Nanoscale imaging of femtosecond magnetization dynamics by scattering of coherent soft x-ray laser harmonics – FEMTO-X-MAG

Magnetization phenomena occurring on nanometer length scale and sub-nanosecond time scale are one of the forefront research areas in solid state physics. Scientifically, these phenomena are challenging due to the often complex interplay of interactions spanning a wide range of strength and length scale. In addition, these activities are strongly motivated by the technological desire for ever smaller and ever faster magnetic devices. In the context of magnetism scientific discoveries and technological progress has always been influenced by the ability so see magnetic domain structures with higher spatial resolution and to follow its temporal evolution on shorter time scales. A recent demonstration of this has been when picosecond time resolution was successfully added to x-ray microscopy. Pushing the time resolution for imaging of magnetization dynamics from the picosecond to the femtosecond time scale while preserving sub 100 nm spatial resolution is a fascinating challenge. Although free-electron lasers (FEL) are currently the most intense femtosecond x-ray sources, they do not represent the most attractive source for the femtosecond pump-probe experiment because of their intrinsic limitation of 100 ' 200 femtosecond precision in synchronizing a femtosecond laser pump with x-ray probe (FEL). We propose to use laser based higher harmonic generation as ultrashort coherent soft x-ray source thanks to their inherent femtosecond synchronization with infrared laser pump beam (both sources starting from the same laser). The project will be in three parts: 1) preparation and tests of the magnetic samples on synchrotron facility, 2) pump-probe experiment on a high average flux soft x-ray source for multiple shot imaging, 3) pump-probe experiment on a high instantaneous flux x-ray source for single shot imaging. Comparison of data acquired on multiple and single shot imaging is mandatory to sort out if the phenomena are erratic or reproducible.