Resolution in near-field optical interactions involving bare tapered optical fibers

Summary form only given. The resolution achievable in near-field scanning optical microscopy (NSOM) with an uncoated fiber used in a conventional collection mode is not significantly below the diffraction limit. The resolution in reflection mode is better because of an equivalent "confocal" advantage. This mode of operation is analyzed using a Huygenian secondary source model with an inverse power law for re-collection of the light that has interacted with a sample. It is shown that in reflection mode a vibrating tip technique can produce an enhancement of the resolution as originally suggested by Buckland et al. Ultimately, as the tip diameter is reduced, the field is expelled from the fiber and insufficient energy remains guided within the fiber to permit further resolution enhancement.