View source for Physical optics

{{Short description|Branch of optics}}
[[File:Laser Interference.JPG|thumb|200px|Physical optics is used to explain effects such as [[diffraction]]]]
In [[physics]], '''physical optics''', or '''wave optics''', is the branch of [[optics]] that studies [[Interference (wave propagation)|interference]], [[diffraction]], [[Polarization (waves)|polarization]], and other phenomena for which the ray approximation of [[geometric optics]] is not valid. This usage tends not to include effects such as [[quantum noise]] in [[optical communication]], which is studied in the sub-branch of [[coherence theory (optics)|coherence theory]].

== Principle ==
''Physical optics'' is also the name of an [[approximation]] commonly used in optics, [[electrical engineering]] and [[applied physics]]. In this context, it is an intermediate method between [[geometric optics]], which ignores [[wave]] effects, and full wave [[electromagnetism]], which is a precise [[theory]]. The word "physical" means that it is more physical than [[geometric]] or [[ray (optics)|ray]] optics and not that it is an exact physical theory.<ref name="Ufimtsev2007">{{cite book|author=Pyotr Ya. Ufimtsev|title=Fundamentals of the Physical Theory of Diffraction|date=9 February 2007|publisher=John Wiley & Sons|isbn=978-0-470-10900-7}}</ref>{{rp|11–13}}

This approximation consists of using ray optics to estimate the field on a surface and then [[integral|integrating]] that field over the surface to calculate the transmitted or scattered field. This resembles the [[Born approximation]], in that the details of the problem are treated as a [[perturbation theory|perturbation]].

In optics, it is a standard way of estimating diffraction effects. In [[radio]], 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.

In [[radar]] [[scattering]] it usually means taking the [[current (electricity)|current]] that would be found on a [[tangent]] [[Plane (mathematics)|plane]] of similar material as the current at each point on the front, i. e. the geometrically illuminated part, of a [[scattering|scatterer]]. 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 smooth [[wikt:convex|convex]] 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 and [[creeping 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.<ref name=Umul>{{cite journal |title=Modified theory of physical optics |first=Y. Z. |last=Umul |journal=Optics Express |date=October 2004 |volume=12 |issue=20 |pages=4959–4972 |doi=10.1364/OPEX.12.004959 |pmid=19484050|bibcode = 2004OExpr..12.4959U |doi-access=free }}</ref><ref>{{cite journal |last1=Shijo |first1=T. |last2=Rodriguez |first2=L. |last3=Ando |first3=M. |title=The modified surface-normal vectors in the physical optics |journal=IEEE Transactions on Antennas and Propagation |volume=56 |issue=12 |pages=3714–3722 |date=Dec 2008 |doi=10.1109/TAP.2008.2007276|bibcode = 2008ITAP...56.3714S |s2cid=41440656 }}</ref> An improved theory introduced in 2004 gives exact solutions to problems involving wave diffraction by conducting scatterers.<ref name=Umul/>

==See also==
*[[Optical physics]]
*[[Electromagnetic modeling]]
*[[Fourier optics]]
*[[History of optics]]
*[[Negative-index metamaterials]]

== References ==
*{{cite book | author1=Serway, Raymond A. | author2=Jewett, John W. | title=Physics for Scientists and Engineers (6th ed.) | publisher=Brooks/Cole | year=2004 | isbn=0-534-40842-7 | url-access=registration | url=https://archive.org/details/physicssciengv2p00serw }}
*{{cite book |author1=Akhmanov, A |author2=Nikitin, S. Yu | title=Physical Optics |publisher= Oxford University Press |year=1997| isbn=0-19-851795-5}}
*{{cite journal |title=A double-edge-diffraction Gaussian-series method for efficient physical optics analysis of dual-shaped-reflector antennas |journal=IEEE Transactions on Antennas and Propagation |date=August 2005 |page=2597 |doi=10.1109/tap.2005.851855 |volume=53 | last1 = Hay | first1 = S.G.|issue=8 |bibcode=2005ITAP...53.2597H |s2cid=10050665 }}
*{{cite journal |title=The physical optics method in electromagnetic scattering |first=J. S. |last=Asvestas |journal=Journal of Mathematical Physics |date=February 1980 |volume=21 |issue=2 |pages=290–299 |doi=10.1063/1.524413|bibcode = 1980JMP....21..290A }}
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==External links==
*{{Commons category-inline|Physical optics}}

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[[Category:Physical optics| ]]
[[Category:Optics]]
[[Category:Electrical engineering]]
[[Category:Christiaan Huygens]]