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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) - Dynamics of Kerr-Like Optical Frequency Combs Generated via Phase-Mismatched Second-Harmonic Generation
摘要： The ability to generate optical frequency combs in nonlinear resonators has attracted significant attention over the last decade. While the majority of studies have considered resonators dominated by the third-order Kerr nonlinearity, more recent investigations have shown that comb generation is also possible through second order nonlinear effects. Experimental works have in particular demonstrated that combs can arise in driven resonators via second-harmonic generation (SHG), both in the presence and absence of a phase-mismatch. Theoretical works have so far focussed almost exclusively on the case of perfect phase-matching. This is somewhat surprising, for it is well-known that phase-mismatched SHG can give rise to a strong effective Kerr nonlinearity coefficient whose sign can be controlled with the phase-mismatch. Here, we theoretically and numerically investigate the generation of Kerr-like frequency combs in resonators under conditions of phase-mismatched SHG. We show that the equations describing intracavity SHG tend towards the Lugiato-Lefever equation of Kerr nonlinear resonators when the phase-mismatch is very large. The resulting effective Kerr nonlinearity coefficient can still exceed that of typical fused silica microcavities. Importantly, the Kerr coefficient is negative if the phase-mismatch is negative, alluding to the possibility of Kerr-like combs in the regime of normal dispersion. In conclusion, we have shown that a cavity subject to phase-mismatched SHG can display pure Kerr cavity dynamics in the regime of very large phase-mismatch. Moreover, we find that localised soliton states can manifest themselves even for intermediate values of phase-mismatch.
关键词： Kerr nonlinearity,optical frequency combs,second-harmonic generation,phase-mismatch,solitons
更新于2025-09-12 10:27:22
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Investigation on intracavity SHG with controllable coherence in a degenerate laser
摘要： We investigate intracavity second harmonic generation (SHG) in a degenerate laser for generating green laser with controllable degree of coherence. It is shown that spatial coherence of the SHG emission can be controlled by varying the diameter of the limiting aperture in the degenerate laser resonator. The pumping power also affects the number of the oscillating transverse modes, so that influences the spatial coherence of the output laser. The laser of low coherence for speckle reduction has been demonstrated. It is shown that the laser of low spatial coherence may find applications in imaging, and laser display etc.
关键词： speckle suppression,lasers,Partially coherent,second harmonic generation,degenerate cavity
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) - Generation of Ultrabroadband Phase-Locked Pulse Pairs in the Ultraviolet by Achromatic SHG
摘要： Two-dimensional electronic spectroscopy (2DES) is a powerful spectroscopic technique for the study of dynamics in coupled multi-chromophore systems, which has been successfully applied in the visible and infrared ranges. Its extension to the UV range (2DUV) is extremely promising for the study of biomolecules but poses several technical challenges: (i) the requirement of phase-locked pulse pairs; (ii) generation of extremely broadband UV pulses; (iii) dispersion management for the UV range. Here we present a setup able to generate ultrabroad phase-locked UV pump pulses with bandwidth from 260 to 310 nm. The UV pump pulse pairs are generated by Achromatic Second Harmonic Generation (ASHG) of a phase-locked, visible pulse pair (Fig. 1(a)). A non-collinear optical parametric amplifier (NOPA) produces 10-μJ, <6-fs-pulses in the 500-640 nm range. Two delayed, phase-locked replicas of the visible pulses are then generated by TWINS [1], a compact ultrastable interferometer consisting of a sequence of β-BBO birefringent wedges that allows varying with extreme accuracy and up to 1 ps the delay between the two replicas. The broadband visible replicas are subsequently chirped in a 45-mm block of SF57 and frequency doubled to the UV range by ASHG [2]. In this scheme, the visible pulse is dispersed by a fused silica (FS) prism and the angular dispersion is converted to a lateral dispersion by a second prism. The resulting collimated beam is focused into a 300-μm β-BBO crystal for SHG. By suitably choosing the prism separation (152 cm) and the focal length (35 mm) we match the propagation direction of each component with its SHG phase-matching angle.
关键词： ultrabroadband UV pulses,UV range,Two-dimensional electronic spectroscopy,Achromatic Second Harmonic Generation,phase-locked pulse pairs
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) - Efficient Nonlinear Metasurfaces using Multiresonant High-Q Plasmonic Arrays
摘要： Nonlinear optical processes are important in many fields of photonics, ranging from biomedical imaging to ultrafast spectroscopy. Thanks to recent progress in nanophotonics and metamaterials, there is a growing demand for smaller and more efficient nonlinear optical components. Unfortunately, it is very challenging to satisfy this demand by using traditional materials, which motivates the search for alternative approaches. Nonlinear plasmonics has recently emerged as a potential solution for enabling more efficient nanoscale nonlinear optics. However, it is not yet clear how nonlinear responses of metamaterials can be enhanced sufficiently to enable practical nonlinear applications. Recent attempts to find the solution to this issue have been focused on two enhancement strategies, which are both based on resonance engineering. First, nanoparticle arrays associated with collective and narrow plasmon resonances with relatively high quality factors (Q-factors) known as surface lattice resonances (SLRs) have been utilized. Second, multiply-resonant nanostructures have been investigated where the resonance enhancement occurring both at the input and output wavelengths results in strong nonlinear response. Here, we combine these two concepts to enable even higher overall enhancement. We numerically study the enhancement of second-harmonic generation (SHG) in multiply-resonant plasmonic metasurfaces consisting of L-shaped aluminium nanoparticles. The array is designed to support two simultaneous high-Q SLRs, termed SLR(cid:90) and SLR2(cid:90), peaking at the fundamental and SHG wavelengths, respectively. The Q-factors of SLR(cid:90) and SLR2(cid:90) were estimated to be 800 and 250, respectively. We perform SHG simulations using an approach based on the nonlinear discrete-dipole approximation, and predict an enhancement of over six orders-of-magnitude of the emitted SHG intensity at doubly-resonant conditions.
关键词： metasurfaces,surface lattice resonances,second-harmonic generation,Nonlinear optics,plasmonics
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) - Femtosecond-Driven Up-Conversion in a Radially Poled LiNbO <sub/>3</sub> Microresonator
摘要： Nowadays, there are plenty of different techniques developed for the generation of Optical Frequency Combs (OFCs), but Mode Locked Laser (MLL) OFC is still the most commonly used and commercially available one [1]. Although MLLs are capable of producing very high-peak power OFCs with femtosecond pulse durations, it is sometimes challenging to apply them directly for a number of reasons. First, MLLs typically produce OFCs with repetition frequencies (fr) below 1 GHz, so additional filtering of the unwanted modes is required for the applications in telecommunications, astrocombs etc. Second, many spectral regions – namely mid-infrared, visible and ultraviolet – are difficult to access by MLLs, which implies the use of external parametric up- and down-conversion. One promising platform for such spectral transfer is high Q-factor optical microresonators based on second order (χ(2)) nonlinear crystals, since not only do they provide the desired spectral transfer, but also open up opportunities for the miniaturization of the system. In addition, such microresonators support whispering gallery modes that possess very low mode volumes, making it possible to enhance nonlinear (χ(2)) processes. This is a significant advantage over the already existing bulk analogs.
关键词： Mode Locked Laser,microresonators,second harmonic generation,femtosecond pulses,Optical Frequency Combs
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) - Optically Engineered Nonlinear Photonic Structures in Ferroelectrics
摘要： Performance of many optical devices based on frequency conversion critically depends on spatial modulation of the nonlinear optical response of the materials. This modulation ensures, via the quasi phase matching (QPM), an efficient energy exchange between optical waves at different frequencies. The QPM structures, also known as the nonlinear photonic crystals, offer a variety of novel properties and functionalities that cannot be obtained in uniform nonlinear crystals. Typically, such nonlinear structures have been fabricated via electric-poling. However, this technique is restricted to particular crystallographic geometries, and does not allow to create isolated structures inside the nonlinear material. This means that one cannot realize fully 3-dimensional nonlinear structures via traditional electrical poling. In this work we discuss our novel technique capable of engineering quadratic nonlinearity, based on all-optical poling of ferroelectrics. This new approach, is similar to traditional laser writing in optical media. It involves a tight focusing of femtosecond infrared beam and subsequent its two photon absorption which heats locally the medium. The large temperature gradient induces thermoelectric field which, if sufficiently high, inverts locally direction of spontaneous polarization, changing the sign of nonlinearity. The method is extremely flexible, can be applied to different crystallographic orientations and enables formation of localised spatially modulated nonlinear response inside optical media. Here, we demonstrate its application to create structures for efficient frequency conversion in Lithium Niobate waveguides and transverse second harmonic generation. Moreover, we provide here the first ever experimental evidence of the 3D Nonlinear Photonic Crystal, fabricated in ferroelectric barium calcium titanate. Finally we show formation of multiple nonlinear photonic crystals in form of fork structures inside the bulk of ferroelectric calcium barium niobate, and demonstrate their application for wave-shaping in frequency doubling process, directly creating second harmonic optical vortices and conical beams.
关键词： frequency conversion,nonlinear photonic structures,ferroelectrics,all-optical poling,second harmonic generation,quasi phase matching
更新于2025-09-12 10:27:22
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Regimes of two-color light bullet formation in a gradient waveguide
摘要： In this paper we concentrate on the remarkable role of a gradient waveguide in two-color light bullet formation. We study generation of the second harmonic in such an inhomogeneous nonlinear medium, taking into account diffraction and relatively weak temporal dispersion. Using the averaged Lagrangian method we consider all possible combinations of the range of group velocities (normal or anomalous dispersion) and waveguide geometry (focusing or defocusing waveguide). Stability conditions for a propagating two-color light bullet are derived analytically. We demonstrate the formation of a stable two-component light bullet in a parabolic planar quadratically nonlinear waveguide either at anomalous or at normal group velocity dispersion. We discuss also the results of numerical simulation con?rming our analytical ?ndings. Besides that, simulation allows us to expand the scope of the study and to show light bullet propagation at a certain phase mismatching and the formation of a stable coupled localized structure from a signal at the fundamental frequency as well.
关键词： diffraction,second harmonic generation,two-color light bullet,waveguide geometry,averaged Lagrangian method,group velocities,stability conditions,gradient waveguide,temporal dispersion,numerical simulation
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) - Nonlinear Microscopy of Lead Iodide Nanosheets
摘要： Lead iodide (PbI2) is a layered material with unique optical and electrical properties, including direct bandgap in the bulk and a layered crystalline structure, consisting of close-packed Pb atoms sandwiched between two layers of Iodine atoms. Compared to the widely-studied TMDCs, 2D PbI2 is a new type of halide semiconductors with a relatively larger visible bandgap (Eg ～ 2.4 eV) which endows its distinct optical properties. Despite being studied for decades and being used as a precursor for perovskite materials, the recently developed PbI2 nanosheets have shown a great promise for high-performance optoelectronic devices, such as ?exible photodetectors and nanolasers. Such 2D nanosheets also show a great potential for low-dimensional nonlinear optical devices, However, their nonlinear properties are still unexplored, while novel applications of PbI2 nanosheets require careful characterization of their crystalline structure, thickness and nonlinearity. Here we demonstrate the nonlinear microscopy of PbI2 nanosheets using the polarization and thickness dependence of the second harmonic generation (SHG) and third harmonic generation (THG) from solution-grown nanosheets. Our measurements allow to precisely determine their thickness and crystalline orientation with a non-invasive optical technique.
关键词： third harmonic generation,nonlinear microscopy,Lead iodide,second harmonic generation,nanosheets
更新于2025-09-11 14:15:04
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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) - Nonlinear Generation of Ultrafast, Higher Order Vector Vortex Beams
摘要： Light beams carrying both spin (polarization) and orbital angular momentum (OAM) can be represented by mapping the total angular momentum onto a higher-order Poincaré sphere [1]. Due to the non-separability of the polarization and OAM degrees-of-freedom, these beams, commonly known as vector vortex beams, find varieties of applications in scientific and technological fields including photon entanglement [2], material processing [3] and microscopy [4]. Such beams are commonly generated using q-plates [5] and liquid crystal based spatial light modulators [6]. However, the limitation of low power handling and restricted wavelength coverage of such techniques can be addressed through the vector vortex beam generation using nonlinear parametric processes. Unfortunately, the dependence of phase-matching of the parametric processes on the polarization of the interacting beams puts the major hindrance to the nonlinear generation of vector vortex beams. Here we report a novel experimental scheme to generate vector vortex beams using single pass second harmonic generation (SHG) of ultrafast higher order vector vortex beams.
关键词： ultrafast,higher order,nonlinear generation,second harmonic generation,vector vortex beams
更新于2025-09-11 14:15:04
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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) - Nonlinear Optics of Multiferroic Materials
摘要： Multiferroics, that is, materials with a coexistence of long-range magnetic and electric order have been attracting tremendous interest because of pronounced coupling effects between magnetic and electric properties that may be the basis for novel devices in which a magnetization is controlled by an electric voltage rather than by energy-intensive electric-current-driven magnetic fields. For monitoring as well as controlling the magnetoelectric coupling, it is essential to have simultaneous access to the magnetic and electric phase of a multiferroic. Only then, the spatial relation between the magnetic and electric domain structures and their response to external perturbations like applied magnetic or electric fields can be studied. Nonlinear optics is particularly well suited for this purpose. The simplest nonlinear optical process is second harmonic generation (SHG) (cid:650) doubling of the frequency of a light wave in a material. SHG is a very symmetry-sensitive process. Any reduction of the symmetry of the frequency-doubling medium can lead to new SHG contributions. Since all types of ferroic order reduce the point group symmetry, SHG can be used as background-free probe of the occurring order. In general, the magnetic and the electric order of a multiferroic change symmetry in different ways so that they are represented by different SHG contributions. These are readily separated by polarization filters so that SHG is an ideal tool to observe the coexistence and correlation between the ferroic phases and their domains in a single experiment. Polarization-dependent SHG spectroscopy and imaging experiments are therefore ideal for analysing the magnetoelectric correlation in a broad variety of multiferroic materials. Some of the most important achievements of nonlinearoptics on multiferroics are: (cid:120) Detection of a coupling between antiferromagnetic and ferroelectric order in hexagonal manganites that occurs in the domain walls rather than in the domains. The result anticipated the current interest in domain walls as functional oxide interfaces [1]. (cid:120) A coupling between magnetic and electric domains in TbMnO3 sustained even across a first-order (cid:120) phase transition [2]. Inversion of a multiferroic domain pattern: The direction of the magnetic or electric order parameter of a multiferroic is reversed across the entire sample, but the domain patterns such is retained [3]. (cid:120) Reversal of a multiferroic domain state without application of external DC fields, just by light [4]. (cid:120) In-situ tracking of the emergence of ferroic order in multiferroic oxide thin films by monitoring the formation of the ordered state by SHG during growth [5]. Optical access in all these experiments involves lasers emitting light pulses of either 100 fs or 5 ns. The laser light can be used to monitor the multiferroic order by nonlinear optics but also, prior to that, to manipulate the ordered state by with an intense pump light beam and analyse the ensuing dynamics. In view of the versatility of the optical access to multiferroics and the generality of the symmetry-based approach to the detection of ferroic phases, it is to be expected that the field of nonlinear optics on multiferroics will continue to develop at the highest speed.
关键词： magnetoelectric coupling,multiferroic materials,second harmonic generation,Nonlinear optics
更新于2025-09-11 14:15:04