Illuminating Molecular Symmetries with Bicircular High-Order-Harmonic Generation

Area of Science:

• Atomic, Molecular, and Optical Physics
• Quantum Optics
• Ultrafast Science

Background:

• High-order harmonic generation (HHG) is a key process for producing coherent extreme ultraviolet and X-ray light.
• Understanding molecular response to intense laser fields is crucial for attosecond science and molecular imaging.
• Bicircular fields offer unique control over HHG, but their interpretation in molecules remains complex.

Purpose of the Study:

• To develop a general theoretical framework for bicircular high-order-harmonic generation (BHG) in molecules.
• To predict the harmonic spectra structure for arbitrary driving frequency ratios.
• To demonstrate the direct identification of molecular rotational symmetries from BHG signals.

Main Methods:

• A general theory based on a rotating frame of reference was developed.
• The theory predicts the complete structure of high-order harmonic spectra.
• Analysis focuses on N-fold rotationally symmetric molecules.

Main Results:

• A universal characteristic fingerprint of rotational molecular symmetries was identified in BHG spectra.
• The method allows direct identification of molecular symmetries from the harmonic signal.
• Predictions are valid for arbitrary driving frequency ratios.

Conclusions:

• BHG provides a powerful tool for probing molecular symmetries.
• The ultrafast response of molecules to strong bicircular fields contains direct information about their structure.
• This work establishes a new pathway for molecular symmetry characterization using laser-driven phenomena.