Part of my professional job is to develop new light sources. So a recent Physical Review Letter on the development of a very special optical parametric oscillator caught my interest. Of course, many of you are now saying "a what?" Relax. As usual, I will bore you with the details.
Almost everyone is familiar with lasers. A laser is just a gain source—a way to get a medium glowing with a particular wavelength of light—surrounded by mirrors to provide feedback. We give the gain medium energy—a lot of energy, in fact—which puts most of the medium into an excited state. Nothing likes being excited for very long, so the atoms or ions or molecules that make up the gain medium relax back to their ground state. As these molecules relax, they emit light, some of which is captured by the mirrors and reflected back and forth through the gain medium. As the light field builds up, this causes the excited gain to emit in sympathy with the existing light field. This process of stimulated emission is one of the things that makes a laser special.
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