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Accurate polarization control in nonorthogonal two-axis Lloyd’s mirror interferometer for fabrication of two-dimensional scale gratings

Abstract. An optical setup for the nonorthogonal two-axis Lloyd’s mirror interferometer, which is composed of a nonorthogonal type of mirror-substrate assembly and a newly designed beam expansion assembly, is proposed to fabricate highly precise two-dimensional (2-D) diffraction scale gratings having uniform pattern structures over a wide area. The beam expansion assembly is designed in such a way that a thin collimated laser beam is at first generated by a small collimating lens to carry out a precise polarization modulation control of subdivided wavefronts in the beam, followed by the generation of a collimated laser beam with the expansion of the thin collimated laser beam by using a beam expander. Since a pair of high-precision half-wavelength plates made of crystalline quartz can be employed in the newly designed optical setup, a much better polarization modulation control can be expected, compared to the conventional optical setup in which low-precision large-size half-wavelength plates made of polycarbonate should have been employed. To verify the effectiveness of the proposed optical setup, theoretical calculations and some basic experiments are carried out by using a prototype optical setup to demonstrate the feasibility of the proposed optical setup for fabrication of highly precise 2-D scale gratings.