Papers by Keyword: Femtosecond Laser

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Authors: Xiao Jun Yang, Ming Li, Li Wang, Hua Long Zhao, Guang Hua Chen
Abstract: Based on the femtosecond laser processing technology and PZT driving scanning technology,high-precision micro- manufacturing technology is developed. By adjusting the laser parameters and scanning parameters to get micro-hole machining on the flat or curved surface. Hole’s size and surface morphology is observed by using phase contrast microscopy and scanning electron microscopy observations, and the surface roughness is analyzed by the surface profile instrument. The feasibility of diesel injector nozzle processing is verified in practical industry applications. The results show that this method of making micro hole has significant advantages, such as high precision, good consistency, without burrs, good surface roughness and high efficiency. These characteristics can meet the practical application requirements and can be used in various industrial fields.
Authors: Dong Zhong, Zhong Ming Li, Ruo Lin Ruan, Chen Chun
Abstract: In the paper, the optical fiber F-P acoustic emission sensing probe has been proposed to monitor online space-time progress of femtosecond laser plasma shock wave for the first time, the structure of sensing probe is microstructure with full optical fiber probes without glue, it can measure weak acoustic emission high frequency signal on femtosecond laser plasma shock wave. In the process of femtosecond laser ablating copper, iron and aluminum, we research and analyze the plasma shock wave acoustic emission signal change regulation under different laser pulse energy and different distance between the laser and the optical fiber sensing probe, and we analyze the feature of the acoustic emission signal spectrum. Experiment establishes a kind of new optical fiber sensing measurement method for femtosecond laser plasma shock wave acoustic emission signal.
Authors: H.S. Sim, K.G. Kang, Seong Hyuk Lee, Jong Min Kim, Young Eui Shin
Abstract: The ultimate goals of this study are to investigate numerically nonequilibrium energy transfer between electrons and phonons, and to predict the crater formation shapes of gold thin film structures irradiated by femtosecond pulse lasers. In particular, the present article expands the onedimensional two-temperature model (1DTTM) to the two-dimensional model (2DTTM) considering wave interference, and it involves the quantum effect to predict thermal and optical properties. The predictions by using 2DTTM are extensively compared with those of 1DTTM, and the influence of film thickness on radiation heat transfer and optical characteristics are also examined. From the results, it is found that the predictions of 2DTTM are in good agreement with those of 1DTTM. As the gold film thickness decreases, the reflectivity decreases dramatically and the absorbed laser intensities at the top surface increases substantially because of wave interference in thin films.
Authors: Hua Long Zhao, Wen Yu Zhu, Xiao Jun Yang, Shi Fang Gao, Hong Yan Zhao
Abstract: Femtosecond laser with the features of ultrashort pulse duration and ultrahigh peak power can achieve “cold” machining. The recast layer and micro-cracks of the hole wall can be ruduced effectively by applying femtosecond laser in processing air-film holes on turbine blades, and the machining accuracy and consistency of the hole shape will increase. In this paper, the high-speed rotating femtosecond laser beam is adopted in several currently used turbine blade materials for air-film holes machining, and high quality air-film holes without hole wall recast layer and micro-cracks are processed through a large number of experiments to optimize machining technology and technological parameter.
Authors: Feng Wang, Jian Jun Luo, Ming Li, Yue Deng
Abstract: To solve the difficulties of processing micro holes on the CMC-SiC, femtosecond laser was used as the drilling tool in this paper. And a new type of laser beam scanning module was studied. The study confirms the feasibility of finishing the processing of micro holes whose diameter is less than 2mm on the new CMC-SiC. And the preliminary optimization of processing parameters is completed. According to the experimental results, the important factors affecting the quality of the micro holes were analyzed, and the factors are the processing power and the scanning speed. The results also show that the femtosecond laser processing technology can solve the difficulties of drilling mirco holes on the new CMC-SiC in our countrys aerospace field.
Authors: Yun Ping Pan, Wen Juan Yang, Yi Min Mo
Abstract: Short pulse lasers, including picosecond laser and femtosecond laser are involved to investigate the ablation characteristics of processing carbon fiber reinforced plastics (CFRPs). The ablation threshold of the femtosecond laser, 0.453 J/cm2, is twice higher than that of the picosecond laser 0.867 J/cm2, since the former generates an intense and shorter pulse and the atoms excitation and multi-photon absorption may occur as short as 10 ps or less. The ablation test also describes the processing qualities, where the femtosecond laser has processing abilities without visible thermal defects or charring over the picosecond laser.
Authors: Ding Kang Tang, Jian Guo Zhang, Yuan Shan Liu
Abstract: We experimentally demonstrate an all-fiber method to generate a high-quality femtosecond pulse train with a repetition rate of 40GHz. A continuous wavelength laser together with an intensity modulator is used to generate an initial pulse train with a repetition rate of 40GHz. Highly nonlinear fiber (HNLF) together with single mode fiber is utilized to compress the initial pulse from 7.8ps to 985fs. The autocorrelation trace has a good sech 2 profile with no pedestal. This pulse source has a potential to be multiplexed to a higher repetition rate for its narrow pulse width. This method is high-quality, cost-effective and can be easily integrated with the fiber system.
Authors: Peng Hui Rao, Bang Lei Huang, Jia Jun Wu, Heng Hu, Peng Fei Wei
Abstract: We investigate the angular distribution of high harmonic generation (HHG) from impulsively aligned CO2 molecules driving by the femtosecond laser. We first observe the HHG spectra under the different aligning angles and the different laser intensities. The angular distribution is found to be sensitive to both the harmonic order and the intensity of the driving laser pulse. At last, we theoretically and experimentally demonstrate the angular distribution with the different harmonic orders and the different laser intensities.
Authors: Chih Hua Hsieh, Po Hsien Tu, Jeng Ywan Jeng
Abstract: This paper proposes an idea for manufacturing internal patterns using a femtosecond laser. The femtosecond laser can easily be focused within transparent materials because of the advantages of multi-photon absorption and high energy density. The parameters of a femtosecond laser can be adjusted to modify the local area inside the glass and to design internal structures. The internal structures can produce optical effects. Through this process, optical plates can be manufactured in glass without wasting excess space.
Authors: Noritaka Kawasegi, Hiroshi Sugimori, Noboru Morita, Min Chao Xue
Abstract: Cutting and friction experiments were conducted in various atmospheres to investigate the chemical effect on textured cutting tools. The cutting experiments indicated that the atmosphere affected the machinability of the textured tools; a larger effect was observed in the presence of gas such as oxygen. A ball-on-disk friction apparatus was developed and used for the friction experiments. Smaller friction coefficients were observed in the presence of oxygen, a trend similar to that observed during the cutting experiments. These results indicate that oxidation is an important factor in determining the texture effect for machining aluminum alloy.
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