Polarisation Control in Arrays of Microlenses and Gratings: Performance in Visible-IR Spectral Ranges.

Microlens arrays (MLAs) which are increasingly popular micro-optical elements in compact integrated optical systems were fabricated using a femtosecond direct laser write (fs-DLW) technique in the low-shrinkage SZ2080TM photoresist. High-fidelity definition of 3D surfaces on IR transparent CaF2 substrates allowed to achieve ∼50% transmittance in the chemical fingerprinting spectral region 2-5 µm wavelengths since MLAs were only ∼10 µm high corresponding to the numerical aperture of 0.3 (the lens height is comparable with the IR wavelength). To combine diffractive and refractive capabilities in miniaturised optical setup, a graphene oxide (GO) grating acting as a linear polariser was also fabricated by fs-DLW by ablation of a 1 µm-thick GO thin film. Such an ultra-thin GO polariser can be integrated with the fabricated MLA to add dispersion control at the focal plane. Pairs of MLAs and GO polarisers were characterised throughout the visible-IR spectral window and numerical modelling was used to simulate their performance. A good match between the experimental results of MLA focusing and simulations was achieved.

Ponderomotive forces in the system of two nanoparticles.

Mechanical consequences of electromagnetic interaction of two nanoparticles have been modeled and simulated. It has been shown that the local field enhancement effect in the studied system causes the appearance of the local field gradients. As a consequence, the local field gradients can lead to ponderomotive forces acting on the nanoparticles near their surface. In the work, the model describing the phenomena has been developed. The model is based on the near-field interaction in the self-consistent system and the effective susceptibility concept. Using the model distribution of the local field in the system of two different-sized nanoparticles has been calculated and ponderomotive forces directions and values were simulated. It has been shown that in the system of two different-sized nanoparticles the forces act mainly on the surface of the bigger nanoparticle and for some systems, the value of its density per volume unit may acquire up to several tens of nano newtons. Possible application of the results to the study of biological systems has been also discussed.

Antiviral Effect of Nonfunctionalized Gold Nanoparticles against Herpes Simplex Virus Type-1 (HSV-1) and Possible Contribution of Near-Field Interaction Mechanism.

The antiviral activity of nonfunctionalized gold nanoparticles (AuNPs) against herpes simplex virus type-1 (HSV-1) in vitro was revealed in this study. We found that AuNPs are capable of reducing the cytopathic effect (CPE) of HSV-1 in Vero cells in a dose- and time-dependent manner when used in pretreatment mode. The demonstrated antiviral activity was within the nontoxic concentration range of AuNPs. Interestingly, we noted that nanoparticles with smaller sizes reduced the CPE of HSV-1 more effectively than larger ones. The observed phenomenon can be tentatively explained by the near-field action of nanoparticles at the virus envelope. These results show that AuNPs can be considered as potential candidates for the treatment of HSV-1 infections.

Electrodynamic interaction between a nanoparticle and the surface of a solid.

We study the interaction between a nanoparticle and the surface of a solid in the framework of the local-field method. Assuming that the nanoparticle is characterized by a finite nonlinear polarizability, we obtain the interaction potential that is repulsive at short range and has an attractive long-range tail. Our numerical analysis shows that this potential strongly depends on the shape and size of the particle. Further, we study the particle-surface interaction in the presence of a surface plasmon polariton propagating along the interface. It is shown that the excitation of the surface wave leads to a drastic (about one order of magnitude) increase in the binding energy. Potential applications of this effect are discussed.

Evaluation of the Mechanism of the Gold Cluster Growth during Heating of the Composite Gold-Polytetrafluoroethylene Thin Film.

Nanocomposite films consisting of gold inclusions in the polytetrafluoroethylene (PTFE) matrix were obtained by thermal vacuum deposition. Annealing of the obtained films with different temperatures was used to measure varying of film morphologies. The dependence of optical properties of the films on their morphology was studied. It was established that absorption and profile of the nanocomposite film obtained by thermal vacuum deposition can be changed with annealing owing to the fact that different annealing temperatures lead to different average particle sizes. A method to calculate the optical properties of nanocomposite thin films with inclusions of different sizes was proposed. Thus, comparison of experimental optical spectra with the spectra obtained during the simulation enables estimating average sizes of inclusions. The calculations give the possibility of understanding morphological changes in the structures.