CN102426061B - Adjusting method of Hartmann wavefront sensor with adjustable dynamic range - Google Patents

Abstract

The invention proposes a Hartmann wavefront sensor with adjustable dynamic range, which is composed of an optical matching system, a wavefront split sampling array, a phase modulator and a photoelectric sensor. The size of the optical beam is smaller than the size of the wavefront split sampling array and the size of the phase modulator, and the phase modulator is placed between the optical matching system and the wavefront split sampling array, and its aperture is larger than the optical aperture of the optical matching system. The constricted incident wave adds aberration, forming many sub-regions in its aperture, which correspond to the sub-aperture aperture and arrangement of the wavefront segmentation sampling array, and add the generated aberration to the passing through Corresponding to the light waves of the sub-apertures, the wavefront division sampling array divides the light waves passing through the phase modulator into multiple sub-beams, and focus them on the target surface of the photoelectric sensor located on the focal plane respectively. The invention can be widely used in wavefront detection under various conditions of large wavefront aberration.

Description

An Adjustment Method of Hartmann Wavefront Sensor with Adjustable Dynamic Range

technical field

The invention relates to a novel optical dynamic wavefront sensor, in particular to a Hartmann wavefront sensor with adjustable dynamic range based on the principle of phase compensation. the

Background technique

The adaptive optics system is mainly composed of a wavefront sensor, a wavefront controller, and a wavefront corrector. The wavefront sensor can be said to be the "eye" of the adaptive optics system. The detection ability of the wavefront sensor directly affects the performance of the adaptive optics system. Calibration performance. The Hartmann wavefront sensor is currently the most popular and widely used wavefront sensor. A Hartmann wavefront sensor disclosed in Chinese Patent Application Publication (Application No. 98112210.8, Publication No. CN1245904A) mainly uses wavefront split sampling array elements such as microlens arrays to divide the wavefront into many sub-aperture before, and the incident light is respectively collected on the array photoelectric sensor to form a light spot array. When a plane wave without aberration is incident, the light spot of each sub-aperture wavefront is located in the center of the corresponding sub-area on the target surface of the photoelectric sensor. When a wavefront with aberration is incident, the corresponding light spot of each sub-aperture will have a certain offset. The offset of each light spot relative to the incidence of the non-aberration plane wave can be processed and calculated by a computer to obtain the wavefront and the entire wavefront aberration information in each sub-aperture. However, the dynamic range of the Hartmann wavefront sensor is generally determined at the time of design. When large aberrations need to be measured, the spot shift often exceeds the design dynamic range, resulting in inaccurate or even impossible detection. If a large dynamic range is used in the design, the overall detection accuracy of the Hartmann wavefront sensor will decrease accordingly. Therefore, how to use the Hartmann wavefront sensor to detect large aberrations and ensure the detection accuracy is a research work that needs to be carried out. the

At present, many Hartmann wavefront sensors with large dynamic range or adjustable dynamic range have been proposed, such as the Chinese patent application publication (application number 02123756.5, publication number CN1212508C) which proposes a sensor with adjustable dynamic range and measurement accuracy. Hartmann wavefront sensor, it adds measurement sub-aperture gating control elements in the Hartmann wavefront sensor structure, controls the gating of sub-apertures to control the sampling period of the wavefront split sampling array, in order to adjust the wavefront sensor measurement for precision and dynamic range purposes. These inventions can achieve the purpose of increasing the dynamic range of the Hartmann wavefront sensor, but the wavefront split sampling array element will always have a certain off-axis aberration. This invention is different from other Hartmann sensors with large dynamic range or adjustable dynamic range. All Mann wavefront sensors inevitably encounter the problem of large spot offset and difficulty in accurate detection of the spot centroid when it is far away from the axis. If this problem is ignored, even if the dynamic range of the Hartmann wavefront sensor is increased, the wavefront detection accuracy will decrease due to the larger detection error of the spot centroid. Therefore, it is very necessary to invent a Hartmann wavefront sensor that can realize adjustable dynamic range and ensure detection accuracy. the

Contents of the invention

The technical problem of the present invention is: to overcome the problem that the Hartmann wavefront sensor has a large dynamic range and high measurement accuracy and it is difficult to balance it, and proposes an adjustable dynamic range, which can guarantee the measurement accuracy, and is easy to meet the centroid algorithm accuracy and wavefront segmentation sampling Off-axis aberration control of array elements requires a Hartmann wavefront sensor. the

The Hartmann wavefront sensor with adjustable dynamic range proposed by the present invention is composed of an optical matching system, a wavefront split sampling array, a phase modulator and a photoelectric sensor. The optical matching system is used to shrink the incident light wave to make the incident light beam The size does not exceed the size of the wavefront split sampling array and the size of the phase modulator. The phase modulator is placed between the optical matching system and the wavefront split sampling array, and its aperture is larger than the optical aperture of the optical matching system. The phase modulator passes through The constricted incident wave adds aberration, forming many sub-regions in its aperture, which correspond to the sub-aperture aperture and arrangement of the wavefront segmentation sampling array, and add the generated aberration to the passing through Corresponding to the light waves of the sub-apertures, the wavefront division sampling array divides the light waves passing through the phase modulator into multiple sub-beams, and focus them on the target surface of the photoelectric sensor located on the focal plane respectively. the

The phase modulator is placed at the front end of the optical matching system, the ratio of the sub-area aperture of the phase modulator to the sub-aperture aperture of the wavefront division sampling array is the same as the beam reduction ratio of the optical matching system, and the arrangement of the sub-areas is the same as that of the sub-apertures. the

The phase modulator can also be placed between the optical matching system and the wavefront division sampling array, and the phase modulator sub-areas have the same aperture and arrangement as the wavefront division sampling array sub-apertures. the

The phase modulator is a transmissive phase modulator, a liquid crystal spatial light modulator with electrical addressing phase modulation.

The wavefront division sampling array adopts a binary Fresnel microlens array, or a continuous surface microlens array, or a gradient refractive index microlens array. the

The photoelectric sensor adopts a CCD detector, or a CMOS detector, or a four-quadrant sensor array. the

Compared with the existing Hartmann wavefront sensor, the Hartmann wavefront sensor with adjustable dynamic range of the present invention can quickly lock each sub-aperture of the wavefront segmentation sampling array to the corresponding light spot on the photoelectric sensor, realize the adjustable dynamic range, and ensure the measurement Accuracy, when measuring large aberrations, even if the spot centroid shift is large, the inherent off-axis aberration of the wavefront split sampling array will affect the centroid detection, but through phase compensation, the large image through the wavefront split sampling array The difference gradually becomes small aberration, and the light spots on the photoelectric sensor return to the vicinity of their respective calibration positions. The accuracy of the Hartmann wavefront sensor is reliable when measuring small aberrations. Therefore, the present invention can reduce the off-axis The requirement of aberration control greatly reduces the influence of off-axis aberration on the final measurement result. the

Description of drawings

FIG. 1 is a schematic structural diagram of an embodiment of a Hartmann wavefront sensor with an adjustable dynamic range according to the present invention. the

Fig. 2 is a schematic diagram of the resetting process of the spot array on the target surface of the Hartmann wavefront sensor with adjustable dynamic range when the spot offset is within the designed dynamic range of the Hartmann wavefront sensor;

Fig. 3 is when some facula offset exceeds the design dynamic range of Hartmann wavefront sensor, the schematic diagram of reset process of spot array on the target surface of Hartmann wavefront sensor with adjustable dynamic range of the present invention;

Fig. 4 is a schematic structural diagram of another embodiment of the Hartmann wavefront sensor with adjustable dynamic range of the present invention. the

Detailed ways

The Hartmann wavefront sensor with adjustable dynamic range of the present invention will be further described below in conjunction with the drawings and embodiments.

Embodiment one

As shown in Figure 1, the wavefront aberration compensation element in the sub-aperture adopts a transmissive phase modulator 3, which is located before the wavefront division sampling array 2, and compensates the oblique aberration of the sub-wavefront in each sub-aperture, which includes an optical matching system 1, a wavefront The front split sampling array 2, the transmissive phase modulator 3 and the photoelectric sensor 4, the incident light wave is narrowed by the optical matching system 1, and passes through the transmissive phase modulator 3 before entering the wavefront split sampling array 2, the transmissive phase modulator Specific aberrations can be added to the light wave. The sub-apertures of the wavefront split sampling array 2 divide the light wave into many sub-beams. The focal plane of which coincides with the target surface of the photoelectric sensor 4, and the sub-beams in each sub-aperture are respectively focused on the photoelectric sensor. 4 on the target surface, where the transmissive phase modulator 3 adopts a liquid crystal spatial light modulator with electrical addressing phase modulation, and the wavefront division sampling array 2 adopts a binary Fresnel microlens array, or a continuous surface microlens array, or a gradient The refractive index microlens array, the photoelectric sensor 4 adopts a CCD detector or a CMOS detector; the transmissive phase modulator 3 adds a specific phase difference to the light wave in each sub-aperture of the wavefront division sampling array 2, and the additional method can be synchronous compensation, that is, simultaneously Adding a specific phase difference to the light waves in each sub-aperture can also be asynchronous compensation. Only add a specific phase difference to the light waves in one or several sub-apertures. When the sub-apertures of the wavefront segmentation sampling array 2 and the light spots can be in one-to-one correspondence, the optical wave tilt aberration in each sub-aperture is obtained according to the offset of the photoelectric sensor 4 light spot centroid during measurement, and the transmission phase modulator 3 is used for synchronous compensation. Finally, the photoelectric Each light spot on the sensor 4 is reset to the initial position determined when the Hartmann wavefront sensor is calibrated, that is, the transmissive phase modulator 3 compensates the wavefront aberration to be measured, and the wavefront aberration to be measured is used for compensation The conjugate value of the aberration amount. The aberrations of each point of the wave surface to be measured and the wave surface used for compensation are inverse numbers to form a conjugate. When the aberration of the wavefront to be measured is large, the centroid of the light spot on the photoelectric sensor 4 is too large, and the sub-apertures of the wavefront segmentation sampling array 2 cannot correspond to the light spots one by one, by controlling the transmissive phase modulator 3 pairs of different sub-apertures Asynchronous compensation of light-wave aberration, observe the change of the centroid of the spot, the spot generated by the centroid corresponds to the sub-aperture with additional aberration, after locking the spot corresponding to each sub-aperture, the centroid offset of the spot can be measured to calculate the oblique image of the light wave in each sub-aperture The size of the difference is compensated synchronously with the transmissive phase modulator 3, and finally each light spot on the photoelectric sensor 4 is reset to the initial position determined when the Hartmann wavefront sensor is calibrated, so that the dynamic range can be realized without being limited by the dynamic range Adjustable and the compensation and measurement of the wavefront aberration, because the spot after the aberration compensation is at or near the initial calibration position, the wavefront aberration of the light entering the wavefront split sampling array 2 is very small, and the small aberration In this case, the measurement of the Hartmann wavefront sensor is reliable, that is, the residual error of phase compensation is very small, so even if the wavefront aberration to be measured is large, the final measurement accuracy can be guaranteed to be consistent with the case of small aberration. the

Embodiment 1 realizes wavefront detection and dynamic range adjustment through the following steps:

(1) On the phase modulator 3, divide corresponding sub-regions for each wavefront division sampling array 2 sub-apertures, the size and arrangement of the phase modulator 3 sub-regions and the size and arrangement of the wavefront division sampling array 2 sub-apertures The distribution is the same, and each phase modulator 3 sub-area adds a certain oblique aberration to the light wave in its corresponding sub-aperture;

(2) Use aberration-free plane wave incident calibration, the transmission phase modulator 3 does not add any aberration, and record the initial calibration position of the light spot corresponding to the sub-aperture of each wavefront segmentation sampling array 2 on the detector;

(3) When measuring the wavefront with aberration, the light spot corresponding to each sub-aperture will be offset on the target surface of the photoelectric sensor 4, and the oblique aberration of the light wave in each sub-aperture is calculated according to the currently measured light spot centroid offset, and the transmission The phase modulator 3 compensates the oblique aberration calculated by the light waves in each sub-aperture, and each spot moves to the calibration position accordingly. Because there is an error in the measurement value of the centroid offset of the spot, only one phase compensation cannot make the spot return to the calibration position. Or in its vicinity, after multiple measurements and compensations, each light spot on the target surface of the photoelectric sensor 4 is finally reset to the vicinity of the calibration position, wherein the phase compensation can be aimed at a specific sub-aperture, and through asynchronous compensation, the sub-aperture can quickly Lock the corresponding spot, so the detection of wavefront aberration is not limited by the dynamic range, and the dynamic range can be adjusted;

(4) When each light spot on the photoelectric sensor 4 is reset to the vicinity of the calibration position, it can be considered that the light wave front aberration of the wavefront division sampling array 2 is very small, which is similar to the aberration-free parallel light used in calibration, that is, the phase The modulator basically compensates the wavefront aberration to be measured, and finally the wavefront aberration to be measured is the conjugate value of the total compensation aberration on the phase modulator. the

The process of adding oblique aberration to the light waves in each sub-aperture by the transmissive phase modulator to reset each light spot on the photoelectric sensor will be further described below with reference to the accompanying drawings. the

As shown in Figure 2, the spot offset corresponding to each sub-aperture is within the design dynamic range of the Hartmann wavefront sensor, and the wavefront segmentation sampling array 2 adopts the spot array formed by 8×8 sub-aperture units on the target surface of the photoelectric sensor 4, The symbol "×" indicates the spot position of the wavefront without aberration, and the black dot "·" indicates the spot formed by the wavefront with aberration. At this time, none of the wavefront aberrations in the sub-aperture exceeds the dynamic range. Taking a single sub-aperture corresponding to the photosensor 4 sub-region as an example, the process of resetting the sub-aperture corresponding to the light spot during phase compensation is described. the

It is assumed that the wavefront approximation in the subaperture contains only tilt aberrations. By measuring the offset of the sub-aperture corresponding to the light spot in the initial state, the sub-aperture wavefront slopes σ _x and σ _y are obtained, and the wavefront in the sub-aperture can be expressed as

W(x, y) = σ _x x + σ _y y (1)

Because there is an error in the detection of the centroid of the off-axis spot, the measured slope also has an error δσ _x , δσ _y relative to the real value, and the real sub-wavefront can be expressed as

W(x,y)=(σ _x +δσ _x )·x+(σ _y +δσ _y )·y (2)

Compensation phase is generated according to the measured value

W(x,y)=-σ _x x-σ _y y (3)

After one compensation, the wavefront in the sub-aperture is

W(x, y) = δσ _x x + δσ _y y (4)

At this time, the position of the spot shifts to the calibrated position of the aberration-free wavefront and enters the paraxial region. Measure the center of mass offset of the spot again, and make supplementary corrections to the previous compensation phase according to the measured amount, and repeat the measurement and compensation until the corresponding spot of each sub-aperture is reset to the calibrated position of the wavefront without aberration or near this position. The allowable range of the specific reset position can be Determined according to allowable error. In this way, the measurement accuracy can be guaranteed even when the wavefront division sampling array 2 has off-axis aberration and the off-axis spot centroid measurement has errors. the

As shown in FIG. 3 , some sub-apertures correspond to spot offsets that exceed the design dynamic range of the Hartmann wavefront sensor and enter the photoelectric sensor 4 sub-regions corresponding to adjacent sub-apertures. By controlling the phase non-synchronous compensation between adjacent sub-apertures, when performing phase compensation in a sub-aperture, in order to determine the light spot corresponding to the sub-aperture, first randomly generate a small tilt compensation aberration for the sub-aperture, and keep The phase of the adjacent sub-aperture remains unchanged, and the light spot corresponding to the sub-aperture can be locked by detecting whether there is a change in the position of the light spot in the corresponding area of the sub-aperture and the adjacent sub-aperture. After the spot is locked, use the same method as in Figure 2 to perform phase compensation on it, so that the spot can return to the sub-area of the photoelectric sensor 4 corresponding to the sub-aperture until it is reset to the vicinity of the calibrated position of the aberration-free wavefront. In this way, the dynamic range limit can be broken through, and the dynamic range can be adjusted. When measuring large aberrations, it also avoids the problem of inaccurate detection of the center of mass caused by the increase of spot offset, ensuring the detection ability and accuracy of large aberrations. Detection accuracy. the

Example two

As shown in Figure 4, the wavefront aberration compensation element in the sub-aperture adopts a transmissive phase modulator 3, which is located in the wavefront division sampling array 2 before the optical matching system, and compensates the wavefront aberration in each sub-aperture, which includes an optical matching system 1. Wavefront split sampling array 2, transmissive phase modulator 3 and photoelectric sensor 4. The incident light wave enters the wavefront split sampling array 2 after being narrowed by the optical matching system 1, and the sub-apertures of the wave front split sampling array 2 split the light wave into many sub-beams, the focal plane of which coincides with the target surface of the photoelectric sensor 4, and the sub-beams in each sub-aperture are respectively focused on the target surface of the photoelectric sensor 4, and the transmissive phase modulator is placed before the optical matching system, which can add light waves Specific aberrations, wherein the transmissive phase modulator 3 adopts an electrically addressable phase-modulated liquid crystal spatial light modulator, and the wavefront division sampling array 2 adopts a binary Fresnel microlens array, or a continuous surface microlens array, or a gradient The refractive index microlens array, the photoelectric sensor adopts CCD detector or CMOS detector; the transmissive phase modulator 3 adds a specific phase difference to the light wave in each sub-aperture of the wavefront division sampling array 2, and the additional method can be synchronous compensation, that is, each Adding a specific phase difference to the light waves in several sub-apertures can also be asynchronous compensation. Only add a specific phase difference to the light waves in one or several sub-apertures. When the sub-apertures of the pre-segmented sampling array 2 and the light spots can correspond one-to-one, the light wave tilt aberration in each sub-aperture can be obtained according to the offset of the light spot centroid of the photoelectric sensor 4 during measurement, and the transmissive phase modulator 3 is used for synchronous compensation, and finally the photoelectric sensor Each light spot on 4 is reset to the initial position determined when the Hartmann wavefront sensor is calibrated, that is, the transmissive phase modulator 3 compensates the wavefront aberration to be measured, and the amount of wavefront aberration to be measured is used for compensation The conjugate value of the aberration amount, when the wavefront aberration to be measured is large, the center of mass of the light spot on the photoelectric sensor 4 is shifted too much, and when the sub-apertures of the wavefront segmentation sampling array 2 cannot correspond to the light spot one by one, by controlling the transmissive The phase modulator 3 asynchronously compensates the light-wave aberration in different sub-apertures, and observes the change of the centroid of the spot. The spot generated by the centroid corresponds to the sub-aperture with additional aberration. After locking the spot corresponding to each sub-aperture, the centroid deviation of the spot can be measured. Calculate the size of the tilt aberration of the light wave in each sub-aperture, and use the transmission phase modulator 3 to compensate synchronously, and finally reset each light spot on the photoelectric sensor 4 to the initial position determined when the Hartmann wavefront sensor is calibrated, so that It can realize the adjustable dynamic range and the compensation and measurement of the wavefront aberration without being limited by the dynamic range, because the light spots after aberration compensation are all at or near the initial calibration position, and enter the optical wavefront image of the wavefront split sampling array 2 The difference is very small, and the measurement of the Hartmann wavefront sensor is reliable in the case of small aberration, that is, the residual error of phase compensation is very small, so even if the wavefront aberration to be measured is large, the final measurement accuracy can also be Guaranteed to be consistent with the case of small aberrations. the

Embodiment 2 realizes wavefront detection and dynamic range adjustment through the following steps:

(1) On the phase modulator 3, the sub-apertures of each wavefront division sampling array are divided into corresponding sub-regions, and the arrangement of the sub-regions of the phase modulator 3 is the same as that of the wavefront division sampling array 2 sub-apertures. Each sub-region The ratio of the aperture to the corresponding sub-aperture is equal to the beam reduction ratio of the optical matching system 1, and each sub-region of the phase modulator 3 adds a certain oblique aberration to the light wave in its corresponding sub-aperture;

(2) Use aberration-free plane wave incident calibration, the transmission phase modulator 3 does not add any aberration, and record the initial calibration position of the light spot corresponding to the sub-aperture of each wavefront segmentation sampling array 2 on the detector;

(3) When measuring the wavefront with aberration, the light spot corresponding to each sub-aperture will be offset on the target surface of the photoelectric sensor 4, and the oblique aberration of the light wave in each sub-aperture is calculated according to the currently measured light spot centroid offset, and the transmission The phase modulator 3 compensates the oblique aberration calculated by the light waves in each sub-aperture, and each spot moves to the calibration position accordingly. Because there is an error in the measurement value of the centroid offset of the spot, only one phase compensation cannot make the spot return to the calibration position. Or in its vicinity, after multiple measurements and compensations, each light spot on the target surface of the photoelectric sensor 4 is finally reset to the vicinity of the calibration position, wherein the phase compensation can be aimed at a specific sub-aperture, and through asynchronous compensation, the sub-aperture can quickly Lock the corresponding spot, so the detection of wavefront aberration is not limited by the dynamic range, and the dynamic range can be adjusted;

(4) When each light spot on the photoelectric sensor 4 is reset to the vicinity of the calibration position, it can be considered that the light wave front aberration of the wavefront division sampling array 2 is very small, which is similar to the aberration-free parallel light used in calibration, that is, the phase The modulator basically compensates the wavefront aberration to be measured, and finally the wavefront aberration to be measured is the conjugate value of the total compensation aberration on the phase modulator. the

Claims (3)

1. An adjustment method of a Hartmann wavefront sensor with adjustable dynamic range, the Hartmann wavefront sensor consists of an optical matching system (1), a wavefront split sampling array (2), a transmissive phase modulator (3 ) and a photoelectric sensor (4), the optical matching system (1) is used to shrink the incident light beam so that the size of the incident light beam does not exceed the size of the wavefront split sampling array (2) and the transmissive phase modulator (3) Size, characterized in that: the transmissive phase modulator (3) is placed between the optical matching system (1) and the wavefront split sampling array (2), and its aperture is larger than the optical aperture of the optical matching system (1). The phase modulator (3) adds aberrations to the beam-contracted incident wave, and forms many sub-regions in its light aperture, which correspond to the sub-aperture aperture and arrangement of the wavefront split sampling array (2) one by one , and add the generated aberrations to the light waves passing through the corresponding sub-apertures, the wavefront split sampling array (2) splits the light waves passing through the transmission phase modulator (3) into multiple sub-beams, and focus them on the focal points respectively on the target surface of the photoelectric sensor (4) on the surface; Specifically, the wavefront detection and dynamic range can be adjusted through the following: (1) On the transmissive phase modulator (3), divide the corresponding sub-areas for each wavefront segmentation sampling array (2) sub-aperture, and the size and arrangement of the sub-areas of the transmissive phase modulator (3) are consistent with the wavefront The sub-apertures of the split sampling array (2) have the same size and arrangement, and each sub-region of the transmissive phase modulator (3) adds a certain oblique aberration to the light waves in its corresponding sub-aperture; (2) Use aberration-free plane wave incident calibration, transmission phase modulator (3) without any aberration, record the initial calibration position of each wavefront segmentation sampling array (2) sub-aperture corresponding to the spot on the detector; (3) When measuring the wavefront with aberration, the light spot corresponding to each sub-aperture will be offset on the target surface of the photoelectric sensor (4), and the oblique aberration of the light wave in each sub-aperture will be calculated according to the currently measured center of mass shift of the light spot , the transmissive phase modulator (3) compensates the oblique aberration calculated by the light waves in each sub-aperture, and each spot moves to the calibration position accordingly. Because there is an error in the measurement value of the centroid offset of the spot, only one phase compensation cannot make the spot return to To reach the calibration position or its vicinity, multiple measurements and compensations are required, and finally all the light spots on the target surface of the photoelectric sensor (4) are reset to the vicinity of the calibration position, and the phase compensation can be aimed at a specific sub-aperture through asynchronous compensation , the sub-aperture can quickly lock the corresponding spot, so the detection of wavefront aberration is not limited by the dynamic range, and the dynamic range can be adjusted; (4) When all the light spots on the photoelectric sensor (4) are reset to the vicinity of the calibration position, it is considered that the light wave front aberration of the wavefront segmentation sampling array (2) is very small, which is similar to the aberration-free parallel light used in calibration, That is to say, the transmission type phase modulator basically compensates the wavefront aberration to be measured, and finally the wavefront aberration to be measured is the conjugate value of the total compensation aberration on the transmission type phase modulator. 2. The adjustment method of the Hartmann wavefront sensor with adjustable dynamic range according to claim 1, characterized in that: the wavefront segmentation sampling array (2) adopts a binary Fresnel microlens array, or a continuous surface microlens array lens array, or gradient index microlens array. 3. The adjustment method of the Hartmann wavefront sensor with adjustable dynamic range according to claim 1, characterized in that: the photoelectric sensor (4) adopts a CCD detector, or a CMOS detector, or a four-quadrant sensor array.

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