A digital signal processor controlled, near-field scanning optical microscope: Analysis, design and development

The design and implementation of a near-field scanning optical microscope that is controlled by a digital signal processor are presented. The description of the theoretical background of the optical near-field provides the motivation for the development. Based on an analysis of the components, the design and development of the instrument are documented. A fiberoptic probe is held close to the surface of the scanned object to detect non-propagating electromagnetic fields. The setup uses a quartz crystal tuning fork as a non-optical distance sensor. Changes in the resonance frequency of the tuning fork that holds the optical probe are measured to control the distance between the probe and the object surface. A piezoelectric scanning tube moves the fiber tip with respect to the sample. The digital control systems for the distance regulation are developed. The required electronic circuits and the control system design are presented. The performance of the near-field scanning optical microscope setup is verified in experiments.