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TexasDude's avatar

How do lasers react with water?

Asked by TexasDude (25274points) January 14th, 2010

What would happen if you fired a high-powered industrial or military laser into or through a container of salt water? What if the water was pond water or distilled water? Does it make a difference? I’m simply curious as to what effect the composition of water would have on a laser beam, if the particles would burn, etc. Thanks.

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6 Answers

Shuttle128's avatar

The light will refract due to the change in density between the air and water, just like any other light. The difference in the speed that light travels in the medium is the cause of the angle change.'s_law

CMaz's avatar

Depending on the power of the laser. Nothing. The reflective properties of the melting container could redirect the laser. The water would get hot and boil keeping the container from burning through.
The laser not penetrating till the water level was lower then the impact point.

TexasDude's avatar

Thanks guys. Much appreciated. +GA

grumpyfish's avatar

However, a high enough powered laser will boil the water. A certain amount of light is absorbed by the water.

To boil 1 gallon of water requires around 9.6MJ of energy (from 25C).

The absorption and effects will vary largely based on what frequency of laser you use. A microwave laser (called a maser) will boil water quite readily, so will a UV laser (Water is relatively opaque in microwave & UV frequencies).

9.6MJ is actually quite a lot—at 1000W of power transmitted INTO the water (e.g., if you had 1% absorption, you’d need 10kW of power) it’d take you 2.6 hours to boil a gallon of water. If you managed to pump 5 megawatts of power (that’s how much a diesel-electric locomotive produces) into the water, you could boil a gallon in 2 seconds.

OTOH, water is mostly transparent to visible light, so any laser you see will have a hard time having much effect. A ruby laser will probably do best—water slightly absorbs red light (which is why it looks a little blue), right about the same frequency as a ruby laser.

TexasDude's avatar

Interesting stuff. I’m definitely not a physicist or a mathematician, but I can appreciate this sort of information. Thanks alot. I was actually wondering about the colors of the lasers too.

loser's avatar

Anyone here point a laser pointer in water? It’s cool!

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