Higher-order harmonic generation from fullerene by means of the plasma harmonic method

Nonlinear optics of graphitic carbon allotropes: from 0D to 3D

The dimensionality of materials fundamentally influences their electronic and optical properties, presenting a complex interplay with nonlinear optical (NLO) characteristics that remains largely unexplored. In this review, we focus on the influence of dimensionality on the NLO properties of graphitic allotropes, ranging from 0D fullerenes, 1D carbon nanotubes, and 2D graphene, to 3D graphite, all of which share a consistent sp2 hybridized chemical bonding structure. We examine the distinct physical and NLO properties across these dimensions, underscoring the profound impact of dimensionality. Notably, dimension-specific physical phenomena, such as Luttinger liquid in 1D and Landau quantization in 2D, play a significant role in shaping NLO phenomena. Finally, we explore the promising potential of NLO properties in systems with mixed dimensionalities, setting the stage for future breakthroughs and innovative applications.

Modeling of High-Harmonic Generation in the C60 Fullerene Using Ab Initio, DFT-Based, and Semiempirical Methods

We report calculations of the high-harmonic generation spectra of the C60 fullerene molecule carried out by employing a diverse set of real-time time-dependent quantum chemical methods. All methodologies involve expanding the propagated electronic wave function in bases consisting of the ground and singly excited time-independent eigenstates obtained through the solution of the corresponding linear-response equations. We identify the correlation and exchange effect in the spectra by comparing the results from methods relying on the Hartree-Fock reference determinant with those obtained using approaches based on the density functional theory with different exchange-correlation functionals. The effect of the full random-phase approximation treatment of the excited electronic states is also analyzed and compared with the configuration interaction singles and the Tamm-Dancoff approximation. We also showcase the fact that the real-time extension of the semiempirical method INDO/S can be effectively applied for an approximate description of laser-driven dynamics in large systems.

Harmonics Generation in the Laser-Induced Plasmas of Metal and Semiconductor Carbide Nanoparticles

Carbon-containing plasma is an attractive medium for generation of harmonics of laser pulses in the extreme ultraviolet range. We ablate two metal carbide (B₄C and Cr₃C₂) nanoparticles and silicon carbide (SiC) nanoparticles and generate harmonics after propagation of 35 fs pulses through the laser-induced plasmas. We analyze the spectra, spectral shifts, and splitting of harmonics from nanoparticles-contained plasmas, which demonstrate the chirp-related harmonic cut-off scaling. In addition, we present the simplified two-color pump model calculations of HHG based on the strong field approximation.

Laser-Induced Molecular Plasma: A Medium for High-Order Harmonics Generation of Ultrashort Pulses

I present a study of laser-induced plasmas (LIPs) produced on the surfaces of molecular targets to create optimal conditions for high-order harmonics generation during the propagation of femtosecond pulses through the LIP. The resonance enhancement of a harmonic, two-color pump of plasma, quasi-phase-matching and nanoparticle-induced growth of the harmonic yield are analyzed, which allows for the formation of sources of coherent extreme ultraviolet radiation based on molecular plasma formation.

Diffractive Imaging of C_{60} Structural Deformations Induced by Intense Femtosecond Midinfrared Laser Fields

Theoretical studies indicated that C_{60} exposed to linearly polarized intense infrared pulses undergoes periodic cage structural distortions with typical periods around 100 fs (1  fs=10^{-15}  s). Here, we use the laser-driven self-imaging electron diffraction technique, previously developed for atoms and small molecules, to measure laser-induced deformation of C_{60} in an intense 3.6  μm laser field. A prolate molecular elongation along the laser polarization axis is determined to be (6.1±1.4)% via both angular- and energy-resolved measurements of electrons that are released, driven back, and diffracted from the molecule within the same laser field. The observed deformation is confirmed by density functional theory simulations of nuclear dynamics on time-dependent adiabatic states and indicates a nonadiabatic excitation of the h_{g}(1) prolate-oblate mode. The results demonstrate the applicability of laser-driven electron diffraction methods for studying macromolecular structural dynamics in four dimensions with atomic time and spatial resolutions.

Generating high-order optical and spin harmonics from ferromagnetic monolayers

High-order harmonic generation (HHG) in solids has entered a new phase of intensive research, with envisioned band-structure mapping on an ultrashort time scale. This partly benefits from a flurry of new HHG materials discovered, but so far has missed an important group. HHG in magnetic materials should have profound impact on future magnetic storage technology advances. Here we introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG carries spin information and sensitively depends on the relativistic spin-orbit coupling; and if they are dispersed into the crystal momentum k space, harmonics originating from real transitions can be k-resolved and carry the band structure information. Geometrically, the HHG signal is sensitive to spatial orientations of monolayers. Different from the optical counterpart, the spin HHG, though probably weak, only appears at even orders, a consequence of SU(2) symmetry. Our findings open an unexplored frontier-magneto-high-order harmonic generation.

Coherent electronic wave packet motion in C(60) controlled by the waveform and polarization of few-cycle laser fields

Strong laser fields can be used to trigger an ultrafast molecular response that involves electronic excitation and ionization dynamics. Here, we report on the experimental control of the spatial localization of the electronic excitation in the C_{60} fullerene exerted by an intense few-cycle (4 fs) pulse at 720 nm. The control is achieved by tailoring the carrier-envelope phase and the polarization of the laser pulse. We find that the maxima and minima of the photoemission-asymmetry parameter along the laser-polarization axis are synchronized with the localization of the coherent electronic wave packet at around the time of ionization.

Strong Field-Induced Frequency Conversion of Laser Radiation in Plasma Plumes: Recent Achievements

New findings in plasma harmonics studies using strong laser fields are reviewed. We discuss recent achievements in the growth of the efficiency of coherent extreme ultraviolet (XUV) radiation sources based on frequency conversion of the ultrashort pulses in the laser-produced plasmas, which allowed for the spectral and structural studies of matter through the high-order harmonic generation (HHG) spectroscopy. These studies showed that plasma HHG can open new opportunities in many unexpected areas of laser-matter interaction. Besides being considered as an alternative method for generation of coherent XUV radiation, it can be used as a powerful tool for various spectroscopic and analytical applications.

Harmonic generation in ablation plasmas of wide bandgap semiconductors

Third and fifth harmonic generation of an IR (1.064 μm) pulsed laser has been produced in ablation plasmas of the wide bandgap semiconductors CdS and ZnS. The study of the temporal behaviour of the harmonic emission has revealed the presence of distinct compositional populations in these complex plasmas. Species ranging from atoms to nanometre-sized particles have been identified as emitters, and their nonlinear optical properties can be studied separately due to strongly differing temporal behaviour. At short distances from the target (<1 mm), atomic species are mostly responsible for harmonic generation at early times (<500 ns), while clusters and nanoaggregates mostly contribute at longer times (>1 μs). Harmonic generation thus emerges as a powerful and universal technique for ablation plasma diagnosis and as a tool to determine the nonlinear optical susceptibility of ejected clusters or nanoparticles.

Multi-µJ coherent extreme ultraviolet source generated from carbon using the plasma harmonic method

We demonstrate intense high-order harmonic generation from plasma that is created from different carbon targets. We obtain high-order harmonic energy in the multi-microjoule range for each harmonic order from the 11th to the 17th harmonic. By analyzing the target morphology and the plasma composition, we conclude that the intense harmonics from the bulk carbon targets originate from nanoparticles target.

Role of autoionizing state in resonant high-order harmonic generation and attosecond pulse production

We suggest a high-order harmonic generation (HHG) model describing enhancement of the generation efficiency for the harmonic resonant with the transition between the ground and autoionizing state of the generating ion. The results of numerical and analytical calculations based on this model are in good quantitative agreement with the experiments showing HHG enhancement up to 2 orders of magnitude. Moreover, this model reproduces well the essential difference in HHG efficiency for different ions. We show that intense but relatively long attosecond pulses can be generated using the enhanced harmonics.