Dopplerjäähdytystä

Dopplerjäähdytystä, also known as Doppler cooling, is a laser-cooling technique used to reduce the temperature of atoms or ions to extremely low levels, approaching absolute zero. This method relies on the Doppler effect, which describes the change in frequency of a wave in relation to an observer who is moving relative to the wave source. In Doppler cooling, atoms are illuminated by laser light tuned slightly below their resonant frequency. When an atom moves towards the laser beam, the Doppler effect causes it to perceive the light at a slightly higher frequency, closer to its resonant frequency. If this perceived frequency matches the atom's resonance, it absorbs a photon.

Upon absorbing a photon, the atom's momentum changes, and it re-emits a photon in a random direction. Because the laser light is tuned below resonance, the atom is more likely to absorb photons when moving towards the laser. Each absorbed photon slows the atom down, and repeated absorption and emission cycles progressively reduce the atom's kinetic energy, and thus its temperature. This process is particularly effective when the laser beams are directed from all opposing directions, effectively trapping and cooling the atoms in a small region. Doppler cooling has been instrumental in the development of Bose-Einstein condensates and other quantum phenomena, enabling precise measurements and new technological applications.