Electro-optic sampling based characterization of broad-band high efficiency THz-FEL

Area of Science:

• Physics, Applied Physics
• Engineering, Electrical and Electronic Engineering

Background:

• Terahertz (THz) free-electron lasers (FELs) offer unique capabilities for generating high-power radiation.
• Achieving high beam-to-radiation energy conversion efficiency is crucial for FEL performance.
• Waveguide-based FELs can enhance interaction by matching velocities, but their dynamics are complex.

Purpose of the Study:

• To report the first electro-optic sampling (EOS) measurements of broadband THz FEL radiation in a zero-slippage resonant condition.
• To investigate the complex dynamics within a waveguide FEL operating at high efficiency.
• To reconstruct THz field waveforms in spatial and temporal domains.

Main Methods:

• Utilizing a strongly tapered helical undulator at the zero-slippage resonant condition.
• Employing a circular waveguide to match radiation group velocity with electron beam velocity.
• Performing multi-shot and single-shot electro-optic sampling (EOS) for THz waveform reconstruction.

Main Results:

• Successfully measured broadband THz FEL radiation pulses using EOS.
• Reconstructed THz field waveforms in both spatial and temporal domains.
• Observed insights into the complex dynamics of waveguide FELs by varying electron beam energy.

Conclusions:

• The zero-slippage resonant condition with a tapered undulator and waveguide enables high THz FEL efficiency.
• EOS is an effective technique for characterizing THz pulses from waveguide FELs.
• The study provides valuable data for understanding and optimizing waveguide FEL performance.