Tunable center point pulse vortex halo continuous laser system

Abstract

The invention discloses a tunable center point pulse vortex halo continuous laser system. Belongs to the technical field of laser, and particularly relates to the technical field of vortex light spot ring pulse continuous laser systems. The problems that at present, an output device for simultaneously obtaining mode-tunable vortex light spot ring pulse continuous laser is too large in size, and the number of needed components is large are solved. The system comprises a 792nm pumping source, a coupling lens group, a plano-concave total reflective mirror, a Tm: YLF crystal, a beam expander and a transmission-type pulse continuous laser modulator, the 792nm pumping source is used for emitting pumping light, the coupling lens group is used for shaping the pumping light, one side, receiving the pumping light, of the plano-concave total reflective mirror is a plane mirror, one side, emitting the pumping light, of the plano-concave total reflective mirror is a concave mirror, and the plano-concave total reflective mirror, the Tm: YLF crystal, the beam expander and the transmission-type pulse continuous laser modulator form a gain cavity. And the pump light is subjected to gain amplification in the gain cavity, and ultrashort pulse laser and vortex light output are generated.

Description

Technical Field

[0001] The invention belongs to the field of laser technology, and in particular relates to the technical field of central point pulse vortex halo continuous laser system. Background Art

[0002] The advancement of laser technology has promoted the development of modern society and made it an important part of modern science and industry. Compared with ordinary light sources, lasers have the advantages of high coherence, high energy density, good monochromaticity and good directionality. These advantages have enabled it to flourish in the past few decades and its application fields have become more and more extensive, including laser cutting, laser welding, laser communications, national defense and military, laser medical treatment and other fields, which has promoted the development of related industries and is becoming more and more worthy of research.

[0003] In the field of laser welding, one of the challenges is the welding defects such as spatter, hump, and porosity generated during welding. In order to improve this defect, various laser hybrid welding and beam shaping welding technologies have been proposed one after another. With the deepening of research, it is found that the spot ring spot has a more uniform temperature distribution and smaller central temperature and temperature gradient changes compared to the Gaussian distribution heat source. This shows that the spot ring spot has great application prospects in reducing welding defects.

[0004] Vortex light has a unique annular light intensity distribution and a spiral wavefront structure, which makes it perform well in laser welding. Specifically, through the computational holography method of light field control, vortex beams can design vortex arrays of arbitrary positions, ring radii, and energy distributions, thereby significantly improving welding efficiency and welding quality; in addition, the application of vortex beams in laser welding also involves real-time observation and quality control of the welding process. By observing the turbulence of the molten pool and steam, real-time monitoring of the weld formation process can be achieved, which is of great significance for improving and enhancing welding quality.

[0005] In summary, in order to improve the welding defects such as spatter, hump, and porosity generated during laser welding, if the mode-tunable vortex spot ring pulse continuous laser output can be obtained at the same time, the welding effect can be better improved.

[0006] At present, there are still many technical difficulties in obtaining mode-tunable vortex spot ring pulse continuous laser output. The most prominent one is that when realizing two modes of laser output at the same time, the device size is too large and many components are required. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a tunable center point pulse vortex light ring continuous laser system.

[0008] The system includes a 792nm pump source, a coupling lens group, a plano-concave total reflection mirror, a Tm:YLF crystal, a beam expander and a transmission type pulse continuous laser modulator; The 792nm pump source is used to emit pump light, the coupling lens group is used to shape the pump light, the side of the plano-concave total reflection mirror that receives the pump light is a plane mirror, and the side that emits the pump light is a concave mirror, the plano-concave total reflection mirror, Tm:YLF crystal, beam expander and transmission type pulse continuous laser modulator form a gain cavity, the pump light is gain amplified in the gain cavity, and ultrashort pulse laser and vortex light output are generated.

[0009] The coupling lens group consists of a group of Kepler collimating and focusing lenses.

[0010] In the group of Kepler collimating and focusing lenses, the focal length of one lens is 25 mm, and the focal length of the other lens is 75 mm.

[0011] The transmission-type pulse continuous laser modulator comprises a liquid crystal panel, a graphene saturable absorber and an annular circuit board. The liquid crystal panel has an opening in the middle, the graphene saturable absorber is placed at the opening in the middle of the liquid crystal panel, and the annular circuit board is connected end to end around the liquid crystal panel.

[0012] The upper and lower surfaces of the liquid crystal panel are both flat and are both provided with PI alignment layers. Through friction alignment and drying and curing operations, the internal liquid crystals all have pre-tilt angles.

[0013] The liquid crystal panel has a film layer with a transmittance of 5% for 1908nm laser on the PI orientation layer on the light path output side.

[0014] The annular circuit board is controlled by a computer, and the computer controls the voltage of the annular circuit board to change the arrangement director of the local liquid crystal in the liquid crystal panel, thereby achieving the effect of light field regulation. The beneficial effects of the system of the present invention are: The total target area of ​​a traditional spatial light modulator is 18×20mm. 2 In addition to the liquid crystal target surface, it also has an internal electronic control system and other devices. The overall size is 60×60×35mm 3The above is particularly complicated from the perspective of optical path construction. The working nature of the traditional spatial light modulator is to fix the internal liquid crystal molecules by applying voltage to the light field of a specific band. Macroscopically, it turns the liquid crystal panel into an isotropic medium, and converts the original light field into light with different phases according to the degree of rotation of each unit liquid crystal and outputs it. Since a specific voltage needs to be applied, the computer must transmit different degrees of phase diagrams to the spatial light modulator. Each phase diagram represents a different form of electric field. Combined with the above working principle, the indispensable devices are only the silicon-based liquid crystal layer and the electronic control panel. The present invention retains the key silicon-based liquid crystal layer and electric control panel of the traditional spatial light modulator, and changes the shape of the liquid crystal panel. The upper and lower surfaces of the liquid crystal panel are both flat, and a graphene saturable absorber is arranged inside the liquid crystal panel. The electric control panel previously attached to the bottom surface of the silicon-based liquid crystal layer is structurally improved and changed into a ring-shaped circuit board that is connected end to end around the liquid crystal panel. The above improvements have two advantages: first, the overall device structure becomes smaller after the improvement, saving space and material share while retaining the necessary laser modulator function required by the present invention; second, the structural improvement of the liquid crystal panel enables it to achieve multi-functional multiplexing. The liquid crystal panel is not only a device for generating ultrashort pulse lasers and vortex light, but also can be used as a flat output mirror, so that the device can be used for oscillating light in the resonant cavity. At the same time, the graphene saturable absorber can be used at the center for pulse modulation and regulation of the surrounding light field, and the center point pulse and continuous vortex light ring laser are emitted.

[0015] The addition of a beam expander and graphene realizes the tunable vortex light spot ring pulse continuous laser output required by the present invention. The beam expander expands the laser and forms a resonant cavity with other devices to increase the light intensity. When the transmission-type pulse continuous laser modulator starts working, a circular specified electric field is formed after a voltage is applied to the liquid crystal panel by controlling the annular circuit board through an external computer. In this way, the absorption and release of light by the graphene surface and the steering of the liquid crystal molecules can be controlled to generate ultrashort pulse laser and vortex light respectively, thereby realizing the mode-tunable vortex light spot ring ultrashort pulse continuous laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a structural diagram of a tunable center point pulse vortex light ring continuous laser system according to an embodiment of the present invention; Figure 2 Schematic diagram of the structure of the transmission type continuous pulse laser modulator described in an embodiment of the present invention; Figure 3 It is an overall diagram of the transmission-type pulse continuous laser modulator described in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0018] Embodiment 1, This embodiment provides a tunable center point pulse vortex light ring continuous laser system, such as Figure 1 As shown, the system includes a 792nm pump source 1, a coupling lens group 2, a plano-concave total reflection mirror 3, a Tm:YLF crystal 4, a beam expander 5 and a transmission type pulse continuous laser modulator 10; The 792nm pump source 1 is used to emit pump light, the coupling lens group 2 is used to shape the pump light, the side of the plano-concave total reflection mirror 3 that receives the pump light is a plane mirror, and the side that emits the pump light is a concave mirror, the plano-concave total reflection mirror 3, Tm:YLF crystal 4, beam expander 5 and transmission type pulse continuous laser modulator 10 form a gain cavity, the pump light is gain amplified in the gain cavity, and ultrashort pulse laser and vortex light output are generated.

[0019] The plano-concave total reflection mirror 3 and the transmissive pulse continuous laser modulator 10 form a resonant cavity for generating laser light. Without adding a beam expander 5, the oscillation spot in the cavity is very small, resulting in a small spot area irradiated on the surface of the transmissive pulse continuous laser modulator 10, and a small number of liquid crystal molecules are fully utilized, which cannot be modulated efficiently. However, with the addition of a beam expander 5 in the cavity, the area of ​​the oscillation spot can be expanded, thereby expanding the utilization range of the liquid crystal panel 6 and achieving the best light field modulation effect.

[0020] The coupling lens group 2 is composed of a group of Kepler collimating and focusing lens groups. Since the numerical aperture of the optical fiber used in the fiber-coupled pump source is generally around 0.22, according to the divergence angle formula, the spot diameter will expand by 4mm when the 792nm laser is emitted at a position of 10mm. In order to shape the laser beam, a group of Kepler collimating and focusing lens groups are used to form a coupling system to shape the pump light, thereby improving the pump coupling efficiency and the output beam quality, and expanding the LD pump light with a core diameter of 200μm to a circular spot of 600μm to enter the Tm:YLF crystal 4.

[0021] In the group of Kepler collimating and focusing lenses, the focal length of one lens is 25 mm, and the focal length of the other lens is 75 mm.

[0022] In the experiment, the Tm:YLF crystal was wrapped with a metal heat sink and connected to a water cooler to dissipate heat so that its side temperature was maintained at around 20°C.

[0023] The transmission type pulse continuous laser modulator 10 comprises a liquid crystal panel 6, a graphene saturable absorber 8 and a ring circuit board 11. The liquid crystal panel 6 has a hole in the middle, the graphene saturable absorber 8 is placed at the hole in the middle of the liquid crystal panel 6, and the ring circuit board 11 is connected end to end around the liquid crystal panel 6. Its structure is as follows: Figure 2 The overall structure after combination is shown as Figure 3 shown.

[0024] The upper and lower surfaces of the liquid crystal panel 6 are both flat and are both provided with a PI alignment layer 7. Through rubbing alignment and drying and curing operations, the liquid crystals inside are all given a pre-tilt angle.

[0025] The liquid crystal panel 6 is coated with a film layer 9 with a transmittance of 5% for 1908nm laser on the PI orientation layer 7 on the output side of the optical path. Tm: YLF crystal 4 has a strong absorption peak at 792nm that is different from other bands of light. The lower energy level particles absorb photon energy to the upper energy level. This stage is called stimulated absorption. The particles at the upper energy level are limited by the energy level life and the external radiation field. After a certain period of time, they will transition to the lower energy level and generate coherent photons. During the transition, a certain amount of energy will be released, which is called stimulated radiation. This part of light is amplified back and forth through the action of the resonant cavity. This is the laser generated after stimulated radiation amplification, corresponding to the strong emission peak of the crystal itself. This laser is at 1.9μm. Laser generation requires three elements: a specific band excitation source, a working substance and a resonant cavity. As long as the resonant mirror film system is selected correctly and the distance between them is within the stable area, laser can be generated.

[0026] The annular circuit board 11 is controlled by a computer. The computer controls the voltage of the annular circuit board 11 to change the arrangement director of the local liquid crystal in the liquid crystal panel 6, thereby achieving the effect of light field regulation.

[0027] The upper and lower surfaces of the liquid crystal panel 6 are both flat, so it can be used as a flat total reflector. This device is used to oscillate the light in the cavity while also using a saturable absorber to perform pulse modulation at the center and regulate the surrounding light field, emitting center point pulse laser and continuous vortex halo laser.

[0028] Specifically, the center point pulse laser is the result of the operation of the graphene saturable absorber 8 at the center. The normal laser emission is continuous, and it will become pulsed light after passing through it. There is no participation of the graphene saturable absorber 8 around it, so it still maintains a continuous mode state. However, it will be controlled by the liquid crystal panel 6 after the electric field is applied to regulate the light field and produce an ideal vortex halo, which is modulated simultaneously.

[0029] The application principle of graphene is further introduced. When the incident light is strong enough, the optical waveguide of graphene material shows nonlinear characteristics. When the incident light intensity is weak, the valence band electrons can jump to the conduction band by absorbing photons, but as the light intensity increases further, the conduction band is easily filled. Due to the effect of the Pauli exclusion principle, the valence band electrons cannot further absorb photons, so it is equivalent to that photons can pass through graphene without loss, that is, under high light intensity, graphene has a higher optical conductivity coefficient. It can be simply understood that when the light intensity is absorbed, it will cause great loss. During this period, no light can be output, but after reaching the saturated absorption state, there is no loss to light, and the laser can pass and output. After the material's own electrons are restored, it can absorb light again. This period is the time to restore the absorption capacity, which is called the recovery time. Therefore, by using the above nonlinear optical properties of graphene, it can be designed as a saturable absorber and used to generate ultrashort pulses to obtain ultrashort pulse laser output. This part is the phenomenon that when the material is in the initial stage and the input light intensity is weak, it can absorb photon energy and make its internal energy level transition spontaneously, and the electrons transition from low energy level to high energy level. Then the light loss is very large and cannot pass through the material. As the input light intensity becomes higher, the energy level of the material reaches a saturated state, which makes the material approach a transparent state on a macro scale and does not absorb light. As a result, light can pass through the material without loss. After that, because the material itself has a certain recovery time, it can return from a transparent state to a state of absorbing light. This recovery stage is the recovery time, so each pulse interval depends on the length of this recovery time. On a long time scale, an ultrashort pulse sequence is formed, which is what we call ultrafast light, generally in the picosecond level or even up to femtoseconds. This pulse form is different from the milliseconds, microseconds, and nanoseconds output of ordinary pulsed lasers.

Claims

1. A tunable center point pulse vortex halo continuous laser system, characterized in that: The system comprises a 792 nm pump source (1), a coupling lens group (2), a plano-concave total reflection mirror (3), a Tm:YLF crystal (4), a beam expander (5) and a transmission-type pulse continuous laser modulator (10); The 792nm pump source (1) is used to emit pump light, the coupling lens group (2) is used to shape the pump light, the side of the plano-concave total reflection mirror (3) that receives the pump light is a plane mirror, and the side that emits the pump light is a concave mirror, the plano-concave total reflection mirror (3), the Tm:YLF crystal (4), the beam expander (5) and the transmission-type pulse continuous laser modulator (10) form a gain cavity, the pump light is gain-amplified in the gain cavity, and ultrashort pulse laser and vortex light output are generated.

2. The tunable center point pulse vortex light ring continuous laser system according to claim 1, characterized in that: The coupling lens group (2) consists of a group of Kepler collimating and focusing lenses.

3. The tunable center point pulse vortex light ring continuous laser system according to claim 2, characterized in that: In the group of Kepler collimating and focusing lenses, the focal length of one lens is 25 mm, and the focal length of the other lens is 75 mm.

4. The tunable center point pulse vortex light ring continuous laser system according to claim 3, characterized in that: The transmission-type pulse continuous laser modulator (10) comprises a liquid crystal panel (6), a graphene saturable absorber (8) and an annular circuit board (11); the liquid crystal panel (6) has an opening in the middle, the graphene saturable absorber (8) is placed at the opening in the middle of the liquid crystal panel (6), and the annular circuit board (11) is connected end to end around the liquid crystal panel (6).

5. The tunable center point pulse vortex light ring continuous laser system according to claim 4, characterized in that: The upper and lower surfaces of the liquid crystal panel (6) are both flat and are both provided with a PI orientation layer (7). Through friction orientation and drying and curing operations, the liquid crystals inside are all given a pre-tilt angle.

6. The tunable center point pulse vortex light ring continuous laser system according to claim 5, characterized in that: The liquid crystal panel (6) is plated with a film layer (9) having a transmittance of 5% for 1908 nm laser light on the PI orientation layer (7) on the light path output side.

7. The tunable center point pulse vortex light ring continuous laser system according to claim 6, characterized in that: The annular circuit board (11) is controlled by a computer, and the computer controls the voltage of the annular circuit board (11) to change the arrangement director of the localized liquid crystal in the liquid crystal panel (6), thereby achieving the effect of light field regulation.

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