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Prove my science teacher wrong!

FreeBee

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I thought it was that the higher the wavelenght, the more easy light is absorbed. What's why (moderate strong) violet lasers can easily burn white paper, whereas a red laser of the same power could not.
 

DrSid

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I thought it was that the higher the wavelenght, the more easy light is absorbed. What's why (moderate strong) violet lasers can easily burn white paper, whereas a red laser of the same power could not.
It's not a rule. It depends on the color of the material. Color, by definition, tells us what wavelengths are absorbed and what are reflected by the material.
In visible spectrum, blue material will reflect blue, and absorb red .. and red material will reflect red and absorb blue. It's better detectable with low power lasers, let's say 200mW. Material being what we would perceive as nice full blue may still absorb 20% of blue light. So with strong laser (like 1W) you can burn almost anything, because almost anything will absorb at least few percent of any wavelength.
White paper nicely sustains laser light on most wavelengths .. but again, every paper absorbs few percent .. and if you get over some treshold, the paper will turn dark, in which moment it will dramatically increase absorbtion over most wavelengths and will get burned instantly.
But this goes beyond visual range. Most common materials absorb UV .. but some reflects them, and it's not easy to find out. On the other hand, for example glass passes most usual wavelengths, but for CO2 lasers you need special materials for lens, because glass does absorb wavelength that LONG.
For red/gree/blue there is almost no difference in amount of materials they are gonna burn. It's simply color, and it's predictable. 405nm will burn most materials better, but sometimes you find an exception.
 




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