Applied optics
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In optical lithography, light diffracted from photo mask structures has been customarily assumed to be constant with the angle of incidence of the light illuminating the photo mask. As numerical aperture increases to unity and beyond, to cope with the continuous demand for shrinking integrated circuits, device dimensions, and densities, this approximation is no longer valid. ⋯ We present a semianalytical model that is fast, accurate, and compatible with existing professional software in this domain. The accuracy of the model is studied using the finite-difference time-domain technique and is shown to be below 5% at the image plane, within angles of incidence between +/-20 degrees .
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Using 180 degrees field-of-view (full-sky) imaging polarimetry, we measured the spatiotemporal change of the polarization of skylight during the total solar eclipse on 29 March 2006 in Turkey. We present our observations here on the temporal variation of the celestial patterns of the degree p and angle alpha of linear polarization of the eclipsed sky measured in the red (650 nm), green (550 nm), and blue (450 nm) parts of the spectrum. ⋯ Practically the same characteristics of celestial polarization were encountered during both eclipses. This shows that the observed polarization phenomena of the eclipsed sky may be general.
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We present a simultaneous dual-wavelength phase-imaging digital holographic technique demonstrated on porous coal samples. The use of two wavelengths enables us to increase the axial range at which the unambiguous phase imaging can be performed, but also increases the noise. ⋯ A comparison to software unwrapping is also presented. A simple way of correcting a curvature mismatch between the reference and the object beams is offered.
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Optical spectroscopy can provide useful diagnostic information about the morphological and biochemical changes related to the progression of precancer in epithelial tissue. As precancerous lesions develop, the optical properties of both the superficial epithelium and underlying stroma are altered; measuring spectral data as a function of depth has the potential to improve diagnostic performance. We describe a clinical spectroscopy system with a depth-sensitive, ball lens coupled fiber-optic probe for noninvasive in vivo measurement of oral autofluorescence and diffuse reflectance spectra. We report results of spectroscopic measurements from oral sites in normal volunteers and in patients with neoplastic lesions of the oral mucosa; results indicate that the addition of depth selectivity can enhance the detection of optical changes associated with precancer.
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A visible wide field multispectral system for comprehensive imaging of skin chromophores and blood vessels has been implemented, and an inhomogeneous Monte Carlo model of photon migration with randomly distributed blood vessels embedded in dermis has been developed. Predetermined nonlinear transforms have been obtained to address the nonlinear interdependent relationship among diffusive reflectance spectra, skin physiology properties, and geometry. For validation, in addition to real skin experiments and phantoms experiments, two alternative methods for blood vessel imaging have been used on the same set of subjects to compensate for the lack of ground truth for skin subsurface imaging.