Spectral and temporal structures of high-order harmonic generation of Na in intense mid-ir laser fields

Abstract

We present a three-dimensional quantum study of high-order harmonic generation ͑HHG͒ of the Na atom in intense mid-ir laser fields. An accurate one-electron model potential is constructed for the description of the Na atom. The time-dependent Schrödinger equation is solved by means of the time-dependent generalized pseudospectral method, allowing nonuniform and optimal spatial grid discretization and accurate and efficient propagation of the wave function in space and time. Excellent agreement of the HHG spectrum in the length and acceleration forms is obtained from the lowest harmonics up to the cutoff. The HHG power spectrum shows fine structures and significant enhancement of the intensities of the lower harmonics due to the strong coupling of the 3s-np states and the 3s-3p multiphoton resonance. We use a wavelet transform to present a detailed time-frequency analysis of the whole range of the HHG power spectrum. The results reveal striking details of the spectral and temporal fine structures of HHG, providing insights into different HHG mechanisms in different energy regimes of Na atoms at long wavelengths.

Correlated few-electron dynamics in intense laser fields

“…2(a) the correlated two-electron continuum spectrum is plotted as a function of the electron velocity components parallel to the laser polarization axis, v 1 ; v 2 . The spectrum is obtained by removing one-and two-electron bound states by applying the filter ½1 À Gðr 1 Þ½1 À Gðr 2 Þ on W with GðrÞ ¼ exp½Àðr=dÞ 6 . In the range 5 6 d 6 14, changes in Fig.…”

“…Solution of the timedependent multi-electron Schrödinger equation is beyond reach [1][2][3]. Approximate methods, such as the time-dependent Hartree-Fock (TD HF) [4], frozen-core (FC) [5], and time-dependent density functional theory [6] neglect all or a part of the electron correlation; their accuracy is not controlled.…”

Optimal control of dissociation of nitrogen molecule with intense ultra-short laser pulse shaping

“…The capability of controlling the dynamics of molecules by an ultra-short laser pulse transferring an initial state to a desired inaccessible state is suggested by different theoretical approaches of the force-optimization [5], Brumer-Shapiro coherent control [6] and genetic algorithms [7]. The pulse shaping techniques have improved impressively to translate this important idea from theory to experiment [8].…”

“…Using TDDFT allows us to reduce this difficulty by performing simulation of a non-interacting system of electrons by considering an effective potential where its density is identical to the real one. For complex quantum systems, a feedback loop, together with an optimization method or learning algorithm are used to achieve the desired controlling goal [7]. Some of these studies employ a mathematical scheme of quantum optimal control theory (QOCT) to optimize a predefined target at the end of finite time interval [11][12][13].…”

Numerical aspects of real-space approaches to strong-field electron dynamics

“…Despite remarkable theoretical achievements [1][2][3][4][5][6][7][8][9], theory overall could not fully keep pace with the experimental advances. Whereas in ground-state electronic structure theory, ab initio or first-principles calculations are a standard and reliable tool to complement experimental investigations, the situation is different in the realm of strong-field excitations.…”