Refraction of space-time wave packets: II. experiments at normal incidence

The refraction of space-time (ST) wave packets offers many fascinating surprises with respect to conventional pulsed beams. In the first paper in this sequence [J. Opt. Soc. Am. A 38, 1409 (2021)], we theoretically described the refraction of all families of ST wave packets at normal and oblique incidence ata planar interface between two nondispersive, homogeneous, isotropic dielectrics. Here, in this second paper in the sequence, we present experimental verification of the refractive phenomena predicted for baseband ST wave packets upon normal incidence on a planar interface. Specifically, we observe group velocity invariance, normal and anomalous refraction, and group velocity inversion leading to group delay cancellation. These phenomena are verified in a set of optical materials with refractive indices ranging from 1.38 to 1.76, including MgF2, fused silica, BK7 glass, and sapphire. We also provide a geometrical representation of the physics associated with anomalous refraction in terms of the dynamics of the spectral support domain for ST wave packets on the surface of the light cone. (c) 2021 Optical Society of America

Automated summary

This paper theoretically described the refraction of ST wave packets at a planar interface in the first paper of the series, and experimentally verified the refraction of baseband ST wave packets at normal incidence in the second paper. The observed phenomena include group velocity invariance, normal and anomalous refraction, and group velocity inversion leading to group delay cancellation.