Bulk-Plasmon-Mediated Free-Electron Radiation Beyond the Conventional Formation Time

Area of Science:

• Physics
• Photonics
• Materials Science

Background:

• Free-electron radiation is a fundamental process involving fast electrons and optical media.
• Historically, this radiation has been confined by a 'formation time,' encompassing Cherenkov and transition radiation mechanisms.
• Existing models describe radiation from bulk media or interfaces.

Purpose of the Study:

• To reveal an alternative free-electron radiation mechanism that extends beyond the conventional formation time.
• To investigate radiation generated when electrons cross the interface between vacuum and a plasmonic medium.
• To clarify the nature of Ferrell radiation.

Main Methods:

• Theoretical analysis of electron-plasmon interactions at interfaces.
• Modeling of bulk plasmon excitation and propagation.
• Comparison with existing models of Cherenkov and transition radiation.

Main Results:

• An alternative free-electron radiation mechanism is identified, operating beyond the established formation time.
• This mechanism involves bulk plasmons forming a 'plasmonic tail' that sustains electron-interface interaction.
• The findings reconcile Ferrell radiation as a phenomenon involving both surface and bulk plasmonic effects.

Conclusions:

• Free-electron radiation can occur via a novel mechanism sustained by bulk plasmons beyond the conventional formation time.
• This extended radiation is linked to the interaction of electrons with a plasmonic tail at the vacuum-medium interface.
• The study resolves the long-standing debate on whether Ferrell radiation is a surface or bulk effect.