Detection of subwavelength slit-width variation with measurements in the far field by use of an embedded-aperture interferometer configuration

The dynamic signature of the subwavelength variation of a rectangular aperture has recently been shown to be determinable from far-field irradiance with a precision better than 1 nm [Opt. Lett. 29, 1045 (2004)]. We have proposed, and have theoretically shown, that detection sensitivity can be greatly enhanced with an embeddedaperture Mach-Zehnder interferometer configuration, after parameter optimization. The sensitivity, in terras of derivative intensity of observed subwavelength variations, could be enhanced approximately 2.7 times, compared with the directly detected method. Another method of detection of subwavelength variation from pattern measurement of far-field diffraction has also been proposed. The associated shifting of the dark line of the diffraction pattern had a good linear correlation to subwavelength variation, which was magnified approximately 150 times, and gave good contrast for measurement.