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<p>We have formulated a mathematical model for a nonlinear photoacoustic (PA) response of two-layer samples. The features of second-harmonic (SH) generation of a nonlinear PA signal by these samples are studied in detail. Simple expressions for the amplitude of this signal, which describe its dependence on the modulation frequency of the incident beam, as well as on the thermal coefficients of thermophysical parameters and emissivity of the samples, are obtained for the most interesting cases. It was found that only for the case where the first layer is highly absorbing and both layers are thermally thick the frequency dependence of the SH amplitude of the PA signal has the form ω<sup>−5/2</sup> and is described by the function ω<sup>−3/2</sup> in all other cases. Only for nontransparent layers does the thermal coefficient of emissivity of the corresponding layer contribute to the amplitude of this signal.</p>

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Theory of Second-Harmonic Generation of a Nonlinear Photoacoustic Response Of Two-Layer Samples With Gas–Microphone Signal Recording

  • 期刊论文

  • 发表日期：

    2025年1月1日

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  • T. H. Salikhov,
  • Yu. P. Khodjaev,
  • A. Makhmalatif,
  • D. M. Sharifov

摘要

We have formulated a mathematical model for a nonlinear photoacoustic (PA) response of two-layer samples. The features of second-harmonic (SH) generation of a nonlinear PA signal by these samples are studied in detail. Simple expressions for the amplitude of this signal, which describe its dependence on the modulation frequency of the incident beam, as well as on the thermal coefficients of thermophysical parameters and emissivity of the samples, are obtained for the most interesting cases. It was found that only for the case where the first layer is highly absorbing and both layers are thermally thick the frequency dependence of the SH amplitude of the PA signal has the form ω−5/2 and is described by the function ω−3/2 in all other cases. Only for nontransparent layers does the thermal coefficient of emissivity of the corresponding layer contribute to the amplitude of this signal.