Ciarán Gray

ZnO nanorods for efficient third harmonic UV generation

ZnO nanorods grown by both high temperature vapour phase transport and low temperature chemical bath deposition are very promising sources for UV third harmonic generation. Material grown by both methods show comparable efficiencies, in both cases an order of magnitude higher than surface third harmonic generation at the quartz-air interface of a bare quartz substrate. This result is in stark contrast to the linear optical properties of ZnO nanorods grown by these two methods, which show vastly different PL efficiencies. The third harmonic generated signal is analysed using intensity dependent measurements and interferometric frequency resolved optical gating, allowing extraction of the laser pulse parameters. The comparable levels of efficiency of ZnO grown by these very different methods as sources for third harmonic UV generation provides a broad suite of possible growth methods to suit various substrates, coverage and scalability requirements. Potential application areas range from interferometric frequency resolved optical gating characterization of few cycle fs pulses to single cell UV irradiation for biophysical studies.

Relativistic laser nano-plasmonics for effective fast particle production

We have studied particle acceleration in different nanostructured targets irradiated by high intensity laser pulses of high contrast. We find that the maximum energy of emitted particles and their directionality is significantly enhanced in the case of nanostructured targets with respect to plane targets. We have studied theoretically in detail the generation and propagation of fast electrons in nanowire targets. Such targets exhibit an extraordinary high conversion efficiency of laser energy into electron kinetic energy. We observe guiding of electron bunches along the wires. Results from theory and simulation compare reasonably well with the experimental data.

Comparison of Linear and Nonlinear Optical Properties of ZnO Nanorods

Photoluminescence emission from, and third harmonic generation by, ZnO nanorod samples grown using both low and high temperature methods are reported. Our results clearly show that PL emission at cryogenic temperatures from low temperature grown samples is both significantly weaker in intensity and spectrally broader than that from high temperature grown samples. The third harmonic generation efficiency of samples grown by both the low temperature and high temperature methods are however comparable to one another, and much larger than third harmonic generation at a bare quartz surface. Intensity dependence and interferometric frequency resolved optical gating measurements are used to study the third harmonic generation from both sample types. Laser pulse parameters are extracted for pulses subjected to both high and low chirp and our results indicate that ZnO nanostructures grown by low temperature methods allow excellent characterization of ultrafast pulses and are efficient for third harmonic generation and thus are excellent candidate materials for a variety of technological applications.