# Wide Bandwidth, Frequency Modulated Free Electron Laser

## TL;DR

This paper introduces a novel wide bandwidth mode for Free Electron Lasers (FELs) that uses frequency modulation to amplify multiple frequencies simultaneously, promising enhanced capabilities for X-ray generation.

## Contribution

It demonstrates, through theory and 3D simulation, a new FEL operation mode with significantly increased bandwidth, analogous to frequency modulation in traditional lasers.

## Key findings

- Achieves at least tenfold increase in FEL bandwidth.
- Supports simultaneous amplification of multiple light frequencies.
- Scales effectively for high-power X-ray applications.

## Abstract

It is shown via theory and simulation that the resonant frequency of a Free Electron Laser may be modulated to obtain an FEL interaction with a frequency bandwidth which is at least an order of magnitude greater than normal FEL operation. The system is described in the linear regime by a summation over exponential gain modes, allowing the amplification of multiple light frequencies simultaneously. Simulation in 3D demonstrates the process for parameters of the UK's CLARA FEL test facility currently under construction. This new mode of FEL operation has close analogies to Frequency Modulation in a conventional cavity laser. This new, wide bandwidth mode of FEL operation scales well for X-ray generation and offers users a new form of high-power FEL output.