Optical diffraction gratings produced by laser interference structuring of amorphous germanium–nitrogen alloys

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We use the interference of two pulsed laser beams (wavelength=355 nm) to produce an optical diffraction grating in amorphous germanium–nitrogen alloy (a-GeN). At the constructive maxima of the interference pattern, the absorption of light leads to crystallization. The crystallized region results of pure microcrystalline germanium (μc-Ge). An indication that Ge–N bonds have broken and nitrogen outdiffused of the film is obtained from infrared spectroscopy and confirmed by Raman spectra. A pattern of alternating a-GeN and μc-Ge lines with a period of about 4 μm acts as an optical diffraction grating due to the difference in optical properties between the two materials, and the three dimensional surface profile, caused by N2 effusion, that is formed on the sample.