Fourier optical route toward multimodal differential microscopy

We experimentally demonstrate a differential microscopy methodology that facilitates simultaneous amplitude, phase, and differential polarization imaging. The proposed optical spatial differentiator is obtained in a remarkably simple setup by placing a glass cover slip, acting as a signum phase mask in the Fourier plane of a standard 4f imaging arrangement. Unlike conventional approaches, the scheme operates without polarized illumination, thereby enabling polarization to serve as an additional contrast within the framework of differential imaging, which facilitates concurrent probing of the phase and polarization gradient information throughout an object. Moreover, the proposed scheme is fully adapted to standard high-resolution microscopy and functions efficiently across a broad wavelength range. The demonstrated simple, low-cost, multifunctional optical spatial differentiator can be easily integrated with conventional bright-field microscopes. It is expected to impact the future of label-free microscopy and optical image-processing techniques, with potential applications in biomedical research, materials science, and several other disciplines.