  A force measurement technique has been developed that utilizes a clamped
fiber optic element both as a cantilever and as a highly sensitive probe of the
static and dynamic displacement of a sample that is mounted near its free end.
Light from a 1.5 mW superluminescent diode coupled into the fiber is used to
detect displacement with 6*10/sup -13 m*Hz/sup -1/2 sensitivity for frequencies
above 40 kHz. This technique has been used to study the interaction between
macroscopic bodies with atomic sensitivity. Here, we report measurements of
stiffness of junctions that form when two gold surfaces are brought into
contact.
