Pulsed laser-induced nucleation of sodium chlorate at high energy densities

We report on a study of laser-induced nucleation (LIN) of sodium chlorate in supersaturated aqueous solutions using focused nanosecond laser pulses at high energy densities (420 kJ cm(-2)). On irradiation with a single laser pulse, optical breakdown was observed in the form of a luminous plasma, and numerous microbubbles were produced. On the basis of the observations, we estimate the energy threshold for optical breakdown in the solutions to be 70 J cm(-2). Remarkably, even at high energy densities, single laser pulses produced on average only one or two crystals. The mean number of crystals obtained was 1.5 (532 nm) and 1.8 (1064 nm) per sample (3 cm(3)). The effect of left circularly polarized (LCP) and right circularly polarized (RCP) light on the nucleation of dextrorotatory (d) versus levorotatory (l) enantiomorphs of cubic (phase I) sodium chlorate crystals was investigated. No significant correlation between the helicity of circular polarization and the chirality of enantiomorph was observed. The results are consistent with a mechanism involving nucleation of the achiral monoclinic phase III followed by solid-solid transformation to the chiral cubic phase I of sodium chlorate, although this transformation was not observed directly. The use of single-pulse LIN at high pulse energy densities may be useful in the exploration of polymorphs or in the production of single crystals for analysis.