Efficient Narrow-Band Terahertz Radiation from Electrostatic Wakefields in Nonuniform Plasmas

Area of Science:

• Plasma physics
• Electromagnetics
• Laser-plasma interactions

Background:

• Plasma wakefield accelerators are a promising technology for future accelerators.
• Controlling radiation emission from plasma wakefields is crucial for applications.
• Previous studies have explored various mechanisms for radiation generation in plasmas.

Purpose of the Study:

• To investigate the radiation generation mechanism in electrostatic plasma wakefields with a positive density gradient.
• To determine the conditions under which efficient terahertz radiation is produced.
• To explore the potential of this mechanism for creating tunable radiation sources.

Main Methods:

• Simulating the interaction of a subluminal driver with a plasma exhibiting a positive density gradient.
• Analyzing the excitation and evolution of electrostatic plasma wakefields.
• Investigating the coupling of wakefields to electromagnetic modes and the resulting radiation spectrum.

Main Results:

• Electrostatic plasma wakefields radiate efficiently at harmonics of the plasma frequency when a positive density gradient is present.
• The wakefield phase velocity increases due to the density gradient, becoming superluminal and coupling to radiative modes.
• Radiation is observed in the terahertz band, with emission characteristics dependent on the gradient scale length and time behind the driver.

Conclusions:

• A positive plasma density gradient provides an efficient mechanism for generating tunable, narrow-band terahertz radiation.
• This effect can potentially lead to the development of novel terahertz sources by allowing wakefields to radiate away nearly all their energy.
• The findings offer a new pathway for controlling and optimizing radiation generation in laser-plasma interactions.