Backward THz Emission from Two-Color Laser Field-Induced Air Plasma Filament

Area of Science:

• Physics
• Optics
• Plasma Physics

Background:

• Two-color laser fields induce plasma filaments, serving as efficient broadband terahertz (THz) sources.
• Intense THz waves are primarily emitted in the forward direction, with backward emission being less studied.

Purpose of the Study:

• To theoretically and experimentally investigate backward terahertz (THz) wave radiation from two-color laser-induced plasma filaments.
• To explore the relationship between plasma filament length and backward THz emission.
• To understand the THz generation mechanisms for both forward and backward emission.

Main Methods:

• Theoretical modeling using a linear dipole array model.
• Experimental setup to generate and detect backward THz radiation from a ~5 mm plasma filament.
• Analysis of THz waveform, spectrum, and dependence of peak THz electric field on pump laser pulse energy.

Main Results:

• A linear dipole array model predicted that backward THz wave proportion decreases with plasma filament length.
• Experimental observation of typical waveform and spectrum for backward THz radiation.
• Peak THz electric field dependence on pump laser energy suggests similar generation processes for forward and backward THz waves.
• Observed peak timing shift in THz waveform indicates plasma position changes due to nonlinear-focusing effects.

Conclusions:

• The study provides insights into the backward THz emission from two-color laser-induced plasma filaments.
• Experimental findings align with theoretical predictions regarding the influence of plasma length.
• The findings suggest potential applications in THz imaging and remote sensing.