A high-resolution and high-brightness backlight photography method based on picosecond laser driving

Abstract

The present invention provides a high-resolution and high-brightness backlight photography method based on picosecond laser driving, which relates to the technical field of backlight imaging, and aims to provide a high-resolution and high-brightness backlight photography method based on picosecond laser driving, which adopts a backlight photography device, and the method comprises placing the object to be photographed between the coding target and the deflection magnet; starting the picosecond laser pulse device and driving the metal luminescent target to emit X-rays through the picosecond laser pulse; photographing the object to be photographed backlight by X-rays, and the X-rays sequentially pass through the magnetic field space formed by the deflection magnet and the metal filter, and then act on the X-ray recording medium to form an original coded image; decoding the original coded image to obtain a restored image of the object to be photographed. The present invention has the advantages of low backlight imaging noise, high resolution and high brightness.

Description

Technical Field

[0001] The invention relates to the technical field of backlight imaging, and in particular to a high-resolution and high-brightness backlight photography method based on picosecond laser driving. Background Art

[0002] In experimental research in fields such as high-energy-density physics, it is crucial to obtain information about the physical process of rapid development and change of high-temperature and high-density materials. With the development of ultra-strong and ultra-short laser pulse technology, the hard X-ray source backlight photography method based on picosecond laser-driven metal microwire targets has been widely used in the diagnosis of related experiments: such as the implosion compression process of the target pellet in inertial confinement fusion (ICF) experiments, and the dynamic photography of the dynamic characteristics of materials under strong loading conditions. This type of X-ray source theoretically has high brightness (>10 10 / sr), high collimation, short duration (~10 picoseconds), and small spatial size (~10 microns), etc. It can provide diagnostic results with high temporal and spatial resolution, and the diagnostic light energy spectrum range can be adjusted from a few keV to more than ten MeV according to different application requirements.

[0003] However, in the actual diagnostic applications of high-energy-density physics experiments, there is usually strong and unavoidable background noise, such as spontaneous radiation of matter under extreme conditions, high-energy particle beams generated during the evolution of matter, and gamma rays generated by the interaction between particle beams and the environment. Background noise will seriously reduce the signal-to-noise ratio of photographic images and damage diagnostic accuracy. Under the condition that such noise cannot be avoided, significantly increasing the brightness of the backlight source is a breakthrough in improving the imaging signal-to-noise ratio. However, the limited laser interception efficiency of the microwire target limits the increase in X-ray yield. At present, the diameter of the microwire target is usually designed to be 10 microns to 30 microns. Under the current focusing conditions of picosecond petawatt laser beams (~100 microns), the laser energy cannot be fully utilized. On the other hand, the diameter of the microwire target a, together with the detector resolution size d, and the imaging system magnification M, together determine the imaging spatial resolution size Bw Therefore, the requirement for imaging spatial resolution limits the feasibility of further increasing the diameter of the wire target.

[0004] In summary, the existing backlight photography method based on microwire targets has the problem of not being able to meet both high spatial resolution and full utilization of laser energy. Summary of the invention

[0005] The purpose of the present invention is to provide a high-resolution and high-brightness backlight photography method based on picosecond laser drive, which solves the problem that the backlight photography method based on microwire target cannot meet the high spatial resolution and fully utilize the laser energy.

[0006] The embodiments of the present invention are implemented by the following technical solutions:

[0007] A high-resolution and high-brightness backlight photography method based on picosecond laser drive, the backlight photography device used includes a picosecond laser pulse device, a coding target, a deflection magnet, a metal filter and an X-ray recording medium;

[0008] The encoding target, the deflection magnet and the X-ray recording medium are coaxially arranged in sequence; the metal filter is coated on a side of the X-ray recording medium close to the deflection magnet; the deflection magnet includes two permanent magnets arranged opposite to each other;

[0009] The coding target includes a metal luminescent target and a non-metallic thin film substrate, wherein the metal luminescent target is a hollow circular tube, and the bottom of the metal luminescent target is attached to the non-metallic thin film substrate; the picosecond laser pulse device is used to generate a picosecond laser pulse to drive the metal luminescent target;

[0010] The method comprises the following steps:

[0011] placing the object to be irradiated between the encoding target and the deflection magnet;

[0012] The picosecond laser pulse device is started and drives the metal luminescent target to emit X-rays through the picosecond laser pulse;

[0013] The X-rays are used to perform backlight photography on the irradiated object, and the X-rays sequentially pass through the magnetic field space formed by the deflection magnet and the metal filter, and then act on the X-ray recording medium to form an original coded image;

[0014] The original encoded image is decoded to obtain a restored image of the illuminated object.

[0015] Preferably, the length of the metal luminescent target is 100-300 microns, the outer diameter is 50-100 microns, and the wall thickness is 2-10 microns.

[0016] Preferably, the material of the metal luminescent target is gold, tantalum, lead or uranium.

[0017] Preferably, the non-metallic film substrate is made of polyethylene or polymethyl methacrylate.

[0018] Preferably, the picosecond laser pulse device adopts a large-scale picosecond petawatt laser device and acts on the front end of the metal luminescent target;

[0019] The maximum output energy of the large-scale picosecond petawatt laser device is in the hundreds of joules or kilojoules level, and its peak power is in the petawatt level.

[0020] Preferably, the X-ray recording medium is an imaging plate or film or an X-ray CCD or a scintillator-coupled CCD.

[0021] Preferably, the thickness of the metal filter is 50 micrometers to 10 millimeters.

[0022] Preferably, the method for the picosecond laser pulse device to start and drive the metal luminescent target to emit X-rays is:

[0023] A large-scale picosecond petawatt laser device is used as the picosecond laser pulse device to emit laser pulses, and the laser pulses hit the surface of the metal luminescent target from the side to form superhot electrons;

[0024] The super-hot electrons are transported along the solid density region of the hollow cylindrical structure and generate bremsstrahlung radiation to form an annular light source having a target cross-section size comparable to that of the metal luminescent target and having a uniform intensity distribution;

[0025] The non-metallic thin film substrate is used to support and fix the metal light-emitting target, and the non-metallic material is used to suppress the bremsstrahlung X-ray background noise excited by the super-hot electrons.

[0026] Preferably, the method for decoding the original encoded image is a Richardson-Lucy iterative algorithm or a Wiener filtering method.

[0027] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0028] The present invention has a reasonable design and a simple structure, and realizes a high-resolution and high-brightness backlight photography device and method that can meet high spatial resolution and fully utilize laser energy by using a picosecond laser pulse device, a coding target, a deflection magnet, a metal filter and an X-ray recording medium.

[0029] The present invention significantly improves the laser interception efficiency by increasing the outer diameter of the hollow circular tube of the luminous metal target, thereby increasing the yield of superthermal electrons accelerated by the laser in the absorption area;

[0030] The present invention utilizes the surface self-generated electromagnetic field generated by the interaction between laser and solid target to effectively confine superhot electrons in the solid region of the luminescent target, thereby enabling them to fully interact with the target material atoms and generate X-rays, significantly increasing the X-ray yield and generating a high-brightness backlight source.

[0031] The present invention generates a coded X-ray source with a certain known structure by controlling the outer diameter and inner diameter of the hollow circular tube of the luminous metal target, performs backlight photography on the irradiated object, and forms an original coded image on the X-ray recording medium;

[0032] The present invention utilizes a mature numerical decoding algorithm to decode the encoded image and obtain a restored image with higher spatial resolution. Its ultimate spatial resolution size is equivalent to the wall thickness of the hollow circular tube of the luminescent metal target, which is significantly superior to the existing backlight photography method based on microwire targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 A schematic structural diagram of a backlight camera device provided in Embodiment 1 of the present invention;

[0035] Figure 2 A schematic diagram of the structure of a metal luminescent target provided in Example 1 of the present invention;

[0036] Figure 3 This is a schematic cross-sectional view of an illuminated object used in Example 7 of the present invention;

[0037] Figure 4 The original coded image obtained in Example 7 of the present invention;

[0038] Figure 5 is the restored image obtained in Example 7 of the present invention;

[0039] Icons: 101-encoded target, 102-picosecond laser pulse device, 103-irradiated object, 104-deflection magnet, 105-metal filter, 106-X-ray recording medium, 101A-non-metallic thin film substrate, 101B-metal luminescent target. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0041] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0043] In the description of the present invention, it should be noted that if the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the application is usually placed when used. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0044] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] Example 1

[0046] See also Figure 1 , the present invention provides a high-resolution and high-brightness backlight photography method based on picosecond laser drive, the backlight photography device used includes a picosecond laser pulse device 102, a coding target 101, a deflection magnet 104, a metal filter 105 and an X-ray recording medium 106;

[0047] The encoding target 101, the deflection magnet 104 and the X-ray recording medium 106 are coaxially arranged in sequence; the metal filter 105 is coated on a side of the X-ray recording medium 106 close to the deflection magnet 104; the deflection magnet 104 includes two permanent magnets arranged opposite to each other;

[0048] The coding target 101 includes a metal luminescent target 101B and a non-metallic thin film substrate 101A, wherein the metal luminescent target 101B is a hollow circular tube, and the bottom of the metal luminescent target 101B is attached to the non-metallic thin film substrate 101A; the picosecond laser pulse device 102 is used to drive the metal luminescent target 101B;

[0049] The method comprises the following steps:

[0050] Placing the object 103 to be irradiated between the encoding target 101 and the deflection magnet 104;

[0051] The picosecond laser pulse device 102 is started and drives the metal luminescent target 101B to emit X-rays through picosecond laser pulses;

[0052] The X-rays are used to perform backlight photography on the irradiated object 103. After the X-rays pass through the magnetic field space formed by the deflection magnet 104 and the metal filter 105 in sequence, they act on the X-ray recording medium 106 to form an original coded image.

[0053] The original encoded image is decoded to obtain a restored image of the illuminated object 103 .

[0054] In simple terms, the working method of this embodiment is:

[0055] The coding target 101 is used to emit X-rays under the action of the picosecond laser pulse device 102, and then irradiate the object placed during shooting. The X-rays pass through the object to be imaged and the magnetic field of the deflection magnet 104 and irradiate the X-ray recording medium 106 to form a coded image. After the coded image is decoded, a restored image with high spatial resolution and high signal-to-noise ratio of the object can be obtained. The function of the metal filter 105 is to filter low-energy X-rays and shield noise.

[0056] In order to shield noise and improve the signal-to-noise ratio of photographic images, this embodiment sets two shielding measures:

[0057] (1) Deflection magnet 104: The picosecond laser pulse device 102 and the metal luminescent target 101B interact with each other, and in addition to generating X-rays, they also generate charged particle beams such as positrons, electrons, and protons. When they are captured by the X-ray recording medium 106, they will also generate signals, thereby reducing the signal-to-noise ratio of the photographic image. In order to eliminate the influence of the charged particle beam, two opposing permanent magnets are set on the side of the X-ray recording medium 106 close to the irradiated object 103 as deflection magnets 104, thereby generating a transverse magnetic field with a longitudinal range of 2cm-20cm and an intensity of 1000G-8000G, which can deflect most high-energy charged particles.

[0058] (2) Metal filter 105: If the object 103 to be irradiated is a high-temperature, high-density material, it will spontaneously radiate a large amount of X-rays with a relatively low energy range but a relatively high brightness during the photographic process, thereby reducing the signal-to-noise ratio of the photographic image. In order to shield such low-energy X-ray background noise, the diagnostic light energy range is selected, and a metal filter 105 is coated on the surface of the X-ray recording medium 106 facing the object 103 to be irradiated. The thickness of the metal filter 105 is preferably 50 microns to 10 mm, and the size is based on the size that can cover the X-ray recording medium 106.

[0059] Example 2

[0060] This embodiment is based on the technical solution of embodiment 1, see Figure 1-Figure 2 , further improve the coding target 101.

[0061] In this embodiment, the length of the metal luminescent target 101B is 100-300 microns, its outer diameter is 50-100 microns, and its wall thickness is 2-10 microns. Its diameter setting is equivalent to the existing picosecond petawatt laser beam focusing size, which can fully intercept the laser and maximize the energy conversion efficiency of the laser to X-ray.

[0062] Furthermore, the material of the metal luminescent target 101B should preferably be an element with a high atomic number and high density, for example, gold, tantalum, lead or uranium.

[0063] On the other hand, the material of the non-metallic thin film substrate 101A should be selected from elements with low atomic number and low density as much as possible, so as to suppress the bremsstrahlung X-ray background noise excited by super-hot electrons in the non-metallic thin film substrate 101A to the greatest extent. At the same time, the interface electromagnetic field formed between the different materials of the metal luminescent target 101B and the non-metallic thin film substrate 101A can be used to limit the super-hot electrons generated in the metal luminescent target 101B from escaping to the non-metallic thin film substrate 101A, thereby reducing the energy loss of the X-ray source. As a preferred embodiment, the material of the non-metallic thin film substrate 101A is polyethylene or polymethyl methacrylate.

[0064] It is particularly noted that the non-metallic thin film substrate 101A needs to be used to support and fix the metal luminescent target 101B, and is connected to the rear half of the metal luminescent target 101B. The contact area should be minimized so that the metal luminescent target 101B can remain fixed and not deformed by gravity. The reason for reducing the contact area is that it can reduce the energy loss of the X-ray source caused by the absorption of super-hot electrons in the metal luminescent target 101B by the non-metallic thin film substrate 101A, and reduce the influence of the bremsstrahlung X-ray background noise excited by super-hot electrons in the non-metallic thin film substrate 101A.

[0065] Example 3

[0066] This embodiment is based on the technical solution of embodiment 1, see Figure 1-Figure 2 , the picosecond laser pulse device 102 is further improved.

[0067] In this embodiment, the picosecond laser pulse device 102 uses a large-scale picosecond petawatt laser device;

[0068] The maximum output energy of the large-scale picosecond petawatt laser device is in the hundreds of joules or kilojoules level, and its peak power is in the petawatt level. Generally speaking, the pulse width is in the range of hundreds of femtoseconds to tens of picoseconds.

[0069] The interaction between the metal luminescent target 101B and the electron beam can accelerate the super-thermal electron beam with a temperature of several hundred keV to several MeV, and then stimulate the bremsstrahlung X-ray beam. In addition, the interaction area with the metal luminescent target 101B should be as close to its front end as possible, which can reduce the propagation distance and self-absorption of X-rays in the metal luminescent target 101B and increase the brightness of the X-ray source.

[0070] Example 4

[0071] This embodiment is based on the technical solution of embodiment 1, see Figure 1-Figure 2 , the X-ray recording medium 106 is further improved.

[0072] As a preferred solution of this embodiment, the X-ray recording medium 106 needs to have a higher spatial resolution, generally with a spatial resolution better than 100 microns as the basic requirement, so the X-ray recording medium 106 described here can be an imaging plate or film or an X-ray CCD or a scintillator-coupled CCD.

[0073] In addition, the thickness of the metal filter 105 is 50 micrometers to 10 millimeters, and its function is to filter low-energy X-rays and shield noise.

[0074] Example 5

[0075] This embodiment is based on the technical solution of embodiment 1, see Figure 1-Figure 2 , further explain the method of generating X-rays.

[0076] In this embodiment, the method of starting the picosecond laser pulse device 102 and driving the metal luminescent target 101B to emit X-rays is:

[0077] A large-scale picosecond petawatt laser device is used as the picosecond laser pulse device 102 to emit laser pulses, and the laser pulses hit the surface of the metal luminescent target 101B from the side to form superhot electrons;

[0078] The super-hot electrons are transported along the solid density region of the hollow circular tube structure and generate bremsstrahlung radiation to form an annular light source having a target cross-sectional size comparable to that of the metal luminescent target 101B and having a uniform intensity distribution;

[0079] The non-metallic thin film substrate 101A is used to support and fix the metal light-emitting target, and the non-metallic material is used to suppress the bremsstrahlung X-ray background noise excited by the super-hot electrons.

[0080] Example 6

[0081] This embodiment is based on the technical solution of embodiment 1, see Figure 1-Figure 2 , further illustrating the method for decoding the initially encoded image.

[0082] As a preferred solution, the method for decoding the original encoded image is Richardson-Lucy iterative algorithm or Wiener filtering method.

[0083] Example 7

[0084] This embodiment provides an imaging test result based on the technical solutions of the above embodiments.

[0085] In the test simulation of this embodiment, the outer diameter of the metal light emitting target 101B used is 50 microns, the inner diameter is 40 microns, the wall thickness is 5 microns, and the length is 100 microns. The size of the generated annular light source is equivalent to the cross-sectional size of the target, that is, the outer diameter of the annular light source is 50 microns, the inner diameter is 40 microns, and the width of the annular band is 5 microns.

[0086] First of all, it should be noted that the photon energy used here is simplified to a monoenergetic light source of 22keV, the luminous intensity is evenly distributed, and the light source brightness is 3×10 11 / sr.

[0087] In the test simulation, the light source is projected onto the illuminated object 103 to form an original coded image. The transverse cross section of the illuminated object 103 used here is as follows: Figure 3 As shown, its width is 130 microns, height is 70 microns, thickness is 20 microns, and the material is tantalum. The original coded image is obtained on the X-ray recording medium 106 as shown in FIG. Figure 4 As shown. Perform numerical decoding to obtain the restored image as Figure 5 It is particularly noted that the simulation software here is Geant4, a calculation tool that uses the Monte Carlo algorithm.

[0088] The test shows that a restored image with high spatial resolution is obtained, the degree of restoration is high, the image is clear and the noise is low.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-resolution and high-brightness backlight photography method based on picosecond laser driving, characterized in that: The backlight photography device used includes a picosecond laser pulse device (102), a coding target (101), a deflection magnet (104), a metal filter (105) and an X-ray recording medium (106); The encoding target (101), the deflection magnet (104) and the X-ray recording medium (106) are coaxially arranged in sequence; the metal filter (105) is coated on a side of the X-ray recording medium (106) close to the deflection magnet (104); the deflection magnet (104) includes two permanent magnets arranged opposite to each other; The coding target (101) comprises a metal luminescent target (101B) and a non-metallic thin film substrate (101A); the metal luminescent target (101B) is a hollow circular tube, and the bottom of the metal luminescent target (101B) is attached to the non-metallic thin film substrate (101A); the picosecond laser pulse device (102) is used to drive the metal luminescent target (101B); The method comprises the following steps: Placing the object to be irradiated (103) between the encoding target (101) and the deflection magnet (104); The picosecond laser pulse device (102) is started and drives the metal luminescent target (101B) to emit X-rays through the picosecond laser pulse; The X-rays are used to perform backlight photography on the irradiated object (103), and after the X-rays sequentially pass through the magnetic field space formed by the deflection magnet (104) and the metal filter (105), they act on the X-ray recording medium (106) to form an original coded image; The original coded image is decoded to obtain a restored image of the illuminated object (103).

2. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The length of the metal luminescent target (101B) is 100-300 microns, the outer diameter is 50-100 microns, and the wall thickness is 2-10 microns.

3. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The material of the metal luminescent target (101B) is gold, tantalum, lead or uranium.

4. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 3 is characterized in that: The material of the non-metallic thin film substrate (101A) is polyethylene or polymethyl methacrylate.

5. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The picosecond laser pulse device (102) adopts a large-scale picosecond petawatt laser device and acts on the front end of the metal luminescent target (101B); The maximum output energy of the large-scale picosecond petawatt laser device is in the hundreds of joules or kilojoules level, and its peak power is in the petawatt level.

6. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The X-ray recording medium (106) is an imaging plate or film or an X-ray CCD or a scintillator-coupled CCD.

7. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The thickness of the metal filter (105) is 50 micrometers to 10 millimeters.

8. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The method of starting the picosecond laser pulse device (102) and driving the metal luminescent target (101B) to emit X-rays is: A large-scale picosecond petawatt laser device is used as the picosecond laser pulse device (102) to emit laser pulses, and the laser pulses strike the surface of the metal luminescent target (101B) from the side to form super-hot electrons; The super-hot electrons are transported along the solid density region of the hollow circular tube structure and generate bremsstrahlung radiation to form an annular light source having a target cross-section size comparable to that of the metal luminescent target (101B) and a uniform intensity distribution; The non-metallic thin film substrate (101A) is used to support and fix the metal luminescent target, and the non-metallic material is used to suppress the bremsstrahlung X-ray background noise excited by the super-hot electrons.

9. The high-resolution and high-brightness backlight photography method based on picosecond laser driving according to claim 1, characterized in that: The method for decoding the original encoded image is a Richardson-Lucy iterative algorithm or a Wiener filtering method.

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