Marcelo F. Ciappina

Beyond carbon K-edge harmonic emission using a spatial and temporal synthesized laser field.

We present numerical simulations of high-order harmonic generation in helium using a temporally synthesized and spatially nonhomogeneous strong laser field. The combination of temporal and spatial laser field synthesis results in a dramatic cutoff extension far beyond the usual semiclassical limit. Our predictions are based on the convergence of three complementary approaches: resolution of the three dimensional time dependent Schrödinger equation, time-frequency analysis of the resulting dipole moment, and classical trajectory extraction. A laser field synthesized both spatially and temporally has been proven capable of generating coherent extreme ultraviolet photons beyond the carbon K edge, an energy region of high interest as it can be used to initiate inner-shell dynamics and study time-resolved intramolecular attosecond spectroscopy.

Strong-Field Resonant Dynamics in Semiconductors.

We predict that a direct band gap semiconductor (GaAs) resonantly excited by a strong ultrashort laser pulse exhibits a novel regime: kicked anharmonic Rabi oscillations. In this regime, Rabi oscillations are strongly coupled to intraband motion, and interband transitions mainly take place when electrons pass near the Brillouin zone center where electron populations undergo very rapid changes. The asymmetry of the residual population distribution induces an electric current controlled by the carrier-envelope phase of the driving pulse. The predicted effects are experimentally observable using photoemission and terahertz spectroscopies.

Interference pattern signatures in fully differential cross sections for single ionization of H2 molecules by fast protons

Electron interference signatures present in fully differential cross sections for single ionization by 6 MeV protons in H2 molecules are investigated. We employ a molecular version of the continuum-distorted wave-eikonal initial state model, where all the interactions present in the exit channel are considered on an equal footing. Calculations of fully differential cross sections are performed for different electron and projectile kinematical conditions and the range of validity of the theoretical approach is discussed. Furthermore, we explore the presence of interference patterns in differential cross sections for both aligned and randomly oriented targets in asymmetric coplanar geometries.

High-order harmonic generation driven by chirped laser pulses induced by linear and non linear phenomena

Abstract We present a theoretical study of high-order harmonic generation (HHG) driven by ultrashort optical pulses with different kind of chirps. The goal of the present work is to perform a detailed study to clarify the relevant parameters in the chirped pulses to achieve a noticeable cut-off extensions in HHG. These chirped pulses are generated using both linear and nonlinear dispersive media. The description of the physical mechanisms origin responsible for this extension is, however, not usually reported with enough detail in the literature. The study of the behaviour of the harmonic cut-off with this kind of pulses is carried out in the classical context, by the integration of the Newton-Lorentz equation complemented with the quantum approach, based on the integration of the time dependent Schrödinger equation in full dimensions (TDSE-3D). Graphical abstract

Two center and Coulomb effects in near-threshold ionization of H+ 2 by short laser pulses

We investigate the influence of the Coulomb potential as well as the two center contribution in the angle-resolved photoelectron spectrum, resulting from the single ionization of H molecules by short laser pulses. We present an extension of the Coulomb–Volkov distorted wave approximation to the H case. This last model can be considered as an improvement beyond the strong-field approximation (SFA) and was capable of reproducing the structures present in near-threshold ionization in atoms.

Strong-field plasmonic photoemission in the mid-IR at <1 GW/cm² intensity.

Strong-field ultrafast photoemission was studied by propagating surface plasmons generated on gold metal layer in Kretschmann configuration at 3.1 microns wavelength. Tunneling photoemission and electron acceleration was demonstrated at an unprecedently low laser intensity (1-5 GW/cm2).

Single- and two-centre effects in fully differential cross sections for single ionization of H2 molecules by 75keV protons

We present theoretical calculations of single ionization of H2 molecules by 75 keV proton impact. The computed fully differential cross sections for different electron ejection geometries and projectile kinematical conditions are compared with recent measurements made by Hasan et al (2014 J. Phys. B: At. Mol. Opt. Phys. 47 215201). We employ a molecular version of the continuum distorted wave-eikonal initial state model, where all the interactions present in the exit channel are considered on an equal footing. In addition, our approach allows us to incorporate different interference terms and to assess their influence. Overall, the agreement between experiment and theory is better than for the case of more sophisticated schemes for coplanar geometries.

Fully differential cross sections for ion-atom impact ionization in the presence of a laser field

We study fully differential cross sections (FDCS) for single ionization of helium by ion impact in the presence of a laser field. The field is assumed to have linear polarization, to be weak compared to the typical atomic field, and we use a frequency corresponding to a CO2 laser. We employ the continuum distorted wave-eikonal initial state (CDW-EIS) to describe our FDCS in the laser background. Analysing our numerical results we explore the dependence of the FDCS on the laser field properties as well as on the ionized electron parameters.

Optical Control of Young’s Type Double-slit Interferometer for Laser-induced Electron Emission from a Nano-tip

Interference experiments with electrons in a vacuum can illuminate both the quantum and the nanoscale nature of the underlying physics. An interference experiment requires two coherent waves, which can be generated by splitting a single coherent wave using a double slit. If the slit-edge separation is larger than the coherence width at the slit, no interference appears. Here we employed variations in surface barrier at the apex of a tungsten nano-tip as slits and achieved an optically controlled double slit, where the separation and opening-and-closing of the two slits can be controlled by respectively adjusting the intensity and polarization of ultrashort laser pulses. Using this technique, we have demonstrated interference between two electron waves emitted from the tip apex, where interference has never been observed prior to this technique because of the large slit-edge separation. Our findings pave the way towards simple time-resolved electron holography on e.g. molecular adsorbates employing just a nano-tip and a screen.

Neutron-impact ionization of He

The time-dependent close-coupling method is used to calculate neutron-impact single and double ionization cross sections of the He atom. We also present the ratio of double to single ionization for He as a guide to experimental checks of theory at low energies and experimental confirmation of the rapid rise of the ratio at high energies unique to neutron-impact ionization of atoms.