Mode growth and competition in the x-ray free-electron laser oscillator start-up from noise

Abstract

We describe the radiation properties of an x-ray free-electron laser (FEL) oscillator, beginning with its start-up from noise through saturation. We first decompose the initially chaotic undulator radiation into the growing longitudinal modes of the composite system consisting of the electron beam, the undulator, and the Bragg mirror resonator cavity. Because the radiation initially comprises several modes whose growth rates are comparable, we find that only after many oscillator passes is the output pulse dominantly characterized by the lowest-order Gaussian mode. We verify our analytic results with a novel, reduced one-dimensional FEL code (derived in the text), and with two-dimensional FEL simulations. Understanding the full longitudinal structure during the initial amplification will be critical in assessing the tolerances on the electron beam, undulator, and optical cavity required for robust operation.

An x-ray regenerative amplifier free-electron laser using diamond pinhole mirrors

“…The utility of an x-ray FEL oscillator (XFELO) has been under study for a decade [7][8][9][10][11][12][13][14] making use of resonators based upon Bragg scattering from high-reflectivity diamond crystals [15][16][17][18][19]. The development of these crystals is a major breakthrough in the path toward an XFELO.…”

Performance of the x-ray free-electron laser oscillator with crystal cavity

“…We also find that the penetration of the x rays into the crystals results in an effective delay that requires compensation via a cavity length reduction of tens of microns. The essential conclusions [4,24] based on 1D arguments and idealized crystal reflectivities have been confirmed: a highquality (" x ¼ 0:2 mm mrad), low-charge (25-50 pC) electron beam of 1 ps duration can produce x rays with 1-10 MW of peak power in an extremely narrow, nearly Fourier-limited bandwidth $1-3 meV FWHM. Additionally, compressing the electron beam by a factor of 10 increases the single-pass gain, and one can consider easing the requirements on the electron beam emittance, the cavity reflectivity, and/or the undulator length.…”

Three-Dimensional, Time-Dependent Analysis of High- and Low-Q Free-Electron Laser Oscillators

“…The utility of an XFELO has been under study for a decade [162,[228][229][230][231][232][233], making use of resonators based upon Bragg scattering from atomic layers within diamond crystals [234][235][236][237][238]. The development of these crystals is a major breakthrough in the path toward an XFELO.…”