Real-time, label-free phase contrast imaging via programmable SLM-based phase mask in off-axis digital holography

Label-free imaging of transparent biological cells is essential for studying native morphology and dynamics without the interference of chemical stains or phototoxic effects. Existing phase contrast methods, however, often rely on computational post-processing, complex optical setups, or mechanical adjustments. In this paper, we propose a real-time, label-free phase contrast imaging method by integrating a programmable spatial light modulator (SLM) into a conventional off-axis digital holographic microscopy (DHM) system. The method introduces a digitally synthesized phase mask at the Fourier plane to modulate the low-frequency spectrum of the object wave, thereby enhancing image contrast directly in the reconstructed intensity. A spectrum-based calibration procedure is employed to ensure accurate mask alignment. Experimental validation on SK-MEL-28 and MCF-7 cell samples further confirms the method's effectiveness. The experimental results demonstrate significant improvement in image clarity across brightfield acquisition, hologram formation, reconstructed intensity and phase images.