Tilted illumination in-line holographic velocimetry: Improvements in the axial spatial resolution

• Published in: Optics and lasers in engineering 2020-11, Vol.134, p.106280, Article 106280
• Main Authors: Lobera, Julia, Palero, Virginia, Roche, Eva, Gómez Climente, Marina, López Torres, Ana M., Andrés, Nieves, Arroyo, M. Pilar
• Format: Article
• Language: English
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2020.106280

•DIH axial resolution improves with a slightly tilted illumination.•The illumination angle effect is explained using optical diffraction tomography.•One-wavelength multiplexed in-line recordings don't improve axial resolution.•Several digital in-line holographic configurations have been compared.•A tilted illumination with a rectangular aperture outperforms other configurations. Two are the main limitations of in-line holography: the twin image problem and the poor spatial resolution in the optical axis direction. The twin image problem can be solved with the introduction of an imaging lens and a knife-edge aperture located at its focal plane. In this work, a theoretical analysis of the axial resolution with and without aperture is provided from the perspective of the Optical Diffraction Tomography. Theoretical analysis and controlled experiments with the different recording options, demonstrate that a small tilt of the illumination beam, together with a centered rectangular aperture, is a key parameter as it improves the spatial resolution along the optical axis during the location and tracking of a particle field.