Optical trapping with photonic nanojet (PNJ) using various sized polystyrene spheres

Photonic nanojets typically require a spherical object onto which a laser beam is illuminated. The presence of the spherical object creates a near-field nanojet where light is emitted in the vicinity of the sphere. We explore the nanojet emanating from various diameters of the spheres and find that two different regimes can be present. In the first regime, the sphere is small when the transverse dimension of the nanojet is smaller than the diffraction limit while the axial dimension is diffraction limited, as has been recently shown. In addition, we find another regime where the sphere diameter is much larger than wavelength, when the axial dimension of the nanojet is now smaller than the diffraction limit keeping the transverse dimension the same as diffraction limit. This yields very high numerical apertures. We also show that we can optically confine particles with a axial corner frequency which is a factor of three larger than regular optical trapping with 100x objective due to the subdiffractive axial nanojet.