Mueller polarimetry as a tool for detecting asymmetry in diffraction grating profiles

Abstract

Reflected Mueller matrix spectra were measured and simulated for asymmetrical photoresist master diffraction gratings in conical mounting (i.e., the direction of grating grooves was not perpendicular to the plane of light incidence). From the electromagnetic reciprocity theorem, Mueller matrix of symmetric grating (composed of only reciprocal materials, and operating in zeroth-order diffraction) is invariant under transposition (M=Mt). For zeroth-order diffraction of asymmetric gratings, the lack of profile rotational symmetry violates this reciprocity and, consequently, breaks the symmetry of the above-mentioned matrix. This property of the Mueller matrix of asymmetric gratings was experimentally observed and numerically modeled at all experimental illumination conditions with the exception of planar mounting (the direction of grating grooves was perpendicular to the plane of light incidence), where there is no cross-polarization effect for the gratings composed of isotropic materials. It was demonstrated that optical nonreciprocity of diffraction gratings can be used for unambiguous detection of grating profile asymmetry. In addition, choosing optimal measurement configuration (i.e., azimuthal angles) considerably increases the sensitivity of the detection technique.