Cooperative two-photon absorption. II

Abstract

In this paper we extend our earlier work on cooperative two-photon absorption to the case of one- and three-photon allowed transitions using the principles of quantum electrodynamics. After deriving a general rate equation we consider two specific molecular systems: (i) van der Waals molecules in which the two centers have a fixed mutual orientation; and (ii) fluid samples with random molecular orientation. Calculations are shown to involve a new type of rotational average which gives rise to two-photon circular dichroism in case (i). The dependence of the rate upon molecular separation is discussed in detail, as is the possibility of resonance enhancement if suitable intermediate energy levels are present. Finally we draw attention to an effect specific to this mode of cooperative absorption and speculate on the possibility of direct observation of the effects of retardation.

The Quantum Electrodynamics of Synergistic Two-photon Processes

“…In the following section, a theory is developed for the former, cooperative, mechanism which relates to transitions allowed under the normal symmetry selection rules for two-photon absorption and Raman scattering . The corresponding theory for the distributive mechanism follows along very similar lines and has been discussed in detail elsewhere [6,10] . The novel features which arise out of virtual photon coupling are essentially identical for both types of mechanism, and it is these which are subsequently examined in section 3 .…”

“…In the latter case, mode 2 is associated with a second laser, and consequently in the final state the occupation number of this mode is decreased by one . The coherence factor which marginally modifies the above treatment in the case where modes 1 and 2 are the same is discussed elsewhere [9,10] .…”

“…Thus the cooperative processes described by the master equations (27) and (28) are now described by [6,8,10] rrr^= tt2l( 60c…”

“…The first process, termed cooperative, corresponds to a case where both photons hw l and hw2 interact with a different molecule as shown in figure 2 [9] . The second mechanism, termed distributive, describes a process in which both photon events occur in a single molecule as in figure 3 [10] . In each case, the energy mismatch for the molecular transitions is transferred by means of a virtual photon which couples with each molecule by electric-dipole coupling .…”

Chiral discrimination in optical binding

“…As we are concerned with a pair interaction with radiation, we require the use of a phased rotational average, accounting for the difference in optical phase of the throughput radiation at each center. [63] In the present case, the relevant phased rotational average takes the generic form;…”