Lensless In-Line Holographic Microscopy With Light Source of Low Spatio-Temporal Coherence

Lensless microscopy is a well known imaging technique, commonly referred as digital in-line holographic microscopy. In the established holography methods, both the spatial and temporal coherence of light play a crucial role in determining the resolution of reconstructed object. This strongly restricts this imaging method to use light sources of high spatio-temporal coherence. We report lensless microscopy with a spatially extended white LED, a light source of low spatial and very low temporal coherence. The wave-field propagation between two parallel planes can be obtained using a convolution operation, where the convolution kernel depends on the object-sensor distance and the characteristics of the light source. For a light source of unknown characteristics, this kernel is an unknown function. In the proposed reconstruction method, we decompose this unknown convolution kernel of very large size (128 × 128) into a small unknown light-source-specific kernel (size 9 × 9) and a large but known light-source-independent kernel (size 128 × 128). This drastically reduces the number of unknown parameters to be estimated at the system identification step, which has been performed here by one time imaging of the known microscopic objects. Final unknown object estimation has been performed using the upper-bound constrained deconvolution. Improvement in resolution has been demonstrated with the imaging of red blood cells.