Laser-plume dynamics during excimer laser nitriding of iron

On the time scale of tens to hundreds of nanoseconds, high intensity pulsed excimer laser irradiation of iron in nitrogen atmosphere produces thin iron nitride layers with high nitrogen concentration. The laser plasma, or laser plume, which plays a crucial role in the complicated interactions within the laser-plasma-metal system, depends strongly on the ambient nitrogen gas pressure. Its influence was investigated in the nitrogen gas pressure range from 0.05 bar to 10 bar. The nitrogen depth profiles were measured via the nuclear resonance reaction N-15(p,alphagamma)C-12, while the phases formed in the surface layer were analyzed by conversion electron Mossbauer spectroscopy and x-ray diffraction. Utilizing sequentially N-15-enriched and natural nitrogen atmospheres, the evolution of the nitrogen depth profiles during the laser nitriding process was traced. The experimental results suggest that the one-dimensional laser-supported combustion wave model reasonably describes the laser-plume dynamics and the nitriding effect. (C) 2003 American Institute of Physics.