Lifetimes of image-potential states on Cu(100) and Ag(100) measured by femtosecond time-resolved two-photon photoemission

We report time-resolved studies of image-potential states on Cu(100) and Ag(100). Femtosecond ultraviolet-pump and infrared-probe techniques combined with two-photon photoemission have been used to measure relaxation dynamics of $n=1,$ 2, and 3 image-potential states. We found the lifetimes of these states on Cu(100) at room temperature to be $40\pm 6,120\pm 15,$ and $300\pm 20\mathrm{fs},$ respectively. The corresponding values for Ag(100) are $55\pm 5,160\pm 10,$ and $360\pm 15\mathrm{fs}.$