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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.

3D orientation angle images of a polycaprolactone film deformed by shearing force
Figure 1. 3D orientation angle images of a polycaprolactone film deformed by shearing force [3]. The azimuthal angle (y) and the axial angle (q) images of an interface region of the quiescent and shear deformed film.
Illustration of 3D orientation angle images of a high-density polyethylene (HDPE) film
Figure 2. Illustration of 3D orientation angle images of a high-density polyethylene (HDPE) film [7]. The color of a rod indicates the axial angle, |q |, and the symbol size represents the order parameter, <P2 >, as indicated. A higher <P2 > means a narrower distribution of the molecular orientation within the image pixel.


[1] 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).

[2] S. Xu, J. Rowlette, Y. J. Lee, Imaging 3D molecular orientation by orthogonal-pair polarization IR microscopy, Opt. Express 30, 8436 (2022).

[3] 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).

[4] 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).

[5] 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).

[6] Y. J. Lee, Theory of birefringence correction for polarization-controlled CARS, Opt. Express 28, 9158 (2020).

[7] 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).

Created May 15, 2019, Updated December 7, 2022