Study Of Excited-state Absorption And Refraction Dynamics Of An Organic Salt Solution Using Time-solved Pump Probe Technique With Phase Object

In recent years, the material with large optical nonlinearities and fast response time has received considerable attention due to their variety of applications in photonics such as all-light switching, optical limiter and optical phase conjugation. In general, organic nonlinear optical materials are superior to their inorganic counterpart for their large nonlinear optical properties and almost unlimited design possibilities.The phenoxazine compound, which is aπ-bridge conjugation unsymmetrical structure, is a kind of organic salt. During the past few years, there are many article reported on the synthesis and characterization of organic phenoxazinium type compounds and their derivatives because of their potential applications in biologically active reagents, fluorescent dyes, DNA probes etc. However, to the best of our knowledge, studies on the optical nonlinearity of these organic compounds are seldom reported, whereas detail experimental reports concerning the exited-state dynamics of the phenoxazine compound are almost non-existent. In this dissertation, the excited-state nonlinear optical properties of a novel phenoxazine compound/ acetonitrile solution are investigated by a modified time-resolved pump-probe technique with phase object at 532 nm with picosecond laser pulse. With the aid of nanosecond Z-scan measurement, the excited state absorptive and refractive parameters of the phenoxazine molecule are determined uniquely.There are three major parts in this dissertation. In the first part, the five-energy-level model and the theory of the time-resolved pump-probe measurement with phase object are presented in detail. And the influences of excited-state parameter variation to the pump-probe result are discussed. In the second part, the experimental detail of the time-resolved pump-probe measurement with phase object is described. It is found that the nonlinear optical response of the phenoxazine compound/ acetonitrile solution is originated from the solute molecule's excited-state mechanism. The sample solution shows reverse saturable absorption and self-focusing effect. In the last part, the theory and experimental detail of the nanosecond Z-scan experiment are presented briefly. All of the compound's excited-state absorptive and refractive parameters are verified by comparing the pump-probe and Z-scan data. The experimental result shows the phenoxazine compound has large absorption cross sections and change of refraction index per unit density for excited-state as well as rather long lifetime, indicating this compound is a good candidate for future photonics applications.