Nonlinear Cherenkov Radiation in an Anomalous Dispersive Medium

Abstract

By using ultrathin nonlinear media, the phase velocity of nonlinear polarization waves can be continuously adjusted. We realized nonlinear Cherenkov radiation (NCR) in an anomalous dispersion medium experimentally, which breaks the minimum speed limit of NCR. This modified nonlinear Cherenkov radiation has two new special states with respect to its prior, i.e., the degenerate state and extreme state. Also, periodically arranged ultrathin nonlinear media can enhance NCR and realize the nonlinear Smith-Purcell effect.

Nonlinear Cherenkov radiation at the interface of two different nonlinear media

“…(3). The SH intensity depends on the sharp change of χ (2) , i.e., if the absolute value of C 1 −C 2 increases, the NCR intensity is enhanced.…”

“…Since we are concerned about the spatial modulation of χ (2) at the medium interface, other properties of media 1 and 2 are supposed to be the same in the simulation. For simplicity and without loss of generality, the dispersion of a β − BaB 2 O 4 crystal (BBO) is assumed for the media on both sides of the interface, unless otherwise stated.…”

“…This angle is determined by the dispersion relation of the nonlinear crystal and generally requires the crystal to be normally dispersive. Previous studies demonstrated that, under anomalous-like dispersion conditions, NCR can also be generated by modulating the phase velocity of the polarization wave [2]. NCR has been thoroughly researched in different nonlinear processes, such as second [3] and cascaded high-order harmonic generation [4][5][6], sum-frequency generation [7], and difference-frequency generation [8].…”

Conical third-harmonic generation in a hexagonally poled LiTaO3 crystal

“…4 In 1998, Berger extended the QPM theory from one dimension to two, proposing the concept of nonlinear photonic crystals. 5 The collinear and noncollinear reciprocal vectors in two-dimensional (2D) nonlinear photonic crystals lead to numerous interesting phenomena, such as nonlinear Talbot self-imaging, 6,7 generation of orbital angular momentum, 8,9 nonlinear generation and manipulation of airy beams, 10 efficient generation of cascaded third harmonic generation (THG), 11 nonlinear Bragg diffraction, 12,13 nonlinear Cherenkov emission, [14][15][16][17][18][19] and nonlinear Raman-Nath diffraction. 20 When an optical beam propagates in a nonlinear photonic crystal, light scattered by the domain walls and defects in the crystal could be involved in the nonlinear optical processes.…”

Tunable diffraction-free array in nonlinear photonic crystal

“…Since the concept of nonlinear photonic crystal, i.e., 2D PPLT crystal, was proposed by Berger27 in 1998, numerous interesting phenomena have been discovered such as non-collinear second-harmonic generation (SHG)28, nonlinear Čerenkov radiations293031, and nonlinear Talbot self-imaging32. Recently, domain engineering in nonlinear photonic crystals for spatial light modulation attracts an increasing research interest.…”