We present a calculation of the chirp generated in laser pulses shorter than 100 fsec on propagation through a saturable absorber (DODCI in ethylene glycol). The calculation takes into account the absorber saturation and the solvent nonlinear refractive index. At pulse energies greater than 10 nJ the chirp tends to be predominantly positive, and it increases rapidly as the pulse duration becomes shorter than 50 fsec. At pulse energies in the 1-7-nJ range the chirp is mostly negative for pulses longer than 30 fsec.
We consider the nonequilibrium thermodynamic aspects of the techno-industrial process of thermal laser Stereolithography. The conditions necessary for a satisfactory process of rapid prototyping to follow are characterized and discussed. We show that the process is best described in terms of modern theories of nonequilibrium thermodynamics of dissipative systems. Nonconservative fluxes need to be introduced as basic variables, quite in the spirit of extended irreversible thermodynamics, to explain the experimental results. We also show that by varying the thermal properties of the material, the restricted domain of validity of the traditional classical irreversible thermodynamics is reached: to have diffusive motion predominating over long-rangepropagating undulatory motion is fundamental for the technique.
ABSTRACT:The development of a new approach for the production of three-dimensional plastic parts, called infrared laser stereolithography, is presented. During the experimentation, a carbon dioxide (CO 2 ) laser beam at 10.6 m (infrared radiation) was focused on a sample composed of an epoxy resin, diethylene triamine (curing agent), and silica powder (filler). The CO 2 laser, adopted for cost reduction, led to no significant shrinkage, and almost no postcure treatment was required. With differential scanning calorimetry, it was possible to determine the reaction rate as a function of the temperature and the activation energy of the curing process. The solution of the heat equation, with the Ansys program simulating this process, was in general agreement with our previous observations of the stereolithography results. The experimental results of the production of solid parts layer by layer in three dimensions are presented.
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