ACS Photonics最新文献

Vertical-cavity surface-emitting laser (VCSEL) has proven value in data communication, optical links, optical sensing, laser printing, and optical computing for its advantages in fabrication cost, energy consumption, temperature stability, and dense-array fabrication complexity. However, the limit of wavelength tunability of VCSEL restricts its application in key areas. Here, we propose a transverse cavity surface emitting laser (TCSEL) with a highly tunable wavelength assisted by a coupled feedback cavity. We presented a prototype bowtie-shaped transversely coupled cavity that emits a laser at 980 nm. Via controlling the injection current in one cavity and the negative bias voltage in the other cavity, we can maneuver the gain and loss and achieve robust wavelength tuning of up to about 5 nm experimentally. Our results represent a significant advancement in VCSEL/TCSEL technology enables a more compact and efficient wavelength tuning scheme for applications in optical communication and sensing.

CsPbBr₃ single crystals have garnered significant attention as one of the most promising candidates for room-temperature semiconductor radiation detectors. However, the current solution-based growth of CsPbBr₃ single crystals suffers from issues of the formation of secondary phases (CsPb₂Br₅) and strain-induced cracks in crystals due to high growth temperatures above the phase transition. In this study, 4-bromobutyric acid (BBA) as an additive was introduced in the precursor, which leads to an effective suppression of secondary phase formation and simultaneously a reduction of the crystal growth temperature. The CsPbBr₃ single crystals grown with BBA exhibited improved crystal quality, with a full width at half-maximum of (200) X-ray rocking curve (XRC) as low as 0.025° and a high hole mobility-lifetime product (μτ_h) of 0.57 × 10^–4 cm²/V. Moreover, the energy resolution for ⁵⁷Co γ-ray spectra was improved to around 15.2%, indicating a great improvement in transport properties for CsPbBr₃ single crystals grown with BBA. This study suggests that the effective suppression of the CsPb₂Br₅ secondary phase is likely one of the most important issues for a spectrometer-grade CsPbBr₃ detector.

Current nanoscale optoelectronic devices can reach femtosecond response times by exploiting highly nonlinear light–matter interactions. Shaping of the field waveform of few-cycle optical pulses allows one to control electron emission from nanotips and nanoparticles as well as to drive electron transport in ≳10 nm wide plasmonic gaps. In this work, we address the less explored optically induced electron transport in much narrower, 1–2 nm metallic gaps of interest in many practical situations such as in light-wave-driven scanning tunneling microscopy or in transduction between electrons and photons for optoelectronic applications. Using the time-dependent density functional theory, model calculations, and semi-classical electron trajectories derived from an analytical strong-field model, we bring robust evidence that the sub-cycle bursts of photoemitted electrons might cross the gap prior to the change of the sign of the optical field and thus without experiencing quiver motion. This leads to a characteristic carrier-envelope phase dependence of the net electron transport. Most importantly, we show that in the optical field emission regime, continuous acceleration of electron bursts moving in the gap by an optical field results in high electron energies. The electron current in a narrow-gap nanocircuit is then associated with hot electron injection into the metallic leads characterized by a non-thermal post-injection energy distribution. This is in contrast with electron transport through wide gaps dominated by low-energy electrons. Our results contribute to the design of optoelectronic devices operating on femtosecond temporal and nanometer spatial scales.

Plasma filaments via femtosecond laser ionization in air have been extensively studied as a significant terahertz (THz) source, based on which one particular objective is to enhance the efficiency and intensity of THz radiation. To this end, various strategies have been explored, including modulating the pump laser through temporal asymmetry of the carrier or envelope, or by tailoring the spectral amplitude profile asymmetrically. Apart from the above “asymmetric” operations in time and frequency domains, here we proposed a straightforward and practical method based on the spatial asymmetry. Specifically, an opaque blade was employed to partially obstruct the cross-section of the pump laser beam, resulting in a notable THz power enhancement of up to 60%. To interpret this improvement, we introduced a spatially asymmetric photocurrent mechanism: the created steep gradient of the inhomogeneous laser field enhances the electron drift motion, which in turn generates a stronger transverse current, leading to the observed increase in THz signal strength. To summarize, the proposed experimental method is highly accessible without requiring additional modulation devices, significantly lowering the application threshold. And its mechanism is also versatile, not only enhancing THz transverse wave radiation in both single- and dual-color field configurations, but also potentially applying to other setups, such as tilting focusing lenses or frequency-doubling crystals, warranting a reevaluation of previous studies. Additionally, our approach optimizes energy usage, enabling stronger THz radiation under low-power laser pump conditions and further allowing the blocked laser energy to be redirected for enhanced functionalities.

Time-varying media offer a platform to realize novel and exotic wave effects, including photonic time crystals characterized by momentum band gaps with exponential wave amplification. Here we focus on the quantum electrodynamic properties of time-varying media, in particular, vacuum amplification and squeezing. For that purpose, we present a theory of photon pair generation in photonic time crystals that unveils the link between the classical and quantum electrodynamical properties of these systems: that is, a direct relation between reflectivity and pair generation through the squeezing parameter. By working within a Hermitian framework, we are able to characterize quantum pair generation processes in photonic time crystals, showing how momentum bandgaps result in an exponential enhancement of dynamical Casimir processes.