Atmospheric turbulence wavefront measuring device

Abstract

The atmospheric turbulence wave front measuring device provided by the application comprises a high-repetition-frequency short pulse laser (1), a laser emission optical unit (2), an atmospheric backwave beacon (3), a receiving optical unit (4), a narrow-band filter (5), a microlens array (6), a high-gain optical enhancer (7) and a high-frame-frequency imaging camera (8). The application uses a high-repetition-frequency short pulse laser to generate a beacon backwave. Since the single pulse time is short and the peak power is high, a high-brightness atmospheric backwave beacon can be generated. The distance gating technology is realized by using a high-speed time sequence controller. By controlling the exposure time matched with the pulse width and combining the narrow-band filtering technology, the background stray light can be reduced by several orders of magnitude. In addition, multiple gating pulses can be superimposed in one frame exposure time. The application mode is flexible, the detection signal-to-noise ratio can be significantly improved, and since the laser active beacon mode does not depend on natural light illumination, it is not affected by the working time and can be applied all day long.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adaptive optics, in particular to an atmospheric turbulence wavefront measurement device. BACKGROUND

[0002] At present, many fields and applications involve atmospheric transmission of light beams, but the system performance is degraded due to the influence of horizontal or oblique range strong atmospheric turbulence, such as imaging detection, wireless laser communication, wireless laser charging, laser directional energy transmission, etc., and it is usually necessary to use adaptive optics technology to overcome the influence of turbulence. One of the core functions of adaptive optics technology is to carry out atmospheric turbulence wavefront measurement first, but the horizontal or oblique range atmospheric turbulence has a short coherence length and a fast change speed, which puts higher requirements on the spatial resolution and time resolution of the wavefront detector.

[0003] At present, the commonly used wavefront measurement method is to use a Shack-Hartmann wavefront detector composed of a microlens array and a focal plane imaging camera. After the light reflected by the target enters the Shack-Hartmann wavefront detector, the energy is evenly distributed to each sub-aperture of the microlens and imaged on the camera target surface, and after the off-target amount of each focal spot is extracted by the image controller, the wavefront is fitted to obtain atmospheric turbulence information.

[0004] Since the Hartmann wavefront detector needs to distribute the received light energy to multiple sub-apertures, the detection capability of each sub-aperture is reduced, but it still cannot meet the strong atmospheric turbulence wavefront detection application due to the following reasons: first, the frame rate of high-sensitivity scientific cameras is relatively low, and the highest is generally 1k-2k FPS (frames per second), which is low in bandwidth after being applied in an adaptive optics system and cannot keep up with the Greenwood frequency of horizontal atmospheric turbulence. If a high-frame-rate ordinary camera is used, its detection capability cannot meet the detection requirements due to short exposure time and poor sensitivity, etc. Moreover, the shortest exposure time of any camera is limited, and it is usually about 1 microsecond, which cannot match the laser pulse width of tens of nanoseconds; second, in order to match the spatial length of atmospheric turbulence, the number of sub-apertures is large, and the energy is more dispersed, so it is difficult for a scientific camera to achieve a high signal-to-noise ratio, and therefore it is required that the brightness of the target be very high, which is usually difficult to meet; third, it is easily disturbed by background stray light, especially in the daytime, the sun's scattered light is strong, which causes the signal-to-noise ratio of detection to decrease significantly. SUMMARY

[0005] In view of this, it is necessary to provide an atmospheric turbulence wavefront measurement device with the advantages of high frame rate, high detection sensitivity, high signal brightness, and high background suppression capability, which can detect horizontal strong atmospheric turbulence in real time.

[0006] To solve the above problems, the technical scheme adopted by the present application is as follows:

[0007] One of the purposes of the present application is to provide an atmospheric turbulence wavefront measurement device, comprising a high-repetition-rate short-pulse laser (1), a laser emission optical unit (2), an atmospheric backscatter beacon (3), a receiving optical unit (4), a narrow-band optical filter (5), a microlens array (6), a high-gain optical amplifier (7), and a high-frame-rate imaging camera (8), wherein:

[0008] The high-repetition-rate short-pulse laser (1) emits laser pulses, which are expanded and focused by the laser emission optical unit (2) to produce a high-brightness atmospheric backscatter beacon (3) through backward scattering. The backscatter beacon light is transmitted through the atmosphere to the receiving optical unit (4) and is shrunk, and then only the light of the laser wavelength is transmitted after passing through the narrow-band optical filter (5). The light of the laser wavelength is divided into several converging sub-beams by each sub-aperture through the microlens array (6) and enters the high-gain optical amplifier (7). The high-gain optical amplifier (7) amplifies the energy of each sub-beam by several times as needed and enters the high-frame-rate special imaging camera (8). The high-frame-rate special imaging camera (8) exposes according to the required sampling frequency to obtain the point spot array image in each sub-aperture, and fits the atmospheric turbulence wavefront information according to the point spot array image data.

[0009] In some embodiments, the high-repetition-rate short-pulse laser (1) can output narrow pulses with a width of several nanoseconds, and the laser emission optical unit (2) can be adjusted to produce a high-brightness atmospheric backscatter beacon.

[0010] In some embodiments, a high-speed timing controller (9) is electrically connected to the high-repetition-rate short-pulse laser (1), the high-gain optical amplifier (7), and the high-frame-rate imaging camera (8). The high-repetition-rate short-pulse laser (1) outputs an electrical pulse signal synchronized with the laser pulses to the high-speed timing controller (9). The high-speed timing controller (9) generates a gating control signal according to the atmospheric turbulence path length, the pulse width, and the required scattering depth, and controls the gating time and the gating time of the high-gain optical amplifier (7) to make the received backscatter echo signal fall within the gating time and the gating time.

[0011] In some embodiments, the imaging detection high-speed timing control mode of the high-speed timing controller (9) is a single-exposure mode, and the frame frequency is consistent with the pulse laser repetition rate.

[0012] In some embodiments, the imaging detection high-speed timing control mode of the high-speed timing controller (9) is a multiple-gating superposition exposure mode, and the exposure frame frequency is less than the pulse laser repetition rate.

[0013] In some embodiments, the high frame rate imaging camera (8) comprises a high-speed CMOS sensor target surface (81), an image readout circuit (82), a wavefront calculation dedicated hardware circuit (83), and a gigabit network output interface (84), wherein the photoelectric effect occurs after the light signal is incident on the high-speed CMOS sensor target surface (81) to generate an electrical signal, the electrical signal is collected by the image readout circuit (82) and converted into a digital signal and sent to the wavefront calculation dedicated hardware circuit (83), the wavefront calculation dedicated hardware circuit (83) calculates the center of mass of the point spot array and fits the wavefront information, and sends the wavefront information in the form of Zernike coefficients to the upper computer user through the high-speed gigabit network interface (84).

[0014] In some embodiments, the wavefront calculation dedicated hardware circuit (83) is composed of a high-speed FPGA.

[0015] The application adopts the above technical solutions, which has the following beneficial effects:

[0016] The atmospheric turbulence wavefront measurement device provided by the application uses high-repetition-rate short-pulse laser to generate beacon echo, and since the single-pulse time is short and the peak power is high, a high-brightness atmospheric beacon echo can be generated. The distance gating technology is realized by using a high-speed time sequence controller, the background stray light can be reduced by several orders of magnitude by controlling the exposure time matched with the pulse width and combining the narrowband filtering technology, and multiple gating pulses can be superimposed in one exposure time, the application mode is flexible, the signal-to-noise ratio of detection can be significantly improved, and since the laser active beacon mode is used, the device is not dependent on natural light illumination, and therefore is not affected by the working time, and can be applied all day long. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments of the application or the prior art description. Obviously, the drawings described below are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 The structure diagram of the atmospheric turbulence wavefront measurement device provided by the embodiments of the application.

[0019] Fig. 2(a) is a wavefront detection high-speed time sequence control schematic diagram provided by an embodiment of the application.

[0020] Fig. 2(b) is a wavefront detection high-speed time sequence control schematic diagram provided by another embodiment of the application.

[0021] Figure 3 The structure schematic diagram of the high frame rate dedicated imaging camera provided by the embodiments of the application. DETAILED DESCRIPTION

[0022] Embodiments of the present application are described below in detail with reference to the accompanying drawings, wherein the same or similar components or components having the same or similar functions are denoted by the same or similar reference numerals throughout the drawings. The embodiments described below by reference to the drawings are exemplary and are intended to explain the present application, and cannot be understood as limiting the present application.

[0023] In the description of the present application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the devices or components referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0024] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise explicitly and specifically limited.

[0025] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments.

[0026] Please refer to Figure 1 A structure schematic diagram of an atmospheric turbulence wavefront measurement device provided for the present embodiment 1, including a high repetition rate short pulse laser (1), a laser emission optical unit (2), an atmospheric backwave beacon (3), a receiving optical unit (4), a narrowband optical filter (5), a microlens array (6), a high gain optical enhancer (7) and a high frame frequency imaging camera (8). The structure of each component and its implementation method are described in detail below.

[0027] The high repetition rate short pulse laser (1) can output narrow pulses with a width of several nanoseconds, has extremely high peak power, and can adjust the laser emission optical unit (2) to focus to produce a high-brightness atmospheric backwave beacon within a certain distance.

[0028] The receiving optical unit (4) is used to collect the atmospheric beacon backscattering echo signal.

[0029] The microlens array (6) is used to divide the received echo signal into several sub-beams.

[0030] The high-gain optical enhancer (7) can amplify the incident optical wave signal by hundreds to tens of thousands of times, so as to improve the detection sensitivity of the whole imaging device.

[0031] The high-frame-rate imaging camera (8) has the ability of real-time high-speed imaging and data transmission, and when a small target surface is operated, the frame rate can be as high as 20k FPS or even higher, and a special hardware circuit is integrated, real-time wavefront information is calculated and fitted, and high-speed sampling of atmospheric turbulence can be realized.

[0032] The atmospheric turbulence wavefront measurement device provided by the above-mentioned embodiments of the present application has the following working mode:

[0033] The high-repetition-rate short-pulse laser (1) emits a laser pulse, which is expanded and focused by the laser emission optical unit (2) and then backscattered to generate a high-brightness atmospheric back beacon (3). The backscattered light of the beacon is transmitted through the atmosphere to the receiving optical unit (4) and is shrunk. Only light of the laser wavelength is transmitted after passing through the narrow-band optical filter (5). The light of the laser wavelength is divided into several converging sub-beams by each sub-aperture through the microlens array (6) and enters the high-gain optical enhancer (7). The high-gain optical enhancer (7) amplifies the energy of each sub-beam by several times as needed and enters the high-frame-rate special imaging camera (8). The high-frame-rate special imaging camera (8) exposes according to the required sampling frequency, obtains the point spot array image in each sub-aperture, and fits the atmospheric turbulence wavefront information according to the point spot array image data.

[0034] In some embodiments, a high-speed timing controller (9) electrically connected to the high-repetition-rate short-pulse laser (1), the high-gain optical enhancer (7) and the high-frame-rate imaging camera (8) is further included. The high-repetition-rate short-pulse laser (1) outputs an electrical pulse signal synchronized with the laser pulse to the high-speed timing controller (9). The high-speed timing controller (9) generates a gating control signal according to the atmospheric turbulence path length, the pulse width and the required scattering depth, and controls the gating time and the gating time of the high-gain optical enhancer (7), so that the received backscattered echo signal falls within the gating time and the gating time.

[0035] Further, the wavefront detection high-speed timing control mode, which is divided into two cases:

[0036] Figure 2(a) is a single exposure mode, the frame rate is consistent with the pulse laser repetition rate, the period of the laser is T, a laser pulse with a pulse width of τ L is emitted at T1. After scattering through a certain depth of atmosphere, the echo pulse with a pulse width of τ RThe high-speed timing controller starts timing after receiving the laser synchronization pulse at time T1, and controls the high-gain optical enhancer to turn on at time T2, and the opening time τ I =τ R The high-speed timing controller simultaneously turns on the high-frame-rate dedicated imaging camera for exposure at time T2, and the exposure time is τ C , τ C The camera's shortest exposure time or τ I The next exposure cycle starts from the next pulse time T3 and repeats the above process.

[0037] Figure 2(b) shows a multiple-shot gate superposition exposure method, where the exposure frame rate is less than the pulse laser repetition rate. The laser period is T, and at time T1, a pulse width of τ is emitted. L The laser pulse, after being scattered by a certain depth of atmosphere, reaches the receiving optical system at time T2, and the echo pulse width is τ R The high-speed timing controller starts timing after receiving the laser synchronization pulse at time T1, and controls the high-gain optical intensifier to start gating at time T2, and the gating time τ I =τ R The high-speed timing controller simultaneously turns on the high-frame-rate dedicated imaging camera for exposure at time T2, and the exposure time is τ C In this diagram, two strobe pulses are superimposed as an example, so τ C =τ I + T. The next exposure cycle starts from the next pulse time T5 and repeats the above process.

[0038] Where: T: laser pulse period, τ L : Laser pulse width, τ R : Received beacon echo pulse width, τ I : High gain optical intensifier gating width, τ C : Camera exposure time, T1: Time when the first pulse is emitted, T2: Time when the first echo pulse arrives at the receiving optical system, T3: Time when the second pulse is emitted, T4: Time when the second echo pulse arrives at the receiving optical system, T5: Time when the third pulse is emitted, T6: Time when the third echo pulse arrives at the receiving optical system, T7: Time when the fourth pulse is emitted, T8: Time when the fourth echo pulse arrives at the receiving optical system.

[0039] See also Figure 3The high-frame-rate imaging camera (8) comprises a high-speed CMOS sensor target surface (81), an image readout circuit (82), a wavefront calculation dedicated hardware circuit (83), and a gigabit network output interface (84), wherein, after the optical signal is incident on the high-speed CMOS sensor target surface (81), a photoelectric effect occurs and an electrical signal is generated, the electrical signal is collected by the image readout circuit (82) and converted into a digital signal and sent to the wavefront calculation dedicated hardware circuit (83), the wavefront calculation dedicated hardware circuit (83) calculates the center of mass of the point spot array and fits the wavefront information, and sends the wavefront information in the form of Zernike coefficients to the upper computer user through the high-speed gigabit network interface (84).

[0040] In some embodiments, the wavefront calculation dedicated hardware circuit (83) is composed of a high-speed FPGA.

[0041] The high-frame-rate imaging camera (8) described above has a high-speed real-time imaging capability, and when a small target surface is used, the frame rate can be as high as 20k FPS or even higher, and the dedicated hardware circuit is integrated to calculate and fit the wavefront information in real time, so that high-speed sampling of atmospheric turbulence can be realized.

[0042] The atmospheric turbulence wavefront measurement device provided by the above-mentioned embodiments of the present application uses a high-repetition-frequency short-pulse laser to generate a beacon echo, and because the single-pulse time is short and the peak power is high, a beacon echo with high brightness can be generated. The distance gating technology is realized by using a high-speed time sequence controller, the background stray light can be reduced by several orders of magnitude by controlling the exposure time matched with the pulse width and combining the narrowband filtering technology, and multiple gating pulses can be superimposed within one exposure time, the application mode is flexible, and the signal-to-noise ratio of detection can be significantly improved; and because the laser active beacon mode does not depend on natural illumination, it is not affected by the working time, and can be applied all day long; the atmospheric turbulence wavefront measurement device provided by the embodiments of the present application has the advantages of high frame rate (≥20k FPS), high detection sensitivity, high beacon brightness, high background suppression capability, and the like, and can realize real-time detection of horizontal atmospheric strong turbulence.

[0043] It can be understood that any combination of the technical features of the above-mentioned embodiments can be made, and in order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0044] The above merely describes preferred embodiments of the present application, and only specifically describes the technical principles of the present application, and these descriptions are only for explaining the principles of the present application, and cannot be explained as limitations on the protection scope of the present application in any way. Based on the explanations here, any modifications, equivalent replacements and improvements made within the spirit and principles of the present application, and other specific embodiments of the present application that can be thought of by those skilled in the art without creative labor, should be included in the protection scope of the present application.

Claims

1. An atmospheric turbulence wavefront measuring device, characterized in that: The invention comprises a high repetition rate short pulse laser (1), a laser emission optical unit (2), an atmospheric echo beacon (3), a receiving optical unit (4), a narrow band filter (5), a micro lens array (6), a high gain optical intensifier (7) and a high frame rate imaging camera (8), wherein: The high repetition rate short pulse laser (1) emits a laser pulse, which is then expanded by the laser emission optical unit (2) and focused and backscattered to generate a high-brightness atmospheric echo beacon (3). The backscattered light of the beacon is transmitted to the receiving optical unit (4) through the atmosphere and is then narrowed. After passing through a narrowband filter (5), only light of the laser wavelength is transmitted. The light of the laser wavelength is divided into a plurality of convergent sub-beams by each sub-aperture through the microlens array (6) and enters the high-gain optical intensifier (7). The high-gain optical intensifier (7) amplifies the energy of each sub-beam by several times as needed and then enters a high-frame rate dedicated imaging camera (8). The high-frame rate dedicated imaging camera (8) performs exposure according to a required sampling frequency to obtain a spot array image in each sub-aperture, and fits atmospheric turbulence wavefront information based on the spot array image data.

2. The atmospheric turbulence wavefront measuring device according to claim 1, characterized in that: The high repetition rate short pulse laser (1) outputs narrow pulses with a width of several nanoseconds, and adjusts the focusing of the laser emission optical unit (2) to generate a high-brightness atmospheric echo beacon.

3. The atmospheric turbulence wavefront measuring device according to claim 1, characterized in that: The invention also includes a high-speed timing controller (9) electrically connected to the high-repetition-rate short-pulse laser (1), the high-gain optical intensifier (7) and the high-frame-rate imaging camera (8). The high-repetition-rate short-pulse laser (1) outputs an electrical pulse signal synchronized with the laser pulse to the high-speed timing controller (9). The high-speed timing controller (9) generates a gating control signal according to the atmospheric turbulence path length, pulse width and required scattering depth, and controls the gating moment and gating time of the high-gain optical intensifier (7) so that the backscattered echo signal to be received falls exactly within the gating moment and gating time.

4. The atmospheric turbulence wavefront measuring device according to claim 3, characterized in that: The imaging detection high-speed timing control mode of the high-speed timing controller (9) is a single exposure mode, and the frame frequency is consistent with the pulse laser repetition frequency.

5. The atmospheric turbulence wavefront measuring device according to claim 3, characterized in that: The imaging detection high-speed timing control mode of the high-speed timing controller (9) is a multiple-gating superposition exposure mode, and the exposure frame frequency is less than the pulse laser repetition frequency.

6. The atmospheric turbulence wavefront measuring device according to claim 1, characterized in that: The high frame rate imaging camera (8) comprises a high-speed CMOS sensor target surface (81), an image readout circuit (82), a dedicated hardware circuit for wavefront calculation (83) and a gigabit network output interface (84), wherein a light signal is incident on the high-speed CMOS sensor target surface (81), a photoelectric effect occurs and an electrical signal is generated, the electrical signal is collected by the image readout circuit (82) and converted into a digital signal and sent to the dedicated hardware circuit for wavefront calculation (83), the dedicated hardware circuit for wavefront calculation (83) calculates the centroid of the spot array from the received image signal and fits the wavefront information, and sends the wavefront information to a host computer user through the gigabit network output interface (84) in the form of Zernike coefficients.

7. The atmospheric turbulence wavefront measuring device according to claim 6, characterized in that: The wavefront calculation dedicated hardware circuit (83) is composed of a high-speed FPGA.

Images