Combined Beam Research Articles

Twenty kilowatts level high beam quality spectral beam combination by dual gratings with distinct groove densities based on conical diffraction structures

We establish a spectral beam combing structure with two distinct diffraction gratings. A theoretical analysis of the beam quality degradation of this beam combining system is given. A six-channel spectral beam combining experiment is constructed based on conical diffraction structure by transmission and reflection gratings. Over 19 kW combined power is achieved with a combining efficiency of about 92%. The six incident fiber amplifiers, ranging from 1040 nm to 1082 nm, can each deliver a 3.5 kW output power laser with about 60 GHz 3 dB linewidth. Both transmission and reflection diffraction gratings, with different grating periods (1000lines/mm, 1170lines/mm), are employed in this work. The combined beam quality factor is controlled to be M2∼2 by effective dispersion compensation. To the best of our knowledge, this is the first time to demonstrate a high power beam combination by two gratings with different types and periods, which verifies the dispersion capability of this structure and provides an alternative approach for high power beam combining.

Real-time fully digital control scheme for pulse coherent beam combining.

A fully digital control scheme for non-polarization-maintaining (non-PM) nanosecond pulse coherent beam combining (CBC) is proposed, where digital locking of optical coherence by single-detector electronic-frequency tagging (LOCSET) for active phase control and stochastic parallel gradient descent (SPGD) for active polarization control is proposed. The fully digital control scheme is integrated on a real-time field-programmable gate array (FPGA) empowered hardware platform and then experimentally validated in a four-channel all-fiber non-fully polarization-maintaining nanosecond pulse CBC system. Consequently, the system can be fully locked in 9.5 ms, and the polarization extinction ratio (PER) of the combined beam is 21.5 dB with a CBC efficiency of 95.3%. The fully digital control scheme integrates the advantages of digital LOCSET and multi-channel active polarization control, enhancing the channel scalability and the potential output power of the non-PM pulse CBC system.

Theoretical Analysis on Active Polarization Control of Fiber Laser Based on Root Mean Square Propagation Algorithm

High-power linearly polarized fiber lasers are widely used in coherent beam combination, nonlinear frequency conversion, and gravitational wave detection. With the increase in output power, it is challenging for fiber lasers to maintain a high polarization extinction ratio (PER). Combined with intelligent techniques, active polarization control is a prospective method to obtain the laser output with high PER and high stability. We demonstrate a comprehensive model of an active polarization control system. The root mean square propagation (RMS-Prop) algorithm is used to control the non-polarization-maintaining (non-PM) fiber laser to generate linearly polarized laser. The parameters of the RMS-Prop algorithm are theoretically analyzed, including cost function, perturbation amplitude, and global learning rate. The simulation results show that PER is the optimal cost function. When the perturbation amplitude is 0.06 and the global learning rate is 0.6, the system can achieve the optimal control speed and accuracy. By comparison with the stochastic parallel gradient descent (SPGD) algorithm, the RMS-Prop algorithm has an advantage in obtaining higher PER.

Study on Fractal Damage of Concrete Cracks Based on U-Net

The damage degree of a reinforced concrete structure is closely related to the generation and expansion of cracks. However, the traditional damage assessment methods of reinforced concrete structures have defects, including low efficiency of crack detection, low accuracy of crack extraction, and dependence on the experience of inspectors to evaluate the damage of structures. Because of the above problems, this paper proposes a damage assessment method for concrete members combining the U-Net convolutional neural network and crack fractal features. Firstly, the collected test crack images are input into U-Net for segmenting and extracting the output cracks. The damage to the concrete structure is then classified into four empirical levels according to the damage index (DI). Subsequently, a linear regression equation is constructed between the fractal dimension (D) of the cracks and the damage index (DI) of the reinforced concrete members. The damage assessment is then performed by predicting the damage index using linear regression. The method was subsequently employed to predict the damage level of a reinforced concrete shear wall–beam combination specimen, which was then compared with the actual damage level. The results demonstrate that the damage assessment method for concrete members proposed in this study is capable of effectively identifying the damage degree of the concrete members, indicating that the method is both robust and generalizable.

Efficient Isolation of Cellulose Nanocrystals from Seaweed Waste via a Radiation Process and Their Conversion to Porous Nanocarbon for Energy Storage System.

This article presents an efficient method for isolating cellulose nanocrystals (CNcs) from seaweed waste using a combination of electron beam (E-beam) irradiation and acid hydrolysis. This approach not only reduces the chemical consumption and processing time, but also improves the crystallinity and yield of the CNcs. The isolated CNcs were then thermally annealed at 800 and 1000 °C to produce porous nanocarbon materials, which were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy to assess their structural and chemical properties. Electrochemical testing of electrical double-layer capacitors demonstrated that nanocarbon materials derived from seaweed waste-derived CNcs annealed at 1000 exhibited superior capacitance and stability. This performance is attributed to the formation of a highly ordered graphitic structure with a mesoporous architecture, which facilitates efficient ion transport and enhanced electrolyte accessibility. These findings underscore the potential of seaweed waste-derived nanocarbon as a sustainable and high-performance material for energy storage applications, offering a promising alternative to conventional carbon sources.

Dual-module combination with littman crosstalk external cavity for narrow-linewidth blue diode laser

The dense spectral beam combination is vital for achieving high power and brightness output in diode lasers. High-power narrow-linewidth laser modules have been widely studied as the fundamental units. This study presents a dual-module shared external cavity linewidth compression structure with a transmission diffraction grating. With a driving current of 2.4 A and a cooling temperature of 20 °C, the blue diode laser’s external cavity achieved an output power of 49.8 W, a spectral linewidth of 0.321 nm, and a tuning range of 0.817 nm, with an external cavity spectrum locked efficiency of approximately 80.6 %. Additionally, it is observed that crosstalk has a significant influence on the linewidth of the two modules. When one module current locked at 2.4 A and the other increased from 0 A to 2.4 A, the linewidth was reduced from 0.377 nm to 0.321 nm, and linewidth locking was implemented over an output power range from 27 W to 49.8 W. This work reports the highest output power for a blue diode narrow-linewidth external cavity laser.

Strong–strong simulations of combined beam–beam and wakefield effects in the Electron–Ion-Collider

Collective wakefield and beam–beam effects play an important role in accelerator design and operation. These effects can cause beam instability, emittance growth, and luminosity degradation, and warrant careful study during accelerator design. In this paper, we studied the combined wakefield and beam–beam effects in an Electron Ion Collider design using strong–strong simulations. The simulation results show that the nonlinear beam–beam effects help suppress wakefield driven instability in the nominal working tune regime. In other tune regimes, the coherent beam–beam modes interact with the wakefields and cause a beam instability. The simulation results also show the importance of maintaining nominal crab cavity voltage. If the crab cavity voltage drops significantly the beam can become unstable.

Surface treatment of metal by combined particle beam

This work is related to modeling of metal surface modification process by combined particles beam. On the basis of thermodynamics of irreversible processes, including equations of state in differential form, a nonlinear model is formulated. The model takes into account the interaction of thermal, diffusion and mechanical waves and finiteness of relaxation times of thermal and diffusion processes. For the combined particle flow such model is proposed for the first time. The numerical algorithm is based on implicit difference schemes. The study of the interaction of waves of different nature is carried out on the example of a copper target treated with nickel and gold particles. It is shown that deformations take the maximal value at the left boundary, which is directly related to the presence of impurity concentration gradients. Depending on the pulse duration, the difference between the extrema on the elastic wave becomes less significant. With increasing temperature, obviously, the diffusion process accelerates. The propagation velocities of the interacting waves are different. The character of distributions of concentrations of introduced particles directly depends on the value of parameters proportional to relaxation times.

High Efficiency High Brightness Spectral Beam Combination Based on Ultra-Broad Area Laser Diode Stack

High Efficiency High Brightness Spectral Beam Combination Based on Ultra-Broad Area Laser Diode Stack

Realizing a kilowatt-level fiber amplifier with a 42 μm core diameter fiber for improved multi-mode performance towards single mode operation output through adaptive spatial mode control utilizing a 3×1 photonic lantern

The photonic lantern, a coherent beam combiner capable of controlling the phase, amplitude, and polarization of input light, has been utilized to enhance the brightness of fiber lasers by managing the output beam’s mode. In this work, a 3×1 photonic lantern-based adaptive spatial mode control system is employed to realize kilowatt-level operation in a 42 μm core fiber laser amplifier. Both simulation and experimental outcomes affirm the ability of this approach to manage modes within large-mode-area fiber laser systems through the use of 3 input arms. The experiment not only streamlines the overall system design but also has the potential to reduce production costs and complexities. Additionally, the spectrum width has been optimized to 10 GHz, striking a balance between the SBS threshold and the coherence of the photonic lantern’s input arms. By implementing this system, we have successfully achieved a stable, improved multi-mode performance towards single mode operation output of 1.08 kW, with a beam quality factor M2 of 2.20. This research furthers our understanding of how photonic lanterns can stabilize and enhance beam quality in high-power fiber lasers, paving the way for potential improvements in their performance and applications.

Monolithic linear array fiber end cap for spectral beam combination

In this study, a fusion splicing system that facilitates the splicing of a monolithic linear array fiber end cap is constructed. The fusion splicing thermal field of the end cap irradiated by a CO2 laser is theoretically simulated using the finite element method. The experimental fusion splicing temperature agrees well with the simulation results. The splicing strength, misalignment, and high-power withstanding capacity of the fusion-spliced monolithic linear 3-fiber end cap are investigated. The use of the fabricated device in a dual-grating spectral beam combination (SBC) is also demonstrated with three-channel laser beams, achieving a combined beam with near-diffraction-limited beam quality M2=1.101. It shows that the development of the monolithic linear array fiber end cap is meaningful for achieving a compact high-brightness SBC system.

High-throughput homogenization of a quasi-Gaussian ultrafast laser beam using a combined refractive beam shaper and spatial light modulator

High-throughput homogenization of a quasi-Gaussian ultrafast laser beam using a combined refractive beam shaper and spatial light modulator

High power spectral beam combining based on four long-wave infrared quantum cascade laser emitters

In this study, we experimentally investigate spectral beam combining based on four long-wave infrared quantum cascade lasers (QCLs) with three dichroic mirrors. The coating curves of the dichroic mirrors were finely designed according to the output spectrum of the four adopted QCLs, whose central wavelength locates in 7.5 μm, 8.3 μm, 9.0 μm and 10.2 μm, respectively. At room temperature the highest combined power reaches as high as 2.39 W, corresponding to a combining efficiency of 83.0 %, and meanwhile, the combined beam keeps a high beam quality with average M2 of 1.78. To the best of our knowledge, this is the highest output power among spectral beam combining for QCLs. Due to the advantage of wide spectral range, high power, high beam quality and compact size, this demonstration may meet the demands of medical diagnosis, remote sensing, free-space optical communication and military application.

High environmentally adaptable phase control with reinforcement learning for coherent beam combination

In contemporary times, the utilization of high-power lasers is progressively expanding. However, the potential of a single laser to generate power confronts inherent physical constraints, leading to limitations in its incremental power augmentation. To address this challenge, coherent beam combining technology has been introduced as a means to achieve amplified power output. In this paper, an intelligent phase control method for coherent beam combining is proposed, which introduces reinforcement learning algorithm to provide assistance for the control problem, designs algorithmic variables based on the physical model of coherent beam combining, deploys it in the environment for multiple interactions, and updates the neural network in real time using the feedback from the environment. The efficacy of the proposed algorithm is validated in a 7-channel coherent beam combining simulation system, and the experiment results show that the synthesized beam is strong and stable under the control of the algorithm, and the convergence of the algorithm as well as the control effect is discussed and validated in different environments, and its performance also exceeds that of the existing mainstream phase control algorithm SPGD.

Efficient distributed architecture and optimized subarray control strategy to facilitate large-scale coherent beam combination

Traditional coherent beam combination (CBC) system architecture has revealed inadequacies in meeting the concurrent demands of large-scale deployment and high-bandwidth requirements. Addressing this challenge, we propose a distributed CBC system architecture based on the optimized stochastic parallel gradient descent (SPGD) algorithm. Our strategy segments the large-scale laser array into multiple independent smaller-scale subarrays, ensuring their efficient phase convergence through the introduction of corresponding reference lasers while avoiding interference when integrating different subarrays. Moreover, the piecewise SPGD algorithm is proposed and the intensity of the reference laser is modulated to further improve the convergence speed and accuracy within subarrays, enhancing the algorithm's compatibility across laser arrays of varying scales. We have validated the feasibility of the distributed CBC architecture through numerical analysis and assessed the strategy's performance in both static and dynamic environments using simulation software. The simulation findings indicate that, compared to traditional CBC systems, distributed architecture with 3, 7, and 19 subarrays and utilizing the piecewise SPGD algorithm, has experienced phase control bandwidth enhancements by factors of approximately 3.6, 10.4, and 32.5 respectively, maintaining superior average power output in dynamic noise environments. The proposed architecture and strategy also accommodate subarrays of variable scales and obviates the necessity for large-aperture optical components on the emitted plane, demonstrating exceptional scalability and adaptability.

Innovative Integration of Dual Quantum Cascade Lasers on Silicon Photonics Platform.

For the first time, we demonstrate the hybrid integration of dual distributed feedback (DFB) quantum cascade lasers (QCLs) on a silicon photonics platform using an innovative 3D self-aligned flip-chip assembly process. The QCL waveguide geometry was predesigned with alignment fiducials, enabling a sub-micron accuracy during assembly. Laser oscillation was observed at the designed wavelength of 7.2 μm, with a threshold current of 170 mA at room temperature under pulsed mode operation. The optical output power after an on-chip beam combiner reached sub-milliwatt levels under stable continuous wave operation at 15 °C. The specific packaging design miniaturized the entire light source by a factor of 100 compared with traditional free-space dual lasers module. Divergence values of 2.88 mrad along the horizontal axis and 1.84 mrad along the vertical axis were measured after packaging. Promisingly, adhering to i-line lithography and reducing the reliance on high-end flip-chip tools significantly lowers the cost per chip. This approach opens new avenues for QCL integration on silicon photonic chips, with significant implications for portable mid-infrared spectroscopy devices.

Concept for power scaling by harmonic beam coaxial combination in an intra-cavity frequency doubling laser.

A new method of harmonic beam coaxial combination (HBCC) from two intra-cavity frequency doubling branches was demonstrated. Firstly, two identical nanosecond (ns) 532 nm green lasers with high power and good beam quality were created. Each green laser was constructed of an intra-cavity frequency doubling branch based on a laser diode (LD) end-pumped acousto-optical (AO) Q-switched 1064 nm Nd:YVO4 laser in a LiB3O5 (LBO) nonlinear crystal. Each branch generated about 45 W green output at a 50 kHz pulse repetition rate (PRR) with diffraction limited beam quality. The first green beam was injected into the LBO crystal in the second branch, and the pulses from the two branches did not exist simultaneously. Then, the HBCC was performed. Consequently, an 83 W combined green output power at 532 nm was obtained with a combination efficiency of 92.2%. The PRR of the HBCC pulse was doubled to be 100 kHz, with a pulse width of about 22 ns, corresponding to a single pulse energy of 0.83 mJ and a peak power of 37.73 kW. The combined beam quality factor was measured to be M x2 = 1.80 in the x direction and M y2 = 1.71 in the y direction, respectively. Moreover, many more beams could also be combined with this method for further scaling the green power.

Bayesian approach to coherent combination of single photon beams

We theoretically investigate the performance of a coherent beam combination of two light beams under relative phase fluctuations in the photon starved regime. We apply a first-principles approach using the optimal Bayesian phase correction protocol. We analyze the efficiency of beam combination as a function of the phase fluctuations strength.

Robust laser phase noise measurement by integration heterodyne for coherent beam combining applications

Phase noise characteristics are critical for coherent beam combination engineering. Heterodyne with integration method for phase noise measurement has been studied numerically and experimentally, which reveals that the method is not only simple to implement with the least equipment but also capable of phase retrieval using under-sampling data. The integration method is compared with the traditional low-pass filter (LPF) method from both numerical and experimental perspectives. By introducing an evaluation criterion of measurement accuracy, the errors of the integration method are 0.44% and 0.08% for white noise and pink noise cases, respectively, which are smaller than that achieved by LPF one (1.52% and 0.25%). The errors of the integration method are below 1.4% when under-sampling data has been employed, which means that large consumption of data processing can be avoided, and the method is robust. Phase noise measurements in quiet laboratory and disturbed conditions are implemented, and the error between the results of the sampling rate of 250 MHz and 31.25 MHz is less than 0.08%, which is consistent with the simulation and demonstrates the excellent performance of the integration method.

Harvesting vibration energy by quad-stable piezoelectric cantilever beam: Modeling, fabrication and testing

The combination of beams with piezoelectric patches has become a prevalent energy harvesting tool due to its ease of use. Typical energy harvesting systems are usually linear, and their efficiency is not satisfying due to low-frequency bandwidth. In this paper, a quad-stable piezoelectric vibration energy harvester is analyzed both numerically and experimentally. The primary purpose of this investigation is to analyze the static and dynamic characteristics of a proposed quad-stable system to consider its potential for application in broadband energy harvesting comprehensively. The harvester system consists of a slotted cantilever beam, a piezoelectric patch, a pair of tip-mass blocks, and a double-sided clip. The cantilever beam is subjected to pre-displacement constraints made by a mutual self-constraint at the free end of it. The nonlinear behaviors of the harvester system, including snap-through and softening phenomena, are analyzed using the assumed modes and finite element method (FEM). The harvester's vibration equation is solved numerically and through an FE model which is made by an in-house finite element software. A prototype is designed and fabricated to validate the mathematical model and FE simulation. The experimental force-displacement diagram of the harvester displays distinct discontinuities, reflecting abrupt transitions occurring while switching its stable states. The prototype dynamics are analyzed by harmonic base excitation with different amplitude levels in two conditions, including the presence and absence of the piezoelectric patch. The results obtained from the mathematical and FEM model demonstrate a satisfactory correlation with the experimental data. Furthermore, the experimental data reveal the occurrence of the snap-through phenomenon, accompanied by a significant widening of the frequency bandwidth at relatively high amplitude levels. The system has the ability to provide an average output electrical power of 0.288 mW for an electrical resistance of 3.262 kΩ at the excitation frequency of 12.695 Hz and base acceleration amplitude of 3g.