Interference effects in the optical second harmonic generation from ultrathin alkali films

Interference effects are shown to strongly modulate the transmission second harmonic signal (fundamental wavelength 1067 nm) from rough alkali island films grown on insulating substrates if one varies the angle of incidence. Depending on growth conditions and substrate thickness, the measured second harmonic dependencies can be interpreted in terms of interference between frontside and rearside adsorbed islands or by taking into account the morph ology of the adsorbed alkali islands. By the use of different polarization combinations of both pump and reflected second harmonic wave we obtain accu rate values of the ratios of the relevant nonlinear optical coefficients. ( C) 2000 Published by Elsevier Science B.V.