Mader D S, Niemann R, Wolf M, Maehrlein S F, Paarmann A
Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany.
J Chem Phys. 2024 Sep 7;161(9). doi: 10.1063/5.0220619.
Nonlinear-optical microscopy and spectroscopy provide detailed spatial and spectroscopic contrast, specifically sensitive to structural symmetry and order. Ferroics, in particular, have been widely studied using second harmonic generation imaging, which provides detailed information on domain structures but typically lacks spectroscopic detail. In contrast, infrared-visible sum-frequency generation (SFG) spectroscopy reveals details of the atomic structure and bonding via vibrational resonances, but conventionally lacks spatial information. In this work, we combine the benefits of nonlinear optical imaging and SFG spectroscopy by employing SFG spectro-microscopy using an infrared free-electron laser. In particular, we demonstrate the feasibility of SFG spectro-microscopy for spectroscopy using in-plane anisotropic wurtzite-type aluminum nitride as a model system. We find the experimental spectra to agree well with our theoretical calculations, and we show the potential of our microscope to provide spatially resolved spectroscopic information in inhomogeneous systems such as ferroics and their domains in the near future.
非线性光学显微镜和光谱学提供了详细的空间和光谱对比度，对结构对称性和有序性特别敏感。特别是，铁电体已被广泛使用二次谐波产生成像进行研究，该成像提供了有关畴结构的详细信息，但通常缺乏光谱细节。相比之下，红外-可见和频产生（SFG）光谱通过振动共振揭示了原子结构和键合的细节，但传统上缺乏空间信息。在这项工作中，我们通过使用红外自由电子激光的SFG光谱显微镜结合了非线性光学成像和SFG光谱学的优点。特别是，我们展示了使用面内各向异性纤锌矿型氮化铝作为模型系统进行SFG光谱显微镜光谱分析的可行性。我们发现实验光谱与我们的理论计算非常吻合，并且我们展示了我们的显微镜在不久的将来为诸如铁电体及其畴等非均匀系统提供空间分辨光谱信息的潜力。
