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.

High average and peak power few-cycle laser pulses delivered by fiber pumped OPCPA system.

Abstract: We report on a high power optical parametric amplifier delivering 8 fs pulses with 6 GW peak power. The system is pumped by a fiber amplifier and operated at 96 kHz repetition rate. The average output power is as high as 6.7 W, which is the highest average power few-cycle pulse laser reported so far. When stabilizing the seed oscillator, the system delivered carrier-envelop phase stable laser pulses. Furthermore, high harmonic generation up to the 33th order (21.8 nm) is demonstrated in a Krypton gas jet. In addition, the scalability of the presented laser system is discussed.

Harmonic generation of radiation in a steep density profile

Abstract: It has been observed experimentally that the CO2‐laser Gemini and Helios systems generate very high harmonics with nearly constant efficiency over several harmonics with a cutoff near the local plasma frequency at the upper density shelf. To understand the experimental results, the strongly nonlinear electron response to a time‐dependent inhomogeneous force is studied. The equation of the electron motion in Lagrangian variables is derived and the conditions on the density scale length and power intensities for wavebreaking are found. By transforming the solution back to Eulerian variables, it is shown that the source of a given high harmonic frequency is localized around the density region where the local plasma wave is at that frequency. Using the numerically obtained nonlinear current density we evaluate the intensity of the radiation coming out of the plasma and verify the nearly constant harmonic production efficiency with a sharp decrease at the local plasma wave frequency at the upper shelf density.

Ultrashort light pulses in hollow waveguides

Abstract: Ultrafast-optics applications of nonlinear-optical processes in gas-filled hollow fibers are briefly reviewed. The main physical processes behind the use of hollow fibers for efficient generation of unprecedentedly short light pulses, enhanced short-wavelength generation, and improvement of the sensitivity of nonlinear-optical gas-phase analysis are considered. These processes include self- and cross-phase modulation, coherent four-wave mixing, high-order harmonic generation, and stimulated Raman scattering. The methods to generate extremely short pulses, including few-cycle field waveforms, and to control such pulses are discussed.

Gas population effects in harmonic emission by plasmonic fields

Abstract: We theoretically investigate the boosts in high-order harmonic generation using fabricated nanostructures and determine that the distribution of an ensemble of gas atoms in the vicinity of nanostructures is substantial for the evaluation of harmonic emission. The distributional behavior is mimicked by a single-atom response as well as by allowing the target atoms to reside in different positions inside the nanogap. For a given population distribution, a maximum photon energy of $\ensuremath{\sim}$25 eV could be observed in qualitative agreement with experiment.

Observation of multiple-harmonic radiation induced from a gold surface by picosecond neodymium-doped yttrium aluminum garnet laser pulses.

Abstract: Illuminating a gold surface by strong (5 GW/${\mathrm{cm}}^{2}$) picosecond neodymium-doped yttrium aluminum garnet laser pulses at grazing incidence, we observed a generation of coherent beams of both even and odd harmonics up to fifth order in the reflected direction with efficiencies ${10}^{\mathrm{\ensuremath{-}}10--}$${10}^{\mathrm{\ensuremath{-}}13}$. The observed decrease of the harmonic efficiencies with increasing harmonic order is much weaker than predicted by perturbative theories.