Real-space observation of photonic nanojet in dielectric microspheres

The three-dimensional real-space observation of photonic nanojet in different microspheres illuminated by a laser is reported. The finite-difference time-domain technique is used to perform the three-dimensional numerical simulation for the dielectric microspheres. The key parameters of photonic nanojet are measured by using a scanning optical microscope system. We reconstruct the three-dimensional real-space photonic nanojets from the collected stack of scanning images for polystyrene microspheres of 3 μm, 5 μm, and 8 μm diameters deposited on a glass substrate. Experimental results are compared to calculations and are found in good agreement with simulation results. The full width at half-maximum of the nanojet is 331 nm for a 3 μm microsphere at an incident wavelength of 633 nm. Our investigations show that photonic nanojets can be efficiently imaged by a microsphere and straightforwardly extended to rapidly distinguish the nano-objects in the far-field optical system.