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Continuous-Wave (CW) Fiber Lasers: Principles and Power Levels
CW fiber lasers operate continuously; they constantly emit light, as opposed to lasers that operate with pulsed pumping. Fiber lasers are often the only ones to operate continuously, as fiber greatly increases gain efficiency. CW lasers typically function with an output power that is constant; however, some power variations may occur due to mode beating; this is mostly true for non-single-frequency lasers.
The continuous nature of a laser beam may be achieved through ionizing gas (like in CO2 lasers) just below a critical level to be in a plasma state; the output of this laser can be turned on and off by controlling the amount of power at the threshold. If the input of power is just above the threshold, the plasma will produce a laser beam. This is one of the principles behind CW fiber laser technology.
Types of CW Fiber Lasers by Power
CW fiber lasers differ by their power levels:
- high power CW lasers;
- medium power CW lasers;
- low power CW lasers.
High-power lasers, including high-power CW fiber lasers, are the most popular variety of all lasers. High power output is required for many different applications, some of which include large laser displays, LIDAR, particle acceleration, material processing, and more. Despite a wide-scale use of these lasers, it is not determined what exactly a high-power laser is. Typically, an output of a few hundred watts will classify a laser as “high powered”. In some areas, however, an output of a few dozen watts is considered high.
High-power CW fiber lasers are inherently brighter than other laser systems due to the high power output. Another important benefit of these lasers is their versatility. Beam switchers, couples, and sharers are readily available for high-powered fiber lasers and can be used for customization.
Applications of High-Power CW Fiber Lasers
High-power CW fiber lasers are most frequently used in optical sensing, optical tweezing, atomic trapping and cooling, spectroscopy, efficient second-harmonic generation, and more.
The design of high-power fiber lasers often involves challenges. Their prime limitation is the thermal degradation of fiber coatings. The thermal effects make it more difficult to achieve high efficiency at high power output.
Other effects that become relevant during the use of high-powered fiber lasers include: 1) Raman scattering; 2) four-wave mixing; 3) Brillouin scattering; 4) conversion of pump power into heat that may potentially lead to laser crystal fracture.