We have measured high-order harmonic generation spectra of D2, N2, and
CO2 by mixing orthogonally polarized 800 and 400 nm laser fields. The
intensity of the high-harmonic spectrum is modulated as we change the
relative phase of the two pulses. For randomly orientated molecules, the
phase of the intensity modulation depends on the symmetry of the
molecular orbitals from which the high harmonics are emitted. This
allows us to identify the symmetry of any orbital that contributes to
high-harmonic generation, even without aligning the molecule. Our
approach can be a route to imaging dynamical changes in
three-dimensional molecular orbitals on a time scale as short as a few
hundred attoseconds.
http://prl.aps.org/abstract/PRL/v105/i5/e053003
