Fig. 10. Energy level hybridization diagram including the photonic (ω_c) and vibrational transitions (ω₀₁,ω₁₂) involved in the formation of linear [LP⁽¹⁾, UP⁽¹⁾] and (effective) transient vibrational polaritons [UP⁽²⁾, and the combination of LP⁽¹⁾ and the 1 → 2 vibrational transition].135 Note the significant interaction between the linear LP mode and the 1 → 2 excitations (represented by the coefficient c) arising from the incoherent population of vibrational modes induced by a pump after sufficiently long probe-delay times.