Combined Beam Research Articles

500-W Average Power, 100-mJ level Pulse Energy by Q-switched 7x7 Multicore Fiber Lasers

This work focuses on achieving high peak and average power through incoherent beam combination of Q-switched 49-core fiber laser. Results show 1.5-MW peak power, and 502-W average power between 1-10 kHz.

Compound laser system based on hybrid beam combination technology

Compound laser system based on hybrid beam combination technology

Seven-shaped beam design for improving the sensitivity of two-dimensional MEMS sensors

The spring constant of the connecting beam is one of the most crucial factors that affect the detection sensitivity of MEMS sensors. Existing researches reduce the spring constant by changing the parameters or number of connecting beams. In this paper, we propose a seven-shaped beam structure to modify the spring constant of MEMS sensors. The acute angle between the two segments of seven-shaped structure lowers spring constant. Compared with the crab-leg beam, it can bring a maximum sensitivity gain of 1.29 times through different angle designs. At the same time, compared with those combined beams, seven-shaped combined beams can bring a maximum sensitivity gain of 1.6 times. The two-dimensional MEMS sensor with seven-shaped beam has been designed and fabricated. According to the experimental results, the sensor reached a detection sensitivity of 25 fF/g. The relative error of the differential capacitance change between the measurement result and the simulation result is only 8.6%.

Investigation of the influence of pulse parameters on the resulting weld seam quality in pulsed electron beam welding of AW 6061

Utilizing pulsed lasers in favor of a continuous wave in laser beam welding is a well-established method to achieve higher process efficiency and reduce heat input into the workpiece, which is especially useful for thin-walled workpieces (Steen, 2005). In addition, pulsed processes have shown to lead to smaller grain sizes due to higher cooling rates, which can lead to a reduction in hot cracks in some aluminum alloys (Beiranvand et al., 2019). Since an electron beam can also be pulsed, a technique industrially utilized in electron beam drilling, the same principles apply (Schultz, 2000). However, pulsed electron beam welding is rarely used in industrial welding applications due to the risk of pores, spiking and sputtering resulting from the pulsed process dynamic, especially in the deep welding regime (Kautz, 1991). This study aims to develop a pulsed electron beam welding process for AW 6061 sheet metal, which is susceptible to hot cracking. The influence of the welding and pulse parameters, as well as the combination of a pulsed beam with high frequency beam oscillation is discussed. Furthermore, suitable welding parameters for pulsed electron beam welding of AW 6061 are developed, and the increased efficiency of pulsed welding is shown by comparison to continuous welds.

Fiber-connectorized ultrafast-laser-inscribed K-band integrated optics beam combiner for the CHARA telescope array.

A fiber-connectorized K-band integrated-optics two-telescope beam combiner was developed for long-baseline interferometry at the CHARA telescope array utilizing the ultrafast laser inscription (ULI) technique. Single-mode waveguide insertion losses were measured to be ∼1.1d B over the 2-2.3µm window. The development of asymmetric directional couplers enabled the construction of a beam combiner that includes a 50:50 coupler for interferometric combination and two ∼75:25 couplers for photometric calibration. The visibility of the bare beam combiner was measured at 87% and then at 82% after fiber-connectorization by optimizing the input polarization. These results indicate that ULI technique can fabricate efficient fiber-connectorized K-band beam combiners for astronomical purposes.

Gyrokinetic turbulence modeling of a high performance scenario in JT-60SA

Local gyrokinetic simulations are used to model turbulent transport for the first time in a representative high-performance plasma discharge projected for the new JT-60SA tokamak. The discharge features a double-null separatrix, 41 MW of combined neutral beam heating and electron cyclotron heating, and a high predicted ratio of the normalized plasma kinetic to magnetic pressure β. When considering input parameters computed from reduced transport models, gyrokinetic simulations predict a turbulent heat flux well below the injected 41 MW. Increasing the background gradients, on the other hand, can trigger a non-zonal transition (NZT), causing heat fluxes to no longer saturate. Furthermore, when considering fast ions in the simulations, a high-frequency mode is destabilized that substantially impacts the turbulence. The NZT is avoided by reducing the electron pressure by 10% below its nominal value, and the fast-ion resonance is removed by reducing the fast-ion temperature. The thus-obtained simulation features broadband frequency spectra and density and temperature fluctuation levels δn/n≈1% –2%, δT/T≈1% –6% that should be measurable with fluctuation diagnostics planned for JT-60SA. The temperature profile is fixed by the critical main-ion temperature gradient as a consequence of the high stiffness; heat fluxes increase by a factor of ten when increasing the main ion temperature gradient by 17%. Despite large gradients, it is demonstrated that, due to the large β, retaining compressional magnetic field fluctuations and in particular, the contribution of the pressure gradient in the ∇B drifts, is crucial to achieving non-zero heat fluxes.

Spectrally resolved ultrafast transient dynamics of a femtosecond fiber-feedback optical parametric oscillator.

We report on spectrotemporal transient dynamics in a femtosecond fiber-feedback optical parametric oscillator (FFOPO) system. Burst modulation of the pump beam in combination with dispersive Fourier transformation sampling allows to record single-pulse signal spectra at 41 MHz sampling rate. Therefore, each individual pulse of the signal transients can be spectrally resolved. We characterize the signal output behavior for anomalous as well as for normal intra-cavity dispersion. Amongst steady state output we observed period-doubling cycles and other attractors, which occured at higher intra-cavity nonlinearity levels. The experimental findings are supported by numerical simulations, in order to identify the linear and nonlinear effects, which govern the wavelength tuning behavior of this FFOPO system. We find that steady state operation is preferred and that the wavelength tuning stability of the FFOPO dramatically increases when using a normal dispersion feedback fiber.

Dynamical behavior of a particle-doped multi-segment dielectric elastomer minimal energy structure

The dynamic behavior of dielectric elastomers (DEs) has significant influence on their performance. The present study investigates the nonlinear dynamics of particle-doped multi-segmented DE minimum energy structures (DEMESs). To simulate the multi-segment DEMES, we consider each segment as a combination of hyperelastic film and elastic beam and obtain the ordinary differential equations governing the system dynamics based on the Euler–Lagrange equations. Due to the difficulty in measuring various physical parameters of DEs in practice, we utilize experimental data from a single-segment DE and employ a physics-informed neural network to predict the unknown parameters of the DE and the framework, such as stiffness K bb and doping volume fraction ϕ. Based on these predictions, nonlinear analysis is performed for the multi-segment system. Stability analyses of the motion equations reveal that the system exhibits a supercritical pitchfork bifurcation with hyperelastic thin film pre-stretching as the bifurcation parameter. For the three-segment DEMES, there are eight stable modes, but only four are illustrated in the bifurcation diagram due to the identical parameter settings for each segment. The amplitude-frequency curves under different AC voltage loads indicate the presence of harmonic, superharmonic, and subharmonic resonances in the system, with varying frequencies and magnitudes depending on the applied load. The Poincaré maps of the time response demonstrate that the system response is predominantly quasiperiodic. Under low voltage loads, the system exhibits periodic oscillations, while under certain high voltage loads, chaotic behavior emerges, characterized by strong nonlinearity in the time-dependent curves and non-periodicity in the Poincaré maps. This study provides insights into the present mathematical model in the motion control of DEMES.

Stress analysis of assembled concrete structures with application of finite element modeling

Abstract In the paper, the finite element model of the assembled concrete structure is constructed based on the finite element method combined with ABAQUS software, including the specific definition of the model material, the boundary condition and contact setting, the analysis step and loading setting, and the validity of the constructed finite element model is verified. In order to deeply explore the stress changes of the assembled concrete structure, four aspects were analyzed, namely, concrete strength grade, load-mid-span displacement curve, stress of tensile and compressive reinforcement, and stress changes of frame combination beams respectively. The results showed that the larger the concrete strength grade, the relative stiffness ratio at the peak point gradually decreased from 0.44 to 0.27, and the specimen of concrete structure with higher steel content reached the maximum load at the mid-span displacement of 12.5 mm. The reinforcement at the end of the steel frame reaches the yield stress only when the lateral displacement is 25.8 mm, while the RC frame reaches the yield stress when the lateral displacement is 16.1 mm. When the load of the assembled concrete structural frame combination beams does not exceed 0.5 times the ultimate load, the stress change is elastic, which can ensure the stability of the assembled concrete structural building. Using the finite element model to model the assembled concrete structure numerically analyzes its stress change, which can better grasp the development of its structural stress during the actual casting process so as to ensure the safety of the building structure.

Arbitrary combinations of helical-conical optical beams in free space.

Helical-conical optical beams (HCOBs) have attracted considerable interest due to their peculiar optical features. Their characteristic helical light intensity distribution has exerted unprecedented advantages in many fields, but multiple combinations of HCOBs have not been reported due to the limitations of algorithms and light field modulation techniques. We propose and experimentally demonstrate arbitrary combinations of multiple HCOBs in free space to construct hybrid HCOB arrays. The similarity between the experimental results and the numerical simulation results is 94.22%. The initial orientation of the HCOBs is flexibly tuned by the rotation factor β, and the optical pen is used to combine the HCOBs. This approach allows multiple parameters in the array to be precisely tuned, including the type, number, and position of HCOBs, adding more design flexibility. The constructed HCOB arrays have a higher degree of modulation freedom and may find applications in fields where dynamic control is in high demand, including optical tweezers, biological cell sorting, and multiparticle manipulation.

Flat Optical Chiral Liquid Crystal Diffractive Elements for Efficient Beam Combiners in Augmented Reality Devices

Flat Optical Chiral Liquid Crystal Diffractive Elements for Efficient Beam Combiners in Augmented Reality Devices

Optimizing geometrical parameters of coherent beam combining in the near and far-field distance

Determining the characteristics of the laser array to improve the performance of a laser system based on coherent beam combination (CBC) has continuously garnered interest. To this end, the parameters of the Gaussian beam waist, array shape, and distance between adjacent beams were studied and numerically investigated in this study. Consequently, the combined beam quality was compared for hexagonal, circular, and square arrays. The observing plane’s location was fixed at 10 km and varied from 0.25 to 10 km to investigate the effect of beam waist on combined beam quality in two modes (near and far field) using the power in the 5 cm bucket metric (PIB5cm). Furthermore, the average PIB5cm was investigated to determine all observing plane distances. The simulation results in two states of fixed and variable observing plane distances demonstrated that the hexagonal array has an advantage in attaining PIB5cm and higher combined beam quality. In addition, the quality of the combined beam degrades as the space between the beams increases. Moreover, the optimal beam waist and aperture diameter are independent of the array geometry and the vacancy between adjacent beams.

On-chip coherent beam combination of waveguide amplifiers on Er3+-doped thin film lithium niobate

We demonstrate on-chip coherent beam combination of two waveguide amplifiers on Er3+-doped thin film lithium niobate (Er:TFLN) platform. Our device is built based on an electro-optic modulator fabricated on Er:TFLN. The output power of the coherently combined amplifiers is measured as high as 12.9 mW, surpassing that of previous single waveguide amplifiers based on an Er3+-doped thin film lithium niobate platform.

Stable control of the phased fiber laser array under varying beam propagation distance

Phased fiber laser array (PFLA) plays an important role in laser propagation applications. However, in many practical scenarios, the beam propagation distance is constantly changing, which makes the metric propagation delay difficult to obtain, and eventually leads to the divergence of existing control algorithms based on metric optimization. In this paper, the laser ranging technique based on PFLA is introduced to estimate the metric propagation delay in real-time. In addition, an iterative algorithm named dynamically delayed stochastic parallel gradient descent (DD-SPGD) is designed to adapt to the varying metric propagation delay, and ensure the stable control of PFLA. Laser ranging and three channel coherent beam combination experiments based on a 7-unit PFLA were conducted to verify the proposed method. The results show that the laser ranging technique can accurately estimate the metric propagation delay with estimation errors of less than 1%. On this basis, the DD-SPGD algorithm can dynamically adjust the delay parameter (from 0 to 2) and realize stable control of PFLA under different metric propagation delays.

Mode attraction, rejection and control in nonlinear multimode optics

Novel fundamental notions helping in the interpretation of the complex dynamics of nonlinear systems are essential to our understanding and ability to exploit them. In this work we predict and demonstrate experimentally a fundamental property of Kerr-nonlinear media, which we name mode rejection and takes place when two intense counter-propagating beams interact in a multimode waveguide. In stark contrast to mode attraction phenomena, mode rejection leads to the selective suppression of a spatial mode in the forward beam, which is controlled via the counter-propagating backward beam. Starting from this observation we generalise the ideas of attraction and rejection in nonlinear multimode systems of arbitrary dimension, which paves the way towards a more general idea of all-optical mode control. These ideas represent universal tools to explore novel dynamics and applications in a variety of optical and non-optical nonlinear systems. Coherent beam combination in polarisation-maintaining multicore fibres is demonstrated as example.

Research on the Shear Performance of Cold-Formed Thin-Walled Steel-Glued Laminated Wood Composite Beams

This paper proposes a new type of composite box beam combined with cold-formed thin-walled steel and glued laminated timber to develop green building structures while improving the load-carrying capacity of a single steel girder and glued timber girder. Two composite beams composed of laminated timber and Q235 cold-formed thin-walled steel were designed and fabricated. Then, the shear performance test with quadratic loading was carried out to analyze the load carrying capacity, damage modes, and deformation characteristics of the test beams, as well as their influencing factors. Subsequently, a finite element model of the composite beam was established, and the loading mode was the same as that of the test to further study the parameters affecting the shear performance of the composite beam. The results of the study indicate that steel and glued timber in composite beams connected by adhesive bonding can work and deform together under load and each give full play to its material properties, especially the composite beams, which exhibit higher shear strength than a steel or timber beam. The effects of parameters such as steel cross-sectional area, shear span ratio, steel skeleton form, and steel cross-sectional strength on the shear capacity of the composite beams were observed, among which the shear span ratio had the greatest effect on the shear capacity of the composite beams. The shear capacity decreased by 14.3% and 19.5% when the shear span ratio was increased from 1.5 to 2.0 and 2.5, respectively. The shear capacity of the combined composite beams increased by 10.6%, 6.3%, and 5.8% when the thickness was increased from 1.5 mm to 2.0 mm, 2.5 mm, and 3.0 mm, respectively. When the combination of the steel cross-section was a box beam, the overall shear-bearing capacity could be increased by 12% compared with the “I” type composite beam, although its shear stiffness was close to that of the “I” section composite beam.

Mismatch analysis of all-fiber coherent beam combiners based on the self-imaging effect

Abstract All-fiber coherent beam combiners based on the self-imaging effect can achieve a near-perfect single laser beam, which can provide a promising way to overcome the power limitation of a single-fiber laser. One of the key points is combining efficiency, which is determined by various mismatches during fabrication. A theoretical model has been built, and the mismatch error is analyzed numerically for the first time. The mismatch errors have been numerically studied with the beam quality and combining efficiency being chosen as the evaluation criteria. The tolerance of each mismatch error for causing 1% loss is calculated to guide the design of the beam combiners. The simulation results are consistent with the experimental results, which show that the mismatch error of the square-core fiber is the main cause of the efficiency loss. The results can provide useful guidance for the fabrication of all-fiber coherent beam combiners.

Design method for laser beam aggregation based on SPGD

This paper proposes a design method for laser beam aggregation based on SPGD, effectively addressing the issue of beam aggregation inconsistency caused by external interferences during the multi-path laser beam combination process. This further enhances the energy density of the combined laser spot. By applying a random binary disturbance vector based on control parameters and employing the stochastic parallel gradient descent (SPGD) algorithm for model control and parallel iteration, the control parameters are halved. This accelerates the iteration speed, enabling rapid aggregation of the combined laser beams and maximizing the energy density of the laser spot.

Real-time low-complexity diversity combining algorithm for free space coherent optical communication systems over atmospheric turbulence channel.

A novel diversity combining scheme, in conjunction with the complex-valued decision-directed least mean square (CV-DD-LMS) algorithm, is evaluated, and a real-time experimental validation is presented. This proposed scheme employs the CV-DD-LMS algorithm to concurrently perform beam combination and carrier phase recovery (CPR), thereby effectively reducing the overall complexity of digital signal processing. Furthermore, in the numerical simulation, under a low signal-to-noise ratio (SNR), a scheme utilizing the CV-DD-LMS algorithm effectively avoids cycle slips (CS) and outperforms schemes employing independent CPR modules. We experimentally validate this novel scheme by implementing it on an FPGA in a real-time 2.5Gb/s QPSK diversity-receiving system with three inputs. The back-to-back sensitivity is assessed using static received optical power, while the dynamic performance is evaluated by employing variable optical attenuators (VOAs) to simulate a power fluctuation at a frequency of 100kHz. The result proves that the implementation of the CV-DD-LMS algorithm yields stable performance while effectively reducing computational complexity.

Quartz-Enhanced Photoacoustic Sensor Based on a Multi-Laser Source for In-Sequence Detection of NO2, SO2, and NH3.

In this work, we report on the implementation of a multi-quantum cascade laser (QCL) module as an innovative light source for quartz-enhanced photoacoustic spectroscopy (QEPAS) sensing. The source is composed of three different QCLs coupled with a dichroitic beam combiner module that provides an overlapping collimated beam output for all three QCLs. The 3λ-QCL QEPAS sensor was tested for detection of NO2, SO2, and NH3 in sequence in a laboratory environment. Sensitivities of 19.99 mV/ppm, 19.39 mV/ppm, and 73.99 mV/ppm were reached for NO2, SO2, and NH3 gas detection, respectively, with ultimate detection limits of 9 ppb, 9.3 ppb, and 2.4 ppb for these three gases, respectively, at an integration time of 100 ms. The detection limits were well below the values of typical natural abundance of NO2, SO2, and NH3 in air.