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云南高美古湍流大气中激光短曝光光斑统计特性研究

Statistical Properties of Short-Exposure Laser Patterns in Turbulent Atmosphere of Gaomeigu, Yunnan Province

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摘要

为了探究激光在自由高空湍流大气中传输的短曝光光斑特性,在云南高美古3200m的高海拔地区,选择远离下垫面的地势条件,开展了532nm固体激光1,2,3,4, 4.7km大气传输光斑成像探测实验。利用4000frame/s采样速率下的短曝光光斑数据,定性地描述了湍流大气中短曝光远场激光光斑的网纹状形态结构以及零星亮点的移动、消散和重构过程,并对激光光斑灰度值进行了定量的统计分析。结果表明:利用二维的光斑图像数据,可以较为方便地获得光强闪烁的孔径平均因子和理想的点闪烁指数,进而得到包括湍流强度和湍流内尺度在内的关键光学湍流参数;同时,也可对激光闪烁频谱、截止频率以及光斑的空间相关特性进行定量的判断。相关数据有助于研究高原或高空长程传输条件下的激光能量在目标靶面上的空间分布及其时间变化特性,为研究激光长程大气传输后光电系统的变化提供了一定的参考。

Abstract

Objective When laser propagates in the atmosphere, it is inevitable that a random change of the refractive index of the atmospheric turbulence causes laser spot broken and distorted, which seriously damages the laser beam quality. Under the conditions of weak- and strong-fluctuating media, the turbulence model has relatively rich theoretical research results. In view of the complexity of the turbulence itself, the current theory of light transmission in random media is not enough to perfectly present the far-field transmission characteristics of the laser spot in the strong-fluctuation region. As for the high-altitude laser transmission engineering applications, the spatial distribution of laser energy on the target surface and its temporal variation characteristics are vital for photoelectric system evaluation. However, the research of long-range high-altitude laser atmospheric transmission faces the following problems: first, there are few transmission tests in high-altitude areas; second, short-exposure laser spot data at high frame-rate sampling are rare; third, two-dimensional imaging methods to obtain more comprehensive laser statistical parameters are still lacking. In this study, we use a high-speed camera to perform laser spot tests at different distances in high-altitude areas. Using the laser short-exposure image data at sampling rate of 4000 frame·s -1, the change characteristics of short-exposure far-field laser spots in the turbulent atmosphere are qualitatively described, and the optical turbulence parameters such as ideal point scintillation indexes, aperture average factors, and inner scales are calculated. Our aim is to use the external field laser transmission test data to understand the spatial laser energy distribution on the target surface as well as its temporal variation characteristics under high-altitude conditions and to simultaneously determine its impact on the laser photoelectric system.

Methods The experiment is performed at an altitude of 3200 m in Gaomeigu, far from the underlying surface. The transmitting terminal is a 532 nm solid-state laser, while the receiving system is consisted of a high-speed CCD camera and a diffuse reflection screen. The camera is placed obliquely in front of the screen at ~9m, the transmitter is located in the balcony in the third floor of the Gaomeigu radar station at ~10m above the ground, and the receiver is located on the open ground at distances of 1, 2, 3, 4, and 4.7km from the transmitting terminal. The selected geographical location can ensure that most of the transmission paths are longer than 15m from the underlying surface and the maximum height is larger than 100m. In addition, the test is also performed in the canyon, far away from the underlying surface. The straight-line distance between two ends is ~2km, and the maximum link distance from the underlying surface is ~300m. The sampling rate of laser spot images is unified to 4000 frame·s -1, each image is 320pixel×240pixel, and the image accuracy is 8bit. For the acquired two-dimensional data of the laser spot, using the imaging method, the scintillation index under different receiving apertures is calculated, and subsequently polynomial fitting is used to obtain the ideal point scintillation index. With the former results, the refractive index structural parameters such as the path, aperture average factor, and inner scale can also be derived. Moreover, this method based on the calculation of the gray value of the light spot can also display the correlation coefficient between the power spectrum and its scaling rate as well as the spatial light intensity distribution.

Results and Discussion At a distance of 1km, with the playback of a short-exposure spot image at a sampling rate of up to 4000 frame·s -1, the broken laser spot shows a clear mesh-like morphological structure, and a few sharp bright spots are scattered. There are irregular shapes and different size holes inside the spot (Fig. 3). As time elapses, these flowing mesh-like structures and scattered bright spots undergo deformation and reconstruction. There is a certain unclear relationship between size of the reticulated texture and the scale of the turbulence. Using the light spot gray value data, the aperture average factor of different receiving radii on the target surface is obtained. The variation of the laser spot aperture average factor with the receiving aperture shows that the aperture average factor is not only a function of the aperture but also is related to the turbulence state (Fig. 6). The daily variation of Cn2 in high-altitude areas is relatively stable, showing a different trend from the “Mexican hat” trend near the ground at low altitudes (Fig. 7). The power spectral distributions of laser scintillation under different transmission distances show that the cutoff frequency of the power spectrum of a single pixel is generally higher than the average cutoff frequency of the circular domain, which indicates that the aperture smoothing effect of light intensity scintillation still exists in the frequency domain. The scaling rate obtained from the power spectrum shows a positive correlation trend with the ideal scintillation index (Figs. 9 and 11). Taking the spot centroid as the point of origin, the normalized spatial correlation coefficient of the light intensity fluctuations at the distance from the origin point shows that the spatial correlation radius increases with the increase of the scintillation index (Fig. 12). It is a completely different concept from the coherence length.

Conclusion The main purpose of designing this experiment is to find the transmission conditions far away from the underlying surface in high-altitude areas and to obtain the characteristics of the laser spot transmitted in high-altitude free atmospheric turbulence. Judging from the fact that there is no obvious “Mexican hat” structure in the daily variation trend of most transmission paths, the underlying surface on the transmission path has little influence, but there are still big differences between the real test conditions and high-altitude “free” atmosphere. In the future, we hope that we will have the opportunity to conduct high frame-rate laser spot image testing on higher and farther platforms to promote the understanding of laser transmission in free turbulent atmospheres.

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中图分类号:O436

DOI:10.3788/CJL202148.0105001

所属栏目:光束传输与控制

基金项目:国家自然科学基金青年项目(11904369)、中国科学院装备预研联合基金(6141A01130202)、脉冲功率激光技术国家重点实验室主任基金(2019ZR07)、安徽省自然科学基金青年项目(1908085QA37)

收稿日期:2020-06-23

修改稿日期:2020-09-04

网络出版日期:2021-01-01

作者单位    点击查看

张骏昕:中国科学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中国科学技术大学研究生院科学岛分院, 安徽 合肥 230026先进激光技术安徽省实验室, 安徽 合肥 230037
梅海平:中国科学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先进激光技术安徽省实验室, 安徽 合肥 230037
沈刘晶:中国科学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先进激光技术安徽省实验室, 安徽 合肥 230037安徽大学物质科学与信息技术研究院, 安徽 合肥 230601
黄印博:中国科学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先进激光技术安徽省实验室, 安徽 合肥 230037
罗福:中国工程物理研究院流体物理研究所, 四川 绵阳 621900
吴小龑:中国工程物理研究院流体物理研究所, 四川 绵阳 621900

联系人作者:梅海平(hpmei@aiofm.ac.cn)

【1】Rao R Z. Modern atmospheric optics[M]. Beijing: Science Press, 2012.
饶瑞中. 现代大气光学[M]. 北京: 科学出版社, 2012.

【2】Tatarski V I. Wave propagation in a turbulent medium[M]. Wen J S: Song Z F, Zeng Z Y, et al, Transl. Beijing: Science Press, 1978.
塔塔尔斯基, [M]. 湍流大气中波的传播理论. 温景嵩: 宋正方, 曾宗泳,等, 译. 北京: 科学出版社, 1978.

【3】Kerr J R, Dunphy J R. Experimental effects of finite transmitter apertures on scintillations [J]. Journal of the Optical Society of America. 1973, 63(1): 1.Kerr J R, Dunphy J R. Experimental effects of finite transmitter apertures on scintillations [J]. Journal of the Optical Society of America. 1973, 63(1): 1.

【4】Rao R Z, Wang S P, Liu X C, et al. Statistical characteristics of laser intensity fluctuation and beam pattern in a real turbulent atmosphere [J]. Chinese Journal of Quantum Electronics. 1998, 15(2): 3-5.
饶瑞中, 王世鹏, 刘晓春, 等. 激光在湍流大气中的光强起伏与光斑统计特征 [J]. 量子电子学报. 1998, 15(2): 3-5.

【5】Rao R Z, Wang S P, Liu X C. Atmospheric turbulence degraded light intensity images: size measurement and description of deformation characteristics [J]. Acta Optica Sinica. 1998, 18(4): 3-5.
饶瑞中, 王世鹏, 刘晓春. 被湍流大气退化的激光光斑: 尺度测量与形变特征描述 [J]. 光学学报. 1998, 18(4): 3-5.

【6】Rao R Z. Pattern characteristics of collimated laser beam in a turbulent atmosphere Ⅰ. characteristic radii [J]. Chinese Journal of Lasers. 2002, 29(10): 889-894.
饶瑞中. 湍流大气中准直激光束的光斑特征Ⅰ.特征半径 [J]. 中国激光. 2002, 29(10): 889-894.

【7】Liu J G, Huang Y B, Wang Y J. Statistical properties of short-exposure images with strong turbulent effects [J]. High Power Laser & Particle Beams. 2005, 17(3): 321-324.
刘建国, 黄印博, 王英俭. 强湍流效应下激光大气传输短曝光光斑统计分析 [J]. 强激光与粒子束. 2005, 17(3): 321-324.

【8】Jing X, Wu Y, Hou Z H, et al. Study of irradiance fluctuations for laser beam propagation in atmosphere [J]. Acta Optica Sinica. 2010, 30(11): 3110-3116.
靖旭, 吴毅, 侯再红, 等. 湍流大气中激光传输光强起伏特征研究 [J]. 光学学报. 2010, 30(11): 3110-3116.

【9】Jiang Y J, Ma J, Tan L Y, et al. Measurement of optical intensity fluctuation over an 11.8km turbulent path [J]. Optics Express. 2008, 16(10): 6963-6973.Jiang Y J, Ma J, Tan L Y, et al. Measurement of optical intensity fluctuation over an 11.8km turbulent path [J]. Optics Express. 2008, 16(10): 6963-6973.

【10】Ke X Z, Jing Y K. Far-field laser spot image detection for use under atmospheric turbulence [J]. Optical Engineering. 2020, 59(1): 016103.

【11】Butts R R, Weaver L D. Airborne laser experiment (ABLEX): theory and simulations [J]. Proceedings of SPIE. 1994, 2120: 10-29.Butts R R, Weaver L D. Airborne laser experiment (ABLEX): theory and simulations [J]. Proceedings of SPIE. 1994, 2120: 10-29.

【12】Weaver L D, Butts R R. ABLEX high-altitude laser propagation experiment [J]. ]. Proceedings of SPIE. 1994, 2120: 30-42.

【13】Washburn D C. ABLE ACE: a high-altitude propagation program [J]. Proceedings of SPIE. 1997, 3065: 296-306.

【14】Vorontsov M A, Carhart G W, Banta M, et al. Atmospheric laser optics testbed (A_LOT): atmospheric propagation characterization, beam control, and imaging results [J]. Proceedings of SPIE. 2003, 5162: 37-48.Vorontsov M A, Carhart G W, Banta M, et al. Atmospheric laser optics testbed (A_LOT): atmospheric propagation characterization, beam control, and imaging results [J]. Proceedings of SPIE. 2003, 5162: 37-48.

【15】Nakamura M, Akiba M, Kuri T, et al. Experimental evaluation of spot dancing of laser beam in atmospheric propagation using high-speed camera [J]. Proceedings of SPIE. 2003, 4976: 149-158.Nakamura M, Akiba M, Kuri T, et al. Experimental evaluation of spot dancing of laser beam in atmospheric propagation using high-speed camera [J]. Proceedings of SPIE. 2003, 4976: 149-158.

【16】Andrews L C, Phillips R L, Hopen C Y, et al. Theory of optical scintillation [J]. Journal of the Optical Society of America A. 1999, 16(6): 1417-1429.

【17】Churnside J H. Aperture averaging of optical scintillations in the turbulent atmosphere [J]. Applied Optics. 1991, 30(15): 1982-1994.

【18】Strohbehn J W. Laser beam propagation in the atmosphere [M]. Heidelberg: Springer. 1978.

【19】Rao R Z, Wang S P, Liu X C, et al. Characteristics of the power spectrum of laser irradiance scintillation in a real atmosphere [J]. Chinese Journal of Lasers. 1999, 26(5): 411-414.
饶瑞中, 王世鹏, 刘晓春, 等. 实际大气中激光闪烁的频谱特征 [J]. 中国激光. 1999, 26(5): 411-414.

【20】Wang Q, Mei H P, Qian X M, et al. Spatial correlation experimental analysis of atmospheric optical turbulence in the near ground layer [J]. Acta Physica Sinica. 2015, 64(11): 114212.
王倩, 梅海平, 钱仙妹, 等. 近地面大气光学湍流空间相关特性的实验研究 [J]. 物理学报. 2015, 64(11): 114212.

引用该论文

Zhang Junxin,Mei Haiping,Shen Liujing,Huang Yinbo,Luo Fu,Wu Xiaoyan. Statistical Properties of Short-Exposure Laser Patterns in Turbulent Atmosphere of Gaomeigu, Yunnan Province[J]. Chinese Journal of Lasers, 2021, 48(1): 0105001

张骏昕,梅海平,沈刘晶,黄印博,罗福,吴小龑. 云南高美古湍流大气中激光短曝光光斑统计特性研究[J]. 中国激光, 2021, 48(1): 0105001

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