The relationship of the two-photon vector model to the coherent excitation of polyatomic molecules

The relationship between multiphoton coherent excitation and the two-photon vector model of Grischkowsky, Loy and Liao is demonstrated. In particular, it is shown that the recent work of Letokhov and Makarov emphasizes the adiabatic following approximation of the vector model while that of Larsen and Bloembergen corresponds to the sudden approximation. © 1977.