Slat laser

Abstract

The invention discloses a slab laser, which comprises a laser medium arranged in a slab shape; the pumping source is arranged on at least one end surface, side surface or large surface of the laser medium; the resonant cavity comprises a first lens, a second lens and a third lens, the first lens and the second lens are arranged on the two sides of the end face of the laser medium respectively, the third lens is arranged between the laser medium and the second lens, the first lens and the second lens form an optical resonant cavity, and the focal points of the first lens and the second lens coincide. The focal length f1 of the first lens and the focal length f2 of the second lens meet the following condition: # imgabs0 #; the third lens is used as a diaphragm inside the resonant cavity and reflects laser to the outside of the resonant cavity; and the Q switch is arranged between the third lens and the second lens. According to the invention, the lath-shaped laser medium is adopted as the oscillator, and the cavity type structure characteristics of the unstable cavity and the application of the third lens are combined, so that the size limitation of a Q switch is broken through, the laser output of the high-power Q-switched lath laser is obtained, and the power upper limit of the existing Q-switched laser is improved.

Description

Technical Field

[0001] The present invention relates to the field of solid laser technology, and more specifically to a high-power large-aperture Q-switched slab laser. Background Art

[0002] Traditional high-power Q-switched rod lasers have obvious thermal effects under high-power pump source pumping conditions due to radial temperature gradients, which not only limits the size of the rod laser gain medium used for rod lasers, but also limits the maximum power that can be obtained by high-power Q-switched rod lasers. At present, the maximum Q-switched output average power that can be obtained by high-power Q-switched rod oscillators is about 1kW. However, when using the master oscillator power amplifier (MOPA) structure, the Q-switched laser output of the high-power rod Q-switched oscillator can be used as the seed light to further increase the laser power, but its device is relatively complex, and the gain medium used in the amplifier in the MOPA structure is generally a slab gain medium.

[0003] Therefore, considering directly using slab lasers to output high-power Q-switched laser output, in the current slab laser Q-switched laser Q-switched structure design, the size of the Q switch needs to match the size of the slab laser gain medium in the width direction, but the slab laser has a larger spot size in the width direction. In slab lasers, higher-power laser output often means a larger slab laser gain medium and a larger laser spot. At present, the maximum aperture of the Q switch is generally around 10mm to 12mm. Only a few Q-switched crystals such as KDP crystals can achieve a maximum aperture of about 25mm, but they are only suitable for electro-optical Q-switching. In addition, when the frequency requirement is reduced to 1kHz, the maximum aperture of the Q switch can be 99mm, but it will limit the frequency of the output laser. Therefore, in the current design of Q-switched slab lasers, the power of the Q-switched laser output obtained by directly using slab lasers is not high, generally in the hundreds of watts. In view of the above situation, we propose a high-power large-aperture Q-switched slab laser device to solve these problems. Summary of the invention

[0004] The object of the present invention is to provide a high-power large-aperture Q-switched slab laser.

[0005] According to one aspect of the present invention, there is provided a slab laser, comprising:

[0006] The laser medium is arranged in a slab shape;

[0007] A pump source is disposed on at least one end face, side face or large face of the laser medium;

[0008] A resonant cavity, comprising a first lens and a second lens respectively arranged on both sides of the end face of the laser medium, and a third lens arranged between the laser medium and the second lens, wherein the first lens and the second lens form an optical resonant cavity, the focal points of the first lens and the second lens coincide, and the focal length f of the first lens 1 and the focal length f of the second lens 2 satisfy: The third lens is used to act as an aperture inside the resonant cavity and reflect the laser light outside the resonant cavity;

[0009] The Q switch is arranged between the third lens and the second lens.

[0010] Optionally, in the resonant cavity, the first lens and the second lens form an unstable cavity in the fast axis direction of the laser, and form an unstable cavity or a stable cavity in the slow axis direction of the laser, and the unstable cavity formed in the fast and slow axis directions is one of a positive branch unstable cavity or a negative branch unstable cavity.

[0011] Optionally, the ratio of the spot size of the parallel light passing through the third lens in the fast and slow axis directions to the full-aperture spot size is greater than or equal to the absolute value of the ratio of the focal lengths of the second lens to the first lens.

[0012] Optionally, the part of the parallel light that passes through the third lens and resonates in the resonance cavity can be diverged to a full aperture when reaching the first lens after being reflected by the second lens.

[0013] Optionally, the ratio of the aperture d of the Q switch, the focal length of the first lens and the second lens is And the width D of the laser medium satisfies the formula:

[0014] Optionally, the shape of the laser medium is a rectangle, a trapezoid or a parallelogram in a cross-section perpendicular to the width direction.

[0015] Optionally, the first lens is a concave mirror, the second lens is a concave mirror or a convex mirror, and the third lens is a plane mirror.

[0016] Optionally, an angle is set between the third lens and the optical axis of the resonant cavity, and the light aperture is adjusted by adjusting the position of the third lens in the light path.

[0017] Optionally, an angle is provided between the third lens and the optical axis of the resonant cavity, and the third lens is provided with a hole for passing light.

[0018] Optionally, the activated ions in the laser medium include at least one of Nd, Yb, Ti, Pr, Cr, Tm or Ho, and / or the matrix material of the laser medium includes at least one of crystal, glass and ceramic.

[0019] The beneficial effects of the present invention are as follows:

[0020] The technical solution provided by the present invention has beneficial technical effects: compared with the prior art, the direct use of slab lasers as oscillators combined with the characteristics of the unstable cavity structure and the application of the third lens breaks through the size limitation of the Q switch, thereby obtaining a high-power Q-switched slab laser output, which increases the power upper limit compared with the traditional Q-switched rod laser and the existing Q-switched slab laser, and has a relatively simple structure compared with the Q-switched laser with MOPA structure. In particular, in the Q-switched laser, the innovative application of the cavity design and the scraper mirror is combined, and the characteristics of the unstable cavity structure part of the laser as the seed light for resonance greatly reduce the demand of the Q-opening aperture of the Q-switched slab laser, so that large-size and high-power slab laser devices can be used to directly generate Q-switched laser output without the need for complex MOPA structure design, thereby providing a guarantee for the realization of high-power Q-switched laser output. In addition, the structural design of the Q-switched slab laser is relatively flexible and can be adjusted according to actual conditions, which is also a major advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0022] Figure 1 A schematic structural diagram of a slab laser embodiment 1 of the present invention is shown.

[0023] Figure 2 A schematic structural diagram of a slab laser embodiment 2 of the present invention is shown.

[0024] Figure 3 A schematic structural diagram of slab laser embodiment 3 of the present invention is shown.

[0025] Figure 4 A schematic structural diagram of slab laser embodiment 4 of the present invention is shown.

[0026] Figure 5 A schematic diagram showing the structure of the slab laser embodiment 1 of the present invention in the slow axis direction.

[0027] Figure 6 A schematic diagram showing the structure of the slab laser embodiment 2 of the present invention in the slow axis direction. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0029] In order to overcome the problem of limited power of Q-switched lasers in the related art, the present disclosure provides a high-power large-aperture Q-switched slab laser. Figures 1 to 5 As shown, Figure 1 A schematic diagram of the fast axis structure of a high-power large-aperture Q-switched slab laser provided in an embodiment of the present invention; Figure 2 A schematic diagram of the fast axis structure of a high-power large-aperture Q-switched slab laser provided in an embodiment of the present invention; Figure 3 A schematic diagram of the fast axis structure of a high-power large-aperture Q-switched slab laser provided in an embodiment of the present invention; Figure 4 A schematic diagram of the fast axis structure of a high-power large-aperture Q-switched slab laser provided in an embodiment of the present invention; Figure 5 A schematic diagram of the slow axis structure of a high-power large-aperture Q-switched slab laser provided in an embodiment of the present invention; Figure 6 A schematic diagram of the slow-axis structure of a high-power, large-aperture Q-switched slab laser provided in an embodiment of the present invention.

[0030] like Figure 1 As shown, the slab laser of the embodiment of the present disclosure includes a slab-shaped laser medium 1, a resonant cavity composed of a first lens 2 and a second lens 3, a third lens 4 and a Q switch 5. The length of the slab-shaped laser medium 1 is greater than the width and greater than the thickness, and it can be a trapezoidal, rectangular and parallelogram slab, wherein the width direction of the slab laser medium is the laser fast axis direction, and the thickness direction is the laser slow axis direction. It has six faces, and the large face usually refers to the face orthogonal to the thickness direction. The large face has the largest area and can be used to install a cooling device and pump from this face. The face orthogonal to the width direction is usually the side face, and sometimes it can also be pumped through this face. The two faces perpendicular to the light transmission direction are end faces, which are the faces of laser output, and sometimes they are also pumped from the end faces. The resonant cavity includes a first lens 2, a second lens 3 and a third lens 4, wherein the first lens 2 and the second lens 3 are respectively arranged on both sides of the end face of the laser medium 1, and the focal length f of the first lens 2 is 1 Greater than the focal length f of the second lens 3 2 , and the two focal points coincide, the focal length of the first lens 2 is f 1 and the focal length f of the second lens 3 2 satisfy: In order to make the laser in the resonant cavity oscillate, the third lens 4 is a scraper mirror, which plays the role of aperture and output laser in the resonant cavity. In the process of the optical path in the cavity, in the direction of the laser fast axis, only a part of the parallel collimated laser emitted from the slat-shaped laser medium 1 passes through the scraper mirror to form resonance. This part of the laser is reflected by the second lens 3, and after passing through the common focus with the first lens 2, it can be diverged to the full aperture of the light spot when it reaches the first lens 2. At this time, the laser reflected back from the first lens 2 becomes parallel collimated light again. An angle is set between the third lens 4 and the optical axis of the resonant cavity, that is, the third lens 4 is tilted on the optical path, and the laser reaches When it reaches the third lens 4, it is reflected outward for output. Since the third lens 4 acts as an aperture, it is different for the positive branch unstable cavity and the negative branch unstable cavity. In the negative branch unstable cavity, the size design of the third lens 4 refers to the size of the parallel laser in the first half of the total laser passing through the third lens 4. In the positive branch unstable cavity, the size design of the third lens 4 refers to the size of the divergent laser in the second half of the third lens 4. In the direction of the laser slow axis, when the cavity type is designed as an unstable cavity, the resonance is the same as the direction of the laser slow axis. When the cavity type is designed as a stable cavity, the laser in the cavity resonates stably between the two cavity mirrors. The Q switch 5 is placed between the third lens 4 and the second lens 3 (rear cavity mirror). This design greatly reduces the size of the laser oscillating in the cavity of the slab laser without destroying the resonance conditions in the cavity, and provides a new technical path for directly applying the size-limited Q switch to large-size slab lasers.

[0031] In some embodiments, the third lens 4 with an opening can be replaced with a solid third lens 4, and the corresponding optical path design needs to be changed. The light aperture can be adjusted by adjusting the position of the third lens 4 in the optical path, such as Figure 1 As shown, in the unstable cavity using the third lens 4 with an opening, the focal points of the first lens 1 and the second lens 2 coincide with the central axis of the parallel light passing through the third lens 4, that is, the central axis perpendicular to the width direction of the slab laser medium 1, so the laser passing through the opening of the third lens 4 is symmetrical about the fast and slow axes of the slab laser gain medium, and the same is true for the laser reflected by the third lens 4 with an opening.

[0032] For an unstable cavity using a solid third lens 4, such as Figure 2 As shown, the overlapping focus of the first lens 1 and the second lens 2 needs to be on the central axis of the parallel light passing through the third lens 4. This is because the solid third lens 4 is different from the open third lens 4 and needs to be placed away from the width direction of the slat-shaped laser medium 1. Therefore, the position of the cavity mirror needs to be adjusted accordingly to achieve the effect of making the parallel collimated light passing through the third lens 4 diverge to the full aperture when it reaches the first lens 1 after being reflected by the second lens 2, that is, the light aperture is adjusted by adjusting the position of the third lens 4 in the optical path.

[0033] In some embodiments, in addition to using the negative branch unstable cavity structure, a positive branch unstable cavity structure can also be used, such as Figure 3 and Figure 4 As shown, the first lens 1 remains unchanged, and the second lens 2 uses a convex mirror. It should be noted that not all parallel light passing through the third lens 4 in the positive branch unstable cavity can form resonance. Only the part of parallel light that can reach the full aperture when it is reflected and diverged to the first lens 1 can form resonance. The ratio of the spot size of the parallel light passing through the third lens 4 in the fast and slow axis directions to the full aperture spot size is greater than or equal to the absolute value of the ratio of the focal length of the second lens 3 to the focal length of the first lens 2.

[0034] Q-switching technology is an effective method to obtain high-energy short pulses. The Q value is an indicator of the quality of the optical resonant cavity in the laser - the "quality factor". Q-switching technology is also called Q-switching technology. It compresses the general output continuous laser into a very narrow pulse width for emission, thereby increasing the peak power of the light source by several orders of magnitude.

[0035] During the Q-switching process, before the gain medium stores enough energy, the entire laser resonant cavity maintains a high cavity loss. At this time, the laser cannot produce laser oscillations due to its high threshold, so the number of upper energy level particles can accumulate in large quantities. When it accumulates to the saturation value, the cavity loss quickly decreases to a very small value. Therefore, in a short period of time, most of the energy stored in the upper energy level particles is converted into laser energy, generating a strong laser pulse output at the output end.

[0036] Q-switching technology is mainly divided into active Q-switching technology and passive Q-switching technology.

[0037] Active Q-switching technologies include acousto-optic Q-switching and electro-optic Q-switching. Acousto-optic Q-switching technology refers to placing an acousto-optic medium in a resonant cavity. When there is no ultrasonic wave, the light beam can pass through the acousto-optic medium freely. The Q value of the cavity is very high (low loss), and laser oscillation is easy to generate. When there is ultrasonic wave, the density of the acousto-optic medium changes periodically, resulting in periodic changes in the refractive index, causing the light beam to deflect. At this time, the Q value of the resonant cavity is very low (high loss), causing the number of particles in the upper energy level to accumulate rapidly. Therefore, we can achieve the effect of controlling the loss in the cavity by controlling the ultrasonic wave, and then obtain pulsed light output.

[0038] Electro-optical Q-switching uses the electro-optical effect of the crystal to add a step voltage to the crystal to adjust the reflection loss of photons in the cavity. When a high voltage is applied to the crystal, the electro-optical Q switch is in the closed state, the resonant cavity is in a low Q state, and the system is in an energy storage state. When the number of inverted particles in the resonant cavity reaches the maximum value, the high voltage on the crystal is suddenly removed, the resonant cavity is in a high Q state, and a pulsed laser output is formed.

[0039] Passive Q-switching technology is to set a saturable absorber (commonly used solid saturable absorber, such as Gr: YAG) in the laser resonant cavity, and use its saturated absorption effect to periodically control the resonant cavity loss to obtain pulsed light output. In the initial stage, the spontaneous fluorescence in the cavity is very weak, the absorption coefficient of the saturable absorber is very large, the light transmittance is very low, and the cavity is in a high loss state, so laser oscillation cannot be formed. With the continued action of the optical pump, the number of inverted particles continues to accumulate, and the fluorescence in the cavity continues to become stronger. When the light intensity reaches a certain value, the saturated absorber absorbs to a saturated value and is suddenly "bleached" to output a laser pulse, and then the light field in the cavity weakens, and the saturable absorber restores its absorption characteristics, and then the above process is repeated to obtain pulsed light output.

[0040] In some embodiments, the Q switch 5 can be an acousto-optic Q switch, an electro-optic Q switch or a Q-switched crystal, and the Q switch 5 is used to increase the peak power of the laser. The maximum aperture of the selected Q switch 5 is determined by the ratio of the focal lengths of the first lens 1 and the second lens 2 of the unstable cavity and the width direction size of the laser medium 1. Accordingly, for a Q switch 5 with a larger aperture, it can be applied to a slab laser of a larger size and higher power under the same cavity type. The aperture d of the Q switch, the ratio of the focal lengths of the first lens 2 and the second lens 3 And the width D of the laser medium 1 satisfies the formula:

[0041] In some embodiments, the shape of the slab-shaped laser medium 1 can be a rectangle, a trapezoid, or a parallelogram. The principle of the present technical solution is applicable to slabs of all shapes. However, in specific applications, the lens angle needs to be adjusted according to the actual designed slab gain medium size structure.

[0042] In some embodiments, the doping particles of the slab-shaped laser medium 1 may include at least one of Nd ions, Yb ions, Tm ions, and Ho ions. In other embodiments, the matrix material may be crystal, glass, or ceramic. Specifically, the material of the gain medium material may include but is not limited to Nd:YAG, Nd:YVO4, Nd:GdVO4, Nd:GSGG, Nd:GYSGG, Nd:LGG, Nd:GGG, Nd:YLF, Nd:YAP, Nd:S-FAP, Yb:YAG, Yb:YVO4, Yb:GGG, Yb:YLF, Yb:YAP, Yb:S-FAP, Tm:YAG, Tm:YVO4, Ho:YAP, Ho:YAG, Ti:Al2O3, Cr:BeAl2O4, Pr:YLF, Pr:YAP, Cr:GSGG, Cr:YAG, ruby ​​crystal, Nd ion doped ceramics, Yb ion doped ceramics, Nd ion doped glass, Yb ion doped glass, Tm ion doped ceramics, Ho ion doped ceramics, Tm ion doped glass, Ho ion doped glass, etc.

[0043] In some embodiments, Figure 5 As shown, it is a schematic diagram of the slow axis direction of the LD stacked array surface pumped negative-branch unstable cavity Q-switched slab laser. This technical solution is applicable to slab lasers with different pumping modes, which can be end pumping, surface pumping or side pumping; this technical solution is also applicable to different types of pump sources, and is mainly used in LD pumped slab lasers.

[0044] In other embodiments, Figure 6 As shown, since the thickness of the slab-shaped laser medium 1 is generally around 10 mm, the cavity type in the laser slow axis direction (slab thickness direction) can be set as an unstable cavity or a stable cavity. It is only necessary to ensure that the size of the Q switch 5 matches the size in the slab thickness direction.

[0045] The slab laser of the present invention is described in detail below based on specific embodiments.

[0046] Example 1

[0047] See also Figure 1 As shown, the laser medium 1 has an isosceles trapezoidal cross section perpendicular to the width direction, an end face cutting angle of 45°, a width of 69 mm, a length of 220 mm, a laser spot size of 69 mm×9 mm emitted from the laser medium 1, and a focal length of the first lens 1 of f 1 is 1500mm, the focal length of the second lens is f 2 The diameter of the laser beam is 500 mm, the zoom ratio is 3, and the laser spot size on the second lens 2 is 23 mm × 3 mm, so the aperture of the hole on the third lens 4 is set to 23 mm × 3 mm, and the Q switch 5 can use a KDP crystal electro-optical Q switch with a aperture of 25 mm. In the traditional slab Q-switched laser design, for the above-mentioned 220 mm × 69 mm × 9 mm slab laser gain medium, a Q switch with a aperture of at least 69 mm is required, which is basically impossible to achieve.

[0048] Example 2

[0049] See also Figure 2 As shown, the cross section of the laser medium 1 perpendicular to the width direction is an isosceles trapezoid, the end face cutting angle is 45°, the width is 60mm, the length is 200mm, the laser spot size emitted from the laser medium 1 is 60mm×10mm, and the focal length of the first lens 1 is f 1 is 1600mm, the focal length of the second lens is f 2 The focal length of the laser beam is 400 mm, the zoom ratio is 4, the laser spot size on the second lens 2 is 15 mm × 2.5 mm, and the size design of the solid third lens 4 is relatively not so strict. It is only necessary to ensure that the part in the optical path is 45 mm × 7.5 mm. The Q switch 5 can use a KDP crystal electro-optical Q switch with a light aperture of 17 mm.

[0050] Example 3

[0051] See also Figure 3 As shown, the laser medium 1 has an isosceles trapezoidal cross section perpendicular to the width direction, an end face cutting angle of 45°, a width of 63 mm, a length of 250 mm, a laser spot size of 63 mm×10.5 mm emitted from the laser medium 1, and a focal length of the first lens 1 of f 1 is 1400mm, the focal length of the second lens is f 2 The aperture of the hole on the third lens 4 can be set to 21mm×3.5mm, and the Q switch 5 can use a KDP crystal electro-optical Q switch with an aperture of 11mm. In the positive branch unstable cavity, the position restriction of the third lens 4 in the light-transmitting direction is stricter than that of the negative branch unstable cavity. Adjusting the position of the third lens 4 forward and backward in the light-transmitting direction will affect the size of the cavity loss.

[0052] Example 4

[0053] See also Figure 4 As shown, the laser medium 1 has an isosceles trapezoidal cross section perpendicular to the width direction, an end face cutting angle of 45°, a width of 74.5 mm, a length of 210 mm, a parallel laser spot size of 74.5 mm×12 mm emitted from the laser medium 1, and a focal length of the first lens 1 of f 1 is 1800mm, the focal length of the second lens is f 2 The optical diameter of the laser beam is -180mm, the zoom ratio is 10, and the laser spot size on the second lens 2 is 7.45mm×1.2mm, so the part of the light reflected by the third lens 4 can be set to 50mm×7.5mm. The Q switch 5 can use a KDP crystal electro-optical Q switch with a light aperture of 10mm.

[0054] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A slab laser, characterized in that: include: The laser medium is arranged in a slab shape; A pump source is disposed on at least one end face, side face or large face of the laser medium; A resonant cavity, comprising a first lens and a second lens respectively arranged on both sides of the end face of the laser medium, and a third lens arranged between the laser medium and the second lens, wherein the first lens and the second lens form an optical resonant cavity, the focal points of the first lens and the second lens coincide, and the focal length f1 of the first lens and the focal length f2 of the second lens satisfy: The third lens is used to act as an aperture inside the resonant cavity and reflect the laser light outside the resonant cavity; The Q switch is arranged between the third lens and the second lens.

2. The slab laser according to claim 1, characterized in that In the resonant cavity, the first lens and the second lens form an unstable cavity in the fast axis direction of the laser, and form an unstable cavity or a stable cavity in the slow axis direction of the laser. The unstable cavity formed in the fast and slow axis directions is one of a positive branch unstable cavity and a negative branch unstable cavity.

3. The slab laser according to claim 2, characterized in that The ratio of the spot size of the parallel light passing through the third lens in the fast and slow axis directions to the full-aperture spot size is greater than or equal to the absolute value of the ratio of the focal lengths of the second lens to the first lens.

4. The slab laser according to claim 2, characterized in that The part of the parallel light that passes through the third lens and forms resonance in the resonance cavity can be diverged to the full aperture when reaching the first lens after being reflected by the second lens.

5. The slab laser according to claim 1, characterized in that The ratio of the aperture d of the Q switch to the focal length of the first lens and the second lens And the width D of the laser medium satisfies the formula:

6. The slab laser according to claim 1, characterized in that The shape of the laser medium is a rectangle, a trapezoid or a parallelogram in a cross section perpendicular to the width direction.

7. The slab laser according to claim 1, characterized in that The first lens is a concave mirror, the second lens is a concave mirror or a convex mirror, and the third lens is a plane mirror.

8. The slab laser according to claim 7, characterized in that An included angle is set between the third lens and the optical axis of the resonant cavity, and the light aperture can be adjusted by adjusting the position of the third lens in the light path.

9. The slab laser according to claim 7, characterized in that An included angle is formed between the third lens and the optical axis of the resonant cavity, and the third lens is provided with a hole for passing light.

10. The slab laser according to claim 1, characterized in that The activated ions in the laser medium include at least one of Nd, Yb, Ti, Pr, Cr, Tm or Ho, and / or the matrix material of the laser medium includes at least one of crystal, glass and ceramic.

Images