Topic
High harmonic generation
About: High harmonic generation is a research topic. Over the lifetime, 11694 publications have been published within this topic receiving 222650 citations. The topic is also known as: HHG.
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TL;DR: In this paper, a review of free-carrier nonlinearities in the hydrodynamic description in both perturbative and non-perturbative regimes, considering also contribution of nonlocal effects is presented.
Abstract: Requirements of integrated photonics and miniaturisation of optical devices demand efficient nonlinear components not constrained by conventional macroscopic nonlinear crystals. Intrinsic nonlinear response of free carriers in plasmonic materials provides opportunities to design both secondand third-order nonlinear optical properties of plasmonic nanostructures and control light with light using Kerr-type nonlinearities as well as achieve harmonic generation. This review summarises principles of free-carrier nonlinearities in the hydrodynamic description in both perturbative and non-perturbative regimes, considering also contribution of nonlocal effects. Engineering of harmonic generation, solitons, nonlinear refraction and ultrafast all-optical switching in plasmonic nanostructures and metamaterials are discussed. The full hydrodynamic consideration of nonlinear dynamics of free carriers reveals key contributions to the nonlinear effects defined by the interplay between a topology of the nanostructure and nonlinear response of the fermionic gas at the nanoscale, allowing design of high effective nonlinearities in a desired spectral range. Flexibility and unique features of free-electron nonlinearities are important for nonlinear plasmonic applications in free-space as well as integrated and quantum nanophotonic technologies.
84 citations
TL;DR: Phase-matched relativistic harmonic generation in plasmas is observed for the first time and the angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma.
Abstract: Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.
84 citations
TL;DR: In this article, a Burgers' equation is used to derive an algorithm for calculating harmonic generation by a continuous plane wave of ultrasound propagating in a nonlinear, lossy, non-invariant medium.
Abstract: A form of Burgers’ equation is used to derive an algorithm for calculating harmonic generation by a continuous plane wave of ultrasound propagating in a nonlinear, lossy, nondispersive medium. The algorithm accounts for attenuation that is not quadratically related to the frequency of the wave. Attenuation strongly affects the rate of harmonic production. The effect of variations of the relationship between attenuation and frequency is shown. Biological tissue is an example of a highly lossy medium where the attenuation does not increase with the square of the frequency. Calculations for several types of tissue and biological fluids are presented that show, for certain conditions, finite amplitude distortion is possible.
84 citations
TL;DR: In this paper, the authors employed femtosecond extreme ultraviolet pulses produced by high harmonic generation to follow how the magnetization of a thin cobalt film evolves after the excitation by a 40-fs laser pulse.
Abstract: The excitation of a ferromagnetic film by a femtosecond laser pulse causes an unexpectedly fast quenching of the film's magnetization on subpicosecond time scales. The microscopic physical mechanisms responsible for this remain a scientific puzzle. The authors employ femtosecond extreme ultraviolet pulses produced by high harmonic generation to follow how the magnetization of a thin cobalt film evolves after the excitation by a 40-fs laser pulse. By measuring the time-, energy-, and angle-resolved magneto-optical response of the Co films across the ${M}_{2,3}$ absorption edge, they obtain a set of time-lapsed magnetic asymmetry spectra, which contain a wealth of information about the different mechanisms at work. When combined with advanced ab initio magneto-optical calculations, they identify two dominant contributions: first, a transient reduction of exchange splitting, and second, magnon excitation. This work thus distinguishes between two fundamental models of magnetism, the Stoner and Heisenberg models, which ascribe magnetization dynamics to an exchange splitting reduction and spin wave excitations, respectively.
83 citations
TL;DR: By considering the tensor and the presence of the other electric field components the possibility of different polarization states of the generated second harmonic as a result of the nonlinear susceptibility tensor is considered, making it possible to generate radially polarized modes with linearly polarized beams.
Abstract: The effects of the axial field components of a focused beam under high NA on the second harmonic generation (SHG) in collagen was examined using a vectorial approach. We find that with high NA, the cross-component terms that are most likely to have an effect on SHG will be ExEx, ExEy, ExEz and EzEz as a result of tight focusing. By considering the tensor and the presence of the other electric field components the possibility of different polarization states of the generated second harmonic as a result of the nonlinear susceptibility tensor making it possible to generate radially polarized modes with linearly polarized beams.
83 citations