Determination of Radiative Fluxes in an Absorbing, Emitting, and Scattering Vapor Formed by Laser Irradiation

Abstract

A two-dimensional computer model is developed to determine the radiative heat flux distributions within the vapor formed above a metal target irradiated by a laser beam. An axisymmetric cylindrical enclosure containing a radiatively participating medium is considered. Scattering is assumed to be isotropic and allowances are made for variation of the radiative properties of the medium and boundaries. The P-1 and P-3 spherical harmonics approximations are used to solve the integro-differential radiative transfer equation. The resulting equations are then solved for the radial and axial heat fluxes using a finite-difference algorithm. The most significant factors affecting the results obtained from both the P-1 and P-3 approximations were the optical thickness of the medium and the type of laser profile incident upon the medium. Using different wall reflectivities and scattering albedos had a smaller effect. Changing the medium temperature had an insignificant effect as long as medium temperatures were below 20,000 K.

Nonlinear effects of laser-plasma interaction on melt-surface temperature

“…The powers of lasers employed in these applications range from a few hundreds of watts to several kilowatts and the power density is about 10 7 W cm −2 and higher. The coupling of the laser energy with the workpiece is determined by the radiative properties of the workpiece [2,3]. At high power densities there is always surface evaporation of the workpiece and subsequent ionization, resulting in a luminous plasma [4,5].…”

Modelling of radiation transfer in low temperature nanosecond laser-induced plasma of Al vapour

“…Also, it was established that radiative losses increase as the laser wavelength increases due to the higher temperature of the plasma [13,16], and are reduced with a decrease in beam radius [16] due to the smaller thickness and effective emissivity of the plasma layer [18]. Plasma radiation transfer for the nanosecond duration case has been studied less extensively [19][20][21][22]. It was established in [19] that under the action of an ultraviolet (UV) laser with a pulse duration of 30 ns and radiation intensity of up to 10 9 W cm −2 the radiative energy losses of the plasma are as high as 35%.…”

“…In [20] expansion and radiation transfer in the air plasma were investigated within the problem of laser shock processing (LSP) under the action of radiation pulses of 1.06 and 0.353 µm and an intensity of 4-17 GW cm −2 . In [21] radiation losses of the stationary plasma are estimated and the problems of inverse bremsstrahlung absorption and heating of the plasma are discussed. In [22] the coefficients of transmission and scattering are determined experimentally for a plasma layer under the action of the eximer laser with an energy density of 1-5 J cm −2 on an Ni target, the energy transfer equation is solved numerically, which leads to conclusions as to the values of the plasma absorption coefficients, the scattering function and typical sizes of scattering centres.…”