Formation of Gratings by Self-Organization of the Chromium Thin Film on the Glass Substrate under Irradiation with Laser Pulses

New features were observed when the laser beam focused to a long and narrow line was applied to remove a thin metal film from the substrate. The infrared Nd:YVO4 laser with the nanosecond pulse duration was used in experiments. The laser beam was focused through the glass substrate on a chromium film with the thickness of 50-200 nm using an acylindrical lens. The partially overlapped laser pulses with the fluence up to two times exceeding the removal threshold caused complex self-organization of the remaining metal. Formation of regular gratings of ripples with the period of 2.5-4 mu m was observed in a certain range of laser fluences and beam overlap. Ripples were orientated perpendicularly to the orientation of the beam stripe and their length increased with every shifted pulse. Diffraction properties of the gratings were investigated. The grating period changed linearly with the laser fluence and it decreased with increasing the shift between pulses. Small period fluctuations caused extension of the non-zero order diffraction maxima in the diffraction image.