Several laser-based techniques are being developed to provide in situ determinations of size, velocity, and elemental composition for individual particulates in combustion environments. Emphasis is placed on composition measurements using laser spark spectroscopy, and data for particulates entrained in gaseous flows are presented. Size and velocity of individual particles are determined by a colinear two-color laser scattering technique. Laser sparks (high-temperature plasmas) are produced from single particles with the use of a Q-switched Nd:YAG laser, and time-resolved emission spectra are observed. Results indicate a high sensitivity of the technique to mineral matter in coal particles. The detection of numerous constituent species is demonstrated, and trends observed in elemental distribution are in agreement with x-ray fluorescence measurements. Initial semi-quantitative results are compared with standard chemical analyses of the bulk material.
D. K. Ottesen, J. C. F. Wang, and L. J. Radziemski, "Real-Time Laser Spark Spectroscopy of Particulates in Combustion Environments," Appl. Spectrosc. 43, 967-976 (1989)