the viewpoints of initial cascade growth of electron number density, absorption of laser energy by the plasmas, and plasma expansion processes.