Argonne National Laboratory

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Time-Delayed Beam Splitting with Energy Separation of X-ray Channels

XSD/IXN Special Presentation
Yuriy Stetsko
August 22, 2013 2:00PM to 3:00PM
Building 401, Room B3100
Time change: 2 p.m.
Location change: Building 401, Rm. B3100 A/B.

Efficiency is a key point of any x-ray optics. Especially, it’s important in the x-ray split-delay optics for the x-ray photon correlation spectroscopy where the complex nanoscale dynamics in condensed matter with low intense scattering properties is studied. Traditional x-ray split-delay optics deals with an equal intensity separation of the x-ray free electron laser or synchrotron radiation beam/pulse of some specific energy between the reference and delayed beams/pulses. This equal intensity separation demands use of a single crystal splitter and mixer of an ultra small thickness, of about 10 micrometers.

Alternatively, we introduce a time-delayed beam splitting method based on the energy separation of x-ray beams. The realization of the reference and delayed beam channels with different individual energies considerably increases efficiency of x-ray split-delay optics, for about four times. It also allows to deal with much thicker, about several tens – one hundred micrometers, splitter and mixer crystals, making easier the crystal manufacturing.

This method is implemented and theoretically substantiated on an example of an x-ray optical scheme similar to that of the classical Michelson interferometer. The splitter uses Bragg-case diffraction from a diamond crystal. Another two diamond crystals are used as back-reflectors. After back reflection of the beams, the splitter works as a mixer. For energy separation of the beams the back-reflectors are set at slightly different temperatures. The small angular deviations from the exact backscattering, for about 10 microradians, provide a high simultaneous beam reflection and transmission on the splitter and mixer for each of beam channels. Due to a minimal number (three) of the optical elements, the split-delay line is simple to operate.

Specifically, the time delay in this scheme is realized by translation of only one back reflecting crystal. It makes the scheme unique in terms of the intensity, angular and spatial stability of the delayed beam channel in contrast to the existing x-ray split-delay schemes, where the synchronization of the translations of two crystals is a key technical issue. In addition, due to the high transparency of diamond crystals, the split-delay line can be used in a beam sharing mode at x-ray free-electron laser facilities.