The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror （SESAM）. Two narrow-band fiber Bragg gratings cent...The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror （SESAM）. Two narrow-band fiber Bragg gratings centered at 1029.9nm and 1032nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9nm and 1032nm. The laser delivers different pulse widths of 7.5ps for 1030nm and 20ps for 1032nm. The maximum output power for both could reach -6.5mW at single pulse operation. The output wavelength couM be tuned to about 0.gnm intervals ranging from 1030.2nm to 1031.1 nm and from 1032.15nm to 1033.7nm with the temperature change of the fiber Bragg grating, respectively.展开更多
The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier...The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.展开更多
We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wav...We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of - 20 nm and from - 0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.展开更多
烟丝的宽度是衡量卷烟质量的重要指标,为了能够实时把控烟丝质量,该文设计一种烟丝宽度实时在线检测方法。该文将YOLOv4中的SPP和PANet结构进行融合,并将输出三种输出尺度改为一种输出尺度,使改进后的YOLOv4算法结构更加简单,在性能几...烟丝的宽度是衡量卷烟质量的重要指标,为了能够实时把控烟丝质量,该文设计一种烟丝宽度实时在线检测方法。该文将YOLOv4中的SPP和PANet结构进行融合,并将输出三种输出尺度改为一种输出尺度,使改进后的YOLOv4算法结构更加简单,在性能几乎不下降的情况下,运算速度提升近35%;烟丝宽度计算方法是该文设计的MCS(Moving Center Search)中心移动搜索法。该方法能够自动搜索出烟丝的两个侧边,并较为精确地计算出烟丝宽度,计算精度可达0.2毫米。将MCS烟丝宽度计算方法与该文改进后的YOLOv4模型相结合,能够进行实时在线的烟丝宽度检测,实时把控烟丝生产质量,提升生产效率。展开更多
我国东北地区气候寒冷,低温事件会严重影响树木生长。水曲柳是东北地区珍贵的用材树种,目前关于其纤维解剖特征对低温的响应与适应策略还知之甚少。为此,以小兴安岭地区水曲柳子代测定林为研究对象,采用树轮年代学和木材解剖学方法,研...我国东北地区气候寒冷,低温事件会严重影响树木生长。水曲柳是东北地区珍贵的用材树种,目前关于其纤维解剖特征对低温的响应与适应策略还知之甚少。为此,以小兴安岭地区水曲柳子代测定林为研究对象,采用树轮年代学和木材解剖学方法,研究水曲柳纤维解剖特征与主要气候因子之间关系,明确低温对木材纤维解剖特征的影响。结果表明,小兴安岭地区水曲柳木纤维解剖特征具有较大的年际变化,木纤维细胞数量(fiber cell number,FN)、木纤维细胞总面积(total fiber cell area,TFA)与年轮宽度(ring width,RW)存在极显著正相关关系,在幼龄林阶段均呈现先升后降的变化趋势。木纤维细胞密度(fiber density,FD)和总体平均木纤维细胞壁增强指数(square of the total-to-bound ratio,(T/B)2)呈现逐年下降的趋势。平均木纤维细胞面积(mean fiber cell area,MFA)和木纤维细胞壁厚度(overall mean thickness of all fiber cell walls,CWTall)呈现逐年增加的趋势。水曲柳纤维解剖特征受温度影响较大,尤其是生长季最低温。低温事件使水曲柳的径向生长受到抑制,年轮宽度、木纤维细胞数量、平均木纤维细胞面积、木纤维细胞总面积和木纤维细胞占比(mean percentage of fiber cell area within xylem,RFTA)较非低温年分别显著下降32.6%、20.3%、22.4%、45.9%和9.4%,而木纤维细胞密度升高11.6%。在面对低温事件时,水曲柳会采取减少木纤维细胞数量、提高木纤维细胞密度这一相对保守的生存策略。研究结果为小兴安岭地区耐寒水曲柳选育提供科学依据。展开更多
基金Supported by the National High Technology Research and Development Program of China under Grant No 2014AA041901NSAF Foundation of the National Natural Science Foundation of China under Grant No U1330134+1 种基金the Opening Project of Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques under Grant No 2012ADL02the National Natural Science Foundation of China under Grant Nos 61308024 and 11174305
文摘The wavelength-tunable and switchable narrow bandwidth mode-locking operation is demonstrated in an all fiber laser based on semiconductor-saturable absorber mirror （SESAM）. Two narrow-band fiber Bragg gratings centered at 1029.9nm and 1032nm respectively with a polarization controller inserted between them are used to realize the wavelength switchable between 1029.9nm and 1032nm. The laser delivers different pulse widths of 7.5ps for 1030nm and 20ps for 1032nm. The maximum output power for both could reach -6.5mW at single pulse operation. The output wavelength couM be tuned to about 0.gnm intervals ranging from 1030.2nm to 1031.1 nm and from 1032.15nm to 1033.7nm with the temperature change of the fiber Bragg grating, respectively.
基金supported by the National Natural Science Foundation of China(Grant Nos.11404404 and 11274385)the Outstanding Youth Fund Project of Hunan Provincethe Fund of Innovation of National University of Defense Technology,China(Grant No.B120701)
文摘The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.
基金Project supported by the National Natural Science Foundation of China(Grant No.61575137)the Program on Social Development by Department of Science and Technology of Shanxi Province,China(Grant No.20140313023-3)
文摘We demonstrate a flexible erbium-doped pulsed fiber laser which achieves the wavelength and pulse width tuning by adjusting an intracavity filter. The intracavity filter is flexible to achieve any of the different wavelengths and bandwidths in the tuning range. The wavelength and width of pulse can be tuned in a range of - 20 nm and from - 0.8 ps to 87 ps, respectively. The flexible pulsed fiber laser can be accurately controlled, which is insensitive to environmental disturbance.
文摘烟丝的宽度是衡量卷烟质量的重要指标,为了能够实时把控烟丝质量,该文设计一种烟丝宽度实时在线检测方法。该文将YOLOv4中的SPP和PANet结构进行融合,并将输出三种输出尺度改为一种输出尺度,使改进后的YOLOv4算法结构更加简单,在性能几乎不下降的情况下,运算速度提升近35%;烟丝宽度计算方法是该文设计的MCS(Moving Center Search)中心移动搜索法。该方法能够自动搜索出烟丝的两个侧边,并较为精确地计算出烟丝宽度,计算精度可达0.2毫米。将MCS烟丝宽度计算方法与该文改进后的YOLOv4模型相结合,能够进行实时在线的烟丝宽度检测,实时把控烟丝生产质量,提升生产效率。
文摘我国东北地区气候寒冷,低温事件会严重影响树木生长。水曲柳是东北地区珍贵的用材树种,目前关于其纤维解剖特征对低温的响应与适应策略还知之甚少。为此,以小兴安岭地区水曲柳子代测定林为研究对象,采用树轮年代学和木材解剖学方法,研究水曲柳纤维解剖特征与主要气候因子之间关系,明确低温对木材纤维解剖特征的影响。结果表明,小兴安岭地区水曲柳木纤维解剖特征具有较大的年际变化,木纤维细胞数量(fiber cell number,FN)、木纤维细胞总面积(total fiber cell area,TFA)与年轮宽度(ring width,RW)存在极显著正相关关系,在幼龄林阶段均呈现先升后降的变化趋势。木纤维细胞密度(fiber density,FD)和总体平均木纤维细胞壁增强指数(square of the total-to-bound ratio,(T/B)2)呈现逐年下降的趋势。平均木纤维细胞面积(mean fiber cell area,MFA)和木纤维细胞壁厚度(overall mean thickness of all fiber cell walls,CWTall)呈现逐年增加的趋势。水曲柳纤维解剖特征受温度影响较大,尤其是生长季最低温。低温事件使水曲柳的径向生长受到抑制,年轮宽度、木纤维细胞数量、平均木纤维细胞面积、木纤维细胞总面积和木纤维细胞占比(mean percentage of fiber cell area within xylem,RFTA)较非低温年分别显著下降32.6%、20.3%、22.4%、45.9%和9.4%,而木纤维细胞密度升高11.6%。在面对低温事件时,水曲柳会采取减少木纤维细胞数量、提高木纤维细胞密度这一相对保守的生存策略。研究结果为小兴安岭地区耐寒水曲柳选育提供科学依据。
文摘采用木材切片法和光学显微技术，研究香椿木材的微观特征，分析年轮宽度、导管及纤维形态的径向变异。结果表明：髓心至第10年年轮宽度迅速增加，1～20 a间均保持旺盛的生长；早材和晚材的导管宽度、双壁厚、腔径由髓心向外逐渐增大，约19 a 后趋于平稳，早材导管宽度121．80μm，晚材导管宽度38．75μm，早材导管双壁厚度10．98μm，晚材导管双壁厚度16．49μm；纤维长度由髓心向外呈逐渐增大的趋势，18 a后纤维长度基本趋于稳定，纤维形态指标平均值分别为：长度1080．94μm，宽度26．76μm，长宽比40．25，双壁厚7．96μm，腔径18．80μm，壁腔比0．43。
