Cantilevers as small as 10 mu m in length are required in order to achieve
a practical data transfer rate in a read-only memory system using cantileve
rs as head. Thus, a new optical lever design concept that can detect the mo
tion 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 nume
rical aperture and to reduce the expansion rate of the projected light sour
ce image on the cantilever surface. As a result, we were able to reduce the
incident laser spot diameter to 5 mu m. It was also possible to expand the
operation bandwidth to 10 MHz while achieving a displacement sensitivity o
f 0.48 Angstrom (when a 10-mu m 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.