CN100486063C - High power pulsed laser maladjustment proof resonant cavity - Google Patents

Abstract

The invention discloses a high-power pulse laser anti-distuning resonant cavity, which includes a total reflection mirror, a plane output mirror and a laser working medium. Combination with the inner surface reflector of the right-angle circular frustum, the central axes of the two reflectors coincide, the height of the right-angle outer conical reflector is greater than the height of the inner surface reflector of the right-angle circular frustum, and the height difference is greater than zero and less than or equal to 2mm. The invention outputs approximately solid parallel light beams, the light intensity distribution of the near-field spot is uniform, the far-field light energy is concentrated, the divergence angle is extremely small, and the mode volume is large; the adjustment is extremely simple and the work is extremely stable; it can be used in high-power gas lasers and solid-state lasers. Especially suitable for high energy pulsed lasers.

Description

High power pulsed laser anti-detuning 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 a stable cavity is that losses are extremely low. 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 of the cavity is not too small. But the stable cavity also has its inherent disadvantages: (1) The mold volume is small. For a typical stable cavity laser, the fundamental mode volume usually only occupies a small part of the volume of the 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 fundamental mode volume have nothing to do with the cavity's lateral size (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. (2) When the Fresnel of the cavity is large, the diffraction losses of several lower-order transverse modes are so small that they can be ignored, so the resonant cavity actually loses the ability to select the transverse mode, which will inevitably lead to multi-mode operation, thereby degrading the 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 effective utilization coefficient of the activated material can be improved, but the beam quality will be lower than that of The fundamental mode beam is much worse.

Unsteady and critical cavities can ensure efficient energy extraction from activated species while obtaining high-quality output beams. The most commonly used unstable cavity 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 flat cavity are: small beam divergence angle and large mode volume. It is relatively easy to obtain single-mode oscillation. Its main disadvantage is that the adjustment accuracy is extremely high and it is easy to get out of adjustment. Strict parallelism and cavity stability requirements severely limit its applications.

Application No. 200610018552.0 discloses a "non-detuned laser resonator". The laser resonator full reflection mirror is formed by a combination of a central right-angled inner conical surface, an outer side of a right-angled circular frustum, and an inner surface of a right-angled circular frustum, and a planar output mirror is used. The laser resonator can eliminate the influence of the uneven distribution of the gain medium, compress the area of the output laser spot, and realize the output of a special annular spot with a central spot. However, the total reflection mirror is formed by combining three conical mirrors, and has a complex structure. In use, three right-angled inner and outer conical mirrors are required to be coaxial, and it is relatively difficult to manufacture.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and provide a high-power pulsed laser anti-offset resonator, which not only has strong anti-offset ability, but also can eliminate the influence of uneven distribution of the gain medium, and has high thermal stability , improves the beam quality, and has a simple structure, easy processing and manufacturing, and no central focal line, so it can be used in high-energy pulsed lasers.

In order to achieve the above object, the technical solution adopted in the present invention is: a high-power pulsed laser anti-detuning resonator, including a total reflection mirror, a plane output mirror and a laser working medium, and the total reflection mirror is a right-angled outer conical mirror and a right-angled circular truncated The combination of inner side mirrors, the central axes of the two mirrors coincide, the height of the right-angle outer conical mirror is greater than the height of the right-angle circular frustum inner side mirror, and the height difference is greater than zero and less than or equal to 2mm.

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

(1) In the present invention, the height of the right-angled outer conical reflector is greater than the height of the inner side reflector of the right-angled circular platform, so the high-power pulsed laser anti-detuning resonator of the present invention does not have a central focal line, avoiding the air on the focal line It is broken down and can be used in high-energy pulse lasers; moreover, it improves the ability of the top part of the right-angle outer conical reflector to resist pulse-intensive laser damage.

(2) In the present invention, the height of the right-angled outer conical surface reflector is greater than the height of the right-angled circular frustum inner side reflector, and the retroreflection characteristics can be used to eliminate the influence of the uneven distribution of gain in the pulsed intensity laser, to solid laser rods, The inhomogeneity of solid laser crystal slabs under excitation, the inhomogeneity of gas discharge, the inhomogeneity of gas refractive index, etc. play an optical compensation role, which fully guarantees the quality and energy of the output beam of solid or gas pulse lasers.

(3) The present invention is simple in structure, easy to process and manufacture.

(4) Strong anti-misalignment ability, the allowable misalignment angle of the total reflection mirror or the output mirror far exceeds the stable cavity, unstable cavity and parallel plane cavity used in the existing high-energy pulse laser, and the use and maintenance are convenient and reliable.

(5) The present invention can also be used in solid or gas high-power continuous lasers.

Description of drawings

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

Fig. 2 is a front view of the total reflection mirror in Fig. 1 .

Fig. 3 is a right view of the total reflection mirror in Fig. 1 .

Detailed ways

As shown in Figures 1 to 3, the high-power pulsed laser anti-detuning resonator of the present invention includes a total reflection mirror 1, a plane output mirror 3 and a laser working medium 2, and the total reflection mirror 1 is a right-angle outer conical reflector 4 and a right-angle The combination of the inner side reflector 5 of the circular frustum, the central axes of the two reflectors coincide, the height h ₁ of the right angle outer conical reflector 4 is greater than the height h ₂ of the inner side reflector 5 of the right angle circular frustum, and the height difference is greater than zero and less than or Equal to 2mm.

The laser medium 2 can be a gaseous medium, such as carbon dioxide; or a solid medium, such as Nd:YAG laser crystal. An anti-reflection film is coated on the outer surface of the plane output mirror 3 .

When the laser resonator is applied to a high-power laser, the total reflection mirror 1 and the planar output mirror 3 are cooled with water to dissipate heat. Generally, a water tank is processed on the back of the total reflection mirror 1, and conventional tap water can be used for cooling. The right-angle outer conical surface reflector 4 and the right-angle circular frustum inner surface reflector 5 are located at the junction gap of the total reflector 1 backside and are sealed to prevent water seepage into the combined reflector. Generally, adhesives or welding are used for sealing.

The central axes of the above-mentioned total reflection mirror 1 and the plane output mirror 3 preferably coincide with the optical axis of the resonant cavity.

The right angle outer conical reflector 4 and the right angle circular frustum inner side reflector 5 are required to have higher surface shape accuracy, right angle accuracy, coaxiality and high reflectivity. Practice has proved that the heat resistance and laser damage resistance of the surface of the oxygen-free copper mirror cut with diamond tools are superior to those of the polished surface. There are difficulties in the uniform reflection film. The diamond machine tool can directly cut the inner and outer cones into a mirror surface, which can be directly used as a reflector without coating a reflective film.

The right-angle outer conical reflector 4 and the right-angle circular frustum inner surface reflector 5 can be detachably connected by threads, keys, splines or adhesives. The right angle outer conical reflector 4 and the right angle circular frustum inner side reflector 5 can also be connected by welding.

The inner surface of the above-mentioned plane output mirror 3 is plated with a ring-shaped total reflection film, the outer diameter of the ring is equal to the diameter of the output mirror, and the ring width is less than half of the diameter of the plane output mirror 3 . In this way, the effect of compressing the output spot radius of the laser can be produced.

The optical property of the total reflection mirror 1 is: after the incident light in any direction is reflected by the total reflection mirror 1, 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 total reflection mirror 1 shakes around the apex of the right-angled outer conical reflector 4, the direction of the reflected light will always remain the same, consistent with the direction of the incident light. According to this property, the direction of the output light of the high-power pulsed laser anti-detuning resonator of the present invention is the same as the normal direction of the plane output mirror 3, and when the apex of the right-angled outer conical mirror 4 is located near the optical axis, the total reflection mirror 1 The light can be emitted when the central axis and the optical axis are approximately coincident, and the light energy and beam quality do not decrease significantly.

Claims (6)

1. A high-power pulsed laser anti-detuning resonator, comprising a total reflection mirror, a plane output mirror and a laser working medium, is characterized in that: the total reflection mirror (1) is a right-angle outer conical reflector (4) and a right-angle circular frustum The combination of side reflectors (5), the central axes of these two reflectors coincide, the height of the right-angled outer conical reflector (4) is greater than the height of the right-angled circular frustum inner side reflector (5), and its height difference is greater than zero and less than or Wait for 2mm. 2. The high-power pulse laser anti-detuning resonator according to claim 1, characterized in that: when the laser resonator is applied to a high-power laser, the total reflection mirror (1) and the plane output mirror (3) are cooled with water to dissipate heat. The gap between the right-angled outer conical surface reflector (4) and the right-angled circular frustum inner surface reflector (5) at the back of the total reflection mirror (1) is sealed. 3. The high-power pulsed laser anti-detuning resonator according to claim 1 or 2, characterized in that: the central axis of the total reflection mirror (1) and the planar output mirror (3) coincides with the optical axis of the resonator. 4. The high-power pulsed laser anti-detuning resonator according to claim 3, characterized in that: the right-angle outer conical reflector (4) and the right-angle circular frustum inner side reflector (5) are threaded, keyed, splined or glued and agent connection. 5. The high-power pulsed laser anti-detuning resonator according to claim 3, characterized in that: the right-angle outer conical reflector (4) and the right-angle circular frustum inner surface reflector (5) are connected by welding. 6. The high-power pulsed laser anti-detuning resonator according to claim 3, characterized in that: the inner surface of the above-mentioned plane output mirror (3) is plated with a ring-shaped total reflection film, and the outer diameter of the ring is equal to the diameter of the output mirror , the ring width is less than half of the diameter of the plane output mirror (3).

Images