Laboratory based laser driven short pulse X-ray sources like laser produced plasmas (LPP) and high harmonic generation (HHG) exhibit a great potential for spectroscopy in the soft X-ray range. These sources are complementary to large scale facilities like synchrotrons or free electron lasers. For applications of LPP or HHG sources for time-resolved X-ray absorption spectroscopy in the water window or beyond a high photon flux is crucial. The available photon flux strongly depends on energy, pulse duration and repetition rate of the pump laser. Depending on the experimental needs in timeresolved experiments pulse durations of the X-ray pulse ranging from nanoseconds to sub-femtoseconds are required. In our contribution we will present a highly brilliant LPP source emitting soft X-rays in the photon energy range between 50 and 1500 eV based on CPA and thin disk laser technology as well as the high average power thin disk laser based OPCPA system for high photon flux HHG. In addition we present a new generation of reflection zone plates on spherical substrates, that promises a remarkable high resolution over a wide spectral range making it an ideal and highly efficient diffractive optic for time-resolved NEXAFS experiments in the lab.
We present advanced instrumentation for the investigation of thin organic films offered by a laboratory X-ray absorption fine structure (XAFS) spectrometer for the soft X-ray range. The transmission spectrometer is based on a laser-produced plasma source in combination with a twin-arm reflection zone plate spectrometer. The efficiency and stability of the spectrometer allow for single shot measurements within 500 ps with a resolving power of E/ΔE ~ 900 in a range between 200 eV and 1300 eV. Through the implementation of an optical pump beam, also transient absorption measurements can be performed. The merits of the spectrometer are demonstrated through the investigation of poly[(9,9-dioctylfluorenyl- 2,7-diyl)-alt-co-(1,4-benzo-{2,1‘,3}-thiadiazole)] (F8BT), a polyfluorene copolymer. Transient optical pump soft X-ray probe spectroscopy with 500 ps time resolution detects changes in the C K edge spectrum which can be attributed to the lowest unoccupied molecular orbitals of the molecules in the benzothiadiazole unit.
Near edge X-ray absorption fine structure (NEXAFS) spectroscopy in the soft X-ray range is feasible in the laboratory using laser-produced plasma sources. We present a study using seven different target materials for optimized data analysis. The emission spectra of the materials with atomic numbers ranging from Z = 6 to Z = 79 show distinct differences, rendering the adapted selection of a suitable target material for specialized experiments feasible. For NEXAFS spectroscopy a 112.5 nm thick polyimide film is investigated as a reference exemplifying the superiority of quasi-continuum like emission spectra.
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