Microscopic response

a)    Model description and method:
We solve the time-dependent Schrödinger equation (TDSE), in the single active electron approximation, on a 1D or 2D Cartesian grid or in 3D spherical geometry. The electron wavepacket (EWP) dynamics is governed here by the static atomic potential and the strong time-dependent laser electric field. The eigenvalues and associated eigenvectors of the stationary Hamiltonian (without laser field) are first computed by means of the imaginary time propagation method, for a soft-core screened Coulomb atomic potential, reproducing the ionization energy of the considered atom or molecule. The laser is then turned on, and the ground state wavefunction is propagated in time, using a split-step or a finite difference method. The interaction with the laser is calculated in the dipolar approximation, in the length or velocity gauge.

b)    Illustrating example: generation of circularly polarized attosecond pulses:
High-order harmonics generated by counter-rotating laser fields at the fundamental (ω) and second harmonic (2ω) frequencies are of particular interest for producing table-top coherent sources of circularly-polarized ultrashort extreme-ultraviolet light. The Lissajous representation of the ω+2ω field has a three-fold rosette shape. The EWP, driven in the continuum by this field, revisits cyclically (each third of the fundamental optical period) its parent ion, resulting in the emission of circularly polarized harmonics with orders 3q+1 and 3q+2 (q = 0, 1…). The movie below illustrates the EWP dynamics in such a bi-chromatic, bi-circular laser field for a hydrogen atom. The nucleus (proton) is in the center of the window.

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#2988 - Màj : 07/11/2018

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