1 北京林业大学水土保持学院, 北京 100083
2 北京林业大学水土保持与荒漠化防治教育部重点实验室, 北京 100083
3 北京林业大学水土保持学院重庆缙云山三峡库区森林生态系统国家定位观测研究站, 北京 100083
4 中国林业科学研究院沙漠林业实验中心, 内蒙古 磴口 015200
防护林是我国荒漠绿洲区主要植被类型, 可为该地区防风固沙、 水盐调控、 水热平衡提供有力保障, 调查防护林空间分布信息十分重要。 然而荒漠绿洲防护林条带较窄、 斑块面积小、 分布广且零散, 不易大尺度准确提取。 为解决此难点, 以磴口县荒漠绿洲为研究区, 基于GF-2号遥感影像, 采用面向对象分类技术提取防护林空间分布信息。 分类前, 首先基于局部方差（LV）和LV变化率（ROC）曲线, 选取分割防护林的最优分割尺度。 然后采用随机森林（RF）算法的袋外误差率（OOB error）及基尼系数（Gini）对包含光谱、 形状和纹理的分类特征进行重要性评估并筛选特征、 优化模型参数; 最后, 基于随机森林、 CART决策树、 支持向量机（SVM）、 K近邻（KNN）四种分类器提取防护林空间分布信息并对比验证。 结果表明: (1）采用ROC-LV曲线方法相比于遍历分割参数, 可更客观更高效地筛选最优分割参数的可能值; (2）基于RF算法计算的袋外误分率和基尼系数可以有效筛除冗余特征, 配合分类器参数优化, 在保证分类精度的同时, 有效提高分类器性能, 大幅提升数据处理速度; (3）基于实测数据集对分类结果进行验证, 结果显示基于随机森林算法的特征优化结合SVM分类器提取的防护林空间分布信息精度最高, 生产者精度达到97.14%, 总体防护林面积为208.99 km2, 与实际210 km2接近, 在小区块中, SVM分类器的分类效果优于其他三种分类器; (4）因GF-2影像分辨率高, 并且含有近红外波段, 通过波段合成得到亚米级信息, 故基于面向对象的方法能够以单条林带为基本单位研究防护林林网属性, 例如提取断带信息等林网结构特征。 研究结论可为荒漠绿洲区带状防护林提取提供重要技术支撑。
防护林带识别 GF-2遥感影像 随机森林 面向对象 Shelterbelt extraction GF-2 remote-sensing imagery Random Forest Object-oriented 光谱学与光谱分析
2022, 42(12): 3896
1 长春理工大学光电工程学院，吉林 长春 130022
2 国家纳米科学中心纳米加工实验室，中国科学院纳米光子材料与器件重点实验室（筹），中国科学院纳米科学卓越创新中心，北京 100190
3 中国环境监测总站国家环境保护环境监测质量控制重点实验室，北京 100012
4 中国科学院大学材料与光电研究中心，北京 100049
报道了一种利用混合抗蚀剂的一步电子束曝光制备表面增强拉曼散射（SERS）基底的新方法。基于氢倍半硅氧烷（HSQ）和聚甲基丙烯酸甲酯（PMMA）电子束抗蚀剂的混合产生相分离形成纳米球体的现象，并利用合适剂量（2000 μC/cm2）电子束曝光、固化纳米球，经显影去除多余残胶后再使用电子束蒸发沉积Au薄膜，得到纳米球型SERS基底。纳米球尺寸分布均匀，相对标准偏差为7.56%，表面粗糙Au层及球之间的间隙能够提供丰富SERS“热点”，从而使其表现出良好的拉曼增强效应。该SERS基底对多种目标物均能表现出良好的检测性能。对4-巯基苯硼酸（4-MPBA）检测的SERS增强因子为5.8×106，检测限为1.06×10-8 mol/L。对罗丹明6G（R6G）和三聚氰胺的检测限分别达到7.08×10-9 mol/L和7.94×10-10 mol/L。三聚氰胺的检测范围为1.0×10-9~1.0×10-5 mol/L，跨度达4个数量级，并呈现良好线性关系（R2=0.952），检测优势十分显著。这种利用不同性质抗蚀剂在纳米尺度独特的分离现象制备纳米球的方法简单、重复性好，对发展新型纳米结构高性能SERS基底及其制备方法具有重要意义。
表面光学 表面增强拉曼散射（SERS） 电子束曝光 痕量检测 三聚氰胺 光学学报
2022, 42(15): 1524002
红外与激光工程
2021, 50(11): 20210116
1 中国科学院合肥物质科学研究院安徽光学精密机械研究所中国科学院大气光学重点实验室，安徽 合肥 230031
2 中国科学技术大学研究生院科学岛分院，安徽 合肥 230026
3 先进激光技术安徽省实验室，安徽 合肥 230037
4 中国科学技术大学环境科学与光电技术学院，安徽 合肥 230026
研究气溶胶辐射强迫和激光大气传输效应，需要掌握气溶胶光吸收特性参数及其垂直分布情况。提出一种基于实测与模式相结合的方法来估测垂直高度上气溶胶吸收系数分布。首先采用太阳辐射计和激光雷达观测的数据分别反演整层气溶胶光学厚度（AOD）和消光廓线，再将辐射传输计算软件moderate spectral resolution atmospheric transmittance algorithm and computer model（MODTRAN）和santa barbara DISORT atmospheric radiative transfer（SBDART）在相应气溶胶模式下的数据结果作为约束条件，得到气溶胶吸收廓线，并通过外场实验测量数据进行反演实验。结果表明，所提方法是可行的，可作为气溶胶吸收系数垂直分布有效获取的一种新的技术途径。
大气光学 气溶胶 吸收系数廓线 激光雷达 太阳辐射计 辐射传输 激光与光电子学进展
2021, 58(19): 1901001
Author Affiliations
Abstract
1 National Laboratory on High Power Laser and Physics
,
Shanghai 201800
,
China
2 Key Laboratory of High Power Laser and Physics
,
Shanghai Institute of Optics and Fine Mechanics
,
Chinese Academy of Sciences
,
Shanghai 201800
,
China
3 University of Chinese Academy of Sciences
,
Beijing 100049
,
China
Polarization mode dispersion (PMD) in fibers for high-power lasers can induce significant frequency modulation to amplitude modulation (FM-to-AM) conversion. However, existing techniques are not sufficiently flexible to achieve efficient compensation for such FM-to-AM conversion. By analyzing the nonuniform transmission spectrum caused by PMD, we found that the large-scale envelope of the transmission spectrum has more serious impacts on the amount of AM. In order to suppress the PMD-induced FM-to-AM conversion, we propose a novel tunable spectral filter with multiple degrees of freedom based on a half-wave plate, a nematic liquid crystal, and an axis-rotated polarization-maintaining fiber. Peak wavelength, free spectral range (FSR), and modulation depth of the filter are decoupled and can be controlled independently, which is verified through both simulations and experiments. The filter is utilized to compensate for the PMD-induced FM-to-AM conversion in the front end of a high-power laser facility. The results indicate that, for a pulse with phase-modulation frequency of 22.82 GHz, the FM-to-AM conversion could be reduced from 18% to 3.2% within a short time and maintained below 6.5% for 3 h. The proposed filter is also promising for other applications that require flexible spectral control such as high-speed channel selection in optical communication networks.
advanced laser technology and applications design fiber laser and applications high-power laser laser facility laser facility and engineering laser systems modeling optimization High Power Laser Science and Engineering
2018, 6(4): 04000e53
Author Affiliations
Abstract
National Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
A high power laser system was used to drive the ignition of inertial confinement fusion (ICF), of which the high energy, the uniform focal spot, the accurate laser waveform, and the synchronization between the laser beams are key parameters. To accomplish this, global laser characteristics control should be assured, which was the main purpose of the injection laser system. In this paper, the key technological progress involved in the improvement of the performance of the injection laser of SG-II is reported, including frequency domain control, time domain control, near-field spatial shaping, pre-amplifier technology, and the optical parametric chirped pulse amplification pump source.
amplifier injection laser pulse shaping spatial shaping synchronization. High Power Laser Science and Engineering
2018, 6(2): 02000e34
Author Affiliations
Abstract
1 Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2 University of Chinese Academy of Science, Beijing 100049, China
A 95 W Nd:YAG laser system pumped by a vertical cavity surface emitting laser (VCSEL) array is described. The laser contains an all-fiber-based seeder, an Nd:YAG regenerative amplifier, and a four-pass amplifier. The laser operates at 300 Hz with energies up to 317 mJ. The beam has a top-hat intensity distribution. The temporal pulse shape is flat in time, and the pulse width can be adjusted in the range of 2–6 ns.
140.3280 Laser amplifiers 140.3295 Laser beam characterization 140.6810 Thermal effects 140.7260 Vertical cavity surface emitting lasers Chinese Optics Letters
2016, 14(12): 121402
Author Affiliations
Abstract
1 National Laboratory on High Power Lasers and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800, China
2 University of the Chinese Academy of Sciences, Beijing 100049, China
A double-clad Yb-doped mode-locked fiber laser that can operate in burst-mode and square-pulse states is experimentally investigated. In the burst-mode state, a burst train with 55 pulses of 500 ps duration is obtained. In the square-pulse state, which is similar to noiselike pulses, the maximum pulse energy is 820 nJ and the duration can be tuned from 15.8 to 546 ns. The square pulses have a narrow and multipeak spectrum, which is quite different from that of normal noiselike pulses. The fiber laser promises an alternative formation mechanism for burst-mode and square-pulse mode-locked fiber lasers.
Collection Of theses on high power laser and plasma physics
2016, 14(1): 052701
Author Affiliations
Abstract
1 National Laboratory on High Power Lasers and Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800, China
2 University of the Chinese Academy of Sciences, Beijing 100049, China
FM-to-AM modulation is an important effect in the front end of high-power lasers that influences the temporal profile. Various methods have been implemented in standard-fiber and polarization-maintaining (PM)-fiber front ends to suppress the FM-to-AM modulation. To analyze the modulation in the front end, a theoretical model is established and detailed simulations carried out that show that the polarizing (PZ) fiber, whose fast axis has a large loss, can successfully suppress the modulation. Moreover, the stability of the FM-to-AM modulation can be improved, which is important for the front end to obtain a stable output. To verify the model, a PZ fiber front end is constructed experimentally. The FM-to-AM modulation, without any compensation, is less than 4%, whereas that of the PM fiber front end with the same structure is nearly 20%. The stability of the FM-to-AM modulation depth is analyzed experimentally and the peak-to-peak and standard deviation (SD) are 2% and 0.38%, respectively, over 3 h. The experimental results agree with the simulation results and both prove that the PZ fiber front end can successfully suppress the FM-to-AM conversion. The PZ fiber front end is a promising alternative for improving the performance of the front end in high-power laser facilities.
Lasers frequency modulated Phase modulation Wave propagation Fusion Collection Of theses on high power laser and plasma physics
2016, 14(1): 8352
Author Affiliations
Abstract
1 National Laboratory on High Power Laser and Physics, Shanghai 201800, China
2 Key Laboratory of High Power Laser and Physics, Shanghai Institute of Optics and fine Mechanics, Chinese Academy of Science, Shanghai 201800, China
3 University of Chinese Academy of Sciences, Beijing 100049, China
A fiber-based，high precision long-term stable time synchronization system for multi-channel laser pulses is presented，using fiber pulse stacker combined with high-speed optical-electrical conversion and electronics processing technology. This scheme is used to synchronize two individual lasers including a mode-lock laser and a time shaping pulse laser system. The relative timing jitter between two laser pulses achieved with this system is 970 fs (rms) in five minutes and 3.5 ps (rms) in five hours. The synchronization system is low cost and can work at over several tens of MHz repetition rate.
ICF OPCPA time synchronization long-term stable Collection Of theses on high power laser and plasma physics
2016, 14(1): 10019
