- 标题
- 摘要
- 关键词
- 实验方案
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2a??10???μm Mida??Infrared Fibera??Based Supercontinuum Laser Source: Experiment and Simulation
摘要： Mid-infrared supercontinuum (mid-IR SC) sources in the 2–20 μm molecular fingerprint region are in high demand for a wide range of applications including optical coherence tomography, remote sensing, molecular spectroscopy, and hyperspectral imaging. Herein, mid-IR SC generation is investigated in a cascaded silica-ZBLAN-chalcogenide fiber system directly pumped with a commercially available pulsed fiber laser operating in the telecommunications window at 1.55 μm. This fiber-based system is shown to generate a flat broadband mid-IR SC covering the entire range from 2 to 10 μm with several tens of mW of output power. This technique paves the way for low cost, practical, and robust broadband SC sources in the mid-IR without the requirement of mid-infrared pump sources or Thulium-doped fiber amplifiers. A fully realistic numerical model used to simulate the nonlinear pulse propagation through the cascaded fiber system is also described and the numerical results are used to discuss the physical processes underlying the spectral broadening in the cascaded system. Finally, recommendations are provided for optimizing the current cascaded system based on the simulation results.
关键词： soft-glass fibers,nonlinear optics and solitons,supercontinuum generation,chalcogenide fibers,fiber lasers,ZBLAN fibers
更新于2025-09-23 15:21:01
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Saturable plasmonic metasurfaces for laser mode locking
摘要： Metamaterials are artificial materials made of subwavelength elementary cells that give rise to unexpected wave properties that do not exist naturally. However, these properties are generally achieved due to 3D patterning, which is hardly feasible at short wavelengths in the visible and near-infrared regions targeted by most photonic applications. To overcome this limitation, metasurfaces, which are the 2D counterparts of metamaterials, have emerged as promising platforms that are compatible with planar nanotechnologies and thus mass production, which platforms the properties of a metamaterial into a 2D sheet. In the linear regime, wavefront manipulation for lensing, holography, and polarization control has been achieved recently. Interest in metasurfaces operating in the nonlinear regime has also increased due to the ability of metasurfaces to efficiently convert incident light into harmonic frequencies with unusual polarization properties. However, to date, the nonlinear absorption of metasurfaces has been mostly ignored. Here, we demonstrate that plasmonic metasurfaces behave as saturable absorbers with modulation performances superior to the modulation performance of other 2D materials and exhibit unusual polarimetric nonlinear transfer functions. We quantify the link between saturable absorption, the plasmonic resonances of the unit cell and their distribution in a 2D metasurface, and finally provide a practical implementation by integrating the metasurfaces into a fiber laser cavity operating in pulsed regimes driven by the metasurface properties. As such, this work provides new perspectives on ultrathin nonlinear saturable absorbers for applications where tunable nonlinear transfer functions are needed, such as in ultrafast lasers or neuromorphic circuits.
关键词： fiber lasers,metamaterials,plasmonic,saturable absorbers,metasurfaces,nonlinear optics
更新于2025-09-23 15:21:01
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Nonlinear Optics
摘要： The mid-infrared atmospheric window of 3–5.5 μm holds valuable information regarding molecular composition and function for fundamental and applied spectroscopy. Using a robust, mode-locked fiber-laser source of < 11 fs pulses in the near infrared, we explore quadratic (χe2T) nonlinear optical processes leading to frequency comb generation across this entire mid-infrared atmospheric window. With experiments and modeling, we demonstrate intrapulse difference frequency generation that yields few-cycle mid-infrared pulses in a single pass through periodically poled lithium niobate. Harmonic and cascaded χe2T nonlinearities further provide direct access to the carrier-envelope offset frequency of the near infrared driving pulse train. The high frequency stability of the mid-infrared frequency comb is exploited for spectroscopy of acetone and carbonyl sulfide with simultaneous bandwidths exceeding 11 THz and with spectral resolution as high as 0.003 cm?1. The combination of low noise and broad spectral coverage enables detection of trace gases with concentrations in the part-per-billion range.
关键词： few-cycle pulses,mid-infrared,frequency comb,spectroscopy,nonlinear optics
更新于2025-09-23 15:21:01
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Highly Conjugated, Fused-Ring, Quadrupolar Organic Chromophores with Large Two-Photon Absorption Cross-Sections in the Near-Infrared
摘要： The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as non-fullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 103 GM) in the near infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (7 rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement and their moderate magnitudes (ca. 10-21 m2) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.
关键词： pump-probe spectroscopy,Nonlinear optics,Z-scan,organic optoelectronics,ultrafast spectroscopy,two-photon absorption
更新于2025-09-23 15:21:01
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Effect of nonlinear cap layer on TM-polarized surface waves in a graphene-based photonic crystal
摘要： In this paper, we investigated the effect of nonlinear cap layer and the chemical potential of the graphene on the p-polarized surface waves (SWs) in a one-dimensional graphene-based photonic crystal (GBPC). Three different cases were considered for the dielectric tensor of the nonlinear cap layer: (1) perpendicular uniaxial approximation, (2) parallel uniaxial approximation and (3) generic case. The results of the study indicated that the effect of nonlinear cap layer on TM SWs may be neglected due to the perpendicular approximation. On the other hand, in parallel approximation as well as generic form of dielectric function, the frequency of the TM SWs within the graphene-induced band gap (GIPBG) may be controlled by the nonlinear cap layer and the chemical potential of the graphene. Moreover, according to the results, in the GIPBG of GBPC with self-defocusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the same direction. However, with respect to the self-focusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the opposite direction. Consequently, by adjusting the chemical potential in the self-defocusing cap layer, the tunability range of the SW frequency may be extended and in the case of self-focusing, optical nonlinear effects may be eliminated.
关键词： Graphene,First integral,Nonlinear optics,Surface waves,Maxwell’s equations,Photonic crystal
更新于2025-09-23 15:21:01
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Topology Optimization-Based Inverse Design of Plasmonic Nanodimer with Maximum Near-Field Enhancement
摘要： The near-field enhancement factor is one of the most significant parameters to evaluate the performance of plasmonic nanostructures. Numerous efforts have been made to maximize the enhancement factor through optimizing the size, shape, and spatial arrangement of metallic nanostructures with simple geometries, such as disk, triangle, and rod. This work implements topology optimization to inversely design a metallic nanoparticle dimer with the goal of optimizing the near-field enhancement factor in its sub-10 nm gap. By optimizing the material layout within a given design space, the topology optimization algorithm results in a plasmonic nanodimer of two heart-shaped particles having both convex and concave features. Full-wave electromagnetic analysis reveals that the largest near-field enhancement in the heart-shaped nanoparticle dimer is originated from the greatest concentration of surface charges at the nano-heart apex. Inversely designed heart-, bowtie-, and disk-shaped nanodimers are fabricated by using focused helium ion beam milling with a “sketch and peel” strategy, and their near-field enhancement performances are characterized with nonlinear optical spectroscopies at the single-particle level. Indeed, the heart-shaped nanodimer exhibits much stronger signal intensities than the other two structures. The present work corroborates the validity and effectiveness of topology optimization-based inverse design in achieving desired plasmonic functionalities.
关键词： topology optimization,near-field enhancement,plasmonic nanostructures,inverse design,nonlinear optics
更新于2025-09-23 15:21:01
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Nonlinear Optics || The Nonlinear Optical Susceptibility
摘要： Nonlinear optics is the study of phenomena that occur as a consequence of the modification of the optical properties of a material system by the presence of light. Typically, only laser light is sufficiently intense to modify the optical properties of a material system in this manner. The beginning of the field of nonlinear optics is often taken to be the discovery of second-harmonic generation by Franken et al. (1961), shortly after the demonstration of the first working laser by Maiman in 1960. Nonlinear optical phenomena are "nonlinear" in the sense that they occur when the response of a material system to an applied optical field depends in a nonlinear manner on the strength of the applied optical field. For example, second-harmonic generation occurs as a result of the part of the atomic response that scales quadratically with the strength of the applied optical field. Consequently, the intensity of the light generated at the second-harmonic frequency tends to increase as the square of the intensity of the applied laser light.
关键词： Material system,Optical properties,Nonlinear optics,Laser light,Second-harmonic generation
更新于2025-09-23 15:21:01
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Nonlinear Optics || Wave-Equation Description of Nonlinear Optical Interactions
摘要： We have seen in the last chapter how nonlinearity in the response of a material system to an intense laser field can cause the polarization of the medium to develop new frequency components not present in the incident radiation field. These new frequency components of the nonlinear polarization act as sources of new frequency components of the electromagnetic field. In the present chapter, we examine how Maxwell’s equations describe the generation of these new components, and more generally we see how the various frequency components of the field become coupled by the nonlinear interaction.
关键词： wave equation,electromagnetic field,frequency components,Maxwell’s equations,nonlinear optics,polarization
更新于2025-09-23 15:21:01
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Nonlinear Optics || Nonlinear Optics in the Two-Level Approximation
摘要： Our treatment of nonlinear optics in the previous chapters has for the most part made use of power series expansions to relate the response of a material system to the strength of the applied optical field. In simple cases, this relation can be taken to be of the form ?P (t) = (cid:2)0χ (1) ?E(t) + (cid:2)0χ (2) ?E(t)2 + (cid:2)0χ (3) ?E(t)3 + · · · . However, there are circumstances under which such a power series expansion does not converge, and under such circumstances different methods must be employed to describe nonlinear optical effects. One example is that of a saturable absorber, where the absorption coefficient α is related to the intensity I = 2n(cid:2)0c|E|2 of the applied optical field by the relation α = α0 / (1 + I /Is), where α0 is the weak-field absorption coefficient and Is is an optical constant called the saturation intensity. We can expand this equation in a power series to obtain α = α0 [1 ? (I /Is) + (I /Is)2 ? (I /Is)3 + · · · ]. However, this series converges only for I < Is, and thus only in this limit can saturable absorption be described by means of a power series of the sort given by Eq. (6.1.1).
关键词： Rabi oscillations,two-level approximation,saturable absorber,optical Stark shifts,nonlinear optics
更新于2025-09-23 15:21:01
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Nonlinear Optics || Processes Resulting from the Intensity-Dependent Refractive Index
摘要： In this chapter, we explore several processes of practical importance that occur as a result of the intensity-dependent refractive index.
关键词： refractive index,self-trapping,laser beam breakup,self-focusing,nonlinear optics
更新于2025-09-23 15:21:01