Phase-Insensitive Scattering of Terahertz Radiation

Mihail Petev,Eleonora Rubino,Matteo Clerici,Daniel Moss,François Légaré,Arnaud Couairon,Daniele Faccio,Roberto Morandotti,Niclaswesterberg Niclaswesterberg

doi:10.3390/photonics4010007

Abstract

The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is principally investigated as a means for the detection of radiation in the hardly accessible THz spectral region. Most studies have targeted second-order nonlinear processes, given their higher efficiencies, and only a limited number have addressed third-order nonlinear interactions, mainly investigating four-wave mixing in air for broadband THz detection. We have studied the nonlinear interaction between THz and NIR pulses in solid-state media (specifically diamond), and we show how the former can be frequency-shifted up to UV frequencies by the scattering from the nonlinear polarisation induced by the latter. Such UV emission differs from the well-known electric field-induced second harmonic (EFISH) one, as it is generated via a phase-insensitive scattering, rather than a sum- or difference-frequency four-wave-mixing process.

Highlights

The far-infrared spectral region suffered for years from the lack of adequate sources and detectors—a fact that led the community to identify this evident underdevelopment as the THz Gap.The potential impact of THz photonics on fields such as bio-imaging, pharmaceutical, chemical identification, and security stimulated the research on this topic [1,2], and the THz Gap in almost closed [3]
We performed a numerical study of the nonlinear waves dynamics, and we identified the unexpected signal as the result of a phase-insensitive scattering (PI) of the THz from the intense NIR
We experimentally investigated the nonlinear interaction between intense NIR pulses and THz fields in diamond by recording the spectrum resulting from their nonlinear mixing

Summary

Introduction

Photonics 2017, 4, 7 detection (ABCD) [8], relies on the EFISH process, which can be interpreted—in the framework of four-wave-mixing—as the beating between sum- and difference-frequency generation processes [9] Such beating leads to a phase- and amplitude-modulated signal at the second harmonic of the optical probe. We performed a numerical study of the nonlinear waves dynamics, and we identified the unexpected signal as the result of a phase-insensitive scattering (PI) of the THz from the intense NIR pump [12,13] These results are in keeping with our previous prediction for the scattering from an effective moving dispersive medium [14]

Experiments

Coupled Nonlinear Envelope Equations

Conclusions