  We are interested in the spectroscopic behaviour of a gas confined in a
micrometric or even nanometric volume. Such a situation could be encountered by
the filling-up of a porous medium, such as a photonic crystal, with an atomic
gas. Here, we discuss the first step of this program, with the generation and
characterization of a self-organized 2D film of nanospheres of silica. We show
that an optical characterization by laser light diffraction permits to extract
some information on the array structure and represents an interesting
complement to electron microscopy.
