Polarization-resolved Off-axis Lensless Microscopy using a Holographic Optical Element

Lensless holographic microscopy offers exceptional simplicity, but in its conventional in-line geometry, the desired object term is superimposed with the unwanted background and conjugate (“twin-image”) terms, limiting proper information recovery. Off-axis digital holography addresses this by including a tilted reference wave to separate these components in the Fourier domain, enabling recovery of the object’s complex field from a single interferogram; though at the cost of bulkier, more expensive setups. This work presents a compact off-axis lensless holographic microscope in which the interferometer is embedded within a volumetric holographic optical element (v-HOE). This element diffracts a single diode-laser beam into object and tilted reference wavefronts, eliminating bulk beam-splitters and alignment optics. The simplicity of the design also facilitates straightforward integration of polarization-resolved imaging, demonstrated here using either a pair of linear polarizers or a polarization-sensitive camera. Quantitative performance was benchmarked against a conventional in-line lensless system and a benchtop off-axis Digital Holographic microscopy (DHM) using a calibrated phase target (50–350 nm). The v-HOE-based system achieved thickness measurement uncertainties of 5.7 nm, comparable to the benchtop reference (8.4 nm) and far surpassing the in-line system (91.2 nm). Biological imaging validation with an onion epidermis sample showed reduced amplitude and phase background fluctuations relative to in-line reconstructions. Finally, polarization measurements with two polarizers yielded clear polarization-dependent contrast, while single-shot Angle-of-Linear-Polarization (AoLP) imaging with a polarization camera produced values in close agreement with theoretical expectations (background: 90.2° ± 1.6° vs. 90°; target: 43.3° ± 1.9° vs. 45°). Together, these results demonstrate a thin-film, alignment-robust approach to twin-image-free quantitative phase and polarization imaging in a compact lensless format, establishing v-HOE off-axis lensless microscopy as a practical alternative to benchtop systems for deployable Quantitative Phase Imaging (QPI).