Portable digital lensless holographic microscope for fieldwork applications using a conventional smartphone sensor and a customized freeform lens

Despite the widespread exploration and application of digital lensless holographic microscopes (DLHMs), there remains a scarcity of portable implementations tailored specifically for fieldwork applications such as remote diagnosis, medical analysis, on-field biological sample study, and even outreach and academic demonstrations. This paper introduces a portable prototype that assembles a digital lensless holographic microscope (DLHM) with a smartphone camera designed specifically for such fieldwork scenarios. The prototype incorporates a customized illumination system, based on a freeform lens, enhancing efficiency and simplifying alignment. A 3D-printed tube houses all components, facilitating easy alignment adjustments by incorporating two axes that keep the optical axis aligned. The design replaces conventional scientific camera sensors with the digital sensor of smartphone cameras. The customized mechanical coupling accommodates the specific light source, and an off-the-shelf microscope and telescope adapter (GoSky) ensures seamless cellphone attachment. The portable freeform-based DLHM assembly requires only a few components, with precise CAD design guiding the production of five 3D-printed parts. The resulting DLHM is compact, measuring 13.6 cm in height, 5 cm in diameter, and weighing about 250 grams. This approach successfully employs the digital sensor of a HUAWEI P8 Lite smartphone after removing its camera lens to ensure free space propagation to the sensor. The system allows recording holograms with variable magnification ranging from 1× to 20× approximately, with a maximum numerical aperture (NA) of 0.12 and resolution of 1.71 µm. To validate the performance of this portable DLHM system, imaging experiments are conducted using a USAF resolution test target and a buccal mucosa sample containing epithelial cheek cells. This study underscores the practicality of the proposed DLHM system for fieldwork applications.