Doppler cooling

Doppler cooling is a technique used to reduce the motion of atoms by controlling how they absorb and emit light. When atoms move toward a light source, they see the light's frequency shifted higher (blue-shifted); if the light is tuned just below the atom's resonance frequency, atoms moving toward the light absorb more photons, which slows them down. When they relax and emit photons spontaneously, they do so in random directions, but overall, this process decreases their average speed. Repeating this cycle effectively cools the atoms, making them less energetic and helping scientists study atomic behavior with higher precision.