Structure of thin fluoride films deposited on amorphous substrates

We have studied the impacts of anisotropic turbulence on the orbital angular momentum (OAM) mode of a partially coherent modified Bessel correlated vortex beam propagation in an oceanic cha...

Effects of anisotropic oceanic turbulence on the propagation of the OAM mode of a partially coherent modified Bessel correlated vortex beam

In order to estimate the multi-layer surface profile and to detect the inter-layer surfaces defects, gated wavefront sensing approach has been proposed in the previous works [1, 2]. However, the proposed methodology measures the wavefront that has been distorted by its prior surfaces (reflected wavefront) or post surfaces (transmitted wavefront). Analysis has to be performed to estimate the multi-layer wavefront sensing by taking into consideration the multi-layer surfaces condition. For reflected wavefront, the bottom layer(s) wavefront is (are) being distorted twice via separate interface points while traveling back to the lenslet arrays through our observation for the slope and phase measurement. The subsequent reconstructed surfaces are not accurate and corrected. Thus, a discrete layer correction technique for the surface reconstruction has been proposed to enhance the reconstruction accuracy by using the upper/top layer’s wavefront information. This paper discusses on the case of 2-layer system, where the reflected wavefront from the bottom layer has been distorted and its surface reconstruction has been corrected. The results show that the distortion is significant and the correction is deemed necessary for industrial application such as in wafer warpage inter-layer profile estimation.

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Method for distortion correction of multi-layered surface reconstruction using time-gated wavefront sensing approach

The use of lateral waves for the examination of weakly absorbing surface films

Tao, Hongdan Ph.D., Purdue University, December 2013. Propagation of Sound in the Vicinity of Rigid Porous Interfaces. Major Professor: Kai Ming Li, School of Mechanical Engineering. Propagation of sound in the vicinity of rigid porous interfaces is investigated systematically to facilitate the acoustical characterization of sound absorption materials for noise reduction applications. Various rigid porous interfaces are considered: (1) a semi-infinite porous layer; (2) a porous hard-backed surface; and (3) a porous impedancebacked layer. A closed-form solution and numerical methods are derived with respect to each rigid porous interface condition. A modified saddle-point method is exploited to investigate the sound field emanating from a monopole source above and below a rigid porous interface. The solutions can be expressed in a form that resembles the classical Weyl-Van der Pol formula. A heuristic method is then proposed to remove the singularity within the asymptotic solution via application of the double saddle-point method. Its relative simplicity and accuracy demonstrates the advantage of the double saddle-point method whenever the approximation is valid. Following this, the sound field within a hardbacked rigid porous medium due to an airborne source is examined. The accuracy of the proposed asymptotic solutions has been confirmed by comparison with benchmark numerical solutions and through indoor sound propagation experiments. Measurement

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Propagation Of Sound In The Vicinity Of Rigid Porous Interfaces

It is known that if a point source is placed in the neighbourhood of a plane boundary, radiation may reach a point on the same side of the boundary by a route which includes a lateral wave path in the second medium. The flux arriving by such a lateral wave path is calculated for two cases, viz. (1) a semi-infinite, absorbing second medium and (2) a very thin absorbing film, placed between identical media.

O.S. Heavens

Papers

The Propagation of Lateral Waves in Absorbing Media and Thin Films