Research On The Measurement Of Third-Order Nonlinear Optical Property A Linear Conjugated Polymer Based On The Attenuated-Total-Reflection Technique

In this dissertation, a new method based on the attenuated-total-re?ection (ATR) technique is proposed for the determination of thethird-order optical nonlinear properties of a linear conjugated polymer,including: (1) Determination of the dispersion of the quadratic electro-optic (QEO) tensor elements for a linear conjugated polymer; (2) Mea-surement of the second hyperpolarizabilityγ(?ω4;ω3,ω2,ω1) of a linearconjugated polymer in the o?-resonant region; (3) Measurement of thecomplex second hyperpolarizability for the QEO e?ect of a linear con-jugated polymer at a wavelength near the absorption.The QEO tensor elements s11 and s12 of a polymer are experimen-tally measured at the o?-resonant region using the ATR technique. Aleast-square fit to the experimental data of the QEO tensor elements11 obtained at di?erent wavelengths yields the frequency-independentcomponents included in the theoretical dispersion of s11, and accordinglythe dispersion of all QEO tensor elements and the dc-Kerr coe?cientare obtained. This method is characterized by the fact that the ex-perimental acquisition of the dispersion of any one among s11, s12 andthe dc-Kerr coe?cient K leads to determining the dispersions of the other two, which is applicable under the condition that only electronicmechanism is taken into account at room temperature.The ATR technique has been applied to determine the second hy-perpolarizabilityγ(?ω4;ω3,ω2,ω1) of a linear conjugated polymer in theo?-resonant region. Based on the ATR technique, the second hyperpo-larizabilityγ(?ω;0,0,ω) of a linear conjugated polymer are measured atdi?erent wavelengths by the QEO e?ect. A least-square fit to the exper-imental data ofγ(?ω;0,0,ω) yields the frequency-independent compo-nents included in the two-level approximation ofγ(?ω4;ω3,ω2,ω1), andaccordingly theγ(?ω4;ω3,ω2,ω1) in the o?-resonant region is obtained.A further exploitation of the ATR technique has been put forwardto measure the complex second hyperpolarizability for the QEO e?ectof a linear conjugated polymer at a wavelength near the absorption.By employing the information obtained from di?erent wave resonancedips, the values as well as the signs of both parts of the complex secondhyperpolarizability are simultaneously obtained, requiring no Kramers-Kronig transformation.Compared with other techniques for measuring the third-order non-linearity of a polymer such as Z-scan, degenerated four wave mixing,the high-power pulse lasers are not required and the lock-in amplifier isno longer needed.