Inphysics,physical optics, orwave optics, is the branch ofoptics that studiesinterference,diffraction,polarization, and other phenomena for which the ray approximation ofgeometric optics is not valid. This usage tends not to include effects such asquantum noise inoptical communication, which is studied in the sub-branch ofcoherence theory.
Physical optics is also the name of anapproximation commonly used in optics,electrical engineering andapplied physics. In this context, it is an intermediate method betweengeometric optics, which ignoreswave effects, and full waveelectromagnetism, which is a precisetheory. The word "physical" means that it is more physical thangeometric orray optics and not that it is an exact physical theory.[1]: 11–13
This approximation consists of using ray optics to estimate the field on a surface and thenintegrating that field over the surface to calculate the transmitted or scattered field. This resembles theBorn approximation, in that the details of the problem are treated as aperturbation.
In optics, it is a standard way of estimating diffraction effects. Inradio, this approximation is used to estimate some effects that resemble optical effects. It models several interference, diffraction and polarization effects but not the dependence of diffraction on polarization. Since this is a high-frequency approximation, it is often more accurate in optics than for radio.
In optics, it typically consists of integrating ray-estimated field over a lens, mirror or aperture to calculate the transmitted or scattered field.
Inradarscattering it usually means taking thecurrent that would be found on atangentplane of similar material as the current at each point on the front, i. e. the geometrically illuminated part, of ascatterer. Current on the shadowed parts is taken as zero. The approximate scattered field is then obtained by an integral over these approximate currents. This is useful for bodies with large smoothconvex shapes and for lossy (low-reflection) surfaces.
The ray-optics field or current is generally not accurate near edges or shadow boundaries, unless supplemented by diffraction andcreeping wave calculations.
The standard theory of physical optics has some defects in the evaluation of scattered fields, leading to decreased accuracy away from the specular direction.[2][3] An improved theory introduced in 2004 gives exact solutions to problems involving wave diffraction by conducting scatterers.[2]
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