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.

Acoustic harmonic generation from fatigue-induced dislocation dipoles

Abstract: A model is presented of the interaction of an acoustic wave with dislocation dipoles and dipole-array approximations to veins and persistent slip bands (substructures) formed during metal fatigue. The model predicts the generation of a substantial acoustic second harmonic that depends on the distance between the glide planes of the dipole pair, on the dipole density, and on the particular arrangement and volume fraction of dipoles in a given substructure of the fatigued solid. Experimental evidence which strongly supports the essential features of the model is presented for fatigued aluminium alloy 2024-T4.

Ionization Dynamics in Strong Laser Fields

Abstract: The behavior of atoms submitted to intense electromagnetic fields is a subject of wide interest and active research. Much of the knowledge in this field is provided by studying the ionization dynamics, the energy and momentum of the photoelectrons, and the spectrum of emitted photons. Multiphoton ionization (MPI) is the process by which an atom is ionized by simultaneous absorption of several photons. The number of photons absorbed is in general even larger than the minimum required by energy conservation. The excess energy can be transferred to the photoelectron whose energy spectrum is composed of a series of lines separated by the photon energy. This process is known as above-threshold ionization (ATI). Alternately, the electron can be recaptured, emitting a series of energetic photons at odd harmonic frequencies of the driving field, dubbed optical harmonic generation (OHG). The particular topics studied in this paper are: Transient Resonances and Excited State Population Trapping; Evolution from Multiphoton to Tunneling; Electron Energy Distributions; Effects of Rescattering on the Photoelectron Energy and Momentum; {open_quotes}Direct{close_quotes} Channel in Multiphoton Double Ionization; {open_quotes}Nonsequential{close_quotes} Channel in Tunneling Double Ionization; and Nonsequential Rate.

High-harmonic generation by field enhanced femtosecond pulses in metal-sapphire nanostructure

Abstract: Plasmonic high-harmonic generation (HHG) drew attention as a means of producing coherent extreme ultraviolet (EUV) radiation by taking advantage of field enhancement occurring in metallic nanostructures. Here a metal-sapphire nanostructure is devised to provide a solid tip as the HHG emitter, replacing commonly used gaseous atoms. The fabricated solid tip is made of monocrystalline sapphire surrounded by a gold thin-film layer, and intended to produce EUV harmonics by the inter- and intra-band oscillations of electrons driven by the incident laser. The metal-sapphire nanostructure enhances the incident laser field by means of surface plasmon polaritons, triggering HHG directly from moderate femtosecond pulses of ∼0.1 TW cm−2 intensities. The measured EUV spectra exhibit odd-order harmonics up to ∼60 nm wavelengths without the plasma atomic lines typically seen when using gaseous atoms as the HHG emitter. This experimental outcome confirms that the plasmonic HHG approach is a promising way to realize coherent EUV sources for nano-scale near-field applications in spectroscopy, microscopy, lithography and atto-second physics. It has been suggested that strong field enhancement for high harmonic generation may be achievable with nano-antennas. Here, the authors show relevant field enhancement using a metal-sapphire nanostructure that provides a solid tip as the high harmonic emitter, replacing commonly used gaseous atoms.

First ultraviolet high-gain harmonic-generation free-electron laser.

Abstract: We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

Nonlinear optics at all-dielectric nanoantennas and metasurfaces

Abstract: Freed from phase-matching constraints, plasmonic metasurfaces have contributed significantly to the control of the optical nonlinearity and enhancing the nonlinear generation efficiency by engineering subwavelength meta-atoms. However, the high dissipative losses and the inevitable thermal heating limit their applicability in nonlinear nanophotonics. All-dielectric metasurfaces, supporting both electric and magnetic Mie-type resonances in their nanostructures, have appeared as a promising alternative to nonlinear plasmonics. High-index dielectric nanostructures, allowing additional magnetic resonances, can induce magnetic nonlinear effects, which along with electric nonlinearities increase the nonlinear conversion efficiency. In addition, low dissipative losses and high damage thresholds provide an extra degree of freedom for operating at high pump intensities, resulting in a considerable enhancement of the nonlinear processes. In this review, we discuss the current state-of-the-art in the intensely developing area of all-dielectric nonlinear nanostructures and metasurfaces, including the role of Mie modes, Fano resonances and anapole moments for harmonic generation, wave mixing, and ultrafast optical switching. Furthermore, we review the recent progress in the nonlinear phase and wavefront control using all-dielectric metasurfaces. We discuss techniques to realize all-dielectric metasurfaces for multifunctional applications and generation of second-order nonlinear processes from CMOS compatible materials.