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Asked by izzywizzyxxx to Mike, Pip, Tianfu, Tim, Tom on 2 Jul 2012.
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Tim Stephens answered on 2 Jul 2012:
There are special crystals which allow you to halve the wavelength of certain types of laser light, which changes its colour. They’re known as harmonic crystals, and are how most green lasers are made (green lasers start out as infrared lasers, whose wavelength is then halved with one of these crystals).
Another way is to use a special type of dye. You shine a laser onto the dye, which absorbs the laser light and then emits light at a new colour. If you put the dye inside another laser cavity, you can change the colour of the laser – this is called a dye laser.
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Philippa Bird answered on 2 Jul 2012:
But most other lasers have just one wavelength which cannot be changed because it is predetermined by the chemicals that produce the light.
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Tom Lister answered on 2 Jul 2012:
Most lasers fire at a few well defined wavelengths and you ‘tune’ the optics until only one wavelength will fire. Some (like Argon) operate at lots of wavelengths and can be tuned to pretty much whatever you want.
Plus you can do what Tim said, although much of the original colour still comes out.
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