Ultrashort laser pulses in metal surfaces: Origin of spurious fluctuations in fully quantal calculations

We use fully quantal methods to solve the time-dependent Schrodinger equation for collision problems. In our particular example, we studied the interaction of ultrashort laser pulses with metal surfaces. We obtained big fluctuations in the photoionization cross sections, and analyzed the possible origin of them. After ruling out the numerical grid effects, we found a way to eliminate the fluctuations, by choosing an appropriate basis set for the continuum eigenfunctions.