Spherical lamellar grating

In the spherical lamellar grating the surface at zero path difference has not a plane but a concave shape. This interferometer operates with a noncollimated beam and is, therefore, limited to lower spectral resolution than the plane version otherwise the spherical configuration is the most simple form of a lamellar grating instrument. Only a source and a detector need to be added adjacent to the center of curvature to form a working far infrared interferometer. 

Hansen, N. P. Strong, J. (1971). Performance of a simple spherical lamellar grating beamsplitter by wavefront division. Aspen International Conference on Fourier Spectroscopy, ed. G. A. Vanasse, A. T. Stair, Jr., D. J. Baker, US Air Force Cambridge Research Laboratory 71-0019. 

Fig. 5.8.17 Lamellar grating interferometers. The upper panel (A) shows the plane version. The lower panel (B) illustrates the spherical configuration.

---