Dependence of two-photon excitation on the relative polarization of intersecting pump beams in a dye solution

Summary form only given. In our current studies of appropriate dye solutions for 3D displays we employ two pump beams derived from two optical parametric oscillators pumped by a single 10 Hz, Q-switched Nd:YAG laser to insure temporal synchronization of the pulses in the medium under test. To determine the geometrical configuration that would lead to the strongest visible emission from 2-photon excitation, the role of the relative polarization of the two pump beams was investigated. Using two linearly polarized pump beams, we varied their relative direction of polarization over the range 0 to 360 degrees. In the non-degenerate case, we observed a strong dependence of the visible emission intensity excited by two-photon absorption (2PA). The strongest signal is obtained when the beams are polarized parallel to one another, and the weakest when the beams have orthogonal polarization. A ratio of 3 between strong and weak visible emission intensity was measured in coumarin 7 and in rhodamine B. We present a semi-classical model that explains the observations, including the absorption strength ratio and the cos/sup 2/ dependence on the relative polarization angle and show that it is related to the Kerr effect describing the effect of an applied DC field on the polarizability of a molecule solution.