The wavefront distortion of a beam from a single-mode violet laser diode (VLD) with a collimator lens was measured and corrected to provide a precise focal spot. This output beam was focused on a plastic plate to which dyestuff or pigments were added to enable color micro-marking without an absorbent. The part irradiated by the laser was marked, and unfixed dyestuff or pigments were removed with ethyl alcohol. Using this VLD, color micro-marking of 100μm font size on the plastic plate was achieved.
