Counting of particles in aqueous solutions by laser-induced photoacoustic breakdown detection

Laser-induced photoacoustic breakdown detection is applied for the determination of particles in aqueous dispersion. Polystyrene (latex), alumina and thoriasol particles of different sizes are investigated for demonstration. Laser pulses at 500 nm with 28 ns pulse width (FWHM), generated by an excimer (λ = 308 nm) pumped dye laser, are focused into aqueous particle dispersions to produce breakdown. The dye laser pulse energy is fixed at a value lower than the breakdown threshold of pure water to initiate a dielectric breakdown only when particles are present in a given focus volume. Focus volume parameters and particle size dependent breakdown thresholds are calculated and the results are compared with data from literature. Dependence of breakdown threshold values on the chemical composition of the particles is determined for polystyrene, alumina and thoriasol particles.