A Michelson interferometer for X-rays capable of high-order measurement

J. Appl. Cryst. (2003). 36, 269–279

Top: Scan of 18 single orders. Middle: Measured Fourier spectrum over a total of 1704 orders of the copper Kα₁–Kα₂ doublet. 4 beat nodes are recognizable. Bottom: Calculated Fourier spectrum of the same order range.

The first Michelson interferometer for hard X-rays [A. Appel and U. Bonse (1991). Phys. Rev. Lett. 64, 1673–1676] featured geometric path-length differences of interfering beams of about 120 nm corresponding to 750 orders at wavelength λ ≈ 0.15 nm. Using the same design principle, i.e. mixing of Laue- and Bragg-case beams diffracted by only one set of Bragg planes of two separate structures of perfect silicon crystals, the scan range could be extended by a factor of 3.6 by modifying the beam-path geometry. 2700 interference orders of the copper Kα₁–Kα₂ doublet, corresponding to six beat nodes of the doublet, were recorded in Fourier spectrometric mode as shown in the diagram. Based on the know-how gained in this study, an extension to 40000 orders, equivalent to a spectroscopic resolution λ/Δλ ≈ 20000, appears feasible.