LASER OPTICS
prevent this by only allowing light to only be transmitted in one direction. Types of optical isolators include polarised, composite, and magnetic. Polarised and composite isolators use polarisation to control light transmission, while magnetic isolators use the Faraday effect to control the polarisation of light. Faraday isolators have three
Prisms are commonly used for beam steering in laser applications g
They are required as, typically, laser sources emit beams with a non-uniform intensity that are not ideal for most applications, and many applications require a beam shape that laser sources cannot naturally produce, such as a line or ring. Some of the many types of beam shapers include: flat top beam shapers, used to convert Gaussian beams into flat top beams with a uniform intensity distribution; cylinder lenses, used to convert an oval or differently shaped profile to a circular one; slow axis collimators and fast axis collimators, used to collimate the light of laser bars and laser diodes, respectively; microlens arrays, for homogenising a variety of light emitters such as line-narrowed excimer lasers and high-power LEDs; diffractive optical elements, which transform laser beams with a nearly-Gaussian profile into a defined 2D shape with uniform intensity distribution at the focal point of a lens; and multi-focus objectives, which can focus laser light to multiple foci along the optical axis, increasing the effective depth of focus (useful in high-speed cutting applications).
Crystals Laser crystals are solid-state materials used as the active medium (or ‘gain media’) in laser devices. They’re designed to amplify light and generate a coherent beam via the process of stimulated emission. These crystals are
highly transparent to prevent scattering and light absorption and must be extremely durable to withstand the thermal effects of a high-power laser. Crystals are often doped with impurities such as rare earth or transition metal ions to alter their properties. The density of this doping, along with the shape of the crystal, influences the characteristics of the laser beam, including its wavelength, power stability and beam coherence. The crystals are known as “host crystals”, with common types including garnets, vanadates, fluorides, sapphires, and chalcogenides. Neodymium-doped yttrium aluminium garnet (Nd:YAG) crystals, for example, are commonly used in high-power Q-switched lasers emitting light in the infrared range, while neodymium-doped vanadate (Nd:YVO4) crystals are suited to mode-locked infrared lasers with high pulse repetition rate; titanium-doped sapphire crystals have particularly broad bandwidths and are often used in tuneable and ultrashort pulse lasers; and chalcogenide crystals have broad absorption and emission bands, meaning they can be used to emit a range of different beam types such as continuous-wave, gain-switched, Q-switched, and mode-locked.
Isolators
When a light beam is passed through an optical fibre it can reflect back on the laser source and damage it. Optical isolators
42 LASER SYSTEMS EUROPE THE 2023 GUIDE TO LASER SYSTEMS
main components: an input and output polariser, and a Faraday rotator. The Faraday rotator rotates the polarisation of light passing through it by 45 degrees, and the input and output polarisers ensure that light can only pass through in one direction. The optical isolator operates in two modes – forward mode and backward mode. In forward mode, light enters the input polariser, becomes linearly polarised, passes through the Faraday rotator, and then exits
“Laser windows are configured to protect users of laser equipment from laser
and are used across a wide range of applications. For example, they can be used to micromachine materials with extreme precision, or observe physical processes that occur at small time scales, such as photosynthesis, human vision, protein folding, and molecular vibrations. Ultrafast lasers are also deployed across medical applications, nonlinear imaging and microscopy, spectroscopy, communications, defence, and more. Ultrafast optics encompass mirrors, lenses, prisms, filters, crystals, gratings, windows, beam expanders, splitters and shapers, all of which are designed to withstand the ultrashort pulse durations, broad wavelength ranges, and extremely high peak powers of ultrafast lasers.
radiation while still allowing them to observe the beam and application”
through the output polariser. In backward mode, light enters the output polariser, is rotated by the Faraday rotator, and then reflected by the input polariser. Isolators can often be
found in laboratory, industrial, and corporate environments being used to improve signal levels and stability in optical communication systems, amplifiers, and laser diodes.
Ultrafast optics Ultrafast optics, as the name suggests, are designed specifically for ultrafast lasers. These lasers are characterised by their ultrashort pulse durations (picoseconds, femtoseconds and even attoseconds)
Windows Laser windows provide a high degree of transmission of specified wavelengths, used in both laser safety and laser applications. For laser safety, windows are configured to protect users from laser radiation while still allowing them to observe the beam and application as a whole. Laser windows are made from a wide array of polymers and glass, available in various shades and colours depending on the wavelength and power of laser light being blocked/transmitted. In laser applications, similar
to a filter, laser windows can offer exceptional transmission of desired wavelengths while effectively reflecting unwanted wavelengths. They can be used to isolate a laser beam, and are available in high-power versions for when particularly high damage thresholds are required. l
For more information on optics and their many different laser applications, visit:
www.lasersystemseurope.com/ technologies/optics
@LASERSYSTEMSMAG |
WWW.LASERSYSTEMSEUROPE.COM
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