Chiral Optofuidics

Chirality in soft matter is emerging as a tool to address innovative concepts in materials science, colloidal systems, optical and photonics devices, optomechanics, opto°uidics etc.. Two examples are presented; the ¯rst one refers to chiral opto°uidics devices and the second one to opto°uidics strategies for nanoparticles assembling and manipulation. We investigate the optical forces and torques on spherical polymeric particles with chiral ar- rangement of the inner structure consisting of supramolecular helices (left or right-handed). The methodological approach used for micro-particles preparation is such that the helical arrange- ment self-organizes in precursor cholesteric liquid crystal droplets by proper selection of a chiral dopant. The helical pitch is adjusted from nanometre to micrometre range by means of the dopant concentration. The helicoidal arrangement can leads to a shell structure of the refrac- tive index and to a selective Bragg phenomenon that makes them to behave as chiral spherical re°ectors for light propagating along the helical axis and wavelength within the stop band. The circularly polarized light component having the same handedness of the chiral arrangement is re°ected leaving its spin state unchanged. On the contrary, the light having opposite handedness is transmitted una®ected. The sign and strength of the optical force depend on the particles re- °ectance. Moreover, in contrast to conventional re°ecting particles, these chiral particles can be set in rotation because of the transfer of spin angular momentum. We investigate the tunability and the coupling of the optical forces and torques by controlling the amount of the re°ected light. Several approaches have been adopted: particle size, optical tweezers wavelength position within the stop band and light ellipticity. Chirality-controlled optical trapping and manipulation opens novel strategies for optomechanics and optical sorting. We exploit chiral photosensitive materials to move nanoparticles-charged disclination lines in anisotropic chiral °uids. We demonstrate the ability to trap nanoparticles and to manipulate them at large range by low power incoherent light. The chirality is introduced at two levels, by the boundary architectures and by a photosensitive chiral dopant. The ¯rst permits to design the topological defects templates, the second to move nanoparticles-charged disclination lines without disrupting them. Full recon¯gurability and time stability make this strategy attractive for future developments and practical applications.