MICROMACHINING Te Glass module shapes the beam geometrically
to deposit the same energy across the thickness of the material, as well as temporally by applying a sequence of pulses. In this way, the technique applies local stress inside the material to make the cut, which Rouffiange noted is low roughness and free from chips. Te femtosecond pulses produce a different effect
Amplitude Systèmes has developed its Glass module for cutting glass or sapphire with femtosecond pulses
different types of glass at different thicknesses, as well as stacks of glass with several layers of either the same or different material. It doesn’t generate dust or particles, because it’s a process that modifies the glass and then separates the glass along a filament. It also gives much higher yield compared to a mechanical process, as well as being more efficient – the laser consumes less power than mechanical processing tools. ‘A laser system can produce many more parts
than one CNC machine, and one laser system can replace many tens of CNC machines,’ Deile stated. Mechanical processes also require water for cooling and separation, which brings complications – you have to recycle the water, clean and dry the part, all of which is not found using laser processing.
Choice of pulse duration Picosecond (10-12
seconds) pulses are the best
choice for filamentation, in terms of the interaction between the laser pulse and the glass, according to Deile. Longer laser-material interaction times are required in order to sustain the filament. Coherent-Rofin uses a burst mode when running its picosecond laser for filamentation, producing a burst of several pulses with a few tens of nanoseconds between them. ‘Te type of laser used depends on the process
quality needed,’ explained Chui. Tere’s also the laser wavelength to consider; a shorter wavelength can focus to a smaller spot and cut finer features. However, there’s a conversion loss moving to shorter wavelengths, so on a cost per watt basis the shorter wavelength is significantly more expensive, according to Chui. In general, shorter wavelengths are better, but economically it might not make sense. ‘A UV nanosecond laser will give a really tight cut,’ he said. ‘If the feature size is less important, but minimising heat affected damage is crucial, then you might go to infrared picosecond or infrared femtosecond.’ Amplitude Systèmes offers a femtosecond (10-15
seconds) process for cutting glass. It launched its Glass module at Photonics West 2017 in January, the result of three years’ work on machining
20 LASER SYSTEMS EUROPE ISSUE 36 • AUTUMN 2017 Sheets of glass can be cut with laser filamentation, a technique that is being adopted by consumer electronics manufacturers @lasersystemsmag |
www.lasersystemseurope.com
transparent materials such as glass or sapphire with femtosecond laser pulses. Te method Amplitude Systèmes employs is different to the standard ultrafast laser processing technique used on metals, and it also differs to filamentation. ‘Metals are much easier to understand in terms of ultrafast processing; with materials like glass and sapphire, the technique is based on non-linear absorption,’ explained Amplitude Systèmes’ Rouffiange. Amplitude Systèmes’ research into the effects of
ultrafast pulses on transparent materials was driven by industry requirements, largely from the consumer electronics sector, according to Rouffiange, for cutting strengthened and unstrengthened glass, as well as sapphire. Te company’s Glass module produces a narrow
filamentation is a mature process and is being adopted right now
[Laser]
and elongated beam so that the pulse energy is absorbed in a very thin channel, typically 2µm wide, throughout the thickness of the material. Te process doesn’t ablate material, explained Rouffiange; instead the high peak power of the femtosecond pulses produces micro-cracks inside the glass or sapphire and, by applying a small amount of stress, the sheet is split in a given direction.
on glass and sapphire than picosecond pulses, according to Rouffiange. Instead of producing local modification, or voids, the technique produces regular oriented and controlled micro-cracks. Tis gives a high-quality cut. Glass and sapphire are transparent at 1,030nm
wavelength. However, the high intensity of femtosecond pulses causes a multiphoton absorption at the focal point. Te peak power of the pulse is therefore quite important, Rouffiange explained, which is why femtosecond pulses are used. Amplitude Systèmes typically receives requests
to cut glass a few hundreds of microns thick for consumer electronics, but has shown that its technique is effective at cutting glass 2mm thick. Tere needs to be sufficient energy deposition across the thickness of the material, and therefore the energy of the laser and the length of the elongated beam have to be adapted depending on the
thickness of the material. Amplitude Systèmes’ setup can be arranged so
that either the beam is fixed and the sample moves, or, if the sample is large and cannot be manipulated, then the Glass module and laser can be moved on a gantry. ‘Our feeling is that ultrafast processing of glass
could be implemented really soon in consumer electronics, because the process improves yield,’ commented Rouffiange, referring to Amplitude
Amplitude Systèmes
Coherent
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