Scanning tunneling microscope (STM) in which the surface of a sample is investigated by variations of the tunneling current between a tip of the needle and the specimen surface. The feedback system moves the needle in the vertical direction keeping the value of the current unchangeable.

The atomic force microscope (AFM) consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever, which is in turn interrogated optically. Fiber optic interferometer Fabry-Perot is used for higher sensitivity of an interrogation system.

Fiber optic atomic force microscope (FOAFM) uses fiber optic interferometer Fabry-Perot to interrogate cantilever displacements. The use of piezoceramic feedback allows the better linearity and the wider dynamic range to be achieved. In this case the optical fiber and needle moves together up and down tracking the profile of the surface.

In FOAFM of resonance type (tapping mode) the atomic force action on the needle are detected by the change of the cantilever resonance frequency. When the tip approaches to the surface, molecular and electrostatic forces changes the cantilever resonant frequency and amplitude of its oscillation diminishes.

Fiber optic interferometer Fabry-Perot can be used directly (without cantilever) for investigation of the reflecting surfaces. An electronic servo uses the piezoelectric actuator to control the height of the fiber tip above the sample. As a result fiber moves up and down tracking the profile of the surface.

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