We have realized an electroluminescent device operating in the light-matter strong-coupling regime based on a GaAs/AlGaAs quantum cascade structure embedded in a planar microcavity. At zero bias, ...reflectivity measurements show a polariton anticrossing between the intersubband transition and the cavity mode. Under electrical injection the spectral features of the emitted light change drastically, as electrons are resonantly injected in a reduced part of the polariton branches. Our experiments demonstrate that electrons can be selectively injected into polariton states up to room temperature.
We analyze the temperature performance of five terahertz (THz)-frequency quantum cascade lasers based on a three-quantum-well resonant-phonon depopulation design as a function of operating frequency ...in the 2.3-3.8-THz range. We find evidence that the device performance is limited by the interplay between two factors: 1) optical phonon scattering of thermal electrons, which dominates at shorter wavelengths, and 2) parasitic current, which dominates at longer wavelengths. We present a simple model that provides an accurate estimate of the parasitic current in these devices and predicts the dependence of the threshold current density on temperature.
Surface plasmons are electromagnetic waves originating from electrons and light oscillations at metallic surfaces. Since freely propagating light cannot be coupled directly into surface-plasmon ...modes, a compact, semiconductor electrical device capable of generating SPs on the device top metallic surface would represent an advantage: not only SP manipulation would become easier, but Au-metalized surfaces can be easily functionalized for applications. Here, we report a demonstration of such a device. The direct proof of surface-plasmon generation is obtained with apertureless near-field scanning optical microscopy, which detects the presence of an intense, evanescent electric field above the device metallic surface upon electrical injection.
We demonstrate a framework to understand and predict the far-field emission in terahertz frequency photonic-crystal quantum cascade lasers. The devices, which employ a high-performance three-well ...active region, are lithographically tunable and emit in the 104-120 microm wavelength range. A peak output power of 7 mW in pulsed mode is obtained at 10 K, and the typical device maximum operating temperature is 136 K. We identify the photonic-crystal band-edge states involved in the lasing process as originating from the hexapole and monopole modes at the G point of the photonic band structure, as designed. The theoretical far-field patterns, obtained via finite-difference time-domain simulations, are in excellent agreement with experiment. Polarization measurements further support the theory, and the role of the bonding wires in the emission process is elucidated.
A scheme for strong coupling between a single atomic spin and the rotational mode of levitating nanoparticles is proposed. The idea is based on spin read-out of NV centers embedded in aspherical ...nanodiamonds levitating in an ion trap. We show that the asymmetry of the diamond induces a rotational confinement in the ion trap. Using a weak homogeneous magnetic field and a strong microwave driving we then demonstrate that the spin of the NV center can be strongly coupled to the rotational motion of the diamond.
Carbon nanotubes are quantum sources whose emission can be tuned at telecommunication wavelengths by choosing the diameter appropriately. Most applications require the smallest possible linewidth. ...Therefore, the study of the underlying dephasing mechanisms is of utmost interest. Here, we report on the low-temperature photoluminescence of high crystalline quality individual single-wall carbon nanotubes synthesized by laser ablation (L-SWNTs) and emitting at telecom-munication wavelengths. A thorough statistical analysis of their emission spectra reveals a typical linewidth one order of magnitude narrower than that of most samples reported in the literature. The narrowing of the PL line of L-SWNTs is due to a weaker effective exciton-phonon coupling subsequent to a weaker localization of the exciton. These results suggest that exciton localization in SWNTs not only arises from interfacial effects, but that the intrinsic crystalline quality of the SWNT plays an important role. Photoluminescence (PL) emission in semiconducting carbon nanotubes arises from exciton recombination 1–3 and has been extensively studied in view of possible applications in opto-electronics, bio-imaging or photovoltaics 4–7. Observation of photon antibunching in the near infrared 8, 9 suggests that SWNTs are also promising single-photon sources for the implementation of quantum information protocols. Interestingly, the PL emission energy (i.e. the excitonic recombination energy) strongly depends on the tube diameter and can be easily tuned in the telecommunication bands at 0.83 eV (1.5µm) by choosing SWNTs with a diameter of about 1-1.2 nm 10. SWNTs could therefore make up a very versatile light source for quantum optics. Several studies suggested that the optical properties of SWNTs at low temperature are best described in terms of localized excitons (zero-dimensional confinement), leading to a quantum dot like behavior 11, 12. Nevertheless, the nature of the traps responsible for this exciton localization is not elucidated yet. In order to address the issue of exciton localization, we studied carbon nanotubes produced by high-temperature synthesis methods such as electric arc or laser ablation methods, which are known for their higher crystalline quality, with a lower density of defects 13–17.
We demonstrate spectrally single-mode, low-divergence surface-emission from photonic-crystal quantum cascade lasers operating in the mid-infrared spectral range (lambda~7.2 mum). The photonic-crystal ...resonator is defined by the sole top metallization. No semiconductor etch is employed. The effective index contrast is induced by the different profiles of surface plasmon and air-confined modes. Numerical electromagnetic simulations show that the resonator Q-factor depends strongly on the r/a ratio. The devices - which operate up to 220 K - exhibit single mode emission with a side mode suppression ratio ges20/25 dB. The far-field emission pattern is doughnut-shaped, with a full divergence angle of ~12 degrees.
We demonstrate single-mode, surface-emitting terahertz lasers at lambdaap110 mum employing photonic-crystal resonators. The devices employ metal-metal waveguides, and the photonic-crystal lattice is ...implemented by the sole patterning of the top metal contact, without deep-etching the semiconductor in the photonic crystal holes. The device emission wavelength correctly tunes with the photonic crystal characteristics. In addition, we elucidate the crucial role played by the boundary conditions of the photonic-crystal resonator.
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