Abstract

Recently, many studies have emerged on optical power limiting (OL) in buckminsterfullerene (C₆₀).¹ OL occurs when the absolute transmittance of a material decreases with increasing laser fluence; in C₆₀, the dominant mechanism for OL is reverse saturable absorption (RSA), in which the absorption cross section from excited-state electronic energy levels is significantly higher than the ground state absorption cross section. For limiting of nanosecond pulses, the lifetime of the excited-state responsible for the nonlinear absorption is a crucial parameter. In this work, we provide a detailed study of the relaxation dynamics of the excited-state absorption for C₆₀ in toluene solution, as a thin solid film, and entrapped within an inorganic sol-gel glass matrix. Our results demonstrate that the microscopic morphology of the C₆₀ molecule plays a crucial role in determining the relaxation dynamics. We find that the dynamics of the C₆₀-glass composite occur on long (ns) timescales, comparable to those in solution; thin film samples, by contrast, show rapid decay (<20 picoseconds). Combined with intensity-dependent transmission measurements on the same samples, these results demonstrate that the C₆₀/sol-gel glass composites contain C₆₀ in a molecular dispersion, and are suitable candidates for solid-state optical limiting.

© 1996 Optical Society of America