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Fiber laser
A fiber laser (or fibre laser in Commonwealth English) is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are related to doped fiber amplifiers, which provide light amplification without lasing.
Fiber nonlinearities, such as stimulated Raman scattering or four-wave mixing, can also provide gain and thus serve as gain media for a fiber laser.[citation needed]
An advantage of fiber lasers over other types of lasers is that the laser light is both generated and delivered by an inherently flexible medium, which allows easier delivery to the focusing location and target. This can be important for laser cutting, welding, and folding of metals and polymers. Another advantage is high output power compared to other types of laser. Fiber lasers can have active regions several kilometers long, and so can provide very high optical gain. They can support kilowatt levels of continuous output power because of the fiber's high surface area to volume ratio, which allows efficient cooling. The fiber's waveguide properties reduce or eliminate thermal distortion of the optical path, typically producing a diffraction-limited, high-quality optical beam. Fiber lasers are compact compared to solid-state or gas lasers of comparable power, because the fiber can be bent and coiled, except in the case of thicker rod-type designs, to save space. They have lower cost of ownership. Fiber lasers are reliable and exhibit high temperature and vibrational stability and extended lifetime. High peak power and nanosecond pulses improve marking and engraving. The additional power and better beam quality provide cleaner cut edges and faster cutting speeds.
Unlike most other types of lasers, the laser cavity in fiber lasers is constructed monolithically by fusion splicing different types of fiber; fiber Bragg gratings replace conventional dielectric mirrors to provide optical feedback. They may also be designed for single longitudinal mode operation of ultra-narrow distributed feedback lasers (DFB) where a phase-shifted Bragg grating overlaps the gain medium. Fiber lasers are pumped by semiconductor laser diodes or by other fiber lasers.
Many high-power fiber lasers are based on double-clad fiber. The gain medium forms the core of the fiber, which is surrounded by two layers of cladding. The lasing mode propagates in the core, while a multimode pump beam propagates in the inner cladding layer. The outer cladding keeps this pump light confined. This arrangement allows the core to be pumped with a much higher-power beam than could otherwise be made to propagate in it, and allows the conversion of pump light with relatively low brightness into a much higher-brightness signal. There is an important question about the shape of the double-clad fiber; a fiber with circular symmetry seems to be the worst possible design. The design should allow the core to be small enough to support only a few (or even one) modes. It should provide sufficient cladding to confine the core and optical pump section over a relatively short piece of the fiber.
Tapered double-clad fiber (T-DCF) has tapered core and cladding which enables power scaling of amplifiers and lasers without thermal lensing mode instability.
Recent developments in fiber laser technology have led to a rapid and large rise in achieved diffraction-limited beam powers from diode-pumped solid-state lasers. Due to the introduction of large mode area (LMA) fibers as well as continuing advances in high power and high brightness diodes, continuous-wave single-transverse-mode powers from Yb-doped fiber lasers have increased from 100 W in 2001 to a combined beam fiber laser demonstrated power of 30 kW in 2014.
High average power fiber lasers generally consist of a relatively low-power master oscillator, or seed laser, and power amplifier (MOPA) scheme. In amplifiers for ultrashort optical pulses, the optical peak intensities can become very high, so that detrimental nonlinear pulse distortion or even destruction of the gain medium or other optical elements may occur. This is generally avoided by employing chirped-pulse amplification (CPA). State of the art high-power fiber laser technologies using rod-type amplifiers have reached 1 kW with 260 fs pulses and made outstanding progress and delivered practical solutions for the most of these problems.
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Fiber laser
A fiber laser (or fibre laser in Commonwealth English) is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are related to doped fiber amplifiers, which provide light amplification without lasing.
Fiber nonlinearities, such as stimulated Raman scattering or four-wave mixing, can also provide gain and thus serve as gain media for a fiber laser.[citation needed]
An advantage of fiber lasers over other types of lasers is that the laser light is both generated and delivered by an inherently flexible medium, which allows easier delivery to the focusing location and target. This can be important for laser cutting, welding, and folding of metals and polymers. Another advantage is high output power compared to other types of laser. Fiber lasers can have active regions several kilometers long, and so can provide very high optical gain. They can support kilowatt levels of continuous output power because of the fiber's high surface area to volume ratio, which allows efficient cooling. The fiber's waveguide properties reduce or eliminate thermal distortion of the optical path, typically producing a diffraction-limited, high-quality optical beam. Fiber lasers are compact compared to solid-state or gas lasers of comparable power, because the fiber can be bent and coiled, except in the case of thicker rod-type designs, to save space. They have lower cost of ownership. Fiber lasers are reliable and exhibit high temperature and vibrational stability and extended lifetime. High peak power and nanosecond pulses improve marking and engraving. The additional power and better beam quality provide cleaner cut edges and faster cutting speeds.
Unlike most other types of lasers, the laser cavity in fiber lasers is constructed monolithically by fusion splicing different types of fiber; fiber Bragg gratings replace conventional dielectric mirrors to provide optical feedback. They may also be designed for single longitudinal mode operation of ultra-narrow distributed feedback lasers (DFB) where a phase-shifted Bragg grating overlaps the gain medium. Fiber lasers are pumped by semiconductor laser diodes or by other fiber lasers.
Many high-power fiber lasers are based on double-clad fiber. The gain medium forms the core of the fiber, which is surrounded by two layers of cladding. The lasing mode propagates in the core, while a multimode pump beam propagates in the inner cladding layer. The outer cladding keeps this pump light confined. This arrangement allows the core to be pumped with a much higher-power beam than could otherwise be made to propagate in it, and allows the conversion of pump light with relatively low brightness into a much higher-brightness signal. There is an important question about the shape of the double-clad fiber; a fiber with circular symmetry seems to be the worst possible design. The design should allow the core to be small enough to support only a few (or even one) modes. It should provide sufficient cladding to confine the core and optical pump section over a relatively short piece of the fiber.
Tapered double-clad fiber (T-DCF) has tapered core and cladding which enables power scaling of amplifiers and lasers without thermal lensing mode instability.
Recent developments in fiber laser technology have led to a rapid and large rise in achieved diffraction-limited beam powers from diode-pumped solid-state lasers. Due to the introduction of large mode area (LMA) fibers as well as continuing advances in high power and high brightness diodes, continuous-wave single-transverse-mode powers from Yb-doped fiber lasers have increased from 100 W in 2001 to a combined beam fiber laser demonstrated power of 30 kW in 2014.
High average power fiber lasers generally consist of a relatively low-power master oscillator, or seed laser, and power amplifier (MOPA) scheme. In amplifiers for ultrashort optical pulses, the optical peak intensities can become very high, so that detrimental nonlinear pulse distortion or even destruction of the gain medium or other optical elements may occur. This is generally avoided by employing chirped-pulse amplification (CPA). State of the art high-power fiber laser technologies using rod-type amplifiers have reached 1 kW with 260 fs pulses and made outstanding progress and delivered practical solutions for the most of these problems.