Extracting the phase of high-order harmonic emission from a molecule using transient alignment in mixed samples

Abstract

We report measurements of both the phase and intensity of high-order harmonic emission from aligned ${\mathrm{CO}}_{2}$ molecules, using a mixture of a molecular and an atomic gas. The molecules are transiently aligned using an ultrashort pulse, and a subsequent stronger pulse is used to generate high-order harmonics from a mixed $\mathrm{Kr}∕{\mathrm{CO}}_{2}$ sample. The high-order harmonic emission from the molecules interferes with the reference emission from the atoms. By monitoring the change in harmonic emission as a function of gas mixture and molecular alignment, we can retrieve the orientational dipole that has general features consistent with a two-center emission model.