High numerical aperture freeform-based illumination for compact lensless holographic microscopy

Abstract Digital lensless holographic microscopy (DLHM) is a simple and cost-effective technique for retrieving label-free microscopic information from transparent samples. However, for onsite applications, there is a growing demand for portable, low-cost, and mechanically robust systems with high-resolution capabilities. Such applications include point-of-care diagnostics, environmental monitoring, and field-based biological research. In this work, a compact DLHM configuration based on a custom-designed freeform (FF) lens is proposed. The FF element is optimized to reshape the astigmatic wavefront of a low-cost laser diode into a highly divergent spherical wavefront, enabling high-numerical-aperture illumination (NA = 0.8) from a minimal optical footprint (56 mm from source to sensor). This FF-DLHM system is validated using a calibrated phase test target and a variety of biological specimens. The results demonstrate single-shot imaging with resolution at the ∼1 µ m scale, confirming the potential of FF-DLHM as a high-performance, miniaturized platform for portable holographic microscopy.