Concept of a new undulator that will suppress the rational harmonics

A basic consideration has been made of an undulator with magnetic poles quasi-periodically aligned in order not to generate higher harmonics of radiation with integrally factored energies, nEf (n: integers, Ef: the fundamental photon energy), that are harmful in some synchrotron radiation experiments. The new undulator generates harmonics with irrational ratios in energy which are never simultaneously diffracted by a crystal or grating monochromator at the same Bragg angle. A combination of the undulator with a high-resolution crystal monochromator is expected to be very useful on beamlines of high energy radiation in which X-ray mirrors would not be suitable because their critical angle of total reflection would be too small. Realistic arrays of magnetic poles are also discussed.