Laser cooling by collisional redistribution of radiation

Abstract

The general idea that optical radiation may cool matter was put forward 80 years ago. Doppler cooling of dilute atomic gases is an extremely successful application of this concept. More recently, anti-Stokes cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids. Collisional redistribution of radiation has been proposed as a different cooling mechanism for atomic two-level systems, although experimental investigations using moderate-density gases have not reached the cooling regime. Here we experimentally demonstrate laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms in argon buffer gas at a pressure of 230 bar. The frequent collisions in the ultradense gas transiently shift a highly red-detuned laser beam (that is, one detuned to a much lower frequency) into resonance, whereas spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, kinetic energy of order k(B)T-that is, the thermal energy (k(B), Boltzmann's constant; T, temperature)-is extracted from the dense atomic sample. In a proof-of-principle experiment with a thermally non-isolated sample, we demonstrate relative cooling by 66 K. The cooled gas has a density more than ten orders of magnitude greater than the typical values used in Doppler-cooling experiments, and the cooling power reaches 87 mW. Future applications of the technique may include supercooling beyond the homogeneous nucleation temperature and optical chillers.

Performance of a quantum heat engine at strong reservoir coupling

“…However, it is of both fundamental and practical importance to understand whether and how thermodynamic treatments can be modified to apply beyond such simplifying assumptions. For example, the strong coupling regime is experimentally accessible in nanoscale devices [20][21][22][23][24][25][26] and exciting technological implications of quantum heat machines have been proposed, such as in laser cooling [27,28]. This motivates the requirement for a greater understanding of heat engines which operate under conditions of strong reservoir coupling [29].…”

Towards redistribution laser cooling of molecular gases: production of candidtate molecules SrH by laser ablation

“…[1][2][3] In fact, we could so far not observe a measurable attenuation of the resonant laser beam crossing the sample cell. WE expect that the yield can be substantially increased by increasing the laser power with a corresponding increase of the laser beam diameter at the target surface in order to keep the laser intensity fixed.…”

Absorption spectroscopy of xenon and ethylene–noble gas mixtures at high pressure: towards Bose–Einstein condensation of vacuum ultraviolet photons

“…Provided that the Kennard-Stepanov relation in the dense system holds, this implies a high quantum efficiency of the involved transitions [37]. Besides photon Bose-Einstein condensation, this would make the system also a promising candidate for collisional redistribution laser cooling starting from room temperature [32].…”

“…A further motivation for the here described work stems from the possibility to carry out collisional redistribution laser cooling of the dense gas samples. In earlier work of our group, collisional laser cooling has been carried out with rubidium gases subject to near 200 bar argon buffer gas pressure, where frequent rubidium-argon collisions shift the alkali atomic transition into resonance with a far red detuned laser beam, while spontaneous decay occurs near the unperturbed resonance frequency [32,33]. The reaching of a sufficient alkali vapour pressure near 1 mbar here requires for a pre-heating of the sample cells, while gases that are gaseous at room temperatures, as ethylene, CO 2 or pure noble gases, could allow for redistribution laser cooling starting from room temperature conditions.…”