ACS Photonics最新文献

Laser-based visible light communication (VLC) has emerged as a rapidly growing technology for underwater wireless optical communication, industrial IoT network, optical interconnection, and other important applications. The development of a high-speed GaN-based laser transmitter becomes critical for VLC links with the increasing demand for data transmission rates. There exists electron leakage and a low differential gain in InGaN quantum well (QW) laser diodes (LDs), limiting their frequency response. In this work, we have studied the impact of structural design and parameters on the modulation bandwidth of blue LDs. A new structure design with a trapezoidal electron blocking layer (EBL) and an unintentionally doped layer adjacent to the QWs was proposed to address those challenges. The fabricated 2 μm ridge waveguide LDs exhibit a relatively low threshold current of 17 mA and a high slope efficiency of 1.6 W/A. A large modulation bandwidth of 7.8 GHz has been measured from 500 μm long cavity LDs, which is a record value in GaN-based LDs, to the best of our knowledge. The LDs show a small damping factor of 0.26 ns while maintaining a wall-plug efficiency exceeding 25%. The work presents a large bandwidth device for visible light transmitters, paving the way for the realization of high-speed laser-based VLC links.

Fundamental knowledge of charge transfer mechanism across the interface of heterostructures has sparked a new revolution of interest for next-generation device applications owing to their strong wave function engineering, interlayer coupling, and enhanced charge separation of photogenerated excitons. Janus-type heterostructures characterized by a well-defined interface between metal halide perovskite and semiconductor quantum dots have gained immense attention in high-performance photovoltaic and optoelectronic applications. In the present investigation, dodecahedron CsPbBr₃/CdS Janus heterostructure has been synthesized using a single-step colloidal hot injection route. High-resolution transmission electron microscope images clearly indicate direct growth between the (002) plane of dodecahedron CsPbBr₃ nanocrystals and the (200) plane of CdS quantum dots. Steady-state optical studies suggest the formation of a charge transfer (CT) complex, which in turn reconfirms the formation of a strong Janus heterostructure between CsPbBr₃ and CdS. Further, femtosecond transient absorption spectroscopy has been employed to unravel the ultrafast charge transfer dynamics at the interface of a CsPbBr₃/CdS heterostructure after exciting the samples at 350 and 490 nm. The appearance of TA bleach after exciting the heterostructure at 490 nm at the CdS position (460 nm) due to electron transfer from CsPbBr₃ to CdS provides compelling evidence for the existence of type II band alignment and affirms the presence of a robust growth in the heterostructure. This study sheds light on the preparation of perovskite-based heterostructures which may pave the way toward high-performance photovoltaic and catalytic applications.

The rescattering of photoemitted electrons with the ionized emitter is a central process in strong-field photoemission from atomic, molecular, and solid-state systems, resulting in characteristic rescattering plateaus in the photoelectron spectra. Recently, the appearance of such plateaus was also observed in the multiphoton photoemission regime from metallic nanostructures, raising questions about their effects on the dynamics of the photoemission process. Here, we analyze the effects of external static electric fields on electron rescattering from tungsten nanotapers illuminated by intense, few-cycle near-infrared laser pulses. In the strong-field regime, we observe distinct changes in the spectral shape of the plateau region. Time-dependent Schrödinger equation simulations of the photoemission dynamics show that this spectral reshaping is a signature of the suppression of recollisions at sufficiently high bias voltages. This suppression predicts the generation of low-energy electron pulses with few-femtosecond subcycle duration and emission characteristics that maintain this pulse duration over mesoscopic propagation distances in the 100 nm range. An experiment is proposed to directly probe the time structure of such subcycle electron pulses.

Exciton-polariton condensation in direct bandgap semiconductors strongly coupled to light enables a broad range of fundamental studies and applications such as low-threshold and electrically driven lasing. Yet, materials hosting exciton-polariton condensation in ambient conditions are rare, with fabrication protocols that are often inefficient and nonscalable. Here, room-temperature exciton-polariton condensation and lasing is observed in a microcavity with embedded formamidinium lead bromide (FAPbBr₃) perovskite film. This optically active material is spin-coated onto the microcavity mirror, which makes the whole device scalable up to large lateral sizes. The sub-μm granulation of the polycrystalline FAPbBr₃ film allows for observation of polariton lasing in a single quantum-confined mode of a polaritonic “quantum dot”. Compared to random photon lasing, observed in bare FAPbBr₃ films, polariton lasing exhibits a lower threshold, narrower line width, and an order of magnitude longer coherence time. Both polariton and random photon lasing are observed under the conditions of pulsed optical pumping and persist without significant degradation for up to 6 and 17 h of a continuous experimental run, respectively. This study demonstrates the excellent potential of the FAPbBr₃ perovskite as a new material for room-temperature polaritonics, with the added value of efficient and scalable fabrication offered by the solution-based spin-coating process.

The Brewster effect, dating back to the pioneering work of Sir David Brewster in 1815, offers a crucial route to achieve 100% energy conversion between the incident and transmitted propagating waves at an optical interface and is of fundamental importance to many practical applications, such as polarization filtering, beam steering, and optical broadband angular selectivity. However, whether the Brewster effect of surface waves can be implemented without the involvement of negative-permittivity or negative-permeability materials remains elusive. This is due to the formidable challenge to fully suppress both the parasitic scattering into propagating waves and the reflection into surface waves under the incidence of surface waves. Here, we reveal a feasible route to achieve a scattering-free plasmonic Brewster effect via isotropic metasurfaces, along with the usage of positive-permittivity and positive-permeability metamaterials with both anisotropic and magnetic responses. In essence, the anisotropic response of metamaterials is judiciously designed to fully suppress the parasitic scattering into propagating waves, while the magnetic response of metamaterials facilitates the full suppression of the reflection into surface waves supported by metasurfaces. Moreover, we find that this plasmonic Brewster effect via metasurfaces can be further engineered to occur for arbitrary incident angles, giving rise to the exotic phenomenon of all-angle scattering-free plasmonic Brewster effect.