Comment

Abstract

In my opinion, there is clear physical distinction between resonant Raman scattering (RRS) and hot luminescence (HL) if we believe there is clear distinction between transverse and longitudinal resonant excitations. It can be shown explicitly for a three-level system that RRS is connected to transverse excitation with its decay governed by transverse relaxation, while HL is connected to longitudinal excitation (excess population in the intermediate state) with its decay governed by longitudinal relaxation. RRS is a direct two-photon process while HL is a two-step process. In magnetic resonances and quantum electronics, similar problems exist and are well-known. For example, consider the case of optical mixing of three beams at ω_ℓ, ω4_S, and ω_ℓ′, in a medium (with ω_ℓ − ω_S ≈ ω_O where ω_O is the resonant frequency of an excitation) to generate an antiStokes field at ω_a = ω_ℓ′ +(ω_ℓ− ω_S). The one-step process gives the so-called coherent antiStokes scattering (discussed by Professor S. A. Akhmanov in this symposium) while the two-step process (creation of longitudinal excitation at ω_O followed by scattering of the probe beam at ω_ℓ^′, off the longitudinal excitation) gives the incoherent spontaneous antiStokes scattering.