Fabrication of microtransmittance grating using laser induced backside dry etching

Laser induced backside dry etching (LIBDE) is a novel technique, which applied in the micromachining and nanomachining of transparent dielectric materials used for optical elements by direct laser irradiation with the assistance of solid mediums as an absorbed layer. On the basis of exploring two different solid mediums, i.e. Al2O3 powder and alumina ceramic wafer as absorbers, LIBDE with 1064 nm central wavelength pulsed ytterbium doped fiber laser as the irradiation source was successfully applied for the fabrication of periodical microscaled structures on fused silica. The threshold of laser fluence to etch fused silica was 7.47 J/cm2 extrapolated from the experimental data. By using alumina ceramic wafer as the absorber, a microbinary dimensional transmittance grating with the constant of 25 μm was obtained on the silica. The depth of the trench is 4.2 μm, and the root mean square roughness of the trench bottom is below 40 nm according to the measurement of 3D profiler. Additionally, diffraction patterns were observed by the normal incidence of a 532 nm diode indicator laser to examine the optical features of the microbinary grating etched under the different laser fluences.