ANALYSIS: ULTRASHORT PULSED LASERS


is used as the display glass of devices for weight reasons. A new field of USP laser processing in the


A structure for print preparation generated using an ultrashort pulse laser


a next step to an all-optical manufacturing system can be provided. In addition to necessary developments


of system components, new laser systems based on fibre lasers and dedicated amplifiers will enable the scaling of the average power and pulse energy of USP lasers. The high average power of the InnoSlab amplifier principle, which is now available, will enable the advantages of these systems to be transferred to macro processing. Other system designs, such as disc lasers with very low phase distortions and low nonlinear effects at high fluences, will allow even further power and energy scaling – which will then result in new application developments.


Taking the tools out of processing The ultimate goal for USP lasers is to use them as a fully flexible digital tool, as an alternative to conventional tool-based processing, with the technology having already proven its advantages across a number of sectors: • Display industry: cutting flexible substrates of OLED-Displays, the drilling and cutting of glass, and the structuring of thin films;


• Automotive industry: machining hydraulic and fuel injection components;


• Printing industry: engraving cylinders for embossing and printing;


• Medical sector: processing cardiovascular stents;


• Aircraft construction: machining carbon fibre composites;


• Tool manufacturing: generating embossing and injection moulding tools;


• Photovoltaics: structuring conductive and dielectric layers of thin-film solar cells and crystalline Si solar cells; and


• Electronics industry: drilling and cutting printed circuit boards.


Display cutting In low-energy and low-power traditional laser processing, the amount of deposited


energy is determined by linear absorption of the laser energy. In USP laser processing, however, very high photon densities can be generated in the focal spot of a processing optic, which enables nonlinear absorption mechanisms to occur. This means that even transparent materials can be processed at wavelengths where the materials do not show any absorption. Display technology has therefore


become one of the fastest growing fields of application for high-power USP lasers, aided by the progressive market penetration of smartphones and tablet computers. Using


“The most important developments have to be carried out in the field of system technology”


nonlinear absorption mechanisms and specially-designed processing principles – such as filament cutting or elongated focus geometries – USP laser energy can be concentrated and deposited into a very thin line in transparent materials. This causes thermal and mechanical stress in the materials, and leads to separation of the parts to be cut. USP lasers are especially being used for the drilling and cutting of hardened display glasses with hardness depths greater than 40µm. The openings in displays for camera lenses, loudspeakers and microphones, as well as the operating units, are mainly cut this way. In principle, however, the USP laser is also suitable for the format cutting of display glasses, although even higher cutting speeds must be achieved. In the future, the range of applications for USP laser cutting systems could be expanded if sapphire, which cannot be cut using conventional cutting methods,


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display industry is the separation of polymer- based OLED displays. For smartphones and tablets, OLED displays are manufactured on polymer films over large areas, for productivity reasons. These large multiple- display sheets have to be separated into single small displays without any thermal damage, discoloration or recondensation of the ablated material being caused. Therefore, USP lasers operating in the UV wavelength are used, which provide low absorption depth, as well as low thermal influence of less than 50µm.


Metalworking USP laser technology is also gaining ground in metal processing, where using pulse durations of 10ps and shorter enables superior processing quality compared to when longer pulses are used. The technology has a long history of


metalworking. One of the first applications explored using USP lasers was the drilling of injection nozzles for diesel injection technology. Even though this application – which requires drilling depths of up to 1mm and bore diameters of 70µm – has not yet established itself, the drilling of injection nozzles using USP lasers for gasoline injection technology has been industrially introduced. Here, the wall thickness is only 0.3mm and the bore diameters range from 70 to 200µm. Compared to conventional eroding processes, higher qualities and processing speeds can be achieved here using USP lasers. New optical set-ups, such as helical drilling optics, can also be used to achieve high-precision bore holes with arbitrary geometries. In the manufacturing of injection moulding


tools for medical products and micro optical components, picosecond and femtosecond lasers are also being used, due to their high precision and the high flexibility of processing they enable, by removing the need for additional tools. In addition, in the printing, engraving and embossing industry – for example, in security printing technology, printing electronic circuits, and embossing light guide foils and scatter foils for display production – the high precision and resolution of USP lasers is enabling new applications. New high-power USP laser systems with


high repetition rates are now being used to achieve metal ablation rates of more than 20mm³/min, with lateral resolutions below 3µm and depth resolutions below 100nm.l


Dr Arnold Gillner is the department manager for ablation and joining at Fraunhofer ILT and managing director of the Fraunhofer Group for Light & Surfaces


SUMMER 2019 LASER SYSTEMS EUROPE 35


Fraunhofer ILT


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