Ignition of Brown Coal Microparticles by Nanosecond Second-Harmonic Pulses from a Neodymium Laser

Irradiation of microparticles of brown coal pressed into tablets with a density of 1 g/cm(3) (particle size less than 63 mu m) by second-harmonic pulses from a neodymium laser (532 nm, 10 ns) leads to the emergence of two stages, which differ in kinetic characteristics and threshold energy densities. At the first stage, when the energy density reaches 0.4 J/cm(2), optical breakdown is initiated and a plasma torch is formed immediately after the laser pulse with a lifetime of similar to 1 mu s. When the energy density reaches a value of 4 J/cm(2), in addition to the processes of the first stage, thermochemical reactions are initiated in the bulk of coal microparticles, and volatile substances and nonvolatile residues are released and ignited in the time interval of 30-500 mu s.