Fiber Laser Heads

History of warheads


The first cutting heads for fiber lasers were created by modifying CO2 laser heads by adding a collimator lens to them. In CO2 lasers, a parallel beam with a diameter of about 10mm is reached to the head. You only need to focus it, for which one focusing lens is enough. Fiber lasers at the output of the fiber emit a divergent beam, so an additional collimator is needed to convert the divergent beam into a parallel one.
Only behind the collimator you can place the lens focusing the laser beam on the surface of the material.
They were heads with a limited range of focal length adjustment because the focusing lens was used to set it, as was the case with CO2 lasers. Only subsequent head designs were able to adjust the focal length with a collimator, which significantly extended the adjustment range, allowing for cutting thicker materials.
The fiber laser head, unlike CO2 lasers, has an additional window between the focusing lens and the nozzle, which helps to protect the lens from contamination and splashes of molten material that could get through the nozzle to the head.

Lenses


The lenses in the laser heads are made of very high purity quartz glass. Most optical lenses are spherical lenses that are relatively easy to manufacture but have spherical aberrations that must be compensated. Therefore, both the converging lens and the collimator lens are in fact often a group of lenses rather than a single lens. Single aspherical lenses can be used in place of spherical lens assemblies, but are more difficult to make and more expensive.
Light radiation falling on the surface of the lens is partially reflected from it, which causes power loss. About 4% of the power reflects off each glass surface. In fiber laser heads there are from 6 to 14 glass surfaces through which light must pass, therefore under normal conditions even half of the power in the head could be lost. The solution to this problem are special anti-reflective coatings that reduce reflection from a single surface by up to 0.1%. Therefore, it is very important to use only the highest quality lenses with high-performance anti-reflective coatings.

Sensors / Consumables


Laser heads are precise and delicate optical devices that need to be kept in proper condition. The most frequently replaced consumables are the nozzle, ceramic insulator and protective window. These are components that are replaced when worn by the operator. The life of the lenses is somewhat dependent on the laser power, but cleanliness when replacing the safety window also has a significant influence. If it is necessary to replace the lenses, use the supplier’s service, but it is possible to prepare the user for their own replacement.

Focal lengths


The heads can be equipped with focusing lenses with different focal lengths depending on the user’s needs. With thin materials and low powers, the focal length is 125mm. They allow you to cut up to 15mm depending on the strength of the materials. The longer 150mm focal length is the most universal choice and is used for cutting materials up to 20mm. 175 and 200mm focal lengths are used only at high powers and cutting materials over 20mm. However, it should be remembered that when increasing the focal length due to the larger diameter of the focused beam, the cutting efficiency of thin materials slightly decreases. There are also heads with variable focal length, but they are more expensive to buy and use due to a much more complex structure and a larger number of lenses.

Connectors


Fiber optic connectors used in laser heads should be made in such a way as to ensure a stable mechanical connection, dustproof, and effective scattering of reflected light. A good fiber optic connector is liquid cooled and can dissipate up to 6kW of reflected power. This enables the cutting of highly reflective materials such as copper or brass.

HSU


For the cutting process to run correctly, the focus of the beam must be at a specific distance from the material surface. Even slight variations in the distance between the nozzle and the material can deteriorate the cut quality. Therefore, it is very important to properly control the head height so that the distance between the nozzle and the material is always the same, regardless of the folds or unevenness on its surface. The most widely used is capacitive distance measurement. The volume between the nozzle and the material is converted into distance and the head position is corrected based on this value. The speed of operation of this system is extremely important because if the adjustment is too slow, the head may not follow the material curvature with fast movements.

Security


To keep the head in optimal condition, it should be monitored on an ongoing basis. This is important especially at higher laser powers, where failure to detect minor damage in time may cause a greater failure. Modern heads use sensors that control essential operating parameters. Temperature sensors independently measure the temperature of the lenses, protective window and nozzle, and the protective window is monitored for the presence and level of contamination. In addition, the condition of the window seal is monitored, because in the event of cutting gas leaks into the interior of the head, the optics could be damaged. It is also useful to monitor the amount of reflected light which helps in detecting the completion of the piercing process. Such a large number of monitored parameters may seem an exaggeration,