The absorptive optical nonlinearity in nanoclusters of Au@hexanethiol and Au@dodecanethiol has been investigated. From the mass spectra, each cluster is estimated to contain about 140 atoms of gold. The optical absorption spectra of the clusters show a gradual increase in absorbance towards the UV region, over which an extremely weak surface plasmon resonance (SPR) is superposed. No plasmon bleach effects are seen when the samples are excited with nanosecond laser pulses at 532 nm. Instead, a reduced transmission behavior is observed, which fits to a three-photon absorption mechanism. We propose that this nonlinearity is caused by two-photon induced excited state absorption occurring in the nanoclusters. Femtosecond pump-probe studies show that when excited and probed at 400 nm, the nonlinearity is very fast with a lifetime of less than 2 ps. © 2005 Elsevier B.V. All rights reserved.

Pradeep Thalappil

Department Of Chemistry

Atoms

Gold

Laser pulses

Photons

Spectrum Analysis

Surface plasmon resonance

Absorbance

Mass spectra

Nanoclusters

Optical nonlinearity

Light absorption

alkane derivative

GOLD DERIVATIVE

thiol derivative

article

Mass spectrometry

Molecular weight

nonlinear system

ultraviolet radiation

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IIT Madras

Chemical Physics Letters

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. © 2013 Optical Society of America.

Fulltext

Optics Express

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

Strong nonlinear absorption is observed in nanocomposite films containing PbS nanocrystals of mean size of 3.3 nm stabilized in a commercial poly(vinyl acetate) glue by a novel and simple chemical route of synthesis. A significant blueshift of the optical absorption edge indicates strong quantum confinement. The mean nanocrystal size was characterized by x-ray diffraction and transmission electron microscopy. The surface structure of nanocrystals is analysed using infrared spectroscopy. The excitonic transitions are probed by photoacoustic spectroscopy and the results are analysed on the basis of theoretical calculations using envelope function formalism. Results of open aperture z-scan experiments suggest a model involving saturable absorption followed by two-photon absorption at a lower concentration while the data for a higher concentration fitted saturable absorption followed by three-photon absorption. Free carrier absorption due to two-photon-assisted excited state absorption appears to be the predominant mechanism of optical nonlinearity. © IOP Publishing Ltd.

Nanotechnology

Two-photon-assisted excited state absorption in nanocomposite films of PbS stabilized in a synthetic glue matrix

We report the spectral and optical limiting properties of two kinds of HA P nanoparticles (pure HA P and HA P@SiO 2 core-shell nanoparticles) that were wetchemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HA P and HA P@SiO 2 nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective threephoton absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core- shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters. © Springer Science+Business Media, LLC 2011.

Journal of Materials Science: Materials in Electronics

Synthesis and optical limiting studies of HAP and HAP@SiO2 core–shell nanoparticles

29 kDa gold cluster molecules with thiol protection were synthesized and size separated by chromatography. Their direct laser desorption leads to large scale clustering and the mass spectral features extend up to 500 kDa. Effect of alkanethiol chain length on clustering suggests that monolayer interaction is the key to this phenomenon. Role of different matrices on clustering in the matrix assisted laser desorption ionization (MALDI) process has been investigated. © 2004 Elsevier B.V. All rights reserved.

Gas phase aggregates of protected clusters

Stable Au and Ag nanoparticles protected with TiO2, ZrO 2, and SiO2 shells show saturable absorption when excited with moderately energetic nanosecond pulses at 532 nm, but exhibit strong optical limiting at higher intensities. The behavior is explained in terms of the induced optical nonlinearity and nonlinear light scattering. The inherent stability of the core-shell structure renders a high laser damage threshold to these materials, making them promising candidates for high energy optical limiting. © 2003 Elsevier B.V. All rights reserved.

Nonlinear light transmission through oxide-protected Au and Ag nanoparticles: An investigation in the nanosecond domain

Monolayer-protected Au, Ag, and Au:Ag alloy nanoclusters have been synthesized using octanethiol and octadecanethiol as capping agents. The particle-size distribution is narrow with an average core size of 3-4 nm. Optical nonlinearity induced by 35 ps pulses at 532 nm has been investigated in these samples using the Z-scan technique. It is found that in general, they behave either as saturable absorbers or reverse saturable absorbers depending on the intensity of excitation. Au and Ag clusters show nearly the same efficiency for optical limiting, but the alloy clusters are found to be less efficient in limiting and are less photostable. The observed effects are explained in terms of the electron dynamics of the excited-state species.

Physical Review B - Condensed Matter and Materials Physics

Picosecond optical nonlinearity in monolayer-protected gold, silver, and gold-silver alloy nanoclusters

Transition from nanoparticle to molecular behavior: a femtosecond transient absorption study of a size-selected 28 atom gold cluster

Surface Science

Clusters as new materials

Observation of a fifth order optical nonlinearity in 29 kDa Au@alkanethiol clusters excited in the visible