One of the central goals of the field of nonlinear optics is to bring the control of light to ultrafast time scales using structures that are easily integrated into nano-optic devices. The ability to design the polarization state of a signal light pulse, with a second control light pulse, at THz rates, will allow new techniques to be developed such as ultrafast polarimetry and quantum state manipulation.
Here we all-optically control, with a femtosecond pulse, the anisotropy of a metamaterial to change the polarization state of signal light at a switching rate of 0.3THz, which is found to be closely linked to the electron temperature distribution within the structure and so can be tuned with the control light wavelength. We experimentally measure more than 60° rotation of the polarization orientation of the signal light. This effect is due to an induced phase shift of the extraordinary wave compared to the ordinary wave of the signal light. Polarization control is observed in both transmission and reflection and shown to be general to any anisotropic metamaterial. Considering only the signal light, its leading edge can alter the polarization state of the pulse allowing the pulse’s incident intensity to be encoded in its transmitted polarization state.
Controlling pulse dispersion in temporal and spectral domains are imperative for modern applications of ultrashort pulses in optical communications, opto-electronics and imaging. In this work we present the detailed study of ultrashort pulse dispersion in a hyperbolic metamaterial. This highly anisotropic structure comprised of plasmonic nanorods promises the flexibility in dispersion engineering beyond the capabilities of classical materials. We show experimentally and theoretically that the delicate balance between local and nonlocal effects play a crucial role in the optical response of the system leading to controlled switching between “superluminal” and stopped light propagation regimes of electromagnetic waves. We compare the effective medium simulations with full vectorial numerical analysis combining split-step Fourier method and finite difference time domain algorithm. The experimental studies were performed with 150 fs pulses in 560-740 nm spectral range. Using the high-resolution spectral interferometry, we were able to retrieve up to third-order dispersion terms of the metamaterial, confirming the theoretical predictions of pulse dynamics, and validate the strength of the effect. The dispersive properties of plasmonic nanorod metamaterials may play a crucial role in advanced dispersion compensation devices in telecommunication applications, supersensitive tuneable interferometers and slow light buffers in all optical systems.
We present a numerical study of the interaction of light with isolated nanoparticles of various symmetry shapes described by the Gielis superformula as well as nanoparticle arrays composed from them. Using the discrete dipole approximation and finite element numerical methods the effects of particle shape symmetry on the spectral properties of gold and silver nanoparticles were investigated. Starting from the spherical and cylindrical geometries and progressing to star-like polygonal shapes, we demonstrate that the variation of the symmetry can significantly enhance the strength of the dipolar resonance and shift the resonance to the red spectral range by hundreds of nanometres. Thus, is possible to tune the optical properties of the nanostructures all across the visible spectral range only by changing their shapes. Finally, we investigate the collective resonances of arrays of interacting nanoparticles of different shapes, elucidating the role of the particle symmetry in the collective response.