eli5: How can a laser burn of rust without melting?

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I just saw a YouTube video by someone with 2000 W laser and now I wonder how can the laser not melt itself when compared to a lense bundeling sunlight its always said cannot get hotter than the sun itself?

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5 Answers

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The sun is a “blackbody” radiator, it generates light based solely on its own temperature, which is hot.

A laser works differently, and a little complex for an ELI5. Basically it’s using a very specific interaction in a specific type of gas molecule to generate exactly one color of light and nothing else.

The lasers interior is highly reflective at this wavelength so most of it gets beamed out instead of absorbed and converted into heat.

The rust is very absorbing at this same wavelength and heats up intensely.

That said, powerful lasers do get extremely hot. It’s probably water jacketed and/or covered with extensive heatsink fins so that it doesn’t overheat during continuous operation.

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