Experimental study of laser-induced plasma in welding conditions with continuous CO2 laser

Abstract

Laser-induced plasmas obtained during a welding process have been studied. Spectroscopic diagnostics and an integrating sphere collecting the reflected CO2 light are the principal diagnostics used in order to determine the spatial variations of the microscopic parameters such as electron density and temperature, and the energy absorption during this process. For several experimental processing conditions of shielding gases, the main perturbing effects such as absorption and refraction of the CO2 laser radiation are quantified. Several possibilities for reducing these perturbing effects are then discussed.

Optical Methods for On-line Quality Assurance of Welding Processes in Nuclear Steam Generators

“…The captured spectrum is then processed to obtain relevant information. The common approach when using plasma spectroscopy in a welding sensor and monitoring system is to calculate the plasma electronic temperature Te, as it is known that there is a correlation between the resulting profiles of this parameter and the quality of their associated welds (Poueyo-Verwaerde et al, 1993). Figure 2 shows the processing steps needed with this "classical" approach of spectroscopic analysis.…”

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

“…In deep welding with a continuous CO 2 laser, PoueyoVerwaerde et al [34] found that the absorption length due to electron-neutral interactions is 0.25 m while that resulting from electron-ionized iron is 0.03 m. Lengths of inverse Brehmstrahlung absorption were around 1 m for plasmas of aluminum and titanium irradiated by a continuous CO 2 laser [35] and pulsed YAG laser, [36] respectively. (7) Radiation in the plasma is neglected.…”

Theoretical peak performance and optical constraints for the deflection of an S-type asteroid with a continuous wave laser

“…Initially, an energy flux on the order of 100GW/m 2 is required to accelerate the free electrons in the vapor by inverse Bremsstrahlung (IB) until their kinetic energy becomes sufficient to ionize the atoms of the vapor by an avalanche process. Indeed, as explained by Poueyo-Verwaerde et al (1993), a necessary condition for the development of this electron avalanche is that the growth rate of electron energy by IB is higher than the losses due to elastic collisions with neutral atoms in the plume. This condition translates in a CW intensity threshold approximately equal to:…”

“…The processes leading to plasma formation under continuous wave laser irradiation have been investigated by Poueyo-Verwaerde et al (1993). Initially, an energy flux on the order of 100GW/m 2 is required to accelerate the free electrons in the vapor by inverse Bremsstrahlung (IB) until their kinetic energy becomes sufficient to ionize the atoms of the vapor by an avalanche process.…”