Double-inline low-coherence digital holographic microscope for 3D nanoparticle positioning and classification

A novel low-coherence digital inline holographic microscope for accurate three-dimensional (3D) position estimation and nanoparticle classification is proposed and validated. Two low-coherence digital inline holograms of a sample containing numerous nanoparticles, generated by two illumination light beams forming a small angle with each other from a low-coherence light source, are employed to determine the nanoparticles’ actual 3D positions. Each nanoparticle’s sub-holograms, extracted from the holograms of the sample, are used to reconstruct the intensity scattering image at its respective actual position using the Rayleigh–Sommerfeld backpropagation method. The intensity scattering image of each nanoparticle is then used to classify particles with similar sizes and shapes. The advantages of the proposed system include rapid and highly accurate 3D nanoparticle position determination and nanoparticle classification without the need to pre-prepare patterns or have prior knowledge of the nanoparticle characteristics.