A laser resonant cavity

Abstract

The present invention discloses a laser resonant cavity, which is composed of a laser output mirror, a concave total reflection mirror and a laser gain medium. The reflectivity curve distribution of the concave total reflection mirror is that the reflectivity gradually decreases from the center to the edge; when the pump source performs side pumping on the laser gain medium, the low-energy level particles in the laser gain medium are converted into high-energy level particles due to stimulated absorption, and as the particle number inversion and stimulated radiation occur, laser oscillation is generated when the gain in the laser resonant cavity is greater than the loss; based on the reflectivity curve distribution characteristics of the concave total reflection mirror, the laser beam radius on the concave total reflection mirror is reduced to ω1, and the number of laser oscillation modes will be reduced. The above-mentioned resonant cavity can prevent high-order modes from oscillating and reduce the number of laser output modes by only designing the reflectivity distribution of the total reflection mirror, thereby achieving beam quality control.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a laser resonant cavity. Background Art

[0002] In the actual application of lasers, it is expected that the output laser beam has high brightness and its transverse mode is as close to the fundamental transverse mode TEM as possible. 00 However, in most laser resonators, there are not only oscillations of this mode, but also other higher-order modes. Therefore, mode control technology is needed to limit the number of oscillation modes, such as the commonly used small hole aperture method, single lens focusing mode selection method and cavity mirror adjustment mode selection method.

[0003] The pinhole aperture method is to insert a pinhole aperture of appropriate size into the resonant cavity. Since the fundamental transverse mode has the smallest beam radius, the pinhole aperture can improve the loss ratio of its high-order mode to the fundamental mode, which can fully suppress the oscillation of the high-order transverse mode, thereby optimizing the beam quality. However, when the energy density in the cavity is too high, the edge of the aperture is easily damaged, affecting the subsequent beam quality control; at the same time, the splashing material caused by the damage of the aperture is easy to cause laser damage to the optical components in the laser resonant cavity. Therefore, the aperture material generally needs to be selected from special materials such as high-melting-point metals or sapphire. This method is not suitable for high-power, high-energy laser light sources.

[0004] The single lens focusing mode selection method is to insert a single lens in the resonant cavity and select the mode with a small aperture diaphragm. The diaphragm is placed at the focus of the lens. When the internal light beam passes through the small aperture diaphragm, the high-order modes at the edge of the light beam are suppressed due to the loss caused by the diaphragm blocking, so the beam quality can be optimized. This structure requires that the center of curvature of the concave reflector must coincide with the focus of the lens, which makes it difficult to adjust the resonant cavity.

[0005] The cavity mirror adjustment method is that when the main optical axis of the reflector of the optical resonant cavity coincides with the axis of the active medium, the diffraction loss of different transverse modes is small. When the mirror axis deviates from the cavity axis, the diffraction loss of different transverse modes will increase accordingly. Because the high-order transverse mode loss is large, it is more affected. The closer the mode is to the TEM, the smaller the diffraction loss of different transverse modes will be. 00 The smaller the mode loss, the easier it is to obtain output. However, due to the tilt of the reflector, it is difficult to obtain a symmetrically distributed laser spot. Summary of the invention

[0006] The purpose of the present invention is to provide a laser resonant cavity, which can maintain the transmission loss of low-order modes, increase the transmission loss of high-order modes, make high-order modes unable to oscillate, reduce the number of laser output modes, and thus achieve control of beam quality by only designing the reflectivity distribution of the total reflection mirror.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] A laser resonant cavity, the laser resonant cavity is composed of a laser output mirror, a concave total reflection mirror and a laser gain medium, wherein:

[0009] The reflectivity of the concave total reflection mirror changes with the position, and the reflectivity gradually decreases from the center to the edge;

[0010] When the pump source performs side pumping on the laser gain medium, low-energy level particles in the laser gain medium are converted into high-energy level particles due to stimulated absorption, and as the population inversion and stimulated radiation occur, laser oscillation is generated when the gain in the laser resonant cavity is greater than the loss;

[0011] Based on the reflectivity curve distribution characteristics of the concave total reflection mirror, the radius of the laser beam on the concave total reflection mirror is reduced to ω1, where ω1 is the radius of the effective high-reflection coating area. The number of laser oscillation modes will be reduced, thereby improving the mode selection ability of the laser resonant cavity and the beam quality of the output laser.

[0012] It can be seen from the technical solution provided by the present invention that the above-mentioned resonant cavity can maintain the transmission loss of the low-order mode and increase the transmission loss of the high-order mode, thereby making the high-order mode unable to oscillate and reducing the number of laser output modes, thereby achieving control of the beam quality, only by designing the reflectivity distribution of the total reflection mirror. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0014] Figure 1 A schematic diagram of the structure of a laser resonant cavity provided in an embodiment of the present invention;

[0015] Figure 2 Schematic diagram of the reflectivity distribution curve of the concave total reflection mirror according to an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] like Figure 1The figure shows a schematic diagram of the structure of a laser resonant cavity provided by an embodiment of the present invention, wherein the laser resonant cavity is composed of a laser output mirror 1, a concave total reflection mirror 2 and a laser gain medium 3, wherein:

[0018] The reflectivity of the concave total reflection mirror 2 changes with the position, and the reflectivity gradually decreases from the center to the edge;

[0019] When the pump source 4 performs side pumping on the laser gain medium 3, the low-energy level particles in the laser gain medium 3 are transformed into high-energy level particles due to stimulated absorption, and as the population inversion and stimulated radiation occur, laser oscillation is generated when the gain in the laser resonant cavity is greater than the loss;

[0020] If the reflectivity curve distribution of the concave total reflection mirror 2 described in the embodiment of the present invention is not adopted, the laser resonant cavity undergoes multi-mode oscillation, and the radius of the multi-mode laser beam on the concave total reflection mirror 2 is ω2, and the value of ω2 can be obtained by solving the Fresnel-Kirchhoff diffraction integral equation describing the optical resonant cavity mode;

[0021] Based on the reflectivity curve distribution characteristics of the concave total reflection mirror 2 described in the embodiment of the present invention, the radius of the laser beam on the concave total reflection mirror 2 can be reduced to ω1, where ω1 is the radius of the effective high-reflection coating area. The number of laser oscillation modes will be reduced, thereby improving the mode selection ability of the laser resonant cavity and improving the beam quality of the output laser.

[0022] like Figure 2 FIG. 1 is a schematic diagram of a reflectivity distribution curve of a concave total reflection mirror according to an embodiment of the present invention. Figure 2 Curve 1 in the figure is the reflectivity distribution of the laser total reflection mirror under normal circumstances, a is the physical radius of the total reflection mirror, and the reflectivity on the entire surface of the total reflection mirror is ≈1.

[0023] The reflectivity curve of the concave total reflection mirror 2 in the embodiment of the present invention is as follows: Figure 2 As shown in curve 2, the reflectivity value of the concave total reflection mirror 2 changes with the position of the lens. When the radial distance r≤ω1 of the concave total reflection mirror 2, the reflectivity ≈1, and then the reflectivity value decreases in a step-by-step manner until it reaches zero.

[0024] The concave total reflection mirror 2 is prepared by thin film deposition, and the specific method is: first, a laser anti-reflection film is plated on the entire area of ​​the concave total reflection mirror 2, and then a baffle is added to shield the area exceeding ω1; then, the thin film deposition preparation in the area r≤ω1 is continued, and the film system is corrected on the basis of the original anti-reflection film, thereby converting it into a laser high-reflection film with a reflectivity ≈1.

[0025] In this way, when the laser oscillates in the resonant cavity, the laser in the region r>ω1 on the mirror surface of the concave total reflection mirror 2 will not be able to operate due to excessive transmission loss, thereby improving the transverse mode identification capability and optimizing the mode of the laser resonant cavity;

[0026] When the ω1 value is closer to the spot radius of the fundamental transverse mode on the concave total reflection mirror 2, the laser resonant cavity is closer to TEM. 00 mode, which is equivalent to reducing the Fresnel number in the cavity.

[0027] The reflectivity curve distribution of the concave total reflection mirror 2 can also be a Gaussian line type or a super Gaussian distribution.

[0028] The laser gain medium 3 is specifically one of laser crystal, laser glass, laser ceramic or laser gas.

[0029] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0030] In summary, the laser resonant cavity described in the embodiment of the present invention can improve the beam quality of the laser output and the mode selection capability of the cavity, while effectively reducing the number of components of the laser resonant cavity and reducing the weight of the resonant cavity. The structure is simpler and is not limited by the laser light intensity in the cavity. A symmetrically distributed output light spot can be obtained, and optical debugging is more convenient and easy to implement.

[0031] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A laser resonant cavity, characterized in that: The laser resonant cavity is composed of a laser output mirror, a concave total reflection mirror and a laser gain medium, wherein: The reflectivity of the concave total reflection mirror changes with the position, and the reflectivity gradually decreases from the center to the edge; When the pump source performs side pumping on the laser gain medium, low-energy level particles in the laser gain medium are converted into high-energy level particles due to stimulated absorption, and as population inversion and stimulated radiation occur, laser oscillation is generated when the gain in the laser resonant cavity is greater than the loss; Based on the reflectivity curve distribution characteristics of the concave total reflection mirror, the radius of the laser beam on the concave total reflection mirror is reduced to ω1, where ω1 is the radius of the effective high-reflection coating area, the number of laser oscillation modes will be reduced, the mode selection ability of the laser resonant cavity will be improved, and the beam quality of the output laser will be improved; The reflectivity value of the concave total reflection mirror changes with the position of the lens. When the radial distance of the concave total reflection mirror is r≤ω1, the reflectivity is ≈1, and then the reflectivity value decreases in a step-by-step manner until it reaches zero. The concave total reflection mirror is prepared by thin film deposition, and the specific method is as follows: First, a laser anti-reflection film is plated on the entire area of ​​the concave total reflector, and then a baffle is added to shield the area exceeding ω1; then, thin film deposition preparation is continued in the area r≤ω1, and the film system is corrected on the basis of the original anti-reflection film, thereby converting it into a laser high-reflection film with a reflectivity ≈ 1; In this way, when the laser oscillates in the resonant cavity, the laser in the region r>ω1 on the surface of the concave total reflection mirror will not be able to operate due to excessive transmission loss, thereby improving the transverse mode identification capability and optimizing the mode of the laser resonant cavity; When the ω1 value is closer to the spot radius of the fundamental mode on the concave total reflection mirror, the laser resonant cavity is closer to TEM. 00 model.

2. The laser resonant cavity according to claim 1, characterized in that: The reflectivity curve distribution of the concave total reflection mirror is specifically a Gaussian line type or a super Gaussian distribution.

3. The laser resonant cavity according to claim 1, characterized in that: The laser gain medium is specifically one of laser crystal, laser glass, laser ceramic or laser gas.

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