Novel laboratory spectrometer for pump-probe NEXAFS spectrometry of bio-molecules in solution

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The proposed development of a NEXAFS (Near edge x-ray absorption fine structure) spectrometer aims to facilitate time-resolved analysis of bio-molecules in solution. The structure-function relationship of photosynthetic pigment-protein complexes will be explored with the help of the model system copper chlorophyllin (CuChl). Additionally the possibility of pump-probe experiments independent on large scale facilities will be shown.The concept is based on a laser-produced plasma (LPP) source for the soft x-ray region which was developed by the applicant, highly efficient reflections zone plates with high energetic resolution, a large scale CCD camera and a transmission liquid cell for solutions. The design of the reflection zone plates as well as the development of the liquid cell is part of the proposed project.The spectrometer will be optimized for the components of CuChl (K absorption edges of C, O, N, and LIII edge of Cu), delivering NEXAFS spectra with high spectral resolution (E/DE~1000), high signal-to-noise ratio (SNR~100) in a few single pulses of the LPP source.The whole setup will thus enable the investigations of biological samples in solution in the laboratory, which up until now had to be performed at synchrotron radiation facilities. The NEXAFS spectrometer will operate in transmission mode, thus, facilitating on-line monitoring of degradation processes during measurements.In addition, to gain information about optically forbidden transitions X-ray optical double resonance (XODR) investigations will be performed by using an optical pump and probing the changes with the soft X-ray pulse. For this purpose a pump channel will be implemented in the setup.The novel spectrometer enables time-resolved measurements, as the optical element if suited for fs-spectroscopy. For the realization of fs-time scales the spectrometer can be used with other sources, for example HHG sources in cooperation with the Max-Born-Institute.