Two-photon operator

In the dipole approximation which happens to be accurate enough for our purposes, an effective two-photon operator Q (E) acting on the states a), 6) and c) is defined as... 

Here, at is the Dirac a-matrix, A(r, t) is the vector potential of the field (divA = 0), and Ho is the Hamiltonian of an isolated atom whose energy in the initial state of the reaction is denoted by Ef. H0 i) = E i). Equation (5) defines the effective two-photon operator Q(2 ui,u> ) which has the dimension of L3 and is a straightforward relativistic generalization of its nonrelativistic counterpart that has been first introduced in [28] to describe the process of two-photon absorption. Generally, the matrix elements of u>,u> ) can be expressed explicitly as... 

Miklailov et have employed TDDFT to design two-photon operated molecular switches built from the diarylethene photoswitching unit and a two-photon absorbing pendant substituent. Both the one- and two-pho-ton absorption spectra were simulated and analyzed in order to understand... 

---

See also in sourсe #XX -- [ ]

---