Grazing-incidence antireflection films. IV. Application to Mössbauer filtering of synchrotron radiation

In principle, a very bright, monochromatic 1-Å signal with ħ Δω≊${10}^{\mathrm{-}8}$–${10}^{\mathrm{-}6}$ eV can be filtered from white synchrotron radiation by multiple reflection at grazing incidence from mirrors coated with grazing-incidence antireflection (GIAR) films in which either the films or substrate contain resonant Mössbauer nuclei. Typically, nonresonant reflectivities can be suppressed to ${10}^{\mathrm{-}4}$–${10}^{\mathrm{-}3}$ while maintaining resonant reflectivities of ≊70%, with half-widths strongly broadened by ‘‘enhancement’’ to ${\Gamma }_{\mathrm{eff}\mathrm{\approxeq }20\mathrm{\Gamma }}$. Effective filtering should be possible with two to four reflections, or alternatively, with one to two reflections plus time resolution.