**9** 0

whitcwa Most lasers are a narrow beam, but all have some divergence. The only rays which are emitted are ones which are travelling nearly parallel to the cavity. Laser diodes have short cavities and have up to 30 degrees divergence. They must be collimated with a lens.

**5** 0

Marlsfarp Well first if all, it isn't just a straight line. Light is a wave and all waves diffract, so it does spread out. There is a theoretical limit to how *little* a wave can spread out, and that is called a "Gaussian beam". In an ideal beam (which a good quality laser will get very close to), the angle it spreads out is given by (wavelength)/(pi * aperture size). This is the size of the "spot," but there are small amounts the radiate in every direction, as well.
Notice that as the aperture size decreases, the angle increases. So as a point source, it really would spread in all directions equally. But it isn't a point source, it's an aperture of finite size, and the "front of point sources" (per Huygens) interfere constructively and destructively.