In-line Optical Lever System for Ultrasmall Cantilever Displacement Detection

Cantilevers as small as 10 µm in length are required in order to achieve a practical data transfer rate in a read-only memory system using cantilevers as head. Thus, a new optical lever design concept that can detect the motion of such small cantilevers is necessary. The new optical lever concept that we propose makes it possible to use an objective lens with a high numerical aperture and to reduce the expansion rate of the projected light source image on the cantilever surface. As a result, we were able to reduce the incident laser spot diameter to 5 µm. It was also possible to expand the operation bandwidth to 10 MHz while achieving a displacement sensitivity of 0.48 Å (when a 10-µm long cantilever was used) by using a small spot position sensor, because the laser spot diameter on the detector could to be reduced to an arbitrary size.