Zeitschriftenaufsätze

Al-AlN composite thin films with surface nanostructures possessing excellent broad-band antireflection properties can be simply fabricated by using a simple sputtering-based method, namely, limited reactive sputtering at elevated temperature. A mixture of Ar and N2 gases with limited gas flow of N2 is used. During the process, the limited amount of the N ions and radicals can only consume some of the sputtered Al atoms for the formation of AlN, so that the Al-AlN composite thin film can finally be deposited on the substrate. Compared to the traditional cosputtering for composite deposition, which works necessarily with two or more targets simultaneously, here only a single Al target is required. When the substrate temperature is higher than 100 &ring;C, surface nanostructures can be evolved because of the different diffusion kinetics of Al and AlN. The total reflection was reduced drastically (<10%) in the spectral range 300-2000 nm. The Al-AlN composite thin films exhibit also a good electric conductivity.

In the present work, a spline-based integration technique for the reconstruction of a freeform wavefront from the slope data has been implemented. The slope data of a freeform surface contain noise due to their machining process and that introduces reconstruction error. We have proposed a weighted cubic spline based least square integration method (WCSLI) for the faithful reconstruction of a wavefront from noisy slope data. In the proposed method, the measured slope data are fitted into a piecewise polynomial. The fitted coefficients are determined by using a smoothing cubic spline fitting method. The smoothing parameter locally assigns relative weight to the fitted slope data. The fitted slope data are then integrated using the standard least squares technique to reconstruct the freeform wavefront. Simulation studies show the improved result using the proposed technique as compared to the existing cubic spline-based integration (CSLI) and the Southwell methods. The proposed reconstruction method has been experimentally implemented to a subaperture stitching-based measurement of a freeform wavefront using a scanning Shack-Hartmann sensor. The boundary artifacts are minimal in WCSLI which improves the subaperture stitching accuracy and demonstrates an improved Shack-Hartmann sensor for freeform metrology application.