CN102035126A - All-solid-state laser for laser texturing of metal - Google Patents

Abstract

An all-solid-state laser for laser texturing, comprising a laser DC power supply, a Q-switch driver, a water cooler, and an all-solid-state texturing laser device, wherein the all-solid-state texturing laser device includes total reflection mirrors connected in series with the optical axis in sequence , Laser generating device, photoelectric gate and laser output mirror and laser power detection device are suitable for roughening of high-quality metal surfaces. The laser in the present invention adopts a small size, low doping concentration double-rod series connection and a thermally induced birefringence compensation device, combined with a thermally unstable cavity design, to skillfully resolve the contradiction between high power and high beam quality. Compared with the prior art, the all-solid-state laser texturing laser of the present invention has high beam energy density and small divergence angle, can increase the laser texturing density, has long service life of the laser module, and is convenient for maintenance.

Description

An all-solid-state laser for metal laser texturing

technical field

The invention relates to the structure and application of a diode-pumped all-solid-state laser, in particular to the structure and application of a high-power, high-beam-quality all-solid-state laser suitable for metal surface texturing.

Background technique

Laser texturing is a cold-rolled steel roll texturing technology developed by the steel industry to produce high-quality steel plates. The Institute of Mechanics, Chinese Academy of Sciences has been researching laser texturing technology since 1990, for example: Chinese patent number: ZL92113223.9, title: "High repetition frequency modulation multi-pulse YAG laser engraving system and processing method"; Chinese patent number: ZL94220848 .X, name: "Laser processing equipment for surface texturing of rolls". The equipment uses a lamp-pumped neodymium-doped yttrium-aluminum garnet (Nd:YAG) laser with high energy density and high repetition rate as the texturing light source for helical scanning. When the laser beam is focused on the surface of the roll, a number of tiny Melt pool: After the light pulse stops, the melt of the micropit cools rapidly to form a surface-hardened micropit and a pit-side boss structure.

But so far, laser texturing devices have used lamp-pumped YAG lasers as the light source. Its disadvantage is that the life of the xenon lamp is limited, and the maintenance period of the equipment in production is relatively short; in addition, the thermal effect of the laser crystal is obvious when the xenon lamp is used as the light source. , not only the electro-optic efficiency is low, but the important thing is that the beam quality of the laser beam is greatly limited. However, with the vigorous development of domestic automobile, home appliance and machinery manufacturing industries, the requirements for surface roughness uniformity and texture density of high-quality steel plates are getting higher and higher, which requires that the laser output beam not only have high power, but also It also has high beam quality at the same time. Some new products require the laser texture density to reach ≥70 dots/mm ² , which is difficult to achieve with conventional lamp-pumped YAG lasers.

Contents of the invention

In order to solve the above-mentioned difficulties in the prior art, the present invention designs an all-solid-state laser texturing laser. An all-solid-state laser for laser texturing, including a laser DC power supply, a Q switch driver, and a water cooler; it also includes an all-solid-state texturing laser device, and the all-solid-state texturing laser device includes all Reflector, laser generating device, photoelectric gate and laser output mirror and laser power detection device.

Further, the laser generating device includes a 45° optical rotator connected in series with the optical axis, an acousto-optic Q switch, and a diode laser side-pumped laser module.

Further, the laser generating device includes an acousto-optic Q switch connected in series with the optical axis, two diode laser side-pumped laser modules, and an optical axis connected in series between the two diode laser side-pumped laser modules. 90° optical rotator.

Further, the diode laser side-pumped laser module is all solid-state, adopts a laser crystal with an ion doping concentration ≤ 0.7% and a diameter ≤ 5mm, and adopts a three-dimensional or five-dimensional symmetrical side-pumped structure of a laser diode.

Further, the distance from the main plane of the laser crystal in the diode laser side-pumped laser module to the cavity mirror is equal to the focal length of the thermal lens generated by the laser crystal when the power of the laser diode is increased to the highest.

Further, the photoelectric gate can turn on or off the operation of the laser at any time; the beam expander and the laser power monitoring device are designed according to the specific needs of the texturing equipment.

Further, the acousto-optic Q switch performs waveform modulation on the laser beam, and controls the morphology of the textured point by controlling the waveform morphology.

Further, the two laser modules are identical, and the distance between the main planes of the two laser crystals is equal to twice the focal length of the thermal lens generated by the laser crystals when the power of the laser diode is increased to the highest.

Further, the diode laser side-pumped laser module uses a laser diode to side-pump a solid laser medium, and the laser medium can be Nd:YAG crystal, Nd:GGG crystal, Nd:GdVO4 crystal or Yb:YAG crystal.

The invention adopts the laser diode (LD) as the laser module series structure of the pump source, adopts the laser crystal with small size and low doping concentration, and combines thermally induced birefringence compensation and thermal near-unstable cavity technology, so that the output beam can be obtained at the same time High power and high beam quality. The laser is used as the light source of the texturing equipment to realize the improvement of the precision of the texturing roll, which is conducive to the localization of low roughness, high density, and high uniformity high-quality automobiles and home appliance panels.

Description of drawings

Fig. 1 is a block diagram of laser of the present invention;

Fig. 2 is a kind of structural light path schematic diagram of laser device of the present invention;

Fig. 3 is another kind of structured optical path schematic diagram of the laser of the present invention;

Figure 4 is the curve of the spot radius at the laser crystal with the thermal lens;

Fig. 5 is a laser output power curve obtained by an example of the laser of the present invention.

Detailed ways

Example 1:

Fig. 1 is a structural block diagram of an all-solid-state laser for metal laser texturing disclosed by the present invention, which includes a laser DC power supply A, a Q switch driver B, an all-solid-state texturing laser device C and a water cooler D. The specific structure of the all-solid-state textured laser device C is shown in Figure 2, including: a total reflection mirror 1, a laser output mirror 2, a 90° optical rotator 8, an acousto-optic Q switch 4, and two diode laser side-pumped laser modules 5, 9, photoelectric gate 6, beam expander and laser power monitoring device 7, wherein total reflection mirror 1 and laser output mirror 2 form a resonant cavity; 90° optical rotator 8, acousto-optic Q switch 4, two diode laser side pumps The Pu laser modules 5 and 9 constitute a laser generating device. Acousto-optic Q switch 4, diode laser side-pumped laser module 5, 90° optical rotator 8, diode laser side-pumped laser module 9, and photogate 6 are sequentially arranged in the resonant cavity in the same optical axis and in series to expand the beam The mirror and laser power monitoring device 7 are arranged outside the output section of the resonant cavity. Diode laser side-pumped laser modules 5 and 9 are two identical diode laser side-pumped laser modules; their power is 300W; LD five-dimensional symmetry and side-pumped Nd:YAG crystals are used, and each diode laser is side-pumped The laser module adopts 30 laser diode arrays, and the maximum output power of each diode array is 40W; the Nd:YAG crystal is 140mm long, 5mm in diameter, and the doping concentration is 0.6%. The two Nd:YAG rods connected in series in the two diode laser side-pumped laser modules are sister rods, and a 90° quartz crystal optical rotation plate is placed in the middle, thereby realizing effective birefringence compensation of the laser, making radial and tangential polarization components have the same phase lag. The total reflection mirror adopts a flat mirror, and part of the output coupling mirror, that is, the laser output mirror 2 in the figure is also a flat mirror, and the transmittance to 1064nm laser is 40%. The laser adopts a symmetrical flat cavity structure. The unstable cavity method is used to accurately measure each laser rod separately, that is, the two Nd:YAG rods are sister rods. After the thermal focal length is generated, the length of the resonant cavity is designed according to the laser stability conditions so that the two end mirrors are total reflection mirrors. 1 and the beam expander are equal to the distances from the end faces of the two nearest diode laser side-pumped laser modules 5 and 9, which are equal to the focal length of the thermal lens generated by the laser crystal when the excitation current of the laser diode is increased to a maximum of 32A. The distance between the main planes of the laser crystal is equal to 350mm, that is to say, it is equal to twice the focal length of the thermal lens generated by the laser crystal when the power of the laser diode in the side-pumped laser module of the diode laser is added to the highest, and the two are sister rods The main planes of the laser crystal are imaged on the main plane of each other, so that the radial and tangential polarization components have the same phase retardation, thereby realizing the effective birefringence compensation of the laser. At this time, the laser cavity operates in the "thermally unstable cavity" mode. In this operating mode, the self-limiting mode effect of the Nd:YAG rod greatly improves the quality of the laser beam. Figure 5 shows the continuous power output curve of the laser obtained in the laboratory. When the highest output power is 623W, the laser beam quality factor M2<10.

Example 2:

As shown in Fig. 2, the laser device of embodiment 2 comprises: total reflection mirror 1, laser output mirror 2, 45 ° optical rotator 3, acousto-optic Q switch 4, diode laser side-pumped laser module 5, photoelectric gate 6; Beam mirror and laser power monitoring device7. The total reflection mirror 1 and the laser output mirror 2 form a resonant cavity, the 45° optical rotator 3, the acousto-optic Q switch 4, and the diode laser side-pumped laser module 5 form a laser generating device. And 45° optical rotator 3, acousto-optic Q switch 4, diode laser side-pumped laser module 5, and photoelectric gate 6; they are arranged in the resonant cavity in series with the same optical axis, beam expander and laser power monitoring device 7 Set outside the output section of the resonant cavity. Diode laser side-pumped laser module 5 is all solid-state, adopts low doping concentration: ion doping concentration ≤ 0.7% and small aperture size: laser crystal with diameter ≤ 5mm, adopts a three-dimensional or five-dimensional symmetrical side pumping structure of a laser diode . The 45° optical rotator 3 is a 45° Faraday optical rotator; it is used to compensate the thermal birefringence effect of the laser crystal: the 45° optical rotator 3 is placed in the middle of the laser module 5 and the total reflection mirror 1, and the laser crystal in the laser module 5 The distance from the principal plane to the resonator mirror is equal to the focal length of the thermal lens produced by the laser crystal when the power of the laser diode is added to the highest value. Then the main plane of the laser crystal is fully mirrored on itself, and when the laser beam passes through the 45° optical rotator 3 back and forth, the radial and tangentially polarized light have the same phase delay, thereby compensating for the thermally induced birefringence effect. The photoelectric gate 6 can turn on or off the operation of the laser at any time; the beam expander and the laser power monitoring device 7 are designed according to the specific needs of the texturing equipment. The acousto-optic Q switch 4 performs waveform modulation on the laser beam, and achieves the purpose of controlling the textured point morphology by controlling the waveform morphology.

The laser structure of the present invention is that in the laser resonator formed by the total mirror 1 and the output mirror 2, a photogate 3 is placed on the same optical axis, and one or two diode laser side-pumped laser modules 5 (and 9), An acousto-optic Q switch 4, an optical rotator 3 (or 8); a beam expander and a laser power monitoring device 7 are installed outside the output resonator mirror. Among them, the laser modules 5 and 9 are all solid-state, and the performance is exactly the same. The laser diode is used as the pumping light source, and the laser crystal is pumped symmetrically from the side by using a three-dimensional or five-dimensional structure.

By rationally designing the distance between the laser diode and the laser crystal, the pumping efficiency of the diode and the uniformity of the gain in the laser crystal are improved. Moreover, the laser crystal geometry, dimensions, doping concentration, and optical grade used are exactly the same. Since a laser crystal with a lower doping concentration can obtain a more uniform pump gain distribution, the thermal effect of the laser crystal, including thermal lens effect, thermally induced birefringence effect and thermal depolarization effect, can be reduced. Therefore, the present invention uses laser crystals with lower doping concentration, for example, ion doping concentration ≤ 0.7%, to obtain higher beam quality while keeping the output power basically unchanged. Simultaneously, the aperture size of the laser crystal adopted in the present invention is small, for example: the diameter of the rod-shaped crystal is usually ≤5mm. When designing the laser cavity structure, it is required that the fundamental mode volume on the laser medium should be as large as possible when the laser is working. At this time, the laser The crystal is equivalent to a self-selecting mode device, so that on the one hand, the effective mode volume is increased, and on the other hand, the lateral size of the laser medium itself can be used to act as a mode-limiting diaphragm, thereby suppressing high-order modes and obtaining low-order mode output , to further improve the beam quality of the oscillating laser.

In order to increase the output power of the laser, the present invention adopts thermally induced birefringence compensation measures. The basic idea of compensating the thermally induced birefringence effect is: in some way, the radially and tangentially polarized radiation passing through each point on the same or the same laser crystal section can obtain equal phase retardation, so that the reduction can be achieved. The purpose of small depolarization loss; at the same time, the stable regions of the two polarized lights overlap each other, so as to achieve the purpose of increasing the pump power and finally increasing the output power. As shown in Figure 2, when two laser modules 5 and 9 with identical performance are connected in series, a 90° optical rotation plate 8 is placed in the middle, and the distance between the main planes of the two laser crystals is equal to adding the laser diode power to At the highest point, the focal length of the thermal lens produced by the laser crystal is twice the focal length, and the main planes of the two sister rods of the laser crystal are imaged on the main plane of each other, so that the radial and tangential polarization components have the same phase lag, thus realizing the laser Effective birefringence compensation. As shown in accompanying drawing 3 again, place 45 ° optical rotator 3 in the middle of laser module 5 and total reflection mirror 1, and the distance from the main plane of laser crystal in laser module 5 to resonant cavity mirror is equal to adding the laser diode power to the highest The focal length of the thermal lens produced by the laser crystal. Then the main plane of the laser crystal is imaged by the total reflection mirror on itself. When the laser light passes through the 45° Faraday rotator 3 back and forth, the radial and tangentially polarized light have the same phase delay, thereby compensating for the thermally induced birefringence effect.

The laser cavity of the present invention adopts a "thermal near-unstable cavity structure", which can alleviate the contradiction between high power and high beam quality. Using the ABCD propagation matrix, the relationship between the laser spot radius at the laser crystal and the thermal lens is numerically simulated, and a U-shaped curve with an upward opening is obtained as shown in Figure 4, and it can be seen from the analysis in Figure 4 that when the laser operates in a stable At the edge of the characteristic curve, the volume of the fundamental mode increases, and better beam quality can be expected. At the same time, the thermal lens of the laser crystal is very short when operating here, indicating that the pumping power of the laser diode can be maximized. It can be seen that the thermal near-unstable cavity structure can make full use of the self-limiting mode effect of the laser medium, and at the same time can maximize the pumping power of the laser diode. Therefore, under the premise of ensuring the output laser power, the thermal lens effect is fully utilized to ensure Laser beam quality has its unique advantages.

The all-solid-state laser of the invention can be used for laser texturing production of metal surfaces, and is mainly used in texturing equipment for laser texturing production of rolls. The laser has stable performance and is easy to maintain. First of all, the laser module is a real modular structure. When the service life is over, it can be directly replaced with a new module without any maintenance work in the middle. Through the acousto-optic Q switch, the waveform of the laser beam is modulated, and the waveform shape is controlled to achieve the purpose of controlling the shape of the textured point. In texturing production, the photoelectric gate can control the operation of the laser at any time. According to the specific texturing equipment, a special beam expander is customized to facilitate the transmission of the laser beam in the texturing equipment. At the same time, in order to monitor the stability of the laser, the laser is also equipped with a laser power monitoring device. In addition, the laser of the present invention adopts corresponding protective measures to ensure its practical application: optical elements with high damage threshold are selected, all cavity optical elements are water-cooled, and the working environment of the laser and its optical path system is guaranteed to be stable, clean, and dry by relying on mechanical design, increasing Low cooling water pressure protection and emergency stop device for emergencies.

To sum up, the laser of the present invention adopts various measures to ensure that the output beam obtains high power and high beam quality at the same time. First of all, the laser module adopted in the present invention has unique advantages. The laser diode is used instead of the xenon lamp as the pumping light source, which greatly improves the utilization efficiency of the light source, thereby reducing the thermal effect of the laser crystal, greatly increasing the pumping power and finally increasing the output power, while reducing waste heat loss and improving Electric energy utilization efficiency reduces loss; the present invention adopts laser crystal with low doping concentration, which can obtain uniform gain distribution, thereby obtaining higher beam quality on the basis of keeping the output power basically unchanged; the laser crystal aperture adopted by the present invention If the size is small, the laser crystal itself is equivalent to a self-selecting mode device, thereby suppressing the high-order mode and improving the beam quality of the oscillating laser. In addition, the present invention utilizes thermally induced birefringence compensation measures, so that the radial and tangentially polarized radiation at each point on the same laser crystal section can obtain equal phase delays, so as to achieve the purpose of reducing depolarization loss; at the same time, the two The stable regions of the polarized light overlap each other, and finally achieve the purpose of increasing the pump power and finally increasing the output power. Finally, the laser cavity of the present invention adopts a "thermally unstable cavity structure", which can alleviate the contradiction between high power and high beam quality, and make full use of the self-limiting mode effect of the laser medium while maximizing the pumping power of the laser diode. , so under the premise of ensuring the output laser power, the thermal lens effect is fully utilized to ensure the quality of the laser beam, which has its unique advantages. Therefore, using the laser of the present invention as the light source of the texturing equipment can improve the precision of the texturing roll, and can be applied to the texturing of high-quality automobiles and home appliance panels with low roughness, high density, and high uniformity.

Claims (9)

1. An all-solid-state laser for laser texturing, comprising a laser DC power supply, a Q switch driver, and a water cooler; it is characterized in that it also includes an all-solid-state texturing laser device, and said all-solid-state texturing laser device includes, coaxial A total reflection mirror, a laser generating device, a photogate, a laser output mirror and a laser power detecting device are connected in series in sequence. 2. The all-solid-state laser according to claim 1, wherein the laser generating device comprises a 45° optical rotator connected in series with the optical axis, an acousto-optic Q switch, and a diode laser side-pumped laser module. 3. The all-solid-state laser according to claim 1, characterized in that, the laser generating device comprises, an acousto-optic Q switch connected in series with the optical axis, two diode laser side-pumped laser modules, in the two There is also a 90° optical rotator connected in series with the optical axis between the diode laser side-pumped laser modules. 4. The all-solid-state laser according to claims 2 and 3, characterized in that the diode laser side-pumped laser module is all-solid-state, adopts laser crystals with ion doping concentration≤0.7% and diameter≤5mm, adopts laser Three-dimensional or five-dimensional symmetrical side-pumped structures of diodes. 5. The all-solid-state laser according to claim 2, characterized in that the distance from the main plane of the laser crystal in the diode laser side-pumped laser module to the resonator mirror is equal to the laser crystal when the power of the laser diode is added to the highest The resulting thermal lens focal length. 6. The all-solid-state laser according to claims 2 and 3, characterized in that the photoelectric gate can turn on or off the operation of the laser at any time; the beam expander and the laser power monitoring device are designed according to the specific needs of the texturing equipment. 7. The all-solid-state laser according to claim 1, characterized in that the acousto-optic Q switch performs waveform modulation on the laser beam, and the purpose of controlling the morphology of the textured point is achieved by controlling the waveform morphology. 8. The all-solid-state laser according to claim 3, characterized in that, the two laser modules are identical, and the distance between the main planes of the two laser crystals is equal to the heat generated by the laser crystal when the power of the laser diode is added to the highest. Twice the focal length of the lens. 9. according to the described all-solid-state laser of claim 2 and 3, it is characterized in that, described diode laser side-pumped laser module adopts laser diode side-pumped solid-state laser medium, and laser medium can be Nd:YAG crystal, Nd:GGG crystal, Nd:GdVO4 crystal or Yb:YAG crystal.

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