Multi-milliwatt average power two-color air-plasma terahertz source at 100 kHz repetition rate

Area of Science:

• Physics
• Optics
• Plasma Physics

Background:

• Ultrafast terahertz (THz) transients are typically generated using two-color air-plasma schemes driven by low-repetition-rate lasers, limiting measurement dynamic range.
• High-power Yb-based lasers and nonlinear temporal compression enable higher repetition rates for THz sources, potentially overcoming previous limitations.

Purpose of the Study:

• Investigate the impact of repetition rate scaling on THz generation efficiency in the two-color air-plasma scheme.
• Analyze the correlation between repetition rate, THz yield, and gas density depletion.
• Validate experimental findings with a developed one-dimensional photocurrent model.

Main Methods:

• Experimentally studied THz generation at repetition rates from 1 kHz to 100 kHz.
• Measured gas density depletion in the filamentation region using interferometry.
• Developed and applied a one-dimensional photocurrent model for efficiency calculations.

Main Results:

• Observed a decrease in optical-to-THz conversion efficiency with increasing repetition rate, correlated with gas density depletion.
• Achieved maximum average THz power of 2.8 mW and peak electric fields of 165 kV/cm at 100 kHz.
• Detected THz frequencies up to 23 THz, confirming the broadband nature of the source.

Conclusions:

• Gas density depletion is a key factor limiting efficiency scaling at higher repetition rates.
• The two-color air-plasma scheme shows promise for MHz repetition rate THz generation.
• The developed THz source offers accelerated measurement times for spectroscopic applications.