Microscopic molecular alignment occurs ubiquitously in various synthetic and natural materials, determining their biological, chemical, and mechanical properties. However, conventional 2D polarization-based imaging methods cannot determine the out-of-plane angle. We have developed the world’s first 3D-orientation imaging method of continuously distributed materials by analyzing two vibrational modes concurrently observed by polarization-controlled IR and Raman microscopy. This rapid, non-invasive imaging technique helps understand the molecular-level structure of highly anisotropic and spatially heterogeneous materials.
We have developed 3D orientation imaging methods for both infrared (IR) and coherent anti-Stokes Raman scattering (CARS) signals. The two approaches are complementary to each other. The IR-based 3D orientation imaging is broadly applicable to any pair of non-parallel IR transition dipole moments, but its spatial resolution is in the several-micrometer scale [1-3]. On the other hand, the analysis of polarization CARS signals is more complicated, but it can provide sub-micrometer resolution [4-7]. These new complementary imaging methods will be able to provide previously unavailable molecular information that can bridge the gap in the relation of [process···structure···property]. This innovative optical metrology will advance plastic manufacturing, 3D printing, medical implants, tissue engineering, and other material sciences and industries.
 Y. J. Lee, Concurrent Polarization IR Analysis to Determine the 3D Angles and the Order Parameter for Molecular Orientation Imaging, Opt. Express 26, 24577 (2018). https://doi.org/10.1364/OE.26.024577
 S. Xu, J. Rowlette, Y. J. Lee, Imaging 3D molecular orientation by orthogonal-pair polarization IR microscopy, Opt. Express 30, 8436 (2022). https://doi.org/10.1364/OE.449667
 S. Xu, C. R. Snyder, J. Rowlette, Y. J. Lee, Three-Dimensional Molecular Orientation Imaging of a Semicrystalline Polymer Film under Shear Deformation, Macromolecules 55, 2627 (2022). https://doi.org/10.1021/acs.macromol.1c02036
 Y. J. Lee, C. R. Snyder, A. M. Forster, M. T. Cicerone, W. Wu, Imaging the Molecular Structure of Polyethylene Blends with Broadband Coherent Raman Microscopy, ACS Macro Lett. 1, 1347 (2012). https://doi.org/10.1021/mz300546e
 Y. J. Lee, Determination of 3D Molecular Orientation by Concurrent Polarization Analysis of Multiple Raman Modes in Broadband CARS Spectroscopy, Opt. Express 23, 29279 (2015). https://doi.org/10.1364/oe.23.029279
 Y. J. Lee, Theory of birefringence correction for polarization-controlled CARS, Opt. Express 28, 9158 (2020). https://doi.org/10.1364/OE.389558
 S. Xu, Y. Jin, Y. J. Lee, 3D orientation imaging of polymer chains with polarization-controlled coherent Raman microscopy, J. Am. Chem. Soc. Published online (2022). https://doi.org/10.1021/jacs.2c10029