Gong Wang

Coherent acoustic waves in the gigahertz‐to‐terahertz regime offer powerful opportunities for nanoscale imaging and quantum technologies, yet their use in solids has been constrained by the intrinsically weak acoustic response to optical excitation, which typically yields transient reflectivity modulations usually below 10 ⁻⁴ . Here we report that cuprous oxide (Cu ₂ O) single crystals support efficient generation of coherent acoustic waves, with transient reflectivity modulations approaching 10 ⁻² . The pronounced response is consistent with a deformation‐potential‐dominated generation mechanism enabled by strong electron‐phonon coupling. In addition, the intrinsically low thermal conductivity and highly symmetric cubic structure of Cu ₂ O are favorable for suppressing phonon dissipation and sustaining acoustic propagation. With this platform, we demonstrate coherent interference of acoustic waves using two‐pulse excitation and show that the resulting strain waves can map variations in interlayer coupling across a WS ₂ /hBN van der Waals heterostructure with nanoscale sensitivity. These results establish Cu ₂ O as an optoacoustic medium for coherent phonon engineering and suggest new opportunities for ultrafast acousto‐photonic imaging and control.

AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs), as a novel solid-state ultraviolet light source, compared with the traditional ones, have competitive advantages over traditional UV sources such as mercury (Hg) pollution free, low energy consumption, small size, and tunable wavelengths. They hold broad prospects for development in critical fields including air purification, water disinfection, biosensing, and communications. Enhancing the electro-optical conversion efficiency of DUV-LEDs is essential for achieving large-scale commercial applications in disinfection and sterilization. Improving the device’s relatively low light extraction efficiency (LEE) has proven to be an effective strategy for boosting electro-optical efficiency and overcoming technical barriers. In this review, the fundamental configurations of the AlGaN DUV-LEDs and the regulatory logic of optical polarization characteristics on LEE are summarized. The detailed discussions include the recent research advances in improving the LEE of the DUV-LEDs via optical polarization—specifically by adjusting quantum well structures, optimizing polarization-dependent light propagation paths, and incorporating additional reflection/diffraction structures. Furthermore, it outlines the challenges and development prospects for improving LEE at the optical polarization level.

Real-time detection of trace gas concentrations has a wide range of applications in industrial processes and monitoring and various complex environments. Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) features high sensitivity and selectivity for the detection of single or multiple gases. It is immune to environmental noise and also boasts advantages such as miniaturization capability, ease of integration, and low cost. However, this technology also faces challenges such as limited laser source performance and the need to optimize quartz tuning fork (QTF) structural parameters. This paper reviews the current research progress in QEPAS, elaborating on its fundamental principle as well as the contributions from both laser source improvements (e.g., power, tuning range, and size) and QTF optimization (e.g., frequency, structure, and coating) to enhanced sensitivity. In addition, this paper systematically evaluates current research on auxiliary enhancement strategies, including relaxant selection, optical path and waveguide optimization, and dual-spectrum fusion. Finally, it summarizes existing technologies and proposes future prospects based on current technical bottlenecks.

An optical waveguide is the basic structure of quantum optics, which has a strong confinement effect on light. It can complete the low-loss transmission of light and the enhancement of the nonlinear effect. Direct writing of optical waveguide structures in transparent crystals can enhance the electro-optic, acousto-optic, and nonlinear optical properties of crystals, making them widely used in the optical field. Femtosecond laser direct writing technology is a non-contact processing technology without thermal damage. The direct writing accuracy is high, and it is easy to fabricate the three-dimensional optical waveguide structure in the crystal. It is the best choice of a direct writing optical waveguide structure in a transparent crystal. This paper reviews the recent progress of femtosecond laser direct writing of transparent crystal materials to form optical waveguide structures. The basic mechanism of optical waveguide fabrication by femtosecond laser direct writing in transparent crystal, the methods of waveguide fabrication combined with different techniques, and the obtained optical waveguide structures are introduced, including single-line waveguides, double-line waveguides, depressed-cladding waveguides, ridge waveguides, and photonic crystal waveguides. The applications of optical waveguide structures in lasers, quantum memories, and quantum telecommunication devices are also presented.

Lasers are increasingly used in the biomedical field because of their concentrated energy, good stability, ease of use, and other advantages, promoting the development of precision medicine to a higher level. Medical laser equipment has transformed from a single therapeutic tool in an intelligent and precise diagnostic system. Existing clinical laser equipment has significant technical bottlenecks regarding soft-tissue ablation precision and multimodal diagnostic compatibility, which seriously restricts its clinical application. High-power thulium-doped fiber lasers with operating wavelengths of 1.9–2.1 μm provide a revolutionary solution for minimally invasive surgery due to their high compatibility with the absorption peaks of water molecules in biological tissues. This study reviews recent advances in high-power thulium-doped fiber lasers for minimally invasive therapies in the biomedical field. Breakthrough results in four major clinical application scenarios, namely, urological lithotripsy, tumor precision ablation, disfiguring dermatological treatment, and minimally invasive endovenous laser ablation, are also summarized. By systematically evaluating its potential for multimodal diagnostic and therapeutic applications and thoroughly exploring the technical challenges and strategies for clinical transformation, we aim to provide a theoretical basis and practical guidance for the clinical transformation and industrialization of new-generation medical laser technology.

Diamond‐based subwavelength antireflective microstructures are corrosion resistant, impact resistant, and possess high transmittance, thereby presenting broad application prospects in special optical windows. Nevertheless, fabricating uniform and highly transmissive subwavelength antireflective microstructures on diamond surfaces poses a significant challenge. The hard and brittle properties of diamond result in a large number of chips and particles, adhering to the surfaces during processing, which subsequently impacts the subsequent processing. Herein, a laser cleaning‐assisted femtosecond laser direct‐write processing technology is reported for fabricating subwavelength antireflective microstructures on diamond. To effectively avert the effects of chip accumulation, an elliptical laser spot is employed to clear the chips and polish the microstructure surface. The resulting highquality midinfrared antireflective microstructures are fabricated on diamond, and high transmittance (94.5%, with a 24.4% increase at 10 μm) within a broadband range (10–12 μm) is obtained, which represents the best results without antireflective coatings to the best of knowledge. Moreover, the antireflective structure possesses no significant angular dependence and maintains good working efficiency even at high temperature.

Gas sensors are now widely employed in many industries due to the rapid speed of industrialization and the growth of the Internet of Things. However, the wearability and mobility of traditional gas sensors are limited by their high reliance on external power sources. Nanogenerators (NGs) can compensate for their power source limitations when paired with gas sensors by transforming the environment’s widely dispersed low-frequency energy into electrical energy, allowing for self-powered gas detection. The paper thoroughly examines the advancements made in the field of NG-based self-powered gas sensor research in recent years. A systematic description is given of the two main types of NG-based self-powered gas sensors. Lastly, the evolution of sensor use in a few typical gas sensing applications is highlighted, and the field’s future development trend is anticipated.

Infrared lasers have an extensive range of applications in sensing, detection, communication, medicine, and other fields. The principle of directly pumping solid-state lasers is simple, and it can easily achieve high-power and high-efficiency laser output, which is one of the important means to obtain infrared lasers. Incorporating rare earth ions into the substrate as the gain medium for directly pumping solid-state lasers can alter their optical performance and further enhance the performance of the laser. Lasers based on rare earth ion doping have a small volume, high conversion efficiency, good beam quality, wide tuning range, and multiple operating modes. Therefore, the proportion of rare earth ions doped as the gain medium for activating ions is currently very large. In this review, Ho³⁺, Tm³⁺, and Er³⁺ are selected as the representative rare earth ions, and their optical properties, such as luminous power and fluorescence lifetime, when doped in different substrates, such as crystals, ceramics, and fibers, are introduced, respectively, to illustrate their feasibility as infrared laser gain media. In addition, we show the different optical properties when doped with two ions, three ions, and four ions, demonstrating their great potential as infrared laser gain media.