Per-atom transition rates between two levels: A_{21} (spontaneous emission), B_{12} ρ(ν) (absorption), B_{21} ρ(ν) (stimulated emission), with the thermodynamic relations A_{21}/B_{21} = 8πhν³/c³ and g_1 B_{12} = g_2 B_{21}.
Per-atom transition rates between two levels: A_{21} (spontaneous emission), B_{12} ρ(ν) (absorption), B_{21} ρ(ν) (stimulated emission), with the thermodynamic relations A_{21}/B_{21} = 8πhν³/c³ and g_1 B_{12} = g_2 B_{21}.