Angela Vasanelli

Investigation of spectral gain narrowing in quantum cascade lasers using terahertz time domain spectroscopy

The spectral gain of bound-to-continuum terahertz quantum cascade lasers (QCLs) is measured as a function of current density using terahertz time-domain spectroscopy. During lasing action the full width at half maximum (FWHM) of the gain is found to monotonically decrease with increasing current density until lasing action stops at which point the FWHM reaches a minimum (0.22 THz for a laser operating at 2.1 THz). Band structure calculations show that the spectral gain narrowing is due to the alignment and misalignment of the injector with the active region as a function of the applied bias field.

Radiative quantum efficiency in an InAs/AlSb intersubband transition

The quantum efficiency of an electroluminescent intersubband emitter based on

Room-temperature 9um photodetectors and GHz heterodyne receivers (Conference Presentation)

mathrm{In}mathrm{As}∕mathrm{Al}mathrm{Sb}

Ultrafast uncooled THz optomechanical bolometers (Conference Presentation)

has been measured as a function of the magnetic field up to

Cyclotron emission in a THz quantum cascade structure

20phantom{rule{0.3em}{0ex}}mathrm{T}

Electron Scattering Spectroscopy by High Magnetic Field in Mid‐Infrared Quantum Cascade Lasers

. Two series of oscillations periodic in

Intersubband Lifetime Magnetophonon Oscillations in GaAs Quantum Cascade Lasers

1∕B

Quantum cascade lasers: The semiconductor solution for lasers in the mid‐ and far‐infrared spectral regions

are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited-state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy-dependent electron effective mass and the optical phonon energy.

GHz Heterodyne generation using Two DFB Mid-IR QCL lasers on a 9μmQWIP

The very short life-time of the excited carriers is a very important intrinsic property of quantum well photodetectors (QWIPs), based on III-V semiconductor materials, that have not been exploited for performances yet. Its typical value is in the order of a ps [7], which leads to two important consequences: the detector frequency response can be up to 100 GHz and its saturation intensity is extremely high in the in the order of 10e7 W/cm2. These two figures are ideal for a heterodyne detection scheme, where a powerful local oscillator (LO) can drive a strong photocurrent, higher than the detector dark current, that can coherently mix with a signal shifted in frequency with respect to the LO. Notably, these unique properties are unmatched in infrared interband detectors based on mercury-cadmium-telluride alloys, which have a much longer carrier lifetime and therefore intrinsic low-speed response. Yet, the performances of all photonic detectors are limited by the high dark current which originates from thermal emission of electrons from the wells, rising exponentially with temperature and imposing cryogenic operation (~ 80K) for high sensitivity. nnIn the present work we show that the intrinsic limitation of QWIP detectors can be overcome by the use of a photonic metamaterial made of metallic resonators. The absorbing region of the detector consists of a 5 period GaAs/AlGaAs QWIP operating at a wavelength 8.9µm (139meV) which has been designed according to an optimized bound to continuum structure. The absorbing region is inserted in an array of double-metal patch resonators [ref], which provide sub-wavelength electric field confinement and act as antennas. The resonant wavelength is fixed by the patch size s through the expression lambda = 2 s neff, with neff = 3.3 the effective index. This allows us to tune the cavity mode in resonance with the absorption peak of the bare detector for values of s between 1.3µm-1.4µm. The detectors obtained in this way have high detectivity up at room temperature, in the order of 3-4 10e7 cmHz1/2/W. Given this his high detectivity we could calibrate the detector using a black body emitting only few µW. Up to date high sensitivity at room temperature, with values comparable to those we are reporting, have been demonstrated, only in the 3-5µm wavelength range, using quantum cascade detectors (QCDs) [9-11] and with MCT standard detectors.nnTo the best of our knowledge this is the best results ever reported for a photoconductive detector at 9µm at room temperature. Since the detector has an extremely fast response of several GHz we built an heterodyne setup tp beat two quantum cascade lasers. We obtained heterodyne signal at high frequencies up to 3GHz, with NEP in the pW range at 300K.

Room temperature 9

The room temperature detection of terahertz (THz) waves remains a challenging task, especially for detectors operating at room temperature. Among the solutions that have been proposed, thermal detectors based on bilayer membranes combined with metamaterial absorbers provide competitive sensitivity and detection speed in the kHz range. We have recently proposed a new device concept, where the photo-thermal interactions take place in a single meta-atom resonator with subwavelength dimensions. Thanks to the compactness of our device, the thermal diffusion time is reduced down to the µs range and the detector speed is increased beyond 10MHz, with 1GHz at reach. I will discuss experimental measurements and dynamical modelling of the detector performance.