Scaling of the Low-Energy Structure in Above-Threshold Ionization in the Tunneling Regime: Theory and Experiment

Spectrum of quasistable states in a strong microwave field

“…If the laser pulse is not over, rescattering of the electron from the core can lead to superponderomotive ATI, recombination and high harmonic generation (HHG), non sequential double ionization (NSDI), and nearly elastic scattering. Nearly elastic scattering can result in a very low energy free electron, as observed recently [6][7][8], or as a bound electron [3,[9][10][11][12]. A striking example of the last process is provided by recent experiments with He in which 10% of the surviving atoms are attributed to states of n < 7 with Kepler orbital periods less than the 30 fs duration of the 1GV/cm laser pulse [12].…”

Rescattering of recolliding electron and low energy structure in few-cycle mid-infrared strong laser field: A 3D-TDSE study

“…When the electric field changes its direction, a few electrons recollide with their parent ion and are elastically back-rescattered to gain more energy from the field, forming the well documented plateau between 2U p and 10U p [5,9]. Recently, unexpected characteristic spike-like low-energy structure (LES) [4,10,11], very-low-energy structure (VLES) [12][13][14] and near-zeroenergy structure (ZES) [15][16][17] were found in the photoelectron energy spectra (PES) when atoms or molecules are exposed to strong mid-infrared laser fields. However, the direct SFA theoretical method which does not include the interaction of electron and parent ion failed to reproduce these experimental observations by generating a smooth photoelectron spectrum.…”

Universal pulse dependence of the low-energy structure in strong-field ionization

“…However, the observation of new structures [10,11] in the electron spectrum at low energies posed a puzzle: reproduced by numerical solutions of the time-dependent Schrödinger equation as well as by classical simulations [11][12][13][14][15][16][17][18], these now called "low" [10] and "very-low" [13] energy structures (LES and VLES) evade the well established three-step model. Early numerical studies [11][12][13] clearly hinted the importance of the Coulomb potential from the parent ion during formation of the low energy structures.…”