Laser breakdown acoustic effect of ultrafine particle in liquids and its application to particle counting

The mechanism of acoustic signal generation from an ultrafine particle in liquids by laser irradiation was found to shift from the photoacoustic effect to optical breakdown of the particle as the power density of the excitation beam increased. The acoustic signal generated from a 0.085 µm polystyrene ultrafine particle in water increased discontinuously at the beam power density of 7.0 ×1010 W/cm2, corresponding to its dielectric breakdown threshold. Then, a novel method in which ultrafine particles were counted individually by counting the breakdown acoustic pulses was proposed, and its counting principle was verified using the polystyrene ultrafine particles.