Hydrogen doped amorphous silicon carbide layers were grown by radiofrequency magnetron sputtering technique using a gas mixture of Ar and H2. The film thickness, the refractive index and the absorption coefficient of the films were obtained by means of optical transmittance in the UV/VIS/NIR spectral region. In order to study the effect of the hydrogen doping on the optical properties of the layers, a constant hydrogen flux was used during the deposition process. The optical bandgap was calculated using different models of the fundamental absorption region. First, a good linear dependency in the Tauc-plot was observed from which the bandgap could be calculated. Second, the E04 iso-absorption optical gap was extracted. Finally, the Urbach rule was used to determine the Urbach energy and the Urbach focus of the films. In order to correlate the bandgap variation with further thermal annealing temperatures and the out diffusion of hydrogen, the vibrational properties of the different bonds were studied through FTIR measurements. Such spectra present the Si-H, the Si-CHn and Si-C bonds. Finally, the material exhibited an enhancement of the optical bandgap when doped with hydrogen. And moreover, a critical annealing temperature is found for which the bandgap reached its maximum value in both cases, doped and undoped samples.
We present several experiments that allow us to show the intensity and phase structure of transverse modal patterns, Hermite-Gaussian and Laguerre-Gaussian laser modes and dynamical transverse patterns. These new spatial configurations of the light depend on the dynamics of laser resonator, and on the boundary conditions. The Laguerre-Gaussian modes are obtained either by the direct conversion of Hermite-Gaussian modes using a modal converter or with a computer-generated hologram. The modal coverter is based on a cavity of cylindrical lenses. We analyze the phase structure and optical phase singularities of laser modes with a Mach-Zehnder interferometer. The resulting interference patterns clearly illustrate the azimuthal phase dependence of the Laguerre-Gaussian modes, which is the origin of the orbital angular momentum associated with each one of them. Moreover, we try to give an explanation of the new modal patterns observed.
The equations for the micromaser are derived without assuming the validity of the rotating- wave approximation (RWA) in the Scully-Lamb model for a single-mode maser off resonance. The treatment is based on Swain's continued fractions approach, by which the eigenvalues and eigenvectors of the Hamiltonian describing the system of atoms plus cavity field can be iteratively determined to any desired order and then used to obtain the micromaser equations. These are valid to second order in the parameter g, the coupling constant of the atom-field interaction. The procedure can be extended, to any desired order in g, by successive iterations. Through numerically evaluating the micromaser spectrum we compare our results with those of the RWA. We predict a relative shift, stemming from the Bloch-Siegert shift, which in case of the spectra corresponding to two-photon correlations should be measurable through atomic selective field ionization.
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