Combined Laser Beam Research Articles

Optical set-up for dynamic superposition of three laser beams for structuring and polishing applications

Structuring by remelting is an innovative approach for structuring metallic surfaces with laser radiation, where no material is removed but reallocated while molten. Based on this remelting principle an innovative structuring technique is investigated, where laser beams are superposed. A melt pool is generated by a cw laser beam with constant feed rate. A pulsed laser is superposed onto the cw laser and evaporates a small amount of molten material and, therefore, generates vapour pressure, which shapes the melt pool surface. The solidification follows this newly shaped surface. For this process a new optical system was designed and built up, which allows the combination of cw and pulsed laser beams.

激光波长合束精度研究

Double laser beam combination accuracy of wavelength multiplexing is carried in this article. Two beams with wavelengths of 532 nm and 515 nm are combined into one in the combination and detection system using light filter with special optical thin films,and the combination accuracy is detected. Based on this system,the corresponding theoretical model is established,and the comprehensive analysis on the error source and the value in combination and detection are given in this paper. When the pointing stability of both beams is 50 μrad,the theoretical value of combination accuracy is 14. 69″,and the proportion of pointing stability is99. 26%. The system gets an excellent anti interference ability against the unstable factor such as the error of centroid location( error rate 3 times),and the variation in accuracy rate is less than 2. 4 ‰. When the laser pointing stability is increased to 23. 51 μrad,the highest theoretical value of combination accuracy is 7. 09″and the proportion of pointing stability is 96. 77%. The system still has a high ability of anti-interference and the variation in the accuracy rate is less than 1%. Factors that affect the beam combination accuracy of near field and small power are laser beam pointing stability,mechanical adjustment and centroid location error are all the factors to affect the combination accuracy of the near field beam with low power,among which the laser pointing stability is the main factor. Adjusting the proportion of each factor,we can control the ability of anti interference of beam combination.

Numerical Analysis of Laser Heating for Laser Assisted Micro Milling Application

The promising processing techniques of micro scale parts are very important in products miniaturization and functions enhancement. Combination of two or more processing techniques gives better processing performance especially when dealing with difficult-to-cut materials. For that reason, the combination of laser beam and micro milling process has been widely studied and proven efficient in reducing cutting force and tool life extension. However, this process needs a precise temperature control in order to eliminate heat effect generated by laser beam irradiation. In this study, temperature distributions are determined numerically to characterize the melted zone and heat affected zone geometry. From the results, the estimation of tool and micro milling cutter distance together with the allowable depth of cut are determined.

Coherent beam combination of fiber lasers with a strongly confined tapered self-imaging waveguide: theoretical modeling and simulation

Coherent beam combination (CBC) of fiber lasers based on self-imaging properties of a strongly confined tapered waveguide (SCTW) is studied systematically. Analytical formulas are derived for the positions, amplitudes, and phases of the N self-images at the output of a SCTW, which are important for quantitative analysis of waveguide-based CBC. The formulas are verified with numerical examples by a finite difference beam propagation method (FDBPM) and the errors of the analytical expressions are studied. This study shows that the analytical formulas agree well with the FDBPM simulation results when the taper angle is less than 1.4° and the phase distortion is less than λ/10. The relative errors increase as the taper angle increases. Based on the theoretical model and the FDBPM, we simulated the CBC of fiber laser array and compared the CBC based on the tapered waveguide with that based on the nontapered one. The effects of input beam number, aperture fill factor, and taper angle on the combination performance have been studied. The study reveals that a beam which has near-diffraction limited beam quality (M2≤1.41) and a single beam without side lobe in the far field can be achieved with tapered-waveguide-based CBC. It is shown that beam quality depends on input beam number, aperture fill factor, and taper angle. There exists a best fill factor which will increase as input beam number increases. The tolerance of the system on the fill factor and the taper angle is studied, which is 0.45<t<0.67 and θ<0.8°, respectively. The results may be useful for practical, high-power fiber laser systems.

Numerical simulation of propagation of laser beams formed by multielement apertures in a turbulent atmosphere under thermal blooming

An algorithm for simulating laser beam propagation in a turbulent atmosphere under conditions of thermal blooming for the case where the beam is formed by a multielement aperture is presented. Coherent and incoherent combining of elementary fields of the multielement aperture is considered. Based on numerical simulation, properties of a combined beam are analyzed in comparison with an equivalent Gaussian beam. A complex diffraction pattern is shown to appear upon coherent combinig as a result of superposition of fields formed by individual elements of the initial aperture. Average values of maximum intensity, both of the Gaussian beam and the combined laser beam, little differ from each other when the nonlinearity parameter N c > 1. Under conditions of strong turbulence and strong nonlinearity, integral radiation characteristics of combined beams are close to characteristics of the Gaussian beam, the effective size of which is determined by sizes of the combined beam. The intensity of combined laser beams in a turbulent atmosphere fluctuates upon incoherent combining of fields to a lesser extent as compared to coherent combining.

Efficient laser operation of diode-pumped Pr3+,Mg2+:SrAl12O19

We report on diode-pumped laser operation of Pr3+,Mg2+:SrAl12O19 at lasing wavelengths of λ L = 724.4 nm, λ L = 643.5 nm, and λ L = 622.8 nm. Furthermore, the laser threshold could be reached in the green spectral range. By pumping the crystal longitudinally from each side with two polarization beam combined InGaN laser diodes, a total pump power of ≈4 W was available. In the deep red spectral range, a maximum output power of 564 mW was achieved with a maximum slope efficiency of 50 % with respect to the absorbed pump power. The maximum possible internal losses were estimated to ≈1 %. Beam quality factors M 2 were in the range of 1.2–1.5.

Ultrabroadband spectral beam combiner spanning over three octaves

We report the design, build, and test of a multispectral laser beam combining collimator with a spectral range in excess of three octaves. The device is based on a sapphire wedge prism, calcium fluoride, and sapphire collimating doublet lens and fiber optic inputs and is designed to operate from ultraviolet (355 nm) to mid-infrared (4075 nm) wavelengths. Five laser sources at different wavelengths were used to validate the concept. The device produced full-angle beam divergence of between 0.1 and 0.2 mrad from 355 to 1908 nm. The bore-sight error with respect to the design wavelength of 1064 nm was 0.07 mrad for 532 nm, 0.14 mrad for 355 and 1908 nm, and 2.4 mrad for 4075 nm. The results presented here represent, to the authors' knowledge, the widest spectral range of a laser beam combiner yet demonstrated.

Orientation dependent coherent anti-Stokes Raman scattering of cylindrical microparticle with focused lasers

We developed a semi-analytical and semi-classical theory for nonlinear scattering of coherent anti-Stokes Raman scattering (CARS) signal from a cylindrical microparticle by paraxial focused laser beams. We study the effects of radius and length of the microparticle, as well as the orientation on the angular distributions of the CARS signal. The waist of the laser beam is found to have a significant effect on the angular distribution. The combination of Gaussian laser beams and cylindrical geometry yields analytical expressions for the orientation factor and the CARS electric field, which permit convenient and efficient computation of the scattering signal versus various physical parameters.

0.4 J/10 ns/10 kHz‐4 kW coherent beam combined laser using stimulated Brillouin scattering phase conjugation mirrors for industrial applications

AbstractA laser system that can produce 0.4 J/10 ns/10 kHz‐4 kW using a coherent beam combination with stimulated Brillouin scattering phase conjugate mirrors (SBS‐PCMs) is proposed. The 4 kW coherent beam combination laser system consists of a front‐end system, a pre‐amplifier module, a coherent beam divider/combiner, and 4 main amplifier modules. The front‐end system produces 1064 nm @ 10 kHz laser pulses, and it is amplified by the pre‐amplifier. After the pre‐amplifier module, the laser beam is divided into 4 sub‐beams. Each sub‐beam is amplified by the main amplifier module in a double‐pass configuration and reflected by SBS‐PCMs. Sub‐beams are combined by a coherent beam combiner, and the output of the total system is designed to be 4 kW. With this 4 kW laser module, high‐speed 2D holographic laser processing will be utilized. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Impact of temporal and spectral aberrations on coherent beam combination of nanosecond fiber lasers

The effects of aberrations on coherent beam combination (CBC) of nanosecond fiber lasers are analyzed in this paper. These effects include imperfect overlap of the pulses, spectral phase shift, and nonlinear phase shift, which are induced by optical path difference and self-phase modulation. A typical system of CBC of two lasers is calculated in detail and design guidelines are given.

Coherent beam combination laser system using SBS-PCM for high repetition rate solid-state lasers

In this paper, the coherent beam combination technique using SBS-PCM for a high repetition rate laser will be demonstrated. It is a novel concept capable of achieving a high energy and high repetition rate laser. A phase conjugation mirror and beam combination laser using a self-phase-controlling technique for coherent beam combination is introduced in this paper. And, a practical demonstration of the coherent beam combination laser using SBS-PCM is presented. With a wave-front dividing scheme, the relative phases are measured to be less than λ/26 even when the amplifier is operating. The coherent beam combination laser using SBS-PCMs has the additional advantage of providing accurate high speed/high rate injection of the fusion target in the LIFE reactor system. The coherent beam combination of 25 100J/10Hz laser modules for the 2.5kJ/10Hz laser beam line for the fusion energy driver is suggested, which is available with the current laser technologies.

激光相干合成光束质量评价

激光相干合成光束质量评价

About comparison of combination of different laser beams at a target to the performance of an equivalent single laser

In this work, it is shown that different lasers’ beams, of the same frequency, having, however, randomly different phases and polarizations at the output, combine at a target by a statistical distribution with a mean and a standard deviation, both, of the same order of magnitude as the incoherent sum of their intensities. This disadvantage does not occur in an “equivalent” single laser operation. Therefore, it delivers a much higher intensity at the target.

Comparison of coherent and incoherent laser beam combination for tactical engagements

The performance of a multibeam laser system is evaluated for coherent and incoherent beam combination under tactical scenarios. For direct comparison, identical aperture geometries are used for both, coherent or incoherent, combination methods. The analysis assumes a multilaser source coupled with a conventional 0.32 m diameter, on-axis, beam director. Parametric analysis includes variations over residual errors, beam quality, atmospheric effects, and scenario geometry. Analytical solutions from previous results are used to evaluate performance for the vacuum case, providing an upper bound on performance and a backdrop for organizing the multitude of effects as they are analyzed. Wave optics simulations are used for total system performance. Each laser in the array has a wavelength of 1.07 μm, 10 kW (25 kW) output power, and Gaussian exitance profile. Both tracking and full-aperture adaptive optics are modeled. Three tactical engagement geometries, air to surface, surface to air, and surface to surface, are evaluated for slant ranges from 2.5 to 10 km. Two near-median atmospheric profiles were selected based upon worldwide climatological data. The performance metric used is beam propagation efficiency for circular target diameters of 5 and 10 cm.

Validation and perspectives of a femtosecond laser fabricated monolithic optical stretcher.

The combination of high power laser beams with microfluidic delivery of cells is at the heart of high-throughput, single-cell analysis and disease diagnosis with an optical stretcher. So far, the challenges arising from this combination have been addressed by externally aligning optical fibres with microfluidic glass capillaries, which has a limited potential for integration into lab-on-a-chip environments. Here we demonstrate the successful production and use of a monolithic glass chip for optical stretching of white blood cells, featuring microfluidic channels and optical waveguides directly written into bulk glass by femtosecond laser pulses. The performance of this novel chip is compared to the standard capillary configuration. The robustness, durability and potential for intricate flow patterns provided by this monolithic optical stretcher chip suggest its use for future diagnostic and biotechnological applications.

Coherent beam combination of fiber lasers with a strongly confined waveguide: numerical model

Self-imaging properties of fiber lasers in a strongly confined waveguide (SCW) and their application in coherent beam combination (CBC) are studied theoretically. Analytical formulas are derived for the positions, amplitudes, and phases of the N images at the end of an SCW, which is important for quantitative analysis of waveguide CBC. The formulas are verified with experimental results and numerical simulation of a finite difference beam propagation method (BPM). The error of our analytical formulas is less than 6%, which can be reduced to less than 1.5% with Goos-Hahnchen penetration depth considered. Based on the theoretical model and BPM, we studied the combination of two laser beams based on an SCW. The effects of the waveguide refractive index and Gaussian beam waist are studied. We also simulated the CBC of nine and 16 fiber lasers, and a single beam without side lobes was achieved.

The Improved Power of the Central Lobe in the Beam Combination and High Power Output

In order to increase the power fraction of the central lobe in the coherent beam combination of lasers in an array, the effects of the distance factor of near-field distribution on far-field interference patterns are calculated and demonstrated experimentally. An improved beam array of interwoven distribution is demonstrated to enable the power in the central lobe to reach 41%. An optimized mirror array is carefully designed to obtain a high duty ratio, which is up to 53.3% at a high power level. By using these optimized methods and designs, the passive phase locking of eight Yb-doped fiber amplifiers with ring cavities are obtained, and a pleasing interference pattern with 87% visibility is observed. The maximum coherent output power of the system is up to 1066 W.

Group delay locking of coherently combined broadband lasers

We demonstrate a method for single-detector coherent sensing and automated coalignment of group delays in a coherently combined laser array, enabling robust coherent combining of broadband sources despite initial path mismatches exceeding the laser coherence length. The method is based on Fourier-domain filtering of the coherently combined laser beam to extract error signals, and it is equally applicable to controlling both spatial and temporal misalignments.

抖动法激光阵列相干合成技术中的性能评价函数研究

抖动法激光阵列相干合成技术中的性能评价函数研究

Experimental investigation on coherent beam combination of a three-element fiber array based on target-in-the-loop technique

A kind of target-in-the-loop (TIL)technique which promises the coherent combination of multi-element laser beams in far field is experimentally demonstrated. The physical model of coherent beam combination (CBC)based on TIL is established. A kind of adaptive fiber optics collimator (AFOC)correcting optical path and tip/tilt errors simultaneously is employed to compensate phase errors between beamlets. The CBC of a 3-element fiber array based on TIL is successfully achieved and a perfect effect of CBC is captured. In this paper, we present a reference for long-distance transmission of multi-element coherent beams in real atmospheric environment.