Functional principle and design of a fiber laser

In EAGLE fiber laser cutting systems, we use IPG Photonics as the power source. In order to go generate high power laser beams with 20kW, for example, we use multi-mode power sources.

The source of an IPG fiber laser is a semiconductor diode pump (as opposed to exciting CO2 with electric current). The excited photons which are emitted by the laser diodes are generated in and sent down a fiber cable.

The fiber laser uses an optical fiber, which is similar to the fiber optic cables used in telecommunications, to create and transfer the photons (light). These fiber cables can be very long, and provide a great deal of flexibility without using mirrors to redirect the laser light. The use of a glass-based fiber is a significant advantage compared to CO2 lasers, since it means that fiber lasers do not rely on perfectly aligned and clean mirrors to ensure the movement of the nozzle tip. Instead, they are flexible, small, and light.

The cross section of the fiber shows three layers, each with specific light refractivity characteristics. The outer layer has special sheathing with the lowest refractive index. The middle layer has a higher refractive index compared to the outer sheathing. Its task is to initiate the operation of the laser, as well as guarantee optimum transmission of the pumping energy. The middle layer is the active optical core, and is coated with rare earth elements, in this case Yb (Ytterbium). This has the highest refractive index of all three layers.

The light traveling through the three-layer fiber must exit the fiber into the open air, where it can come into contact with and cut material. A collimating lens is used to convert the beam into a collimated beam, in which all of the photons move in parallel to each other.
This collimated beam is then led an optical system, which focuses it on a certain point (where the target material can be found) and set to a certain diameter.
The thin structure of the long beam makes the cooling process easier and more effective than with other types of laser, and the amount of heat generated by pumping the beam of the laser with energy is minimal. These two attributes allow the fiber laser to achieve an extremely good conversion ratio from electrical power to beam power. Fiber lasers are very efficient.

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