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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.
Terahertz (THz) sideband generation on a near-infrared (NIR) carrier has been recently demonstrated using quantum cascade lasers (QCL), with potential applications in wavelength shifting and THz up-conversion. However, the NIR wavelength range and nonlinear efficiency were severely limited by absorption. Here we overcome this drawback through a novel reflection geometry, whilst preserving a large...
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.
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...
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 show the coherent detection of the laser emission from seeded terahertz (THz) quantum cascade lasers (QCL) with metal-metal waveguides using free-space coupling of a THz pulses to the sub-wavelength waveguide. We implement a simple, monolithic planar horn antenna design on the metalmetal waveguide that reduces the impedance mismatch to the waveguide. The laser emission is seeded and coherently...
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 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.
Background Critical limb ischemia (CLI) caused by peripheral arterial disease is associated with significant morbidity and mortality. This condition is associated with a 30 % amputation rate as well as mortality levels which might be as high as 25 %. There is no pharmacological therapy available, but several reports have suggested that mesenchymal stem cells (MSCs) may be a useful therapeutic option...
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.
The emission of a quantum cascade laser can be synchronized to the repetition rate of a femtosecond laser through the use of coherent injection seeding. This synchronization defines a sampling coherence between the terahertz laser emission and the femtosecond laser which enables coherent field detection. In this contribution the sampling coherence is measured in the time-domain through the use of...
The transient terahertz radiation emitted by a spin coherence optically generated in CdMnTe two-dimensional electron gases is directly measured in the time domain using electro-optic sampling. The spin radiation decays in a few ps at high magnetic fields. We also provide a full theoretical description within first principle calculations of both the generation of spin waves, precession and emission...
We use injection seeding to study the emission of THz quantum cascade lasers (QCLs) on picosecond time-scales. We find pulsed regimes for THz QCLs suggesting a gain recovery times from 10 to 40ps.
Phase-matched difference frequency mixing between a resonant bandgap near-infrared beam and a THz wave is demonstrated within a quantum cascade laser using second order non-linearities. Conversion efficiencies up to 0.16% are shown.
Modelocking of a Terahertz Quantum Cascade Laser is achieved using multimode injection seeding. Contrarily to standard methods that rely on gain modulation, a fixed phase relationship is here directly imprinted to the QCL modes.
We measure the sampling coherence between a quantum cascade laser and a reference femtosecond laser. In addition to complete and incomplete sampling coherence, quantum cascade lasers can exhibit partial sampling coherence that varies with time.
A quantum-cascade-laser (QCL) is used as an integrated injection seeded source and amplifier for terahertz (THz) pulses. A coupled-cavity scheme is implemented to generate THz pulses on the QCL and to saturate the amplified pulse.
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