On the realization of microscopic grids for local strain measurement by direct interferometric photolithography

In order to extend the application range of the so-called “grid method” to the micron scale and thus quantitatively characterize the micromechanical behavior of metallic alloys, we report in this paper on the optimization of microscopic 2D gratings with pitches ranging from 1 to 10μm. After an overview of the state of the art on full-field kinematic measurements at the micron scale, the direct interferometric photolithography technique, used to produce such gratings, is introduced. The shape of the gratings has been characterized using an atomic force microscope and compared with the theoretical profiles. An optimization of the parameters involved in the marking process is then presented. One of the goals lies in the measurement of displacement fields using spatial phase-shifting concept which is briefly recalled. This optimization is achieved for two different optical techniques used to observe the grids namely optical microscopy and white light confocal interferometry. Finally, a first evaluation of the performance of the measurement technique is given and discussed.