We experimentally engineer Nanojets produced by dielectric spheres by varying the illumination and observe the effect with a high-resolution interference microscope (HRIM). Converging and diverging spherical wavefronts and Bessel- Gauss beams are considered. We find that the diverging wavefront pushes Nanojets away from the surface of the sphere without change of the spot size. This allows earning several micrometers of working distance contrary to the Nanojet confined at the sphere's surface. When the radius of curvature of the incident wavefront is greater than about 5 times the sphere size, the Nanojet moves back to the sphere surface like it is found for plane wave incidence. On-axis Bessel- Gauss beam illumination with the central lobe covering the whole sphere leads to the same results as the plane wave case. Off-axis Bessel beam illumination can generate multiple-spot Nanojets. We demonstrate the separation of such spots of about 220 nm at 642 nm. This separation is smaller than the feature sizes defined by the diffraction limit at this wavelength. We discuss briefly applications of engineered Nanojets for nano-lithography and near-field sensing.

Date Published: 17 January 2011
PDF: 8 pages
Proc. SPIE 7941, Integrated Optics: Devices, Materials, and Technologies XV, 794115 (17 January 2011); doi: 10.1117/12.887604

Published in SPIE Proceedings Vol. 7941:
Integrated Optics: Devices, Materials, and Technologies XV
Jean Emmanuel Broquin; Gualtiero Nunzi Conti, Editor(s)