Small particle analysis by laser induced incandescence

A method of analyzing submicron sized particles in a defined volume of gas, comprising steps of:

• generating a pulsed laser light beam of energy high enough to heat the particles to incandescence;
• passing the laser beam through an aperture to select a portion of the beam with a substantially constant fluence;
• forming a relay image of the aperture at a measurement location located within the defined volume of gas;
• measuring incandescence from the particles at the measurement location at two or more wavelengths at a plurality of time intervals;
• calculating temperatures of the particles from the measured incandescence;
• and
• analyzing the calculated temperatures to determine characteristics of the particles.

An apparatus for analyzing submicron sized particles in a defined volume of gas by laser induced incandescence, comprising:

• a laser for generating a pulsed laser light beam of a predetermined fluence;
• an optical arrangement including an aperture in an optical path of the pulsed laser light beam for limiting the transmitted pulse to an area of substantially constant fluence;
• imaging optics for forming a relay image of the aperture at a measurement location located within the defined volume of gas so that one or more particles in the defined volume of gas are heated by a constant fluence of the pulsed laser light beam and incandesce;
• at least one photodetector for measuring incandescence from the particles at two or more wavelengths at a plurality of time intervals;
• a signal processing unit for calculating temperatures of the particles at a plurality of time intervals;
• and
• a signal analyzer for analyzing a time dependent decaying of the calculated temperatures to obtain characteristics of the particles.

An apparatus for analyzing submicron sized particles in a defined volume of gas by laser induced incandescence comprising:

• a laser for generating a pulsed laser light beam of a predetermined fluence;
• an optical arrangement including attenuating means for directing the pulsed laser light beam at an energy sufficient to heat the particles to a temperature high enough for the particles to incandesce but lower than an evaporation level of the particles;
• at least one photodetector for measuring incandescence from the particles at two or more wavelengths at a plurality of intervals;
• a signal processing unit for calculating temperatures of the particles at a plurality of intervals;
• and
• a signal analyzer for analyzing a time dependent decaying of the calculated temperatures to obtain characteristics of the particles.