A simple model is presented that allows calculation of the image produced by a spherical absorbing particle illuminated by monochromatic, coherent laser light. Results are restricted to a single-lens imaging system, although generalization to more complex imaging system configurations would be straightforward. The method uses classic Lorenz-Mie scattering theory to obtain the electro-magnetic field external to an absorbing spherical particle and a Fourier optics approach to calculate the intensities in the image plane. Experimental results evaluating focus characteristics are examined for 50 μm diam water droplets using an N2 laser imaging system in conjunction with a digital image processor, and the experimental images are compared to the results of the theoretical model. Comparative focus criteria results are useful in aerosol science research involving dynamic particle size measurements in which criteria for focus and depth of field must be established.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics