Probing an Optical Field with Atomic Resolution

This paper describes the investigation of an optical field with atomic resolution. The probe is a single trapped ion in a linear Paul trap. The trap allows the longitudinal direction to be scanned by displacing the ion along the trap axis. In the two transversal directions the ion is confined by the trap potential and therefore the optical field is scanned by displacement of the sample using a piezo drive. The method is demonstrated by measuring particular modes of an optical cavity.