Beam focusing characteristics effect on energy reflection and absorption in a drilling or welding cavity of paraboloid of revolution

Wei, P. S.; Ho, Ching-Yen

doi:10.1016/s0017-9310(98)00036-2

Cited by 26 publications

(24 citation statements)

References 10 publications

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“…Evidently, the absorbed energy flux is quite different from the incident flux, as found by Wang and Wei,[14] Ho and Wei, [15] Wei and Ho, [16] and this work accounting for the effects of wavelength and polarization on energy absorption. The difference in using a constant specular reflectivity and c-polarized Fresnel reflectivities, which are independent and dependent of incident angle, respectively, to predict energy absorption is presented in Figure 6.…”

Section: Dimensionless Diffuse Radiositymentioning

confidence: 50%

“…[16] and substituting r j for r n+2 , the location of the first impinging point, r jn , can be obtained…”

Section: Dimensionless Diffuse Radiositymentioning

confidence: 99%

“…The refractive and absorptive indices are independent [33] parameters due to dependence of frequencies of laser, plasma or electron-phonon interactions, impurities, phase change, and temperatures in the workpiece, etc. Instead of using s 1,2 ϭ s 1,2// ϭ (u Ϫ n 1 sin 2 tan 2 ) 2 ϩ v 2 (u ϩ n 1 sin 2 tan 2 ) 2 ϩ v 2 s 1,2Ќ convergence angle, spot size, and focal location to define energy flux, [15,16] the incident flux is specified by the wave- [34] length, spot size, and focal location of the laser beam. For a given location, specular reflectivities are determined by (c) Reflectivities for c-polarization Fresnel's relations as functions of the incident angle and indices of refraction and absorption.…”

Section: Dimensionless Diffuse Radiositymentioning

confidence: 99%

“…The variation of specular reflectivity for p-polarization with incisd 1,2Ќ ϭ (n 1 cos d 2 Ϫ u) 2 ϩ v 2 (n 1 cos d 2 ϩ u) 2 ϩ v 2 , [39] dent angle, therefore, reduces with decreasing refractive analysis; incident flux is also shown. specular reflection from the virtual point source, [16] can be determined by…”

Section: Dimensionless Diffuse Radiositymentioning

confidence: 99%

“…Ho and Wei [15] and Wei C.Y. HO, Associate Professor, is with the Mechanical Engineering and Ho [16] further included beam focusing characteristics to absorbed at a critical radius for the focal spot above the cavity base. The focusing effect is pronounced for the focal absorption.…”

mentioning

confidence: 99%

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Absorption in a paraboloid of revolution-shaped welding or drilling cavity irradiated by a polarized laser beam

Wei

2001

Metall Mater Trans B

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Energy flux absorbed by a paraboloid of revolution-shaped cavity subject to a focused polarized laser beam is systematically and quantitatively investigated. The incident flux is considered to be TEM 00 mode of a Gaussian distribution specified by the wavelength, spot size, and focal location of the laser beam. By neglecting absorption and scattering within the plasma in the cavity and accounting for diffuse and Fresnel specular reflections of the wall, the predicted results show that in contrast to cutting or etching, energy absorbed near the critical radius for a deep welding or drilling cavity is higher for s-polarization than that for p-polarization. On the other hand, absorption for p-polarization is higher than that for s-polarization in a shallow cavity. The critical radius indicating the jump of energy flux absorbed is independent of polarization and optical properties of the workpiece. The use of constant specular reflectivity instead of more elaborate c-polarized Fresnel reflectivities to predict absorption is accurate. A decrease in the wavelength of the laser beam and increase in cavity depth reduce the critical radius and enhance the peak of energy flux absorbed. As the focal distance and spot size decrease, both the critical radius and peak of energy flux absorbed increase. The predicted energy flux absorbed from the Monte Carlo method agrees well with an asymptotic solution.

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Section: Dimensionless Diffuse Radiositymentioning

confidence: 50%

“…[16] and substituting r j for r n+2 , the location of the first impinging point, r jn , can be obtained…”

Section: Dimensionless Diffuse Radiositymentioning

confidence: 99%