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All-solid-state passively Q-switched lasers have advantages that include simple structure, high peak power, and short sub-nanosecond pulse width. Potentially, these lasers can be applied in multiple settings, such as in miniature light sources, laser medical treatment, remote sensing, and precision processing. Cr4+:YAG crystal is an ideal Q-switch material for all-solid-state passively Q-switched lasers owing to its high thermal conductivity, low saturation light intensity, and high damage threshold. This study summarizes the research progress on all-solid-state passively Q-switched lasers that use Cr4+:YAG crystal as a saturable absorber and discusses further prospects for the development and application of such lasers. [ABSTRACT FROM AUTHOR]

The excellent characteristics of transparent hard materials such as high hardness, high transparency, corrosion resistance, and high temperature resistance enable their applications in microfluidic substrates even in harsh environments. Microchannels are important parts in microfluidic systems, and the preparation of microchannel structures in transparent hard materials deserves further in‐depth study. The traditional processing method is contact processing with large thermal influence and low processing efficiency, so it is impossible to obtain complex microchannels with high quality and high aspect ratio. The femtosecond laser processing is a non‐contact processing approach with no thermal damage, high processing accuracy, and easy to form complex microchannels, making it the best choice for processing microchannels in transparent hard materials. This work reviews the recent advances in femtosecond laser processing of transparent hard materials to form microchannel structures, focusing on the reaction mechanism, processing methods, and the obtained microchannel structures, including surface microchannels, 2D microchannels, and 3D microchannels. Furthermore, the application of microchannel structure in microfluidic field, including optical inspection and biochemical reaction, is also described. [ABSTRACT FROM AUTHOR]

Past decades have witnessed the generation of new stretchable photodetectors in electronic eyes, health sensing, wearable devices, intelligent monitoring and other fields. Stretchable devices require not only outstanding performance but also excellent flexibility, adaptability and stability. Innovative strategies have been proposed to realize the stretchability of devices. In addition, novel functional materials including zero‐dimensional nanomaterials, one‐dimensional inorganic nanomaterials, two‐dimensional layered materials, organic materials, and organic‐inorganic composite materials with excellent properties are emerging to continuously improve the performance of devices. Here, the recent research progress of stretchable photodetectors in terms of both various design methods and functional materials is outlined. The optical performance and stretchable properties are also comprehensively reviewed. Finally, a summary and the challenges associated with the application of stretchable photodetectors are presented. [ABSTRACT FROM AUTHOR]

• We achieved a tunable, multi-wavelength CWML fiber seed with a large dynamic range. • We proposed an all-fiber SA and comb filter device based on a GIMF twined into PC. • We achieved the stable CWML, pulse bunches, and harmonic mode-locked operation. • The output spectrum of six-wavelength mode-locked span range is up to 28 nm. We have demonstrated a tunable, multi-wavelength mode-locked fiber laser with a large dynamic range based on polarization controller (PC) coiled graded index multimode fiber (GIMF) as a saturable absorber (SA) and comb filter for the first time. The SA device that consists of a section of GIMF coiled into a polarization controller and two sections of single mode fibers aim to mitigate the technical difficulty of multimode fiber (MMF) in the length accuracy requirements and tune multi-wavelength operation in an Yb-doped fiber laser. Nonlinear multimode interference and transverse light field evolution in multimode fiber are simulated. Experimentally, we achieved the stable continuous-wave mode-locked (CWML), pulse bunches, and high-harmonic mode-locked (HML) operation. Furthermore, the PC-based GIMF structure can also be used as a filter to tune the laser line numbers. Continuously tunable multi-wavelength mode-locked operation with a large dynamic range was demonstrated by varying the polarization orientation of MMF. The range of six-wavelength spectrum is up to 28 nm. Our results indicate that the PC coiled GIMF could serve as an SA and a filter, which makes it beneficial to realize tunable, multi-wavelength mode-locked laser with a large dynamic range. [ABSTRACT FROM AUTHOR]

The nonlinear effect of fiber limits the further increase in pulse energy, and Mamyshev oscillator shows outstanding advantages in managing nonlinearity in waveguide medium, which is now associated with high peak power and high pulse energy. The potential applications of these laser sources based on Mamyshev mechanism have facilitated aggressive research and innovative ideas by researchers around the world. Here, we focus on the mode-locked principle and starting dynamics of Mamyshev oscillator. The review of Mamyshev technology is summarized from two starting modes of seed source injection and self-starting. Initial research and significant progress in this field, plus new insights and challenges of Mamyshev oscillator for ultrafast fiber laser technology are analyzed. [ABSTRACT FROM AUTHOR]

We demonstrate a continuous-wave single-frequency diamond Raman laser operating at 1178 nm by using a linear resonator that is stabilized using an intracavity χ (2) element. Optimization of the single-frequency power was realized by tuning the phase matching in the χ (2) element away from the second-harmonic peak to suppress neighboring modes via sum frequency generation but avoid large losses to the intracavity primary Stokes mode. A maximum single-longitudinal-mode power of 20 W at 1178 nm with an instrument-limited linewidth of 67 MHz was obtained using a 12 GHz multi-longitudinal-mode Yb-doped fiber pump laser at 1018 nm with power of 82 W. This work provides an interesting route for producing single-frequency high-power lasers near 1.2 μm utilizing diamond Raman conversion combined with broadband, high-power, low-cost YDF lasers. [ABSTRACT FROM AUTHOR]

We have demonstrated the dual-wavelength domain-wall pulse operation in an Er-doped mode-locked fiber laser based on single-mode fiber (SMF)–graded index multimode fiber (GIMF)–SMF as the saturable absorber for the first time. The domain-wall dark–bright pulse pairs exhibited two peaks, which were located at 1604.6 and 1606 nm. The pulse repetition rate was maintained at 16.5 MHz throughout the dark–bright pulse pairs operation. Besides, dark–bright pulse pairs operation was demonstrated at a relative stability with the signal to noise ratio of 55.3 dB. Moreover, the dark–bright pulse pairs could be converted into bright–dark pulse pairs by adjusting the polarization state, which has potential advantages for the development of wavelength division multiplexing and optical fiber sensing technology. [ABSTRACT FROM AUTHOR]

• Different nonlinear lasers and different resonator structures for yellow laser. • Stimulated Raman scattering laser for obtaining yellow light output. • Output characteristics including nonlinear frequency conversion, conversion efficiency and output power for yellow laser. Yellow lasers have always attracted much attention in the fields of biomedicine, lidar, adaptive optics and nano-guide stars. Different application scenarios also have differences in the selection of yellow light wavelengths and various indicators. For example, the Coarse Star and Nano-guide technologies require a narrow yellow light linewidth of 589 nm. According to the generation method, it can be divided into dye excitation, semiconductor excitation and nonlinear frequency conversion excitation. Non-linear frequency conversion technology can be divided into sum frequency generation (SFG), second harmonic generation (SHG), optical parametric oscillation (OPO) and stimulated Raman scattering (SRS). Among them, SRS has become a current research hotspot due to its high beam quality, high wavelength scalability and high conversion efficiency. The development and research status of non-linear frequency conversion technology are expatiated in this article, which is useful reference for the future in this field. [ABSTRACT FROM AUTHOR]

• A novel YDFL proposed based on NLMMI-NPR hybrid mode-locked mechanism. • Stable single-pulse mode-locked state is achieved with the repetition rate of 12.8 MHz. • Obtain Multi-pulse bunches, harmonic mode-locked, harmonic pulse bunches, and chaotic state. • The mode-locked pulse bunches containing a maximum of 10 pulses. In this study, we propose a novel Ytterbium-doped ultrafast fiber laser based on nonlinear multimode interference-nonlinear polarization rotation (NLMMI-NPR) hybrid mode-locked mechanism. Stable single-pulse mode-locked state is achieved in the linear cavity, with a repetition rate of 12.8 MHz. By adjusting the polarization state and pump power inside the cavity, various characteristic modes are obtained, including multipulse bunches, second- and third-harmonic mode-locked states, second- and third-harmonic multipulse bunches states, and a chaotic multipulse state. This is the first exploration of multipulse bunches in Ytterbium-doped ultrafast fiber lasers based on the NLMMI-NPR hybrid mode-locked mechanism. And multipulse mode-locked fiber lasers have unique advantages in numerous fields owing to their higher energy and wider pulse width. [ABSTRACT FROM AUTHOR]

High-order vortex lasers are important for high angular momentum quantum entanglement and high-resolution spatial detection. However, traditional spatial phase modulation for Gaussian beams have difficulties achieving high-order and continuously adjustable optical vortex output. In this study, a high-order vortex laser output of continuously adjustable topological charges between 1 and 9 was obtained by adjusting the cavity length in a side-pumped Nd:YAG oscillator with circular spot defects of different sizes etched on the surface of the cavity mirror. Its chirality was also controlled by slightly tilting the cavity mirror, and the mode changes under different cavity parameters and the factors limiting the output optical-vortex order in the side-pumping structure were analyzed. In addition, the generation of optical vortex lattice modes with multiple spatially separated OAMs was obtained based on the spot defect method by displacing the cavity mirror. • This study develops a high-order vortex laser with continuously adjustable topological charges by adjusting the cavity length in a side-pumped Nd: YAG oscillator with circular spot defects. • Chiral control of the output vortex laser and optical vortex lattice modes with two spatially separated orbital angular momenta were obtained. • The side-pump approach offers enhanced flexibility in terms of vortex tuning and the potential for power expansion. [ABSTRACT FROM AUTHOR]

Linear polarization effects on laser drilling were investigated by the use of a picosecond laser system. It was observed that the exit shapes of stainless steel were placed perpendicular to the direction of polarization. According to theoretical analysis, the main factor that determines the exit hole shape is the difference between Rs and Rp. When this gap is large enough, the bulges on the exit hole will be easily observed. Inversely, when the gap is small, bulges can be barely spotted on the exit hole. This is further confirmed by comparative experiment and calculation conducted on a copper sheet. [ABSTRACT FROM AUTHOR]

• A stress measurement method based on laser heterodyne technology for optical elements is proposed. • Three algorithms used to extract the phase accuracy of heterodyne signal are discussed. • The experimental results show that the phase measurement accuracy is better than 0.001 rad and the relative error is better than 0.01%. Common stress measurement methods of optical elements often suffering from complex process and limited aperture. To meet this challenge a new method based on laser heterodyne technology is proposed. In this method the stress measurement is transformed into the measurement of optical path difference induced by birefringence according to the stress birefringence effect, and the signal light is demodulated by laser heterodyne detection. This method has simple measurement process, and solves the problem of large-aperture measurement by combining with MEMS scanning technology. The basic structure of the measurement system is established, and its theoretical model is derived in detail. The experiment result of a fused silica sample with thickness of 2 mm reach an accuracy as high as 1.8 kPa, and the relative error is less than 0.01%. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the influence of Semiconductor Saturable Absorber Mirror (SESAM) parameters on pulse evolution of passively mode-locked fiber laser at different repetition rates. Based on the Nonlinear Schrodinger Equation, the mode-locked process of the SESAM passively mode-locked fiber laser and the pulse evolution were simulated. Furthermore, the impact of modulation depth of a SESAM together with saturation intensity on mode-locking at different repetition rates have been analyzed. According to the simulation, at low repetition rate, when the laser operates at mode-locked state, the modulation depth of SESAM is larger, while the modulation depth is smaller when pulse modulation phenomenon caused by excessive modulation depth occurs in the cavity. At high repetition rate, the range of saturation intensity is much larger when the laser operates at mode-locked state. The presented numerical study provides valuable guidance for the design and development of mode-locked fiber lasers operating at different repetition rates. [ABSTRACT FROM AUTHOR]

A continuous-wave narrow linewidth diamond Raman laser based on an intracavity frequency doubling structure was demonstrated. Linewidth narrowing and power enhancement were realized by tuning the phase matching in the second-harmonic generation element through temperature control. A maximum output power of 5 W at 592 nm with a linewidth of 72 MHz was obtained using a Yb doped fiber laser with a power of 40 W and a linewidth of >4 GHz, an enhancement of the linewidth by a factor of about 65. The results indicate that high-power and narrow linewidth lasers can be produced utilizing diamond Raman conversion combined with the phase matching in the second-harmonic generation element. [Display omitted] • A linewidth compressed CW diamond Raman laser with 5 W at 592 nm laser output is proposed. • A temperature-power model of diamond frequency doubling laser is established. • Phase matching and nonlinear process in SRS and SHG conversion has been analyzed by linewidth changes. [ABSTRACT FROM AUTHOR]

• This research explores a 1.5 μm passively Q-switched pulse burst microchip laser, which is end-pumped by a 940 nm laser diode. • The laser utilizes Er:Yb:glass as the gain medium and Co:MALO as the passively Q-switched component. The performance of this pulse burst laser was exhaustively examined and optimized across a range of parameters. • A pulse train of up to 12 pulses, with a total pulse burst energy of 2 mJ was achieved. • A single pulse energy of 272 μJ was realized, featuring a pulse width of 6.2 ns, corresponding to a peak power of 43.9 kW. Burst mode lasers, characterized by a sequence of high-intensity pulses, are integral to applications such as the examination of turbulent flows and optical metrology. This study investigates a 1.5 μm passively Q-switched pulse burst microchip laser, end-pumped by a 940 nm laser diode. Utilizing Er:Yb:glass as the gain medium and Co:MALO for passive Q-switching, delivering a pulse width of 5.5 ms and a repetition rate of 10 Hz. When the initial transmittance of the saturable absorber was 93 % and the maximum absorbed pump energy reached 85 mJ, we successfully generated up to 12, 8, and 4 pulses within a burst at 1.5 μm. These results corresponded to cavity lengths of 12 mm, 13 mm, and 14 mm, respectively. By using a saturable absorber with an initial transmittance of 90.5 %, a higher single pulse energy and a narrower pulse width were realized. The narrowest pulse width was reduced to 6.2 ns, with a corresponding single pulse energy of 272 μJ. The peak power in the Er:Yb:glass/Co:MALO pulse burst laser reached an estimated 43.9 kW. This research provides valuable experimental and theoretical insights for the development of human eye-safe lasers with adjustable pulse sequences. [ABSTRACT FROM AUTHOR]

• Order controllable cascaded diamond Raman laser has been established. • The first-order to fifth-order output with wavelengths of 573.0, 620.3, 676.1, 743.0 and 824.7 nm has been achieved. Controllable multi-wavelength gets worse efficiency and quality at high orders and high energy, remaining cascade Raman laser a challenge. Here, we establish an order controllable multi-wavelength cascaded diamond Raman laser to achieve the first-order to fifth-order Raman lasers output with wavelengths of 573.0, 620.3, 676.1, 743.0 and 824.7 nm. At a 532.8 nm pump energy of 1.60 mJ, the total Stokes output energy of 0.51 mJ with a slope efficiency of 36.5% has been achieved. Meanwhile, a Stokes output threshold model of all order is proposed under short pulse pumping for the first time. The threshold energy of the first-order to fifth-order was 256, 298, 320, 494, 1100 μJ separately, which is in consistent with the simulation results perfectly. [ABSTRACT FROM AUTHOR]

• The 2 μm tunable SLM all-solid-state pulsed laser is low cost and compact. • The laser can simultaneously achieve SLM, tunability, and pulsed laser output. • The laser can output 1.37 mJ, 139 ns pulses with a SLM rate of 99.5 %. • The laser has an extensive wavelength tuning range of 116 nm around 2 μm. Single-longitudinal-mode pulse lasers operating at a wavelength of 2 μm are extensively utilized as lidar light sources in gas detection applications. We demonstrated a tunable single-longitudinal-mode acousto-optic Q-switched Tm:YAP laser by a birefringent filter and etalon. With the absorbed pump power of 8.95 W, the laser achieved a pulse duration of 139 ns and a single pulse energy of 1.37 mJ at 1 kHz repetition rate, with an SLM ratio exceeding 99.5 %. The central wavelength was tunable over a wide range from 1887 nm to 2003 nm by adjusting the birefringent filter. Our results provide an effective approach for developing compact mid-infrared solid-state lasers with high power, wide tuning and excellent performance. [ABSTRACT FROM AUTHOR]

Miniaturized sub-nanosecond laser is critical to the applications such as medical treatment, Lidar and manufacturing. In this paper, a high repetition rate hundred picosecond pulse oscillator based on Nd:YAG/Cr4+:YAG bonded crystal is demonstrated, and its output pulse characteristics are studied. It is found that the stability of amplitude and frequency of Q-switched pulse can be improved effectively by pulsedpumping. A satellite-free sub-nanosecond laser with a pulse width of 663 ps and an average power of 80 mW at the repetition rate of 1 kHz was developed, while the 50 μs pulse width of the pump was employed. Meanwhile, the near-diffraction limit output beam (M 2 =1.03 ± 0.02) with pulse energy instability of less than 2 % was obtained. This study provides a reference for the development of highly stable satellite-pulse-free passive Q-switched lasers with a high repetition rate. [ABSTRACT FROM AUTHOR]

To enable active control of rogue waves after pumping a pulse into an optical fiber, adding a weak trigger is necessary. However, this process typically involves numerous numerical simulations based on the nonlinear Schrodinger equation, which can be computationally intensive. Using neural networks to predict complex nonlinear propagation in optical fibers avoids the need for numerical solutions during research. We show a neural network using long short-term memory to predict the temporal and spectral evolutions of the mid-infrared supercontinuum generation in the near-zero dispersion region under weak triggering, simply by determining the input pulse strength in the time and frequency domains. • Add seed pulse can improve spectrum performance. • Wavelength has different effects on spectrum in different dispersion regions. • We use neural network to predict mid infrared supercontinuum with no parameter. • The highest root mean squared error value in training results is 0.15. [ABSTRACT FROM AUTHOR]

Nanostructures, novel materials, optoelectronic performance, photodetectors, stretchable devices The preparation methods, optoelectronic materials and performance parameters of these photodetectors are discussed. Keywords: nanostructures; novel materials; optoelectronic performance; photodetectors; stretchable devices EN nanostructures novel materials optoelectronic performance photodetectors stretchable devices 1 1 1 03/03/23 20230301 NES 230301 B The development of novel optoelectrical materials b is an effective way to achieve high-performance stretchable photodetectors. [Extracted from the article]

We experimentally demonstrate a novel, linear-cavity mode-locked Yb-doped fiber laser based on the graded-index multimode fiber (GIMF) as saturable absorber, and propose the use of varying gain levels by doubling gain fiber length to mitigate the technical difficulty of multimode fiber as a saturable absorber in the length accuracy requirements. It provides a more flexible solution to achieve a highly stable mode-locked fiber laser based on GIMF. By analogy to dispersion management, we refer to this scheme as gain management. By adopting the two mechanisms of flexible GIMF length and gain management simultaneously, a stable mode-locked pulse train with the repetition rate of 10.96 MHz and pulse duration of ∼83.4 ps at 1064.07 nm was generated. Stable pulse bunches with pulse numbers up to 12 in a single bunch were obtained when increasing the pump power. The proposed gain management method opens a promising way for practical highly stable mode-locked technology based on nonlinear multimode interference mechanism. [ABSTRACT FROM AUTHOR]

Orange–red lasers (∼ 590–625 nm) are of tremendous interest in biomedicine, astronomy, spectroscopy, and laser scanning. So far, the implementation of tunable is still based on the mode-selecting elements in the laser, but it is difficult to achieve a wide range of tuning due to the limited ability to select the optical elements. Here, we report a continuously tunable diamond Raman laser with output from 592–624 nm based on an all-fiber tunable ytterbium-doped laser. A maximum output power of 4.5 W is obtained at 40 W of pump power with a maximum slope efficiency of 17%. Also, we found the anti-Stokes spectrum in the output spectrum. To the best of our knowledge, this is the first discovery in a continuous-wave diamond Raman laser. The work demonstrated that continuously tunable multispectral outputs can be achieved with the same technique. • A continuously tunable diamond Raman laser with output from 592–624 nm​ based on an all-fiber tunable ytterbium-doped laser was fabricated. • A maximum output power of 4.5 W is obtained at 40 W of pump power with a maximum slope efficiency of 17%. • The anti-Stokes spectrum in the output was firstly reported in a continuous-wave diamond Raman laser. [ABSTRACT FROM AUTHOR]

• With the continual development of laser-based applications, there is growing demand for laser sources with high pulse energy, pulse durations in the picosecond range and with high repetition rates. These sources are particularly important for applications such as laser ignition, laser processing of materials and supercontinuum generation. While it is possible to generate high repetition rate, picosecond pulse duration emission from passively q-switched microchip lasers, the maximum pulse energy is limited and must be amplified. • In this work we undertake comprehensive theoretical modelling of the characteristics of the seed beam as it is injected into the amplifier slab, and we model the expected amplification characteristics of the system. This theoretical modelling is supported by a comprehensive experimental investigation of the system performance and optimization. • With this MOPA system design, we demonstrate a maximum amplification factor of ∼90 times and generate amplified seed laser output with a pulse energy of 99.58 mJ, and a pulse duration of 491 ps at a repetition rate of 200 Hz. Laser sources which generate high peak-pulse energy, picosecond pulse duration outputs at high repetition rates are of particular interest for applications including laser ignition and space fragment detection. In this work, we demonstrate the design and operation of a zig-zag slab, solid-state master oscillator power amplifier (MOPA) which yields high energy amplification. The system uses a weakly-doped Nd:YAG slab as the amplifier medium, to amplify laser pulses from a passively Q-switched microchip seed laser. The seed laser beam undergoes four passes of the slab amplifier resulting in an amplified output pulse with hundreds of picoseconds pulse duration. We investigate the relationship between the angle of incidence of the seed laser beam into the amplifier slab and its effect on the slab fill-factor and overall laser field amplification. We also investigate the impact that the temperature of the laser diode array (LDA) which is used to pump the slab amplifier, has on the amplification efficiency of the MOPA. Experimentally, we demonstrate an amplification factor of ∼90 times from the optimized slab amplifier, and a resultant output laser field with a pulse energy of 99.58 mJ, a pulse duration of 491 ps, and a repetition rate of 200 Hz. We believe that this work will pave the way towards the development of novel all-solid-state amplifier designs for the generation of high-energy, high repetition frequency, sub-nanosecond laser outputs. [ABSTRACT FROM AUTHOR]

Mode-locked erbium-doped fiber lasers (EDFL) with the low repetition rate and high pulse energy play an important role in many fields, such as micromechanical processing, ophthalmic surgery, biological sample detection, and LiDAR detection. However, in the 1550 nm band, due to the anomalous dispersion and nonlinear effects of erbium-doped fiber lasers (EDFLs), it is difficult to achieve mode-locked pulses especially in long cavities, which brings many difficulties to engineering applications. We analyze and simulate the pulse formation and evolution process in a mode-locked EDFL at a low repetition rate of sub-megahertz. The results show that by decreasing the gain or increasing modulation depth/saturation light intensity of saturable absorber in a specific range, a stable single-pulse mode-locked state can be achieved. Then a multipulse mode-locked state can be achieved by gradually increasing the gain or decreasing the saturation light intensity. In addition, the pulse width can be compressed by adjusting the second-order dispersion coefficient. The numerical simulation results are instructive for the design and development of EDFL at a low repetition rate of sub-megahertz. [ABSTRACT FROM AUTHOR]

The far-field distribution is measured by a scientific grade CCD in a single-shot nanosecond-level high power Nd:glass laser system based on a vertical truss structure. The beam-pointing drift of the laser system is analyzed in two methods by calculating the geometric center and the energy centroid of the far-field spots. Results show that the RMS value of the long-term angle drift of the output laser beam is less than 17 μrad. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a spatial beam shaping method to achieve high-quality near-field for a high-power frequency tripling laser system by using a liquid crystal spatial light modulator (SLM). Considering the nonlinear relationship between the output 3 ω intensity and the input 1 ω intensity of the frequency conversion system and the transmittance nonuniformity of the whole laser system, we introduce an efficient spatial beam shaping method that improves the output near-field beam quality of frequency tripling laser dramatically. Results show that the near-field peak-to-mean value of the frequency tripling laser improves from 1.83:1 to 1.42:1 after spatial beam shaping within four shots. This method provides effective guidance for spatial beam shaping of high-power frequency tripling laser systems. [ABSTRACT FROM AUTHOR]

• The theoretical model of diamond temperature field is established according to the initial boundary conditions, Gaussian pump distribution and heat transfer mode. • Based on the theoretical model, the temperature gradient, temperature distribution, stress distribution and thermal deformation distribution of diamond are simulated and calculated. • Through the design and construction of the diamond Raman laser, the output of 1240 nm with132 W is realized. The temperature difference between the diamond and the environment is 7 K, which is in accordance with the theoretical simulation result of 7.15 K. Thermal effects are some of the most significant factors limiting power scalability and beam quality of laser systems. In this work we examine both theoretically and experimentally, the degree by which thermal loading impacts the performance of an external cavity diamond Raman laser (DRL). Specifically, we formulate a model to study the temperature, thermal stress and thermal deformation that occurs within a diamond Raman medium in response to increasing levels of laser pumping. Experimentally, we demonstrate a DRL generating Stokes emission at 1240 nm with output power of up to 132 W and output beam quality of M2 = 1.1. [ABSTRACT FROM AUTHOR]

One major setback in the applications of high-power solid-state lasers in areas like high energy density physics is the beam quality that deteriorates with increasing pump power. To solve this problem, we proposed to develop a high beam quality and stable stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) using a filtration approach and a carefully designed geometry that includes a rotating wedge to operate under a high repetition rate laser. Upon reducing the micro-impurities to 100 nm, the accumulated heat at the focus reduced greatly, resulting in improved beam quality and better phase fidelity. At 6.5 mJ input energy and below 100 Hz repetition rates, there is no observable optical breakdown or obvious thermal effects as opposed to the unfiltered medium that experience optical breakdown at 0.5 mJ and 50 Hz repetition rate. The simulated temperature gradient at the focus shows that the material absorbed the laser within a short distance from the irradiation side, and the temperature probe reveals that the temperature increases with pumping power and time due to heat accumulation at the focus. To disperse the heat accumulation through a large area within the SBS cell, we design and introduce a rotating wedge. The impact of the rotating wedge was much more noticeable when the system works at higher pump power. • The mathematical equation connecting laser incidence angle and radius of focus rotation for a rotating-wedge-based SBS-PCM is conducted. • The process of heat transfer from the laser and accumulated in the liquid SBS gain medium is stimulated. • A stable ∼380 ps Stokes beam is generated with the rotating-wedge-based SBS-PCM at a repetition rate up to 100 Hz. [ABSTRACT FROM AUTHOR]

• The GIMF-YDF structure was used as the SA in a mode locked fiber laser. • The harmonically mode-locking (HML) pulses and bunched pulses could be obtained. • The HML pulses with pulse width of 105 ps and bandwidth of 0.093 nm were realized. An Yb-doped mode-locked fiber laser with controllable multiple-pulse dynamic patterns is experimentally demonstrated by use of an all-fiber saturable absorber (SA) based on graded index multimode fiber (GIMF)-Yb-doped fiber (YDF) structure. In addition to stable fundamentally mode locked pulses with 11 MHz, multi-pulse patterns operated in bunched pulses could be obtained with different pump powers. Besides, harmonically mode-locked pulses with pulse width of 105 ps and bandwidth of 0.093 nm are realized. The harmonically mode-locking operation exhibited a high stability and worked at a wide range of pump power. To our knowledge, this is also the first report of both harmonically mode-locked pulses and bunched pulses in a fiber laser with a GIMF-YDF based SA. The results reveal the versatility and flexibility of the GIMF-YDF structured device in controlling the pulse dynamics for different experimental requirements. [ABSTRACT FROM AUTHOR]

• The properties of periodically poled lithium niobate (PPLN) and the methods in which it has been used have been reviewed. • Development and demonstration of nonlinear wavelength conversion using PPLN are summarized. Laser gain media offer a limited number of radiative wavelengths. With the continued development of laser applications, there has grown a need for a diversity of laser wavelengths. This is where the process of nonlinear wavelength/frequency conversion can be used as an effective means of extending the range of obtainable wavelengths from existing laser sources. Lithium niobate is a commonly used nonlinear optical frequency conversion crystal, particularly when structured via the periodic poling process (periodically poled lithium niobate (PPLN)). The application of periodic poling to achieve quasi-phase-matching (QPM) within a nonlinear optical crystal maximizes the nonlinear conversion efficiency throughout the length of the crystal, minimizes beam walk-off and depending on the poling configuration, can be used to convert a range of wavelengths. The diversity of PPLN is such that it has been used for wavelength conversion of laser fields across the visible, near-infrared and mid-infrared regions. This paper reviews research which has been conducted on PPLN and in particular examines the application of PPLN across a range of laser cavity structures. [ABSTRACT FROM AUTHOR]

• The categories of OAM beams are summarized, including common OAM beams and novel OAM beams. • For intracavity generation method and extracavity conversion method, techniques for generating OAM beams in space are systematically reviewed. The advantages and disadvantages of each OAM beam generation technology are summarized. And the parameter performance comparison of each OAM generation technology is shown in the form of a table. • The application fields of OAM beams are summarized, and the development trend and potential of their applications are pointed out. • This article will be helpful to provide reference and guidance for related experiments of OAM beams in the future. In recent years, vortex beams with orbital angular momentum (OAM) have attracted more and more attention. The wavefront of the OAM beams is helical, the intensity at the center of the beam is zero, and there is a phase singularity. Because of the novel phase characteristics of OAM beams, they have a wide application prospect in the fields of optical communication, rotating body detection and particle manipulation. Therefore, the research on the generation technology of OAM beams and their application range are of instructive significance to the future experiments. In this paper, the common beams carrying OAM are introduced, and the techniques of generating OAM beams in free space are summarized, including intracavity conversion method and extracavity conversion method. The application range of OAM beams studied at present is discussed, and the development trend of OAM beams is prospected. The purpose of this paper is to provide reference and guidance for related experiments of OAM beams in the future. [ABSTRACT FROM AUTHOR]

In a high-power Pr:YLF solid-state laser, the thermal effect of gain medium is one of the prime limiting factors, and its thermal damage has become the major concern. The thermal effect of Pr:YLF crystal was analyzed theoretically, and the distribution of temperature, thermal stress, thermal focal length, and pump polarization effects of the Pr:YLF crystal were simulated. The thermal effect investigation indicates that under reasonable pumping power density, crystal length, and beam waist size and location, the temperature rise and nonuniformity of thermal distortion are not intensified under high-power operation. Additionally, the relationship between Gauss or Super-Gaussian pump mode and thermal focal length of Pr:YLF crystal was simulated. To the best of our knowledge, this analysis is the first to examine the thermal effect of Pr:YLF crystal for power scaling, and this thermal effect investigation of Pr:YLF crystal provides first-hand data for a high-power, visible, solid-state laser that could be helpful for high-power Pr:YLF solid-state laser design. [ABSTRACT FROM AUTHOR]

The accurate measurement of high-power laser near-field fluence distribution leads to a correct assessment of the output beam quality. In this paper, the nearfield fluence distribution is measured by a scientific-grade CCD in a hundred-Joule-level laser system. The experimental method of filtering the background noise in original near-field image is studied. Compared with the other method of filtering background noise, the experimental method is simple and accurate. Results show that this method can measure and correctly extract the image of near-field distribution in high-power lasers. [ABSTRACT FROM AUTHOR]

• The common LMA fiber amplifier achieving peak power above 0.2 MW with ps pulses. • The maximum pulse energy of 12.36 μJ was achieved. • Output pulse spectra and temporal trace was simulated and agree with experiment. We demonstrated the generation of narrow spectral bandwidth, high energy picosecond pulses from a low repetition rate SESAM mode-locked laser seeded Yb-doped fiber MOPA system. A short large mode field diameter gain fiber (DCF-30/250) was adopted to efficiently reduce the influence of nonlinear effects. The maximum pulse energy of 12.36 μJ, ∼60 ps pulses with a narrow bandwidth was obtained at a repetition rate of 5 MHz, corresponding to the peak power of 0.2 MW and average output power of 64 W. The optical-to-optical conversion efficiency was ∼64% in such a low repetition rate all-fiber laser design. The output pulse spectra and temporal trace of the MOPA system for different output powers was investigated by simulation. The simulation results were in agreement with experiment but further showed that the spectral splitting would occur as output power increased. [ABSTRACT FROM AUTHOR]

• We reviewed the research progress of NL-MMI mode-locking technology based on multimode fibers. • We gave the theoretical principle of NL-MMI, and the working principles of various SAs based on GIMFs are introduced. • The soliton molecules, noise-like pulse or multi-wavelength operation in NL-MMI mode-locked fiber lasers are discussed. • The present limitation and solutions of using GIMF as the SA are analysized. We review the research status of the mechanism and technology of all-fiber mode-locked ultrafast laser with multimode fiber based saturable absorber. Using novel all-fiber structured mode-locking modulation device with high damage threshold, the single pulse energy and pulse width of conventional soliton can up to the order of nJ and fs in 1 μm, 1.5 μm, 2 μm, switchable and tunable dual or multi-wavelength mode-locked operation can be realized. At the same time, fascinating nonlinear optical phenomena such as soliton molecules and noise-like pulses were achieved, which provided an excellent platform for the study of nonlinear optics. Thus, using the multimode fiber as an all-fiber nonlinear saturable absorber has important research significance and wide application, which further promotes the development of ultrafast laser technology and nonlinear optics. [ABSTRACT FROM AUTHOR]

• SESAM mode-locked fiber laser achieving repetition rate about 1 MHz with ps pulses. • Pulses stretches from 33 ps to 102 ps employing different FBGs. • Pulse dynamics and behavior with low repetition rates are discussed. • The effect of gain on pulse evolution at different repetition rates was simulated. We demonstrated a SESAM mode-locked Yb-doped fiber laser with pulse duration of 57 ps, bandwidth of 41 pm at repetition rate of 1.04 MHz. In addition, we numerically investigated the effect of the gain on pulse evolution of passively mode-locked fiber laser at different repetition rates. Experimentally, pulses stretches from 33 ps to 102 ps and linewidth ranges from 60 pm to 25 pm employing different bandwidth-limited FBGs under different repetition rates. The experiment results were nearly in agreement with simulation but further showed the pulse formation and evolution related to the decreasing repetition rate. [ABSTRACT FROM AUTHOR]

• We reviewed the research progress of 589 nm sodium-guided star lasers. • We gave the comparison between different 589 nm laser techniques. • We emphasized the key technical innovation points for 589 nm lasers. • The limitations on 589 nm laser output performances were comment. In recent years, 589 nm lasers have attracted much attention in the fields of laser sodium guide star, laser radar, and adaptive optics. Therefore, the sodium guide star technology at 589 nm has been particularly topical. The sodium guide star technology requires that the average power should be Watt-level for the continuous-wave yellow laser which having narrow-linewidth and are capable of being tuned to match transition lines accurately. According to the generation method, the sodium guided star laser can be divided into four types: dye lasers, solid-state lasers, optically pumped semiconductor lasers, and fiber lasers. Solid-state laser includes sum-frequency generation, stimulated Raman scattering and optical parametric amplifier. Among them, sum-frequency generation lasers are used mostly. The development history and state of the art of them are expatiated, which is useful reference for the future research in this field. [ABSTRACT FROM AUTHOR]

In recent years, the quasi-2D perovskite material ((PEA) 2 (CsPbBr3) n -1 PbBr 4 ) has exhibited outstanding optoelectronic performance and environmental stability due to its unique structure, presenting a broad range of potential applications. However, structural differences arising from varying values of " n " result in distinct nonlinear effects in perovskite materials, which have not been thoroughly investigated to date. We conducted a comparative analysis of the mode-locked characteristics of 2D and n = 3, 4, 5, and 6 quasi-2D perovskite materials within an Erbium-doped fiber laser (EDFL). All materials exhibited excellent saturable absorption effects. Besides, the superior performance of the n = 5 quasi-2D perovskite material, with an SNR of 72.59 dB, performed best in terms of the average power and single pulse energy. The five-layer quasi-2D perovskites offer a suitable bandgap, exciton binding energy, and moderate quantum confinement, leading to effective laser operation. Additionally, the optimal nonlinear absorption, refractive index, and thermal stability contribute to stable and high-power laser performance, while suppressing surface states and interface effects. Experimental results indicate that quasi-2D perovskite materials hold significant potential for applications in the realm of ultrafast optics.

The near flat-top Gaussian beam, which finds significant applications in energy amplification, laser processing, nonlinear frequency transformation, and atmospheric turbulence studies, has received limited attention regarding its transverse mode field distribution characteristics during spatial transmission and amplification. In this study, we simulated the spatial transmission and amplification processes of the near flat-top Gaussian beam using the Collins diffraction equation and a traditional side-pumping gain model. To validate our simulations, we conducted experiments employing a gradual soft-edged aperture to produce a near flat-top Gaussian beam. Our findings revealed that during free transmission, the near flat-top Gaussian beam evolved into a Gaussian-like beam, and a secondary peak emerged when amplified by a conventional laser diode side-pumping amplifier. These results underscored the necessity of using an image transfer system to maintain the energy uniformity of the near flat-top Gaussian beam during amplification. Furthermore, we identified the optimal shaping parameter of the Gaussian beam with a soft-edged aperture to be approximately 2.3. By utilizing an image transfer system and a two-stage amplifier, we successfully amplified the beam energy post-shaping. Ultimately, we achieved a near flat-top Gaussian beam with an energy of 219.5 mJ and an energy root-mean-square (RMS) normalized deviation of 0.144, compared to the initial Gaussian beam, which had an energy of 52.3 mJ and an energy RMS normalized deviation of 1.434.

In September 2022, rice spikelets rot disease (RSRD) was investigated in Songjiang District (30.94132N, 121.18393E), China, leading to a 26.77% yield loss. At the heading stage, infected spikelets exhibited small, yellowish-brown dots with water-stained husks, subsequently coalescing to form irregular brown to black lesions. Later, the lesions were enlarged and rotted, which eventually caused blighted grains. About 10% of husked grains showed black spots. 30 infected grains and 30 husked grains with black spots were surface sterilized in 75% ethanol for 2 min, then rinsed with ddH 2 O and plated on PDA medium at 28°C in darkness for 4 d. 22 and 13 fungal isolates with similar morphology were obtained in shriveled and husked grains, respectively. Three isolates (SJTU1, SJTU2 and SJTU3) were selected by the single-spore isolation method. The colonies were brown to blackish green, smooth, and contained a large number of stolons with a few aerial mycelia in the center. Hyphae and conidiophores were blackish green, thick-walled, branched with septa. Conidia were 14.77 to 26.82×4.74 to 11.36 μm (average 20.42×8.58 μm, n= 100) in size, lightly curved with blackish green. Conidia with three septa and four cells, apical and basal cells transparent, middle cell unequal in size. Based on morphological characteristics, the isolates were preliminarily identified as Curvularia plantarum (Raza et al. 2019). The genomic DNA of the three isolates (SJTU1 to 3) was extracted for molecular identification. 3 pairs of primers ITS1/TTS4 (Peever et al. 2004), gpd1/gpd2 (Berbee et al. 1999), and EF-983F/EF-2218R (Rehner and Buckley 2005) were used to amplify ITS, GAPDH, and EF1-α genes, respectively. These sequences were all uploaded in GenBank (ITS: OR726053 to 55; EF1-α: OR732471 to 73; GAPDH: OR732474 to 76). According to data in GenBank, the ITS, EF1-α, and GAPDH genes of 3 isolates (SJTU1 to 3) showed 99-100% identity (573/575 bp, 542/543 bp, and 531/531 bp) to the ITS (MW581905, MN044755, and MN215690), 99-100% identity (869/869 bp, 868/869 bp, and 855/856 bp) to the EF1-α (MN263982 to 83, and MT628901), and 99-100% identity (543/544 bp, 528/528 bp, and 540/540 bp) to the GAPDH (MT628902, MN264120, and MT432926) gene of C. plantarum , respectively. The phylogenetic analysis by Maximum Likelihood (ML) method based on the concatenated sequences of ITS, EF1-α, and GAPDH genes showed that the three isolates (SJTU1 to 3) clustered with C. plantarum . According to morphology and molecular identification, these fungal isolates were identified as C. plantarum . Pathogenicity tests were conducted in the field used only for inoculation with pathogens by spraying 30 spikelets of rice cultivar 'Song1013' at the heading stage with conidial suspension (5 × 10 5 conidia/mL). 30 spikelets sprayed with ddH 2 O were designated as control. The test was conducted 3 times at 22 to 31°C with 78 to 89% RH. All the inoculated spikelets exhibited similar symptoms to those of the infected spikelets in paddy at 10 d after spraying, while the control spikelets remained healthy. All reisolated strains from infected spikelets were identified the same as the original inoculated strains by morphology and ITS sequences, fulfilling Koch's postulates. To our knowledge, this is the first report of C. plantarum causing RSRD in China. The discovery of this new disease and its pathogens will facilitate the provision of pathogenically relevant information vital for management strategies to RSRD caused by C. plantarum in the future.

High-frequency, high-power picosecond lasers have important and wide-ranging applications in laser ranging, optoelectronic countermeasures, and ultrafine industrial processing. Pulse compression based on stimulated Brillouin scattering (SBS) can achieve a highly efficient picosecond laser output, while improving the peak power and beam quality of the laser. In this paper, a generator-amplifier two-cell structure with frequency-detuning was proposed to achieve a pulse output that combines high compression ratio and high energy reflectivity. The experiment proved that under a pump pulse width of 15 ns and repetition frequency of 10 Hz, when the generator cell and amplifier cell media were selected as HT-230, the highest energy reflectivity of 46% and narrowest compression pulse width of 1.1 ns were achieved, and the pulse compression ratio was 13.6. When the amplifier cell was selected as FC-770 and the generator cell was selected as HT-230, an energy reflectivity of 52% and a compression pulse width of 840 ps could be achieved simultaneously, and the pulse compression ratio was 18.

Analyzing the longitudinal-mode of a pump can significantly prevent optical damage to solid media and expand the applications of solid media in high repetition rate stimulated Brillouin scattering (SBS). In this study, a Fabry-Pérot etalon was used to control the number of longitudinal-mode in a pump laser output. We studied the output characteristics of SBS in fused silica by considering both single- and multi-longitudinal-mode pumping. We analyzed and compared variations in the SBS threshold, energy reflectivity, linewidth, and waveform characteristics. The experimental results indicated that a pump operating in a single-longitudinal-mode had a 14% lower SBS threshold than one operating in a multi-longitudinal-mode. The proportion of the weak longitudinal-mode in the multi-longitudinal-mode was close to the threshold difference. The damage threshold of the multi-longitudinal-mode pumps was approximately 35 mJ (@12 ns, f = 300 mm). The Stokes linewidth and waveform exhibited opposite trends as the energy changed. Due to the time-bandwidth product, the linewidth and waveform tended to converge towards the pump. This study emphasizes the importance of using a single-longitudinal-mode pump in the development and use of solid-state SBS gain media.

Rice false smut, caused by Ustilaginoidea virens , has become one of the most devastating grain diseases of rice worldwide. Understanding the genetic diversity of U. virens is essential for efficient disease control and breeding for disease resistance. However, little is known about the genetic variation of U. virens from different rice cultivars. We investigated the genetic diversity and pathogenic variation of U. virens isolates from 10 rice cultivars in Zhejiang, China. A total of 260 polymorphic loci and 27 haplotypes were identified based on the 2,137-bp combined DNA fragments of all individuals; hap_4 was the most common haplotype, represented by 41 isolates. Phylogeny indicated that all isolates were divided into four genetic groups. Group I was the largest, with 98 isolates, distributed mainly in eight cultivar populations, whereas 90% of the isolates collected from a Changxiang cultivar were clustered in Group IV. Furthermore, the pairwise F ST values exhibited significant genetic differentiation in 27 of the pairwise comparisons between populations, accounting for 23.21% of the total genetic variation. The genetic composition of the isolates of the CX population was distinguishable from that of the other nine populations, and genetic recombination was found in a few isolates. Finally, 27 haplotype representative isolates showed high variation in pathogenicity, and the isolates from the genetic subpopulation I were likely to be more virulent than those from genetic subpopulations II and III. Collectively, these findings suggest that differences in rice cultivars play an important role in the genetic variation of U. virens .