高真空条件下的激光诱导白炽光研究
Laser-Induced Incandescence (LII) occurs when a high-energy pulsed laser beamencounters graphitic particulate matter particles like soot or carbon black. Theparticles absorb laser energy from the beam and see an increase in their internalenergy, resulting in an increase of temperature. At the same time, the particles looseenergy through heat transfer mechanisms. If the energy absorption rate is sufficientlyhigh, particle temperature will rise to levels where significant incandescence(blackbody emission) can occur .Typically, Laser-Induced Incandescence produces50ns to 1μs long light pulses at atmospheric pressure.So far, LII measurements had been restrained to conduction-dominated conditions,whereby signals are short-lived (less than one microsecond) and require sensitivenanosecond resolution instrumentation. This thesis introduces a novel LII – basedmeasurement method performed under high vacuum conditions. The novelty of LIIunder vacuum resided in the fact that heat conduction away from the soot particlebecomes negligible below 10-2 mbar and this constituted a step away from the typicalsituation, whereby laser absorption is followed by heat conduction from the particlesto the surrounding medium. Instead, sublimation and radiative heat transfer wouldfollow laser absorption. The consequence was the obtention of long-lived LII signals(up to 100 microseconds) and a large gain of photons (ranging between 50 to 300)emitted per primary soot particle during LII temperature decays. Furthermore, therefractive index function E(m) value could be determined directly from measuredradiative temperature decays, with potentially an uncertainty of circa 7%, whichoutperformed current soot extinction measurements. In addition, for laser fluencesbelow 0.06 J/cm2, a regime where only laser energy absorption and radiative heattransfer apply would be reached and LII signals became independent of particle size.