Beam expanders use lenses to increase the size of laser or light beams without affecting their color or focus. They are used in various scientific applications, from microscopes to astronomical measurements, and can handle light from ultraviolet to infrared regions. Beam expanders are essentially telescopes, with Galilean designs preferred to prevent distortion from laser heat. Extra-cavity hybrid optical designs produce prismatic beams used in interferometry procedures and physics experiments.
A laser or light beam expander is a scientific instrument that allows parallel laser or light beams to expand an input beam to become a larger output beam. The instrument is used in a similar way to using a telescope and produces straight-line telescopic beams or prismatic beams, such as the beams you can see when light is reflected off the facets of a crystal. Beam expanders are used in laser physics and nearly a dozen scientific applications that use their output beams for measurements, such as laser micromachining, solar cell cutting, remote sensing, and other scientific experiments in various fields. Their beam magnification, without affecting the chromatic and deliberately avoiding focusing, allows applications from the smallest, such as in microscopes, to the largest astronomical measurements. Developed from established telescope optics, they have high transmission and low distortion.
The features available in most beam expanders are for standard inlet apertures and can preserve precise columns of light regardless of wavelength. Expanders can handle light from the ultraviolet spectrum through all visible regions and into the infrared regions and can reduce the amount of length needed in a telescope. They are designed for both variable and fixed output configurations with column trim controls.
For some background, optical telescopes are refractory or reflective. Refractor telescopes refract light using lenses that bend or refract light, while reflector telescopes use large optical mirrors to reflect light. A beam expander is essentially a telescope with the principle that the beam divergence and beam spread ratios are by the same factor. The lower power beam expanders are built on the Galileo telescope design with a negative input, positive output lens set. There are models of Kepler telescopes available, however, that have an intermediate, pinhole, focusing lens and two positive lenses that are very long, telescopic, beam-expanding.
Designs for laser beam expanders produce imaging lens and objective lens placements that are the opposite of their placement inside a Kepler telescope. The incoming columnar beam is focused to a point between the lenses where heat from the laser builds up and heats the air leading to wavefront distortion, therefore, the Galilean design is often preferred to prevent distortion. Since a laser beam expander will enlarge the laser input by a set expansion power, it will reduce the output beam divergence by the same power, and at great distances, the columnar beam will be smaller.
So-called extra-cavity hybrid optical designs in beam expanders follow the standard beam expander with a convex lens, shaped like the curvature of a human eye, which produces a multiple prismatic effect. These expanded beams can be radiated very long distances and yet appear very thin when viewed from an angle. These line illuminations are used in interferometry procedures to make measurements in optical and engineering metrology and are also used in nuclear, particle and plasma physics.
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