Second-order nonlinear-optical tensor properties of poled films under stress

The orientational distribution function of a poled, doped polymer film under stress is measured using polarized second-harmonic generation. The four interface nonlinear boundary conditions are solved, and both the magnitude of the second-order susceptibility and the ratio of the tensor components of the second-order susceptibility, χ113(2)/χ333(2)(≡a), are shown to vary with poling field and stress. Further, the sign of the order parameter ratio, 〈P3〉/〈P1〉, as measured directly by polarized second-harmonic generation of these materials, shows that the materials fall into a regime of order unlike other material classes such as Langmuir–Blodgett films and liquid crystals. For a one-dimensional dopant molecule, the order parameters 〈P1〉, 〈P2〉, 〈P3〉, and 〈P4〉 can be estimated. Materials processed in this way are shown to result in a range of tensor ratios of a = 0.33 with a film under no stress to a = 0.7 with a film under moderate stress.