All-optical measurement of high-harmonic amplitudes and phases in aligned molecules

We report a new all-optical approach to measuring the phase and amplitude of high-harmonic emission from aligned molecules. We combine the transient grating technique with a continuous rotation of the molecular alignment axis and develop an analytical model that enables the simultaneous determination of phases and amplitudes. Measurements in N(2) molecules are shown to be in qualitative agreement with the results of ab initio quantum scattering calculations.