A target-shooting device and method for obtaining ultra-high contrast laser.

Abstract

This invention discloses a target-shooting device and method for obtaining ultra-high contrast laser beams, comprising a first plasma mirror (1), a second plasma mirror (2), and a target (3), wherein the first plasma mirror (1) reflects the laser beam to the second plasma mirror (2), and the second plasma mirror (2) reflects the laser beam to the target (3). The device and method for obtaining ultra-high contrast laser beams according to this invention have many advantages, such as high laser reflectivity, high contrast enhancement, small footprint, and fewer optical path components.

Description

Technical Field

[0001] This invention relates to a laser target-shooting device and method, and more particularly to a laser target-shooting device and method for obtaining ultra-high contrast, belonging to the field of laser technology. Background Technology

[0002] Ultra-high power density laser bombardment of thin-film targets is an important method for obtaining ultrafast high-energy particle beams and rays. Ultra-high power density lasers exhibit a Gaussian temporal distribution, with pulse widths ranging from picoseconds to femtoseconds and even attoseconds. Their main pulse possesses extremely high instantaneous peak power. Before and after the main pulse, the light intensity remains high enough to cause material damage; therefore, the ratio of the peak power of the main pulse to the light intensity at a given moment is defined as the laser contrast ratio at that moment. Laser contrast ratio is an important indicator of high-power lasers, defined as CR(t) = I(t) / I(t=0), where I(t) is the laser intensity at time t, and I(t=0) is the peak laser intensity.

[0003] Target-hitting experiments require lasers with high temporal contrast (i.e., signal-to-noise ratio) to prevent shock waves generated at the pulse leading edge from damaging the target surface or pre-plasmizing the target surface, thus affecting the interaction between the main pulse and the target surface. For example, in laser proton acceleration, to improve particle beam yield, cutoff energy, and reduce particle beam divergence, the laser's contrast at the nanosecond scale must reach 10. 9 The contrast ratio at the picosecond scale reaches 10. 5 Furthermore, as lasers reach petawatt levels and their peak focused power increases further, the requirements for laser contrast will become even more stringent. Different acceleration mechanisms also have different requirements for laser contrast. The RPA mechanism, which promises to significantly improve particle beam yield, cutoff energy, and reduce particle beam divergence, places particularly stringent demands on laser contrast. Other research areas also require lasers with high contrast, such as suppressing thermionic temperature, increasing characteristic X-ray yield, and obtaining high-order harmonics.

[0004] Improving laser contrast can be achieved by addressing the laser itself, specifically by optimizing the contrast of the laser front-end pulses. This results in a higher contrast even after the laser energy is amplified. Techniques such as XPW (cross-polarization filtering), Pockels cells, OPCPA, and optimizing compression gratings can be employed. However, these methods are only suitable for low-energy applications, and the optimized contrast still falls short of the requirements of many experiments.

[0005] On the other hand, contrast enhancement CI=R can be achieved through plasma mirror technology. sf / R wf , where R sf R is the reflectivity of a strong-field laser. wfThe reflectivity is for weak-field lasers. Plasma mirrors typically come in two forms: one is a stand-alone plasma mirror system, which offers better performance but requires a separate vacuum cavity and two OAPs; the other is a target-front plasma mirror, which embeds the plasma mirror into the optical path, eliminating the need for additional optical components. However, the close spatial proximity of the plasma mirror and the target can be mutually restrictive, making it difficult to achieve a good balance between contrast enhancement and target-hitting convenience.

[0006] Therefore, it is necessary to study a laser target-shooting device and method to solve the above problems. Summary of the Invention

[0007] In order to overcome the above problems, the inventors have conducted in-depth research and, on the one hand, provided a target-shooting device for obtaining ultra-high contrast laser, including a first plasma mirror 1, a second plasma mirror 2 and a target 3.

[0008] Furthermore, the first plasma mirror 1 reflects the laser beam to the second plasma mirror 2, and the second plasma mirror 2 reflects the laser beam to the target 3.

[0009] In a preferred embodiment, the laser beam irradiating the first plasma mirror 1 is a laser with power of TW or higher, preferably a laser with power of PW, and more preferably, the laser beam is focused by an off-axis parabolic mirror.

[0010] In a preferred embodiment, the mirror surface of the first plasma mirror 1 forms a 45° angle with the centerline of the laser beam path.

[0011] In a preferred embodiment, the laser reflected by the first plasma mirror 1 is vertically upward or vertically downward.

[0012] In a preferred embodiment, the centerline of the laser beam illuminating the first plasma mirror 1 is set horizontally, and the second plasma mirror 2 reflects the laser beam reflected by the first plasma mirror 1 back onto the horizontal surface.

[0013] In a preferred embodiment, the first plasma mirror 1 is fixed on the first support 4, and the second plasma mirror 2 is fixed on the second support 5, such that the defocus positions of the first plasma mirror 1 and the second plasma mirror 2 are appropriate. The appropriate defocus position means that the laser can trigger the plasma mirror within 3ps before the pulse peak.

[0014] In a preferred embodiment, the device further includes a target mount 31 and a mirror target support 6, wherein the target 3 is fixed on the target mount 31, and the target mount 31 is fixed on the mirror target support 6.

[0015] The first bracket 4 and the second bracket 5 are fixedly connected to the target support 6.

[0016] In a preferred embodiment, the device further includes a displacement stage 7, which is a platform capable of movement and / or rotation.

[0017] The first support 4, the second support 5 and / or the target support 6 are placed on the displacement stage 7 and move or rotate with the displacement stage 7.

[0018] On the other hand, the present invention also provides a method for obtaining ultra-high contrast laser for target firing: the laser is focused and reflected by at least two plasma mirrors before firing at the target.

[0019] This method is compatible with both target aiming devices and detection devices.

[0020] The beneficial effects of this invention include:

[0021] (1) The target-shooting device for obtaining ultra-high contrast laser according to the present invention adopts a plasma mirror placed in front of the target, which eliminates the need for a separate vacuum cavity and focusing and re-collimating optical elements, as well as a laser polarization conversion device.

[0022] (2) The target-hitting device for obtaining ultra-high contrast laser according to the present invention adopts a continuous dual plasma mirror, the incident laser and the outgoing laser do not change direction, and the laser contrast is improved by more than 4 orders of magnitude.

[0023] (3) According to the target-hitting device for obtaining ultra-high contrast laser as described in the present invention, the two mirrors are placed vertically. This device does not need to change the polarization of commonly used P lasers, so that the plasma mirror can achieve a higher reflectivity than the equivalent S-polarized laser, and thus obtain a higher laser reflectivity.

[0024] (4) According to the target-hitting device for obtaining ultra-high contrast lasers as described in the present invention, the dual mirrors adopt a simple combination of coated and uncoated, which can accurately achieve the output of three contrast lasers, while the laser end is difficult to accurately control the laser contrast.

[0025] (5) The target-hitting device for obtaining ultra-high contrast laser according to the present invention can realize high-repetition-rate target hitting;

[0026] (6) The target shooting device for obtaining ultra-high contrast laser according to the present invention is compatible with the aiming device and the detection device. Attached Figure Description

[0027] Figure 1 A schematic diagram of a target-shooting device for obtaining ultra-high contrast laser according to a preferred embodiment of the present invention is shown.

[0028] Figure 2 A schematic diagram of a traditional laser target ablation device is shown.

[0029] Figure 3A schematic diagram of a traditional laser target-shooting device is shown.

[0030] Explanation of icon numbers:

[0031] 1-First plasma mirror;

[0032] 2-Second plasma mirror;

[0033] 3-target;

[0034] 31-Target mount;

[0035] 4-First support;

[0036] 5-Second support;

[0037] 6-Mirror target support;

[0038] 7-Displacement stage;

[0039] 8-Targeting camera. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent.

[0041] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0042] On one hand, the present invention provides a target-shooting device for obtaining ultra-high contrast lasers, the device comprising a first plasma mirror 1, a second plasma mirror 2, and a target 3, as shown below. Figure 1 As shown.

[0043] Furthermore, the first plasma mirror 1 reflects the laser beam to the second plasma mirror 2, and the second plasma mirror 2 reflects the laser beam to the target 3, thereby completing the target hitting.

[0044] Traditional laser target ablation typically employs a separate plasma mirror system. First, a half-wave plate laser beam is converted from P-polarization to S-polarization. Then, an off-axis parabolic mirror (OAP1) focuses the beam onto the plasma mirror. After reflection, the beam diverges. An OAP2 then recollides the beam into parallel light, which is then transmitted to the target cavity and refocused by an OAP3 to ablate the target. Figure 2 As shown, this method requires a separate vacuum chamber and two OAPs, which takes up a lot of space;

[0045] Another approach is to place a plasma mirror in front of the target, such as... Figure 3As shown, this method makes it difficult to adjust the position and angle of the plasma mirror, and the scheme will change the laser emission direction, which often results in ordinary rectangular houses not being able to meet the layout requirements or increasing the required interior area of ​​the house, leading to increased costs. In addition, this method uses P-polarized laser to act on the plasma mirror, and the reflectivity will be low due to plasma resonance absorption.

[0046] In this invention, two plasma mirrors are set in the optical path in front of the target, so that the laser emission direction does not need to be changed and the position and angle of the plasma mirrors are easy to adjust.

[0047] According to the present invention, the laser beam irradiating the first plasma mirror 1 is a laser with power of TW or higher, preferably a laser with power of PW, and more preferably, the laser beam is focused by an off-axis parabolic mirror.

[0048] In a preferred embodiment, the mirror surface of the first plasma mirror 1 forms a 45° angle with the center line of the laser beam path, thereby ensuring the flatness of the mirror surface and reducing stress-induced deformation.

[0049] In this invention, the shape of the first plasma mirror 1 is not particularly limited. In a preferred embodiment, the first plasma mirror 1 is an isosceles right-angled prism. When the bottom surface of the isosceles right-angled prism is placed horizontally, its inclined surface forms a 45° angle with the horizontal plane, which is convenient for adjustment.

[0050] In a preferred embodiment, the mirror surface flatness PV value of the first plasma mirror 1 is less than one-tenth of a laser wavelength.

[0051] More preferably, the laser reflected by the first plasma mirror 1 is vertically upward or vertically downward, so that the P-polarized light has no electric field component on the mirror surface. When the laser at the leading edge of the pulse is weak, the first plasma mirror 1 is a low reflectivity mirror. When the pulse reaches a higher power, the mirror surface is ionized to generate a plasma plane, which strongly reflects the laser. This achieves the effect of weakening the intensity of the laser pulse leading edge, thereby improving the contrast of the laser.

[0052] More preferably, the centerline of the optical path of the laser beam irradiating the first plasma mirror 1 is set horizontally, and the second plasma mirror 2 reflects the laser reflected by the first plasma mirror 1 back onto the horizontal surface, thereby improving the laser contrast for the second time and realizing the P-polarization equivalent to the S-polarization laser acting on the plasma mirror to obtain a higher reflectivity.

[0053] Experiments have shown that this method can achieve a higher reflectivity for plasma mirrors than for equivalent S-polarized lasers without changing the polarization of commonly used P-lasers, thereby improving laser contrast by more than four orders of magnitude. At the same time, compared with traditional methods, it eliminates the need for a separate vacuum plasma mirror cavity and focusing and re-collimating optical elements, as well as a laser polarization conversion device, greatly reducing the overall space requirements of the device.

[0054] According to the present invention, the first plasma mirror 1 and the second plasma mirror 2 can be coated with anti-reflection film or not coated as needed. By combining the first plasma mirror 1 and the second plasma mirror 2 with different coating conditions, three different contrast lasers can be output, and the output laser energy is basically consistent.

[0055] Traditional target-shooting devices rely on adjusting the laser contrast at the laser end. However, once the laser design is complete, it is difficult to accurately adjust the laser contrast. This invention solves this problem by addressing the coating of the plasma mirror, greatly improving the applicability of the device.

[0056] According to a preferred embodiment of the present invention, the device further includes a first support 4 and a second support 5.

[0057] The first plasma mirror 1 is fixed on the first support 4, and the second plasma mirror 2 is fixed on the second support 5, so that the defocus positions of the first plasma mirror 1 and the second plasma mirror 2 are appropriate. Appropriate defocus positions mean that the laser can trigger the plasma mirror within 3 ps before the pulse peak, allowing the laser to trigger the plasma, but not too early. Furthermore, for a femtosecond laser with a power density of 10... 15 W / cm 2 ~10 16 W / cm 2 .

[0058] In this invention, the specific structure of the first support 4 and the second support 5 is not particularly limited. They can be any structure that can fix the plasma mirror, such as a structure that is fixedly connected to the side of the plasma mirror or a structure that is fixedly connected to the bottom of the plasma mirror.

[0059] Furthermore, in this invention, the fixed connection can be made in any way, such as snap-fit, sleeve, or connection based on pressure, friction, gravity, etc., as long as there is no relative movement between the two fixedly connected devices.

[0060] According to the present invention, the device further comprises a target base 31 and a mirror target support 6, wherein the target 3 is fixed on the target base 31 and the target base 31 is fixed on the mirror target support 6.

[0061] In this invention, the structure and material of the target 3 are not particularly limited. It can be any kind of target material, such as a thin film target material of metal, plastic or DLC, or a liquid target material or a gas target material. The specific form of the target material, as well as the specific parameters such as material and thickness, can be determined by those skilled in the art according to actual needs and laser conditions.

[0062] Typically, the thickness of a thin-film target is at the micrometer or nanometer level. In this invention, the contrast is greatly improved after the laser passes through the first plasma mirror 1 and the second plasma mirror 2. Therefore, a thin-film target with a thickness of less than 1 nanometer can be used for target hitting in this application.

[0063] In this invention, the material of the target 31 is not particularly limited. For example, it can be made of metal or insulating material, and aluminum is commonly used.

[0064] Furthermore, in this invention, the target holder 31 can be placed at an angle on the mirror target support 6, so that the laser reflected by the second plasma mirror 2 can strike the target 3 at different angles.

[0065] More preferably, the first support 4, the second support 5, and the mirror-target support 6 are fixedly connected, so that the first plasma mirror 1, the second plasma mirror 2, and the target 3 are coupled together, making the optical path easier to adjust.

[0066] In a preferred embodiment, the first plasma mirror 1 and the second plasma mirror 2 are elongated, and the mirror target support 6 has multiple targets 3 or the target base 31 is provided with multiple targets 3, so that when the first support 4, the second support 5 and the mirror target support 6 move horizontally perpendicular to the optical path direction, the laser can strike multiple targets 3 through the first plasma mirror 1 and the second plasma mirror 2.

[0067] According to a preferred embodiment of the present invention, the device further includes a target camera 8, which is used to locate and optimize the focal spot of the focused laser beam.

[0068] Furthermore, the target camera 8 is a high-magnification camera, which magnifies the image after capturing the focal spot image to achieve more accurate positioning of the focal spot. The specific structure or model of the target camera 8 will not be described in detail in this invention. Those skilled in the art can design or select it as needed. For example, the target camera 8 is a combination of a MindVision MV-GED200M CCD and a Nikon TPlan EPI SLWD 10X microscope lens.

[0069] Furthermore, when the first plasma mirror 1 moves out of the laser beam path, the target camera 8 takes a picture facing the direction of laser beam propagation, which can locate the accurate position of the focal spot, thereby assisting in locating the positions of the first plasma mirror 1 and the second plasma mirror 2, so that the laser beam falls exactly on the center line of the mirror surface of the first plasma mirror 1 and the second plasma mirror 2.

[0070] Furthermore, by capturing the intensity of the light spot at the target using a target-aiming camera, the exact contrast enhancement factor of the laser can be determined.

[0071] According to a preferred embodiment of the present invention, the device further includes a displacement stage 7, which is a platform capable of movement and / or rotation.

[0072] The first support 4, the second support 5 and / or the mirror-target support 6 are placed on the displacement stage 7. As the displacement stage 7 moves or rotates, the plasma mirror and the target are moved out of the laser light path by the displacement stage 7, so that the target-aiming camera 8 can help determine the focal spot position, laser light path and other information, thereby helping to locate the position of the first plasma mirror 1 and the second plasma mirror 2.

[0073] Furthermore, the displacement stage 7 also moves the first plasma mirror 1, the second plasma mirror 2, and the target holder 31 that are coupled together during the target firing process, so that the laser can strike multiple targets 3, thereby achieving high-frequency target firing.

[0074] Preferably, the displacement stage 7 is a five-dimensional displacement platform, such as the ASM25XY-RTV5 five-dimensional combined displacement stage, the APFP-XYZT five-dimensional displacement stage, etc.

[0075] On the other hand, the present invention also provides a method for obtaining ultra-high contrast laser beams during target firing.

[0076] The laser is focused and reflected by at least two plasma mirrors before hitting the target.

[0077] Furthermore, the laser is a laser with power of TW or higher, preferably a laser with power of PW, and more preferably, the laser beam is focused by an off-axis parabolic mirror.

[0078] Preferably, the surface flatness (PV) value of the plasma mirror is less than one-tenth of the laser wavelength.

[0079] Preferably, the centerline of the laser beam path forms a 45° angle with the surface of the first plasma mirror.

[0080] Preferably, the laser reflected by the first plasma mirror is vertically upward or vertically downward.

[0081] More preferably, the centerline of the laser beam irradiating the first plasma mirror is set horizontally, and the second plasma mirror reflects the laser beam reflected by the first plasma mirror back onto the horizontal surface.

[0082] Preferably, the first and second plasma mirrors are configured to be coated with anti-reflection films to achieve laser outputs with different contrast ratios.

[0083] Preferably, the laser triggers the plasma mirror within 3 ps before the pulse peak.

[0084] Preferably, the power density corresponding to the femtosecond laser is 10. 15 W / cm 2 ~10 16 W / cm 2 .

[0085] According to a preferred embodiment of the present invention, two plasma mirrors and a target holder for a fixed target are fixedly connected by a mirror-target support to achieve mirror-target coupling. During the target firing process, the mirror-target support is moved as a whole to achieve the attack on targets on multiple target holders or multiple targets on one target holder.

[0086] Preferably, the position of the focal spot is located by a target-aiming camera, thereby assisting in the positioning of the plasma mirror.

[0087] Specifically, the target camera will clearly image the surface with a shallow depth of field. The plasma mirror is moved out of the laser beam path, and the target camera takes pictures in the direction of laser beam propagation. Moving the target camera up and down and left and right can allow the laser to enter the camera. During the movement, the camera images a certain defocused surface. Moving the camera back and forth can clearly image surfaces with different depths of field. The size of the image spot is different at different camera positions. The point with the smallest image spot, that is, the focal point with the smallest spot size, is the focal spot of the incident laser. The position of this spot is the initial focal position of the incident laser.

[0088] Furthermore, based on the initial focal position of the laser and the defocusing of the plasma mirror, the position to be placed for the first plasma mirror can be obtained. The specific calculation method for obtaining the placement position of the plasma mirror is a conventional technique for those skilled in the art and will not be elaborated in this invention.

[0089] Furthermore, after the first plasma mirror is placed in the accurate position, the laser is reflected, and the position of the focal spot changes. The placement position of the second plasma mirror can be determined in the same way.

[0090] Furthermore, after placing the second plasma mirror in the accurate position, the target camera is moved to determine the new focal spot position of the laser, and the target is moved to that focal spot position.

[0091] In this invention, the target aiming method for obtaining ultra-high contrast laser is compatible with existing aiming devices, and can achieve target aiming using existing aiming devices and methods.

[0092] Furthermore, the target-shooting method for obtaining ultra-high contrast laser according to the present invention is compatible with existing laser detection devices, and can realize the detection of laser in the device of the present invention without designing or purchasing new laser detection devices.

[0093] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0094] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0095] The present invention has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present invention based on these embodiments, all of which fall within the scope of protection of the present invention.

Claims

1. A target-shooting device for obtaining ultra-high contrast laser, characterized in that, It includes a first plasma mirror (1), a second plasma mirror (2), and a target (3), eliminating the need for focusing and recollimating optical elements; The first plasma mirror (1) reflects the laser beam to the second plasma mirror (2), and the second plasma mirror (2) reflects the laser beam to the target (3). The mirror surface of the first plasma mirror (1) forms a 45° angle with the center line of the laser beam path; The laser reflected by the first plasma mirror (1) is vertically upward or vertically downward; The center line of the laser beam illuminating the first plasma mirror (1) is set horizontally, and the second plasma mirror (2) reflects the laser beam reflected by the first plasma mirror (1) back onto the horizontal surface; The first plasma mirror (1) is fixed on the first bracket (4), and the second plasma mirror (2) is fixed on the second bracket (5), so that the defocus positions of the first plasma mirror (1) and the second plasma mirror (2) are appropriate. The appropriate defocus position means that the laser can trigger the plasma mirror within 3ps before the pulse peak. The first plasma mirror (1) and the second plasma mirror (2) can be coated with anti-reflection film or not coated as needed. By combining the first plasma mirror (1) and the second plasma mirror (2) with different coating conditions, three different contrast laser outputs can be achieved.

2. The target-shooting device for obtaining ultra-high contrast laser according to claim 1, characterized in that, The laser beam irradiating the first plasma mirror (1) is a laser with a power of TW or higher.

3. The target-shooting device for obtaining ultra-high contrast laser according to claim 1 or 2, characterized in that, The device also has a target mount (31) and a mirror target support (6), wherein the target (3) is fixed on the target mount (31) and the target mount (31) is fixed on the mirror target support (6). The first bracket (4), the second bracket (5), and the target support (6) are fixedly connected.

4. The target-shooting device for obtaining ultra-high contrast laser according to claim 3, characterized in that, The device also includes a displacement stage (7), which is a platform capable of movement and / or rotation. The first support (4), the second support (5) and / or the target support (6) are placed on the displacement stage (7) and move or rotate with the displacement stage (7).

5. A method for obtaining ultra-high contrast laser beams during target firing, characterized in that, The laser is focused and reflected by at least two plasma mirrors before hitting the target, eliminating the need for focusing and collimating optical components; The first plasma mirror reflects the laser beam to the second plasma mirror, and the second plasma mirror reflects the laser beam to the target; The mirror surface of the first plasma mirror forms a 45° angle with the center line of the laser beam path; The laser reflected by the first plasma mirror is vertically upward or vertically downward; The centerline of the laser beam illuminating the first plasma mirror is set horizontally, and the second plasma mirror reflects the laser beam reflected by the first plasma mirror back onto the horizontal plane. The first plasma mirror is fixed on the first bracket, and the second plasma mirror is fixed on the second bracket, so that the defocus positions of the first and second plasma mirrors are appropriate. The appropriate defocus position means that the laser can trigger the plasma mirror within 3ps before the pulse peak. By determining whether the first and second plasma mirrors are coated with anti-reflection films, laser outputs with different contrast ratios can be achieved.

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