Working principle and construction of fiber laser

In an EAGLE fiber laser cutting systems, we use IPG Photonics as a power source. To generate ultrahigh power laser light, such as 20kW, we use multi-mode power sources.

The feed source of an IPG fiber laser is a semiconductor diode pump (as opposed to exciting CO2 with electrical current). The excited photons that are emitted from the laser diodes are created in and sent down a fiber cable.

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

The cross section of the fiber shows three layers, each with specific characteristics of light refractivity. The outer layer has a special cladding with the lowest refractive index. The middle layer has a higher refractive index compared to the outer cladding, and its’ goal is to initiate the work of the laser as well as guarantee optimal transmission of the pumping energy. The center layer is the active optical core and is doped with rare earth elements, in this case Yb (Ytterbium). It has the highest refractive index of all three layers.

The light traveling through the three-layer fiber must exit the fiber and enter free-space where it can contact and cut material. A collimating lens is used to transform the beam into a collimated beam where all the photons are traveling parallel to each other.
Finally, this collimated beam is transferred to an optical system where it is focused to a certain point (where the intended target material will be) and set to a certain diameter.
The thin construction of the long beam makes the cooling process easier and more effective than other types of lasers, and the amount of heat generated by pumping the laser’s beam with energy is minimal. These two attributes enables the fiber laser to achieve extremely good power conversion ratio of electrical power to beam power. Fiber lasers are very efficient.