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

Abstract

The invention discloses a laser targeting local irradiation flux mapping method and device based on phase plate positioning, belongs to the field of laser targeting experiments, and aims to solve the problem that in existing optical element damage test analysis, flux data only takes average flux as a result, and target surface beam flux cannot correspond to damage points. The method comprises a calibration step for obtaining an affine transformation matrix and a step for carrying out a laser targeting experiment to obtain local irradiation flux of a target material, a phase plate is inserted between a lens of a targeting experiment light path and the target material, array damage points are formed on the rear surface of the target material, the affine transformation matrix is constructed, the phase plate is removed, and the target material local irradiation flux is obtained. Performing a laser targeting experiment by using the original experiment light path; mapping the target shooting laser beam near-field image to the target material damage image according to the affine transformation matrix, and superposing the target shooting laser beam near-field image and the target material damage image to obtain the position of the phase mark point corresponding to the target material damage point; and obtaining the local irradiation flux of laser targeting at the position of each damage point on the target material.

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, and because impurities and defects are inevitably introduced 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, and 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 sampled from the same processing batch before being put on the shelf for use, to test their damage threshold and damage resistance, and to obtain the initial damage and damage development law of the rear surface of the optical component. This test is of great 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 tests 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 problem, 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, in order 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 a 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 damage point on the target surface for subsequent damage analysis.

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

[0006] Step 1: A calibration step for obtaining an affine transformation matrix, specifically comprising:

[0007] Step 11, inserting a phase plate 2 between the lens 1 and the target material 3 in the target shooting experiment optical path, wherein N discrete Fresnel zone plates arranged 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 rear surface of the target material;

[0008] Step 12, recording a laser light field distribution image having a phase point between the phase plate 2 and the target 3;

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

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

[0011] Step 2: Conducting 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 use the original experimental optical path to perform the laser target shooting experiment;

[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, recording 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 to 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, 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 adopts 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 2.5-5mm, the etching depth is 364±40nm, 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] In another aspect, the present invention provides a laser target local irradiation flux mapping device based on phase plate positioning, which is used to implement the laser target local irradiation flux mapping method based on phase plate positioning, and 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;

[0025] 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;

[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 reflected to the second CCD 9 through the second beam splitter 7 and the first beam splitter 6. 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 reflected to the second CCD 9 through the second beam splitter 7 and the first beam splitter 6; the transmission 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 moved away 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 plates, inducing 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, with 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 by using the obtained affine transformation matrix, and finally obtain the specific laser irradiation flux borne by the damage point position on the target surface in combination with the light field distribution and the energy value.

[0033] The light field is modulated by using a Fresnel zone plate, and the contrast between the local irradiation flux of the positioning mark point constructed on the target surface and the irradiation flux of 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 correspond the target material damage image with the laser beam near-field image with high spatial accuracy and calculate the affine transformation matrix. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] Figure 2 It is a principle diagram of 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 diagram of the structure of an apparatus for implementing the method of the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are 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 in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

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

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

[0045] Step 11, inserting a phase plate 2 between the lens 1 and the target material 3 in the target shooting experiment optical path, wherein N discrete Fresnel zone plates arranged 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 rear surface of the target material;

[0046] Step 12, recording a laser light field distribution image having a phase point between the phase plate 2 and the target 3;

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

[0048] Step 14: establishing an affine transformation matrix according to the laser light field distribution image with phase marking points and the target material damage image for calibration, 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 use the original experimental optical path to perform the laser target shooting experiment;

[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, recording 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 to 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, 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 target shooting optical path, the laser beam flux is relatively high, and its purpose is to be able to create damage points on the target material 3. The target shooting optical path basically constitutes that the laser directly hits the target material 3 through the lens 1, and the present invention is after the lens 1 (the phase plate 2 is inserted between the lens 1 and the target material 3), its purpose is to induce the generation of a local strong area in the laser near field, and this principle can be used to create a local strong point of the light field to achieve spot positioning.

[0058] The full name of the phase plate is the phase mask plate. It is generally based on a parallel flat plate, and the corresponding vector height that meets the requirements is processed on its surface, or a film layer with corresponding thickness or refractive index is coated to change the phase of light. An optical element of the phase plate element works based on the convergence effect of the Fresnel zone plate on the light beam. When the optical path difference between each two adjacent half-wave bands of the Fresnel zone plate to the main focus is λ / 2, according to the Fresnel Kirchhoff diffraction theory, it can converge the incident light beam to the main focus, and λ is the laser wavelength. Using the Fresnel zone plate, a focal spot can be formed on the focal plane for the incident monochromatic light, and the intensity of each focus on the focal plane is the same.

[0059] The phase plate 2 of this embodiment adopts a quartz element. Figure 4 , 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 4.88mm, the etching depth is 364nm, and the focal planes of lens 1 and phase plate 2 are matched with 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 is matched with the rear surface of the sample, ensuring the accurate focusing of the laser and the effective implementation of the damage test.

[0060] In this embodiment, the phase plate 2 is introduced into the target optical path for positioning. The Fresnel zone plate can achieve a higher contrast after focusing. Under the irradiation of a lower laser flux, a higher flux to the target can be achieved at the phase mark point, and a damage point can be left on the target material 3. Based on the correspondence between the damage point at the target material 3 and the near-field CCD recording spot, the correspondence between the irradiation spot and the target material 3 can be obtained, and an affine transformation matrix can be constructed. At the same time, the laser irradiation flux data is measured according to the laser energy value, and then the energy data is distributed according to the light field distribution to obtain the distribution result of the target laser flux, and the correlation between the irradiation flux distribution-target surface damage point distribution position-phase mark point distribution position is established. The correlation between the irradiation flux and the damage point is obtained, and the high-precision matching of the laser near-field light intensity distribution and the damage point flux is achieved. This method not only improves the accuracy of the flux data, but also helps to reduce the error introduced in the 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] The insertion position of phase plate 2 is determined by:

[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, the sum of the two D is a known quantity, S is an intermediate variable, and L can be obtained according to the equation, that is, the insertion position of the phase plate 2 is determined. Based on the above formula, the distance between the phase plate 2 and the lens 1 and the focal length parameters of the phase plate 2 and the lens 1 determine the position of the target surface, that is, the strongest focusing point of the Fresnel zone plate. If the position of the focus of the phase plate 2 is not accurately located in the experiment, the contrast of the strong modulation point will be far less than expected, and the accuracy of the affine transformation will be reduced. Therefore, the position of the phase plate should be determined according to the above equation to ensure the experimental effect.

[0066] Specific implementation method 2: The following is combined Figure 5The present embodiment is described. The present embodiment describes a laser target local irradiation flux mapping device based on phase plate positioning, which is used to implement the laser target local irradiation flux mapping method based on phase plate positioning described in the first embodiment. 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] 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;

[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 reflected to the second CCD 9 through the second beam splitter 7 and the first beam splitter 6. The transmitted beam of the second beam splitter 7 is incident on the energy meter 5.

[0070] The second CCD9 records the laser light field distribution image with phase points, and the data monitored by the energy meter 5 during calibration is not used. The multiple phase marking points made by the phase plate 2 roughly form a quadrilateral. This embodiment uses five Fresnel zone plates to make phase marking points to realize an arbitrary quadrilateral. The second-order Fresnel zone plate induces a local strong area in the laser near field, and converges N high-flux sites that have been positioned on the surface of the target material to form a damage point. The spatial position relationship between the phase marking point and the damage point is established using the five phase marking points of known positions and the target material damage map recorded by the first CCD8, and an affine transformation matrix is ​​established. The purpose of setting the shielding plate 12 in front of the microscope 13 is to prevent the high-power laser from causing damage to the microscope 13.

[0071] The movable reflector 11 and the illumination light source 10 are not used in the calibration stage and are first removed from the optical 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 reflected to the second CCD 9 through the second beam splitter 7 and the first beam splitter 6; the transmission 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 moved away 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 of 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 based on 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 examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for local irradiation flux mapping of laser target shooting based on phase plate positioning, characterized in that: The method comprises the following steps: Step 1: A calibration step for obtaining an affine transformation matrix, specifically comprising: Step 11, inserting a phase plate (2) between the lens (1) and the target material (3) in the target shooting experiment optical path, wherein N discrete Fresnel zone plates arranged 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 surface of the target material; Step 12, recording a laser light field distribution image having a phase point between the phase plate (2) and the target material (3); Step 13, recording an image of the target material (3) having array damage points as a target material damage image for calibration; Step 14: establishing an affine transformation matrix according to the laser light field distribution image with phase marking points and the target material damage image for calibration, 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 to 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, 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 is 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 five 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, and the etching depth is 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 is 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 irradiation flux mapping device based on phase plate positioning, used to implement the laser target local irradiation 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) through the second beam splitter (6) and the second beam splitter (7); the transmission 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 material (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 transmission beam of the second beam splitter (7) is incident on the energy meter (5); After the target shooting is completed, the shielding plate (12) is moved away 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).

Images