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19 February 2010 Coherent transfer functions and extended depth of field
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To preserve the speed advantage of Fourier Domain detection in Optical Coherence Microscopy (OCM), extended depth of field (DOF) is needed. To assess and improve the DOF and the lateral resolution, we analyzed the coherent transfer function (CTF) of OCM. In the spectral domain detection, each wavelength has its own specific CTF, sampling a different part of the object's spatial frequency spectrum. For classical optics and increasing numerical apertures these regions start to overlap and bend, which limits the depth of field. Bessel-like beams produced by axicon lenses circumvent these detrimental effects, but introduce side lobes. Decoupling the detection and the illumination apertures gives more flexibility in engineering a CTF and optimizes the lateral resolution and the DOF at the same time all while reducing these side lobes. We evaluated different combinations of Gaussian and Bessel-like illumination and detection optics. Using Bessel-like beams as well in the illumination as in the detection paths, but with different side-lobe radii, we obtained a lateral resolution of 2μm invariant over an extended depth of field of more than 300μm, at a signal penalty of only 12dB compared to classical Gaussian optics.
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M. Villiger, C. Pache, Rainer A. Leitgeb, and Theo Lasser "Coherent transfer functions and extended depth of field", Proc. SPIE 7554, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XIV, 755417 (19 February 2010);

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