CN115883952B - Polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system and method - Google Patents
Polarization splitting frequency domain reconstruction ultra-high-speed multi-framing imaging system and method Download PDFInfo
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Abstract
The invention relates to a polarization beam-splitting frequency domain reconstruction ultra-high speed multi-frame imaging system and a method thereof, which are used for solving the technical problem that the image quality of the conventional pulse sequence is long and the image quality of a multi-exposure frequency identification algorithm is reduced. The system comprises a pulse light source for emitting pulses, a structured light pulse sequence generating unit, a polarization beam splitting unit and a high-speed scene generating unit which are sequentially arranged along the pulse transmission direction, wherein a control unit is respectively connected with the pulse light source and an image acquisition unit, signals output by the high-speed scene generating unit are received by the image acquisition unit, and the image acquisition unit is connected with a data processing unit. The method comprises the steps of 1, obtaining N structural light pulses after pulse light source emission pulses pass through a beam splitter, 2, obtaining 2N polarized structural light pulses through a double refraction delay crystal, 3, irradiating a high-speed scene generating unit to obtain images of a target scene at 2N moments, 4, generating a superimposed image, and 5, reconstructing to obtain image information of different moments of a dynamic scene.
Description
Technical Field
The invention relates to the technical field of high-speed imaging, in particular to a polarization beam-splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system and method.
Background
In a wide scientific research field, the ability to record fast transient events in real time is critical to understanding the topic at hand, such as delays in photoemission, molecular motion, and photosynthetic systems. To meet this demand, high speed cameras have been developed, but there is an upper limit to the speed of the high speed camera due to the limit in the speed at which the actual detector reads out and prepares to capture the next frame.
In order to achieve higher frame rates, a method that does not rely on a fast detector is needed. For example, a pump detection method, in which a transient event is initiated by a pump pulse and detected by another pulse after a controllable time delay, the process being repeated a number of times with different time delays, the process of the event being captured by a time resolution set by the probe pulse length. However, events that cannot be repeated, due to random events, cannot be studied in this way. Based on this, various single exposure techniques have been developed for irradiating a sample with a series of short laser pulses. Because the laser pulses are temporally separated, they encode image information that is each used to study a temporally different portion of the event. In order to retrieve image information for a single pulse, each pulse must be unique in certain characteristics, which may be, for example, angle, spatial position, or wavelength. Multiple exposure frequency identification algorithms (FRAMEs) rely on encoding a unique spatial modulation into each pulse of a 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 superimposed modulation of the pulses. This allows reconstructing the frame sequence carried in the pulse sequence component.
Since the size of the 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. Thus, as the sequence becomes longer, the FRAME faces the difficulty of image quality degradation.
Disclosure of Invention
The invention provides a polarization beam splitting frequency domain reconstruction ultrahigh-speed multi-frame imaging system and method for solving the technical problem that the image quality of the conventional pulse sequence is long and the image quality of a multi-exposure frequency identification algorithm is reduced.
The technical scheme provided by the invention is as follows:
The ultra-high-speed multi-frame imaging system for reconstructing the polarized light splitting frequency domain is characterized by comprising a pulse light source, a structured light pulse sequence generating unit, a polarized light splitting unit, a high-speed scene generating unit, an image acquisition unit, a data processing unit and a control unit;
The pulse light source is used for transmitting a pulse, and a structural light pulse sequence generating unit, a polarization beam splitting unit and a high-speed scene generating unit are sequentially arranged along the pulse transmission direction;
The structured light pulse sequence generating unit comprises a K-stage beam splitter and N delay units, wherein K is more than or equal to 1, K is an integer, and N=2 K;
The beam splitter is used for receiving the pulse and splitting the pulse step by step to obtain N light pulses, and 2N is equal to the framing number of the target scene to be detected in the high-speed scene generating unit;
The delay units comprise an incident reflector, a sinusoidal intensity grating and an emergent reflector which are sequentially arranged along the propagation direction of the light pulse, wherein sinusoidal stripes with different periods and directions are carried on the sinusoidal intensity grating in each delay unit;
The incident reflector in the delay unit is used for receiving the light pulses output by the beam splitter, and the light pulses are combined into N structural light pulses after passing through the sinusoidal intensity grating and the emergent reflector and output to the polarization beam splitter;
The polarization beam splitting unit comprises a birefringent delay crystal and is used for outputting N structural light pulses into 2N polarized structural light pulses;
The control unit is respectively connected with the pulse light source and the image acquisition unit, receives a signal started by 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;
The signal output by the high-speed scene generating unit is received by the image acquisition unit, and the image acquisition unit is connected with the data processing unit;
the data processing unit is used for receiving the image signals acquired by the image acquisition unit and reconstructing high-speed multi-frame images.
Further, 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 detected in the high-speed scene generating unit;
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 larger than the pulse width of the structured light pulse.
The second beam splitter divides the received light pulse signal into a reflected light pulse signal and a transmitted light pulse signal, and inputs the reflected light pulse signal and the transmitted light pulse signal to a third beam splitter, and sequentially transmits the reflected light pulse signal and the transmitted light pulse signal to a Kth beam splitter;
the K-th beam dividing mirror divides the received optical pulse signals into reflected optical pulse signals and transmitted optical pulse signals respectively and inputs the reflected optical pulse signals and the transmitted optical pulse signals to the corresponding delay units.
Further, the pulse is circularly polarized light or linearly polarized light.
Further, the material of the birefringent delay crystal is quartz glass.
Further, the image acquisition unit is a polarization camera.
The invention also provides a polarization beam-splitting frequency domain reconstruction ultra-high speed multi-frame imaging method, which is characterized by comprising the following steps of:
S1, a pulse light source emits pulses, the pulses are divided into N paths of light pulses after passing through a K-stage beam splitter, the N paths of light pulses respectively enter N delay units to generate N structural light pulses, K is more than or equal to 1, K is an integer, and N=2 K, wherein 2N is equal to the framing number of a target scene to be detected in a high-speed scene generating unit;
the time interval of the structured light pulse is t;
S2, enabling N structural light pulses to pass through a birefringent delay crystal in a polarization beam splitting unit, enabling light pulses with 0-degree polarization and 90-degree polarization in the same structural light pulse to generate delay, wherein the delay time is N multiplied by t, and obtaining 2N polarized structural light pulses comprising N0-degree polarized structural light pulses and N90-degree polarized structural light pulses;
s3, 2N polarized structured light pulses irradiate the target scene to be detected generated by the high-speed scene generating unit, and images of the target scene at 2N moments are output;
S4, the control unit controls the image acquisition unit to start according to the starting time of the pulse light source, images of the target scene at 2N times are overlapped on the image acquisition unit, and the image acquisition unit performs one-time exposure to generate an overlapped image;
s5, the data processing unit receives the superimposed image output by the image acquisition unit, processes the superimposed image by adopting a frequency domain reconstruction algorithm, and obtains image information of different moments of the dynamic scene after reconstruction.
Further, 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;
the time interval of the structured light pulse is equal to the frame interval of the target scene to be detected in the high-speed scene generating unit.
The invention has the beneficial effects that:
1. The ultra-high-speed multi-frame imaging system for reconstructing the polarized light splitting frequency domain generates a structured light pulse sequence from a terahertz stage (10 12 Hz) to a beat Hz stage (10 15 Hz) frame frequency by setting delay lines of sinusoidal intensity gratings of sinusoidal stripes in different directions and periods so as to realize spectrum separation of each frame of images of a target, and the structured light pulse sequence frames the polarization of a birefringent delay crystal, so that the quantity of the structured light pulse is doubled and the frequency spectrum is further dispersed.
2. The polarization beam splitting method provided by the invention can enable the frequency spectrum distribution to be more dispersed, solves the problem that the imaging quality is easy to be reduced when the FRAME is provided with multiple FRAMEs, and can increase the number of FRAMEs by more than two times and does not reduce the image reconstruction quality compared with the traditional FRAME image system.
Drawings
FIG. 1 is a schematic diagram of an embodiment of a polarization beam-splitting frequency domain reconstruction ultra-high speed multi-frame imaging system according to the present invention;
FIG. 2 is a schematic diagram of a structure of a pulse train generating unit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a polarizing beam-splitting unit for circularly polarized light according to an embodiment of the present invention;
Fig. 4 is a schematic diagram of a 45 ° linear polarized light passing polarization splitting unit according to an embodiment of the present invention.
The reference numerals are as follows:
the device comprises a 1-pulse light source, a 2-structured light pulse sequence generating unit, a 3-polarization beam splitting unit, a 4-high-speed scene generating unit, a 5-image acquisition unit, a 6-data processing unit, a 71-first-stage beam splitter, a 72-second-stage beam splitter, an 81-incident reflector, an 82-emergent reflector, a 9-sinusoidal intensity grating, 10-pulses, 11-birefringent delay crystals, a 12-control unit and 13-structured light pulses.
Detailed Description
Referring to fig. 1 and 2, the present embodiment provides a polarized light 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 polarized light 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;
The pulse light source 1 is used for emitting a pulse 10, and the pulse 10 is circularly polarized light or linearly polarized light, and the pulse light source is sequentially provided with a structured light pulse sequence generating unit 2, a polarization beam splitting unit 3 and a high-speed scene generating unit 4 along the transmission direction of the pulse 10;
The structural light pulse sequence generating unit 2 comprises a K-stage beam splitter and N delay units, wherein K is larger than or equal to 1, K is an integer, N=2 K, the beam splitter is used for receiving the pulse 10 and carrying out stage-by-stage beam splitting on the pulse 10 to obtain N light pulses, 2N is equal to the framing number of a target scene to be detected in the high-speed scene generating unit 4, the two-stage beam splitter and four delay units are adopted in the embodiment, the structural light pulse sequence generating unit specifically comprises 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 to be output to the two second stage beam splitters 72, and the second stage beam splitter 72 divides the received light pulse signal into the reflected light pulse signal and the transmitted light pulse signal to be output to the corresponding delay units.
The delay units comprise an incident reflecting mirror 81, a sinusoidal intensity grating 9 and an emergent reflecting mirror 82 which are sequentially arranged along the propagation direction of the light pulse, and sinusoidal fringes with different periods and directions are mounted on the sinusoidal intensity grating 9 in each delay unit, so that different delay times are generated to separate the frequency spectrums of target images of each frame.
The incident reflector 81 in the delay unit is used for receiving the light pulses output by the beam splitter, and the light pulses are combined into four structural light pulses 13 through the sinusoidal intensity grating 9 and the emergent reflector 82 and output to the polarization beam splitter unit 3, the time interval of the structural light pulses 13 is equal to the frame interval of the target scene to be detected in the high-speed scene generating 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 larger than the pulse width of the structural light pulses 13.
The polarization beam splitting unit 3 includes a birefringent delay crystal 11, where in this embodiment, the material of the birefringent delay crystal 11 is quartz glass, and in other embodiments, other birefringent materials may be used to output four structural light pulses 13 as eight structural light pulses, so as to further diffuse the spectrum of the target image, and avoid introducing adjacent frame strings into the reconstructed image.
The control unit 12 is respectively connected with the pulse light source 1 and the image acquisition unit 5, and the control unit 12 receives a signal started by 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;
The signal output by the high-speed scene generating unit 4 is received by the image collecting unit 5, the image collecting unit 5 is connected with the data processing unit 6, the image collecting unit 5 is a polarized camera, and in other embodiments, other image collecting devices which can receive polarized structured light pulses to irradiate the target scene to be detected generated by the high-speed scene generating unit 4 and then output eight time images of the target scene can be adopted.
By adopting the polarization beam-splitting frequency domain reconstruction ultra-high-speed multi-frame imaging system provided by the embodiment, a single camera is used for single exposure, so that a high-speed picture in a target scene to be detected can be acquired, and the system can be expanded according to the needs of the system, and a plurality of cameras are adopted. The data processing unit 6 is used for receiving the image signals acquired by the image acquisition unit 5 and reconstructing high-speed multi-frame images.
The imaging method of the polarization beam-splitting frequency domain reconstruction ultra-high speed multi-frame imaging system comprises the following steps:
s1, referring to FIG. 2, a pulse light source 1 emits a pulse 10, the pulse 10 shown in the figure is circularly polarized light or linearly polarized light with the angle of 45 degrees, the pulse width of the pulse 10 is equal to the time resolution of the pulse 10, the pulse 10 is divided into four paths of light pulses after passing through a two-stage beam splitter, the four paths of light pulses enter four delay units respectively to generate four structural light pulses 13, the time interval of the structural light pulses 13 is t, the time interval of the structural light pulses 13 is equal to the frame interval of a target scene to be detected in a high-speed scene generating unit 4, and the frame interval of the pulse 10 is larger than the pulse width of the structural light pulses 13.
S2, referring to fig. 3 and 4, four structural light pulses 13 pass through a birefringent delay crystal 11 in a polarization beam splitting unit 3, and the same structural light pulse 13 has 0-degree polarization and 90-degree polarization to generate delay, and the delay time is 4×t, so that eight polarized structural light pulses including four 0-degree polarized structural light pulses and four 90-degree polarized structural light pulses are obtained;
s3, eight polarized structured light pulses irradiate the target scene to be detected generated by the high-speed scene generating unit 4, and images of the target scene at eight moments are output;
S4, the control unit 12 controls the image acquisition unit 5 to start according to the starting time of the pulse light source 1, images of eight times of the target scene are overlapped on the image acquisition unit 5, and the image acquisition unit 5 performs one-time exposure to generate an overlapped image;
S5, the data processing unit 6 receives the superimposed image output by the image acquisition unit 5, processes the superimposed image by adopting a frequency domain reconstruction algorithm, and obtains image information of different moments of the dynamic scene after reconstruction.
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| US5612812A (en) * | 1995-08-31 | 1997-03-18 | The United States Of America As Represented By The Secretary Of The Air Force | Method and apparatus for photorefractive pirouette display and processing of analog signals |
| CN112902866A (en) * | 2021-01-18 | 2021-06-04 | 武汉大学 | Spatial framing device, all-optical ultrafast imaging system and method |
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| WO2013076531A1 (en) * | 2011-11-23 | 2013-05-30 | Nokia Corporation | An apparatus and method comprising a beam splitter |
| WO2021114034A1 (en) * | 2019-12-09 | 2021-06-17 | 深圳大学 | Ultra-high-speed optical parametric amplification optical imaging system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5612812A (en) * | 1995-08-31 | 1997-03-18 | The United States Of America As Represented By The Secretary Of The Air Force | Method and apparatus for photorefractive pirouette display and processing of analog signals |
| CN112902866A (en) * | 2021-01-18 | 2021-06-04 | 武汉大学 | Spatial framing device, all-optical ultrafast imaging system and method |
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