Beam divergence


Beam divergence

The beam divergence of an electromagnetic beam is an angular measure of the increase in beam diameter with distance from the optical aperture or antenna aperture from which the electromagnetic beam emerges. The term is relevant only in the "far field", away from any focus of the beam. Practically speaking, however, the far field can commence physically close to the radiating aperture, depending on aperture diameter and the operating wavelength.

Beam divergence is often used to characterize electromagnetic beams in the optical regime, for cases in which the aperture from which the beam emerges is very large with respect to the wavelength. That said, it is also used in the Radio Frequency (RF) regime for cases in which the antenna is operating in the so-called optical region and is likewise very large relative to a wavelength.

Beam divergence usually refers to a beam of circular cross section, but not necessarily so. A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, for example with respect to the major or minor axis of the elliptical cross section.

The divergence of a beam can be calculated if one knows the beam diameter at two separate points ("Di", "Df"), and the distance ("l") between these points. The beam divergence is given by :Divergence=2 arctanleft(frac{D_f-D_i}{2 l} ight).

If the beam has been collimated using a lens or other focusing element, the divergence expected can be calculated from two parameters: the diameter, D_m, of the narrowest point on the beam before the lens, and the focal length of the lens, f. The divergence is then given by :Divergence=frac{D_m}{f}.,

Like all electromagnetic beams, lasers are subject to divergence, which is measured in milliradians (mrad) or degrees. For many applications, a lower-divergence beam is preferable. Neglecting divergence due to poor beam quality, the divergence of a laser beam is proportional to its wavelength and inversely proportional to the diameter of the beam at its narrowest point. For example, an ultraviolet laser that emits at a wavelength of 308 nm will have a lower divergence than an infrared laser at 808 nm, if both have the same minimum beam diameter. The divergence of good-quality laser beams is modeled using the mathematics of Gaussian beams.

ee also

*Laser beam profiler

External links

* [http://www.pseudonomen.com/lasers/calculators Laser divergence calculator]
* [http://www.columbia.edu/cu/mechanical/mrl/ntm/level1/ch02/html/l1c02s02.html Interactive beam divergence graph]
* [http://www.uslasercorp.com/envoy/diverge.html Measuring laser beam divergence]


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • beam divergence — pluošto skėstis statusas T sritis radioelektronika atitikmenys: angl. beam divergence vok. Bündeldivergenz, f rus. расходимость пучка, f pranc. divergence du faisceau, f ryšiai: palygink – spindulių skėstis …   Radioelektronikos terminų žodynas

  • beam divergence angle — pluošto skėsties kampas statusas T sritis radioelektronika atitikmenys: angl. beam divergence angle vok. Bündeldivergenzwinkel, m rus. угол расходимости пучка, m pranc. angle de divergence du faisceau, m …   Radioelektronikos terminų žodynas

  • laser beam divergence — lazerio pluošto skėstis statusas T sritis radioelektronika atitikmenys: angl. laser beam divergence; laser ray divergence vok. Laserstrahldivergenz, f rus. расходимость лазерного луча, f; расходимость лазерного пучка, f pranc. divergence du… …   Radioelektronikos terminų žodynas

  • Divergence (disambiguation) — Divergence can refer to: In mathematics: Divergence, a function that associates a scalar with every point of a vector field Divergence (computer science), a computation which does not terminate (or terminates in an exceptional state) Divergence… …   Wikipedia

  • Beam diameter — The beam diameter or beam width of an electromagnetic beam is the diameter along any specified line that is perpendicular to the beam axis and intersects it. Since beams typically do not have sharp edges, the diameter can be obtained in many… …   Wikipedia

  • divergence du faisceau de laser — lazerio pluošto skėstis statusas T sritis radioelektronika atitikmenys: angl. laser beam divergence; laser ray divergence vok. Laserstrahldivergenz, f rus. расходимость лазерного луча, f; расходимость лазерного пучка, f pranc. divergence du… …   Radioelektronikos terminų žodynas

  • divergence du faisceau — pluošto skėstis statusas T sritis radioelektronika atitikmenys: angl. beam divergence vok. Bündeldivergenz, f rus. расходимость пучка, f pranc. divergence du faisceau, f ryšiai: palygink – spindulių skėstis …   Radioelektronikos terminų žodynas

  • Beam parameter product — In laser science, the beam parameter product (BPP) is the product of a laser beam s divergence angle (half angle) and the radius of the beam at its narrowest point (the beam waist).cite web|url=http://www.rp photonics.com/beam parameter… …   Wikipedia

  • Laser beam profiler — A laser beam profiler captures, displays, and records the spatial intensity profile of a laser beam at a particular plane transverse to the beam propagation path. Since there are many types of lasers ultraviolet, visible, infrared, continuous… …   Wikipedia

  • Gaussian beam — In optics, a Gaussian beam is a beam of electromagnetic radiation whose transverse electric field and intensity (irradiance) distributions are well approximated by Gaussian functions. Many lasers emit beams that approximate a Gaussian profile, in …   Wikipedia