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We report saturable absorption in multilayer epitaxial graphene at 4.7 μm wavelength using mid-infrared quantum cascade laser. From z-scan and differential transmittance measurements, we demonstrate an enhancement of the transmittance of 9 %, attributed to the Pauli blocking effect in the graphene layers. We found that the saturation intensity is in the range of MW/cm2. Our results show the potential...
Interdigitated photoconductive (IPC) switches are convenient sources and detectors for terahertz (THz) time domain spectroscopy. However, reflection of the emitted or detected radiation within the device substrate can lead to echoes that inherently limits the spectroscopic resolution achievable. In this work, we design and realize low-temperature-grown-GaAs (LT-GaAs) IPC switches for THz pulse generation...
We demonstrate the generation of 11ps terahertz pulses from spectrally broad metal-metal quantum cascade lasers at 77K via active modelocking, and show the critical role of phase-matching between the terahertz pulse and the microwave modulation.
The far-field emission profile of terahertz quantum cascade lasers (QCLs) in metal-metal waveguides is controlled in directionality and form through planar horn-type shape structures, whilst conserving a broad spectral response.
A novel terahertz photoconductive antenna that totally suppresses unwanted echoes is demonstrated. This is achieved with a buried metal plane placed below the surface antenna structure and active layer, realizing a sub-wavelength cavity.
We investigate the conductivity of epitaxial multilayer graphene in the THz range at various temperatures using time-domain THz spectroscopy. We demonstrate an increase of the THz conductivity as the temperature is increased, indicating Fermi energy of quasi-neutral layers close to the Dirac point. We also highlight phonon-assisted conduction at high temperature.
We demonstrate the generation of short terahertz pulses from spectrally broad metal-metal quantum cascade lasers at 77 K via active mode-locking, and show the limiting role of phase-matching between the terahertz pulse and the microwave modulation. Furthermore a new concept of THz pulse dispersion control is proposed to go beyond the limitation of the current modulation scheme.
Room temperature terahertz generation is demonstrated in graphene under femtosecond optical excitation. This is induced by dynamical photon drag, which relies on the transfer of light momentum to the carriers by ponderomotive and magnetic forces.
We demonstrate the generation of 11ps terahertz pulses from metal-metal (MM) quantum cascade lasers (QCLs) at 77K via active mode-locking. Contrary to popular belief that a long gain recovery time is required, we demonstrate that the dominant factor necessary for active pulse generation is in fact the synchronization between the propagating electronic microwave modulation and the generated THz pulses...
We demonstrate broadband coherent THz emission at room temperature from epitaxial graphene under femtosecond optical excitation induced by photon drag effect. We interpret the emitted THz radiation characteristics with a model describing the electron and hole states beyond the usual massless relativistic scheme. This second-order nonlinear effect relies on the dynamical transfer of light momentum...
The far-field of metal-metal terahertz quantum cascade lasers is greatly improved through integrated and stable planar horn antennas on top of the QCL ridge. The antenna structures introduce a gradual change in the high modal confinement of metal-metal waveguides and permit an improved far-field, showing a five times increase in the emitted output power. The two dimensional far-field patterns are...
We demonstrate a reduction of loss and group velocity dispersion (GVD) of THz plasmonic waveguides by using a low-loss thin flexible substrate. We present a numerical calculation of the effect of the substrate thickness on the GVD. We show experimentally low absorption and weak distortion of the propagated THz pulses along a THz plasmonic waveguide on a flexible 58µm-thick polyimide substrate.
We compare the THz pulses generated by photoconductive antennas made from two different materials: ErAs:GaAs and Br-irradiated InGaAs. The THz pulses were generated using the same 1550 nm THz time-domain spectroscopy set-up. The detection was realized with an electro-optic crystal, allowing a direct comparison of the performance from the different antennas.
Optical sidebands are generated by difference frequency mixing between a resonant bandgap near-infrared beam and a terahertz (THz) wave. This is realized within the cavity of a THz quantum cascade laser using resonantly enhanced non-linearities. Multiple order optical sidebands and conversion efficiencies up to 0.1% are shown.
Quantum Cascade Lasers are promising sources of Terahertz radiation. Picosecond pulses generation with these lasers is currently at its infancy and their detection is difficult. An intensity electro-optic sampling method is used here to demonstrate 19ps FWHM pulses from a QCL via active modelocking.
We show that shrinking the transverse size of metallic waveguides always leads to solutions with extreme field confinement at THz frequencies, regardless of the materials used and of the system geometry. We provide a unified framework to understand such universal behaviors, which will benefit future developments in THz science and technology.
We study the generation of broadband THz radiation (∼18 THz) with high peak electric field (∼0.5 kV/cm) using a low temperature GaAs interdigitated photoconductive antenna and a high-power, high repetition rate, 15 femtosecond Ti:Sapphire oscillator.
Difference frequency mixing between a resonant bandgap near-infrared beam and a THz wave is demonstrated within the cavity of a quantum cascade laser using a resonantly enhanced second order non-linearity. Conversion efficiencies up to 0.13% are shown that are comparable to those shown by Free Electron Laser measurements.
We compare the photocarrier lifetime measured in Br-irradiated InGaAs and cold Fe-implanted InGaAsP. We also demonstrate the possibility of a two-photon absorption (TPA) process in ErAs:GaAs. The lifetime and the TPA were measured with a fiber-based 1550 nm time-resolved differential transmission (?T) set-up. The InGaAs-based materials show a positive ?T with sub-picosecond lifetime, whereas ErAs:GaAs...
We review the most important developments in the technology of THz photoconductive antennas made from ion-bombarded semiconductors. We describe the structural, optical and electrical properties of various ion-bombarded semiconductors and discuss the nature of the defects introduced by the ion bombardment technique and their impact on the characteristics of THz photoconductive antennas. Finally, we...
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