Transient surface electric fields induced by femtosecond laser irradiation of an aluminum film were investigated directly by ultrashort electron pulses. At pump intensities of 2.9~7.1 * 10^10 W/cm2, the transient electric fields last at least one nanosecond with a maximum field strength of 3.2~5.3 * 10^4 V/m at 120 micro m above the aluminum surface. The transient electric fields and the associated evolution of photoelectrons were explained by a "three-layer" model. The potential influence of such fields on reflection ultrafast electron diffraction and time-resolved angle-resolved photoemission spectroscopy were evaluated.
Comment: 24 pages, 6 figures, 3 tables