CN102778300A - Method for stably measuring atmospheric coherence length - Google Patents

Method for stably measuring atmospheric coherence length Download PDF

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CN102778300A
CN102778300A CN2012102643285A CN201210264328A CN102778300A CN 102778300 A CN102778300 A CN 102778300A CN 2012102643285 A CN2012102643285 A CN 2012102643285A CN 201210264328 A CN201210264328 A CN 201210264328A CN 102778300 A CN102778300 A CN 102778300A
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apertures
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coherence length
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宣丽
胡立发
穆全全
曹召良
彭增辉
杨程亮
陈浩
刘永刚
姚丽双
李大禹
夏明亮
鲁兴海
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Changchun Institute of Optics Fine Mechanics and Physics of CAS
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Abstract

The invention belongs to the field of optical technology, and particularly relates to a method for stably measuring atmospheric coherence length r0. According to space-time probability consistency characteristic of atmospheric turbulence, multiple pairs of sub-apertures which are in regular polygon symmetrical distribution on a Hartman wave front detector are selected, so as to increase the space statistic probability and simultaneously reduce the sampling time; In order to continue to calculate r0 by use of a formula (1), the method of selecting the multiple pairs of sub-apertures is as follows: the distance between centers of each pair of sub-apertures is strictly the same and simultaneously meets the principle of selecting one pair of sub-apertures, the regular polygon symmetrical distribution of the multiple pairs of sub-apertures is simplified as square distribution under the structure restriction of the Hartman wave front detector; and by utilizing hundreds of light spot array signals of a turbulence wave surface collected within one second, the difference movement of multiple pairs of image points which are in square symmetrical distribution on each light spot array signal is substituted into the formula (1) so as to be subjected to identical statistic average, so that an accurate atmospheric coherence length r0 value with an instant characteristic can be obtained.

Description

大气相干长度的稳定测量方法A Stable Measurement Method of Atmospheric Coherence Length

技术领域 technical field

本发明属于自适应光学领域,涉及大气通道的自适应校正效果的评价参数,具体地说是大气湍流强度参数即大气相干长度的稳定测量方法。The invention belongs to the field of adaptive optics, and relates to an evaluation parameter of an adaptive correction effect of an atmospheric channel, in particular to a stable measurement method of an atmospheric turbulence intensity parameter, that is, an atmospheric coherent length.

背景技术 Background technique

地球表面垂直方向上有10~20公里的大气层,由于温度的不均匀变化使得空气局部密度不同,即而导致大气折射率不均匀,从而形成大气湍流对光波前的动态扰动现象。利用天文望远镜对空间目标观测成像时,天文望远镜接收到的目标光波受到大气湍流的动态扰动而产生不同程度的波前畸变,严重影响成像质量。因此,自适应波前校正系统成为米级以上口径望远镜的必要设施。为了评价自适应波前校正系统应对大气湍流的能力,大气湍流强度的测量一直是自适应光学领域的重要课题。There is an atmosphere of 10-20 kilometers in the vertical direction on the earth's surface. Due to the uneven temperature change, the local density of the air is different, which leads to the uneven refractive index of the atmosphere, thus forming the dynamic disturbance phenomenon of atmospheric turbulence on the light wavefront. When astronomical telescopes are used to observe and image space targets, the target light waves received by the astronomical telescopes are subject to dynamic disturbances of atmospheric turbulence, resulting in varying degrees of wavefront distortion, which seriously affects the imaging quality. Therefore, the adaptive wavefront correction system has become a necessary facility for telescopes with apertures above the meter level. In order to evaluate the ability of adaptive wavefront correction system to cope with atmospheric turbulence, the measurement of atmospheric turbulence intensity has always been an important topic in the field of adaptive optics.

大气相干长度r0的数值能够表达光束在大气湍流中传输的空间相干性及大气湍流动态扰动的综合强度。大气相干长度r0的值越小,表征大气湍流的动态扰动越剧烈,取值范围一般在几个厘米至几十厘米之间。r0值的定义为:光学波面在大气相干长度r0为直径的圆域或者说是子孔径内位相起伏的均方根值RMS是1rad。当光学波面的直径超过大气相干长度r0值的尺度时,光学波面的畸变量将降低光学接收系统的成像分辨率。The value of the atmospheric coherence length r 0 can express the spatial coherence of the light beam propagating in the atmospheric turbulence and the comprehensive strength of the dynamic disturbance of the atmospheric turbulence. The smaller the value of the atmospheric coherence length r 0 , the more severe the dynamic disturbance representing atmospheric turbulence, and the value range is generally between a few centimeters and tens of centimeters. The value of r 0 is defined as: the RMS value of the phase fluctuation of the optical wavefront in a circle with the diameter of the atmospheric coherence length r 0 is 1 rad. When the diameter of the optical wavefront exceeds the scale of the atmospheric coherence length r0 , the distortion of the optical wavefront will reduce the imaging resolution of the optical receiving system.

通常采用两种方法测量大气相干长度r0:一种是通过测量大气湍流折射率结构常数进而求出大气相干长度r0,需要经过长期观测才能得到折射率结构常数的统计规律;另一种是通过测量畸变波前的位相信息求出大气相干长度r0,就是所谓的差分星点像运动法(DIMM),已被广泛采用。Two methods are usually used to measure the atmospheric coherence length r 0 : one is to obtain the atmospheric coherence length r 0 by measuring the structural constant of the refractive index of the atmospheric turbulence, and it takes long-term observations to obtain the statistical law of the structural constant of the refractive index; the other is The atmospheric coherence length r 0 is obtained by measuring the phase information of the distorted wavefront, which is the so-called differential satellite image motion method (DIMM), which has been widely used.

差分星点像运动法(DIMM)由Stock和Keller于1960年提出,其测量原理为:在天文望远镜的入瞳位置处放置一块挡板,挡板上开具有两个子孔径,两个子孔径之间的距离远大于子孔径直径。来自大气通道另一端的点目标光束经过两个子孔径到达观测CCD相机后会分为两个独立的星点像。在一定时间内,通过实时记录由大气湍流动态扰动导致的两个像点之间相对距离的变化,就能够计算出大气相干长度r0的值。F.Roddie在Fried理论研究的基础上,推导出计算大气相干长度r0的基本公式【F.Roddier,The effects of atmospheric turbulence inoptical astronomy,[J].Prog.Optics,1981,19:281~376】:The differential star point image motion method (DIMM) was proposed by Stock and Keller in 1960. Its measurement principle is: a baffle is placed at the entrance pupil of the astronomical telescope, and there are two sub-apertures on the baffle, and the gap between the two sub-apertures is The distance is much larger than the sub-aperture diameter. The point target beam from the other end of the atmospheric channel will be divided into two independent star point images after reaching the observation CCD camera through two sub-apertures. In a certain period of time, the value of the atmospheric coherence length r0 can be calculated by recording the change of the relative distance between two image points caused by the dynamic disturbance of atmospheric turbulence in real time. F.Roddie deduced the basic formula for calculating the atmospheric coherence length r 0 on the basis of Fried's theoretical research [F.Roddier, The effects of atmospheric turbulence inoptical astronomy, [J].Prog.Optics,1981,19:281~376 】:

rr 00 == [[ 22 ff 22 ll 22 (( 0.3580.358 DD. -- 11 // 33 -- 0.2420.242 ZZ -- 11 // 33 )) << ZZ qq 22 >> -- << ZZ qq >> 22 ]] 33 // 55

其中,f为测量系统的焦距,λ为接收光的中心波长,D为子孔径的直径,Z为两子孔径的中心间距,且Z>>r0,Zq为两子孔径的成像点质心间距,〈〉为时间统计平均符号。像点质心坐标(cx,cy)的求算方法依据【Francois Roddier,Adaptive optics in astronomy,Cambridge University Press,1999,Part two,pp99】:Among them, f is the focal length of the measurement system, λ is the central wavelength of the received light, D is the diameter of the sub-aperture, Z is the center distance between the two sub-apertures, and Z>>r 0 , Z q is the centroid of the imaging point of the two sub-apertures The interval, <> is the time statistical average symbol. The calculation method of the centroid coordinates (c x , c y ) of the image point is based on [Francois Roddier, Adaptive optics in astronomy, Cambridge University Press, 1999, Part two, pp99]:

cc xx == &Sigma;&Sigma; ii ,, jj xx ii ,, jj II ii ,, jj &Sigma;&Sigma; ii ,, jj II ii ,, jj ,, cc ythe y == &Sigma;&Sigma; ii ,, jj ythe y ii ,, jj II ii ,, jj &Sigma;&Sigma; ii ,, jj II ii ,, jj -- -- -- (( 22 ))

其中i,j是CCD相机像素构成的直角坐标系上像素的序号,xi,j与yi,j分别为(i,j)像素的两个坐标分量,Ii,j为(i,j)像素的光强。Where i, j are the serial numbers of pixels on the Cartesian coordinate system composed of CCD camera pixels, x i, j and y i, j are the two coordinate components of (i, j) pixels respectively, and I i, j is (i, j ) pixel light intensity.

实际上采用Shack-Hartmann波前探测器即可对r0进行DIMM法的测量【饶长辉,姜文汉,凌宁.应用哈特曼-夏克波前传感器测量大气湍流参数[J].光学学报,2000,20(9):1201~1207】。使用约千赫兹采样频率的Shack-Hartmann波前探测器,选择其上距离足够远的两个子孔径,通常这两个子孔径的位置在接收波面上呈中心对称。测量时连续采集10s、约10000幅大气通道上的光点阵列,然后只考虑每一幅上被选择的两个子孔径的星点像质心距离,按照(1)式统计计算r0In fact, r 0 can be measured by the DIMM method using the Shack-Hartmann wavefront detector [Rao Changhui, Jiang Wenhan, Ling Ning. Measuring atmospheric turbulence parameters using the Hartmann-Shack wavefront sensor[J]. Acta Optics Sinica, 2000, 20(9):1201~1207]. Using a Shack-Hartmann wavefront detector with a sampling frequency of about kilohertz, select two sub-apertures with a sufficient distance on it, and usually the positions of these two sub-apertures are centrally symmetrical on the receiving wave surface. During the measurement, about 10,000 light point arrays on the atmospheric channel are continuously collected for 10s, and then only the centroid distances of the star point images of the two selected sub-apertures are considered in each frame, and r 0 is statistically calculated according to formula (1).

但是,采用DIMM法在某一个时刻测得的大气相干长度r0值经常会在数秒之后突然跃升二、三厘米,偶然还可跃升近十厘米。这种现象与大气湍流的速度特性并不相符。分析其原因,应该是统计量不够造成的,因为波前的起伏剧烈程度在各个方位上都是不同的,DIMM法只统计固定位置上的两个子孔径像点质心的运动,要想统计全面必须花费较长时间。如果统计1万次也难以保证r0测量的准确性,说明1万次的统计量还不够;但是再增加统计量,也有可能造成采样时间过长,超过r0保持恒定的时间,平均掉r0的变化。因此传统测量大气相干长度r0的DIMM方法是有缺陷的。However, the r 0 value of atmospheric coherence length measured at a certain moment by using the DIMM method often suddenly jumps by two or three centimeters after a few seconds, and sometimes it can jump by nearly ten centimeters. This phenomenon does not match the velocity characteristics of atmospheric turbulence. Analyzing the reason, it should be caused by insufficient statistics, because the intensity of wavefront fluctuations is different in all directions, and the DIMM method only counts the movement of the center of mass of the two sub-aperture image points at fixed positions. In order to make comprehensive statistics, it is necessary take a long time. If it is difficult to guarantee the accuracy of r 0 measurement after counting 10,000 times, it means that the statistics of 10,000 times are not enough; but if the statistics are increased, it may also cause the sampling time to be too long, exceeding the time when r 0 remains constant, and the average loss of r 0 changes. Therefore, the traditional DIMM method of measuring the atmospheric coherence length r 0 is flawed.

2000年饶瑞中采用三孔、即三对星点像差分运动法【饶瑞中,王世鹏,刘晓春,等.湍流大气中的激光束漂移的实验研究[J].中国激光,2000,27(11):1011-1015.】,尝试弥补一对星点像运动统计的不全面。2007年饶瑞中研究组又报道了采用互为垂直的两对孔(四孔)、即六对星点像差分运动法【黄宏华,姚永帮,饶瑞中,四孔差分像运动测量大气相干长度的方法研究[J].强激光与粒子束,2007,19(3):357-360.】,并在2010年的文章中【倪志波,黄宏华,黄印博,朱文越,饶瑞中[J].Dome效应对四孔大气相干长度仪系统性能的影响,强激光与粒子束,2010,22(11):2551-2555.】统计了6对星点像×200幅图的差分结果,测得的r0变化速度大幅减缓,约0.6~0.7cm/min,但仍然无法证实这个统计量是否充分,即r0的变化是否真实,是否有波前局地异性随时间变化的影响;另外这6对孔径中每两子孔径的中心间距不尽相同,须改造公式(1)的统计计算方法,使计算量增加。In 2000, Rao Ruizhong adopted the differential motion method of three holes, that is, three pairs of star point images [Rao Ruizhong, Wang Shipeng, Liu Xiaochun, et al. Experimental study of laser beam drift in turbulent atmosphere[J]. China Laser, 2000, 27(11): 1011-1015. ], trying to make up for the incompleteness of a pair of star-like motion statistics. In 2007, Rao Ruizhong’s research group also reported the method of differential motion using two pairs of holes (four holes) that are perpendicular to each other, that is, six pairs of star point images [Huang Honghua, Yao Yongbang, Rao Ruizhong, Research on the method of four-hole differential image motion to measure atmospheric coherence length[ J]. Intense Laser and Particle Beam, 2007,19 (3): 357-360.], and in the article in 2010 [Ni Zhibo, Huang Honghua, Huang Yinbo, Zhu Wenyue, Rao Ruizhong [J]. Dome effect on four holes Influence of Atmospheric Coherence Length Meter System Performance, Intense Laser and Particle Beam, 2010, 22(11): 2551-2555.] The difference results of 6 pairs of star images × 200 images were counted, and the measured r 0 change speed was greatly Slow down, about 0.6~0.7cm/min, but it is still impossible to confirm whether this statistic is sufficient, that is, whether the change of r 0 is real, and whether there is an influence of wave front local anisotropy changing with time; The center spacing of the apertures is not the same, so the statistical calculation method of formula (1) must be modified to increase the amount of calculation.

发明内容 Contents of the invention

本发明为了克服大气相干长度r0统计方法的缺陷,提出在Shack-Hartmann波前探测器测得的光斑阵列上选取正多边形对称分布的多对子孔径,大幅增加系综统计几率,同时保持公式(1)的统计计算方法有效,目的是提供一种准确而简便的大气相干长度r0的稳定测量方法。In order to overcome the defect of atmospheric coherence length r 0 statistical method, the present invention proposes to select multiple pairs of sub-apertures with symmetrical distribution of regular polygons on the spot array measured by the Shack-Hartmann wavefront detector, greatly increasing the probability of ensemble statistics, while maintaining the formula The statistical calculation method in (1) is effective, and the purpose is to provide an accurate and simple stable measurement method of the atmospheric coherence length r0 .

下面详述本发明。将Shack-Hartmann波前探测器与一天文望远镜光学对接,使望远镜接收到的任意一恒星的光束能够全口径、且与Shack-Hartmann波前探测器接收口径相同、平行入射Shack-Hartmann波前探测器。根据大气湍流的时空几率一致特性,在Shack-Hartmann波前探测器测得的光斑阵列上选取正多边形对称分布的多对子孔径,以增加空间统计几率,同时减少采样时间。为了继续利用公式(1)来计算r0,选取多对子孔径的方法是保持公式(1)中的Z值不变,即每一对子孔径的中心间距都严格相同,且远大于r0。这样在Shack-Hartmann波前探测器结构的限制下正多边形对称分布的多对子孔径就只能简化为如图1所示的正方形、或六角形分布,选择其上10~14对子孔径。Shack-Hartmann波前探测器的采样频率不得小于500Hz,连续采集300~500幅湍流波面的光斑阵列信号。将300~500幅阵列上每一对像点的质心间距Zq均代入公式(1)中进行统计平均,得出误差小于3%的、带有即时特征的大气相干长度r0值。The present invention is described in detail below. The Shack-Hartmann wavefront detector is optically connected to an astronomical telescope, so that the light beam of any star received by the telescope can be detected with full aperture and the same receiving aperture as the Shack-Hartmann wavefront detector, and parallel incident Shack-Hartmann wavefront detection device. According to the uniform characteristics of temporal and spatial probability of atmospheric turbulence, multiple pairs of sub-apertures with regular polygonal symmetrical distribution are selected on the spot array measured by the Shack-Hartmann wavefront detector to increase the spatial statistical probability and reduce the sampling time. In order to continue to use formula (1) to calculate r 0 , the method of selecting multiple pairs of sub-apertures is to keep the Z value in formula (1) unchanged, that is, the distance between the centers of each pair of sub-apertures is strictly the same, and is much larger than r 0 . In this way, under the restriction of the Shack-Hartmann wavefront detector structure, the multiple pairs of sub-apertures distributed symmetrically in a regular polygon can only be simplified to a square or hexagonal distribution as shown in Figure 1, and 10 to 14 pairs of sub-apertures are selected on it. The sampling frequency of the Shack-Hartmann wavefront detector shall not be less than 500Hz, and continuously collect 300-500 spot array signals of the turbulent wavefront. Substituting the centroid spacing Z q of each pair of image points on the 300-500 arrays into the formula (1) for statistical average, the atmospheric coherence length r 0 value with an error of less than 3% and real-time characteristics is obtained.

附图说明 Description of drawings

图1为本发明中利用大气湍流模拟器测量大气相干长度r0的室内实验光路示意图。其中1为卤素灯点光源,2为785nm波长的单色滤光片,3为第一透镜,将点光源的光准直为直径合适的平行光,4为大气湍流模拟器的旋转位相板,5为孔径光阑,6为第二透镜,7为第三透镜,二者组成缩束透镜组,8为Shack-Hartmann波前探测器,全口径接收大气湍流模拟器扰动后的光束,9为与Shack-Hartmann波前探测器8相连的计算机,读出与存储所采集的光斑阵列图数据。Fig. 1 is a schematic diagram of an indoor experimental optical path for measuring the atmospheric coherence length r 0 by using an atmospheric turbulence simulator in the present invention. Among them, 1 is a halogen lamp point light source, 2 is a monochromatic filter with a wavelength of 785nm, 3 is the first lens, which collimates the light of the point light source into parallel light with a suitable diameter, and 4 is the rotating phase plate of the atmospheric turbulence simulator, 5 is the aperture stop, 6 is the second lens, 7 is the third lens, the two form a narrowing lens group, 8 is the Shack-Hartmann wavefront detector, which receives the beam disturbed by the atmospheric turbulence simulator at full aperture, and 9 is The computer connected to the Shack-Hartmann wavefront detector 8 reads out and stores the collected light spot array image data.

图2为本发明中在Shack-Hartmann的光斑阵列图上12对点的选取方法。在光斑阵列两个垂直方向上分别选择间距12个光斑即12倍r0的6对光斑,形成正方形分布的12对子孔径的星点像,用字母标记成对光点:a与a′,b与b′,c与c′,d与d′,e与e′,f与f′,g与g′,h与h′,i与i′,j与j′,k与k′,l与l′。Fig. 2 is the selection method of 12 pairs of points on the Shack-Hartmann spot array diagram in the present invention. In the two vertical directions of the spot array, select 6 pairs of spots with a spacing of 12 spots, that is, 12 times r 0 , to form a star point image of 12 pairs of sub-apertures in a square distribution, and mark the paired spots with letters: a and a′, b with b', c with c', d with d', e with e', f with f', g with g', h with h', i with i', j with j', k with k', l and l'.

图3为本发明具体实施例中在Shack-Hartmann的光斑阵列图上分别选取1对点和12对点,获得的r0随统计量的变化曲线,其中曲线A是1对点的结果,曲线B是12对点的结果。Fig. 3 selects 1 pair of points and 12 pairs of points respectively on the light spot array figure of Shack-Hartmann in the specific embodiment of the present invention, and the r obtained varies with the curve of statistics, wherein curve A is the result of 1 pair of points, curve B is the result of 12 pairs of points.

具体实施方式 Detailed ways

1)按照图1搭建测量r0的实验光路。其中卤素灯点光源1发出的球面光波经波长为785nm,经单色滤光片2成为单色光,再经第一透镜3准直为平行光后入射到大气湍流模拟器的旋转位相板4上,孔径光阑5设置在紧靠大气湍流模拟器的旋转位相板的通光口径处,孔径光阑5的孔径设置为10mm,通过孔径光阑5的光束再经第二透镜6、第三透镜7缩束2.5倍成为4mm口径的平行光束进入到Shack-Hartmann波前探测器8的通光窗口内切圆上,计算机9与Shack-Hartmann波前探测器8相连,读出与存储所采集的光斑阵列图数据。1) Set up the experimental optical path for measuring r 0 according to Figure 1. Among them, the spherical light wave emitted by the halogen lamp point light source 1 has a wavelength of 785nm, becomes monochromatic light through the monochromatic filter 2, and then collimates into parallel light through the first lens 3, and then enters the rotating phase plate 4 of the atmospheric turbulence simulator. Above, the aperture stop 5 is set close to the aperture of the rotating phase plate of the atmospheric turbulence simulator. The lens 7 shrinks the beam by 2.5 times to become a parallel light beam with a 4mm diameter and enters the inscribed circle of the light transmission window of the Shack-Hartmann wavefront detector 8. The computer 9 is connected with the Shack-Hartmann wavefront detector 8, and the readout and storage are collected. The spot array image data.

2)步骤1)中所述大气湍流模拟器为Lexltek公司产品,通过控制位相板上的通光口径来确定大气相干长度r0,通过控制位相板转动速度来确定湍流频率即格林武德频率:首先设定湍流中心波长为785nm,然后设定望远镜口径为500mm,大气相干长度r0设定为5.0cm,在该产品的使用手册上查找到相应位相板上的光斑直径为10mm,选择湍流频率即格林武德频率31Hz,在该产品的使用手册上查找到相应位相板转速为20转/min。2) The atmospheric turbulence simulator described in step 1) is a product of Lexltek Company. The atmospheric coherence length r 0 is determined by controlling the aperture of the phase plate, and the turbulence frequency, namely the Greenwood frequency, is determined by controlling the rotation speed of the phase plate: First set the center wavelength of turbulence to 785nm, then set the aperture of the telescope to 500mm, and set the atmospheric coherence length r0 to 5.0cm. Find the spot diameter on the corresponding phase plate as 10mm in the user manual of the product, and select the turbulence frequency That is, the Greenwood frequency is 31Hz, and the corresponding phase plate speed is found to be 20 rpm in the user manual of the product.

3)孔径光阑5的孔径可以在1mm到15mm范围内连续调节,能够控制入射到大气湍流模拟器旋转位相板4上的光束直径。3) The aperture of the aperture diaphragm 5 can be continuously adjusted within the range of 1 mm to 15 mm, which can control the diameter of the beam incident on the rotating phase plate 4 of the atmospheric turbulence simulator.

4)Shack-Hartmann波前探测器8帧频为1020Hz,感光元件为Intevac Photonics公司的MicroVista-NIR背照明式CMOS相机,该相机的像素数达到1280×1024个,微透镜数为20×20个、以方格阵列排列,每个微透镜对应7×7个像素,共使用CMOS相机的像素数为140×140个,对应窗口为4mm×4mm。4) The Shack-Hartmann wavefront detector 8 has a frame rate of 1020Hz, and the photosensitive element is a MicroVista-NIR back-illuminated CMOS camera from Intevac Photonics. The number of pixels of this camera reaches 1280×1024, and the number of microlenses is 20×20 , Arranged in a grid array, each microlens corresponds to 7×7 pixels, the total number of pixels used in the CMOS camera is 140×140, and the corresponding window is 4mm×4mm.

5)第一透镜3、第二透镜6、第三透镜7均为消色差双胶合透镜,其中第一透镜3的口径为40mm,焦距为270mm,使到达位相板上的光斑直径为10mm,以模拟口径为500mm的波前;第二透镜6、第三透镜7的口径分别为40mm和25mm,焦距分别为250mm、100mm,以使光束缩束2.5倍,其口径与Shack-Hartmann波前探测器8的通光口径相同。5) The first lens 3, the second lens 6, and the third lens 7 are all achromatic doublet lenses, in which the diameter of the first lens 3 is 40mm, and the focal length is 270mm, so that the diameter of the light spot reaching the phase plate is 10mm, with Simulate a wavefront with a caliber of 500mm; the calibers of the second lens 6 and the third lens 7 are 40mm and 25mm respectively, and the focal lengths are 250mm and 100mm respectively, so that the beam is shrunk by 2.5 times, and its caliber is the same as that of a Shack-Hartmann wavefront detector 8 have the same aperture.

6)开启点光源1后,Shack-Hartmann波前探测器8获得的光斑阵列如图2,在光斑阵列两个垂直方向上分别选择间距12个光斑即12倍r0的6对光斑,形成正方形分布的12对子孔径的星点像,如图2中标记字母的成对光点。6) After turning on the point light source 1, the spot array obtained by the Shack-Hartmann wavefront detector 8 is shown in Figure 2. In the two vertical directions of the spot array, select 6 pairs of spots with a distance of 12 spots, that is, 12 times r 0 , to form a square The star point images of the distributed 12 pairs of sub-apertures are shown as the paired light points marked with letters in Figure 2.

7)开启大气湍流模拟器旋转位相板4后,连续采集10000幅光斑阵列数据,在光斑阵列图上分别选取1对点和12对点,计算出每对星点像的质心间距Zq代入公式(1)中,获得的r0随统计量的变化曲线如图3所示,其中曲线A是12对点的结果,曲线B是1对点的结果,看出曲线A中300幅光斑阵列数据统计出来的r0已经收敛,为5.1cm,与r0设定值5.0cm相比只有2%误差,而曲线B则到6500幅以后才收敛,且收敛到5.5cm,与r0设定值5.0cm相比有10%的误差。7) After turning on the rotating phase plate 4 of the atmospheric turbulence simulator, continuously collect 10,000 pieces of spot array data, select 1 pair of points and 12 pairs of points on the spot array map, and calculate the centroid distance Z q of each pair of star point images and substitute them into the formula In (1), the variation curve of r 0 obtained with statistics is shown in Figure 3, where curve A is the result of 12 pairs of points, and curve B is the result of 1 pair of points. It can be seen that the data of 300 spot arrays in curve A The calculated r 0 has converged, which is 5.1cm, which is only 2% error compared with the r 0 set value of 5.0cm, while the curve B does not converge until after 6500 pieces, and converges to 5.5cm, which is the same as the r 0 set value There is a 10% error compared to 5.0cm.

Claims (3)

1.大气相干长度r0的稳定测量方法,其特征是将Shack-Hartmann波前探测器与一天文望远镜光学对接,使望远镜接收到的任意一恒星的光束能够全口径、且与Shack-Hartmann波前探测器接收口径相同、平行入射Shack-Hartmann波前探测器;在Shack-Hartmann波前探测器测得的光斑阵列上选取正方形对称分布的10~14对子孔径,以增加空间统计几率,同时减少采样时间;利用公式 r 0 = [ 2 f 2 l 2 ( 0.358 D - 1 / 3 - 0.242 Z - 1 / 3 ) < Z q 2 > - < Z q > 2 ] 3 / 5 来计算r0,公式中的f为测量系统的焦距,λ为接收光的中心波长,D为子孔径的直径,Z为每对子孔径的中心间距,且Z>3r0,Zq为两子孔径的成像点质心间距,〈〉为时间统计平均符号;选取多对子孔径的方法是保持公式中的Z值不变,即每一对子孔径的中心间距都严格相同;Shack-Hartmann波前探测器的采样频率不得小于500Hz,连续采集300~500幅湍流波面的光斑阵列信号;将300~500幅阵列上每一对像点的质心间距Zq均代入公式中进行统计平均,得出稳定的、带有即时特征的大气相干长度r0值。1. The stable measurement method of the atmospheric coherence length r 0 is characterized in that the Shack-Hartmann wavefront detector is optically connected with an astronomical telescope, so that the light beam of any star received by the telescope can be full-aperture and compatible with the Shack-Hartmann wave The front detector receives the same aperture and parallel incident Shack-Hartmann wavefront detector; 10-14 pairs of sub-apertures with square symmetrical distribution are selected on the spot array measured by the Shack-Hartmann wavefront detector to increase the probability of spatial statistics. Reduce sample time; utilize formula r 0 = [ 2 f 2 l 2 ( 0.358 D. - 1 / 3 - 0.242 Z - 1 / 3 ) < Z q 2 > - < Z q > 2 ] 3 / 5 To calculate r 0 , f in the formula is the focal length of the measurement system, λ is the central wavelength of the received light, D is the diameter of the sub-aperture, Z is the center distance of each pair of sub-apertures, and Z>3r 0 , Z q is two The centroid spacing of the imaging points of the sub-apertures, <> is the time statistical average symbol; the method of selecting multiple pairs of sub-apertures is to keep the Z value in the formula unchanged, that is, the center spacing of each pair of sub-apertures is strictly the same; the Shack-Hartmann wave The sampling frequency of the front detector shall not be less than 500Hz, and continuously collect 300-500 spot array signals of turbulent wave fronts; Substituting the centroid distance Z q of each pair of image points on the 300-500 arrays into the formula for statistical average, it is obtained Stable atmospheric coherence length r 0 values with instantaneous features. 2.根据权利要求1所述的大气相干长度r0的稳定测量方法,其特征是:Shack-Hartmann波前探测器帧频为1020Hz。2. the stable measuring method of atmospheric coherence length r 0 according to claim 1 is characterized in that: the Shack-Hartmann wavefront detector frame frequency is 1020Hz. 3.根据权利要求2所述的大气相干长度r0的稳定测量方法,其特征是:在Shack-Hartmann波前探测器上获得的光斑阵列图,其两个垂直方向上分别选择间距12个光斑即12倍r0的6对光斑,形成正方形分布的12对子孔径的星点像,连续采集300幅光斑阵列数据,将每对星点像的质心间距Zq代入权利要求1所述的公式中,统计计算出r03. the stable measuring method of atmospheric coherence length r according to claim 2 is characterized in that: the spot array figure that obtains on the Shack-Hartmann wavefront detector, selects spacing 12 spots respectively on its two perpendicular directions That is, 6 pairs of light spots with 12 times r 0 form star point images of 12 pairs of sub-apertures in a square distribution, continuously collect 300 pieces of light spot array data, and substitute the centroid distance Z q of each pair of star point images into the formula described in claim 1 , statistically calculated r 0 .
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