Optics11 CHIARO NANOINDENTER, User Manual, Page: 38 / 65

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5. WORKING PRINCIPLE OF THE PIUMA
NANOINDENTER INSTRUMENT
The goal of performing indentation experiments with the Piuma is to measure the mechanical
properties of a sample under st
udy. These properties include the Young’s Modulus (or modulus of
elasticity) and visco-elastic properties. These experiments are performed by gradually deforming
the sample, while accurately measuring the reaction force. From the load-displacement curves,
where the load is plotted against the sample deformation, the mechanical properties are derived
using mechanical models.
5.1 Principle of operation
The Piuma Nanoindenter uses proprietary optical probes
in combination with the Optics11’s
OP1550 interferometer, to precisely detect sample deformation by detecting cantilever bending.
The Piuma’s unique probes are at the heart of what makes the Piuma instrument so easy to operate
and provide unparalleled precision at the same time. The next paragraphs briefly describe the
physics behind this optical probe design.
Interferometric displacement sensing
The Piuma interferometer contains a laser source, of which light is coupled into the optical fiber.
The laser wavelength, 1550 nm, is highly defined (a narrowband source). The light is trapped inside
the optical fiber by a refractive index difference between the core and the cladding. As the fiber
terminates in the probe, a sudden change in refractive index (fiber-to-air/medium) occurs. This
causes the interface to reflect a part of the light back into the fiber. The remaining light is coupled
to the air or medium, and is reflected by the next interface, the cantilever. This reflection is also
coupled back into the fiber (Figure 31).