An evanescent wave is an electromagnetic wave that decays exponentially with distance. Evanescent waves are observed in total internal reflection. Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... A wave crashing against the shore A wave is a disturbance that propagates. ... A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ...

The effect has been used to exert radiation pressure on small particles in order to trap them for experimentation, or to cool them to very low temperatures, and to illuminate very small objects such as biological cells for microscopy (as in the total internal reflection fluorescence microscope). The evanescent wave from an optical fiber can be used in a gas sensor. Electromagnetic radiation exerts a pressure upon any surface exposed to it. ... Refrigeration (from the Latin frigus, frost) is generally the cooling of a body by the transfer of a portion of its heat away from it. ... Cells in culture, stained for keratin The cell is the structural and functional unit of all living organisms. ... 1852 microscope Compound microscope made by John Cuff in 1750 A microscope (Greek: micron = small and scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. ... Principle of the TIRFM A total internal reflection fluorescence microscope (TIRFM) is a type of microscope with which a thin region of a specimen, usually less than 200 nm, can be observed. ...

In optics, evanescent waves are formed when sinusoidal waves are (internally) reflected off an interface at an angle greater than the critical angle so that total internal reflection occurs. The physical explanation for their existance is that the electric and magnetic fields cannot be discontinuous at a boundary, as would be the case if there were no evanescent field. See also list of optical topics. ... In trigonometry, an ideal sine wave is a waveform whose graph is identical to the generalized sine function y = Asin[ω(x − α)] + C, where A is the amplitude, ω is the angular frequency (2π/P where P is the wavelength), α is the phase shift, and C is the... In geometric optics, at a refractive boundary, the critical angle is the smallest angle of incidence at which total internal reflection occurs. ... The larger the angle to the normal, the smaller is the fraction of light transmitted, until the angle when total internal reflection occurs. ...

"Evanescent" means "tending to vanish", which is appropriate because the intensity of evanescent waves decays exponentially (rather than sinusoidally) with the distance from the interface at which they are formed. A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. ...

Mathematically, evanescent waves are characterized by having an imaginary value of the wavenumber, k. In mathematics, an imaginary number (or purely imaginary number) is a complex number whose square is a negative real number or zero. ... Wavenumber in most physical sciences is a wave property inversely related to wavelength, having units of inverse length. ...

See also

• quantum tunneling

Quantum tunneling Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...

External link

• Evanescent waves