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Transparency and absorption
All commonly used polymers are more or less trans-parent in undoped condition in the infrared wavelength range of the laser sources (except CO2 lasers).
Filler materials, like pigments, provide for the absorption of laser energy. Many colour pigments absorb within the infrared range and can be used for laserwelding. Even simpler, and therefore most common, is the use of carbon black particles acting as absorbers, typically in a concentration of 0.05 - 0.5 %. However, this results in darker colours. There are already standard solutions for black-black and transparent-black welding availabe.
For clear and bright colours, colorants,
which are flexible in use, are also available.
They absorb only within a certain wavelength
range and have no significant influence on
the colour. The slight colour changes due to
the additives can be adjusted by colour
matching.
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Most polymers (lighter blue curve) are usually transparent or translucent in the visible and near IR range. By adding pigments (darker blue curve), suitable absorption of the laser wavelength is achieved.
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