Image Processing Reference
Figure 3.8 Shearing interferometer created from a glass plate. Light from the front
and back sides of the plate is displaced, creating interference at the point of over-
The popularity of interferometers arises from the fact that they provide some of the
least ambiguous displays of phase information in the form of intensity change.
A Ronchi grating is a uniform, low-linear-density series of lines that either block or
pass light in a manner similar to the effect of looking through the teeth of a comb.
When collimated light passes though the Ronchi grating, the light is diffracted from
the edges of the lines. The diffracted light from the grating can be focused and
recollimated onto a screen. The pattern on the screen is the central diffraction order,
with a first order on either side of the central beam. The overlap regions between
the central beam and diffracted orders make a laterally sheared beam that shows in-
terference fringes. This is shown in Fig. 3.9.
Ronchi gratings can also be used with a converging beam to produce the dif-
fracted orders. The Ronchi grating is an example of an indirect wavefront sensor.