Abstract
We develop an integrated system of holographic optical trapping and multimodal nonlinear microscopy and perform simultaneous three-dimensional optical manipulation and non-invasive structural imaging of composite soft-matter systems. We combine different nonlinear microscopy techniques such as coherent anti-Stokes Raman scattering, multi-photon excitation fluorescence and multi-harmonic generation, and use them for visualization of long-range molecular order in soft materials by means of their polarized excitation and detection. The combined system enables us to accomplish manipulation in composite soft materials such as colloidal inclusions in liquid crystals as well as imaging of each separate constituents of the composite material in different nonlinear optical modalities. We also demonstrate optical generation and control of topological defects and simultaneous reconstruction of their three-dimensional long-range molecular orientational patterns from the nonlinear optical images.
Highlights
Soft materials often combine properties such as fluidity, intrinsic to conventional liquids, with the properties and structural features typically associated with solid crystals, such as elasticity, orientational and positional order, anisotropy, and topological defects
We demonstrate 3D manipulation and nonlinear imaging capabilities of the integrated setup by using an example of a system consisting of cholesteric Liquid crystals (LCs) as the host medium and colloids of spherical and anisometric shapes dispersed in it
We illustrate manipulation of melamine resin spherical microparticles dispersed in cholesteric LCs based on nematic 5CB in a series of vertical cross-sectional images obtained in coherent anti-Stokes Raman scattering (CARS) and 3PEF (Fig. 2)
Summary
Soft materials often combine properties such as fluidity, intrinsic to conventional liquids, with the properties and structural features typically associated with solid crystals, such as elasticity, orientational and positional order, anisotropy, and topological defects. Characterization of physical properties and experimental study of various physical phenomena in such materials is a challenging task, as all properties depend on the details of structural organization, presence of defects, etc. Liquid crystals (LCs) are a classic example of soft materials, typically possessing long-range orientational order combined with varying degree of positional order [1]. The simplest type of LCs, the so-called nematic LC, is composed of rod-shaped molecules whose local average orientation is described by the molecular director, n(r), which is the local optical axis of these materials. In the cholesteric LC, the molecules show a uniform twist along a helical axis, giving rise to a periodic lamellar-like ground state
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