Nanosecond pulsed laser irradiation is shown to be effective for cleaning contaminant particles as small as 0.3 μm in diameter from NiP magnetic hard disk substrates. A micron-thick liquid film is deposited on the disk surface just before the laser irradiation. The cleaning threshold and efficiency are investigated for the fundamental and frequency-tripled Nd:YAG laser harmonics (wavelengths λ=1064 and 355 nm). The rapid phase-change and thin liquid film ablation processes are examined in order to elucidate the cleaning mechanism. Optical reflectance and photoacoustic beam deflection probes are employed for monitoring the vaporization threshold and the acoustic transients generated. The plume evolution and acoustic wave propagation into the ambient air are visualized by laser flash photography. A jet composed of vapor and liquid columns/droplets is expelled from the laser-irradiated area. The pressure enhancement accompanying the explosive-vaporization process and the momentum supplied by the ablation plume are the main sources of the augmented cleaning efficiency at moderate laser energy densities.
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She et al. (1999) studied this question.
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