hi tech Bern University of Applied Sciences Engineering and Information Technology
2/2012 The Magazine
Laser: Lightwave of the Future The laser beam – a universal tool Gwatt on Lake Thun – a Mecca for laser professionals Well-prepared to start international business with Fit2GlobalizeTM
Focus
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EDITORIAL
The laser beam – a universal tool
Lightwave of the Future
The laser beam – a universal tool|
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Gwatt on Lake Thun – a Mecca for laser professionals
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Gwatt – where laser professionals develop new ideas
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The Janus-faced aspects of applied research
It is well-known that mankind differs from the animal world in three distinct characteristics: abstract thinking by means of concepts, language, and the use of tools made by man himself. A lot of the world in which we live today has been created by tools such as the computer to process ideas, or by machines to process materials.
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What is less well-known is the fact that our region (more precisely, the Alemannic area that once stretched from Augsburg to Geneva, and from Chiavienna to Strassbourg), has been and still is the global leader in the inventing and manufacturing of new precision mechanical tools as well as in their use in machines.
25 years of collaboration: a Russian-Swiss success story
14 Cutting metal with laser is like cutting through butter 16 Harvesting the sun more efficiently 18 Joining Forces: Doctoral Research at BUAS and University of Bern 20 Swept-Source laser sources at the BUAS OptoLab 23
Z-LASIK – eye surgery without blades
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Fiber lasers: Processing material with glass fibers
Dr. Christoph Harder President Swisslaser.Net Photo : Swisslaser.Net
26 ROFIN-LASAG: Pioneers in laser welding of copper 28 SILITEC – more efficiency and fewer costs thanks to sand 30 Well-prepared to start international business with Fit2GlobalizeTM
Cover: Impressions from the laser lab Photo: BUAS-EIT
When laser technology was invented in California 50 years ago, Switzerland was soon looking into ways of using this intense beam of light as a contact-free tool. A contact-free tool never wears out and thus carries immense advantages such as high precision at all times and no downtimes for replacement. Soon some institutes and companies around Bern came together and researched the use of laser technology for the purpose of processing materials. They developed processes and beam tools, and then sold them worldwide. Today Switzerland is one of the leading nations in the manufacturing of laser beam tools in competition with Germany, Japan and the USA.
Laser beam sources developed further: in raw power and strength, through beam guidance in fibers, in their precision, and in their modulation. As a result, new applications continue to be created for use in, for example, medical operations, the manufacture of bio-compatible surfaces on implanted pieces of metal, and in the processing of synthetics. 50 years after the invention of laser technology, the progress of beam tools continues unabated. Bern University of Applied Sciences is in a good position to continue the very old Alemannic tradition of developing mechanical tools, and to contribute to our quality of life with newly developed laser beam tools.
Dr. Christoph Harder President Swisslaser.Net
Since the 90’s, Bern University of Applied Sciences in Burgdorf, first at the IALT, now at the ALPS, has been researching and developing new laser beam tools and ways of processing materials in close co-operation with industry. The first development phase looked into ways of using laser to minimie tool wear. In a later phase, researchers sought ways to cut the materials more exactly and then weld them in such ways that lighter and yet safer cars could be produced, and motors that need less fuel could be built.
I m p r e ssu m Editors Patrick Studer, Diego Jannuzzo Translation Carmel Widmer-O'Riordan, Patrick Studer Adress BFH-TI, hitech-Redaktion, Postfach, 2501 Biel, E-Mail Editor hitech@bfh.ch Homepage hitech.bfh.ch Circulation 1500 issues Graphics and layout Ingrid Zengaffinen Print Stämpfli Publikationen AG, Wölflistrasse 1, Postfach CH-3001 Bern – hitech 2/2012, Special Edition English: September 2012
This magazine is available in German and French under: www.hitech.bfh.ch
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F O C U S | lightwa v e of the future
Gwatt on Lake Thun – a Mecca for laser professionals Physicists from the University of Bern built the first Swiss solid-state laser as far back as 1963. They continued to develop it further and mounted a stronger version on an astronomical telescope, allowing observation of satellites through laser beams at Zimmerwald Observatory. This was a huge success. Nobody could have anticipated that the Canton of Bern would become a leader in the field of laser technology, which it did thanks to the know-how of the University of Bern and, later, Bern’s University of Applied Sciences.
Laser scanningproblem solver in action Photo: BUAS-EIT
Prof. Dr. Franz Baumberger Head of Research and Development at BUAS-EIT Photo: Arteplus Sàrl
Abraham Maiman was not well pleased when his son, Theodore Harold, decided to become a physicist instead of a doctor. In a laboratory owned by the millionaire, Howard Hughes, Theodore worked tirelessly in the interests of pure research to develop a piece of equipment that would eventually be able to concentrate light. Einstein had already promoted the principle of stimulated emissions back in 1917. By 1960 had come up with the solution and presented the world’s first ever functioning ruby laser. Other researchers were a little sceptical at first. Even Maiman’s assistant, Irnee D’Haenens, joked that the laser was «a solution looking for a problem». Since then the laser has conquered the world. Optical and laser technologies have become leading disciplines involved in innovation around the globe. Universities teach fundamental elements of physics such as the production of laser beams, laser guidance and the design of laser optics. It is also the remit of the Universities of Applied
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Sciences to instruct students on the options of using the laser as a tool, its application in the welding and cutting of laser beams, as well as on aspects of laser safety or the simulation of laser-led processes.
Lasers win over the world of industry The number of laser welding applications has risen constantly over the last 20 years. Thanks to the controllability of laser energy and the reaction time of the material, it may soon be possible to weld metallic materials at high melting temperatures or high thermal conductivity. Laser welding is interesting in so far as it enables the combination of similar or different elements without having to apply supplementary material. In contrast to other, more conventional methods of welding technology, the laser directs heat precisely onto the object itself. Interaction with the material lasts a matter of milliseconds. The range of materials that can be used in laser welding is quite wide; from high-alloyed steels, tungsten, molybdenum, and tantalum to nickel and beryllium as well as aluminium and titan and, thanks to a discovery made by Swiss researchers from the Gwatt-Thun region, also to non-ferrous heavy metal such as copper.
Researchers at the University of Bern have been developing lasers for use in both pure and applied research for over 50 years. The first Swiss laser was set up in the laboratory of the IAP (Institute of Applied Physics, University of Bern). Today they are working on new types of highly stabilised or pulsed models such as fiber or x-ray lasers. As a result, the Canton of Bern has become a strong and highly competent player in the laser and optics industry with an annual turnover of 500m Swiss Francs.
ALPS-the problem solvers The Institute for Applied Laser, Photonics and Surface Technologies (ALPS) at Bern University of Applied Sciences, Engineering and Information Technology (BUASEIT) is the ideal partner for organisations. It has a team of highly specialised experts working with industrial partners to develop new processes and techniques in the manufacturing of elements and their analysis in ways that save both material and energy. The symbol for this technology transfer is IAP’s and BUAS's joint Centre of Competence «Fiber and Fiber Lasers». While the IAP concentrates on developing fundamental elements, the ALPS deals with applications, which then lead to cooperation with business firms. On the basis of their competence in this field, the Bern University of Applied Sciences decided to invite scientists and researchers from all over the world to the 20th International Congress on Advanced Laser Technology at the beginning of September 2012. This ALT event, first held in
Material processing with laser Photo: photolook-Fotolia.com
1993, focuses on the latest developments and findings in laser technology applications. It offers internationally recognised experts a platform to present their results and the opportunity to exchange ideas. Whether they are optimising combustion engines, making a profit for the scanner industry, breathing life into our CD’s and DVD’s, luring us into a speed trap or working their magic in the 2 million cases of glaucoma every year, lasers are here to stay and have become a fixed part of our everyday lives. It’s just as well that Theodore Harold went against his father’s wishes and became a physicist instead of a doctor! Contact: > franz.baumberger@bfh.ch > Further information: www.alps.ti.bfh.ch www.alt12.org
ALPS – who we are The Applied Laser, Photonics and Surface Technologies group (ALPS) at BUAS-EIT has a long tradition in the field of materials processing and is the leading group in materials micro-processing in Switzerland. Our main experience lies in processing absorbing as well as dielectric materials with short (nanosecond) and ultrashort (picosecond and below) pulses of different wavelengths. Typical applications comprise the surface micro-structuring of metals, ultra-hard materials like diamond, hard metals, diamond-like carbon and ultra-hard coatings for tribological applications and the selective ablation of thin films on various substrates. ALPS operates a «Fiber and Fiber Lasers Center of Competence» together with the Institute of Applied Physics at the University of Bern. This center of competence started its activity in 2009 and runs fiber-technological equipment for fiber prototype drawing, fiber characterisation, fiber cleaving, fiber tapering. Contact: Prof. Dr. Patrick Schwaller, Head of ALPS, patrick.schwaller@bfh.ch
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F O C U S | lightwa v e of the future
Gwatt: where laser professionals develop new ideas From September 2 – 6, 2012, the International Conference on Advanced Laser Technologies ALT12 will be held in the Gwatt Center at Lake Thun. Scientists from all over the world will be presenting their latest research findings and demonstrating the opportunities that laser technology has to offer to industry.
From the innovative idea to the marketable product
Prof. Dr. Patrick Schwaller Head of ALPS at BUAS-EIT Photo: BUAS-EIT
Von der innovativen Idee zum marktfähigen Produkt
STI - We support innovation The Foundation for Technological Innovation offers financial support to founders of start-up companies in the form of a long-term and interest-free loan. The Foundation promotes technological innovation with economic potential.
STI - Wir unterstützen Innovationen
The renowned Russian General Physics Institute in Moscow launched the first ALT Conference in 1993, and since then these have been held annually around the globe, receiving great acclaim along the way. This year it is Switzerland’s turn to be the host country and welcome foreign researchers to the shores of Lake Thun.
Glimpse behind the scenes This year’s organisers are researchers from the Institute for Applied Laser, Photonics and Surface Technologies (ALPS) of the Bern University of Applied Sciences in cooperation with their Russian counterparts. Thanks to their international connections, they were able to attract renowned researchers from the USA, France, Germany, Japan, Russia and Switzerland for the plenary lectures. In addition, other speakers will be giving talks that will offer an excellent overview of the state of research in laser
Die Stiftung für technologische Innovation gewährt Gründern von Start-up-Firmen eine finanzielle Unterstützung in Form langfristiger zinsloser Darlehen. Gefördert werden technologische Innovationen mit wirtschaftlichem Potential. www.sti-stiftung.ch
High-temperature ellipsometer at the ALPS Institute of the BUAS-EIT Photo: BUAS-EIT
technologies and their applications. The scientific conferences will be divided into various thematically-linked sessions. The more fundamental themes such as biophotonics, non-linear optics, photo-acoustics or terahertz laser sources and their applications will be dealt with, and there will also be sessions aimed specifically at people from the world of industry. Here the focus will be on laser systems and fiber lasers, laser diagnostics and spectroscopy, micro-and nanophotonic appliances and components as well as special laser-material interactions and process technologies. The poster session will take place on the large sundeck of the MS Stadt Thun, one of the largest motor boats on Lake Thun. This will give participants the opportunity to discuss scientific findings and exchange views in elegant surroundings. Contact: > patrick.schwaller@bfh.ch > Further information: www.alt12.org www.alps.ti.bfh.ch
F O C U S | lightwa v e of the future
The Janus-faced aspects of applied research There has been a long tradition of bottom-up co-operation between BUAS-EIT and the Institute of Applied Physics of the University of Bern in the area of lasers and laser materials interaction, despite a slight undertone of opposition from the «purist» corner. Researchers working on applied projects quickly realised that a successful solution to an applied research task has two complementary sides; namely, an understanding of the basic processes as well as the ability to apply them.
Dr. Valerio Romano Professor of Applied Photonics Head of the Applied Fiber Technology Group Photo: BUAS-EIT
Universities are responsible for the basic understanding of knowledge, a task that reflects their expertise in fundamental research. Universities of Applied Sciences, on the other hand, are responsible for applying this basic knowledge. The tasks complement each other. Like the Janus face, each one looks in a different direction; the Universities looking back at fundamentals, the Universities of Applied Sciences looking forward towards the social and industrial relevance of an application. This can be exemplified by the research on optical glass fiber that was once used mainly for optical communication, while today it is a key element of many modern lasers both for generating laser light and delivering it to the workpiece.
Infrared image of the active fiber in a ytterbium fiber laser. Although the fiber emits a 10 Watt output, it doesn’t need to be cooled. To demonstrate this more clearly, it has been loosely wound around a plastic roll Photo: IAP Bern
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Co-operation works better when tasks are divided correctly Co-operation between the Institute ALPS at the BUAS-EIT and the IAP at the University of Bern has become much closer. One of the fruits of this co-operation is the joint Centre of Competence for Fiber and Fiber Laser. This is made up of two laboratories; one at the IAP in Bern and the other at the BUAS-EIT in Burgdorf. Tasks are divided according to competence. While the IAP carries out fundamental research on fibers and comes up with designs for new fiber laser systems, the BUAS-EIT examines how these can be integrated into machines. The co-operation goes much further than in other similar projects. Though the research tasks are separated and adapted to the strengths of the two institutions, the project leadership is undertaken in close collaboration with representatives from both laboratories, or by a person who operates in both institutions. Both teams also run a fiber drawing tower at the IAP, which is where they work on producing prototypes of original, microstructured glass fibers in co-operation with industry. At present many of the of the laser systems under examination are being produced with commercially available glass fibers, but their own glass fibers should be ready for use in the foreseeable future. Other joint activities in the area of education are also in the pipeline.
Preform of a microstructured optical glass fibers Photo : Silitec SA
Building on sand is not always the worst idea One of the projects being run by the two institutes is «built on sand», though this is not meant to be understood quite in the same way as in the well-known expression. The story begins with a small, creative company from Boudry, called Silitec. In an effort to cut down on costs, this company began searching for ways of producing optical glass fibers more cheaply without affecting the quality of the product. They managed to develop and then patent a process whereby the manufacture of non-critical parts of the fiber preform is based on quartz sand. This reduces the costs and stimulates the imagination of researchers! This method makes it very easy to produce microstructured fibers. The structures replace the simple refractive index difference of traditional glass fibers, and allow light to be transmitted in the fiber core. Such fibers are based on a brilliant idea that researchers from MIT had in the late 80’s; namely the photonic crystal effect. More specifically, these fibers can actually implement a characteristic which is highly relevant for materials processing. Given the appropriate structure, the core can be enlarged without losing beam quality. This is of interest in so far as it allows light to be transported with far fewer non-linear effects. It would, of course, be ideal to be able to enlarge the core diameter to a few hundredths or even tenths instead of a few thousandths millimetres. If you do this with a traditional fiber, you end up with a choice between two evils: either the beam quality suffers, or the radiation can no longer be guided in the core at bending points and escapes from the fiber. This is where microstructured fibers can be of help. There are special hole patterns around the core that facilitate its enlargement without any loss of beam quality during delivery transportation (photonic crystal and leakage channel fibers).
Infrared image of a ytterbium fiber laser Photo: IAP Bern
Passive today … Passive fibers of this kind have been developed by the IAP in co-operation with the company Silitec, and then tested and successfully applied by the BUAS. They lay the foundation for the possible integration of laser technology into machinery, allowing more freedom and flexibility of design through flexible beam guidance as well as greater eyesafety for the user. … Active tomorrow And what about active fibers? Active fibers are fibers in which the core is doped with a material that allows laser light to be generated or amplified within the fiber core. These should also be able to profit from the sand method. The necessary doping material can be added to the quartz sand in powder form. This would result in a fiber with a structure that, at present, cannot be achieved by traditional methods, and all within a matter of hours rather than weeks. The IAP has proved that this simple principle actually works. The losses are higher than anticipated but we are on the right track. Contact: > valerio.romano@bfh.ch > Further information: www.alps.ti.bfh.ch www.iap.unibe.ch
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F O C U S | lightwa v e of the future
Ultrashort and small Ultrashort in the jargon of laser machining means that the laser radiation is only applied for an extremely short time to produce very small structures. Do you need a hole that is thinner than a strand of human hair? Maybe you require surface structures with dimensions that are even smaller than 1/10mm, or perhaps cut pieces of similar dimensions? In the laser micro-processing laboratory, these and other wishes can be fulfilled using laser systems with ultrashort pulses.
Swiss topography in copper and detailed images of the Eiger, Mönch and Jungfrau mountains Picture: J. Zürcher, BUAS-EIT
Dr. Beat Neuenschwander Professor of Applied Laser Technology Head of the Laser Surface Engineering Group Photo: Andreas Marbot
What does ultrashort mean? Ultrashort laser pulses are «laser flashes» that last only a matter of pico or femto seconds. Light takes about 1.3 s to cover the distance between the earth and the moon. In 10 picoseconds it covers 3mm, and in 200 femtoseconds just about the thickness of a strand of human hair. In other words, here we are talking about an unimaginably short time. Because of the ultrashort pulse duration, theses pulses show, even at a low pulse energy level, outstanding peak powers that can amount to several GW’s, which is more than that of a nuclear power station although, of course, only during this extremely short time. Advantages The short exposure time means that the energy is not only precisely deposited locally, which is a general feature of laser radiation anyway, but it does not then flow into the surrounding area. This makes it the perfect tool to evaporate
the material, and practically all materials can be treated with these pulses in a way both precise and that minimises theheat-affected zone. This does away with the often tiresome post-processing of parts that have been treated with a laser, and leads to an essential increase in precision.
Relevant to industry While ultrashort pulses were only relevant in an academic context 10 years ago, today the situation has changed radically. The arrival of industrial-strength laser systems has boosted industry’s interest in applications. This has opened new perspectives, especially for Swiss companies with a tradition in micro- and precision engineering. Possible areas for application could be, for example, in mould-making, embossing templates, tribological surfaces, laser-drilling in nozzles and micro-cutting, to name but a few. Other materials that are generally considered to be more difficult to process, such as glass or crystal, very hard materials (hard metals, polycrystalline diamond), ceramics or even layered thin films (such as thin-film solar cells) can be machined using ultrashort pulses.
Micro-dino with pattern Photo: B. Joss, ALPS BUAS-EIT
Challenges While they may be fascinating in themselves, the fact is that, in practice, ultrashort laser pulses face competition from other processing methods. Only when their use finally results in money being saved or made for the company will this technology be applied by industry. In various projects (CTI, direct commissions and student project papers), we examine the use of ultrashort laser pulses for industrial processes. Besides the actual process development, the focus is also strongly on increasing efficiency. Results from our group’s work on this clearly show that the material removal rate pro laser energy can be maximised when moderate
pulse energy is applied. We have also developed structuring strategies that guarantee a minimal surface roughness (e.g. R a <100nm with copper) at very high precision. Additionally, our findings show that shorter pulse durations lead to higher ablation rates for most materials. This advantage, however, needs to be measured against the higher system prices. In order to remain close to maximum possible process efficiency at the high average powers necessary for high throughput, either a large focus diameter, fast-moving rays or parallel processes need to be employed. The first variation runs the risk of delivering less precision, the second is hampered by the limits of today’s beam guiding systems, while the third makes completely new demands on the optical components being used. On top of that, the mechanical axes have to be synchronised with the laser pulse train if they are to work at the highest possible precision; ie. the laser works as a master and the axes as slaves. We value co-operation when attempting to surmount challenges like these, be it within our department (for example, with the Institute for Mechatronic Systems) or with external institutions such as the Institute of Applied Physics at the University of Bern, or the Institute for Product- and Product Engineering at the FHNW. We are convinced that this is how we can make our contribution to establishing ultrashort pulses in Swiss industry. Contact: > beat.neuenschwander@bfh.ch > Further information: www.alps.ti.bfh.ch
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Micro-dino made of sheet steel (100 micrometers thick) Photo: B. Joss, ALPS BUAS-TI
TUX, grayscale image translated in height information, structured in copper with ps-pulses Figure: B. Jäggi, BUAS-EIT
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F O C U S | lightwa v e of the future
25 years of collaboration: a Russian Swiss success story This year’s International Conference on Advanced Laser Technologies (ALT12) returns to Switzerland, exactly ten years after its first successful organisation in the Bernese Oberland. The conference builds on 25 years of intense research collaboration between the Russian Academy of Sciences, the University of Bern, and a dedicated team of researchers at BUAS.
It is exactly 10 years since the ALT02 conference was held in the town of Adelboden, a famous tourist resort in the centre of the western Bernese highlands. The conference was the tenth in a series of events dedicated to the advancement of the theory and application of laser technology. The prestigious series was established by the Prokhorov General Physics Institute of the Russian Academy of Sciences in 1993. The institute was named after Nobel laureate Alexander Mikhailovich Prokhorov, who received the Nobel Prize for his research in the field of quantum electronics in 1964. This year’s ALT conference returns to the gate of the Bernese highlands – the historic city of Thun – bringing together leading scientists and researchers from all over the world.
Successful partnership since 1987 The organisation of the ALT conference is only the latest event in a long and successful history of joint activities between Russia and Switzerland: Exactly 25 years ago, in 1987, a first collaboration was established between the General Physics Institute in Moscow and the Institute of Applied Physics in Bern. The collaboration aimed at exploring new ways of developing and processing laser materials. The laser material of greatest interest to the IAP at that time was erbium-doped crystal. This material made it possible to generate laser radiation in mid-infrared (i.e. at 3 micrometer) wavelength. Light of this wavelength is absorbed very efficiently within one-thousandth of a millimeter in water, and hence in human tissue; it can therefore cut tissue efficiently and very precisely at low energy and with minimum heat-affected zone. Prof. Weber, at that time head of the laser depart-
Sergei Pimenov and Valerio Romano Photo: courtesy of Sergei Pimenov, GPI RAS
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3x3 array of graphitic micro-channels formed in a 0.68-mm-thick single crystal diamond plate using 1-ps-pulses (from the current project).
ment at the IAP, was investigating the use of laser radiation in medicine. These interests coincided with the interests of Prof. Konov and Prof. Shcherbakov at the GPI, which resulted in fruitful joint work in the study of laser interaction with human tissue, as well as the spectroscopic analysis of laser materials, for the purpose of generating those wavelengths. In 1996, this initial collaboration led to the start of a joint research project funded by the Swiss National Science Foundation. The project was a great success and institutional partnership projects followed, facilitating regular exchange visits between Russia and Switzerland. Recently, the General Physics Institute in Moscow, the Institute for Single Crystals (Ukraine) and Institute for Applied Laser, Photonics and Surface Technologies at BUASEIT launched a new Swiss National Science Foundation project, which is led by Prof. Valerio Romano at BUAS-EIT.
Advances in ultrashort-pulse laser technology The present collaboration between Russia, the Ukraine and Switzerland forms a continuous line of research from the activities in the past. The joint SNF project, which is due to be completed in 2012, springs from the recent interest in ultrashort-pulse laser technology. The project aims at exploring new possibilities in material processing with ultrashort pulses required for applications in photonics, data storage, micro-mechanical and micro-optical devices. Ultrashort laser pulses, for example, can be used to produce inscribed «wires» inside diamond for electronic or photonic applications. For this purpose, a variety of advanced optical materials including diamond, sapphire, lithium niobate, and nanocrystalline films of silicon carbide (nc-SiC) are currently being studied. A particular goal of each potential application is to demonstrate how much the material properties can be changed by only ‹small› changes induced by ultrashort pulses in micrometer- and submicrometer-sized regions of transparent materials.
SEM picture of two holes into human hair. Photo: Courtesy of Prof. W. Lüthy, IAP, University of Bern
Joint research activities in the project focus on the synthesis of nanocrystalline SiC films, the investigation of structure and optical properties, as well as laser modification of crystals and thin films. Ultrashort-pulse laser technology will be the subject of intense interest in the research community for a long time to come. And there is little doubt that the Russian-Swiss partnership will continue to be at the forefront of these developments. Text: Patrick Studer Contact: > valerio.romano@bfh.ch beat.neuenschwander@bfh.ch > Further information: www.alps.ti.bfh.ch
Two-dimensional structure (arrays of craters) with the period of 4 µm in diamond to change its optical properties Photos: Courtesy of GPI RAS
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F O C U S | lightwa v e of the future
Cutting metal with laser is like cutting through butter Because of their ability to cut through 25mm thick metal plates, lasers are going to play a major role in the future of metalworking. However, depending on the metal, the plate thickness and the wavelength, the quality of the cut is not always satisfactory and the workpiece needs some reworking afterwards. The Institute ALPS at the BUAS-EIT and its partners are looking for solutions to this problem. Figure 2: Measurement structure with vacuum chamber Photo: BUAS-EIT
Dr. phil. nat. Marc Schmid Senior Researcher ALPS, BUAS-EIT Photo: BUAS-EIT
Lasers are the ideal tool when it comes to cutting plateshaped metals because they produce complex forms, work quickly and precisely, and are profitable even in small batches. In an effort to increase the quality of the cut, researchers from the Institute for Applied Laser Photonics and Surface Technologies (ALPS) at the BUAS-EIT got together with colleagues from the Institute of Applied Physics (IAP) from the University of Bern as well as with an industrial partner, Bystronic AG in Niederönz. Their aim was to optimise the cutting process through simulation.
Figure 3: Liquid aluminium in the vacuum chamber Photo: BUAS-EIT
Ellipsometry as basic measurement Anyone wanting to achieve meaningful simulations first needs to understand the optical material properties. For example, during the laser-cutting process, a thin layer of liquid metal forms at the cut front, which mainly absorbs the energy of the laser beam. For a simulation to work, one needs to know how much of the laser beam’s energy is absorbed by the metal and how deep the beam penetrates into it. Consequently, refraction and absorption indices of the metal in its liquid form are important indicators. These material properties are only known in the case of a few pure metals such as silver, gold or mercury in their liquid phase, but not for metal alloys like steel, which is widely used by the industry. Therefore one of the aims of the project was to measure the complex refraction index of liquid metals and alloys. This was achieved with the help of ellipsometry, a method which has been known about for more than a century. The basic idea is that a defined polarised laser beam hits a sample at an angle φ and is reflected (see Figure 1). The polarisation of the laser beam changes through the reflection on the material’s surface. Generally, elliptically polarised light forms after the reflection, hence the name ellipsometry. By analysing the change of polarisation after the reflection, one can calculate the optical properties of the material. The theoretical background of ellipsometry has been well investigated , and the method is routinely used in the analysis of solids and thin layers. The crux of the measurement When determining the optical properties of liquid metals, the main challenge is the handling and measuring of liquid metals. On the one hand, the surface (topology and roughness) of the metal samples changes continuously when it is heated and liquefied. On the other hand, every change on the surface has an effect on the reflected beam, which has to be taken into consideration when applying ellipsometry. In order to avoid unwanted reactions between the liquid metal surface and atmospheric gases, we constructed a vacuum chamber (Figure 2) for the experimental setup that achieves a vacuum of about 105 mbar. Additionally, the vacuum chamber can be flooded with an inert gas such as argon as well. The vacuum chamber has various viewports to which
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the ellipsometer arms and other measuring equipment can be attached. The ellipsometer itself, which was specially constructed for this experimental setup, is made up of a source and a detector arm. A super-luminescent LED with a wavelength of 1070 nm and a bandwidth of about 100 nm serves as the light source, and a fiber-coupled spectrometer serves as detector. The optical components of the ellipsometer, for example the polarisers, of both the ellipsometer arms are mounted on motorised rotating mounts, which can be controlled thanks to software we have developed ourselves. One important part of the experimental setup is the heating. To achieve high temperatures – the steel under examination only begins to melt at 1660˚C – the experimental setup has two heat sources. An electrically driven, adjustable heating plate allows an adjustment of the metal samples during the heating phase. This allows the samples to be heated to about 1000˚C. Materials such as aluminium and silver melt at these temperatures. The second heat source is a fibercoupled laser diode that emits at 800 nm and achieves an output power of roughly 350 W. In this way, metals such as copper, which melt at 1060˚C, or steel can be liquefied.
New questions for research During our experiments, we were confronted with questions that were entirely new. We needed to clarify how curved surfaces affect the ellipsometry, because the rectangularshaped sample became semi-spherical during the melting process (Figure 3). On top of that, slag from the liquid metal resulted from contamination of the sample in the vacuum chamber. This slag needs to be removed before the measurement takes place. A skilful heating strategy, however, allows the slag to be broken up and shoved to one side. To date, simulations with our results have been promising. Currently we are working on measuring further metals and alloys in their liquid states so that we can extend the range of applications of laser processing. Contact: > marc.schmid@bfh.ch > Further information: www.alps.ti.bfh.ch
Figure 1: Principle of ellipsometer measurement: linear polarised light beam changes polarisation after reflection on the sample surface. The reflected beam is analysed using λ/4-plate and polariser Graphic: BUAS-EIT
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F O C U S | lightwa v e of the future
Harvesting the sun more efficiently
Why are interconnects necessary? The most important performance determining factor beside the absorber material is the electrical connection of the solar cell. While the back contact can be a thin metal film, the front contact must be transparent to the sunlight. Often, transparent conductive oxides (TCO) layers like aluminumdoped zinc-oxide (Al:ZnO) are used for this purpose. A problem arises when the area of the solar cell is scaled up: the electric current scales with the cell area (L x W) but the TCO cross section scales with the width of the cell. Consequently the current density in the TCO increases and so do the Ohmic losses.
Thin-film photovoltaic (PV) technologies are gaining ground despite their lower efficiency compared to silicon wafer-based technologies. This trend is mostly economy-driven and based on key advantages inherent to the technology.
Dr. Andreas Burn Senior researcher ALPS, BUAS-EIT Photo: BUAS-EIT
The advantages of thin-film PV technologies are obvious: The production process for thin-film PV cells can be scaled up easily to streamlined, high-volume manufacturing, and the amount of absorber material needed (1-3 µm thick layer) is much lower than for crystalline silicon cells. This leads to dramatically lower fabrication costs per Watt peak power in high-volume production. Thin-film PV cells show a greater efficiency in diffuse weather conditions and high temperatures than other materials. The enormous potential of the thin-film PV market is best illustrated by the projected annual growth rate between 2009 and 2020, which is at a spectacular 24 %.1
Innovation in the thin-film solar industry Despite these advantages, cost reduction remains a major challenge for companies trying to make the technology profitable. Let’s take the thin-film solar industry as a case in point. Continuous developments need to address ways of producing more efficient solar modules at lower cost with less energy. Besides the obvious – the optimisation of the absorber material – there is also an enormous potential for improvement in module patterning, i.e. the scribing of thin films between production steps in order to build electrical interconnects (see «why interconnects are necessary»). Solneva Swiss Solar Tools SA in Aarberg is a young and highly innovative company which is entering the global market for industrial laser scribing machines. Solneva’s unique concept rests on their core competencies in machine and laser integration, controller development, and application know-how. Their machines are fast, reliable, energy efficient and have a small footprint.
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In the scribing process, the thin films are removed selectively along narrow lines on the panel. Three scribes per sub-cell strip are necessary and their arrangement allows a back-to-front electrical connection (see Figure 1). One industrial-sized solar module can contain hundreds of scribe meters. Therefore, it is necessary to develop highly reliable scribing processes. The zone between the three scribes is a non-productive area, also termed «deadzone», which has to be kept as small as possible. Laser scribing addresses these problems and is rapidly emerging as one of the most significant processes for photovoltaic elements production. It enables high-volume production of next-generation thin-film devices, surpassing mechanical scribing methods in quality, speed, and reliability.
scribing for the P2 and P3 process. Mechanical scribing produces up to 500 µm wide dead-zones mainly due to chipping of the thin-films, which broadens the scribe substantially. Calculations have shown that module efficiency can be increased by 4 % if the dead-zone width is reduced to below 200 µm. Scientific articles published in the past few years gave rise to the assumption that high-quality CIGS laser-ablation could be achieved using picosecond laser pulses.
In thin-film solar modules, interconnects are typically formed from three scribes (lines where the films are selectively removed) that are made between thin film deposition process steps in industrial solar module production. An optimisation process yields the best compromise between the reduction of Ohmic losses and the total active area loss caused by the non productive «dead zone» at the interconnects. This optimisation process obviously profits from a reduction of the dead zone.
Laser scribing in CIGS solar modules Solneva SA developed machines and processes for structuring amorphous and micromorph silicon (a-Si, µ-Si) thin-film cells and is now working on a solution for Copper Indium Gallium (di-)Selenide (CIGS) cells. CIGS absorberbased products are the fastest-growing branch in the thin-film family thanks to their favorable properties. But there is one important drawback: CIGS is a particularly difficult material for laser-structuring and there is no industrial laser-based solution available for module patterning to date. Manufacturers fall back on mechanical needle Figure 2 Electron Micrograph of the scribing region on a functional mini-module. On this mini-module we demonstrated the feasibility of a dead-zone <200 µm. Photo: J. Zürcher
Figure 1 Cross-section through an interconnect with the three scribes P1-P3 made between the three main process steps. The P1 scribe is applied on the molybdenum-coated sheet glass substrate. Then the CIGS layer is grown on top followed by the P2 scribe which removes the CIGS and exposes the moly back contact. In the third step, the front contact – a transparent conductive oxide (TCO) layer – is deposited and patterned in the P3 scribing process. Together, the three scribes form an electrical back-to-front contact as indicated by the dashed arrow. Figure: A. Burn
Increasing the TCO thickness is not an option as this increases optical transmission losses. A solution to the problem is the subdivision of the solar cell into strips (sub-cells) that are connected in series.
Research collaboration with the industry In 2010, Solneva SA started collaboration with the ALPS institute at Bern University of Applied Sciences to benefit from our expertise in short- and ultrashort pulse material processing. The collaboration is funded by the Commission for Technology and Innovation (CTI). The first results of the study are very promising. were able to prove the existence of stable process windows for all three process steps P1-P3 with picosecond laser sources. We further demonstrated that dead-zone widths smaller than 200 µm can be realis ed on functional mini-modules
using these processes for structuring. An electron micrograph of the scribing zone on the finished mini-module is shown in Figure 2. The ultimate goal of the project is to develop and build a working prototype of an industrial all-laser scribing machine that is adapted to the specific needs of the industry. Contact: > andreas.burn@bfh.ch > Further information: www.alps.ti.bfh.ch
«Thin Film Photovoltaic Cells Market Analysis to 2020», GB
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F O C U S | lightwa v e of the future
Joining Forces: Doctoral Research at BUAS and University of Bern Dereje Etissa, a PhD student from Ethiopia, is currently working on a research project aimed at minimising fiber scattering losses. Parts of his doctoral thesis on the material improvement of fiber optics are carried out jointly by BUAS and the University of Bern.
Dereje Etissa PhD Candidate at Institute of Applied Physics, University of Bern Photo: Institute of Applied Physics (IAP), University of Bern
Dereje Etissa received his Bachelor degree in physics from the University of Addis Ababa and after a few years of work experience as a physicist in the Ministry of Education in Ethiopia he continued his studies at the Institute of Radiation Physics at the University of Stuttgart. There he received his Master of Science in Sensor Technology and in Physics. After the successful completion of his Master degrees in Stuttgart, Dereje Etissa took up a research position at EMPA in Switzerland, working in the field of exhaust gas soot particle research, before he was offered a PhD scholarship at the Institute of Applied Physics of the University of Bern.
Rare-earth activated optical fibers Dereje Etissa is currently conducting his doctoral research in the framework of an ongoing project at the Institute of Applied Physics. This is aimed at studying and improving the production of rare-earth activated microstructured optical fibers by the granulated silica method for laser applications. The results of his present research will form the basis for a broader project in the same field that will lead to fibers with large cores for fiber lasers and amplifiers. Rare-earth (e.g. neodymium, erbium or ytterbium) doped optical fibers are the active elements for fiber lasers and amplifiers; they are incorporated in their trivalent ionic form into the glass matrix of the fiber core where they act as active laser media. The core of a fiber is the region in which the light is guided, i.e. it is responsible for the waveguiding effect. The non-uniformities and material impurities of the core are responsible for the fiber losses through scattering and absorption. Two different methods are used for the production of the doped materials: i) granulated oxides of the different species are mixed, put into adequate silica tubes and directly drawn to fibers; ii) the sol-gel method is used to produce a porous glass that is already doped with the desired dopants, densified and then milled to a granulate. Method ii) leads to improvements in homeogeneity and hence to fewer scattering losses.
Production of doped granualted optical fiber core material using CO2-laser at the Institute of Applied Physics, University of Bern. Photo: IAP Bern
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Minimising fiber scattering losses Dereje Etissa has chosen the sol-gel method because it is very attractive if one wants to draw fibers with complicated optical fiber geometries including, multicore or microstructured fibers. In both methods, after the inclusion of dopants into a glass matrix, milling and melting is applied to obtain homogenous core material. This helps to avoid fluctuation of refractive index and scattering losses. Typically a fiber is then drawn by appropriately filling a glass tube with the previously produced granulated silica (doped silica for the core, undoped for the cladding and empty capillaries for the holes) and evacuating the preform while heating it in the drawing tower’s furnace. The optical properties of the fabricated fiber will be characterised by different analytical techniques (energy dispersive x-ray, electron probe microanalyses, x-ray diffraction analysis and refractive index profilometry). In this work, particular emphasis is given to the minimisation of fiber scattering losses.
Refractive index profile of Yb+3, Al+3, P+5 doped optical fiber. Figure: IAP Bern
Dereje Etissa does not know yet where his research will take him, but he does know that his passion for physics will guide his way wherever he goes – in Switzerland, Europe, or, indeed, Ethiopia. Contact: > dereje.etissa@iap.unibe.ch > Further information: www.iap.unibe.ch
F O C U S | lightwa v e of the future
Swept-Source laser sources at the BUAS OptoLab In the world of medicine, Optical Coherence Tomography (OCT) is a reliable procedure in the areas of ophthalmic examinations, skin disease and early tumor diagnosis. Researchers at the BUAS OptoLab are taking this to a new level with Swept-Source OCT, significantly faster and potentially cost-efficient laser systems for which they are developing miniature solutions.
Since researchers from the Massachusetts Institute of Technology (MIT) developed the concept of Optical Coherence Tomography in the early 1990’s, it has become firmly established as a diagnostic tool in medicine. OCT supports the measurement of the inside of light scattering samples. Biological samples, which scatter light quite strongly, are particularly suitable for examination using OCT. «This allows non-invasive, 3-D images of live tissue to be created with a resolution of just a few micrometers», says Professor Christoph Meier, Head of OptoLab. OptoLab is a joint group made up of researchers from the Institutes for Applied Laser, Photonics and Surface Technologies (ALPS) and Human Centered Engineering HuCE. «In contrast to the ionising radiation of x-ray tomography, OCT only emits a low light intensity, which does not affect the biological samples in any way.»
Breeding ground for new laser applications Not only is OptoLab a specialist in OCT, it is also performing innovative pioneer work in this field. One such area is the so-called Swept Source Laser (SSOCT), which engineers from OptoLab and MicroLab have integrated into an OCT system as part of a research project with the firm EXALOS AG in Schlieren. EXALOS first became known through its design, development and distribution of super-luminescent light emitting diodes (SLED’s), hi-tech products that are used in various markets. The firm has an interest in semiconductor lasers that can be quickly tuned, as their wavelength can be altered rapidly and precisely with the help of micromechanic elements. These semiconductors present a good signal-to-noise ratio and are ahead of the competition when it comes to
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speed. Swept Source OCT systems are made up of such a fast tunable laser source, an interferometer, the differential amplifiers and an imaging software. «The current coherence length determines the measuring range within which Swept Source measuring methods like OCT can be used for interferometric measurements,» explains Tim von Niederhäusern. He examined swept source lasers as part of his Master Thesis, and came up with a new and original measuring method that could characterise the laser at full operating speed. Researchers at OptoLab make good use of a broad spectrum of competence available at the Institute for Human Centered Engineering (HuCE), especially in the areas of hardware algorithms, microelectronics, signal processing and control engineering. Applications for swept source laser have been demonstrated especially in ophthalmology; for example, in the Lasik technique (see article on Page 23). The use of swept source laser outside the world of medicine has also been recognised; for example, in material testing, where a significantly higher resolution can be achieved than with ultrasound. «They are also being used for strain measurement to monitor and guard buildings and bridges, and, more recently, for offshore windmills, an economically attractive market,» explains Professor Christoph Meier.
Hi-tech with potential for the future Christoph Meier recognises the potential of improving the measurement system to achieve an even higher speed and a wider range, especially in the areas of data acquisition.
Christoph Meier Professor of Optics, Head of OptoLab, and scientific researchers Photo: BUAS-EIT
3-D, non-invasive imaging methods are growing more and more important around the world. «What’s needed is a monochromatic laser, a large tunable spectral range as well as a high sweep frequency. The laser must also be easily focused or, in other words, it must be possible to connect it to a single mode fiber,» summarises Christoph Meier. When you leave the breeding ground that is the OptoLab in Biel/Bienne, you won’t have to worry about getting a job. The market is crying out for well-educated engineers in optical technology. One example is that of former Master student, Tim von Niederhäusern, who is now bringing his ideas and creativity to life for our industrial partner EXALOS. The firm launched its new, high performance swept source laser sources in January. Featuring individually adjustable tuning ranges of up to 200 nanometers, and wobble frequencies of from 2kHz to 150 kHz in a 1550 nanometer spectrum, the new swept sources offer flexible system designs for application in fiber-optical processing and optical imaging in the frequency range. In order to maintin a global
OCT measurement of the iris and lens of a pig's eye at OptoLab, processed with a speckle-reduction-algorithm Photo: OptoLab BUAS-EIT
lead in the future, the EXALOS team is relying on its skilled research colleagues. Co-operation with the OptoLab is, therefore, about to go to the next level. Original text in German by Elsbeth Heinzelmann CST Communication Science & Technology GmbH
Contact: > christoph.meier@bfh.ch > Further information: www.alps.ti.bfh.ch www.huce.bfh.ch www.arcoptix.com www.exalos.com
BUAS-EIT’s OptoLab The OptoLab at the BUAS-EIT comprises a joint research group from thei Institutes ALPS and HuCe. Its core competence is optical measurement techniques, particularly optical coherence tomography (OCT), as well as opto-electric and opto-mechanical design. The team has the necessary infrastructure available to be able to carry out feasibility studies or test measurements in optical sensors within a very short time scale. In January 2005 engineers from OptoLab and from the University of Lausanne founded the spin-off firm Arcoptix as a joint project, which offers various optical measuring and analysis tools.
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“Exciting technical projects”
Z-LASIK – eye surgery without blades LASIK (laser assisted in situ keratomileusis) is a laser operation on the eye that corrects vision impairment. At present, it is the most commonly used procedure to achieve sharp vision without the aid of spectacles or contact lenses. The guiding principle of LASIK is that it changes the form and refractive power of the cornea and therefore eliminates vision impairment.
Nora Kleisli, Business IT, Business Engineer
Imagine that your bathroom mirror could tell you where and when it is going to rain today. You would know what clothes to put on, even before you’re fully awake. Mirrors can’t do that yet, but they might be able to soon. Help shape the future with us and develop innovative solutions that inspire our customers! Information on our trainee programme, internships and job vacancies: www.swisscom.ch/students
LASIK eye correction is performed in two steps. Firstly, the doctor creates a thin film, known as a flap, over the cornea and then folds this to one side. A femtosecond laser is most often used at this point as it guarantees precision and safety. Using the second laser, known as the excimer laser, the tissue under the flap is then removed. The flap is afterwards repositioned and grows back without stitches.
Z-LASIK- the latest generation The FEMTO LDV TM being produced by Ziemer works exclusively with a very high frequency of over 5 million pulses per second as well as extremely low pulse energies. Very small and regular laser spots can therefore be placed side by side, resulting in a very smooth tissue section. The low pulse energy also preserves the cornea. Furthermore, the precise and thin Z-LASIK flap cuts of between 90 and 140 um thickness allow a cut where the cornea is thinner or in the case of greater vision impairment. Over one and a half million Z-LASIK operations have been carried out to date worldwide. It holds the record as the method that results in the fewest complications, and the post-operative recovery phase, known as «visual recovery», is also by far the fastest. The latest generation of Ziemer femtosecond lasers, FEMTO LDV Z-Models, is fitted with new improved technology, and also has a modular structure. The advantage of a modular construction is that it allows upgrades. In fact, all Z-lasers can be upgraded. As a result, customers can now not only order a laser system that is tailor-made to their needs, but also have access to enhanced functionalities without having to buy a new laser system. Other functions that are not yet available on the market, such as integrated imaging for cut monitoring (OCT based), or other surgical applications, can be added as upgrades. Femtosecond laser systems are among the technologically most sophisticated surgical instruments being used in ophthalmology, perhaps even in any kind of surgery. As
well as the robust production of femtosecond pulses (in one femtosecond, light covers a distance of only 300 nm), and the precise and speedy scanning, it also requires diffraction-limited, high-performance optics. It further needs steering hardware and software that is built with real-time capability and is technologically safety redundant. Other special features of Ziemer’s FEMTO LDV TM are a «a hand-held laser applicator, and a compact basis station» with integrated running gear, the only device which allows mobile application. Due to its highly complex nature, only the most highly trained staff, used to interdisciplinary work and international communication modes, can be employed in the development, manufacturing and distribution of this system. Clearly, Switzerland is capable of maintaining its cutting-edge position alongside international competitors. Text by Ziemer Opthalmology Contact: > info@ziemergroup.com > Further information: www.ziemergroup.com
Lorenz Klauser, Product Manager R+D, and Lukas Kohler, Product Manager HW/R+D with the latest FEMTO LDV Z model. Photo: Ziemer Ophthalmic Systems AG
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F O C U S | lightwa v e of the future
Fiber lasers: Processing material with glass fibers When fiber lasers were first discovered about 50 years ago, shortly after the first laser had been presented to the world, nobody really expected them to be put to any serious use in the area of industrial applications. The maximum performance emitted lay in the area of thousandths of a watt, and the fiber laser was deemed a curiosity, a toy for experimental physicists.
Dr. Valerio Romano Professor of Applied Photonics, Head of the Applied Fiber Technology Group Photo: BUAS-EIT
First laughed at, then considered suitable for work that doesn’t require finesse The research paid off. With an output of several kilowatts in continuous wave operation, displaying optimal beam quality and highest efficiency, continuous wave fiber lasers have become an alternative to conventional systems, even to the point of replacing them on the market. At present, fiber laser systems like these are being optimised for use in macro processing in areas like metal sheet cutting, hardening and welding. These are often applications that benefit from the good beam quality of the fiber laser at high average output. The new, smaller fiber lasers, which are easier to integrate and more efficient, are gradually replacing the dinosaurs of the first generation.
Micro processing: highest intensity for less ablation In many ways, micro processing makes more demands on lasers than macro processing. While for the latter high continuous power output and good beam quality are sufficient, micro processing needs low average power but very high peak intensities. This can be achieved by pulsing the light at a pulse duration in the area of picoseconds (1 ps is a millionth of a millionth second). In microprocessing applications fiber lasers are therefore pushed to their limit. This is because what is needed is not high average power, but very high peak power being emitted from a surface that is smaller than the cross-sectional surface of a strand of hair. It doesn’t take expert knowledge to recognise what the problem is: on the one hand,
the generated light of such high intensity is able to ablate steel or even diamond, on the other hand the same light should be generated and transported at the same time in a glass fiber laser without any side-effects (absorbtion or non-linear effects). This is a challenge. The company Onefive has taken up the challenge and is developing a series of fiber lasers for micro material processing. It is working closely with the University of Bern (IAP) and the University of Applied Sciences (ALPS, BUAS-EIT in Burgdorf) in the frame of a CTI project. The aim is to get the most out of the fibers in ways that are cost effective, efficient, and that allow easy integration into machinery. Onefive enjoys working with research institutes. Sometimes the universities don’t function the way industry would wish for, but diligence and skillful coordination has produced very positive results. The BUAS has wide expertise in
Photo: Victoria-Fotolia.com
the area of laser application development and has become an invaluable partner for companies like Onefive. Contact: > valerio.romano@bfh.ch > Further information : www.onefive.com
Institute for Applied Laser, Photonics and Surface Technologies We develop new methods and techniques for the energy- and material-saving production of materials and their analysis.
1 Lightwaves that are doped with the rare metal erbium can strengthen the light signals that are transmitted by way of glass fibers without the need of an electronic amplifier. (Source: T. Seilnacht, PH Luzern) 2 The laser beam is produced in a continuous wave operation using a constant supply of energy. The laser transmits a laser light of constant intensity. (Source: Technical Information, TRUMPF GmbH Ditzingen)
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ORIGAMI - Low-noise femtosecond laser modules Photo: onefive
Our core competencies are • Fiber technologies for laser applications • Material processing with lasers • Changes in the properties of boundary layers with heat or laser treatment • Application of thin films • Development of optical measuring systems for the
analysis, processes control and quality assurance • Materials and surface analysis • Topographic measurements in the µm and nm range We use our know-how to develop solutions jointly with our industrial partners in research and development projects. These solutions contribute to the efficient production of goods and ensure or improve their quality.
alps.ti.bfh.ch
F O C U S | lightwa v e of the future
ROFIN-LASAG: Pioneers in laser welding of copper When it comes to cutting, welding, drilling or ablating materials, ROFIN-LASAG, with headquarters in Thun, is one of the global leaders in lasers for high-precision materials processing. The company has done pioneer work with the GreenMix laser, which facilitates reliable and reproducible copper welding, an area which even today continues to pose a challenge to industrial applications.
The story of Swiss laser technology only really began in January 1965, when the company known as Watch Stones AG in Thun, producer of rubies for watch bearings, commissioned the University of Bern to research possibilities for drilling watch stones with lasers. 7 years later, a Laser Development Center was set up in Thun, followed by the company LASAG in 1974.
Non-ferrous metals: a hard nut to crack Their lasers are in demand all over the world in almost all areas of manufacturing industry. However, laser welding of copper materials continues to challenge the experts. All efforts to solve the problem to date have resulted in processes that were not efficient enough and had a low reproducibility. The challenge with non-ferrous metals is that, due to their high reflectivity at the common laser wavelength of 1 micrometer, the welding results can vary enormously, which reduces the level of processing reliability. Because a high proportion of the induced radiation is reflected, the metal hardly heats up at all. Yet a requirement for thermal laser material processing is the direct
interaction between focussed laser beam and copper surface, as the metal has to melt. Engineers at ROFIN-LASAG came up with the clever idea of merging a laser pulse of 532 nm wavelength (green) with a laser pulse of 1 micrometer wavelength (infrared). «Because the green wavelength is initially better absorbed than the infrared one, the copper surface heats up, the temperature of the copper rises and thus the absorption of both wavelengths is achieved,» explains the Head of Development, Dr Christoph Rüttimann. If the absorption values are high enough, the variations of the surface characteristics (e.g. oxide layers) are less notable. The clever solution lies in the amalgamation of both pulses: using the pure infrared on its own could mean that the copper surface doesn’t melt, whereas it is visible when the pure green is used. Merging the pulses results in a considerably enlarged molten pool.
Minimum investment for maximum effect To start with, a high intensity of the laser pulses is aimed at through use of a skilful process. The combined infrared and green beams warm the surface of the copper until the infrared absorption is high enough and the metal begins to melt. Then the pulse power is reduced. «Although only a little green is converted, the absorption of infrared is high enough during the melting phase and welding with infrared can continue,» says Christoph Rüttimann. The extension and the penetration depth of the weld spot depends on the length of the welding phase. At the end of the pulse, the performance can be shut down in a given time period, as this determines the cooling phase and, as a result, the metallurgical and mechanical properties of the weld. A comparison between welding done with infrared alone and with a mixture of infrared and green shows that the reproducibility of the welding is considerably higher when done with the combined model, and that no flaws appear. The innovative aspect of this is the converting module, the so-called GreenMix Add-on-Box. This takes over the conversion of the green at the output of the laser resonator, and looks after the programmable wavelength mix between 532 nm and 1064 nm via intelligent pulse shaping. The laser beam is safely fed into highly reflective materials like copper and precious metals through an optical fiber and a processing head, which ensures efficient use of the total laser energy available for the welding process. Precision welding on the tiniest diameters of 25 micrometers is suited for medical applications, for example for cardiac pacemakers, and in the electronics industry, for example for copper bonds or electrical contacts.
Welding laser in action Photo: uwimages-Fotolia.com
What makes it interesting for the user is the fact the ROFINLASAG system only needs one laser source to produce the wavelength mix, which has a positive effect on investment costs. Contact: > lasers@lasag.ch > Further information: www.lasag.com
The ROFIN-LASAG AG LASAG AG has been developing and producing industrial solid-state lasers for almost 40 years. Their products for precision cutting, spot welding, drilling and scribing are used in medical equipment, in electronics and precision mechanics as well as in the automotive and aviation industries. The October 2010 takeover by ROFIN-SINAR allowed the traditional Thun-based company to become even more dynamic and, in line with the company's vision, to be the most successful producer of solid-state solutions for precision processing.
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ROFIN-LASAG's solid-state lasers performing precision work on the smallest surface area. Photo: ROFIN-LASAG AG
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F O C U S | lightwa v e of the future
SILITEC – more efficiency and fewer costs thanks to sand Industrial manufacturers have only been using the high beam quality of fiber lasers for the last few years. Their high power density on the workpiece enables speedy processing when using suitably designed systems. Special fibers are necessary to produce suitable lasers, and this is where production has hit a barrier. The company Silitec in Boudry is in a position to offer a way over it.
The production of optical fibers is a delicate operation but it always starts with the so-called preform, which is equipped with the characteristics of the subsequent fiber. This cylinder made of quartz glass is coated on the inside. Using the Modified Chemical Vapour Deposition (MCVD process), gases are repeatedly fed through it and modified until the raw materials in the inner surface of the cylinder have melted, and layers with a different refractive index have been formed.
The trick with the sand The last 10 years have seen an increase in the performance of fiber lasers, during which time they have become a real alternative to solid-state lasers. On the negative side, however, non-linear disruptions such as inelastic scattering severely affect efficiency. A single-mode laser beam is necessary to evenly distribute the power of the light on the inside of the beam. Active Large Mode Area (LMA) fibers can enlarge the core diameter, afford a more exact control of the core and, especially, the refractive index, which has to be uniform and homogeneous. A microstructured fiber technique with the «stack and draw» method allows the beam to be evenly distributed and, in combination with the Multidrawing Method, a diameter of 60 micrometers. However, such sophistication is hardly possible when using a classic procedure like MCVD.
In 1978, Silitec was one of the first companies in the world to produce optical fibers. Today, their highly original sand technology enables them to produce optical fibers that perform at the highest end of the scale. Photo: Silitec SA
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This is why the company SILITEC, based in Boudry, is breaking new ground with its patented sand technology. A tube made out of silicone dioxide is filled with sand, which is, for example, doped with rare earth elements, particularly with ytterbium and erbium. Silitec engineers place a second tube, this time of larger diameter, over the first one and fill the space between the two with pure or doped sand. They then remove the inner tube, which leaves a good interface between the inner sand core and the outer sand layer which later make up the cladding. The Silitec team then heats up the whole structure and, at the same time, begins a pure gas treatment. This guarantees that all of the sand is glazed and that a solid preform results.
The need for flexibility «The sand method is a flexible process which allows the core to be doped with rare earth oxides, the difference in the refractive index to be perfectly set, and finally to achieve a larger core diameter,» explains plant manager Frédéric Sandoz. Sand technology also makes it possible to produce multi-core fibers, in which the Silitec team mount various doped core rods. «This process is particularly suited to achieving non-symmetrical structures, such as polarisation maintenance or an eccentric arrangement of the core materials.» Thanks to their new manufacturing method of using doped silicone dioxide powder, researchers from Silitec are breaking new ground in the area of manufacturing active fibers for laser applications. Now they are in a position to provide large and highly active cores with a very uniform refractive index without the need for expensive production equipment. «The index difference between the core and the cladding can be achieved in a smaller and more homogeneous way than with traditional methods,» says Frédéric Sandoz. This allows the realisation of fiber lasers which have a 74% higher degree of efficiency in relation to the initial pump
Preform for a microstructured fiber. The sand that has not yet been melted is visible in the upper part of the preform. Photo: Silitec SA
capacity. The production process is the key to the manufacturing of highly doped, large cores with a very high index contrast, and cost-efficient, high-performance Large-ModeArea (LMA) fibers with a single mode management. Original text in German by Elsbeth Heinzelmann CST Communication Science & Technology GmbH Contact: > info@silitec.ch > Further information: www.silitec.ch
SILITEC When today’s plant manager at SILITEC, Frédéric Sandoz, developed the first optical fiber with his fellow-workers in 1978, he became one of the first producers worldwide that dared enter this new territory. Since then, innovation has become a watchword, and the partnership with Professor Valerio Romano from the Institute for Applied Laser, Photonics and Surface Technologies at the BUAS-EIT has become an extremely important element of this philosophy. Today, the company has become a pioneer with its patented sand technology, a method which stands for high performance and cost-efficiency. SILITEC’s special optical fibers are used in the worlds of industry as well as in telecommunications, medicine, the military and aviation. They are equally used in measuring equipment and instruments, but are especially valued for client-specific applications
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interantional business
Well-prepared to start international business with Fit2GlobalizeTM Economic growth has shifted to the emerging economies. These new markets are also attractive to the many Swiss companies. At the same time, the opportunities in the enormous market potential are often accompanied by risks to which the companies in the traditional export markets are less exposed. To ideally examine the opportunities and risks associated with a market entry, the Market Entry Evaluation Method Fit2Globalize™ was developed in the Management Center of Bern University of Applied Sciences BUAS in a research project supported by the BUAS Department of Engineering and Information Technology research fund.
Jan Richard M.Sc., EMBA Management Center Bern
There are enormous opportunities for Swiss exporters in the emerging economies. The exports to the BRIC countries are expected to increase by 11% to 19% per annum. This means that exports to the BRIC states are expected to almost triple within seven years. By extrapolating these developments until 2030, the BRIC countries will make up a market share of nearly 45% of the Swiss exports1. In addition to the opportunities in the new markets, it is also important to examine the potential risks which could lead to problems when entering the emerging markets, such as legal security, bureaucracy or poorly developed logistics, as well as the lack of internal readiness to do business with the emerging markets. It is important to identify the potential risks in good time in order to be prepared for them and to be able to react correctly.
Fit2GlobalizeTM -Portfolio
+ Market Attractiveness
Dr. Paul Ammann Head of Program EMBA-IM Management Center Bern Photos: BUAS-EIT
The Fit2GlobalizeTM method helps companies to assess all the relevant factors associated with a market entry. Using this method, companies can process the relevant information in order to develop a country-specific market entry strategy. The method incorporates two dimensions: the external dimension shows the opportunities and risks in a foreign market, whereas the internal dimension demonstrates one’s own strengths and weaknesses with regard to international business. It is this latter dimension which is often underestimated: one of the strengths of this method is that it also clearly shows, apart from the potential of a foreign market, whether a company is actually ready to work at an international level. On the basis of the answers to two sets of 25 questions2, each pertaining to the market situation in a country and the internal situation of the company, the opportunities and risks, as well as the strengths and weaknesses are compiled. The questions related to the foreign market deal with the political, social, economic, legal and technological situation of a target country. The customer and competitive situation and the market potential are also the topics of the external analysis. Using the questions related
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2. Do homework
1. Develop Market
CHINA ITALY
3. Process as 4. Do not develop third level priority the market Readiness for + international business Diameter of the circle representing the market potential of a country
Source: Credit Suisse, Exportindustrie Schweiz – Erfolgsfaktoren und Ausblick, 2011 See www.fit2globalize.ch for the list of questions 3 SWOT: Strengths, Weaknesses, Opportunities and Threats 1
2
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Illustration 1: The Market Attractiveness / Readiness Portfolio of Fit2GlobalizeTM Figure: M. Signer
to the internal situation of a company, its management, core business and support processes are assessed with regard to its readiness for international business. Many of the questions related to the individual export markets are answered by accessing the evaluations of specialist information providers, such as the World Bank, the IMF, EulerHermes, Transparency International, doingbuisness.org, Human Development Index, heritage.org, WTO, geerthofstede.com and others. This ensures that decisions are not made on the basis of a «gut feeling», but on the basis of neutral evaluations. The results of the method include an Attractiveness/Readiness Portfolio, a SWOT3 analysis and a To-do-List with regard to the identified weaknesses and risks. Finally, different markets are compared in order to facilitate decision-making when it comes to prioritising external business. In the Market Attractiveness/Readiness Portfolio (Illustration 1), depending on the position of the analysed market, four standard approaches are suggested: for the company taken as an example in Illustration 1, «Italy» is a market which should be developed because the market is attractive and the company is ready to do business with Italy. The potential is, however, limited. In contrast, although China displays great potential, the company is not yet ready to do business in China. Therefore, the standard strategy «Do homework» would be effective in this case. The homework is defined based on the risks of a market and the weaknesses of a company, which are the results of the answers given to the questions listed in the method. The «homework» is displayed as suggested actions in a To-do-List. The companies should concentrate on the markets in the first and second quadrant. The markets in the fourth quadrant should not be dealt with for the time being, and those in the third quadrant only at a subordinated level – e.g. in case of very low entry barriers.
Executive MBA program based on the concept of lifelong learning The Management Center in Bern (www.mzbe.ch) supports university graduates with customised post-graduate education programs based on the concept of lifelong learning throughout their entire career after their first degree. One of these programs is the Executive MBA in International Management (www.emba.ch), which prepares the students for international challenges. Fit2GlobalizeTM is an integral component of this post-graduate study.
Sooner or later, many engineers deal intensively with the development of foreign markets – since most of the Swiss small and medium-sized enterprises (SMEs) are heavily dependent on the export trade. Therefore, to assist the said SMEs, the Management Center in Bern offers the Executive MBA in International Management based on the concept of lifelong learning. Fit2GlobalizeTM is used in this course (www.emba.ch) and in consultancy projects. The students use the methods in the course of a market entry study to be written by them during their stays abroad in China, Russia or the USA. The findings are very often of great interest to the companies. The key benefits of the method are that all the relevant questions and topics come to light, the findings are neutral and can be successfully used as a basis both for discussions and for the definition of a market entry strategy. Contact: > paul.ammann@bfh.ch > Further information: www.emba.ch www.fit2globalize.ch China is a market with great potential for Swiss companies. View of Hongkong. Photo: Fotolia.com
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