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.

Topological strong field physics on sub-laser cycle time scale

Abstract: Sub-laser cycle time scale of electronic response to strong laser fields enables attosecond dynamical imaging in atoms, molecules and solids. Optical tunneling and high harmonic generation are the hallmarks of attosecond imaging in optical domain, including imaging of phase transitions in solids. Topological phase transition yields a state of matter intimately linked with electron dynamics, as manifested via the chiral edge currents in topological insulators. Does topological state of matter leave its mark on optical tunneling and sub-cycle electronic response? We identify distinct topological effects on the directionality and the attosecond timing of currents arising during electron injection into conduction bands. We show that electrons tunnel across the band gap differently in trivial and topological phases, for the same band structure, and identify the key role of the Berry curvature in this process. These effects map onto topologically-dependent attosecond delays in high harmonic emission and the helicities of the emitted harmonics, which can record the phase diagram of the system and its topological invariants. Thus, the topological state of the system controls its attosecond, highly non-equilibrium electronic response to strong low-frequency laser fields, in bulk. Our findings create new roadmaps in studies of topological systems, building on ubiquitous properties of sub-laser cycle strong field response - a unique mark of attosecond science.

Optical second‐harmonic scattering in rat‐tail tendon

Abstract: The angular dependence of optical second-harmonic generation by native, wet, rat-tail tendon is found to display a sharp, intense, forward peak superimposed on a broad background. The sharp peak is shown to imply long-range polar order, while the broad background corresponds to that predicted for the random “up”/“down” array of collagen fibrils seen with the electron microscope. The degree of polar order is determined, and the dependence of the fibril diameter distribution on age and state of hydration is measured. The coherence length of tendon for harmonic generation and the absolute magnitude of the nonlinear susceptibility of the collagen fibril are also determined. The biological significance of these various findings is discussed.

Energetic sub-2-cycle laser with 216 W average power

Abstract: Few-cycle lasers are essential for many research areas such as attosecond physics that promise to address fundamental questions in science and technology. Therefore, further advancements are connected to significant progress in the underlying laser technology. Here, two-stage nonlinear compression of a 660 W femtosecond fiber laser system is utilized to achieve unprecedented average power levels of energetic ultrashort or even few-cycle laser pulses. In a first compression step, 408 W, 320 μJ, 30 fs pulses are achieved, which can be further compressed to 216 W, 170 μJ, 6.3 fs pulses in a second compression stage. To the best of our knowledge, this is the highest average power few-cycle laser system presented so far. It is expected to significantly advance the fields of high harmonic generation and attosecond science.

Near- and Extended-Edge X-Ray-Absorption Fine-Structure Spectroscopy Using Ultrafast Coherent High-Order Harmonic Supercontinua

Abstract: Recent advances in high-order harmonic generation have made it possible to use a tabletop-scale setup to produce spatially and temporally coherent beams of light with bandwidth spanning 12 octaves, from the ultraviolet up to x-ray photon energies >1.6 keV. Here we demonstrate the use of this light for x-ray-absorption spectroscopy at the K- and L-absorption edges of solids at photon energies near 1 keV. We also report x-ray-absorption spectroscopy in the water window spectral region (284-543 eV) using a high flux high-order harmonic generation x-ray supercontinuum with 10^{9} photons/s in 1% bandwidth, 3 orders of magnitude larger than has previously been possible using tabletop sources. Since this x-ray radiation emerges as a single attosecond-to-femtosecond pulse with peak brightness exceeding 10^{26} photons/s/mrad^{2}/mm^{2}/1% bandwidth, these novel coherent x-ray sources are ideal for probing the fastest molecular and materials processes on femtosecond-to-attosecond time scales and picometer length scales.

Towards enabling femtosecond helicity-dependent spectroscopy with high-harmonic sources

Abstract: Recent advances in high-harmonic generation gave rise to soft X-ray pulses with higher intensity, shorter duration and higher photon energy One of the remaining shortages of this source is its restriction to linear polarization, since the yield of generation of elliptically polarized high harmonics has been low so far We here show how this limitation is overcome by using a cross-polarized two-colour laser field With this simple technique, we reach high degrees of ellipticity (up to 75%) with efficiencies similar to classically generated linearly polarized harmonics To demonstrate these features and to prove the capacity of our source for applications, we measure the X-ray magnetic circular dichroism (XMCD) effect of nickel at the M2,3 absorption edge around 67 eV There results open up the way towards femtosecond time-resolved experiments using high harmonics exploiting the powerful element-sensitive XMCD effect and resolving the ultrafast magnetization dynamics of individual components in complex materials