25 February 2013 Direct model for thin wetting film focusing
Author Affiliations +
We demonstrated that the use of thin wetting film focusing allows detection of single micrometer-size objects with 24 mm2 lensfree imaging. In order to refine the technique and push the detection limit down to the nanometer scale, a deep insight in the imaging mechanisms is necessary. We constructed a model based on wetting film microfluidics and Fresnel diffraction of light. This model properly fits the intensity measurements acquired on micro-particles with our lensfree imaging setup. When the particle diameter is 1 µm, a microlens is formed by a liquid surface deformation of about 100 nm in height over few microns radial distance. The measured point spread function of the light deflected by such microlens presents a constant beam intensity over a long range, between 50 µm and 250 µm from the object plane. This is very similar to what is obtained by illuminating an axicon with a Gaussian beam, i.e. the central beam propagates for several Rayleigh ranges without appreciable divergences. In the lensfree imaging setup, the detector plane is far apart from the object (≈500 µm). Thus, it is a true advantage to form axicon lens that can propagate strong intensity beams up to the detector plane. Most important, our model predicts that the detection of smaller objetcs needs thinner films. These results are important for further detecting viruses with lensfree imaging techniques.
© (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
D. Migliozzi, D. Migliozzi, C. P. Allier, C. P. Allier, Y. Hennequin, Y. Hennequin, J.-C. Coutard, J.-C. Coutard, J.-M. Dinten, J.-M. Dinten, "Direct model for thin wetting film focusing", Proc. SPIE 8591, Optical Diagnostics and Sensing XIII: Toward Point-of-Care Diagnostics, 85910N (25 February 2013); doi: 10.1117/12.2001812; https://doi.org/10.1117/12.2001812

Back to Top