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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...
Metal-stripe surface grating structure presents a stable single-mode operation for THz quantum cascade lasers due to its strong coupling mechanism and easy tuning. We use sampled metal-stripe gratings to establish a distributed feedback and scale the single-mode power by tune the grating parameters. Record single-mode power more than 500 mW at 10 K is achieved.
We present the first direct observation of 26.5 GHz direct modulation of mid infrared buried heterostructure quantum cascade laser (QCL) emitting at 9 μm. For these measurements we have used an ultra-fast QWIP detector with 65 GHz bandwidth. As expected the modulation frequency bandwidth increases by increasing the laser driving DC current. Finally, we demonstrate that the laser cavity round trip...
Dispersion compensation is vital for the generation of ultrashort and single cycle pulses from modelocked lasers across the electromagnetic spectrum. However, no such scheme have been successfully applied to terahertz (THz) quantum cascade lasers (QCL) for short and stable pulse generation in the THz range. Here we show a monolithic on-chip compensation scheme for a modelocked QCL, permitting THz...
We report on Doppler-free spectroscopy using a free-running terahertz quantum-cascade laser at 3.3 THz in a pumpprobe configuration with a fast Ge:Ga detector. The sensitivity of the setup allows for the observation of a Lamb dip in deuterated water with a resolution of less than 1 MHz and an acquisition time of only 10 ms.
A unique feature of Quantum Cascade lasers is the possibility to stack active regions. Using a three stack heterogeneous Quantum Cascade laser ultra broadband amplification and short pulse generation is demonstrated. High power output is achieved by two stacked symmetric active regions.
We have demonstrated a new approach to realize a continuous wave room temperature THz laser source: a low-pressure molecular gas is optically pumped by a solid-state mid-infrared source. A tunable quantum cascade laser allows to have access to transitions that are not accessible to CO2 lasers. Here we present our last results concerning NH3: pure inversion transitions allows emission around 1 THz...
In this paper, the state of the art and progress towards building a complete plasmonic front-end for Terahertz communications is described. The discussed system architecture, whose components rely on the properties of graphene and III/V semiconductors, is able to generate, modulate, radiate and, reciprocally, detect and demodulate THz signals with multi-GHz bandwidths, needed for next generation communication...
Simultaneous stabilization of two quantum cascade lasers operated at 2 and 3 THz has been demonstrated by using a multi-frequency THz source based on Mach-Zehnder-modulator-based flat comb generator (MZ-FCG) combined with a programmable optical filter.
Molecular gases like ammonia (NH3) and deuterium oxide (D2O) can be used as active media for optically pumped terahertz lasers (OPTL). In this paper we present spectroscopic measurement of chosen NH3 and D2O lasing lines near 1 THz. Rotational-vibrational transitions are pumped by mid infrared quantum cascade laser (MIR QCL) which offers more precise tunability in MIR spectral range than standard...
We have developed a phase-locking system of a terahertz quantum cascade laser (THz-QCL) using a hot electron bolometer mixer (HEBM) and a terahertz reference such as an amplifier/multiplier chain (AMC) or an optical-comb generator followed by a UTC-PD. We have demonstrated simultaneous phase-locking of two THz-QCLs. The phase-locked THz-QCLs can be used as local oscillators (LOs) of an HEBM. This...
We report on a new design of room-temperature terahertz quantum cascade lasers (THz QCLs) based on ZnMgSe/ZnSe material systems employing two-well design schemes with alternating quantum barrier heights and n-type delta-doping of the injector well. Our calculations show that this new THz QCLs achieves high optical gain at the emission frequency of 1.33 THz at room-temperature.
Three dimensional chemical and structural information from an Al0.25Ga0.75As/GaAs terahertz quantum cascade laser heterostructure obtained by atom probe tomography is used to demonstrate the impact of diffusion-induced chemical roughening of the AlGaAs barrier layers on the optoelectronic characteristics of the laser by recalculating the band structure of the QCL and comparing the relevant parameters...
Germanium-on-silicon waveguides are designed, fabricated and characterized with a novel near-field infrared spectroscopy technique that allows on-chip investigation of the in-coupling efficiency. On-chip propagation along bends and straight sections up to 0.8 mm is demonstrated around λ = 6 μm.
We demonstrate a novel architecture for a THz near-field probe, which enables coherent imaging with subwavelength spatial resolution using THz quantum cascade lasers. An InAs nanowire acting as a THz detector based on the field effect transistor concept is integrated inside a subwavelength input aperture of the near-field probe to detect intensity of the THz field and its phase. To determine the phase...
We present the results on the emission characteristics of both Quantum Cascade Laser based frequency combs and combs based on optical rectification in photoconductive antennas operating at Terahertz frequencies using intensity autocorrelation by electro-optic sampling. We find the emission to be amplitude modulated when the laser operates in comb and in the dispersed regime. We further emphasize on...
In the following work, we present the study and plans for the realization of a THz QCL based Polarimeter for fusion plasma diagnostics. The device is being developed taking into consideration a reduced footprint, reliability and ease of operation and maintenance.
We propose a novel design of monolithic facet-emitting terahertz-quantum-cascade-laser (THz-QCL) array. The simulation shows the stable phase-locked range for coherent lasing, which is determined by the external cavity length. And its far-field beam divergence can be reduced when compared with the non-locked array. Such a monolithic QCL array with mutual injection of optical fields may provide not...
We study the feasibility of dispersion compensated terahertz quantum cascade lasers combs operating around 2.65–2.95 THz to perform multiheterodyne spectroscopy. The devices show short-term intermode beat note frequency drift after 30 μs, which indicates that reliable multiheterodyne spectroscopy over extended time-scale requires phase and timing correction to allow for coherent averaging.
We present THz surface emission by difference frequency generation in nonlinear quantum cascade lasers operating at room temperature. The device comprises two separate, transversely superimposed gratings, one for selective feedback of the mid-infrared modes and one for surface emission of the generated THz radiation. The mid-infrared grating is realized as a higher order, loss-coupled distributed...
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