Compact high-power ring light spot pulse laser and working method thereof

Abstract

The invention discloses a compact high-power ring light spot pulse laser and a working method thereof. The annular light spot pulse laser comprises a pumping source, a gain medium, a first cavity mirror, a second cavity mirror, a scraper mirror and a Q switch. Based on the lath gain medium, a confocal unstable cavity structure is adopted, kilowatt-level ring light spot pulse laser is directly generated through modulation of the large-clear-aperture acousto-optic Q switch, the structural complexity of a main oscillation power amplification technology commonly used by a high-power pulse laser is overcome, the power upper limit of an existing Q-switched laser is improved, and the energy consumption of the Q-switched laser is reduced. And ring light spot output can be obtained without an additional beam shaping device, so that the laser is more compact in structure and higher in stability, and can be applied to the fields of laser surface treatment, laser welding and the like.

Description

Technical Field

[0001] The invention relates to a compact high-power annular spot pulse laser and a working method thereof, belonging to the technical field of lasers. Background Art

[0002] The rapid development of laser processing technology has put forward higher requirements for its core component - laser. In order to further improve processing efficiency, it is necessary to develop higher-power lasers. However, with the increase of laser power, the thermal effect in the processing process becomes more serious, which is destructive to the substrate of the workpiece, affecting the engineering application of high-power lasers.

[0003] In laser cleaning and laser welding applications, in order to overcome the adverse effects of thermal effects, on the one hand, short pulse lasers are used instead of traditional continuous lasers to reduce heat accumulation during processing through extremely high laser peak power and extremely short laser pulse action time. On the other hand, an annular spot is used instead of the traditional point spot to reduce the energy at the center of the spot and avoid problems such as explosion holes and spatter caused by excessive temperature of the laser molten pool. In the prior art, in order to obtain kilowatt-level short-pulse laser output, a rod-shaped gain medium Q-switched laser is usually used as the seed light, and the power is amplified by the main oscillator power amplifier structure to increase the laser power. In order to obtain an annular spot, an axicon lens is usually used to shape the beam. The laser using the above technical means is large in size, complex in structure, and has poor stability, which is not conducive to engineering applications. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a compact high-power annular spot pulse laser.

[0005] The present invention also provides a working method of the annular spot pulse laser.

[0006] The technical solution of the present invention is:

[0007] A compact high-power annular spot pulse laser comprises a pump source, a gain medium, a first cavity mirror, a second cavity mirror, a scraper mirror and a Q switch;

[0008] Wherein, the pump source is arranged on the upper side or the lower side of the gain medium; the cross section of the gain medium perpendicular to its end face is a trapezoid or a parallelogram, and the cross section perpendicular to its length direction is a rectangle;

[0009] The first cavity mirror is arranged on the left side of the left end surface of the gain medium, the scraper mirror is arranged on the right side of the right end surface of the gain medium, the Q switch is arranged on the right side of the scraper mirror, and the second cavity mirror is arranged on the right side of the Q switch;

[0010] The first cavity mirror and the second cavity mirror form a confocal resonant cavity; specifically, the curvature radius R1 of the first cavity mirror, the curvature radius R2 of the second cavity mirror and the cavity length L of the resonant cavity satisfy R1+R2=L, and the focal positions of the first cavity mirror and the second cavity mirror coincide.

[0011] The scraper mirror, the first cavity mirror and the second cavity mirror form a confocal unstable resonant cavity;

[0012] After the scraper mirror is inserted into the resonant cavity, the light in the resonant cavity is reflected by the scraper mirror and escapes from the resonant cavity after a finite number of round trips, and the resonant cavity becomes an unstable resonant cavity. (In the prior art, if the light will not escape laterally from the resonant cavity any number of times it goes back and forth in the resonant cavity, such a resonant cavity is a stable cavity. If a beam of light cannot exist in the cavity forever, and must escape laterally from the cavity after a finite number of round trips, it is called an unstable cavity).

[0013] The center of the scraper mirror transmits the laser, and the edge reflects the laser;

[0014] The focal length f1 of the first cavity mirror and the focal length f2 of the second cavity mirror satisfy

[0015] The pump source provides the energy required for particle number inversion; the gain medium is a crystal that realizes particle number inversion and generates laser light; the scraper mirror is a partial reflector that transmits laser light at the center and reflects laser light at the edge; the large-aperture acousto-optic Q switch realizes the modulation of the large-aperture laser beam in the cavity.

[0016] Preferably, the angle between the scraper mirror and the optical axis in the confocal resonant cavity is 10° to 60°.

[0017] Preferably, the gain medium is one of yttrium aluminum garnet crystal, yttrium vanadate crystal, sapphire crystal, glass, and ceramic; or the above substances doped with a laser ion; the laser ions include Nd, Yb, Ti, Pr, Cr, Tm, and Ho.

[0018] Preferably, the first cavity mirror is a plano-concave spherical reflector with a curvature radius of 1200 mm and a focal length f1=600 mm; the second cavity mirror is a plano-concave spherical reflector with a curvature radius of 600 mm and a focal length f2=300 mm; the focal length ratio

[0019] The scraper mirror is a coated scraper mirror, and a scraper mirror anti-reflection film coated area is arranged at the center of the front surface of the scraper mirror, and the area outside the scraper mirror anti-reflection film coated area is a scraper mirror high-reflection film coated area.

[0020] Further preferably, the second cavity mirror is configured as a plano-convex spherical reflector with a curvature radius of 400 mm, a focal length f2 = -200 mm, and a focal length ratio

[0021] The scraper mirror is a perforated scraper mirror, and a scraper mirror perforated area is arranged at the center of its front surface; the scraper mirror perforated area runs through the front and rear surfaces of the scraper mirror; the area on the front surface of the scraper mirror without a perforation is the scraper mirror high-reflection film-coated area.

[0022] Preferably, the light-transmitting area of ​​the Q switch is greater than 10 mm×20 mm, and greater than the area of ​​the laser transmission area in the center of the scraper mirror; the average diffraction efficiency is ≥80%. The maximum size of the light-transmitting aperture of the common acousto-optic Q switch in the prior art is about 12 mm. The present invention adopts the latest developed acousto-optic Q switch, and the light-transmitting aperture is greater than 10 mm×20 mm.

[0023] A working method of the above-mentioned annular spot pulse laser, wherein the activated particles in the gain medium produce a population inversion under the stimulation of the pump source 1, and photons are generated when the particles at the high energy level transition to the low energy level, and laser oscillation amplification is formed in the confocal resonant cavity formed by the first cavity mirror and the second cavity mirror;

[0024] The parallel light outputted from the right end face of the gain medium, the central part of the laser passes through the central transmission area of ​​the scraper mirror 5, passes through the Q switch, and is reflected back to the gain medium by the second cavity mirror;

[0025] The parallel light outputted from the right end face of the gain medium, the edge part of the laser is outputted through the edge reflection area of ​​the scraper mirror, and the output light spot is a "U"-shaped ring light spot, that is, the ring light spot described in the present invention;

[0026] When the Q switch is turned off, the confocal resonant cavity oscillation fails and the activated particles in the gain medium continue to accumulate; when the Q switch is turned on, photons are released instantaneously, generating high-energy spike pulse lasers; when the Q switch is turned on and off periodically at the nanosecond level, high-power nanosecond lasers are generated.

[0027] The beneficial effects of the present invention are as follows:

[0028] The present invention is based on a slab gain medium and adopts a confocal unstable cavity structure. It directly generates a kilowatt-level annular spot pulse laser through large-aperture acousto-optic Q-switch modulation, which overcomes the structural complexity of the main oscillator power amplification technology commonly used in high-power pulsed lasers, improves the power upper limit of existing Q-switched lasers, and can obtain annular spot output without the need for additional beam shaping devices, making the laser structure more compact and more stable, and can be applied to laser surface treatment, laser welding and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the optical structure of the laser 1 described in Example 3;

[0030] Figure 2 This is a schematic diagram of the optical structure of the laser 2 described in Example 4;

[0031] Figure 3 This is a schematic diagram of the shape of the “U”-shaped ring light spot;

[0032] Figure 4 This is a schematic diagram of the structure of the coating scraper mirror of the present invention;

[0033] Figure 5 This is a schematic diagram of the structure of the hole-opening scraper mirror of the present invention;

[0034] Figure 6 This is a screenshot of the power meter interface for the pulse laser power test described in Example 6;

[0035] Figure 7 This is a screenshot of the oscilloscope interface for the pulse width test of the pulse laser described in Example 6;

[0036] Among them, 1. Pump source; 2. Gain medium; 3. First cavity mirror; 4. Second cavity mirror; 5. Scraper mirror; 6. Q switch; 7. Scraper mirror high-reflection film-coated area; 8. Scraper mirror anti-reflection film-coated area; 9. Scraper mirror opening area. DETAILED DESCRIPTION

[0037] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0038] Example 1

[0039] like Figure 1 shown.

[0040] A compact high-power annular spot pulse laser comprises a pump source 1, a gain medium 2, a first cavity mirror 3, a second cavity mirror 4, a scraper mirror 5, and a Q switch 6;

[0041] The pump source 1 is arranged on the upper side of the gain medium 2; the cross section of the gain medium 2 perpendicular to its end face is a trapezoid, and the cross section perpendicular to its length direction is a rectangle;

[0042] The first cavity mirror 3 is arranged on the left side of the left end surface of the gain medium 2, the scraper mirror 5 is arranged on the right side of the right end surface of the gain medium 2, the Q switch 6 is arranged on the right side of the scraper mirror 5, and the second cavity mirror 4 is arranged on the right side of the Q switch 6;

[0043] The first cavity mirror 3 and the second cavity mirror 4 form a confocal resonant cavity;

[0044] The scraper mirror 5, the first cavity mirror 3 and the second cavity mirror 4 form a confocal unstable resonant cavity;

[0045] The center of the scraper mirror 5 transmits the laser, and the edge reflects the laser;

[0046] The focal length f1 of the first cavity mirror and the focal length f2 of the second cavity mirror satisfy

[0047] The gain medium is one of yttrium aluminum garnet crystal, yttrium vanadate crystal, sapphire crystal, glass, ceramics; or the above substances doped with a laser ion; the laser ions include Nd, Yb, Ti, Pr, Cr, Tm, Ho. The gain medium 2 material of this embodiment is neodymium-doped yttrium aluminum garnet Nd:YAG; the length, width and height of the gain medium 2 are 130mm×5mm×50mm.

[0048] Example 2

[0049] As in the compact high-power annular spot pulse laser described in Example 1, further, the angle between the scraper mirror 5 and the optical axis in the confocal resonant cavity is 30°.

[0050] Example 3

[0051] As described in the compact high-power annular spot pulse laser of Example 1, further, the first cavity mirror 3 is a plano-concave spherical reflector with a curvature radius of 1200 mm and a focal length f1=600 mm; the second cavity mirror 4 is a plano-concave spherical reflector with a curvature radius of 600 mm and a focal length f2=300 mm; the focal length ratio

[0053] The scraper mirror 5 is a coated scraper mirror, such as Figure 4 As shown, a scraper mirror anti-reflection film coating area 8 is arranged at the center of the front surface, and the area outside the scraper mirror anti-reflection film coating area 8 is a scraper mirror high-reflection film coating area 7. In this embodiment, the scraper mirror anti-reflection film coating area 8 is a rectangular area of ​​2mm×20mm.

[0054] Example 4

[0055] The compact high-power annular spot pulse laser as described in Example 1 is different in that the second cavity mirror 4 is configured as a plano-convex spherical reflector with a radius of curvature of 400 mm, a focal length f2 = -200 mm, and a focal length ratio

[0056] The scraper mirror 5 is a perforated scraper mirror, such as Figure 5 As shown, a scraper mirror opening area 9 is provided at the center of the front surface; the scraper mirror opening area 9 penetrates the front and rear surfaces of the scraper mirror 5; the area on the front surface of the scraper mirror 5 without opening is the scraper mirror high-reflection film-plated area 7. In this embodiment, the scraper mirror opening area 9 is a square hole of 1.5 mm×15 mm in size.

[0057] Example 5

[0058] As described in the compact high-power annular spot pulse laser of Example 1, further, the light-transmitting area of ​​the Q switch 6 is larger than 10 mm×20 mm, and larger than the area of ​​the central laser transmission area of ​​the scraper mirror 5; the average diffraction efficiency is ≥80%. In this embodiment, the Q switch 6 adopts the SGQ27 acousto-optic Q switch, and its light-transmitting aperture is 12 mm×30 mm.

[0059] Example 6

[0060] A working method of the ring spot pulse laser as described in Example 1, wherein the activated particles in the gain medium 2 produce a population inversion under the stimulation of the pump source 1, and photons are generated when the particles at the high energy level transition to the low energy level, and laser oscillation amplification is formed in the confocal resonant cavity formed by the first cavity mirror 3 and the second cavity mirror 4;

[0061] The parallel light outputted from the right end face of the gain medium 2, the central part of the laser passes through the central transmission area of ​​the scraper mirror 5, then passes through the Q switch 6, and is reflected back to the gain medium 2 by the second cavity mirror 4;

[0062] The parallel light outputted from the right end face of the gain medium 2 has its edge laser outputted through the edge reflection area of ​​the scraper mirror 5, and the output light spot is a "U"-shaped ring light spot, i.e., the ring light spot described in the present invention; Figure 3 As shown;

[0063] When the Q switch 6 is turned off, the confocal resonant cavity oscillation fails, and the activated particles in the gain medium 2 continue to accumulate; when the Q switch 6 is turned on, the photons are released instantly, generating high-energy spike pulse lasers; when the Q switch 6 is turned on and off periodically at the nanosecond level, high-power nanosecond lasers are generated. This embodiment achieves high-power nanosecond laser output with an average power of 2180W and a pulse width of 51ns. Figure 6 As shown, it is a screenshot of the power test of the pulse laser in this embodiment. Figure 7 This is a screenshot of the pulse width test of the pulse laser in this embodiment.

Claims

1. A compact high-power annular spot pulse laser, characterized in that: The invention comprises a pump source, a gain medium, a first cavity mirror, a second cavity mirror, a scraper mirror and a Q switch; wherein the pump source is arranged on the upper side or the lower side of the gain medium; the cross section of the gain medium perpendicular to its end face is a trapezoid or a parallelogram, and the cross section perpendicular to its length is a rectangle; the first cavity mirror is arranged on the left side of the left end face of the gain medium, the scraper mirror is arranged on the right side of the right end face of the gain medium, the Q switch is arranged on the right side of the scraper mirror, and the second cavity mirror is arranged on the right side of the Q switch; the first cavity mirror and the second cavity mirror form a confocal resonant cavity; the scraper mirror, the first cavity mirror and the second cavity mirror form a confocal unstable resonant cavity; the center of the scraper mirror transmits laser light, and the edge reflects laser light; the focal length f1 of the first cavity mirror and the focal length f2 of the second cavity mirror satisfy 2. The compact high-power annular spot pulse laser according to claim 1, characterized in that: The angle between the scraper mirror and the optical axis in the confocal resonant cavity is 10° to 60°.

3. The compact high-power annular spot pulse laser according to claim 1, characterized in that: The gain medium is one of yttrium aluminum garnet crystal, yttrium vanadate crystal, sapphire crystal, glass, and ceramic; or the above substances doped with a laser ion; the laser ions include Nd, Yb, Ti, Pr, Cr, Tm, and Ho.

4. The compact high-power annular spot pulse laser according to claim 1, characterized in that: The first cavity mirror is a plano-concave spherical reflector with a curvature radius of 1200 mm and a focal length f1=600 mm; the second cavity mirror is a plano-concave spherical reflector with a curvature radius of 600 mm and a focal length f2=300 mm; the focal length ratio The scraper mirror is a coated scraper mirror, and a scraper mirror anti-reflection film coated area is arranged at the center of the front surface of the scraper mirror, and the area outside the scraper mirror anti-reflection film coated area is a scraper mirror high-reflection film coated area.

5. The compact high-power annular spot pulse laser according to claim 1, characterized in that: The second cavity mirror is set as a plano-convex spherical reflector with a curvature radius of 400 mm and a focal length f2 = -200 mm. The scraper mirror is a perforated scraper mirror, and a scraper mirror perforated area is arranged at the center of its front surface; the scraper mirror perforated area runs through the front and rear surfaces of the scraper mirror; the area on the front surface of the scraper mirror without a perforation is the scraper mirror high-reflection film-coated area.

6. The compact high-power annular spot pulse laser according to claim 1, characterized in that: The light-transmitting area of ​​the Q switch is larger than 10 mm×20 mm, and larger than the area of ​​the central laser transmission area of ​​the scraper mirror; the average diffraction efficiency is ≥80%.

7. A method for operating the annular spot pulse laser according to any one of claims 1 to 6, characterized in that: The activated particles in the gain medium produce a population inversion under the stimulation of the pump source 1, and the particles at the high energy level generate photons when they transition to the low energy level, forming laser oscillation amplification in the confocal resonant cavity formed by the first cavity mirror and the second cavity mirror; The parallel light outputted from the right end face of the gain medium, the central part of the laser passes through the central transmission area of ​​the scraper mirror 5, then passes through the Q switch, and is reflected back to the gain medium by the second cavity mirror; The parallel light outputted from the right end face of the gain medium, the edge part of the laser is outputted through the edge reflection area of ​​the scraper mirror, and the output light spot is a "U"-shaped ring light spot, that is, the ring light spot described in the present invention; When the Q switch is turned off, the confocal resonant cavity oscillation fails and the activated particles in the gain medium continue to accumulate; when the Q switch is turned on, photons are released instantaneously, generating high-energy spike pulse lasers; when the Q switch is turned on and off periodically at the nanosecond level, high-power nanosecond lasers are generated.

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