The Influence Of Exciton Effect And Gold Nanoparticles On The Nonlinear Optical Properties Of Quantum Wells

Since the advent of laser,nonlinear optics has been a broad research field,which has brought a wide range of fascinating functions and applications.Low dimensional semiconductor materials with great potential,such as superlattices,quantum wells,quantum wires,quantum dots and so on,have been studied because of their low threshold power,fast response rate and obvious nonlinear optical coefficient.At the same time,people pursue the semiconductor devices with higher accuracy,faster response,more durable,more stable and smaller structure volume.The theory and technology application of nonlinear optics are in line with expectations.The continuous advancement of nanoprocessing technology has enabled more and more new materials to be prepared,which has brought us more challenging research topics.Based on the above factors,this article has carried out two researches on the nonlinear optics of low dimensional semiconductors.The first one is the influence of exciton effects on optical absorption coefficient and refractive index changes in Morse quantum wells.The second one is the influence of gold nanoparticles on optical absorption coefficient and refractive index in Morse quantum wells.In order to demonstrate these two works,this article is divided into the following four chapters to elaborate.The first chapter is the introduction.This chapter introduces the background of nonlinear optics,including the principle of nonlinear optics,and the research content and object of nonlinear optics.The research content of this article is also introduced(the effects of exciton effect and gold nanoparticles on optical absorption coefficient and refractive index changes in Morse quantum wells are studied).Finally,the research methods are introduced,including diagonalization,variational method,density matrix method,iterative method,MNPBEM toolbox,etc.The second chapter studies the influence of exciton effect on optical absorption coefficient and refractive index changes in Morse quantum wells.First of all,the diagonalization and variational method are used to calculate the energy and wave function of exciton state in Morse quantum wells.And then,the density matrix method and iterative method are used to analyze the exciton effect on optical absorption coefficient and refractive index.This chapter analyzes the influence of the exciton effect in Morse quantum wells from four aspects: the presence or absence of excitons,aluminum concentration,width parameters,and electric field strength.The calculation results show that the exciton effect significantly increases the optical absorption coefficient and refractive index changes.The increase of aluminum concentration and width parameters can also increase the optical absorption coefficient and cause blue shift.But the enhancement of the electric field will lead to a completely different phenomenon: the optical absorption coefficient and refractive index changes are suppressed.The third chapter studies the influence of gold nanoparticles on optical absorption coefficient and refractive index changes in Morse quantum wells.This part of the research work is to undertake the research work of the second chapter.The first step is to use diagonalization and variational methods to calculate the energy and wave function of exciton state in Morse quantum well.After that,we consider the correction effects of excitonplasmon coupling and Purcell effect on the energy level and relaxation rate.Finally,the density matrix method and iterative method are used to analyze the influence of gold nanoparticles on optical absorption coefficient and refractive index changes.This chapter analyzes the influence of gold nanoparticles in Morse quantum wells from three aspects: the presence or absence of gold nanoparticles,the center distance between gold nanoparticles and quantum wells,and the size of gold nanoparticles.The calculation results show that the placement of gold nanoparticles will cause the optical absorption coefficient to weaken.At the same time,the increase in the diameter of the gold nanoparticles and the decrease in the distance between the gold nanoparticles and the quantum well will make the optical absorption coefficient weaker more obvious.Chapter 4 summarizes the full text.