Objective lens for a miniature endoscopic confocal microscope
El Ferradi, Nabil
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This thesis presents the design and testing of a micro-objective lens for a miniature endoscopic confocal microscope. The advance of confocal endo-microscopy for in-situ imaging can lead to considerable improvements in inspection, analysis, and diagnosis, especially in the biomedical field. The dimensions of the objective lens developed are 4.0 mm long and 2.0 mm in diameter incorporated into a probe that is 2.0 mm in diameter and 10.0 mm long. The size of the probe will allow it to be inserted in some of the smallest channels in an endoscope. The objective lens features a 0.33 numerical aperture, a 4x magnification, and 200 æm field of view and a sub-micron spot size. The optical system is compensated at two wavelengths, 488 nm and 515 nm. Chromatic and spherical aberrations are minimized through the use of 3 refractive planoconvex elements and an 8-level fused silica diffractive optical element. Details of the lens design, its simulation using computer ray tracing software, fabrication of the diffractive optical element and experimental characterization of the assembly are presented.