Revisiting multi-center interferences in carbon dioxide through high-harmonic spectroscopy

We present high-harmonic spectroscopic measurements of the spectral intensity and phase of multi-center interferences in carbon dioxide where we observe a wavelength-dependent change in the interference mechanism. We use molecular impulsive alignment combined with four different driving wavelengths, ranging from the near-infrared to mid-infrared, and a range of intensities at each wavelength for high-harmonic generation. In our measurements we observe an intensity-dependent, multi-orbital interference at near-infrared driving wavelengths and an intensity-independent, two-center interference at mid-infrared driving wavelengths. Our assignment of two different interference mechanisms is supported by a change in sign and intensity-dependence of the spectral phase jump between near-infrared and mid-infrared driving wavelengths. These results resolve a long-standing discrepancy in prior publications and provide new insight about geometric two-center interferences and dynamic multi-orbital interferences.