Reflection near-field scanning optical microscopy: an interferometric approach

An all-fiber near-field scanning optical microscope (NSOM) is demonstrated which allows significant signal enhancement through interferometric mixing and permits phase contrast. An uncoated fiber tip is used both as source and detector in a reflection mode configuration. Pseudoheterodyne detection in a Mach-Zehnder interferometer used in conjunction with the reflection mode NSOM allows the imaging of both opaque and transparent samples with a large signal enhancement. A phase contrast can be observed that may prove useful in the imaging of certain samples such as biological specimens. Images of a diffraction grating and red blood cells are presented in three different operating modes: conventional reflection, reflection with enhanced amplitude contrast, and reflection with phase contrast.