OPTICAL-PROPERTIES OF LOW-DENSITY FOAMS CONSIDERED AS TARGETS FOR INERTIAL CONFINEMENT FUSION

An optical method for measuring scattered light, namely by analyzing t he transmitted light, is used to characterize the optical properties o f low-density foams that are candidates as targets for inertial confin ement fusion. This method allows us to simultaneously measure both sca ttering and intrinsic absorption in the foam. Three types of foams hav e been examined: two have similar chemistries and are based on either ethylene glycol dimetacrylate (EGDM) or trimethylolpropane trimethacry late (TMPT), The other one is based on resorcinol formaldehyde (RF). W e observe that while the RF foams are orange in color and nearly trans parent, the EGDM/TMPT based foams are white and opaque. The opacity of these foams is shown to be due to light scattering by particles havin g dimensions on the order of 200 nm. In contrast, the light scattering from the RF foams indicates that the structures scattering light are on the order of 20 nm. The orange color of the RF foams is shown to be due to intrinsic absorption of light by the polymer comprising the fo am. The onset of absorption is seen to shift towards the blue as the f oams age, Index matching to the TMPT foam using ethanol is shown to si gnificantly reduce the scattering. (C) 1998 American Vacuum Society.