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Electrically Driven Microcavity Exciton-Polariton Optomechanics at 20 GHz
2021, Kuznetsov, Alexander S., Machado, Diego H.O., Biermann, Klaus, Santos, Paulo V.
Microcavity exciton polaritons enable the resonant coupling of excitons and photons to vibrations in the super-high-frequency (SHF, 3–30 GHz) domain. We introduce here a novel platform for coherent SHF optomechanics based on the coupling of polaritons and electrically driven SHF longitudinal acoustic phonons confined in a planar Bragg microcavity. The highly monochromatic phonons with tunable amplitudes are excited over a wide frequency range by piezoelectric transducers, which also act as efficient phonon detectors with a very large dynamical range. The microcavity platform exploits the long coherence time of polaritons as well as their efficient coupling to phonons. Furthermore, an intrinsic property of the platform is the backfeeding of phonons to the interaction region via reflections at the sample boundaries, which leads to quality factor × frequency products (Q×f) exceeding 1014 Hz as well as huge modulation amplitudes of the optical transition energies exceeding 8 meV. We show that the modulation is dominated by the phonon-induced energy shifts of the excitonic polariton component. Thus, the large modulation leads to a dynamical switching of light-matter nature of the particles from a mixed (i.e., polaritonic) one to photonlike and excitonlike states at frequencies up to 20 GHz. On the one hand, this work opens the way for electrically driven polariton optomechanics in the nonadiabatic, sideband-resolved regime of coherent control. Here, the bidirectionality of the transducers can be exploited for light-to-sound-to-rf conversion. On the other hand, the large phonon frequencies and Q×f products enable phonon control with optical readout down to the single-particle regime at relatively high temperatures (of 1 K).
Dynamically tuned arrays of polariton parametric oscillators
2020, Kuznetsov, Alexander S., Dagvadorj, Galbadrakh, Biermann, Klaus, Szymanska, Marzena H., Santos, Paulo V.
The spatially varying strain field of the wave induces state-dependent energy shifts of discrete polariton levels with the appropriate symmetry for OPO triggering. The robustness of the dynamic acoustic tuning is demonstrated by the synchronous excitation of an array of confined OPOs using a single wave, which thus opens the way for the realization of scalable nonlinear on-chip systems. © 2020 Optical Society of America
Effective group dispersion of terahertz quantum-cascade lasers
2020, Röben, Benjamin, Lü, Xiang, Biermann, Klaus, Schrottke, Lutz, Grahn, Holger T.
Terahertz (THz) quantum-cascade lasers (QCLs) are based on complex semiconductor heterostructures, in which the optical gain is generated by intersubband transitions. Using the spacing of the laser modes in the emission spectra, we have determined the effective group refractive index for more than one hundred THz QCLs of the hybrid design with Fabry-Pérot resonators based on single-plasmon waveguides. The experimentally obtained values of for emission frequencies between 2.5 and 5.6 THz generally follow the trend of derived from electromagnetic simulations. However, for a certain number of QCLs, the experimental values of exhibit a rather large deviation from the general trend and the simulation results. From a thorough analysis, we conclude that differences in the optical gain/loss spectra are responsible for this deviation, which lead to a modification of the dispersion in the active region and consequently to altered values of. The analysis also provides evidence that these differences in the gain/loss spectra originate from both, the details of the design and the gain broadening due to interface roughness. © 2020 The Author(s). Published by IOP Publishing Ltd.
Application of electron tomography for comprehensive determination of III-V interface properties
2021, Nicolai, Lars, Biermann, Klaus, Trampert, Achim
We present an electron tomography method for the comprehensive characterization of buried III-V semiconductor interfaces that is based on chemical-sensitive high-angle annular dark-field scanning transmission electron microscopy. For this purpose, an (Al,Ga)As/GaAs multi-layer system grown by molecular beam epitaxy is used as a case study. Isoconcentration surfaces are exploited to obtain topographic height maps of 120 nm × 120 nm area, revealing the interface morphology. By applying the height-height correlation function, we are able to determine important interface properties like root mean square roughness and lateral correlation length of various interfaces of the (Al,Ga)As/GaAs system characterized by different Al concentrations. Height-difference maps based on isosurfaces corresponding to 30% and 70% of the total compositional difference at the interfaces are used to create topographic maps of the interface width and to calculate an average interface width. This methodology proves differences in the properties of direct and inverted interfaces and allows the observation of interfacial anisotropies. © 2021
High-Performance GaAs/AlAs Terahertz Quantum-Cascade Lasers for Spectroscopic Applications
2020, Schrottke, Lutz, Lü, Xiang, Röben, Benjamin, Biermann, Klaus, Hagelschuer, Till, Wienold, Martin, Hübers, Heinz-Wilhelm, Hannemann, Mario, van Helden, Jean-Pierre H., Röpcke, Jürgen, Grahn, Holger T.
We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm$^2$. These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications. © 2011-2012 IEEE.