Abstract

From the early days of free-electron lasers (FELs), the idea of lasing at wavelengths where gain media had not previously existed was one of the most attractive aspects of these devices. The spectral region in the soft X-ray was both inviting, due to the exciting physics one could do with such a source, and challenging, due to the need for a very bright electron beam (high charge density), very high gain to overcome cavity losses, and the cost of providing all this at very high electron beam energies with high-duty-cycle electron beams. Electron beam brightness is defined as the ratio of the peak current to the product of the horizontal and vertical normalized emittances. The normalized electron beam emittance is the product of the rms transverse size and momentum spread. High gain is usually obtained using a very long undulator, which requires a very small energy spread in addition to the small transverse emittance. Electron beams in the 1970s generally provided either low peak current or large energy spread and very low charge density. Even the VUV spectral range was considered too difficult for the accelerators and optics available then. Early FELs therefore operated in the infrared range. FEL oscillators were eventually pushed into the visible and ultraviolet but could not push into the VUV due to either low gain or poor mirror reflectivity.

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 call

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.