Abstract
Geometrical chirality is a property of objects that describes three-dimensional mirror-symmetry violation and therefore it requires a non-vanishing spatial extent. In contrary, optical chirality describes only the local handedness of electromagnetic fields and neglects the spatial geometrical structure of optical beams. In this manuscript, we put forward the physical significance of geometrical chirality of spatial structure of optical beams, which we term "Kelvin's chirality". Further, we report on an experiment revealing the coupling of Kelvin's chirality to optical chirality upon transmission of a focused beam through a planar medium. Our work emphasizes the importance of Kelvin's chirality in all light-matter interaction experiments involving structured light beams with spatially inhomogeneous phase and polarization distributions.
Highlights
Since its first definition by Lord Kelvin in 1893 [1], the term “chiral” has found its use across the fields of physics, mathematics, chemistry, and biology
We investigate a system of two dry aplanatic microscope objectives (MO1 and MO2) in confocal alignment, as sketched in Fig. 1, with an incident monochromatic beam propagating along the z axis
To comprehend the role of Kelvin’s chirality K it is worth discussing our result from the point of view of geometry, material composition, and conservation laws
Summary
Since its first definition by Lord Kelvin in 1893 [1], the term “chiral” has found its use across the fields of physics, mathematics, chemistry, and biology. These include knotted and linked polarization and phase singularities [27,28,29] and even polarization Möbius strips [30] Some of these peculiar field topologies are structurally asymmetric upon parity inversion [31], rendering the optical beams geometrically chiral. Since the definition of C only refers to a local arrangement of E and H, it fails to describe any form of chirality originating from the spatial extent of the beams This geometrical chirality of the spatial polarization and phase structure of optical beams (hereinafter referred to as Kelvin’s chirality or K) may be directly involved in chiral light-matter interaction. Our work calls for a careful evaluation of Kelvin’s chirality as a crucial component of all light-matter interaction experiments that involve light beams with spatially inhomogeneous phase or polarization distributions
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