Direct Fabrication of Planar Grating by Ultrafast Laser Beam

Femtosecond laser pulse has been used for the machining of the gratings primarily due to its superior advantages over conventional continuous wave (CW) and long pulse lasers for micromachining. In this paper, we develop a novel technique for the fabrication of planar gratings by colliding two beams to generate interference fringes. This technique is simple, fast and low cost. We have successfully fabricated planar gratings on a copper substrate. INTRODUCTION The recent development of femtosecond pulsed lasers has stimulated interest in the field of optical devices, for instance, fiber Bragg gratings , waveguides , micro-optics etc. The fabrication of planar Bragg grating by colliding a pair of femtosecond laser pulses in a transparent material has been reported. The reported experimental setup consists of a regeneratively amplified pulse of ML-Ti sapphire laser, split into two beams by using a half mirror. The two beams, which form an angle (θ ) of 10 to 30° to each other are focussed beneath a top surface of a single crystal diamond. The timing of the pulse is adjusted by using optical delay line. The irradiation induces morphological changes on surface or nearsurface regions of the specimen. A periodic line pattern with a constant spacing of ~2.5μm has