Macroenergy optical fiber coupling laser for impact strengthening

Abstract

The invention relates to the technical field of laser, in particular to a macro-energy optical fiber coupling laser for shock peening, which comprises a Cassegrain unstable resonant cavity and a Cassegrain unstable resonant cavity endoscope, the Cassegrain unstable resonant cavity endoscope comprises a plano-convex total reflection mirror and a Gaussian output mirror, and the plano-convex total reflection mirror is connected with the Gaussian output mirror. A laser pulse modulation assembly, a first laser gain assembly and a polarization assembly are arranged between the plano-convex total reflection mirror and the Gaussian output mirror; the frequency doubling assembly comprises a beam shrinking system and a frequency doubling crystal, and a second laser gain assembly is arranged between the frequency doubling assembly and the Cassegrain unstable resonant cavity; the optical fiber coupling assembly with the homogenizer comprises an attenuator and a beam expanding system, a honeycomb mirror is arranged behind the beam expanding system, and a focus lens is further arranged behind the honeycomb mirror; and the optical fiber is arranged behind the focus lens. The problem that high-strength laser pulses damage the inlet surface of the optical fiber and the interior of a core material can be solved.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to a high-energy fiber-coupled laser for shock strengthening. Background Art

[0002] In practical production applications, metal materials often develop defects due to factors such as fatigue, corrosion and wear. Severe defects may significantly reduce the service life of components and even cause operational failure of facilities, resulting in huge economic losses.

[0003] A Chinese patent with publication number CN110320593A discloses a fiber laser coupler, comprising: a laser input optical cable, a laser shaping coupling device and a multi-beam mode energy transmission optical fiber; the multi-beam mode energy transmission optical fiber comprises: a circular fiber core and an annular fiber core, each annular fiber core is coaxial with the circular fiber core; a fluorine-doped layer is arranged between the circular fiber core and the annular fiber core, and a fluorine-doped layer is also arranged between adjacent annular fiber cores; an adjustable collimating lens group and an adjustable focusing lens group of the laser shaping coupling device can be horizontally moved along the direction of the laser beam in the housing of the laser shaping coupling device; the laser shaping coupling device is used to couple the laser beam input by the laser input optical cable into different cores in the multi-beam mode energy transmission optical fiber to obtain output laser beams of different beam modes; but in actual use, the fiber laser coupler has the problem that the laser pulse causes damage to the entrance surface of the optical fiber and the inside of the core material. Summary of the invention

[0004] To this end, the present invention provides a high-energy fiber-coupled laser for shock strengthening, which is used to improve the problem in the prior art that laser pulses cause damage to the entrance surface of the optical fiber and the inside of the core material.

[0005] To achieve the above-mentioned object, the present invention provides a high-energy fiber-coupled laser for shock strengthening, comprising a Cassegrain unstable resonant cavity, including a Cassegrain unstable resonant cavity mirror, wherein the Cassegrain unstable resonant cavity mirror comprises a plano-convex total reflector and a Gaussian output mirror, and a laser pulse modulation component, a first laser gain component and a polarizing component are arranged between the plano-convex total reflector and the Gaussian output mirror; A frequency doubling component, comprising a beam reduction system and a frequency doubling crystal, wherein a second laser gain component is provided between the frequency doubling component and the Cassegrain unstable resonant cavity; An optical fiber coupling assembly with a homogenizer includes an attenuator and a beam expansion system, a honeycomb mirror is arranged behind the beam expansion system, and a focusing mirror is also arranged behind the honeycomb mirror; The optical fiber is arranged behind the focusing mirror.

[0006] Furthermore, the plano-convex total reflection mirror includes a first convex surface, the Gaussian output mirror includes a second convex surface, and the first convex surface is arranged opposite to the second convex surface.

[0007] Furthermore, the laser pulse modulation component includes a 1 / 4 wave plate, an electro-optical Q switch and a first polarizer, the convex direction of the first convex surface is the laser emission direction, and the 1 / 4 wave plate, the electro-optical Q switch and the first polarizer are arranged in sequence along the laser emission direction.

[0008] Furthermore, the first laser gain component includes a first side pump gain module, a second side pump gain module and a first optically active crystal, and the first side pump gain module, the first optically active crystal and the second side pump gain module are sequentially arranged behind the first polarizer along the laser emission direction.

[0009] Furthermore, the polarizing component includes a first half-wave plate and a second polarizer, the first half-wave plate and the second polarizer are sequentially arranged behind the second side pump gain module along the laser emission direction, and the second polarizer is hinged in the Cassegrain unstable resonant cavity.

[0010] Furthermore, a reflective beam expansion component is provided between the second laser gain component and the Cassegrain unstable resonant cavity, and the reflective beam expansion component includes a first reflector and a second reflector that are arranged opposite to each other, and a first plano-concave lens and a first plano-convex lens are provided in sequence between the first reflector and the second reflector.

[0011] Furthermore, the second laser gain component comprises a first side-pumped rod-shaped crystal module and a second side-pumped rod-shaped crystal module, and a second optically active crystal is disposed between the first side-pumped rod-shaped crystal module and the second side-pumped rod-shaped crystal module.

[0012] Furthermore, the beam reduction system comprises a second plano-convex lens and a second plano-concave lens sequentially arranged along the laser emission direction, and a third reflector and a fourth reflector relatively arranged along the laser emission direction are defined between the beam reduction system and the second laser gain assembly.

[0013] Furthermore, the attenuator includes a second half-wave plate and a third polarizer, and a first beam splitter and a second beam splitter are arranged relatively between the attenuator and the frequency doubling crystal mirror along the laser emission direction, the second half-wave plate is arranged behind the second beam splitter, and the third polarizer is hinged behind the second half-wave plate.

[0014] Furthermore, the fiber coupling assembly with homogenizer includes only one honeycomb mirror, and the beam expansion system includes a third plano-concave lens and a third plano-convex lens, wherein the third convex surface of the third plano-convex lens faces the plane of the third plano-concave lens.

[0015] Compared with the prior art, the beneficial effects of the present invention are that the seed light with a laser intensity approximately having a flat-top distribution is output through the Cassegrain unstable resonant cavity, and the intensity of the seed light after subsequent amplification and frequency doubling is more evenly distributed than that of the resonant cavity form of the prior art; and, before coupling, the laser beam is first expanded and then divided into several beams using a honeycomb mirror, the spatial distribution of the average laser power density is then averaged, and the sub-beams are superimposed and output through a focusing mirror to achieve homogenization of the beam, which is then coupled into the optical fiber to alleviate the damage caused by high-intensity laser pulses to the entrance surface of the optical fiber and the inside of the core material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of a high-energy fiber-coupled laser for shock strengthening in this embodiment; Figure 2 This is a comparison chart of the intensity of flat-top distribution and Gaussian distribution. DETAILED DESCRIPTION

[0017] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0019] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0020] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] See also Figure 1 As shown, it is a schematic diagram of the structure of a high-energy fiber-coupled laser for shock strengthening in this embodiment, and the high-energy fiber-coupled laser for shock strengthening includes: A Cassegrain unstable resonant cavity 1, comprising a Cassegrain unstable resonant cavity mirror, wherein the Cassegrain unstable resonant cavity mirror comprises a plano-convex total reflector 101 and a Gaussian output mirror 102, wherein a laser pulse modulation component 103, a first laser gain component 104 and a polarizing component 105 are arranged between the plano-convex total reflector 101 and the Gaussian output mirror 102; The frequency doubling component 2 comprises a beam reduction system 201 and a frequency doubling crystal 202, wherein a second laser gain component 7 is provided between the frequency doubling component 201 and the Cassegrain unstable resonant cavity 1; The optical fiber coupling assembly 3 with a homogenizer includes an attenuator 301 and a beam expansion system 302. A honeycomb mirror 4 is disposed behind the beam expansion system 301. A focusing mirror 5 is also disposed behind the honeycomb mirror 4. The optical fiber 6 is arranged behind the focusing mirror 5 .

[0022] Specifically, the device is used for laser strengthening of materials underwater. The high-energy fiber-coupled laser for impact strengthening of the present invention outputs seed light with a laser intensity approximately flat-top distribution through a Cassegrain unstable resonant cavity 1, and the seed light is more evenly distributed in intensity after subsequent amplification and frequency doubling compared with the resonant cavity form of the prior art; and before coupling, the laser beam is first expanded and then divided into several beams using a honeycomb mirror 4, the spatial distribution of the average laser power density is then averaged, and the sub-beams are superimposed and output through a focusing mirror 5 to achieve homogenization of the beam, which is then coupled into the optical fiber to alleviate the damage caused by high-intensity laser pulses to the entrance surface of the optical fiber and the inside of the core material.

[0023] Specifically, in this embodiment, the cavity length L of the Cassegrain unstable resonant cavity 1 is 600 mm.

[0024] Specifically, the plano-convex total reflection mirror 101 includes a first convex surface 1011 , and the Gaussian output mirror 102 includes a second convex surface 1021 , and the first convex surface 1011 and the second convex surface 1021 are arranged opposite to each other.

[0025] Specifically, the curvature R1 of the plano-convex total reflection mirror 101 is 6 m; the Gaussian output mirror 102 has 2a=6, 2b=0, a curvature R2=1.5 m, and a transmittance T=70%.

[0026] Specifically, the laser pulse modulation component 103 includes a 1 / 4 wave plate 1031, an electro-optical Q switch 1032 and a first polarizer 1033, the convex direction of the first convex surface 1011 is the laser emission direction, and the 1 / 4 wave plate 1031, the electro-optical Q switch 1032 and the first polarizer 1033 are arranged in sequence along the laser emission direction.

[0027] Specifically, before laser oscillation is formed, the transmitted light emitted by the first laser gain component 104 passes through the first polarizer 1033, the electro-optical Q switch 1032 and the 1 / 4 wave plate 1031 in sequence. The pulsed laser can be modulated by the 1 / 4 wave plate 1031, the electro-optical Q switch 1032 and the first polarizer 1033 arranged in sequence, thereby realizing nanosecond laser output.

[0028] Specifically, the modulation of the pulsed laser means that when the number of energy level inversion particles on the laser accumulates to a preset level, a 1 / 4 wave voltage is applied to the electro-optical Q switch 1032 through a high-voltage driving power supply, and the longitudinal electro-optical effect is used to put the laser oscillator used to release the laser in an open-door working state, thereby achieving nanosecond laser output.

[0029] Specifically, the first laser gain component 104 includes a first side pump gain module 1041, a second side pump gain module 1043 and a first optical rotation crystal 1042. The first side pump gain module 1041, the first optical rotation crystal 1042 and the second side pump gain module 1043 are sequentially arranged behind the first polarizer 1033 along the laser emission direction.

[0030] Specifically, the first side pump gain module 1041 and the second side pump gain module 1043 are both Nd:YAG crystal rods with a diameter of 7 mm, a length of 94 mm, and a doping concentration of 0.8%at. The first optically active crystal 1042 can compensate for the thermally induced birefringence in the crystal; and cooperate with the plano-convex total reflection mirror 101 and the Gaussian output mirror 102 to generate pulsed lasers.

[0031] Specifically, the polarizing component 105 includes a first half-wave plate 1051 and a second polarizer 1052, which are sequentially arranged behind the second side pump gain module 1043 along the laser emission direction, and the second polarizer 1052 is hinged in the Cassegrain unstable resonant cavity 1.

[0032] Specifically, by setting the first half-wave plate 1051 and the second polarizer 1052 for polarization selection and polarization, a laser with high energy output and high polarization ratio can be obtained.

[0033] Specifically, a reflective beam expander component 8 is provided between the second laser gain component 7 and the Cassegrain unstable resonant cavity. The reflective beam expander component 8 includes a first reflector 801 and a second reflector 802 that are relatively arranged. A first plano-concave lens 803 and a first plano-convex lens 804 are provided in sequence between the first reflector 801 and the second reflector 802.

[0034] Specifically, the direction of the laser is changed by the first reflector 801 and the second reflector 802 to guide the laser to the second laser gain component 7, wherein the first reflector 801 and the second reflector 802 are both 45° reflectors. When the laser passes through the first plano-concave lens 803 and the first plano-convex lens 804 in sequence, the combination of these two lenses can shape the light beam. By adjusting the parameters and relative positions of the two lenses, a light beam output with a specific shape and characteristics can be obtained.

[0035] Specifically, the second laser gain assembly 8 includes a first side-pumped rod-shaped crystal module 701 and a second side-pumped rod-shaped crystal module 703 , and a second optically active crystal 702 is disposed between the first side-pumped rod-shaped crystal module 701 and the second side-pumped rod-shaped crystal module 703 .

[0036] Specifically, the first side-pumped rod-shaped crystal module 701 and the second side-pumped rod-shaped crystal module 703 are both Nd:YAG crystal rods with a diameter of 8 mm, a length of 140 mm, a doping concentration of 0.8% at, and an end face cutting angle of 2°, which can avoid the return of the light along the original path to damage the preceding optical path components. The second optically active crystal 702 is similar to the seed light, which can reduce the depolarization effect caused by thermally induced birefringence and improve the polarization degree of the amplified laser.

[0037] Specifically, the beam reduction system 201 includes a second plano-convex lens 2012 and a second plano-concave lens 2011 sequentially arranged along the laser emission direction, and a third reflector 9 and a fourth reflector 10 relatively arranged along the laser emission direction are defined between the beam reduction system 201 and the second laser gain assembly 7.

[0038] Specifically, the third reflector 9 and the fourth reflector 10 are both 45° reflectors, which can adjust the direction of the laser and guide the laser into the beam reduction system so as to reduce the laser through the second plano-convex lens 2012 and the second plano-concave lens 2011.

[0039] Specifically, the attenuator 301 includes a second half-wave plate 3011 and a third polarizer 3012. A first beam splitter 11 and a second beam splitter 12 are arranged relatively along the laser emission direction between the attenuator 301 and the frequency doubling crystal mirror 202. The second half-wave plate 3011 is arranged behind the second beam splitter 12, and the third polarizer 3012 is hinged behind the second half-wave plate 3011.

[0040] Specifically, after the laser passes through the frequency doubling crystal 202, the fundamental frequency light in the laser is filtered out by the first beam splitter 11 and the second beam splitter 12, wherein the frequency doubling crystal 202 is an LBO crystal mirror, and the LBO crystal mirror is a lithium triborate crystal with a size of 6×6×20cm, θ=90°, φ=9.6°, and a 532nm&1064nm anti-reflection film coated on the front and rear end faces. It adopts temperature phase matching and uses a temperature controller to control the temperature with a temperature control accuracy of ±0.1°C.

[0041] Specifically, the fiber coupling assembly with homogenizer 3 includes only one honeycomb mirror 4 , and the beam expansion system 302 includes a third plano-concave lens 3021 and a third plano-convex lens 3022 , wherein the third convex surface 3023 of the third plano-convex lens 3022 faces the plane 3024 of the third plano-concave lens 3021 .

[0042] Specifically, the third plano-concave lens 3021 and the third plano-convex lens 3022 can expand the laser beam.

[0043] Specifically, after the laser passes through the third plano-concave lens 3021 and the third plano-convex lens 3022 to be expanded, it is then divided into several light beams by the honeycomb mirror 4, and then the sub-beams are superimposed and output through the focusing mirror 5 to achieve light beam homogenization, weaken the scattered strong points, and alleviate the damage caused by high-intensity laser pulses to the entrance surface of the optical fiber 6 and the inside of the core material.

[0044] See also Figure 2 As shown, it is a comparison diagram of the intensity of flat-top distribution and Gaussian distribution. The ordinate is relative intensity and the abscissa is position. It can be seen from the figure that the relative intensity of the flat-top distribution is half that of the Gaussian distribution.

[0045] Specifically, under the same conditions, the honeycomb mirror 4 homogenizes the light spot so that the fiber coupling output power is doubled, while avoiding the problem of air breakdown after the focusing mirror 5 focuses the light beam.

[0046] Specifically, the parameters of the honeycomb mirror 4 are: focal length f=100mm, pitch=1000um, sub-unit shape is hexagonal, ~ SINα=0.005; the parameters of the focusing mirror 5 are: its focal length f=50mm, and it is coated with a 532nm anti-reflection film.

[0047] Specifically, the pitch refers to the distance between the centers of two adjacent subunits. ~ SINα refers to the approximation of the sine of the angle associated with the focusing characteristic.

[0048] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A high-energy fiber-coupled laser for shock peening, characterized in that: include, A Cassegrain unstable resonant cavity, comprising a Cassegrain unstable resonant cavity mirror, wherein the Cassegrain unstable resonant cavity mirror comprises a plano-convex total reflector and a Gaussian output mirror, and a laser pulse modulation component, a first laser gain component and a polarizing component are arranged between the plano-convex total reflector and the Gaussian output mirror; A frequency doubling component, comprising a beam reduction system and a frequency doubling crystal, wherein a second laser gain component is provided between the frequency doubling component and the Cassegrain unstable resonant cavity; An optical fiber coupling assembly with a homogenizer includes an attenuator and a beam expansion system, a honeycomb mirror is arranged behind the beam expansion system, and a focusing mirror is also arranged behind the honeycomb mirror; The optical fiber is arranged behind the focusing mirror.

2. The high-energy fiber-coupled laser for shock strengthening according to claim 1, characterized in that: The plano-convex total reflector includes a first convex surface, and the Gaussian output mirror includes a second convex surface, and the first convex surface is arranged opposite to the second convex surface.

3. The high-energy fiber-coupled laser for shock strengthening according to claim 2, characterized in that: The laser pulse modulation component includes a 1 / 4 wave plate, an electro-optical Q switch and a first polarizer, the convex direction of the first convex surface is the laser emission direction, and the 1 / 4 wave plate, the electro-optical Q switch and the first polarizer are arranged in sequence along the laser emission direction.

4. The high-energy fiber-coupled laser for shock strengthening according to claim 3, characterized in that: The first laser gain component includes a first side pump gain module, a second side pump gain module and a first optically active crystal. The first side pump gain module, the first optically active crystal and the second side pump gain module are sequentially arranged behind the first polarizer along the laser emission direction.

5. The high-energy fiber-coupled laser for shock strengthening according to claim 4, characterized in that: The polarizing component includes a first half-wave plate and a second polarizer, which are sequentially arranged behind the second side-pumped gain module along the laser emission direction, and the second polarizer is hinged in the Cassegrain unstable resonant cavity.

6. The high-energy fiber-coupled laser for shock peening according to claim 3, characterized in that: A reflective beam expansion component is also provided between the second laser gain component and the Cassegrain unstable resonant cavity. The reflective beam expansion component includes a first reflector and a second reflector arranged opposite to each other. A first plano-concave lens and a first plano-convex lens are also provided in sequence between the first reflector and the second reflector.

7. The high-energy fiber-coupled laser for shock peening according to claim 6, characterized in that: The second laser gain component comprises a first side-pumped rod-shaped crystal module and a second side-pumped rod-shaped crystal module, and a second optically active crystal is disposed between the first side-pumped rod-shaped crystal module and the second side-pumped rod-shaped crystal module.

8. The high-energy fiber-coupled laser for shock peening according to claim 7, characterized in that: The beam reduction system comprises a second plano-convex lens and a second plano-concave lens sequentially arranged along the laser emission direction, and a third reflector and a fourth reflector oppositely arranged along the laser emission direction are defined between the beam reduction system and the second laser gain assembly.

9. The high-energy fiber-coupled laser for shock peening according to claim 8, characterized in that: The attenuator includes a second half-wave plate and a third polarizer. A first beam splitter and a second beam splitter are arranged opposite to each other along the laser emission direction between the attenuator and the frequency doubling crystal. The second half-wave plate is arranged behind the second beam splitter, and the third polarizer is hinged behind the second half-wave plate.

10. The high-energy fiber-coupled laser for shock peening according to claim 1, characterized in that: The fiber coupling assembly with homogenizer includes only one honeycomb mirror, and the beam expansion system includes a third plano-concave lens and a third plano-convex lens, wherein the third convex surface of the third plano-convex lens faces the plane of the third plano-concave lens.

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