Comparison of laser cooling of the lattice of wide-band-gap semiconductors using nonlinear or linear optical excitations

A generalized nonlocal energy-balance equation for excited carriers and phonons is established for studying the laser cooling of a lattice of a wide-band-gap semiconductor such as AlN using a He-Ne laser through a three-photon nonlinear excitation process. The power-exchange densities of the system are calculated and compared for different strengths of the excitation field. When the power-exchange density is positive, it implies laser cooling of the lattice. The effects of initial lattice temperature and field-frequency detuning on the laser-cooling phenomenon under the three-photon nonlinear excitation process are described. The power-exchange densities are compared for both laser cooling and heating using linear and nonlinear excitations. We find that the linear excitation seems more favorable than the nonlinear excitation for laser cooling. However, the resonant three-photon nonlinear absorption will allow us the use of a common He-Ne laser for laser cooling of the lattice in AlN, rather than a more expensive ultraviolet laser.