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-Harmonic Generation of Attosecond Pulses in the “Single-Cycle” Regime

Abstract: High-harmonic generation with excitation pulses shorter than 25fs is studied theoretically using a 3D model For very short excitation pulses, a new regime of harmonic generation by a {open_quotes}single-cycle{close_quotes} of the driver pulse can be reached In this regime, the temporal coherence of the adjacent harmonic orders is dramatically improved compared with longer excitation pulses, even though the discrete harmonic structure in the emission disappears X-ray pulses as short as 100attoseconds can be emitted, with increased conversion efficiency of laser-to-harmonic radiation {copyright} {ital 1997} {ital The American Physical Society}

High-harmonic generation in graphene enhanced by elliptically polarized light excitation

Abstract: The electronic properties of graphene can give rise to a range of nonlinear optical responses. One of the most desirable nonlinear optical processes is high-harmonic generation (HHG) originating from coherent electron motion induced by an intense light field. Here, we report on the observation of up to ninth-order harmonics in graphene excited by mid-infrared laser pulses at room temperature. The HHG in graphene is enhanced by an elliptically polarized laser excitation, and the resultant harmonic radiation has a particular polarization. The observed ellipticity dependence is reproduced by a fully quantum mechanical treatment of HHG in solids. The zero-gap nature causes the unique properties of HHG in graphene, and our findings open up the possibility of investigating strong-field and ultrafast dynamics and nonlinear behavior of massless Dirac fermions.

Short‐pulse laser harmonics from oscillating plasma surfaces driven at relativistic intensity

Abstract: The generation of harmonics by interaction of an ultrashort laser pulse with a step boundary of a plane overdense plasma layer is studied at intensities Iλ2=1017–1019 W cm−2 μm2 for normal and oblique incidence and different polarizations. Fully relativistic one‐dimensional particle‐in‐cell (PIC) simulations are performed with high spectral resolution. Harmonic emission increases with intensity and also when lowering the plasma density. The simulations reveal strong oscillations of the critical surface driven by the normal component of the laser field and by the ponderomotive force. It is shown that the generation of harmonics can be understood as reflection from the oscillating surface, taking full account of retardation. Describing the oscillations by one or more Fourier components with adjustable amplitudes, model spectra are obtained that well reproduce the PIC spectra. The model is based on relativistic cold plasma equations for oblique incidence. General selection rules concerning polarization of odd and even harmonics depending on incident polarization are derived.

High-harmonic generation from an atomically thin semiconductor

Abstract: Observations of high-harmonic generation from a single layer of a transition metal dichalcogenide opens the door to studying strong-field and attosecond phenomena in two-dimensional materials. High-harmonic generation (HHG) in bulk solids permits the exploration of materials in a new regime of strong fields and attosecond timescales1,2,3,4,5,6. The generation process has been discussed in the context of strongly driven electron dynamics in single-particle bands7,8,9,10,11,12,13,14. Two-dimensional materials exhibit distinctive electronic properties compared to the bulk that could significantly modify the HHG process15,16, including different symmetries17,18,19, access to individual valleys20,21 and enhanced many-body interactions22,23,24,25. Here we demonstrate non-perturbative HHG from a monolayer MoS2 crystal, with even and odd harmonics extending to the 13th order. The even orders are predominantly polarized perpendicular to the pump and are compatible with the anomalous transverse intraband current arising from the material’s Berry curvature, while the weak parallel component suggests the importance of interband transitions. The odd harmonics exhibit a significant enhancement in efficiency per layer compared to the bulk, which is attributed to correlation effects. The combination of strong many-body Coulomb interactions and widely tunable electronic properties in two-dimensional materials offers a new platform for attosecond physics.

Generation of intense uv radiation by subharmonically seeded single-pass free-electron lasers.

Abstract: We present a detailed analysis of a subharmonically seeded single-pass free-electron laser (FEL) utilizing two wiggler magnets separated by a dispersion section. To be specific, suppose the seed to be laser light at 300 nm. A first wiggler is used to energy modulate the electron beam. This is followed by a dispersion section to produce spatial bunching, and a second wiggler resonant to 100 nm. Upon passing through the second wiggler, the prebunched electron beam first radiates coherently, and then this radiation is exponentially amplified. Finally, a tapered section is used to extract additional power from the electron beam. In this manner we can achieve pulses of duration {approx}10 psec with 1 mJ per pulse in 10{sup {minus}4} bandwidth, with continuously tunable wavelength in the range 100--300 nm. We present the analytical tools we have employed for the preliminary estimate of the system performance and of the optimization of the parameters. We describe our modification of the simulation code TDA to include harmonic generation and discuss its use in analyzing the subharmonically seeded FEL. The analytic and computer-simulation calculations are in good agreement. We discuss in detail the physical process in the system and the optimization of parameters.