Ultrafast photoinduced enhancement of nonlinear optical response in 15-atom gold clusters on indium tin oxide conducting film

TL;DR

This study demonstrates that contact with indium tin oxide significantly boosts the third-order nonlinear optical response of 15-atom gold clusters, revealing ultrafast photoinduced enhancements in their optical properties.

Contribution

It introduces a novel system where gold clusters on ITO exhibit greatly enhanced nonlinear optical responses due to excited state energy transfer, differing from previous charge transfer mechanisms.

Findings

Two-photon absorption coefficient increased by an order of magnitude.

Nonlinear optical refraction coefficient enhanced by approximately three times.

Photo-induced excited state absorption also increased by an order of magnitude.

Abstract

We show that the third order optical nonlinearity of 15-atom gold clusters is significantly enhanced when in contact with indium tin oxide (ITO) conducting film. Open and close aperture z-scan experiments together with non-degenerate pump-probe differential transmission experiments were done using 80 fs laser pulses centered at 395 nm and 790 nm on gold clusters encased inside cyclodextrin cavities. We show that two photon absorption coefficient is enhanced by an order of magnitude as compared to that when the clusters are on pristine glass plate. The enhancement for the nonlinear optical refraction coefficient is ~3 times. The photo-induced excited state absorption using pump-probe experiments at pump wavelength of 395 nm and probe at 790 nm also show an enhancement by an order of magnitude. These results attributed to the excited state energy transfer in the coupled gold cluster-ITO system are different from the enhancement seen so far in charge donor-acceptor complexes and nanoparticle-conjugate polymer composites.