# An X-Ray Regenerative Amplifier Free-Electron Laser Using Diamond Pinhole MIrrors

## TL;DR

This paper proposes and analyzes a diamond-pinhole mirror regenerative amplifier free-electron laser (RAFEL) design for x-ray wavelengths, demonstrating potential for high power output at specific energies using advanced simulation tools.

## Contribution

It introduces a novel RAFEL design with diamond pinhole mirrors for x-ray FELs and demonstrates its feasibility through detailed simulations.

## Key findings

- Substantial power levels achievable at 3.05 keV and 9.15 keV.
- Effective out-coupling of over 90% using diamond pinhole mirrors.
- Simulation results support the design's potential for LCLS-II applications.

## Abstract

Free-electron lasers (FELs) have been built ranging in wavelength from long-wavelength oscillators using partial wave guiding through ultraviolet through hard x-ray FELs that are either seeded or start from noise (SASE). Operation in the x-ray spectrum has relied on single-pass SASE due either to the lack of seed lasers or difficulties in the design of x-ray mirrors. However, recent developments in the production of diamond crystal Bragg reflectors point the way to the design of regenerative amplifiers (RAFELs) which are, essentially, low-Q x-ray free-electron laser oscillators (XFELOs) that out-couple a large fraction of the optical power on each pass. A RAFEL using a six-mirror resonator providing out-coupling of 90% or more through a pinhole in the first downstream mirror is proposed and analyzed using the MINERVA simulation code for the undulator interaction and the Optics Propagation Code (OPC) for the resonator. MINERVA/OPC has been used in the past to simulate infrared FEL oscillators. For the present purpose, OPC has been modified to treat Bragg reflection from diamond crystal mirrors. The six-mirror resonator design has been analyzed within the context of the LCLS-II beamline under construction at the Stanford Linear Accelerator Center and using the HXR undulator which is also to be installed on the LCLS-II beamline. Simulations have been run to optimize and characterize the properties of the RAFEL, and indicate that substantial powers are possible at the fundamental (3.05 keV) and third harmonic (9.15 keV).

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Source: https://tomesphere.com/paper/1905.06279