  We couple a laser-based, space-resolved dynamic light scattering apparatus to
a universal testing machine for mechanical extensional tests. We perform
simultaneous optical and mechanical measurements on polyether ether ketone, a
semi-crystalline polymer widely used in the industry. Due to the high turbidity
of the sample, light is multiply scattered by the sample and the diffusing wave
spectroscopy (DWS) formalism is used to interpret the data. Space-resolved DWS
yields spatial maps of the sample strain and of the microscopic dynamics. An
excellent agreement is found between the strain maps thus obtained and those
measured by a conventional stereo-correlation bench. The microscopic dynamics
reveals both affine motion and plastic rearrangements. Thanks to the extreme
sensitivity of DWS to displacements as small as 1 nm, plastic activity and its
spatial localization can be detected at an early stage of the sample
deformation, making the technique presented here a valuable complement to
existing material characterization methods.

Soft Condensed Matter