We introduce a measure of the local density of chirality of the electromagnetic field. This optical chirality determines the asymmetry in the rates of excitation between a small chiral molecule and its mirror image, and applies to molecules in electromagnetic fields with arbitrary spatial dependence. A continuity equation for optical chirality in the presence of material currents describes the flow of chirality, in a manner analogous to the Poynting theorem for electromagnetic energy. "Superchiral" solutions to Maxwell's equations show larger chiral asymmetry, in some regions of space, than is found in circularly polarized plane waves.

A molecule or larger body is chiral if it cannot be superimposed on its mirror image (enantiomer). Electromagnetic fields may be chiral, too, with circularly polarized light (CPL) as the paradigmatic example. A recently introduced measure of the local degree of chiral dissymmetry in electromagnetic fields suggested the existence of optical modes more selective than circularly polarized plane waves in preferentially exciting single enantiomers in certain regions of space. By probing induced fluorescence intensity, we demonstrated experimentally an 11-fold enhancement over CPL in discrimination of the enantiomers of a biperylene derivative by precisely sculpted electromagnetic fields. This result, which agrees to within 15% with theoretical predictions, establishes that optical chirality is a fundamental and tunable property of light, with possible applications ranging from plasmonic sensors to absolute asymmetric synthesis.

Fluorescent imaging of single helicene molecules is applied to study the optical activity of chiral fluorophores. In contrast to the previous report by Hassey et al. (Science 2006, 314, 1437), the dissymmetry factors of single chiral fluorophores are found not to differ significantly from the bulk value of |g| < 10(-4) at 457 nm. Linear dichroism and birefringence of the dichroic mirror inside the fluorescence microscope change the polarization state of the incoming laser beam significantly; i.e., circular polarized light sent into the microscope becomes highly elliptically polarized after reflection from the dichroic mirror. Compensation for this effect should be made to avoid artifacts brought by linear dichroism in single immobilized molecules.

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Fine-tuning of whispering gallery modes in on-chip silica microdisk resonators within a full spectral range Appl. Phys. Lett. 102, 041104 (2013) The plasmonic J-pole antenna Appl. Phys. Lett. 102, 033106 (2013) Electro-optic sensor for specific absorption rate measurements Appl. Phys. Lett. 102, 033502 (2013) Cavity piezooptomechanics: Piezoelectrically excited, optically transduced optomechanical resonators Appl. Phys. Lett. 102, 021110 (2013) Sub-diffraction optical coherent control of ultrafast electrical currents in antenna devices on GaAs Appl. Phys. Lett. 101, 251119 (2012) Additional information on Appl. Phys. Lett. We image the chiroptical response of crossed nanowire junctions as a function of the vertical offset between the nanowires and the incident wavelength. These samples show chiroptical "hot spots" with strongly localized circular differential scattering at the nanowire crossing points. These chiroptical hot spots are not apparent in the spatially averaged spectra. The sign and magnitude of the chiroptical enhancement show a complex dependence on sample geometry, which we reproduce with a fully retarded analytical scattering model. These results suggest strategies for engineering devices with enhanced chiral light-matter interactions. V C 2013 American Institute of Physics.