Optical EngineeringInvestigation of diffractive optical element fabricated on diamond film by use of focused ion beam direct milling
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A novel method of direct transfer of microstructure into diamond films is presented. A diffractive optical element (DOE) with continuous relief and six annuli was directly fabricated on the diamond films by use of focused ion-beam milling (FIBM). The diamond film was coated via hot filament chemical vapor deposition (HFCVD) on a substrate of fused silica. It is shown by the measurement results of Raman spectrum, transmission, and the refractive index of the diamond film before and after the FIBM that little diamond compound is transferred to the graphite during the FIBM, and the influence of the FIBM on the optical properties of the film can be ignored. The surface roughness of the DOE with an Ra value of 2.374 nm is derived by use of an atomic force microscope (AFM) in a partial square area of 1×1 μm2. By the two-dimensional (2-D) profile and three-dimensional (3-D) topography of the DOE it is shown that the surface is smooth and neat, and the relief depth and annulus width of the DOE are in accordance with the design.