1,721,408 research outputs found
Low-threshold quantum-cascade lasers at 3.5 THz (lambda=85 mu m)
No full textChirped-superlattice quantum-cascade lasers are reported that emit at lambda similar to 85 mum (3.5 THz), which is to the authors' knowledge the longest wavelength demonstrated so far with this technology. Collected peak output powers of 1.5 mW per facet were measured at liquid-helium temperature, and a maximum operating temperature of 45 K was reached. Record low-threshold-current densities of 95 and 115 A cm(-2) were observed in pulsed and continuous-wave operation, respectively. For the latter, output powers of a few hundred microwatts are estimated at low temperatures. (C) 2003 Optical Society of America
Quantum cascade lasers emitting at lambda greater than 100 mu m
No full textQuantum-cascade lasers based on a bound-to-continuum transition and emitting at lambda similar to 106 mum (2.8 THz) are reported. They produce peak output powers of a few milliwatt and can be operated up to a heatsink temperature of 65K. The devices demonstrate the feasibility of this technology for frequencies below 3 THz
Terahertz quantum cascade lasers - first demonstration and novel concepts
Full text linkQuantum cascade (QC) lasers operating at terahertz frequencies were demonstrated two years ago, and, since then, their development has proceeded at a very rapid pace. The gain medium of the first devices was based on chirped superlattices, and a resonator relying on the surface plasmon concept was employed to achieve a large optical confinement with concomitant low propagation losses. Laser action was obtained at 4.4 THz, in pulsed mode and at temperatures up to 50 K. Improved fabrication allowed continuous-wave (cw) operation and increased the operating temperature to 75 K. Using a similar active region, lasing at 3.5 THz was achieved. More recently, various groups have introduced several new design concepts such as bound-to-continuum transitions and extraction of carriers via resonant phonon scattering, leading to pulsed operation up to 140 K, output powers of up to 50 mW, and cw operation up to 93 K. The lowest emission frequency is now 2.1 THz, tackling the technologically important region of 1.5-2.5 THz. Stable single-mode emission under all operating conditions has also recently become a reality thanks to the adoption of distributed feedback resonators. This rapid and substantial progress underlines the growing potential of QC lasers in THz photonics
High-intensity interminiband terahertz emission from chirped superlattices
Full text linkElectroluminescence at lambdasimilar to69 mum (4.3 THz) is reported from interminiband transitions in quantum-cascade structures with superlattice active regions. Spontaneous emission gives a low-temperature linewidth of 2 meV (0.48 THz) with linear light-current characteristics observed up to high-current densities (625 A/cm(2)), resulting in record output powers of 500 pW. Devices operate up to above liquid-nitrogen temperature, with both emission wavelength and current-voltage characteristics in good agreement with theoretical predictions. (C) 2002 American Institute of Physics
Terahertz quantum cascade lasers
No full textUnipolar semiconductor injection lasers emitting at THz frequencies (from 4.3 THz down to 2.8 THz) are discussed. The devices are based on interminiband transitions in chirped GaAs/AlGaAs superlattices that are arranged in a quantum-cascade scheme. The core, featuring about 100 repetitions of this type of superlattice, is embedded into a novel kind of waveguide loosely based on the surface plasmon concept, which allows low absorption losses and high confinement factors. These devices operate in pulsed mode up to a maximum temperature of 75 K (50 K in continuous wave) with several mW of output power and threshold current densities as low as 100 A/cm(2). A promising structure based on an interdigitated cascade is presented that allows operation above 90 K with high emitted powers. (C) 2003 Elsevier B.V. All rights reserved
Single-mode operation of terahertz quantum cascade lasers with distributed feedback resonators
Full text linkDistributed feedback terahertz quantum-cascade lasers emitting at 4.34 and 4.43 THz are presented. Mode selection is based on a complex-coupling scheme implemented into the top-contact layer by a combination of wet chemical etching and ohmic-contact deposition. Single-mode emission stable at all injection currents and operating temperatures is shown, with a side-mode suppression ratio exceeding 20 dB. Peak output powers of up to 1.8 mW are obtained at low temperatures. (C) 2004 American Institute of Physics
Terahertz semiconductor-heterostructure laser
No full textSemiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radiofrequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz 5 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications-for example, chemical detection, astronomy and medical imaging(1-4). Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources(5-9). Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems
Vertical subwavelength mode confinement in terahertz and mid-infrared quantum cascade lasers
No full textWe exploit the modal confinement properties of metal-metal ridge waveguides to investigate the effect of reducing the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 55 times thinner than the free-space emission wavelength are demonstrated. They show only a modest increase in threshold current density compared with conventional-thickness devices. The limited increase in threshold is possibly due to a parasitic current channel in addition to the radiative current channel. These structures could be useful for the development of ultra-low volume lasers
Terahertz quantum cascade laser as local oscillator in a heterodyne receiver
Full text linkTerahertz quantum cascade lasers have been investigated with respect to their performance as a local oscillator in a heterodyne receiver. The beam profile has been measured and transformed in to a close to Gaussian profile resulting in a good matching between the field patterns of the quantum cascade laser and the antenna of a superconducting hot electron bolometric mixer. Noise temperature measurements with the hot electron bolometer and a 2.5 THz quantum cascade laser yielded the same result as with a gas laser as local oscillator. (C) 2005 Optical Society of America
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