  We experimentally determine tensile force-elongation diagrams of tapered
optical fibers with a nanofiber waist. The tapered optical fibers are produced
from standard silica optical fibers using a heat and pull process. Both, the
force-elongation data and scanning electron microscope images of the rupture
points indicate a brittle material. Despite the small waist radii of only a few
hundred nanometers, our experimental data can be fully explained by a nonlinear
stress-strain model that relies on material properties of macroscopic silica
optical fibers. This is an important asset when it comes to designing
miniaturized optical elements as one can rely on the well-founded material
characteristics of standard optical fibers. Based on this understanding, we
demonstrate a simple and non-destructive technique that allows us to determine
the waist radius of the tapered optical fiber. We find excellent agreement with
independent scanning electron microscope measurements of the waist radius.
