Search results for "Monochromatic color"
showing 10 items of 62 documents
High-contrast white-light Lau fringes
2004
We present a new optical assembly with which to achieve Lau fringes with totally incoherent illumination. Gratinglike codification of the spatially incoherent source combined with an achromatic Fresnel diffraction setup allows us to achieve Lau fringe-pattern visibility of almost 100% with broadband light. The white-light character to our proposed setup is in stark contrast to previous monochromatic implementations. Potential implications of this fact are identified.
Chromatic Sums for Colorings Avoiding Monochromatic Subgraphs
2013
Abstract Given graphs G and H, a vertex coloring c : V ( G ) → N is an H-free coloring of G if no color class contains a subgraph isomorphic to H. The H-free chromatic number of G, χ ( H , G ) , is the minimum number of colors in an H-free coloring of G. The H-free chromatic sum of G , Σ ( H , G ) , is the minimum value achieved by summing the vertex colors of each H-free coloring of G. We provide a general bound for Σ ( H , G ) , discuss the computational complexity of finding this parameter for different choices of H, and prove an exact formulas for some graphs G. For every integer k and for every graph H, we construct families of graphs, G k with the property that k more colors than χ ( …
Organic Dye Bearing Asymmetric Double Donor-π-Acceptor Chains for Dye-Sensitized Solar Cells
2011
A novel efficient metal free sensitizer containing asymmetric double donor-π-acceptor chains (DC) was synthesized for dye-sensitized solar cells (DSSCs). Comparing to 3.80%, 4.40% and 4.64% for the DSSCs based on the dyes with single chain (SC1, SC2) and cosensitizers (SC1 + SC2), the overall conversion efficiency reaches 6.06% for DC-sensitized solar cells as a result of its longer electron lifetime and higher incident monochromatic photon-to-current conversion efficiency.
Optical properties and quantum yield determination in photocatalytic suspensions
2006
Knowledge of the optical properties of photocatalytic suspensions is vital for a correct comparison of their energetic efficiency. In this work, the determination of both absorption and scattering coefficients of aqueous suspensions of commercial TiO2 powders irradiated by monochromatic light was carried out by measuring only one quantity—the transmitted photon flow—as a function of the catalyst mass and by applying an asymptotic form of the Kubelka–Munk solution of the radiative transfer equation. Applying a nonlinear fitting procedure the evaluation of the actual values of absorption and scattering coefficients was carried out. The limit for optically thick media of the Kubelka–Munk equat…
Volumetric multiple optical traps produced by Devil's lenses
2010
We propose the use of a new diffractive optical element coined Devil's Vortex-Lens (DVL) to produce optical tweezers. In its more general form it results as the combination of a Devil’s lens and a helical vortex phase mask. It is shown that under monochromatic illumination a DVL generates a focal volume with several concatenated doughnut modes that are axially distributed according to the self-similarity of the lens. The orbital angular momentum associated to each link in the chain is investigated.
Optical-sectioning microscopy by patterned illumination
2010
We propose a very simple method for the flexible production of 1D structured illumination for high resolution 3D microscopy. Specifically, we propose the insertion of a Fresnel biprism after a monochromatic point source for producing a pair of twin, fully coherent, virtual point sources. The resulting interference fringes are projected into the 3D sample and, by simply varying the distance between the biprism and the point source, one can tune the period of the fringes, while keeping their contrast, in a very versatile and efficient way.
Absence of lightness constancy as a deficit of monochromatic vision
1995
Dark-adapted human subjects arranged a collection of colored papers in a sequence according to their lightness. The sequence of the papers (which appeared gray to the subjects) varied under different illuminant spectra. These variations could be predicted quantitatively from the radiometric data and human scotopic spectral sensitivity. By substitution of natural daylight spectra in the computation it was shown that monochromats cannot perceive lightness reliably under the changing illuminant spectra of our planet. Animals need some degree of lightness constancy to detect figures against a background reliably. This can be achieved only with the help of additional light receptors of different…
Polychromatic, continuous-wave mirrorless lasing from monochromatic pumping of cesium vapor
2019
We report on studies of simultaneous continuous-wave mirrorless lasing on multiple optical transitions, realized by pumping hot cesium vapor with laser light resonant with the 6$S_{1/2}\rightarrow 8$P$_{3/2}$ transition. The multiplicity of decay paths for the excited atoms to their ground state is responsible for the emergence of lasing in a number of transitions, observed here in at least seven wavelengths in the infrared (IR), and at two wavelengths in the blue. We study the properties of the fields generated in the cesium vapor, such as optical power, directionality and optical linewidth.
Smartphone snapshot mapping of skin chromophores under triple-wavelength laser illumination
2017
Abstract Chromophore distribution maps are useful tools for skin malformation severity assessment and for monitoring of skin recovery after burns, surgeries, and other interactions. The chromophore maps can be obtained by processing several spectral images of skin, e.g., captured by hyperspectral or multispectral cameras during seconds or even minutes. To avoid motion artifacts and simplify the procedure, a single-snapshot technique for mapping melanin, oxyhemoglobin, and deoxyhemoglobin of in-vivo skin by a smartphone under simultaneous three-wavelength (448–532–659 nm) laser illumination is proposed and examined. Three monochromatic spectral images related to the illumination wavelengths …
Snapshot RGB mapping of skin melanin and hemoglobin.
2015
The concept of snapshot red-green-blue (RGB) multispectral imaging was applied for skin chromophore mapping. Three monochromatic spectral images have been extracted from a single RGB image dataset at simultaneous illumination of skin by 473-, 532-, and 659-nm laser lines. The spectral images were further transformed into distribution maps of skin melanin, oxyhemoglobin, and deoxyhemoglobin, related to pigmented and vascular skin malformations. The performance and clinical potential of the proposed technique are discussed