Barrier potentials including a harmonically time-dependent term are frequently used in order to investigate the modulation of tunneling probabilities in nanoscale systems due to the interaction with laser light. In this work, a novel approach to calculate these probabilities based on a partial Fourier transform of the wave-function in an extended coordinate space is derived. Numerical results will be compared to analytical as well as previous numerical calculations for two prototype barrier systems. (c) 2005 Elsevier B.V. All rights reserved.