<title>Femtosecond excited-state absorption dynamics and optical limiting in fullerene solutions, sol-gel glasses, and thin films</title>

Abstract

Los Alamos National Laboratory, an affirmative actiodequal opportunity employer, is operated by the University of California for the US. Department of Energy under contract W-7405-ENG-36. By acceptance of this article, the publisher recognizes that the US. Government retains a nonexclusive, royalty-free license to publish or reproduce the published form of this contribution, or to allow others to do so, for US. Government purposes. The Los Alamos National Laboratory requests that the publisher identify this article as work performed under the auspices of the US. Department of Energy. Form No. 836 R5 ST2629 10191 ~. ~. DfsTRIBUflON OF THIS D Q C-'. Femtosecond excited-state absorption dynamics and optical limiting in fullerene solutions, sol-gel glasses, and thin films

Optical Limiting Properties of [60]Fullerene and Methano[60]fullerene Derivative in Solution versus in Polymer Matrix: The Role of Bimolecular Processes and a Consistent Nonlinear Absorption Mechanism

“…In addition to PMMA polymer films, other solid-state matrixes such as sol−gel glasses also have significant effects on the optical limiting performance of fullerenes, resulting in substantially weaker optical limiting responses. − Mechanistic explanations including a change in nonlinear scattering from solution to solid-state matrix 18,19 and thermal effects 20 have been proposed. While there may be contributions to the optical limiting of fullerenes from these mechanisms in addition to nonlinear absorptions, especially at high input fluences, the contributions are likely insignificant compared to the effects that are associated with the bimolecular excited-state processes discussed above.…”

“…Among the most promising optical limiters under active investigations are materials showing strong nonlinear absorptions, which are commonly referred to as reverse saturable absorbers. − The primary mechanism for the nonlinear absorptive optical limiting is a large ratio of excited-state to ground-state absorption cross sections. Thus, potent reverse saturable absorbers are typically molecules with weak ground-state absorptions, such as metallophthalocyanines, , mixed metal complexes and clusters, and fullerenes. ,− …”

“…Since Tutt and Kost first reported 7 that [60]fullerene (C 60 ) in toluene solution is an excellent optical limiter toward a nanosecond pulsed Nd:YAG laser at 532 nm, there have been extensive investigations of fullerene optical limiting properties. − The optical limiting performance of C 60 in solution was reported to be concentration independent, though the experimental results on which the report was based apparently contain large uncertainties . For C 60 in room-temperature toluene solution, McLean et al used a five-level model for reverse saturable absorption (Figure ) to correlate the observed optical limiting responses with the ground- and excited-state absorption cross sections of C 60 .…”

“…Significant contributions from other nonlinear optical processes, such as nonlinear scattering, , have been suggested. Important experimental evidence for possible contributions from mechanisms other than reverse saturable absorption includes the observation that the optical limiting performance of fullerenes in solid matrixes is rather different from that in solution. − For example, it was reported that the optical limiting responses of C 60 dispersed in a poly(methyl methacrylate) (PMMA) matrix are much weaker than those in room-temperature toluene solution . The dramatic difference in the optical limiting performance of C 60 from solution to PMMA matrix cannot be attributed to changes in the nonlinear absorptive behavior because the ground-state and triplet−triplet transient absorption spectra of C 60 in PMMA polymer film are similar to those in room-temperature toluene solution 22a.…”

Fullerene-Based Organic−Inorganic Nanocomposites and Their Applications

“…Methanofullerenes for application in sol−gel materials were synthesized by the group of Los Alamos, in particular phenyl-C 61 -butyric acid choleteryl ester (PCBCR) with the cholesteryl side chain attached via a 6−6 cycloaddition and 1-(3-methoxycarbonyl)propyl)-1-phenyl-[6,6]-C 61 (PCBM). The general advantage of methanofullerenes is their larger solubility in polar media.…”