  Parabolic and spherical mirrors are constructed of aluminized PET polyester
film on urethane foam. During construction, the chosen shape of the mirror is
created by manipulating the elastic/plastic behavior of the film with air
pressure. Foam is then applied to the film and, once hardened, air pressure is
removed. At an f-number of 0.68, preliminary models have an optical angular
spread of less than 0.25 degrees, a factor of 3.3 smaller than that for a
perfectly spherical mirror. The possibility exists for creating
large-lightweight mirrors with excellent shape and stiffness. These
"film-on-foam" construction techniques may also be applicable to
parabolic-trough solar concentrators but do not appear to be suitable for
optical imaging applications because of irregularities in the film.

Optics