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Добірка наукової літератури з теми "Beam quality, Beam Profile, High power laser"

Автор: Grafiati

Опубліковано: 6 вересня 2023

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Статті в журналах з теми "Beam quality, Beam Profile, High power laser"

Hou, Guanyu, Lijie Wang, Jian Feng, Andreas Popp, Berthold Schmidt, Huanyu Lu, Shili Shu, Sicong Tian, Cunzhu Tong, and Lijun Wang. "Beam Control in an Intracavity Frequency-Doubling Semiconductor Disk Laser." Applied Sciences 9, no. 8 (April 17, 2019): 1584. http://dx.doi.org/10.3390/app9081584.

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In this paper, we have demonstrated a 1.3 W green laser using a V-shaped intracavity frequency doubling 1036 nm semiconductor disk laser. The beam quality of the fundamental and second harmonic generation (SHG) laser is investigated. It has been found that the output lasers at the fundamental and SHG wavelength both suffer from reduced beam quality along with power scaling. The measured beam profile is elliptical under high power operation. In order to improve the SHG laser beam, an intracavity aperture is employed to control the mode characteristics of fundamental frequency light. By fine-tuning the aperture, a nearly circular beam profile with improving beam quality and brightness is realized.

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Nguyen, Thanh-Phuong. "Characterization of High-power DFB-MOPA Diode Lasers Emitting at 1064 nm." Communications in Physics 29, no. 1 (February 5, 2019): 47. http://dx.doi.org/10.15625/0868-3166/29/1/13221.

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Detail characterization of the such laser diode is important for the applications. Electro-Optical and spectral characteristics of the high power 1064 nm DFB-MOPA lasers are investigated at room temperature as function of injection current. Beam quality is characterized by waist diameter and far-field divergence angle versus average optical output power. Beam propagation ratio M2 is defined at difference intensity levels from lateral beam profile giving more detail laser behaviors at high power.

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Coroado, Julio, Supriyo Ganguly, Wojciech Suder, Stewart Williams, Sonia Meco, and Goncalo Pardal. "Selection of parameters in nanosecond pulsed wave laser micro-welding." International Journal of Advanced Manufacturing Technology 115, no. 9-10 (May 31, 2021): 2929–44. http://dx.doi.org/10.1007/s00170-021-07251-8.

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AbstractThe digital control of the latest nanosecond pulsed wave (PW) fibre lasers allows very high flexibility in controlling the application of the total energy to a workpiece, which brings several advantages to the joining process. By choosing different pulse shapes in different spatial profiles, it is possible to apply low energy per pulse with high precision and accuracy resulting in lower heat input. Since the energy of each pulse is insufficient to generate melting, these lasers operate at very high pulse repetition frequencies near continuous wave (CW) regime. Nevertheless, the peak powers of PW lasers are much higher than CW. In this research, the effect of peak power, pulse energy, pulse width, pulse repetition frequency and duty cycle has been studied. The experimental work was conducted in bead on plate of austenitic stainless steel to investigate the effect of laser on the weld geometry, i.e. depth of penetration and width. An empirical model, previously established for CW mode, which enables the achievement of a particular penetration depth independent of the beam diameter, was redesigned and tested for PW mode. The “pulse power factor model” allows the laser user to select a weld profile that meets certain quality and productivity requirements independent of the laser system. It was shown that identical depth of penetration but different weld metal profile can be obtained for a specific beam diameter for a range of different system parameters by keeping a constant trade-off between pulse power factor and interaction time.

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Ihama, Masahiro, Yuji Sato, Yuta Mizuguchi, Norio Yoshida, Sasitorn Srisawadi, Dhritti Tanprayoon, Tetsuo Suga, and Masahiro Tsukamoto. "Suppression of denudation zone using laser profile control in vacuum selective laser melting." Journal of Laser Applications 35, no. 1 (February 2023): 012004. http://dx.doi.org/10.2351/7.0000749.

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A vacuum selective laser melting method with a beam profile control was developed to fabricate the high quality 3D object. To investigate the quality of 3D fabrication, the denudation zone (DZ) as a quality indicator was evaluated to make a single bead. The main challenge is to clarify the correlation between the DZ and beam profiles. The beam profiles, such as a Gaussian mode, a doughnut mode, and a flat-top mode, were formed in several modes, by a dioptric system with a beam shaper. A stainless steel 316L (SS316L) powder was irradiated in arbitrary pressure to form a single bead, and then the DZ was measured. As a result, it was found that the flat-top mode recorded the minimum value of the DZ under atmospheric pressure. Thus, the dynamics of the metal vapor while the laser irradiation were observed by the Schlieren imaging technique under atmospheric pressure. The average velocity of metal vapor with flat-top mode was the slowest, i.e., 0.199 m/s. It was found that the DZ becomes small depending on the dynamics of metal vapor. The ambient pressure was reduced to 300 Pa in order to reduce the gas movement, and the DZ with flat-top mode was improved to record a minimum value of 0.048 mm, 1/3 of the DZ at atmospheric pressure.

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LUKISHOVA, SVETLANA G. "NONLINEAR OPTICAL RESPONSE OF CYANOBIPHENYL LIQUID CRYSTALS TO HIGH-POWER, NANOSECOND LASER RADIATION." Journal of Nonlinear Optical Physics & Materials 09, no. 03 (September 2000): 365–411. http://dx.doi.org/10.1142/s0218863500000212.

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Results from investigations are summarized into: (1) transient refractive and absorptive (two-photon) nonlinearities at 0.532 μm by the Z-scan method, and (2) reflective nonlinearity in the near-IR, of linearly nonabsorbing cyanobiphenyl liquid crystals under nanosecond laser irradiation. (1) For isotropic liquid crystals at the several-nanosecond time scale and several tens-micrometers beam-waist-diameter, transient molecular-reorientation and thermal/density refractive nonlinearities compete in changing the sign of the total transient refractive nonlinearity. For the different, given pulse durations, the influence of coupled thermal and density effects on nonlinear refraction depends, through buildup time, on the beam-waist diameter. Nonlinear absorption coefficients depend on the incident intensity. For planar nematic layers, cumulative effects in heating (and in refractive nonlinearity) were observed even at low, 2–10 Hz pulse repetition rate. These results are useful for optical power limiting applications, and for intensity and beam-quality sensors of pulsed, high-power lasers. (2) Reflective nonlinearity of chiral-nematic (cholesteric) mirrors near selective reflection conditions for circular polarized light at λ=1.064 μm was studied both under free space irradiation and inside a laser resonator. Specially chosen experimental irradiation conditions make it possible to attribute the observed changing of reflectivity to athermal helix unwinding by the optical field. The results can find applications in laser-resonator mirrors, Q-switches and soft apertures for beam-profile formation, and also in showing the limits of use cholesteric optical elements in high-power laser beams.

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Morimoto, Junji, Yutaka Katoh, Shinji Fukuhara, Nobuyuki Abe, Masahiro Tsukamoto, and Shigeru Tanaka. "Micro-Hardening of Carbon Steel with a Direct Diode Laser." Solid State Phenomena 118 (December 2006): 197–200. http://dx.doi.org/10.4028/www.scientific.net/ssp.118.197.

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Surface treatments, surface modification and surface engineering are required to improve the wear resistance, erosion resistance, friction resistance and corrosion protection. Transformation hardening of metals has been used since ancient times to increase the hardness and thereby vastly reduce the wear rate of metal surfaces in use. Today several processes are in use to achieve the controlled heating and rapid cooling required for transformation process. Transformation hardening is one of the most attractive processes for high power diode lasers, since their moderate beam quality and their low power density is sufficient for many applications. Generally laser hardening generates less distortion than conventional methods. In this study, the effect of laser beam characteristics (beam profile, power density, power etc) was examined on the micro hardening of carbon steel.

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Krainara, Siriwan, Shuya Chatani, Heishun Zen, Toshiteru Kii, and Hideaki Ohgaki. "Manipulation of Laser Distribution to Mitigate the Space-Charge Effect for Improving the Performance of a THz Coherent Undulator Radiation Source." Particles 1, no. 1 (November 7, 2018): 238–52. http://dx.doi.org/10.3390/particles1010018.

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A THz coherent undulator radiation (THz-CUR) source has been developed at the Institute of Advanced Energy, Kyoto University. A photocathode Radio-Frequency (RF) gun and a bunch compressor chicane are used for generating short-bunch electron beams. When the electron beam energy is low, the space-charge effect strongly degrades the beam quality, such as the bunch length and the energy spread at the high bunch charge condition at around 160 pC, and results in the reduction of the highest frequency and the maximum radiated power of the THz-CUR. To mitigate the space charge effect, we have investigated the dependence of the electron beam quality on the laser distribution in transverse and longitudinal directions by using a numerical simulation code, General Particle Tracer GPT. The manipulation of the laser distribution has potential for improving the performance of the THz-CUR source. The electron bunch was effectively compressed with the chicane magnet when the laser transverse distribution was the truncated Gaussian profile, illuminating a cathode. Moreover, the compressed electron bunch was shortened by enlarging the laser pulse width. Consequently, an enhancement of the radiated power of the THz-CUR has been indicated.

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Nahr, Florian, Dominic Bartels, Richard Rothfelder, and Michael Schmidt. "Influence of Novel Beam Shapes on Laser-Based Processing of High-Strength Aluminium Alloys on the Basis of EN AW-5083 Single Weld Tracks." Journal of Manufacturing and Materials Processing 7, no. 3 (May 9, 2023): 93. http://dx.doi.org/10.3390/jmmp7030093.

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The commonly used Gaussian intensity distribution during the laser-based processing of metals can negatively affect melt pool stability, which might lead to defects such as porosity, hot cracking, or poor surface quality. Hot cracking is a major factor in limiting production rates of high-strength aluminium alloys in laser-based processes such as welding or the powder bed fusion of metals (PBF-LB/M). Going away from a Gaussian intensity distribution to ring-shaped profiles allows for a more even heat distribution during processing, resulting in more stable melt pools and reduced defect formations. Therefore, the aim of this study is to investigate the influence of different laser beam profiles on the processing of high-strength aluminium alloys by using a multicore fiber laser, allowing for in-house beam shaping. Single weld tracks on the aluminium alloy EN AW-5083 are produced with varying laser powers and weld speeds, as well as different beam profiles, ranging from Gaussian intensity distribution to point/ring profiles. The molten cross sections are analyzed regarding their geometry and defects, and the surface roughness of the weld tracks is measured. By using point/ring beam profiles, the processing window can be significantly increased. Hot cracking is considerably reduced for weld speeds of up to 1000 mm/s compared to the Gaussian beam profile. Furthermore, the melt pool width and depth are more stable, with varying parameters for the point/ring profiles, while the Gaussian beam tends to keyhole formation at higher beam powers. Finally, a strong decrease in surface roughness for the point/ring profiles, accompanied by a significantly reduced humping effect, starting even at lower beam powers of 200 W, can be observed. Therefore, these results show the potential of beam shaping for further applications in laser-based processing of high-strength aluminium alloys.

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Laptev, Alexei V., Gleb V. Kuptsov, Vladimir A. Petrov, and Victor V. Petrov. "ASTIGMATISM COMPENSATION IN BLOCK OF TEMPORAL BROADENING OF PULSE FOR PUMP CHANNEL OF HIGH POWER LASER SYSTEM." Vestnik SSUGT (Siberian State University of Geosystems and Technologies) 25, no. 4 (2020): 205–12. http://dx.doi.org/10.33764/2411-1759-2020-25-4-205-212.

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A high peak and high average power femtosecond laser system based on media doped with Yb3+ ions is being developed at the Institute of Laser Physics of the SB RAS. For efficient laser amplification and to avoid optical damage is actually to compensate wave front distortion caused by grating astigmatism in pump channel. Based on theory of propagation of gaussian beam in space and through optical elements the calculation of optimal parameters of two lenses telescope and comparison with experimental data has been performed. The obtained results can be used for decrease of astigmatic effect on beam profile quality in design of laser systems with elements involving astigmatism.

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Li, Peizhi, Yu Fan, Chonghao Zhang, Zhiyuan Zhu, Wenteng Tian, and Anmin Liu. "Research on Heat Source Model and Weld Profile for Fiber Laser Welding of A304 Stainless Steel Thin Sheet." Advances in Materials Science and Engineering 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/5895027.

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A heat source model is the key issue for laser welding simulation. The Gaussian heat source model is not suitable to match the actual laser weld profile accurately. Furthermore, fiber lasers are widely recognized to result in good-quality laser beam output, a narrower weld zone, less distortion, and high process efficiency, compared with other types of lasers (such as CO2, Nd : YAG, and diode lasers). At present, there are few heat source models for fiber laser welding. Most of researchers evaluate the weld profile only by the bead width and depth of penetration, which is not suitable for the laser keyhole welding nail-like profile. This paper reports an experimental study and FEA simulation of fiber laser butt welding on 1 mm thick A304 stainless steel. A new heat source model (cylindrical and cylindrical) is established to match the actual weld profile using Marc and Fortran software. Four bead geometry parameters (penetration depth, bead width, waist width, and depth of the waist) are used to compare between the experimental and simulation results. The results show that the heat source model of cylindrical and cylindrical can match the actual shape of the fiber laser welding feasibly. The error range of the penetration depth, bead width, waist width, and depth of the waist between experimental and simulation results is about 4.1 ± 1.6%, 2.9 ± 2.0%, 13.6 ± 7.4/%, and 18.3 ± 8.0%, respectively. In addition, it is found that the depth of penetration is more sensitive to laser power rather than bead width, waist width, and depth of the waist. Welding speed has a similar influence on the depth of penetration, weld width, waist width, and depth of the waist.

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Більше джерел

Дисертації з теми "Beam quality, Beam Profile, High power laser"

Lang, Lei. "Investigation of optical filtering techniques for improving the beam quality of high-power semiconductor laser diodes." Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546489.

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Zeghuzi, Anissa. "Analysis of Spatio-Temporal Phenomena in High-Brightness Diode Lasers using Numerical Simulations." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/22016.

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Breitstreifenlaser haben eine breite Emissionsapertur, die es ermöglicht eine hohe Ausgangsleistung zu erreichen. Gleichzeitig führt sie jedoch zu einer Verringerung der lateralen Strahlqualität und zu ihrem nicht-stationären Verhalten. Forschung in diesem Gebiet ist anwendungsgetrieben und somit ist das Hauptziel eine Erhöhung der Brillanz, die sowohl die Ausgangsleistung als auch die laterale Strahlqualität beinhaltet. Um die zugrunde liegenden raumzeitlichen Phänomene zu verstehen und dieses Wissen zu nutzen, um die Kosten der Brillanz-Optimierung zu minimieren, ist ein selbst-konsistentes Simulationstool notwendig, welches die wichtigsten Prozesse beinhaltet. Zunächst wird in dieser Arbeit ein quasi-dreidimensionales elektro-optisch-thermisches Model präsentiert, welches wesentliche qualitative Eigenschaften von realen Bauteilen gut beschreibt. Zeitabhängige Wanderwellen-Gleichungen werden genutzt, um die inhärent nicht-stationären optischen Felder zu beschreiben, welche an eine Ratengleichung für die Überschussladungsträger in der aktiven Zone gekoppelt sind. Das Model wird in dieser Arbeit um eine Injektionsstromdichte erweitert, die laterale Stromspreizung und räumliches Lochbrennen korrekt beschreibt. Des Weiteren wird ein Temperaturmodel präsentiert, das kurzzeitige lokale Aufheizungen in der Nähe der aktiven Zone und die Formierung einer stationären Temperaturverteilung beinhalten. Im zweiten Teil wird das beschriebene Modell genutzt, um die Gründe von Brillanz-Degradierung, das heißt sowohl die Ursprünge der Leistungssättigung als auch des nicht diffraktionslimitierten Fernfeldes zu untersuchen. Abschließend werden im letzten Teil Laserentwürfe besprochen, welche die laterale Brillanz verbessern. Hierzu gehört ein neuartiges “Schachbrettlaser” Design, bei dem longitudinal-laterale Gewinn-Verlust-Modulation mit zusätzlicher Phasenanpassung ausgenutzt wird, um eine sehr geringe Fernfeld-Divergenz zu erhalten.
Broad-area lasers are edge-emitting semiconductor lasers with a wide lateral emission aperture that enables high output powers, but also diminishes the lateral beam quality and results in their inherently non-stationary behavior. Research in the area is driven by application and the main objective is to increase the brightness which includes both the output power and lateral beam quality. To understand the underlying spatio-temporal phenomena and to apply this knowledge in order to reduce costs for brightness optimization, a self-consistent simulation tool taking into account all essential processes is vital. Firstly, in this work a quasi-three-dimensional opto-electronic and thermal model is presented, that describes well essential qualitative characteristics of real devices. Time-dependent traveling-wave equations are utilized to describe the inherently non-stationary optical fields, which are coupled to dynamic rate equations for the excess carriers in the active region. This model is extended by an injection current density model to accurately include lateral current spreading and spatial hole burning. Furthermore a temperature model is presented that includes short-time local heating near the active region as well as the formation of a stationary temperature profile. Secondly, the reasons of brightness degradation, i.e. the origins of power saturation and the spatially modulated field profile are investigated and lastly, designs that mitigate those effects that limit the lateral brightness under pulsed and continuous-wave operation are discussed. Amongst those designs a novel “chessboard laser” is presented that utilizes longitudinal-lateral gain-loss modulation and an additional phase tailoring to obtain a very low far-field divergence.

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Panda, Binodbihari. "A simple method for measurement of high power, inline beam quality of high-power lasers." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4793.

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Over the past few decades, applications of high-power fiber laser in the area of material processing, medicine, defence, high precision micro-machining etc., is rapidly increasing. The primary reason behind thriving applications is the exceptional power scaling which is due to unique advantages like better thermal management, compact size, cost effectiveness, high quantum efficiency and excellent beam quality. High power fiber laser has a gain medium which is a long cylindrical geometry of optical fiber and thus, provides a high surface to volume ratio. The heat generated during lasing is distributed over longer fiber length and provides better thermal management as compared to other solid-state and gas-based lasers. However, power scaling of high-power fiber lasers has required the use of Large Mode Area(LMA) fibers to increase the dimension of gain medium(fiber core) to accommodate more power. The excitation mechanism of those lasers is also becoming more complex, which is leading to the presence of higher order waveguide modes supported by these larger fibers in the output beam profile. Therefore, the measurement of the beam quality of the laser (represented by the parameter M2 ) is imperative. Conventional M2 measurement methods such as moving knife-edge, variable aperture, moving slit method etc. uses CCD, CMOS or InGaAs detectors and these detector-based methods are not reliable at high power, because of their very low saturation powers. Therefore, with these measurement techniques, high-power beams need to be attenuated and this attenuation has the potential for substantial distortion of the inherent beam profile thereby degrading the beam quality. Other methods using modal decomposition of different constituent eigenmodes are also suggested to measure M2. However, they are complex and not very accurate. In this work, a high power 100Watt Ytterbium doped fiber laser is built, and its beam profile is characterized with a newly proposed method. A simple, cost-effective and alternative thermal imaging-based measurement technique is implemented to measure both beam profile and beam quality of high-power laser beam at full power without additional attenuation or beam diversion. This technique is wavelength agile, robust and can be easily implemented in any high-power laser laboratory where the thermal camera is readily available.

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Cai, Yu-Liang, and 蔡宇亮. "Improving the beam quality of high power laser field and the application on laser drilling." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/86657528133454940210.

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碩士
國立清華大學
物理系
100
In amplification of high-power laser, the high-spatial-frequency components are generated usually, causing the defect in laser beam profile. Therefore, we design an optical spatial filter to improve the beam profile of narrow-band Nd:YAG laser in our experimental system. According Fourier optics, Fourier power spectrum is produced in the focal plane of lens. The higher spatial-frequency components are located at the position far from optical axis. Thus, an aperture with proper size can be used to remove high-spatial-frequency noise so that the beam profile is improved. We apply an aperture with conical shape. This design can increase the interaction area of incident beam and material surface lead to longer lifetime for aperture. In order to reduce the air plasma and damage of aperture, we fix the aperture in a glass vacuum tube. The minimum aperture size is 380 μm and material is stainless steel. Experimental results show the beam profile is improved obviously and the aperture can tolerate intensity 16.9 TW/cm2. Besides, we apply this spatial filter to the phase measurement system and laser processing. The spatial stability of interference pattern and the quality of laser processing are better than before.

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Частини книг з теми "Beam quality, Beam Profile, High power laser"

Schildbach, K. "Resonator Design and Beam Quality of High Power YAG-Lasers." In Laser/Optoelektronik in der Technik / Laser/Optoelectronics in Engineering, 327–31. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-83174-4_69.

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Bakker, J., and J. G. van der Laan. "A Diagnostic Device for Beam Profile Measurements of Pulsed High Power Solid State Lasers." In Laser/Optoelektronik in der Technik / Laser/Optoelectronics in Engineering, 438. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-48372-1_92.

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Eichler, Hans J., Andreas Haase, Baining Liu, and Jörg Schwartz. "Phase-Conjugating SBS Mirrors for Realisation of High-Power Laser Systems with Diffractation-Limited Beam Quality." In Laser in Forschung und Technik / Laser in Research and Engineering, 800–810. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-80263-8_161.

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Komori, Hiroshi, Hidetomi Ochi, Toshihiro Nishisaka, Ryoichi Nodomi, Yasuo Itakura, Kazuaki Sajiki, and Shuji Murai. "High-power high beam quality ArF laser." In Laser and Ion Beam Modification of Materials, 193–98. Elsevier, 1994. http://dx.doi.org/10.1016/b978-0-444-81994-9.50044-0.

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Jin, Hong, Seong Ku, Jin Woo, Jae Sung, and Sangwoo Park. "Stimulated Brillouin Scattering Phase Conjugate Mirror and its Application to Coherent Beam Combined Laser System Producing a High Energy, High Power, High Beam Quality, and High Repetition Rate Output." In Advances in Lasers and Electro Optics. InTech, 2010. http://dx.doi.org/10.5772/8640.

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Тези доповідей конференцій з теми "Beam quality, Beam Profile, High power laser"

Tatum, Jim A., Roman Strozewski, Harvey B. Serreze, and Duncan L. MacFarlane. "Beam quality in high-power visible-region diode lasers." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/oam.1993.fcc.4.

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Applications of visible diode lasers such as laser pumping, plastic fiber optics, optical storage, and laser printing rely on the ability to control the spatial profile and precise positioning of laser radiation.

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Somkuarnpanit, S., D. Su, D. R. Hall, and J. D. C. Jones. "High-quality CO2 laser beam delivery using dielectric-coated metallic hollow waveguides." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/cleo_europe.1994.cthi21.

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Over the past decade, a number of different types of hollow waveguides have been used for the delivery of CO2 laser radiation.1-3 However, much of the previous work has been concentrated on beam attenuation and the power transmission characteristics of the waveguide, whereas to take full advantage of the available CO2 laser technology, i.e., a combination of high power and high beam quality, it is necessary to try to preserve beam quality in the passage of the beam through the fibre. The principal object of this paper is to investigate the transmission properties of hollow wave guides for the case when high-quality CO2 laser beams are launched efficiently at the input. In a number of important applications of carbon dioxide lasers, beam quality issues are very important, not only in terms of the achievable spot size, but also as regards the transverse intensity profile.

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Perrone, M. R., and D. Diso. "Time evolution of the beam quality factor in Gaussian cavities of different length." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.ctui16.

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The improvement of the optical quality of the laser radiation delivered by high-power excimers is strongly demanded to achieve a greater utilization of their laser energy. Moreover, in applications in which excimers are used for precision drilling, cutting and writing diffractive optical elements, laser beams of low divergence and with a quite uniform intensity profile are needed. Recently, plane-parallel cavities with a Gaussian-reflectivity-profile mirror as full reflector have been applied to a XeCl laser and it has been shown that excimer lasers fitted with plane-parallel Gaussian cavities deliver laser beams with quite uniform intensity profiles and with beam-quality-factor M2 more than 50% smaller than that of laser beams delivered by plane-parallel cavities using conventional high reflectivity mirrors as full reflectors [1].

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Dai, Zheng, and Peter Unger. "Simulation of Beam Filamentation in High-Power Semiconductor Amplifiers." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.cthi30.

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The suppression of beam-profile filamentation is a challenging task for semiconductor laser amplifiers. In recent times, diffraction-limited, high-power amplification up to 5 W CW and 21 W under pulsed operation has been achieved [1]. In order to obtain high-power amplification with good beam quality, we have used the beam propagation method (BPM) to simulate the disturbance of the refractive index variation. In this paper, we will discuss different mechanisms of the beam filamentation and methods to avoid it.

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Wen, Shaoyi, and Yung C. Shin. "Modeling of the Off-Axis High Power Diode Laser (HPDL) Cladding Process." In ASME 2009 International Manufacturing Science and Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/msec2009-84049.

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Off-axis high power diode laser (HPDL) cladding is commonly used for surface quality enhancement such as coating, part repairing, etc. Although some laser cladding models are available in the literature, little has been reported on modeling of powder flow and molten pool for a rectangular beam with side powder injection. In this article, a custom-designed flat nozzle delivers the powder material into a distinct molten pool formed by a high power diode laser (HPDL) with a rectangular beam. A powder model is first presented to reveal the powder flow behavior below the flat nozzle. Key parameters such as the nozzle inclination angle, the rectangular beam profile, shielding gas flow rates and powder feed rate are incorporated so that spatial powder density, powder velocity and temperature distribution are distinctly investigated. Then in order to describe thermal and fluidic behavior around the molten pool formed by the rectangular beam, a three dimensional self-consistent cladding model is developed with the incorporation of the distributed powder properties as input. The level set method is adopted to track the complex free surface evolution. Temperature fields and fluid motion in the molten pool area resulting from the profile of rectangular beam are distinctly revealed. The effect of continuous mass addition is also embedded into the governing equations, making the model more accurate. A HPDL cladding with little dilution is formed and the simulated result agrees well with the experiment.

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Saltarelli, F., D. Koenen, L. Lang, I. J. Graumann, C. R. Phillips, and U. Keller. "Beam quality in high-power thin-disk lasers: influence and measurement of the radial inversion profile." In Advanced Solid State Lasers. Washington, D.C.: OSA, 2019. http://dx.doi.org/10.1364/assl.2019.jm5a.35.

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Kubacki, Frank, Dirk Hauschild, Mikhail Ivanenko, Jens Meinschien, Andreas Bayer, and Vitalij Lissotschenko. "Dynamic Thermal Thin Film Processing of Large Areas With High Power Laser Sources." In ASME 2009 International Manufacturing Science and Engineering Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/msec2009-84105.

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High power laser sources are used in various production tools for cutting, welding and hardening of metal parts and patterning, annealing and lithography of flat panel displays, solar cells and microelectronic devices. Beside the right choice of the laser source suitable high performance optical beam delivery and shaping systems are needed for generating the appropriate beam profile and intensity distribution are of high importance for the right processing speed, quality and yield. In addition to the typical laser processes with circular beam shapes LIMO has developed laser sources with line shaped beams for large area processing for e.g. crystallization and tempering of conducting and semi-conducting films on glass for FPD, PV and thermal processing of semiconductor wafer, coated float glass and sheet metal. Due to the high power density of several 100kW/cm2 and line length up to several hundred millimetres a treatment capacity of several m2 per minute and processing speeds up to 1 m/s can be achieved per laser head with typical scan & repeat processes. The use of multiple laser heads in one machine scales the productivity to the individual needs. The high scanning speed together with line widths of 0,01mm to 0,1mm is the basis for heating only a few microns of the surfaces layers and no costly cooling time is needed like with regular heating technologies. With this controlled surface heating even more sensitive materials can be processes like inks on polymers and paper for RFIDs, printed solar absorbers and coatings. For industrial applications equally important is an adequate understanding of the physics of the light-matter interaction behind the process. In advance simulations of the tool performance can minimize technical and financial risk as well as lead times for prototyping and introduction into series production. Based on this knowledge together with a unique free-form micro-lens array production technology and patented micro-optics beam shaping designs a number of novel production tool sub-systems have been built by LIMO: 1. a multi-kilowatt direct diode illumination modules for solar cell annealing, and crystallization; 2. a novel green laser beam line for the annealing of silicon thin films on glass; 3. a novel wavefront shaping optics that generates a top hat beam profile from a TEM00 high-power laser source for accurate thin film structuring. For each of these sub-system basic functionalities, design principles and performance results are presented with a special emphasis on resilience, cost reduction and process reliability.

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Schoeffel, Kevin C., and Yung C. Shin. "Laser Cladding of Two Hardfacing Alloys Onto Cylindrical Low Alloy Steel Substrates With a High Power Direct Diode Laser." In ASME 2007 International Manufacturing Science and Engineering Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/msec2007-31112.

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Blown-powder laser cladding is an efficient method for enhancing the surface properties of engineering components while preserving the properties of the base material. High power direct diode lasers (HPDDLs) offer wide beams with nearly uniform intensity distribution, allowing the deposition of wide clad tracks with flatter profiles than those produced with a Gaussian beam. In this work, a 4.0 kW HPDDL is used to perform blown-powder cladding on AISI 4140 and AISI 5150 steel shafts. The first part of the experiments concerns two-layer circumferential tracks created from two commonly used hardfacing alloys: Stellite 6 (Co-Cr alloy) and Nistelle 625 (Ni-Cr alloy). The effects of laser power and powder feed rate on the clad geometry are assessed. Increasing the powder feed rate and holding constant all other parameters decreases the track width-to-thickness aspect ratio. All tracks exhibit dendrite microstructures that are characteristic of powder-based clad tracks. The tracks exhibit no cracks or porosity. Energy dispersive X-ray (EDX) analysis reveals dilution of five percent or less between the clad and substrate materials. The second part of the experiments concerns overlapping of single-layer clad tracks in a continuous helical pattern on the substrate to form a layer that covers a large area. Clad layer thickness and inter-track porosity are measured to determine the optimum degree of overlap for producing a high-quality clad layer. The thickness of the resulting Stellite 6 and Nistelle 625 clad layers decreases as the overlap percentage decreases. No inter-track, interfacial, or bulk pores are present for any tests, comprising overlap percentages of 50% and lower.

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Chazan, P., and J. D. Ralston. "Beam Propagation Model of Tapered Amplifiers including Non-Linear Gain and Carrier Diffusion." In Semiconductor Lasers: Advanced Devices and Applications. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/slada.1995.tuc.5.

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Recent interest in high-power single-mode diode lasers has led to the evaluation of a variety of semiconductor amplifier geometries [1], integrated master oscillator power amplifier (MOPA), designs and flared oscillator devices. Flared amplifiers and oscillators have been found to be less sensitive to filamentation effects than broad area devices, although filamentation still ultimately limits the performance of such devices [2]. Using a FD-BPM model we investigate the performance to be expected from various flared laser structures in terms of both output power and beam quality. We clarify the influence of such material parameters as the number of quantum wells, the differential quantum efficiency and the linewidth enhancement factor on the output beam profile of the amplifier. We point out the influence of the linewidth enhancement factor showing that a reduction of this factor improves the output beam quality, the resistance to inhomogeneous injection, and the output farfield. Furthermore, a simulation of a 2D integrated elliptical lens is presented, showing the possibility of ‘on chip’ correction of the astigmatism for low α-factor structures. Such a lens would spare the use of an external cylindrical lens for collimation of the output signal.

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Bu¨ttner, Lars, and Ju¨rgen Czarske. "Multimode Laser Doppler Anemometer for Turbulence Measurements With High Spatial Resolution." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45598.

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The advantageous employment of multimode fibres for beam delivery in laser Doppler anemometers (LDA) is presented. Turbulent boundary layers can be investigated with high precision and high spatial resolution. For measurements of turbulence data usually hot wire anemometers are employed which, however, do not fulfil the requirement of non-intrusiveness. Therefore laser Doppler anemometers are employed which are limited by the size of their measurement volume of usually about 50 μm × 100 mm. The spatial resolution can be improved by a stronger focusing or by using a side receiver, which restricts the detection area. Furthermore, the measurement of turbulence data is limited by the varying fringe spacing, which pretends a non-existing degree of turbulence (“virtual turbulence”) and is caused by the wave-front curvature of the employed Gaussian laser mode. In this contribution it is demonstrated, that the employment of multimode-light with beam quality factors M2 >> 1 the length of the measurement volume is reduced to a few percent compared to the intersection volume length of the two laser beams because of the low spatial coherence of the multimode light. The uniformity of the fringe spacing is significantly improved. The variation of fringe spacing (“virtual turbulence”) is less than 0.05%. The multimode-fibre LDA (MMF-LDA) combines the advantages of both a short measurement volume guaranteeing a high spatial resolution as well as low virtual turbulence in one device. It is therefore well suited for high accurate determination of velocity gradients in laminar or turbulent boundary layers. A MMF-LDA with about 100 fringes and 5·10−4 fringe spacing variation within a measurement volume of length 80 μm was used to perform fluid measurements in a wind tunnel. The remaining turbulence intensity of the free wind tunnel stream was determined to 0.3%. Boundary layer measurements on a well-known laminar velocity profile, the Blasius boundary layer, were performed and the wall shear stress was determined. All results are in excellent agreement with the theory. Measurements of turbulent boundary layers are presented. Multimode fibres allow the transfer of significantly higher power into the LDA measurement volume and need lower alignment effort compared to the usually employed single-mode fibres. Powerful laser diodes can now be applied for LDA set-ups, enabling sensitive velocity measurements of fluid flows.

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