system
Given the following post, respond as if you're commenting on Reddit:
human
For light to qualify as a laser does it have to be emitted in a beam or does it just have to be of one wavelength?

If it does have to be a beam, what is the maximum spread it can have and still qualify?
gpt
Laser has nothing to do with colour or beam divergence. Lasers are just good for making tight beams, and they inherently make a rather monochromatic source. You can have a really wide laser beam, and you can have a rather narrow focus with lenses or mirrors. 



L.A.S.E.R. is actually an acronym. It's Light Amplification by Stimulated Emission of Radiation. To be a laser, it has to be light amplification done by stimulating the emission of radiation. Basically you energize certain types of materials so much so that more electrons are in the energetic state than the ground state, and then as light passes it causes electrons to emit basically identical photons, amplifying the light. The coherence of this light is what makes laser have a narrow wavelength band and allows for tight beams if desired.  


This is opposed to spontaneous emission, which is most other sources, like an from a hot object like an incandescent bulb or fluorescence like in a fluorescent lamp or white LED. Here a minority of electrons are energized, and they randomly emit leading to a less coherent light source. Some spontaneously emitted photons may trigger stimulated emission, but it's a minority effect. Once you pass a point called population inversion (more electrons energized than not) stimulated emission takes over as a dominant effect as you can start lazing.