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Articles you may be interested inDispersion properties and low infrared optical losses in epitaxial AlN on sapphire substrate in the visible and infrared range A prism coupling method was used to measure the ordinary (n o ) and extraordinary (n e ) refractive indices of Al x Ga 1Ϫx N films, grown by hydride vapor phase epitaxy ͑HVPE͒ and metalorganic chemical vapor deposition ͑MOCVD͒ on sapphire, at several discrete wavelengths from 442 nm to 1064 nm. In addition, spectroscopic transmittance and reflectance, correlated with the prism coupling results, were used to measure n o as a continuous function of wavelength between the band gap of each sample ͑255 nm to 364 nm, depending on Al fraction͒ and 2500 nm. The Al mole fractions ͑x͒, determined by energy dispersive x-ray spectroscopy ͑EDS͒, were xϭ0.144, 0.234, 0.279, 0.363, 0.593, and 0.657 for the HVPE-grown samples, and xϭ0.000, 0.419, 0.507, 0.618, 0.660, and 0.666 for the MOCVD-grown samples. The maximum standard uncertainty in the EDS-determined value of x was Ϯ0.02. The maximum standard uncertainty in the refractive indices measured by prism coupling was Ϯ0.005 and a one-Sellmeier-term equation was adequate to fit the wavelength dependence of n e from 442 nm to 1064 nm. Due to the spectral proximity of the absorption edge, the wavelength dependence of n o measured by spectroscopic transmittance/ reflectance ͑correlated with the prism-coupling results͒, from the band gap of each sample to 2500 nm, was fit with a two-Sellmeier-term equation.

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We consider unsteady heat transfer in a one-dimensional harmonic crystal surrounded by a viscous environment and subjected to an external heat supply. The basic equations for the crystal particles are stated in the form of a system of stochastic differential equations. We perform a continualization procedure and derive an infinite set of linear partial differential equations for covariance variables. An exact analytic solution describing unsteady ballistic heat transfer in the crystal is obtained. It is shown that the stationary spatial profile of the kinetic temperature caused by a point source of heat supply of constant intensity is described by the Macdonald function of zero order. A comparison with the results obtained in the framework of the classical heat equation is presented. We expect that the results obtained in the paper can be verified by experiments with laser excitation of low-dimensional nanostructures.