排序方式: 共有34条查询结果,搜索用时 15 毫秒
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层析成像图像重建算法综述 总被引:1,自引:0,他引:1
介绍了层析成像技术的图像重建算法,并从正向问题数学模型的简化和反向问题数学模型的映射结构的角度比较了各种算法的特点和优劣。研究表明:用本质是线性算法的各种变换方法重建图像存在严重失真,而卷积滤波的引入可以使变换方法的重建效果有所改善;基于导数搜索的迭代算法对初始值依赖性强、收敛速度慢并且容易陷入局部最优解;基于Fourier变换的方法具有本质的局限性;小波变换则可以同时刻画图像时域和频域的细节特征;有限元法通过重建对象像素的智能划分可以简化正问题的复杂性;而具有物理背景的蒙特卡罗法、模拟退火法、遗传算法、粒子滤波法及神经网络法更适合于复杂且非线性的图像重建;智能化、仿生化、并行化以及各种算法的融合是层析成像图像重建算法的发展趋势。 相似文献
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Two semiconductor saturable absorber mirrors (SESAMs), of which one is coated with 50% reflection film on the top and the other is not, were contrastively studied in passively mode-locked solid-state lasers which were pumped by low output power laser diode (LD). Experiments have shown that reducing the modulation depth of SESAM by coating partial reflection film, whose reflectivity is higher than that between SESAM and air interface, is an effective method to get continuous wave (CW) mode-locking instead of Q-switched mode-locking (QML) in low power pumped solid-state lasers. A simple Nd:YVO4 laser pumped by low power LD, in which no water-cooling system was used, could obtain CW mode-locking by the 50% reflector coated SESAM with average output power of ~ 20 mW. 相似文献
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We have demonstrated passive mode-locking in a diode-end-pumped Nd:YV04 laser using two kinds of semiconductor absorbers whose relaxation region comes from Ino.2sGao.75As grown at low temperature (LT) and GaAs/air interface respectively. Mode-locking, using absorbers of the GaAs/air interface relaxation region, has the characteristics of less Q-switching tendency and higher average output power than that using absorbers of LT In0.25Ga0.75As relaxation region, but is not as stable as the latter. 相似文献
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An L-shaped very-small-aperture laser (VSAL) with high power output and field enhancement effect is fabricated and characterized. As a comparison, a conventional rectangular VSAL and a double-aperture VSAL containing one L-aperture and one rectangular aperture are also fabricated and measured. The confined optical fields in the vicinity of apertures of VSAL are detected using an apertured near-field scanning optical microscope. The experimental results reveal that the power output from the L-shaped VSAL increases about 13 times than the rectangular VSAL with a comparable aperture area. It is indicated that the L-shaped VSAL has strong power output enhancement effect. The near-field distribution of the double-aperture VSAL indicates that the L-aperture has the field confinement and enhancement effect stronger than the rectangular aperture. 相似文献
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激光调频光纤位移传感器多路复用技术的研究 总被引:3,自引:1,他引:2
叙述了运用半导体激光器连续波调频外差干涉和频域多路复用原理,研究了光纤位移传感器多路复用技术。已研制成的分频与分幅相结合四路复用光纤位移传感器,可同时进行对多点、多维位移和多种物理量的测量,各路位移测量范围大于1mm,测量精度优于0.1μm及位移分辨率为0.01μm。 相似文献
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The longitudinal optical field is a peculiar physical phenomenon that is always involved with the domain of near-field optics. Due to its extraordinary properties, it has recently attracted increasing attention in research and application. In this work, the longitudinal fields generated by the evanescent illumination of tightly focused, different polarized hollow beams are investigated. The focused light fields are numerically simulated according to vector diffraction theory, and their vector analysis is also carried out. The longitudinal fields on the focal plane are demonstrated experimentally using tip-enhanced scanning near-field microscopy. The simulation and experimental results show that the tightly focused radially polarized beam is suited to generating a stronger and purer longitudinal optical field at the focus. 相似文献