Combined Laser Beam Research Articles

Optimal spectral combination of spectrally combined laser beams in the turbulent atmosphere.

The optimal spectral combination of spectrally combined laser beams (SCLBs) propagating from the ground to orbit in the turbulent atmosphere is studied, where the atmospheric effects (e.g., turbulence, extinction and nonlinear self-focusing) are considered. The analytical propagation formulae are derived. It is found that there exists the intensity maximum at the target when the optimal central wavelength λc-opt arrives, and λc-opt is always located around 3.8µm, 8.9µm, or 10.6µm. The λc-opt depends on the spectral width, the initial beam size, and the turbulence strength. Based on λc-opt, the beam quality may be further improved by the method of removing sub-beams with low atmospheric transmittance. However, this method is invalid when the self-focusing is strong enough, while it can significantly improve the beam quality for the large initial beam size.

Corrosion behavior of combination of laser beam welded UNS S32304 + SS304L in 3.5% NaCl solution

This study investigates the corrosion behavior of laser beam-welded UNS S32304 and SS304L in 3.5% NaCl solutions, focusing on the effects of temperature. The primary objective is to enhance the understanding of corrosion resistance in welded materials and inspire advancements in corrosion mitigation strategies. The methodology involves assessing corrosion resistance under varying temperatures and comparing the performance of laser beam welding (LBW) with that of the base metals. Scanning electron microscopy analysis reveals effective passivation, while quantitative analysis indicates differences in chloride ion coverage between the weld metal and base metals. Tafel plots and electrochemical impedance spectroscopy demonstrate enhanced corrosion potential and improved barrier properties for the weld metal. Results indicate a marginal reduction in corrosion resistance at 50 °C for both base metals. LBW metals corrosion resistance demonstrates superior performance, with only 5% reduction in breakdown potential compared to 10% in base metals. Compared to the base metal, it exhibits a substantial reduction in corrosion rate, ranging from 60 to 75%. This supports enhanced corrosion resistance and material stability. Additionally, similar results are observed after the analysis with scanning electron microscopy images, reinforcing the efficacy of LBW in improving corrosion resistance of LBW UNS S32304 and SS304L. These findings underscore the potential of LBW for applications requiring robust corrosion performance. By contributing to the understanding of the corrosion behavior of laser beam-welded materials, this study addresses a critical research gap in material science and corrosion engineering. Future research may explore long-term durability and corrosion resistance under diverse environmental conditions to further elucidate the mechanisms driving the observed differences in corrosion behavior.

The effect mechanism of laser beam defocusing on the surface quality of IN718 alloy prepared by laser powder bed fusion

The surface quality issue of the laser powder bed fused (LPBF-ed) parts deteriorates the mechanical properties. Laser beam defocusing (LBD) can effectively improve the surface quality. To reveal the effect mechanism of LBD on the surface quality of the LPBF-ed parts, a laser powder bed fusion (LPBF) numerical model is established. Based on the calculated results, the formation process of the surface defects such as bulges, depressions, partially melted powders and spatters and the corresponding melt pool dynamic behaviors are investigated. The effects of LBD on the melt pool dynamic behaviors during the surface defects formation and the track width are discussed. The results show that LBD can improve the surface quality by reducing Marangoni force and recoil pressure to reduce bulge height and depression depth, increasing track width to decrease partially melted powders, and increasing surface tension and reducing kinetic energy to decrease spatters.

Assessing the feasibility of laser ablation coating removal (LACR) on legacy bridge steel: Coating removal and adhesion, and effects on mechanical properties

The application of protective organic coatings is one of the most effective and commonly used corrosion mitigation strategies. To maintain the protective nature of coatings on long-term-exposed surfaces such as steel bridge components, coatings must be periodically removed and reapplied. A relatively new method called laser ablation coating removal (LACR), which incorporates a high energy nanosecond pulsed laser beam in combination with a high efficiency filtration system, allows for safe and effective removal of coatings and contamination from metal surfaces. In this study, LACR cleaning is tested on legacy bridge steel components to investigate the effect on substrate cleanliness and steel mechanical properties. These bridge sections were never blasted and contain a 20–100 μm thick mill-scale layer (iron oxide) below several coating layers (including lead-rich coatings). The top micron of the oxide layer is melted by LACR and also thermally insulates the underlying steel and prevents any melting within the metallic substrate. The resulting surfaces are analyzed using microscopy, hardness testing, tensile, and fatigue testing, and it is shown that LACR does not cause any measurable detrimental effects to the bulk mechanical properties of the bridge steel, as well as effectively removes all paint coatings. Furthermore, adhesion testing on LACR-cleaned substrates shows excellent adhesion, qualifying above adhesion requirements for coated steel.

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.

Analytical propagation formulae of spectrally combined laser beams in nonlinear Kerr media.

The analytical propagation formulae of spectrally combined laser beams (SCLBs) in nonlinear Kerr media are derived, and the analytical expression of the ratio of the effect of the photorefractivity to the diffraction of SCLBs propagating in nonlinear Kerr media is also obtained. The validity of the analytical propagation formulae of SCLBs in nonlinear Kerr media is confirmed, and the error of the analytical propagation formulae is also discussed. It is shown the calculation time is reduced greatly by using the analytical propagation formulae. Therefore, a useful method is presented to study the propagation of SCLBs in nonlinear Kerr media.

Dysprosium optogalvanic spectroscopy in a hollow cathode lamp

This work presents data obtained from optogalvanic spectroscopy (OGS) of dysprosium (Dy) using a commercial hollow cathode lamp. Combining laser beams from two tunable dye lasers, it was possible to identify 13 electronic transitions from excited states of the atom not observed or registered in published papers and the NIST database; these lines were observed between 555–575 nm and 585–615 nm. The study of 13 two-step transitions found in this work complement the available data for the Dy which may support other research or any work using this atom.

Wavelength selection for spectrally combined laser beams propagating in free space and the atmosphere

Wavelength selection has a major impact on spectral beam combining (SBC) of laser beams that propagate in free space and in the atmosphere. We derive analytical expressions for the intensity and four characteristic quality parameters of free-space SBC beams. We show that the peak intensity, the mean-square beam width, and the M 2 factor of an SBC beam at the target are all larger than those of one single laser beam of the same power and average wavelength. The peak intensity can be made higher by increasing the wavelength spacing but reducing the mean wavelength. However, when an SBC laser beam propagates in the atmosphere, the beam quality depends on the absorption coefficient of the multi-wavelength field due to thermal blooming. A thermal distortion number is introduced for an SBC beam and its validity is confirmed. We show that the power proportion of a high-absorption element within an SBC beam should be as low as possible to reduce the thermal blooming effect.

New approach for multi-material design: Combination of laser beam and electromagnetic melt pool displacement by induced Lorentz forces

Multimaterial structures are a promising solution to reduce vehicle weight and save fuel or electric energy in automotive design. However, thermal joining of steel and aluminum alloys is a challenge to overcome due to different material properties and the formation of brittle intermetallic phases. In this study, a new joining approach for producing overlap line-shaped joints is presented. The lower joining partner (EN AW 5754) is melted by a laser beam, and this melt is displaced into a line-shaped cavity of the upper joining partner (1.0330) by induced Lorentz forces. The melt solidifies in the cavity to a material and form-fitting joint. This approach needs no auxiliary joining elements or filler materials. Previous investigation to produce spot-shaped joints by using this approach showed that quality and reproducibility were limited by known melt pool dynamics of aluminum alloys (keyhole collapses). For line-shaped joints, the melt displacement can take place behind the keyhole. This allows the displacement process to be spatially uncoupled from the influence of keyhole collapses. The study shows that this improved the process stability and the quality of the joint. The created line-shaped joints were microstructurally characterized by transversal sections. Intermetallic phases were identified by electron backscatter diffraction and EDX analysis. The detected intermetallic phases consist of a 5–6 μm compact phase seam of Al5.6Fe2 and a needle-shaped phase of Al13Fe4. Tensile shear tests were carried out to quantify the load capacity. It was possible to create a joint with a load capacity of about 2 kN.

Watt-level beam combined diode laser systems in a chip-scale hybrid photonic platform.

Scaling up the power of on-chip diode lasers is of great importance for many emerging applications, such as integrated nonlinear optics, remote sensing, free space communication, infrared countermeasure, and light detection and ranging (LIDAR). In this manuscript, we introduce and demonstrate photonic integrated circuits (PIC) based beam combining methods to create power scalable, integrated direct diode laser systems. Traditional laser beam combining, including coherent beam combining (CBC) and wavelength beam combining (WBC), usually requires free space or fiber optical components, leading to bulky and complex systems. Instead, PIC based beam combining methods can greatly reduce the cost, size, weight, and power consumption (CSWaP) of next generation direct diode laser systems. We experimentally demonstrate four channel chip-scale CBC and WBC with watt-level on-chip power by using III/V-Si3N4 hybrid integration. Our results show that PIC based beam combining is very suitable for power scaling in a chip-scale platform.

Efficient waveguide-type four-color (red–green–blue–infrared) laser beam combiner for compact laser beam scanning image projectors

Efficient waveguide-type four-color (red–green–blue–infrared) laser beam combiner for compact laser beam scanning image projectors

Modal decomposition of an incoherent combined laser beam based on the combination of residual networks and a stochastic parallel gradient descent algorithm.

With the increase of the superimposed eigenmodes number, the traditional numerical modal decomposition (MD) technique will inevitably suffer from ambiguity and local minima problems and thus is typically unsuitable for conducting modal decomposition of an incoherent combined laser beam. In this paper, we propose a novel, to the best of our knowledge, MD algorithm, named ResNet-SPGD, which combines the advantages of residual networks (ResNet) and stochastic parallel gradient descent (SPGD) algorithm. Via setting the modal mode coefficients obtained from the CNN model as the initial value of the SPGD algorithm, such algorithm shows an attractive solution to mitigate the problem of modal ambiguity. The proposed algorithm is preliminarily applied to the modal decomposition of an incoherent combined laser beam, and the feasibility is demonstrated via numerical simulations. Complete MD is performed with high accuracy, and the only cost is the sacrifice of some real-time capacity.

Phenomenology and capabilities of mutually guided laser and neutral particle beams for deep space propulsion

Here we present a detailed analysis of a new concept for beam propulsion that extends the propagation range through space by circumventing fundamental limitations on the beam divergence. Using a combination of spatially overlapped continuous laser and neutral particle beams, opto-mechanical forces and light refraction are simultaneously exploited to produce self-guided modes. The aim of the present work is to elucidate the relevant physical phenomena, their relation to the conditions for self-guiding, and practical considerations for the design parameters of such a propulsion system. Methods for computing the lowest order axisymmetric self-guided modes are presented along with the resulting spatial mode structure. Key non-dimensional parameters are derived, including the use of linear stability analysis to determine features of the dynamic interaction. Based on these findings, a beam parameter optimization framework is proposed and applied to a 100-year interstellar flyby mission to Proxima b. With 200 GW of combined laser and particle beam power, we find that a 0.3 kg spacecraft could be accelerated to 0.044c over a distance of 4.37×106 km (0.029 AU) using a small 1 m2 beam cross-section. Compared to an equivalent particle beam with no self-guiding, this represents an over 50× increase in payload. Similar payload mass would be possible by laser propulsion with an approximately 104 m2 area laser array. These results suggest that self-guided beam propulsion possesses unique attributes that could enable the acceleration of larger spacecraft to relativistic velocities and enhance scientific capabilities for future interstellar and interstellar-precursor missions.

10 kW rectangular laser beam generation with incoherent space combiner

In this paper, we report an incoherent space laser beam combiner for rectangular beam combination with 18 fiber-transmitted semiconductor lasers at 972 nm wavelength. The coupled thermo-mechanical properties of all the optical lenses in the combiner were analyzed to evaluate the long-term reliability of the combiner subjected to beyond 10 kW high-power laser irradiation. An experiment-based numerical model was developed on the basis of the multi-beam laser volumetric heat source, and the performance of lenses irradiated by 10 kW combined laser for 1000 s was studied with finite element method (FEM). The maximum temperature among all lenses was 427.27 K which is much lower than the softening point temperature of fused silica material made of lenses. And the 0.1 aperture number corresponding to the maximum thermal deformation of 4.53 µm is much smaller than the conventional optical lens processing tolerance. The maximal stress of 12.73 MPa is far less than the yield stress of 4.5 GPa for the material. The manufactured laser beam combiner realized a highest output power of 10.641 kW at a power combination efficiency of 98.5%, a combination length of 200 mm and a rectangular focal beam spot of 30 mm × 10 mm. Our method provides a valuable choice for realizing fast and flexible laser surface heat treatment.

비등방성 로킹을 위한 금속의 하이브리드 마이크로 텍스쳐링 가공법

In this paper, a novel hybrid micro texturing method that combines laser beam machining and electrochemical etching was suggested. In this new machining process, tungsten anisotropic micro channel that was used for directional locking was fabricated. First, laser beam machining on a tungsten workpiece with tilted condition was adopted to rough texturing. Subsequently, a recast layer with tungsten oxide was generated that covered the original anisotropic channel shape, causing a low surface quality. For this reason, electrochemical etching was carried out to elute the recast layer into electrolyte. Moreover, EDS analysis that observed the atomic distribution of textured micro channel was performed to verify the principle of the suggested hybrid process. In the finally fabricated anisotropic micro channel after the hybrid texturing process, the interlocking force (maximum 133.44 N, 5×5 mm²) was measured using the load cell.

High-Efficiency Ignition Laser Source Based on Diode Laser Beam Combination Technology

High-Efficiency Ignition Laser Source Based on Diode Laser Beam Combination Technology

Design of optical Fabry–Perot filters for spectral combination of laser beams

Types of spectral combinations of beams of industrial lasers are considered. The optical Fabry–Perot filters are demonstrated to be an acceptable alternative to surface and volume diffraction gratings and edge dichroic filters. Known methods for designing Fabry–Perot filters for spectral multiplexing of channels in fiber-optic telecommunications are updated considering peculiarities of industrial lasers such as different emission power, transmission and suppression bandwidths of filters, and maintenance of minimum power loss. The applicability of the proposed approach is demonstrated using filters for combination of beams of ytterbium fiber lasers as an example.

Prediction study on in-situ reduction of thermal stress using combined laser beams in laser powder bed fusion

High thermal stress induced by extremely high temperature gradient significantly hinders the development of the laser powder bed fusion (LPBF). In this study, an in-situ stress control method based on the combined laser beams was proposed, in which a second laser beam was added to release the thermal stress during the process. The effect of the combined laser beams on the temperature distribution and thermal stress in LPBF was studied. A definition of the equivalent scan length was adopted to simulate the effect of the scan length. It was found that when the second beam was used, the post-heating strategy can reduce the residual stress better than the pre-heating strategy. The stress relief effect was close to the scan direction of the second beam and the vertical post-heating pattern was recommended to in-situ reduce the thermal stress. More obvious thermal stress cycles and the thermal stress peaks appeared in the long scan length. The stress release effect caused by the second beam decreased with the increase of the scan length, indicating that the scan length should be also reduced even if the second beam was used. The simulated results were indirectly verified by the experimental data with different re-scanning strategies and scan lengths. The purpose of this paper is expected to significantly in-situ reduce the thermal stress during the process without increasing the manufacturing time.

Coherent beam combination of seven 1.5 µm fiber amplifiers through up to 1 km atmospheric turbulence: near- and far-field experimental analysis.

A laser testbed based on active coherent beam combination (CBC) of seven 1.5 µm, 3 W fiber amplifiers was developed for applications requiring high power such as power density deposition on targets or free space laser communication. For the first time to our knowledge, the frequency-tagging locking of optical coherence by single-detector electronic-frequency tagging technique was implemented in the field in real atmospheric turbulence conditions in a target-in-the-loop configuration. Successful combination was achieved after horizontal propagation of 311 m and 1 km, at 1.5 m above the ground, while the estimated average turbulence strength was Cn2∼4.10-14m-2/3. We present the CBC laser bench and an embedded near-field interferometer called PISTIL (PISton and TILt) able to measure the relative phase shift of each emitter. We show that this measurement can provide information on relative turbulence-induced phase variation of the combined laser beams. In particular, the far-field beam envelope wandering can be estimated through this diagnosis. Results are supported by an analytical model and confirmed by numerical post-analysis of measured far-field interference. This additional interferometer may improve CBC beam pointing through turbulence.

Theoretical and experimental research on crosstalk in spectral beam combining of a laser diode bar with a high fill factor.

Spectral beam combining is an important way to improve the brightness of semiconductor laser beams. For a spectral beam combining system, crosstalk between different emitters would cause the deterioration of beam quality and the reduction of beam combining efficiency, especially for the laser diode bar with a high fill factor. In this paper, an analysis model of the spectral beam combining system with crosstalk is established. The most important advantage of this model is that it can analyze the spectral distribution of the combined beam and also give a relatively good estimation for the beam quality parameters, such as beam size and far-field divergence angle. This model is verified by the experimental results. Furthermore, based on the theoretical model, a method for eliminating crosstalk is developed. By introducing a spatial filter inside the grating external cavity, the crosstalk between different emitters is blocked in the far field, and the beam quality is improved. In the experiment of beam combining of five emitters, after crosstalk is eliminated, the divergence angle of the combined laser beam is reduced from 10.09 to 4.73 mrad, the beam parameter product is reduced from 2.95 to 0.91 mm⋅mrad, and the power of the main lobe is improved from 1.77 to 2 W.