In this work, we reported a high-performance-based ultraviolet-visible (UV-VIS) photodetector based on a TiO₂@GaO_xN_y-Ag heterostructure. Ag particles were introduced into TiO₂@GaO_xN_y to enhance the visible light detection performance of the heterojunction device. At 380 nm, the responsivity and detectivity of TiO₂@GaO_xN_y-Ag were 0.94 A/W and 4.79 × 10⁹ Jones, respectively, and they increased to 2.86 A/W and 7.96 × 10¹⁰ Jones at 580 nm. The rise and fall times of the response were 0.19/0.23 and 0.50/0.57 s, respectively. Uniquely, at 580 nm, the responsivity of fabricated devices is one to four orders of magnitude higher than that of the photodetectors based on TiO₂, Ga₂O₃, and other heterojunctions. The excellent optoelectronic characteristics of the TiO₂@GaO_xN_y-Ag heterojunction device could be mainly attributed to the synergistic effect of the type-Ⅱ band structure of the metal–semiconductor–metal heterojunction and the plasmon resonance effect of Ag, which not only effectively promotes the separation of photogenerated carriers but also reduces the recombination rate. It is further illuminated by finite difference time domain method (FDTD) simulation and photoelectric measurements. The TiO₂@GaO_xN_y-Ag arrays with high-efficiency detection are suitable candidates for applications in energy-saving communication, imaging, and sensing networks.

超材料吸波体可以将入射电磁波集中在亚波长尺度内并进行高效吸收，因此在光电探测、热发射器、能量收集等领域具有广泛的应用前景。迄今报道的多波段超材料吸波体主要为某一波长范围内多个相近波长的完美吸收，想要实现大光谱范围内的多波长吸收则需要多个结构的联合工作。基于钛十字形谐振器-氮化硅介质层-钛反射层三层结构，设计并数值模拟了一种工作波长范围跨越中波红外、长波红外以及甚长波红外的三波段超材料吸波体。利用超材料吸波体激发的传播型表面等离激元谐振、局域型表面等离激元谐振以及氮化硅本征吸收模式，实现了4.8 μm、9.1 μm和18 μm三个波长处97.3%、94.4%和93.6%的高吸收率。超材料吸波体的工作波长可以通过改变其几何参数进行调节，且具有偏振和入射角不敏感性。该工作中所用材料均为现有工艺中的常用材料，在气体检测、红外成像等领域具有应用前景。

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

Q-switched lasers have occupied important roles in industrial applications such as laser marking, engraving, welding, and cutting due to their advantages in high pulse energy. Here, SnS₂-based Q-switched lasers are implemented. Considering that SnS₂ inherits the thickness sensitive optical characteristics of TMD, three kinds of SnS₂ with different thickness are characterized in terms of nonlinearity and used to realize the Q-switched pulses under consistent implementation conditions for comparison tests. According to the results, the influence of thickness variation on the nonlinear performance of saturable absorber, such as modulation depth and absorption intensity, and the influence on the corresponding laser are analyzed. In addition, compared with other traditional saturable absorbers, the advantage of SnS₂ in realizing ultrashort pulses is also noticed. Our work explores the thickness-dependent nonlinear optical properties of SnS₂, and the rules found is of great reference value for the establishment of target lasers.

Recent years have witnessed the exploration of fiber laser technology focused on numerous pivotal optoelectronic applications from laser processing and remote sensing to optical communication. Here, using cobalt oxyfluoride (CoOF) as the nonlinear material, a 156 fs mode-locked fiber laser with strong stability is obtained. The rapid thermal annealing technique is used to fabricate the CoOF, which is subsequently transferred to the tapered region of the microfiber to form the effective pulse modulation device. CoOF interacts with the pulsed laser through the evanescent field to realize the intracavity pulse shaping, and then the stable mode-locked pulse is obtained. The mode-locked operation is maintained with the pulse duration of 156 fs and repetition rate of 49 MHz. In addition, the signal-to-noise ratio is about 90 dB. Those experimental results confirm the attractive nonlinear optical properties of CoOF and lay a foundation for the ultrafast application of low-dimensional transition metal oxides.

Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensed matter. However, the only way to determine crystal structures of materials above 100 GPa, namely, X-ray diffraction (XRD), especially for low Z materials, remains nontrivial in the ultrahigh-pressure region, even with the availability of brilliant synchrotron X-ray sources. In this work, we perform a systematic study, choosing hydrogen (the lowest X-ray scatterer) as the subject, to understand how to better perform XRD measurements of low Z materials at multimegabar pressures. The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254 GPa at room temperature [C. Ji et al., Nature 573, 558–562 (2019)]. We present our discoveries and experiences with regard to several aspects of this work, namely, diamond anvil selection, sample configuration for ultrahigh-pressure XRD studies, XRD diagnostics for low Z materials, and related issues in data interpretation and pressure calibration. We believe that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures, eventually testing structural models of metallic hydrogen.