Fig. 1. Experimental system

Fig. 2. Emission spectrum region

Fig. 3. The result of spectral diagnosis

Fig. 4. Effect of power on emission spectrum

Fig. 5. Emission spectrum region
(a): 2.0 kW; (b): 2.5 kW

Fig. 6. Effect of defocus distance on emission spectrum

Fig. 7. Effect of scanning speed on emission spectrum

Fig. 8. The surface of nitride layer

Fig. 9. Cross section of nitride layer

Fig. 10. Depth of nitride layer and heat effected zone

Fig. 11. Effect of nitrogen argon ratio on emission spectrum

Fig. 12. Effect of nitrogen argon ratio on emission spectrum