Modeling of Momentum Transfer to a Surface by Laser-Supported Absorption Waves

Abstract

A simplified parametric model of the flowfield produced by impingement of a high-energy laser pulse onto a nonablative surface in a static environment is described. An attempt has been made to account for the twodimensional effects arising out of the rarefaction structure within the laser-heated gases. An optimization model is developed to indicate the laser spot size, pulse width, and intensity dependencies of the efficiency of delivery of both impulse and mechanical energy to the target surface.velocity u(x) = axial velocity v = velocity behind shock in LSC model V w = LSC wave speed W = nondimensional particle velocity x = axial coordinate a =(Kt) y = ratio of specific heats in plasma 70 = ratio of specific heats in air p = density o = target material density Tf) = pulse length T Z = axial relaxation time T 2D = radial relaxation time T = normalized pulse time (= r p /r 2D ) T O = pressure relaxation time $0 = incident laser flux intensity, W/cm 2 Subscripts LSC = laser supported combustion condition LSD = laser supported detonation condition 0 = ambient r = condition behind rarefaction s = surface, spot

Ultrasonic Nondestructive Evaluation Using Laser Transducers

“…Reilly, Ballantine, and Woodroffe (1979) have modeled this mechanism, and they predict pressures of about 10 7 newtons/m 2 for this mechanism for power densities of lOll W/m 2 • This is very comparable to the steam ablation predictions. The amount of the aluminum removed is so small (10-7 m thick) as to be almost invisible.…”

Origin of nitrogen depth profiles after laser nitriding of iron

“…The nitrogen depth profiles achieved by laser nitriding of pure iron were measured with high accuracy by resonant nuclear reaction analysis and described by two superimposed diffusion profiles. Using simple estimates, together with the results of marker experiments and laser treatments in 15 N-isotopically enriched atmospheres, the development of these profiles with the number of pulses can be simulated in excellent agreement with the experimental results. © 1999 American Institute of Physics.…”

“…The time constant t 2 ϭ209 ns for the second diffusion profile is well below the 293 ns for which the surface remains liquid. According to the model of laser supported combustion ͑LSC͒ waves, a high plasma pressure of about 49 MPa above the liquid surface is generated, [14][15][16] which remains constant for z ϭ113 ns when the rarefaction fan from the top reaches the surface, and then slowly drops until 2D ϭ265 ns when the rarefaction fan a͒ Electronic mail: pschaaf@uni-goettingen.de from the lateral borders of the laser spot reaches the center. 15 The diffusion time t 2 ϭ209 ns lies in between these two values.…”

Mechanisms of Pulsed Laser Ablation of Biological Tissues

“…Like the steady-state vaporization models, the first comprehensive attempt at integrating mechanical effects into a steady-state model of the tissue ablation process drew upon models developed for the ablation of metals. [334][335][336][337][338] This approach for tissue ablation was pioneered by Zweig, Frenz, and co-workers, starting in the late 1980s. 244,280,284,[288][289][290] In this model, tissue is considered to be capable of undergoing two phasechange processes: (a) a transition from a solid to a liquid phase and (b) a transition from a liquid to a vapor phase.…”