Ultraviolet supercontinuum generation driven by ionic coherence in a strong laser field.

Area of Science:

• Quantum optics
• Strong-field physics
• Spectroscopy

Background:

• Supercontinuum (SC) light sources are crucial for applications like imaging and frequency comb metrology.
• Generating SC in the ultraviolet (UV) spectrum remains a significant challenge.
• Existing SC sources are primarily limited to the visible and near-infrared regions.

Purpose of the Study:

• To demonstrate a novel method for generating UV supercontinuum radiation.
• To explore the underlying quantum phenomena responsible for UV SC generation in molecular nitrogen ions.
• To showcase the application of the generated UV SC in absorption spectroscopy.

Main Methods:

• Utilizing strong field ionization and quantum resonance in molecular nitrogen ions.
• Investigating dynamic Stark-assisted multiphoton resonances following tunneling ionization.
• Analyzing the creation and evolution of quantum coherences in ionic levels.

Main Results:

• Achieved unexpected UV continuum radiation with a 100 nm bandwidth in molecular nitrogen ions.
• Identified quantum coherences in ionic levels created by dynamic Stark-assisted multiphoton resonances.
• Demonstrated that laser-assisted continuum emission and free-induction decay contribute to SC generation, along with fifth harmonics.
• Successfully applied the UV SC radiation for absorption spectroscopy.

Conclusions:

• The joint effect of strong field ionization and quantum resonance provides an alternative route for generating exotic SC sources.
• This work establishes ionic quantum optics in the strong-field regime.
• The developed method offers a new approach for accessing the UV spectrum with supercontinuum light.