Coherent nonlinear vibrational microscopy

Coherent nonlinear vibrational microscopy has emerged as a powerful platform for label-free, chemically specific imaging by probing intrinsic chemical bond vibrations. This review comprehensively examines the principles and applications of three foundational techniques: vibrational sum-frequency generation for interfacial and chiral analysis; coherent Raman scattering, encompassing coherent anti-Stokes Raman scattering and stimulated Raman scattering, for bond-selective chemical visualization; and stimulated Brillouin scattering for biomechanical mapping. We highlight recent transformative advances including hyperspectral multiplexing, super-resolution implementations, and AI-integrated analysis, which have significantly enhanced imaging capabilities. These developments have enabled unique applications in diverse fields such as biomedicine, physical chemistry, materials science, and environmental science. While challenges in imaging depth and system portability remain, we discuss promising solutions based on ongoing instrumental and computational developments. Collectively, these coherent nonlinear vibrational imaging techniques bridge molecular spectroscopy and functional microscopy with unprecedented analytical and diagnostic capabilities.