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Some energy resolution tests on BL I311

The performance of the monochromator at beamline I311 has been tested using X-ray absorption spectroscopy on gases. The examples shown below illustrate the excellent energy resolution of the monochromator. (The absolute energy scales have not been calibrated).

This spectrum shows a small region of the double excitation resonance in He where the 1s² ¹S - (sp, 2n ± ) ¹P^o transition can be followed up to at least n = 21+. The step length in this recording is 1 meV. In this energy range the resolving power of the monochromator is in excess of 15000.

The "standard" resolution test using the N₂ 1s - p * transition. Curve fitting using a Lorenzian life-time width of 119 meV yields a Gaussian monochromator contribution of 32 meV, i.e. a resolving power of 12500.

The same excitation in N₂ recorded in 2^nd order diffraction. The energy resolution in this case is 22 meV, corresponding to a resolving power of 18000.

An absorption spectrum from Ne at the 1s threshold. Assuming a life-time width of 250 meV a monochromator contribution of 132 meV is obtained, i.e. a resolving power of 6600.

Jesper Andersen and Ralf Nyholm, MAX-lab

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