Beam expanders are

optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultravio ...

devices that take a

collimated beam A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...

of light and expand its size (or, used in reverse, reduce its size). In

laser physics Laser science or laser physics is a branch of optics that describes the theory and practice of lasers. Laser science is principally concerned with quantum electronics, laser construction, optical cavity design, the physics of producing a popula ...

they are used either as intracavity or extracavity elements. They can be telescopic in nature or prismatic. Generally prismatic beam expanders use several prisms and are known as multiple-prism beam expanders. Telescopic beam expanders include refracting and reflective telescopes. A refracting telescope commonly used is the

Galilean telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and a ...

which can function as a simple beam expander for

collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...

light. The main advantage of the Galilean design is that it never focuses a collimated beam to a point, so effects associated with high power density such as

dielectric breakdown Electrical breakdown or dielectric breakdown is a process that occurs when an electrical insulating material, subjected to a high enough voltage, suddenly becomes an electrical conductor and electric current flows through it. All insulating mate ...

are more avoidable than with focusing designs such as the

Keplerian telescope A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and as ...

. When used as intracavity beam expanders, in laser resonators, these telescopes provide two-dimensional beam expansion in the 20–50 range. In

tunable laser A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength ran ...

resonators intracavity beam expansion usually illuminates the whole width of a

diffraction grating In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structur ...

. Thus beam expansion reduces the beam divergence and enables the emission of very narrow linewidths which is a desired feature for many analytical applications including laser spectroscopy.

Multiple-prism beam expanders

Multiple-prism beam expanders usually deploy two to five prisms to yield large one-dimensional beam expansion factors. Designs applicable to tunable lasers with beam expansion factors of up to 200 have been disclosed in the literature. Initially multiple-prism grating configurations were introduced in narrow-linewidth liquid dye lasers but eventually were also adopted in gas, solid-state, and diode laser designs. The generalized mathematical description of multiple-prism beam expanders, introduced by Duarte, is known as the

multiple-prism dispersion theory The first description of multiple-prism arrays, and multiple-prism dispersion, was given by Newton in his book ''Opticks''. Prism pair expanders were introduced by Brewster in 1813. A modern mathematical description of the single-prism dispersio ...

. Multiple-prism beam expanders and arrays can also be described using ray transfer matrices. The multiple-prism dispersion theory is also available in 4 × 4 matrix form. These matrix equations are applicable either to prism pulse compressors or multiple-prism beam expanders.

Extra-cavity beam shaping

Extra cavity hybrid beam transformers: using a telescopic beam expander, followed by a convex lens, followed by a multiple-prism beam expander, a laser beam (with a circular cross section) can be transformed into an extremely elongated beam, in the plane of propagation, while extremely thin in the orthogonal plane. The resulting plane illumination, with a near one-dimensional (or line) cross section, eliminates the need of point-by-point scanning and has become important for applications such as N-slit interferometry,

microdensitometry A microdensitometer is an optical instrument used to measure optical densities in the microscopic domain. J. C. Dainty and R. Shaw, ''Image Science'' (Academic, New york, 1974).T. H. James, ''The Theory of the Photographic Process'' (Eastman Kodak ...

, and microscopy. This type of illumination can also be known in the literature as light sheet illumination or selective plane illumination.

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Schematics of practical multiple-prism arrangements.
{{Lasers Optical devices Laser science

Multiple-prism beam expanders

Extra-cavity beam shaping

See also

References

External links