Study Of Optical Nonlinearity Dynamics In Toluene (C₇H₈) Solution

In the rapidly growing field of the organic functional materials, organic nonlinear optical (NLO) materials, especially of the third-order, are at the forefront of research activities. Organic third-order nonlinear optical materials have numerous applications, such as optical fiber communication, optical computing, optical data storage, dynamic holography, laser medical treatment, laser weapon and so on. In this dissertation, the interaction between laser and molecular system is studied in terms of micro-mechanism, and some new principles concerning nonlinear absorption and refraction are discussed.In this paper, we studied the impact of organic solution's parameter and laser condition on Z-scan curve, and got a set of assay parameter to determine nonlinear absorption and nonlinear refraction of organic solution. The nonlinear refractive index of toluene was measured using the Z-scan technique with 4f coherent imager technique and laser radiation of various pulse durations( 150fs,21 ps,4ns). We observed the growth of ywith the increase of the pulse duration( from 3.7×10¹⁶cm²/W at 150 fs to 2.6×10^-14cm²/W at4 ns ) . We analyzed the simultaneous influence of mechanisms leading to nonlinear refraction and in toluene.We discovered the reverse saturation absorptive behavior in Toluene when irradiatedby intensity of 4.73×10¹⁴W/m² under the picosecond pulse excitation at the wavelength of532nm .Two-photon absorption is proved to be the predominant mechanism causing the reverse saturation absorptive behavior. The TPA absorption cross-section is measured at 532nm by using an open aperture Z-scan system.