A KDP frequency doubling crystal structure

Abstract

The present invention discloses a KDP frequency doubling crystal structure, which includes a crystal fixing structure, a KDP crystal, a π polarization tube, and a σ polarization tube; the π polarized light with a central wavelength of 800 nm passes through the π polarization tube, enters the KDP crystal, and the KDP crystal doubles the π polarized light with a central wavelength of 800 nm into σ polarized light with a central wavelength of 400 nm, and finally outputs from the σ polarization tube. The inclined surfaces of the closed ends of the π polarization tube and the σ polarization tube are both designed with Brewster angles. The KDP crystal is placed in a vacuum closed cavity formed by the π polarization tube, the σ polarization tube, and the crystal fixing structure, eliminating the cumbersome process of crystal coating, avoiding the deliquescence of the KDP crystal in the air, and overcoming the problems that the coating layer of the existing KDP crystal is easily damaged by high-intensity fundamental frequency light, resulting in a short service life of the crystal, an increase in coating difficulty, and an improvement in coating technical requirements. The structure of the present invention is simple, can be obtained through simple mechanical processing, and has a low manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and particularly to a KDP frequency doubling crystal structure. Background Art

[0002] The chirped pulse amplification (CPA) technology for generating ultra-intense and ultra-short laser pulses is one of the most innovative and potential amplification technologies at present. Combined with the discovery of gain media with excellent performance, the laser peak power that can be achieved on a common optical platform has increased by 7 orders of magnitude in just a few years, and currently has reached the order of 10 PW (petawatt, 1 PW = 10 15 W). A CPA system with Nd:glass as the amplification medium has achieved a pulse output of 1.5 PW with a central wavelength of 1064 nm; a CPA system with Ti:sapphire (titanium-doped sapphire crystal) as the amplification medium has currently obtained 10 PW and has become the mainstream development direction of the current CPA amplification system. The pulse output of this amplification system has a central wavelength of 800 nm. Such a pulse with a peak power of the TW order (terawatt, 1 TW = 10 12 W) and a pulse width of the fs order (femtosecond, 1 fs = 10 -15 s) can generate a laser intensity that has exceeded 10 20 W / cm 2 ², and such ultra-intense pulses have extensive applications in high-order harmonic emission, obtaining ultra-high-density plasmas, generating ultrafast X-rays, inertial confinement fusion, miniaturized high-gradient particle accelerators, etc., providing a powerful means for obtaining these extreme conditions.

[0003] However, the output wavelength band of such ultra-intense pulses is generally in the infrared and near-infrared regions, and it is necessary to expand its frequency to the visible, and even the ultraviolet band. Currently, the most commonly used technology is to achieve wavelength down-conversion through a type of phase-matching frequency doubling method. Such a frequency-doubled ultra-short pulse can effectively reduce the background noise and pre-pulse amplitude, which is beneficial to more clearly understanding the physical essence of the interaction between the main pulse and matter. Since the group velocity mismatch coefficient of the crystal KDP is very small (83 fs / mm), and at the same time the acceptance angle is large (4 min / cm), and the acceptance bandwidth (1.6 nm / cm) is much larger than that of BBO crystals, LBO crystals, etc., it has thus become the preferred frequency doubling crystal for broadband high-intensity pulses. There is a serious group velocity mismatch between the fundamental wave and the frequency-doubled wave during the frequency doubling process of ultra-short pulses, which greatly limits the length of the frequency doubling crystal. Generally, the length is between 1 and 2 mm. To obtain a high conversion efficiency with such a short crystal, it is necessary to increase the intensity of the fundamental frequency light, and its intensity is generally greater than (100 GW / cm 2) Such a strong fundamental frequency light can easily cause damage to the coating layer, thereby affecting the service life of the KDP crystal. This poses very high requirements for the coating of the crystal. At the same time, since thin KDP is very prone to deliquescence in air, the crystal must be placed in a vacuum-sealed box, and the KDP is coated by sol-gel, which further increases the coating difficulty of the crystal.

[0004] Therefore, it is necessary to propose a new crystal design solution to address the drawbacks of the current KDP crystal coating layer being vulnerable to damage by high-intensity fundamental frequency light, resulting in a short service life of the crystal, increased coating difficulty, and higher coating technology requirements. Summary of the Invention

[0005] The object of the present invention is to provide a KDP frequency doubling crystal structure, which utilizes the characteristic that when linearly polarized light is incident at the Brewster angle in the P plane, there is theoretically no loss. The π polarization tube and the σ polarization tube are respectively used to design the vacuum sealing of the incident surface and the exit surface of the KDP crystal, replacing the existing crystal coating, and overcoming the problems that the existing KDP crystal coating layer is vulnerable to damage by high-intensity fundamental frequency light, resulting in a short service life of the crystal, increased coating difficulty, and higher coating technology requirements.

[0006] To achieve the above object, the present invention provides the following solution:

[0007] The present invention provides a KDP frequency doubling crystal structure, including:

[0008] Crystal fixing structure;

[0009] A KDP crystal, the KDP crystal is fixed on the crystal fixing structure, and the incident surface and the exit surface of the KDP crystal are respectively exposed on both sides of the crystal fixing structure; the KDP crystal is used to double the frequency of the π polarized laser with a central wavelength of 800 nm into a σ polarized laser with a central wavelength of 400 nm;

[0010] A π polarization tube, one end of the π polarization tube is open, and the other end is closed by a Brewster angle inclined plane, and a vacuum pumping port is provided on the tube wall of the π polarization tube; the open end of the π polarization tube is hermetically connected to one side of the crystal fixing structure to seal the incident surface of the KDP crystal; the π polarization tube can have high transmittance for the π polarized laser with a central wavelength of 800 nm;

[0011] A σ polarization tube, one end of the σ polarization tube is open, and the other end is closed by a Brewster angle inclined plane, and a vacuum pumping port is provided on the tube wall of the σ polarization tube; the open end of the σ polarization tube is hermetically connected to the other side of the crystal fixing structure to seal the exit surface of the KDP crystal; wherein, the Brewster angle inclined plane of the σ polarization tube is perpendicular to the Brewster angle inclined plane of the π polarization tube, and the σ polarization tube can have high transmittance for the σ polarized laser with a central wavelength of 400 nm;

[0012] A hollow clip, a cylindrical mounting hole is provided at the center of the hollow clip, a retaining ring for preventing the crystal from falling out is provided at one axial end of the cylindrical mounting hole, the cylindrical crystal is disposed in the cylindrical mounting hole, and one axial end of the cylindrical crystal abuts against the retaining ring, and the inner ring of the retaining ring is used to expose one of the incident surface and the exit surface;

[0013] A fixing member, the fixing member is connected to the other end of the cylindrical mounting hole and abuts against the other axial end of the cylindrical crystal to fix the cylindrical crystal in the cylindrical mounting hole; a hollow hole is provided at the center of the fixing member for exposing the other of the incident surface and the exit surface.

[0014] Optionally, the hollow clip is a cylindrical hollow clip, and the cylindrical mounting hole is coaxially arranged with the cylindrical hollow clip; a stepped ring protrudes radially outward in the middle of the cylindrical hollow clip, the open end of the π-polarization tube is sleeved on one end of the cylindrical hollow clip and is hermetically connected to one side end face of the stepped ring, and the open end of the σ-polarization tube is sleeved on the other end of the cylindrical hollow clip and is hermetically connected to the other side end face of the stepped ring.

[0015] Optionally, the open end of the π-polarization tube is adhesively sealed to one side end face of the stepped ring; the open end of the σ-polarization tube is adhesively sealed to the other side end face of the stepped ring.

[0016] Optionally, a plurality of through holes parallel to its axis are provided in the side wall of the cylindrical hollow clip, all the through holes are uniformly distributed along the circumferential direction of the cylindrical hollow clip, and both ends of any one of the through holes penetrate through both axial ends of the cylindrical hollow clip to realize the communication between the π-polarization tube and the σ-polarization tube.

[0017] Optionally, the fixing member is threadedly connected to the cylindrical mounting hole.

[0018] Optionally, both the π-polarization tube and the σ-polarization tube are cylindrical polarization tubes, and the cylindrical crystal, the π-polarization tube and the σ-polarization tube are coaxially arranged.

[0019] Optionally, both the π-polarization tube and the σ-polarization tube are quartz glass tubes; the angle between the Brewster angle inclined plane of the π-polarization tube and the axis of the π-polarization tube is 34.5°, and the angle between the Brewster angle inclined plane of the σ-polarization tube and the axis of the σ-polarization tube is 34.2°.

[0020] Optionally, a kind of phase matching angle of the cylindrical crystal is 43°42′, the cross-sectional diameter is 7 mm, and the axial length is 2 mm.

[0021] Optionally, the material of the crystal fixing structure is polytetrafluoroethylene.

[0022] The present invention has achieved the following technical effects compared with the prior art:

[0023] The present invention provides a high-power KDP frequency doubling crystal structure. The π-polarized light with a central wavelength of 800 nm passes through a π-polarized tube and then enters a KDP crystal. The KDP crystal doubles the π-polarized light with a central wavelength of 800 nm into σ-polarized light with a central wavelength of 400 nm, and finally outputs from the σ-polarized tube. The inclined planes of the closed ends of the π-polarized tube and the σ-polarized tube are both designed with Brewster angles. The KDP crystal is placed in a vacuum-sealed cavity formed by enclosing the π-polarized tube, the σ-polarized tube, and the crystal fixing structure, eliminating the cumbersome process of crystal coating and avoiding the deliquescence of the KDP crystal in the air. It overcomes the problems that the coating layer of the existing KDP crystal is vulnerable to damage by high-intensity fundamental frequency light, resulting in a short service life of the crystal, an increase in coating difficulty, and a higher requirement for coating technology. The components in the entire crystal structure, such as the π-polarized tube, the σ-polarized tube, and the crystal fixing structure, have simple structures and can be obtained through simple mechanical processing, with low manufacturing costs.

[0024] The KDP frequency doubling crystal structure proposed by the present invention can be used efficiently for a long time, providing a feasible new technical approach for obtaining a KDP crystal with a high damage threshold under high-power frequency doubling, and having strong practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0026] Figure 1 It is a schematic exploded view of the KDP frequency doubling crystal structure disclosed in the embodiments of the present invention;

[0027] Figure 2 It is a schematic overall structure view of the KDP frequency doubling crystal structure disclosed in the embodiments of the present invention;

[0028] Figure 3 It is a ray tracing diagram simulated by using TracePro software disclosed in the embodiments of the present invention;

[0029] Figure 4 It is a schematic diagram of π-polarized laser incident on a π-polarized tube simulated by using TracePro software disclosed in the embodiments of the present invention;

[0030] Figure 5The polarization analysis diagram of the laser emitted from the π polarization tube for the π polarized laser disclosed in the embodiment of the present invention;

[0031] Figure 6 The schematic diagram of the σ polarized laser incident on the σ polarization tube simulated by TracePro software disclosed in the embodiment of the present invention;

[0032] Figure 7 The polarization analysis diagram of the laser emitted from the σ polarization tube for the σ polarized laser disclosed in the embodiment of the present invention.

[0033] Among them, the reference numerals are:

[0034] 100, KDP frequency doubling crystal structure;

[0035] 1, crystal fixing structure; 11, hollow clamp; 12, cylindrical mounting hole; 13, fixing member; 14, hollow hole; 15, stepped ring; 16, through hole; 17, retaining ring; 2, KDP crystal; 3, π polarization tube; 4, Brewster angle inclined plane; 5, vacuum pumping port; 6, σ polarization tube. Specific embodiments

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] One of the purposes of the present invention is to provide a KDP frequency doubling crystal structure, which utilizes the characteristic that when linearly polarized light is incident at the Brewster angle in the π plane, there is theoretically no loss, and uses a π polarization tube and a σ polarization tube to respectively perform vacuum sealing design on the incident surface and the exit surface of the KDP crystal, replacing the existing crystal coating, and overcoming the problems that the coating layer of the existing crystal KDP is easily damaged by high-intensity fundamental frequency light, resulting in a short service life of the crystal, an increase in coating difficulty, and an improvement in coating technical requirements.

[0038] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] Embodiment 1

[0040] As Figures 1 to 2As shown in the figure, this embodiment provides a KDP frequency doubling crystal structure 100, which mainly includes a crystal fixing structure 1, a KDP crystal 2, a π polarization tube 3, and a σ polarization tube 6. The KDP crystal 2 is fixed on the crystal fixing structure 1, and the incident surface and the exit surface of the KDP crystal 2 are respectively exposed on both sides of the crystal fixing structure 1. The first type phase matching angle of the KDP crystal 2 is 43°42′, which is used to double the frequency of the π polarization laser with a central wavelength of 800 nm into a σ polarization laser with a central wavelength of 400 nm. One end of the π polarization tube 3 is open, and the other end is closed by a Brewster angle inclined plane 4. A vacuum pumping port 5 is arranged on the tube wall of the π polarization tube 3. The open end of the π polarization tube 3 is hermetically connected to one side of the crystal fixing structure 1 to hermetically seal the incident surface of the KDP crystal 2. The π polarization tube 3 is the part of the 800 nm fundamental frequency light entering end, and its Brewster angle inclined plane 4 is the incident surface of the π polarization tube 3, which can make the fundamental frequency light with a central wavelength of 800 nm be P polarization relative to this incident surface, so as to have high transmittance for the π polarization laser with a central wavelength of 800 nm. One end of the σ polarization tube 6 is open, and the other end is closed by a Brewster angle inclined plane 4. A vacuum pumping port 5 is arranged on the tube wall of the σ polarization tube 6. The open end of the σ polarization tube 6 is hermetically connected to the other side of the crystal fixing structure 1 to hermetically seal the exit surface of the KDP crystal 2. Among them, the Brewster angle inclined plane 4 of the σ polarization tube 6 is perpendicular to the Brewster angle inclined plane 4 of the π polarization tube 3. The σ polarization tube 6 is the part of the 800 nm fundamental frequency light after frequency doubling and exiting end, and its Brewster angle inclined plane 4 is the exit surface of the σ polarization tube 6, which can make the σ polarization light with a central wavelength of 400 nm be P polarization relative to this exit surface, so as to have high transmittance for the σ polarization laser with a central wavelength of 400 nm. The above KDP frequency doubling crystal structure 100 relates to a design method of a high damage threshold frequency doubling crystal under the first type phase matching for ultra-strong and ultra-short pulses: different from the crystal coating technology, it mainly uses the characteristic that when linearly polarized light is incident at the Brewster angle in the π plane, there is theoretically no loss to conduct a sealing design for the incident and exit surfaces of the crystal. The π polarization laser with a central wavelength of 800 nm is incident on the π polarization tube, and the Brewster angle is used to replace the high-transmission dielectric film to achieve high transmittance for the laser with a central wavelength of 800 nm. The transmitted laser is incident on the KDP crystal 2 to double the frequency of the π polarization laser with a central wavelength of 800 nm into a σ polarization laser with a central wavelength of 400 nm, and finally is efficiently output from the Brewster angle σ polarization tube. This KDP frequency doubling crystal structure 100 proposes a new crystal design scheme for the current deficiencies of KDP crystals, such as being prone to deliquescence, difficult coating, high technical requirements, and short service life. It omits the complicated procedures of crystal coating and only involves simple mechanical processing to form a π polarization tube and a σ polarization tube with Brewster angle inclined planes, and then a high-efficiency KDP frequency doubling crystal beneficial for long-term use can be obtained, providing a feasible new technical approach for obtaining a KDP crystal with a high damage threshold under high-power frequency doubling.

[0041] In this embodiment, the KDP crystal 2 is preferably a cylindrical crystal, and its incident surface and exit surface are respectively located at both axial ends of the cylindrical crystal.

[0042] In this embodiment, based on the above-mentioned cylindrical KDP crystal 2, the crystal fixing structure is specifically arranged to include a hollow clamp 11 and a fixing member 13, as Figure 1 shown. A cylindrical mounting hole 12 is provided at the center of the hollow clamp 11. A retaining ring 17 for preventing the crystal from slipping out is provided at one axial end of the cylindrical mounting hole 12. The cylindrical crystal is arranged in the cylindrical mounting hole 12, and one axial end of the cylindrical crystal abuts against the retaining ring 17. The inner ring of the retaining ring 17 is used to expose one of the incident surface and the exit surface; the fixing member 13 is connected to the other end of the cylindrical mounting hole 12 and abuts against the other axial end of the cylindrical crystal to fix the cylindrical crystal in the cylindrical mounting hole 12; a hollow hole 14 is provided at the center of the fixing member 13 for exposing the other of the incident surface and the exit surface. In this specific embodiment, it is preferred that the exit surface of the cylindrical KDP crystal 2 abuts against the retaining ring 17, and the incident surface abuts against the fixing member 13. The inner rings of the above-mentioned retaining ring 7, retaining ring 17, and the hollow hole 14 are all circular structures, and it is preferred that the inner rings of the above-mentioned retaining ring 7, retaining ring 17, the hollow hole 14, and the cylindrical KDP crystal 2 are coaxially arranged.

[0043] In this embodiment, the above-mentioned hollow clamp 11 is a cylindrical hollow clamp, that is, the outer shape structure of the hollow clamp 11 is cylindrical, and the cylindrical mounting hole 12 is coaxially arranged with the cylindrical hollow clamp. A stepped ring 15 protrudes radially outward at the middle position of the outer wall of the cylindrical hollow clamp 11, as Figure 2 shown. The open end of the π polarization tube 3 is sleeved on one end of the cylindrical hollow clamp and is hermetically connected to one side end face of the stepped ring 15. The open end of the σ polarization tube 6 is sleeved on the other end of the cylindrical hollow clamp and is hermetically connected to the other side end face of the stepped ring 15. Thus, it can be seen that the incident surface of the KDP crystal 2 is sealed in the vacuum tight space enclosed by the π polarization tube 3 and the cylindrical hollow clamp, and the exit surface is sealed in the vacuum tight space enclosed by the σ polarization tube 6 and the cylindrical hollow clamp. In actual use, by evacuating the vacuum tight space enclosed by the π polarization tube 3 and the cylindrical hollow clamp and the vacuum tight space enclosed by the σ polarization tube 6 and the cylindrical hollow clamp to an appropriate vacuum degree through the vacuum port 5, it can be ensured that the KDP crystal 2 is enclosed in this vacuum tight environment, and the KDP crystal 2 can be effectively prevented from deliquescing.

[0044] In this embodiment, the open end of the π polarization tube 3 is adhesively sealed to one side end face of the stepped ring 15; similarly, the open end of the σ polarization tube 6 is adhesively sealed to the other side end face of the stepped ring 15.

[0045] In this embodiment, the vacuum-sealed space formed by the π-polarization tube 3 and the cylindrical hollow clamp and the vacuum-sealed space formed by the σ-polarization tube 6 and the cylindrical hollow clamp can be isolated from each other or communicated with each other. As a preferred solution, in this embodiment, a plurality of through holes 16 parallel to the axis of the hollow clamp are opened in the side wall of the cylindrical hollow clamp, as Figure 1 shown. All the through holes 16 are evenly distributed along the circumferential direction of the cylindrical hollow clamp 11, and both ends of any through hole 16 penetrate through the axial two ends of the cylindrical hollow clamp 11, so as to realize the communication inside the π-polarization tube 3 and the σ-polarization tube 6. Thus, the incident surface and the exit surface of the KDP crystal 2 are equivalent to being located in the same vacuum-sealed space.

[0046] In this embodiment, the fixing member 13 is preferably cylindrical, and preferably threadedly connected to the cylindrical mounting hole 12, which is convenient for disassembly and assembly and has a reliable connection.

[0047] In this embodiment, the above-mentioned π-polarization tube 3 and σ-polarization tube 6 are both preferably cylindrical polarization tubes, and the cylindrical KDP crystal 2, π-polarization tube 3 and σ-polarization tube 6 are coaxially arranged. In actual operation, the π-polarization tube 3 and the σ-polarization tube 6 are both preferably quartz glass tubes. The refractive index of quartz glass for the laser with a central wavelength of 800 nm is 1.453371, and the Brewster angle is 55.5°. In order to meet this Brewster angle, the Brewster angle inclined plane 4 of the π-polarization tube 3 needs to be set at an angle of 34.5° with respect to the axis of the π-polarization tube 3, that is, 90° - 55.5°; correspondingly, the refractive index of quartz glass for the laser with a central wavelength of 400 nm is 1.46968, and the Brewster angle is 55.8°. In order to meet this Brewster angle, the Brewster angle inclined plane 4 of the σ-polarization tube 6 needs to be set at an angle of 34.2° with respect to the axis of the σ-polarization tube 6, that is, 90° - 55.8°.

[0048] In this embodiment, the material of the above-mentioned crystal fixing structure 1 is polytetrafluoroethylene, that is, the aforementioned fixing member 13 and the hollow clamp 11 are both polytetrafluoroethylene, and the retaining ring 17 and the stepped ring 15 are both preferably integrally formed with the hollow clamp 11. In actual operation, the cross-sectional diameter Φ of the cylindrical crystal is preferably 7 mm. Correspondingly, the inner diameter of the retaining ring 17 and the diameter of the hollow hole 14 are both preferably 7 mm or slightly less than 7 mm; the axial length of the cylindrical crystal, that is, the crystal thickness, is preferably 2 mm. This thickness ensures the maximum conversion efficiency under the condition of group velocity non-mismatch. The corresponding effective aperture of the above-mentioned cylindrical crystal is 5 mm, which can support the frequency doubling of CPA laser with a frequency above 50 fs.

[0049] Next, in combination with the structural design of the above-mentioned KDP frequency doubling crystal structure 100, its installation method and working principle will be specifically described.

[0050] The installation method of the KDP frequency doubling crystal structure 100 is as follows: First, place the KDP crystal 2 into the cylindrical installation hole 12 of the hollow clamp 11, and press the KDP crystal 2 with the fixing member 13; then, put the π polarization tube 3 on the left side of the hollow clamp 11, and the σ polarization tube 6 on the right side of the hollow clamp 11, and ensure that the Brewster angle inclined surface 4 of the π polarization tube 3 is perpendicular to the Brewster angle inclined surface 4 of the σ polarization tube 6. After assembly, use sealant to tightly bond and seal the docking part of the π polarization tube 3 and the stepped ring 15 and the docking part of the σ polarization tube 6 and the stepped ring 15; finally, evacuate the inside of the π polarization tube 3 and the σ polarization tube 6 through the vacuum port 5 on the π polarization tube 3 or the σ polarization tube 6, or evacuate the inside of the π polarization tube 3 and the σ polarization tube 6 simultaneously through the vacuum ports 5 on the π polarization tube 3 and the σ polarization tube 6. After the vacuum degree meets the standard, stop evacuating, and block the vacuum ports 5 on the π polarization tube 3 and the σ polarization tube 6 with structures such as rubber plugs, then a finished KDP frequency doubling transistor device, that is, the KDP frequency doubling crystal structure 100, is obtained.

[0051] The application principle of the KDP frequency doubling crystal structure 100 in this embodiment will be described in detail below with specific examples.

[0052] During use, the π polarized laser with a central wavelength of 800 nm is incident on the Brewster angle inclined surface 4 of the π polarization tube 3. Using the Brewster angle to replace the high-transmission dielectric film, high transmission of the laser with a central wavelength of 800 nm is achieved. The transmitted laser is incident on the KDP crystal 2, and the KDP crystal 2 doubles the π polarized laser with a central wavelength of 800 nm into a σ polarized laser with a central wavelength of 400 nm, and finally outputs efficiently from the Brewster angle inclined surface 4 of the σ polarization tube 6.

[0053] In optical experiments, the numerical simulation technology of computers has been widely used. Optical simulation experiments can describe abstract and difficult optical concepts and laws in the form of images through the simulation interface. Professional optical design software has more powerful simulation functions and can provide more intuitive and realistic simulation effects. TracePro is a non-sequential ray tracing software based on the Monte Carlo method, developed by Lambda Research Corporation in the United States, and is commonly used in lighting systems, optical analysis, radiation analysis, and photometric analysis. TracePro has the ability to handle complex geometric problems, can define and trace millions of rays, constructs the optical path system with solid objects, and simulates the interaction between rays and solid surfaces by calculating behaviors such as reflection, refraction, absorption, and diffraction, and can calculate and display real scenes.

[0054] In this embodiment, use the Solidworks mechanical drawing software to establish the assembly drawing of the KDP frequency doubling crystal structure 100, asFigure 2 As shown. Next, the assembly drawing is imported into TracePro software. The materials of the π-polarization tube 3 and the σ-polarization tube 6 are defined as fused quartz. The refractive indices of the π-polarization tube 3 and the σ-polarization tube 6 are 1.453371 and 1.46968 respectively, and the absorption loss is zero. The incident light source is parallel natural light with a wavelength of 800 nm, and the total number of rays is 1000. The σ-polarized light is reflected by the π-polarizer, so as to ensure that the light incident on the Brewster angle inclined plane 4 of the π-polarization tube 3 is all π-polarized light with a central wavelength of 800 nm, as Figure 3 shown. Figure 4 and Figure 6 are the ray tracing diagrams of the π-polarization tube 3 and the σ-polarization tube 6 respectively. From the light polarization analysis diagrams of Figure 5 and Figure 7 , the polarization state of the light when it is incident on the observation surface can be known. Figure 5 and Figure 7 are π-polarization and σ-polarization respectively.

[0055] It can be seen that the design method of the high-damage-threshold frequency-doubling crystal KDP under the above-mentioned phase matching proposed by this technical solution is to pass the π-polarized light (polarized laser) with a central wavelength of 800 nm through the π-polarization tube 3, and then enter the KDP frequency-doubling crystal to double the π-polarized light with a central wavelength of 800 nm into σ-polarized light (polarized laser) with a central wavelength of 400 nm, and finally output from the σ-polarization tube. The closed-end inclined planes of the π-polarization tube and the σ-polarization tube adopt the Brewster angle design. The KDP crystal is placed in the vacuum sealed tube cavity formed by the π-polarization tube, the σ-polarization tube and the hollow clamp 11, which omits the complicated process of crystal coating and also avoids the deliquescence of the KDP crystal in the air. The whole device only involves simple mechanical processing, and a high-efficiency KDP frequency-doubling crystal structure beneficial to long-term use can be obtained, providing a feasible new technical approach for obtaining a KDP crystal with a high damage threshold under high-power frequency doubling.

[0056] It should be noted that for those skilled in the art, obviously, the present invention is not limited to the details of the above-mentioned exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0057] In the present invention, specific examples are used to illustrate the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A KDP frequency doubling crystal structure, characterized in that, It includes a crystal fixing structure, a KDP crystal, a π polarization tube, and a σ polarization tube, where: The KDP crystal is fixed on the crystal fixing structure. The KDP crystal is a cylindrical crystal, and the incident surface and the exit surface of the KDP crystal are respectively located at the two axial ends of the cylindrical crystal. The KDP crystal is used to double-frequency the π polarization laser with a central wavelength of 800 nm into a σ polarization laser with a central wavelength of 400 nm. The crystal fixing structure includes a hollow clamp and a fixing member. A cylindrical mounting hole is provided at the center of the hollow clamp. A retaining ring for preventing the crystal from coming out is provided at one axial end of the cylindrical mounting hole. The cylindrical crystal is arranged in the cylindrical mounting hole, and one axial end of the cylindrical crystal abuts against the retaining ring. The inner ring of the retaining ring is used to expose one of the incident surface and the exit surface. The fixing member is connected to the other end of the cylindrical mounting hole and abuts against the other axial end of the cylindrical crystal to fix the cylindrical crystal in the cylindrical mounting hole. A hollow hole is provided at the center of the fixing member for exposing the other of the incident surface and the exit surface. One end of the π polarization tube is open, and the other end is closed by a Brewster angle inclined plane. A vacuum pumping port is provided on the tube wall of the π polarization tube. The open end of the π polarization tube is hermetically connected to one side of the crystal fixing structure to seal the incident surface of the KDP crystal. The π polarization tube can highly transmit the π polarization laser with a central wavelength of 800 nm. A σ polarization tube. One end of the σ polarization tube is open, and the other end is closed by a Brewster angle inclined plane. A vacuum pumping port is provided on the tube wall of the σ polarization tube. The open end of the σ polarization tube is hermetically connected to the other side of the crystal fixing structure to seal the exit surface of the KDP crystal. Among them, the Brewster angle inclined plane of the σ polarization tube is perpendicular to the Brewster angle inclined plane of the π polarization tube, and the σ polarization tube can highly transmit the σ polarization laser with a central wavelength of 400 nm.

2. The KDP frequency doubling crystal structure according to claim 1, wherein The hollow clamp is a cylindrical hollow clamp, and the cylindrical mounting hole is coaxially arranged with the cylindrical hollow clamp. A stepped ring protrudes radially outward in the middle of the cylindrical hollow clamp. The open end of the π polarization tube is sleeved on one end of the cylindrical hollow clamp and is hermetically connected to one end face of the stepped ring. The open end of the σ polarization tube is sleeved on the other end of the cylindrical hollow clamp and is hermetically connected to the other end face of the stepped ring.

3. The KDP frequency doubling crystal structure according to claim 2, wherein, The open end of the π polarization tube is adhesively sealed to one end face of the stepped ring; the open end of the σ polarization tube is adhesively sealed to the other end face of the stepped ring.

4. The KDP frequency doubling crystal structure according to claim 2, characterized in that, A plurality of through holes parallel to its axis are provided in the side wall of the cylindrical hollow clamp. All the through holes are evenly distributed along the circumferential direction of the cylindrical hollow clamp, and both ends of any one of the through holes penetrate through the two axial ends of the cylindrical hollow clamp to realize the communication between the π polarization tube and the σ polarization tube.

5. The KDP frequency doubling crystal structure according to any one of claims 1 to 4, characterized in that, The fixing member is threadedly connected to the cylindrical mounting hole.

6. The KDP frequency doubling crystal structure according to any one of claims 1 to 4, characterized in that Both the π-polarization tube and the σ-polarization tube are cylindrical polarization tubes, and the cylindrical crystal, the π-polarization tube, and the σ-polarization tube are coaxially arranged.

7. The KDP frequency doubling crystal structure according to claim 6, characterized in that, Both the π-polarization tube and the σ-polarization tube are quartz glass tubes; the angle between the Brewster angle inclined plane of the π-polarization tube and the axis of the π-polarization tube is 34.5°, and the angle between the Brewster angle inclined plane of the σ-polarization tube and the axis of the σ-polarization tube is 34.2°.

8. The KDP frequency doubling crystal structure according to claim 6, characterized in that, One type of phase matching angle of the cylindrical crystal is 43°42′, the cross-sectional diameter is 7 mm, and the axial length is 2 mm.

9. The KDP frequency doubling crystal structure according to any one of claims 1 to 4, characterized in that, The material of the crystal fixing structure is polytetrafluoroethylene.

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