Phase-shift anomaly caused by subwavelength-scale metal slit or aperture diffraction

Abstract

Terahertz time-domain spectroscopy probes anomalous phase-shift caused by wave diffraction from a subwavelength-scale metal slit or aperture. Carrier frequency phase measurements in the far-field region reveals that nearly 30 degrees phase advance is induced from a subwavelength slit diffraction and that 180 degrees phase-advance from a subwavelength aperture. These results indicate that the conventional 90 degrees phase advance of diffracted waves in the far-field region, known as the Gouy phase shift, is not valid for subwavelength diffraction phenomena. The physical origin of these phase-shift anomalies is attributed to induced electric currents or magnetic dipole radiation, and theoretical analyses based on these factors are in good agreement with the experimental results. (C) 2013 Optical Society of America