Dual beam-shear differential interference microscopy for full-field surface deformation gradient characterization

Subnanometer accuracy of surface characterization by reflected-light differential interference microscopy

“…The phase tuning and beam shearing module consists of prisms and linear phase retarders, which can spatially differentiate the propagation directions of light beams with orthogonal polarizations and gain the desirable phase lag with respective to each other. This module is similar to the Nomarski prism [25] used for many commercial DIC microscopes, but the phase lag between the two orthogonally polarized beams can be precisely tuned [23] and the beam-shear angle is variable by using the prisms with different birefringence properties. The functional modules such as the localization module and the imaging module are switchable and work independently.…”

“…The microscope we developed is similar to most differential interference contrast (DIC) microscopes [13][14][15][16][17][18][19][20], but we aim at quantitative measures of surface height variation instead of producing phase contrast images. We utilize the localization analysis [21] to precisely determine the shear distance between two orthogonally polarized light rays, by which we measure the surface topography from the phase lag between the differentiated light path [22,23]. Since the phase contrast of an image is no longer the scope here, we name our optical system as Differential Interference Microscopy (DInM).…”

“…Since the phase contrast of an image is no longer the scope here, we name our optical system as Differential Interference Microscopy (DInM). Our previous works have successfully demonstrated submicron axial and lateral resolutions for measuring the full-field deformation gradient of phase-changing metals [23] and the thin film buckling on soft substrate [24].…”