Ultrafast multidimensional spectroscopy with field resolution and noncollinear geometry at mid-infrared frequencies

in New Journal of Physics (2022)

Energetic correlations and their dynamics govern the fundamental properties of condensed matter materials. Ultrafast multidimensional spectroscopy in the mid infrared is an advanced technique to study ... [more ▼]

Energetic correlations and their dynamics govern the fundamental properties of condensed matter materials. Ultrafast multidimensional spectroscopy in the mid infrared is an advanced technique to study such coherent low-energy dynamics. The intrinsic many-body phenomena in functional solid-state materials, in particular few-layer samples, remain widely unexplored to this date, because complex and weak sample responses demand versatile and sensitive detection. Here, we present a novel setup for ultrafast multidimensional spectroscopy with noncollinear geometry and complete field resolution in the 15–40 THz range. Electric fields up to few-100 kV cm−1 drive coherent dynamics in a perturbative regime, and an advanced modulation scheme allows to detect nonlinear signals down to a few tens of V cm−1 entirely background-free with high sensitivity and full control over the geometric phase-matching conditions. Our system aims at the investigation of correlations and many-body interactions in condensed matter systems at low energy. Benchmark measurements on bulk indium antimonide reveal a strong six-wave mixing signal and map ultra- fast changes of the band structure with access to amplitude and phase information. Our results pave the way towards the investigation of functional thin film materials and few-layer samples. [less ▲]

Field-resolved detection of the temporal response of a single plasmonic antenna in the mid infrared

in Optica (2021), 8(6), 898-903

Unveiling the spatial and temporal dynamics of a light pulse interacting with nanosized objects is of extreme importance to widen our understanding of how photons interact with matter at the nanoscale and ... [more ▼]

Unveiling the spatial and temporal dynamics of a light pulse interacting with nanosized objects is of extreme importance to widen our understanding of how photons interact with matter at the nanoscale and trigger physical and photochemical phenomena. An ideal platform to study light–matter interactions with an unprecedented spatial resolution is represented by plasmonics, which enables an extreme confinement of optical energy into sub-wavelength volumes. The ability to resolve and control the dynamics of this energy confinement on the time scale of a single optical cycle is at the ultimate frontier towards a full control of nanoscale phenomena. Here, we resolve in the time domain the linear behavior of a single germanium plasmonic antenna in the mid-infrared by measuring the complex optical field response in amplitude and phase with sub-optical-cycle precision, with the promise to extend the observation of light–matter interactions in the time domain to single quantum objects. Accessing this fundamental information opens a plethora of opportunities in a variety of research areas based on plasmon-mediated photonic processes and their coherent control, such as plasmon-enhanced chemical reactions and energy harvesting. [less ▲]

Ultrafast all-optical switching enabled by epsilon-near-zero-tailored absorption in metal-insulator nanocavities

in Communications Physics (2020), 3

Ultrafast control of light−matter interactions is fundamental in view of new technological frontiers of information processing. However, conventional optical elements are either static or feature ... [more ▼]

Ultrafast control of light−matter interactions is fundamental in view of new technological frontiers of information processing. However, conventional optical elements are either static or feature switching speeds that are extremely low with respect to the time scales at which it is possible to control light. Here, we exploit the artificial epsilon-near-zero (ENZ) modes of a metal-insulator-metal nanocavity to tailor the linear photon absorption of our system and realize a nondegenerate all-optical ultrafast modulation of the reflectance at a specific wavelength. Optical pumping of the system at its high energy ENZ mode leads to a strong redshift of the low energy mode because of the transient increase of the local dielectric function, which leads to a sub-3-ps control of the reflectance at a specific wavelength with a relative modulation depth approaching 120%. [less ▲]

Ultrafast carrier recombination in highly n-doped Ge-on-Si films

in APPLIED PHYSICS LETTERS (2019), 114(24),

We study the femtosecond carrier dynamics of n-type doped and biaxially strained Ge-on-Si films which occurs upon impulsive photoexcitation by means of broadband near-IR transient absorption spectroscopy ... [more ▼]

We study the femtosecond carrier dynamics of n-type doped and biaxially strained Ge-on-Si films which occurs upon impulsive photoexcitation by means of broadband near-IR transient absorption spectroscopy. The modeling of the experimental data takes into account the static donor density in a modified rate equation for the description of the temporal recombination dynamics. The measurements confirm the negligible contribution at a high n-type doping concentration, in the 10(19)cm(-3) range, of Auger processes as compared to defect-related Shockley-Read-Hall recombination. Energy resolved dynamics reveal further insights into the doping-related band structure changes and suggest a reshaping of direct and indirect conduction band valleys to a single effective valley along with a significant spectral broadening of the optical transitions. [less ▲]

Field-resolved response of plasmonic antennas

in Proceedings 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference (2019)

We introduce a new experimental strategy to investigate the transient resonant behavior of plasmonic nanostructures. Our approach allows to access their full-time field-resolved response in amplitude and ... [more ▼]

We introduce a new experimental strategy to investigate the transient resonant behavior of plasmonic nanostructures. Our approach allows to access their full-time field-resolved response in amplitude and phase. [less ▲]

Sub-femtosecond electron transport in a nanoscale gap

in Nature Physics (2019)

The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared ... [more ▼]

The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion. [less ▲]

Switchable dissociation of excitons bound at strained CdTe/CdS interfaces

in Nanoscale (2018)