Ignition of brown coal microparticles by the pulses of the second harmonic of nanosecond neodymium laser

Abstract: Under the action of pulses of neodymium laser second harmonic (532 nm, 10 ns) on microparticles of brown coal in the form of the tablets with 1 g/cm³ density (particle size being less than 63 μm), two stages different in kinetic characteristics and threshold energy densities were distinguished.At the first stage, when the energy density reaches 0.4 J/cm², there occurs an optical breakdown and a plasma torch is formed immediately after the laser pulse with a lifetime of ∼1 μs. When the energy density reaches 4 J/cm², in addition to the processes of the first stage thermochemical reactions are initiated in the volume of coal microparticles, and volatile substances and non-volatile residue are released and ignited in the time interval of 30–500 μs.

Keywords: laser ignition, optical breakdown, brown coal, emission spectra, emission kinetics, carbon plasma.