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Research on the influence of alignment error on coupling efficiency and beam quality for Gaussian beam to multimode fiber
摘要： The effect of alignment error on the coupling efficiency and beam quality of a Gaussian beam coupled into a large-core multimode fiber is studied in this paper. The equations for evaluating the effect of alignment error on the coupling efficiency are derived separately, and verified with the method of simulation. The calculation and simulation results obtained are highly consistent. In the same way, the effects of alignment error on the beam power distribution are discussed. The results show that the lateral error will change the path of partial light to a large extent, and have a greater influence on the power distribution of the Gaussian beam than the longitudinal error and angular error do.
关键词： Multimode fiber,Coupling efficiency,Beam quality,Alignment error
更新于2025-09-23 15:23:52
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2nd-order random lasing in a multimode diode-pumped graded-index fiber
摘要： Raman lasing in a graded-index fiber (GIF) attracts now great deal of attention due to the opportunity to convert high-power multimode laser diode radiation into the Stokes wave with beam quality improvement based on the Raman clean-up effect. Here we report on the cascaded Raman generation of the 2nd Stokes order in the 1.1-km long GIF with 100-μm core directly pumped by 915-nm diodes. In the studied all-fiber scheme, the 1st Stokes order is generated at 950–954 nm in a linear cavity formed at GIF ends by two fiber Bragg gratings (FBGs) securing beam quality improvement from M2 ≈ 30 to M2 ≈ 2.3 due to special transverse structure of FBGs. The 2nd Stokes wave is generated either in linear (two FBGs) or half-open (one FBG) cavity with random distributed feedback via Rayleigh backscattering. Their comparison shows that the random lasing provides better beam quality and higher slope efficiency. Nearly diffraction limited beam (M2 ≈ 1.6) with power up to 27 W at maximum gain (996 nm), and 17 W at the detuned wavelength of 978 nm has been obtained, thus demonstrating that the 2nd-order random lasing in diode-pumped GIF with FBGs provides high-efficiency high-quality beam generation in a broad wavelength range within the Raman gain spectral profile.
关键词： laser diode,fiber Bragg gratings,beam quality,graded-index fiber,Raman lasing,random distributed feedback
更新于2025-09-23 15:21:21
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Evaluating the Potential of Laser Beam Quality Improvement by Adaptive Optics System
摘要： AO (adaptive optics) systems have been extensively used to improve the beam quality in high-energy lasers; however, few studies have focused on how much the beam quality could be improved. A novel evaluation criteria and factor is presented in this paper. The factor, defined as power in ring (PIR), is expressed by distinguishing the low- and high-spatial frequency components in the far-field laser intensity distribution. Beams with different PIR values are generated in our model, and then they are compensated by AO systems. Calculation result shows that the PIR factor could evaluate a laser beam’s improvement potential by an AO system quantitatively.
关键词： high-energy lasers,power in ring,adaptive optics,beam quality,spatial frequency
更新于2025-09-23 15:19:57
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High-Brightness Low-Divergence Tapered Lasers with a Narrow Taper Angle
摘要： High-brightness tapered lasers with photonic crystal structures are designed and fabricated. A narrow taper angle is designed for the tapered section. The device delivers an output power of 3.3 W and a maximum wall-plug efficiency of 43%. The vertical beam divergence is around 11° at different currents. Nearly diffraction-limited beam qualities for the vertical and lateral directions are obtained. The lateral beam quality factor ?? 2 is below 2.5 and the vertical ?? 2 value is around 1.5 across the whole operating current range. The maximum brightness is 85 MW·cm?2sr?1. When the current is above 3.3 A, the brightness is still above 80 MW·cm?2sr?1.
关键词： photonic crystal structures,tapered lasers,High-brightness,brightness,beam quality
更新于2025-09-23 15:19:57
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Calculation of kQ factors for Farmer-type ionization chambers following the recent recommendations on new key dosimetry data
摘要： Purpose: To calculate by Monte Carlo simulations kQ factors for Farmer-type ionization chambers in megavoltage photon beams using the new key dosimetry data recommended by the International Commission on Radiation Units and Measurements (ICRU) Report 90. Methods: Monte Carlo calculations were performed with the EGSnrc code system using both the ICRU 90 and the ICRU 37 data. Farmer-type ionization chambers with graphite and plastic walls and with graphite wall and a plastic waterproofing sleeve were considered (Nuclear Enterprise NE 2571, IBA FC65-G and FC65-P). kQ factors were calculated for photon beams in the range 6–25 MV using phase-space files as input radiation sources. The photon beam qualities in terms of TPR20,10 and %dd(10)x were established by simulating the depth-dose curves in water. Absorbed doses to the air cavity and to water were calculated using the egs_chamber user code with a target statistical uncertainty below 0.1%. Results: The update of key dosimetry data according to the ICRU report 90 had an impact of ?0.2% in the absorbed dose to water and up to 0.5% in the absorbed dose to the air cavity. Nevertheless, changes partially offset each other when entering in kQ as ratio, and the final impact on the kQ values was below 0.3%. Conclusions: The calculated values of kQ tend to be lower than the current values in the IAEA TRS-398 protocol with differences up to about 0.5%. A slightly better agreement (within 0.3%) is observed with the Monte-Carlo calculated values provided by the addendum to the AAPM’s TG-51 protocol.
关键词： Monte-Carlo calculated kQ,Beam quality correction factor,kQ,Radiotherapy dosimetry,ICRU 90
更新于2025-09-19 17:15:36
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Proof-of-Principle Experiment for Nanoparticle-Assisted Laser Wakefield Electron Acceleration
摘要： Laser electron accelerators have paved the way to build compact electron accelerators, but the quality of the electron beam should be improved to enable efficient use in various specialized applications. We demonstrate a proof-of-principle experiment for nanoparticle-assisted laser wakefield acceleration (NA LWFA) to improve the quality of the electron beam. Nanoparticles are generated through laser ablation of an aluminum target and introduced into a helium plasma to trigger the injection of electrons into the nonlinear plasma wake excited by 70 TW femtosecond laser pulses. We observe a significant enhancement of the electron beam energy, energy spread, and divergence compared with the case of self-injection. For instance, the best quality electron bunches present a maximum energy of up to 340 MeV, with a relative energy spread of 4.7% and a vertical divergence of 5.9 mrad. The initial results on NA LWFA are very promising and motivate further theoretical and experimental research into developing nanoparticle-assisted laser wakefield acceleration.
关键词： femtosecond laser pulses,electron beam quality,plasma wake,nanoparticle-assisted,laser wakefield acceleration
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Accurate, Fast and Robust Beam Characterization for Fiber Beams Based on Deep Learning
摘要： Fiber beam characterization based on deep learning, including mode decomposition and M2 evaluation, has been simulation and experiment. Deep learning enables not only high accuracy and speed but also high anti-noise ability.
关键词： Beam Quality,Mode Decomposition,Beam Characterization,Deep Learning
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Shenzhen, China (2019.9.3-2019.9.6)] 2019 IEEE 4th Optoelectronics Global Conference (OGC) - Ultra-High-Power and High-Efficiency 905nm Pulsed Laser for LiDAR
摘要： We report the design, fabrication and characterization of ultra-high-power and high-efficiency 905-nm pulsed lasers with four epitaxially stacked emitters connected by tunnel junctions for LiDAR application. The P-side-up submounted multimode lasers produce as high as 150 W at the current of 35 A and environmental temperature of 25°C. At the output power of 111.5 W, the Wall-Plug Efficiency and slope efficiency reach 41.4% and 4.66 W/A, respectively. The measurement shows 284-μm beam width and 12.6-degree horizontal far-field angle (95% power enclosure), indicating high brightness for this device, making it well-suited for long-distance and high-spatial-resolution range finding.
关键词： tunnel junction,temperature performance,ultra-high power,lidar,beam quality,semiconductor laser
更新于2025-09-16 10:30:52
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Photonic crystal spatial filtering in broad aperture diode laser
摘要： Broad aperture semiconductor lasers usually suffer from low spatial quality of the emitted beams. Due to the highly compact character of such lasers, the use of conventional intracavity spatial ?lters is problematic. We demonstrate that extremely compact photonic crystal spatial ?lters, incorporated into a laser resonator, can improve the beam spatial quality and, correspondingly, increase the brightness of the emitted radiation. We report the decrease in the M2 value from 47 down to 28 due to photonic crystal spatial intracavity ?ltering and the increase in the brightness by a factor of 1.5, giving a proof of principle of intracavity photonic crystal spatial ?ltering in broad area semiconductor lasers.
关键词： photonic crystal,spatial filtering,beam quality,broad aperture diode laser,brightness
更新于2025-09-16 10:30:52
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Optical Electronics (An Introduction) || 4. Optical fiber lasers
摘要： Because of their numerous advantages and potential applications, fiber lasers have attracted considerable attention since they first appeared in the 1960s. However, the output power of the early device was small, which restricted its application to a great extent. In the 1990s, with the invention of the double-clad fiber, the output of fiber lasers was greatly improved, which was comparable to that of the bulk lasers. Moreover, the characteristics of fiber lasers such as compact structure, high efficiency, and high beam quality are far superior than that of the traditional rod lasers. Therefore, in recent years, fiber laser technology and its applications have developed rapidly, becoming a new hot spot in the laser field.
关键词： double-clad fiber,laser technology,output power,fiber lasers,beam quality
更新于2025-09-16 10:30:52