Seminars Archive

Stimulated X-ray emission in the condensed phase

Abstract
The invention of the laser in the optical regime has triggered a breakthrough in spectroscopic techniques and enabled a multitude of methods involving beams of different photon energy, direction and arrival time. X-ray spectroscopy in turn has the power to deliver much more specific information than optical methods through the shorter wavelength - making it sensitive for order on the length scales of the atomic lattice and especially through the ability to tune the photon energy to elemental resonances, strongly enhancing the signal from selected sites, for example the active site in a chemical reaction. Combining the non-linear methods from optical spectroscopy with the specificity and sensitivity of X-rays is a dream of many experimentalists and has the ability to trigger another breakthrough in the way we can understand matter. X-ray free-electron lasers promise to enable this breakthrough. In the recent past, it has turned out that approaches towards this dream are feasible and some pioneering experiments will be discussed, especially the signal enhancement by one order of magnitude in X-ray emission spectroscopy will be presented. It also became obvious that a further development can only be achieved with an exquisite control over the photon parameters especially in the time-energy Fourier space. Here, the common SASE FELs are reaching fundamental limits and instructive experimental results will be discussed. FERMI - in contrast - as a seeded FEL, is unique in delivering photon beams with the desired properties. A proposed experiment will be shown that has the power to increase signal levels in X-ray emission spectroscopy by up to eight orders of magnitude and thus has the ability to revolutionize X-ray spectroscopies.