Nonlinear focusing of Terahertz laser beam using layered superconductor

TL;DR

This paper theoretically demonstrates that a layered superconductor can nonlinear focus a Terahertz laser beam, with the focal properties depending on beam intensity and exhibiting hysteresis, suggesting new control mechanisms for THz beam shaping.

Contribution

It introduces a theoretical model showing nonlinear focusing and hysteresis effects of THz beams in layered superconductors, a novel approach in THz optics.

Findings

Layered superconductor supports lensing of THz beams instead of divergence.

Focal length and waist depend on incident beam intensity.

Hysteresis behavior observed in beam focusing properties.

Abstract

We theoretically study the propagation of a Terahertz (THz) Gaussian beam through a thin sample of layered superconductor. We consider the beam axis and the superconducting layers to be perpendicular to the sample interface, while the electric field in the beam is perpendicular to the layers. We show that, in such a geometry, the Josephson current between the superconducting layers supports lensing of the beam instead of divergence on the Rayleigh range. Moreover, due to the nonlinearity, the focal length and waist of the transmitted beam depend on the incident beam intensity. These dependences demonstrate nontrivial hysteresis behavior that can be observed in experiments with THz lasers.