• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    A Hartmann wavefront sensor employing different-time exposure comprises a spectroscope, an optical power density measurer, a step-by-step acquisition controller, a microlens array, a CCD (Charge Coupled Device) camera, a center-of-mass calculator and a wavefront restorer, wherein the optical power density measurer measures the optical power density of incident wavefront at first; the step-by-step acquisition controller calculates the exposure time of step-by-step acquisition of the CCD camera to a light spot array according to the characteristics of the optical power density of the incident wavefront and the response sensitivity of the CCD camera, and then controls the center-of-mass calculator to calculate the center of mass of the light spot array step by step after the completion of acquisition; and finally, the wavefront restorer restores the incident wavefront according to the center-of-mass matrix obtained by the center-of-mass calculator. The Hartmann wavefront sensor acquires the array of the light spots at the CCD camera step by step by different exposure time by means of the step-by-step acquisition controller, thereby improving the signal-to-noise ratio of light spot center-of-mass detection in a single sub-aperture when the incident light intensity is uneven, enhancing the accuracy of center-of-mass detection and providing a solution for restoring the incident wavefront with high accuracy under the condition with uneven lighting.
    公开号:NL2010461A
    申请号:NL2010461
    申请日:2013-03-15
    公开日:2013-09-23
    发明作者:Xiaoyu Ma；Changhui Rao；Xuejun Rao
    申请人:Inst Optics & Elect Cn Acad；
    IPC主号:
    专利说明:

    Title: HARTMANN WAVEFRONT SENSOR ADOPTING TIME-DIVISION EXPOSURE Technical Field
    [0001] The present disclosure relates to a Hartmann wavefront sensor applicable to an adaptive optics system. In particular, the present disclosure relates to a Hartmann wavefront sensor adopting time-division exposure.
    Background
    [0002] The Hartmann wavefront sensor was initially applied in astronomical adaptive optics because it can provide real-time measurement with suitable measurement accuracy. With development of technology, the Hartmann wavefront sensor has been widely used as a precise wavefront measuring instrument in mirror surface type detection, laser parameter diagnosis, flow field CT reconstruction, human-eye aberration diagnosis, and optical path alignment, etc., due to its simple structure and principle. The Hartmann wavefront sensor generally comprises micro-lenses and a CCD camera. It performs wavefront measurement based on wavefront slope measurement.
    [0003] In operation of the Hartmann wavefront sensor, an array of micro-lenses divides a wave surface to be measured into a plurality of sample units. The sample units are converged onto separate focuses by the respective high-quality lenses and received by the CCD camera, respectively. Wavefront slant within each sub-aperture will cause displacement of a corresponding light spot in x and y directions. The displacement of the centroid of the light spot in the x and y directions reflects a wavefront slope of a corresponding sample unit in the two directions. In the Zernike modal wavefront reconstruction algorithm, Zernike coefficients of reconstructed wavefront are obtained by multiplying a wavefront slope vector with a reconstruction matrix. Thus, error of the reconstructed wavefront will decrease if the reconstruction matrix can be calculated properly (Chaohong Li, Hao Xian, “Measuring Statistical error of Shack-Hartmann Wavefront Sensor with Discrete Detector Arrays,” Journal of Lightwave Technology, 2007).
    [0004] The Hartmann wavefront sensor, as a precise wavefront measuring instrument, suffers from noises. Thus, error may occur in measurement of the centroid of the light spot by the Hartmann wavefront sensor. Generally the measurement accuracy of the centroid of the light spot can be improved by increasing the Signal-to-Noise-Ratio (SNR) of the light spot (Wenhan Jiang, Hao Xian, Feng Shen, “Detection Error of Shack-Hartmann Wavefront Sensor," Journal of Quantum Electronics, 1998). However, because the CCD camera is limited in its dynamic range, the SNR of the CCD camera is low within a sub-aperture where light intensity is relatively weak in case where light power density of incident wavefront is less uniform. As a result, the centroid of the light spot calculated from the light power density of the light spot within the sub-aperture may have a significant error, thus affecting the accuracy of reconstructed wavefront.
    [0005] In view of the foregoing problems, it has become an important research topic to improve the SNR of the light spot within each sub-aperture when the Hartmann wavefront sensor operates under non-uniform light illumination, without causing local saturation of the CCD camera, so as to improve reconstruction accuracy of the Hartmann wavefront sensor under the non-uniform light illumination.
    Summary
    [0006] In view of the foregoing problems of the prior art, the present disclosure provides, among others, a Hartmann wavefront sensor adopting time-division exposure to improve accuracy of light spot centroid measurement and thus accuracy of wavefront reconstruction.
    [0007] According to an aspect of the present disclosure, there is provided a Hartmann wavefront sensor adopting time-division exposure. The sensor may comprise a splitter, a light power density measuring instrument, a step-wise collection controller, a micro-lens array, a CCD camera, a centroid calculator, and a wavefront reconstruction device. The splitter can be configured to divide an incident wavefront into a portion for wavefront energy measurement and a portion for wavefront slope measurement. The light intensity distribution measuring instrument can be configured to receive the portion for wavefront energy measurement, and also to measure light power density of the incident wavefront and transfer light power density data to the step-wise collection controller. The micro-lens array can be configured to divide the portion for wavefront slope measurement, which, thus divided, generates a light spot array at the CCD camera. The step-wise collection controller can be configured to determine a plurality of sub-aperture sets, for which light spot data are to be collected step-wisely by the CCD camera from the light spot array, and exposure time for each of the sub-aperture sets based on light power density characteristics of the incident wavefront and response sensitivity of the CCD camera. The step-wise collection controller can be further configured to control the CCD camera to step-wisely collect the light spot data according to the exposure time for each of the sub-aperture sets and transfer the data to the centroid calculator. The step-wise collection controller can be further configured to control the centroid calculator to calculate centroids of sub-apertures in each of the sub-aperture sets and transfer the same to the wavefront reconstruction device. The wavefront reconstruction device can be configured to arrange the centroids calculated by the centroid calculator as a centroid vector and calculate a slope vector of the incident wavefront from the centroid vector to reconstruct the incident wavefront.
    [0008] The step-wise collection controller can be configured to determine the plurality of sub-aperture sets, for which the light spot data are to be collected step-wisely by the CCD camera from the light spot array, and the exposure time for each of the sub-aperture sets based on the light power density characteristics of the incident wavefront and the response sensitivity of the CCD camera by: calculating a minimum value Emin of incident light energy required by a SNR lower limit for measurement of the centroid of the light spot within a single sub-aperture of the micro-lens array and also a maximum value Emax of the incident light energy required to make the maximum value of the light spots reach a measurement upper limit of the CCD camera; integrating a portion of the light intensity measured by the light power density measuring instrument (2) corresponding to each of the sub-apertures to derive incident light power Pk within the sub-aperture, where k is a number of the sub-aperture; dividing the light power in each of the sub-apertures by the required maximum and minimum values of the incident light energy, respectively, to derive an exposure time lower limit
    for the sub-aperture and an exposure time upper limit
    for the sub-aperture; and classifying the sub-apertures into the plurality of sub-aperture sets according to their exposure time ranges defined by the respective exposure time lower limits and the respective exposure time upper limits, and determining the exposure time for each of the sub-aperture sets based on the exposure time ranges.
    [0009] The step-wise collection controller can be configured to classify the sub-apertures into the plurality of sub-aperture sets by: (a) associating the number k of each of the sub-apertures and the exposure time upper limit tkmax for this sub-aperture and the exposure time lower limit tkmin for this sub-aperture to generate a sub-aperture number vector K, an exposure time upper limit vector Tmax and an exposure time lower limit vector Tmin; (b) searching the exposure time upper limit vector Tmax for a minimum value tmax to find a sub-aperture number corresponding to this minimum value tmax, and searching the exposure time lower limit vector Tmin for values less than tmax to find sub-aperture numbers corresponding to those values, so as to form a sub-aperture set including sub-apertures corresponding to those found sub-aperture numbers and set the exposure time for this sub-aperture set as tmax; (c) removing the sub-aperture numbers found in the step (b) from the sub-aperture number vector K, and removing elements ^maxand^min corresponding to those sub-aperture numbers from the exposure time upper limit vector Tmax and the exposure time lower limit vector Tmin; and (d) repeating the step (b) and the step (c) until all the sub-apertures have been removed.
    [0010] The measurement upper limit of the CCD camera can be smaller than a full measuring range of the CCD camera, and preferably 80%-90% of the full measuring range of the CCD camera, in order to avoid saturation of the CCD camera.
    [0011] According to the present disclosure, the light power density measuring instrument and the step-wise collection controller are incorporated into the Hartmann wavefront sensor to control the exposure time for each of the sub-apertures. Under the control of the step-wise collection controller, the CCD camera adopts a relatively short exposure time for the sub-aperture with a relatively high light intensity so as to avoid saturation. Further, for the sub-aperture with a relatively low light intensity, the CCD camera adopts a relatively long exposure time to improve SNR. In this way, a solution is provided for improving accuracy of wavefront reconstruction of the Hartmann wavefront sensor under non-uniform light illumination.
    [0012] The present disclosure can provide the following advantages, for example. A conventional Hartmann wavefront sensor based on single exposure is limited by the dynamic range of the CCD camera under non-uniform light illumination. It is possible that the light spot signal within a sub-aperture having a relatively high light intensity has reached a saturation level while the light spot signal within a sub-aperture having a relatively low light intensity is still very weak. Due to inevitable noise in the process of measuring the centroid of the light spot, the SNR in the sub-aperture having the weak light spot signal is low, which degrades the measurement accuracy of the centroid of the light spot and thus the accuracy of wavefront reconstruction. The present technology uses multiple exposures in a time-division manner (by means of the step-wise collection controller) to collect centroid data of different light spots with different exposure time each time, so as to ensure the SNR in collecting the centroid of each of the light spots. In this way, the accuracy in measuring the centroid and thus the wavefront reconstruction can be improved.
    Brief Description of Drawings
    [0013] Fig. 1 is a schematic view showing a Hartmann wavefront sensor adopting time-division exposure according to an embodiment of the present disclosure;
    [0014] Fig.2 is a schematic view showing a conventional Hartmann wavefront sensor;
    [0015] Fig. 3 is a schematic view showing arrangement and numbering of sub-apertures according to an embodiment;
    [0016] Fig.4 is a histogram of incident light power density according to an embodiment;
    [0017] Fig.5 is a histogram of incident light power density corresponding to each sub-aperture number according to an embodiment;
    [0018] Fig.6 is an image of a light spot array under non-uniform light illumination (t=50ms) according to an embodiment;
    [0019] Fig.7 is a schematic view showing a wavefront to be measured according to an embodiment;
    [0020] Fig.8 is a histogram of upper and lower limits of exposure time required for each sub-aperture according to an embodiment; and
    [0021] Fig.9 is a plot showing errors of a wavefront reconstructed by the conventional light spot centroid collection method based on single-exposure and the light spot centroid collection method based on multiple-exposure according to the present disclosure, respectively.
    1 splitter 2 light power density measuring instrument 3 step-wise collection controller 4 micro-lens array 5 CCD camera 6 centroid calculator 7 wavefront reconstruction device 8 wavefront to be measured 9 portion for wavefront energy measurement 10 portion for wavefront slope measurement
    Detailed Description of Embodiments
    [0022] According to an embodiment of the present disclosure, a CCD camera 5 may have a full measuring range of 4095ADU (12-bit), a mean square root of noise of 20ADU, and a sensitivity of 50nJ/ADU. A light spot may have an Airy Disk diameter of 10 pixels. A Hartmann wavefront sensor may have a 10x10 micro-lens array 4, and may have a single sub-aperture size of 1mmx1mm. Fig.3 shows numbering of the sub-apertures, wherein only valid ones of the sub-apertures are shown..
    [0023] According to light intensity distribution characteristics of the light spot (Xiaoyu Ma, Hanqing Zheng, Changhui Rao, Optimal Spot Centroid Position during Shack-Hartmann Wavefront Sensor Calibration in Adaptive Optics System, "ACTA OPTICA SINICA, 2009), when the Airy disk diameter of the light spot is 10 pixels and the maximum value point of the light spot is 1ADU, the light spot has about 26ADUs in total, and desired incident light energy is: 26ADUx50nJ/ADU =1.3uJ.
    [0024] As shown in Fig.2, a conventional Hartmann wavefront sensor comprises: an array of micro-lenses 4, a CCD camera 5, a centroid calculator 6, and a wavefront reconstruction device 7. In case where incident light power density has a distribution as shown in Fig.4, incident light power at a kth sub-aperture is:
    (1) where: is light power density (in unit of W/mm2) at a point with coordinates (m, n) within the kth sub-aperture; M and N are numbers of measurement points of the light power density along two directions in a plane within a single sub-aperture, respectively, so that there are MxN measurement points within the single sub-aperture; and / is a side length of the single sub-aperture.
    [0025] Fig.5 is a histogram of incident light power density for the respective sub-apertures numbered as above. As shown in Fig.5, a maximum value of the incident light power among the individual sub-apertures is 96.05mW, and a minimum value of the incident light power within among the individual sub-apertures is 22.10mW. The ratio of the minimum value to the maximum value is 23%.
    [0026] Fig.6 shows an image of a light spot array for exposure time of 50ms. A light spot in a sub-aperture with the maximum incident light power has a maximum gray value of about 96.05mWx50ms/1,3uJ=3694ADU, which is up to 90% of the saturation power value (4095ADU) of the CCD camera 5. That is, an SNR limit for the light spot centroid collection method based on single-exposure has been reached.
    [0027] Fig.7 shows a wavefront 8 to be measured having an out-of-focus aberration of Fig.9 shows, by a dotted line, errors of reconstructed wavefront obtained by performing 100 times of the single-exposure method on the out-of-focus wavefront as shown in Fig.7. The errors have an average value of 0.18λ%.
    [0028] Fig. 1 shows a Hartmann wavefront sensor adopting time-division exposure according to an embodiment of the present disclosure. The Hartmann wavefront sensor may comprise a splitter 1, a light power density measuring instrument 2, a step-wise collection controller 3, an array of micro-lenses 4, a CCD camera 5, a centroid calculator 6, and a wavefront reconstruction device 7. An incident wavefront 8 is divided into a portion 9 for wavefront energy measurement and a portion 10 for wavefront slope measurement. The portion 9 for wavefront energy measurement enters the light power density measuring instrument 2. The portion 10 for wavefront slope measurement is divided via the array of micro-lenses 4 and then generates an array of light spots at the CCD camera 5. The time-division exposure can be performed as follows.
    (1) The light power density measuring instrument 2 measures light power density of the wavefront 8 to be measured to obtain a light power density graph of the wavefront 8 to be measured, for example, one as shown in Fig.4.
    (2) The sub-apertures are each assigned a number, for example, as shown in Fig.3. The step-wise collection controller 3 calculates incident light power Pk for each of the sub-apertures based on the light power density measured by the light power density measuring instrument 2, where k is the number of the sub-aperture. Specifically, the step-wise collection controller 3 can calculate the incident light power Pk by integrating a portion of the light intensity measured by the light power density measuring instrument 2 corresponding to the kth sub-aperture, for example, using the equation (1),.
    (3) The step-wise collection controller 3 calculates desired light energy when the light spot has a maximum value point of 1ADU based on sensitivity of the CCD camera 5 and an Airy Disk diameter of the light spot. In this embodiment, because the Airy Disk diameter of the light spot is 10 pixels, the light spot has about 26ADUs in total when the maximum value point of the light spot is 1 ADU, and thus the desired incident light energy is 26ADU*50nJ/ADU =1.3uJ.
    (4) The step-wise collection controller 3 calculates an upper limit and a lower limit of exposure time for each of the sub-apertures based on a suitable SNR for the CCD camera 5. In this embodiment, the maximum value of the light spot in a single sub-aperture is at least 60%, but at most up to 90%, of the full measuring range of the CCD camera 5.
    The lower limit tkmin and the upper limit ^“^of the desired exposure time for the kth sub-aperture may be calculated by
    Here, Emin indicates a minimum value of the incident light energy required by a SNR lower limit (in this example, 60%) for proper measurement of the centroid of the light spot within a single sub-aperture, and Emax indicates a maximum value of the incident light energy required to make the maximum value of the light spots reach a measurement upper limit (in this example, 90%) of the CCD camera 5.
    Fig.8 shows the upper limits and the lower limits of the desired exposure time for the respective sub-apertures calculated by the equation (2).
    (5) The sub-aperture number k is associated with the upper limit tkmax and the lower limit tkmin of the exposure time to generate a sub-aperture number vector K = [1,2,3......76]', an exposure time upper limit vector ^ = [rlmax,r2max,r3max,......t16max]' and an exposure time lower limit vector Tmia = [tlmhl,t2min,t3min,......t76^ .
    (6) Some sub-apertures are processed together. In this embodiment, first a sub-aperture corresponding to a minimum value in the exposure time upper limit vector Tmax can be found . In this example, the minimum value in the exposure time upper limit vector Tmax is =A9ms, with a corresponding sub-aperture numbered 33. Then, sub-aperture(s) corresponding to value(s) in the exposure time lower limit vector Tmin less than the minimum value found as above can be found. In this example, sub-apertures corresponding to values in the exposure time lower limit vector Tmin less than 49ms are those numbered: 34, 43, 44, 23, 24, 32, 35, 42, 45, 53, 54, 22, 25, 52, 55, 14, 15, 31, 36, 41,46, 62, and 63. Thus, the exposure time of the first exposure for the CCD camera 5 can be set as tmax (49ms in this example), and a sub-aperture set for the first exposure can be determined as including the above found sub-apertures (a set of [33, 34, 43, 44, 23, 24, 32, 35, 42, 45, 53, 54, 22, 25, 52, 55, 14, 15, 31, 36, 41, 46, 62, 63] in this example). The set of sub-apertures for the first exposure can be removed from the sub-aperture number vector K, and their corresponding elements in the exposure time upper limit vector Tmax and the exposure time lower limit vector Tmin can also be removed from the exposure time upper limit vector Tmax and the exposure time lower limit vector Tmin, respectively. The foregoing process can be repeated until all the sub-apertures have been processed. In this example, the CCD camera needs to perform four exposures in a time-division manner. The exposure time and sub-aperture set for each of the exposures are shown in the following table.
    (7) The step-wise collection controller 3 controls the CCD camera 5 to collect light spot data in a time-division manner corresponding to that of the exposures. In this example, the CCD camera 5 needs to collect the light spot data for four times. Integration time for each collection of the light spot data can be set as corresponding to the respective exposure time tmax as determined above. In this example, integration time for the first collection of the light spot data is 49ms, integration time for the second collection of the light spot data is 79ms, integration time for the third collection of the light spot data is 138ms, and integration time for the fourth collection of the light spot data is 216ms.
    (8) The step-wise collection controller 3 controls the centroid calculator 6 to calculate, for four times in this example, centroid of the light spot at a sub-aperture z by:
    where Xc^ and (z) represent the positions of the centroid of the light spot at the sub-aperture z in x and y directions, respectively; represent the positions of a pixel in x and y directions; ^i] is a gray value at the pixel within a sub-aperture;
    T r A//V
    and ’ represent the sizes of the sub-aperture in x and y directions in unit of pixel.
    In this example, the sub-apertures for the first centroid calculation are those numbered: [33, 34, 43, 44, 23, 24, 32, 35, 42, 45, 53, 54, 22, 25, 52, 55, 14, 15, 31, 36, 41,46, 62, 63], the sub-apertures for the second centroid calculation are those numbered: [16, 21, 26, 51, 56, 61, 64, 7, 8, 12, 17, 30, 37, 40, 47, 60, 65, 69, 70, 6, 9, 20, 27, 50, 57, 68, 71], the sub-apertures for the third centroid calculation are those numbered: [10, 11, 18, 59, 66, 67, 72, 2, 3, 29, 38, 39, 48, 74, 75], and the sub-apertures for the fourth centroid calculation are those numbered: [1,4, 19, 28, 49, 58, 73, 76], (9) The wavefront reconstruction device 7 arranges the centroid data calculated by the centroid calculator 6 in accordance with the sub-aperture numbers as a centroid vector Q = [xc(l),_yc(l),xc(2),yc(2),,....xc(76),yc(76),]', and converts the centroid vector Q to a slope vector G = where f is a focus length of a single micro-lens in the micro-lens array 4.
    (10) The wavefront reconstruction device 7 calculates a Zernike vector A of the reconstructed wavefront based on a reconstruction matrix D+ and the slope vector G by: A = D+G, so as to derive the reconstructed wavefront. Calculation of the reconstruction matrix D+ can be done as described in CN Application No. 201210072934.7, entitled “HARTMANN WAVEFRONT MEASURING INSTRUMENT ADAPTED FOR NON-UNIFORM LIGHT ILLUMINATION.”
    [0028] Fig.9 shows, by a solid line, errors of reconstructing wavefront with the out-of-focus aberration as shown in Fig.7 by 100 times of time-division exposures. The errors have an average value 0.15λ% , which is lower than that obtained by the single-exposure method.
    [0029] In summary, in case where the wavefront 8 to be measured has a incident light in a non-uniform distribution, the time-division Hartmann wavefront sensor according to the present disclosure improves the SNR in detecting the light spot centroid within a single sub-aperture and thus the accuracy of centroid calculation. Therefore, a solution is provided for improving the measurement accuracy of the Hartmann wavefront sensor in case where the wavefront 8 to be measured has a light intensity in a non-uniform distribution.
    权利要求:
    Claims (4)
    [1]
    A time-divided exposure Hartmann wavefront sensor, comprising a splitter (1), a light power density measuring instrument (2), a step-by-step collective controller (3), a micro-lens array (4), a CCD camera (5), a centroid calculator (6) and a wave front reconstruction device (7), wherein the splitter (1) is arranged to divide an incident wave front (8) into a wave front energy measurement part (9) and a wave front slope measurement part (10); the light intensity distribution measuring instrument (2) is adapted to receive the wave front energy measurement part (9) and also to measure light power density from the incident wave front (8) and transfer light power density data to the stepwise collection controller (3); the micro-lens array (4) is adapted to divide the wave front slope measurement portion (10) that, thus distributed, generates a light spot array on the CCD camera (5); the step-by-step collection controller (3) is adapted to determine a plurality of sub-aperture groups for which light-spot data from the light-spot array is to be collected step by step by the CCD camera (5), and exposure time for each of the sub-aperture groups based on light power density properties of the incident wavefront (8) and response sensitivity of the CCD camera (5); controlling the CCD camera (5) for stepwise collecting the light spot data according to the exposure time for each of the sub-aperture groups and transferring the data to the centroid calculator (6); and controlling the centroid calculator (6) for calculating centroids of partial apertures in each of the partial aperture groups and transferring them to the wavefront reconstruction device (7); and the wavefront reconstruction device (7) is arranged to arrange the centroids calculated by the centroid calculator (6) as a centroid vector and calculate a slope vector of the incident wavefront (8) from the centroid vector for reconstructing from the incident wavefront.
    [2]
    A time-divided exposure Hartmann wavefront sensor according to claim 1, wherein the step-by-step collection controller (3) is adapted to determine the plurality of sub-aperture groups for which the light spot data from the light spot array is to be collected step by step by the CCD camera (5), and the exposure time for each of the sub-aperture groups based on the light power density properties of the incident wavefront (8) and the response sensitivity of the CCD camera (5) by calculating a minimum value Emin of incident light energy required by a lower SNR limit for measuring the centroid of the light spot within a single sub-aperture of the micro lens array and also a maximum value Emax of the incident light energy required to cause the maximum value of the light spots to reach an upper measuring limit of the CCD camera (5); integrating a part of the light intensity measured by the light power density measuring instrument (2) corresponding to each of the partial apertures to derive incident light power Pk into the partial aperture, wherein k is a number of the partial aperture; dividing the light power in each of the partial apertures by respectively the required maximum and minimum values of the incident light energy, to derive a lower exposure time limit tkmin = Pk / Emax for the partial aperture and an upper exposure time limit tkmax = Pk / Emin for the partial aperture; and classifying the sub-apertures in the plurality of sub-aperture groups according to their exposure time defined by the respective lower exposure time limits and the respective upper exposure time limits, and determining the exposure time for each of the sub-aperture groups based on the exposure time ranges.
    [3]
    The Hartmann wavefront sensor with time-divided exposure according to claim 2, wherein the step-by-step collective controller (3) is adapted to classify the sub-apertures in the plurality of sub-aperture groups by (a) associating the number k of each of the sub-apertures and the upper exposure time limit tkmax for this partial aperture and the lower exposure time limit tkmin for this partial aperture to generate a partial aperture number vector K, an upper exposure time limit vector Tmax and a lower exposure time limit vector Tmin; (b) searching the upper exposure time limit vector Tmax for a minimum value tmax to find a partial aperture number corresponding to this minimum value tmax, and searching the lower exposure time limit vector Tmin for values smaller than tmax to find partial aperture numbers corresponding to these values, thus forming of a sub-aperture group comprising sub-apertures corresponding to those found sub-aperture numbers and setting the exposure time for this sub-aperture group 31S tmax, (c) removing the sub-aperture numbers found in step (b) from the sub-aperture number vector K and removing elements tkmax and tkmin corresponding to those sub-aperture numbers from the upper exposure time limit vector Tmax and the lower exposure time limit vector Tmin; and (d) repeating step (b) and step (c) until all partial apertures have been removed.
    [4]
    Hartmann wavefront sensor with time-divided exposure according to claim 2, wherein the upper measuring limit of the CCD camera (5) is smaller than a full measuring range of the CCD camera (5) and preferably 80% -90% of the full measuring range of the CCD camera (5).
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    CN201210071732|2012-03-19|
    CN2012100717320A|CN102607718B|2012-03-19|2012-03-19|Hartmann wavefront sensor employing different-time exposure|
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