Picosecond laser with high beam quality

Abstract

The invention relates to a picosecond laser with high beam quality, comprising: a pumping source for providing pumping energy to an amplification crystal; the laser oscillator is used for providing signal light with high light beam quality for the amplification crystal; the amplification crystal is used for amplifying the signal light power; the pump light shaping system comprises a first lens group and a third plano-convex lens, the first lens group is arranged between the pump source and the amplification crystal and formed by combining a first plano-convex lens and a second plano-convex lens, the third plano-convex lens and the first lens group are arranged at intervals, and the pump light is subjected to quasi-collimation processing through the first lens group; third plano-convex lenses which are arranged at intervals are used for focusing, so that the Rayleigh length of the pump light after focusing completely falls into the amplification crystal; the signal light shaping system comprises a fourth plano-convex lens arranged on the upstream of the light path of the amplification crystal and a second lens group formed by combining a fifth plano-convex lens and a first plano-concave lens, and the signal light is focused through the fourth plano-convex lens. After beam expansion and collimation are carried out through the second lens group, the Rayleigh length of the signal light completely falls into the amplification crystal, the pump light and the signal light are in a uniform distribution state in the amplification crystal, and the amplification crystal generates uniform heat distribution to eliminate the thermal lens effect. The generation probability of a thermally induced birefringence effect and a thermally induced teratosis effect is reduced, and the amplification efficiency of the light beam and the quality of the output light beam are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of picosecond lasers, and in particular to a picosecond laser with high beam quality. Background Art

[0002] Traditional high-energy single-pulse lasers face the problem of limited amplification power when their energy exceeds 1mJ and is on the order of ten picoseconds, accompanied by severe high-order mode effects, resulting in poor beam quality.

[0003] For high-energy diode-pumped solid-state lasers, under high-power pumping conditions, the laser crystal will produce significant thermal effects. Part of the pump light is effectively converted into laser output, while the other part of the pump light is converted into heat and deposited inside the laser crystal. This heat deposition will cause uneven temperature distribution inside the crystal, which in turn causes a refractive index gradient distribution. This gradient distribution will further produce a series of thermal effects, including thermal lens effect, thermally induced birefringence effect, and thermally induced distortion effect.

[0004] It is worth noting that the thermal lens focal length of the laser crystal will change with the change of pump power, which in turn will lead to corresponding changes in the equivalent resonant cavity and the fundamental mode volume. These changes will have an adverse effect on the further improvement of the beam quality and power of the output laser.

[0005] Beam quality, as an important parameter of laser, largely determines the overall performance of the laser. In many laser applications, laser beam quality is often more critical than laser power. For a laser with a certain output power, the better the beam quality, the higher the laser brightness. High beam quality can bring higher laser brightness, thereby improving nonlinear conversion efficiency.

[0006] In laser processing applications such as laser cutting and drilling, high-quality laser beams can form smaller convergent spots, which means that when processing the same material, less laser power is required and less material waste is caused. At the same time, when the convergent spot size is the same, the laser with high beam quality has a smaller divergence angle and a greater processing depth.

[0007] In military applications, high-quality laser beams are also of great significance. They can form smaller far-field light spots, thereby enhancing the effect of the laser. Therefore, controlling and improving the quality of laser beams is a key technical issue to be solved in this field. Summary of the invention

[0008] Based on this, in order to solve the above problems, the present invention provides a picosecond laser with high beam quality, which greatly improves the quality of the laser output beam.

[0009] To achieve the above-mentioned purpose, the present invention provides a picosecond laser with high beam quality, comprising: a pump source, used to provide pump energy to an amplifying crystal; a laser oscillator, used to provide signal light with high beam quality to the amplifying crystal; an amplifying crystal, used to amplify the signal light power; a pump light shaping system, comprising a first lens group formed by a first plano-convex lens and a second plano-convex lens and arranged between the pump source and the amplifying crystal, and a third plano-convex lens arranged at intervals from the first lens group, wherein the pump light is subjected to quasi-collimation treatment by the first lens group, and then focused by the third plano-convex lens arranged at intervals so that the Rayleigh length of the focused pump light completely falls within the amplifying crystal; a signal light shaping system, comprising a fourth plano-convex lens arranged upstream of the amplifying crystal optical path, and a second lens group formed by a fifth plano-convex lens and a first plano-concave lens, wherein the signal light is focused by the fourth plano-convex lens, and then expanded and collimated by the second lens group so that the Rayleigh length of the signal light completely falls within the amplifying crystal.

[0010] In one specific embodiment, the diameter of the collimated light spot output by the lens group in the pump light shaping system is 1-1.5 mm, the spaced plano-convex lenses are located at a position where the diameter of the light spot is 3 mm, and the second lens group in the beam shaping system is placed at a position where the light spot is 1-1.3 mm.

[0011] In one specific embodiment, the power of the signal light provided by the laser oscillator is 1mw~10mw, M2 is less than 1.1, the pulse width is 10~100 picoseconds, and the repetition frequency is 20~50KHZ.

[0012] In one specific embodiment, the amplifying crystal includes at least three stages of amplifying crystals connected in series on an optical path, wherein each stage of the amplifying crystal is independently provided with a pump source, and the signal light shaping system is provided before each stage of the amplifying crystal.

[0013] In one specific embodiment, the optical distance between each stage of amplification crystal is more than 1 m.

[0014] In one specific embodiment, it also includes an output light shaping system, including an eighth plano-convex lens and a ninth plano-convex lens confocally arranged along the optical path and an aperture at the real focus of the eighth plano-convex lens and the ninth plano-convex lens. After the signal light is focused by the eighth plano-convex lens, it passes through the aperture and is then transmitted to the ninth plano-convex lens to output the light beam.

[0015] In one specific embodiment, the pump source is an LD pump source, and the wavelength of the output laser is 888 nm.

[0016] In one specific embodiment, the amplifying crystal is Nd:YVO4, with a length of L. The amplifying crystal is subjected to gradient doping treatment, with a doping concentration of 0% in the first section and a length of L / 6, a doping concentration of 0.1%~0.2% in the second section and a length of L / 6, a doping concentration of 0.3%~0.5% in the third section and a length of L / 3, a doping concentration of 0.6%~0.8% in the fourth section and a length of L / 3, the first section is an end close to a pump source, and the fourth section is an end far from the pump source.

[0017] In one specific embodiment, the substance doped into the amplifying crystal is one of Er3+, Yb3+, Nd3+, Tm3+ or Pr3+.

[0018] In one of the specific embodiments, the amplifying crystal is arranged on a crystal seat, TEC temperature control is arranged around the crystal seat, and a water channel is arranged on the TEC heating surface for heat dissipation.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The pump light shaping system makes the Rayleigh length of the focused pump light fall completely inside the amplifying crystal, and the signal light shaping system makes the Rayleigh length of the signal light also fall completely inside the amplifying crystal. Therefore, inside the amplifying crystal, the pump light and the signal light can achieve efficient and uniform interaction. The pump light provides energy and the signal light is amplified. What is particularly important is that the pump light and the signal light are both evenly distributed inside the amplifying crystal. Therefore, during the laser amplification process, the heat generated by the amplifying crystal is also uniform. The uniform heat distribution eliminates the thermal lens effect, reduces the probability of thermally induced birefringence effect and thermally induced distortion effect, and greatly improves the amplification efficiency of the light beam and the quality of the output light beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a schematic diagram of the structure of a picosecond laser with high beam quality according to the present invention. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0022] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like 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 an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0025] like Figure 1 As shown, this embodiment provides a picosecond laser with high beam quality, including: a pump source 10, used to provide pump energy to the amplifying crystal 20, after the pump energy is absorbed by the amplifying crystal 20, the particles inside the amplifying crystal are excited to a high energy level, providing a basis for subsequent laser generation; a laser oscillator 30, used to provide a signal light with high beam quality to the amplifying crystal 20, the power of the signal light is 1mw, M 2The pump light shaping system 40 comprises a first lens group formed by a first plano-convex lens 401 and a second plano-convex lens 402 arranged between the pump source 10 and the amplifying crystal 20, and a third plano-convex lens 403 arranged at intervals from the first lens group. The pump light is collimated by the first lens group, and then focused by the third plano-convex lens 403 arranged at intervals so that the Rayleigh length of the focused pump light completely falls within the range of Inside the amplifying crystal 20, the pump light can be ensured to be uniformly distributed inside the amplifying crystal 20; the signal light shaping system 50 includes a fourth plano-convex lens 501 disposed upstream of the amplifying crystal optical path, a fifth plano-convex lens 502 located at 1-1.3 mm of the light spot, and a first plano-concave lens 503 to form a second lens group. The signal light is focused by the fourth plano-convex lens 501, and then expanded and collimated by the second lens group so that the Rayleigh length of the signal light completely falls inside the amplifying crystal 20, ensuring that the signal light is uniformly distributed inside the amplifying crystal 20. In this embodiment, the pump light shaping system 40 and the signal light shaping system 50 are provided. Inside the amplifying crystal 20, the pump light and the signal light interact with each other, the pump light provides energy, and the signal light is amplified. Since the pump light and the signal light are uniformly distributed inside the amplifying crystal 20, the heat generated by the amplifying crystal is also uniform. The uniform heat distribution can greatly eliminate the thermal lens effect, thereby improving the amplification efficiency of the light beam and the quality of the output light beam.

[0026] In one specific embodiment, the diameter of the collimated light spot output by the first lens group in the pump light shaping system 40 is 1-1.5 mm, more specifically, the diameter of the collimated light spot is 1.3 mm, the third plano-convex lens 403 is located at a position where the spot diameter is 3 mm, and the final shaped pump light spot diameter is 2 mm, and the Rayleigh length is 160 mm.

[0027] In one specific embodiment, the power of the signal light provided by the laser oscillator 30 is 1mw~10mw, M2 is less than 1.1, the pulse width is 10~100 picoseconds, and the repetition frequency is 20~50KHZ.

[0028] In one specific embodiment, the amplifying crystal 20 includes at least three stages of amplifying crystals connected in series on the optical path, wherein each stage of the amplifying crystal is individually provided with a pump source, and the signal light shaping system is provided before each stage of the amplifying crystal. Exemplarily, a secondary signal light shaping system 51 and a secondary amplifying crystal 52 are also connected to the optical path downstream of the amplifying crystal 20, and the secondary signal light shaping system 51 includes a sixth plano-convex lens 511 provided on the optical path upstream of the secondary amplifying crystal, a seventh plano-convex lens 512 located at 1 mm of the light spot, and a third lens group formed by combining a second plano-concave lens 513, the signal light is focused by the sixth plano-convex lens 511, and then expanded and collimated by the third lens group so that the Rayleigh length of the signal light completely falls inside the secondary amplifying crystal 52, the secondary pump source 10' provides pump light to the secondary amplifying crystal 52, and a secondary pump light shaping system 40' is also provided between the secondary pump source 10' and the secondary amplifying crystal 52, and its specific structure and working principle are the same as those in the above embodiment, and will not be repeated here. Furthermore, a three-stage signal light shaping system 53 and a three-stage amplifying crystal 54 are connected to the optical path downstream of the two-stage amplifying crystal 52. The three-stage pump source 10'' provides pump light to the three-stage amplifying crystal 54. A three-stage pump light shaping system 40'' is also arranged between the three-stage pump source 10'' and the three-stage amplifying crystal 54. The specific structure and working principle of the three-stage signal light shaping system 53 and the three-stage pump light shaping system 40'' are the same as those in the above embodiment, and will not be repeated here.

[0029] In one specific embodiment, the optical path between each stage of amplifying crystals is more than 1 m, and when the signal light is transmitted in the optical path, the high-order modes at the edge will diverge and be lost during the transmission process, so the high-order modes at the edge of the amplified light spot can be eliminated, and the edge high-order modes can be prevented from entering the next stage of amplifying crystals and being further amplified, generating heat and causing the beam quality to deteriorate. Exemplarily, the optical path between each stage of amplifying crystals is 2 m, 3 m, 4 m, 5 m, 6 m, 7 m, 8 m, 9 m, or more than 10 m.

[0030] In one specific embodiment, it also includes an output light shaping system 60, including an eighth plano-convex lens 601 and a ninth plano-convex lens 602 that are confocally arranged in sequence along the optical path, and an aperture 603 at the real focus of the two plano-convex lenses. After the signal light is focused by the eighth plano-convex lens 601, it passes through the aperture 603 and is then transmitted to the ninth plano-convex lens 602 to output the light beam. The aperture 603 is used to eliminate high-order modes in the light beam. The output light beam is transmitted through the real focus, so that better light beam quality can be obtained.

[0031] In one of the specific embodiments, the pump sources at each stage are LD pump sources, and the wavelength of the output laser is 888nm, so that the absorption coefficients of the amplifying crystals at each stage to the pump light in each polarization direction can be equal, and the absorption coefficient of the YVO4 crystal to the 888nm pump light is small. A longer crystal can be used so that the heat can be diffused in a larger volume, alleviating the thermal effect in the crystal, which is conducive to achieving high beam quality and high-power laser output.

[0032] In one specific embodiment, the amplifying crystal is Nd:YVO4, with a length of L. The amplifying crystal is subjected to gradient doping treatment, with a doping concentration of 0% in the first section and a length of L / 6, a doping concentration of 0.1% to 0.2% in the second section and a length of L / 6, a doping concentration of 0.3% to 0.5% in the third section and a length of L / 3, a doping concentration of 0.6% to 0.8% in the fourth section and a length of L / 3, the first section being the end close to the pump source, and the fourth section being the end far from the pump source. The amplifying crystal in this embodiment is subjected to gradient doping treatment, with the doping concentration gradually increasing from the end face close to the pump source, and the farther from the pump end face, the higher the doping concentration. By gradually increasing the doping concentration, the absorption efficiency of the pump light inside the crystal is kept relatively stable, which can fully ensure that the heat generated by each section of the crystal is uniform, so that the heat of the pump light and the signal light is more evenly distributed along the axial direction of the amplifying crystal, eliminating the thermal lens effect, and improving the amplification efficiency of the light beam and the quality of the output light beam. Exemplarily, the substance doped into the amplifying crystal is one of Er3+, Yb3+, Nd3+, Tm3+ or Pr3+.

[0033] In one of the specific embodiments, the amplifying crystal is arranged on a crystal seat, and TEC temperature control is arranged around the crystal seat. The TEC heating surface is provided with water channels for heat dissipation, and the temperature control accuracy, temperature control effect and temperature control speed are greatly improved. The temperature control accuracy can reach 0.1°C, and the temperature around the crystal seat can be kept consistent. As the pump power increases, the heat generated by the crystal will continue to increase. The use of TEC temperature control can respond quickly and control the temperature quickly, and feedback adjustment will be performed according to the real-time heat and the cavity environment, thereby making the crystal temperature control more stable.

[0034] It should be noted that it is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any figure mark in the claims should not be regarded as limiting the claims involved.

[0035] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A picosecond laser with high beam quality, characterized in that: include: A pump source, used to provide pump energy to the amplifying crystal; A laser oscillator for providing high beam quality signal light to the amplifying crystal; Amplifying crystal, used to amplify the signal light power; A pump light shaping system comprises a first lens group formed by a first plano-convex lens and a second plano-convex lens and a third plano-convex lens arranged at intervals from the first lens group, wherein the pump light is subjected to quasi-collimation treatment by the first lens group and then focused by the third plano-convex lens arranged at intervals so that the Rayleigh length of the focused pump light completely falls within the amplifying crystal; The signal light shaping system comprises a fourth plano-convex lens arranged upstream of the amplifying crystal optical path and a second lens group formed by a fifth plano-convex lens and a first plano-concave lens. The signal light is focused by the fourth plano-convex lens and then expanded and collimated by the second lens group so that the Rayleigh length of the signal light falls completely inside the amplifying crystal.

2. A picosecond laser with high beam quality according to claim 1, characterized in that: The diameter of the collimated light spot output by the lens group in the pump light shaping system is 1-1.5 mm, the plano-convex lenses arranged at intervals are located at a position where the diameter of the light spot is 3 mm, and the second lens group in the beam shaping system is placed at a position where the light spot is 1-1.3 mm.

3. The picosecond laser with high beam quality according to claim 1, characterized in that: The power of the signal light provided by the laser oscillator is 1mw~10mw, M 2 Less than 1.1, pulse width is 10~100 picoseconds, and repetition frequency is 20~50KHZ.

4. The picosecond laser with high beam quality according to claim 1, characterized in that: The amplifying crystal comprises at least three stages of amplifying crystals connected in series on an optical path, wherein each stage of the amplifying crystal is independently provided with a pump source, and the signal light shaping system is provided before each stage of the amplifying crystal.

5. The picosecond laser with high beam quality according to claim 4, characterized in that: The optical distance between each level of amplification crystal is more than 1m.

6. The picosecond laser with high beam quality according to claim 4, characterized in that: It also includes an output light shaping system, including an eighth plano-convex lens and a ninth plano-convex lens confocally arranged along the optical path and an aperture at the real focus of the eighth plano-convex lens and the ninth plano-convex lens. After the signal light is focused by the eighth plano-convex lens, it passes through the aperture and is then transmitted to the ninth plano-convex lens to output the light beam.

7. The picosecond laser with high beam quality according to claim 1, characterized in that: The pump source is an LD pump source, and the wavelength of the output laser is 888nm.

8. The picosecond laser with high beam quality according to claim 1, characterized in that: The amplifying crystal is Nd:YVO4, and its length is L. The amplifying crystal is subjected to gradient doping treatment, wherein the doping concentration of the first section is 0%, and the length is L / 6; the doping concentration of the second section is 0.1%-0.2%, and the length is L / 6; the doping concentration of the third section is 0.3%-0.5%, and the length is L / 3; the doping concentration of the fourth section is 0.6%-0.8%, and the length is L / 3; the first section is the end close to the pump source, and the fourth section is the end far from the pump source.

9. The picosecond laser with high beam quality according to claim 8, characterized in that: The substance doped into the amplifying crystal is one of Er3+, Yb3+, Nd3+, Tm3+ or Pr3+.

10. The picosecond laser with high beam quality according to claim 1, characterized in that: The amplifying crystal is arranged on a crystal seat, TEC temperature control is arranged around the crystal seat, and a water channel is arranged on the TEC heating surface for heat dissipation.

Images