Direct measurement of the angular dependence of ionization for N2, O2, and CO2 in intense laser fields.

We experimentally measure the ionization probability as a function of alignment angle of three molecules in intense laser fields: nitrogen, oxygen, and carbon dioxide. Unlike atoms, molecules have a rotational degree of freedom. By controlling the alignment of the molecule relative to the laser field, molecules offer additional ways to understand strong-field ionization. The angular dependence of ionization directly maps to the orbital symmetry of each molecule. Carbon dioxide is seen to have a very sharp preference for ionization when aligned at 45 degrees to the laser field, in significant disagreement with current theories.