Ichihashi Hayato, Ueno Shoya, Fukunaga Takumi, Takayanagi Shinji, Matsukawa Mami
IEEE Trans Ultrason Ferroelectr Freq Control. 2022 Jun;69(6):2152-2161. doi: 10.1109/TUFFC.2022.3165519. Epub 2022 May 26.
A pump-probe system with a subnanosecond pulsed laser is expected to be a compact and inexpensive transient spectroscopic system that enables nondestructive and noncontact evaluations of the physical properties. However, an improvement in the sensitivity and a theoretical model to complement the measurement signal are necessary to obtain the transient signal precisely because of the low sensitivity and large time resolution. We have developed a highly sensitive pump-probe system with a subnanosecond pulsed laser that combines signal amplification based on surface plasmon resonance (SPR) in this study. An integrated theoretical model of the transient response obtained by a subnanosecond pump-probe under the SPR condition was proposed. Our model consisted of the profile descriptions of the used pulse source, temperature change, generated thermoelastic stress, estimated permittivity change in the metal film, and estimated reflectivity change. The theoretical estimations in the time domain and the incident angle dependence were compared with those of the experimental results to verify our theory. As a result, the estimations were well in agreement with the experimental results. Moreover, the signal-amplification mechanism based on SPR was discussed using our theory. The amplification was caused by the broadening of the resonant curve of SPR and the shift of the resonant angle, which seemed to come from the increase in the electron-phonon scattering rate and the thermal expansion of the metal film, respectively. A clear mechanism of SPR-based signal amplification of the subnanosecond pump-probe was identified through experimental and theoretical approaches.
具有亚纳秒脉冲激光的泵浦 - 探测系统有望成为一种紧凑且廉价的瞬态光谱系统，能够对物理性质进行无损和非接触式评估。然而，由于灵敏度低和时间分辨率大，要精确获得瞬态信号，就需要提高灵敏度并建立一个补充测量信号的理论模型。在本研究中，我们开发了一种具有亚纳秒脉冲激光的高灵敏度泵浦 - 探测系统，该系统结合了基于表面等离子体共振（SPR）的信号放大技术。提出了在SPR条件下由亚纳秒泵浦 - 探测获得的瞬态响应的综合理论模型。我们的模型包括所用脉冲源的轮廓描述、温度变化、产生的热弹性应力、金属膜中估计的介电常数变化以及估计的反射率变化。将时域和入射角依赖性的理论估计与实验结果进行比较，以验证我们的理论。结果，这些估计与实验结果吻合良好。此外，利用我们的理论讨论了基于SPR的信号放大机制。这种放大是由SPR共振曲线的展宽和共振角的移动引起的，这似乎分别源于电子 - 声子散射率的增加和金属膜的热膨胀。通过实验和理论方法确定了亚纳秒泵浦 - 探测基于SPR的信号放大的清晰机制。
