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Novel Sources for Synchrotron Light

100%

Weckert E.

Acta Physica Polonica A

2002

vol. 101

issue 5

565-581

During the past decades synchrotron radiation has become an amazingly versatile tool for a very large range of applications ranging from basic physics, materials science, condensed matter physics, chemistry to life sciences, just to mention a few. The properties most widely exploited are high brilliance or flux, tunability, polarisation, and temporal resolution. More recently with the advent of third generation synchrotron sources providing very small source sizes partially coherent radiation even in the X-ray regime is available which enables a large number of new experiments. However, as far as it concerns pulse length and coherence traditional storage ring based sources encounter limits that cannot easily be surpassed. Having also these applications in mind new concepts have been developed. Mainly in the US plans are worked out for linac driven storage rings. In these devices electrons circulate only once in a storage ring after they have been accelerated by a high current/power linac. The emittance of such a source would be considerably smaller than that of a normal storage ring of the same size. A totally coherent beam down in wavelengths to theÅ-regime will be delivered by so-called X-ray free electron lasers proposed in the US (Stanford), in Germany (DESY, Hamburg), and in Japan (Spring8/KEK). In these systems the beam of a linac is directly fed through very long undulators where X-rays are generated according to the so-called self-amplified spontaneous emission process. The radiation after such a device will be fully coherent in the transverse direction and the pulse length will be in the 0.1 ps regime. These are properties unseen so far. The peak (average) brilliance of such an X-ray free electron laser will be about ten (five) orders of magnitude higher compared to the most advanced present day synchrotron radiation sources.

Experimental Determination of Reflection Phases by Three-Beam Diffraction and its Applications

51%

Hümmer K., Schwegle W., Weckert E.

Acta Physica Polonica A

1992

vol. 82

issue 1

83-102

Information on phase relationships between Bragg reflections can be obtained by the interference of Bragg waves. In the three-beam case, phase difference is given by a structure invariant triplet phase relationship. The intensity variation due to the three-beam interaction can be best measured by a ψ-scan experiment. The resulting ψ-scan diffraction profiles scanning through a three-beam position uniquely depend on the triplet phase relationship involved. In principle each three-beam profile is given by a superposition of a symmetrical phase-independent and a phase-dependent profile. Thus, triplet phases can be determined experimentally with an accuracy of about 45 degrees. The ψ-scan method is discussed and some examples of applications to the determination of the absolute structure as well as to the structure determination by combination of measured triplet phases with direct methods are given.

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2 Acta Physica Polonica A

1 2002

1 1992

2 Weckert E.

1 Hümmer K.

1 Schwegle W.

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Novel Sources for Synchrotron Light

Experimental Determination of Reflection Phases by Three-Beam Diffraction and its Applications