Visualization of pure phase objects with optical spatial differentiation operations.

Phase distributions typically contain richer information about the morphology, structure, and organizational properties of a sample than intensity distributions. However, due to the weak scattering and absorption properties of pure phase objects, intensity measurements are unable to provide information about the phase, making it more challenging to reveal phase structure from the incident light background. Here, we propose a method for visualizing phase objects through simple optical reflection occurring at a glass interface. By exploiting the spin-orbit interaction of light and the Brewster effect, it is possible to perform a two-dimensional differentiation operation on the input light field. This enables high-contrast, isotropic differential images for pure phase objects. Experimental measurements are conducted on pure phase masks with different phase jumps to verify the superiority of our method. Additionally, bias retardation is introduced based on the differential system, thereby enabling phase reconstruction of low-contrast phase objects. The proposed mechanism for visualizing pure phase objects may lead to important applications in versatile and high-contrast bioimaging.