I read laser beams get wider, like a few feet wide by the time they hit the moon, Is that a manufacturing limit, or just something about the physics of laser light? Is a perfect laser beam that doesn’t get wider possible?

Question

I read laser beams get wider, like a few feet wide by the time they hit the moon, Is that a manufacturing limit, or just something about the physics of laser light? Is a perfect laser beam that doesn’t get wider possible?

In: 5280

Answer 1

A laser beam pointed at the moon (from earth’s surface) will get much wider because the photons are hitting other particles as it goes – air, dust, etc – causing the light to diffuse. So no, we can’t manufacture a laser that won’t get wider when used practically in our environment.

~~Even in a perfect vacuum with no other particles, the photons themselves will interfere with each other over a long distance causing the beam to widen. But this is quite negligible, so the beam will indeed stay mostly the same size for a long distance.~~

Edit: see u/jaa101 comment below on what happens in a vacuum, who probably knows more than I do.