and fifth chapters respectively, show how these principles can be applied to model and understand various aspects of the pyrolytic and photolytic LCVD processes.

The most widely used high power industrial lasers are the Nd:YAG and CO2 lasers. The chemical oxygen iodine laser (COIL), whose wavelength (1.315 μm) is between that of the Nd:YAG (1.06 μm) and CO2 (10.6 μm) lasers, is another high power laser for industrial applications. The cutting capability of these lasers is investigated in this paper. The cut depth strongly depends on the absorptivity of the cut material, kerf width and cutting speed. The absorptivity is an unknown parameter for which experimental data at high temperatures are currently unavailable. Theoretical values of the absorptivities of various metals are obtained using the Hagen-Ruben relationship. It is found that the absorptivity of a metal is linearly proportional to the square root of its resistivity and also inversely proportional to the square root of the wavelength. The absorptivities of the COIL and Nd:YAG lasers are 2.84 and 3.16 times larger than that of the CO2 laser, respectively. Based on these theoretical values of the absorptivity, the cut depths for several metals are analyzed at various laser powers and cutting speeds for these lasers. For identical cutting parameters, the cut depths for stainless steel and titanium are deeper than those of most other metals. Due to the wavelength dependence of the absorptivity, the cut depths for COIL and Nd:YAG lasers are expected to be 2.84 and 3.16 times deeper than that for the CO2 laser.

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A two-dimensional model is developed for material damage caused by melting and vaporization during pulsed laser irradiation. The problem is formulated by using the energy conservation equation (the Stefan condition) at various points on the solid-liquid and liquid-vapor interfaces. The effect of curvature of the solid-liquid and liquid-vapor interfaces are taken into account and the problem is solved numerically by using the Runge–Kutta method. For determining the maximum damage that can occur during laser irradiation, the laser energy is considered to be utilized only to melt and vaporize the material. The effect of various laser parameters, such as the laser power, laser beam diameter, pulse-on time, and the number of pulses per second on the depth and the radius of the crater is presented. Also, the tapering angle of the crater and the formation of recast layer in the crater during laser irradiation are examined in this study. Finally, a linear relationship between the maximum crater depth and the ‘‘gross’’ laser intensity is derived phenomenologically and verified by using the numerical results of this study.

A nanosecond pulsed laser direct-write and doping (LDWD) technique is used for the fabrication of carbon-rich silicon carbide nanoribbons heterostructure in a single crystal 4H–SiC wafer. Characterization by high-resolution transmission electron microscope and selected area electron diffraction pattern revealed the presence of nanosize crystalline ribbons with hexagonal graphite structure in the heat-affected zone below the decomposition temperature isotherm in the SiC epilayer. The nanoribbons exist in three layers each being approximately 50–60 nm thick, containing 15–17 individual sheets. The layers are self-aligned on the (0001) plane of the SiC epilayer with their c axis at 87° to the incident laser beam. The LDWD technique permits synthesis of heterostructured nanoribbons in a single step without additional material or catalyst, and effectively eliminates the need for nanostructure handling and transferring processes.

Nanoelectrospray laser deposition (NELD) of nanoparticles (NPs) on various substrates has attracted considerable attention as a fast, cost-effective, and scalable technique for precise control of heating time and zone. In this work, NELD-assisted sintering of titanium dioxide (TiO2) NPs on borosilicate glass and quartz substrates is addressed. A [Formula: see text] CO2 laser was used for patterning and sintering titania nanoparticles in ambient air. The effects of laser dose and deposition process parameters on the morphological, structural, and optical characteristics of the sintered TiO2 patterns were characterized using optical microscopy, scanning electron microscopy, and x-ray diffraction. The results point out that the anatase phase was preserved after laser sintering, without the appearance of any TiO2 rutile traces. We show that the improvement in the morphological properties of TiO2 patterns is due to the laser sintering of a dense layer of ceramic with enhanced interconnectivity and connection between single nanoparticles. A theoretical model was developed to select the temperature required to sinter TiO2 nanoparticles and to correlate it with the laser power and scanning speed to prevent cracking on the substrate and sintered nanoparticles and also to get transparent TiO2 films. An optical transmittance of [Formula: see text] was achieved. The experimental data were in accordance with the theoretical model, predicting the success of the model.

Impact response and dynamic strength of partially melted aluminum alloy J. Appl. Phys. 112, 053511 (2012) Study of strain fields caused by crystallization of boron doped amorphous silicon using scanning transmission electron microscopy convergent beam electron diffraction method J. Appl. Phys. 112, 043518 (2012) A theory for time-dependent solvation structure near solid-liquid interface J. Chem. Phys. 136, 244502 (2012) A new model of chemical bonding in ionic meltsMelting is encountered in almost all laser materials processing. This article deals with a one-dimensional heat conduction problem to investigate the melting rate during laser materials processing. The problem is solved approximately to obtain a correlation among melt depth, power density, and laser irradiation time. Based on this correlation, the dynamics of melting, a relationship between the melt depth and power density and an average melting velocity are expressed by simple analytic formulas. These expressions are further simplified for high power densities ͑I у 10 9 W/m 2 ͒. The times to reach the melting and boiling temperatures at the surface of the workpiece are also calculated.

Almost all laser-assisted materials processing involves melting, vaporization and plasma formation which affect the utilization of laser energy for materials processing. To account for the effect of these phases, an effective absorptivity is defined, and a simple mathematical model is developed for the cutting of thick-section stainless steel using a high power chemical oxygen—iodine laser (COIL). The model is based on an overall energy balance, and it relates the cutting depth with various process parameters that can be used to predictively scale the laser materials processing performance to very thick sections. The effects of various process parameters such as laser power, spot size, cutting speed and cutting gas velocity on the cutting depth are discussed. The results of the mathematical model are compared with experimental data. Such a comparison provides a means of determining the effective absorptivity during laser materials processing.