The effects of varying Co thickness on the mass resolving power for Cu in a multilayer stack are characterized by laser-assisted atom probe. As the Co layer thickness increased, Cu exhibited poorer mass resolving power. By reducing the pulse repetition rate from 250 kHz to 10 kHz, the mass resolving power improved to match that of Cu with no Co underlayer. These results support that thermal mechanisms for field evaporation dominate in this Co-Cu multilayer, which is a common architecture in giant magneto-resistance thin film devices. (C) 2013 Elsevier B.V. All rights reserved.