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Nanometer size field effect transistors can operate as efficient resonant or broadband terahertz detectors, mixers, phase shifters and frequency multipliers at frequencies far beyond their fundamental cut-of frequency. This work is an overview of some recent results concerning the low temperatures operation, linearity, and circular polarization studies of nanometer scale field effect transistors for the detection of terahertz radiation. Also first results on graphene transistors are discussed. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Antenna-coupled field effect transistors have been developed as plasma-wave THz detectors in both InAs nanowire and graphene channel materials. Room temperature operation has been achieved up to 3 THz, with noise equivalent power levels

Quantum cascade lasers (QCLs) are powerful testing grounds for the fundamental physical parameters determined by their quantum nature. The associated wealth of unique physical properties makes the QCL a subject of extensive research, especially across the far-infrared, where the electron-phonon relaxation dynamics, the gain mechanisms and the related intrinsic QCL features need to be extensively investigated. Here, we report a complete overview of the frequency-noise power spectral density of a THz QCL, giving an experimental and analytical evaluation of its intrinsic linewidth and a full investigation of the physics beyond it, offering a new perspective of use of ultra-narrow THz QCL sources as a metrological grade tool for a widespread range of photonic applications.

Graphene is a promising candidate for the development of detectors of Terahertz (THz) radiation. A well-known detection scheme due to Dyakonov and Shur exploits the confinement of plasma waves in a field-effect transistor (FET), whereby a dc photovoltage is generated in response to a THz field. This scheme has already been experimentally studied in a graphene FET [L. Vicarelli et al., Nature Mat. 11, 865 (2012)]. In the quest for devices with a better signal-to-noise ratio, we theoretically investigate a plasma-wave photodetector in which a dc photocurrent is generated in a graphene FET. The rectified current features a peculiar change of sign when the frequency of the incoming radiation matches an even multiple of the fundamental frequency of plasma waves in the FET channel. The noise equivalent power per unit bandwidth of our device is shown to be much smaller than that of a Dyakonov-Shur detector in a wide spectral range., 5 pages, 4 figures

Phase-locked multi-terahertz transients map out the full photonic bandstructure of a one-dimensional photonic crystal while a 12-fs control pulse activates ultrastrong interaction on a sub-cycle time scale with quantized electronic transitions in semiconductor quantum wells. We trace the build-up dynamics of a large vacuum Rabi splitting and observe an unexpected asymmetric formation of the upper and lower polariton bands. The pronounced flattening of the photonic bands causes a slow-down of the group velocity by one order of magnitude on the time scale of the oscillation period of light. published

A great interest in the study of exciton-photon coupling in resonant optical media such as semiconductor microcavities is currently developing both in experiments and in theory. We investigate the spectral response of a new semiconductor quantum system in which the cavity material itself is the active medium. If the Fabry-Perot quasi-mode is carefully tuned on the excitonic transition of the cavity bulk material, strong exciton-photon coupling takes place and produces new features such as a Rabi-like splitting as large as that observed in quantum well microcavities and comparable optical absorption. In addition, the polaritonic spatial dispersion and the quantization of the centre-of-mass motion introduce remarkable fine structures which are absent in the quantum well case. We demonstrate the above effects from a spectroscopic analysis of GaAs cavities, using standard reflectance and photoluminescence techniques. The experimental results are further clarified with theoretical calculations performed with an adapted transfer-matrix approach. The case of semi-cavities is finally considered and a new way to control the exciton-photon interaction in our system is achieved tailoring the photonic wave function with a change in the reflectivity phase of the mirrors.

We show how to compute the optical properties (reflection and absorption) of anisotropic semiconductors in the exciton energy region, taking into account polariton and electron-hole coherence effects. The method is applied to a GaAs/Ga1−xAl x As superlattice, and the modifications in the optical properties with respect to GaAs are related to the anisotropy.

Antenna-coupled field effect transistors have been developed as plasma-wave THz detectors in both InAs nanowire and graphene channel material. Room temperature operation has been achieved up to frequencies of 1.5 THz, with noise equivalent powers as low as a few 10-11 W/Hz1/2, and high-speed response.

The unique optoelectronic properties of graphene [1] make it an ideal platform for a variety of photonic applications [2], including fast photodetectors [3], transparent electrodes [4], optical modulators [5], and ultra-fast lasers [6]. Owing to its high carrier mobility, gapless spectrum, and frequency-independent absorption coefficient, it has been recognized as a very promising element for the development of detectors and modulators operating in the Terahertz (THz) region of the electromagnetic spectrum (wavelengths in the hundreds of micrometers range), which is still severely lacking in terms of solid-state devices. Here we demonstrate efficient THz detectors based on antenna-coupled graphene field-effect transistors (FETs). These exploit the non-linear FET response to the oscillating radiation field at the gate electrode, with contributions of thermoelectric and photoconductive origin. We demonstrate room temperature (RT) operation at 0.3 THz, with noise equivalent power (NEP) levels < 30 nW/Hz^(1/2), showing that our devices are well beyond a proof-of-concept phase and can already be used in a realistic setting, enabling large area, fast imaging of macroscopic samples., 6 pages, 5 figures

Optical frequency comb synthesizers have represented a revolutionary approach to frequency metrology, providing a grid of frequency references for any laser emitting within their spectral coverage. Extending the metrological features of optical frequency comb synthesizers to the terahertz domain would be a major breakthrough, due to the widespread range of accessible strategic applications and the availability of stable, high-power and widely tunable sources such as quantum cascade lasers. Here we demonstrate phase-locking of a 2.5 THz quantum cascade laser to a free-space comb, generated in a LiNbO3 waveguide and covering the 0.1-6 THz frequency range. We show that even a small fraction (< 100 nW) of the radiation emitted from the quantum cascade laser is sufficient to generate a beat note suitable for phase-locking to the comb, paving the way to novel metrological-grade terahertz applications, including high-resolution spectroscopy, manipulation of cold molecules, astronomy and telecommunications.

We report the realization of a confocal THz microscope based on a ∼ 3 THz quantum cascade laser source. A resolution as low as 67 µm is achieved, with a large contrast enhancement allowed by the confocal geometry. The capability of imaging overlayed objects on close-by planes is also demonstrated.

This work reports a detailed study of quasi-guided mode resonances in metallodielectric photonic crystal slabs, focusing on the interaction with the intersubband transition supported by a multiple quantum well embedded in the photonic crystal itself. The strong light-matter coupling regime is obtained at room temperature in the mid-infrared spectral range, and its spectral fingerprints are analyzed in the framework of a Fano line-shape model. We propose an estimate of the light-matter coupling coefficient for arbitrarily shaped resonant cavities embedding multiple quantum wells supporting intersubband transitions, obtaining good agreement between theoretical calculations and experimental results.

We demonstrate the phase-locking of a 2.5 THz Quantum Cascade Laser (QCL) to an air-propagating, 6 octaves-spanning, THz Optical Frequency Comb Synthesizer (OFCS). We directly observe the beating signal using a commercial detector, therefore proving that this approach provides a mature metrological tool in the THz region. We show that only a small fraction (

We map out the band structure of a one-dimensional photonic crystal while a 12-fs control pulse activates ultrastrong interaction with quantized electronic transitions in semiconductor quantum wells. Phase-locked multi-terahertz transients trace the buildup of a large vacuum Rabi splitting and an unexpected asymmetric formation of the upper and lower polariton bands. The pronounced flattening of the photonic bands causes a slow-down of the group velocity by one order of magnitude on the time scale of the oscillation period of light.

We report on the transition from the strong to the weak light-matter coupling regime between an intersubband excitation and a photonic crystal resonance in a nanostructured semiconductor membrane. Such a transition is induced by varying the intensity of an ultrafast light pulse, which is employed for pumping and probing the system eigenmodes. The phenomenon is interpreted in terms of the saturation of the intersubband transition due to the large number of photoexcited electrons in the quantum well, as confirmed by a thorough analysis performed both in frequency and time domain.

We report a complete overview of the frequency-noise power spectral density of THz QCLs, giving an experimental evaluation and a theoretical explanation of their intrinsic linewidth and a thorough investigation of the physics behind it.

We demonstrate two different Terahertz (THz) rectification mechanisms by graphene field effect transistors: 1) a standard rectification mechanism where THz radiation modulates simultaneously the carrier density and the carrier velocity, and 2) a mesoscopic rectification due to the existence of the nonlinearity associated to the quantum interference effects.

We investigated the transport properties of lateral gate field effect transistors (FET) that have been realized by employing, as active elements, (111) B-oriented InAs nanowires grown by chemical beam epitaxy with different Se-doping concentrations. On the basis of electrical measurements, it was found that the carrier mobility increases from 103 to 104 cm2/(V × sec) by varying the ditertiarybutyl selenide (DtBSe) precursor line pressure from 0 to 0.4 Torr, leading to an increase of the carrier density in the transistor channel of more than two orders of magnitude. By keeping the DtBSe line pressure at 0.1 Torr, the carrier density in the nanowire channel measures ≈ 5 × 1017 cm-3 ensuring the best peak transconductances (> 100 mS/m) together with very low resistivity values (70 Ω × μm) and capacitances in the attofarad range. These results are particularly relevant for further optimization of the nanowire-FET terahertz detectors recently demonstrated. PACS: 73.63.-b, 81.07.Gf, 85.35.-p

We coupled linearly polarized and azimuthally polarized Terahertz quantum cascade lasers (QCLs) to the low-loss optical modes of hollow core waveguides having a sequence of different metallic or dielectric inner coatings. The latter waveguides have been specifically designed to force the propagation of a dominant optical mode once the thickness (d) of the inner dielectric coating is properly chosen. Our results demonstrate that both the TE01 and the TE11 modes can be easily converted to a hybrid one when d > 6 mu m allowing the propagation of THz QCL beams with transmission losses as low as 1.5 dB/m, bending losses < 1.1 dB and reasonably high coupling efficiencies (87%).

We report experimental evidence of intrinsic linewidth values approaching the quantum limit in far-infrared quantum cascade lasers through the measurement of their frequency-noise power spectral density and a thorough investigation of the physics behind it.

Quantum cascade lasers (QCL) are unipolar injection lasers based on intersubband transitions in a modular semiconductor heterostructure. The first THz QCL, operating at 67 mu m (4.3 THz), was demonstrated in 2002; the wavelength range now extends beyond 250 mu m (1.2 THz) and is entering the sub-terahertz frequency range for devices operated in external magnetic field. Although a number of different quantum designs have been demonstrated, increasing the operating temperature remains a major challenge: the maximum temperature is still similar to 195 K, and recently approached 225 K in high magnetic fields. Nevertheless, compact continuous wave systems operating within Sterling coolers already ensure ample portability and turn-key operation and QCLs represent then the THz solid-state radiation source that actually shows the best performance in terms of optical output power, which can reach more than 100 mW average, and linewidth, typically in the tens of kHz for single mode devices. THz QCLs have then a realistic chance to deeply impact technological applications such as process monitoring, security controls, and bio-medical diagnostics. They are ideally suited though for plasma polarimetry and interferometry, thanks to their high polarization selectivity, excellent stability and ruggedness, and ease of high-speed modulation. Their compact size and monolithic cavity arrangement allows placement in the very proximity of the plasma to be monitored, easing requirements of stability against vibrations etc. Furthermore, the long coherence lengths should be easily compatible with interferometric arms of even very different lengths, a geometry ideal for coupling to a plasma reactor. The possibility of direct current modulation at MHz if not GHz frequencies ensures then an excellent temporal resolution of the meaurements, and a large low-frequency noise rejection. New analysis schemes also become feasible, for instance employing two-color lasers, operating at the same time at two appropriately chosen wavelengths, or exploiting the laser emission tunability for implementing frequency modulation techniques. This paper will discuss the current state-of-the-art in THz QCL technology and applications, focusing on those aspects of greatest relevance for plasma diagnostics. Quantum cascade lasers (QCL) are unipolar injection lasers based on intersubband transitions in a modular semiconductor heterostructure. The first THz QCL, operating at 67 μm (4.3 THz), was demonstrated in 2002; the wavelength range now extends beyond 250 μm (1.2 THz) and is entering the sub-terahertz frequency range for devices operated in external magnetic field. Although a number of different quantum designs have been demonstrated, increasing the operating temperature remains a major challenge: the maximum temperature is still ∼ 195 K, and recently approached 225 K in high magnetic fields. Nevertheless, compact continuous wave systems operating within Sterling coolers already ensure ample portability and turn-key operation and QCLs represent then the THz solid-state radiation source that actually shows the best performance in terms of optical output power, which can reach more than 100 mW average, and linewidth, typically in the tens of kHz for single mode devices. THz QCLs have then a realistic chance to deeply impact technological applications such as process monitoring, security controls, and bio-medical diagnostics. They are ideally suited though for plasma polarimetry and interferometry, thanks to their high polarization selectivity, excellent stability and ruggedness, and ease of high-speed modulation. Their compact size and monolithic cavity arrangement allows placement in the very proximity of the plasma to be monitored, easing requirements of stability against vibrations etc. Furthermore, the long coherence lengths should be easily compatible with interferometric arms of even very different lengths, a geometry ideal for coupling to a plasma reactor. The possibility of direct current modulation at MHz if not GHz frequencies ensures then an excellent temporal resolution of the meaurements, and a large low-frequency noise rejection. New analysis schemes also become feasible, for instance employing two-color lasers, operating at the same time at two appropriately chosen wavelengths, or exploiting the laser emission tunability for implementing frequency modulation techniques. This paper will discuss the current state-of-the-art in THz QCL technology and applications, focusing on those aspects of greatest relevance for plasma diagnostics. © 2012 IOP Publishing Ltd and SISSA.

We report on the experimental observation of non-equilibrium longitudinal (LO) and interface transverse-like (IF-TO) optical phonons populations associated with electron transport in resonant-phonon THz quantum-cascade lasers. The measured LO-phonon occupation numbers are in excellent agreement with the result of Monte Carlo simulations at a phonon in-plane wave number q = 4.2 x 10(+4) cm(-1), and they remain about 40% larger than the IF-TO ones. (C) 2012 American Institute of Physics. [doi:10.1063/1.3687913]

The growth of semiconductor nanowires (NWs) has recently opened new paths to silicon integration of device families such as light-emitting diodes, high-efficiency photovoltaics, or high-responsivity photodetectors. It is also offering a wealth of new approaches for the development of a future generation of nanoelectronic devices. Here we demonstrate that semiconductor nanowires can also be used as building blocks for the realization of high-sensitivity terahertz detectors based on a 1D field-effect transistor, configuration. In order to take advantage of the low effective mass and high mobilities achievable in III-V compounds, we have used InAs nanowires, grown by vapor-phase epitaxy, and properly doped with selenium to control the charge density and to optimize source drain and contact resistance. The detection mechanism exploits the nonlinearity of the transfer characteristics: the terahertz radiation field is fed at the gate-source electrodes with wide band antennas, and the rectified signal is then read at the output in the form of a DC drain voltage. Significant responsivity values (>1 V/W) at 0.3 THz have been obtained with noise equivalent powers (NEP) < 2 x 10(-9) W/(Hz)(1/2) at room temperature. The large existing margins for technology improvements, the scalability to higher frequencies, and the possibility of realizing multipiixel arrays, make these devices highly competitive as a future solution for terahertz detection.

We demonstrate that azimuthally polarized micro-ring THz quantum-cascade lasers can be coupled to hollow metallic waveguides with efficiencies ≥96% and perfectly matched with the TE 01 waveguide mode, giving attenuation losses < 3dB/m. The use of Ag coated-flexible pipe waveguides allows propagation of either vertically polarized or azimuthally polarized QCL beams with propagation losses as low as 2.1–4.4 dB/m and bending losses lower than 1.2 dB.

Various resonators for surface emission are reviewed that have recently been developed to improve radiative- and collection-efficiencies of terahertz quantum cascade lasers (THz QCL). While the fabrication of waveguides for long wavelengths is challenging in terms of molecular beam epitaxy, long wavelengths also provide a wonderful testbed for new photonics structure concepts, since these can be easily produced by conventional optical lithography because of the typically large size of the required features. This led to novel geometries, like one-and two-dimensional non-periodic photonic crystals, or circular gratings for microdisk- and ring-lasers, which are all implemented by simply patterning the top metal cladding of a metal-metal wave-guide. The modeling of such resonators with the finite element method is also described, highlighting the importance of this tool for the engineering of surface losses and far-field patterns.

As part of a study for a second generation heterodyne spectrometer on SOFIA we are developing a 2.5-THz frontend which is implemented in a pulse-tube cooler . It consists of a quantum-cascade laser as local oscillator and a phonon-cooled NbN hot electron bolometric mixer. Frequency stabilization to below 300 kHz full width at half maximum is achieved by locking to a molecular absorption line. We will present the design and performance of the frontend and discuss the prospects for an application on board of SOFIA.

We present a planar laser diode based on a simple fabrication scheme compatible with virtually any geometry accessible by standard semiconductor lithography technique. We show that our lasers exhibit similar to 1 GHz -3 dB-modulation-bandwidth already in this prototypical implementation. Directions for a significant speed increase are discussed. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3672438]

Nanowire diodes have been realized by employing an axial heterojunction between InAs and InSb semiconductor materials. The broken-gap band alignment (type III) leads to a strong rectification effect when the current-voltage (I-V) characteristic is inspected at room temperature. The additional insertion of a narrow InP barrier reduces the thermionic contribution, which results in a net decrease of leakage current in the reverse bias with a corresponding enhanced rectification in terms of asymmetry in the I-V characteristics. The investigated diodes compare favorably with the ones realized with p-n heterostructured nanowires, making InAs/InP/InSb devices appealing candidates to be used as building blocks for nanowire-based ultrafast electronics and for the realization of photodetectors in the THz spectral range.

Self-assembled nanowires represent a new interesting technology to be explored in order to increase the cutoff frequency of electronic THz detectors. They can be developed in field effect transistor (FET) and diode geometries exploiting non-linearities of either the transconductance or the current-voltage characteristic as detection mechanism.

Imaging arrays of direct detectors in the 0.5-5 THz range are being experimentally developed. Terahertz active imaging with amplitude-modulated quantum cascade lasers emitting at 2.5 and 4.4 THz performed by using an antenna-coupled superconducting microbolometer. We then present two room-temperature terahertz detector technologies compatible with monolithic arrays: i) GaAs Schottky diodes with air-bridge sub-micron anodes; ii) high electron mobility transistors with sub-micron Schottky gate. Performances, requirements and fabrication costs of the different detector technologies are compared.

Intersubband cavity polaritons in a quantum well waveguide structure are optically generated within less than one cycle of light by a 12-femtosecond near-infrared pulse. Mid-infrared probe transients trace the nonadiabatic switch-on of ultrastrong light-matter coupling and the conversion of bare photons into cavity polaritons directly in the time domain. Future perspectives of room-temperature subcycle control of ultrastrong electron-photon interaction are discussed. (C) 2011 American Institute of Physics. [doi :10.1063/1.3578341]

We present the observation of the strong light–matter coupling regime between intersubband transitions of semiconductor quantum wells and the plasmonic-like resonances of a one dimensional metallic grating. Polariton spectra have been recorded in transmission employing a suspended membrane sample and are consistent with theoretical calculations. This arrangement, avoiding the complexity of dispersive substrate, is particularly attractive for the development of time-resolved pump–probe experiments.

An "injectorless" quantum-cascade (QC) laser is presented. The requirement of using injector regions to transport electrons from the lower laser level and other low-lying energy levels of one active region to the upper laser level of the next electron-downstream active region was eliminated by using an appropriately designed double-quantum-well "chirped" superlattice active region. The major advantage of the "injectorless" QC laser is the close packing of the active regions and the concomitant large optical confinement factor. Using a cascade of 75 consecutive active regions, designed for emission at lambda = 11.5 mum, a pulsed peak output power of 270 mW is achieved at 7 K and approximately 10 mW at the maximum operating temperature of 195 K. (C) 2001 American Institute of Physics.

The local temperature of quantum-cascade lasers operating in continuous wave mode is reported. This information is extracted from the thermal shift of the band-to-band photoluminescence peaks in the AlInAs and InP cladding layers of quantum-cascade laser facets using a high-resolution microprobe setup. Interpolation by means of a two-dimensional heat diffusion model allows to obtain the temperature profile and the thermal conductivity in the waveguide core. Comparison between substrate and epilayer-side mounted lasers shows the superior thermal dissipation capability of the latter, and explains their better performance with respect to threshold current and maximum operating temperature. (C) 2001 American Institute of Physics.

Terahertz-range intracenter silicon lasers have demonstrated significant progress over past decade in expanding the frequency operation range, in manipulation of a silicon matrix as well as in lowering of optical pump threshold. While terahertz gain realized in silicon lasers has been already defined, optical losses in the active media have not been yet measured experimentally. We applied continuous wave terahertz quantum cascade lasers, operating at 2.5 THz and 3.1 THz for direct measurements of the light losses at conditions of optical pumping with pump intensities exceeding laser thresholds for corresponding media. These measurements allow estimates of THz losses as well as determination of physical mechanisms mainly contributing for total THz absorption in optically excited silicon. It was found that absorption by so called D --centers, dynamically induced in optically excited silicon, cause major loss of THz emission. These losses, however, can be significantly reduced by a proper procedure of crystal growth and doping.

Surface emission from distributed feedback terahertz quantum cascade lasers operating in double-metal waveguides is investigated. After analyzing the origin of vertical out-coupling in linear second-order gratings, the enhancement of radiative efficiency achieved with quasi-periodic and circular gratings is presented. Linear Fibonacci resonators and microdisk lasers have been realized allowing great flexibility in tailoring the surface emission intensity and profile. Finally, ring lasers showing high power collimated emission in the vertical direction by employing a double-slit grating configuration will be discussed.

We have realized a differential Near-field Scanning Optical Microscope (NSOM) working with subwavelength resolution in the THz spectral region. The system employs a quantum cascade laser emitting at lambda approximately 105 microm as source, and the method, differently from conventional NSOM, involves diffracting apertures with size comparable to the wavelength. This concept ensures a higher signal-to-noise level at the expense of an additional computational step. In the implementation here reported lambda/10 resolution has been achieved; present limiting factors are investigated through finite difference time domain simulations.

Although lasers have found numerous applications, their design is often still based on the concept of a gain medium within a mirror cavity. Exceptions to this are distributed feedback lasers1, in which feedback develops along a periodic structure, or random lasers, which do not require any form of cavity2. Random lasers have very rich emission spectra, but are difficult to control. Distributed feedback devices, conversely, have the same limited design possibilities of regular lasers. We show, by making use of a quasi-crystalline structure in an electrically pumped device, that several advantages of a random laser can be combined with the predictability of a distributed feedback resonator. We have constructed a terahertz quantum cascade laser based on a Fibonacci distributed feedback sequence, and show that engineering of the self-similar spectrum of the grating allows features beyond those possible with traditional periodic resonators, such as directional output independent of the emission frequency and multicolour operation. Researchers have constructed a terahertz quantum cascade laser using quasi-periodic distributed feedback gratings based on the Fibonacci sequence. Features that go beyond traditional distributed feedback lasers are demonstrated, such as directional output independent of the emission frequency and multicolour operation.

We show that a distributed-feedback terahertz quantum cascade laser can be tuned with a coupled microcavity by anti-crossing of the respective eigenfrequencies. In this proof-of-concept experiment, a tuning range of 20 GHz is obtained, in good agreement with a simple finite element model, which shows that the tuning is determined by the coupling strength between the resonators. The concept could be applied to any laser cavity, but becomes progressively more attractive the lower the emission frequency.

A superconducting bolometer with an on-chip lithographic terahertz antenna has been characterized in passive and active mode. Direct detection measurements made with 300K/77K blackbody sources yeld an optical efficiency of 10%. Time response of the bolometer has been obtained at 2.5 and 4.4 THz by illuminating the detector with quantum cascade lasers (QCL) showing a time constant of 1.2 mus. Here we report on the fabrication and the optical characterization of an antenna-coupled hot-spot microbolometer operating in vacuum at liquid helium temperature.

We evaluate 2 thermopile sensors as convenient detector options for a modern integrated THz imaging system. Both a commercial single pixel device and a 32x32 pixel FPA are utilized in a simple setup with a single optical element to achieve an outstanding resolution and SNR performance. Either a cryogenically cooled quantum cascade laser (QCL) or a room temperature electronic THz multiplier chain is used as source., Comment: 2 pages, 6 figures, distilled by Acrobat Distiller 7.0.5, IRMMW-THz 2008. 33rd International Conference on. Date:15-19 Sept. 2008

In this work we demonstrate the achievement of light-matter strong coupling regime between an intersubband transition and the photonic bandlike mode supported by a metallic grating. Polaritonic resonances have been identified in the reflectivity spectra at 10 degrees incidence, with a clear anticrossing appearing when the photonic mode is tuned across the transition line. Experimental results are in good agreement with the simulations performed with a scattering-matrix approach. This cavity design can be further optimized and is likely to open the way to a new class of time-resolved measurements, as it allows pump-and-probe measurements to be performed in collinear geometries. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3524823]

In this paper we investigate, both theoretically and experimentally, nonequilibrium electron and phonon effects in quantum-cascade devices. In particular, we have developed a Monte Carlo-based global kinetic approach describing the complete interacting electronic subsystem (i.e., the full set of active-region and injector subbands) coupled to out-of-equilibrium longitudinal polar-optical (LO) phonons, which in turn will decay anharmonically into thermalized acoustic modes. Simulated results obtained for a prototypical terahertz emitting device show a very good agreement with measured data, evidencing how the nonequilibrium LO phonon population affects the electro-optical device performances. The latter may be qualitatively reproduced in terms of a global effective temperature of the heated phononic system. (C) 2010 American Institute of Physics. [doi:10.1063/1.3464977]

A superconducting bolometer with an on-chip lithographic terahertz antenna has been illuminated by two quantum cascade lasers operating at 2.5 and 4.4 THz to be used for wide dynamic range Terahertz imaging applications.

The longest wavelength III–V semiconductor laser to date has been realized employing a quantum cascade configuration for the active material. It operates at λ∼19 μm on interminiband transitions in graded superlattices. The waveguide is based on surface plasmon modes confined at a metal–semiconductor interface. The devices emit peak output powers of 14 mW per facet at 10 K and laser action is achieved up to the maximum temperature of 145 K.

Single-mode tunable quantum-cascade distributed feedback lasers emitting at 4.6–4.7 μm wavelength are reported. The lasers employ strained heterostructure material with global strain compensation to provide the large band offset needed for high-performance short wavelength operation. Pulsed, continuously tunable single-mode emission is achieved from 90 to 300 K with a tuning range of 65 nm. Peak output power levels of 100 mW at room temperature are obtained. In continuous-wave operation, current tunable single-mode emission is demonstrated around liquid-nitrogen temperature with a tuning range of 20 nm (over a current range of 450 mA). The maximum output power in continuous wave at 80 K is 150 mW.

The gain recovery time of a bound-to-continuum terahertz quantum cascade laser is measured using a stimulated emission photocurrent technique. At low temperatures a value $\ensuremath{\sim}50\text{ }\text{ps}$ is found. This tends to decrease with rising temperature, and suggests that class B laser dynamics should be expected from these devices. Both the value and the trend in the gain recovery time are found to be consistent with hopping transport through the miniband. Power-dependent measurements of the photocurrent clearly show the effects of inhomogeneous broadening of the gain transition.