- Bessel beam
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**Bessel beam**is a field ofelectromagnetic radiation whose amplitude is described by aBessel function . A true Bessel beam is non-diffractive. This means that as it propagates, it does notdiffract and spread out; this is in contrast to the usual behavior of light, which spreads out after being focussed down to a small spot.As with a

plane wave a true Bessel beam cannot be created, as it is unbounded and therefore requires an infinite amount ofenergy . [*cite web|url=http://www.st-andrews.ac.uk/~atomtrap/Research/reconstruct.htm| author=Kishan Dholakia| coauthors= David McGloin, and Vene Garcés-Chávez| title=Optical micromanipulating using a self-reconstructing light beam| year=2002| accessdate=2007-02-06*] Reasonably good approximations can be made, however, and these are important in many

See also cite journal|author=V. Garcés-Chávez| coauthors= D. McGloin, H. Melville, W. Sibbett and K. Dholakia| title=Simultaneous micromanipulation in multiple planes using a self-reconstructing light beam| journal=Nature| volume= 419| year=2002| url=http://sinclair.ece.uci.edu/Papers/Optics/Orbital%20angular%20momentum/Garces-Chavez%20Nature%20419%20pp145-148%202002%20(Simultaneous%20micromanipulation%20in%20multiple%20planes%20using%20a%20self-reconstructing%20light%20beam).pdf| accessdate=2007-02-06| doi=10.1038/nature01007| pages=145optical applications because they exhibit little or no diffraction over a limited distance. Bessel beams are also "self-healing", meaning that the beam can be partially obstructed at one point, but will re-form at a point further down thebeam axis .These properties together make Bessel beams extremely useful to research in optical tweezing, as a narrow Bessel beam will maintain its required property of tight focus over a relatively long section of beam and even when partially occluded by the dielectric particles being tweezed.

The mathematical function which describes a Bessel beam is a solution of

Bessel's differential equation , which itself arises from separable solutions toLaplace's equation and theHelmholtz equation in cylindrical coordinates.Approximations to Bessel beams are made in practice by focusing a

Gaussian beam with anaxicon lens to generate a Bessel-Gauss beam.**References**

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