Optical EngineeringInvestigation of direct milling of micro-optical elements with continuous relief on a substrate by focused ion beam technology
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A novel method of manufacturing micro-optical elements with continuous relief by focused ion beam (FIB) is described in detail. Microfabrication of diffractive optical elements (DOEs) with feature sizes as small as the submicronmeter range is realized in this way. Making use of direct milling by FIBs, the microstructure on any substrate (metal and nonmetal) and the mold used for micro-optical element replication are realized easily without any other procedures. The DOEs are duplicated by hot-embossing with relief surface roughness [root mean square (rms) value] of 3 nm measured in a 2 x2 µm2 area, which is higher than the 5 nm achieved with conventional methods. In addition, other examples such as a microlens mold, a microcylindrical lens, and a 3 x3 DOE array are introduced briefly.