Optical Second-Harmonic Generation of Terahertz Field from n-type InSb Semiconductors
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Optical Second-Harmonic Generation of Terahertz Field from n-type InSb Semiconductors Devki Nandan Gupta1 Received: 21 May 2020 / Accepted: 15 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this paper, optical second-harmonic generation of terahertz field from n-type InSb semiconductors is investigated. The inter-band transitions generate electron-hole charge carriers in narrow bandgap semiconductors. The nonlinear interaction of terahertz fields with charge carriers within the absorption depth produces a nonlinear current at twice of the fundamental THz frequency, which generates second-harmonic terahertz photons. The conversion efficiency of second-harmonic generation is enhanced by the resonant density perturbations of the charge carriers. The results based on computational fluid dynamics show the generation of second-harmonic radiation spectrally centered at 2 THz frequency with 8 MeV energy. This mechanism for optical second-harmonic generation of terahertz may open new realms of semiconductor characterization, for which terahertz techniques are ideally suited. Keywords Terahertz radiation · Semiconductors · Nonlinear current
Introduction The interaction of terahertz (THz) field with semiconductors is a fascinating field of research. The semiconductor crystal characterization by THz field has been one of the crucial processes in material science over the last several decades [1–3]. The generation of electromagnetic radiation in THz frequency band is of significant interest at present due to a growing number of applications such as imaging, surface characterization, photo-conductive switch, and biomedical applications [4–7]. In narrow bandgap semiconductors, the inter-band transitions create high-density charge carriers (electronhole) [8]. At this high-density, these charge carriers show the collective behaviors to form a plasma [9]. The electronhole plasma is a nonlinear Kerr medium, which shows the nonlinear response to the electromagnetic fields [10, 11]. The charge carrier density perturbations associated with the pump field generate oscillations at plasma frequency (which may be comparable or twice to the
Devki Nandan Gupta
[email protected] 1
Department of Physics and Astrophysics, University of Delhi, Delhi, 110 007, India
THz frequency). The generation of THz radiation from n-type InSb semiconductors has attracted much attention from researchers for a long time [12–14]. The InSb semiconductor surface emission has been proved to be a relatively bright source of pulsed THz radiation. THz field has also been shown to be a successful tool to induce and probe the scattering dynamics in bulk semiconductors such as indium-arsenide (InSb) [15, 16]. Optical second-harmonic generation (SHG) of THz radiation in narrow bandgap semiconductors has been proved to be a method of frequency up-conversion of THz for crystal characterization [17, 18]. The fundamental wave at THz frequency imparts oscillatory velocity to the electron charge carriers (as the hol
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