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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Knowledge-aided Color Loading Sparse Recovery STAP Algorithm
摘要： We numerically study the dynamics of supercontinuum generation (SCG) for a variety of possible combinations of photonic crystal fibers (PCFs) and ultrafast fiber laser pulses that the current technologies offer. Three types of PCFs typically used in SCG and four representative types of ultrafast fiber laser pulses are considered for this combinatorial study. We numerically model and qualitatively discuss the nonlinear evolution of the pulses for their whole 12 combinatorial cases. We also quantitatively analyze their output spectra and organize a performance chart for them in terms of spectral bandwidth, flatness, and degree of spectral coherence. Finally, we suggest the most viable combinations among the given PCFs and ultrafast fiber laser pulses in order for generating a target supercontinuum spectrum for various specific cases.
关键词： Optical fiber laser,nonlinear optics,supercontinuum generation,ultrashort pulse
更新于2025-09-23 15:19:57
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Nonlinear optics with resonant metasurfaces
摘要： The field of nonlinear optics is a well-established discipline that relies on macroscopic media and employs propagation distances longer than a wavelength of light. Recent progress with electromagnetic metamaterials has allowed for the expansion of this field into new directions of new phenomena and novel functionalities. In particular, nonlinear effects in thin, artificially structured materials such as metasurfaces do not rely on phase-matching conditions and symmetry-related selection rules of natural materials; they may be substantially enhanced by strong local and collective resonances of fields inside the metasurface nanostructures. Consequently, nonlinear processes may extend beyond simple harmonic generation and spectral broadening due to electronic nonlinearities. This article provides a brief review of basic concepts and recent results in the field of nonlinear optical metasurfaces.
关键词： frequency conversion,high-harmonic generation,resonances,metasurfaces,nonlinear optics
更新于2025-09-23 15:19:57
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Microcavity Nonlinear Optics with an Organically Functionalized Surface
摘要： We report enhanced optical nonlinear effects at the surface of an ultrahigh-Q silica microcavity functionalized by a thin layer of organic molecules. The maximal conversion efficiency of third harmonic generation reaches ～1680%=W2 and an absolute efficiency of 0.0144% at pump power of ～2.90 mW, which is approximately 4 orders of magnitude higher than that in a reported silica microcavity. Further analysis clarifies the elusive dependence of the third harmonic signal on the pump power in previous literature. Molecule-functionalized microcavities may find promising applications in high-efficiency broadband optical frequency conversion and offer potential in sensitive surface analysis.
关键词： Nonlinear Optics,Microcavity,Third Harmonic Generation,Surface Functionalization,Organic Molecules
更新于2025-09-23 15:19:57
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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) - Hot Electrons Modulation of Third Harmonic Generation in Graphene
摘要： Hot-electrons dominate the ultrafast (～fs-ps) optical and electronic properties of metals and semiconductors and they are exploited in a variety of applications including photovoltaics and photodetection. Here we perform power-dependent third harmonic generation (THG) measurements on gated single layer graphene (SLG) and we show that hot-electrons modulate significantly the power-law dependence of THG, inducing a large deviation from the expected cubic power-law. We use a Chemical Vapor Deposition (CVD) SLG sample transferred on Fused Silica (FS) and gated by ionic liquid (IL), Fig.1(a). We excite the sample with the idler beam of an Optical Parametric Oscillator (OPO, Coherent) at a photon energy of ?ω0=0.69eV. The OPO is seeded by a mode-locked Ti:Sa laser (Coherent) with 150fs pulse duration and 80MHz repetition rate. The OPO idler spot-size is～4.7μm and the pulse duration ～300fs.
关键词： Hot electrons,nonlinear optics,third harmonic generation,graphene
更新于2025-09-23 15:19:57
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Femtosecond-laser direct-writing volume phase gratings inside Gea??Asa??S chalcogenide glass
摘要： In this study, volume-phase gratings (VPGs) were fabricated inside Ge–As–S chalcogenide glasses (ChG) with femtosecond-laser writing technology. VPGs with high thicknesses were obtained through single-step writing by exploiting the self-focusing effect of highly nonlinear ChGs. The clear diffraction patterns and high diffraction efficiency of the prepared gratings indicated their high optical performance. Testing results showed that the diffraction efficiency of VPGs first increased with laser pulse energies and then decreased when the laser damage threshold of the glass reached 9.42 nJ. Grating thickness also exhibited the same trend as laser pulse energies and reached the maximum value of 28 μm at 9.42 nJ. The changes in the refractive indexes of volume gratings fabricated under different laser pulse energies were carefully investigated. The changes in the refractive indexes of the gratings remained at the same level while laser pulse energy was increased. Meanwhile, grating thickness played a key role in diffraction efficiency. The maximum diffraction efficiency of the prepared VPGs reached 50% at 808 nm under optimized laser parameters.
关键词： chalcogenide glass,volume-phase grating,laser direct-writing,nonlinear optics
更新于2025-09-23 15:19:57
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Active control of multiple, simultaneous nonlinear optical processes in plasmonic nanogap cavities
摘要： Plasmonic structures are promising to enhance and control nonlinear optical processes as the subwavelength-scale elements not only increase the local electric field intensities but also result in relaxed phase matching conditions. This opens the possibility to observe and further manipulate multiple nonlinear optical processes simultaneously which would be forbidden in bulk crystals due to incompatible phase matching requirements. Here we enhance and control the relative strength between third harmonic generation (THG), sum frequency generation (SFG) and four wave mixing (FWM) arising from 1-7 nm Al2O3 layers sandwiched between a gold film and silver nanorectangles. We demonstrate that the relative strength of the three, simultaneous nonlinear optical processes can be precisely controlled by either the ratio between the powers of the two excitations or the thickness of the Al2O3 layer. Furthermore, enhancements up to 106-fold for THG and FWM are observed along with 104-fold enhancements for SFG response when the resonance of the transverse and longitudinal mode of the cavity are matched to the two pump excitations. The ability to obtain and control multiple, nonlinear optical processes simultaneously opens new capabilities for advanced on-chip manipulation and processing of optical signals on the deep nanoscale.
关键词： metasurface,frequency conversion,plasmonics,tuning,nonlinear optics
更新于2025-09-23 15:19:57
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A simple FBG Fabry-Perot sensor system with high sensitivity based on fiber laser beat frequency and Vernier effect
摘要： We numerically study the dynamics of supercontinuum generation (SCG) for a variety of possible combinations of photonic crystal fibers (PCFs) and ultrafast fiber laser pulses that the current technologies offer. Three types of PCFs typically used in SCG and four representative types of ultrafast fiber laser pulses are considered for this combinatorial study. We numerically model and qualitatively discuss the nonlinear evolution of the pulses for their whole 12 combinatorial cases. We also quantitatively analyze their output spectra and organize a performance chart for them in terms of spectral bandwidth, flatness, and degree of spectral coherence. Finally, we suggest the most viable combinations among the given PCFs and ultrafast fiber laser pulses in order for generating a target supercontinuum spectrum for various specific cases.
关键词： Optical fiber laser,supercontinuum generation,nonlinear optics,ultrashort pulse
更新于2025-09-23 15:19:57
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Off-Resonance Control and All-Optical Switching: Expanded Dimensions in Nonlinear Optics
摘要： The theory of non-resonant optical processes with intrinsic optical nonlinearity, such as harmonic generation, has been widely understood since the advent of the laser. In general, such effects involve multiphoton interactions that change the population of each input optical mode or modes. However, nonlinear effects can also arise through the input of an off-resonant laser beam that itself emerges unchanged. Many such effects have been largely overlooked. Using a quantum electrodynamical framework, this review provides detail on such optically nonlinear mechanisms that allow for a controlled increase or decrease in the intensity of linear absorption and fluorescence and in the efficiency of resonance energy transfer. The rate modifications responsible for these effects were achieved by the simultaneous application of an off-resonant beam with a moderate intensity, acting in a sense as an optical catalyst, conferring a new dimension of optical nonlinearity upon photoactive materials. It is shown that, in certain configurations, these mechanisms provide the basis for all-optical switching, i.e., the control of light-by-light, including an optical transistor scheme. The conclusion outlines other recently proposed all-optical switching systems.
关键词： absorption,nonlinear optics,all-optical switch,resonance energy transfer,fluorescence,FRET,optical transistor,multiphoton process,laser action,second harmonic generation
更新于2025-09-23 15:19:57
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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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The TeraFERMI Electro-Optic Sampling Set-Up for Fluence-Dependent Spectroscopic Measurements
摘要： TeraFERMI is the THz beamline at the FERMI free-electron-laser facility in Trieste (Italy). It uses superradiant Coherent Transition Radiation emission to produce THz pulses of 10 to 100 μJ intensity over a spectral range which can extend up to 12 THz. TeraFERMI can be used to perform non-linear, ?uence-dependent THz spectroscopy and THz-pump/IR-probe measurements. We describe in this paper the optical set-up based on electro-optic-sampling, which is presently in use in our facility and discuss the properties of a representative THz electric ?eld pro?le measured from our source. The measured electric ?eld pro?le can be understood as the superimposed emission from two electron bunches of different length, as predicted by electron beam dynamics simulations.
关键词： THz spectroscopy,free-electron-lasers,nonlinear optics
更新于2025-09-23 15:19:57