Tailoring photonic strength in monolithic macroporous silica for random media

A systematic method of tuning the photonic strength of disordered dielectric media has been demonstrated in monolithic silica (SiO) with interconnected macropores prepared by the sol-get method. Macroporous SiO2 gels are obtained in a system containing tetramethoxysilane, poly(ethylene glycol) (PEG), acetic acid, and water. The macroporous structure is formed when the transient structure of phase separation developed during the hydrolysis and polycondensation of alkoxysilane is chemically frozen-in by the sol-gel transition. The sizes of pores and skeletons, which are determined by the relative rate of phase separation to that of the sol-gel transition, can be controlled by the PEG content. The coherent. backscattering measurement, together with the theoretical calculation based on the independent scattering approximation, reveals that the transport mean free path of light in the porous SiO2 can be tuned by adjusting the density and size of the pores.