Second harmonic characteristics of Disperse Red 1 doped polysulfones
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Ping Yu, Lap-Tak Cheng,a) and George K. L. Wong Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong (Received 16 June 1995; accepted 1 August 1995)
Polysulfones, such as poly(oxy-l,4-phenylenesulfonyl-l,4-phenyleneoxy-1,4phenyleneisopropylid-ene-l,4-phenylene), poly(phenylene ether sulfone), poly(phenylene sulfone), and aliphatic polysulfone, poly(bicycloheptene sulfone), were employed as a host resin. N-ethyl-N-hydroxyethyl-4-(4'-nitrophenylazo)phenylamine (Disperse Red 1) acted as a guest molecule and was dispersed in those hosts with a concentration of 5 wt. % to 10 wt. %. Their second harmonic generation properties were characterized and compared. Xijk values obtained varied from 11 pm/V to 21 pm/V. The merits of polysulfones as a host material are good optical clarity, easy film forming, and fairly high glass transition Tg temperature (140 °C to 190 °C). Chemically, compared to polyimides they have good resistance to moisture, i.e., less vulnerable to hydrolysis. It is a good candidate for electro-optical materials.
Besides linear response, the interaction of light with molecules can be in a nonlinear manner. This is illustrated in the molecular polarization expression'^ as below. /"-; = /J'oj + ottjEj + f3ijkEjEk
+ yijklEjEkEi
+ (1)
Polarizability a ( / is responsible for those linear events, like absorption, etc. Both pijk and y,^; are higher order hyperpolarizabilities and responsible for nonlinear optical phenomenon. In terms of bulk materials, the bulk polarization is re-expressed as follows'" 4 : p. = p . + J:l)E- + x2kE-Ek
+ y(3) E E E + ••• (2)
Linear processes depend on the linear susceptibility Xij • Nonlinear processes depend on those higher order susceptibilities, such as xijk and xijki, e t c - Second harmonic generation (SHG) is based on the coefficients
(5ijk and xfjlMolecules consisting of a conjugated structure with large dipole moment have large fiijk value. For a bulk material of considerable Xijk value, dipoles in the system are aligned with the result of nonzero dipole moment. In terms of mathematical expressions,
a) Permanent
address: CR&D, The Du Pont Company, Wilmington,
Delaware. J. Mater. Res., Vol. 10, No. 11, Nov 1995 http://journals.cambridge.org
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is related to /3,7/t in the following manner.1-2
X
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