A nonlinear optical method to determine the transverse relaxation time of excitonic molecules by means of two-photon echo is proposed. In the case of two-photon transition such as excitonic molecule one needs three pulses to obtain an echo signal. When the wave-vector and frequency of the three successive pulses are denoted by k1,ω1, k2,ω2 and k3,ω3, the two-photon echo can be observed in the direction of 4k2-2k1-k3 with frequency 4ω2-2ω1-ω3. Tuning both ω1 and ω2 to be two-photon resonant with excitonic molecule, we can satisfy the phase-matching condition rather easily for appropriate values of ω3 due to the large dispersion of excitonic polaritons. From the correlation trace of the two-photon echo we can determine directly the transverse relaxation time of excitonic molecules.
ASJC Scopus subject areas
- 化学 (全般)