MICROSCOPIC EXPRESSION OF NONLINEAR SUSCEPTIBILITY IN A SIX-LEVEL MODEL
六能级分子系统非线性极化率的微观描述

Adopting density matrix theory and a six-energy-level model,the microscopic expression nonlinear susceptibility,nonlinear absorption coefficient and nonlinear refraction indices are deduced.All of them are proportional to the linear sum of the population in each energy-leveI. The parameters,refraction volume and absorption cross - section, are introduced into describing the characteristic of refraction and absorption.