Bessel beam

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A Bessel beam is a beam of electromagnetic radiation whose intensity is described by a Bessel function. A true Bessel beam is non-diffractive. This means that as it propagates, it does not diffract and spread out; this is in contrast to the usual behavior of light, which spreads out after being focussed down to a small spot. A true Bessel beam cannot be created, because it would require an infinite amount of energy.^[1] Reasonably good approximations can be made, however, and these are important in many optical 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 the beam 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 to Laplace's equation and the Helmholtz equation in cylindrical coordinates.

Bessel beams are made in practice by focusing a Gaussian beam with an axicon lens.

[edit] References

1. ^ Kishan Dholakia; David McGloin, and Vene Garcés-Chávez (2002). Optical micromanipulating using a self-reconstructing light beam. Retrieved on 2007-02-06.
   See also V. Garcés-Chávez; D. McGloin, H. Melville, W. Sibbett and K. Dholakia (2002). "Simultaneous micromanipulation in multiple planes using a self-reconstructing light beam". Nature 419. Retrieved on 2007-02-06.