# High-efficiency broadband THz emission via diffraction-radiation cavity

## TL;DR

This paper proposes and experimentally demonstrates a novel scheme for high-efficiency broadband terahertz emission using diffraction radiation in an optical cavity, significantly enhancing radiation output via stimulated processes.

## Contribution

The paper introduces a new cavity-based diffraction-radiation scheme with stimulated emission, achieving efficient broadband THz generation in an accelerator setting.

## Key findings

- Observation of a sharp THz resonance signal indicating stimulated radiation.
- Experimental validation of efficient beam-to-radiation energy conversion.
- Successful demonstration of broadband THz emission in an ERL setup.

## Abstract

Accelerator-based terahertz (THz) radiation has been expected to realize a high-power broadband source. Employing a low-emittance and short-bunch electron beam at a high repetition rate, a scheme of coherent diffraction-radiation in an optical cavity layout is proposed. The scheme's stimulated radiation process between bunches can greatly enhance the efficiency of the radiation emission. We performed an experiment with a superconducting linac constructed as an energy recovery linac (ERL) test facility. The electron beam passes through small holes in the cavity mirrors without being destroyed. A sharp THz resonance signal, which indicates broadband stimulated radiation correlated with beam deceleration, was observed while scanning the round-trip length of the cavity. This observation proves the efficient beam-to-radiation energy conversion due to the stimulated radiation process.