Raman Cooling of Solids through Photonic Density of States Engineering

TL;DR

This paper proposes a novel approach to laser cooling of solids by engineering the photonic density of states to suppress heating transitions and enhance cooling efficiency, enabling potential refrigeration of semiconductors like silicon.

Contribution

It introduces a general model for DoS modification to Raman scattering, demonstrating the feasibility of net Raman cooling in transparent semiconductors through DoS engineering.

Findings

Photonic DoS engineering can suppress Stokes transitions.

Enhanced anti-Stokes scattering enables net cooling.

Potential to cool silicon and other semiconductors without optical absorption.

Abstract

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.