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Layered Hybrid Perovskites for Highly Efficient Three-Photon Absorbers: Theory and Experimental Observation
摘要： Multiphoton absorption may find many technological applications, such as enhancing the conversion efficiency of solar cells by the utilization of sub-band-energy photons, below-bandgap photodetection through the simultaneous absorption of several infrared photons for photocurrent generation, or light frequency upconversion for high-resolution, 3D imaging. To enhance multiphoton absorption in semiconducting materials, one of the strategies is to explore low-dimensional excitons. Here, a quantum perturbation theory on a giant enhancement in three-photon absorption (3PA) arising from 2D excitons in multilayered crystals of organic–inorganic hybrid perovskites is presented. The maximal 3PA coefficient is predicted to be in the range of 2–7 cm3 GW?2 at 1100 nm, the largest values reported so far for any 2D and bulk semiconductors at room temperature. Excellent agreement between theory and the experimental findings unambiguously demonstrates a pivotal role in the enhancement of 3PA played by 2D excitons. The theory predicts that the resonant 3PA coefficient should be enhanced further by at least two orders of magnitude with very low temperature. The findings are essential for understanding giant 3PA arising from 2D excitons in layered hybrid perovskites and may open new pathways for highly efficient conversion from infrared light energy to either electrical energy or higher-frequency light emission/lasing.
关键词： nonlinear optics,three-photon absorbers,2D excitons,hybrid perovskites
更新于2025-09-04 15:30:14
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First Hyperpolarizability of 1,3-Thiazolium-5-Thiolates Mesoionic Compounds
摘要： The first hyperpolarizabilities of the mesoionic compounds (MICs) 2-(4-chlorophenyl)-3-methyl-4-phenyl-1,3-thiazole-5-thiolate (MIC-1), 2-(4-chlorophenyl)-3-methyl-4-(4-methylphenyl)-1,3-thiazole-5-thiolate (MIC-2), and (2-(4-chlorophenyl)-3-methyl-4-(4-methoxyphenyl)-1,3-thiazole-5-thiolate) (MIC-3), dissolved in dimethyl sulfoxide (DMSO), are reported here for the first time to our knowledge. Hyper-Rayleigh scattering experiments were performed with an excitation source operating at ?? =1180 nm (?? = 8475 cm?1). The measured hyperpolarizability, ??(2??), was used to calculate the static hyperpolarizability, ??(0), by applying the classical two-level model. The values obtained for ??(0) were 10.1 × 10?30 esu (MIC-1), 8.7 × 10?30 esu (MIC-2) and 10.4 × 10?30 esu (MIC-3) which are smaller than previous theoretical predictions that did not consider features related to the liquid phase.
关键词： nonlinear optics,Hyper-Rayleigh scattering,mesoionic compounds,hyperpolarizability,DMSO
更新于2025-09-04 15:30:14
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Controlling steady-state second harmonic signal via linear and nonlinear Fano resonances
摘要： Nonlinear signal even from a single molecule becomes visible at hot spots of plasmonic nanoparticles. In these structures, Fano resonances can control the nonlinear response in two ways. (i) A linear Fano resonance can enhance the hot spot field, resulting enhanced nonlinear signal. (ii) A nonlinear Fano resonance can enhance the nonlinear signal without enhancing the hot spot. In this study, we compare the enhancement of second harmonic signal at the steady-state obtained via these two methods. Since we are interested in the steady-state signal, we adapt a linear enhancement which works at the steady-state. This is different than the dark-hot resonances that appear in the transparency window due to enhanced plasmon lifetime.
关键词： Fano resonance,nonlinear optics,Quantum plasmonics
更新于2025-09-04 15:30:14
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Continuous wave pumped supercontinuum assisted by a weak femtosecond pulse seed
摘要： We numerically investigate the effects of a weak coherent femtosecond (fs) pulse seed on the continuous wave (CW) pumped supercontinuum (SC) generation. We analyze the evolution of CW pumped SC generation with various random noises and we observe the instabilities, which are initiated by modulation instability, in the spectrum of the SC. To actively control the instabilities, we introduce a weak coherent fs pulse seed to improve the properties of CW pumped SC in terms of spectral bandwidth and pulse-to-pulse stability. The detailed numerical results corroborate that the frequency shift and the peak power of the seed signi?cantly decide the properties of the SC. The present investigation would be highly useful for realizing a broad CW pumped SC with enhanced coherence and SNR.
关键词： ?bers,nonlinear optics,supercontinuum,modulation instability
更新于2025-09-04 15:30:14
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Intermixed Superlattices
摘要： The enhancement of stimulated Raman scattering (SRS) with a GaAs/AlAs intermixed superlattice that works as a χ (3)-quasi-phase-matched structure is studied, where such Kerr-induced effects as four-wave mixing (FWM), self-phase-modulation (SPM), cross-phase-modulation (XPM), and two-photon absorption (TPA) are included. In particular, the efficiency of anti-Stokes generation is enhanced here; anti-Stokes generation inherently has an extremely small efficiency due to a phase mismatch in the interaction of the pump, Stokes, and anti-Stokes waves (while the efficiency of Stokes generation is sufficiently large because of no such phase mismatch). The superlattice enhances the anti-Stokes efficiency up to the order of 103 when compared with that without the superlattice, particularly at a small pump intensity. In this enhancement, it is seen that there is an efficiency boost via simultaneous FWM. In this situation, it is shown how much SPM and XPM degrade the efficiency enhancement. Furthermore, an optimal superlattice length is identified that provides the highest efficiency. The degradation of the efficiency at the optimized length due to TPA is also analyzed. Finally, to gain more anti-Stokes efficiency (or control the sizes of the Stokes and anti-Stokes efficiencies), a photonic-band-gap cavity structure is proposed.
关键词： anti-Stokes generation,nonlinear optics,quasi-phase-matching,GaAs/AlAs superlattice,stimulated Raman scattering
更新于2025-09-04 15:30:14