Speaker
Description
Orbital angular momentum (OAM) photon beams provide a unique tool for nondestructive photon-matter interactions in a broad photon energy range. Here, we report the first experimental demonstration of coherently mixed OAM beams from an oscillator free-electron laser (FEL). With wavelength tunability, free-electron lasers (FELs) are well-suited for generating OAM beams in a wide photon energy range. Lasing around 458 nm, we have generated OAM FEL beams up to the fourth order, as a coherent superposition of two pure OAM modes with opposite helicities. These coherently mixed OAM beams are generated with high quality in terms of beam quality factors and mode components, high degree of circular polarization, and high power. We have also developed a pulsed mode operation of the OAM beam with a highly reproducible temporal structure for a range of modulation frequencies from 1 to 30 Hz. This development can be extended to short wavelengths, for example to x-rays using a future x-ray FEL oscillator. The operation of such an OAM FEL also paves the way for the generation of OAM gamma-ray beams via Compton scattering. We will also discuss the challenges of producing high-flux OAM gamma-ray beams with the Compton scattering scheme using an electron beam and an OAM laser beam.
This research is supported in part by the U.S. Department of Energy under Grant No. DE-FG02-97ER41033.
