Absorption of a photon whose energy is E₂-E. Absorption of a photon whose energy is E₁-E₂. =) Emission of a photon whose energy is E₁-E₁. Emission of a photon whose energy is E3-Ep. s) Emission of a photon whose energy is E4-E- Absorption of a photon whose energy is E4-Ei.12

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