Observing molecular structures by using high-order harmonic generation in mixed gases

We demonstrate that the structure of CO2 molecules can be determined by measuring the phases of harmonics from them. This is evidenced by observing a phase jump of harmonics generated in a mixed gas of aligned CO2 molecules and their reference Kr atoms, which serve to extract the net contribution due to the structure of CO2 molecules. Furthermore, in the strong field approximation model, we derive the exact conditions of quantum interference during high-order harmonic generation in CO2 molecules analytically and we propose a method to control harmonic pulse duration.