Enhancement And Applications Of Second Harmonic Generation In Several One-dimensional ?-? Group Nano-materials

Due to the excellent optical and electrical properties of one dimensional?-?group semiconductor nano-structures,they have played an important role as interconnects and functional units in microelectronic devices,integrated optoelectronic devices,and micro-electromechanical systems.Generally,?-?group semiconductors such as ZnS and CdS,have large second-order nonlinear susceptibilities.Recently,the second harmonic generation?SHG?of?-?group semiconductors has achieved important applications in bio-imaging and optical detection,which has become one of the research hotspots in optical detection technologies.The lattice orientations of a crytal can be obtained by measuring the relationship between the SHG intensity and the polarization state of the excitation light.Compared with the electron diffraction methods which are commonly used in the detection of crystal structures,this optical method has lower environmental requirements and makes no damage to the samples.However,previous researches only studied the effects of one crystal axis on the SHG responses,and the effects of the rest two axes were usually ignored.Improving the measurement precision of the polarization-dependent SHG responses,and realizing the precise determination of all the three crystal axes'orientations,will further expand the application scope of the optical method.Because of the small interaction volume between the nano-materials and photons,the low SHG conversion efficiency of nano-materials is also an urgent issue.Surface Plasmon Polaritons?SPPs?have been widely applied in the enhancement of localized field and the breakthrough of the optical diffraction limit.The traditional excitation and detection methods for SPPs have some problems,such as the low excitation efficiency,and the expensive detection equipments.If the excitation of SPPs can be achieved efficiently in subwavelength scale,and the observation of SPPs can be realized by an ordinary optical microscope,which will promote the researches and applications of SPPs in nano-photonics.Based on these problems,the main research works of this thesis are as follows:?1?Three kinds of one dimensional?-?group semiconductor nano-structures with high crystal qualities were synthesized by the chemical vapor deposition method,and these ZnS,CdS,and CdSe nanowires or nanobelts were then characterized by SEM and XRD.After dispersing the nanowires on a quartz substrate,we measured the photoluminescence properties of the single CdS nanowires and the single CdSe nanowires.?2?The SHG properties of single ZnS nanowires were studied by a self-built optical microscope system.Based on the polarization-dependent SHG responses,namely the relationship between the SHG intensity and the polarization state of the pump laser,we developed an all optical method for in-situ determination of all the three crystal axes'orientations.The crystal orientations of the ZnS nanowires measured by the optical method,are in good agreement with the HRTEM results.In addition,we have also studied the SHG conversion efficiency of a ZnS nanowire,which is in the order of 10^-6.?3?We fabricated a hybrid nanostructure combining the Al film with ZnS nanobelts to form an???shape,and studied the influence of the hybrid nanostructure on its SHG intensity.Using the lift-off process and the electronic beam evaporation method,we covered one part of a single ZnS nanobelt with the Al film,and remained the rest part as bare.The SHG enhancement factors of the Al-ZnS hbrid nanostructures were precisely measured.The results showed that the SHG enhancement factors were influenced not only by the polarization state of the pump laser,but also by the cross-section size of the ZnS nanobelt.In the experiments,the hybrid nanostructures have obtained the highest SHG enhancement factor exceeding 60 times.It is found that the enhanced foundmental optical field and the increased collection efficiency of the SHG signal,are the main factors that are responsible for the SHG enhancement.?4?In the hybrid nanostructures that consist of an Ag film and a CdSe nanowire,we have proved the feasibility that exciting the SPPs efficiently on the Ag film by the fluorescence signals of the CdSe nanowires,and observing the propagative SPPs with an ordinary optical microscope.Besides,we have designed a CdSe microcavity laser based on the above hybrid nanostructure,and simulated the field distributions of the resonant frequency in the microcavity.