The Zn-to-Cu ratio in brass was measured by laser ablation inductively coupled plasma atomic emission spectroscopy. The influence of laser beam properties (pulse width, wavelength, and power density) on fractional laser ablation was investigated. The behavior of the Zn/Cu ratio vs. laser power density shows that there are different mechanisms influencing ps and ns laser ablation. With the use of a 30 ns pulse duration from an excimer laser, thermal vaporization appears to be the dominant process in the low-power density region. The Zn/Cu ratio approaches stoichiometry at higher power density, but the ablated mass still remains Zn rich. With a 35 ps pulse Nd:YAG laser, a nonthermal mechanism appears to govern the laser ablation process. When a 3 ns Nd:YAG laser is used, both thermal and nonthermal processes exist. For both 3 ns and 30 ps Nd:YAG lasers, stoichiometric ablation can be achieved at higher power densities.
X. L. Mao, A. C. Ciocan, and R. E. Russo, "Preferential Vaporization during Laser Ablation Inductively Coupled Plasma Atomic Emission Spectroscopy," Appl. Spectrosc. 52, 913-918 (1998)