What is optical pumping in physics?
Optical pumping is a process where we use light to transfer atoms from one energy level to another, aligning their magnetic moments in a specific direction. Imagine an atom as a small solar system: electrons orbit a nucleus, and each orbit has a fixed energy, like steps on a staircase. By shining circularly polarized light of a precise frequency, we can 'pump' electrons from a lower step to a higher one, but only if the light's angular momentum matches the atom's spin. This creates a population imbalance—more atoms in one spin state than another—which we can then probe with radio waves to study Hertzian resonances. I first demonstrated this with mercury vapor in 1950, and it became a cornerstone for masers and lasers. The method is elegant because it uses light, a tool we can control precisely, to reveal the hidden structure of matter.
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