R.H. Magruder

Picosecond nonlinear optical response of a Cu:silica nanocluster composite

We describe the picosecond nonlinear optical response of a metal-dielectric composite made by implanting Cu ions in fused silica. The implanted Cu ions aggregate during implantation to form nanometer-diameter clusters in a dense, thin (~150 nm) layer just beneath the surface of the substrate. The third-order susceptibility X((3)) has an electronic component with a magnitude of the order of 10(-8) esu and is enhanced for laser wavelengths near the surface plasmon resonance of the copper colloids.

Physical and optical properties of Cu nanoclusters fabricated by ion implantation in fused silica

Cu clusters of nanometer dimensions were created by implantation of Cu ions into pure fused silica substrates at energies of 160 keV. The sizes and size distributions of the Cu clusters were measured by transmission electron microscopy, and were found to be determined by the ion‐beam current during implantation. Optical‐absorption spectra of these materials show the size‐dependent surface plasmon resonance characteristic of noble‐metal clusters. There are also significant size‐dependent effects in both the nonlinear index of refraction and two‐photon absorption coefficients. The distinctive variations in linear and nonlinear optical properties with Cu nanocluster sizes and size distributions affords potentially interesting possibilities for using these materials in nonlinear optical devices.

Nonlinear optical properties of metal-quantum-dot composites synthesized by ion implantation

Abstract Over a decade ago, it was demonstrated that composites comprising metal clusters embedded in dielectric hosts could be synthesized by ion implantation. The optical properties of these metal-cluster composites are dominated by two phenomena which alter the susceptibilities from those of bulk metals: One is a classical field enhancement effect, dielectric confinement, which leads to the characteristic surface plasmon resonance of the metal clusters seen in absorption spectra. The other effect is quantum confinement of the conduction-band electrons which enhances the nonlinear susceptibility of the metal clusters for diameters smaller than about 10 nm and makes them behave as quantum dots with electronic properties which approximate those of independent electrons confined in a spherical potential well. This paper reviews our studies of the nonlinear optical behavior of quantum-dot composites synthesized by ion implantation. We also consider the potential of these quantum-dot composites as materials for nonlinear waveguide devices.

Non-linear optical properties of nanometer dimension AgCu particles in silica formed by sequential ion implantation

Abstract Nanometer dimension metal colloids were formed in silica by sequential implantation of Ag and Cu ions. The Ag and Cu were implanted with Ag to Cu ratios of 9:3, 6:6 and 3:9 and total nominal dose 12 × 10 16 ions/cm 2 . The linear optical response was measured from 200 to 900 nm. The non-linear optical properties were measured using the Z-scan technique at a wavelength of 570 nm. The linear and non-linear optical properties were found to be dependent upon the Ag to Cu ratio.

Wavelength tunability of the surface plasmon resonance of nanosize metal colloids in glass

Abstract It is demonstrated that the wavelength of the surface plasmon resonance of nanosize metal colloids embedded in silica can be changed by the alloying of metal ions using sequential implantation of different metal elements. Cu and Ag ions were sequentially implanted in silica to doses of 6 and 12×1016 ions/cm2. Both Ag- and Cu-rich metal alloy colloids ∼ 20 nm in diameter were formed in the silica matrix. The position of the surface plasmon resonance frequency was shifted to a frequency that depends on the elements implanted and their relative concentrations. These results have implications for the tunability of non-linear optical waveguide devices and switches.

Size dependence of the third-order susceptibility of copper nanoclusters investigated by four-wave mixing

We report on the observation of the forward degenerate four-wave mixing in four composite samples with Cu nanoclusters embedded in fused silica. The mean diameters of the copper particles in the four samples were 5, 7, 10, and 13 nm. The independent tensor elements of optical Kerr susceptibility were measured with different wave-mixing polarizations by use of 35-ps laser pulses from a mode-locked, frequency-doubled Nd:YAG laser. The measured third-order susceptibilities were on the order of 10−9–10−8 esu; the response time of the nonlinearity is faster than the laser pulse duration. The experimental results are consistent with a d−3 size dependence predicted for quantum-confined conduction band electrons in Cu nanoclusters.

Probing interface properties of nanocomposites by third-order nonlinear optics

We describe the exploitation of third-order nonlinear optical response — particularly nonlinear absorption and the nonlinear index of refraction — to probe interface dynamics, modifications and relaxation processes in granular materials consisting of metal quantum dots embedded in such dielectrics as fused silica and sapphire. Many features of these materials can be interpreted in terms of the quantum-mechanical model of the “particle-in-a-box”. Electronic and thermal relaxation processes in these novel nanocomposites are dominated by interactions of conduction-band electrons at the boundary between the quantum dot and its surrounding host material. Experimental examples presented include measurements of thermal and electronic relaxation rates, dephasing due to electron collisions at the nanocluster surface, effects of local structural order, changes in the saturation parameter due to chemical modification of the substrate, and one-and two-dimensional heat-transfer effects.

GaAs nanocrystals formed by sequential ion implantation

Sequential ion implantation of As and Ga into SiO2 and α‐Al2O3 followed by thermal annealing has been used to form zinc‐blende GaAs nanocrystals in these two matrices. In SiO2, the nanocrystals are nearly spherical and randomly oriented, with diameters less than 15 nm. In Al2O3, the nanocrystals are three dimensionally aligned with respect to the crystal lattice. Infrared reflectance measurements show evidence for surface phonon modes in the GaAs nanocrystals in these matrices.

Modification of the optical properties of glass by sequential ion implantation

The linear and nonlinear optical properties of a series of samples formed by the sequential implantation of Ti, O and Au are examined. Energies of implantation for each ion were chosen using TRIM calculations to insure overlap of the ion distributions. The Ti was implanted with nominal doses of 1.2 and 2 {times} 10{sup 17} ions/cm{sup 2}. The samples were implanted with oxygen to the same nominal dose as the Ti. Au was then implanted with a nominal dose of 6 {times} 10{sup 16} ions/cm{sup 2}. The samples were subsequently annealed in oxygen at 900 C for two hours. The Ti and O are incorporated into the host network, while the Au forms nanosize colloids. The presence of the Ti in the substrate causes a shift in the surface plasmon resonance frequency of the Au metal colloids as well as an increase in the nonlinear response of the composites. The results are interpreted in terms of effective medium theory.

Electron paramagnetic resonance spectroscopy of titanium‐ion‐implanted silica

Silica substrates were implanted with titanium ions, in the +1 charge state, to nominal doses of 1×1016, 3×1016, and 6×1016 ions/cm2 at an energy of 160 keV and a current of 2.5 μA/cm2. The implanted ion depth profiles were measured by backscattering techniques. Components in the vacuum ultraviolet absorption and electron paramagnetic resonance (EPR) spectra are attributed to a fraction of the implanted titanium in the Ti3+ state. The intensity of the Ti3+ EPR component has a Boltzmann temperature dependence between 490 and 5 K. The fraction of implanted titanium ions producing this EPR component ranges from 10% for doses of 6×1016 and 3×1016 ions/cm2 to 38% for a dose of 1×1016 ions/cm2. Based on the relative intensities of the Ti3+ charge transfer band resolved in optical absorption measurements, the fraction of Ti ions in the 3+ state is larger than the fraction estimated from the EPR spectral component. The Ti3+ ions not contributing to the EPR spectra are assumed to be antiferromagnetically (or spero...