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.

Soft-x-ray harmonic comb from relativistic electron spikes

Abstract: We demonstrate a new high-order harmonic generation mechanism reaching the "water window" spectral region in experiments with multiterawatt femtosecond lasers irradiating gas jets. A few hundred harmonic orders are resolved, giving μJ/sr pulses. Harmonics are collectively emitted by an oscillating electron spike formed at the joint of the boundaries of a cavity and bow wave created by a relativistically self-focusing laser in underdense plasma. The spike sharpness and stability are explained by catastrophe theory. The mechanism is corroborated by particle-in-cell simulations.

Harmonic generation beyond the Strong-Field Approximation: the physics behind the short-wave-infrared scaling laws.

Abstract: The physics of laser-mater interactions beyond the perturbative limit configures the field of extreme non-linear optics. Although most experiments have been done in the near infrared (λ≤1µm), the situation is changing nowadays with the development of sources at longer wavelengths (<5µm), opening new perspectives in the synthesis of shorter XUV attosecond pulses and higher frequencies. The theory of intense-field interactions is based either on the exact numerical integration of the time-dependent Schrodinger equation or in the development of models, mostly based on the strong-field approximation. Recent studies in the short-wave infrared show a divergence between the predictions of these models and the exact results. In this paper we will show that this discrepancy reveals the incompleteness of our present understanding of high-order harmonic generation. We discuss the physical grounds, provide a theoretical framework beyond the standard approximations and develop a compact approach that accounts for the correct scaling of the harmonic yield.

Measurement of the duration of high harmonic pulses

Abstract: Summary form only given. High harmonics are generated during the ionization of an atomic gas and therefore the probability of ionization, the number of unionized atoms, and the phase matching effects will impose a natural temporal envelope on the harmonic generation. We made some simulations which showed the maximal, minimal, and averaged possible values of the intensity of the harmonic as a function of the angular frequency detuning multiplied by the length of the harmonic pulse. From the envelope of the maximum signal we can extract the high harmonic pulse duration.

Optical properties of cluster plasma

Abstract: It is shown that unlike a gas plasma or an electron plasma in a metal, an ionized clustered material (“cluster plasma”) permits propagation below the plasma cut-off of electromagnetic (EM) waves whose phase velocity is close to but below the speed of light. Its unique properties allow a variety of applications, including direct acceleration of particles with its EM fields and the phase matching of waves of high harmonic generation (HHG). The particle-in-cell simulation demonstrates the new optical mode, the cluster mode.