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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Second-Harmonic Generation in Lithium Niobate Metasurfaces
摘要： Lithium niobate (LN), a birefringent crystal, is an attractive material for nonlinear photonics due to its wide transparency range and high second-order nonlinearity. Among other applications, it has been used for fabrication of fast optical modulators and nonlinear frequency converters. However, almost all implementations to date were using bulk LN crystals or waveguides. Although isolated Mie-type nanoresonators in lithium niobate have been shown very recently [1], functional metasurfaces based on densely packed arrangements of such nanoresonators have not yet been demonstrated. In order to close this gap, we have designed, fabricated and experimentally investigated a nonlinear metasurface consisting of an array of nanocubes featuring Mie-type resonances.
关键词： metasurfaces,nonlinear photonics,Mie-type resonances,second-harmonic generation,Lithium niobate
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - All-Optical Ultrafast Control of Second Harmonic Generation in AlGaAs Nanopillars
摘要： All-dielectric nanophotonics has recently raised an increasing interest because the optical response of high-permittivity dielectric nanoparticles exhibits negligible dissipative losses and strong magnetic multipole resonances [1-4] in the visible and near-IR. We recently reported a second harmonic generation (SHG) conversion efficiency higher than 10-5 at (cid:79)= 1554 nm (pump intensity (cid:124) 1.6 GW/cm2; pulse width (cid:124) 150 fs; repetition rate = 80 MHz) in all-dielectric Al0.18Ga0.82As-on-AlOx nanodisks [5-7]. Such a remarkable efficiency is achieved thanks to the exploitation of magnetic and electric resonances emerging at coincidence with both the pump and SHG wavelength. In addition, the choice of both the pump and, consequently, the SHG ((cid:124) 777 nm) wavelength, set below the energy of the material bandgap, allow minimizing the two-photon absorption of the pump and the re-absorption of the SHG. Here, we demonstrate the potential for the all-optical modulation of the SHG. First, we study the behavior of the emitted SHG signal when the nanoantennas are concurrently illuminated with a low-power (< 300 (cid:80)W) continuous wave (CW) laser with energy above the bandgap ((cid:124) 3.2 eV, 405 nm wavelength). We observe variations in the SHG yield of the nanoantennas up to 60%. Figure 1a shows the SHG differential map acquired on an array of nanopillars with variable radius (r). Figure 1b shows the overall SHG intensity (dashed line) as well as the SHG modulation (solid blue line) as a function of r. While SHG from the smaller nanopillar (r = 205 nm) is decreased by about 60% under a 300 (cid:80)W CW pump beam, the 220-nm-radius nanopillar show a 30% SHG enhancement. We also investigated the ultrafast modulation of the SHG in a pump-probe experiment, where the pump is an ultrashort pulse at (cid:79)= 510 nm (above material bandgap), while the probe is a time-delayed pulse at (cid:79)= 1550 nm generating the SHG, to study the SHG dynamics when the pillars are brought out of equilibrium and a transient plasma is photoinjected in the dielectric. Time-traces of the SHG as a function of the pump-probe delay are shown in Figure 1c. We measured an ultrafast SHG quenching (< 0.5 ps) and slower (10 to 100 ps) recovery times, which strongly depend on the nanopillars, hence on the resonances involved. Our results allow gaining further insight into the photophysics of the nonlinear emission in these nanoscale systems and pave the way to the all-optical control of nanoscale nonlinear photonic devices for data storage with AlGaAs-on-insulator all-dielectric platforms.
关键词： Second harmonic generation,All-optical modulation,Nanopillars,All-dielectric nanophotonics,AlGaAs,SHG
更新于2025-09-12 10:27:22
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Quantum-enhanced tunable spin-valley dependent excitonic second harmonic generation in molybdenum disulfide quantum dots
摘要： Developing a robust system with a strong tunable nonlinear second harmonic generation (SHG) is desirable. In this work, we calculate SHG arising from the excitonic states of monolayer molybdenum disulfide quantum dots (MoS2 QDs) with a parabolic confinement potential within massive Dirac fermion model using the density matrix formalism. We theoretically demonstrate that MoS2 QDs can exhibit a giant and tunable Spin-Valley dependent excitonic SHG, which can be tuned from 0 to ～107 pm/V and realized by biasing nanostructured gates or by position-dependent doping. Remarkably, the strength of SHG response is more than two orders of magnitude higher than that in monolayer MoS2. Furthermore, robust excitonic effects together with strong spin-valley coupling in monolayer transition metal dichalcogenides quantum dots (TMDC QDs), which are tunable depending on the strength of the quantum confinement, make them as a promising candidate for ultrathin nonlinear optical materials with large nonlinearities. We believe that this study could spark interest in the nonlinear optical properties of TMDC QDs and open up a variety of new avenues for versatile novel 2D nonlinear photonics and optoelectronic nanodevices.
关键词： second harmonic generation,spin-valley coupling,TMDC QDs,excitonic nonlinear optical properties
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Tailoring Second-Harmonic Generation in Plasmonic Radial Trimers using Cylindrical Vector Beams
摘要： Collective effects in assemblies of plasmonic nanostructures are attracting widespread interest. Such effects are governed by the interactions among the constituents of the overall structure, providing an alternative path to modify plasmon resonances [1]. A particularly interesting collective effect in these structures is the so-called dark plasmon mode, which has a net zero dipole moment and cannot be accessed using plane waves or linearly polarized light under normal incidence. An emerging way to excite collective dark modes in such structures is through the use of cylindrical vector beams (CVB) that exhibit inhomogeneous states of polarization such as azimuthal or radial polarizations [2,3]. The use of CVBs to excite collective nonlinear optical effects such as second-harmonic generation (SHG) in oligomers has started only recently [4]. Here, we demonstrate a similar possibility by tailoring SHG in plasmonic radial trimers using CVBs.
关键词： dark plasmon mode,second-harmonic generation,cylindrical vector beams,plasmonic nanostructures
更新于2025-09-12 10:27:22
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Tailoring the longitudinal electric fields of high-order laser beams and their direct verification in three dimensions
摘要： We demonstrate the tailoring of longitudinal electric fields that arise from tight focusing of spatially phase-shaped high-order laser beams, and verify their spatial distribution in three dimensions. To tailor the three-dimensional (3D) spatial distribution of longitudinal electric fields, we precisely control the relative phase delay between the two lobes of a HG10 laser beam using a spatial light modulator (SLM) before tight focusing. To verify the longitudinal electric fields in the focal volume, we employ 3D microscopic mapping of second-harmonic generation (SHG) from a single semiconductor nanowire that is extremely sensitive to the orientation of the longitudinal electric field. The technique is direct, general and expected to be useful in harnessing and in probing longitudinal electric fields with arbitrary spatial intensity distributions in the 3D focal volume.
关键词： Second-harmonic generation,Polarization,Longitudinal electric field,3D microscopy,Semiconductor nanowire
更新于2025-09-12 10:27:22
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Formation Rules and Dynamics of Photoinduced χ <sup>(2)</sup> Gratings in Silicon Nitride Waveguides
摘要： Silicon nitride has emerged as a prominent platform for building photonics integrated circuits. While its nonlinear properties based on third-order effects have been successfully exploited, an efficient second harmonic generation in standard stoichiometric silicon nitride (Si3N4) waveguides can also be achieved after all-optical poling as was recently shown. The root of such phenomenon has been attributed to the inscription of a self-organized periodic space-charge grating along the waveguide, allowing an effective χ(2) and automatic quasi-phase-matching of pump and second harmonic. However, the different parameters and their role in increasing the efficiency of the process are still not fully comprehended. In this work, we use optical means to identify the general conditions of mode matching occurring during all-optical poling. The overlap integral between pump and second harmonic optical modes is shown to be the governing parameter in determining the features of the χ(2) gratings. Two-photon microscopy measurements of the χ(2) gratings reveal the presence of a secondary periodicity in some of the waveguides used in the study. According to overlap integral simulations such effect can occur due to mode mixing in the waveguide bends. From a study of poling dynamics, we observe that poling efficiency and rate increase as a function of optical pump power and waveguide length. However, in order to initiate poling, a critical pump intensity, which is lower for longer waveguides, must be coupled into waveguide. Temporal and thermal stability tests reveal the nature of charge traps responsible for grating inscription. After applying thermally activated hopping as conductivity mechanism in our samples, we show that only shallow traps seem to be activated during the all-optical poling process.
关键词： stoichiometric silicon nitride,nonlinear optics,all-optical poling,second harmonic generation,quasi-phase-matching
更新于2025-09-12 10:27:22
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - A Tentative Comprehensive Overview of the Second Harmonic Generation from Plasmonic Nanoparticles
摘要： We report in this work a detailed analysis of the competition that takes place between size and symmetry in the second harmonic generation (SHG) response from nanoparticles. SHG, the physical phenomenon entailing the conversion of two photons at a fundamental frequency into a single photon at the harmonic frequency is highly sensitive to symmetry. SHG is indeed forbidden in centrosymmetric materials within the electric dipole approximation. This feature can be exhibited by nanoparticles at the level of their material crystalline structure or their nanoparticle shape. Furthermore, the electric dipole approximation breaks down as the nanoparticles size increases. It is therefore critical to assess carefully both, i.e. material and shape symmetry as well as size, to fully uncover the SHG response from these nanoscale systems. After a discussion on the specific features of the SHG response in nanoparticles at the nanoscale, nanoparticles are classified according to the centrosymmetry or non centrosymmetry of the material they are made of and their geometrical shape. Finally, the role of size in the breaking of the electric dipole approximation is discussed.
关键词： size,nanoparticles,centrosymmetry,second harmonic generation,shape,plasmonics
更新于2025-09-12 10:27:22
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Second harmonic generation by circularly polarized laser beam propagating in obliquely magnetized plasma
摘要： An analytical study of intense radiation generation at second harmonic frequency, by a circularly polarized laser beam propagating in plasma, in presence of an obliquely applied magnetic field, has been presented. Considering a mildly relativistic regime, a perturbation scheme is used for evaluation of transverse components of current density. The current density oscillating at twice the fundamental frequency of the laser field, drives the second harmonic radiation. The amplitude of the circularly polarized second harmonic radiation is derived and its variation with obliqueness of the applied magnetic field is graphically depicted.
关键词： obliquely magnetized plasma,perturbation scheme,mildly relativistic regime,second harmonic generation,circularly polarized laser beam
更新于2025-09-12 10:27:22
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Second-harmonic generation by a chirped laser pulse with the exponential density ramp profile in the presence of a planar magnetostatic wiggler
摘要： Second-harmonic generation of the relativistic self-focused chirped laser pulse in plasma has been studied with the exponential plasma density ramp profile in the presence of a planar magnetostatic wiggler. It is evident that the exponential plasma density ramp is helpful in enhancing second-harmonic generation as, with the introduction of the exponential plasma density ramp, self-focusing becomes stronger and hence, it leads to enhance the harmonic generation of the second order in the plasma. Also, it is observed that the efficiency of second-harmonic generation enhances significantly with an increase in the value of the chirp parameter. Further, the magnetostatic wiggler helps in enhancing the harmonic generation of the second order. This is due to the fact that dynamics of the oscillating electrons is altered due to the Lorentz force which, in turn, modifies the plasma wave and, hence, results in the efficient second-harmonic generation.
关键词： Chirped laser pulse,magnetostatic wiggler,second-harmonic generation,exponential density ramp profile
更新于2025-09-12 10:27:22
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Quasi-Phase-Matching Method Based on Coupling Compensation for Second Harmonic Generation in GaN Waveguides
摘要： We report a novel quasi-phase-matching method based on coupling compensation for second harmonic generation in GaN/AlGaN waveguides on sapphire substrates. The proposed method can overcome limitations of periodically oriented GaN waveguides because of spatial periodic modulation of the light intensity along the propagation direction, rather than the conventional spatial periodic modulation of the nonlinear optical coefficients of GaN. The method can be realized by using a dual-planar or dual-ridge waveguide frequency doubler structure. This concept has the potential to open a new range of applications for broadband on-chip nonlinear frequency conversion.
关键词： second harmonic generation,directional couplers,GaN and AlGaN waveguides,quasi-phase-matching,supermode dispersion,integrated optics
更新于2025-09-12 10:27:22