The growth of thin K films on Si(111)-7 x 7 has been investigated by selecting the input and output polarizations of second-harmonic generation (SHG) at room temperature (RT) and at an elevated temperature of 350 degrees C. The SH intensity at 350 degrees C showed a monotonic increase with K coverages up to a saturated level, where low energy electron diffraction (LEED) showed a 3 x 1 reconstructed structure. The additional deposition onto the K-saturated surface at 350 degrees C showed only a marginal change in the-SH intensity. These variations are different from the multicomponent variations up to 1 ML and orders of magnitude increase due to excitation of plasmons in the multilayers at RT. The variations of SHG during desorption of K at 350 degrees C showed a two-step decay with a marked shoulder which most likely corresponds to the saturation K coverage of the Si(111)-3 x 1-K surface. The dominant tensor elements contributing to SHG are also identified for each surface. (c) 2005 Elsevier B.V. All rights reserved.