Metals are heat resistant materials, marking metals requires high density laser irradiation. Basically, the average laser power leads to melting and the peak power causes evaporation of the material .
The best traditional engraving materials started out being the worst laser-engravable materials. This problem has now been solved using lasers at shorter wavelengths than the traditional 10,640 nm wavelength CO2 laser. Using Yb: Fiber Lasers, Nd:YVO4 or Nd:YAG lasers at 1,064 nm wavelength, or its harmonics at 532 and 355 nm, metals can now easily be engraved using commercial systems.