The Study Of Light Intensity And Energy Transmission Of Non-paraxial Vector Diffraction Beam

The movement law of light wave, electromagnetic wave, is described by the Maxwell equations, so light field is the vector field in nature. Along with the development of near-field optics and the gradually increased using of small-scale but large divergence angle light, the scalar approximation of diffraction theory is no longer useful and vector diffraction theory must be applied. Light intensity has many definitions and it is defined as the average energy flowing through the unit area within unit time in light vector theory. Light intensity in the cross section perpendicular to the optical axis (z-axis) is equivalent to the z component of the average Poynting vector. Also light intensity is traditionally defined as the square of the absolute value of the complex vibration amplitude of light I =|E_x |~2 +| E_y |~2 + | E_z|~2. This research compared the two light intensity definitions in detail and analyzed the validity of the traditionally defined light intensity I and characteristics of axial light intensity of Gaussian beam diffracted by a circular aperture. Taken the non-paraxial diffraction of a small circular aperture as an example, the formulae for three different kinds of light intensity I , J zand S z at transverse plane are obtained. Detailed numerical calculation is performed and the different results are compared and analyzed the characteristics of axial light intensity.In the study of light beam energy transmission, the energy focusability of light beam is a very important physical unit to describe the characterization of energy transmission. Based on the accurate expression of light intensity of non-paraxial vector diffraction beam at the transverse plane and the rigorous vectorial diffraction theory, the energy focusability of small circular aperture are analyzed in this paper. Numerical calculation results show the dependence of energy focusability of the diffraction beam on the transmission distance, diffraction aperture, facula radius. It showed that appropriate energy focusability can be got by controlling parameters of optical system, the results have some reference value to the research of energy transmission of the fiber probe.