Laser induced incandescence under high vacuum conditions

This paper reports on a study of laser-induced incandescence of carbon particles in free space within a high vacuum (< 10(-3) mbar) excited by an Nd:YAG laser pulse. We have conducted an experimental study using samples of carbon black placed within an evacuated, sealed glass vessel which is slowly tumbled to cause a cascade of carbon black particles in free space. Our experiments show that under a high vacuum two important phenomena are observed. Due to the absence of gaseous conduction, in comparison to particles in ambient air, incandescence lifetime in a vacuum is dramatically extended to more than 50 mu s with a corresponding increase of a factor of over 10(4) in the integrated or total number of photons emitted by each soot primary particle. For large aggregates and/or agglomerates in a vacuum after a delay of the order of 2 to 10 mu s, the large particles fragment into smaller entities. We have also modelled the incandescence behaviour using well established methods.