  In disordered materials under mechanical stress, the produced deformation can
deviate from the affine one already in the elastic regime. The nonaffine
contribution was observed and characterized in numerical simulations for
various systems. However, low amplitude of nonaffinity and its local character
makes the experimental study challenging. We present a novel method on the
based on a phase compensation of the wave scattered from a dilated amorphous
material using fine wavelength tuning of the optical probe beam. Using a glass
frit as a sample, we provide complete reversibility of the material deformation
which enables to confirm the occurrence of nonaffinity in the elastic regime.
We develop a model for the coupled effect of the thermal expansion/contraction
of the material and the dilatation of the incident wavelength which allows us
to estimate the magnitude of the nonaffine displacement and the spatial extent
of its correlation domain.
