No abstract

We report the observation and analysis of the gain curve of amplified Kα x-ray emission from solutions of Mn(II) and Mn(VII) complexes using an x-ray free electron laser to create the 1s core-hole population inversion. We find spectra at amplification levels extending over 4 orders of magnitude until saturation. We observe bandwidths below the Mn 1s core-hole lifetime broadening in the onset of the stimulated emission. In the exponential amplification regime the resolution corrected spectral width of ~1.7 eV FWHM is constant over 3 orders of magnitude, pointing to the buildup of transform limited pulses of ~1 fs duration. Driving the amplification into saturation leads to broadening and a shift of the line. Importantly, the chemical sensitivity of the stimulated x-ray emission to the Mn oxidation state is preserved at power densities of ~1020 W/cm2 for the incoming x-ray pulses. Differences in signal sensitivity and spectral information compared to conventional (spontaneous) x-ray emission spectroscopy are discussed. Our findings build a baseline for nonlinear x-ray spectroscopy for a wide range of transition metal complexes in inorganic chemistry, catalysis, and materials science.

No abstract

Beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics for the installation of the new permanent CAMP end-station, a multi-purpose instrument optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments. An overview of the layout, beam transport, focusing capabilities, and experimental possibilities of this new end-station, as well as results from its commissioning and first experiments, are presented.

No abstract

With the invention of femtosecond X-ray free-electron lasers (XFELs), studies of light-induced chemical reaction dynamics and structural dynamics reach a new era, allowing for time-resolved X-ray diffraction and spectroscopy. To ultimately probe coherent electron and nuclear dynamics on their natural time and length scales, coherent nonlinear X-ray spectroscopy schemes have been proposed. In this contribution, we want to critically assess the experimental realisation of nonlinear X-ray spectroscopy at current-day XFEL sources, by presenting first experimental attempts to demonstrate stimulated resonant X-ray Raman scattering in molecular gas targets.

We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a high-intensity free-electron laser pulse in a cell filled with Xe or Kr gas, the medium is quasi instantaneously population-inverted by inner-shell ionization on the giant resonance followed by Auger decay. On the timescale of 100 ps a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe and Kr lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission shows an exponential growth of over 4 orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation.Superfluorescence [1] is the spontaneous, collective decay of an extended ensemble of atoms that have been prepared in a population-inverted state, resulting in collimated, highintensity radiation pulses. The pulses are emitted at a certain delay following excitation and have a duration that can be several orders of magnitude smaller than the typical upper-state lifetimes. Long before the advent of short-wavelength free-electron lasers (FELs), strong superfluorescence in optically thick media was proposed as a source of highly intense and pulsed extreme-ultraviolet (XUV) or X-ray radiation [2]. Strong X-ray K-α superfluorescence following ionization of the 1s shell with a focused X-ray FEL (XFEL) beam was demonstrated in neon gas [3,4], solid copper [5] and manganese salts in aqueous solution [6]. Extremely high gains were observed in these experiments [3,6], with exponential amplification factors surpassing 20 compared to spontaneous emission. In the vacuum ultraviolet and XUV regions, superfluorescence following inner-shell ionization has so far not been demonstrated.The difficulty to obtain transient gain in this wavelength regime is a consequence of the very different time scales of two competing processes: on the one hand, short (fs) Auger lifetimes of inner-valence vacancies, and, on the other hand, comparatively long (ns) radiative transition times -a highly unfavorable combination to sustain a sizable population inversion and gain. Here, we present combined experimental and theoretical work, giving strong evidence for XUV superfluorescence of Xe and Kr gases. Population inversion is

No abstract