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Title
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Wide‐bandgap organic crystals : enhanced optical‐to‐terahertz nonlinear frequency conversion at near‐infrared pumping
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Author
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Abstract
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| Enhanced terahertz (THz) wave generation was demonstrated in nonlinear organic crystals through refractive index engineering, which improved phase matching characteristics substantially. Unlike conventional low-bandgap nonlinear organic crystals, the newly designed benzimidazolium-based HMI (2-(4-hydroxy-3-methoxystyryl)-1,3-dimethyl-1H-benzoimidazol-3-ium) chromophore possesses a relatively wide bandgap. This reduces the optical group index in the near-infrared, allowing better phase matching with the generated THz waves, and leads to high optical-to-THz conversion. A unique feature of the HMI-based crystals, compared to conventional wide-bandgap aniline-based crystals, is their remarkably larger macroscopic optical nonlinearity, a one order of magnitude higher diagonal component in macroscopic nonlinear susceptibility than NPP ((1-(4-nitrophenyl)pyrrolidin-2-yl)methanol) crystals. The HMI-based crystals also exhibited much higher thermal stability, with a melting temperature Tm above 250 C, versus aniline-based crystals (116 C for NPP). With pumping at the technologically important wavelength of 800 nm, the proposed HMI-based crystals boosted high optical-to-THz conversion efficiency, comparable to benchmark low-bandgap quinolinium crystals with state-of-the-art macroscopic nonlinearity. This performance is due to the excellent phase matching enabled by decreasing optical group indices in the near-infrared through wide-bandgap chromophores. The proposed wide-bandgap design is a promising way to control the refractive index of various nonlinear organic materials for enhanced frequency conversion processes. |
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Language
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English
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Source (journal)
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Advanced Optical Materials. - -
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Publication
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2020
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ISSN
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2195-1071
[online]
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DOI
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10.1002/ADOM.201902099
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Volume/pages
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8
:10
(2020)
, p. 1-13
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Article Reference
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1902099
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ISI
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000536081600017
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Medium
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E-only publicatie
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Full text (Publisher's DOI)
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Full text (open access)
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Full text (publisher's version - intranet only)
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