In this work, a detailed investigation is carried out on copper oxide, in the form of cupric oxide (CuO) nanocrystals. Particular attention is paid to the bandstructure and ultrafast charge-carrier dynamics. Transient absorption spectroscopy is carried out with an above-bandgap pump beam and below-bandgap probe beam to glean insight on the relaxation and recombination dynamics of the CuO nanocrystals at various pump fluences. Three time constants are apparent. The first time constant varies with pump fluence from 330 fs to 630 fs, and it is attributed to momentum relaxation via carrier-carrier scattering in the valence band as well as exciton-exciton annihilation. The second time constant is constant at 2 ps, and it is attributed to energy relaxation via carrier-phonon scattering within the valence band. The third time constant is constant at 50 ps, and it is attributed to trapping and recombination, due to the high density of trap states within the CuO nanocrystals. Such findings lay the foundation for future studies and applications of the emerging CuO material system.

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Nanophotonic all-optical switching is anticipated to replace electronic processing in future optical fibre front-end systems-unlocking capabilities for all-optical terabit-per-second processing. This work introduces a new all-optical switch (AOS) as a fundamental element for such processing. The AOS applies a nanophotonic superlens, in the form of a dielectric microsphere, to form an intense nonevanescent subdiffractional focus called a photonic nanojet. The photonic nanojet materializes in a coating of semiconductor nanoparticles at the rear of the microsphere. The AOS is refined using Lorenz-Mie theory simulations and free-carrier dynamical modelling. Experiments with microspheres coated by Si, CdTe, InP, and CuO nanoparticles, having radii of 40, 30, 20, and 20 nm, reveal switching energies of 1 pJ, 500 fJ, 400 fJ, and 300 fJ, and switching times of 2 ps, 2.3 ps, 900 fs, and 350 fs, respectively. The realized AOS meets the ultimate goals of femtojoule switching energies and femtosecond switching times.