Differential holographic reconstruction for lensless in-line holographic microscope with ultra-broadband light source illumination

We propose a differential holographic reconstruction (DHR) method for lensless in-line holographic microscope (LIHM) with ultra-broadband light source illumination. Using the DHR method, the deterioration of imaging resolution and contrast because of insufficient temporal coherence can be noticeably compensated. In our LIHM setup, the sample was illuminated by an ultra-broadband light source without any spectral filters, and the in-line hologram was recorded by a CMOS imaging sensor located behind the sample. The enhanced-resolution sample image was achieved by subtracting two low-resolution sample images, which were obtained by back-propagating the hologram numerically to the sample plane and another plane with slightly different back-propagation distance. The DHR method was studied theoretically, and the resolution enhancement capability was verified by both numerical simulations and imaging experiments. The U.S. air force target and a lily anther as bio-sample were used in the imaging experiments. The results showed that the proposed DHR method achieved better resolution with ultra-broadband light sources such as sunlight and incandescent light sources, which could reduce the cost for compact imaging systems.