Picosecond acoustics in single quantum wells of cubic GaN/(Al,Ga)N

A picosecond acoustic pulse is used to study the photoelastic interaction in single zinc-blende GaN/AlxGa1−xN quantum wells. We use an optical time-resolved pump-probe setup and demonstrate that tuning the photon energy to the quantum well’s lowest electron-hole transition makes the experiment sensitive to the quantum well only. Because of the small width, its temporal and spatial resolution allows us to track the few-picosecond-long transit of the acoustic pulse. We further deploy a model to analyze the unknown photoelastic coupling strength of the quantum well for different photon energies and find good agreement with the experiments

Controlled lasing from active optomechanical resonators

Planar microcavities with distributed Bragg reflectors (DBRs) host, besides confined optical modes, also mechanical resonances due to stop bands in the phonon dispersion relation of the DBRs. These resonances have frequencies in the sub-terahertz (10E10-10E11 Hz) range with quality factors exceeding 1000. The interaction of photons and phonons in such optomechanical systems can be drastically enhanced, opening a new route toward manipulation of light. Here we implemented active semiconducting layers into the microcavity to obtain a vertical-cavity surface-emitting laser (VCSEL). Thereby three resonant excitations -photons, phonons, and electrons- can interact strongly with each other providing control of the VCSEL laser emission: a picosecond strain pulse injected into the VCSEL excites long-living mechanical resonances therein. As a result, modulation of the lasing intensity at frequencies up to 40 GHz is observed. From these findings prospective applications such as THz laser control and stimulated phonon emission may emerge

Systematic study of the influence of coherent phonon wave packets on the lasing properties of a quantum dot ensemble

Kohärente Phononen können die Licht-Materie-Wechselwirkung in Halbleiter Nanostrukturen stark ändern. Bei einem Ensemble von Quantenpunkten (QP) als aktivem Lasermedium sind Phononen im Stande, die Laserintensität deutlich zu verstärken oder abzuschwächen. Die Physik des gekoppelten Phonon-Exziton-Licht-Systems wird von verschiedenen Mechanismen dominiert, die im Experiment nicht eindeutig unterschieden werden können, da die komplizierte Probenstruktur zu einem komplexen Verspannungspuls führt, der auf das QP-Ensemble trifft. Hier zeigen wir durch eine umfassende theoretische Studie, wie die Laseremission durch Phononpulse verschiedener Form und QP-Ensembles verschiedener spektraler Verteilung beeinflusst wird. Dies erlaubt einen Einblick in die grundlegenden Wechselspiele des gekoppelten Gesamtsystems. Dadurch können wir zwischen zwei Mechanismen unterschieden: der adiabatischen Verschiebung des Ensembles und dem Schüttel-Effekt. Dies ebnet den Weg zu einer gezielten Kontrolle der Laser Emission durch kohärente Phononen.Coherent phonons can greatly vary light–matter interaction in semiconductor nanostructures placed inside an optical resonator on a picosecond time scale. For an ensemble of quantum dots (QDs) as active laser medium, phonons are able to induce a large enhancement or attenuation of the emission intensity, as has been recently demonstrated. The physics of this coupled phonon–exciton–light system consists of various effects, which in the experiment typically cannot be clearly separated, in particular, due to the complicated sample structure a rather complex strain pulse impinges on the QD ensemble. Here we present a comprehensive theoretical study how the laser emission is affected by phonon pulses of various shapes as well as by ensembles with different spectral distributions of the QDs. This gives insight into the fundamental interaction dynamics of the coupled phonon–exciton–light system, while it allows us to clearly discriminate between two prominent effects: the adiabatic shifting of the ensemble and the shaking effect. This paves the way to a tailored laser emission controlled by phonons.</p

Picosecond control of quantum dot laser emission by coherent phonons

A picosecond acoustic pulse can be used to control the lasing emission from semiconductor nanostructures by shifting their electronic transitions. When the active medium, here an ensemble of (In,Ga)As quantum dots, is shifted into or out of resonance with the cavity mode, a large enhancement or suppression of the lasing emission can dynamically be achieved. Most interesting, even in the case when gain medium and cavity mode are in resonance, we observe an enhancement of the lasing due to shaking by coherent phonons. In order to understand the interactions of the nonlinearly coupled photon-exciton-phonon subsystems, we develop a semiclassical model and find an excellent agreement between theory and experiment

Impact of nanomechanical resonances on lasing from electrically pumped quantum dot micropillars

The work was sponsored by the German Ministry of Education and Research (BMBF) within the RELQUSA project (FKZ: 13N12462) and the Deutsche Forschungsgemeinschaft (Ba1549/14-1 and Collaborative Research Centre TRR 142). The work was also supported by the state of Bavaria. A.V.A. acknowledges the Alexander-von-Humboldt Foundation. S.H. acknowledges support by the Royal Society and the Wolfson Foundation. Date of Acceptance: 06/01/2015We use a picosecond acoustics technique to modulate the laser output of electrically pumped GaAs/AlAs micropillar lasers with InGaAs quantum dots. The modulation of the emission wavelength takes place on the frequencies of the nanomechanical extensional and breathing (radial) modes of the micropillars. The amplitude of the modulation for various nanomechanical modes is different for every micropillar which is explained by a various elastic contact between the micropillar walls and polymer environment.Publisher PDFPeer reviewe

Coherent acoustic phonons in colloidal semiconductor nanocrystal superlattices

The phonon properties of films fabricated from colloidal semiconductor nanocrystals play a major role in thermal conductance and electron scattering, which govern the principles for building colloidal-based electronics and optics including thermoelectric devices with a high <i>ZT</i> factor. The key point in understanding the phonon properties is to obtain the strength of the elastic bonds formed by organic ligands connecting the individual nanocrystallites. In the case of very weak bonding, the ligands become the bottleneck for phonon transport between infinitively rigid nanocrystals. In the opposite case of strong bonding, the colloids cannot be considered as infinitively rigid beads and the distortion of the superlattice caused by phonons includes the distortion of the colloids themselves. We use the picosecond acoustics technique to study the acoustic coherent phonons in superlattices of nanometer crystalline CdSe colloids. We observe the quantization of phonons with frequencies up to 30 GHz. The frequencies of quantized phonons depend on the thickness of the colloidal films and possess linear phonon dispersion. The measured speed of sound and corresponding wave modulus in the colloidal films point on the strong elastic coupling provided by organic ligands between colloidal nanocrystals

Picosecond ultrasonics with miniaturized semiconductor lasers

There is a great desire to extend ultrasonic techniques to the imaging and characterization of nanoobjects. This can be achieved by picosecond ultrasonics, where by using ultrafast lasers it is possible to generate and detect acoustic waves with frequencies up to terahertz and wavelengths down to nanometers. In our work we present a picosecond ultrasonics setup based on miniaturized mode-locked semiconductor lasers, whose performance allows us to obtain the necessary power, pulse duration and repetition rate. Using such a laser, we measure the ultrasonic echo signal with picosecond resolution in a 112 nm thick Al film deposited on a semiconductor substrate. We show that the obtained signal is as good as the signal obtained with a standard bulky mode-locked Ti-Sa laser. The experiments pave the way for designing integrated portable picosecond ultrasonic setups on the basis of miniaturized semiconductor lasers

Supplement 1: Acousto-optical nanoscopy of buried photonic nanostructures

Supplemental Content Originally published in Optica on 20 June 2017 (optica-4-6-588