Glow spectral characteristics of the hard coal particles surface during the action of laser pulses in the free generation mode

The luminescence spectra of coal fractions with dimensions $d\le$ 63 $\mu$m were studied directly during the action of neodymium laser pulses ($\tau_i$ = 120 $\mu$s). Depending on the radiation energy density $H$, the luminescence spectra have a different character. The glow at minimum values of the laser pulse energy density $H_{cr}^{(1)}$ is associated with the ignition of fine coal particulates ($\sim$1 $\mu$m) present in the fractions, and with the ignition of reactive microprotrusions on the surface of larger coal particles. The luminescence spectra at this stage are of a non-thermal nature and are associated with the radiation of volatile molecules in the gas phase and their oxidation products. With an increase in the laser pulse energy density $H$, a thermal glow of the surface of larger coal particles is observed, which is described by the Planck formula at $T$ = 3100 K. When $H=H_{cr}^{(2)}$ is reached, the surface of the coal particles ignites during the action of the laser pulse. Contributions to the spectra are the glow of the surface of coal particles, emitted carbon particles, and the glow associated with the emission of excited molecules H$_{2}$, H$_{2}$O, CO$_{2}$. With an increase in $H>H_{cr}^{(2)}$, the processes leading to the glow of coal particles during a laser pulse are similar to those described above for $H_{cr}^{(2)}$, but the glow intensity increases.