[en] We have made direct absorption measurements of the transition probability and collision broadening of the 1.3-μm ²P/sub 1/2/ → ²P/sub 3/2/ transition of atomic iodine. Atomic iodine was generated in heated iodine vapor, and the spectrum was obtained with a Fourier-transform spectrometer. A transition probability was measured that corresponds to a ²P/sub 1/2/ radiative lifetime of 125 msec. Broadening coefficients of 1.4, 1.7, 3.1, and 1.3 MHz/Torr at 1000 K were found for argon, oxygen, molecular iodine, and atomic iodine, respectively. The intensity of the (2, 4) forbidden electric-quadrupole line was measured and yielded the ratio of electric-quadrupole to magnetic dipole transition probability of 2.7 x 10^-3. Molecular absorption spectra of IO and SiI were seen in high-temperature spectra of a quartz cell containing and I₂/O₂ mixture

[en] The self-focusing phenomenon of powerful Gaussian CO₂-laser beams in collisional plasmas is analyzed using a new technique based on geometrical optics. The problem of self-focusing is reduced to a nonlinear differential equation in the beam width parameter, which is then numerically solved by using a computational technique and assuming that the laser beam and the plasma are either coupled or decoupled along the propagation path. The beamwidth parameter is, in general, a function of propagation distance, radial position, collisional-energy-loss to conduction-energy-loss ratio, initial beamwidth, laser power, and electron concentration to its critical-concentration ratio. The effect of variation of each of these parameters on the variation of the beam width parameter is investigated

[en] An arbitrary source function cannot be determined fully from projection data that are limited in number and range of viewing angle. There exists a null subspace in the Hilbert space of possible source functions about which the available projection measurements provide no information. The null-space comp]onents of deterministic solutions are usually zero, giving rise to unavoidalbe artifacts. It is demonstrated that these artifacts may be reduced by a Bayesian maximum a posteriori (MAP) reconstruction method that permits the use of significant a priori information. Since normal distributions are assumed for the a priori and measurement-error probability densities, the MAP reconstruction method presented here is equivalent ot the minimum-variance linear estimator with nonstationary mean and covariance ensemble characterizations. A more comprehensive Bayesian approach is suggested in which the ensemble mean and covariance specifications are adjusted on the basis of the measurements

[en] We present the results of degenerate four-wave mixing (DFWM) studies in three samples of p-type Ge with a wide range of absorptive properties. Three mechanisms for DFWM are observed in this material. A model, which includes the mechanisms of the inhomogeneously broadened saturable absorption of p-type Ge and the optical Kerr effect that is due to bound electrons in Ge but not the mechanism of bulk plasma formation that occurs only at extremely high pump intensities, is developed and compared with the experimental results. Pump-beam attenuation by the medium is shown to be an important effect in modeling DFWM. The model, which has no free parameters, fits the experimental data well for samples with small-signal transmission of greater than 20%

[en] Precise wavelength predictions are presented for the 3s3p ³P₁-3s3p ³P₂ magnetic-dipole transitions, the 3s3p ³P₀-3s3p ³P₂ electric-quadrupole transitions, and the 3s²¹S₀-3s3p ³P₁ intercombination lines for all members of the Mg isoelectronic sequence with Z< or =45. Magnetic-dipole and intercombination transitions of this type have recently been observed in tokamak spectra and have applications for localized diagnostics in high-temperature plasmas. The predictions are based on interpolations and extrapolations of empirical regularities, which also provide insights into the dynamics of these atomic systems

[en] Precise transition energies for several transitions in singly ionized erbium are presented, together with lifetimes for a number of excited levels. The lifetime results obtained make possible a general correction to the oscillator strength previously reported by Corliss and Bozman [Nat. Bur. Stand. (U.S.) Monogr. 53 (1982)]

[en] We have used optical pumping to produce a substantial ²³⁵U enrichment in the metastable levels of UI in the discharge afterglow of a hollow-cathode vapor generator. The measured isotope-enrichment factor for the level at 3800 cm^-1 is approximately 20

[en] We calculate the power-dependent propagation constant of a surface-plasma wave as a function of the thickness of the metal film on which it propagates when the metal film is bounded by a nonlinear semiconductor. In the case of a Cu film bounded by InSb at a wavelength of approx.5 μm and a temperature of 5 K, we find that the effect of the nonlinearity on the propagation constant is enhanced by a factor of 10 as the metal thickness decreases from 120 to 15 nm

[en] The far-field asymptotic solution for the diffraction of an electromagnetic plane wave by a cylinder-tipped half-plane is derived from the direct solution. It is demonstrated that the Fresnel diffraction plays an important role in the transition regions where the solution of the geometrical theory of diffraction fails. The asymptotic solution not only simplifies the numerical calculations but also gives a physical model of the exact solution

[en] High-resolution spectra of a ²³²ThI₄/²³⁰ThI₄ electrodeless discharge lamp were obtained from 5600 to 36000 cm^-1 with a Fourier-transform spectrometer. The splittings of more than 2800 Th I isotopic doublets were measured to an accuracy of 0.001 cm^-1. Level isotope shifts were determined for 274 even and 318 odd levels of Th I