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Microscopic molecular anisotropy is universally and heterogeneously present from biomaterials to medical implants to 3D printed polymer products, determining their biological, chemical, and mechanical properties [1]. However, current 2D-projection based measurements cannot quantitatively characterize molecular anisotropy inside 3D-structured materials, neither during manufacturing nor after final production. We are developing the world’s first 3D-orientation microscope, which will be a rapid, non-invasive, optical method with diffraction-limited spatial resolution.


The 3D-orientation spectroscopy based on concurrent polarization analysis of vibrational spectra is applied to imaging of complex, anisotropic materials. This new imaging method will be able to bridge the gap in the relation of [process···(molecular structure)···property] by providing real-time, direct, molecular-level, microscopic images on molecular structure during manufacturing and failure. This innovative optical metrology will advance not only additive manufacturing and tissue engineering but also materials science and various US manufacturing sectors.

We have proposed analytical solutions to concurrent polarization IR and CARS spectroscopy data [2,3]. These approaches are used to analyze experimental results from semicrystalline polymers and other complex materials.

Figure 1
Figure 1. Schematic hierarchy of microscopic structure of PE blend spherulites consisting of semi-crystalline lamellar ribbons. Green in the composite image indicates D-HDPE and red indicates H-LLDPE, acquired by circularly polarized light excitation.  The dotted rectangular box in the molecular structure indicates the unit cell of crystalline PE, with the unit cell parameters (a, b, c) as indicated [1].

Figure 2
Figure 2. A flow chart of the concurrent polarization analysis method for determination of the 3D angles of the mean molecular orientation and the order parameter <P2> of the local orientation distribution using polarization profiles of two orthogonal IR modes [3].


[1] 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).

[2] 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).

[3] 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).

Created May 15, 2019