Laser Performance Research Articles

Buried depressed cladding waveguides in neodymium-doped yttrium aluminate crystals fabricated by femtosecond laser writing: Raman properties and laser performance

Buried depressed cladding waveguides in neodymium-doped yttrium aluminate crystals fabricated by femtosecond laser writing: Raman properties and laser performance

Prediction of laser beam spatial profiles in a high-energy laser facility by use of deep learning

We adapt the significant advances achieved recently in the field of generative artificial intelligence/machine-learning to laser performance modeling in multipass, high-energy laser systems with application to high-shot-rate facilities relevant to inertial fusion energy. Advantages of neural-network architectures include rapid prediction capability, data-driven processing, and the possibility to implement such architectures within future low-latency, low-power consumption photonic networks. Four models were investigated that differed in their generator loss functions and utilized the U-Net encoder/decoder architecture with either a reconstruction loss alone or combined with an adversarial network loss. We achieved inference times of 1.3 ms for a 256 × 256 pixel near-field beam with errors in predicted energy of the order of 1% over most of the energy range. It is shown that prediction errors are significantly reduced by ensemble averaging the models with different weight initializations. These results suggest that including the temporal dimension in such models may provide accurate, real-time spatiotemporal predictions of laser performance in high-shot-rate laser systems.

Performance Prediction of High-Entropy Perovskites La0.8Sr0.2MnxCoyFezO3 with Automated High-Throughput Characterization of Combinatorial Libraries and Machine Learning.

Perovskite oxides form a large family of materials with applications across various fields, owing to their structural and chemical flexibility. Efficient exploration of this extensive compositional space is now achievable through automated high-throughput experimentation combined with machine learning. In this study, we investigate the composition-structure-performance relationships of high-entropy La0.8Sr0.2MnxCoyFezO3±𝞭 perovskite oxides (0 < x, y, z <1; x+y+z≈1) for application as oxygen electrodes in Solid Oxide Cells. Following the deposition of a continuous compositional map using thin-film combinatorial pulsed laser deposition, compositional, structural, and performance properties are characterized using six different techniques with mapping capabilities. Random forests effectively model electrochemical performance, consistently identifying Fe-rich oxides as optimal compounds with the lowest area-specific resistance values for oxygen electrodes at 700 °C. Additionally, the models identify a statistical correlation between oxygen sublattice distortion-derived from spectral analysis of Raman-active modes-and enhanced performance.

Ultrafast Polarization‐Maintaining Fiber Lasers: Design, Fabrication, Performance, and Applications

AbstractUltrafast polarization‐maintaining fiber lasers (UPMFLs), with superior optical performance and high immunity to environmental disturbances, are highly preferable in a variety of industrial and scientific applications such as high‐precision micromachining and biomedical imaging. Especially, the utilization of PM fibers endows the laser intrinsic stability, thereby enabling the construction of robust and low‐noise optical frequency comb systems. To meet more demanding application challenges, continuous efforts have been invested in the design and fabrication of UPMFLs, aiming to reach unprecedented levels of various pulse parameters, that is, to achieve shorter pulse duration, higher or lower repetition rate, and higher pulse energy. This review presents a detailed overview of different passive mode‐locking techniques for pulsed operation and the most significant achievements in UPMFLs. Representative advances at 1.0, 1.55, and 2.0 µm spectral regions are presented and summarized. The state‐of‐the‐art lasing performance is application‐oriented, and conversely, optical improvements in all‐PM pulsed lasers promote emerging applications, which are also discussed and analyzed. How to overcome the bottlenecks of UPMFLs in terms of pulse duration, repetition rate, emission wavelength, and pulse energy to make them powerful tools for physical, medical, and biological applications remains challenging in the future.

Effects of defects on the high-temperature performance of selective laser melting K418 superalloys: An in-situ 3D X-ray analysis

Defects are inevitable in selective laser melting process, significantly impacting the mechanical properties of materials and reducing their service life. In this study, the effects of various defects and their distribution on the high-temperature mechanical performance of the selective laser melted K418 superalloys were investigated via an in-situ 3D X-ray analysis and finite element method. The results showed that the selective laser melting process can significantly enhance the strength of the K418 sample, while degrading the fracture elongation. The sphericity and location of defects are the two key parameters influencing the mechanical performance. The defects with low sphericity at the sub-surface resulted in elevated local stress and strain, accounting for the significant degradation in fracture elongation. Locally increased stress and accumulated strain around lack of fusion defects at the sub-surface contribute to the initiation and propagation of crack. This study provides inspiration for understanding the correlation between the defects and mechanical properties.

Investigation on high-temperature tribological performance of laser directed energy deposited Inconel 625 for aerospace applications

Laser directed energy deposition (LDED) is an emerging technique for fabricating superalloy based aero engine components. Hence, the current work investigates the tribological performance of LDED processed IN625 at room temperature (RT) and high temperature (HT) conditions of 850 °C to replicate the operating environment of aero engine components. The comparison with conventionally processed (CP) sample confirmed that as-deposited (AD) sample showed similar friction behavior to the CP sample but slightly improved wear performance. The COF and wear rate of AD sample reduced significantly at HT compared to RT due to the evolution of stable oxide layer. NiO, Fe2O3, and Cr2O3 were the major phases in oxide layer. The work indicates suitability of LDED to fabricate wear resistant surfaces.

Enhancing yellow-green emission in Eu/Tb co-doped tellurite glasses controlled by Lu2O3

In this research, Lu2O3 was incorporated into Eu3+ and Tb3+ co-doped tellurite glasses to enhance structural stability and modify the yellow-green emission. A series of microstructural analyses, including Differential Scanning Calorimetry (DSC), Raman spectroscopy, and density measurements, confirmed that the addition of Lu2O3 causes the long-chain or cyclic Te-O-Te network structure to break, resulting in the formation of more [TeO3], which in turn leads to an increase in non-bridging oxygens (NBO) and lowers the phonon energy of the matrix material. Fluorescence spectral characterization revealed that both green and yellow luminescence intensities peaked when Lu2O3 concentration reached 15 %. Additionally, the Judd-Ofelt theory supports its superior laser performance. With the addition of Lu2O3,The radiative transition probability (Arad), lifetime (τrad), and branching ratio (β) of the excited states of Tb3+ and Eu3+ have all been enhanced.Under the regulation of 15% Lu2O3, The maximum absorption cross-section of at 544 nm is 1.88×10-20 cm2, and the maximum emission cross-section is 2.14×10-20 cm2. At 611 nm, the maximum absorption cross-section is 1.05×10-20 cm2, and the maximum emission cross-section is 1.44×10-20 cm2. The decay curve indicates a fluorescence lifetime enhancement from 0.6 ms to 1 ms with Lu2O3. These results underscore the potential of Lu2O3 modulated Eu3+/Tb3+ co-doped tellurium glass as an effective yellow-green laser gain medium.

Enhanced optical properties and laser performance of Yb:LuScO3 transparent ceramics fabricated with ZrO(NO3)2

This work aims to fabricate the Yb:LuScO3 sesquioxides transparent ceramics for use in ultrafast and ultrashort laser technology. 1 at.% Yb:LuScO3 nanopowders were fabricated using the glycine-nitrate process. ZrO(NO3)2 was selected as the precursor of ZrO2 which functions as a sintering aid. Yb:LuScO3 transparent ceramics with different ZrO2 content were fabricated by vacuum sintering at 1780°C and HIPing at 1650°C, among which the ceramic with 7 at.% ZrO2 showed the highest transmittance, reaching 81% at 2000 nm. The ceramic achieved a maximum output power of 1.5 W at 1038 nm with a slope efficiency of 34.8% and tunable wavelength range exceeding 22 nm. The results demonstrated that Yb:LuScO3 transparent ceramics can be considered as promising materials in 1 μm solid-state laser applications.

Optimizing Diode Laser Performance: Effective Noise Reduction in a Three-Dimension Printing Machine

Optimizing Diode Laser Performance: Effective Noise Reduction in a Three-Dimension Printing Machine

Effect of Ce co-doping on radiation resistance behavior and laser performance of Er/Yb/Ce co-doped high-phosphorous polarization-maintaining silica fiber

Er/Yb/Ce co-doped high-phosphorus silica fiber core glasses with varying Ce2O3 concentrations were prepared and systematically studied. Based on this research, optimized Er/Yb/Ce co-doped high-phosphorus polarization-maintaining silica fibers were subsequently fabricated using the modified chemical vapor deposition (MCVD) technique and hole drilling method. The study confirmed that there is an optimal range of Ce doping concentrations for spectral performance, Ce doping effectively suppressing the formation of P-related defects during X-ray irradiation, and the dynamic valence state transformation of Ce3+/Ce4+ ions during irradiation enhanced the radiation-resistant properties, as demonstrated through radiation-induced absorption (RIA), electron paramagnetic resonance (EPR), and L3-edge X-ray absorption near edge structure (XANES) spectra. The homemade fiber, with optimized element concentrations, exhibited high laser efficiency comparable to commercial high-power fibers. Furthermore, the radiation-induced background loss of the fiber was 0.16 dB/m under 60 krad γ-rays at a low dose rate of 100 rad/h, and the radiation-induced gain variation (RIGV) was 0.019 dB/krad.

Effect of polydimethylsiloxane content on the electrothermal performance and tensile strength of laser induced graphene films: Experimental and theoretical

BackgroundSince its discovery in 2014, laser induced graphene (LIG) has gained a lot of interest from research institutions and the industry as a result of its single-step fabrication process and tailorable properties. Nonetheless, LIG's brittle nature makes it susceptible to any mechanical disturbances thus shearing off from the polyimide (PI) sheet surface. This limits its applicability in electrothermal heating and other applications requiring high flexibility. Therefore, there is a need to enhance LIG's robustness on the precursor surface. MethodsTo overcome this, LIG films were fabricated from PI using a 10.6 µm CO2 laser machine and polydimethylsiloxane (PDMS) contents were infused into the LIG structure by spin coating to form LIG/PDMS films. Furthermore, the adhesion strength of LIG/PDMS films was further improved by making micro scratches on the substrate surface by pressing the PI sheets in between the jaws of a Universal Testing Machine (UTM). The joule heating of LIG and LIG/PDMS heaters was evaluated before, during, and after mechanical testing. Theoretical models (heat balance and Ansys Finite Element, FE) were also performed to validate experimental results. Significant findingsAt an input DC voltage of 8 V, the LIG/PDMS with 50 μL PDMS and LIG heaters generated saturation temperatures of 250 and 308.86 °C, respectively. Much as the saturation temperatures were lower for LIG/PDMS heaters, their mechanical strength was enhanced in comparison with the LIG heaters. LIG/PDMS films could undergo more bending cycles (4800) than LIG films (2400). Additionally, LIG/PDMS film accommodated more stress (⁓ 0.16 Mpa) than LIG film (⁓ 0.04 Mpa) after tensile tests. Interestingly, the LIG/PDMS heater's electrothermal performance was better than that of LIG heater after tension. The heat balance equation and simulation results showed a tight match with experimental generated temperatures, verifying the approach's trustworthiness. Hence, the demonstrated effectiveness and efficiency of LIG-based heaters with high flexibility under various mechanical stresses open new possibilities for diverse electronic applications.

Low-threshold CW eye-safe vortex generation from an intracavity pump-wave off-axis pumped OPO.

A low-threshold efficient setup for CW wavelength versatile vortex generation is proposed. The intracavity optical parametric oscillator is utilized for low-threshold operation. By using the pump-wave off-axis pumping for the signal-wave oscillator, high-order Hermite-Gaussian modes at the eye-safe region can be obtained, which can further generate a vortex via an astigmatism mode converter. The overall laser performance is additionally verified to be better by comparing it with the diode off-axis pumping method where the TEM1,0 pump wave was generated first for the signal-wave TEM1,0 mode oscillation. This method is expected to be further applied for more complicated structured light generation.

Self-frequency-doubling Yb:GdCOB laser intracavity-pumped Pr:YAP laser

Abstract We present for the first time a Pr:YAlO3 (Pr:YAP) laser emitting at 547 nm intracavity-pumped by a self-frequency-doubling Yb3+:Ca4GdO (BO3)3 (Yb:GdCOB) blue laser at 488 nm. We carried out a model to design the system properly, and the laser performance was experimentally investigated. Intracavity sum-frequency mixing at 547 and 488 nm was then realized in a CsLiB6O10 (CLBO) nonlinear crystal to reach the ultraviolet laser at 258 nm. We obtained a continuous wave output power of 575 mW at 258 nm with a pump source, which is a diode-pumped quasi-three-level Sr1-x La x -y Nd y Mg x Al12-x O19 (Nd:ASL) laser emitting 11.2 W at 902 nm.

Enhanced performance of GaN based VCSELs through graded electron-blocking layer design

Electron leakage from the active region to the p-type region restricts the performance of GaN-based Vertical-Cavity Surface-Emitting Lasers (VCSELs). AlGaN EBL can decrease the leakage current, but also raises the hole injection barrier and reduce the hole injection efficiency. Then, it is important to design EBL structures that can enhance both electron blocking and hole injection. In this study, VCSEL devices with three different EBL, basic structure Al0.6Ga0.4N EBL labeled as Device A, newly proposed 16 nm thick Al0.75–0.80Ga0.25–0.20N EBL labeled as Device B, and 18 nm thick Al0.75–0.80Ga0.25–0.20N EBL labeled as Device C, respectively, are designed and analyzed using PICS 3D simulation. Device A represents a basic VCSEL structure, while Device C incorporates a graded electron-blocking layer (EBL) with adjusted thickness. Through simulation results, it is observed that the introduction of a graded EBL in Device C leads to significant performance enhancements compared to the basic structure of Device A. Specifically, the graded EBL effectively reduces band bending and increases the electron barrier height, thereby improving carrier confinement and reducing electron leakage. Additionally, the utilize of a Graded structure in Device C aids in strain relief at the layout between the QB and EBL, resulting in improved electron-blocking capability and potentially enhanced hole transport characteristics. These findings underscore the importance of EBL grading in optimizing the performance of VCSELs, highlighting its potential for advancing the efficiency and functionality of these semiconductor devices. Power of the device C is being improved upto 4.16%, similarly the conduction band barrier height is improved upto 26.6% which is beneficial for better VCSEL performance as it enhances electron confinement in the active region, leading to increased efficiency and reduced carrier leakage and valance band barrier height decreases upto 6.52% and threshold current is decreased upto 4.8% so if valence band barrier height decrease the hole injection efficiency increases and if threshold current decreases the emitting power of the device increase.

Evaluating Nd3+:Na4Y6F22 single crystals as a promising active medium for diode-pumped lasers

The optical and spectroscopic properties and laser performances of Nd3+:Na4Y6F22 fluoride single crystals were systematically examined. The quasi-CW laser action in Nd3+:Na4Y6F22 disordered crystals was realized for the first time under 796 nm-diode pumping. The slope efficiency was 5.8 % with a lasing threshold approximately 19 mW in terms of absorbed pumping power. The reasons for the discrepancy between the promising spectral-kinetic characteristics and pure lasing efficiency under diode pumping were elucidated.

Anisotropic Laser Performance in an Optically Isotropic Crystal by Phonon Engineering

Symmetry is an eternal motif in understanding the characteristics of nearly all the laws and courses of science. The symmetry‐breaking in the optical crystal will generate a rich variety of unprecedented physical phenomena and create new functional properties. Herein, the symmetry‐breaking in a photon–phonon collaboratively pumped laser, dominated by the anisotropic lattice vibrations is investigated. Using an optically isotropic Nd:YAG crystal as an example, the phonon‐assisted electronic transitions accompanied by anisotropic fluorescence emission are observed, beyond the intrinsic structural symmetry ruled by Neumann's principle. For the first time, the phonon‐assisted new‐wavelength lasers at 1151 and 1166 nm are achieved in Nd:YAG with divergent light polarization, determined by the vibrational direction of involved phonons. These results provide a flexible degree of freedom for photonics by phonon engineering and pave the way to new frontiers in the field of laser generation and manipulation.

Yb:YSAG ceramics: An attractive thin-disk laser material alternative to a single crystal?

The 8.3 at.% Yb-doped yttrium-scandium-aluminum garnet (YSAG) ceramics were fabricated by a modified reverse co-precipitation method followed by uniaxial and cold isostatic pressing, annealing in air and high-temperature sintering in vacuum. Spectroscopic and lasing properties were investigated in dependence on Y/Sc/Al ratio in ceramic composition. Optical transmission of Yb:YSAG ceramics in visible and near-infrared spectral range exceeds 80 % that indicates a high quality of the Yb:YSAG samples. Among all the ceramics, the Y2.35Yb0.25Sc1.00Al4.40O12 composition demonstrates the best lasing performance and the highest slope efficiency up to 75 %.

Micro-welding of non-optical contact sapphire/metal using Burst femtosecond laser

Recently, welding of dissimilar material, such as transparent material to metal material, is widely used in aerospace, microelectronic packaging, medicine, etc. Ultrafast laser welding provides a new method for high-performance dissimilar material welding, in which the non-optical contact dissimilar material welding has become a new research hot spot. In this paper, we report the effective welding of Fe-36Ni with roughness as high as 1.1 µm to sapphire, which, to our knowledge, is the roughest dissimilar material welding achieved in ultrafast laser. A 238 fs, 1035 nm, 200 kHz Burst mode femtosecond laser (4 sub-pulses with a total energy of 132.5μJ) yields a smooth and uniform interface with a welding strength up to 11 MPa. In this context, the welding performance and mechanism of Burst mode and single pulse mode ultrafast laser are systematically analyzed. The relevant research results are expected to provide theoretical guidance for the welding of high-strength and high-stability dissimilar materials.

High power continuous-wave, Q-switched, and quasi-continuous-wave operation of a diode-pumped Tm,Ho:YAG laser oscillator at 2.09 μm

A high-power diode-pumped 2.09 μm Tm,Ho:YAG laser oscillator with multi-regime operation is demonstrated. In the continuous-wave (CW) regime, it delivers 44.68 W output power with M2 = 3.47, yielding a record-high brightness of 87.57 MW/cm2·sr. In the Q-switched mode, stable laser performance across pulse repetition frequencies (PRFs) from 1 kHz to 4 kHz is achieved. At a PRF of 1 kHz, single pulse energy reaches 22.85 mJ with a pulse width of 443.4 ns and M2 = 3.50. In the quasi-continuous-wave (QCW) operation, a pulse energy of 31.85 mJ is obtained at 200 Hz with a 370 μs pulse width and M2 = 4.49. These pulse energies are the highest reported to date for Tm-Ho co-doped laser oscillators at high PRF. This also marks the first demonstration of a versatile 2 μm laser that can operate at room temperature while delivering high-energy, high-repetition-rate pulses in both nanosecond and microsecond durations within a single device, making it highly appealing for scientific and industrial applications.

Stable random laser of perovskite quantum dots based on SiO2-QDs-SiO2 composite nanostructure

In recent years, metal halide perovskite has gradually become a hotspot in the field of optoelectronics. However, the inherent instability of CsPbX3 quantum dots (QDs) seriously affects the amplified spontaneous emission (ASE) or lasing performance. Herein, the highly stable CsPbBr3 random laser is realized in SiO2-QDs-SiO2 (SQS) composite nanostructure doped with Ag nanoislands. The strong scattering generated by SQS composite nanostructure and the localized surface plasmon resonance (LSPR) of metal silver nanoislands provide optical feedback for the formation of random laser. Then a coherent random laser with low threshold (∼2.2 mJ/cm2) is obtained. SiO2 microspheres anchor QDs to avoid photoinduced regeneration and fluorescence quenching caused by QDs clusters. The inner QDs of SQS are effectively protected from water erosion, thus resulting that the samples have higher water resistance. The luminescence intensity still maintains 70 % of the original intensity after 40 days with the addition of pure water. Our research provides an effective method for improving the water stability of perovskite QDs. The highly stable random laser based on perovskite quantum dot film has a wide application prospect in integrated optoelectronics, display imaging and sensing measurement.