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从热传导方程出发，研究了脉冲激光作用下因样品线性和非线性吸收引起热效应而产生的折射率变化．从理论分析得出，当仅存在线性吸收时，非线性折射率的概念在通常情况下并不适合于由热效应产生的非线性，但在所用的激光脉冲很短的情况下，类似于其它非线性的各种效应，对热效应也可定义时间平均非线性折射率，并可用Z－scan法对这两类吸收感生的不同非线性折射率进行测量．所得结论符合实验结果．
Based on the heat conduction equation, the change of refractive index due to the thermal effect caused by the linear and nonlinear absorption of the sample under pulsed laser irradiation was studied. The theoretical analysis shows that when there is only linear absorption, the concept of nonlinear refractive index is not suitable for the nonlinearity caused by thermal effect under normal circumstances. However, when the laser pulse is very short, it is similar to other non-linear The various effects of linearity also define the time-averaged nonlinear refractive index for the thermal effects and the different nonlinear refractive indices induced by these two types of absorption can be measured by Z-scan. The conclusion is in line with the experimental results.