Broadband Anisotropic Optical Properties of the Terahertz Generator HMQ-TMS Organic Crystal

Annalisa D’Arco,Luca Tomarchio,Paola Di Pietro,Massimo Petrarca,Andrea Perucchi,Valerio Dolci,Sen Mou,Stefano Lupi

doi:10.3390/condmat5030047

Annalisa D’Arco, Luca Tomarchio + Show 6 more

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https://doi.org/10.3390/condmat5030047

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Abstract

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the x 1 and x 3 axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm − 1 . We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two x 1 and x 3 axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region.

Highlights

THz radiation (1 THz∼33 cm−1 or 4 meV photon energy) has gained over the years a considerable interest due to its broad variety of applications
A rapid development of both THz generators and detectors has been made possible thanks to novel technologies that have become available in these last two decades, such as quantum cascade lasers, photoconductive antennas, Gunn lasers, and sources based on nonlinear optical (NLO) effects
From the T measurements, one can notice a broad transparent spectral region extending from the mid-IR to the VIS region (5000–20,000 cm−1) for both axes, with a plateau at 83% along x1 and up to 80% along x3, respectively

Summary

Introduction

THz radiation (1 THz∼33 cm−1 or 4 meV photon energy) has gained over the years a considerable interest due to its broad variety of applications. A rapid development of both THz generators and detectors has been made possible thanks to novel technologies that have become available in these last two decades, such as quantum cascade lasers, photoconductive antennas, Gunn lasers, and sources based on nonlinear optical (NLO) effects. The latter realm has been the starting point for the production of single cycle, high-intensity THz signals comparable to those obtained from free-electron facilities [13,14].

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