Femtosecond Laser Modulated into Bessel Beam by Spatial Light Modulator for Fresnel Zone Plate Processing

Abstract

Femtosecond laser processing is an important machining method for micro-optical components such as Fresnel zone plate (FZP). However, the low processing efficiency of femtosecond laser restricts its application. In this paper, Femtosecond laser Bessel beam was proposed to process FZPs, which is modulated from Gaussian beam to annular beam. The processing time for FZP with outer diameter of 60 μm is reduced from 30 minutes to 1.5 minutes on Gallium arsenide, which significantly improves the processing efficiency. In the modulation process, a central ablation hole which has an adverse effect on the diffraction performance is produced, and the adverse effect is completely eliminated by superimposing the shining grating hologram. Meanwhile, The FZP machined by spatial light modulator has good morphology and higher diffraction efficiency, which provides a strong guarantee for the application of micro-FZPs in computed tomography and solar photovoltaic cells.

Keywords: Femtosend laser, Fresnel zone plate, spatial light shaping, Bessel beam