Chiral optofluidics

Chirality in soft matter is emerging as a tool to address innovative concepts in materials science, colloidal systems, optical and photonics devices, optomechanics, optofluidics etc. Two examples are presented; the first one refers to chiral optofluidic devices and the second one to optofluidics strategies for nanoparticles assembling and manipulation. We investigate the optical forces and torques on spherical polymeric particles with chiral arrangement 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 arrangement self-organizes in precursor cholesteric liquid crystal droplets by proper selection of a chiral dopant. The helical pitch is adjusted from nanometer to micrometer range by means of the dopant concentration. The helicoidal arrangement can leads to a shell structure of the refractive index and to a selective Bragg phenomenon that makes them to behave as chiral spherical mirrors 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 reflected leaving its spin state unchanged. On the contrary, the light having opposite handedness is transmitted unaffected. The sign and strength of the optical force depend on the particles reflectance. Moreover, in contrast to conventional reflecting 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 reflected light. 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 fluids. We demonstrate the ability to trap nanoparticles and to manipulate them at large scale by low power incoherent light. The chirality is introduced at two levels, by the boundary architectures and by a photosensitive chiral dopant. The first permits to design the topological defects templates, the second to move nanoparticles-charged disclination lines without disrupting them. Full reconfigurability and time stability make this strategy attractive for future developments and practical applications.