With this article, we would like to start a monograph of laser ablation technology, as we know it from everyday challenges and experience. In this way, we will try to "disenchant" LASER for you.
We have been working with laser processing technology for selective cleaning and surface preparation for a long time. We deal with complex surface engineering problems in technological processes on a daily basis. So why have we decided to give our article this fairy-tale title? We will try to introduce you to issues, the understanding of which will help to “disenchant” the technology. Because lasers are not just about cleaning, cutting or welding. Above all, lasers increase the productivity, precision and quality of processing.
Let’s start with the basics. Lasers, or electromagnetic radiation generators, are devices that use the phenomenon of forced emission of radiation. They operate by the excitation of an active medium by various types of pumping, such as electrical, optical, chemical or electron collisions. The excited medium emits energy in the form of quanta of coherent radiation.
Based on the type of the active medium, lasers are divided into gas, liquid, organic and inorganic, solid-state and semiconductor types. Laser radiation is characterised by monochromaticity, high coherence – temporal and spatial – and directionality of beam propagation. Moreover, laser beams can be focussed by optical systems even to diameters of several micrometres, which results in very high power densities.
The application of lasers is wide. I n military technology, they are found in weapons sights, range finders, missile and rocket guidance systems, target tracking systems and bomb igniters. Lasers are common in surveying, distance measurement, geometric structure analysis of the surface layer, airborne reconnaissance systems and navigation. They are successfully used in medicine and cosmetics, environmental protection, and telecommunications.
Most often, however, laser technology is used in a variety of industrial processes involving the processing of metals and composites such as welding, melting, hardening, and cutting. They are also used for marking, drilling holes and applying coatings. In recent years, lasers have also been used in the conservation of works of art for the removal of contaminants and layers from stone, ceramics, metal details and polychrome.
The source, or the heart of a LASER
The laser source is commonly called the active medium where the laser action is generated. In order not to exaggerate with a detailed description and distinction between different types of active media, we will focus mainly on fibre lasers.
The active element of fibre lasers is an optical fibre doped with rare earth ions, such as erbium, ytterbium or neodymium. These sources are characterised by high efficiency and excellent beam quality. The radiation is generated directly in the optical fibre core and transmitted to the processing head via the optical fibre directly and without loss. This eliminates unreliable and complicated beam path control systems as well as the risk of beam weakening through misaligned or dirty mirrors or lenses. A laser system based on a fibre optic source is also resistant to temperature changes and various types of shock. Another unquestionable advantage is the long lifetime of these sources of at least 100,000 hours.