The out of phase or quadrature component of the fluorescent emission of a material ???i??? at a wavelength ?? is given by: I i ?? = I o ??? ??? A ??? ??? ( ?? ?? 2 + ?? i 2 ) ( 8 ) where I0 is the excitation peak amplitude, A is a factor that depends on the material active density, other rates and optical cross section. ??i is the relaxation rate of the optically emitting level and includes non ra