Research Themes 

Dynamical processes in quantum materials

Dynamics of fundamental excitations (e.g., electron-phonon and phonon-phonon interactions, excitons etc.) in materials and artificially engineered structures and the ways these are modified in reduced dimensionalities.

We use femtosecond time-resolved non-linear optical spectroscopy, such as the Optical Pump Terahertz Probe and other time-resolved methods, to observe the interactions between electrons and phonons, as well as phonon-phonon interactions and other fundamental excitations like excitons and polaritons including the study of the carrier recombination and the dynamics of photoluminescences in semiconductors. This helps us gain insights into the relaxation dynamics of these excitations, which play a crucial role in determining the optical and electronic properties of materials on a nanoscale. 


THz Photonics

Terahertz generation and modulation by artificial nanostructures created either lithographically or photoimprinted using ultrafast near IR pulses.  The terahertz spectral regime, ranging from about 0.1–15 THz, is one of the most technologically transformative spectral regions.

We develop novel methods to generate and modulate terahertz radiation (THz). In particular, we demonstrate:

·     a single-cycle broadband THz generation, ranging from about 0.1–4 THz, from a thin layer of split-ring resonators with a thickness of just a few tens of nanometers, that was achieved with excitation of a wavelength of 1.5μm.

·     a modulation of THz radiation by an optical modulator consisting of randomly stacked trilayer graphene deposited on an oxidized silicon substrate

·    ultrafast reversible modulation of resonant terahertz (THz) response in strongly photoexcited metamaterials.

·   photo-imprinted diffractive elements in the THz range by projecting the optical image of a periodic arrangement of metallic elements onto a thin GaAs substrate using a femtosecond pulsed laser source. 

Polaritonics


Control of the dielectric function can be obtained by anatomically thick superlattices using polar materials, by nanostructures, or by isotopically enriched a polar material such as the hexagonal boron nitride. 

Phonon polaritons (PhPs) are long-lived electromagnetic modes that result from the interaction of infrared (IR) photons with the bound ionic lattice of a polar crystal. These polaritons are sustained within the Reststrahlen band, which is a spectral range located between the transverse and longitudinal optical phonon modes. Phonon polaritons confine light to subdiffractional dimensions on polar surfaces, enhancing light-matter interactions. Phonon polaritons offer immense technological opportunities for nanophononics in the infrared spectral region. These include surface-enhanced infrared absorption for molecular sensing, super-resolution imaging enhanced spectroscopy narrow-band thermal emitters for infrared optical sources.  The modulation of the Reststrhlen band can be achieved by i) a random array of nanostructures in cubic boron nitride, ii) by changing the frequencies of the optical phonon modes employing atomic-scale superlattices of polar semiconductors such as AlN/GaN. Moreover, the lifetime of the phonon polaritons can be controlled, using isotopic enrichment of polar a material.