Construction of a pump‐probe system for observing time‐resolved sum frequency images

We combined a pump‐probe technique with optical sum frequency microscopy, and demonstrated a time‐resolved SF intensity image observation of an HSi(111) surface in ultrahigh vacuum (UHV) conditions. After pump‐light irradiation of photon energy 2.33 eV, pulse duration ∼30 ps, and the width of the spot ∼304 µm, SF intensity image resonant to the SiH stretching vibration with IR probe wavenumber of 2085 cm −1 was darkened dramatically at 0 ps and then gradually recovered. Nonresonant SF signals with IR probe wavenumber of 2020 cm −1 increased at the probe delay time ∼0 ps, and then decreased with the life time of ∼1 ns. The width of the spatial profile of the nonresonant signal was at a minimum of ∼436 µm at the delay time 26 ps, and then increased to ∼673 µm at 930 ps. The origins of these behaviors of the SF intensity images are discussed. Copyright © 2010 John Wiley & Sons, Ltd.