Measurement of laser absorptivity for operating parameters characteristic of laser drilling regime

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. AbstractLaser drilling in the percussion regime is commonly used in the aircraft industry to drill sub-millimetre holes in metallic targets. Characteristic laser intensities in the range of 10 MW cm −2 are typically employed for drilling metallic targets. With these intensities the temperature of the irradiated matter is above the vaporization temperature and the drilling process is led by hydrodynamic effects. Although the main physical processes involved are identified, this process is not correctly understood or completely controlled. A major characteristic coefficient of laser-matter interaction for this regime, which is the absorptivity of the laser on the irradiated surface, is still unknown, because of the perturbing effects due to laser beam geometrical trapping inside the drilled hole. So, by using time resolved experiments, this study deals with the direct measurement of the variation of the intrinsic absorption of aluminium, nickel and steel materials, as a function of the incident laser intensity up to 20 MW cm −2. We observe that for this incident intensity, the absorptivity can reach up to 80%. This very high and unexpected value is discussed by considering the microscopic behaviour of the heated matter near the vapour-liquid interface that undergoes possible Rayleigh-Taylor instability or volume absorption.

Analysis and possible estimation of keyhole depths evolution, using laser operating parameters and material properties

“…Then if the welding speed is decreased, the surface temperature reaches the evaporation one T v , and the surface below the laser spot begins to be depressed by the recoil pressure [ Fig. 1(b)], but the reflected incident beam is still reflected upwards, which carries away about typically 60% from the incident laser power (at 1.06 μm, on steel alloys 15 ). By a further reduction of the welding speed, due to the resulting increase in surface temperature and the subsequent recoil pressure, the deformation of the melt pool surface increases and the inclination of what will be the KH front can reach 45°[ Fig.…”

Modeling laser drilling in percussion regime using constraint natural element method

“…In order to avoid the modelling of these complex effects, the absorption coefficients measured in [30] is used for several laser peak power corresponding to the percussion regime (Fig. 5a).…”

“…Every values of thermophysical properties were found in the litterature [25]. Only the absorption coefficient (0.68) and the laser beam radius (150μm) come from experimental measurements done in [30]. The initial domain is a 400×800μm 2 rectangular and the simulation duration is set to 150μs.…”

Surface oxidation of nickel base alloys and stainless steel under pure oxygen atmosphere: Application to oxygen safety

“…A conventional way 5,6 for the determination of the surface absorption coefficient for a specific laser wavelength consists in the use of an integrating sphere (Ulbricht sphere). The internal surface of the integrating sphere is sandblasted and coated with BaSO 4 for a good diffusion and reflectivity of the light inside.…”