School of Science Department of Physics 67 Femtosecond Laser Pulse Induced Air-plasma Filament for Generating THz Radiation: Experiment and Simulation Supervisor: ZHANG Jingdi / PHYS Student: LIN Yuchen / COSC Course: UROP3100, Fall Following the previous UROP 2100 research, a series of numerical simulations on the terahertz generation induced by the Orbital Angular Momentum (OAM) modulated light and TEMlm wave have been performed for UROP 3100. Because the original two dimensional numerical model is inadequate when applying to systems with no rotational symmetry, a new three dimensional simulation program has been developed and tested this semester. Meanwhile, the assembly of the femtosecond laser pulse induced terahertz generation system and the alignment of optical instruments were also carried out. In the coming winter period, experiments will be performed to generate the terahertz wave which serve as a prerequisite for the investigation of terahertz generated by polarized light, and we aim to verify our proposed model clarifying the dynamics of terahertz generation in future experiments. Femtosecond Laser Pulse Induced Air-plasma Filament for Generating THz Radiation: Experiment and Simulation Supervisor: ZHANG Jingdi / PHYS Student: PENG Huaiyue / PHYS Course: UROP1100, Spring UROP2100, Summer Lorentz oscillator is a classical model to describe the motion of the phonons when a material is polarized by the electric field brought by the input light wave, where a guassian pulse is adopted. In this program, we stimulate the nonlinear polarization process in SiC via FDTD algorithm inMATLAB. The modulated equations are derived from the Lagrangian by assuming the varying permittivity and effective charge. After getting the dispersion spectrum and compare it with the classical one, we find that dispersion of the nonlinear phonon oscillator differs from the linear oscillator, which arouses our interests to research deeper in this field. Optical Parametric Amplification of Femtosecond Laser Pulse Supervisor: ZHANG Jingdi / PHYS Student: YANG Yiguang / PHYS Course: UROP1000, Summer This report includes two parts that I mainly pay attention to during this period. The first part is optical parametric amplification, including collinear OPA and noncollinear OPA, which can help to enhance the power of laser pulse. Also, a basic model for 3 stage OPA will be shown in the report. The second part is using MATLAB to do the simulation for photonic and ionic Raman scattering for diamond, ErFeO3 and BiFeO3. Raman scattering is a kind of inelastic scattering between photon and particle. During this process, energy exchange will happen, which result in the wavelength change of photon.