Laser target local irradiation flux mapping method and device based on phase plate positioning

Abstract

The method and device for mapping the local irradiation flux of laser target shooting based on phase plate positioning belong to the field of laser target shooting experiments. The present invention aims to solve the problem that the flux data in the existing optical element damage test analysis only uses the average flux as the result, and cannot achieve the correspondence between the target surface beam flux and the damage point. The present invention includes a calibration step for obtaining an affine transformation matrix and a step for performing a laser target shooting experiment to obtain the local irradiation flux of the target material. A phase plate is inserted between the lens and the target material in the target shooting experiment optical path, an array of damage points is formed on the rear surface of the target material, and an affine transformation matrix is ​​constructed. The phase plate is removed and the laser target shooting experiment is performed using the original experimental optical path; the near-field image of the target shooting laser beam is mapped to the target material damage image according to the affine transformation matrix, and the near-field image of the target shooting laser beam and the target material damage image are superimposed to obtain the position of the phase mark point corresponding to the target material damage point; and then the local irradiation flux of the laser target shooting at the location of each damage point on the target material is obtained.

Description

Technical Field

[0001] The invention relates to a technology for obtaining accurate laser irradiation flux of a target material damage point in a target shooting experiment, and belongs to the field of laser target shooting experiments. Background Art

[0002] In high-power laser systems, components need to be exposed to high-intensity laser irradiation. In addition, due to the inevitable introduction of impurities and defects during the production and processing of optical components, the surface of the optical components will be damaged under high-power laser irradiation. Once the damage is formed, the component's absorption rate of the laser will be greatly increased. The damage size will rapidly increase under subsequent laser irradiation, and its splashes will adhere to the surfaces of other subsequent optical components, causing new damage, and paralyzing the entire laser system in a chain reaction. Therefore, the working optical components in the high-power laser system need to be randomly inspected before being put into use. The components of the same processing batch need to be tested for their damage threshold and damage resistance, and the initial damage and damage development rules of the rear surface of the optical component are obtained. This test has important guiding significance for accurately evaluating the operating status of the components in the device and formulating the operating strategy of the entire high-power optical system.

[0003] In existing optical component damage testing and damage research experiments, the analysis of the acquired laser damage test data generally takes the average laser irradiation flux within a certain area as the flux value of the area. However, due to the coherence of the laser beam itself and the actual beam quality issues, the light field inevitably has local modulation, which makes the distribution of the light flux on the beam cross section fluctuate. In actual operation, the uneven distribution of the local irradiation flux of the target beam will make the measurement of the damage probability and damage threshold inaccurate, resulting in a decrease in the confidence of the damage data, and introduce certain errors in the final damage probability and damage growth analysis. In the current laser-induced damage research, the probability of initial damage to optical components and the subsequent damage growth rate are highly correlated with the laser irradiation flux. Therefore, to conduct a more in-depth study of laser-induced damage, it is necessary to obtain more accurate damage flux data. Summary of the Invention

[0004] In order to solve the problem that the flux data in the existing optical component damage test and analysis only uses the average laser irradiation flux as the parameter basis, and cannot achieve the correspondence between the actual local irradiation flux to the target and the specific damage point position, the present invention provides a laser target shooting local irradiation flux mapping method and device based on phase plate positioning, which can accurately provide the beam flux data of the target surface damage point for subsequent damage analysis.

[0005] In one aspect, the present invention provides a method for mapping local irradiance flux of laser target shooting based on phase plate positioning, the method comprising the following steps:

[0006] Step 1: Calibration step for obtaining the affine transformation matrix, specifically including:

[0007] Step 11: inserting a phase plate 2 between the lens 1 and the target 3 in the target shooting experiment optical path. The N discrete Fresnel zone plates provided on the phase plate 2 form N discrete phase marking points in the light field, thereby forming an array of damage points on the rear surface of the target.

[0008] Step 12: Recording the laser light field distribution image with the phase mark point between the phase plate 2 and the target 3;

[0009] Step 13: Record an image of the target material 3 having the array damage points as a target material damage image for calibration;

[0010] Step 14: establishing an affine transformation matrix based on the laser light field distribution image with phase marking points and the calibration target material damage image, and establishing a spatial correspondence between N discrete phase marking points and array damage points;

[0011] Step 2: Conducting a laser target shooting experiment to obtain the local irradiation flux of the target material, specifically including:

[0012] Step 21: Remove the phase plate 2 and perform the laser target shooting experiment using the original experimental optical path;

[0013] Step 22: Recording the irradiated laser light field distribution image corresponding to the target damage event;

[0014] Step 23, recording the irradiation laser pulse energy corresponding to the target damage event;

[0015] Step 24: Record the image of the target material 3 as a target material damage image;

[0016] Step 25: Mapping the irradiation laser light field distribution image corresponding to the target damage event onto the target material damage image according to the affine transformation matrix, and superimposing the irradiation laser light field distribution image corresponding to the target damage event and the target material damage image to obtain the position of the phase mark point corresponding to the target material damage point;

[0017] Step 26: Distribute the irradiation laser pulse energy corresponding to the target damage event obtained in step 23 according to the light field distribution displayed by the irradiation laser light field distribution image corresponding to the target damage event to obtain the laser irradiation flux distribution of the irradiation laser beam, and then obtain the local irradiation flux of the laser target at the location of each damage point on the target material.

[0018] Preferably, the N discrete Fresnel zone plates on the phase plate 2 form an arbitrary quadrilateral, where N≥5.

[0019] Preferably, the phase plate 2 uses a quartz element, and 5 adjacent second-order Fresnel zone plate structures are etched on the quartz element. The outer ring zone plate diameter of each second-order Fresnel zone plate is 2.5-5 mm, the etching depth is 364±40 nm, and the focal planes of the lens 1 and the phase plate 2 are matched with the rear surface of the target material 3.

[0020] Preferably, the insertion position of the phase plate 2 is determined by:

[0021] The distance L between the phase plate 2 and the lens 1 is obtained by the following equation:

[0022]

[0023] Where f is the focal length of the lens, S is the equivalent optical path, and R c is the focal length of the phase plate, d is the distance between the phase plate 2 and the target 3, and D is the distance between the lens 1 and the target 3.

[0024] On the other hand, the present invention provides a local irradiation flux mapping device for laser target shooting based on phase plate positioning, which is used to implement the local irradiation flux mapping method for laser target shooting based on phase plate positioning. The device includes a lens 1, a phase plate 2, a target material 3, a laser 4, an energy meter 5, a first beam splitter (6), a second beam splitter 7, a first CCD 8, a second CCD 9, an illumination light source (10), a movable reflector 11, a shielding plate 12, a microscope 13 and a filter 14;

[0025] The laser 4, the phase plate 2, the first beam splitter (6), the movable reflector 11, the target 3, the shielding plate 12, the microscope 13, the filter 14 and the first CCD 8 are arranged in sequence along the optical axis;

[0026] During calibration, the shielding plate 12 is placed in front of the microscope 13 and the movable reflector 11 is removed from the optical path;

[0027] The laser beam emitted by the laser 4 is incident on the target 3 through the phase plate 2. The laser beam passing through the phase plate 2 is split twice by the first beam splitter (6) and the second beam splitter 7 and is reflected to the second CCD 9. The transmitted beam of the second beam splitter 7 is incident on the energy meter 5.

[0028] During the target shooting experiment, phase plate 2 was removed;

[0029] The laser beam emitted by the laser 4 hits the target 3, and the laser beam is split twice by the first beam splitter (6) and the second beam splitter 7 and reflected to the second CCD 9; the transmitted beam of the second beam splitter 7 is incident on the energy meter 5;

[0030] After the shooting is completed, the shielding plate 12 is removed from the front of the microscope 13, and the movable reflector 11 is moved in front of the target material 3. The illumination light output by the illumination light source (10) is projected onto the target material 3 through the movable reflector 11, and the target material 3 is imaged in the first CCD 8 through the microscope 13 and the filter 14.

[0031] Beneficial effects of the present invention: The present invention utilizes a phase plate to be inserted into the optical path of a target shooting experiment, and N Fresnel zone plates are made on the phase plate as phase marking points. The light field is modulated by the Fresnel zone plate to induce the generation of a local strong area in the laser near field, and N positioned high-flux sites are gathered on the surface of the target material, thereby creating damage points with spatial position characteristics on the target surface, so as to realize the construction of an affine transformation matrix at a flux far lower than that of normal laser target shooting, and put less pressure on the entire optical path system.

[0032] In the formal target shooting test, the present invention can obtain the damage point position of the target material using the obtained affine transformation matrix, and then combine the light field distribution and energy value to finally obtain the specific laser irradiation flux borne by the damage point position on the target surface.

[0033] The light field is modulated using a Fresnel zone plate, and the contrast between the local irradiation flux at the positioning mark point on the target surface and the irradiation flux in other areas is greater than 20:1, making the positioning mark point more obvious.

[0034] The size of the phase plate positioning point is small, and the diameter of the phase mark point of the present invention can be less than 100 microns, which makes it easy to match the target material damage image with the laser beam near-field image with high spatial precision and calculate the affine transformation matrix. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a calibration principle diagram of the local irradiation flux mapping method for laser targeting based on phase plate positioning according to the present invention;

[0036] Figure 2 This is a schematic diagram of a laser target shooting experiment using the method of the present invention;

[0037] Figure 3 is a schematic diagram of the structure of the phase plate;

[0038] Figure 4 Schematic diagram of the structure of the second-order Fresnel zone plate used in the present invention;

[0039] Figure 5 It is a schematic structural diagram of an apparatus for implementing the method of the present invention. DETAILED DESCRIPTION

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0041] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0043] Specific implementation method 1: Figures 1 to 3 This embodiment describes a method for mapping local irradiance flux of laser target shooting based on phase plate positioning, which includes the following steps:

[0044] Step 1: Calibration step for obtaining affine transformation matrix, see Figure 1 , specifically including:

[0045] Step 11: inserting a phase plate 2 between the lens 1 and the target 3 in the target shooting experiment optical path. The N discrete Fresnel zone plates provided on the phase plate 2 form N discrete phase marking points in the light field, thereby forming an array of damage points on the rear surface of the target.

[0046] Step 12: Recording the laser light field distribution image with the phase mark point between the phase plate 2 and the target 3;

[0047] Step 13: Record an image of the target material 3 having the array damage points as a target material damage image for calibration;

[0048] Step 14: establishing an affine transformation matrix based on the laser light field distribution image with phase marking points and the calibration target material damage image, and establishing a spatial correspondence between N discrete phase marking points and array damage points;

[0049] Step 2: Perform laser target shooting experiment to obtain the local irradiation flux of the target material, see Figure 2 , specifically including:

[0050] Step 21: Remove the phase plate 2 and perform the laser target shooting experiment using the original experimental optical path;

[0051] Step 22: Recording the irradiated laser light field distribution image corresponding to the target damage event;

[0052] Step 23, recording the irradiation laser pulse energy corresponding to the target damage event;

[0053] Step 24: Record the image of the target material 3 as a target material damage image;

[0054] Step 25: Mapping the irradiation laser light field distribution image corresponding to the target damage event onto the target material damage image according to the affine transformation matrix, and superimposing the irradiation laser light field distribution image corresponding to the target damage event and the target material damage image to obtain the position of the phase mark point corresponding to the target material damage point;

[0055] Step 26: Distribute the irradiation laser pulse energy corresponding to the target damage event obtained in step 23 according to the light field distribution displayed by the irradiation laser light field distribution image corresponding to the target damage event to obtain the laser irradiation flux distribution of the irradiation laser beam, and then obtain the local irradiation flux of the laser target at the location of each damage point on the target material.

[0056] See also Figure 3 , the N discrete Fresnel zone plates on the phase plate 2 form an arbitrary quadrilateral, N≥5.

[0057] In a normal laser targeting optical path, the laser beam flux is relatively high, and its purpose is to create a damage point on the target material 3. The targeting optical path basically constitutes the laser directly hitting the target material 3 through the lens 1. However, the present invention is behind the lens 1 (a phase plate 2 is inserted between the lens 1 and the target material 3). Its purpose is to induce a local strong area in the laser near field. This principle can be used to create a local strong point in the light field to achieve spot positioning.

[0058] A phase plate, or phase mask, is an optical element that alters the phase of light by machining a surface with a desired sag, or coating it with a film of appropriate thickness or refractive index, based on a parallel flat plate. Phase plates operate based on the converging effect of Fresnel zone plates on light beams. When the optical path difference between each two adjacent half-wave zone of a Fresnel zone plate to the principal focal point is λ / 2, according to Fresnel Kirchhoff diffraction theory, the incident light beam can be converged at the principal focal point, where λ is the laser wavelength. Using a Fresnel zone plate, incident monochromatic light can be focused on the focal plane, with the same intensity at each focal point.

[0059] The phase plate 2 of this embodiment is a quartz element. Figure 4 Five adjacent second-order Fresnel zone plates were etched on the quartz element. The outer zone of each second-order Fresnel zone plate had a diameter of 4.88 mm and an etching depth of 364 nm. The focal planes of lens 1 and phase plate 2 were matched to the surface of target 3. By adjusting the distance between phase plate 2 and the surface of target 3, the focal plane of the phase plate and lens combination was matched to the rear surface of the sample, ensuring accurate laser focusing and effective damage testing.

[0060] This embodiment introduces a phase plate 2 into the target optical path for positioning. The Fresnel zone plate can achieve high contrast after focusing, achieving a high target flux at the phase mark point under low laser flux irradiation, and leaving a damage point on the target material 3. Based on the correspondence between the damage point on the target material 3 and the near-field CCD recording spot, the correspondence between the irradiation spot and the target material 3 is obtained, and an affine transformation matrix is ​​constructed. At the same time, laser irradiation flux data is measured based on the laser energy value. The energy data is then distributed according to the light field distribution to obtain the distribution result of the target laser flux. The correlation between the irradiation flux distribution, the target surface damage point distribution position, and the phase mark point distribution position is established. The correlation between the irradiation flux and the damage point is obtained, achieving high-precision matching between the laser near-field light intensity distribution and the damage point flux. This method not only improves the accuracy of the flux data but also helps reduce the errors introduced in damage analysis. Through this sophisticated data acquisition and analysis method, accurate laser flux data analysis of the target surface damage point position is achieved.

[0061] Determination of the insertion position of phase plate 2:

[0062] The distance L between the phase plate 2 and the lens 1 is obtained by the following equation:

[0063]

[0064] Where f is the focal length of the lens, S is the equivalent optical path, and R c is the focal length of the phase plate, d is the distance between the phase plate 2 and the target 3, and D is the distance between the lens 1 and the target 3.

[0065] In the above equation, f, R c is a known quantity, L and d are unknown quantities to be determined, their sum D is a known quantity, and S is an intermediate variable. This equation allows us to determine L, which in turn determines the insertion position of phase plate 2. Based on the above equation, the distance between phase plate 2 and lens 1, as well as the focal length parameters of phase plate 2 and lens 1, determine the position of the target surface, i.e., the point of strongest focus of the Fresnel zone plate. Failure to accurately locate the focal point of phase plate 2 during the experiment will result in a contrast ratio far below expectations at the strongest modulation point and reduce the accuracy of the affine transformation. Therefore, the phase plate's position should be determined according to the above equation to ensure optimal experimental results.

[0066] Specific implementation method 2: The following is combined Figure 5This embodiment is described. The embodiment described herein is a device for mapping local irradiance flux of laser target shooting based on phase plate positioning, which is used to implement the method for mapping local irradiance flux of laser target shooting based on phase plate positioning described in Embodiment 1. The device includes a lens 1, a phase plate 2, a target material 3, a laser 4, an energy meter 5, a first beam splitter 6, a second beam splitter 7, a first CCD 8, a second CCD 9, an illumination light source 10, a movable reflector 11, a shielding plate 12, a microscope 13, and a filter 14.

[0067] The laser 4, the phase plate 2, the first beam splitter (6), the movable reflector 11, the target 3, the shielding plate 12, the microscope 13, the filter 14 and the first CCD 8 are arranged in sequence along the optical axis;

[0068] During calibration, the shielding plate 12 is placed in front of the microscope 13 and the movable reflector 11 is removed from the optical path;

[0069] The laser beam emitted by the laser 4 is incident on the target 3 through the phase plate 2. The laser beam passing through the phase plate 2 is split twice by the first beam splitter (6) and the second beam splitter 7 and is reflected to the second CCD 9. The transmitted beam of the second beam splitter 7 is incident on the energy meter 5.

[0070] CCD 2 records the laser light field distribution image with phase markings, and the data monitored by energy meter 5 is not used for calibration. The multiple phase marking points produced by phase plate 2 roughly form a quadrilateral. This embodiment uses five Fresnel zone plates to produce phase marking points to achieve an arbitrary quadrilateral. The second-order Fresnel zone plate induces a localized strong area in the laser near field, converging N positioned high-flux sites on the target surface to form damage points. The spatial positional relationship between the phase marking points and the damage points is established using the five phase marking points at known positions and the target damage map recorded by CCD 1, thereby creating an affine transformation matrix. The purpose of placing the shielding plate 12 in front of the microscope 13 is to prevent damage to the microscope 13 caused by the high-power laser.

[0071] The movable reflector 11 and the illumination light source 10 are not used in the calibration stage and are first removed from the light path.

[0072] During the target shooting experiment, phase plate 2 was removed;

[0073] The laser beam emitted by the laser 4 hits the target 3, and the laser beam is split twice by the first beam splitter (6) and the second beam splitter 7 and reflected to the second CCD 9; the transmitted beam of the second beam splitter 7 is incident on the energy meter 5;

[0074] After the shooting is completed, the shielding plate 12 is removed from the front of the microscope 13, and the movable reflector 11 is moved in front of the target material 3. The illumination light output by the illumination light source (10) is projected onto the target material 3 through the movable reflector 11, and the target material 3 is imaged in the first CCD 8 through the microscope 13 and the filter 14.

[0075] During the target shooting experiment, the irradiated laser causes local damage to the surface of the target material 3 due to its own non-uniformity. The second CCD9 records the target material damage image. Since the laser emission has stopped at this time, the microscope 13 is no longer worried about being damaged. The shielding plate 12 is first moved away from the front of the microscope 13. At the same time, in order to provide the light intensity for imaging, the movable reflector 11 is moved in front of the target material 3. The illumination light output by the illumination light source (10) is projected onto the target material 3 through the movable reflector 11 and an image is formed on the CCD.

[0076] At this time, the position of the damage point in the target material damage image is unknown. The present invention can obtain the specific damage position by using the previously established affine transformation matrix and the target material damage image recorded during the target shooting experiment.

[0077] The data monitored by the energy meter 5 is the irradiation laser pulse energy corresponding to the target damage event. The energy value is distributed according to the light field distribution to obtain a distribution diagram of the laser flux. The local laser flux at different positions can be displayed, and the laser flux at the damage point can be read out according to the distribution diagram of the laser flux.

[0078] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the invention. It should be understood that many modifications may be made to the illustrative embodiments, and that other arrangements may be devised, without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in ways other than those described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in conjunction with other described embodiments.

Claims

1. A method for mapping local irradiance flux in laser targeting based on phase plate positioning, characterized in that: The method comprises the following steps: Step 1: Calibration step for obtaining the affine transformation matrix, specifically including: Step 11: inserting a phase plate (2) between the lens (1) and the target (3) in the target shooting experiment optical path, wherein N discrete Fresnel zone plates provided on the phase plate (2) form N discrete phase marking points on the light field, so as to form an array of damage points on the target surface; Step 12: Recording a laser light field distribution image with phase points between the phase plate (2) and the target (3); Step 13, recording an image of the target material (3) having the array damage points as a calibration target material damage image; Step 14: establishing an affine transformation matrix based on the laser light field distribution image with phase marking points and the calibration target material damage image, and establishing a spatial correspondence between N discrete phase marking points and array damage points; Step 2: Conducting a laser target shooting experiment to obtain the local irradiation flux of the target material, specifically including: Step 21: Remove the phase plate (2) and use the original experimental optical path to perform the laser target shooting experiment; Step 22: Recording the irradiated laser light field distribution image corresponding to the target damage event; Step 23, recording the irradiation laser pulse energy corresponding to the target damage event; Step 24, recording the image of the target material (3) as a target material damage image; Step 25: Mapping the irradiation laser light field distribution image corresponding to the target damage event onto the target material damage image according to the affine transformation matrix, and superimposing the irradiation laser light field distribution image corresponding to the target damage event and the target material damage image to obtain the position of the phase mark point corresponding to the target material damage point; Step 26: Distribute the irradiation laser pulse energy corresponding to the target damage event obtained in step 23 according to the light field distribution displayed by the irradiation laser light field distribution image corresponding to the target damage event to obtain the laser irradiation flux distribution of the irradiation laser beam, and then obtain the local irradiation flux of the laser target at the location of each damage point on the target material.

2. The laser target local irradiation flux mapping method based on phase plate positioning according to claim 1, characterized in that: The N discrete Fresnel zone plates on the phase plate (2) form an arbitrary quadrilateral, where N≥5.

3. The method for local irradiation flux mapping of laser target shooting based on phase plate positioning according to claim 2, characterized in that: The phase plate (2) adopts a quartz element, and 5 adjacent second-order Fresnel zone plate structures are etched on the quartz element. The outer ring zone plate of each second-order Fresnel zone plate has a diameter of 2.5-5 mm and an etching depth of 364±40 nm. The focal planes of the lens (1) and the phase plate (2) are matched with the rear surface of the target material (3).

4. The method for local irradiation flux mapping of laser target shooting based on phase plate positioning according to claim 3, characterized in that: The insertion position of the phase plate (2) is determined by: The distance L between the phase plate (2) and the lens (1) is obtained by the following equation: Where f is the focal length of the lens, S is the equivalent optical path, and R c is the focal length of the phase plate, d is the distance between the phase plate (2) and the target (3), and D is the distance between the lens (1) and the target (3).

5. A laser target local irradiance flux mapping device based on phase plate positioning, used to implement the laser target local irradiance flux mapping method based on phase plate positioning according to any one of claims 1 to 4, characterized in that: The device comprises a lens (1), a phase plate (2), a target material (3), a laser (4), an energy meter (5), a first beam splitter (6), a second beam splitter (7), a first CCD (8), a second CCD (9), an illumination light source (10), a movable reflector (11), a shielding plate (12), a microscope (13) and a filter (14); A laser (4), a phase plate (2), a first beam splitter (6), a movable reflector (11), a target (3), a shielding plate (12), a microscope (13), a filter (14) and a first CCD (8) are sequentially arranged along the optical axis; During calibration, the shielding plate (12) is placed in front of the microscope (13) and the movable reflector (11) is removed from the optical path; The laser beam emitted by the laser (4) is incident on the target material (3) through the phase plate (2); the laser beam passing through the phase plate (2) is reflected to the second CCD (9) after being split twice by the first beam splitter (6) and the second beam splitter (7); the transmitted beam of the second beam splitter (7) is incident on the energy meter (5); During the target shooting experiment, the phase plate (2) was removed; The laser beam emitted by the laser (4) hits the target (3), and the laser beam is reflected to the second CCD (9) after being split twice by the first beam splitter (6) and the second beam splitter (7); the transmitted beam of the second beam splitter (7) is incident on the energy meter (5); After the shooting is completed, the shielding plate (12) is removed from the front of the microscope (13), and the movable reflector (11) is moved in front of the target material (3). The illumination light output by the illumination light source (10) is projected onto the target material (3) through the movable reflector (11), and the target material (3) is imaged in the first CCD (8) through the microscope (13) and the filter (14).

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