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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.
Quantum cascade lasers (QCLs) are compact and powerful sources that cover a wide spectral range from infrared to terahertz (THz) radiation. The emission characteristics of QCLs depend on design parameters such as layer thickness, material composition and doping. Therefore, the material system has to be chosen accurately. Most commonly used material systems for THz QCLs are GaAs/AlGaAs and InGaAs/InAlAs...
Quantum cascade lasers (QCLs) are powerful sources of coherent radiation covering the frequency range from mid-infrared to terahertz. In the terahertz frequency range the active region is normally realized using a GaAs/AlxGa1−xAs semiconductor heterostructure. This material system enables a variable conduction band offset by changing the Al-content in the barrier layers without introducing a significant...
Terahertz (THz) quantum-cascade lasers (QCLs) constitute a very promising candidate for compact, wide bandwidth, integrated frequency combs [1, 4-7]. QCLs based on heterogeneous cores display the widest spectral coverage reaching more than one octave [2]. The possibility to engineer the gain profile turns out to be fundamental also with respect to dispersion compensation in order to extended the comb...
The development of InGaAs based terahertz quantum cascade lasers is reported. This material system is an attractive alternative to the used GaAs/AlGaAs due the smaller effective mass. Using a symmetric quantum cascade design allows to understand the barrier interface and to realize high performance devices.
In this contribution we study the fundamental interactions of a metamaterial system built of dipole elements in the THz regime. We investigate the coupling between the elements for different geometries, as well as symmetric and asymmetric structures and analyze the response of the system with changing refractive index of the surrounding medium. Finally, we use these structures to access intersubband...
By introducing side-absorbers to metal-metal waveguides of broadband terahertz quantum cascade lasers, we are able to control and completely suppress higher-order lateral waveguide modes. This change leads to an octave spanning laser spectrum with a 600 GHz wide flat top. In addition, the absence of higher order lateral modes has a strong effect on the pulse generation of injection seeded QCLs. We...
Time-domain terahertz spectroscopy (THs-TDS) has demonstrated its power in last two decades. With technological development of ultra-fast lasers and THz photonics, the sensitivity, signal dynamic range and the speed of acquisition of spectral information have been continuously improved. Here we present a proof of the principle of a confluence of THz-TDS and quantum cascade laser that holds promise...
Availability of coherent and relatively powerful terahertz sources — quantum cascade lasers (QCL) [1, 2] — opens the terahertz frequency range to application. However massive usage of THz-QCLs is hindered by necessity to cool them bellow 200 K, or if decent THz output power is required even to level of 77K or less. The reason for limited operation temperature range of THz-QCL lays in low energy of...
The generation of few-cycle Terahertz radiation into the free space from a biased photoconductive gap illuminated by an ultrashort laser pulse is known more than a decade [1]. Since then, many attempts were presented to increase the generated THz power without compromising the bandwidth of the output radiation [2, 3]. In this contribution, we report on a low-temperaturegrown GaAs (LT GaAs) based photoconductive...
High power terahertz quantum cascade lasers with symmetric, wafer bonded active regions are presented, which are ideally suited for object illumination for real-time terahertz imaging using a microbolometer camera.
We demonstrate an amplification of broadband terahertz pulses in the bandwidth of 500 GHz centered at 2.5 THz. The amplification is based on gain switched quantum cascade structure width the heterogeneous active region.
We present high performance quantum cascade lasers with a peak output power of 0.94 W. This development is based on new materials and new symmetric designs for the active region. The devices are fabricated by a wafer-bonding technique of two symmetric active regions.
We demonstrate terahertz quantum cascade lasers based on arrays of subwavelength micropillar structures, corresponding to scaled-down photonic crystals. Stimulated emission is measured at 4 THz for devices operating in the effective medium regime of the photonic bands.
Quantum cascade lasers (QCLs) operating at terahertz frequencies (1–10 THz) become a powerful radiation source with potential applications in medicine, environmental monitoring, security applications and communication. The development of QCLs is strongly focused on the optimization of unipolar carrier transport with prospect of high temperature operation (i.e. above cryogenic temperatures). Therefore,...
We are presenting results from the fabrication and characterization of GaAs/Al0.15Ga0.85As micropillar arrays formed by structuring a terahertz quantum cascade laser heterostructure. The micropillar arrays are arranged in a double metal waveguide for providing electrical contacts and collection of terahertz radiation. The diameters of the micropillars are about one order of magnitude smaller then...
We present experimental results on coupled pairs of microdisk quantum cascade lasers (QCLs) emitting in the terahertz (THz) spectral region. This resonator type allows to control and to strongly confine the optical mode within the cavity. The coupling is based on the evanescent field of whispering gallery modes (WGMs) formed in each disk [1].
Metallic wire grids (WG) are popular terahertz (THz) polarizing elements. For freestanding structures, the near perfect properties of metals provide high transmission efficiency and extinction ratio over a wide frequency range. For substrate-supported structures however, these nearly ideal properties are lost as the transmission efficiency is dictated by the refractive index of the substrate. Recently,...
In this contribution, effective coupling between intersubband optical transitions and planar metallic resonators is presented. We discuss and demonstrate features unique to such a system and point out the consequences for active terahertz metamaterial devices.
The interaction of metamaterials and terahertz intersubband transitions is investigated in the strong coupling regime. We demonstrate that the resonant frequency of the metamaterial can be tuned by etching without destroying the strong interaction.
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