Study On The Magneto-Photovoltaic And The Hyper-Raman Tensors Of Crystals

The macroscopic physical properties of materials are connected with their inner structure and their symmetry. The symmetry of crystal is perfect, and various devices used of crystal material are widely applied in communications, photography, space navigation, medicine and other industries, and the base of these applications is the physical properties of crystals. The macroscopic physical properties of materials are always expressed by tensors. The calculation method of tensor invariants is used in this thesis. The magneto-photovoltaic and the hyper-Raman tensors are calculated through the C language programming of this method, and their properties are studied in this thesis.There are many methods in the tensors calculation, among which the method of invariants can be applied in a wide range, and easy to program. The calculation of high rank tensor can be completed accurately and quickly through the programming of method of invariants. In this thesis the programming is achieved through C language under the complied environment of Visual C++ 6.0. With the program the general bases of sixth-rank of some point groups are calculated. Also, the invariants theories of static tensor and dynamic tensor are analyzed separately, which is helpful for realization of the calculation of tensors of different types by invariants method.The influences of magnetic field on photorefractive processes have gradually attracted attentions of researchers. By the use of magneto-photorefractive effect, the photorefractive processes can be modulated by the magnetic field. The magneto- photovoltaic effect is an important transfer mechanism in the magneto-photorefractive effect. The associated magneto-photovoltaic tensor is a fourth-rank static pseudo-tensor, which can be divided in two parts, the linear magneto-photovoltaic tensor which is symmetric in the latter two subscripts, and the circular magneto-photovoltaic tensor which is antisymmetric in the latter two subscripts. For static pseudo-tensor, a new simple method based on invariants method is obtained through theoretical deduction in this thesis, by which the static pseudo-tensor of different rank can be obtained just using the bases in coordinate form. In this way the magneto-photovoltaic tensors of 32 crystal point groups are calculated, and the nonvanishing independent tensor components of these tensors are tabulated.Hyper-Raman scattering is a three-photons nonlinear scattering, which occurs when the incidence light is great and has a very special selection rule. When the photons explored in medium, more abundant spectrum information can be gained from this effect than those from Raman scattering and infrared absorption. The selection rule of hyper-Raman scattering can be obtained according to hyper-Raman tensor. Hyper-Raman tensor refers to lattice vibration, which is a third-rank dynamic tensor, and symmetric in the latter two subscripts. Using the programmed invariants method, the hyper-Raman tensors for C₅, C_5h, S₁₀, D₅, C_5v, D_5h and D_5d point groups with fivefold rotation axes are calculated in this thesis, and found that in the non-centre-symmetry point groups, except individual mode, most modes are active in hyper-Raman scattering; in the centre-symmetry point groups, those u mode which is silent in Raman scattering are active in hyper-Raman scattering.