Direct laser writing of relief diffraction gratings into a bulk chalcogenide glass

We inscribed relief diffraction gratings with periods of 6, 14, and 24 mu m into the surface of Ge15Ga3Sb12S70 bulk glass by the material's ablation using a femtosecond lambda = 800 nm Ti:sapphire pulsed laser. The laser writing was done with sample implemented on a computer-controlled stage employing surface-to-beam alignment, laser power, and raster pattern control. Pulse energies of 1.5, 3.0, and 4.5 mu J were focused on spot diameter of 1.5 mu m, resulting in channel widths, measured on the surface, of around 4, 5, and 6 mu m and depths up to 1.7 mu m. The first-order diffraction efficiency of the fabricated gratings was up to 10% at lambda = 650 nm. We have also fabricated a "composite" grating combining the three relief diffraction gratings inscribed in the same position, but with a mutual tilt. The composite grating provides complex multidirectional diffraction of the light in accordance with geometrical arrangement and grating period of all the gratings inscribed. We propose practical applications of femtosecond pulsed-laser surface patterning, for example, surface-relief diffraction microgratings integrated at the ends of multimode mid-IR chalcogenide optical waveguides or on the surfaces of bare core chalcogenide glass optical fibers used for chemical sensing. (c) 2012 Optical Society of America