推导了调制的平顶光束激励下基于Fresnel衍射积分的表面热透镜理论,通过数值模拟,比较了平顶光束和高斯光束激励下样品内部温度场、表面形变场和探测光衍射信号的径向分布,分析了影响表面热透镜信号的实验参数.结果表明,在最佳探测位置,平顶光束激励下的表面热透镜系统比相同情况下高斯光束激励下的灵敏度高,最高时约2倍,更有利于薄膜吸收测量. The theory of surface thermal lens based on Fresnel diffraction integral under the modulated flat-top beam excitation is deduced. The radial distribution of the internal temperature field, the surface deformation field and the diffraction signal of the probe light under the excitation of the flat-top beam and the Gaussian beam is compared by numerical simulation , The experimental parameters affecting the signal of the surface thermal lens are analyzed.The results show that the surface thermal lens system excited by the flat-top beam is higher than the Gaussian beam excitation under the same conditions at the best detection position, about 2 times the maximum, Conducive to film absorption measurement.