
186 OPTICS FOR ENGINEERS
and the contribution of the cell to the geometric-optics distance is
geom
=
c
n
. (7.16)
With light arriving via both paths, we expect interference to occur according to
Equations 7.1 and 7.3. Our next problem then is to determine how changes, , in OPL, vary
with x and y for a given . These changes will result in a fringe pattern, the details of which
will be related to , and thus to the index of refraction.
7.1.3 Viewing an Extended Source
7.1.3.1 Fringe Numbers and Locations
From the viewer’s point of view, the distance to a point in an extended source is
r =
x
2
+y
2
+z
2
. (7.17)
A small change, in z results in a change, to ...