DIRECT OBSERVATION OF SIZE-DEPENDENT FEATURES OF THE OPTICAL NEAR-FIELD ON A SUBWAVELENGTH SPHERICAL SURFACE

We investigate the characteristics of the optical near field of a subw avelength dielectric sphere by using a nanometric fiber tip and a sens itive technique of wavelength conversion. The decay length of the near field induced around the single sphere is directly measured to be 0.3 of its radius, obtained by precise positioning of the probe tip. A nu merical calculation of the optical near field based on the Mie scatter ing theory is in good agreement with the experimental results. The enh ancement of fluorescence collection efficiency in the near-field regio n is also observed. (C) 1996 Optical Society of America