RU2243620C1 - Laser, slab-laser, gas laser (alternatives), and gas slab-laser - Google Patents

Abstract

FIELD: laser engineering; high-power rectangular gas discharge geometry lasers.

SUBSTANCE: proposed laser has two elongated surfaces with laser active medium in-between, pumping means, and plane incorporating closed axial loop of traveling wave optical cavity. The latter is optically unstable in mentioned plane and optically stable in certain direction. Modes of optically unstable and optically stable cavities jointly dictate propagation characteristics inside cavity and radiation beam output therefrom. Active medium of laser may be gas, solid material, or liquid.

EFFECT: reduced sensitivity of cavity to maladjustment of its inner components without no unwanted effect due to high light intensity in focal plane when focusing beam inside cavity.

101 cl, 6 dwg

Description

Technical field

The present invention relates to the generation of coherent radiation in the form of one or more lower transverse modes in a large volume of a laser active medium having an asymmetric cross section, to obtain an output beam that is diffractically output and has a continuous cross section. This is achieved by using a hybrid unstable traveling wave resonator. Generally speaking, it is well known that unstable standing wave resonators having an axisymmetric or asymmetric cross section have higher characteristics, in the sense of discrimination of the transverse modes, in comparison with stable standing wave resonators. The present invention shows that the use of hybrid unstable ring resonators allows you to obtain properties that cannot be obtained using hybrid unstable optical standing-wave resonators. For example, it is widely known that hybrid unstable standing-wave resonators belonging to the negative branch have a uniquely low level of sensitivity to misalignment of end mirrors due to the inversion of the beam occurring in the focal plane of a pair of concave mirrors. It is this property that is the reason why hybrid unstable standing wave resonators related to the negative branch are considered more promising in a number of laser applications compared to hybrid standing wave resonators related to the positive branch. However, the present invention shows that the desired property of the intracavity flip of the beam, leading to the replacement of the left by the right, and low sensitivity to misalignment of the resonator can be obtained in a hybrid traveling wave resonator without compromising the characteristics associated with the presence of a focal waist inside the resonator. In addition, due to the fact that the resonator is a traveling-wave resonator, the effects of spatial “hole burning out” characteristic of some laser media are reduced to zero. In addition, since the present invention is limited to resonators that are unstable in only one plane, does not use branched waveguides and is mainly based on the use of fully reflective optics, the concept presented in it is easily scalable to a very high level of average laser output power. Accordingly, the overall objective of the present invention is to develop new and more advanced methods and devices of this type.

General Description of Prior Unstable Resonators

Since the first appearance of unstable resonators in the literature [1] and their first systematic experimental and analytical studies in 1965, unstable resonators have been used in excimer, ion, molecular, solid-state lasers, as well as in non-liquid active media lasers and free electron lasers. All of these lasers collectively emit in the spectral range from ultraviolet to infrared.

In this pioneer article, using the ad hoc geometric-optical approach, it was shown that the mode losses are independent of the size of the end mirrors, and that although the experimental losses in the resonator turned out to be large, as expected, it was suggested that the diffraction conclusion radiation could be useful for the selection of transverse modes. In 1967, in the second paper [2], three general properties of unstable resonators were listed: "1) Unstable resonators can have a large mode volume even with a very short cavity; 2) The unstable configuration of the resonator makes it easy to vary the diffraction output of the radiation; 3) The analysis shows "that unstable resonators should provide a high degree of discrimination with respect to higher order transverse modes."

The first experimental evidence of a high degree of discrimination of transverse modes in a laser with an unstable cavity was given in [3]. Over time, these three properties of unstable resonators have been repeatedly demonstrated experimentally and theoretically. In 1967 and 1969, the concept of unstable resonators was extended to confocal unstable resonators, and several new types of ring unstable resonators were proposed for the first time [4]. The comments on a brief discussion of their properties [5, 6] pointed to the emergence of “a new possibility of creating unidirectional ring generators [5, p. 1002]”. In these publications [4–6], unstable ring resonators were introduced for the first time with or without focal constriction inside the resonator. These ring resonators were investigated in [5, 6], and it was shown for the first time that “although the losses of modes propagating in opposite directions are identical, a significant difference in the volume of modes in such resonators can contribute to unidirectional generation [5, p. 1002] "

Although the active medium of a CO ₂ laser was considered as one of the ideal candidates for use in combination with an unstable resonator system, it took almost five years after the first discussion of unstable resonators in the literature [1] for the details of such a resonator system to be presented in [7] in 1969. In this work, we reported the use of a confocal unstable resonator of the positive branch to generate continuous radiation with an output power of 22 W and an annular output mirror to output a collimated main mode from the laser, which has the shape of a ring in the near zone. Within a year from the first publication in 1970 shedding light on the true values of the loss of the first six lower modes in unstable standing wave resonators with round mirrors, a paper [9] was published that reported the creation of a continuous CO based on an unstable resonator system ₂ lasers with an output power of 30 kW.

In 1972, an unmatched ring unstable resonator was patented for the first time [10]. Around the same time, a number of experimental works on CO ₂ lasers were published, in which the characteristics of confocal unstable standing wave resonators [11], unidirectional symmetric confocal ring resonators [12], asymmetric confocal ring resonators [13], and unstable standing and traveling wave resonators operating in the mode of radiation injection and regenerative amplification [14]. It was shown [11] that, in confocal unstable standing wave resonators, the measured diffraction losses, without any exceptions, are in full agreement with the losses predicted by the strict diffraction theory [8]. This correspondence also includes details of the behavior of mode losses in the cavity near the transition point from the lowest symmetric mode to the next symmetrical mode in terms of loss [11, Fig. 17]. Similarly, the unidirectional mode of operation of an unstable traveling-wave resonator, proposed in mid-1968 in [4], was implemented for the first time in [12, 13], as was previously predicted [5], only by placing the amplifying medium in a place for which the volumes of the forward and backward waves are different, which gives the advantage of a traveling wave of only one direction. Moreover, it was shown that the use of unstable traveling-wave resonators is a powerful resonator approach in relation to the concept of laser regenerative amplification [14]. In this case, as was shown, the degree of unidirectional generation is significantly enhanced due to the output mirror of the laser injecting radiation [14, Fig. 35], which serves as a return mirror for the ring resonator [10, Fig. 24, element 24]. It was shown that in regenerative amplifiers based on ring optical unstable resonators, unidirectional mode is achieved more easily than in the case of using unstable standing wave resonators, since an insulator is not required in this case [10, Fig. 29].

As follows from what has been said, over the decade since the introduction of unstable resonators and their first analysis, understanding of unstable resonators has gone from the initial geometrical-optical approach [1] to the approach based on iterative calculations in the diffraction approximation [8]. During this decade of theoretical studies, the output power of CO ₂ lasers ultimately increased from 20 W in the first standing wave devices [7] to a level of continuous output power of presumably several hundred kilowatts when using an asymmetric ring resonator [12, 13].

From a historical point of view, it is interesting to note that the original concept of an unstable optical resonator [1], proposed by Sigman in 1965, has never been claimed for patenting anywhere. Apparently this was due to the fact that in the first period of discussion and development there was no reliable diffraction model of an unstable resonator. Meanwhile, the substantial practical value of confocal unstable resonators was independently predicted in 1968 in [7] and experimentally demonstrated in [15] in 1969. As a result of these studies, the confocal unstable cavity of the positive branch (telescopic cavity) was patented in Russia [16] with a priority date of March 18, 1968, but for a long time remained unknown to the international community. The idea of a ring unstable resonator, proposed in 1968 in [4], was never announced for patenting until 1972. From a retrospective point of view, this could be due to a general misunderstanding of how completely the backward wave propagating in the resonator can be suppressed. In 1972, unstable ring resonators were patented in [10] due to the development of effective methods for ensuring unidirectional operation of lasers with such resonators. In any case, a review of works on unstable resonators, reflecting the views of that time, can be found in [6, 17], and the most complete discussion of all the mentioned, as well as other types of unstable resonators, along with a detailed bibliography, in [18, 19] .

Stable ring resonators have been widely known in laser technology since the second half of the sixties, because even earlier it was proposed, along with other applications, to use them to measure the rotation of objects in an inertial gravitational field [20]. As was shown specifically for these applications, the difference frequency between the waves propagating along the ring in the forward and reverse directions is proportional to the angular velocity of rotation of the ring laser system. Unstable ring resonators are fundamentally different from stable ring resonators in that, in unstable ring resonators, the diameters of the modes of the forward and reverse directions are generally different, and the same in stable ring resonators. This circumstance serves as the basis for one of the methods for achieving unidirectional operation [5, 6] by using the diaphragm inside the cavity. In addition, the suppression of waves propagating in one of the possible directions, both in symmetric [12] and asymmetric [6, 12, 13] ring unstable resonators, can be achieved by reasonably placing the active medium inside the resonator. To achieve this, the active medium is placed inside the resonator in the region where the mode volume of one of the traveling waves is large and exceeds the volume of the other traveling wave [17, Fig. 16, 17]. In a near-symmetric unstable ring resonator, the ratio of the output powers of the forward and backward waves turned out to be close to 20 in the experiments [12, Fig.6]. Another way to achieve unidirectional mode is to use a return mirror [10, figure 2], placed outside the resonator. It should be noted that the unidirectional aspect, both in stable and unstable resonators with a symmetrical aperture, is central to the idea of achieving regenerative amplification without introducing an optical isolator between the master oscillator and the regenerative amplifier [14, Fig. 8, 29]. Similarly, in applications such as a variety of plasma diagnostic methods [21] or analysis of the spectral composition of laser radiation [22], the use of ring resonators is highly desirable or even fundamental. Therefore, it is not surprising that in the description of all these applications, inventions and devices, without exception, one or another discussion of both directions of propagation inside the ring always takes place.

Obviously, if, when considering the optical device of a traveling wave, in which waves of two opposite directions of propagation leave the device in different and unique directions for each wave, we discuss only one of the directions of propagation, then this is equivalent to discussing only half of the optical problem. Indeed, without such a discussion it is impossible even to say with certainty which of the two modes propagating towards each other is used for output, i.e. in which direction the radiation will go. Conversely, if there is no discussion about the two possible directions of distribution in the description of an invention or device, such inventions or devices should be considered as inventions and devices based, in their nature and applications, on the concept of a standing wave.

In contrast to the obvious difference in the direction of generation, which is considered the most distinguishing feature when comparing stable ring resonators and stable standing wave resonators, the differences between unstable ring resonators and stable ring resonators are much richer and more complex. For example, in a stable ring resonator, the diameter of the mode in the forward and backward waves in any section inside the resonator, as well as the total volumes of the modes are the same for both waves. In contrast, the diameters of the mode for the forward and backward waves, measured in any cross section inside the unstable resonator, as well as the total volumes of the mode in these two waves propagating towards each other, are generally different.

For illustrative purposes, suppose that an unstable ring resonator is both confocal and asymmetric. In our consideration, the term “confocal” means that the design of the resonator is chosen in such a way that either the direct or backward wave leaves the resonator in the form of a collimated beam. The term “asymmetric” in this case means that the distance between the optical elements expanding the beam is greater (or less) than the remaining part of the perimeter of the resonator. For such an asymmetric confocal case [10], the resonator is confocal in only one of the directions along the ring. In other words, “this type of asymmetry of directions can only be realized in a [unstable] ring resonator” [19, p. 839, lines 28, 29]. Therefore, in order to fully and unambiguously describe the mode properties of unstable ring resonators, these resonators must be considered completely separate from stable standing wave resonators, stable traveling wave resonators, and also unstable standing wave resonators.

Therefore, when considering inventions whose novelty is the use of certain types of unstable resonators with a symmetrical aperture or hybrid unstable resonators, it cannot be argued that these inventions include ring unstable resonators, unless the patent itself contains a discussion of how the mode is effectively suppressed, propagating along an unstable ring resonator in one of the directions. Similarly, any discussion should be presented on how the shape of the beam cross section in the generating traveling mode is related to the cross section of the laser amplifying medium if this mode remains unpressed, since, if not suppressed, this mode determines the direction in which Significant laser output will be emitted. In this regard, US patent No. 5097479 [23] is fully consistent with this remark, because describes the suppression of one of the traveling waves in a two-mirror branched unstable ring resonator with respect to CO ₂ slab type laser medium. Similarly, US patent No. 3824487 [10] meets the specified requirement, since it discusses both the backward wave and the problem of matching another, not suppressed wave with a large volume of active medium. On the other hand, US patent No. 4719639 [24] and No. 5048048 [25] are unsatisfactory in this regard, and, thus, their applicability is fundamentally self-limited and applies only to hybrid unstable standing wave resonators.

As shown below, a laser with a traveling wave resonator, in which for one transverse direction the traveling wave mode corresponds to the mode of an unstable resonator, and in the orthogonal transverse direction corresponds to the waveguide mode or the Gaussian mode characteristic of propagation in free space, can be ideally suited for efficient energy removal from an active medium of any type having an elongated cross section. This, of course, suggests that generation in one of the directions along the ring of an unstable ring resonator can be effectively suppressed. If this is the case, the use of the present invention can be beneficial in combination with excimer, ionic, molecular, solid-state and liquid active media, as well as a free-electron laser medium emitting in the whole spectrum from the ultraviolet to the infrared. Such media can be pumped by high-frequency discharge, direct current, electron beam, incoherent light, coherent light or a source of free electrons, or any combination of these methods.

Description of known waveguide and slab lasers with high-frequency excitation

The present invention can be used, for example, in high-power CO or CO ₂ lasers with a rectangular discharge geometry, although its practical applicability is not limited to these applications. In the general case, the rectangular geometry of the discharge is considered to be such that the discharge cross section is elongated and the discharge occurs in the most typical case either along a smaller transverse size (slab device) or along a larger section size (slice device). In slice devices, there is also a special case where the discharge is carried out in a direction perpendicular to the elongated transverse aperture. In all these cases, the ratio of the long side of the cross section to its short side is large and is selected so that in the direction along the long side the mode of the unstable traveling wave resonator can be supported. Due to the elongation of the cross section in such lasers, optical resonators that have different functional characteristics, as well as propagation characteristics in two different transverse dimensions, can be successfully used. For the first time, an optical resonator of similar geometry was experimentally investigated in [26] as a part of a neodymium-glass slab laser. The resonator included one plane and one convex cylindrical mirror, so that the resonator was unstable along the large transverse slab dimension (240 mm) and equivalent to the Fabry-Perot resonator along the short side of the cross section (20 mm). Subsequently, such resonators were called hybrid [27]. Thus, two types of hybrid resonators to which the present invention is particularly well applicable are those in which the field along the short transverse dimension is described by either i) the waveguide mode or ii) the Gaussian mode of free space, while along the larger transverse dimension it functionally described by the mode of an unstable resonator.

In preferred embodiments of the present invention, the proposed optical configuration can find practical application in high-power waveguide gas lasers with diffusion cooling of gas using a discharge with a slab-type geometry in accordance with the '639 [24] patent or slice geometry in accordance with the' 663 [28].

The waveguide slab laser, excited by a transverse high-frequency electric discharge, contains a waveguide formed by the reflective surfaces of two elongated electrodes arranged in parallel facing each other. The electrodes are made of a material that reflects laser radiation well, which ensures low radiation losses in the waveguide. The space between the electrodes is filled with a gas active medium excited by a transverse electric discharge created in the active medium by applying high-frequency excitation power to the electrodes. Near the ends of the waveguide formed by the surfaces of the electrodes, mirrors are installed that form the laser resonator. In addition to the excitation of gas by an electric discharge and the formation of the upper and lower walls of the optical waveguide, the electrodes serve as cooling elements and provide heat removal from the active medium. To ensure good diffusion heat removal from the discharge region, the electrodes are made of a material with high thermal conductivity, and the gap between them is chosen small and usually does not exceed several millimeters.

The electric field in such a discharge is directed substantially perpendicular to the surfaces of the cooling elements and is oriented substantially in the direction of the height of the cross section of the active medium. Typical examples of such lasers are waveguide lasers with high-frequency excitation on CO ₂ [29, 30], CO [31], and Xe [32]. Slice lasers made in accordance with the '663 patent [28] are also characterized by a gas amplifying medium excited by a high-frequency electric discharge and having an elongated cross section with short and long sides. Unlike waveguide lasers, the discharge region is determined in them by an electric field created in a direction perpendicular to the short side of the cross section. In slice lasers, the discharge is limited by the space enclosed between a pair of closely spaced non-conductive cooling elements. These cooling elements are located opposite each other so that the gap between their facing each other surfaces is not only small enough to provide diffusion cooling of the gas filling the gap, but is also acceptable from the point of view of creating a fiber for the propagation of laser radiation between non-conducting surfaces. Thus, a discharge in a gas is excited by a system of electrodes arranged so that the electric field in the discharge chamber is substantially parallel to the surfaces of the cooling elements, i.e. directed transversely with respect to the height (smaller dimension) of the cross section of the active medium. As indicated in the '663 patent [28], such slice lasers have a number of advantages over conventional waveguide lasers. These advantages, among others, include the independent selection and optimization of the gas pressure in the discharge and the excitation frequency, the possibility of using both high-frequency sources and direct current sources to excite the discharge, as well as the relatively weak influence of the boundary layers formed near the electrodes.

It is clear that the device based on the high-frequency transverse discharge in a small-diameter tube, in the microwave and high-frequency versions, described in 1980 in [33], and the strip geometry device, described in 1984 in [34], preceded the application for the slab device geometry '639 [24] in 1987. Due to previous inventions of the time, slab lasers, from the point of view of patentability, were limited to the case in which only the waveguide mode is realized in the direction of the smaller of the two transverse measurements of the discharge, and direction larger - only the operating mode inherent in an unstable resonator. In a waveguide slab laser, the modes of light propagating along the opposite surfaces of the electrodes are determined entirely by these surfaces and their relative positions. The geometry of a slice laser in accordance with the patents '663 [28] and' 256 [35], on the other hand, was a completely new type of transverse discharge organization, which became known only after the filing of the corresponding patent application. The laser slice geometry is one in which a much wider choice of types of hybrid resonators can be used.

Therefore, for example, when describing the slice lasers considered in [32, 35], the term “fiber”, when applied to slice lasers, has a broader meaning than just a waveguide.

Thus, in the case of a slice laser, the propagation of light can be either waveguide, as in a slab device, or such that the radiation propagates inside the resonator without any interaction with the walls of the slice camera. One of such cases is realized when, in the direction corresponding to the small slice measurement, the intracavity mode does not touch the walls and is best described by the Gaussian mode of free space in terms of its functional features. This case occurs, for example, in stable resonators, where the laser beam is kept from expanding by means of the cavity mirrors and does not touch the walls of the fiber, since any boundary conditions for this type of mode in the cavity should not be satisfied.

In the present invention, the term “fiber” is used in the most general sense, and is intended to include all propagation methods, from the waveguide mode to the propagation of a Gaussian beam in free space.

To increase the volume of the active medium of a conventional waveguide laser with a symmetrical aperture and thereby the laser output power while maintaining a small gap between the electrodes, US Pat. . The surface of the electrodes reflecting the radiation in this laser forms the upper and lower walls of the large-width optical waveguide, in which the radiation propagating between the electrodes is limited by this waveguide only in directions perpendicular to the electrode surfaces. In the directions parallel to the surfaces of the electrodes, the waveguide is open, so that the radiation beam propagating along the waveguide can expand in these directions in both opposite directions as in free space. Near the ends of the waveguide, confocal convex and concave mirrors are installed that form an unstable cavity of the positive branch with an increase in M> 1. In such a resonator, at each complete passage of the radiation beam from one mirror to another and back, this beam expands approximately M times in two opposite directions, in which the beam is not limited by the surfaces of the electrodes and can expand as in free space. To form a single output beam of a continuous section in a laser with such a resonator, the mirrors are usually set so that the axis of the unstable resonator formed by them is shifted to one of the open lateral sides of the interelectrode gap. The output laser beam is extracted from the resonator on the other side of the interelectrode gap, near the edge of the convex mirror, covering only part of the cross section of the waveguide. Such a “half” configuration of the cavity makes it possible to form a continuous beam of approximately rectangular cross section with a divergence close to the limit determined by diffraction in each of the transverse directions, even with a sufficiently large width of the electrodes. The large width of the electrodes makes it possible to excite a large volume of the active medium and, due to this, a high output laser power.

However, it is known that waveguide lasers with an unstable resonator of a positive branch, having a small increase in M, are characterized by high sensitivity to misalignment of the mirror mirrors, in particular to a change in their angular position in a plane parallel to the electrodes [25], as well as to optical inhomogeneities such as a wedge in that the same plane, which usually occurs in the active medium of a laser when it is pumped. This cannot be considered unexpected if we take into account previously published works on ordinary unstable resonators [6, 7]. In CO ₂ slab and slice lasers, as a rule, M does not exceed 1.2-1.5. Therefore, if special measures are not taken that increase the rigidity of the structure and the optical uniformity of the active medium and, consequently, increase the cost of the laser, misalignment of the mirrors and inhomogeneities of the active medium in such lasers lead to a significant deformation of the structure of the radiation mode, accompanied by a sharp decrease in the output power and a decrease in the directivity and angular displacement of the output beam, which is unacceptable in a number of applications. The need to take measures to solve these problems leads to an increase in the cost of the laser.

It is well known to those skilled in the art of slab lasers that shifting the axis of an unstable cavity of the positive branch to one of the sides of the electrode will convert the cavity from a full cavity to a half configuration. However, it is not always taken into account that part of the radiation propagating inside the resonator still leaves the resonator near the edge of the electrode gap, to which the axis of the resonator is shifted. Thus, although the shift of the axis of the resonator makes it possible to obtain essentially one output beam of a continuous cross section instead of two output beams, this positive property is achieved at the cost of removing some of the radiation from the side of the resonator where this radiation cannot be combined with a useful output beam. For the cavity, this means introducing passive radiation losses, which reduce the overall laser efficiency. And even worse, this radiation can again interact with the desired resonator mode due to mirror reflections and cause the appearance of undesirable higher modes that compete with the main mode in terms of gain in the entire active volume and, therefore, in terms of output power. To address these shortcomings, US Pat. No. 5,048,048 [25] proposed the use of an unstable negative-branch resonator with an increase in M <-1 in a wide-aperture waveguide laser. The proposed resonator is formed by two concave mirrors with different radii of curvature having a common focus located inside the resonator.

The confocal resonator of the negative branch can form a continuous output beam that emerges from only one side, as a result of replacing the left to the right (inversion), which occurs in the common focal plane of two concave mirrors of the resonator.

The laser beam propagating along the waveguide between the mirrors of the unstable resonator of the negative branch, at each passage through the focal point (focal "constriction" of the beam) is turned over in section so that the beam rays propagating on one side of the cavity axis, after passing the focal point, are the other side of this axis (which is the common normal to the surfaces of both mirrors). Due to such alternating passage of laser radiation, on one or the other side of the cavity axis, with | M | of the order of 1.2-1.5, there is an effective compensation of misalignments due to deviation of the angular position of the resonator mirrors in a plane parallel to the electrodes, as well as effective compensation of optical inhomogeneities such as a wedge in an active medium, which makes the resonator insensitive to such misalignments and optical inhomogeneities [6, 7].

To ensure a one-way output of radiation from a hybrid unstable resonator of the negative branch made according to the '048 patent [25], the dimensions of one of the resonator mirrors are chosen so that the distance from the resonator axis to the opposite edges of this mirror in a plane parallel to the reflective surfaces of the electrodes differs by more than in | M | time. The dimensions of the other resonator mirror are chosen large enough so that it does not limit the expansion of the beam in the waveguide. In this case, the radiation that propagates through the resonator from the side from its axis that is opposite to the output side of the radiation, as a result of the flip of the beam section occurring in the focal constriction, at the next pass of the resonator enters the output side of the radiation and is removed from the resonator in the form of a useful output beam. Due to this, the output laser beam is a single beam of a continuous cross section, leaving the cavity from only one side of it, despite the free expansion of the beam in the cavity in two opposite directions. Thus, the presence of a focal waist in the unstable cavity of the negative branch reduces passive radiation losses from this resonator, compared with the “half” unstable cavity of the positive branch, in which beam expansion in two opposite directions inevitably leads to radiation loss from the cavity on the other side which is opposite to the output side of the useful output beam.

However, the presence of a focal constriction in the volume of the gas active medium in the unstable cavity of the negative branch can lead, due to the high local density of the radiation power, to undesirable nonlinear effects in the active medium and to the breakdown of the gas, especially in high-power pulsed lasers. In addition, the efficiency of using the volume of the active medium in such a resonator is reduced compared to the resonator of the positive branch due to the uneven filling of the active medium by the radiation beam. The reduction in laser dimensions, which is usually achieved by breaking the optical axis of the laser resonator with an additional mirror, is also difficult in this case, since the mirror placed in the resonator of the negative branch to break its axis is close to the focal waist and does not withstand the action when the laser power is increased powerful radiation. In addition, the mirrors of the unstable resonator of the negative branch should have a large curvature - their radii of curvature in order of magnitude should be equal to the distance between the mirrors. As a result, to reduce the influence of the curvature of these mirrors on the formation of the field along the height of the waveguide, i.e. in the direction of the normals to the surfaces of the electrodes, it is necessary to use mirrors of complex shape with different curvatures in two mutually perpendicular planes, or to take special measures to match the wave fronts, as a result of which, as indicated in US Pat. No. 5123028 [36], additional losses occur in the resonator. In addition, with a significant increase in the width of the electrodes, an increase in the width of mirrors having a large curvature is accompanied by a rapid increase in spherical aberration, which leads to a significant increase in the divergence of radiation, which also complicates the use of unstable negative-branch resonators in high-power waveguide lasers.

Indeed, as can be seen from figure 4 in US patent '048 [25], in the area where the negative branch resonator has an advantage over the positive branch resonator, the output power level is relatively low. At present, some evidence has been obtained that at a power level of several kW in such CO ₂ slab lasers, there is a significant instability in the direction of the output beam, which can be caused by gas heating or other nonlinear effects in the common focal region of a pair of confocal mirrors.

US Pat. No. 5,097,479 [23] proposed a wide-aperture waveguide gas laser with an unstable ring resonator of a positive branch, equipped with means for performing unidirectional generation in the cavity [23, Fig. 10, element 80]. This embodiment of a waveguide gas laser is pumped by a high-frequency power applied to a pair of spaced electrodes. Due to the fact that only two intracavity mirrors are used in this ring resonator, a complete round-trip along the ring resonator can only be achieved through a sequence of distributed reflections in a precisely curved branched waveguide structure. In this waveguide structure consisting of two branches, an annular unstable optical resonator with a closed axial contour is formed, which ensures the output beam of a continuous cross section from the laser.

The ring resonator proposed in '479 [23] is formed by combining into two optical units adjacent to each other precisely curved segments of the optical waveguide. Both halves of the curved branching waveguide structure are optically coupled to each other by means of a pair of mirrors located at the ends of the segments in such a way that they direct the radiation incident on the mirror from one segment of the waveguide to its other segment.

Each of the mirrors thus provides a rotation of the incident radiation beam in a plane transverse to the waveguide walls. Thus, a pair of mirrors and two curved segments of the waveguide in this laser provide the formation of a ring resonator with a closed axial contour lying in a plane that intersects the waveguide walls at a substantially right angle. The formation of a ring resonator in this plane provides a compact laser design, since these segments of the waveguides have a small, compared with the width and length, height.

However, since the creation of any type of traveling-wave resonator is impossible using only two mirrors, the optical path of the ring resonator must be ensured by the correct choice of the waveguide curvature, which is the same with high accuracy for both segments of the waveguide. Obviously, the distributed radiation reflections in these two branching sections of the waveguide add significant intracavity losses, and the proper organization of these reflections leads to a significant complication of the laser manufacturing process. This becomes especially clear if we recall that one of the electrodes of a high-frequency-pumped slab laser must be at a high high-frequency potential. Summing up the balance, one should weigh on the scales, on the one hand, the obvious simplicity of using only two mirrors for organizing a ring resonator and, on the other hand, the difficulties arising from the requirement to achieve very low distributed power losses when organizing reflections in both curved sections of the waveguide. It should be noted that a small value of these distributed losses should be achieved under conditions of holding the high-voltage high-frequency electrode from shorting it to a grounded electrode. In addition, in order to provide a one-way beam exit from the indicated annular unstable resonator, the axial contour of this resonator must be shifted so that it passes near one of the open edges of the interelectrode gap. As can be seen from the optical scheme given in '479 [23], this approach to creating a hybrid resonator cannot be applied to plane waveguides or plane radiation-directing structures, since it uses only two optical elements. Another disadvantage is that this ring resonator cannot be made asymmetric due to the presence of a branching waveguide structure.

Due to the fact that the unstable traveling-wave resonator, made in accordance with '479 [23], does not have focal constrictions inside the resonator, the one-sided diffraction output of radiation from the laser is ensured only by shifting the axial contour to one of the open edges of the discharge gap.

Therefore, such a laser is characterized by the disadvantages discussed above, which are characteristic of lasers with a “half” unstable cavity of a positive branch. These include high sensitivity to misalignment of the cavity mirrors and optical inhomogeneities of the wedge type in the active medium, as well as the useless loss of radiation from the cavity on the side to which the axis of the cavity is shifted when radiation is output from the cavity in the form of a single beam.

Summing up, it should be said that the unstable traveling-wave resonator with a branched waveguide proposed in '479 [23] rather adds to rather than eliminates the difficulties of creating compared to other single-slot type slab lasers using a hybrid resonator.

SUMMARY OF THE INVENTION

The main objective of the present invention in relation to powerful gas lasers with high-frequency excitation and diffusion cooling is the creation of a hybrid ring resonator system, characterized by a reduced sensitivity to misalignment of the laser cavity mirrors and optical inhomogeneities such as a wedge in the active medium, as well as reduced useless radiation losses from the resonator during output radiation from the resonator in the form of a single beam of a continuous section.

This goal is achieved by the fact that in a gas laser with high-frequency excitation and collision (diffusion) cooling mechanism containing a pair of gap-separated cooling elements, each of which has an extended surface, arranged so that their opposite surfaces form a fiber for optical radiation in the gap between these surfaces, a gaseous medium placed in the specified gap to generate laser radiation when this medium is excited by an electric discharge by supplying and to it a high-frequency electric power, and mirrors forming an annular traveling-wave optical resonator having a closed axial contour for forming a laser beam in said optical fiber according to the invention, said mirrors are arranged so that said axial contour of the resonator they form lies essentially in a plane passing between these surfaces forming a fiber for optical radiation, and facing its sides to the indicated surfaces of the cooling elements, while The traveling-wave ring resonator is unstable in the indicated plane, so that part of the specified beam expanding in the specified cavity is output in the form of a continuous-section output beam, the curvature of the mirrors, and the number of these mirrors is such that any ray belonging to the laser beam propagating through the fiber , and located on the inner side of the axial contour of the resonator, after a complete round-trip of the resonator, it appears on the outer side of the axial contour of the resonator, and any beam belonging to the laser beam polar radiation propagating through the optical fiber, and located on the outer side of the axial cavity contour after a complete traversal of the resonator is on the inside of the axial cavity contour.

The passage of the closed axial contour of the ring resonator in a plane lying between the surfaces of the cooling elements means that each of the mirrors of this ring resonator provides, when a radiation beam is reflected from it, rotation of the radiation beam in the specified plane. As a result of each such rotation of the beam, that part of the beam that propagated along the optical fiber from the inside from the closed axial contour of the resonator turns out to be from the outside from this circuit and vice versa. Due to such a “flip” of the beam by each of the mirrors, with the appropriate choice of their number and curvature, after a complete round-trip of the resonator, any laser beam propagating through the optical fiber from the inside from the axial contour of the resonator will be outside from the axial contour of the resonator. And vice versa, any beam of a laser beam propagating through the fiber from the outside from the axial contour of the resonator will be on the inside from the axial contour of the resonator, i.e. any ray passing at a distance from the axial contour of the resonator, after going around the resonator, will change its position relative to this axial contour in the plane in which the radiation expands as in free space.

Thus, in the proposed ring resonator of the traveling wave, alternating passage of the laser beam rays lying in the specified plane, then on one, then on the other side of the axial contour of the ring resonator, is ensured. The location of the axial contour of the ring resonator in a plane lying between the surfaces of the reflecting elements, or essentially in this plane, for unstable ring resonators of a positive branch is a necessary condition for reducing the sensitivity of the resonator to wedge disturbances existing in the resonator and oriented in this plane. If the axial contour of the resonator lies in the transverse plane, i.e. in the plane transverse to the surfaces of the cooling elements, such as, for example, in a laser with an unstable ring resonator of a positive branch made according to US Pat. , which is necessary to reduce the sensitivity of the resonator to wedge disturbances in the specified plane.

Due to the alternate passage of the beams of the laser beam from one or the other side of the axial contour of the ring resonator, the laser made according to the invention provides compensation for misalignment due to deviation of the angular positions of the resonator mirrors in the plane passing between the electrodes, as well as compensation for optical inhomogeneities type of wedge in an active environment. Therefore, the proposed laser is relatively insensitive to such misalignment of the mirror mirrors and optical inhomogeneities, as compared with the known lasers with a hybrid resonator of a positive branch, in which the axial contour of the unstable ring resonator lies in a plane perpendicular to the surfaces of the electrodes, as a result of which the sensitivity of the resonator to wedge disturbances is not ensured oriented in the plane of free expansion of the beam.

In addition, due to the alternating passage of the beams of the laser beam from one or the other side of the axial contour of the ring resonator, in the proposed laser, the output beam of a continuous cross section is removed from the resonator from only one side of the axial contour, despite the fact that the beam is freely expanding in the cavity occurs in both opposite directions, in which this expansion is not limited to the surfaces of the electrodes. For example, a part of the laser beam propagating along the inner edge of the cavity, i.e. from the side internal from the axial contour, it passes after bypassing the resonator to its external side, where it can be removed from the resonator in the form of a useful output beam. Useless radiation losses from the cavity on the inside from the axial contour are practically eliminated. Thus, according to the invention, the useless losses of radiation from the resonator are reduced compared to the known annular unstable resonators of the positive branch, in which the axial contour lies in a plane transverse to the surface of the electrodes, and as a result, beam expansion in two opposite directions leads to the useless loss of radiation from the resonator from the side that is opposite to the output side of the output beam of a continuous section from the resonator.

In contrast to the previously known waveguide laser with a linear unstable resonator of the negative branch, the proposed laser, due to the use of a ring resonator of a traveling wave of a positive branch with an axial contour lying in a plane passing between the surfaces of the cooling elements, ensures alternating passage of the beam from different sides from the axial circuit does not require the use of focal beam constriction in the resonator. Since the laser made according to the invention does not require the use of a focal beam constriction, this laser prevents unwanted non-linear effects caused by such a constriction and breakdowns in the active medium. In addition, in the proposed laser, high efficiency of using the volume of the active medium due to its uniform filling with laser radiation can be ensured. The reduction in laser dimensions is also facilitated by breaking the optical axis of the laser resonator. In addition, it is not necessary to use spherical mirrors of large curvature and apply appropriate measures to reduce the influence of these mirrors on the formation of the field along the height of the waveguide.

In a preferred embodiment of the proposed laser, the number of these mirrors forming a ring resonator is odd, and their curvature is such that the laser beam propagating along the waveguide does not have focal constrictions. If there are no focal constrictions in the laser beam, then to ensure proper beam overturn when the cavity is completely circumvented, the number of mirrors forming a ring resonator should be odd.

In accordance with this invention, only one of the mirrors of the ring resonator must be convex to provide the desired increase in the unstable resonator. In this implementation, for reasons of design simplicity and cost reduction, the remaining mirrors forming the resonator may be flat.

In another embodiment, one of the mirrors of the ring resonator may be convex, the other concave, and the remaining mirrors may be flat. The use of at least one concave mirror in a ring resonator simplifies the formation of a wavefront with the required curvature at the laser output.

Compared with the slab laser made in accordance with the previous patent '479 [23], in a preferred embodiment of the proposed laser, said surfaces of the cooling elements are essentially plane parallel. This simplifies the design of the laser and also improves its efficiency compared to a laser containing curved sections of waveguides. The latter consideration is obvious, since the introduction of curved sections of the waveguide into the laser usually leads to the “pressing” of the waveguide mode field to the electrode facing the discharge gap with its concave surface, as a result of which the part of the excited active medium located near the opposite electrode is used less efficiently.

In a preferred embodiment of the proposed laser, the distances from the intersection of the axial contour of the resonator with the surface of each of the mirrors forming the resonator to the edges of these mirrors are such as to ensure that radiation is emitted from the resonator in the form of a single continuous beam near one of the edges of one of these mirrors and thereby limiting the expansion of the beam in the cavity.

However, in other embodiments of the invention, the resonator may be equipped with a means of deflecting a portion of the radiation adjacent to the edge of the laser beam generated by the mirrors of the optical resonator to remove this portion of the radiation from the resonator and thereby limit the expansion of the beam in the resonator.

The proposed laser preferably includes means that ensure the predominant propagation of radiation through the ring resonator in one of two possible opposite directions of bypassing this resonator. Such means make it possible to provide substantially unidirectional generation of radiation in a traveling-wave laser ring resonator, which makes it possible to obtain maximum radiation power in one compact output beam.

These means, providing the predominant propagation of radiation in one of two directions, may contain a feedback mirror (return mirror), installed so that it essentially does not affect the radiation propagating through the resonator in the first of two directions, but reflects in the opposite direction, at least a portion of the radiation propagating through the resonator in a second direction opposite to the first, such that at least a portion of the radiation is directed along the resonator in the first direction.

In another possible embodiment of the invention, a hole may be made in one of the resonator mirrors at the intersection of its surface with the axial contour of the resonator, and these means, which provide the predominant propagation of radiation in one of two directions, may include a feedback mirror mounted behind this hole so that it reflects in the opposite direction passed through the specified hole part of the radiation propagating through the resonator in the second direction, so that this Part of the radiation passes through said opening and is guided through the resonator in the first direction.

Thanks to the feedback mirror, a bond is introduced between two waves propagating towards each other, leading to an additional amplification of one of these waves. As a result of mode competition in the amplifying medium at the stage of generation in the cavity, preferential conditions are created for a beam propagating in the first direction, and the laser begins to operate essentially in a unidirectional mode.

In yet another embodiment of the present invention, the radiation of a low-power laser can be injected into a high-power laser so that the coherent radiation of a low-power laser determines the wavelength of the radiation of a high-power laser. In one embodiment, the output beam of a low-power laser can be introduced in the opposite direction in the plane of the output mirror of a high-power laser. In another embodiment, low-power radiation can be introduced into the cavity of a high-power laser using an opening in one of the mirrors of an unstable resonator. In any of these embodiments of the present invention, the low-power laser will be optically decoupled in the direction from the radiation propagating in the high-power laser.

The parameters of the fiber in the options discussed above in General, and, therefore, the mode of propagation of radiation in the fiber can be different. In some embodiments, said traveling wave ring resonator may be stable in a direction perpendicular to said plane of the axial contour of the resonator, so that the radiation beam is practically not guided by the surfaces of the cooling elements.

In other embodiments, said cooling elements may be arranged so that they determine a waveguide mode of propagation of radiation in said fiber.

Brief Description of the Drawings

The invention is illustrated by drawings, in which:

figure 1 in perspective shows a gas laser with diffusion cooling, made according to one of the embodiments of the invention;

figure 2 presents a top view, in section along the interelectrode gap, of the laser with diffusion cooling, shown in figure 1;

figure 3 shows another embodiment of a gas laser with diffusion cooling according to the invention;

figure 4 shows another embodiment of a gas laser with diffusion cooling according to the invention;

on figa and 5b is explained one of the possible schemes for providing unidirectional generation in a gas laser with diffusion cooling, made according to the invention;

figure 6 shows another embodiment of a gas laser with diffusion cooling according to the invention, having 5 mirrors.

In conventional waveguide slab lasers, cooling elements simultaneously play the role of electrodes. In slice lasers, the discharge is excited by additional electrodes (not shown in the drawings).

The drawings are given without observing the scale relationships between the sizes of the laser elements for a clearer presentation of the invention.

Description of Embodiments

The gas laser with high-frequency excitation and diffusion (collision) cooling, shown in Fig. 1, contains a pair of cooling elements 1 and 2, separated by a gap 3, in which a gas active medium (not shown) is placed, for example, a typical gas medium of a waveguide CO ₂ laser including CO ₂ , N ₂ , He and other gases.

Opposite surfaces of the cooling elements 1 and 2 are located close enough to each other, so that they form a light guide for the propagation of optical radiation. The electrodes are connected to a high-frequency generator (not shown) to supply high-frequency pump power to the active medium. The cooling elements 1 and 2 may also be provided with cooling means (not shown) to improve heat removal from the cooling elements.

The external contour of each of the cooling elements 1, 2 has the shape of a triangle with cut vertices, near which, in the immediate vicinity of the outer edge of the interelectrode gap 3, mirrors 4, 5 and 6 are installed, forming an unstable annular optical resonator of a traveling wave of a positive branch, a closed axial contour which lies in a plane passing between the surfaces of the cooling elements 1 and 2 and facing them with their opposite sides.

As shown in figure 2, for the formation of a ring optical resonator, the mirrors 4, 5 and 6 are mounted relative to each other so that they close the triangular axial contour (shown by the dot-dash line). The bisectors of the angles at the vertices of this triangular contour (shown by dashed lines) are simultaneously normals to the surfaces of the mirrors. Thus, the angle of incidence of the axial ray incident on the mirror is equal to the angle of reflection for each of the mirrors. The axial contour of the resonator, shown in figures 1 and 2, lies in the median plane (plane of symmetry), equidistant from the opposite surfaces of the cooling elements 1 and 2, forming the fiber.

As can be seen in FIGS. 1 and 2, the formation of a closed axial contour of the ring resonator in a plane passing between the surfaces of the cooling elements makes it possible to provide a compact structure compared to the known linear resonators with an equal area of these elements. Moreover, since the propagation of laser radiation is not limited in the plane passing between the surfaces of the cooling elements 1 and 2, the possibility of additional rotation of the radiation in this plane by bending the walls of the waveguide is essentially absent, and, therefore, there are no additional distributed losses on the curved walls of the waveguide taking place in known prototypes.

Therefore, in comparison with the known device made in accordance with '479, where two mirrors and two complex and precisely curved waveguide surfaces are used, and the formation of a closed loop of a ring resonator occurs due to distributed reflections from four curved walls of the waveguide, in the present invention to realize a circular The passage of radiation through the resonator uses three mirrors and the simplest resonator axial contour. By eliminating distributed reflections during propagation along the curved surfaces of the waveguide and replacing them with reflection from a single intracavity optical element, the resonator made in accordance with the present invention will have significantly lower intracavity losses compared to the losses of the known ring resonator using two mirrors. In addition, even in the three-mirror design of the ring resonator, in the present invention, the beam-expanding part of the resonator can include, for example, mirrors 5 and 6 in FIG. 2. This allows you to make the ring resonator, made in accordance with the invention, confocal and asymmetric. This cannot be done in the well-known two-mirror symmetrical device, made in accordance with '479 [23]. And finally, the change of left to right, i.e. the inversion of the radiation beam inside the resonator, in the present invention can be carried out without using the focal constriction inside the resonator, which is necessary for this in the known linear unstable resonators.

In order for the traveling traveling ring optical resonator shown in FIG. 2 to be an unstable positive branch resonator, in this embodiment, the mirror 4 is convex, the mirrors 5 and 6 are flat. The convex mirror 4 may be, for example, spherical with a radius of curvature R selected so as to provide an optimal increase in M of the unstable resonator. The increase in the ring resonator shown in Fig. 2 (which approximately coincides with the increase in the transverse size of the beam in the plane of symmetry of the waveguide with a complete round-trip of this ring resonator) is determined, with a sufficiently small angle of incidence of the beams on the convex mirror, by the expression

where L is half the length of the axial contour of the resonator. The magnification M of the unstable resonator is usually chosen so as to ensure optimal energy removal efficiency in the active medium of the laser. To determine the optimal value of M, known methods for calculating the parameters of unstable resonators in waveguide gas lasers can be used. In a typical diffusion-cooled waveguide CO ₂ laser having a gap between electrodes of 2 mm with an axial contour length of 3.5 m and a pump frequency of 81 MHz, the optimal value of M can be, for example, of the order of 1.3-1.4.

The distances from the intersection of the axial contour of the resonator with the surface of each of the mirrors 4, 5 and 6 forming the resonator to the edges of these mirrors are such as to ensure that radiation is emitted from the resonator in the form of a single continuous beam near the edge of one of the mirrors, for example, edge 6a of the mirror 6, and thereby limiting the expansion of the beam in the cavity.

So, the sizes of mirrors 4, 5 and 6 in the direction of the normals to the surfaces of the cooling elements approximately correspond to the size of the gap between them or slightly exceed it, in order to avoid leakage of laser radiation from the edges of the mirrors. In the direction transverse to the indicated normals, the size of mirror 6 is chosen in such a way that the distance from the point of intersection of the axial contour of the resonator with the surface of mirror 6 to the first edge 6a of this mirror, measured in the symmetry plane of the waveguide, is less than the distance to the second edge 6b of this mirror not less than in M time. The dimensions of the remaining mirrors 4 and 5 in the indicated transverse direction are large enough so that the laser beam propagating in the resonator and incident on these mirrors does not go beyond their edges, i.e. so that they do not limit the beam expansion in the cavity.

The laser shown in FIG. 1 also includes means for predominantly propagating radiation in one of two possible opposite directions around the cavity, in this example, clockwise. For this, a small hole 8 is made in the mirror 4 on the resonator axis (under typical conditions of a CO ₂ laser, the hole size can be, for example, 1 mm). The hole 8 is oriented so that the continuation of the section of the axis of the resonator going from mirror 5 to mirror 4, i.e. in the direction of bypassing the resonator counterclockwise, passes through this hole. Behind this hole 8, on the reverse side of the reflecting surface of the mirror 4, there is a small flat feedback mirror 9 that intersects the specified extension of the section of the axis of the resonator and oriented transversely to it. The mirror 9 is aligned so that the wave propagating counterclockwise in the resonator passing through the hole 8 is reflected from the mirror 9, again passes through the hole 8 back to the resonator and is summed there with the wave propagating in the resonator clockwise.

The laser shown in FIGS. 1 and 2 also includes means for deflecting the output laser beam in the desired direction, formed by a planar mirror 10, as well as a concave mirror 11, which serves to give the wave front of the beam the required curvature.

The laser design shown in FIGS. 1 and 2 is provided by way of example only. So, for example, in other embodiments of the invention, more than one of the mirrors forming the ring resonator can be made convex. One or more of the resonator mirrors may be concave to collimate the output beam or impart the required curvature to its wavefront.

The number of mirrors forming a ring resonator in a laser made according to the invention may be more than three. For example, in the waveguide gas laser shown schematically in FIG. 3, the number of mirrors forming a ring resonator is four, while mirrors 12, 13 are concave and mirrors 14, 15 are convex.

In a gas laser with diffusion cooling, shown schematically in FIG. 6, the number of mirrors in the traveling wave ring cavity is five (mirrors 21-25). The curvature of the mirrors and their sizes are chosen so that the ring resonator, being unstable in the plane lying between the surfaces of the cooling elements, has the desired increase in M, and the distribution of the radiation field inside the resonator ensures good filling of the active medium 26. In the embodiment of the invention shown in FIG. 6, mirrors 21 and 24 are convex, mirrors 22, 23 are concave, and mirror 25 is flat.

It should also be noted that at least some of the mirrors forming the ring resonator may not be separate elements, as shown in the attached drawings, but sections of a single mirror surface. In addition, in addition to mirrors, the ring resonator may include other known elements used to form such resonators.

The cooling elements 1 and 2 do not have to be plane parallel. For example, the surfaces of the cooling elements 1 and 2 may have some bend of the opposite sign in the plane transverse to the walls of the fiber and passing through the segments of the axial contour. The closed axial contour of the resonator in this case still lies essentially in the same plane, as in the above embodiment. In other embodiments of the invention, the distance between the cooling elements may vary depending on the transverse coordinates in order to control the curvature of the wavefront of the beam in the plane of symmetry of the waveguide.

It is also obvious that the axial contour of the traveling-wave ring resonator can deviate to a small extent from the plane passing between the surfaces of the cooling elements, until such a deviation leads to a significant deterioration in the laser output parameters.

Cooling elements can also be made of separate sections. When cooling elements are used as electrodes, the pump power can be supplied to each of the sections separately, as is done in known waveguide slab lasers with high-frequency excitation or slice lasers.

The output of laser radiation from the resonator does not have to be provided near the edge of one of the mirrors, as shown in FIGS. 1-3. For example, in the gas laser according to the invention with diffusion cooling, shown schematically in FIG. 4, the resonator is provided with a separate means for outputting radiation from the resonator in the form of a mirror 16 mounted on the outside of the axial contour of the resonator.

Ensuring unidirectional generation in a ring resonator does not require the mandatory use of holes in the cavity mirrors. So, in the waveguide gas laser, schematically shown in figa and fig.5b, the feedback mirror 17 is located behind the output mirror of the resonator near its edge, in the "shadow" region for the wave propagating clockwise in the resonator. At the same time, the feedback mirror 17 is aligned so as to reflect in the opposite direction the wave incident on it, traveling counterclockwise along the resonator. As the output mirror, near the edge of which the radiation is removed from the resonator, in this embodiment, a convex mirror 4 is used.

In the embodiment of the invention shown schematically in FIG. 6, another possible feedback injection scheme is shown in which an intermediate mirror 27 and a dihedral corner reflector 28 are used in the feedback path. As shown in FIG. 6, the polished side surface of the mirror 21 is used as a mirror 27, directing radiation 20 incident on it back into the resonator, propagating counterclockwise, after it is reflected from the dihedral angular reflector 28 placed accordingly.

When operating a ring laser of a traveling wave with diffusion cooling, shown in Figs. 1 and 2, a high-frequency pump power is supplied to the medium to excite a gas active medium by electric discharge using an external generator. In the case of a conventional waveguide laser, this is done using cooling elements 1 and 2, which are made in this case from a conductive material and play the role of electrodes. In order not to pump areas that are not filled with radiation, and thus increase the laser efficiency, a recess 7 can be made in one of the electrodes, which prevents the discharge from being excited in the recess area.

When operating a slice laser with a traveling wave resonator shown in FIGS. 1 and 2, high-frequency power (or a combination thereof with direct current power) is supplied to additional electrodes (not shown in the figures). In both cases, when the active medium is excited, optical radiation is generated that propagates in the waveguide (fiber) formed by the gap between the opposite surfaces of the cooling elements 1 and 2. Radiation whose propagation direction coincides with the direction of the axial contour of the ring resonator propagates along this path along a closed path, amplifying in the active medium, which leads to self-excitation of the laser beam near the axial contour of the resonator. When propagating through an unstable ring resonator, the width of this laser beam in the median plane between the cooling elements (in the plane of the drawing of FIG. 2) increases M times with each complete round-trip of the resonator due to the curvature of the convex mirror 4, i.e. the radiation beam expands in free space. In directions transverse to the surfaces of the cooling elements, the beam expansion is limited by these surfaces, as a result of which a main waveguide mode or a Gaussian mode is formed, depending on the height of the fiber.

Each of the three mirrors 4, 5 and 6 of the resonator provides a rotation of the laser beam in the plane of symmetry of the fiber passing between the indicated electrodes. As a result of each such rotation, any beam beam changes its position with respect to the axial contour of the resonator to the opposite. In the intervals between mirrors 4, 5, and 6, no beam flips occur, since there are no concave mirrors in this resonator and, therefore, there are no focal beam constrictions. Since the number of mirrors in such a resonator is odd, any beam propagating along the waveguide on one side of the axial contour of the resonator, after a complete round-trip of the resonator, is on the other side of the axial contour of the resonator. As, for example, shown in figure 2, the beam passing clockwise through the waveguide through point A, located on the inner side of the axial contour, after a complete round-trip of the resonator, as a result of successive reflection from mirrors 5, 6 and 4, appears at the point B, located on the outside of the axial contour.

The width of the laser beam propagating through the unstable ring resonator increases in the symmetry plane of the waveguide at each complete round-trip of the resonator by M times until after one round-trip of the resonator one of the beam edges exits, as shown in Fig. 2, beyond edge 6a of mirror 6 However, the radiation does not extend beyond the other edge 6b of this mirror 6, since the distance from the axial contour to the edge 6b is at least M times greater than the distance from the axial contour to the edge 6a. After the next full passage of the beam through the resonator and the beam width is increased by a factor of M again, that part of the laser beam that was near the second edge 6b of mirror 6, due to the flipping of the beam in the ring resonator made according to the invention, will be on the other side of the axial contour beyond the first edge 6a of the mirror 6 and will be removed from the resonator. Thus, the output of radiation from the resonator near the first edge 6a of the mirror 6 limits the further expansion of the beam in both opposite directions in which it expands in free space. In this case, the edges of the remaining mirrors 4 and 5 are sufficiently far from the axial contour of the resonator so that the beam propagating in the resonator does not go beyond the edges of these mirrors, which ensures that radiation is emitted from the resonator in the form of one beam, and not two or more. The part of the expanded beam that extends beyond the edge 6a of the mirror 6, after successive reflection from the mirrors 10 and 11, is removed from the laser in the form of an output beam 18 of a continuous section, close to rectangular. The curvature of the concave mirror 11 ensures the collimation of the output beam in the transverse plane or, if necessary, the formation of a converging beam from a diverging beam emerging from the annular unstable resonator.

Thus, in the proposed laser, made as shown in FIGS. 1 and 2, the one-way radiation output from the resonator is achieved due to the alternate passage of the rays forming the laser beam from different sides of the axial contour of the resonator, similar to the way in linear unstable resonators of the negative branch one-sided output of radiation is provided due to the alternate passage of rays from different sides from the axis of the linear resonator. In linear unstable resonators of the negative branch, this avoids the useless loss of radiation from the resonator that occurs in the “half” unstable resonator of the positive branch with one-sided radiation output. At the same time, unlike the known linear unstable resonators of the negative branch, the flip of the beam cross section in the ring resonator made according to the invention does not require the use of a focal beam waist, but is ensured by the orientation of the axial contour of the ring resonator in a plane passing between the surfaces of the cooling elements 1 and 2, with the appropriate choice of the number and curvature of the mirrors 4, 5 and 6, forming a ring resonator. The absence of focal constrictions of the beam in the resonator shown in FIGS. 1 and 2 ensures high uniformity of radiation intensity and, therefore, high efficiency of using the volume of the active medium and prevents undesirable nonlinear effects and breakdowns in the active medium.

Due to the fact that the rays forming the radiation beam in the ring resonator made according to the invention fall on any of the mirrors 4, 5 and 6, alternately from one or the other from the axial contour, possible deviations of these mirrors in the median plane of the fiber from them the required positions are compensated in the same way as in linear unstable negative-branch resonators with a focal constriction. Optical wedge inhomogeneities in the active medium are compensated in a similar way, since the positive path difference acquired in one pass by the outer part of the beam due to its propagation, for example, along the “thick” side of such a wedge oriented in the plane of symmetry of the fiber, will be compensated in the next pass as a result of acquisition the same part of the beam of the negative path difference, since the outer part of the beam will now become internal and will spread along the “thin” side of the same wedge. Thus, the alternate passage of the rays forming the laser beam from different sides of the axial contour of the ring resonator provides a significant decrease in the sensitivity of the ring resonator made according to the invention to the misalignments of the mirrors 4-6 forming the resonator and to optical inhomogeneities such as a wedge in an active medium, without using the focal constrictions of the beam in the cavity for this purpose.

Thus, the proposed diffusion-cooled waveguide laser with a traveling-wave ring resonator combines the advantages of known waveguide lasers with a positive branch resonator associated with the absence of a focal waist of the laser beam inside the resonator with the advantages of the known linear unstable negative branch resonators, such as low sensitivity to misalignment and wedge inhomogeneities and one-sided output of radiation from a solid-beam beam resonator.

As follows from the foregoing, to flip the beam cross section in a laser made according to the invention, it is preferable to use an odd number of resonator mirrors (3, 5, 7, etc.). In this case, the flip of the beam section in the direction of the larger cross-section is ensured without the need for a focal constriction inside the resonator. However, in those cases where a negative branch resonator having a focal constriction inside the resonator is intentionally used in a ring laser made according to this invention in order to maintain a revolution in the beam cross section after a full round-trip of the resonator, the number of mirrors is made even. Conversely, in accordance with this invention it is possible to design a ring resonator, which should have an even number of intracavity mirrors. In such a situation, shown in figure 3, due to the fact that the flip of the beam cross-section with the left to the right being replaced seems to be preferable for a resonator with an even number of mirrors, in order to carry out such a flip, it is necessary to create a focal constriction inside the resonator.

For example, in figure 3, such a constriction 19, formed by focusing the beam with a concave mirror 12, is located between the mirrors 12 and 13. However, unlike lasers with linear unstable resonators of the negative branch, the region of the waist in the laser with a ring resonator can be moved outside of the pumped region of the active medium, therefore, the presence of such a constriction will not lead to a significant deterioration of the laser parameters due to the appearance of undesirable nonlinear effects.

In contrast to the laser shown in FIG. 2, where the beam expansion in the cavity is limited by the mirror 6 of the resonator, in the laser shown schematically in FIG. 4, the beam is limited by the additional mirror 16, which is set so that it deflects and leads out of the resonator the part of the radiation adjacent to the edge of the laser beam formed by the mirrors of the optical resonator, and located on the outside of the axial contour of the resonator. The use of such a separate means of deflecting the beam for its output from the cavity simplifies the alignment of the optical system of the laser and makes it easy to control the width of the output beam by corresponding transverse movement of the mirror 16.

The feedback mirror 9 shown in FIGS. 1 and 2 provides a predominant propagation of radiation in the cavity in a clockwise direction, which allows achieving substantially unidirectional generation. The hole 8 in the mirror 4, due to its small size, does not significantly affect the wave propagating along the resonator in a clockwise direction. A relatively small part of the power of this wave passing through the hole 8 is deflected by the mirror 9 and does not fall back into the resonator. At the same time, part of the wave propagating counterclockwise in the resonator passes through the hole 8, is reflected from the mirror 9 and is directed through the hole 8 back to the resonator, propagating in it clockwise. Thus, between two waves propagating towards each other, a certain connection is introduced, leading to an additional amplification of one of these waves; in this example, amplification of a wave propagating clockwise occurs. As a result of mode competition in the amplifying medium, which occurs at the stage of generation of oscillations in the cavity, preferential conditions are created for a beam propagating in a clockwise direction, and the laser begins to operate in essentially unidirectional mode. Such a feedback mirror is especially effective in the case of media with a uniformly broadened gain line, such as YAG or CO ₂ . As the calculations and experiments performed by the authors show, the presence of even a relatively weak coupling between the waves propagating in the cavity in opposite directions is quite sufficient to ensure essentially unidirectional operation of the laser.

In the laser, the circuit of which is shown in FIGS. 5a and 5b, unidirectional generation is achieved without using holes in the cavity mirrors, the presence of which in waveguide lasers with a small interelectrode gap is not always desirable. On figa shows a beam 18 of useful radiation, propagating in the resonator clockwise, on figb - beam 20 going counterclockwise, which must be suppressed. The mirror 17, due to its location behind the output mirror 4, in the region of the "shadow" does not introduce distortion into the radiation beam 18, propagating clockwise. At the same time, the radiation beam 20, propagating counterclockwise, leaves the resonator at a different angle than the beam 18, and as a result is partially intercepted by the mirror 17. The radiation incident on the mirror 17 is reflected in the opposite direction and added to the wave traveling in the resonator clockwise. As a result, as in the laser shown in FIGS. 1 and 2, advantageous conditions are created for a beam propagating in a clockwise direction, and the laser begins to operate essentially in a unidirectional mode.

In the laser shown schematically in FIG. 6, another embodiment of feedback is shown. In it, a beam propagating counterclockwise undergoes additional reflection from the side surface 27 of the mirror 21 before it is reflected from the feedback reflector 28. The angle between the surfaces of the mirrors 27 and 21 near their common edge 29 can be chosen so as to increase the angle between beams 20 and 18. An increase in this angle simplifies the interception of the beam 20, propagating counterclockwise, by the feedback reflector 28 and its reflection back into the ring resonator.

The use of a dihedral corner reflector 28 instead of the feedback mirror 17 significantly reduces the requirements for the accuracy of the angular adjustment of the reflector, provided that its edge 30 is properly positioned relative to the edge 29.

In a first practical embodiment of the present invention, an output power of 350 watts was continuously obtained in a CO ₂ slab laser with a three-mirror ring unstable resonator. The components of the ring hybrid unstable traveling wave resonator were two flat fully reflecting mirrors and one convex spherical fully reflecting mirror with a radius of curvature of 60 meters. These mirrors formed a resonator with a perimeter of 2L = 1.3 m and a geometric magnification of 1.3. At a discharge gap of 2 mm, the laser operated on a mixture of He-N ₂ -CO ₂ 6: 1: 1 gases at a pressure of 70 torr. With a resonator having a configuration similar to that shown in Fig. 5a, the measured value of the suppressed backward wave was approximately 100 times, i.e. 20 decibels weaker in intensity than the 350 W output wave propagating in the forward direction. As the experiments showed, the divergence of the output beam of a continuous cross section, emerging on one side of the mirror and having a cross section of 2 mm by 12 mm, turned out to be very close to the diffraction limit for each of the two measurements of the output beam.

The above constructions of a gas laser with diffusion cooling and high-frequency excitation are given only as examples. For the implementation of the invention can be used any suitable types of elements that limit the gap, mirrors, active media, means of pumping and other components used in such devices. For specialists in the field of laser technology, it is obvious that instead of mirrors or along with them, any equivalent optical means can be used, providing the required transformation and changing the direction of the optical radiation beams. Therefore, although the options described above are preferred embodiments of the invention, various modifications and replacements can be made in these embodiments without departing from the spirit and spirit of the invention. Accordingly, it should be understood that the description of the present invention is illustrative and not restrictive.

Literature

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Claims (101)

1. A laser, including the first and second extended surfaces, between which there is a gap characterized by an average value in a certain direction, and these surfaces form a space between them to accommodate the laser active medium, the specified space has a plane containing a closed axial contour of the traveling wave optical resonator, the specified plane is located in the middle between the indicated surfaces, and the indicated direction is oriented mainly perpendicular to the indicated surface Ostam; laser active medium located in the specified space; means for pumping at least a portion of the laser medium located between said first and second surfaces to create an inverse population in said active medium; wherein said resonator is optically unstable in the indicated plane and optically stable in the indicated direction, the modes of the optically unstable and optically stable resonators together determine the characteristics of light propagation inside the laser, as well as the output of radiation from it. 2. The laser according to claim 1, in which the output of radiation from the specified unstable resonator is carried out only on one side of the closed axial contour. 3. The laser according to claim 1, including a non-resonant element, making it preferable to close the axial contour of the resonator in the counterclockwise direction. 4. The laser according to claim 1, including a non-resonant element, making it preferable to close the axial contour of the resonator in a clockwise direction. 5. The laser according to claim 1, including a non-resonant element, forcing the axial modes of the traveling wave resonator to oscillate in the counterclockwise direction. 6. The laser according to claim 1, including a non-resonant element, forcing the axial modes of the traveling wave resonator to oscillate in a clockwise direction. 7. The laser according to claim 1, in which the active medium is placed in such a way as to make preferred one direction of propagation in the specified traveling wave resonator. 8. The laser according to claim 1, in which the optically stable mode is a Gaussian stable mode in the indicated direction, transverse to the gap. 9. The laser according to claim 1, wherein said first and second surfaces are reflective. 10. The laser according to claim 9, in which the optically stable mode in the direction transverse to the gap is a stable waveguide mode. 11. The laser according to claim 1, in which the closed axial contour has an odd number of vertices. 12. The laser according to claim 1, in which the closed axial contour has an even number of vertices. 13. The laser according to claim 1, in which the unstable resonator of the traveling wave is an unstable resonator of the negative branch. 14. The laser according to claim 1, in which the unstable resonator of the traveling wave is an unstable resonator of the positive branch. 15. The laser according to claim 1, in which the active medium is gas. 16. The laser according to claim 1, in which the active medium is a solid. 17. The laser according to clause 15, in which the emitting medium is CO ₂ . 18. The laser of claim 15, wherein the emitting medium is CO. 19. The laser of claim 15, wherein the emitting medium is an excimer medium. 20. The laser according to claim 1, in which the active medium emits in the visible range of the spectrum. 21. The laser according to clause 15, in which the active medium emits in the far infrared range of the spectrum. 22. The laser of claim 15, wherein the pumping means is a radio frequency current. 23. The laser of claim 15, wherein the extended reflective surfaces are conductive. 24. The laser of claim 23, wherein the pumping means is a radio frequency current applied between the first and second extended surfaces. 25. The laser according to claim 1, in which the pumping means is a light source. 26. The laser according to claim 1, in which the pumping means is a laser light source. 27. The laser of claim 15, wherein the pumping means is a light source. 28. The laser of claim 15, wherein the pumping means is a laser light source. 29. A slab laser, including the first and second extended reflective surfaces having a gap between them and arranged so that they form a light guide between said surfaces, said surfaces defining a space between them to accommodate an active medium, said active medium space having a plane containing a closed axial contour of the traveling wave optical cavity, and said plane is located in the middle between said surfaces; an active medium located at least in part of the specified space; means for pumping said active medium located between said first and second surfaces to create an inverse population in said active medium, the cavity being unstable in said plane and, together with the gap between the first and second extended surfaces, determines the propagation of resonator modes of light inside the laser, which ensures diffraction radiation output. 30. The slab laser according to clause 29, in which the diffraction output of radiation is carried out only on one side of the specified axial contour. 31. The slab laser according to clause 29, including the non-resonant element to provide unidirectional laser operation. 32. The slab laser according to clause 29, including an extra-resonant element that closes the axial circuit in the counterclockwise direction. 33. The slab laser according to clause 29, including the non-resonant element that closes the axial circuit in a clockwise direction. 34. The slab laser according to clause 29, in which the closed axial contour has an odd number of vertices. 35. The slab laser according to clause 29, in which the closed axial contour has an even number of vertices. 36. The slab laser according to clause 29, in which the unstable resonator of the traveling wave is an unstable resonator of the negative branch. 37. The slab laser according to clause 29, in which the unstable traveling wave resonator is an unstable positive branch resonator. 38. The slab laser according to clause 29, in which the active medium is a gas. 39. The slab laser according to clause 29, in which the active medium is a solid. 40. The slab laser according to clause 29, in which the active medium is a liquid. 41. The slab laser according to claim 38, wherein the emitting medium is CO ₂ . 42. The slab laser according to claim 38, wherein the emitting medium is CO. 43. The slab laser according to claim 38, wherein the radiating medium is an excimer medium. 44. The slab laser according to claim 38, wherein the active medium emits in the visible range of the spectrum. 45. The slab laser according to claim 38, wherein the active medium emits in the far infrared range of the spectrum. 46. The slab laser of claim 38, wherein the extended reflective surfaces are conductive. 47. The slab laser according to claim 46, wherein the pumping means is a radio frequency current applied between the first and second extended surfaces. 48. The slab laser according to clause 29, in which the pumping means is a light source. 49. The slab laser according to claim 38, wherein the pumping means is a laser light source. 50. The slab laser according to claim 38, wherein the pumping means is a light source. 51. A gas laser, including the first and second extended reflective surfaces having a gap between them, arranged so that they form a light guide between these surfaces, said gap defining a space for accommodating an active medium, said space having a plane containing a closed axial contour of the optical resonator a traveling wave, and the indicated plane is located in the middle between the indicated surfaces; laser gas placed in the indicated space; means for pumping said laser gas located between said first and second surfaces and creating an inverse population in said gas between said surfaces, said resonator being unstable in said plane and together with the gap between the first and second extended surfaces determines the propagation of light modes inside the laser providing a diffraction output of radiation. 52. The gas laser according to paragraph 51, in which the diffraction output of radiation is carried out only on one side of the specified axial contour. 53. The gas laser according to paragraph 51, in which the closed axial contour has an odd number of vertices. 54. The gas laser according to paragraph 51, in which the closed axial contour has an even number of vertices. 55. The gas laser according to claim 51, wherein the unstable traveling wave resonator is an unstable negative branch resonator. 56. The gas laser according to paragraph 51, in which the unstable resonator of the traveling wave is an unstable resonator of the positive branch. 57. The gas laser according to paragraph 51, in which the emitting medium is CO ₂ . 58. The gas laser according to paragraph 51, in which the emitting medium is CO. 59. The gas laser according to paragraph 51, in which the emitting medium is an excimer medium. 60. The gas laser according to paragraph 51, in which the active medium emits in the visible range of the spectrum. 61. The gas laser according to paragraph 51, in which the active medium emits in the far infrared range of the spectrum. 62. The gas laser according to Claim 57, wherein the pumping means is a radio frequency current. 63. The gas laser according to claim 58, wherein the pumping means is a radio frequency current. 64. The gas laser according to clause 57, in which the pumping means is a light source. 65. The gas laser according to clause 57, in which the means of pumping is a laser light source. 66. The gas laser according to claim 58, wherein the pumping means is a light source. 67. The gas laser according to claim 58, wherein the pumping means is a laser light source. 68. The gas laser according to clause 57, in which the extended reflective surfaces are conductive. 69. The gas laser according to Claim 57, wherein the pumping means is a radio frequency current applied between the first and second extended surfaces. 70. The gas laser according to § 58, in which the pumping means is a radio frequency current applied between the first and second extended surfaces. 71. A gas slab laser comprising first and second extended electrodes having a gap between them, each of which includes a light reflecting surface arranged so that a light guide is formed between said surfaces, said electrodes having a gap between them define a space, filled with a discharge, said discharge space has a plane containing a closed axial contour of the traveling wave optical resonator, and said plane is located in the middle between said electrons childbirth; laser gas located in the specified gap; means for applying a radio frequency current between said first and second electrodes and exciting a discharge in said laser gas between said electrodes; in which the specified resonator is unstable in the specified plane and together with the gap between the first and second extended electrodes determines the propagation of light modes inside the laser, providing a diffraction output of radiation. 72. The gas slab laser according to claim 71, wherein the diffraction output of radiation is carried out only on one side of said closed axial contour. 73. The gas slab laser of claim 71, wherein the closed axial contour has an odd number of vertices. 74. The gas slab laser according to claim 71, wherein the closed axial contour has an even number of vertices. 75. The gas slab laser of claim 71, wherein the unstable traveling wave resonator is an unstable negative branch resonator. 76. The gas slab laser of claim 71, wherein the unstable traveling wave resonator is an unstable positive branch resonator. 77. The gas slab laser according to claim 71, wherein the emitting medium is CO ₂ . 78. The gas slab laser according to claim 71, wherein the emitting medium is CO. 79. The gas slab laser according to claim 71, wherein the emitting medium is an excimer medium. 80. The gas slab laser according to claim 71, in which the active medium emits in the visible range of the spectrum. 81. The gas slab laser according to claim 71, wherein the active medium emits in the far infrared range of the spectrum. 82. The gas slab laser according to claim 77, wherein the pumping means is a radio frequency current. 83. The gas slab laser according to claim 78, wherein the pumping means is a radio frequency current. 84. The gas slab laser according to Claim 77, wherein the pumping means is a light source. 85. The gas slab laser according to Claim 77, wherein the pumping means is a laser light source. 86. The gas slab laser of claim 78, wherein the pumping means is a light source. 87. The gas slab laser of claim 78, wherein the pumping means is a laser light source. 88. The gas slab laser of claim 77, wherein the extended reflective surfaces are conductive. 89. The gas slab laser of claim 88, wherein the pumping means is a radio frequency current applied between the first and second extended surfaces. 90. A gas laser with high-frequency excitation and diffusion cooling, comprising a pair of gap-separated cooling elements, each of which has an extended surface, located opposite each other so as to form a fiber for the propagation of optical radiation in the gap between these surfaces; a gas active medium placed in the indicated interval for generating laser radiation upon excitation of this medium by an electric discharge by supplying high-frequency electric power to said medium; mirrors forming an annular traveling-wave optical cavity with a closed axial contour for forming a laser beam in said optical fiber in which said mirrors are arranged so that the closed axial contour of the resonator formed by them lies essentially in a plane passing between said surfaces of said cooling elements and facing its opposite sides to the indicated surfaces of the cooling elements, wherein said traveling wave resonator is made unstable in said plane so that part of the specified beam, expanding in the specified resonator, is removed from the laser in the form of an output beam of a continuous cross section, and the curvature of the mirrors and the number of these mirrors are such that any ray belonging to the laser beam propagating through the fiber and located with the inner side of the axial contour of the resonator, after a complete round-trip of the resonator, it appears on the outer side of the axial contour of the resonator, and any beam belonging to the laser beam propagating through the fiber, and which extends from the outer side from the axial contour of the resonator, after a complete bypass of the resonator, it appears from the inner side from the axial contour of the resonator. 91. The gas laser according to claim 90, in which the number of said mirrors forming an annular resonator is odd, and their curvature is such that the laser beam propagating through the optical fiber does not have focal constrictions inside the resonator. 92. The gas laser according to claim 90 or 91, wherein at least one of the mirrors of the ring resonator is convex and the remaining mirrors are flat. 93. The gas laser of claim 90 or 91, wherein at least one of the mirrors of the ring resonator is convex and at least one of the mirrors of the ring resonator is concave. 94. A gas laser according to any one of claims 90-93, wherein said surfaces of the cooling elements are substantially plane parallel. 95. A gas laser according to any one of claims 90-94, wherein the distances from the intersection of the axial contour of the resonator with the surface of each of the mirrors forming the resonator to the edges of these mirrors are such that radiation is emitted from the resonator in the form of a single continuous beam near one of the edges of one of these mirrors and thereby limiting the expansion of the beam in the resonator. 96. The gas laser according to any one of paragraphs.90-94, in which the resonator is equipped with a means of deflecting a portion of the radiation adjacent to the edge of the laser beam generated by the mirrors of the optical resonator, to remove this part of the radiation from the resonator and thereby limit the expansion of the beam in the resonator. 97. The gas laser according to any one of paragraphs.90-96, wherein said laser includes means that provide preferential conditions for the propagation of radiation through a ring resonator in one of two possible opposite directions around the cavity. 98. The gas laser according to p. 97, in which the said means, which provide the predominant propagation of radiation in one of these two opposite directions, include a feedback mirror, installed so that it essentially does not affect the radiation propagating through the resonator in the first from the indicated directions, but reflects in the opposite direction at least part of the radiation propagating along the resonator in the second direction opposite to the first, so that the specified part of the radiation is directed along the resonance torus in the first direction. 99. The gas laser according to claim 97, in which a hole is made in one of the resonator mirrors at the intersection of its surface with the axial contour of the resonator, and said means, which provide the predominant propagation of radiation in the first of two possible directions, include a feedback mirror mounted behind the specified hole so that it reflects in the first direction at least part of the radiation transmitted through the hole in the second direction, so that at least part of this radiation passes back through the decree hole and propagates through the resonator in the first direction. 100. A gas laser according to any one of claims 90-99, wherein said traveling wave ring resonator is made stable in a direction perpendicular to said plane of said axial contour. 101. A gas laser according to any one of claims 90-99, wherein said surfaces of said cooling elements provide a waveguide mode of light propagation in said light guide.

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