Bi-pass amplifier structure and laser

Abstract

The bi-pass amplifier structure comprises a gain crystal of a lath-shaped structure, and seed light is arranged outside the end of the gain crystal; the two ends, oppositely arranged in the axial direction, of the gain crystal are inclined planes, the inclined plane at one end faces the seed light and is plated with an anti-reflection film layer, and the inclined plane at the other end is plated with a high-reflection film layer. The gain crystal further comprises a first reflecting surface and a second reflecting surface which are arranged on two axial sides in parallel at an interval; seed light enters the gain crystal through the antireflection film layer, is reflected by the first reflecting surface, the second reflecting surface and the high-reflection film layer, forms a zigzag back-and-forth light path in the gain crystal, and finally exits from the antireflection film layer. Thus, seed light passes through the gain crystal back and forth, bi-pass amplification of gains is achieved, back-and-forth light paths are different, reverse propagation of returned light is solved, meanwhile, arrangement of optical elements such as an isolator is omitted, overall light path arrangement is greatly simplified, the overall structure is simplified, and cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lasers, and in particular to a double-pass amplifier structure and a laser. Background Art

[0002] Optical amplification is an important link in laser technology. To achieve a high-energy pulsed laser, various amplification techniques are usually adopted, such as a master oscillator power amplification (MOPA) structure, a double-pass optical path that travels back and forth twice, etc., to increase the energy; double-pass amplification allows the optical signal to pass through the gain medium twice, thereby obtaining higher gain and significantly increasing the output energy of the laser. Double-pass amplification can make more full use of the population inversion distribution in the gain medium, thereby improving the energy conversion efficiency.

[0003] In the existing double-pass amplified laser system, since part of the light will be reflected back from the output end during the propagation of the light in the resonant cavity, the total reflection mirror of the round-trip optical path is also prone to form a resonant cavity with the oscillator, thus damaging the device. Therefore, an isolator needs to be added to protect the optical elements in the resonant cavity, avoid the reflected light from returning to the laser resonant cavity and causing frequency changes, and maintain the stable output of the laser energy. The isolator is like a "one-way valve", which only allows light to propagate in one direction (the direction from the inside of the laser to the outside), and blocks the reflected light from returning to the inside of the laser.

[0004] In the prior art, one or even two optical isolators need to be added between the oscillator and the amplifier to prevent the laser from returning and entering the resonant cavity in the reverse direction; multiple optical isolators greatly increase the cost, and greatly reduce the energy input from the oscillator to the amplifier, reducing the efficiency of the amplifier. In addition, generally, multiple mirrors need to be inserted into the amplification optical path to make the light beam incident on the same gain material at different angles multiple times, so as to fully extract the pump light energy stored in the gain material, block the transmission path of the reverse light while improving the isolation degree of the optical isolator, resulting in a complex overall optical path layout, a large geometric structure system, and high costs. Summary of the Invention

[0005] To solve the above problems, the present invention provides a double-pass amplifier structure and a laser with a reasonable structure, thereby eliminating the setting of optical elements such as isolators while solving the reverse propagation of the returned light, greatly simplifying the overall optical path layout, simplifying the overall structure, and reducing the cost.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A double-pass amplifier structure includes a gain crystal in a strip structure, and a seed light is arranged outside the ends of the gain crystal. The two ends of the gain crystal arranged axially opposite are set as inclined planes. One inclined plane faces the seed light and is coated with an antireflection film layer, and the other inclined plane is coated with a high-reflection film layer. The gain crystal also includes a first reflecting surface and a second reflecting surface that are spaced parallel on both sides of the axis. The seed light is incident into the gain crystal through the antireflection film layer, and the seed light is reflected by the first reflecting surface, the second reflecting surface, and the high-reflection film layer to form a zigzag reciprocating optical path in the gain crystal, and finally exits from the antireflection film layer.

[0008] As a further improvement of the above technical solution:

[0009] The optical axis of the emitted light of the seed light is consistent with the axis of the gain crystal.

[0010] The incident point and the exit point of the seed light on the gain crystal are both the midpoints of the antireflection film layer.

[0011] The seed light is the fundamental frequency light generated by a laser oscillation cavity, and the gain medium in the laser oscillation cavity is the same as the gain medium of the gain crystal.

[0012] The gain medium is one of Nd:YAG, Nd:YVO4, and Nd:YLF.

[0013] When the gain medium is Nd:YAG, the included angle between the antireflection film layer and the axis of the gain crystal is >55°.

[0014] The antireflection film layer and the high-reflection film layer are parallel to each other to form a gain crystal in a parallelogram structure; or, the antireflection film layer and the high-reflection film layer are each inclined relative to the axis of the gain crystal to form a gain crystal in a trapezoid structure.

[0015] The high-reflection film layer is a total reflection film layer for the seed light, and the antireflection film layer is an antireflection film layer for the seed light; the seed light located inside the gain crystal forms total reflection on the first reflecting surface, the second reflecting surface, and the high-reflection film layer.

[0016] The seed light is reflected at the midpoint of the high-reflection film layer, and the optical path of the seed light from the antireflection film layer towards the high-reflection film layer and the optical path from the high-reflection film layer towards the antireflection film layer are staggered from front to back.

[0017] A laser includes the double-pass amplifier structure described in any one of the above.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention enables the seed light to pass through the gain crystal back and forth, realizing double-pass amplification of the gain. The round-trip optical paths are different. While solving the problem of the reverse propagation of the return light, the setting of optical components such as isolators is eliminated, greatly simplifying the overall optical path layout, simplifying the overall structure, and reducing costs.

[0020] The present invention also has the following advantages:

[0021] The seed light forms different round-trip optical paths in the plate-shaped gain crystal, fully realizing double-pass amplification of the optical signal. Moreover, the return optical path is not coaxial with the laser oscillation cavity, eliminating the need to set an isolator in the optical path and eliminating the need to set complex optical components in the optical path, fundamentally solving the problem of the reverse propagation of the return light.

[0022] The reflections of the seed light in the gain crystal are all total reflections, effectively reducing the loss of laser energy. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of the present invention (the gain crystal is in the shape of a parallelogram).

[0024] Figure 2 It is a schematic principle diagram of the seed light of the present invention passing through the gain crystal.

[0025] Figure 3 It is Figure 2 A partial optical path schematic diagram at the antireflection coating layer in

[0026] Figure 4 It is a schematic structural diagram of the present invention (the gain crystal is in the shape of a symmetric trapezoid).

[0027] Figure 5 It is a schematic structural diagram of the present invention (the gain crystal is in the shape of an asymmetric trapezoid).

[0028] Wherein: 1. Seed light; 2. Gain crystal; 21. High-reflection coating layer; 22. Antireflection coating layer. Detailed Embodiments

[0029] The following combines the drawings to illustrate the detailed embodiments of the present invention.

[0030] As shown in Figure 1 , Figure 4 and Figure 5As shown in the figure, a dual-pass amplifier structure according to this embodiment includes a gain crystal 2 in a strip structure, and a seed light 1 is arranged outside the ends of the gain crystal 2; both ends of the gain crystal 2 arranged axially opposite to each other are set as inclined surfaces, one inclined surface faces the seed light 1 and is coated with an antireflection film layer 22, and the other inclined surface is coated with a high-reflection film layer 21; the gain crystal 2 also includes a first reflection surface and a second reflection surface that are spaced parallel on both sides of the axis; the seed light 1 is incident into the gain crystal 2 through the antireflection film layer 22, and the seed light 1 is reflected by the first reflection surface, the second reflection surface, and the high-reflection film layer 21 to form a zigzag round-trip optical path in the gain crystal 2, and finally exits from the antireflection film layer 22.

[0031] In this embodiment, the seed light can form a zigzag round-trip optical path in the gain crystal 2, which not only fully realizes the gain dual-pass amplification of the optical signal, but also makes the return optical path non-coaxial with the incident optical path through the formation of different round-trip optical paths, so that there is no need to set an isolator in the optical path, nor is there a need to set complex optical elements in the optical path, fundamentally solving the problem of reverse propagation of the return light.

[0032] The optical axis of the outgoing light of the seed light 1 is consistent with the axis of the gain crystal 2, so that in combination with the obliquely arranged antireflection film layer 22, it helps to effectively ensure the formation of a zigzag round-trip optical path of the seed light 1 in the gain crystal 2 and ensure the difference of the round-trip optical paths.

[0033] The incident point and the outgoing point of the seed light 1 on the gain crystal 2 are both the midpoints of the antireflection film layer 22 to ensure that the seed light will not overflow outside the cavity in the dual-pass amplifier.

[0034] The seed light 1 is the fundamental frequency light generated by the laser oscillation cavity, and the gain medium in the laser oscillation cavity is the same as the gain medium of the gain crystal 2.

[0035] The gain medium is one of Nd:YAG, Nd:YVO4, and Nd:YLF.

[0036] When the gain medium is Nd:YAG, the included angle (α) between the antireflection film layer 22 and the axis of the gain crystal 2 > 55°.

[0037] The antireflection film layer 22 and the high-reflection film layer 21 are parallel to each other to form a gain crystal 2 in a parallelogram structure; alternatively, the antireflection film layer 22 and the high-reflection film layer 21 are each obliquely arranged relative to the axis of the gain crystal 2 to form a gain crystal 2 in a trapezoidal structure.

[0038] In Figure 1 the embodiment shown in the figure, the gain crystal 2 is in a parallelogram structure.

[0039] In Figure 4 the embodiment shown in the figure, the antireflection film layer 22 and the high-reflection film layer 21 are symmetrically arranged to form a gain crystal 2 in a symmetric trapezoidal structure, that is, an isosceles trapezoidal structure.

[0040] In Figure 5 the illustrated embodiment, the antireflection film layer 22 and the high-reflection film layer 21 have different tilt angles, forming a gain crystal 2 with an asymmetric trapezoidal structure.

[0041] The high-reflection film layer 21 is a total reflection film layer for the seed light 1, and the antireflection film layer 22 is an antireflection film layer for the seed light 1; the seed light 1 located inside the gain crystal 2 forms total reflection on the first reflection surface, the second reflection surface, and the high-reflection film layer 21, effectively reducing the laser energy loss.

[0042] In this embodiment, the seed light 1 located inside the gain crystal 2 is obliquely incident on the first reflection surface, the second reflection surface, and the high-reflection film layer 21, respectively forming reflections, effectively ensuring the formation of the round-trip optical path.

[0043] The seed light 1 is reflected at the midpoint of the high-reflection film layer 21. The optical path of the seed light 1 from the antireflection film layer 22 towards the high-reflection film layer 21 and the optical path from the high-reflection film layer 21 towards the antireflection film layer 22 are staggered from front to back, thus solving the problem of the reverse propagation of the return light.

[0044] In this embodiment, the thickness of the gain crystal 2 can be 3 - 6 mm.

[0045] In this embodiment, the seed light is incident on the gain crystal 2 horizontally through the antireflection film layer 22, refracts at the antireflection film layer 22, and then is reflected by the first reflection surface, the second reflection surface, and in combination with the high-reflection film layer 21 to form a round-trip optical path. The return light is incident on the antireflection film layer 22 and exits from the antireflection film layer 22, and part of the light is reflected at the antireflection film layer 22 and returns to the inside of the gain crystal 2. As Figure 2 and Figure 3 shown, the tilt angle of the antireflection film layer 22, that is, the angle between the antireflection film layer 22 and the axis is α, the thickness of the gain crystal 2 is 2h, the refraction angle is ε, the incident angle is β; the complementary angle of the reflection angle of the seed light 1 on the reflection surface in the gain crystal 2 is η; the reflection angle of the return light of the seed light 1 on the reflection surface in the gain crystal 2 is θ; the incident angle ε' of the return light of the seed light 1 on the antireflection film layer 22 inside the gain crystal 2, and by reflection ε = ε';

[0046] L is the axial distance between the first reflection contact point of the seed light 1 incident on the gain crystal 2 and the center of the antireflection film layer 22, and l is the axial distance between the last reflection contact point of the seed light 1 in the gain crystal 2 and the center of the antireflection film layer 22;

[0047] The seed light 1 is incident on the gain crystal 2 along the horizontal direction. According to the law of refraction:

[0048]

[0049] n 1 and n2 are the refractive indices of the crystal and air respectively; at this time, the gain medium is set as Nd:YAG.

[0050] It can be known from the triangle geometric relationship that:

[0051] θ = 90° - ε - β (2)

[0052] η = β - ε (3)

[0053]

[0054] α = 90° - β (6)

[0055] Set L / l = N, then:

[0056]

[0057] To ensure total internal reflection in the gain crystal 2, it is necessary to satisfy 1.82sinθ = 1, that is, θ ≥ 33.3°.

[0058] In Figure 2 In the illustrated embodiment, when the gain crystal 2 has a parallelogram structure, its length T is:

[0059] T = 4KL;

[0060] where K is a positive integer; when K is a multiple of N, the above equation has a solution.

[0061] Thus, by adjusting the parameter N, the adjustment of the aspect ratio of the gain crystal 2 and the adjustment of the reflection angle θ can be achieved.

[0062] In this embodiment, according to actual requirements, the length of the gain crystal 2 can be adjusted so that in the round-trip optical path after the seed light 1 enters the gain crystal 2, one or more than two reflections are formed.

[0063] When N = 4, ε is solved as 14.8°, β is 27.7°, and the minimum reflection angle θ of the optical path on the upper and lower surfaces of the crystal is 47.5°, which is greater than the total internal reflection critical angle, and it can ensure that all the laser is reflected.

[0064] When N is odd, in the case where the simultaneous equations (2) and (3) have a solution, the gain crystal 2 can be made into an isosceles trapezoid structure as Figure 4 shown. For example, when N = 3, the gain crystal 2 can be an isosceles trapezoid structure with a base angle α = 62.3°.

[0065] In Figure 4 In the illustrated embodiment, when the gain crystal 2 has an isosceles trapezoid structure, its length T' is:

[0066]

[0067] Example 1:

[0068] Taking the center wavelength of the seed light 1 as 1064 nm, the angles α between the two end faces of the laser crystal 2 and the axis are both 62.3°, and the thickness of the laser crystal is 4 mm as an example;

[0069] According to the angle α, β (27.7°), ε (14.8°), and η (12.9°) can be calculated in sequence. Combining with h = 2 mm, l (2.18 mm) and L (8.73 mm) are obtained; thus, the length T of the gain crystal 2 with a parallelogram structure is calculated to be 34.9 mm, or an integer multiple of 34.9 mm.

[0070] The gain medium is set as Nd:YAG. The high-reflection film layer 21 is designed as HR@1064 nm, R > 99.9%, and the antireflection film layer 22 is designed as AR@1064 nm, R < 0.5%.

[0071] Through the above settings and selections, it can be ensured that total reflection and refraction output occur at the center positions of the two end faces of the gain crystal 2, which helps to ensure that the seed light 1 forms a zigzag optical path in the plate-shaped crystal, and total internal reflection of the laser can be achieved within the gain crystal 2, reducing the loss of the laser.

[0072] A laser in this embodiment includes the double-pass amplifier structure in any one of the above.

[0073] The double-pass amplifier structure in this embodiment has the following advantages:

[0074] The round-trip optical paths are different, and an isolator does not need to be set, so the cost is low. The gain medium of the double-pass amplifier is set as a plate shape. By designing the angles between the two inclined planes and the axis, when the seed light is incident horizontally, different round-trip optical paths are formed in the gain medium, and the problem of reverse propagation of the returned light can be fundamentally solved without setting an isolator in the optical path, realizing double-pass amplification of the optical signal.

[0075] The optical elements are simple and compact. This double-pass amplifier structure does not need to set multiple total reflection mirrors and wave plates in the optical path. The two inclined end faces of the plate-shaped gain medium can be used to ensure that the seed light passes through the amplified gain medium twice.

[0076] Zigzag optical path. The double-pass amplification structure is set as a plate-shaped gain medium. By designing the angles between the two inclined planes and the axis, the seed light can form a zigzag optical path in the gain medium, making full use of the population inversion distribution of the gain medium to realize double-pass gain amplification of the optical signal.

[0077] The present invention enables the seed light to pass through the gain crystal back and forth, realizing double-pass amplification of the gain. Since the round-trip optical paths are different, while solving the problem of the reverse propagation of the return light, the setting of optical components such as isolators is eliminated, greatly simplifying the overall optical path arrangement, simplifying the overall structure, and reducing costs.

[0078] In the present specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the various embodiments, reference may be made to each other.

[0079] The above description is an interpretation of the present invention, not a limitation thereof. For the scope defined by the present invention, reference may be made to the claims. Any form of modification may be made within the protection scope of the present invention.

Claims

1. A dual-pass amplifier structure, characterized in that: The invention comprises a gain crystal (2) of a slat-shaped structure, wherein a seed light (1) is arranged outside the end of the gain crystal (2); two ends of the gain crystal (2) arranged opposite to each other along the axial direction are arranged as inclined surfaces, one end inclined surface is arranged toward the seed light (1) and is coated with an anti-reflection film layer (22), and the other end inclined surface is coated with a high-reflection film layer (21); the gain crystal (2) also comprises a first reflection surface and a second reflection surface which are spaced and parallel and located on both sides of the axial direction; the seed light (1) is incident into the gain crystal (2) through the anti-reflection film layer (22), and the seed light (1) is reflected by the first reflection surface, the second reflection surface, and the high-reflection film layer (21), forming a zigzag round-trip optical path in the gain crystal (2), and finally exits from the anti-reflection film layer (22).

2. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The light-emitting optical axis of the seed light (1) is consistent with the axial direction of the gain crystal (2).

3. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The incident point and the exit point of the seed light (1) on the gain crystal (2) are both the midpoint of the anti-reflection film layer (22).

4. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The seed light (1) is fundamental frequency light generated by a laser oscillation cavity, and the gain medium in the laser oscillation cavity is consistent with the gain medium of the gain crystal (2).

5. A dual-pass amplifier structure as claimed in claim 4, characterized in that: The gain medium is one of Nd:YAG, Nd:YVO4 and Nd:YLF.

6. A dual-pass amplifier structure as claimed in claim 4, characterized in that: When the gain medium is Nd:YAG, the angle between the anti-reflection film layer (22) and the axial direction of the gain crystal (2) is greater than 55°.

7. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The anti-reflection film layer (22) and the high-reflection film layer (21) are parallel to each other, forming a gain crystal (2) with a parallelogram structure; or the anti-reflection film layer (22) and the high-reflection film layer (21) are each arranged obliquely relative to the axial direction of the gain crystal (2), forming a gain crystal (2) with a trapezoidal structure.

8. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The high-reflection film layer (21) is a total reflection film layer for the seed light (1), and the anti-reflection film layer (22) is an anti-reflection film layer for the seed light (1); the seed light (1) located inside the gain crystal (2) is totally reflected on the first reflection surface, the second reflection surface, and the high-reflection film layer (21).

9. A dual-pass amplifier structure as claimed in claim 1, characterized in that: The seed light (1) is reflected at the midpoint of the high-reflection film layer (21), and the optical path of the seed light (1) from the anti-reflection film layer (22) toward the high-reflection film layer (21) and the optical path from the high-reflection film layer (21) toward the anti-reflection film layer (22) are staggered.

10. A laser, characterized in that: The dual-pass amplifier structure comprises the dual-pass amplifier structure as described in any one of claims 1 to 9.

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