Laserkyla

Laserkyla, or laser cooling, refers to techniques that reduce the thermal motion of atoms and ions by interacting them with near-resonant laser light. The basic idea is to use photon momentum to apply a gentle, velocity-dependent force that removes kinetic energy from the particles.

In Doppler cooling, light is tuned slightly to the red of an atomic resonance. An atom moving toward a laser beam sees the light closer to resonance and is more likely to absorb a photon, slowing its motion. After spontaneous emission, the emitted photon has no preferred direction, yielding a net cooling effect. A configuration with counter-propagating beams, called optical molasses, creates viscous damping and temperature limits known as the Doppler limit. Sub-Doppler cooling exploits the internal structure of atoms (and polarization gradients) to reach temperatures below this limit.

The common implementation for neutral atoms is a magneto-optical trap (MOT), which combines red-detuned laser beams with a magnetic field gradient to capture and pre-cool samples to the microkelvin range. For ions, cooling is performed in electrostatic traps and can reach near the motional ground state through resolved-sideband cooling. More recently, laser cooling has been extended to certain molecules and to techniques such as cavity cooling, which use coupling to an optical cavity.

Limitations include recoil heating from spontaneous emission and the finite linewidth of the cooling transition. The Doppler limit sets a practical floor, typically in the tens to hundreds of microkelvin for common alkali atoms; sub-Doppler methods can reach lower temperatures, down to microkelvin and below in specialized setups. Laser cooling has enabled precision atomic clocks, quantum simulators, ultracold quantum gases, and advances in quantum information processing, and it played a central role in the development of Bose-Einstein condensation. The field matured in the 1980s–1990s and earned the Nobel Prize in Physics.