How are green lasers visible in mid-air?

Question

i dont get how it can show up in midair with no smoke or anything for it to reflect off of. why dont red lasers?

Answer 1

There is stuff in the air (smoke, dust, atoms, etc) that scatters the laser light out of the beam and toward your eye.  It's just that you need a very bright light so that enough of it gets scattered to be visible to you eye.  There are two reasons why green lasers do this while red lasers "don't".  The first reason is that it is easier to make a high power green laser than a high power red laser.  For this reason, the common green laser pointer will have a a couple times more power than a common red laser pointer.  The other reason is that your eye is by far most sensitive to green light.  Your eye is far less sensitive to red light.  So if your green and red lasers were equal power, the green would look much brighter and needs to scatter less for you to see it.

That being said, red lasers also scatter in air and can be seen if they are powerful enough (or if the room is dark enough).  I have a couple red lasers in my lab that are easily visible in the very clean lab air, but they are more than 100 times more powerful than a typical laser pointer.

Answer 2

it has to do with the wavelength of green light.

Answer 3

The smoke and/or dust is there; you just need an intense light to make it visible.