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BEAM DELIVERY Galvanometer or ‘galvo’ scanners have long


been the primary scanning tool. Tey use one or more reciprocating (elements move back and forth to drive motion) servo-controlled galvo motors with mounted mirrors to deflect and position a beam. But they can’t keep up with more powerful and faster-pulsed lasers. Te alternative is polygon scanners, which use a multifaceted or polygon mirror to deflect the beam to its target. Polygon scanners operate at a fast, constant speed, as opposed to a galvo’s reciprocating motion and its non-linear effects on position. Tey can achieve scan speeds an order of magnitude greater than traditional galvo scanners. Lightweight mirrors help to increase speed in


An SEM image of an anti-resonant fibre made by the University of Bath. The parts that appear black are air, and the rest is glass. The core guiding region is in the centre. The curved ‘walls’ surrounding the core are less than 1µm thick


the fibre’s Eigenmode has to match the fundamental mode of the laser beam. Terefore, a single mode beam can be maintained over a fibre’s length, while higher order modes are suppressed. Wedel explains that ‘using the optical fibre


output, people have a perfect reference for the laser beam’. Photonic Tools offers a product that includes a beam launching system, easily adaptable to any laser source, fibre type, and processing head. ‘If you deal with ultrafast components, you have to pay more attention to preserving all parameters of the beam. Tis must be engineered into the processing head as well.’ Clients can therefore use the technology to


integrate any kind of laser within their machining, welding, or micromachining system. New interface soſtware will allow for greater ease in using hollow fibres for a variety of applications. ‘We look forward to introducing this


technology to a wide laser manufacturing base,’ Wedel concludes.


Integrated ultrafast systems In France, Amplitude Systèmes offers a fully coupled ultrafast laser with hollow core fibre output, which can be directly integrated in a micromachining station and coupled to a scanner. ‘Imagine that, until now, when machine manufacturers wanted to integrate an ultrafast laser, had they been using a standard fibre laser, they would have had to redesign the machine completely to integrate free-space optics,’ said Vincent Rouffiange, vice president of sales. ‘Free


www.lasersystemseurope.com | @lasersystemsmag


space optics would be a nightmare, in terms of design, for a scanning head installed on a rotating axis.’ With fibre delivery, design is simplified and


there’s no need for cleaning optics or a covered beam path. A scanning system can be mounted on a rotation or translation axis; and the laser itself can sit outside of the machine, if so desired. ‘Fibre delivery in ultrafast is a real revolution. It


can open new machine design and new applications, for example, using an ultrafast laser with a robot.’ Rouffiange tells of one company with a machine designed for a CW fibre laser. Tis company had a request from a customer to integrate an ultrafast laser in order to achieve better ablation quality, reduce the heat affected zone, and increase accuracy. Tis company purchased Amplitude’s Satsuma fibre-coupled solution, removed the old connector, and their customer was set to go.


modern galvo scanners, but offer minimal heat sinking, creating problems for high-power lasers. Another issue is that galvo scanners use an analogue or digital encoder to determine mirror position. However, flexing of the motor shaſt and mirror, when scanning at high speed, causes the mirror to point in a different direction from that indicated by the encoder. In contrast, polygon scanners do not use


encoders to determine mirror position. Rather, a ‘start of scan’ detector triggers a timer when the beam approaches the target. Since the polygon rotates at a constant speed, beam location is determined by elapsed time, with a new timer triggered for each passing facet of the rotating polygon. Te mirror’s heſty mass helps maintain speed stability, while serving as a heat sink and improving the laser damage threshold. Polygon scanning


these [fibres for ultrashort pulse delivery] to become standard in the next few years


I would expect


technology was originally investigated by Xerox in the mid-1970s. Te company needed to scan a line very rapidly, and so became Lincoln Laser’s first customer for polygon scanners, which became commonplace in laser printers. While polygon scanners for laser printers don’t


Faster scanners Ultrashort pulsed lasers make possible applications unfeasible with longer pulses, providing high precision in micromachining. Here, ultrafast lasers remove a small quantity of material per pulse. To achieve industrial-scale throughput, scanners that deflect and position the beam need to work at high rates. Hence, it’s also essential to have very high speed beam scanning to prevent damage from thermal effects.


need to be able to handle high energy beams, the technology is still a possible option for the higher powers found in materials processing. ‘Polygon scanners are for brighter beams,’ says


George Helser, president of Precision Laser Scanning in Arizona. Tat includes high power lasers that need to scan rapidly to avoid thermal damage to the target, such as drilling holes in a thin film while removing minimal material. Helser points out that materials processing


system engineers might be aware of polygon scanners, but not how to implement them. When making the transition from galvo to polygon, his


ISSUE 33 • WINTER 2016 LASER SYSTEMS EUROPE 19


University of Bath


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