  We analyze properties of electromagnetic radiation in helical undulators with
a particular emphasis on orbital angular momentum of the radiated photons. We
demonstrate that all harmonics higher than the first one radiated in a helical
undulator carry an angular momentum. We discuss some possible applications of
this phenomenon and the ways of effective generation of these photons in a
helical undulator. We call for review of results of experiments performed where
the higher harmonics radiated in a helical undulator might be involved.
