Phase-sensitive lock-in detection for high-contrast mid-infrared photothermal imaging with sub-diffraction limited resolution
Phase-sensitive lock-in detection for high-contrast mid-infrared photothermal imaging with sub-diffraction limited resolution
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DOI：
10.1364/oe.27.002643
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发表时间：
2019-02-04
期刊：
影响因子：
3.8
通讯作者：
Sander, Michelle Y.
中科院分区：
文献类型：
--
作者：
Samolis, Panagis D.;Sander, Michelle Y.
首次结合非线性解调展示了中红外光热振动显微镜中锁定放大器的相位输出成像。一般来说，热模糊和热传输现象有助于中红外光热成像的分辨率和灵敏度。对于具有多种吸收特征的异质样品，如果在与其嵌入介质吸收相当的光谱范围内成像，则证明与光热振幅信号的标准成像相比，从锁定放大器获得的相位信号的互补成像实现了高对比度的区分。具体来说，通过研究异相锁定信号的相对贡献，可以提取基于热传输速率变化的信息，并且可以以高灵敏度和亚衍射有限分辨率来映射整个样品平面的热扩散特性的不均匀性。在这些成像条件下，可以识别波数范围，其中热扩散贡献被最小化，并且实现了空间分辨率的增强，超出了相应相位图像中探测光束的衍射极限光斑尺寸。通过将相对扩散相位成像与二次谐波非线性解调相结合，证明嵌入 4-辛基-4'-氰基联苯 (8CB) 液晶薄层中的 1μm 大小的三聚氰胺珠可以以 1.3μm 空间半峰全宽 (FWHM) 分辨率进行检测。因此，成像分辨率超过探针衍射极限光斑尺寸 2.5 倍，这为中红外超分辨率、无标记成像铺平了道路。 (C) 2019 年美国光学学会根据 OSA 开放获取出版协议条款
Imaging of the phase output of a lock-in amplifier in mid-infrared photothermal vibrational microscopy is demonstrated for the first time in combination with nonlinear demodulation. In general, thermal blurring and heat transport phenomena contribute to the resolution and sensitivity of mid-infrared photothermal imaging. For heterogeneous samples with multiple absorbing features, if imaged in a spectral regime of comparable absorption with their embedding medium, it is demonstrated that differentiation with high contrast is achieved in complementary imaging of the phase signal obtained from a lock-in amplifier compared to standard imaging of the photothermal amplitude signal. Specifically, by investigating the relative contribution of the out-of-phase lock-in signal, information based on changes in the rate of heat transport can be extracted, and inhomogeneities in the thermal diffusion properties across the sample plane can be mapped with high sensitivity and subdiffraction limited resolution. Under these imaging conditions, wave number regimes can be identified in which the thermal diffusion contributions are minimized and an enhancement of the spatial resolution beyond the diffraction limited spot size of the probe beam in the corresponding phase images is achieved. By combining relative diffusive phase imaging with nonlinear demodulation at the second harmonic, it is demonstrated that 1-mu m -size melamine beads embedded in a thin layer of 4-octyl-4'-cyanobiphenyl (8CB) liquid crystal can be detected with a 1.3-mu m spatial full-width at half-maximum (FWHM) resolution. Thus, imaging with a resolving power that exceeds the probe diffraction limited spot size by a factor of 2.5 is presented, which paves the route towards super-resolution, label-free imaging in the mid-infrared. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement