FEATURE: CO2
LASERS
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market. In one sense CO2 lasers haven’t had to evolve over the last two decades; they’ve still got a very healthy market and they’re the right tool for the job.’ Stephen Fazeny, CTO for laser sources
at Trotec, added that the CO2 laser market is still growing at a rate faster than GDP and faster than the standard machine tool market. ‘The CO2 market has a future because CO2 laser applications are replacing some mechanical non-laser applications,’ he said. Working with ceramics is another area
where CO2 lasers are used and, May said, ‘they’re frankly the only obvious choice for nearly all organic materials.’ Jobs like cutting leather trim for cars or thin plastics for automotive dashboards. The longer 10.6µm wavelength of CO2 lasers is better absorbed by organic materials than the 1µm fibre laser wavelength, which results in a cleaner cut. Kristen Hill, senior product line manager
at Novanta, recalled a customer that came to them after trying to cut foam with a fibre laser, which had severely burned the material. ‘We were able to cut the material with a Synrad CO2 laser with very minimal discoloration, and the customer was happy
with the result,’ she said. Synrad is one of the Novanta brands. On the other hand, solid-state lasers
have replaced CO2 lasers in the field of sheet metal processing, where the 1µm wavelength is better absorbed by metals.
‘CO2 is more or less gone for metal processing in the kilowatt power range,’ Fazeny confirmed. In addition to being preferable for
processing metals, fibre lasers have a factor of 10 smaller spot size than CO2
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g CHALLENGES OF BAND-SELECTED CO₂ LASERS
Standard CO2 lasers emit at 10.6µm, but other CO2 wavelength bands are available that might prove advantageous for processing thin films, for instance. Luxinar offers 10.6, 10.25 and 9.3µm sealed CO2 laser sources ranging from 80 to 450W. In thin films less than
100µm, processing speed can be enhanced using the correct wavelength, while the heat-affected zone can be the decisive factor for moving to a different wavelength on films greater than 250µm.
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In any case, the optics used in the laser cavity to select the wavelength have to be carefully chosen. Band-selected cavity optics need robust coatings with a high flux density, proximity to RF discharge and the ability to suppress the neighbouring branch without reducing gain at the required wavelength. Polarisation, absorption in air and loss are the main integration challenges for wavelength band-selected CO2 lasers, Luxinar advises. The firm states that standard 10.6µm dielectric
mirrors can depolarise circular polarised light, whereas isolation mirror solutions are lambda specific. At 9.3µm, especially at
high powers, lens effects due to absorption distort the beam; these can be removed by nitrogen purging or by moving dry air.
Loss per surface on standard 10.6µm AR or AR transmissive optics is approximately 3 to 5 per cent at 9.3µm operation, and can cause back reflections or heating of optic mounts.
AUTUMN 2021 LASER SYSTEMS EUROPE 9
Trotec
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