A portable, rugged, inexpensive shearing interferometer is described and evaluated. Originally intended for application to plasma and flow analysis, it is also a suitable instructional aid. The shearing is obtained by the offset of the reflection from the first surface of a mirror relative to the reflection from the second surface when the mirror is set at an angle to the illuminating beam. The sensitivity is equivalent to that of a schlieren system. However, no schlieren quality components are involved and there are no critical adjustments or dimensions.
J. G. Kelley and R. A. Hargreaves, "A Rugged Inexpensive Shearing Interferometer," Appl. Opt. 9, 948-952 (1970)