How does a Laser Work?
Although optical designers make use of laser light in many systems they design (such as supermarket product scanners and CD players), the basic principle of a laser depends on the photon nature of light. Photons are particles of energy that can be absorbed into and emittted from atoms and molecules. When an atom absorbs a photon of light energy, the atom stores this extra energy temporarily (we say the atom is in a higher energy state). When the atom “relaxes” to its natural low-energy state, it gives up the excess energy in the form of another photon (we call this spontaneous emission — it just happens). Lasers are possible because of another type of photon emission called stimulated emission. If you can somehow get a LOT of atoms into specific higher energy states, you can use light to trigger or “stimulate” all of them into releasing their excess-energy photons at the same time (we say these photons are in phase, or coherent). There are various ways to get a lot of atoms into the s
