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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Optical Generation of High-power Terahertz Pulses for Tunable Wave Source
摘要： High-power terahertz pulse generation and its polarization and frequency control by optical rectification with nonlinear organic crystals were studied. Terahertz pulses up to 730 nJ/pulse was generated from a DAST crystal pumped by 250 μJ femotosecond laser pulses with a central wavelength of 1500 nm. The terahertz peak electric field is estimated as 860 kV/cm if we focus the terahertz beam to φ=300 μm spot, which is expected to nonlinear material control application. We proposed the high-power terahertz polarization pulse shaping using the double stacked nonlinear organic crystals excited with tailored pump pulses. Through the terahertz modulation of pump pulses, the waveform shaping of the high-power terahertz pulses are expected, which leads to selective excitation of molecules or spin waves.
关键词： optical rectification,terahertz pulses,nonlinear organic crystals,polarization control,DAST crystal
更新于2025-09-23 15:21:01
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Widea??Bandgap Organic Crystals: Enhanced Opticala??toa??Terahertz Nonlinear Frequency Conversion at Neara??Infrared Pumping
摘要： Enhanced terahertz (THz) wave generation is demonstrated in nonlinear organic crystals through refractive index engineering, which improves 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 exhibit 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 boost 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.
关键词： organic crystals,terahertz,refractive index engineering,phase matching,nonlinear optics
更新于2025-09-23 15:19:57
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Xa??Shaped Alignment of Chromophores: Potential Alternative for Efficient Organic Terahertz Generators
摘要： Efficient broadband organic terahertz (THz) generators using X-shaped alignment of the nonlinear optical chromophores, as an alternative to the parallel alignment of chromophores in benchmark organic crystals, are reported. All the developed six organic benzothiazolium crystals exhibit an isomorphic X-shaped alignment of chromophores, resulting in an unprecedentedly large off-diagonal optical nonlinearity (>100 × 10?30 esu), which presents one of the largest off-diagonal optical nonlinearity of organic crystals. The benzothiazolium crystals exhibit efficient broadband THz wave generation employing the off-diagonal optical nonlinearity, in contrast to the present state-of-the-art organic THz generators that mostly utilize diagonal optical nonlinearity. For using off-diagonal and diagonal optical nonlinearities, the polarization of the optical pump is perpendicular and parallel, respectively, to the polar axis of crystals. In addition to a large THz wave generation efficiency with one order of magnitude higher peak-to-peak THz electric field than that generated in a 1.0-mm-thick inorganic benchmark ZnTe crystal, the benzothiazolium crystals generate broadband THz spectra with an upper cut-off frequency of near 8 THz, and the absence of strong absorption dimples in the range of 0.5?4 THz. Therefore, the X-shaped alignment of chromophores presents an interesting potential alternative for efficient broadband organic THz generators.
关键词： nonlinear optical crystals,THz generators,organic crystals
更新于2025-09-19 17:13:59
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Fluorinated Organic Electro-Optic Quinolinium Crystals for THz Wave Generation
摘要： Fluorinated electro-optic crystals with state-of-the-art second-order nonlinear optical response and excellent characteristics for terahertz (THz) wave generation are reported. The fluorinated organic ionic crystals consist of optically highly nonlinear fluorinated HM6FQ (6-fluoro-2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) or HM7FQ (7-fluoro-2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) cations and 4-methylbenzenesulfonate (T) counter anions. Compared to benchmark electro-optic crystals based on nonfluorinated HMQ (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) cations, introducing fluorine substituent on HM6FQ cations creates additional hydrogen bonds (ArF···HC). Such a molecular engineering leads to an enhanced thermal stability and significant modulations of phonon vibrational modes of crystals in THz frequency region, while excellent π–π stacking and space filling characteristics of HM6FQ cations in crystals lead to state-of-the-art diagonal component of the macroscopic nonlinear optical susceptibility, similar to the case of HMQ cations. HM6FQ-based crystals exhibit a very high optical-to-THz conversion efficiency, comparable to benchmark HMQ-based crystals. In addition, due to additional hydrogen bonds induced by fluorine substituents, the spectral shape of the generated THz wave is remarkably modified; e.g., the largest spectral gap is near 1.5 and 2.0 THz for HM6FQ- and HMQ-based crystals, respectively. The fluorinated cationic engineering on nonlinear optical crystals having benchmark nonlinear optical response is, as far as is known, reported for the first time.
关键词： organic crystals,nonlinear optics,terahertz waves,electro-optics
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Exceptionally high THz energy densities generated from organic crystals pumped with mid-infrared pulses
摘要： Optical Parametric Chirped-Pulse Amplification (OPCPA) is an emerging laser technology, providing a flexibility in operating wavelengths and power upscaling. Here, we investigate THz generation in organic crystals (DAST) by optical rectification (OR) of intense Mid–Infrared (MIR) pulses. The broadband spectrum exceeds several octaves when pumped by 100 fs, 3.9 μm OPCPA pulses. We report on an extraordinarily high THz energy density of 3.1 mJ/cm2 and crystal damage threshold > 150 mJ/cm2.
关键词： optical rectification,OPCPA,mid-infrared pulses,THz generation,organic crystals
更新于2025-09-11 14:15:04