X-Ray Laser Research – The University of Wisconsin- Milwaukee

The world’s first X-ray free electron laser (XFEL) goes to the USA, however there is due to come online a European XFEL in Hamburg in 2017, which will be superior in many ways to the one in the US (Stanford) as it will have a much higher repetition rate allowing many more diffraction patterns to be measured per experimental shift. This will allow novel applications that are not possible at the Stanford XFEL. It is perhaps fitting that the European XFEL is sited in Germany as a reflection of the seriousness with which Germans take their scientific research, as the accompanying article makes clear.

Unfortunately, most of time-resolved crystallography to date happens in crystals. A molecule is crystallized and the time resolved changes in the structure at very fast time scales can be studied by a time-resolved experiment using the difference Fourier method 2 which requires an identification of corresponding Bragg spots in an excited state and ground state crystal. The problem is that since all these reactions take place in crystals, steric hindrance may make the reactions of the molecules different from what takes place in real life where the molecules are swimming more or less freely in liquid water. Fortunately a method has been developed recently 3 that enables the visualization of chemical reactions of individual molecules even if they are not all aligned in the form of crystals.

Aiding this development has been the development of a brand new form of X-rays produced by a brand new instrument called an X-ray free electron laser (XFEL). Being a form of laser, it produces X-rays with very different properties than ordinary X-rays, just as laser light is fundamentally different in quality than everyday light. Indeed, an XFEL produces light that is so coherent that the brightness of X-rays from an XFEL is many orders of magnitude greater than X-rays from any previous source.


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