Editing Electromagnetic radiation (section)

=== Wave model ===

[[File:Circular.Polarization.Circularly.Polarized.Light Right.Handed.Animation.305x190.255Colors.gif|thumb|right|Representation of the electric field vector of a wave of circularly polarized electromagnetic radiation]] In homogeneous, isotropic media, electromagnetic radiation is a [[transverse wave]],<ref>{{cite book |title=Electromagnetic Theory |first=Julius Adams|last=Stratton|publisher=McGraw-Hill Book Company, New York, NY |year=1941 |chapter-url=https://books.google.com/books?id=zFeWdS2luE4C&q=%22electromagnetic+theory%22+stratton |chapter=Chapter V Plane waves in unbounded, isotropic media|isbn=978-0-470-13153-4}}</ref> meaning that its oscillations are perpendicular to the direction of energy transfer and travel. It comes from the [[Electromagnetic wave equation|following equations]]:<math display="block">\begin{align}
\nabla \cdot \mathbf{E}  &= 0\\
\nabla \cdot \mathbf{B}  &= 0
\end{align}</math>These equations predicate that any electromagnetic wave must be a transverse wave, where the electric field {{math|'''E'''}} and the magnetic field {{math|'''B'''}} are both perpendicular to the direction of wave propagation. The electric and magnetic parts of the field in an electromagnetic wave stand in a fixed ratio of strengths to satisfy the two [[Maxwell's equations]] that specify how one is produced from the other. In dissipation-less (lossless) media, these {{math|E}} and {{math|B}} fields are also in phase, with both reaching maxima and minima at the same points in space.

In the [[Near and far field|far-field]] EM radiation which is described by the two source-free Maxwell [[curl operator]] equations, a time-change in one type of field is proportional to the curl of the other. These derivatives require that the {{math|E}} and {{math|B}} fields in EMR are in phase.{{anchor|frequency}} An important aspect of light's nature is its [[frequency]]. The frequency of a wave is its rate of oscillation and is measured in [[hertz]], the [[SI]] unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as [[Dispersion relation|dispersion]].

A monochromatic wave (a wave of a single frequency) consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the [[wavelength]]. Waves of the electromagnetic spectrum vary in size, from very long radio waves longer than a continent to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength, according to the equation:<ref>{{Cite web|url=https://astronomy.swin.edu.au/cosmos/E/Electromagnetic+Radiation|title=Electromagnetic Radiation {{!}} COSMOS|website=astronomy.swin.edu.au|access-date=29 March 2020|archive-date=19 March 2020|archive-url=https://web.archive.org/web/20200319090846/https://www.astronomy.swin.edu.au/cosmos/E/Electromagnetic+Radiation|url-status=live}}</ref>
: <math>\displaystyle v=f\lambda</math>
where ''v'' is the speed of the wave ([[speed of light|''c'']] in a vacuum or less in other media), ''f'' is the frequency, and ''λ'' is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant.

Electromagnetic waves in free space must be solutions of Maxwell's [[electromagnetic wave equation]]. Two main classes of solutions are known, namely plane waves and spherical waves. The plane waves may be viewed as the limiting case of spherical waves at a very large (ideally infinite) distance from the source. Both types of waves can have a waveform which is an arbitrary time function (so long as it is sufficiently differentiable to conform to the wave equation). As with any time function, this can be decomposed by means of [[Fourier analysis]] into its [[frequency spectrum]], or individual sinusoidal components, each of which contains a single frequency, amplitude, and phase. Such a component wave is said to be ''monochromatic''.

Interference is the superposition of two or more waves resulting in a new wave pattern. If the fields have components in the same direction, they constructively interfere, while opposite directions cause destructive interference. Additionally, multiple polarization signals can be combined (i.e. interfered) to form new states of polarization, which is known as parallel polarization state generation.<ref>{{cite journal |last1=She |first1=Alan |last2=Capasso |first2=Federico |date=17 May 2016 |title=Parallel Polarization State Generation |journal=Scientific Reports |volume=6 |pages=26019 |arxiv=1602.04463 |bibcode=2016NatSR...626019S |doi=10.1038/srep26019 |pmc=4869035 |pmid=27184813}}</ref>