DETECTION OF PARTICULATES IN A RF PLASMA BY LASER EVAPORATION AND SUBSEQUENT DISCHARGE FORMATION

Nd:YAG-laser-induced evaporation of particulates formed in an Ar-CCl2F 2 rf plasma and the subsequent discharge in the vapor have been invest igated in situ by means of optical emission spectroscopy. The estimate d threshold for discharge formation is 5 X 10(6) W/cm2. The maximum la ser-induced emission intensity is observed when the laser is operated in the long-pulse mode (about 200 mus pulse duration) at the fundament al frequency. The wavelength integrated intensity of this continuum em ission has been compared with light scattering intensity at the same l aser energy. It has been found that the laser-induced emission intensi ty can be more than ten times higher than the scattering intensity, es pecially for particulates with a diameter much smaller than the wavele ngth of the laser. Therefore, this effect provides a sensitive particu late detection method.