Session R5: Wilson Prize Session

Robert R. Wilson Prize for Achievement in the Physics of Particle Accelerators Lecture: Frontiers of FEL Physics and Technology

For much of the past 40 years, efforts to advance the capabilities of FELs have focussed on the frontiers of operation at high average power and short wavelengths with impressive and gratifying results. But a number of potentially important additional frontiers remain to be explored. I will briefly describe several of the new areas in which we have worked relating to the exploitation of boundary conditions to enhance oscillator phase coherence and stability, the exploitation of phase coherence to reduce the quantum fluctuations in amplitude of the coherent harmonics, the elucidation of the classical Wheeler-Feynman coherent radiation reaction force in single pass radiation sources, the development of the precision, robust high peak and average power optical elements needed for the reliable operation of these sources and the application of these advances to the development of optimized inverse-Compton x-ray and gamma ray sources.   

Challenges of Seeded Free-Electron Lasers

A principle advantage of the free-electron laser (FEL) over the more conventional atomic-transition based laser is its ability to be tuned to an arbitrary wavelength. In fact this advantage is even more pronounced as wavelengths extend into the x-ray regime. Early FELs operated in an oscillator configuration, i.e. similar to conventional laser, and so relied heavily on mirrors. This configuration gave the FEL output both good transverse and longitudinal coherence properties. But mirrors have limitations, and if one wants to construct an FEL that can operate in the x-ray regime then one is forced to rethink the FEL configuration. Over the past decade electron beam sources and beam control have achieved beam qualities sufficient for the FEL to operate in the x-ray regime; however, present devices are not configured as oscillators and indeed the process in these single pass configurations start from synchrotron radiation shot noise. As such, even though the FEL process saturates and the transverse beam quality is almost completely coherent, longitudinally the coherence is poor. If one could seed the FEL and operate the system in an amplifier mode then the longitudinal coherence could be greatly improved. In this talk we will review the status of the FEL and then dive into the issue one faces when attempting to seed the FEL at very short wavelengths. We will also touch upon some other interesting opportunities that seeding provides as well as highlight some interesting seeding concepts presently being explored.