BEAM DELIVERY
ALL IN THE DELIVERY
With new fibre delivery options now available, along with advances in scanning solutions, ultrafast lasers are becoming a much more practical tool for industrial machining, as Rachel Berkowitz discovers
U
ltrashort pulsed lasers are now an established industrial machining tool, but delivering such picosecond and femtosecond pulses of light to the
workpiece can still present challenges. By moving away from solid-core fibres and toward hollow- core fibres for beam delivery, updating tried-and- true techniques for scanning the beam onto the target, and developing lenses that focus faster than ever before, technology is meeting these challenges.
An alternative to solid-core More than 75 per cent of macro laser applications employ beam delivery methods using solid-core fibres. Tat’s because they’re straightforward to integrate with existing systems for companies using YAG, diode, disk and fibre laser beams in applications such as cutting or welding. But while solid-core fibre optics have become
the norm for lasers that pulse at nanosecond timescales, they’re not suitable for delivering high power lasers that pulse at picosecond to femtosecond timescales. ‘Tis is now changing with the availability of so-called anti-resonant fibres,’ said Duncan Hand, professor of applied photonics at Heriot-Watt University in Edinburgh, Scotland. Anti-resonant fibres have a hollow core and
allow the delivery of much higher peak powers than earlier designs. Tey can deliver 100W average power and high energy (>100μJ) picosecond pulses. Current research focuses on evaluating whether different designs are truly single mode or have some level of guidance for
18 LASER SYSTEMS EUROPE ISSUE 33 • WINTER 2016
Scanlab’s digital encoder technology in a galvanometer scanner, enabling it to meet future market needs
other modes, and on understanding how this might affect transmission efficiency and bend sensitivity. Hand is optimistic about this technology’s
future. ‘Fibres for single-mode delivery of high power, ultrashort pulses are becoming available commercially, and so I would expect these to become standard in the next few years.’
Commercial hollow-core fibres Solid-core fibres are plagued by beam dispersal and damaged fibre materials when used to deliver high-power laser light. To address these issues, Germany-based Photonic Tools has introduced a fibre with a hollow core through which to guide
the beam. Tis means the light travels through ‘nothing’, a vacuum. ‘It’s possible to deliver ultrafast lasers in free
space, but it’s more complicated to maintain and to service. And you have stability issues,’ said Bjorn Wedel, Photonic Tools co-founder. Typically, ultrafast lasers have been guided by complicated optical systems that must be assembled piece by piece. Hollow fibres offer a free-space solution within a stable, sheltered cable. Guiding the beam through a hollow region at
the fibre’s centre results in a flexible medium with minimal dispersion, reduced nonlinearity, and less laser-induced damage. To make this work,
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