Although energy generated by stimulated emission is always at the exact frequency of the field which has stimulated it, the above rate equation refers only to excitation at the particular optical frequency ν ν 0 corresponding to the energy of the transition. At frequencies offset from ν ν 0 the strength of stimulated (or spontaneous) emission will be decreased according to the so-called line shape. Considering only homogeneous broadening affecting an atomic or molecular resonance, the spectral line shape function is described as a Lorentzian distribution g ′ ( ν ν ) = 1 π π ( Γ Γ / 2 ) ( ν ν − − ν ν 0 ) 2 + ( Γ Γ / 2 ) 2 where Γ Γ is the full width at half maximum or FWHM bandwidth.