Second poled polymer films

The electro-optic coefficient in a poled polymer film can be related to the second-order susceptibility as shown in Equation 5. 

Second order, polyazomethine possesses both donor and acceptor groups at the molecular level, which when aligned gives a poled polymer. Tatsuura et al. fabricated an as-deposited poled polymer film by applying anin-situ electric field during CVD and reported on the second order nonlinear optical properties of the obtained film. The polymer film refractive index was reported to be about 1.68 at 632.8 nm. Second order NLO susceptability, p, was found to be... 

Also, Zhu and coworkers reported preparing of two high Tg (250° and 258°) polyimides embedded with triphenyl imidazole chromophores. Simultaneous polymerization and poling was carried in situ. The second harmonic generation measurements technology yielded moderate das values of 15 pnW and 16 pnvV. The signals of these poled polymer films were reported to be without any decay at < 150° The relaxation starts rapidly over 195°. The half-decay temperatures, of the samples orientation are as high as 240° and 224° respectively. 

The electrical response of a piezoelectric material is a function of the electrode configuration relative to the direction of the applied mechanical stress. For a coefficient dy, the first subscript is the direction of the electric field or charge displacement, and the second subscript gives the direction of the mechanical deformation or stress. The C2v crystallographic symmetry typical of S5mthetic oriented, poled polymer film leads to cancellation of all but five of the dtj components W31, ds2, ds3, di5, and 24)- If the film is poled and biaxially oriented or unoriented, dsi = ds2 and di5 = 24. Most natural biopolymers possess Pco symmetry which yields a matrix that possesses only the shear piezoelectricity components dis and 25. Because the dss constant is difficult to measure without constraining the lateral dimension of the sample, it is typically determined from equation 7 which relates the constants to the hydrostatic piezoelectric constant, dsh. 

Singer KD, Sohn JE et al (1986) Second harmonic generation in poled polymer films. Appl Phys Lett 49(5) 248-250... 

H. E., and Schilling, M. L., Electro-optic phase modulation and optical second-harmonic generation in corona-poling polymer films, Appl. Phys. Lett., 53, 1800, 1988. 

The susceptibility tensors measure the macroscopic compliance of the electrons. Since the second order polarization is a second rank tensor, SHG is zero in a centrosymmetric or randomly oriented system. To make the material capable of SHG, the NLO dopants must be oriented noncentrosymmetricaly in the polymer matrix (2-3). When modeling the poled, doped films using a free gas approximation, the poled second order susceptibilities are given by (2.19)... 

In the limit of the oriented gas model with a one-dimensional dipolar molecule and a two state model for the polarizability (30). the second order susceptibility X33(2) of a polymer film poled with field E is given by Equation 4 where N/V is the number density of dye molecules, the fs are the appropriate local field factors, i is the dipole moment, p is the molecular second order hyperpolarizability, and L3 is the third-order Langevin function describing the electric field induced polar order at poling temperature Tp - Tg. 

Sckkat, Z., Aust, E. F., and Knoll, W. Photo-induced poling of polar azo dyes in polymer films. In G. Lindsay and K. Singer, Eds. Polymers for Second-Order Nonlinear Optics, ACS Symp. Set. 601, Ch. 19, 1995. 

Figure 6.7. Upper linUts of x values reported for second harmonic generation of poled polymers, crystals, and LB films compared with those of inorganic crystals. Also noted is x /or the linear electrooptic effect in LiNbOa-...

The requirement of non-centrosymmetry is not restricted to the molecular level, but also applies to the macroscopic nonlinear susceptibility, which means that the NLO molecules have to be organized in a non-centrosymmetric alignment. The first measurements of the macroscopic second-order susceptibility, have been performed on crystals without centrosymmetry [5]. However, many organic molecules crystallize in a centrosymmetric way. Other condensed oriented phases such as Langmuir-Blodgett (LB) films and poled polymers therefore seem to be the most promising bulk systems for NLO applications. 

Blanchard PM, Mitchell GR. 1993a. A comparison of photoinduced poling and thermal poling of azo dye doped polymer films for second order nonlinear optical applications. Appl Phys Lett 63(15) 2038 2040. 

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