Here k ≡ ω / c, and the complete solution is now given by Ψ Ψ ( r , ω ω ) = ∑ ∑ l m [ A l m ( 1 ) h l ( 1 ) ( k r ) + A l m ( 2 ) h l ( 2 ) ( k r ) ] Y l m ( θ θ , ϕ ϕ ) , where h l (kr) and h l (kr) are the spherical Hankel functions.