Photonic nanojets

We report what we believe to be the first evidence of localized photonic nanojets generated at the shadow-side surfaces of micron-scale, circular dielectric cylinders illuminated by a plane wave. Using high-resolution finite-difference time-domain (FDTD) numerical modeling, we have found that photonic nanojets have waists smaller than the diffraction limit and propagate over several optical wavelengths without significant diffraction. We have further found that such nanojets can enhance, by several orders of magnitude, the backscattering of visible light by nanometer-scale dielectric particles located within the nanojets. Not involving evanescent fields and not requiring mechanical scanning, photonic nanojets may provide a new means to detect and image nanoparticles of size well below the diffraction limit. This may provide a new ultramicroscopy technique for using visible light to detect and image nanoparticles, such as proteins, viral particles, and even single molecules; and to monitor molecular synthesis and aggregation processes of importance in many areas of biology, chemistry, material sciences, and tissue engineering.