Abstract
Three-dimensional simulation codes genesis and opc are used to investigate the dependence of the resonator stability of free-electron laser (FEL) oscillators on the stability parameter, laser wavelength, outcoupling hole size and mirror tilt. We find that to have stable lasing over a wide range of wavelengths, the FEL cavity configuration should be carefully chosen. Broadly, the concentric configuration gives near-Gaussian modes and the best performance. At intermediate configurations the dominant mode often switches to a higher-order mode, which kills lasing. For the same reason, the outcoupled power can also be less. We have constructed a simple analytic model to study resonator stability which gives results that are in excellent agreement with the simulations. This suggests that modes in FEL oscillators are determined more by the cavity configuration and radiation propagation than by the details of the FEL interaction. We find (as in experiments at the CLIO FEL) that tilting the mirror can, for some configurations, lead to more outcoupled power than a perfectly aligned mirror because the mode is now a more compact higher-order mode, which may have implications for the mode quality for user experiments. Finally, we show that the higher-order mode obtained is usually a single Gauss-Laguerre mode, and therefore it should be possible to filter out the mode using suitable intracavity elements, leading to better FEL performance.
Highlights
Most infrared free-electron laser (FEL) facilities around the world use thermionic electron sources with modest currents (≈10–100 A) [1,2,3,4,5] and operate the FEL in the oscillator configuration, very often with on-axis hole outcoupling
We find that to have stable lasing over a wide range of wavelengths, the FEL cavity configuration should be carefully chosen
They suggest that the FEL cavity configuration should be chosen carefully, in order to have stable lasing over a wide range of wavelengths, and concentric or confocal configurations may be preferable
Summary
Most infrared free-electron laser (FEL) facilities around the world use thermionic electron sources with modest currents (≈10–100 A) [1,2,3,4,5] and operate the FEL in the oscillator configuration, very often with on-axis hole outcoupling. The shape of the dominant mode on the outcoupling mirror determines the outcoupled power It is well known [6,7,8] that mode competition and mode beating affect the stability of optical modes in FEL oscillators and constrain the operating parameters of the FEL. This can be a concern for FEL facilities, because one of the important advantages of FELs is the ability to provide tunable coherent radiation over a large wavelength range. This identification suggests that the use of intracavity elements for suppressing the higher-order modes can lead to better operation of the FEL, in terms of greater outcoupled power and operation over a wider range of wavelengths
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Physical Review Special Topics - Accelerators and Beams
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
