Clayton W. Bates

Line-width and tuning effects in resonant excitation

Effects deriving from the finite spectral line width of an irradiation source are investigated for the resonant excitation process and found to be of particular interest when the irradiation spectral width is comparable with atomic (or molecular) line widths. An application of high current interest is laser isotope separation using relatively broad band but tunable dye lasers for selective excitation. Expressions are derived in systematic fashion for the absorption coefficient and for the yield, taking into account three independent line shapes—the first describing the irradiation source, the other two describing Lorentz and Doppler broadening of the atomic (or molecular) medium. Saturation effects are included, but propagation effects are neglected. It is shown that the customary distinction between homogeneous and inhomogeneous atomic-line broadening must be modified if the irradiation is not monochromatic. A further result of practical importance is that there exists an optimum irradiation line width that maximizes the yield for resonant transfer. In this respect, the relatively broad spectral widths characteristic of dye lasers are to be regarded as an advantageous feature, contrary to what is generally assumed.

Solution Chemistry in the Formation of Single‐Phase CuInSe2 by Spray Pyrolysis

Depot de CuInSe 2 par pulverisation chimique sur un support de Molybdene. Bonne reproductibilite de la methode si le pH de la solution est controle, si les solutions sont conservees dans le noir, et si la contamination par O 2 est reduite au minimum

Optical properties of inhomogeneous composite materials

Abstract Using the condition that the forward scattering amplitude S(0) = 0, we extend the treatment of composite media to optical frequencies and to a model system of metal island spheres suspended in a dielectric. Our results are in good agreement with experimental data from cermets of Au in SiO2 for volume fractions from 10 to 80% Au in SiO2.

Strain-induced room temperature photoluminescence in CsI and CsI(Na)

Abstract The photoluminescence produced from mechanically deformed crystals of pure CsI and the photoluminescence increase of CsI(Na) crystals similarly prepared, where the amount of sodium is considerably less than that required for maximum photoluminescence efficiency was measured. Several interpretations of the results are suggested.

Temperature dependence of the absorption edge of vitreous silica

During an investigation of the optical properties of high-purity vitreous silica (fused quartz), which is being developed by NASA as a reflective and ablative heat shield, some interesting properties of theoretical and experimental nature have become apparent which otherwise may have remained unnoticed. Of particular interest for the NASA application is the shift of the absorption edge toward longer wavelengths with increasing temperature. The results of studies of this shift and of the spectral dependence of the absorption edge are summarized in the present paper. Plots of the absorption edge and the absorption spectrum of fused quartz vs temperature are given and discussed.

Characterization of structural defects in the presence of In2O3 in CuInSe2 prepared by spray pyrolysis

Abstract Structural defects in CuInSe2 films prepared by chemical spray pyrolysis are characterized by electrical resistivity, Hall mobility and optical absorption. This work revealed that incorporation of oxygen contributes to the formation of intrinsic defects, thus reducing the resistivity and mobility of the material. Optical absorption coefficients between 104 and 105 cm−1 were measured at 1.02 eV. Two distinct acceptor defect levels were measured at 20 and 110 meV above the valence band. A third level, believed to be a deep donor level, is located 220 meV below the conduction band.

Information Transfer Using Thin Transparent Membranes

Using a first order expression for the angular flux distribution of energy emitted by a phosphor, we are able to calculate the modulation transfer function of thin transparent membranes that are used for transferring images from the phosphor to photosensitive materials, such as photographic emulsions or photocathodes, where the phosphor and photographic emulsions or photocathodes are on opposite sides of the membrane. The loss in information in going through the membrane is due to the scattering and diffusion of light. This loss is shown to depend upon the angular distribution of light emitted by the phosphor, the degree of optical contact between the phosphor and membrane, the membrane thickness, and the ratio of the indexes of refraction of the membrane and phosphor. The results appear to be in good agreement with experiment.

Absorption and emission due to localized excitons in CsI:Na

Abstract The absorption spectra and the characteristic emission and excitation spectra of CsI:Na bulk crystals at temperatures between 300 K and 4.2 K are reported. Localized exciton energies were calculated by considering a Born-Haber cycle. The results were compared with the experimental results and the origins of the absorption bands were identified. The characteristic emission spectrum consists of two bands, one peaking around 4200 A, the other around 3800 A. The corresponding excitation spectra show that this emission is due to the recombination of a relaxed exciton which was created by transferring an electron from an iodine ion to a substitutional sodium ion in an otherwise perfect CsI lattice.

Electron spin resonance studies of reduced and unreduced lead silicate glasses

Abstract A measurement of the electron spin resonance spectrum of unreduced and reduced lead silicate glasses containing 50 mole per cent of PbO indicates that in addition to iron impurity signals occuring with g-values of 4.28 and 2.01, there is a signal at g = 1.915 which only occurs in the reduced samples. The intensity of the signal varies directly with the induced surface conductivity and, hence can be used as a tool to study the surface conductivity variation as a function of reducing schedules. At present the origin of this signal has not been definitely established.

Second phases in CdS/CuInSe2 solar cells

Though second phases consisting of Cu2-xSe or In2O3 are known to occur in CuInSe2 deposited by various methods and on a variety of substrates, establishing whether these second phases are present in CdS/CuInSe2 heterojunction solar cells has been complicated by the additional material layers in the solar cells. Hence the effect of second phases on the electrical properties and device performance has not been specified in detail in previous studies of this structure. In this paper the authors investigate the use of x-ray diffraction to determine whether second phases are present in CdS/CuInSe2 solar cells prepared by chemical spray pyrolysis. On phase in the CuInSe2 of the solar cells. An attempt to remove Cu2-xSe by chemically selective etches failed, perhaps because the diffraction peak attributed to Cu2-xSe actually had a different cause. Future studies will attempt to determine this cause. If a second phase is the cause, both removing it or preventing its formation will be studied in an effort to determine its effect on solar cell efficiency.