Laser harmonics from 2000 Å to 100 Å

Abstract

It is possible to bunch a relativistic electron beam in a storage ring using a powerful laser in conjunction with a periodic undulator magnet. Such a spatially bunched beam passing through a periodic undulator magnet radiates much more strongly than a normal unbunched beam. This optical klystron effect also generates significant harmonic output, much as in a conventional microwave klystron, only in this case, the output wavelengths are in the extreme ultraviolet (XUV). It is useful to think of the relativistic electron beam in the storage ring as a kind of non-linear medium for generating harmonics. Conversion efficiencies from laser power to harmonic output in the range 2000 Å to 100 Å vary from 10−3 down to 10−8 for a practical experiment using the National Synchrotron Light Source (NSLS) 700 MeV storage ring at Brcokhaven. This exceeds by several orders of magnitude any other technique for generating tunable coherent light in the XUV region, and will make possible a practical coherent light source for high resolution spectroscopy, microscopy, lithography, and holography. The physics of the bunching and harmonic generation process will be discussed, as well as some details of a computer simulation of the proposed NSLS Brookhaven experiment. In addition, a proposal for a tunable XUV light source based on this technique will be presented.