A grating interferometer for high-resolution displacement measurements is presented. To decrease interferometer sensitivity to inaccuracy of the grating guide, application of divergent light beam is proposed. The effect of the interferometer geometry on the direction and constant of fringes is analyzed. Comparison is drawn between results of applying plane and spherical wavefronts. The advantages of spherical wavefront application are theoretically evaluated and experimentally proved. An acceptable value of the angular instability of the grating illuminated by spherical wavefront is equal to about ±3 arcmin.
"Application of a divergent laser beam in a grating interferometer for high-resolution displacement measurements," Optical Engineering 33(3), (1 March 1994). http://dx.doi.org/10.1117/12.160893