Photoacoustic spectroscopy (PAS) measures the photon absorption spectrum of a sample through detection of the acoustic wave generated by the photothermal effect as one modulates the intensity of the incident radiation at each wavelength. We have recently demonstrated the implementation of PAS in a microscopy configuration with mid-infrared radiation (microPAS). In the present work, we describe the performance of microPAS using synchrotron radiation (SR) in diffraction-limited spectromicroscopy and imaging experiments. Spectra were obtained for polystyrene beads, polypropylene fibres, and single fibres of human hair. SR produced microPAS spectra of much higher intensity as compared with those obtained using conventional mid- and near-infrared sources. For hair samples, the penetration depth of mid-infrared light, even with bright SR, is significantly shorter than the probed sample thickness at very low modulation frequencies resulting in saturated PAS spectra. In contrast, microPAS spectra of polymer beads were in general of much better quality than those obtained with conventional sources. We also demonstrated the capability to collect line profiles and line spectra at diffraction limited spatial resolution. The microPAS spectra of beads appear free from appreciable bandshape distortions arising from the real part of the refractive index of the sample. This observation confirms microPAS as an absorption-only technique and establishes it as a valuable new tool in the microspectroscopic analysis of particulates and of samples with a complex topography.

中文翻译：

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用微光声光谱法和同步加速器辐射对微结构样品的红外光谱进行分析。

光声光谱法（PAS）通过检测由光热效应产生的声波来测量样品的光子吸收光谱，因为它可以调制每个波长下的入射辐射强度。我们最近在具有中红外辐射（microPAS）的显微镜配置中演示了PAS的实现。在目前的工作中，我们描述了在衍射极限光谱学和成像实验中使用同步辐射（SR）的microPAS的性能。获得了聚苯乙烯珠，聚丙烯纤维和人发单纤维的光谱。与使用传统的中红外和近红外光源相比，SR产生的microPAS光谱具有更高的强度。对于头发样品，即使在明亮的SR情况下，中红外光的穿透深度也是如此，它在非常低的调制频率下比所探测的样品厚度要短得多，从而导致PAS光谱饱和。相比之下，聚合物珠粒的microPAS光谱通常质量要好于常规来源的光谱。我们还展示了在衍射受限的空间分辨率下收集线轮廓和线谱的能力。珠子的microPAS光谱看起来没有明显的由样品折射率的实数部分引起的带状畸变。这一观察结果证实了microPAS是仅吸收技术，并使其成为具有复杂形貌的微粒和样品的显微光谱分析中有价值的新工具。聚合物珠粒的microPAS光谱质量通常比使用常规来源获得的质量好得多。我们还展示了在衍射受限的空间分辨率下收集线轮廓和线谱的能力。珠子的microPAS光谱看起来没有明显的由样品折射率的实数部分引起的带状畸变。这一观察结果证实了microPAS是仅吸收技术，并使其成为具有复杂形貌的微粒和样品的显微光谱分析中有价值的新工具。聚合物珠粒的microPAS光谱质量通常比常规来源的质量好得多。我们还展示了在衍射受限的空间分辨率下收集线轮廓和线谱的能力。珠子的microPAS光谱看起来没有明显的由样品折射率的实数部分引起的带状畸变。这一观察结果证实了microPAS是仅吸收技术，并使其成为具有复杂形貌的微粒和样品的显微光谱分析中有价值的新工具。珠子的microPAS光谱看起来没有明显的由样品折射率的实数部分引起的带状畸变。这一观察结果证实了microPAS是仅吸收技术，并使其成为具有复杂形貌的微粒和样品的显微光谱分析中有价值的新工具。珠子的microPAS光谱看起来没有明显的由样品折射率的实数部分引起的带状畸变。这一观察结果证实了microPAS是仅吸收技术，并使其成为具有复杂形貌的微粒和样品的显微光谱分析中有价值的新工具。