Reflection gratings as polarization converters

An experimental and theoretical modelling study of corrugated gold surfaces, where the refractive index of the upper medium is varied to change the effective wavelength of the incident radiation, is presented. For certain corrugation amplitudes we show that it is possible to convert nearly 100% of plane polarized light incident normal to the average plane of the grating surface into the orthogonal polarization. Investigations of the incident radiation's E-fields immediately above the corrugated surface show that the physical origin of this phenomenon rests with the phase retardation introduced by reflection. It is found that optimum polarization conversion occurs when the component of the optical E-field parallel to the grating wavevector is retarded by 180° with respect to the component parallel to the grooves.