Figure 1From: The resonance fluorescence cascade of a laser-excited two-level atomEnergy diagram of the atom (g for the ground state, e for the excited one) dressed by laser photons (number n). States (blue lines) are grouped in two-fold nearly degenerate multiplicities in which they are coupled by reversible absorption and stimulated emission processes (green shaded ellipses). Spontaneous-emission processes are irreversible jumps down the ladder of multiplicities (red arrows)Back to article page