where ℏ ℏ is the reduced Planck constant, ω ω is the angular frequency, T is the thermodynamic temperature, n ( ω ω , T ) = ( 1 / 2 ) [ coth ⁡ ⁡ ( ℏ ℏ ω ω / 2 k b T ) − − 1 ] is the Bose function, k b is the Boltzmann constant, and