A laser is a device that emits light through a process of optical amplification based on the stimulated emission of radiation. The term "laser" is an acronym for "Light Amplification by Stimulated Emission of Radiation." Lasers produce coherent light, which means that the light waves are organized in a consistent phase relationship, resulting in a narrow, focused beam that can be very intense.
Articles by others on the same topic
What makes lasers so special: Lasers vs other light sources.
How Lasers Work by Scientized (2017)
Source. An extremely good overview of how lasers work. Clearly explains the electron/photon exchange processes involved, notably spontaneous emission.
Talks about the importance of the metastable state to achieve population inversion.
Also briefly explains the imperfections that lead to the slightly imperfect non punctual spectrum seen in a real laser.
- youtu.be/_JOchLyNO_w?t=188 says LED is "also monochromatic", but that is not strictly true, it has way way larger frequency band than a laser. Only narrower compared to other sources such as incandescent light bulbs.
- youtu.be/_JOchLyNO_w?t=517 stimulated emission. This is the key to laser formation as it produces coherent photons.
- youtu.be/_JOchLyNO_w?t=581 spontaneous emission happens too fast (100 ns), which is not enough time for stimulated emission to happen. Metastable electrons to the rescue.
- youtu.be/_JOchLyNO_w?t=832 the parallel mirrors select perpendicular photons preferentially