Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA.
J Chem Phys. 2021 Dec 7;155(21):214202. doi: 10.1063/5.0071944.
Infrared photothermal heterodyne imaging (IR-PHI) is an all-optical table top approach that enables super-resolution mid-infrared microscopy and spectroscopy. The underlying principle behind IR-PHI is the detection of photothermal changes to specimens induced by their absorption of infrared radiation. Because detection of resulting refractive index and scattering cross section changes is done using a visible (probe) laser, IR-PHI exhibits a spatial resolution of ∼300 nm. This is significantly below the mid-infrared diffraction limit and is unlike conventional infrared absorption microscopy where spatial resolution is of order ∼5μm. Despite having achieved mid-infrared super-resolution, IR-PHI's spatial resolution is ultimately limited by the visible probe laser's diffraction limit. This hinders immediate application to studying samples residing in spatially congested environments. To circumvent this, we demonstrate further enhancements to IR-PHI's spatial resolution using a deep learning network that addresses the Abbe diffraction limit as well as background artifacts, introduced by experimental raster scanning. What results is a twofold improvement in feature resolution from 300 to ∼150 nm.
红外光热外差成像（IR-PHI）是一种全光学桌面方法，可实现超分辨率中红外显微镜和光谱学。IR-PHI 的基本原理是检测样品因吸收红外辐射而引起的光热变化。由于使用可见（探针）激光检测由此产生的折射率和散射截面变化，因此 IR-PHI 的空间分辨率约为 300nm。这明显低于中红外衍射极限，与传统的红外吸收显微镜不同，后者的空间分辨率约为 5μm。尽管已经实现了中红外超分辨率，但 IR-PHI 的空间分辨率最终受到可见探针激光衍射极限的限制。这阻碍了其在研究位于空间拥挤环境中的样品中的直接应用。为了克服这一问题，我们使用深度学习网络进一步提高了 IR-PHI 的空间分辨率，该网络解决了阿贝衍射极限以及由实验光栅扫描引入的背景伪影。结果是特征分辨率从 300nm 提高到约 150nm，提高了两倍。
