Nonlinear and quantum optics on the nature of sugar emission excited by the first harmonic of a Nd laser

The physical nature of emissions excited in pressed-sugar samples by the first harmonic of a neodymium laser (1064 nm, 12 ns) is studied. The spectral, kinetic, spatial, and amplitude characteristics of emissions upon single- and multipulse irradiation with energy densities of 0.012–3.2 J/cm$^2$ are measured. It is found that excitation of a sample by the first pulse causes two emission types, namely, emission of the second harmonic of a Nd laser (532 nm) and glowing of dense low-temperature plasma formed as a result of a low-temperature optical breakdown on absorbing inhomogeneities. Multipulse excitation leads to annealing of absorbing inhomogeneities and to an increase in the optical breakdown threshold.