Advanced Photonics Research最新文献

GaN-Based Blue Laser Diodes

In article number 2400119, Wenyu Kang, Junyong Kang, and co-workers develop an anti-aging technology for high-power GaN LD from mechanism investigation to degradation suppression. This cover depicts a person in different aging stages, indicating the severe degradation issues in high-power LD and the effectiveness of this anti-aging technology.

Spintronic Terahertz Emitters

In article number 2400064, Mathias Vanwolleghem and co-workers experimentally demonstrate a close to 100-fold improvement of the power efficiency of inverse spin Hall emitters by maximizing the impact of the electromagnetic environment of the nanometric emitter. As a result, by moving from a basic emitter on a bare substrate to one functionalized by a resonant crystal cavity and an impedance matched emitting substrate, the emitted THz field pulses can reach several MV/cm peak strengths without any echo behavior.

2D Layered Superconductors

In article number 2400045, Kaveh Delfanazari showcases methods for the realization of ultrafast terahertz (THz) metamaterial photonic switches on a few nanometer-thick layered high-temperature superconductor van der Waals (vdWs). The metamaterial array offers active modulation of THz amplitude and phase with an ultrafast-picosecond-switching timescale. The device holds promise for the development of future THz communication circuits and systems operating at cryogenic temperatures.

Core–Shell Particles

Essential features of functional optical materials are their interaction with light and underlying structures. In article number 2400091, Markus Gallei and co-workers report the combination of structural colors with cellulose, a renewable and biodegradable biopolymer. The latter acts as reinforcement agents, maintaining the polymer opal film’s structural color and mechanochromic material behavior.

Polymer-Network Liquid Crystals

In article number 2300340, Dan Luo, Kun-Lin Yang, and co-workers show that after partially completed photopolymerization, the polymer network liquid crystal undergoes a secondary polymerization to form an isotropic polymer network when it is heated beyond its clearing point, resulting in an irreversible optical appearance change from transparent to cloudy. It enables applications such as a heating stopwatch and oxygen sensing.

Coherent Perovskites Emitters

In article number 2400033, Kwangdong Roh and co-workers provide a comprehensive overview of the historical progress in perovskite lasers and light-emitting didoes, along with important design considerations essential for their development.

Owing to their excellent optoelectronic properties, halide perovskites (HPs) have garnered significant attention in the field of optoelectronics. However, conventional HPs-based optoelectronic devices primarily are fabricated using solution-based processes, implying that extremely time-consuming needs to individually synthesize their composition-dependent optoelectronic properties. This study demonstrates the feasibility of combining first-principles simulations with combinatorial synthesis, comparing the effects of HP properties on optoelectronic devices using this combined approach. The first-principles simulations confirm that increasing the ratio of small halide ions increased the band gap by k·p perturbation theory and harmonic oscillator models. By fabricating HP thin films with compositional gradients using combinatorial synthesis, it is confirmed that an increase in band gap corresponds to a decrease in static relative permittivity. Furthermore, HP-based optoelectronic devices are fabricated to measure their photoelectric conversion efficiency and responsivity based on the simulated and measured relative permittivity, including time-resolved photoluminescence. The findings demonstrate the influence of the relative permittivity on device performance, elucidating the relationship between band structure and relative permittivity. Therefore, in this study, the potential of combining first-principles simulations with combinatorial synthesis is confirmed by comparing the relative permittivity characteristics of optoelectronics developed using this combined approach.

Gallium nitride (GaN)-based semiconductor laser diodes (LDs) have garnered significant attention due to their promising applications. However, high-power LDs face serious degradation issues that limit their practical use. This study investigates the degradation factors of 437 nm and 6.3 W LDs by comparing light–current–voltage (L–I–V) characteristics, transmission electron microscopy (TEM), cathodoluminescence (CL), and secondary ion mass spectroscopy (SIMS) before and after 1000-h aging. The diffusion of mirror coating from the resonant cavity surface is identified as a key factor contributing to high-power LD degradation, which has not been reported in milliwatt-level LDs. Meanwhile, the mechanisms behind the LD degradation are profiled and summarized together with the diffusion and other factors. On basis of the mechanism exploration, an anti-aging technology for high-power GaN-based LDs is developed by using aluminum nitride for passivation layer and sapphire materials for mirror film. This anti-aging technology has been verified, and a nearly ten-time degradation suppression is achieved from 1000 h. This study elucidates the degradation mechanisms of high-power GaN LDs and provides an effective technology to extend their lifespan, thereby prompting the practical applications of high-power LDs.

Optically pumped spintronic terahertz emitters (STEs) have, in less than a decade, strongly impacted terahertz (THz) source technology, by the combination of their Fourier-limited ultrafast response, their phononless emission spectrum and their wavelength-independent operation. However, the intrinsic strength of the inverse spin Hall effect governing these devices introduces a challenge: the optical-to-terahertz conversion efficiency is considerably lower than traditional sources. It is therefore primordial to maximize at least their electromagnetic efficiency independently of the spin dynamics at play. Using a rigorous time-domain treatment of the electromagnetic generation and extraction processes, an optimized design is presented and experimentally confirmed. With respect to the strongest reported spintronic THz emitters it achieves a 250% enhancement of the emitted THz field and therefore an 8 dB increase of emitted power. This experimental achievement brings STE close to the symbolic barrier of mW levels. The design strategy is generically applicable to any kind of ultrafast spin-to-charge conversion (S2C) system. On a broader level, our work highlights how a rigorous handling of the purely electromagnetic aspects of THz spintronic devices can uncover overlooked aspects of their operation and lead to substantial improvements.

Carbon dots (CDs) show great application potential with their unique and excellent performances. Coal and its derivatives are rich in aromatic ring structure, which is suitable for preparing CDs in microstructure. Coal-burning dust from coal-fired power plants can be utilized as a rich resource to separate and extract CDs. It is shown in the results that there are two main possible mechanisms for the formation of CDs in coal-burning dust. One is the self-assembly of polycyclic aromatic hydrocarbons contained in coal or produced by incomplete combustion of coal. The other mechanism is that the bridge bonds linking different aromatic structures in coal break, which will form CDs with different functional groups when the coals burn at high temperature. Under violet light excitation at 310–340 nm or red light at 610–640 nm, CDs extracted from coal-burning dust can emit purple fluorescence around 410 nm. The mechanism of up-conversion fluorescence emission of CDs is due to a two-photon absorption process. The recycling of CDs from coal-burning dust from coal-fired power plants are not only good to protect environment but will also be helpful for mass production of CDs.