Zone Plates for Hard X-Ray Free-Electron Lasers

Hard x-ray free-electron lasers are novel sources of coherent x-rays with unprecedented brightness and very short pulses. The radiation from these sources enables a wide range of new experiments that were not possible with previous x-ray sources. Many of these experiments require the possibility to focus the intense x-ray beam onto small samples. This Thesis investigates the possibility to use di ractive zone plate optics to focus the radiation from hard x-ray free-electron lasers. The challenge for any optical element at free-electron laser sources is that the intensity in a single short pulses is high enough to potentially damage the optics. This is especially troublesome for zone plates, which are typically made of high Z elements that absorb a large part of the incident radiation. The rst part of the Thesis is dedicated to simulations, where the temperature behavior of zone plates exposed to hard x-ray free-electron laser radiation is investigated. It is found that the temperature increase in a single pulse is several hundred Kelvin but still below the melting point of classical zone plate materials, such as gold, tungsten, and iridium. Even though the temperature increases are not high enough to melt a zone plate it is possible that stresses and strains caused by thermal expansion can damage the zone plate. This is rst investigated in an experiment where tungsten gratings on diamond substrates are heated to high temperatures by a pulsed visible laser. It is found that the gratings are not damaged by the expected temperature uctuations at free-electron lasers. Finally, a set of tungsten zone plates are tested at the Linac Coherent Light Source where they are exposed to a large number of pulses at varying uence levels in a prefocused beam. Damage is only observed at uence levels above those typically found in an unfocused x-ray free-electron laser beam. At higher uences an alternative is to use a diamond zone plate, which has signi cantly less absorption and should be able to survive much higher uence. Damage in diamond structures is investigated during the same experiment, but due to a remaining tungsten etch mask on top of the diamond the results are di cult to interpret.