Optics for 1 microm Fiber Lasers

The use of fiber lasers in metal processing industry for cutting applications is becoming increasingly popular due to the advantages versus other laser technologies. Fiber lasers do an excellent job cutting metals thinner than 3 mm (0.12 in).Thin metal processing times are faster than CO₂ lasers with comparable edge quality. Typical CO₂ laser cut edge quality for 10 mm (0.4 in.) Stainless steel (Courtesy of Fraunhofer ILT Aachen Germany).

The output optical assembly of a fiber optic beam delivery system consists usually of a collimating lens, a focusing lens and a protective window. The optical lenses featured in the fiber laser cutting head are made of fused silica and are specially coated to minimize absorption and maximize transmittance of the 1 micron wavelength laser beam onto to the metal sheet.

The collimating lens captures the highly divergent output from the optical fiber and creates a parallel (collimated) beam with reduced divergence enabling moderate propagation distances.

Similar to other laser systems for metal processing applications, the main role of the focusing lens is to concentrate the energy of the laser beam output to spot at a specific distance (focal length) - depending on the application. The focal length - defined by the radius of curvature of the lens - is the most important feature of a focusing lens.

The first lens (collimator lens - L1) takes the rapidly diverging beam from the Fiber exit, and straightens, or collimates, it. This lens should be placed at a distance exactly equal to its focal length from the fiber exit face. If this is not done, the beam will not be collimated, and the imaging convention described below is void. The second lens (focusing lens - L2)acts as an objective, and focuses the beam to form an image of the fiber face.

The contamination of the focusing lens is one of the prime reasons for poor laser performance and potential down time of laser operations. No nozzle system is perfect and some debris, fume or backspatter can occasionally reach the lens.

This situation occurs for many high power laser systems, including fiber lasers. Collimating lenses as well as focusing lenses present in fiber laser cutting head are very sensitive to any type of contamination. For this reason, the majority of fiber laser systems employ protective optical windows to protect the focusing lens against contamination. The protective window is positioned in front of the focusing lens, and serves as a barrier between the lens and the metal sheet. Protective windows are the most consumed optical element in fiber laser systems.

Ophir Fiber Laser Optics offering includes:- Fiberlens™ - UV grade fused silica Focusing and Collimator Lenses- UV grade fused silica Protective Windows used as a debris shield to protect the 1 micron lenses from contamination. Ophir Fiberlens™ optics are the world's most innovative optics for use in high power, 1-micron Fiber Laser Systems. This family of optics is applicable for all 1 micron range application of 1030-1080 nm range including fiber lasers, disc lasers and YAG lasers. Ophir Fiberlens™ optics deliver the best performance for 1-micron lasers thanks to ultra-low absorption material (<100 ppm at 1.03-1.08 microns), tight focal length tolerances (±0.5%) and a laser-damage threshold >10J.