Interferometry

The electric field of plane wave propagates as and differences in the path traversed by two different beams will produce an interference pattern on recombination. The following two results are important for calculation of phase differences between two light beams.

Consider reflection of a ray of light as it approaches a denser material from a lighter material. We have, where is density and is the refractive index. Then where is the phase angle. (Figure 4.3)

Consider reflection of light as it approaches a lighter material from the denser side. We have,. Then , i.e. the reflected ray has the same phase as the incident ray. These results can be proved by considering reflection of a transverse wave at a fixed end and a free end respectively.

Figure 4.3: Phase Differences Owing to Reflection at Material Interfaces.

Figure 4.4: Wedge Fringes (right) created by an Air Gap of Varying Thickness (left)