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ANALYSIS: DIODE LASERS


Direct diode lasers today: better integration drives applications growth


Coherent’s Dr Jörg Neukum highlights how the ease of integration and maintenance of direct diode lasers has contributed towards their increased uptake in industry


The use of high-power, direct diode lasers is increasing in many manufacturing applications, including those for producing automobiles, medical devices, and consumer products. Typical tasks include metal cladding and other additive applications, soldering, surface heat treatment, brazing and plastics welding. Several factors contribute to this


growth, most notably the availability of integrated product platforms – sub- systems – equipped with processing heads for optical beam shaping and other application-specific accessories, together with advanced cooling schemes that do not need de-ionised water and deliver 24/7 reliability in any manufacturing location.


Sub-systems optimised for integration The advantages of diode lasers include compact size, high electrical efficiency, and scalable architectures. But diode laser output is less ‘well behaved’ than other lasers, thus requiring more complex beam shaping and delivery optics. Consequently, after many years of emphasis on the development of higher brightness devices, it is the availability of lasers that include integration-friendly features that has proved most critical to penetrating real- world manufacturing applications. A typical integrated system, therefore, includes a beam shaping module, often with a fibre-based processing head, a power supply, and possibly a chiller. The goal is to simplify life for the user, allowing them to just specify the beam, rather than all the photonic components required to generate that beam. In automotive manufacturing applications, these sub-systems are


14 LASER SYSTEMS EUROPE AUTUMN 2019


then integrated into a robotic tool by a speciality tool builder or by the automotive manufacturer, for example, for applications such as brazing two galvanised steel body components.


Scalable power – from plastics to metal applications Direct diode lasers can range from single emitters outputting a few watts, to bars at hundreds of watts, and stacks of bars up to a kilowatt and beyond. This broad power scalability enables diode laser systems to be optimally configured for a wide range of applications. In the tens to a few hundred watts range, diode laser systems are used mainly for plastics welding in numerous applications, where they compete with traditional bonding technologies, such as adhesives and ultrasonic welding. Here, medical devices represent a fast-growing market segment because ultrasonic welding creates particles that require cleaning, and adhesives need regulatory approval. Another interesting segment is smart car key fobs, where ultrasonic welding might damage the sensor electronics. Laser welding is also used for sealing devices with plastic coatings to make them immune to


damage from liquid (for example, hot tea/ coffee) as in the illuminated exit strips on the aisles of commercial aircraft. Process development is key in many


of these applications, starting with the choice of the optimum wavelength – this is particularly important for transparent and white plastics, for example. Direct diode lasers are currently available over a broad range of wavelengths from 1,400 to 1,500nm, 780 to 1,060nm, and even blue diode lasers at 450nm have begun to emerge in recent years – for processing highly reflective metals such as copper, gold and aluminium. Extensive experience in a variety of applications can also be pivotal in product selection, and as such Coherent maintains a network of global applications facilities for this purpose. At hundreds of watts, diode laser


systems are used in brazing/soldering applications. And at the kilowatt level, diode laser systems are used for additive manufacturing and heat treating (case hardening) applications where large areas must be rapidly processed, and where the fine resolution of a fibre laser, for example, is not required. Such applications include the processing of heavy machinery for shipping, military, and mining and drilling (gas/coal/oil) applications.


Customised beam shaping Diode lasers have a large area output profile that is ideal for use in applications that need illumination over a specified broad area, and additive manufacturing (such as cladding) provides a simple illustration of the value of beam shaping. As shown in the simplified schematic in figure 1, in cladding the output is often shaped to a line focus of


Figure 1: cladding is optimally performed using a line focused beam shape


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