“…An optical grating can be encoded on a sample surface by two-beam interference using a single near-infrared femtosecond laser pulse [1,2]. Diffraction gratings have been commonly fabricated on silver halide emulsion, photoresist, and photopolymer optical materials, for example [3][4][5]. With individual femtosecond laser pulses, permanent gratings have been encoded on surfaces of glass, crystal, and silicon dioxide thin film [6][7][8][9].…”