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tasks such as laser illumination, scanning, welding, cutting, and other types of material processing. These tasks require a variety of lens types in a range of wavelengths, such as spherical, aspherical, plano-convex, cylindrical, conical, and line- generating lenses. These lenses have different focal distances for different applications. The smaller the beam diameter, the higher the energy density of the laser beam, which results in a more aggressive beam. Like laser mirrors, laser lenses are also coated with numerous exotic materials to ensure they perform their intended task with the highest performance and greatest reliability and longevity.
Prisms Perhaps most recognisable from the cover of a Pink Floyd album, prisms have been around for centuries. Indeed, it was Sir Isaac Newton who discovered that glass prisms could be used to steer, direct, and disperse light – something he demonstrated by splitting a beam of sunlight into the seven colours of the rainbow. Lasers, however, are usually only one colour. So instead of being split like in Newton’s experiment, laser beams tend to bend when shined through a prism. For this reason, laser prisms are often designed to internally reflect a laser beam off of multiple surfaces in order to redirect the beam path, making them useful for beam steering or beam manipulation applications. As with laser mirrors and
lenses, laser prisms come in a wide range of forms, including: right-angle, dispersion, penta,
“Ultrafast optics are designed to withstand the ultrashort pulse durations and extremely high peak powers of ultrafast lasers”
Lenses are used in a wide range of combinations and set-ups to focus laser beams into spots, lines, rings and other shapes
image rotation, retroreflection, wedge, and more. All these prisms can be found in various scientific and industrial settings for tasks such as laser tracking, alignment, and range finding, as well as atmospheric monitoring.
Filters Laser filters are used to essentially ‘clean up’ laser systems by selectively transmitting or blocking specific wavelengths of light, depending on which are required for the application at hand. By screening out interference such as background radiation, ambient light, and noise, filters can prevent damage to optical components caused by changes in power levels or temperature. More specifically, laser line and shortpass edge filters improve the signal quality at the laser source, while longpass edge and laser rejection filters tackle unwanted noise at a detector. Notch and dichroic filters are also commonly deployed in laser systems. Similar to the lasers
themselves, laser filters are deployed across a wide range of applications, including material processing, spectroscopy (measuring chemical and physical properties of samples), medical
40 LASER SYSTEMS EUROPE THE 2023 GUIDE TO LASER SYSTEMS
and life sciences (surgical procedures, diagnostics, and therapeutics), and optical communications (efficient data transfer over optical fibres). They are also used to improve the contrast and resolution of images and protect sensitive optical systems in the defence industry, while in astronomy they are used in telescopes to collect the right types of light required to capture stars, galaxies, and other celestial objects in perfect clarity.
Beam splitters and expanders Beam splitters and expanders are used to change the radius of collimated laser beams. These components often constitute a series of mirrors, prisms, lenses, and filters. Beam splitters split a light beam into two or more beams, usually by wavelength or polarity. They can also work in reverse to combine multiple light beams into one. There are various types of beamsplitters: dichroic beamsplitters reflect some wavelengths while transmitting others; polarising beam splitters split light beams based on polarity while non-polarising splitters do so independently of the polarity; and lateral beam splitters divide an incident beam into two parallel beams.
Beam expanders, on the other hand, increase the diameter of a light beam to reduce laser power density and prevent damage to optical components. They can maintain beam collimation in long-path systems and are useful for remote sensing, interferometry, laser scanning and more. Like their light-splitting counterpart, beam expanders can also be used in reverse to reduce the radius of the beam. Beam expanders often
come in the form of optical telescopes that have two lenses or curved mirrors. Keplerian and Galilean telescopes are the two most common types of beam expanders. A Keplerian telescope has two focusing lenses separated by their combined focal lengths, with a beam waist between them. This means that changing the focal length of the lenses changes the beam radius. A Galilean telescope, which is a little more compact, uses a focusing lens and a defocusing lens, with the distance between them equal to the sum of their focal lengths, where one is negative.
Beam shapers Laser beam shapers are used to collimate laser beams, transform beam profiles, convert beam shapes and more.
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