CN1268043C - Perpendicular internal conical surface reflector laser resonant cavity - Google Patents

Abstract

The present invention discloses a laser resonant cavity of a right-angle inner conical surface reflecting mirror, which comprises a total reflecting mirror, a plane output mirror and a laser working medium, wherein the total reflecting mirror is a right-angle inner conical surface reflecting mirror; an apex corner of the total reflecting mirror is at a right angle, and an axial line of the apex corner is perpendicular to the bottom plane; the inner surface of the total reflecting mirror is a reflecting surface which is plated with a highly reflecting membrane. The apex of the right-angle inner conical surface reflecting mirror is positioned on an optical axis of a laser cavity, and the bottom plane is perpendicular to the optical axis. The laser resonant cavity has the advantages of solid parallel light beam output, uniform near-field light spot intensity distribution, far-field light energy centralization, small divergence angle, large mode volume, convenient adjustment and stable operation. The present invention can be used for a gas laser, a solid laser, a high power laser, a medium power laser or a small power laser.

Description

Right angle inner conical mirror laser resonator

technical field

The invention relates to a laser resonant cavity.

Background technique

The main problem in the design of high-energy laser devices is how to obtain the largest possible mode volume and good transverse mode discrimination ability to achieve high-energy single-mode operation, so as to extract energy efficiently from the active material while maintaining high beam quality.

Commonly used laser resonators include stable cavity, unstable cavity and critical cavity. The main advantage of stable cavities is low loss. In all stable cavities, the geometric deflection loss of paraxial rays is zero, and the diffraction loss is usually negligibly small as long as the Fresnel number of the cavity is not too small. The main disadvantage of the stable cavity is that the mode volume is small. For a typical stable cavity laser, the fundamental mode volume usually only accounts for a small part of the volume of the entire active medium. In fact, the Gaussian mode of the stable cavity is like a long and thin ribbon near the axis of the activated material, and most of the activation energy cannot be effectively converted into the laser energy of the Gaussian mode. It is particularly worth pointing out that for a stable cavity with a large Fresnel number, the spot radius and the fundamental mode volume have nothing to do with the lateral size of the cavity (which is usually determined by the diameter of the gas discharge tube or solid-state laser rod). Therefore, when the cavity length is constant, it is impossible for us to increase the volume of the fundamental mode by increasing the lateral size of the active material, thereby increasing the output power of the laser. Conversely, the larger the lateral dimension of the active substance, the lower the utilization coefficient of the working substance. Another disadvantage of the stable cavity is that when the Fresnel number of the cavity is large, the diffraction losses of several lower-order transverse modes are negligibly small, so the resonant cavity actually loses the transverse mode selection ability. This will inevitably lead to multimode operation, thereby reducing beam quality. Stable cavity operating in a multi-mode state can increase the mode volume, thereby improving the utilization factor of the activated material and increasing the output power. Because the volume of the stable cavity mode increases with the order of the mode, when enough Hermitian-Gaussian (or Laguerre-Gauerian) modes form oscillations, the utilization factor of the activated material can be improved, but the beam quality will be lower than that of The fundamental mode beam is much worse.

The most important and most commonly used unstable cavity in practice is the virtual confocal unstable cavity. It consists of a concave mirror and a convex mirror. The real focus of the concave mirror coincides with the virtual focus of the convex mirror, and the common focus is outside the cavity. By choosing the dimensions of the mirrors, the plane wave will efficiently pass through the entire working substance. At this time, the utilization efficiency of the active substance is the highest and a collimated and uniform output beam can be obtained. The far-field pattern of a circular mirror cavity is the diffraction pattern of a ring uniformly illuminated by a plane wave. The disadvantage of the virtual confocal unstable cavity is that the energy distribution of the circular ring diffraction pattern will have a considerable energy distribution on the surrounding bright ring compared with the circular hole diffraction, and the far-field energy distribution is not concentrated enough. The adjustment process of the virtual confocal unstable cavity is complex and demanding.

The parallel plane cavity is composed of a plane total reflection mirror and a plane output mirror. Two plane mirrors are parallel to each other. Output a uniform parallel beam. The main advantages of the flat cavity are: the beam divergence angle is small, the mode volume is large, and it is relatively easy to obtain single-mode oscillation. Its main disadvantages are: the adjustment accuracy is extremely high and it is easy to get out of adjustment, and the strict parallelism requirement severely limits its application.

Application No. 99816848.3 discloses a "Laser with Gyro-shaped Conical Prism in Resonant Cavity". The total reflection mirror of the parallel plane cavity is replaced by a right-angle conical prism, and the right-angle conical prism cavity is formed by using the retroreflection characteristic of the right-angle conical prism, which can greatly reduce the adjustment requirements of the cavity. At the same time, due to the quasi-phase conjugate characteristic of the cavity, the inhomogeneous light intensity distribution caused by the inhomogeneous distribution of the active medium gain can also be compensated, thereby improving the beam quality. In addition to the advantages of large mode volume and small divergence angle of the parallel plane cavity, the rectangular conical prism cavity also has high stability. However, the right-angle conical prism cavity has the following disadvantages: the prism absorbs more light energy than the plane reflector or spherical reflector and generates heat, and heat dissipation and cooling are difficult, so the right-angle conical prism cavity has low thermal stability and cannot be used in high-energy laser situations; in addition , because prisms working in certain wavelength bands require optical crystals to be manufactured, and these optical crystals are expensive.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of the above-mentioned prior art, such as difficulty in heat dissipation and cooling, low thermal stability, and inability to be used for high-energy lasers, and provide a laser resonator with a right-angle inner conical mirror, which not only has the ability to resist misalignment Strong, free of debugging, improved beam quality, and has high thermal stability, can be used in high-power lasers.

In order to achieve the above object, the technical solution adopted by the present invention is: a right-angle inner conical mirror laser resonator, including a total reflection mirror, a plane output mirror and a laser working medium, and the total reflection mirror is a right-angle inner conical mirror.

Compared with the prior art, the present invention has the following advantages and effects:

1. The invention has large mode volume, small divergence angle, plane wave light field and quasi-phase conjugation property, and the cavity is easy to cool and dissipate heat, and its laser output has high energy, high beam quality and high stability at the same time.

2. Since there is no refraction phenomenon in the right-angle inner conical mirror, the near-field light spots are evenly distributed, the far-field light energy is concentrated, the optical cavity is easier to adjust, and the work is more stable.

3. The manufacturing cost can be reduced by using the right-angle inner conical reflector.

Description of drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 is a schematic diagram of an installation structure of the right angle inner conical reflector in Fig. 1 .

FIG. 3 is a schematic structural view of an embodiment of the right-angled inner conical reflector in FIG. 1 .

Fig. 4 is a left side view of Fig. 3 .

Fig. 5 is a schematic structural diagram of another embodiment of the present invention.

Detailed ways

As shown in Fig. 1 and Fig. 2, a laser resonator of a right-angled inner conical reflector comprises a total reflection mirror 1, a plane output mirror 2 and a laser working medium 3, the total reflector 1 is a right-angled inner conical reflector, and the reflection The vertex angle of the mirror 1 is a right angle, and its inner surface is a reflective surface, which can be coated with a reflective film, and the axis is preferably perpendicular to the bottom plane. When installing, the apex of the right-angle inner conical reflector 1 is preferably located on the optical axis of the laser cavity, and the bottom plane is perpendicular to the optical axis. The right-angle inner conical reflector 1 can be fixed on the seat plate 4 through threaded connection or fixed with screws, etc., and then the seat plate 4 can be fixed on the optical bridge support seat 5 through bolts, etc., and the center of the light hole of the seat plate 4 Line coincides with the center line of the optical cavity of the support seat 5. The plane output mirror 2 is placed perpendicular to the optical axis, its outer surface can be coated with an anti-reflection coating, and its inner surface can be coated with a partial reflection coating. The optical properties of the right-angle inner conical reflector 1 are: after the incident light in any direction is reflected by the inner conical surface, the reflected light is parallel to the incident light. In other words, as long as the direction of the incident light remains unchanged, no matter how the right-angled inner conical reflector 1 shakes around its apex, the direction of the reflected light remains unchanged, consistent with the direction of the incident light. According to this property, the direction of the light output by the resonator is the same as the normal direction of the plane output mirror, and when the apex of the right-angled inner conical mirror 1 is located near the optical axis, and the bottom plane is approximately perpendicular to the optical axis, the light can be emitted, and the light energy with no apparent degradation in beam quality.

As shown in Fig. 3 and Fig. 4, when the present invention is applied to a high-power laser, the right-angle inner conical mirror 1 and the plane output mirror 2 should be cooled with water to prevent damage due to overheating. Common structure can be adopted: a water tank 6 is provided on the right-angle inner conical reflector 1, which is cooled with flowing tap water. The right-angle inner conical reflector 1 and the plane output mirror 2 can be made of materials with good thermal conductivity, such as copper and silicon crystals, so that the thermal deformation of the reflector 1 and the output mirror 2 can be kept at a low level. And when it is used for medium and small power lasers, it does not need to be cooled.

Due to machining accuracy, there is a microhole on the top of the right-angled inner conical mirror 1, the diameter of which is related to the tool of the diamond ultra-precision optical machining lathe, and is required to be as small as possible. Now the precision has reached the nanometer level, and the holes are through holes or blind holes. If a through hole is made, the through hole is sealed with a light-transmitting lens. At this time, the oscillation power or energy of the resonant cavity can be detected through the light energy released from the small hole.

As shown in FIG. 5 , when the present invention is used in a solid-state laser, the output end of the laser rod 7 is coated with a partial reflection film to replace the flat output mirror 2 . In addition, it is better to coat the input end of the laser rod 7 with an anti-reflection coating, and the centerline of the laser rod 7 is the optical axis of the laser cavity.

The invention can be used in gas lasers, solid lasers, high power lasers or medium and small power lasers and the like.

Claims (7)

1. A right-angle inner conical reflector laser resonator, comprising a total reflection mirror, a plane output mirror and a laser working medium, characterized in that the total reflection mirror is a right-angle inner conical reflector (1). 2. The laser resonator according to claim 1, characterized in that: the apex of the right-angle inner conical reflector (1) is located on the optical axis of the laser cavity, and the bottom plane is perpendicular to the optical axis. 3. The laser resonator according to claim 1 or 2, characterized in that a water groove (6) is opened on the right-angle inner conical reflector (1). 4. The laser resonator according to claim 1 or 2, characterized in that: the reflective surface of the right-angled inner conical mirror (1) is coated with a reflective film. 5. The laser resonator according to claim 1 or 2, characterized in that there is a through hole at the top of the right-angle inner conical reflector (1), and the through hole is sealed with a light-transmitting lens. 6. The laser resonator according to claim 1 or 2, characterized in that: the output end of the laser rod (7) is coated with a partial reflection film to replace the flat output mirror (2). 7. The laser resonator according to claim 6, characterized in that an anti-reflection coating is coated on the input end of the laser rod (7), and the center line of the laser rod (7) is the optical axis of the laser cavity.

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