Polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system and method

Abstract

The present invention relates to a polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system and method, in order to solve the current technical problem that the pulse sequence is long and the image quality of the multiple exposure frequency recognition algorithm is reduced. The system includes a pulse light source that emits pulses and a structured light pulse sequence generation unit, a polarization splitting unit, and a high-speed scene generation unit that are sequentially arranged along the pulse transmission direction; the control unit is respectively connected to the pulse light source and the image acquisition unit; the signal output by the high-speed scene generation unit is received by the image acquisition unit, and the image acquisition unit is connected to the data processing unit. The method includes 1. The pulse light source emits pulses and obtains N structured light pulses after passing through a beam splitter; 2. 2N polarization structured light pulses are obtained through a birefringent delay crystal; 3. The high-speed scene generation unit is irradiated to obtain images of the target scene at 2N moments; 4. A superimposed image is generated; 5. Image information of the dynamic scene at different moments is reconstructed.

Description

Technical Field

[0001] The present invention relates to the technical field of high-speed imaging, and in particular to a polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system and method. Background Art

[0002] In a wide range of scientific research, the ability to record fast transient events in real time is critical to understanding the subject at hand, such as delayed photoemission, molecular motion, and photosynthetic systems. High-speed cameras have been developed to meet this need, but their speed has an upper limit due to the speed at which practical detectors can read out and prepare to capture the next frame.

[0003] To achieve higher frame rates, a method that does not rely on fast detectors is needed. For example, pump-probe methods, in which a transient event is initiated by a pump pulse and detected by another pulse after a controllable time delay, can be repeated multiple times with different time delays. The course of the event can be captured with a temporal resolution set by the probe pulse length. However, events that do not repeat, as they are random events, cannot be studied with this method. Based on this, various single-exposure techniques have been developed that illuminate the sample with a series of short laser pulses. Because the laser pulses are separated in time, they encode image information for different temporal parts of the event that are used to study them. In order to retrieve the image information of a single pulse, each pulse must be unique with respect to some characteristics, which can be, for example, angle, spatial position or wavelength. The frequency recognition algorithm of multiple exposures (FRAME), relies on encoding a unique spatial modulation into each pulse of the pulse train. Although all pulses arrive at the same part of the detector, the image information carried by the individual pulses is separated in Fourier space according to the superposition modulation of the pulses. This allows the reconstruction of the frame sequence carried in the components of the pulse train.

[0004] Since the size of Fourier space is constant for a given sensor, if more frames are added, fewer Fourier components must be used to reconstruct each frame to avoid introducing adjacent frame crosstalk in the reconstructed image. Therefore, FRAME faces the problem of image quality degradation as the sequence becomes longer. Summary of the invention

[0005] In order to solve the current technical problem of long pulse sequence and degraded image quality of multiple exposure frequency recognition algorithm, the present invention proposes a polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system and method.

[0006] The technical solution provided by the present invention is:

[0007] A polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system, which is special in that it includes a pulse light source, a structured light pulse sequence generation unit, a polarization splitting unit, a high-speed scene generation unit, an image acquisition unit, a data processing unit and a control unit;

[0008] The pulse light source is used to emit a pulse, and a structured light pulse sequence generating unit, a polarization splitting unit, and a high-speed scene generating unit are sequentially arranged along the pulse transmission direction;

[0009] The structured light pulse sequence generating unit comprises K-level beam splitters and N delay units, K≥1 and K is an integer, N=2 K ;

[0010] The beam splitter is used to receive pulses and split the pulses step by step to obtain N light pulses, and 2N is equal to the number of frames of the target scene to be measured in the high-speed scene generation unit;

[0011] The delay unit comprises an incident reflector, a sinusoidal intensity grating and an exit reflector which are sequentially arranged along the propagation direction of the light pulse, and the sinusoidal intensity grating in each delay unit carries sinusoidal fringes with different periods and directions;

[0012] The incident reflector in the delay unit is used to receive the light pulse output by the beam splitter, and after passing through the sinusoidal intensity grating and the output reflector, it is combined into N structured light pulses and output to the polarization splitter unit;

[0013] The polarization splitting unit includes a birefringent delay crystal, which is used to output N structured light pulses into 2N polarization structured light pulses;

[0014] The control unit is connected to the pulse light source and the image acquisition unit respectively, and the control unit receives a signal for starting the pulse light source and transmits the signal to the image acquisition unit for controlling the image acquisition unit to start after the polarized structured light pulse passes through the high-speed scene generation unit;

[0015] The signal output by the high-speed scene generation unit is received by the image acquisition unit, and the image acquisition unit is connected to the data processing unit;

[0016] The data processing unit is used to receive the image signal collected by the image collection unit to reconstruct a high-speed multi-frame image.

[0017] Furthermore, the time interval of the structured light pulses output by the structured light pulse sequence generating unit is equal to the frame interval of the target scene to be measured in the high-speed scene generating unit;

[0018] The pulse width of the pulse emitted by the pulse light source is equal to the time resolution of the pulse, and the frame interval of the pulse is greater than the pulse width of the structured light pulse.

[0019] Furthermore, the K-level beam splitter is specifically a first-level beam splitter that receives pulses emitted by a pulse light source, and divides the pulses emitted by the pulse light source into reflected light pulse signals and transmitted light pulse signals, which are input to two second-level beam splitters; the second-level beam splitter divides the received light pulse signals into reflected light pulse signals and transmitted light pulse signals, respectively, and inputs them to a third-level beam splitter, which are sequentially transmitted to the K-th-level beam splitter;

[0020] The Kth beam splitter respectively divides the received optical pulse signal into a reflected optical pulse signal and a transmitted optical pulse signal and inputs them into the corresponding delay units.

[0021] Furthermore, the pulse is circularly polarized light or linearly polarized light.

[0022] Furthermore, the material of the birefringent delay crystal is quartz glass.

[0023] Furthermore, the image acquisition unit is a polarization camera.

[0024] The present invention also provides a polarization splitting frequency domain reconstruction ultra-high speed multi-frame imaging method, which is special in that, based on the above-mentioned polarization splitting frequency domain reconstruction ultra-high speed multi-frame imaging system, the method comprises the following steps:

[0025] S1. The pulse light source emits a pulse, which is divided into N light pulses after passing through a K-level beam splitter. The N light pulses enter N delay units to generate N structured light pulses, where K≥1 and K is an integer, and N=2 K ; 2N is equal to the number of frames of the target scene to be measured in the high-speed scene generation unit;

[0026] The time interval of the structured light pulse is t;

[0027] S2, N structured light pulses pass through the birefringent delay crystal in the polarization beam splitting unit, so that the light pulses with 0° polarization and 90° polarization in the same structured light pulse are delayed, and the delay time is N×t, and 2N polarization structured light pulses including N 0° polarization structured light pulses and N 90° polarization structured light pulses are obtained;

[0028] S3, 2N polarized structured light pulses illuminate the target scene to be measured generated by the high-speed scene generation unit, and output images of the target scene at 2N moments;

[0029] S4, the control unit controls the image acquisition unit to start according to the start time of the pulse light source, and the images of the target scene at 2N times are superimposed on the image acquisition unit, and the image acquisition unit performs one exposure to generate a superimposed image;

[0030] S5. The data processing unit receives the superimposed image output by the image acquisition unit, and processes the superimposed image using a frequency domain reconstruction algorithm to obtain image information of the dynamic scene at different times after reconstruction.

[0031] Furthermore, in step S1, the pulse width of the pulse is equal to the time resolution of the pulse, and the frame interval of the pulse is greater than the pulse width of the structured light pulse;

[0032] The time interval of the structured light pulses is equal to the frame interval of the target scene to be measured in the high-speed scene generation unit.

[0033] Beneficial effects of the present invention:

[0034] 1. The polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system proposed in the present invention generates terahertz-level (10 12 Hz) to petahertz level (10 15 Hz) frame rate to separate the spectrum of each frame of the target image. The structured light pulse sequence is framed by polarization of the birefringent delay crystal to double the number of structured light pulses and further disperse the spectrum.

[0035] 2. The polarization splitting method proposed in the present invention can make the spectrum distribution more dispersed, solving the problem that the imaging quality is easily reduced when there are multiple FRAME frames. Compared with the traditional FRAME imaging system, the invention can increase the number of frames by more than two times without reducing the image reconstruction quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of an embodiment of a polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system of the present invention;

[0037] Figure 2 Schematic diagram of the structure of a structured light pulse sequence generating unit in an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of circularly polarized light passing through a polarization splitting unit in an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of 45° linearly polarized light passing through a polarization splitting unit in an embodiment of the present invention.

[0040] The reference numerals are as follows:

[0041] 1-pulse light source, 2-structured light pulse sequence generating unit, 3-polarization splitting unit, 4-high-speed scene generating unit, 5-image acquisition unit, 6-data processing unit, 71-first stage beam splitter, 72-second stage beam splitter, 81-incident reflector, 82-exit reflector, 9-sine intensity grating, 10-pulse, 11-birefringence delay crystal, 12-control unit, 13-structured light pulse. DETAILED DESCRIPTION

[0042] See also Figure 1 and Figure 2 , This embodiment provides a polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system, which includes a pulse light source 1, a structured light pulse sequence generating unit 2, a polarization splitting unit 3, a high-speed scene generating unit 4, an image acquisition unit 5, a data processing unit 6 and a control unit 12;

[0043] The pulse light source 1 is used to emit a pulse 10, and the pulse 10 is circularly polarized light or linearly polarized light; a structured light pulse sequence generating unit 2, a polarization splitting unit 3, and a high-speed scene generating unit 4 are sequentially arranged along the transmission direction of the pulse 10;

[0044] The structured light pulse sequence generating unit 2 includes K-level beam splitters and N delay units, K≥1 and K is an integer, N=2 K ; The beam splitter is used to receive the pulse 10 and obtain N light pulses after splitting the pulse 10 step by step, and 2N is equal to the number of frames of the target scene to be measured in the high-speed scene generation unit 4; In this embodiment, a two-stage beam splitter and four delay units are used, specifically including a first-stage beam splitter 71 and a second-stage beam splitter 72, the first-stage beam splitter 71 receives the pulse 10 emitted by the pulse light source 1, and divides the pulse 10 into a reflected light pulse signal and a transmitted light pulse signal and outputs them to two second-stage beam splitters 72; the second-stage beam splitter 72 respectively divides the received light pulse signal into a reflected light pulse signal and a transmitted light pulse signal and outputs them to the corresponding delay units.

[0045] The delay unit includes an incident reflector 81, a sinusoidal intensity grating 9 and an exit reflector 82 which are arranged in sequence along the propagation direction of the light pulse. The sinusoidal intensity grating 9 in each delay unit is equipped with sinusoidal stripes with different periods and directions, thereby generating different delay times to separate the frequency spectrum of each frame of the target image.

[0046] The incident reflector 81 in the delay unit is used to receive the light pulse output by the beam splitter, which is combined into four structured light pulses 13 after passing through the sinusoidal intensity grating 9 and the output reflector 82 and output to the polarization splitting unit 3; the time interval of the structured light pulses 13 is equal to the frame interval of the target scene to be measured in the high-speed scene generation unit 4; the pulse width of the pulse 10 is equal to the time resolution of the pulse 10, and the frame interval of the pulse 10 is greater than the pulse width of the structured light pulse 13.

[0047] The polarization splitting unit 3 includes a birefringent delay crystal 11. In this embodiment, the material of the birefringent delay crystal 11 is quartz glass, and in other embodiments, it can also be other birefringent materials. It is used to output the four structured light pulses 13 as eight polarized structured light pulses, further diffuse the spectrum of the target image, and avoid introducing adjacent frame strings into the reconstructed image.

[0048] The control unit 12 is connected to the pulse light source 1 and the image acquisition unit 5 respectively. The control unit 12 receives a start signal of the pulse light source 1 and transmits the signal to the image acquisition unit 5 for controlling the image acquisition unit 5 to start after the polarized structured light pulse passes through the high-speed scene generation unit 4.

[0049] The signal output by the high-speed scene generation unit 4 is received by the image acquisition unit 5, and the image acquisition unit 5 is connected to the data processing unit 6; the image acquisition unit 5 is a polarization camera. In other embodiments, other image acquisition devices that can receive polarization structured light pulses to irradiate the target scene to be measured generated by the high-speed scene generation unit 4 and then output images of the target scene at eight moments can be used.

[0050] By using the polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system provided in this embodiment, a single camera can be used for single exposure to capture high-speed images of the target scene to be measured, and it can also be expanded according to the needs of the system to use multiple cameras. The data processing unit 6 is used to receive the image signal collected by the image acquisition unit 5 to reconstruct a high-speed multi-frame image.

[0051] The imaging method of the polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system comprises the following steps:

[0052] S1. See Figure 2 , the pulse light source 1 emits a pulse 10, and the pulse 10 shown in the figure is circularly polarized light or 45° linearly polarized light; the pulse width of the pulse 10 is equal to the time resolution of the pulse 10; the pulse 10 is divided into four light pulses after passing through the two-stage beam splitter, and the four light pulses enter four delay units respectively to generate four structured light pulses 13; the time interval of the structured light pulses 13 is t, and the time interval of the structured light pulses 13 is equal to the frame interval of the target scene to be measured in the high-speed scene generation unit 4; the frame interval of the pulse 10 is greater than the pulse width of the structured light pulse 13.

[0053] S2, see Figure 3 and Figure 4 , four structured light pulses 13 pass through the birefringent delay crystal 11 in the polarization beam splitting unit 3, and a delay is generated for the 0° polarization and 90° polarization light pulses in the same structured light pulse 13, and the delay time is 4×t, and eight polarization structured light pulses including four 0° polarization structured light pulses and four 90° polarization structured light pulses are obtained;

[0054] S3, eight polarized structured light pulses illuminate the target scene to be measured generated by the high-speed scene generation unit 4, and output images of the target scene at eight moments;

[0055] S4, the control unit 12 controls the image acquisition unit 5 to start according to the start time of the pulse light source 1, and the images of the target scene at eight moments are superimposed on the image acquisition unit 5, and the image acquisition unit 5 performs one exposure to generate a superimposed image;

[0056] S5. The data processing unit 6 receives the superimposed image output by the image acquisition unit 5 and processes the superimposed image using a frequency domain reconstruction algorithm to obtain image information of the dynamic scene at different times after reconstruction.

Claims

1. A polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system, characterized by: It comprises a pulse light source (1), a structured light pulse sequence generating unit (2), a polarization light splitting unit (3), a high-speed scene generating unit (4), an image collecting unit (5), a data processing unit (6) and a control unit (12); The pulse light source (1) is used to emit a pulse (10), and a structured light pulse sequence generating unit (2), a polarization light splitting unit (3), and a high-speed scene generating unit (4) are sequentially arranged along the transmission direction of the pulse (10); The structured light pulse sequence generating unit (2) comprises K-level beam splitters and N delay units, K≥1 and K is an integer, N=2 K ; The beam splitter is used to receive the pulse (10) and to obtain N light pulses after performing step-by-step beam splitting on the pulse (10), and 2N is equal to the number of split frames of the target scene to be measured in the high-speed scene generation unit (4); The delay unit comprises an incident reflector (81), a sinusoidal intensity grating (9) and an exit reflector (82) which are arranged in sequence along the propagation direction of the light pulse, and the sinusoidal intensity grating (9) in each delay unit is equipped with sinusoidal fringes with different periods and directions; The incident reflector (81) in the delay unit is used to receive the light pulse output by the beam splitter, and after passing through the sinusoidal intensity grating (9) and the output reflector (82), the light pulse is combined into N structured light pulses (13) and output to the polarization splitting unit (3); The polarization splitting unit (3) comprises a birefringent delay crystal (11) and is used for outputting N structured light pulses (13) into 2N polarization structured light pulses; The control unit (12) is connected to the pulse light source (1) and the image acquisition unit (5) respectively. The control unit (12) receives a signal for starting the pulse light source (1) and transmits the signal to the image acquisition unit (5) so as to control the image acquisition unit (5) to start after the polarized structured light pulse passes through the high-speed scene generation unit (4). The signal output by the high-speed scene generation unit (4) is received by the image acquisition unit (5), and the image acquisition unit (5) is connected to the data processing unit (6); The data processing unit (6) is used to receive the image signal collected by the image collection unit (5) to reconstruct a high-speed multi-frame image.

2. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to claim 1, characterized in that: The time interval of the structured light pulses (13) output by the structured light pulse sequence generating unit (2) is equal to the frame interval of the target scene to be measured in the high-speed scene generating unit (4); The pulse width of the pulse (10) emitted by the pulse light source (1) is equal to the time resolution of the pulse (10), and the frame interval of the pulse (10) is greater than the pulse width of the structured light pulse (13).

3. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to claim 2, characterized in that: The K-level beam splitter is specifically a first-level beam splitter (71) that receives a pulse (10) emitted by a pulse light source (1), and divides the pulse (10) into a reflected light pulse signal and a transmitted light pulse signal, which are input to two second-level beam splitters (72); the second-level beam splitter (72) respectively divides the received light pulse signal into a reflected light pulse signal and a transmitted light pulse signal, and inputs the signals to a third-level beam splitter, which are then sequentially transmitted to the K-level beam splitter; The Kth beam splitter respectively divides the received optical pulse signal into a reflected optical pulse signal and a transmitted optical pulse signal and inputs them into the corresponding delay units.

4. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to claim 3, characterized in that: The pulse (10) is circularly polarized light or linearly polarized light.

5. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to claim 4, characterized in that: The material of the birefringent time-delay crystal (11) is quartz glass.

6. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to claim 5, characterized in that: The image acquisition unit (5) is a polarization camera.

7. A polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging method, characterized in that: The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system according to any one of claims 1 to 6 comprises the following steps: S1. A pulse light source (1) emits a pulse (10). The pulse (10) is divided into N light pulses after passing through a K-level beam splitter. The N light pulses enter N delay units respectively to generate N structured light pulses (13). K≥1 and K is an integer, and N=2 K ; 2N is equal to the number of frames of the target scene to be measured in the high-speed scene generation unit (4); The time interval of the structured light pulse (13) is t; S2, N structured light pulses (13) pass through the birefringent time-delay crystal (11) in the polarization beam splitting unit (3), so that light pulses with 0° polarization and 90° polarization in the same structured light pulse (13) are delayed, and the delay time is N×t, thereby obtaining 2N polarization structured light pulses including N 0° polarization structured light pulses and N 90° polarization structured light pulses; S3, 2N polarized structured light pulses illuminate the target scene to be measured generated by the high-speed scene generation unit (4), and output images of the target scene at 2N moments; S4, the control unit (12) controls the image acquisition unit (5) to start according to the start time of the pulse light source (1), and the images of the target scene at 2N times are superimposed on the image acquisition unit (5), and the image acquisition unit (5) performs one exposure to generate a superimposed image; S5. The data processing unit (6) receives the superimposed image output by the image acquisition unit (5), and processes the superimposed image using a frequency domain reconstruction algorithm, thereby obtaining image information of the dynamic scene at different times after reconstruction.

8. The polarization splitting frequency domain reconstruction ultra-high-speed multi-frame imaging method according to claim 7, characterized in that: In step S1, the pulse width of the pulse (10) is equal to the time resolution of the pulse (10), and the frame interval of the pulse (10) is greater than the pulse width of the structured light pulse (13); The time interval of the structured light pulses (13) is equal to the frame interval of the target scene to be measured in the high-speed scene generation unit (4).

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