I know you take light and bounce it somehow but how do they get the intensity so high
In: Physics
Imagine you have a tube. At one end is a mirror that reflects 100% of light that hits it. At the other end is a mirror that is slightly transparent. Inside this tube we put a material called a *gain medium*. There are all sorts of gain mediums: crystals, gases, glass, etc. What’s important is that the material of the gain medium can be put into a state where it creates more ~~energy~~ **light** than it absorbs. The gain medium is energized so that the majority of its electrons go into an excited state.
As the light travels back and forth between the mirrors, it continually passes through the gain medium. When light passes through the gain medium, the medium *radiates* more light traveling in the same direction, which amplifies the light. This is called *stimulated emission*.
Eventually the light is amplified enough that the small portion of the light that escapes through the semi-transparent mirror is a powerful beam. This beam is made of **l**ight **a**mplified by **s**timulated **e**mission of **r**adiation, or a laser.
*Edit: In this house we obey the laws of thermodynamics!*
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