Yu-Hsiang Tsai

Measurement for temperature on a LED lamp

LED demonstrates a number of benefits compared to traditional incandescent lamps and fluorescent lamps. However, the thermal problem that is brought by heat generated within the LED itself is still a bottleneck that limits the stability, reliability and lifetime of high power LED. In order to understand the temperature characteristics of the LED lamp, this paper utilized the thermocouples to measure the temperature on LED lamp. The effects of the ambient temperature on the surface temperature of the LED lamp were presented.

Nanoscale Removal of Picosecond Laser Ablation for Polymer.

This paper analytically investigates the picosecond laser ablation of polymer. Laser-pulsed ablation is a well-established tool for polymer. However the ablation mechanism of laser processing for polymer has not been thoroughly understood yet. This study utilized a thermal transport model to analyze the relationship between the ablation rate and laser fluences. This model considered the energy balance at the decomposition interface as the ablation mechanisms and is applied to predict the laser-ablated depth of Acrylonitrile Butadiene Styrene/PolyVinyl Chloride (ABS/PVC). The calculated variation of the ablation rate with the logarithm of the laser fluence agrees with the measured data. The effects of material properties and processing parameters on the ablation depth per pulse are discussed for picosecond laser processing of ABS/PVC.

Analysis on ultrashort-pulse laser ablation for nanoscale film of ceramics

This paper uses the dual-phase-lag model to study the ablation characteristics of femtosecond laser processing for nanometer-sized ceramic films. In ultrafast process and ultrasmall size where the two lags occur, a dual-phase-lag can be applied to analyse the ablation characteristics of femtosecond laser processing for materials. In this work, the ablation rates of nanometer-sized lead zirconate titanate (PZT) ceramics are investigated using a dual-phase-lag and the model is solved by Laplace transform method. The results obtained from this work are validated by the available experimental data. The effects of material thermal properties on the ablation characteristics of femtosecond laser processing for ceramics are also discussed.

Effect analysis of material properties of picosecond laser ablation for ABS/PVC

This paper analytically investigates the picosecond laser ablation of ABS/PVC. Laser-pulsed ablation is a wellestablished tool for polymer. However the ablation mechanism of laser processing for polymer has not been thoroughly understood yet. This study utilized a thermal transport model to analyze the relationship between the ablation rate and laser fluences. This model considered the energy balance at the decomposition interface and Arrhenius law as the ablation mechanisms. The calculated variation of the ablation rate with the logarithm of the laser fluence agrees with the measured data. It is also validated in this work that the variation of the ablation rate with the logarithm of the laser fluence obeys Beer’s law for low laser fluences. The effects of material properties and processing parameters on the ablation depth per pulse are also discussed for picosecond laser processing of ABS/PVC.

Thermal characteristics of region surrounding laser welding keyhole

This paper investigates the thermal characteristics of region surrounding laser welding keyhole. The thermal characteristics of region surrounding laser keyhole play an important role on the mechanical properties after welding. The welding keyhole produced by laser welding is assumed to be a paraboloid of revolution. The laser beam with Gaussian distribution of intensity irradiates on the keyhole. Considering the phase change at solid-liquid interface, this study utilized the finite difference method to numerically calculate the thermal fields in the solid and liquid region surrounding laser welding keyhole.

Comparison of ultrashort-pulse-laser ablation characteristics for different ceramics

This paper analytically investigates the ultrashort-pulse-laser ablation characteristics for different ceramics. Ceramics processing is difficult due to its hard and brittle properties. Noncontact ultrashot-pulse-laser is widely recognized to be a applicable tool. The optical property, thermal conductivity, and thermal expansion coefficient of AhO3 Ceramics are obviously different from these of AlN ceramics and are significantly relevant to the ablation characteristics of these ceramics. Therefore, the ablation for Al2O3 and AlN ceramics is quantitatively analyzed in this study. The effects of the ceramics properties on the ablation characteristics are discussed by comparing the ablation of Al2O3 with AlN.

Nonlinear Characteristics of Plasma Induced by an Electron Beam Irradiating the Target Material

This paper studies the nonlinear characteristics of plasma induced by an electron beam irradiating the target material. Poissons equation, the equations of continuity, and momentum equation are employed to investigate the nonlinearity of the electron beam-induced plasma. The steady-state three equations are combined into a nonlinear second-order ordinary differential equation. The physical phenomena resulted from the nonlinear second-order ordinary differential equation are analyzed and presented in this paper. The effects of parameters on the nonlinear characteristics are also discussed.

Pressure Effect on Thermal Diffusion in Aluminum Powders Composed of Nanometer- and Micrometer-Sized Particles

Nanoparticles show a variety of size-dependent properties due to the dramatic changes in the ratio of surface area to volume. The characteristics of nanoparticles different from the bulk material make the properties of the powders composed of these nanoparticles attract more attention. The thermal diffusion in the powder composed of nanoparticles is experimentally investigated in this paper. The powder is wrapped up in the slender tube made of insulating material. One end of the slender tube filled with powder is maintained at low temperature and the other end is kept at room temperature. The temperature histories at two different locations in the slender tube are recorded using thermalcouples. The results show that the heat transfer depends on the bed porosity and the thermal conductivities of the solid and the gas. The pressure on the Al powders enhances the rate of heat transport due to the decrease of the bed porosity and a small fraction of gas.

Scattering signals of monochromatic light incident on a rectangular microchannel

In this paper, the transition process of scattering signals is investigated as an incident monochromatic light irradiates rectangular channels with sizes from micrometers to submicrometers. Monochromatic light scattering from open groove cavities is important in many design analyses for such fields as optical communications, display, storage, sensing, MENS and nano-technology. The distribution of scattering signals for light incident on the groove starts to change due to the diffraction as the opening width of the groove is close to the wavelength of monochromatic light. This study revealed the transition process of scattering signals of monochromatic light irradiating rectangular microchannels with sizes from micrometers to submicrometers. The results showed that the profile for the intensity of scattering signals changes from concave to convex shape in the direction of width and from irregular to regular wave in the direction of depth if the opening width of the rectangular microchannel reduces from micrometer to submicrometer.

Deformation in Thin Metal Films Irradiated by Femtosecond Laser

This paper utilizes the parabolic two-step model and dynamical theory of thermoeslasticity to investigate the deformation in thin metal films irradiated by femtosecond laser. In the femtosecond-laser processing of thin metal films, the hot electrons blast exerting on the metal lattices occurs because the metal lattices stay and almost thermally undisturbed at the stage of nonequilibrium energy transfer. The blasting force could be so strong that the cold lattices are impelled into the domain for damage. This study directly adds the driving force derived from the thermal field of hot electrons blast into the equation of dynamical theory of thermoelasticity that describes the dynamic response of the metal lattices. The results from this analysis show that the deformation of thin metal films decreases with the increasing electron thermal conductivity, optical penetration depth and film thickness.