Nearly diffraction-limited picosecond pulse amplification from LMA fluoride fiber at 2.8 µm.

We demonstrated the generation of a nearly diffraction-limited picosecond pulse from a large-mode-area (LMA) fluoride fiber amplifier. Seeded with a mode-locked fiber oscillator at 2.8 µm, the LMA Er:ZBLAN fiber amplifier delivered the pulse of 16 µJ with a duration of 70 ps at 5 kHz. The nearly diffraction-limited beam was obtained from the 50 µm LMA fiber using the fundamental mode excitation technique, with a measured M2 value of 1.25 for x axis and 1.27 for y axis, respectively. This high-beam-quality high-energy picosecond fiber-based system of 2.8 µm exhibits a great potential in the high-precision biomaterial processing.

Efficient continuous wave and passively Q switched Er:GdScO3 laser using Fe:ZnSe at 2.8 µm.

We report on diode-pumped continuous wave and passively Q switched Er:GdScO3 crystal lasers at around 2.8 µm. A continuous wave output power of 579 mW was obtained with a slope efficiency of 16.6%. Using Fe:ZnSe as a saturable absorber, a passively Q switched laser operation was realized. A maximum output power of 32 mW was generated with the shortest pulse duration of 286 ns at a repetition rate of 157.3 kHz, leading to a pulse energy of 204 nJ and a pulse peak power of 0.7 W.

Red-diode-clad-pumped CW and mode-locked Er:ZBLAN fiber laser at 3.5†µm.

We report on a red-diode-clad-pumped continuous-wave (CW) and mode-locked Er:ZBLAN fiber laser at 3.5 µm for the first time. Numerical simulation shows that a heavily-doped Er:ZBLAN fiber is favorable for effective generation of 3.5 µm laser through 658 nm laser diode pumping. Using a 7.0 mol.% Er:ZBLAN fiber, CW output power of 203 mW was experimentally obtained at 3462 nm. By incorporating a home-made semiconductor saturable absorber mirror into the cavity, diode-pumped CW mode-locked 3.5 µm Er:ZBLAN fiber laser was first demonstrated with an average power of 19 mW, a pulse duration of 18.1 ps, and a repetition rate of 46 MHz. The research results show that red-diode-clad-pumping provides a simple and potential scheme for 3.5 µm CW and mode-locked Er:ZBLAN fiber laser.

Semiconductor saturable absorber mirror in the 3-5†µm mid-infrared region.

Semiconductor saturable absorber mirrors (SESAMs) have been regarded as a revolutionary technology for ultrafast mode-locked lasers, producing numerous landmark laser breakthroughs. However, the operating wavelength of existing SESAMs is limited to less than 3 µm. In this study, we create a 3-5 µm mid-infrared (MIR) SESAM by engineering an InAs/GaSb type-II superlattice. Bandgap engineering and the strong coupling between potential wells in a superlattice enable a broadband response of saturable absorption in the 3-5 µm spectral range. Using the fabricated SESAM, we realize a SESAM mode-locked Er:ZBLAN fiber laser at 3.5 µm, which delivers MIR ultrashort pulses with high long-term stability. The breakthrough of SESAM fabrication in the MIR will promote the development of MIR ultrafast coherent sources and related application fields.

Real-time detection method of gear contact fatigue pitting based on machine vision.

This paper proposes a real-time detection method for gear contact fatigue pitting based on machine vision in order to improve the detection accuracy and detection efficiency of specimen fatigue pitting in gear contact fatigue tests and to realize the visualization, quantification, and real-time detection of gear pitting. Under the principle of gear meshing and the shooting principle of a line-scan camera, a test detection system for gear contact fatigue is established, and the optimal centrifugal shooting distance for the gear tooth surface is obtained by analyzing the gear rotation process. In response to the phenomenon of image overlap caused by the inconsistency between the speed of each point on the gear tooth profile and the line frequency set by the camera, an image correction algorithm of the gear meshing surface has been proposed, which has been proven to have improved the accuracy of the detection results of gear contact fatigue pitting corrosion. The detection accuracy of fatigue pitting corrosion is improved by combining the preliminary detection and the accurate detection of the fatigue features. The depth information of the extracted contour pitting pits is extracted by the sequential forward selection (SFS) algorithm. The experimental results showed that 0.1216mm2 is the average absolute error of pitting corrosion detection, the average relative error is 2.2188%, and the detection accuracy is 97.7812%. The proposed pitting corrosion detection system advances in visualization, quantification, real-time monitoring, and failure judgment with a new, to the best of our knowledge, experimental approach for gear contact fatigue pitting corrosion detection.

2-MW peak-power pulses from a dispersion-managed fluoride fiber amplifier at 2.8 µm.

We report on a scheme of pulse amplification and simultaneous self-compression in fluoride fiber for generating a high-peak-power pulse at 2.8-µm wavelength. We find dispersion management plays a key role for the amplification and self-compression process. Through dispersion management with a Ge rod, pulse amplification and simultaneous pulse self-compression were realized in the small anomalous dispersion region. A 2-MW peak-power pulse was achieved through amplification and self-compression in Er:ZBLAN fiber, with pulse energy of 101 nJ and pulse duration of 49 fs. To the best of our knowledge, this is the highest peak power obtained from fluoride fiber at 2.8 µm, and will benefit a series of applications.

Generation of a mid-infrared femtosecond vortex beam from an optical parametric oscillator.

Mid-infrared femtosecond vortex beams generated by optical parametric oscillators (OPO) are reported for the first time, to the best of our knowledge. Order-tunable femtosecond Hermite-Gauss beams from the first to sixth order are produced from a synchronously pumped OPO and then converted into the corresponding first through sixth-order femtosecond vortex beams by a cylindrical lens mode converter. By slightly tuning the cavity length, the wavelength of the vortex beam can be continuously tunable in the range from 2323 to 2382 nm, and the pulse duration can be changeable from ${\sim}{400}\;{\rm fs}$∼400fs to ${\sim}{1.1}\;{\rm ps}$∼1.1ps. The work provides a flexible and reliable way to generate mid-infrared femtosecond vortex beams, and is of special significance for expanding the wavelength range of femtosecond vortex beams and their application fields.

Highly-efficient mid-infrared CW laser operation in a lightly-doped 3 at.% Er:SrF2 single crystal.

3 at.% Er:SrF2 laser crystals with high optical quality were successfully grown using the temperature gradient technique (TGT). The intense mid-infrared emission was observed around 2.7 µm with excitation by a 970 nm LD. Based on the Judd-Ofelt theory, the emission cross-sections of the 4I13/2-4I11/2 transition were calculated by using the Fuchtbauer-Ladenburg (FL) method. Efficient continuous-wave laser operation at 2.8 µm was achieved with the lightly-doped 3 at.% Er:SrF2 crystal pumped by a 970 nm laser diode. The laser output power reached up to 1.06 W with a maximum slope efficiency of 26%.

Black phosphorus Q-switched and mode-locked mid-infrared Er:ZBLAN fiber laser at 3.5 µm wavelength.

With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 µm have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 µm. Here, we fabricated a 3.5-µm saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 µm. To the best of our knowledge, it is the first time to achieve passively Q-switched and mode-locked pulses in 3.5 µm spectral region. The research results will not only promote the development of 3.5-µm pulsed fiber lasers but also open the photonics application of two-dimensional materials in this spectral region.

Spectroscopic characteristics, continuous-wave and mode-locking laser performances of Tm,Y:CaF2 disordered crystal.

The spectroscopic characteristics, continuous-wave (CW) and mode-locking laser performances of Tm,Y:CaF2 disordered crystal were studied. A maximum CW output power of 586 mW was obtained with a slope efficiency of 26%. The Tm,Y:CaF2 mode-locked laser could operate in two states: single-wavelength mode locking or dual-wavelength synchronous mode locking. The single-wavelength mode-locked laser generated pulses with pulse duration of 22 ps, repetition rate of 99 MHz, and pulse energy of 1.15 nJ at 1887 nm. Alternatively, the laser could also be mode-locked simultaneously at 1880.7 nm and 1889.0 nm wavelengths. The beating modulation in autocorrelation trace shows that the dual-wavelength pulses were temporally synchronous.

Ultraclean femtosecond vortices from a tunable high-order transverse-mode femtosecond laser.

Femtosecond optical vortices open a variety of fascinating applications, ranging from femtosecond micro-nano manipulation to vortex strong-field physics. A basic requirement for these applications is that the femtosecond vortex has a clean intensity node for capturing or trapping particles. Thus far, the generation of clean femtosecond vortices remains a challenge. Here, we report on ultraclean femtosecond vortex generation by a femtosecond mode-locked laser operating in a single high-order transverse mode. By controlling the oscillation thresholds of various-order transverse modes in a laser, a pure and mode-order-tunable femtosecond Hermite-Gaussian beam is generated from the mode-locked laser and, subsequently, is converted into the femtosecond vortex by a cylindrical lens mode converter. The obtained femtosecond vortex has an unprecedented ring-to-center intensity contrast of 36 dB measured with a near wavelength-spatial-resolution detecting device, which approaches the theoretical limit of an ideal vortex beam. This Letter may open a wide range of application prospects for femtosecond vortices and motivate novel femtosecond structured beam generation directly from mode-locked lasers.

Mid-infrared mode-locked pulse generation with multilayer black phosphorus as saturable absorber.

A mid-infrared saturable absorber mirror is successfully fabricated by transferring the mechanically exfoliated black phosphorus onto the gold-coated mirror. With the as-prepared black phosphorus saturable absorber mirror, a continuous-wave passively mode-locked Er:ZBLAN fiber laser is demonstrated at the wavelength of 2.8 µm, which delivers a maximum average output power of 613 mW, a repetition rate of 24 MHz, and a pulse duration of 42 ps. To the best of our knowledge, this is the first time a black phosphorus mode-locked laser at 2.8 µm wavelength has been demonstrated. Our results demonstrate the feasibility of black phosphorus flake as a new two-dimensional material for application in mid-infrared ultrafast photonics.

Black phosphorus as saturable absorber for the Q-switched Er:ZBLAN fiber laser at 2.8 µm.

Black phosphorus, a newly emerged two-dimensional material, has attracted wide attention as novel photonic material. Here, multilayer black phosphorus is successfully fabricated by liquid phase exfoliation method. By employing black phosphorus as saturable absorber, we demonstrate a passively Q-switched Er-doped ZBLAN fiber laser at the wavelength of 2.8 µm. The modulation depth and saturation fluence of the black phosphorus saturable absorber are measured to be 15% and 9 µJ/cm(2), respectively. The Q-switched fiber laser delivers a maximum average power of 485 mW with corresponding pulse energy of 7.7 µJ and pulse width of 1.18 µs at repetition rate of 63 kHz. To the best of our knowledge, this is the first time to demonstrate that black phosphorus can realize Q-switching of 2.8-µm fiber laser. Our research results show that black phosphorus is a promising saturable absorber for mid-infrared pulsed lasers.

Watt-level passively mode-locked Er(3+)-doped ZBLAN fiber laser at 2.8 µm.

We experimentally demonstrated a stable, high-average-power, continuous-wave (CW) passively mode-locked Er(3+)-doped ZBLAN fiber laser at 2.8 µm based on a semiconductor saturable absorber mirror. A stable mode-locked laser with a signal-to-noise ratio of 52 dB and a slope efficiency of 14% was obtained. The highest average output power in excess of 1 W was generated at the incident pump power of 8.2 W, with a pulse repetition rate of 22.56 MHz and pulse duration of 25 ps. To the best of our knowledge, this is the highest average output power of a CW mode-locked ZBLAN fiber laser in the mid-infrared wavelength regime up to now.

8.5 W mode-locked Yb:Lu1.5Y1.5Al5O12 laser with master oscillator power amplifiers.

We report on a diode-pumped passively mode-locked Yb:Lu(1.5)Y(1.5)Al(5)O(12) (Yb:LuYAG) laser for the first time to our knowledge. With the mixed crystal of Yb:LuYAG as gain medium, the mode-locked laser generated 2.2 W of average output power with a repetition rate of 83.9 MHz and pulse duration of 2.4 ps at the wavelength of 1030 nm. In order to obtain higher output power, the output from the mode-locked oscillator was further amplified to 8.5 W by two-stage single-pass amplifiers. The high-power picosecond laser is very useful for applications such as pumping of midinfrared optical parametric oscillators, material microprocessing, and UV light generation.

Deep learning-based automatic measurement system for patellar height: a multicenter retrospective study.

BACKGROUND: The patellar height index is important; however, the measurement procedures are time-consuming and prone to significant variability among and within observers. We developed a deep learning-based automatic measurement system for the patellar height and evaluated its performance and generalization ability to accurately measure the patellar height index. METHODS: We developed a dataset containing 3,923 lateral knee X-ray images. Notably, all X-ray images were from three tertiary level A hospitals, and 2,341 cases were included in the analysis after screening. By manually labeling key points, the model was trained using the residual network (ResNet) and high-resolution network (HRNet) for human pose estimation architectures to measure the patellar height index. Various data enhancement techniques were used to enhance the robustness of the model. The root mean square error (RMSE), object keypoint similarity (OKS), and percentage of correct keypoint (PCK) metrics were used to evaluate the training results. In addition, we used the intraclass correlation coefficient (ICC) to assess the consistency between manual and automatic measurements. RESULTS: The HRNet model performed excellently in keypoint detection tasks by comparing different deep learning models. Furthermore, the pose_hrnet_w48 model was particularly outstanding in the RMSE, OKS, and PCK metrics, and the Insall-Salvati index (ISI) automatically calculated by this model was also highly consistent with the manual measurements (intraclass correlation coefficient [ICC], 0.809-0.885). This evidence demonstrates the accuracy and generalizability of this deep learning system in practical applications. CONCLUSION: We successfully developed a deep learning-based automatic measurement system for the patellar height. The system demonstrated accuracy comparable to that of experienced radiologists and a strong generalizability across different datasets. It provides an essential tool for assessing and treating knee diseases early and monitoring and rehabilitation after knee surgery. Due to the potential bias in the selection of datasets in this study, different datasets should be examined in the future to optimize the model so that it can be reliably applied in clinical practice. TRIAL REGISTRATION: The study was registered at the Medical Research Registration and Filing Information System (medicalresearch.org.cn) MR-61-23-013065. Date of registration: May 04, 2023 (retrospectively registered).

Comparison of the efficacy of Oxford unicondylar replacement for the treatment of spontaneous osteonecrosis of the knee versus medial knee osteoarthritis: a meta-analysis.

OBJECTIVE: Meta-analysis of the comparative efficacy of Oxford unicompartmental knee arthroplasty (OUKA) for the treatment of spontaneous osteonecrosis of the knee (SONK) and medial knee osteoarthritis (MKOA). METHODS: A computerized search was conducted for literature related to OUKA treatments of SONK and MKOA across various databases, including the China National Knowledge Infrastructure, WAN FANG, VIP, SinoMed, Cochrane Library, PubMed, Embase, and Web of Science, covering the period from each database's inception to September 2023. Literature screening, quality assessment and data extraction were performed according to the inclusion and exclusion criteria. After extracting the literature data, RevMan 5.4 software was applied to analyse the postoperative knee function score, postoperative knee mobility, postoperative pain, bearing dislocation rate, aseptic loosening, postoperative progression of posterolateral arthritis, and revision rate. RESULT: A total of 9 studies were included, including 6 cohort studies and 3 matched case‒control studies. A total of 1544 knees were included, including 183 in the SONK group and 1361 in the MKOA group. The meta-analysis results showed that the SONK and MKOA groups showed a significant difference in postoperative knee function scores [MD = 0.16, 95% CI (- 1.20, 1.51), P = 0.82], postoperative knee mobility [MD = - 0.05, 95% CI (- 1.99. 1.89), P = 0.96], postoperative pain [OR = 0.89, 95% CI (0.23, 3.45), P = 0.87], rate of bearing dislocation [OR = 1.28, 95% CI (0.34, 4.81), P = 0.71], aseptic loosening [OR = 2.22, 95% CI (0.56, 8.82), P = 0.26], postoperative posterolateral arthritis progression [OR = 2.14, 95% CI (0.47, 9.86), P = 0.33], and revision rate [OR = 1.28, 95% CI (0.53, 3.04), P = 0.58] were not statistically significant. CONCLUSION: OUKA treatment with SONK and MKOA can achieve similar satisfactory clinical results.

A novel array-type microdroplet parallel-generation device.

In this study, the innovative design of a new array microdroplet parallel-generation device is proposed based on the principle of fluid inertial force using a capillary glass needle. The entire device used an electromagnetic actuator as the power source. It was designed as a 9-channel parallel array of glass needles. All glass needles feed independently, allowing different solutions to be sprayed simultaneously while effectively avoiding cross-contamination. We achieved non-contact parallel precision dispensing of nanoliter-sized microdroplet arrays using a relatively simple method. In this study, we first investigated the homogeneity of the generated droplet arrays and the stability of the device over long periods of operation. Then, the influence of the driving-voltage amplitude of the electromagnet and nozzle diameter on microdroplet generation was analyzed. Finally, a prediction model for the droplet size was developed using regression analysis to investigate the on-demand generation of droplets. In summary, the device designed in this study had a novel design, low cost, and modular assembly. It has excellent potential for applications in high precision and low-volume microdroplet-array generation.

Icariin improves cognitive impairment by inhibiting ferroptosis of nerve cells.

AIM: We investigated the effect and mechanism of Icariin (ICA) on improving neurobehavioral ability of mice with Alzheimer's disease (AD). METHODS: We selected 10-month-old APP/PS1 mice (AD) and wild-type C57BL/6J mice (Normal). After intragastric administration of ICA, Morris water maze was employed to detect neurobehavioral improvements, and to assay key ferroptosis indicators and oxidative stress levels. The common target of ICA for resisting ferroptosis and AD was predicted by network pharmacology. RESULTS: ICA could improve the neurobehavioral, memory and motor abilities of AD mice. It could lower the ferroptosis level and enhance the resistance to oxidative stress. After inhibition of MDM2, ICA could no longer improve the cognitive ability of AD mice, nor could it further inhibit ferroptosis. Network pharmacological analysis revealed that MDM2 might be the target of ICA action. CONCLUSIONS: We found that ICA can inhibit ferroptosis of nerve cells, thereby ameliorating neural damage in mice with AD.

Pushing Optical Switch into Deep Mid-Infrared Region: Band Theory, Characterization, and Performance of Topological Semimetal Antimonene.

The existing pulsed laser technologies and devices are mainly in the infrared spectral region below 3 µm so far. However, longer-wavelength pulsed lasers operating in the deep mid-infrared region (3-20 µm) are desirable for atmosphere spectroscopy, remote sensing, laser lidar, and free-space optical communications. Currently, the lack of reliable optical switches is the main limitation for developing pulsed lasers in the deep mid-infrared region. Here, we demonstrate that topological semimetal antimonene possesses an ultrabroadband optical switch characteristic covering from 2 µm to beyond 10 µm. Especially, the topological semimetal antimonene shows a very low saturable energy fluence (only 3-15 nJ cm-2 beyond 3 µm) and an ultrafast recovery time of ps level. We also demonstrate stable Q-switching in fiber lasers at 2 and 3.5 µm by using topological semimetal antimonene as passive optical switches. Combined with the high environmental stability and easy fabrication, topological semimetal antimonene offers a promising optical switch that extends pulsed lasers into deep mid-infrared region.