473 research outputs found
The Linfield Review Staff
No full textThe Linfield Review staff gathers around Ms. A. Osterlund at the typewriter. This image can also be found on page 76 of the 1947 Oak Leaves.
(left to right): R. Shcmalz, W. Bishop, H. Dyer, C. Anderson, A. Osterlund, P. Schupp, D. Havill, H. Robinson, E. Heberthttps://digitalcommons.linfield.edu/lca_photos/1103/thumbnail.jp
High-performance operation of single-mode terahertz quantum cascade lasers with metallic gratings
No full textA periodic array of thin slits opened on a metallic surface can act as a one-dimensional photonic crystal for the propagation of surface-plasmon waves. We have used such structure for the implementation of distributed feedback resonators in quantum cascade lasers emitting near 2.5 THz. Single-mode emission, stable at all injection currents and operating temperatures, was achieved both in pulsed and continuous wave. The devices exhibited output powers of several milliwatts with low threshold current densities of ∼100 A cm2
THz semiconductor heterostructure laser
No full textThe terahertz region (1-10THz) of the electromagnetic spectrum offers ample opportunities in spectroscopy, free space communications, remote sensing and medical imaging. Yet, the use of THz waves in all these fields has been limited by the lack of appropriate, convenient sources. We here report on a semiconductor heterostructure injection laser that emits at THz frequencies (4.44THz, lambda similar to 67 mum) and has the potential for device-like implementation. It is based on the quantum cascade scheme employing interminiband transitions in the technologically mature AlGaAs/GaAs material system and features a novel kind of waveguide loosely based on the surface plasmon concept. The electron dynamics in the structure is analysed with the help of Monte-Carlo simulations including both carrier-carrier and carrier-phonon scattering. The lasers emit more than 2 mW of peak optical power and can be operated in pulsed mode up to 60 K with threshold current densities of few hundred A/cm(2). Continuous-wave operation is achieved at temperatures below 30K with output powers of 150 muW
Terahertz quantum cascade lasers
No full textThe terahertz region (1-10 THz) of the electromagnetic spectrum offers paramount opportunities in spectroscopy, remote sensing, medical imaging and free space communications. Yet, the use of THz waves in all these fields has been limited by the lack of appropriate, convenient sources. We here report on unipolar semiconductor injection lasers that emit at THz frequencies (4.3 THz, lambda similar to 69mum and 3.5 THz, lambda similar to 85mum) and possess the potential for device-like implementation. They are based on the quantum cascade scheme employing interminiband transitions in the technologically mature AlGaAs/GaAs material system and feature a novel kind of waveguide loosely relying on the surface plasmon concept. Continuous-wave laser emission is achieved with low tresholds of a few hundred A/cm2 up to 45 K heat sink temperature and maximum output powers of more than 4 mW. Under pulsed excitation, peak output powers of 4.5 mW at low temperatures and still 1 mW at 65 K are measured. The maximum operating temperature is 67 K
Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings
No full textWe have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0° and 50° was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers
Vertical sub-wavelength mode confinement in THz quantum cascade lasers
No full textWe exploit the modal confinement properties of metal-metal ridge waveguides to reduce the thickness of the active laser cores in both terahertz and mid-infrared quantum cascade lasers. Devices with active regions over 60 times thinner than the free-space emission wavelength are demonstrated. The devices surprisingly show only a modest increase in threshold current density compared with conventional-thickness devices
Terahertz semiconductor heterostructure laser
No full textThe terahertz region (1-10THz) of the electromagnetic spectrum offers ample opportunities in spectroscopy, free space communications, remote sensing and medical imaging. Yet, the use of THz waves in all these fields has been limited by the lack of appropriate, convenient sources. We here report on a semiconductor heterostructure injection laser that emits at THz frequencies (4.44THz, lambda similar to 67 mum) and has the potential for device-like implementation. It is based on the quantum cascade scheme employing interminiband transitions in the technologically mature AlGaAs/GaAs material system and features a novel kind of waveguide loosely based on the surface plasmon concept. The electron dynamics in the structure is analysed with the help of Monte-Carlo simulations including both carrier-carrier and carrier-phonon scattering. The lasers emit more than 2 mW of peak optical power and can be operated in pulsed mode up to 60 K with threshold current densities of few hundred A/cm(2). Continuous-wave operation is achieved at temperatures below 30K with output powers of 150 muW
Continuous-wave highly-efficient low-divergence terahertz wire lasers
No full textTerahertz (THz) quantum cascade lasers (QCLs) have undergone rapid development since their demonstration, showing high power, broad-tunability, quantum-limited linewidth, and ultra-broadband gain. Typically, to address applications needs, continuous-wave (CW) operation, low-divergent beam profiles and fine spectral control of the emitted radiation, are required. This, however, is very difficult to achieve in practice. Lithographic patterning has been extensively used to this purpose (via distributed feedback (DFB), photonic crystals or microcavities), to optimize either the beam divergence or the emission frequency, or, both of them simultaneously, in third-order DFBs, via a demanding fabrication procedure that precisely constrains the mode index to 3. Here, we demonstrate wire DFB THz QCLs, in which feedback is provided by a sinusoidal corrugation of the cavity, defining the frequency, while light extraction is ensured by an array of surface holes. This new architecture, extendable to a broad range of far-infrared frequencies, has led to the achievement of low-divergent beams (10°), single-mode emission, high slope efficiencies (250 mW/A), and stable CW operation
Magnetization studies of Landau level broadening in two-dimensional electron system
No full textWe have used a torque magnetometer to measure de Haas-van Alphen oscillations in the magnetization of two-dimensional electrons in GaAs/AlGaAs heterostructures and multiple quantum well systems for temperatures ranging from 0.125 K to 4.2 K and in magnetic fields of up to 15 T. Our results indicate that for high magnetic fields the density of states can be described by a series of Lorentzian broadened Landau levels with a broadening that is independent of the magnetic field, B, and Landau level index, n. However, at low magnetic fields the Lorentzian broadened density of states becomes indistinguishable from a Gaussian one with a broadening that is proportional to B½. The high field behaviour of the Landau level line-shape is shown to differ appreciably from the low field case as reported by other workers using both magnetization and other experimental methods. The reliability of this and other experimental techniques is discussed
Photonic quasi-crystal terahertz lasers
No full textQuasi-crystal structures do not present a full spatial periodicity but are nevertheless constructed starting from deterministic generation rules. When made of different dielectric materials, they often possess fascinating optical properties, which lie between those of periodic photonic crystals and those of a random arrangement of scatterers. Indeed, they can support extended band-like states with pseudogaps in the energy spectrum, but lacking translational invariance, they also intrinsically feature a pattern of ‘defects’, which can give rise to critically localized modes confined in space, similar to Anderson modes in random structures. If used as laser resonators, photonic quasi-crystals open up design possibilities that are simply not possible in a conventional periodic photonic crystal. In this letter, we exploit the concept of a 2D photonic quasi crystal in an electrically injected laser; specifically, we pattern the top surface of a terahertz quantum-cascade laser with a Penrose tiling of pentagonal rotational symmetry, reaching 0.1–0.2% wall-plug efficiencies and 65 mW peak output powers with characteristic surface-emitting conical beam profiles, result of the rich quasi-crystal Fourier spectrum
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