Laser cooling by spontaneous anti-Stokes scattering (A)

David J. Wineland, Wayne M. Itano

Various aspects of the laser cooling of atoms are investigated theoretically. More generally, the authors investigate a process through which the kinetic energy of a collection of resonant absorbers can be reduced by irradiating these absorbers with near-resonant electromagnetic radiation. The process is described here as anti-Stokes spontaneous Raman scattering. Cooling mechanisms, rates, and limits are discussed for both free and bound atoms.

Christopher Corder, Brian Arnold, Harold J. Metcalf

Xuanwen Bu, Li Li, Xinlu Zhang +1 more

A theoretical scheme for laser cooling thulium doped solids with optical superradiance is presented. The superradiance is coherent, sharply directed spontaneous emission of photons by an ensemble of excited ions in the solid-state host, the properties of which are much different from the conventional, incoherent anti-Stokes fluorescence radiating through all directions. In this paper, we consider a thulium doped ZBLAN sample pumped with continuous-wave laser at 1.9 μm and pulse laser at 1.8 μm. The induced anti-Stokes superrandiance at 1.8 μm removes the matrical phonons energy much effectively and quickly, because of the intensity of superradiance proportional to the square of the number of excited Tm ions. The numerical evaluations of the superradiance cooling performance, especially in the net cooling power and the cooling efficiency, is discussed.

S. V. Petrushkin, Vitali V. Samartsev

Ulrich Vogl, Martin Weitz

Yin-Chung Chen, Gaurav Bahl

The laser cooling of vibrational states of solids has been achieved through photoluminescence in rare-earth elements, optical forces in optomechanics, and the Brillouin scattering light-sound interaction. The net cooling of solids through spontaneous Raman scattering, and laser refrigeration of indirect band gap semiconductors, both remain unsolved challenges. Here, we analytically show that photonic density of states (DoS) engineering can address the two fundamental requirements for achieving spontaneous Raman cooling: suppressing the dominance of Stokes (heating) transitions, and the enhancement of anti-Stokes (cooling) efficiency beyond the natural optical absorption of the material. We develop a general model for the DoS modification to spontaneous Raman scattering probabilities, and elucidate the necessary and minimum condition required for achieving net Raman cooling. With a suitably engineered DoS, we establish the enticing possibility of refrigeration of intrinsic silicon by annihilating phonons from all its Raman-active modes simultaneously, through a single telecom wavelength pump. This result points to a highly flexible approach for laser cooling of any transparent semiconductor, including indirect band gap semiconductors, far away from significant optical absorption, band-edge states, excitons, or atomic resonances.