Terahertz pulse generation by multi-color laser fields with linear versus circular polarization

Area of Science:

• Laser-induced terahertz (THz) radiation generation
• Nonlinear optics and plasma physics

Background:

• Femtosecond laser pulses interacting with gases can generate THz radiation.
• The polarization state of the laser pulse is a critical parameter influencing this process.

Purpose of the Study:

• To investigate how the polarization of multi-color femtosecond laser pulses influences the THz radiation emitted from ionized gases.
• To determine the optimal polarization for maximizing THz energy yield based on the number of laser harmonics used.

Main Methods:

• Theoretical modeling using a local-current model and plane wave evaluations.
• Comprehensive 3D numerical simulations of gas jet experiments.
• Analysis of THz energy yields and polarization states.

Main Results:

• A crossover in THz energy yields was predicted and confirmed, where circular polarization is more efficient for fewer laser harmonics, and linear polarization becomes favorable for more than six harmonics.
• This polarization-dependent efficiency was observed in both singly and multiply ionized gases.
• Rotation of the THz polarization ellipse under circular laser polarization was attributed to phase shifts altering harmonic phase angles.

Conclusions:

• The polarization state of multi-color femtosecond laser pulses plays a crucial role in optimizing THz radiation generation.
• Understanding this polarization dependence allows for tailored laser-gas interactions to control THz output.
• The findings provide insights into controlling THz emission through laser polarization manipulation.