Laserjäähdytyksessä

Laserjäähdytys, known in English as laser cooling, is a technique used to slow down atoms and ions to extremely low temperatures. This is achieved by using lasers tuned to a specific frequency. When atoms absorb photons from the laser, they lose momentum, and consequently, their speed decreases. This process can be repeated multiple times, effectively cooling the atoms down to temperatures near absolute zero.

The principle behind laser cooling relies on the Doppler effect. Lasers are directed at atoms from multiple directions. If an atom is moving towards a laser, it perceives the laser's frequency as higher (blue-shifted). The laser is tuned slightly below the atomic resonance frequency. This means that when the atom is moving towards the laser, the Doppler shift brings the laser's frequency into resonance, causing the atom to absorb a photon. This absorption imparts a momentum kick opposite to the atom's direction of motion, slowing it down. Atoms moving away from the laser see the frequency as lower (red-shifted), and thus do not absorb photons as readily.

Once an atom absorbs a photon, it is excited to a higher energy state. It then spontaneously emits another photon in a random direction and returns to its ground state. While this emission imparts a random momentum kick, on average, the decelerating kicks from the absorption process dominate. Over many cycles, this leads to significant cooling.

Laser cooling has been instrumental in various scientific fields. It is crucial for atomic clocks, which achieve unprecedented precision by trapping and cooling atoms. It is also a fundamental technique in quantum simulation and the study of Bose-Einstein condensates and other quantum degenerate matter. The development of laser cooling led to the 1997 Nobel Prize in Physics awarded to Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips for their work on this phenomenon.