JPH08148739A - Laser resonator and laser apparatus provided with said laser resonator - Google Patents

Abstract

PURPOSE: To make phase distribution uniform so that it may be considered to be a spherical wave emitted from a certain point, by designing second and third total reflection mirrors so that the virtual image of a center circle at the center of the beam waist of a laser beam being in the ring cylindrical part in a laser medium gathers at a point near above the central axis of the laser medium. CONSTITUTION: A total reflection mirror parts of whose conical surface are the surfaces of total reflection mirrors 3 and 4 is thought of. On this occasion, beams emitted from wave directing path ends 24 and 25 and reflected by the total reflection mirrors 3 and 4 can be considered to be beams emitted from a virtual image 26 at the upper part of a wave directing path end and that 27 at the lower part of the wave directing path end. At this time, it is possible to make the center coincide with the end surfaces of the virtual images 26 and 27 by adjusting the angles of the total reflection mirrors 3 and 4. When design is done in this way, it is possible to treat a beam emitted from the end of a circular wave directing path equally with one emitted from a certain point effectively. Namely, its wave surface is considered to be a spherical wave, and can be made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser resonator for extracting a high-quality beam from a ring-shaped laser medium and a laser device equipped with the laser resonator.

[0002]

2. Description of the Related Art FIG. 18 is a sectional view showing a conventional laser resonator using a mirror called a waxicon, which is disclosed in, for example, Japanese Patent Laid-Open No. 3-62579.
Reference numeral 1 is a ring-cylindrical (or simply cylindrical) laser medium, 2 is a total reflection mirror, 5 is a partial reflection mirror for emitting laser light, and 42 is a mirror called a waxicon. In FIG. 18, the laser resonator is shown in a sectional view in a plane including the central axis thereof. Waxicon is a vertical angle 9
This is a mirror having a configuration in which a 0-degree conical shape (axicon) is doubled, and the waxicon mirror 42 is bent around a laser beam having a circular cross section generated by the ring-cylindrical laser medium 1, The structure is such that it is converted into a circular beam that is substantially parallel at the center.

By the way, various advantages of the ring-cylindrical laser medium have been reported in terms of cooling, excitation, miniaturization and the like. For example, gas lasers can be efficiently cooled by a gas cooling method using heat conduction, and can be miniaturized. In solid-state lasers, highly efficient pumping is possible. And the like.

In practical use of a laser device having such a ring-cylindrical laser medium, the biggest problem is to extract a highly focused circular beam close to a Gaussian mode from the ring-cylindrical gain space. Is. Various laser resonators have been proposed for this purpose, and the conventional laser resonator shown in FIG. 18 is one example.

Next, the characteristics of the laser medium having a ring-cylindrical shape will be described. For example, in a CO ₂ laser, it is essential to cool the laser gas that is the laser medium. This is because the CO ₂ laser has the property that its output sharply decreases as the gas temperature rises. Therefore, all CO ₂ lasers always have some kind of gas cooling mechanism, which in most cases is CO ₂
It is a very large part of the laser structure.

For example, in a high output CO ₂ laser, the laser gas is circulated outside the laser resonator and is forcibly cooled through a blower or a heat exchanger so that the laser gas is always cooled and supplied into the laser resonator. The method that is done is taken. However, although this method is easy to achieve high output, it requires parts such as a blower and a heat exchanger, which makes the apparatus large in size, and has many problems in terms of cost and reliability.

On the other hand, there are some small CO ₂ lasers that do not have a gas circulation system but have a system of cooling the electrode and cooling the gas by heat conduction. However, in this method, the laser gas is cooled by heat conduction, so if the beam diameter is increased, the temperature at the center of the beam rises,
It has a drawback that the beam diameter cannot be increased to increase the output.

In order to solve these problems, a laser device having a flat type laser medium with a short gap has been proposed. The flat plate type electrodes are opposed to each other with a short gap, and the electrodes are cooled, whereby cooling by heat conduction is efficiently performed, and the output can be increased by increasing the area of the flat plate.

A laser device having a ring-cylindrical laser medium, which is the object of the present invention, is obtained by rolling such a flat plate type laser into a cylindrical shape. This type of laser device can be made smaller than the flat plate type, and the structure of the vacuum device can be simplified.

Further, the laser medium having a ring-cylindrical shape has various advantages in lasers other than the CO ₂ laser. For example, in a YAG laser, a laser medium is excited by a flash lamp, but when the flash lamp is inserted inside a ring-shaped YAG rod, the light of the lamp is very efficiently absorbed in the laser medium, and highly efficient oscillation is generated. It will be possible.

As described above, the ring-cylindrical laser medium is
It has very attractive features, especially with respect to cooling and excitation, but the biggest problem is in beam extraction. In order to extract a highly focused circular beam suitable for practical use from a ring-cylindrical laser medium, it is necessary to configure a complicated laser resonator as shown in FIG. 18, for example.

Next, the operation of the resonator using the wax control mirror shown in FIG. 18 will be described. The ring-cylindrical laser medium 1 is formed as a gap between two inner and outer concentric cylindrical electrodes (not shown), and the ring-cylindrical laser medium 1 is excited by the discharge between them. The inner and outer electrodes are water-cooled from the inner and outer sides, respectively. The discharge space between the electrodes functions as a beam waveguide.

The laser beam generated and amplified by the ring-shaped cylindrical laser medium 1 propagates in the axial direction of the cylinder. The ring-shaped laser beam that has reached the waxicon mirror 42 is first redirected inward by the outer conical mirror 421, and then turned back by the inner conical mirror 422 in the direction exactly opposite to the incident direction to the waxicon. . At this time, the laser beam, which was circular in shape at the time of incidence, is collected in the central portion at the time of reflection by the waxicon and becomes circular. In this way, the annular laser beam can be converted into a circular shape. The laser resonator is composed of a waxicon mirror 42, a total reflection mirror 2 and a partial reflection mirror 5, and a circular beam is extracted from the partial reflection mirror 5.

[0014]

Since the conventional laser resonator including the laser resonator using the above-mentioned wax-type mirror is constructed as described above, the emitted beam is emitted from each point of the ring of the laser medium. It is a combination of the emitted light, and therefore the wavefront inevitably becomes distorted.

FIG. 19 is a schematic diagram for explaining such a problem, and this diagram is an enlarged view of how the beam propagates through the waxicon mirror 42.

In FIG. 19, the wavefronts of light emitted from the upper end (waveguide end) 24 and the lower end (waveguide end) 25 of the cylindrical waveguide are the light from all points on the waveguide end according to Huygens' principle. It will add up the wavefront. Here, the width of the waveguide is considered to be sufficiently smaller than the radius of the cylinder, and the wavefront of the light from the center of the waveguide is considered as a representative. Each light is reflected twice by the wax concentrator mirror 42 and is reflected back to the side opposite to the incident direction. These are waveguide ends 24, 25 in which the waveguide ends 24, 25 are respectively folded by the wax concentrator 42.
Is equivalent to the light emitted from the virtual images 26 and 27. That is,
The light emitted from the annular waveguide ends 24 and 25 and reflected by the wax conical mirror 42 can be considered as light emitted from circular light sources such as the virtual images 26 and 27.

Considering the propagation of the wavefront of the light emitted from such a light source, the one emitted from the virtual image 26 is a spherical wave 43, and the one emitted from the virtual image 27 is a spherical wave 44.
It is thought that it propagates like. When these lights are added together, spherical waves 4 from two points with different wavefronts as shown in FIG.
It can be seen that the sum of 3,44 is added and the wavefront of the output wave is distorted.

As described above, as long as the wax conical mirror 42 constituted by the combination of right and left conical side surfaces is used, there is a limit to the improvement of the beam quality, and there is a problem that sufficient condensing performance cannot be realized. .

Various attempts have been made to extract a circular high-quality beam from a ring-cylindrical laser medium, but in addition to the above example, a drastic solution method including accurate design of the wavefront has not been proposed yet. is the current situation.

The present invention has been made in order to solve the above problems, and has a Cassegrain type mirror structure, which makes it possible to make uniform the wavefront of the emitted beam of laser light, that is, the phase distribution. The objective is to obtain a simple laser resonator.

Another object of the present invention is to obtain a laser resonator capable of selecting an oscillating transverse mode by a difference in resonator loss.

Further, the present invention is a laser device in which a ring-cylindrical laser medium serves as a waveguide for a laser beam, and it is possible to provide a beam with minimum waveguide loss and excellent symmetry and stability. The purpose is to obtain a laser device.

Further, the present invention is a laser device in which a ring-cylindrical laser medium serves as a waveguide for a laser beam, and the phase distribution of an outgoing beam of laser light can be made uniform, and the waveguide is provided. It is an object of the present invention to obtain a laser device which can emit a beam symmetric with respect to the center thereof without changing its shape.

Another object of the present invention is to obtain a laser device which can make the phase distribution of the emitted beam of the laser light uniform and can hold the mirror without hindering the propagation of the laser beam. .

Another object of the present invention is to obtain a laser device which can obtain a laser beam having a large output while making the phase distribution of the outgoing beam of the laser beam uniform.

[0026]

According to a first aspect of the present invention, there is provided a laser resonator, which is installed at a predetermined distance from the other end of a laser medium, and which allows light passing through the laser medium to be emitted near the central axis of the laser medium. A second total reflection mirror for focusing light in a certain direction,
A third total reflection mirror for converting the light collected by the second total reflection mirror into substantially parallel light, the second and third total reflection mirrors cooperating with each other. ,
The shape and arrangement that substantially collects the virtual image of the circle at the center of the annulus, which is the cross-sectional shape of the light at the position of the beam waist, where the wavefront of the light in the ring-cylindrical portion in the laser medium is closest to the plane. Have a relationship.

Second aspect of the laser resonator according to the invention of claim 2
And the surface shape of the third total reflection mirror is expressed by a linear expression or a quadratic expression relating to the distance from the center of the mirror.

In the laser resonator according to the third aspect of the present invention, for the beam on the third total reflection mirror, the distance b from the central position of the beam to the central axis of the laser medium and the beam diameter ω _m of the beam. The value of the ratio b / ω _m is defined as an index for selecting the transverse mode of the output beam of the laser resonator.

In the laser resonator according to the invention of claim 4, when the order of the output beam of the laser resonator in the cylindrical coordinate system in the angular direction is n, with respect to the beam on the third total reflection mirror, Ratio b of the distance b from the central position of the beam to the central axis of the laser medium and the beam diameter ω _m of the beam
The value of / ω _m is 0.5n + 0.9 <b / ω _m <0.5n
The relationship of +1.8 is satisfied.

A laser device according to a fifth aspect of the present invention includes a laser medium having an annular cylindrical shape, and the third or fourth aspect.
The laser medium described in 1) is used, and the ring-cylindrical laser medium serves as a waveguide of the laser beam, and the laser resonator outputs a beam corresponding to TEM _0n ^* polarized in the circumferential direction. The value of b / ω _m is specified.

A laser device according to a sixth aspect of the present invention has a ring-cylindrical laser medium, and is provided with the laser resonator according to any one of the first to fourth aspects. The ring-cylindrical laser medium serves as a waveguide for the laser beam, and the waveguide gap length d and the waveguide length L are L = n × d ² / λ (n is an arbitrary integer, λ is Laser wavelength) is satisfied.

A laser device according to the invention of claim 7 has a ring-shaped cylindrical laser medium, and claims 1 to 4
The laser resonator according to any one of the above is provided, and the third total reflection mirror is configured to be held from the inside of the laser medium.

A laser device according to the invention of claim 8 has a ring-cylindrical gas as a laser medium, and is provided with the laser resonator described in any one of claims 1 to 4. In this configuration, the gas is allowed to flow in the axial direction of the ring-shaped optical space, the gas is guided to the outside of the laser resonator, and the gas is returned to the optical space again. And a cooling means.

[0034]

In the laser resonator according to the first aspect of the invention, the laser beam emitted in the axial direction from the ring-shaped laser medium is emitted by the second total reflection mirror, which is, for example, a ring-shaped aspherical surface. Collected near the central axis of the medium. At this time, a virtual image of the center circle of the center of the beam waist of the laser beam in the ring-cylindrical portion in the laser medium, which is formed by the second and third total reflection mirrors, almost gathers at a point on the vicinity of the central axis of the laser medium. As such, the second and third total internal reflection mirrors must be designed. further,
The light collected at the center is converted into circular substantially parallel light by the following third total reflection mirror which is, for example, an aspherical surface. The laser light converted into the substantially parallel light is incident on the partial reflection mirror, a part of the laser light is returned to the inside of the laser resonator, and the other part is emitted from the laser resonator to the outside. In this way, the virtual image of the central circle of the center of the beam waist of the laser beam in the ring-cylindrical portion in the laser medium is collected at the above-mentioned one point on the vicinity of the central axis of the laser medium so that the second and third images can be collected. Since the total reflection mirror is designed, the wavefront of the emitted beam of the laser light, that is, the phase distribution can be made uniform so that it can be regarded as a spherical wave emitted from a certain point.

The laser resonator according to the invention of claim 2 is
The surface shape of each of the second and third total reflection mirrors is an aspherical surface and is formed as represented by a linear expression or a quadratic expression regarding the distance from the center of the mirror. This shape is the simplest and practical one for realizing the resonator of claim 1, and similarly, a virtual image of the central circle of the center of the beam waist of the laser beam in the ring-cylindrical shape portion in the laser medium Almost all of them can be collected at one point on the vicinity of the central axis of the medium, and the wavefront of the emitted beam of the laser light, that is, the phase distribution can be made uniform.

The laser resonator according to the invention of claim 3 is
Design using the ratio b / ω _m of the beam diameter ω _m of the beam and the distance b from the central position of the beam to the central axis of the laser medium for the beam on the third total reflection mirror. Allows the transverse mode of the output beam of the laser cavity to be selected by the difference in cavity loss.

The laser resonator according to the invention of claim 4 is
Similarly, the value of the ratio b / ω _m is set to the order n of the mode,
By defining 0.5n + 0.9 <b / ω _m <0.5n + 1.8, the transverse mode to oscillate is selected according to the difference in resonator loss.

In the laser device according to the invention of claim 5, the value of the ratio b / ω _m is defined so that the laser resonator outputs a beam corresponding to TEM _0n ^* polarized in the circumferential direction. The polarized light of is also parallel to the waveguide wall at all locations, the waveguide loss is minimum, and a beam with excellent symmetry and stability is obtained.

In the laser apparatus according to the sixth aspect of the invention, the waveguide gap length d and the waveguide length L are L = n × d ² / λ.
Since the relationship of is satisfied, the beam symmetrical with respect to the center of the waveguide is emitted without changing its profile.

In the laser apparatus according to the invention of claim 7, the ring-shaped cylindrical laser medium and the output beam are coaxial with each other.
It is effective for holding the third total reflection mirror without hindering the propagation of the beam.

The circulating means of the laser device in the eighth aspect of the invention causes a flow in the gas enclosed in the optical space to circulate the gas. When the gas circulated by the circulation means reaches the cooling means, it is cooled there, and is guided again into the optical space. Therefore, in the laser device having such a configuration, it is not necessary to cool the gas that is the laser medium by heat conduction from the cylindrical electrode or the like, so that the gap length of the cylinder that defines the size of the laser medium is increased. It is possible to obtain a laser beam with a larger output.

[0042]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram schematically showing a configuration of a laser resonator according to an embodiment of the present invention. In the figure, 1 is a ring-cylindrical laser medium, and 2 is total reflection provided at one end of the laser medium 1. Mirrors (first total reflection mirrors) 3 are provided at the other end of the laser medium 1, and collect the laser light emitted from the ring-shaped laser medium 1 near the central axis of the laser medium 1. (Second total reflection mirror), 4
Is a total reflection mirror (third total reflection mirror) for converting the laser light reflected from the total reflection mirror 3 into circular substantially parallel light, and 5 is a circular beam formed by the total reflection mirrors 2, 3 and 4. Is a partial reflection mirror that emits laser light by reflecting a part of the light and transmitting the remaining part.

The total reflection mirror 3 is an annular aspherical mirror, and a through hole is formed in the center thereof. The total reflection mirror 4 is an aspherical mirror that cooperates with the total reflection mirror 3 to convert the light collected by the total reflection mirror 3 into circular substantially parallel light. The laser resonator according to this embodiment includes a total reflection mirror 3 and 4 and a total reflection mirror 2.
And a partial reflection mirror 5. The combination of the ring-shaped total reflection mirror 3 and the total reflection mirror 4 is an application of the Cassegrain type mirror structure used in the concave mirror of the astronomical telescope.

Next, the operation will be described. A laser beam emitted from the ring-shaped cylindrical laser medium 1 in its axial direction is collected near the central axis of the laser medium 1 by a ring-shaped aspherical total reflection mirror 3. At this time, the virtual image of the center circle of the center of the beam waist of the laser beam in the ring-cylindrical portion of the laser medium 1 by the total reflection mirrors 3 and 4 is almost gathered at one point on the vicinity of the central axis of the laser medium 1. In addition, the total reflection mirrors 3 and 4 must be designed.

FIG. 2 is a perspective view schematically showing the beam waist and the central circle of the beam waist. In FIG.
Is a beam waist, and 51 is a central circle. As is apparent from this figure, the beam waist 50 of the light beam in the ring-shaped laser medium 1 is the constricted portion of the beam, and the wave front of the ring-shaped light beam is closest to the plane. The central circle 51 of the center of the beam waist 50 of the cylindrical portion is a circle formed by the center of the width of the ring which is the sectional shape of the light beam at the position of the beam waist 50 of the cylindrical portion, that is, A circle formed by the center of the beam diameter when considered in the radial direction.

Further, the light collected at the center is converted into circular substantially parallel light by the next aspherical total reflection mirror 4 installed closer to the total reflection mirror 3 than the roughly collected points. It The laser light converted into substantially parallel light passes through the through hole in the center of the annular total reflection mirror 3 and is incident on the partial reflection mirror 5, and a part of the laser light is returned to the inside of the laser resonator and the rest. Part of the light is emitted from the laser resonator to the outside.

The advantage of the laser resonator according to this embodiment is that
Not only this mirror structure, but also the surface shape such as the curvature of the mirror is designed in detail, so that a high quality circular highly focused beam can be taken out. In addition, the mirrors can be designed to extract various desired transverse and polarization modes of the beam.

Next, a method of designing the mirror of the laser resonator according to this embodiment will be described. FIG. 3 is a configuration diagram showing a configuration of a main part of a laser resonator according to this embodiment. In the figure, reference numerals 24 and 25 respectively denote an upper end and a lower end of a cylindrical waveguide which is a laser medium, and a total reflection mirror 3.
It is the end of the waveguide folded back at. 26 is a virtual image of the waveguide end 24, and 27 is a virtual image of the waveguide end 25.

In the case of the conventional laser resonator using the above-mentioned waxicon mirror, there has been a problem that the wavefront at the time of outputting the waxicon mirror is distorted due to the addition of spherical waves generated from multiple points. . In order to solve this problem, it is sufficient that the centers of spherical waves emitted from multiple points are substantially coincident with each other.

The waveguide ends 24, 25 can be approximated as plane mirrors, assuming the beam does not change during waveguide propagation. Since the end of the waveguide approximated by the plane mirror is one end of the laser resonator, the beam has a beam waist on the faces 24 and 25 of the end of the waveguide. In general, the beam that spreads through the beam waist is sufficiently far from the beam waist,
It can be regarded as a spherical wave emitted from the center of the beam waist. That is, the position of the center of the beam waist may be considered as the center of the spherical wave. The light emitted from each point at the end of the waveguide is regarded as a spherical wave, and in order to make the centers thereof substantially coincide, the virtual images at the centers of the waveguide ends may be made coincident.

The most important point in the design of the mirror of the laser resonator according to this embodiment is to design the optical system so that the light emitted from the end of the waveguide seems to be emitted from one point.

The total reflection mirrors 3 and 4 are generally aspherical total reflection mirrors, but here, as the first stage of design, consider a total reflection mirror whose surface is a part of a conical surface. In this case, the light emitted from the waveguide ends 24 and 25 and reflected by the total reflection mirrors 3 and 4 is effectively combined with the light emitted from the virtual image 26 above the waveguide end and the virtual image 27 below the waveguide end. I can think. At this time, the centers of the end faces of the virtual images 26 and 27 can be matched by adjusting the angles of the total reflection mirrors 3 and 4. When designed in this way, the light emitted from the end of the annular waveguide can be effectively treated as if emitted from a certain point. That is, the wavefront is considered to be exactly a spherical wave. After that, as a second stage of designing, a stable resonator can be configured by providing the total reflection mirror 4 or the total reflection mirror 3 and the partial reflection mirror 5 with an appropriate curvature.

Usually, since the annular laser medium and the mirror forming the resonator are arranged coaxially, the surface shapes of the respective mirrors, especially the total reflection mirrors 3 and 4 which are generally aspherical surfaces, are axisymmetric. is there. Further, as described above, the shape is based on a part of the conical surface and has a predetermined curvature. Therefore, the surface shape of the total reflection mirrors 3 and 4 is a linear expression of the distance r from the center or 2
It is given by the curve given by However, when careful design is performed, a mirror whose surface shape expression changes depending on the range of r may be required.

Various mirror combinations and structures are conceivable in an actual laser resonator. For example, when the portion of the ring-shaped cylindrical laser medium is not a waveguide, there may be a case where the total reflection mirror 2 which is an end mirror is a plane mirror or a case where it has a curvature. In any case, as shown in FIG. 2, since the laser beam has the beam waist 50 somewhere in the annular beam portion farther than the total reflection mirror 3, the total reflection mirror of the central circle 51 of the beam waist 50 is shown. It may be designed so that the virtual images of 3 and 4 coincide with one point. By doing so, as described above, a point sufficiently separated from the beam waist 50, for example, the partial reflection mirror 5
In the above, the laser beam can be treated as if it were a spherical wave emitted from a single point.

Next, especially when the ring-shaped portion of the laser medium acts as the waveguide of the laser, when using such a ring-shaped laser medium, the transverse mode of the output beam is selected, and especially the circular mode is selected. The importance of outputting a transverse mode that is a ring-shaped polarization mode polarized in the direction, that is, close to the TEM ₀₁ ^* mode will be described.

When the beam is reflected by the waveguide wall, the reflectance is different between s-polarized light and p-polarized light. The waveguide loss of the parallel-plate waveguide is large for p-polarized light, that is, polarized light perpendicular to the waveguide wall, and small for s-polarized light, that is, polarized light parallel to the waveguide wall. As a result, in the cylindrical waveguide, the polarized light in the radial direction suffers more loss, and the polarized light in the circumferential direction is easily selected.

As a result, when the laser resonator according to this embodiment is assembled and a beam close to a Gaussian beam is to be emitted, if the 0th-order mode is to be emitted, the polarization selectivity in the waveguide portion is inevitable. Therefore, it is conceivable that a ring mode, for example, a mode close to the TEM ₀₁ ^* mode can be easily produced.

FIG. 4 shows the relationship between the transverse mode and the polarized light. FIG. 4 (a) shows a case where the 0th-order Gaussian beam 28 is emitted. At this time, polarized light in the waveguide is perpendicular to the waveguide wall at some places and parallel to the waveguide wall at some places. You can see that it has become. Propagating the waveguide in such a polarized state results in a large waveguide loss, resulting in poor symmetry and stability.

On the other hand, FIG. 4B shows a case where the beam 29 corresponding to the TEM ₀₁ ^* mode which is polarized in the circumferential direction is emitted. In this case, since the polarized light is in the circumferential direction, the polarized light in the waveguide is also parallel to the waveguide wall at all locations, and a beam with minimal waveguide loss and excellent symmetry and stability can be obtained.

Next, how to select the lateral mode will be described. A normal CO ₂ laser is composed of a Fabry-Perot resonator composed of two concave mirrors and an aperture. The mode is selected by the curvature of the concave mirror and the size of the aperture. At this time, the selection of the mode is determined not only by the difference in the loss of the resonator including the aperture but also by the competition of the gain between the resonator loss and the mode. For example, when the value of the resonator loss of each transverse mode is calculated, the loss of the low-order mode is smaller than that of the higher-order mode in any resonator configuration. Nevertheless, higher-order single-mode oscillation is possible because of gain competition. However, in the laser resonator according to the present invention, since the portion having the gain is the portion of the waveguide, it cannot be expected that the mode is selected by the competition of the gain.

The laser resonator according to this embodiment has a remarkable feature that the transverse mode to be oscillated can be selected by the difference in resonator loss. Next, a method of designing the resonator and mirror shapes so as to select a specific mode will be described.

In FIG. 3, the beam emitted from the end of the waveguide is reflected by the aspherical total reflection mirror 3 and reaches the aspherical total reflection mirror 4. At that time, the beam on the total reflection mirror 4 is reflected. Let b be the distance between the center of the laser beam and the center axis of the laser medium. Further, in FIG. 3, the upper waveguide end face 24 and the partial reflection mirror 5 constitute a stable resonator as described above if the total reflection mirror 4 is effectively regarded as a convex lens, but the actual oscillation is generated. The mode is considered to be the addition of the modes formed by this stable resonator, and therefore, it cannot be approximated. At this time, the beam diameter at the position of the total reflection mirror 4 is uniquely determined by the distance between the total reflection mirror 4 and the waveguide and the curvature given to the total reflection mirror 4 and the like. Let this beam diameter be ω _m .

In the design of the laser resonator of this embodiment, the ratio between the beam diameter ω _m and the distance b between the center of the beam and the central axis on the total reflection mirror 4 is important for determining the transverse mode of the beam to be extracted. I know it's a parameter.

FIG. 5 shows that b and ω under certain conditions.
0 when changing the ratio of _m as a variable parameter
It is a graph showing the values of the resonator loss of the second, first, and second modes (where ω _m is the radius such that the intensity becomes 1 / e ² ). The ratio of b to ω _m changes depending on the configuration of the resonator and the mirror shape, but it is easiest to understand that the value of b is changed by changing the inclination of the cone of the total reflection mirror 3.

As is apparent from FIG. 5, b / ω _m = 1.
In the range 30 of 65 or less, the 0th order is b / ω _m = 1.65 to
It can be seen that the first-order mode is in the range 31 of 2.1 and the second-order mode is in the range 32 where b / ω _m = 2.1 or more is the lowest resonator loss mode. It can be seen that the transverse mode to be oscillated can be selected by changing the resonator loss of each transverse mode by changing the parameter b / ω _m .

The horizontal mode selection method will be described below. First, b / ω _m = 1.65 or less (region 30 in FIG. 5)
Then, the 0th-order mode is selected. In this case, inconvenience may occur due to the polarization dependence when passing through the annular medium as described above, but when the annular medium does not function as a waveguide, there is no polarization dependency, Alternatively, when the polarization dependence can be ignored, the 0th-order mode gives a high-quality beam with the best focusing property.

Next, b / ω _m = 1.65 to 2.1 (see FIG.
In the area 31) of 1), the primary mode is selected. When the annular medium has a strong polarization dependency, it is considered that the generation of a beam of a mode corresponding to TEM ₀₁ ^* polarized in the circumferential direction is the best, as shown in FIG. 4B. .

Further, when b / ω _m = 2.1 or more (region 32 in FIG. 5), a second or higher order mode is generated, but it is used for uniform irradiation in a wide range such as surface modification. Then, it is necessary to generate such a transverse mode.

The above discussion regarding the transverse mode selection depending on the value of the ratio b / ω _m of the distance b between the center of the beam and the central axis on the reflecting mirror 4 and the beam diameter ω _m is based on a certain condition. It is derived based on the calculated FIG. Therefore, when the calculation is performed for another condition, that is, for a system having a different medium shape and a different resonator configuration, the characteristic curve shown in FIG. 5 changes slightly and becomes different. However, it is empirically known that when b / ω _m is used as a parameter, a result almost equal to that shown in FIG. 5 is obtained under any condition. The intersection of the three curves shown in FIG. 5 may change slightly depending on the conditions,
When generating the nth mode, empirically, b / ω _m is
Experience has shown that the following inequalities must be satisfied.

0.5n + 0.9 <b / ω _m <0.5n + 1.8 That is, the resonator loss is large in the region where b / ω _m is smaller than 0.5n + 0.9, and it is not suitable for selecting that mode. When b / ω _m is larger than 0.5n + 1.8, the resonator loss increases past the minimum value, and at the same time, the loss of another higher-order mode becomes sufficiently small. , You cannot select the mode.

In this way, the transverse mode of the output beam can be selected according to the value of the ratio b / ω _m of the distance b between the center of the beam and the central axis on the total reflection mirror 4 and the beam diameter ω _m .

Example 2. FIG. 6 is a configuration diagram showing a configuration of a laser resonator according to another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 3 denote the same or corresponding components.

As described in the laser resonator according to the first embodiment, the transverse mode of the output beam is such that the distance b between the center of the beam on the total reflection mirror 4 and the central axis and the beam diameter ω.
_It can be selected according to the ratio b / ω _m value to _m . Also, this b
The value of / ω _m can be changed by adjusting the inclination of the cone of the total reflection mirror 3 and changing the value of b when the structure of the resonator is roughly fixed.
On the other hand, the laser resonator according to this embodiment is configured to change the value of ω _m by changing the resonator length and execute the transverse mode selection of the output beam.

Next, the operation will be described. The value of ω _m is determined by the curvature attached to the total reflection mirror 4 and the resonator length. Therefore, as shown in FIG. 6, z indicated by the arrow A in the figure, which is the optical axis direction provided on the partial reflection mirror 5.
If the position of the partial reflection mirror 5 that is a take-out mirror is changed by using a z-direction stage (not shown) that translates the mirror in the direction, the resonator length is changed, and the value of ω _m is changed. Can be changed.

Such a laser resonator is effective in that the output mode can be changed without changing the surface shapes of the aspherical total reflection mirrors 3 and 4. That is, the mode of the output beam can be changed only by changing the position of the partial reflection mirror 5, which is a take-out mirror, without replacing the mirror.
This is very useful in practice in that various modes can be extracted with a set of mirrors.

Example 3. 7 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 designate the same or corresponding constituent elements.

As shown in FIG. 7, in the laser resonator according to this embodiment, the ring-shaped total reflection mirror 3 and the partial reflection mirror 5 are integrally formed. When these two mirrors are integrated, their base materials are different (CO
_In the case of ₂ lasers, the Au-coat C
u, ZnSe) in the partial reflection mirror, they may be accurately fitted together, or the base material may be unified to that of the partial reflection mirror 5 and a coating may be applied thereon. Since the operation of the laser resonator according to this embodiment is similar to that of the laser resonator according to the first embodiment, its explanation is omitted here.

When a plurality of mirrors are integrally formed in this manner, the whole structure is simplified, the number of parts is reduced, and the fine adjustment mechanism of the mirror is not necessary. Ease of use and stability are improved.

Example 4. FIG. 8 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 denote the same or corresponding components, and 34 Is a roof reflector.

As shown in FIG. 8, the laser resonator according to this embodiment includes a roof reflector 34 instead of the partial reflection mirror 5. The roof reflector 34 is 2
It is a combination of two plane mirrors at an angle of 90 degrees.
Light rays that are incident on a plane that makes an angle of 90 degrees with each mirror are emitted so that the left and right are inverted with respect to the line of intersection of the mirrors.

Next, the operation will be described. Since the laser resonator according to this embodiment has such a configuration, the beam is switched up and down every time it is reflected by the roof reflector 34, and the propagation path in the waveguide of the beam is changed every time the laser resonator makes a round trip. Change. In other words, the effect of mixing the beams inside the laser resonator is produced, so that the coherency of the beams can be easily improved with a small number of round trips. As a result, the stability and alignment tolerance of the laser resonator are improved. Further, such an effect can be obtained by using a corner reflector, an axicon mirror, or the like instead of the roof reflector described here. Also, depending on the structure of the resonator and the method of extracting the laser, it goes without saying that when extracting the laser from this mirror, the roof reflector, the corner reflector, the axicon mirror, or the like of the extraction portion is composed of a partial reflection mirror. .

Example 5. FIG. 9 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 designate the same or corresponding constituent elements.

As shown in FIG. 9, in the laser resonator according to this embodiment, the total reflection mirror 4 is disposed inside the ring-shaped laser medium 1. Since the operation of the laser resonator according to this embodiment is similar to that of the laser resonator according to the first embodiment, its explanation is omitted here.

With such a structure, the laser resonator can be further miniaturized.

Example 6. 10 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 designate the same or corresponding components.

As shown in FIG. 10, in the laser resonator according to this embodiment, the annular total reflection mirror 3 and the partial reflection mirror 5 are integrally formed as in the third embodiment. The aspherical total reflection mirror 4 and the total reflection mirror 2 are integrally formed. As already described in the fifth embodiment, when the total reflection mirror 3 and the partial reflection mirror 5 are integrated, the base materials thereof are different (in the case of a CO ₂ laser, the total reflection mirror has Au-coat Cu, It is conceivable that the partial reflection mirror is made of ZnSe) and they are accurately fitted to each other, or the base material is unified to that of the partial reflection mirror 5 and a coating is applied thereon. Since the operation of the laser resonator according to this embodiment is similar to that of the laser resonator according to the first embodiment, its explanation is omitted here.

With this configuration, the number of mirrors is substantially two, which is the same as that of a normal simple Fabry-Perot resonator, and the alignment and stability are improved.

Example 7. FIG. 11 is a sectional view showing in detail the structure of a laser device according to an embodiment of the present invention. In the figure, the same reference numerals as those shown in FIG. 1 denote the same or corresponding components, and 6 , 7 is an electrode, 8 is a matching box, 9 is a power source, 10 is a ceramic electrode,
Reference numeral 11 is an outer tube of the electrode 6, 12 is an inner tube of the electrode 6, 13 is a water cooling jacket, 14 is an electrode holding and adjusting mechanism, 15 is an invar, 16 is a window, 17 is xyz of the total reflection mirror 3.
Fine adjustment mechanism, 18 is an xyz fine adjustment mechanism of the partial reflection mirror 5,
Reference numeral 19 is a micrometer for finely adjusting the total reflection mirror 2, 20 is a micrometer for fine adjustment of the total reflection mirror 4, 21 is a micrometer for fine adjustment of the total reflection mirror 4, and 22 is a partial reflection mirror. A micrometer for finely adjusting 5 and a vacuum pump 23.

FIG. 11 shows, as an example, a discharge-excited gas laser equipped with a cooling mechanism, particularly a CO ₂ laser. The laser resonator shown in the first embodiment is incorporated in this laser device. There is.

The ring-cylindrical laser medium 1 is formed as a gap between the cylindrical inner electrode 6 and the ring-shaped ceramic electrode 10. This gap is a vacuum container, and a laser gas is introduced as the laser medium 1 having a ring-cylindrical shape in the container and kept at a constant pressure. The outer electrode 7 is provided on the outer side of the ceramic electrode 10, and the outer electrode 7 and the inner electrode 6 are discharged via the ceramic electrode 10.
Occurs between and. Due to the structure of the device, the inner electrode 6 is grounded so as to be electrically equipotential to the device housing, and the outer electrode 7 is connected to the power supply 9.

Normally, as the power source 9, an RF (radio f
A power supply is used. The power source 9 is connected to the outer electrode 7 via the matching box 8.
Metal-D discharge between ceramic and metal
This is a discharge at the ielectric boundary, but a uniform discharge can be obtained. Further, this type of discharge is effective in that the structure is simple.

The inner electrode 6 is formed of a double tube structure of an outer tube 11 and an inner tube 12, and is constructed so that the inner electrode 6 can be water-cooled from the inside. A water cooling jacket 13 is also provided on the outer side of the outer electrode 7, so that the outer side of the outer electrode 7 is water cooled.

Since the inner electrode 6 is supported at one end of the device by the electrode holding and adjusting mechanism 14 and the inclination thereof can be adjusted, it is necessary to adjust the inner electrode 6 so as to be exactly coaxial with the ceramic electrode 10. You can

Laser medium 1 in the shape of a circular cylinder, which is a vacuum container
Both ends of are vacuum-sealed by the total reflection mirror 2 and the window 16. Since the constituent elements of the laser resonator also contain the vacuum at the same time, the number of windows can be reduced, the structure can be simplified, and the performance can be improved.

The total reflection mirror 2 is provided with the micrometer 19, so that the total reflection mirror 2 can be maintained without damaging the vacuum.
The angle of can be fine-tuned.

Further, the aspherical total reflection mirror 4 is attached to the window 16 so as to be integrated with the window 16, and the total reflection mirror 4 is provided with a fine adjustment mechanism 20 such as a micrometer.
It enables fine adjustment of. Further, the total reflection mirror 4 needs to be configured so as to be integrally attached to the window 16 so as to be held from at least the inside, and if it is configured to be held from the outside, the propagation of the laser beam is hindered. become.

FIG. 12 is a perspective view showing in more detail the above-mentioned integrated structure with the window 16 for holding the total reflection mirror 4. As is clearer from FIG. 12, when the ring-cylindrical laser medium 1 and the output beam are coaxial, if the total reflection mirror 4 is held from the outside of the laser medium 1 due to the structure of the resonator, the beam is emitted. Will interfere with the propagation of. Further, if the output medium is not coaxial with the ring-shaped laser medium 1, the structure of the laser resonator becomes complicated and the mirror design becomes difficult. Therefore, in order to make the ring-shaped cylindrical laser medium 1 and the output beam coaxial, it is necessary to hold the total reflection mirror 4 from the inside. In this embodiment, as an example of the solution, the window 16 and the total reflection mirror 4 are integrally formed, which simplifies the structure.

The components of the above-described laser device including the total reflection mirror 2 and the total reflection mirror 4 integrally attached to the window 16 are the Invar 1 having a small thermal expansion coefficient.
5, the distance between the total reflection mirror 2 and the total reflection mirror 4 is always kept constant.

The ring-shaped aspherical total reflection mirror 3 is held by a mirror holder, and this mirror holder requires an angle fine adjustment mechanism 21 such as a micrometer and an xyz direction fine adjustment mechanism 17. Further, as described above, since the mirror 3 allows the beam to pass through in the middle, it needs to have an annular shape having a through hole in the center. Similarly,
The mirror holder of the partial reflection mirror 5 is also provided with an angle fine adjustment mechanism 22 such as a micrometer and an xyz direction fine adjustment mechanism 18.
Must be provided.

Although the CO ₂ laser has been described here, it goes without saying that the laser resonator according to this embodiment can also be applied to other gas lasers such as CO lasers which also require gas cooling by discharge excitation.

Example 8. FIG. 13 is an explanatory view showing a case where a ring-cylindrical medium serves as a laser waveguide for explaining a laser device according to another embodiment of the present invention. CO
_For gas lasers such as ₂ gas lasers, it is necessary to cool from the side of the cylinder, so the width of the cylinder (gap length) should be short, and a waveguide is effective for the laser to propagate in such a short gap space. Is.

However, since the propagation mode in the waveguide is different from the propagation mode in the free space, when it is intended to design the beam shape and the wavefront in detail like the laser resonator according to the present invention, the The effect of the propagation mode must also be considered.

The propagation mode in the waveguide is derived by a very simple model. First, assume a slab type waveguide having a gap length d and both walls made of metal. As shown in FIG. 14, the coordinate system has an x-axis in the gap direction and a z-axis in the wave traveling direction. At this time, assuming that ∂ / ∂y = 0 and assuming that a wave propagates with a wave number β in the z direction, that is, an electric field is represented by the following equation,

[0104]

[Equation 1]

The following wave equation should hold in the space of the waveguide.

[0106]

[Equation 2]

Here, k ₀ = ω / c, n ₀ (= 1) is the refractive index of the waveguide. Also, from the boundary conditions at the waveguide wall, E (0, y) = E (d, y) = 0 (3) holds, so the solution of equation (2) is

[0108]

(Equation 3)

It becomes: n is an arbitrary integer of 1 or more,
When n is an even number, it shows an even function, that is, a mode asymmetric with respect to the waveguide center, and when n is an odd number, it shows a symmetric mode.

The calculation of the propagation mode of the waveguide in the simplest case as described above has revealed that the propagation mode in the waveguide is a sine function and the value of the propagation coefficient β differs depending on the mode. This indicates that the propagation speed also differs depending on the mode.

The eigenmode of propagation in free space is a Gaussian function, as is well known. The beam of the Gaussian function does not change its shape due to propagation. However, when a Gaussian beam is incident from the end of the waveguide, it is expanded by the natural propagation mode in the waveguide, and the expanded natural modes are propagated in the waveguide at different speeds and are added together at the end of the waveguide. Go to. Therefore, the beam shape generally changes due to passage through the waveguide.

However, under certain conditions, this change can be minimized. The condition is determined by the gap length of the waveguide and the waveguide length. When the length of the waveguide is L, the phase change generated between the inlet and the outlet of the waveguide is given by Lβ. Therefore, the phase change φ _n of each eigenmode is

[0113]

[Equation 4]

Is given by However, n ₀ = 1 and k ₀ =
ω / c.

When this value deviates by an integer multiple of 2π for each mode, it can be said that the beam shapes at the entrance and exit of the waveguide become equal. It is not possible to obtain L of such a condition for general n, but it is shown that such a condition can be obtained if the incident beam is symmetrical with respect to the center.

A beam symmetric with respect to the center is n = 1,
3, 5, ... = 2m-1 (m is an arbitrary integer of 1 or more). From this, the following equation holds.

[0117]

(Equation 5)

Here, the insides of the two parentheses in the following equation are both integers, and the difference between them is 2m−1, which is an odd number, so either one is an even number. Therefore, in order for this expression to be an integral multiple of 2π, it is sufficient that L and d satisfy the relationship of L = nd ² / λ (7). Conversely, when this relationship is satisfied, the waveguide A beam symmetrical with respect to the center of is emitted without changing its contour. Here, n is an arbitrary integer and λ is the wavelength of the laser.

In an actual waveguide, both waveguide walls are often not made of metal, and the beam entering the waveguide is not strictly symmetrical with respect to the waveguide center. However, even when the waveguide wall is a dielectric, the penetration length of the electric field into the dielectric is sufficiently small, and it can be obtained here because it can be sufficiently approximated by the above mode obtained assuming a metal boundary. It can be considered that the relational expression is sufficiently practical.

Example 9. FIG. 15 is a cross-sectional view showing the structure of a laser device including the laser resonator described in the above embodiment according to the embodiment of the present invention.
The same reference numerals as those shown in 1 denote the same or corresponding components, and 33 is a ceramic tube provided around the inner electrode 6.

As described in the eighth embodiment, in the laser device in which the laser resonator shown in the first embodiment or the like is incorporated, it is very effective that the ring-cylindrical laser medium 1 serves as a laser waveguide. On the other hand, as described in the first embodiment, on the other hand, in the propagation of the waveguide, the propagation characteristic changes depending on the polarization of the beam.

The waveguide is preferably designed to minimize such distortion. This distortion greatly depends on the material of the waveguide wall, and becomes very large in a metal having a large difference in reflection characteristics between s-polarized light and p-polarized light, and the difference in reflection characteristics between s-polarized light and p-polarized light is sufficiently small in a dielectric. If the waveguide has an asymmetric structure such as a metal on one side and a dielectric on the other side, the effect that the traveling direction deviates from the axis of the waveguide occurs. Therefore, it is concluded that a symmetric dielectric waveguide, where the waveguide walls are dielectric on both sides, is optimal.

FIG. 15 shows an example of a laser device according to FIG. 11 in which the waveguide walls on both sides are dielectrics. A ceramic tube 33 is provided around the inner electrode 6, and between the inner electrode 6 and the outer electrode 7, the inner electrode 6-the inner ceramic tube 33-the discharge space 1a-
The structure is such that the outer ceramic tube 10a-the outer electrode 7. This structure is as shown in FIG.
Although it is structurally more complicated than the one-sided dielectric or one-sided metal electrode structure, such double-sided dielectrics are used when polarization dependence becomes significant, such as when a cylindrical discharge space acts as a waveguide. This structure is more advantageous.

Example 10. FIG. 16 is a sectional view showing the structure of the main part of a laser device according to another embodiment of the present invention. In the figure, 35 is a flash lamp, 36 is a cylindrical YAG rod, 37 is an outer shell, and 38 is inner cooling water. , 39
Is the outer cooling water.

The laser device according to this embodiment is obtained by applying the laser resonator shown in the first embodiment or the like to a solid-state laser. The cylindrical YAG rod 36 corresponds to the above-mentioned annular cylindrical laser medium 1 shown in FIG. A flash lamp 35 for excitation is inserted inside the cylindrical YAG rod 36. The inner surface of the outer shell 37 of the laser medium is a reflection mirror having a high reflectance. The entire laser device is water-cooled by the inner cooling water 38 and the outer cooling water 39.

Next, the operation will be described. In the solid-state laser having such a structure, the flash lamp 3
All of the light of No. 5 directly reaches the cylindrical YAG rod 36 which is the laser medium of the solid-state laser without passing through reflection, and most of it is absorbed by the rod. YAG rod 3 excited by the absorbed light of flash lamp 35
6 causes laser oscillation. Then, as shown in the first embodiment and the like, the laser light amplified in the YAG rod 36 is converted into a circular beam by the total reflection mirrors 3 and 4 shown in FIG. 1, and the partial reflection mirror 5 and the like. Exit through.

As described above, the laser device according to the present embodiment is provided with the ring-cylindrical laser medium 1, and in order to efficiently pump the laser medium, a pump source such as a flash lamp is housed inside the laser medium. Since a reflection mirror for returning the light emitted from the excitation source and transmitted through the laser medium back to the laser medium is provided outside the laser medium, it is possible to perform the excitation with extremely high efficiency, and also the first embodiment described above. A high-quality laser beam can be generated by applying a laser resonator based on the above.

Example 11. FIG. 17 is a sectional view showing the structure of the main part of a laser device according to another embodiment of the present invention. In the figure, 40 is a heat exchanger (cooling means) and 41 is a blower (circulation means).

The laser device according to the present embodiment is a gas laser such as a CO ₂ laser. The laser gas is not confined in the discharge space (optical space) having a ring-cylindrical shape, but the gas is flowed in the axial direction and the gas is externally supplied. It is equipped with a mechanism for circulation.

Next, the operation will be described. Blower 41
Generates a flow in the gas enclosed in the discharge space in the direction of the arrow shown in FIG. 17 to circulate the gas. Blower 41
When the gas circulated by the heat exchanger reaches the heat exchanger 40, it is cooled there and is guided again into the discharge space. In the laser device having such a configuration, it is not necessary to cool the laser gas from the electrodes by heat conduction, so that the gap length of the cylinder can be increased. Therefore, the laser device according to this embodiment is equivalent to a conventional high-speed axial flow type laser arranged in an annular shape, and it is possible to oscillate an ultrahigh-power laser by using the conventional technique. A high-quality laser beam can be generated by applying the laser resonator according to the first embodiment described above.

Needless to say, such a structure can also be applied to a CO laser that requires gas cooling by discharge excitation.

[0132]

As described above, according to the first aspect of the invention, the light which is installed at a predetermined distance from the other end of the laser medium and which has passed through the laser medium is directed in the direction near the central axis of the laser medium. A second total reflection mirror for condensing and a third total reflection mirror for converting the light collected by the second total reflection mirror into substantially parallel light are provided.
The total reflection mirrors of the above cooperate with each other so that the wavefront of the light of the ring-cylindrical portion in the laser medium becomes the closest to the plane.
The wavefront of the output beam of the laser beam, that is, the phase The effect is that the distribution can be made uniform.

According to the second aspect of the invention, since the structure is represented by a linear expression or a quadratic expression relating to the distance from the center of the mirror, similarly, the wavefront of the outgoing beam of the laser light, that is, the phase distribution. There is an effect that can be made uniform.

According to the third aspect of the invention, for the beam on the third total reflection mirror, the distance b from the central position of the beam to the central axis of the laser medium and the beam diameter ω of the beam.
_Since the value of the ratio b / ω _m with respect to _m is defined as an index for selecting the transverse mode of the output beam of the laser resonator, the transverse mode to oscillate is selected by the difference in the resonator loss. There is an effect that can be.

According to the invention of claim 4, when the order of the output direction of the laser resonator in the cylindrical coordinate system in the angular direction is n, the center of the beam on the third total reflection mirror is set. The value of the ratio b / ω _m of the distance b from the position to the central axis of the laser medium and the beam diameter ω _m of the beam satisfies the relationship of 0.5n + 0.9 <b / ω _m <0.5n + 1.8. With this configuration, there is an effect that the transverse mode to oscillate can be selected according to the difference in resonator loss.

According to the fifth aspect of the present invention, the laser medium has a ring-cylindrical laser medium, and the laser resonator according to claim 3 or 4 is provided. Since it serves as a beam waveguide and the laser resonator is configured so that the value of the ratio b / ω _m is regulated so as to output a beam corresponding to TEM _0n ^* polarized in the circumferential direction,
There is an effect that a beam with a minimum waveguide loss and excellent symmetry and stability can be obtained.

According to the invention of claim 6, the laser medium has a ring-cylindrical laser medium, and the laser resonator according to any one of claims 1 to 4 is provided,
The ring-cylindrical laser medium serves as a waveguide for the laser beam, and the waveguide gap length d and the waveguide length L are L.
= N × d ² / λ (n is an arbitrary integer, λ is the laser wavelength)
Since it is configured so as to satisfy the above relationship, there is an effect that a beam symmetric with respect to the center of the waveguide can be emitted without changing its shape.

According to the invention of claim 7, a laser medium having a ring-cylindrical shape is provided, and the laser resonator according to any one of claims 1 to 4 is provided. Since the total reflection mirror of No. 3 is configured to be held from the inside of the laser medium,
There is an effect that the total reflection mirror can be held.

According to the eighth aspect of the present invention, a ring-cylindrical gas is used as the laser medium, and the first to fourth aspects are provided.
The laser resonator according to any one of 1 to 3 is provided, and the gas is caused to flow in the axial direction of the ring-shaped optical space and the gas is guided to the outside of the laser resonator to return the gas into the optical space again. Since the circulating means and the cooling means for cooling the gas guided to the outside by the circulating means are further provided, it is possible to increase the gap length of the cylinder that defines the size of the laser medium, and to increase the size. There is an effect that an output laser beam can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing the structure of a laser resonator according to an embodiment of the present invention.

FIG. 2 is a perspective view for explaining a beam waist of a laser beam generated in the laser resonator shown in FIG.

FIG. 3 is a diagram for explaining a method of designing a mirror that constitutes a laser resonator according to an embodiment of the present invention.

FIG. 4 is a diagram showing a polarization state in a waveguide that changes according to a transverse mode in a laser resonator according to an embodiment of the present invention.

FIG. 5 is a graph showing a change in propagating transverse mode resonator loss with respect to a mirror design parameter b / ω _m in a laser resonator according to an embodiment of the present invention.

FIG. 6 is a configuration diagram showing a configuration of a laser resonator according to another embodiment of the present invention.

FIG. 7 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention.

FIG. 8 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention.

FIG. 9 is a sectional view showing the structure of a laser resonator according to another embodiment of the present invention.

FIG. 10 is a sectional view showing a structure of a laser resonator according to another embodiment of the present invention.

FIG. 11 is a sectional view of a laser device according to another embodiment of the present invention in a plane including the central axis.

12 is a diagram illustrating a method for holding total reflection mirror 4 in the laser device shown in FIG.

FIG. 13 is a diagram showing how a laser propagates using a ring-cylindrical medium as a waveguide in a laser device according to another embodiment of the present invention.

FIG. 14 is a cross-sectional view showing a slab-type waveguide in which both walls are made of metal.

FIG. 15 is a sectional view of a laser device according to another embodiment of the present invention in a plane including the central axis.

FIG. 16 is a sectional view showing the structure of a flash lamp-pumped solid-state laser which is a laser device according to another embodiment of the present invention.

FIG. 17 is a sectional view showing a structure of a main part of a laser device according to another embodiment of the present invention.

FIG. 18 is a configuration diagram showing a laser resonator using a conventional waxicon.

19 is a configuration diagram showing an enlarged view of a portion of a waxicon mirror in the laser resonator using the waxicon shown in FIG.

[Explanation of symbols]

1 ring-shaped laser medium, 2 total reflection mirror (first
Total reflection mirror of 3), an annular aspherical total reflection mirror (second total reflection mirror), 4 aspherical total reflection mirror (third total reflection mirror), 5 partial reflection mirrors, 16
Window, 40 heat exchanger (cooling means), 41 blower (circulation means).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Yoshizawa 8-1-1 Tsukaguchihonmachi, Amagasaki-shi Central Research Laboratory, Mitsubishi Electric Corporation

Claims (8)

[Claims] 1. A laser resonator used in a laser device having an annular cylindrical laser medium, wherein a first total reflection mirror installed at one end of the laser medium and a predetermined total distance from the other end of the laser medium. A second total reflection mirror, which is installed at a distance and focuses light passing through the laser medium in a direction near the central axis of the laser medium, and light collected by the second total reflection mirror A third total reflection mirror for converting the light into parallel light; and a part of the substantially parallel light provided substantially perpendicular to the substantially parallel light converted by the third total reflection mirror. A beam having a partial reflection mirror for transmitting light, wherein the second and third total reflection mirrors cooperate with each other so that a light wavefront of a ring-cylindrical portion in the laser medium is closest to a plane. At the waist A laser resonator having a shape and an arrangement relationship such that a virtual image of a circle at the center of an annulus, which is a cross-sectional shape of light, is substantially collected at one point. 2. The surface shape of each of the second and third total reflection mirrors is expressed by a linear expression or a quadratic expression relating to the distance from the center of the mirror, respectively. Laser resonator. 3. The ratio b of the beam diameter ω _m of the beam on the third total reflection mirror to the distance b from the central position of the beam to the central axis of the laser medium.
3. The laser resonator according to claim 1, wherein the value of / ω _m is defined as an index for selecting the transverse mode of the output beam of the laser resonator. 4. When the order in the angular direction of the output beam of the laser resonator in the cylindrical coordinate system is n, then the third
Of the beam on the total reflection mirror, the ratio b / ω _m of the distance b from the central position of the beam to the central axis of the laser medium and the beam diameter ω _m of the beam is 0.5 n.
The laser resonator according to claim 3, wherein the relationship of +0.9 <b / ω _m <0.5n + 1.8 is satisfied. 5. The ring-cylindrical laser medium serves as a waveguide for a laser beam, and the laser resonator outputs a beam corresponding to TEM _0n ^* polarized in the circumferential direction so that the ratio b / ω _m. The laser device having the laser resonator according to claim 3 or 4, wherein the value of is defined. 6. The ring-shaped cylindrical laser medium serves as a waveguide for a laser beam, and a gap length d of the waveguide is used.
And the waveguide length L is L = n × d ² / λ (n is an arbitrary integer,
5. A laser device having a laser resonator according to claim 1, wherein λ substantially satisfies a relationship of (laser wavelength). 7. The laser resonator according to claim 1, wherein the third total reflection mirror is supported from the inside of the ring-shaped cylindrical laser medium. Equipped laser device. 8. The circulation, wherein the laser medium is a gas, the gas is caused to flow in the axial direction of the ring-shaped optical space, and the gas is guided to the outside of the laser resonator to return the gas into the optical space again. 5. A laser device having a laser resonator according to claim 1, further comprising: a cooling means for cooling the gas guided to the outside by the circulation means.