Advances in Vibrationally Resonant Sum-frequency Generation Microscopy

Abstract

Vibrationally resonant sum-frequency generation microscopy is a member of the family of nonlinear optical microscopy techniques. It enables chemically selective imaging of non-centrosymmetric structures. We present the latest advances in this field.

Imaging Orientation of a Single Molecular Hierarchical Self-Assembled Sheet: The Combined Power of a Vibrational Sum Frequency Generation Microscopy and Neural Network

“…The hyperspectral microscope was based on VSFG spectroscopy, a second-order nonlinear optical phenomenon. As an even-order nonlinear optical process, only noncentrosymmetric systems produce VSFG responses, such as the air/liquid, air/solid, and solid/liquid interfaces. ,− Furthermore, VSFG is also sensitive to materials without inversion centers, − many of which are MSAs, including collagen, , amyloid fibers, artificial materials used in drug delivery, − metal–organic frameworks, − and piezoelectric crystals …”

“…Thus, traditional VSFG spectroscopy will probe multiple MSAs in an ensemble-averaged manner which does not accurately reflect the molecular structure of an individual MSA . The development of VSFG spectroscopy into a hyperspectral imaging technique ,− ,,,− overcame this challenge with 1 μm or submicrometer resolution being obtained, which offered a platform that could resolve multiple micrometer-sized MSAs individually.…”

Multimodal Nonlinear Vibrational Hyperspectral Imaging

“…32 While both are sensitive to structural arrangement, VSFG has the additional advantage of extracting chemical specific information because it measures molecular vibrational modes. 22,29,30,[40][41][42][43][44][45][46][47][48] Broadband VSFG employs a resonant femtosecond IR pulse spatially and temporally overlapped with a nonresonant visible or NIR beam to coherently generate a signal at the sum of the energy of the two input beams. With the availability of tunable IR sources, in the form of optical parametric amplifiers (OPAs) and optical parametric oscillators (OPOs), VSFG can cover any VSFG active vibrational modes.…”

“…Our group and others have developed the VSFG microscopy platform to accept biomimetic and biological materials. 22,29,30,40,41,43,44,46,47,52,53 Briefly, we have implemented a point-scanning VSFG microscope and used it to demonstrate superior phase stability for heterodyne detected VSFG images 41 , and the importance of visualizing local ordering in an overall disordered system. We further used it to resolve hydration levels of self-assembled biomimetic sheets at the single domain level 29 , and even conducted the first ultrafast vibrational dynamics of individual self-assembled sheets and reveal the heterogeneous hydration among sheets 22 .…”