Image Processing Reference
Figure 3.3 Interference fringes created from two diffraction-limited optical systems.
The structure of the Airy disk and first ring are clearly visible.
similar to the approach used in Young's historic double-slit experiment (Born and
Wolfe 1999); however, Young's experiment was performed well before the
invention of the laser.
The basic approach of any interferometer is to compare a wavefront to a refer-
ence wavefront such that constructive and destructive interference between the
wavefronts occurs, showing the phase difference between them as a change in in-
tensity. Wavefront sensors constructed from interferometers require that the refer-
ence beam be generated out of the aberrated wavefront entering the interferometer
in order to maintain the coherence of the light. In the next sections several different
interferometer configurations are outlined.
3.3.1 Mach-Zehnder interferometer
One of the most versatile interferometers is the Mach-Zehnder, which can generate
interference both in the focal and pupil planes. However, in its standard form, it is
not really a wavefront sensor as based on our earlier definition. The Mach-Zehnder
interferometer is included here because it is an excellent example of how an inter-
ferometer works and, in modified form, can be used as a wavefront sensor.
A Mach-Zehnder interferometer is characterized by having two separate, but
similar paths through the optics. The two beams exit the interferometer and overlap
generating an interferogram that shows any difference in phase between the two
beams as changes in intensity. Figure 3.4 shows a Mach-Zehnder interferometer con-
figured to produce an interferogram in a focal plane. The resulting interferogram
shows the general shape of an Airy Function with alternating dark and light lines
through it showing that there is a change in tilt between the two beams. Figure 3.5