Random Laser Control And Surface Plasmon Enhancement Of Nanoparticles Scattering System

Random laser is produced in disordered media with gain.It is characterized with tiny footprint because the feedback is provided by light scattering rather than well-defined cavity in conventional lasers.This provides an idea for the design of micro lasers.However,up to now,random lasers do not achieve wide acceptance of conventional lasers.This is because their lasing mechanisms are not thoroughly understand yet,and their output characteristics are not appropriately regulated due to their randomness and unpredictability.In this thesis,the basic characteristics of random lasers,the mode control based on redistributing gain,the effect of local surface plasmon on the characteristics of random lasers are studied in the random lasers system of random distributed nanoparticles in gain medium by using the finite-difference time-domain(FDTD)method.First,the influence of the radius and refractive index of nanoparticles on the quasi-mode is studied based on FDTD.Localized mode and weakly Localized mode are observed at different refractive indexes.The four level model is used to describe the gain of the medium.The threshold characteristics of the random laser system doped with dielectric nanoparticles and the influence of filling factor on the threshold characteristics are studied.The relationship between the quasi-mode and the lasing mode is also observed.The influence of gain distribution on the lasing mode of random lasers is also studied.By adjusting the gain distribution to approach the field distribution of threshold lasing mode,the lasing modes for above threshold are suppressed,and the threshold mode is realized in a large range of pump rate.In addition,the effect of refractive index of dielectric nanoparticles on the above operation of mode control is also studied.Finally,the random lasing properties of the gain medium with randomly dispersed silver nanoparticles are studied.The metal nanoparticles doped random laser systems have been reported,but there is no theoretical or numerical work to study their mechanisms and laser characteristics systemmatically.This work investigates the spectrum and threshold characteristics of laser,and the influence of the size and the filling factor on these characteristics.We also discuss and confirm the contributions of localized surface plasmon to the optical feedback of laser.