Measuring the intensity and phase of high-order harmonic emission from aligned molecules

High-order harmonic emission from aligned molecules can be used as a probe of molecular structure with ultrafast time resolution. In this paper, we review past work, and also present new measurements of the intensity and phase of harmonic emission from N2O and N2 molecules. We find that high harmonic emission from CO2 and N2O molecules is well described by a simple two-center interference model. In contrast, high harmonic emission from N2 exhibits a very different behavior, not readily explained by assuming that the electron responsible for the high-order harmonic emission recollides with the molecule as a plane wave. These data clearly emphasize the need for more comprehensive models of high harmonic generation from molecules.