Classical description of laser light?

[dipole]

It occurred to me today that I really don't know much about lasers. When dealing with electromagnetic waves, we always talk about plane waves, which are infinite in extent, or spherical waves, which spread out as they travel.

What then is laser light? A finite plane wave? How do you treat laser light mathematically using the wave picture?

 

[Simon Bridge]

You have plane waves in the direction of the beam but to get a beam the amplitude of the waves has to go to zero radially. The profile used is usually gaussian - which is close to actual measurements. But we don't normally use the classical description for lasers.