Modulation Of Photoluminescence And Random Laser Based On Weak Localizaiton Of Light In PLZT Ceramics

When photons propagate in an inhomogeneous medium,multiple scattering of light occurs inevitably.If multiple scattering is strong enough,there are chances that light can be localized in limited regions.As one of the hot topics in these years,Anderson localization of light has been studied in powder materials,one and two dimensional photonic crystals,cold atomic gas and other disordered materials,which are applied to data storage,biomedical detection,laser modulation and some other related fields.Laser modulation has attracted growing attention,especially in the aspects of transferring efficiency,miniaturization and integration of photonics devices.Rare earth(RE)doped lead lanthanum zironate titanate ceramics,as a family of excellent laser gain materials,have been used in researching novel type lasers.Weak localization of light would be formed under certain conditions based on the abundant intrinsic traps and photon induced charge accumulation in the PLZT ceramics,which play crucial roles in modulation of the luminescence and random lasers,and provide a new approach to improve the laser 's efficiency and miniaturization.Especially,random lasing is one of the most frontier research directions in recent years.In this thesis,based on the weak localization of light observed in RE doped PLZT ceramics,up and down frequency conversion luminescence,optical amplification and random lasing would be modulated.Along this line,high efficiency lasers with compact size are expected to be generated.In addition,the exploration to distribution of traps in the PLZT ceramics provide theoretical basis for the study of the weak localization and random las ing action.Taking distribution of traps as the foundation,weak localization was studied firstly.The distribution of the traps was investigated through analyzing the material components,structure and the variation of the spectrum upon exposing to different light radiations.The trap energy level distribution model was established based on the analysis of dynamics of the transmission spectrum and transmittance of the specimen upon exposing to light radiation of various powers.The transition rate equation was written based on the model established and the phenomena observed.The numerical simulation results by using the transition rate equation confirmed validity of the trap distribution model.An improved trap distribution model was established through analysing the variation of the transmission spectrum upon exposing to short wavelength light,which provides theoretical basis for dealing with the weak localization and random lasing action in the PLZT ceramics.Consisting with the picture illustrated in the trap distribution model,weak localization of light was observed in the Nd3+ doped bulk PLZT at the expense of 808 nm laser,which is discussed in details in the second part of this thesis.A laser with center wavelength of 1064 nm was selected as the signal light to study the amplification of light based on the analysis of the scattering and absorption cross sections.As high as 670% optical amplification was obtained.To explain the high optical amplification,on one hand,strong scattering theory was used for quantitative analysis;On the other hand,theoretical interpretation was proposed based on the trap distribution model and related electron transition processes.Besides,the dynamic process of the optical amplification was analyzed by using weak localization of light.The charge accumulation model was confirmed through monitoring the photoinduced current in the specimen.Based on the experiments and analysis above,a tunable optical amplification could be realized by changing the density of the scatterer via adjusting the pumping power.To improve the multiple scattering intensity of light and hence to improve light localization,powder PLZT specimen was prepared and studied in the third part of this thesis.Based on the weak localization of light,the multiphoton upconversion experiment was devised in the Er3+/Yb3+ codoped ceramics at the expense of 1480 nm laser and strong three-photon upconversion luminescence was observed.Based on the trap distribution model,the upconversion process was discussed by making use of weak localization and energy level transition structure.The emission intensity and the output light color could be adjusted by changing the degree of the weak localization througth adjusting the pumping power on the specimen.To further improve the multiple scattering and hence to lower the pumping power threshold of the weak localization of light,in the last part of this thesis,a nanometer structured array was obtained on the surface of the bulk ceramics by using the technique of femtosecond laser ablation.Coherent feedback random lasing action in the Nd3+ doped PLZT ceramics was observed by using a nanosecond laser with center wavelength 532 nm.Remarkably narrowed emission peak,which is a hallmark feature of random lasing was observed.The laser emission spectrum,laser oscillation curve and apparent directional emission were investigated and discussed under different pumping power and pumping direction.The oscillation process was simulated by using the rate equations and oscillation frequency equations.T he coherent feedback random laser model was established and the narrow peak character of random lasing emission spectrum was discussed based on weak localization of light.