Peter Zijlstra

Five-dimensional optical recording mediated by surface plasmons in gold nanorods.

Multiplexed optical recording provides an unparalleled approach to increasing the information density beyond 1012 bits per cm3 (1u2009Tbitu2009cm-3) by storing multiple, individually addressable patterns within the same recording volume. Although wavelength, polarization and spatial dimensions have all been exploited for multiplexing, these approaches have never been integrated into a single technique that could ultimately increase the information capacity by orders of magnitude. The major hurdle is the lack of a suitable recording medium that is extremely selective in the domains of wavelength and polarization and in the three spatial domains, so as to provide orthogonality in all five dimensions. Here we show true five-dimensional optical recording by exploiting the unique properties of the longitudinal surface plasmon resonance (SPR) of gold nanorods. The longitudinal SPR exhibits an excellent wavelength and polarization sensitivity, whereas the distinct energy threshold required for the photothermal recording mechanism provides the axial selectivity. The recordings were detected using longitudinal SPR-mediated two-photon luminescence, which we demonstrate to possess an enhanced wavelength and angular selectivity compared to conventional linear detection mechanisms. Combined with the high cross-section of two-photon luminescence, this enabled non-destructive, crosstalk-free readout. This technique can be immediately applied to optical patterning, encryption and data storage, where higher data densities are pursued.

White light scattering spectroscopy and electron microscopy of laser induced melting in single gold nanorods.

We present the first measurements of laser induced melting and reshaping of single gold nanorods. Using a combination of white light scattering spectroscopy and electron microscopy we find a melting energy of 260 fJ for nanorods with an average size of 92 x 30 nm. Contrary to previous reports on ensembles of nanorods, this melting energy corresponds well to the theoretical prediction of 225 fJ. We observe a gradual shape change from a long and thin rod to a shorter and wider rod, which eventually collapses into a sphere when enough laser energy is deposited. We also observe that higher aspect ratio particles are thermodynamically less stable, leading to a greater reduction of the aspect ratio at lower laser pulse energy densities.

Effect of heat accumulation on the dynamic range of a gold nanorod doped polymer nanocomposite for optical laser writing and patterning.

Even though gold nanorod doped dielectrics have been widely used for optical laser writing and patterning there has been no attempt to study the dynamic range of these nanocomposites, let alone exploring ways to improve this property. Here we study the dynamic range of a gold nanorod doped polyvinyl alcohol film for various laser spot sizes at two different laser pulse repetition rates and show that when a high repetition rate laser source is employed the dynamic range of the nanocomposite is severely limited due to accumulative heating inside the focal volume. This problem could be solved by silica-coating the nanorods inside the polymer matrix. This method does not compromise the high repetition rate of the laser writing source and yet retains the attractive flexible properties of the polymer matrix. The silica-coated gold nanorod doped polymer nanocomposite could be an attractive medium for future high-speed, high repetition rate pulsed laser writing and patterning applications.

Two-photon-induced photoenhancement of densely packed CdSe∕ZnSe∕ZnS nanocrystal solids and its application to multilayer optical data storage

We report on a two-photon absorption-induced photoenhancement effect on a densely packed CdSe∕ZnSe∕ZnS core-shell semiconductor nanocrystal solid film. The enhancement is found to be irreversible without a noticeable blueshift in emission spectra, hence we attribute the enhancement to the photoannealing of interface defects rather than to the photo-oxidation or surface passivation by other molecules. The two-photon enhancement allows us to record the enhanced spots three dimensionally, hence demonstrating the feasibility of its application to multilayered optical data storage based on nanocrystal solids.

Wavelength Multiplexed Optical Storage in Plasmonic Gold Nanorods

In this paper we propose the use of wavelength as an extra recording dimension by exploiting the plasmonic properties of anisotropic gold nanorods. The wavelength of the longitudinal absorption band can be tuned from the visible to near infrared wavelength region by changing the aspect ratio of the nanorod. Data bits are recorded by femtosecond laser induced reshaping of nanorods in the focal volume. The data can be read out in transmission by monitoring the change in absorption at the recording wavelength.

Functionalisation of gold nanorods and its application to optical data storage

In this report we show the application of silica coated gold nanorods to optical data storage. We show controlled growth of a thick silica shell onto gold nanorods. The coated nanorods are transferred into a PVA matrix and data patterns are recorded. A silica layer on the nanorods dissipates the heat and the matrix does not melt, allowing reliable data storage.

Numerical optimization of gold-dielectric nanoparticle heterostructures for surface plasmon resonance engineering

Metallic nanoparticles are a very attractive and fascinating material due to their multifunctional properties, such as surface plasmon resonance absorption and excitation band tuning. In particular, these properties are proved to be valuable in photothermal therapeutic applications, where the tunable, efficient near-field enhanced ablation or photothermal energy conversions can be used to destroy cancerous cells. A similar mechanism can be applied for three-dimensional multilayer nanopatterning of polymer matrix doped with NPs, where the field enhancement and photothermal energy conversion are utilised to produce micro-explosions and voids. Previously, it was reported that engineering the morphology of nanoparticles (rod and shell shape) can greatly enhance the field enhancement and photothermal conditions. Here, we numerically study the field enhancement efficiencies of nanparticles with heterogeneous morphologies (such as metal - dielectric - metal core-shell structures), and compare their efficiencies to conventional nanosphere and nanoshell structures. Unlike the previous approximate analytical models, the SPR excitation and field enhancement efficiencies are numerically simulated, using the frequency-dependent finite-difference time domain method under tightly focused ultrashort pulse laser irradiation to accurately emulate the experimental conditions.