Improved fiber-optic interferometer for atomic force microscopy

A high-sensitivity fiber-optic displacement sensor for atomic force microscopy is described. The sensor is based on the optical interference occurring in the micron-sized cavity formed between the cleaved end of a single-mode optical fiber and the microscope cantilever. As a result of using a diode laser light source and all-fiber construction, the sensor is compact, mechanically robust, and exhibits good low-frequency noise behavior. Peak-to-peak noise in a dc to 1 kHz bandwidth is less than 0.1 Å. Images are presented demonstrating atomic resolution of graphite and magnetic force imaging of bits written on a magnetic disk.