Combining Cubic Spline Interpolation and Fast Fourier Transform to Extend Measuring Range of Reflectometry

The reflectometry is a common method used to measure the thickness of thin films. Using a conventional method,its measurable range is limited due to the low resolution of the current spectrometer embedded in the reflectometer.We present a simple method, using cubic spline interpolation to resample the spectrum with a high resolution,to extend the measurable transparent film thickness. A large measuring range up to 385 m in optical thickness is achieved with the commonly used system. The numerical calculation and experimental results demonstrate that using the FFT method combined with cubic spline interpolation resampling in reflectrometry, a simple,easy-to-operate, economic measuring system can be achieved with high measuring accuracy and replicability.

Thermomechanical response of aluminum alloys under the combined action of tensile loading and laser irradiations

This study reports the investigation of the thermomechanical behavior of aluminum alloys （AI-1060, A1-6061, and A1-7075） under the combined action of tensile loading and laser irradiations. The continuous wave ytterbium fiber laser （wavelength 1080 nm） was employed as the irradiation source, while tensile loading was provided by the tensile testing machine. The effects of various pre-loading and laser power densities on the failure time, temperature distribution, and the deformation behavior of aluminum alloys are analyzed. The experimental results represent the significant reduction in failure time for higher laser power densities and for high preloading values, which implies that preloading may contribute a significant role in the failure of the material at elevated temperature. Fracture on a microscopic scale was predominantly ductile comprising micro-void nucleation, growth, and coalescence. The AI-1060 specimens behaved plastically to some extent, while A1-6061 and A1-7075 specimens experienced catastrophic failure. The reason and characterization of ma- terial failure by tensile and laser loading are explored in detail. A comparative behavior of under-tested materials is also investigated. This work suggests that studies considering only combined loading are not enough to fully understand the mechanical behavior of under-tested materials. For complete characterization, one should consider the effect of heating as well as loading rate and the corresponding involved processes with the help of thermomechanical coupling and the thermal elastic-plastic theory.

A single-phase full-color phosphor Sr_(2)Ca_(2)La(PO_(4))_(3)O:Eu^(2+),Tb^(3+),Mn^(2+):Photoluminescence and energy transfer

A single-phase full-color emitting phosphor Sr_(2)Ca_(2)La(PO_(4))_(3)O:Eu^(2+),Tb^(3+),Mn^(2+) was synthesized by the high temperature solid-state method.The phase formation,luminescence properties,thermal stability,and energy transfer from Eu^(2+)to Tb^(3+) and Eu^(2+)to Mn^(2+) in Sr_(2)Ca_(2)La(PO_(4))_(3)O were investigated in details.Tunable emission color from blue to blueish green or orange can be observed under 365 nm near-ultraviolet excitation based on the energy transfer from Eu^(2+) to Tb^(3+)or Mn^(2+) ions by varying the ratio of Eu^(2+)/Tb^(3+)or Eu^(2+)/Mn^(2+) ions.White light was obtained with chromaticity coordinates of(0.3558,0.3500)in the Sr_(2)Ca_(2)La(PO_(4))_(3)O:0.04Eu^(2+),0.08Tb^(3+),0.40Mn^(2+) phosphor,suggesting their potential applications in white light emitting diodes.

Numerical simulation and experimental investigation of Ti-6Al-4V melted by CW fiber laser at different pressures

The interaction of continuous wave （CW） fiber laser with Ti-6A1-4V alloy is investigated numerically and experi- mentally at different laser fluence values and ambient pressures of N2 atmosphere to determine the melting time threshold of Ti-6A1-4V alloy.＇ A 2D-axisymmetric numerical model considering heat transfer and laminar flow is es- tablished to describe the melting process. The simulation results indicate that material melts earlier at lower pressure （8.0 Pa） than at higher pressure （8.8x 104 Pa） in several milliseconds with the same laser fluence. The experimental results demonstrate that the melting time threshold at high laser fluence （above 1.89x 108 W/m2） is shorter for lower pressure （vacuum）, which is consistent with the simulation. While the melting time threshold at low laser fluence （below 1.89x 108 W/m2） is shorter for higher pressure. The possible aspects which can affect the melting process in- clude the increased heat loss induced by the heat conduction between the metal surface and the ambient gas with the increased pressure, and the absorption variation of the coarse surface resulted from the chemical reaction.