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Physical optics, or wave optics, is the branch of optics that studies interference, diffraction, polarization, and other phenomena for which the ray approximation of geometric optics is not valid.

• ## 2: Reflection and Transmission at Boundaries and the Fresnel Equations

When a ray of light encounters an interface between two media of different refractive indices, some of it is reflected and some is transmitted. This chapter will concern itself with how much is reflected and how much is transmitted. (Unless the media are completely transparent, some of the light will also be absorbed - and presumably degraded as heat - but this chapter will concern itself only with what happens at the interface, and not in its passage through either medium.)
• ## 3: The Cornu Spiral

Cornu’s spiral is a graphical device that enables us to compute and predict the Fresnel diffraction pattern from various simple obstacles.