| During the interaction of a uniformly distributed scalar light field with an isotropic nonlinear Kerr media,since the homogeneous polarization state,in general,the magnitude of the third-order nonlinearity excited by nonlinear optical materials mainly depends on the change of the intensity of the inident light field.In recent years,the vetorial light fields with inhomogenous polarization distribution become a research hotspot.During the action of a vectorial light field with the structured polarization and nonlinear Kerr media,the third-order nonlinear refractive index is modulated by both the light intensity and the polarization state of the incident light field,therefore,structured intense laser interacting with matter results in a varity of novel nonlinear optical effects,reflects the nonlinear optical property of material,and modulates the light propagation behavior.In this thesis,we investigate the isotropic Kerr nonlinearities and anisotropic Kerr nonlinearities induced by scalar and vectorial optical fields,respectively.The main contents and research results are listed below:(1)Due to the orientation nonlinearity of an anisotropic nonlinear Kerr medium,we theoretically investigate the far-field vectorial self-diffraction pattern of radially polarized beam modulated by the anisotropic nonlinearity based on the vectorial Rayleigh-Sommerfeld formulas.The results show that the far-field vectorial self-diffraction pattern has four-fold rotational symmetry,and the optical field is modulated from radially polarized beam to hybridly polarized beam.Furthermore,the radially polarized beam interacting with the anisotropic nonlinear Kerr media results in the redistribution of the spin angular momentum on the far-field observational plane.(2)The elliptically polarized vector beams modulated by isotropic Kerr nonlinearities,the polarization state of the far-field observational plane exhibits a radial-variant nonlinear ellipse rotation.Specifically,on the far-field observational plane,along the radial direction,both the orientation angle and ellipticity angle of the local polarization ellipse show a gradient distribution.Numerical simulation results show that the self-diffraction intensity pattern,the distribution of the state of polarization,and the spin angular momentum distribution of an elliptically polarized vector beams could be manipulated by tuning both the isotropic optical nonlinearity and the chirality parameter of the vectorial light field.After the scalar elliptically polarized light passing through the anisotropic nonlinear Kerr media,the rotation angle induced by nonlinear ellipse rotation depends on the nonlinear phase shift,ellipticity as well as crystal orientation angle.The elliptically polarized vector beam modulated by the anisotropic nonlinear Kerr media,the intensity pattern and spin angular momentum present nonuniform distribution,what’s more,with the ellipticity decreases,the far-field light intensity gradually increases and the spin angular momentum redistributes..(3)We theoretically investigate the spatial self-phase modulation effect,nonlinear ellipse rotation,and spin angular momentum redistribution of hybridly polarized vector beams through isotropic nonlinear Kerr nonlinearities.Experimentally,we observe the spatial self-phase modulation of the femtosecond-pulsed hybridly polarized vector beam in carbon disulfide at 800 nm,which is in agreement with the theoretical predictions.Our results show that the spatial self-phase modulation intensity pattern,the distribution of state of polarization,and the spin angular momentum of a hybridly polarized vector beam could be manipulated by tuning the isotropic optical nonlinearity.The anisotropic third-order nonlinear refraction indexes based on the left-hand and right-hand base vectors,which depend on the ellipticity,the dichroism coefficient,the nonlinear anisotropy coefficient,as well as the crystal orientation angle.Experimentally,we develop the elliptically polarized light Z-scan technique for characterizing third-order nonlinear susceptibility tensor in anisotropic nonlinear Kerr media.With the known nonlinear optical parameters,we numerically simulated both the vectorial self-diffraction behaviors and spin angular momentum characteristics of hybridly polarized beams induced by an anisotropic Kerr nonlinearity.The results shown that the anisotropic Kerr nonlinearity offers a new approach to manipulate the polarization-structured light field.(4)We report a theoretical investigation on polarization rotation and singularity evolution of focused fundamental Poincaré beams in free-space propagation and through isotropic and anisotropic nonlinear Kerr media.It is shown that when propagation in free-space,the basic Poincaré beams only exhibits overall polarization rotation,and after passing through the nonlinear Kerr medium,due to the existence of optical nonlinearity,the polarization rotation characteristics of the fundamental Poincaré beams are enhanced.It is worth mentioning that the anisotropy of optical nonlinearity leads to the symmetry breaking of the polarization distribution.Further studies show that the C-point and L-line singularities of the lemon Poincaré beams do not change while propagating in free space or through the isotropic nonlinear Kerr medium.Interestingly,the anisotropic Kerr nonlinearity evokes the C-point singularity splitting,and the distortion and birth of L-line singularities.However,the total singularity index always remains the conservation within the light field,regardless of the optical nonlinearity. |
