基于表面热透镜的薄膜弱吸收测量的调制频率研究

Research of Modulation Frequency in Surface Thermal Lens Technique for Coatings Weak Absorption Measurement

激励光辐照薄膜的表面热透镜效应中,调制频率的大小影响样品内热波的热扩散深度。通过频率控制热波扩散深度可以探测不同薄膜层面的吸收和热缺陷分布。理论分析了不同薄膜厚度下调制频率对热扩散深度的影响。结果表明,薄膜的热导率越小、膜厚越厚,基底中的热扩散深度就越浅,不同材料的基底对吸收测量带来的影响就越小;在膜厚一定的情况下,调制频率越高,基底中的热扩散深度越浅,不同基底样品的光热信号将趋于相等。

The modulation frequency affects the thermal diffusion depth in sample during the coatings absorption measurement. The absorption value and thermal defects in various depth of the sample can be measured using proper modulation frequency. Theoretical analysis of the impact of modulation frequency on thermal diffusion depth at certain thickness of the coatings is presented. The results show that the thermal diffusion depth is shorter while the thermal conductivity is smaller and the coating is thicker,meanwhile the influence of the substrate is weaker. When the thickness of the coatings does not change,the thermal diffusion depth is shorter while the modulation frequency is higher,and the photothermal signals of different substrates tend to be same.