Numerical and experimental research on the near-field optical virtual probe.

A near-field optical virtual probe (NFOVP) is a type of immaterial tip based on the principle of near-field evanescent wave interference. Evanescent wave interference and the aperture type play very significant roles in generating near-field optical virtual probes. Two evanescent waves, propagating in opposite directions, will interfere to generate the confinement field. The central peak of the wave distribution carries the preponderance of energy. An aperture can be used to suppress the sidelobe in the energy distribution while forming the NFOVP. In this paper, the NFOVP is investigated numerically by means of the three-dimensional (3-D) finite-difference time-domain (FDTD) method. Some significant factors in the creation of the NFOVP, such as the shape and size of the aperture, the incident light, and the specimen (nanoparticle), are studied and discussed. The optical field of the evanescent wave interference has been measured by near-field scanning optical microscopy (NSOM), and the preliminary experimental results are shown.