Combined pulsed laser (CPL), introduced in 1975 for target damage, integrates different lasers to achieve high peak power and pulse energy. However, despite decades of research, CPL remains unused for long-range target damage due to the challenge of maintaining high peak power density over long distances. We note that a potential solution lies in leveraging the air filament generated by femtosecond laser, which can transmit peak power densities higher than 10 14 W/cm 2 under the power clamping effect. To address this, a concept of a femtosecond laser induced air filament-CW CPL for surface damage of ceramics was introduced. We found no surface changes in ceramic targets when irradiated with a CW laser alone. By way of contrast, the target can be penetrated in a very short time (20 ms) with the assistance of the femtosecond laser induced air filament. In this context, we employ high-speed shadow imaging, cross-timescale simulation models and macro-microscopic characterization, to elucidate the CPL damage mechanism. The optimal CPL, combining a 1 mJ femtosecond laser and a 500 W CW laser, yields a damage rate of 1.51×10 7 μm 3 /J, representing an improvement of approximately 175% compared to single femtosecond laser ablation and around 59% enhancement compared to coating-assisted CW laser ablation. Furthermore, the efficacy of the proposed femtosecond-CW CPL method is demonstrated in causing penetration damage of ceramic/metal composite material or direct damage of sapphire, showcasing its versatility in damaging applications. Consequently, the femtosecond-CW CPL ablation method presented in this paper holds great promise as a new type of damage method for transparent hard and brittle materials.

The presence of manganese ions (Mn2+) in Yb/Er-co-doped nanomaterials results in suppressing green (545 nm) and enhancing red (650 nm) upconversion (UC) emission, which can achieve single-red-band emission to enable applications in bioimaging and drug delivery. Here, we revisit the tunable multicolor UC emission in a single Mn2+-doped β-NaYF4:Yb/Er microcrystal which is synthesized by a simple one-pot hydrothermal method. Excited by a 980 nm continuous wave (CW) laser, the color of the single β-NaYF4:Yb/Er/Mn microrod can be tuned from green to red as the doping Mn2+ ions increase from 0 to 30 mol%. Notably, under a relatively high excitation intensity, a newly emerged emission band at 560 nm (2H9/2 → 4I13/2) becomes significant and further exceeds the traditional green (545 nm) emission. Therefore, the red-to-green (R/G) emission intensity ratio is subdivided into traditional (650 to 545 nm) and new (650 to 560 nm) R/G ones. As the doped Mn2+ ions increase, these two R/G ratios are in lockstep with the same tunable trends at low excitation intensity, but the tunable regions become different at high excitation intensity. Moreover, we demonstrate that the energy transfer (ET) between Mn2+ and Er3+ contributes to the adjustment of R/G ratio and leads to tunable multicolor of the single microrod. The spectroscopic properties and tunable color from the single microrod can be potentially utilized in color display and micro-optoelectronic devices.

In this manuscript, we studied the thermal properties of hundred-watt fiber laser oscillator by real-time in-situ distributed temperature measurement. Optical frequency domain reflectometry (OFDR) was introduced to measure the temperature distribution of gain fiber core. The fiber laser oscillator operated at 1080 nm and the wavelength of detecting signal from OFDR was ~1550 nm. The maximum output power of this fiber oscillator was 100 W. The fiber core temperature distributions in experiment agree well with our theoretical simulation. The temperature measurement of gain fiber core in oscillator has always been a problem because the backward laser from the oscillator may reduce the signal-to-noise ratio in OFDR. To the best of our knowledge, this is the first temperature distribution measurement of fiber core in hundred-watt oscillator. By the experimental measurement and theoretical model, we also analyzed the thermal properties of laser oscillator respectively pumped by 915 nm and 976 nm LD sources. We found fiber laser oscillator pumped by 976 nm LD sources experienced not only higher maximum thermal load but also higher average thermal load than that pumped by 915 nm LD sources at the same level output power. We also analyzed the fiber core temperature of other components in system, such as combiners and fiber Bragg gratings (FBG). These results are meaningful for us to improve the thermal design and management in fiber lasers.

Er³⁺-sensitized upconversion nanoparticles (UCNPs) have attracted great attention due to their tunable upconversion (UC) emissions, low cytotoxicity, high resistance to photobleaching and especially multiple effective excitation wavelengths. However, detailed energy conversion between Er³⁺ and Tm³⁺ ions in Y₂O₃ UCNPs is still a problem, especially under multi-wavelength and variable pulse width excitation. In this work, we successfully fabricated a series of Er³⁺-sensitized Y₂O₃ nanocrystals by a spray flame synthesis method with a production rate of 40.5 g h⁻¹. The as-prepared UCNPs are a pure cubic phase with a mean size of 14 nm. Excited by both 980 and 808 nm lasers, the tunable upconversion luminescence (UCL) from Er³⁺ ions was achieved by increasing the Er³⁺ doping concentration, co-doping Tm³⁺ ions and extending excitation pulse-width. The investigations of the lifetimes and the laser power dependence of UC emissions further support the proposed mechanism, which provides guidance for achieving effective color control in anticounterfeiting and multiplexed labeling applications. In addition, the red UC emission at about 5 mm beneath the tissue surface was observed in an ex vivo imaging experiment under the excitation of 808 nm laser, indicating that the Y₂O₃:Er³⁺/Tm³⁺ UCNPs have great prospects in further biological applications.

Dimeric acceptors (DMAs) exhibit significant potential for optimizing both the efficiency and stability of organic solar cells (OSCs). However, medium band-gap DMAs with a high open-circuit voltage (V_oc) for efficient OSCs remain underexplored. In this study, we designed and synthesized a medium bandgap dimeric acceptor, designated DYO-1, through the strategy of alkoxy side-chain substitutions. The resultant DYO-1 exhibited an upshifted lowest unoccupied molecular orbital (LUMO) level and blue-shifted absorption. Notably, an o-xylene (o-XY) processed OSC with a PM6:DYO-1 binary blend achieved an ultra-high V_oc of 1.022 V and a fill factor (FF) of 73.9%, resulting in a power conversion efficiency (PCE) of 15.1%. To our knowledge, this is the highest PCE reported thus far for dimer-based OSCs with a V_oc exceeding 1.0 V. Furthermore, DYO-1 was incorporated into a PM6:L8-BO-X blend film, effectively reducing excessive aggregation of the host blend film, thus improving the carrier transport efficiency and enhancing both the short-circuit current (J_sc) and FF. Alongside the improvement in V_oc, the PM6:L8-BO-X:DYO-1 based ternary OSC, which is prepared using an o-XY solvent, achieved a prominent PCE of 19.6%. Additionally, a module device with an effective area of 13.5 cm² exhibited a PCE of 15.8%, highlighting the potential for large-area fabrications. Our study unveils the importance of medium bandgap dimeric acceptors in achieving efficient and stable OSCs, providing valuable insights into the design of high-performance electron acceptors.