Brida, Daniele
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Passively phase-locked Er:fiber source of single-cycle pulses in the near infrared with electro-optic timing modulation for field-resolved electron control
A single-cycle light source in the near infrared is demonstrated enabling sensitive applications of ultrafast optical field control of electronic transport. The compact Er:fiber system generates passively phase-locked pulses with broadband spectra covering 150 THz to 350 THz at a duration of 4.2 fs and 40 MHz repetition rate. A second output arm is equipped with an electro-optic modulator that switches the arrival time of the pulses by 700 ps at arbitrary frequencies up to 20 MHz, enabling timing modulation of the pump pulse without changing the average intensity. As a benchmark demonstration, we investigate the carrier relaxation dynamics in low-temperature-grown InGaAs using quantum interference currents.
Magneto-Optical Activity in Nonmagnetic Hyperbolic Nanoparticles
Active nanophotonics can be realized by controlling the optical properties of materials with external magnetic fields. Here, we explore the influence of optical anisotropy on the magneto-optical activity in nonmagnetic hyperbolic nanoparticles. We demonstrate that the magneto-optical response is driven by the hyperbolic dispersion via the coupling of metallic-induced electric and dielectric-induced magnetic dipolar optical modes with static magnetic fields. Magnetic circular dichroism experiments confirm the theoretical predictions and reveal tunable magneto-optical activity across the visible and near infrared spectral range.
Field-resolved detection of the temporal response of a single plasmonic antenna in the mid-infrared
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.
Broadband Pulse Generation at Infrared Frequencies Based on a multi-kHz Ytterbium Amplifier
Two-stage optical parametric amplification enables the generation of sub-20 fs pulses at near- to mid-infrared frequencies, spanning from 1.5 to 2.5 µm (120 – 200 THz) and tunable up to 5 µm (60 THz).
Sub-three-cycle pulses at 2 µm from a degenerate optical parametric amplifier
In this work we present a compact two-stage optical parametric amplifier (OPA) pumped at degeneracy by the fundamental of a Yb:KGW laser system. The output pulses span from 1.7 to 2.5 µm (120-176 THz) and are compressed to a sub-20 fs duration. This parametric amplifier exploits the broad phase-matching bandwidth at the degeneracy point in bismuth triborate (BiBO) and periodically poled lithium tantalate (PPLT). The result drastically expands the availability of ultrashort pulses with few-microjoule energy from near-infrared (NIR) to even longer wavelengths in the mid-infrared (MIR) spectral region.
Ge-on-Si based mid-infrared plasmonics
In the last decade, silicon photonics has undergone an impressive development driven by an increasing number of technological applications. Plasmonics has not yet made its way to the microelectronic industry, mostly because of the lack of compatibility of typical plasmonic materials with foundry processes. In this framework, we have developed a plasmonic platform based on heavily n-doped Ge grown on silicon substrates. We developed growth protocols to reach n-doping levels exceeding 1020 cm-3, allowing us to tune the plasma wavelength of Ge in the 3-15 μm range. The plasmonic resonances of Ge-on-Si nanoantennas have been predicted by simulations, confirmed by experimental spectra and exploited for molecular sensing. Our work represents a benchmark for group-IV mid-IR plasmonics.
Probing free-carrier and exciton dynamics in a bulk semiconductor with two-dimensional electronic spectroscopy
We employ partially collinear two-dimensional electronic spectroscopy to disentangle precisely the ultrafast dynamics of excitons and free carriers in gallium selenide. Femtosecond temporal and meV energy resolution in the visible spectral region allows us to observe ultrafast bleaching at the exciton resonance with a relaxation time of 112 fs that corresponds to the thermal dissociation of excitons at room temperature, and is orders of magnitude faster than carrier relaxation in the bulk crystal. Our method is applicable to other functional materials, two-dimensional systems, and nanostructures.
Second Harmonic Generation in Germanium Quantum Wells for Nonlinear Silicon Photonics
Second-harmonic generation (SHG) is a direct measure of the strength of second-order nonlinear optical effects, which also include frequency mixing and parametric oscillations. Natural and artificial materials with broken center-of-inversion symmetry in their unit cell display high SHG efficiency, however, the silicon-foundry compatible group IV semiconductors (Si, Ge) are centrosymmetric, thereby preventing full integration of second-order nonlinearity in silicon photonics platforms. Here we demonstrate strong SHG in Ge-rich quantum wells grown on Si wafers. Unlike Si-rich epilayers, Ge-rich epilayers allow for waveguiding on a Si substrate. The symmetry breaking is artificially realized with a pair of asymmetric coupled quantum wells (ACQW), in which three of the quantum-confined states are equidistant in energy, resulting in a double resonance for SHG. Laser spectroscopy experiments demonstrate a giant second-order nonlinearity at mid-infrared pump wavelengths between 9 and 12 μm. Leveraging on the strong intersubband dipoles, the nonlinear susceptibility χ(2) almost reaches 105 pm/V, 4 orders of magnitude larger than bulk nonlinear materials for which, by the Miller’s rule, the range of 10 pm/V is the norm.
Probing Free Carrier and Exciton Dynamics in a Bulk Semiconductor with Two-Dimensional Electronic Spectroscopy
Ultrafast spectroscopy employing a sequence of phase-locked pump pulses provides a unique method to precisely track the exciton dynamics in bulk gallium selenide with sub-10 fs temporal and 4 meV (1 THz) spectral resolution.
Coherent Multidimensional Spectroscopy with Field Resolution and Noncollinear Geometry at Multi-THz Frequencies
Noncollinear two-dimensional spectroscopy in the 10-40 THz range enables background-free and phase-sensitive investigation of coherent low-energy dynamics in semiconductors and strongly correlated materials in a perturbative excitation regime. Measurements on bulk indium antimonide explore the capabilities of the setup and pave the way toward the investigation of functional thin film materials and few-layer samples.