EFFECT OF LASER REPETITION RATE ON THE MELTING AND ABLATION OF NI24ZR76 ALLOY RIBBON

An amorphous Ni24Zr76 metallic ribbon 35 mu m thick, prepared by plana r flow casting, was furnace recrystallized and subsequently laser anne aled in a vacuum of 2 x 10(-3) Pa. The fluences of the laser pulses we re 1.4 and 1.9 J cm(-2), the number of pulses directed to the same irr adiation site was between 1 and 300. The repetition rate of the laser pulses varied between 5 and 100 Hz. The temperature evolution in the i rradiated samples in one- and multipulse regimes were numerically calc ulated. The samples were analysed by X-ray diffraction, X-ray fluoresc ence spectroscopy, scanning electron microscopy and differential scann ing calorimetry. A strong increase of the laser damage level, manifest ed by melting and ablation with the increase of the pulse repetition r ate, was observed. This effect is attributed to the heat accumulation in the sample at higher pulse repetition rate. Additional effects, suc h as roughening of the sample surface, increase of the optical absorpt ion, decrease of the thermal diffusivity, and decrease of the thicknes s of irradiated sample can also amplify this effect.