CN109212743B - Rotating shaft reflection type pulse laser beam combiner and pulse beam combining laser system - Google Patents

Abstract

The invention relates to a rotating shaft reflection type pulse laser beam combiner and a pulse beam combining laser system. In order to overcome the defect that a transmission type element is difficult to adapt to the deficiency of high-power laser in the existing pulse time sequence beam combination or other beam combination methods influence the quality of the combined beam, the invention provides a beam combiner for pulse laser, which comprises a rotating shaft and a reflecting mirror fixed on the rotating shaft, wherein the axial lead of the rotating shaft is parallel to the combined beam, and the reflecting mirror is arranged at intervals along the axial lead direction of the rotating shaft and is arranged in a radially staggered manner along a circle taking the axis as the center of circle; and a plurality of beams of pulse laser are reflected by corresponding reflectors and are emitted along an output optical path after being spatially combined. The invention also provides a pulse beam combination laser system which consists of the beam combiner, a plurality of pulse lasers and a plurality of turning mirrors, wherein the pulse lasers emit laser according to a set time sequence, and the laser is reflected by the turning mirrors and then enters the reflecting mirrors to form beam combination laser emission.

Description

Rotary Shaft Reflective Pulse Laser Beam Combiner and Pulse Combined Laser System

technical field

The invention belongs to the technical field of lasers, and in particular relates to a rotating shaft reflection type pulsed laser beam combiner and a pulsed beam combined laser system.

Background technique

With the continuous development and maturity of laser technology, high-power lasers have become more and more widely used, which has profoundly affected the development of many industries. According to the working mode, high-power lasers are mainly divided into high-peak power lasers (ie high-energy pulsed lasers) and high-average power lasers.

For high-energy pulsed lasers, lasers are required to have a certain repetition frequency in various application fields. However, directly increasing the repetition frequency of high-energy pulsed lasers will cause serious thermal effects, which will affect the performance of the laser, and even cause the laser output pulse energy to drop or can not work. For high average power lasers, application requirements continue to put forward higher requirements for laser output power, and the single-channel laser power is limited, making it difficult to achieve higher average output power. Therefore, whether for high-energy pulsed lasers or high-average power lasers, increasing the repetition frequency of pulsed lasers is an urgent problem to be solved.

A single laser achieves the output of high power, high beam quality and high efficiency. Due to the increase of power, the beam quality will decrease nonlinearly, and the nonlinear relationship is very complicated. Therefore, under certain basic conditions, the output of a single laser will Capability is always limited, but people's demand for "three-high" laser output is endless. To achieve higher power output, the best way is multi-beam synthesis technology.

Existing beam combining methods include coherent combining, spectral combining and pulsed laser time-sharing. "Research on Incoherent Synthesis of Pulsed Lasers" published in "Laser Technology" in March 2015 disclosed a method for combining pulsed lasers based on the rotation of the turntable, and the lasers of different timings are obliquely incident on crystals of different thicknesses. When the offset occurs, the coaxial output is coaxial after being refracted by the crystal to realize the beam combination of the pulsed laser and achieve the purpose of increasing the repetition frequency and average power of the laser output. The problem with this solution is that the strong laser needs to be transmitted through the crystal, and the optical components have limited ability to withstand the laser power, making it difficult to meet the incident requirements of high-power and high-energy lasers.

The Chinese invention patent application "A method of combining pulsed laser beams" (Publication No.: 201210078189.7) proposes a method of using a rotating mirror to combine multiple pulsed laser beams with lower repetition rates into a single beam of high repetition rate pulsed lasers The reflective optical element and the optical path structure adopted by the method are simple, and the combined beam can have high power. According to the description of its technical effect, all optical elements of the polygon mirror system can be reflective optical elements, the device can withstand any high-power laser, and as long as the input laser power is high enough, it can output any high-power pulsed laser beam. However, the problem with this scheme is that the quality of the composite beam is degraded due to the continuous movement of the mirror during the pulsed laser light emission. The resulting composite beam quality is reduced by 1/10, which affects its popularization and application.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a rotating shaft reflection in order to overcome the shortcomings of the existing pulse timing beam combining that the transmission-type elements are difficult to adapt to high-power lasers or that other beam combining methods have an impact on the beam quality after the beam combination. The pulsed laser beam combiner and pulsed beam combining laser system greatly improve the average output power and repetition frequency of a single laser, basically keep the beam quality of the original laser unchanged, and have good power and laser quantity scalability. .

The technical scheme of the present invention is:

A rotating shaft reflection type pulse laser beam combiner, comprising a rotating shaft and a plurality of mirrors fixed on the rotating shaft, the axis of the rotating shaft is arranged in parallel with the output beam after the beam combination, and the reflecting mirrors are along the axis of the rotating shaft. The line direction is spaced and arranged along the outer circle with the axis of the rotating shaft as the center. The output light path exits.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, the reflecting mirror is fixed on the rotating shaft by means of a support rod or a hollow rotating cylinder structure.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, the mirror surface of the reflecting mirror is a partial conical surface, and the conical surface takes the axis of the rotating shaft as the axis of rotation.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, the cone angle of the conical surface is 30-60°.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, the cone angle of the conical surface is 45°.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, the reflecting mirror and the rotating drum are integrally formed and processed, and the mirror surface is mirror-polished by a diamond lathe.

Further, in the above-mentioned rotating shaft reflection type pulsed laser beam combiner, a plurality of counterweight blocks or weight reduction holes are arranged on the rotating drum or the rotating shaft.

A pulsed beam combining laser system, which is special in that it includes n pulsed lasers and i×n reflecting mirrors, the pulsed laser emits laser light according to a set time sequence, and is incident on the reflecting mirror to form a beam-combining laser output. The foldback mirror is a parabolic mirror, where n is a positive integer greater than 1, and i is a positive integer.

Further, it also includes that the pulsed laser with n fold-back mirrors is folded back by the fold-back mirror and then incident on the reflector.

Beneficial effects of the present invention:

1. In the present invention, a plurality of conical surface mirrors arranged at intervals along the axial and circumferential directions of the rotating shaft are arranged on the rotating shaft. On the premise of not changing the quality of the original laser beam, the power and repetition frequency of the output laser can be greatly improved, and the number of laser beams can be expanded. important application value;

2. The present invention adopts the total reflection method of the reflector and other optical circuit devices, so as to avoid the shortage of limited power tolerance of the device and influence on the quality of the beam when the transmission optical element is used, and the heat is easily transferred to the hollow drum for export or It is convenient to adopt a variety of thermal management measures to improve the laser tolerance of the mirror, especially suitable for high-power, long-term light output, and can achieve high-repetition-frequency pulsed laser beam combining by changing the rotational speed of the rotating shaft;

3. The present invention adopts the method of directly mechanically chamfering the conical surface on the metal base to manufacture the reflector, which can be directly processed by a diamond lathe, and has the characteristics of simple processing, high surface finish, reliable application, and easy engineering implementation;

4. The present invention uses a special parabolic mirror as a return mirror to realize the matching coupling between the incident laser and the conical mirror, which matches the optical characteristics of the circular conical mirror, thereby ensuring that the incident laser beam and the combined laser beam are The cross-sectional shape remains the same.

Description of drawings

Fig. 1 is the working principle and idea schematic diagram of the pulse beam combiner of the present invention;

Fig. 2 is the timing chart of n pulse lasers before the present invention combines beam;

Fig. 3 is a schematic diagram of the output power of the laser after the pulse combining of Fig. 2;

FIG. 4 is a schematic diagram of the mirror shift principle according to the first embodiment of the present invention;

Fig. 5 is the three-dimensional structure schematic diagram of the rotating shaft reflection type beam combiner of the present invention;

Fig. 6 is the sectional view of the beam combiner of Fig. 5;

Fig. 7 is the side view of coating 5 beam combiner;

8 is a schematic diagram of the beam combining principle of the rotating shaft type beam combiner of the present invention;

9 is a side view of the rotating drum when the mirrors of the present invention are overlapped;

10 is a schematic structural diagram of a rotating-axis reflection beam combiner of multiple groups of mirrors according to the present invention;

11 is a schematic structural diagram of a conical surface mirror and a matching folding mirror of the present invention in a direction perpendicular to the rotation axis;

12 is a schematic structural diagram of a conical surface mirror and a matching folding mirror in the direction parallel to the rotation axis of the present invention;

FIG. 13 is a schematic diagram of the composition of the pulsed beam combining laser system of the present invention.

The reference numerals are: 1—shift device, 2—reflector, 21—hollow drum, 22—mirror body, 23—rotating shaft, 24—mirror surface, 25—folding mirror, 3—mirror shifting direction, 30—laser, 31—incident laser beam, 32—outgoing laser beam, 33—focusing spot, 4—output optical path, 5—shift control unit, 6—electrically controlled displacement stage, 7—laser timing control unit, 8—synchronized trigger signal;

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 1, FIG. 2 and FIG. 3, the principle idea of the pulse beam combining of the present invention is: on the same output optical path 4, n mirrors 2 are arranged obliquely, and each mirror 2 is arranged on the shift device 1, The mirror 2 can be moved out of the beam-combining optical path along the mirror-moving direction 3 in the figure and moved back to the beam-combining optical path, and the combined beam path is the output optical path 4; the shifting device 1 can be an integral mechanism or a separate body The mechanism can realize the independent movement of each mirror 2 in and out.

Each mirror 2 corresponds to the incident laser beam 3, wherein the laser is a pulsed laser with repeated frequency output, and the light-emitting sequence of each laser is shown in Figure 2, and the "Research on the Incoherent Synthesis of Pulsed Laser" in the Background Art can be used. The programmable logic array generates electrical signals with pulse width, frequency and time delay that meet the requirements, and then drives the seed laser with this electrical signal and amplifies or drives the pulsed pump laser, so that the output light of each laser The pulses are kept with different delays to meet the requirements of pulse bundling.

In FIG. 1, when n lasers are incident on the corresponding mirror 2, the shift device 1 moves the mirror 2 away and returns to the original position according to the set timing according to the incident timing, so that when the laser incident from the rear is reflected and output, the front The reflecting mirror 2 will not block the incident beam behind, so that the beam combining of multiple pulsed lasers can be realized. For example, the light-emitting pulse of the 2# laser has a certain delay compared with the 1# laser. When the 2# laser is incident on the 2# mirror, as long as the front 1# mirror is removed by the shifting device so that it is not blocked on the optical path, At this moment, there is only one laser on the combined beam path, that is, the pulsed laser of 2#. Similarly, the output pulse of the 3# laser has a certain delay compared with the 2#. When the 3# laser is incident on the 3# mirror, the As long as the front 1# mirror and 2# mirror are removed by the shifting device and are not blocked on the optical path, the laser output on the combined beam path at this moment is the 3# pulsed laser, and so on. After the incident is completed, the cycle starts from 1# again, and the high repetition frequency or quasi-continuous laser output as shown in Figure 3 is obtained.

In practical application, due to the action delay of the displacement mechanism, the front mirror will inevitably block a small part of the rear when the mirror is displaced, and it is difficult to achieve seamless timing synthesis, so it is difficult to achieve continuous output, but it is possible to achieve continuous output. To achieve quasi-continuous output or increase the repetition frequency of the original laser. Since each pulsed laser is output with a certain duty cycle, the combined laser is the synthesis of n lasers, and the average laser power is the sum of the average powers of all n lasers, thus greatly improving the average output power of the laser. The reflected beams are coaxial, and the quality of the combined beam will not change due to the movement of the mirror, which determines that the combined laser can be emitted and transmitted over long distances with high efficiency and high quality.

The significance of this kind of pulse combining is that it is difficult to improve the average power output of a single laser, especially for continuous output lasers, due to the influence of nonlinear effects and thermal effects, whether for solid-state lasers, fiber lasers or semiconductor lasers. . The purpose of using pulsed beam combining is to make a single laser a pulsed laser with a certain repetition frequency output and a small duty cycle. Although it is affected by nonlinear effects and thermal effects, the average power cannot be too high, but the pulse peak value Power can be very high. Then, the pulse sequence characteristics of each laser are adjusted through the scheme of pulse beam combining, and then the beam combiner of the present invention is used to combine the n laser beams and output them as high repetition frequency laser or quasi-continuous laser. n times, and still maintain the original beam quality, and theoretically this beam combining method has no upper limit of power, which has important application value in industry and other fields.

As shown in FIG. 4 , the displacement device 1 in the first embodiment of the present invention is a plurality of electronically controlled displacement stages 6 that are only electrically connected to the displacement control unit 5 . The working mode of the hydraulic cylinder, under the control of the shift control unit 5, drives the corresponding mirror 2 to move out of the output optical path 4 in sequence according to the time sequence, and then moves back to the original position, and ensures that the mirror 2 in front of the optical path at each moment The following beams will not be blocked, and only one laser beam can be output along the output optical path 4 at the same time. At the same time, in order to match the output timing of the laser, the shift control unit 5 outputs the synchronization trigger signal 8 to the laser timing control unit 7, or the laser timing control unit 7 outputs the synchronization trigger signal 8 to the shift control unit 5, so as to realize the Matching of displacement and pulsed laser timing. The mirror surface of the reflector 2 is a plane, and the included angle with the output optical path 4 is 30-60 degrees, preferably 45 degrees.

If the effective incident area of the mirror (that is, the area after oblique projection) is much larger than the spot of the laser beam, the mirror will always reciprocate under the action of the electronically controlled displacement stage from the start time to the end time of the laser pulse. In the moving state, the laser pulse width and displacement speed are controlled to ensure that the incident beam does not leak out of the mirror surface. If the effective incident area of the reflector is only slightly larger than the spot of the laser beam, the program-controlled setting of the electronically controlled displacement stage makes the reflector remain stationary at the moment of laser emitting, and then quickly move away from the position of the output beam after the emitting light to avoid the Occlusion of reflected light behind. The moving method of this electronically controlled stage can in principle meet the requirements of the above-mentioned pulse combining power superposition, constant beam quality and total reflection device on the optical path, but it is limited by the weight and size of the mirror. Due to the inertial effect of the moving mechanism, it cannot reciprocate quickly, so it can only be used for the beam combining requirements of Hz-level low-repetition pulsed lasers at present.

In order to meet the beam combining requirements of high repetition frequency laser, the laser output with high average power can be realized. The present invention provides a second embodiment, that is, a rotating shaft beam combiner. As shown in Figures 5-7, the displacement device 1 of the present invention is a rotating shaft 23 whose axial direction is parallel to the output optical path 4, the reflector 2 is fixed on the rotating shaft 23 by means of a support rod or a hollow rotating cylinder structure, and a plurality of reflecting mirrors 2 are located on the rotating shaft 23. They are arranged at intervals along the axis line direction of the rotating shaft 23 , and are dislocated along the outer circle direction centered on the axis of the rotating shaft 23 .

Figures 5-7 only show the structure in which the reflector 2 is fixed on the rotating shaft by means of a hollow rotating cylinder. In the figure, the reflector 2 is fixed on the outer ring of the rotating drum 21 through the mirror body 22, and n reflectors 2 are arranged at intervals along the axis direction of the rotating drum 21, and at the same time, they are arranged in a dislocation along the outer circle direction of the rotating drum 21. The reflecting mirrors 2 The mirror surface 24 is no longer the plane in the first embodiment, but a part of a conical surface with the axis of the rotating shaft 23 as the axis of rotation. The cone angle of the cone is 30-60°, preferably 45°. This is because the theoretical analysis shows that if the reflective surface of the mirror is a plane, the beam will spread during the rotation process, which will affect the beam quality after the beam combination.

As shown in FIG. 8 , when the rotating drum 21 rotates at a high speed, each reflecting mirror 2 passes through the output optical path 4 in turn, and the corresponding laser outputs optical pulses at this time, and when the reflecting mirror moves and turns out of the output optical path 4, the optical pulse stops; At this time, the other mirror rotates into the output optical path 4, and the corresponding laser outputs optical pulses, and so on, and finally realizes the combined output of n lasers, and repeats the cycle to realize the output of the next group of pulse sequences. Since the mirrors 2 are staggered and arranged in the outer circumference direction of the rotating drum 21 , they will not block the combined output of the following pulsed laser light. Figure 8 shows the situation where the 1# mirror is in the output optical path 4. Similarly, when the drum 21 is turned to another position, the 1# mirror moves out of the output optical path 4, and the 2# mirror enters the optical path, and so on..., As long as the laser pulse timing is matched, the spatial beam combining output of the laser can be completed. When the mirrors 2 are staggered, adjacent mirrors 2 may overlap slightly, as shown in FIG. 9 . At this time, as long as the timing of the pulsed laser is controlled, the pulsed laser beam combining effect can still be achieved.

In actual processing, the mirror can be chamfered by machining, which is mirror-polished on the metal or non-metal mirror body 22 by a diamond lathe, and a reflective film is coated on the mirror surface as required to delay the oxidation of the mirror surface and realize reflection. Mirror's long-term work. The reflector 2 can be integrally processed with the rotating drum 21. The purpose of this is to ensure the surface accuracy and installation accuracy of the reflector 2, so as to ensure the quality of the reflected beam, and to facilitate heat dissipation. It is suitable for high power and long-term use. laser light out. It is also possible to use a strut to fix the mirror 2 on the rotating shaft 23 after processing. In addition, the rotating shaft 23 or the rotating drum 21 is provided with a number of counterweight blocks or weight-reducing holes, so that the rotational inertia of the rotating shaft is balanced and the belt is reduced during high-speed rotation. Vibration to come.

As shown in Fig. 10, the reflector 2 can be one set or multiple sets of structures. The difference between Fig. 10 and Fig. 5 is that on the same drum, six reflectors 2 are arranged in Fig. 5, in the form of a single helix Line shape distribution; while Figure 10 arranges twelve mirrors 2, which are distributed in a double helix shape. That is to say, when the shaft rotates once, there will be two mirrors corresponding to the same laser. The purpose of this is to reduce the rotation rate of the mechanism, or to meet the beam combining requirements of high repetition frequency lasers. As long as the pulse timings are properly matched, normal pulse laser beam combining can be achieved.

As shown in FIG. 11 and FIG. 12 , since the mirror surface 24 in the second embodiment is a conical surface, when a laser beam with a circular beam cross-section is incident on the mirror surface 24 of the conical surface, a light spot perpendicular to the direction of the center line of the rotating shaft will be caused Diffusion occurs, but the light spot parallel to the centerline of the rotating shaft does not diffuse, which is equivalent to the mirror return in the direction of the cone angle. For example, the 45° mirror only changes the direction, and does not expand or shrink the beam.

In order to overcome this problem, a fold-back mirror 25 is added between the laser exit and the mirror 2, and each laser corresponds to a fold-back mirror 25 to correct the parameters of the laser beam incident on the mirror, so that the beam incident on the fold-back mirror 25 The cross-section parameters are consistent with the beam cross-section parameters after combining by the beam combiner. The folding mirror 25 adopts a special-shaped paraboloid structure. The specific structural parameters need to be determined according to the spot parameters of the incident beam and the parameters of the mirror 2 after optical design.

Figure 13 shows the composition principle diagram of the pulsed beam combining laser system. Since the folding mirror 25 is fixed at the exit of the laser 30 and does not rotate with the rotating shaft, the folding mirror 25 can be accurately adjusted by the multi-dimensional optical adjustment frame. The correction of the combined beam, and the system is easy to implement in the direction perpendicular to the combined beam, which makes the entire system compact and realizes the combination of more pulsed lasers.

Claims (8)

1. A rotating shaft reflection type pulsed laser beam combiner is characterized in that: comprising a rotating shaft (23) and several mirrors (2) fixed on the rotating shaft (23), the axis of the rotating shaft (23) The line and the combined output beam are arranged in parallel, the mirrors (2) are arranged at intervals along the axis of the rotating shaft (23), and are arranged in a staggered direction along the outer circle with the axis of the rotating shaft as the center; The multiple beams of pulsed lasers are reflected by not less than one corresponding mirror (2), and then exit along the output optical path (4) after spatial combination; The reflecting mirror (2) is fixed on the rotating shaft (23) by means of a support rod or a hollow rotating cylinder (21); The mirror surface (24) of the reflector is a partial conical surface, and the conical surface takes the axis of the rotating shaft (23) as the axis of rotation. 2 . The rotating shaft reflection type pulsed laser beam combiner according to claim 1 , wherein the cone angle of the conical surface is 30-60°. 3 . 3 . The rotating shaft reflection type pulsed laser beam combiner according to claim 2 , wherein the cone angle of the conical surface is 45°. 4 . 4 . The rotary shaft reflection pulse laser beam combiner according to claim 3 , wherein the mirror ( 2 ) and the hollow drum ( 21 ) are integrally formed and processed, and the mirror surface is mirror-polished by a diamond lathe. 5 . 5 . The rotating shaft reflection type pulsed laser beam combiner according to claim 4 , wherein the hollow rotating drum ( 21 ) is provided with a number of counterweight blocks or weight reduction holes. 6 . 6 . The rotating shaft reflection type pulsed laser beam combiner according to claim 5 , wherein the rotating shaft ( 23 ) is provided with a number of counterweight blocks or weight reduction holes. 7 . 7. A pulsed beam-combining laser system composed of the rotating shaft reflection type pulsed laser beam combiner according to claim 1, characterized in that: it comprises n pulsed lasers (30) and i*n reflecting mirrors (2) , the pulsed laser (30) emits laser light according to the set timing, and is incident on the reflector (2) to form a combined beam of laser light. The reflector is a parabolic reflector, where n is a positive integer greater than 1, and i is a positive integer . 8 . The pulsed beam combining laser system according to claim 7 , further comprising n folding mirrors ( 25 ), and the pulsed laser ( 30 ) is folded back by the folding mirror ( 25 ) and then incident on the reflecting mirror ( 2 ). 9 .

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