Cluster matter: the transition of optical elastic scattering to regular reflection

The optical response of many-cluster systems (cluster matter) depends strongly on the mean filling factor and on its local variations. This is shown from Au clusters of various sizes which form coagulation systems. Measured spectra of the extinction, the absorbance, the integral scattering, the angle resolved scattering, the regular reflection and corresponding TEM micrographs are presented. It is demonstrated that by varyingf from 10−6 to 0.5 the incoherent Mie scattering is transformed into regular geometric-optical transmission and reflection (“Oseen-transition”) while the spectral features even of the most densely packed samples still differ strongly from those of a bulk Au film.