Molecular orbital tomography using short laser pulses

Recently, a method to image molecular electronic orbitals using high-order harmonic generation was introduced by Itatani et al. [Nature 432, 876 (2004)]. We show that, while the tomographic reconstruction of general orbitals with arbitrary symmetry cannot be performed with long laser pulses, this becomes possible when extremely short pulses are used. This statement is shown both in a simplified wave-packet picture and more formally within the strong-field approximation. We present an analytical formula for the wave-packet composition of the recollision electron. An alternative reconstruction equation based on momentum matrix elements, rather than on dipole matrix elements, is proposed. We present simulations of the procedure for two-dimensional model systems based on numerical solutions of the time-dependent Schrodinger equation.