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Synthesis of second-order nonlinear optical chromophores with conjugated steric hindrances for electro-optics @850 nm
摘要： Electro-optic materials at the shortwave infrared window (850 nm) of optical fiber is significant for free-space telecommunication and short-distance local area network. However, most of current high-performance organic nonlinear optical chromophores (absorption bandgap ~1.5 eV) are designed for the operation windows of 1310 nm (O band) or 1550 nm (C band), which are not transparent at 850 nm (bandgap ~1.45 eV). The design and synthesis of chromophores for 850 nm is more challenging because regular bandgap engineering to improve microcroscopic nonlinearity (μβ value) might be not available due to the bandgap restriction (optical transparency) @ 850 nm. In this respect, this manuscript utilizes the strategy of suitable site-isolation in molecular engineering to optimize comprehensive performance of chromophores for electro-optics @850 nm. Vilsmeier formylation is facilitated on symmetric or asymmetric donor-π-donor intermediate dyes to form donor-π-acceptor (D-π-A) chromophores C1 and C2 with tuneable conjugated steric hindrance (site-isolator). Without significant red-shift of absorption spectra, conjugated steric hindrance groups contribute to large enhancement of chromophores’ μβ values and ensure optical transparency @ 850 nm. The μβ values of C1 (6706 ? 10-48 esu) and C2 (7279 ? 10-48 esu) with conjugated site-isolation groups are much higher than previously reported chromophores for 850 nm. The structure-property relation reveals that a suitable site-isolator is extremely significant for realizing highly efficient translation of microscopic hyperpolarizability into macroscopic electro-optic coefficients. As a results, electro-optic coefficients of 94 pm/V @ 830 nm are achieved. To the best of our knowledge, this is the highest value for organic electro-optics materials @ 850 nm.
关键词： Electro-optic materials,Vilsmeier formylation,conjugated steric hindrance,site-isolation,nonlinear optical chromophores
更新于2025-09-23 15:19:57
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LiGa0.54In0.46S2: A New Infrared Nonlinear Optical Material with Large Laser Damage Threshold Designed by Gallium substitution in LiInS2
摘要： Larger second-order harmonic generation (SHG) efficiency and high laser damage threshold (LDT) are two crucial requirements for the practical applications of IR nonlinear optical (NLO) materials. Li-(Ga, In)-Q2 (Q = S, Se) is a well-known IR NLO materials system, in which In–Q bonds are more covalent than Ga–Q bonds and benefit larger SHG efficiency. However, the incompatibility between LDT and SHG leads to a smaller LDT of LiInS2 than that of LiGaS2. A new IR NLO compound LiGa0.54In0.46S2 was successfully synthesized by the introduction of gallium in LiInS2, where mixing Ga3+ in In3+ sites result in a wider band-gap of 3.86 eV and a smaller thermal expansion anisotropy value (0.26) compared with LiInS2, leading to the large LDT of 12 times that of commercial AgGaS2 under 1064 nm at room temperature. Meanwhile, the title compound had a relatively strong SHG efficiency of about 0.6 times that of AgGaS2 under a 1910 nm laser radiation. This work highlights the strategy of pursuing IR NLO materials with high LDTs by atom doping in classic material systems.
关键词： laser damage threshold,Infrared nonlinear optical,second-order harmonic generation
更新于2025-09-23 15:19:57
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Q-switched all-fiber laser based on MoSe <sub/>2</sub> films with chemical vapor deposition method
摘要： In this work, MoSe2 ˉlm is synthesized by the chemical vapor deposition method. Saturable absorber (SA) is assembled with the tapered ˉber and MoSe2 ˉlms. Q-switched operation is achieved with the MoSe2-based SA. The experimental result reveals that the MoSe2-based SA has excellent saturable absorption characteristic with 23.41% modulation depth. When the pump power is greater than 289.2 mW, Q-switched all-ˉber lasing action is demonstrated. The repetition rate of the Q-switched pulses varies from 185.6 to 252.8 kHz. The shortest pulse duration is 801.9 ns, and the largest output energy is 69.3 nJ. Results indicate that MoSe2 ˉlms can provide new opportunities for large-modulation-depth optical modulators in ultrafast photonics.
关键词： Q-switched,saturable absorbers,ˉber laser,Nonlinear optical materials
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Difference-frequency generation in the cavity of a dual-wavelength semiconductor disk laser: Effect of absorption of the short-wavelength radiation in the a??long-wavelengtha?? active region on the operation point stability
摘要： A difference-frequency generation in the external cavity of a dual-wavelength semiconductor disk laser (SDL) is numerically studied. The dual-wavelength SDL itself has been designed to emit two optical beams simultaneously – the short-wavelength beam (usually referred to as the pump) and the long-wavelength beam (signal). The study is performed with the help of the mathematical model based on a set of ordinary differential equations with a time delay. The model takes into account possible absorption of the pump radiation in the active region designed to provide gain for the signal. The steady state operation point, its stability, and transient dynamics of intra-cavity difference-frequency generator (ICDFG) are analyzed. As the pump radiation absorption exceeds the critical value, the operation point is shown to lose the stability within the certain interval of the primary pomp power. The steady-state instability of the ICDFG develops to the multi-scaled oscillations of high amplitude.
关键词： semiconductor disk laser,difference-frequency generation,intracavity nonlinear optical interaction
更新于2025-09-23 15:19:57
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Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna
摘要： We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.
关键词： quantum emitter,plasmonics,nonlinear optical response,Second-harmonic generation,electromagnetic coupling
更新于2025-09-23 15:19:57
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Nonlinear optical properties of colloidal CdSe/ZnS quantum dots in PMMA
摘要： The colloidal CdSe/ZnS quantum dots (QDs) in the PMMA polymer film with different QDs concentrations were fabricated. The influence of QDs concentration and excitation pump energy on nonlinear optical (NLO) properties of PMMA capped CdSe/ZnS QDs was investigated by the Z-scan technique with nanosecond laser pulses in the near-infrared spectral band. A large effective nonlinear absorption coefficient (βeff～?10?13 esu) due to the saturable absorption was observed. It was found that the appropriate concentration could lead to the reinforcement of NLO effect. In addition, the impact of the excitation energy on the nonlinear refractive index n2, real and imaginary parts of the third-order nonlinear optical susceptibility was also performed. This study involving the light–matter interactions in the colloidal quantum dots will benefit potential NLO-based applications of optoelectronics, optical modulation and photonics.
关键词： nanophotonics,semiconductor colloidal quantum dots,impact behavior,Z-scan technique,nonlinear optical (NLO) properties
更新于2025-09-23 15:19:57
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Enhanced Broadband and Harmonic Upconversion from Coupled Semiconductor and Metal Nanoparticle Films
摘要： The enhancement of the nonlinear optical properties of hybrid nanoparticle ?lms by coupling between metallic and plasmonic semiconducting nanoparticles is shown. A heterostructure comprising CuS and Au nanoparticle ?lms separated by a thin layer of insulating ligands enhanced the yield of second-harmonic light by a factor of 3.3 compared with the sum of the constituent nanoparticles on their own. Heterostructures were fabricated with scalable solution-processing techniques that can create devices of arbitrary geometry. In addition to harmonic generation, the multiple-photon photoluminescence response of Au, CuS, and heterostructured ?lms is also explored.
关键词： plasmon,heterostructure,copper sul?de nanoparticle,second-harmonic generation,gold nanoparticle,multiphoton photoluminescence,nonlinear optical material
更新于2025-09-23 15:19:57
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Hydrogen order at the surface of ice I <sub/>h</sub> revealed by vibrational spectroscopy
摘要： Among numerous crystalline phases of ice, the Ih phase is the most stable above 72 K at atmospheric pressure. It is well established that the orientations of water molecules in the bulk of ice Ih are statistical without long-range order. However, the orientational order of water at the surface of ice Ih has been enigmatic. Here we show that the surface of ice Ih at 100 K has hydrogen order with the OH group pointing upward to the air (‘‘H-up’’ orientation). We applied nonlinear optical spectroscopy and theoretical modeling to the surface of isotopically pure and diluted ice Ih and observed OH stretch vibrational signatures attributed to H-up ordering. Furthermore, we found that this hydrogen order takes place despite a more inhomogeneous microenvironment at the surface than in the bulk. Our results suggest the prominent role of the surface to allow the reorientation of water molecules for hydrogen ordering that is virtually prohibited in the bulk.
关键词： surface structure,ice Ih,hydrogen order,nonlinear optical spectroscopy,vibrational spectroscopy
更新于2025-09-23 15:19:57
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Semiconducting Polymer Dots as Broadband Saturable Absorbers for Q-switched Fiber Lasers
摘要： Semiconducting polymer dots (Pdots) have attracted much attention due to their outstanding optical properties. However, Pdots potential in laser technology is rare. Here, we first report the benzobisthiadiazole (BBT)-based Pdot as a single broadband nonlinear saturable absorber (SA) for passively Q-switched fiber lasers at 1, 1.5, and 2 μm. The Pdots-SA possesses a strong saturable absorption, broadband nonlinear optical response, and large modulation depth. Once the Pdots-SA is integrated into the ytterbium-, erbium-, and thulium-doped fiber laser cavities, stable Q-switched operations are observed at the central wavelengths of 1036, 1561, and 1951 nm. Our results verify that the Pdots are promising nonlinear media for Q-switched pulses generation, and highlight the potential of Pdots for relevant nonlinear optical applications.
关键词： Saturable absorber,Semiconducting polymer dots,Q-switched fiber lasers,Broadband nonlinear optical response
更新于2025-09-23 15:19:57
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Enhancement of nonlinear optical and thermal properties of polyurethanes by modifying the chromophores with fused heterocyclic and pyrimidine rings
摘要： This article describes the synthesis of substituted triazolo[3,4-b]-thiadiazole heterocycles based nonlinear optical (NLO) responsive chromophores. To enhance the NLO properties of the chromophores, the pyrimidine ring was introduced with an appropriate π-bonding. With these chromophores, different series of polyurethanes were prepared by condensation with tolylene-2,4-diisocyanate and 3,30-dimethoxy-4,40-biphenylene diisocyanate. The structure of the resulting chromophores and polyurethanes was confirmed using Fourier transform infrared, proton nuclear magnetic resonance, and Carbon Hydrogen Nitrogen (CHN) analyzer. The inherent viscosities (ηinh) of the polyurethanes measured by Ubbelohde viscometer were in the range of 0.2324–0.2760 dl/g. Thermal behavior of the polyurethanes was investigated using differential scanning calorimetry and thermogravimetric analysis. The molecular orientation in polyurethane films was induced by a corona poling, and this was ascertained using ultraviolet-visible spectrophotometer and atomic force microscope. The thicknesses and refractive indices of thin films were determined by an Ellipsometer. Polyurethanes exhibited excellent solubility in most of the common organic solvents. The second harmonic generation (SHG) coefficients (d33) of the poled polyurethanes ranged from 63.20 and 95.32 pm/V at 532 nm. None of the polyurethanes showed SHG decay below 100°C, and retained 95% of the signal even up to 500 h. The resulting enhanced NLO efficiency and longer temporal stability make these polyurethanes as promising candidates for photonic devices.
关键词： Polyurethanes,Second harmonic generation,Chromophores,Thermal stability,Nonlinear optical materials
更新于2025-09-23 15:19:57