Free electron lasers

Abstract

Data storage applications of magnetism utilize dynamic processes on sub-nanosecond time scales and on length scales of less than 100 nanome-ters. Magnetization dynamics on the sub-picosecond time scale has been observed and may lead the way to novel devices. In order to investigate these processes it is essential to have a method-combining sub-micrometer spatial with sub-picosecond temporal resolution. Ultrafast x-ray pulses now offer this possibility. The radiation of free electron lasers (FELs) consists of sub-picosecond x-rays with unprecedented peak brightness. This chapter explains the basic principles of FELs. The peak intensity offers the possibility of imaging a fluctuating system (for example a ferromagnetic domain struc-ture) within a single pulse. These imaging techniques as well as spectroscopic methods are explained. In order to perform time resolved experiments using large scale facilities it is essential to understand the techniques used to determine the timing between the pump laser and the x-ray probe pulses, a topic laid out.