Laser and resonant cavity design method

Abstract

The invention relates to the technical field of laser, and discloses a laser and a resonant cavity design method.The laser comprises a resonant cavity, the resonant cavity comprises an upper supporting arm and a lower supporting arm which are arranged in parallel, and a prism assembly is arranged between the upper supporting arm and the lower supporting arm; the upper support arm comprises a total reflection mirror, a gain module and a polaroid, the gain module is arranged close to the total reflection mirror, and the polaroid is arranged in the emergent direction of the total reflection mirror; the prism assembly comprises a first multi-face reflecting prism arranged in the emitting direction of the polaroid and a second multi-face reflecting prism forming reflection matching with the first multi-face reflecting prism. The lower support arm comprises a lambda / 4 wave plate, a Q-switched crystal, an optical wedge and an output mirror which are sequentially arranged from the incident end to the emergent end; according to the invention, the problem that the pulse width of a large-energy pulse laser of more than 120mJ is small is solved, and the mechanical length of the laser is still maintained in a small range.

Description

Technical Field

[0001] The present application relates to the field of laser technology, and in particular to a laser and a resonant cavity design method. Background Art

[0002] Laser light finder is an important component of laser semi-active homing guided weapon system, and the core component of laser light finder is pulse solid laser. For this laser, the main technical route at home and abroad is to use LD pumped Nd:YAG crystal electro-optical Q-switching technology to achieve pulsed laser output of a certain energy, which belongs to all-solid-state laser. Different specific design methods are derived according to different crystal shapes, different pumping methods and whether amplification is used. Different design schemes are suitable for different carrying platforms and have their own advantages and disadvantages.

[0003] For the design of high-energy (here, laser energy greater than 120mJ is defined as high energy) pulsed lasers, the most feasible solution in theory and engineering is to adopt the MOPA (master oscillator power amplifier) ​​design solution, which usually designs the oscillation level to be 50~80mJ laser output, and then amplifies it to more than 120mJ through one or more stages. This solution can take into account three indicators such as laser energy, beam quality and laser pulse width, and can simultaneously achieve laser parameters such as laser energy greater than 120mJ, small laser beam divergence and pulse width maintained at 15ns±5ns. However, due to the increase in the amplification stage, this solution does not have an advantage in laser volume, and increases hardware costs. In some occasions with strict requirements on volume, weight and cost, there are application limitations. Therefore, scientific research engineers usually use another technical route, using LD side-pump crystal rods or side-pump slab crystals, to directly output energy output of more than 120mJ without amplification. This solution can save the LD pump module and other devices in the amplification stage, and has cost advantages. However, this solution has an obvious flaw: the laser pulse width is relatively small, usually in the range of 5ns~8ns, which strictly speaking does not meet the 15ns±5ns required for laser guidance. The laser pulse width is an important indicator in the laser terminal guidance process. The laser spot tracker on the laser-guided missile or artillery seeker generally uses a four-quadrant detector to detect the return light signal, and its detection response rising edge is usually around 10ns. Therefore, the laser pulse width needs to be designed to be within the range of 15ns±sns, that is, it needs to be greater than 10ns, to ensure that each pulse laser can be detected. If the pulse width is too small, there is a certain probability that the seeker will lose the code, and the laser cannot be detected by the seeker under certain codes. It can be seen that a small laser pulse width not only affects the accuracy of laser guidance, but is also likely to cause off-target phenomena and fail to accurately hit the target.

[0004] The main reason why the pulse width is too small due to the above-mentioned technical route is that: with the increasing requirements for miniaturization of the laser light meter, the overall unit is generally limited to a length of 200mm~300m or less, which limits the size of the laser. The conventional solution is to use a right-angle prism or a corner cone prism to fold once or twice to form a U-shaped cavity to increase the physical cavity length, but the cavity length is still limited and can usually only be controlled within 30mm. According to the theoretical calculation of the pulse width expression derived from the Degnan electro-optical Q-switching classical physical model, the pulse width is inversely proportional to the intracavity gain. The greater the gain, the smaller the pulse width; and it is proportional to the transit time of the photons in the cavity, and the transit time depends on the actual physical cavity length of the resonant cavity. The larger the cavity length, the larger the pulse width. The length of the conventional U-shaped folded cavity is about 300mm. For a laser light meter of the order of 80mJ, the pulse width can still be maintained above 10ns. However, for a laser light meter of more than 120mJ, when the LD pump energy increases, the intracavity gain increases, and the pulse width decreases accordingly, and it is impossible to achieve a pulse width greater than 10ns. At this time, to increase the pulse width, in theory, the volume of the crystal rod can be increased (such as using a crystal rod with a larger diameter), but this method increases the mode volume, which is not conducive to the subsequent beam expansion of the laser light meter and will increase the volume of the beam expander. Therefore, the pulse width can only be increased by increasing the physical cavity length of the resonant cavity. At present, one or two folds of the length of the U-shaped folded cavity are still not enough to widen the pulse width to more than 10ns when the energy is greater than 120mJ. Summary of the invention

[0005] The purpose of the present application is to provide a laser and a resonant cavity design method that solves the problem of small pulse width of high-energy pulse lasers above 120mJ, while maintaining the mechanical length of the laser within a relatively small range.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A laser of the present invention comprises a resonant cavity, wherein the resonant cavity comprises an upper arm and a lower arm arranged in parallel, and a prism assembly is arranged between the upper arm and the lower arm; The upper arm includes a total reflection mirror, a gain module and a polarizer, wherein the gain module is arranged close to the total reflection mirror, and the polarizer is arranged in the emission direction of the total reflection mirror; The prism assembly includes a first multi-faceted reflecting prism arranged in the emitting direction of the polarizer, and a second multi-faceted reflecting prism forming a reflection match with the first multi-faceted reflecting prism; The lower arm comprises a λ / 4 wave plate, a Q-switched crystal, an optical wedge and an output mirror which are arranged in sequence from the incident end to the output end.

[0007] Furthermore, the first multi-faceted reflecting prism includes a first reflecting surface M 1 , the second reflecting surface M 2 and the third reflecting surface M 3, the first reflecting surface M 1 , the second reflecting surface M 2 and the third reflecting surface M 3 From top to bottom, the first reflecting surface M 1 The angle between the second reflecting surface M and the horizontal direction is 38°. 2 The angle between the third reflecting surface M and the horizontal direction is 73°. 3 The angle between the first reflecting surface M and the horizontal direction is 104°. 1 The second reflecting surface M 2 The angle between the second reflecting surface M and the 2 With the third reflecting surface M 3 The angle is 177°; The second multi-faceted reflecting prism includes a fourth reflecting surface M 4 and the fifth reflecting surface M 5 , the fourth reflecting surface M 4 and the fifth reflecting surface M 5 From top to bottom, the angle between the fourth reflecting surface M4 and the horizontal direction is 50°, and the fifth reflecting surface M 5 The angle between the fourth reflecting surface M and the horizontal direction is 133°. 4 With the fifth reflecting surface M 5 The angle is 177°.

[0008] Furthermore, the first reflecting surface M 1 The size of the second reflective surface M is 10 mm × 10 mm. 2 The size of the third reflective surface M is 12 mm × 10 mm. 3 The size of the fourth reflective surface M is 16 mm × 10 mm. 4 The size of the fifth reflective surface M is 10 mm × 10 mm. 5 The size is 12mm×10mm.

[0009] Furthermore, a spot correction cylindrical mirror is movably arranged between the polarizer and the prism assembly.

[0010] Furthermore, the first multi-faceted reflecting prism and the second multi-faceted reflecting prism are both integrated prisms.

[0011] Furthermore, the gain module includes two first Nd:YAG crystal rods arranged between the total reflection mirror and the polarizer, the two first Nd:YAG crystal rods are arranged in parallel along the optical path direction, the two first Nd:YAG crystal rods are respectively provided with a first LD pump source module, and the two first LD pump source modules are respectively located on both sides of the corresponding first Nd:YAG crystal away from each other.

[0012] Furthermore, the gain module includes a Nd:YAG slab crystal arranged between the total reflection mirror and the polarizer, and a second LD pump source module arranged above the Nd:YAG slab crystal, and the Nd:YAG slab crystal is a trapezoidal table with an upper end area larger than a lower end area.

[0013] Furthermore, the gain module includes a second Nd:YAG crystal rod arranged between the total reflection mirror and the polarizer, and a coupling mirror group arranged at the incident end of the total reflection mirror, and a third LD pump module is arranged at the incident end of the coupling mirror group.

[0014] A resonant cavity design method, according to the requirement of sufficient space between the incident light path 1 and the outgoing light path 6, an upper arm and a lower arm are arranged; According to the horizontal incidence of the incident light path 1 and the horizontal emission of the outgoing light path 6, the first reflecting surface M of the first multi-faceted reflecting prism in the prism assembly is designed. 1 , the second reflecting surface M 2 , the third reflecting surface M 3 The angle of the fourth reflecting surface M of the second multi-faceted reflecting prism 4 and the fifth reflecting surface M 5 Angle The upper arm horizontal incident light path enters the second reflection surface M 2 ; Through the second reflecting surface M 2 Reflect the light path 2 to the fourth reflection surface M 4 , the angle between the optical path 2 and the optical path 1 is 34°, and the second reflection surface M 2 The angle with the horizontal direction is 73°; Through the fourth reflecting surface M 4 Reflect the light path three to the first reflection surface M 1 , the angle between optical path 3 and optical path 2 is 12°, and the fourth reflection surface M 4 The angle with the horizontal direction is 50°; Through the first reflecting surface M 1 Reflect the light path 4 to the fifth reflecting surface M 5 , the angle between optical path 4 and optical path 3 is 12°, the first reflection surface M 1 The angle with the horizontal direction is 38°, and the first reflecting surface M 1 With the second reflecting surface M 2 The angle is 145°; Through the fifth reflecting surface M 5 Reflect the light path five times to the third reflecting surface M 3 The angle between the optical path 5 and the optical path 4 is 30°, and the fifth reflecting surface M 5 The angle with the horizontal direction is 133°, and the fifth reflecting surface M 5With the fourth reflecting surface M 4 The angle is 177°; Through the third reflecting surface M 3 The light path 6 is emitted horizontally to the lower arm, and the angle between the light path 6 and the light path 5 is 28°. 3 The angle with the horizontal direction is 104°, and the third reflecting surface M 3 With the second reflecting surface M 2 The angle is 177°; Design the spatial dimensions of the prism assembly based on the outer envelope dimensions of the laser energy and the volume of the entire laser; According to the spatial size of the prism assembly, the distance between the first multi-faceted reflecting prism and the second multi-faceted reflecting prism in two directions is designed; According to the distance between the first multi-faceted reflecting prism and the second multi-faceted reflecting prism in two directions, the first reflecting surface M of the first multi-faceted reflecting prism in the prism assembly is designed. 1 , the second reflecting surface M 2 , the third reflecting surface M 3 The size of the fourth reflecting surface M of the second multi-faceted reflecting prism 4 and the fifth reflecting surface M 5 The size of the prism assembly is such that the total optical path of the optical path in the prism assembly is greater than or equal to 300 mm; The spatial dimensions of the prism assembly are 55 mm × 55 mm, and the first reflecting surface M 1 The size of the second reflective surface M is 10mm×10mm. 2 The size of the third reflective surface M is 12mm×10mm. 3 The size of the fourth reflective surface M is 16mm×10mm. 4 The size of the fifth reflective surface M is 10 mm × 10 mm. 5 The size is 12mm×10mm.

[0015] Furthermore, a spot correction cylindrical mirror is arranged between the polarizer and the prism assembly to reshape the elliptical spot deformed after reflection back into a nearly circular shape; The major axis size of the elliptical spot deformed by the angle between the optical paths is calculated by the angle between the optical paths greater than 20°; According to the size of the major axis of the elliptical spot, the curvature radius of the spot correction cylindrical mirror is calculated; The output light spot is fine-tuned by moving the spot correction cylindrical mirror so that the output light spot remains as circular as possible.

[0016] Compared with the prior art, the beneficial effects of this application are: 1. Through two reflective prisms designed with precise angles, five optical path foldings are achieved, and the physical cavity length of the resonant cavity is expanded to more than 500mm within the mechanical length of the laser of 200m. Compared with the conventional U-shaped folded cavity, the pulse width is greatly improved; 2. The first multi-faceted reflecting prism and the second multi-faceted reflecting prism are designed as multi-mirror integrated prisms. Multiple reflecting surfaces are designed on the same prism. Compared with the conventional reflection optical path constructed by multiple plane reflecting mirrors, the reflection optical path is more stable, and the error of each reflecting mirror surface is controlled within a smaller error range (can reach the arc second level) by prism processing, which greatly reduces the error caused by manual debugging of the optical path and is more conducive to laser debugging; 3. A spot correction cylindrical mirror is inserted into the cavity. The radius of curvature matches the deformation of the spot produced by the large incident angle of each mirror surface of the reflecting prism assembly in the direction perpendicular to the optical path, thereby compensating and correcting the spot, so that the laser mode in the cavity maintains high beam quality oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the implementation methods of the present application, the drawings required for use in the implementation methods will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 is a schematic diagram of a resonant cavity according to the first embodiment of the present application; Figure 2 is a schematic diagram of the resonant cavity structure of the first embodiment of the present application; Figure 3 is a schematic diagram of a resonant cavity according to the second embodiment of the present application; Figure 4 is a schematic diagram of the resonant cavity structure of the second embodiment of the present application; Figure 5 is a schematic diagram of the resonant cavity of the third embodiment of the present application; Figure 6 is a schematic diagram of the resonant cavity structure of the third embodiment of the present application; Figure 7 is a schematic diagram of geometric parameter design of the first multi-faceted reflecting prism of the present application; Figure 8 is a schematic diagram of geometric parameter design of the second multi-faceted reflecting prism of the present application; Fig. 9 It is a schematic diagram of the reflected light path of the prism assembly of the present application.

[0019] Reference numerals: total reflection mirror 1; first Nd:YAG crystal rod 2; polarizer 3; spot correction cylindrical mirror 4; first multi-faceted reflection prism 5; second multi-faceted reflection prism 6; λ / 4 wave plate 7; Q-switched crystal 8; wedge 9; output mirror 10; first LD pump source module 11; second LD pump source module 12; Nd:YAG slab crystal 13; second Nd:YAG crystal rod 14; coupling mirror group 15; third LD pump module 16; first reflection surface M 1 ; Second reflecting surface M 2 ; The third reflecting surface M 3 ; Fourth reflecting surface M 4 ; Fifth reflecting surface M 5 . DETAILED DESCRIPTION

[0020] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0021] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show the layers related to the present invention rather than being drawn according to the number, shape and size of the layers in actual implementation. In actual implementation, the type, quantity and proportion of each layer may be changed arbitrarily, and the layer layout may also be more complicated.

[0022] In the following description, numerous details are discussed to provide a more thorough explanation of embodiments of the present invention; however, it is apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details.

[0023] Example 1: Please refer to Figure 1 and Figure 2 , a laser, comprising a resonant cavity, wherein the resonant cavity comprises an upper arm and a lower arm arranged in parallel, and a prism assembly is arranged between the upper arm and the lower arm; The upper arm includes a total reflective mirror 1, a gain module and a polarizer 3, wherein the gain module is arranged close to the total reflective mirror 1, and the polarizer 3 is arranged in the emission direction of the total reflective mirror 1; The prism assembly includes a first multi-faceted reflecting prism 5 arranged in the emission direction of the polarizer 3, and a second multi-faceted reflecting prism 6 that forms a reflection match with the first multi-faceted reflecting prism 5; The lower arm comprises a λ / 4 wave plate 7, a Q-switched crystal 8, an optical wedge 9 and an output mirror 10 which are arranged in sequence from the incident end to the output end.

[0024] The resonant cavity of the present invention adopts a concave-convex unstable cavity design, the total reflection mirror 1 of the upper arm adopts a plano-concave mirror, and forms a resonant cavity with an output mirror 10; the gain module is used to provide gain for the incident light signal; the polarizer 3 is used to generate linear polarization, and emits a horizontal incident light path to the prism assembly; the first multi-faceted reflection prism 5 and the second multi-faceted reflection prism 6 of the prism assembly are used to fold and reflect the horizontal incident light path multiple times and then emit it horizontally into the lower arm; the λ / 4 wave plate 7 and the Q-switching crystal 8 of the lower arm are used as intra-cavity Q-switching devices, and work together to generate nanosecond pulse light output; the optical wedge 9 is used to fine-tune the intra-cavity light path, so that the intra-cavity light path takes into account both high beam quality and high energy output; the output mirror 10 adopts a concave-convex mirror, and forms an unstable cavity with the total reflection mirror 1. The optical paths of the upper arm and the lower arm both oscillate in the horizontal direction. Through the reflection matching between the first multi-faceted reflection prism 5 and the second multi-faceted reflection prism 6 of the prism assembly, the intracavity optical path is horizontally incident in the upper arm and enters the first multi-faceted reflection prism 5 to form a reflection, and performs multiple folding reflections inside the prism assembly. Finally, it is reflected by the first multi-faceted reflection prism 5 and horizontally emitted into the lower arm to maintain the intracavity oscillation, thereby significantly increasing the physical cavity length and the transit time of the photons in the cavity, thereby achieving the purpose of increasing the laser pulse width. The intracavity optical path of the present invention forms multiple reflections under a limited mechanical length to increase the physical cavity length of the resonant cavity, thereby extending the transit time of the oscillating photons in the cavity, thereby achieving the purpose of increasing the laser pulse width.

[0025] See also Figure 7 and Figure 8 The first multi-faceted reflecting prism 5 includes a first reflecting surface M 1 , the second reflecting surface M 2 and the third reflecting surface M 3 , the first reflecting surface M 1 , the second reflecting surface M 2 and the third reflecting surface M 3 From top to bottom, the first reflecting surface M 1 The angle between the second reflecting surface M and the horizontal direction is 38°. 2 The angle between the third reflecting surface M and the horizontal direction is 73°. 3 The angle between the first reflecting surface M and the horizontal direction is 104°. 1 The second reflecting surface M 2 The angle between the second reflecting surface M and the 2 With the third reflecting surface M 3 The angle is 177°; The second multi-faceted reflecting prism 6 includes a fourth reflecting surface M 4 and the fifth reflecting surface M5 , the fourth reflecting surface M 4 and the fifth reflecting surface M 5 The fourth reflecting surface M is arranged sequentially from top to bottom. 4 The angle between the fifth reflecting surface M and the horizontal direction is 50°. 5 The angle between the fourth reflecting surface M and the horizontal direction is 133°. 4 With the fifth reflecting surface M 5 The angle is 177°.

[0026] The mirror angle is counterclockwise rotation from the horizontal direction to the reflective mirror surface. The mirror surfaces of the first multi-faceted prism and the second multi-faceted prism are both 1064nm high-reflection films, HR@1064nm, R≥99.9%, the incident angle is 0°~20°, and the damage threshold is not less than 10J / cm2 (@10ns, 20Hz); the oscillating light path of the upper arm in the resonant cavity enters the second reflective surface M as the horizontal incident light path 2 , realize the first reflection, through the second reflection surface M 2 Reflected to the fourth reflection surface M 4 , realize the second reflection, through the fourth reflection surface M 4 Reflected to the first reflection surface M 1 , realize the third reflection, through the first reflection surface M 1 Reflected to the fifth reflecting surface M 5 , realize the fourth reflection, through the fifth reflection surface M 5 Reflected to the third reflection surface M 3 , realize the fifth reflection, form a five-fold reflection light path, and pass through the third reflection surface M 3 The reflected light is horizontally emitted to the lower arm, thereby maintaining the photon oscillation in the cavity, thereby significantly increasing the physical cavity length and the photon transit time in the cavity, thereby achieving the purpose of increasing the laser pulse width.

[0027] See also Figure 7 and Figure 8 , the first reflecting surface M 1 The size of the second reflective surface M is 10 mm × 10 mm. 2 The size of the third reflective surface M is 12 mm × 10 mm. 3 The size of the fourth reflective surface M is 16 mm × 10 mm. 4 The size of the fifth reflective surface M is 10 mm × 10 mm. 5 The size is 12mm×10mm.

[0028] See also Figure 7 , Figure 8 and Fig. 9The space of the prism assembly is about 55mm×55mm, which has a volume advantage while increasing the pulse width. The oscillating light path completes five light path reflections in the prism assembly. During the reflection process, the optical path of each light path is about 50mm, and the total optical path length is about 300mm. Combined with the optical path of the upper arm and the lower arm of about 200mm, the total physical cavity length of the entire laser resonant cavity can reach 500mm; in actual design, according to the outer envelope size of the laser energy and the volume of the entire laser, the spacing between the first multi-faceted reflection prism 5 and the second multi-faceted reflection prism 6 in two directions can be adjusted, and the optical path length of the reflected light path can be appropriately reduced or increased, so as to achieve a pulse width of more than 10ns when a large energy output of 120mJ is achieved.

[0029] For a conventional laser with a physical cavity length of 200mm~300mm, when the laser light detector energy is designed at the order of 120mJ and the pulse width is 5ns~8ns, the physical cavity length is increased to 500mm in the present invention, and the cavity length is expanded to 1.67~2.5 times of that in the conventional design method. According to the laser pulse width expression of the electro-optical Q-switched laser derived by Degnan, the pulse width is proportional to the transit time in a square, and the pulse width can also be expanded by 1.67~2.5 times, which can reach 12ns. When the cavity length is increased, the pulse width can be further widened by optimizing the transmittance of the output mirror 10, increasing the laser energy output, and reducing the intracavity gain.

[0030] See also Figure 1 and Figure 2 A spot correction cylindrical mirror 4 is movably arranged between the polarizer 3 and the prism assembly.

[0031] The spot correction cylindrical mirror 4 is a positive lens used to properly converge the elliptical spot and correct it back to a nearly circular spot. When debugging the laser, the spot correction cylindrical mirror 4 is moved for fine adjustment so that the output spot remains as round as possible.

[0032] The first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 are both integrated prisms.

[0033] The first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 are designed as multi-mirror integrated prisms, and multiple reflecting surfaces are designed on the same prism. Compared with the conventional reflecting light path constructed by multiple plane reflecting mirrors, it is more stable.

[0034] See also Figure 1 and Figure 2The gain module includes two first Nd:YAG crystal rods 2 arranged between the total reflection mirror 1 and the polarizer 3, the two first Nd:YAG crystal rods 2 are arranged in parallel along the optical path direction, the two first Nd:YAG crystal rods 2 are respectively provided with a first LD pump source module 11, and the two first LD pump source modules 11 are respectively located on both sides of the corresponding first Nd:YAG crystal away from each other.

[0035] The LD side pump Nd:YAG crystal rod pumping module including the first Nd:YAG crystal rod 2 and the two first LD pumping source modules 11 has small packaging requirements and good beam quality.

[0036] Example 2: Please refer to Figure 3 and Figure 4 The gain module includes a Nd:YAG slab crystal 13 arranged between the total reflection mirror 1 and the polarizer 3, and a second LD pump source module 12 arranged above the Nd:YAG slab crystal 13, and the Nd:YAG slab crystal 13 is a trapezoidal table with an upper end area larger than a lower end area.

[0037] The LD side pump Nd:YAG slab crystal 13 pumping module including the Nd:YAG slab crystal 13 and the second LD pump source module 12 has good heat dissipation performance and higher laser light-to-light conversion efficiency.

[0038] See also Figure 5 and Figure 6 The gain module includes a second Nd:YAG crystal rod 14 arranged between the total reflection mirror 1 and the polarizer 3, and a coupling mirror group 15 arranged at the incident end of the total reflection mirror 1, and a third LD pump module 16 is arranged at the incident end of the coupling mirror group 15.

[0039] The gain module including the second Nd:YAG crystal rod 14 , the coupling mirror group 15 and the third LD pump module 16 adopts an end pump design, which effectively increases the cavity length of the upper arm and increases the pulse width. At the same time, the second Nd:YAG crystal rod 14 can also further improve the beam quality.

[0040] See also Figure 7 , Figure 8 and Fig. 9 , a resonant cavity design method, according to the requirement of sufficient space between the incident light path 1 and the outgoing light path 6, an upper arm and a lower arm are set; According to the horizontal incidence of the incident light path 1 and the horizontal emission of the outgoing light path 6, the first reflecting surface M of the first multi-faceted reflecting prism 5 in the prism assembly is designed. 1 , the second reflecting surface M 2 , the third reflecting surface M 3The angle of the fourth reflecting surface M4 and the fifth reflecting surface M of the second multi-faceted reflecting prism 6 is 5 Angle The upper arm horizontal incident light path enters the second reflection surface M 2 ; Through the second reflecting surface M 2 Reflect the light path 2 to the fourth reflection surface M 4 , the angle between the optical path 2 and the optical path 1 is 34°, and the second reflection surface M 2 The angle with the horizontal direction is 73°; Through the fourth reflecting surface M 4 Reflect the light path three to the first reflection surface M 1 , the angle between optical path 3 and optical path 2 is 12°, and the fourth reflection surface M 4 The angle with the horizontal direction is 50°; Through the first reflecting surface M 1 Reflect the light path 4 to the fifth reflecting surface M 5 , the angle between optical path 4 and optical path 3 is 12°, the first reflection surface M 1 The angle with the horizontal direction is 38°, and the first reflecting surface M 1 With the second reflecting surface M 2 The angle is 145°; Through the fifth reflecting surface M 5 Reflect the light path five times to the third reflecting surface M 3 The angle between the optical path 5 and the optical path 4 is 30°, and the fifth reflecting surface M 5 The angle with the horizontal direction is 133°, and the fifth reflecting surface M 5 With the fourth reflecting surface M 4 The angle is 177°; Through the third reflecting surface M 3 The light path 6 is emitted horizontally to the lower arm, and the angle between the light path 6 and the light path 5 is 28°. 3 The angle with the horizontal direction is 104°, and the third reflecting surface M 3 With the second reflecting surface M 2 The angle is 177°; Design the spatial dimensions of the prism assembly based on the outer envelope dimensions of the laser energy and the volume of the entire laser; According to the spatial size of the prism assembly, the distance between the first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 in two directions is designed; According to the distance between the first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 in two directions, the first reflecting surface M of the first multi-faceted reflecting prism 5 in the prism assembly is designed. 1 , the second reflecting surface M 2 , the third reflecting surface M 3The size of the fourth reflecting surface M of the second multi-faceted reflecting prism 6 4 and the fifth reflecting surface M 5 The size of the prism assembly is such that the total optical path of the optical path in the prism assembly is greater than or equal to 300 mm; The spatial dimensions of the prism assembly are 55 mm × 55 mm, and the first reflecting surface M 1 The size of the second reflective surface M is 10mm×10mm. 2 The size of the third reflective surface M is 12mm×10mm. 3 The size of the fourth reflective surface M is 16mm×10mm. 4 The size of the fifth reflective surface M is 10 mm × 10 mm. 5 The size is 12mm×10mm.

[0041] See also Figures 1 to 6 , by setting a spot correction cylindrical mirror 4 between the polarizer 3 and the prism assembly, the elliptical spot deformed after reflection is shaped back to a nearly circular shape; The major axis size of the elliptical spot deformed by the angle between the optical paths is calculated by the angle between the optical paths greater than 20°; According to the size of the major axis of the elliptical light spot, the curvature radius of the light spot correction cylindrical mirror 4 is calculated; The output light spot is finely adjusted by moving the light spot correction cylindrical mirror 4 so that the output light spot remains as circular as possible.

[0042] See also Figures 1 to 9 The laser includes an upper arm, a lower arm and a prism assembly, and the resonant cavity adopts a concave-convex unstable cavity design. The upper arm includes a total reflection mirror 1, a gain module, a polarizer 3 and a spot correction cylindrical mirror 4; the lower arm includes a λ / 4 wave plate 7, a Q-switched crystal 8, an optical wedge 9 and an output mirror 10, and the prism assembly includes a first multi-faceted reflection prism 5 and a second multi-faceted reflection prism 6. The optical paths of the upper arm and the lower arm are both oscillating in the horizontal direction. By reasonably designing the angles and relative distances of each mirror surface of the prism assembly, the light path in the cavity is horizontally incident in the upper arm and enters the first multi-faceted reflection prism 5 to form a reflection. After five folding reflections inside the prism assembly, it is finally reflected by the first multi-faceted reflection prism 5 and emitted horizontally into the lower arm to maintain the intracavity oscillation, thereby significantly increasing the physical cavity length and the photon transit time in the cavity, thereby achieving the purpose of increasing the laser pulse width.

[0043] In order to realize the functions of horizontal incidence and horizontal emission of the light path in the cavity, the light path reflection between the first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 is as follows: Fig. 9 The oscillating light path of the upper arm in the resonant cavity enters the second reflection surface M of the first multi-faceted reflection prism 5 as a horizontal incident light path. 2 , the central incident point is O2 , reflected via the optical path 2 to the fourth reflection surface M of the second multi-faceted reflection prism 6 4 The center reflection point is O 4 , and so on, until it finally forms a horizontal outgoing light path 6 and enters the lower arm of the resonant cavity, thereby maintaining the photon oscillation in the cavity. That is, the incident light path 1 passes through the second reflection surface M of the prism assembly in turn. 2 →Fourth reflecting surface M 4 →First reflecting surface M 1 →Fifth reflecting surface M 5 →The third reflecting surface M 3 , forming a five-fold reflection light path, the corresponding central reflection points are O 2 →O 4 →O 1 →O 5 →O 3 The angles of each light path are: 1) Light path 1 enters the second reflecting surface M in a horizontal direction 2 ; 2) The angle between optical path 2 and incident optical path 1 is 34°; 3) The angle between optical path 3 and optical path 2 is 12°; 4) The angle between optical path 4 and optical path 3 is 12°; 5) The angle between optical path 5 and optical path 4 is 30°; 6) The angle between the horizontal outgoing light path six and the light path five is 28°.

[0044] According to the above optical path design, only about 55mm×55mm space can be used in the laser resonant cavity to complete five optical path reflections. The optical path of each optical path from optical path 1 to optical path 6 can be designed to be about 50mm. The sum of the optical paths of the six optical paths is 300mm. Adding the optical paths of the upper arm and the lower arm of about 200mm, the total physical cavity length of the entire laser resonant cavity can reach 500mm. In actual design, according to the outer envelope size of the laser energy and the volume of the entire laser, the spacing between the two reflecting prisms in two directions can be adjusted to appropriately reduce or increase the optical path of the reflected optical path, so as to achieve a pulse width of more than 10ns when the energy output is large at the order of 120mJ.

[0045] Due to the multiple folding of the optical path, another problem that needs to be solved is: when the angle of the optical path is controlled within 20°, there will be no obvious deformation of the light spot. However, in order to ensure that there is enough spacing between the horizontal output optical path six and the horizontal incident optical path one to facilitate the placement of the upper arm and the lower arm of the resonant cavity, the angle of part of the optical path must be increased. At this time, when the angle between the optical paths exceeds 20°, it will cause obvious deformation of the light spot, and the light spot will appear elliptical in the vertical direction of the figure. In order to reshape the elliptical light spot deformed after reflection back to a nearly circular shape, the present invention inserts a light spot correction cylindrical mirror 4 in the resonant cavity. The light spot correction cylindrical mirror 4 is designed as a positive lens, which can appropriately converge the elliptical light spot and correct it back to a nearly circular light spot. The curvature radius of the light spot correction cylindrical mirror 4 is calculated according to the size of the major axis of the ellipse caused by the increased angle. The angles in the optical path greater than 20° include the angle between the optical path one and the optical path two of 34°, the angle between the optical path four and the optical path five of 30°, and the angle between the optical path five and the optical path six of 28°. These three angles will obviously cause the laser spot to change from a circle to an ellipse. After folding at these three angles, the equivalent major axis size of the elliptical light spot is equal to A=D / (cos34°×cos30°×cos28°), then the curvature radius of the compensation lens is R=D / A After the radius of curvature is determined, when actually debugging the laser, the spot correction cylindrical mirror 4 can be moved to fine-tune the output spot so that it remains as circular as possible.

[0046] On the basis of the design of electro-optical Q-switched pulse laser, for conventional lasers with a physical cavity length of 200mm~300mm, when the laser light meter energy is designed at the order of 120mJ, the pulse width is 5ns~8ns. In the present invention, the physical cavity length is increased to 500mm, and the cavity length is expanded to 1.67~2.5 times of the conventional design method. According to the laser pulse width expression of electro-optical Q-switched laser derived by Degnan, the pulse width is proportional to the transit time, so the pulse width can also be expanded by 1.67~2.5 times, which can reach about 12ns. And in practical applications, when the cavity length is increased, by optimizing the transmittance of the output mirror 10, increasing the laser energy output, and reducing the intracavity gain, the pulse width can be further widened. Therefore, the present invention has substantial reference value for the design of increasing the pulse width of the laser light meter.

[0047] Compared with the prior art, the present invention has the following advantages: 1. Through two reflective prisms designed with precise angles, five optical path foldings are achieved, and the physical cavity length of the resonant cavity is expanded to more than 500mm within the mechanical length of the laser of 200m. Compared with the conventional U-shaped folded cavity, the pulse width is greatly improved; 2. The first multi-faceted reflecting prism 5 and the second multi-faceted reflecting prism 6 are designed as multi-mirror integrated prisms. Multiple reflecting surfaces are designed on the same prism. Compared with the conventional reflecting optical path constructed by multiple plane reflecting mirrors, the reflection optical path is more stable, and the error of each reflecting mirror surface is controlled within a smaller error range (can reach arc second level) by prism processing, which greatly reduces the error caused by manual debugging of the optical path and is more conducive to laser debugging; 3. A spot correction cylindrical mirror 4 is inserted into the cavity, and the radius of curvature matches the deformation of the spot generated by the large incident angle of each mirror surface of the reflecting prism assembly in the direction perpendicular to the optical path, thereby compensating and correcting the spot, so that the laser mode in the cavity maintains high beam quality oscillation.

[0048] In the above-mentioned embodiments, although the present invention has been described in conjunction with the specific embodiments of the present invention, many replacements, modifications and variations of these embodiments will be apparent to those of ordinary skill in the art based on the foregoing description. The embodiments of the present invention are intended to cover all such replacements, modifications and variations falling within the broad scope of the appended claims.

[0049] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A laser comprising a resonant cavity, characterized in that: The resonant cavity comprises an upper arm and a lower arm arranged in parallel, and a prism assembly is arranged between the upper arm and the lower arm; The upper support arm comprises a total reflection mirror (1), a gain module and a polarizing plate (3), wherein the gain module is arranged close to the total reflection mirror (1), and the polarizing plate (3) is arranged in the emission direction of the total reflection mirror (1); The prism assembly comprises a first multi-faceted reflecting prism (5) arranged in the emission direction of the polarizing plate (3), and a second multi-faceted reflecting prism (6) forming a reflection match with the first multi-faceted reflecting prism (5); The lower arm comprises a λ / 4 wave plate (7), a Q-switched crystal (8), an optical wedge (9) and an output mirror (10) which are arranged in sequence from the incident end to the output end.

2. A laser according to claim 1, characterized in that: The first multi-faceted reflecting prism (5) comprises a first reflecting surface M1, a second reflecting surface M2 and a third reflecting surface M3, wherein the first reflecting surface M1, the second reflecting surface M2 and the third reflecting surface M3 are arranged in sequence from top to bottom, the angle between the first reflecting surface M1 and the horizontal direction is 38°, the angle between the second reflecting surface M2 and the horizontal direction is 73°, the angle between the third reflecting surface M3 and the horizontal direction is 104°, and the angle between the first reflecting surface M1 and the second reflecting surface M2 is 145°, and the angle between the second reflecting surface M2 and the third reflecting surface M3 is 177°; The second multi-faceted reflecting prism (6) comprises a fourth reflecting surface M4 and a fifth reflecting surface M5, which are arranged in sequence from top to bottom, the angle between the fourth reflecting surface M4 and the horizontal direction is 50°, the angle between the fifth reflecting surface M5 and the horizontal direction is 133°, and the angle between the fourth reflecting surface M4 and the fifth reflecting surface M5 is 177°.

3. A laser according to claim 2, characterized in that: The size of the first reflection surface M1 is 10 mm×10 mm, the size of the second reflection surface M2 is 12 mm×10 mm, the size of the third reflection surface M3 is 16 mm×10 mm, the size of the fourth reflection surface M4 is 10 mm×10 mm, and the size of the fifth reflection surface M5 is 12 mm×10 mm.

4. A laser according to claim 2, characterized in that: A light spot correction cylindrical mirror (4) is movably arranged between the polarizing plate (3) and the prism assembly.

5. A laser according to claim 1, characterized in that: The first multi-faceted reflecting prism (5) and the second multi-faceted reflecting prism (6) are both integrated prisms.

6. A laser according to claim 1, characterized in that: The gain module comprises two first Nd:YAG crystal rods (2) arranged between the total reflection mirror (1) and the polarizer (3), the two first Nd:YAG crystal rods (2) being arranged in parallel along the optical path direction, the two first Nd:YAG crystal rods (2) being respectively provided with a first LD pump source module (11), and the two first LD pump source modules (11) being respectively located on two sides of the corresponding first Nd:YAG crystal rod (2) that are away from each other.

7. A laser according to claim 1, characterized in that: The gain module comprises a Nd:YAG slab crystal (13) arranged between the total reflection mirror (1) and the polarizer (3), and a second LD pump source module (12) arranged above the Nd:YAG slab crystal (13); the Nd:YAG slab crystal (13) is in the form of a trapezoidal platform with an upper end area larger than a lower end area.

8. A laser according to claim 1, characterized in that: The gain module comprises a second Nd:YAG crystal rod (14) arranged between the total reflection mirror (1) and the polarizer (3), and a coupling mirror group (15) arranged at the incident end of the total reflection mirror (1), wherein a third LD pump module (16) is arranged at the incident end of the coupling mirror group (15).

9. A resonant cavity design method, characterized in that: According to the requirement that there needs to be enough space between the incident light path 1 and the outgoing light path 6, an upper support arm and a lower support arm are provided; According to the horizontal incidence of the incident light path 1 and the horizontal emission of the outgoing light path 6, the angles of the first reflecting surface M1, the second reflecting surface M2 and the third reflecting surface M3 of the first multi-faceted reflecting prism (5) in the prism assembly, and the angles of the fourth reflecting surface M4 and the fifth reflecting surface M5 of the second multi-faceted reflecting prism (6) are designed; The horizontal incident light path of the upper arm is incident on the second reflecting surface M2; The light path 2 is reflected to the fourth reflection surface M4 by the second reflection surface M2, the angle between the light path 2 and the light path 1 is 34°, and the angle between the second reflection surface M2 and the horizontal direction is 73°; The light path three is reflected to the first reflection surface M1 by the fourth reflection surface M4, the angle between the light path three and the light path two is 12°, and the angle between the fourth reflection surface M4 and the horizontal direction is 50°; The light path 4 is reflected to the fifth reflection surface M5 by the first reflection surface M1, the angle between the light path 4 and the light path 3 is 12°, the angle between the first reflection surface M1 and the horizontal direction is 38°, and the angle between the first reflection surface M1 and the second reflection surface M2 is 145°; The light path 5 is reflected to the third reflection surface M3 through the fifth reflection surface M5, the angle between the light path 5 and the light path 4 is 30°, the angle between the fifth reflection surface M5 and the horizontal direction is 133°, and the angle between the fifth reflection surface M5 and the fourth reflection surface M4 is 177°; The light path 6 is emitted horizontally to the lower arm through the third reflection surface M3, the angle between the light path 6 and the light path 5 is 28°, the angle between the third reflection surface M3 and the horizontal direction is 104°, and the angle between the third reflection surface M3 and the second reflection surface M2 is 177°; Design the spatial dimensions of the prism assembly based on the outer envelope dimensions of the laser energy and the volume of the entire laser; The distances between the first multi-faceted reflecting prism (5) and the second multi-faceted reflecting prism (6) in two directions are designed according to the spatial dimensions of the prism assembly; According to the distances between the first multi-faceted reflecting prism (5) and the second multi-faceted reflecting prism (6) in two directions, the sizes of the first reflecting surface M1, the second reflecting surface M2, and the third reflecting surface M3 of the first multi-faceted reflecting prism (5) in the prism assembly, and the sizes of the fourth reflecting surface M4 and the fifth reflecting surface M5 of the second multi-faceted reflecting prism (6) are designed so that the total optical path of the light path in the prism assembly is greater than or equal to 300 mm; The spatial dimensions of the prism assembly are 55mm×55mm, the dimensions of the first reflection surface M1 are 10mm×10mm, the dimensions of the second reflection surface M2 are 12mm×10mm, the dimensions of the third reflection surface M3 are 16mm×10mm, the dimensions of the fourth reflection surface M4 are 10mm×10mm, and the dimensions of the fifth reflection surface M5 are 12mm×10mm.

10. A resonant cavity design method according to claim 9, characterized in that: By arranging a light spot correction cylindrical mirror (4) between the polarizing plate (3) and the prism assembly, the elliptical light spot deformed after reflection is shaped back to a nearly circular shape; The major axis size of the elliptical spot deformed by the angle between the optical paths is calculated by the angle between the optical paths greater than 20°; According to the size of the major axis of the elliptical light spot, the curvature radius of the light spot correction cylindrical mirror (4) is calculated; The output light spot is finely adjusted by moving the light spot correction cylindrical mirror (4) so ​​that the output light spot remains as circular as possible.

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