Investigation of Interferences in Carbon Dioxide through Multidimensional Molecular-Frame High-Harmonic Spectroscopy

Area of Science:

• Quantum optics
• Molecular spectroscopy
• Attosecond science

Background:

• High-harmonic generation (HHG) is a key process for creating ultrashort light pulses.
• Understanding interference mechanisms in HHG is crucial for controlling light-matter interactions.
• Carbon dioxide (CO2) is a relevant molecule for studying fundamental HHG processes.

Purpose of the Study:

• To investigate the spectral intensity and group delay in molecular-frame high-harmonic spectroscopy of CO2.
• To characterize the wavelength and intensity dependence of a distinct minimum in harmonic emission.
• To differentiate between structural two-center interference and dynamic multichannel interference using experimental data.

Main Methods:

• Performed molecular-frame high-harmonic spectroscopic measurements on CO2.
• Utilized four different driving wavelengths and varied intensities for high-harmonic generation.
• Measured spectral intensity and group delay across a range of experimental conditions.
• Employed ab initio time-dependent density functional theory (TD-DFT) calculations for validation.

Main Results:

• Observed a well-characterized minimum in harmonic emission with clear wavelength and intensity dependence.
• Classified the interference minimum as either structural two-center or dynamic multichannel interference based on intensity dependence.
• Demonstrated that the sign of the group delay excursion across the interference acts as a sensitive probe of the underlying mechanism.
• Experimental findings were corroborated by theoretical TD-DFT calculations.

Conclusions:

• The study provides a detailed molecular-frame characterization of high-harmonic generation in CO2.
• Group delay measurements offer a powerful new method for distinguishing interference mechanisms in HHG.
• The combination of experiment and theory advances the understanding of light-matter interactions in molecules.