Trajectory-based models in strong-field physics

Abstract

We review various semiclassical models for strong-field physics. These semiclassical models employ ensembles of classical trajectories to simulate electron motion in the continuum after being released from an atom or molecule by an external laser field. We discuss different approaches to trajectory-based simulations and identify their advantages and shortcomings. We also review some of the recent applications of semiclassical models to the key strong-field phenomena: above-threshold ionization, high-order harmonic generation, nonsequential double ionization, and frustrated tunneling ionization.

Figures (7)

• Figure 1: The three-step model of strong-field ionization involves (i) electron tunneling through the effective potential barrier, (ii) acceleration by the laser field, and (iii) recollision with the parent ion, which can lead to high-order above-threshold ionization (via elastic scattering), high-harmonic generation (via recombination), or nonsequential double ionization (via the liberation of a second electron). The effective potential barrier (solid blue curve) results from the superposition of the Coulomb potential (dashed green curve) and the laser field potential (solid red curve).
• Figure 2: Two-dimensional momentum distributions for the H atom ionized by a laser pulse with a duration of $8$ cycles, wavelength of $800$ nm, and peak intensity of $0.9\times10^{14}$ W/cm$^2$ obtained from (a,d) solution of the TDSE, (b,e) QTMC, and (c,f) the SCTS model. Panels (d), (e), and (f) show the maginifications for $\left|k_z\right|$, $\left|k_z\right|<0.3$ a.u. of the distributions presented in (a), (b), and (c), respectively. The distributions are normalized to the total ionization yield. A logarithmic color scale in arbitrary units is used. The laser field is linearly polarized along the $z$-axis.
• Figure 3: Electron energy spectra calculated for the H atom ionized by a laser pulse with an intensity of $0.9\times10^{14}$ W/cm$^2$ and duration of $8$ cycles using numerical solution of the TDSE (thick light orange curve), the QTMC model (dotted green curve), and the SCTS model (solid red curve). Panels (a), (b), and (c) correspond to the wavelengths equal to 800 nm, 1000 nm, and 1200 nm, respectively. The energy spectra are normalized to the peak value. The dashed vertical lines show the energy equal to ponderomotive potential in panels (a) and (b).
• Figure 4: Scheme of the two routes leading to the formation neutral excited H atoms: Pathway A (a) and pathway B (b). Black curves and gray dashed lines show the time-dependent position of electrons and ions, respectively. From https://doi.org/10.1103/PhysRevA.85.011402
• Figure 5: Experimental (dashed curve) and CTMC-QUEST high-order harmonics spectra obtained for a laser pulse with a wavelength of 1380 nm and a peak intensity of $1.0\times10^{14}$ W/cm$^2$. From https://doi.org/10.1103/PhysRevA.83.053401