A new method for fabrication of diffractive structures, which we call quasi-direct writing, is illustrated. The diffractive structures can be generated by changing the pixel spacing along the direction of the cross scan (with zero overlap) and keeping the pixel spacing constant along the other scan direction, with a normal overlap of 50%–60%, while the substrate surface is scanned with a focused ion beam (FIB). Quasi-direct writing is a method for achieving special customer designs when the milling machine has no computer programming function. Diffractive structures with various periods and depths can be derived by controlling the parameters of pixel spacing, beam current, ion incidence angle, and the scan time or ion dose. The method is not restricted to any one material and can be used for metals, insulators, and semiconductors.
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