More information about the HRM can be found here.

Context

In additional to the fundamental wavelength, the The generation of x-ray by electron electrons passing through undulators also produces produces, in addition of the fundamental energy, higher order radiation (. Because of symmetry, only the odd orders in fact). For are allowed, so for example, for a fundamental at 5keV, photons at 15keV, 25keV, etc. are also generated.

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