Laser Oscillator

Abstract

The laser oscillator comprises an output mirror (1), a reflecting mirror (2) that reflects the laser light (A) output from the output mirror (1), and electrodes (3) that are arranged in pairs at a distance D in the direction of the y-axis, which is an axis perpendicular to the z-axis, which is the optical axis of the laser light (A), and have a length of W in the direction of the x-axis, which is an axis perpendicular to the z-axis and y-axis. The outer surface (11) of the output mirror (1) is an inclined surface that is inclined with respect to the xy plane perpendicular to the z-axis. If the angle between the y-axis and an inclined line that intersects with the optical axis on the outer surface (11) of the output mirror (1) and that makes the maximum angle θ with the xy plane is defined as angle α, then angle α can be calculated by tan -1 (W / D) is greater than π-tan -1 (W / D) or less than tan -1 (W / D)-π or greater, -tan -1 Less than (W / D).

Description

[Technical field]

[0001] The present disclosure relates to laser oscillators. [Background technology]

[0002] Conventionally, a laser oscillator is known that includes an output mirror from which a laser beam is output, a reflecting mirror that reflects the laser beam output from the output mirror, and electrodes arranged in pairs at intervals in a direction perpendicular to the optical axis of the laser beam. When unnecessary parasitic oscillation light is generated by light reflection on the outer surface of the output mirror, the transverse mode, which is the intensity distribution, deteriorates and the output of the laser beam decreases. For example, the optical resonator disclosed in Patent Document 1 tilts the outer surface of the front mirror, which is the output mirror, and uses a roof mirror with two mutually intersecting reflecting surfaces as a reflecting mirror. The inclination direction of the outer surface of the front mirror and the valley line of the roof mirror are arranged in parallel to suppress the parasitic oscillation light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-98814 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the technology disclosed in Patent Document 1, the inclination direction of the outer surface of the front mirror and the valley line of the roof mirror are perpendicular to the electrodes arranged in pairs, so that the light reflected by the outer surface of the front mirror heads toward the electrodes and may become parasitic oscillation light when reflected by the electrodes.

[0005] The present disclosure has been made in view of the above, and has an object to provide a laser oscillator capable of suppressing parasitic oscillation light generated due to reflection from the electrodes. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the laser oscillator according to the present disclosure comprises an output mirror from which laser light is output, a reflecting mirror which reflects the laser light output from the output mirror, and electrodes arranged in pairs at a distance D in the direction of the y-axis which is an axis perpendicular to the z-axis which is the optical axis of the laser light, and having a length W in the direction of the x-axis which is an axis perpendicular to the z-axis and y-axis. An optical resonator is formed by the inner surface of the output mirror and the inner surface of the reflecting mirror facing the inner surface of the output mirror. The outer surface of the output mirror is an inclined surface which is inclined with respect to the xy plane which is perpendicular to the z-axis. If the angle between the y-axis and a straight line within the outer surface of the output mirror which intersects with the optical axis and which makes the maximum angle with the xy plane is defined as angle α, angle α can be calculated by tan -1 (W / D) is greater than π-tan -1 (W / D) or less than tan -1 (W / D)-π or greater, -tan -1 Less than (W / D). Effect of the Invention

[0007] The laser oscillator according to the present disclosure has an advantage in that it is possible to suppress parasitic oscillation light caused by reflection from the electrodes. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an overall configuration of a laser oscillator according to a first embodiment; [Diagram 2] FIG. 1 is a perspective view showing an optical resonator of a laser oscillator according to a first embodiment; [Diagram 3] FIG. 11 is a plan view showing an optical resonator according to a comparative example; [Figure 4] FIG. 13 is a front view showing an optical resonator according to a comparative example; [Diagram 5] FIG. 1 is a front view showing a state in which parasitic oscillation light is generated between the outer surface of the output mirror, the inner surface of the reflecting mirror, and the electrodes in an optical resonator of a comparative example. [Figure 6]FIG. 1 is a plan view showing an optical resonator of a laser oscillator according to a first embodiment; [Figure 7] FIG. 1 is a front view showing an optical resonator of a laser oscillator according to a first embodiment; [Figure 8] FIG. 8 is a plan view showing light reflected on an outer surface of an output mirror in an optical resonator of the laser oscillator according to the first embodiment. [Figure 9] An illustration showing the output mirror as seen from the y-axis direction [Figure 10] FIG. 10 is an explanatory diagram showing an enlarged view of a part of the outer surface of the output mirror as viewed from the white arrow X shown in FIG. [Figure 11] FIG. 1 is an explanatory diagram showing the electrodes of the laser oscillator according to the first embodiment as viewed from the z-axis direction, with the angle α of the inclined straight line being tan-1(W / D). [Figure 12] FIG. 1 is an explanatory diagram showing the electrodes of the laser oscillator according to the first embodiment as viewed from the z-axis direction, with the angle α of the inclined straight line being π-tan-1(W / D). [Figure 13] FIG. 1 is a perspective view showing an optical resonator of a first modified example of the laser oscillator according to the first embodiment; [Figure 14] FIG. 11 is an explanatory diagram showing an output mirror of a second modified example of the laser oscillator according to the first embodiment; [Figure 15] FIG. 13 is an explanatory diagram showing an output mirror of a laser oscillator according to a second embodiment. [Figure 16] FIG. 11 is an explanatory diagram showing an output mirror of a modified example of the laser oscillator according to the second embodiment; [Figure 17] FIG. 13 is a perspective view showing an optical resonator of a laser oscillator according to a third embodiment. [Figure 18] 11 is a graph showing the power of light reflected by the output mirror, the electrodes, and the retroreflection mirror when the angle α is changed in the laser oscillator according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Laser oscillators according to embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings.

[0010] Embodiment 1 FIG. 1 is a perspective view showing the overall configuration of a laser oscillator according to the first embodiment. As shown in FIG. 1, a laser oscillator 200 is disposed inside a vacuum vessel 300. The laser oscillator 200 includes an output mirror 1, a reflecting mirror 2, a pair of electrodes 3, a heat exchanger 4, and a blower 5. In the following description, the output mirror 1, the reflecting mirror 2, and the electrodes 3 are collectively referred to as an optical resonator 100. The laser oscillator 200 shown in FIG. 1 illustrates a case in which a discharge occurs in the direction of the y axis (y-axis direction) perpendicular to the z axis, which is the optical axis of the laser light A output from the output mirror 1, and a gas flow F in the discharge space S occurs in the direction of the x axis (x-axis direction) perpendicular to the z axis and the y axis. The laser oscillator 200 shown in FIG. 1 is called a three-axis orthogonal laser in which the optical axis of the laser light A, the direction of the discharge, and the direction of the gas flow F are mutually orthogonal.

[0011] FIG. 2 is a perspective view showing an optical resonator of the laser oscillator according to the first embodiment. As shown in FIG. 2, in the optical resonator 100, an output mirror 1 and a reflecting mirror 2 are arranged facing each other with a gap therebetween, and an optical resonator is formed by an inner surface 10 of the output mirror 1 and an inner surface 20 of the reflecting mirror 2 that face each other. In the optical resonator 100, a laser beam A is output from the output mirror 1. The output mirror 1 has an inner surface 10 that faces the inside of the optical resonator, and an outer surface 11 that faces the outside. The inner surface 10 of the output mirror 1 is coated with a coating that provides a desired reflectance for the wavelength of the laser beam A, for example. The outer surface 11 of the output mirror 1 is coated with a coating that provides a high transmittance for the wavelength of the laser beam A, for example.

[0012] The reflection mirror 2 has an inner surface 20 that faces the inside of the optical resonator, and an outer surface 21 that faces the outside. The inner surface 20 of the reflection mirror 2 is coated with a coating that provides high reflectance to the wavelength of the laser light A, for example.

[0013] The pair of electrodes 3 are arranged with a distance D in the y-axis direction. Each electrode 3 has a length W in the x-axis direction and a length L in the z-axis direction. Between the pair of electrodes 3 is a discharge space S in which the laser gas is excited by discharge. The volume of the discharge space S can be expressed as W×D×L using W, D, and L. A laser gas that functions as a laser medium is supplied between the pair of electrodes 3. The laser gas is, for example, a mixed gas containing some or all of CO2, N2, He, CO, Xe, O2, H2, etc. In the laser gas, for example, a CO2 laser having a wavelength of 10.6 μm or 9.3 μm, or a CO laser having a wavelength of 5 μm to 6 μm, etc., oscillates.

[0014] In the optical resonator 100, the laser light A travels back and forth between the inner surface 10 of the output mirror 1 and the inner surface 20 of the reflecting mirror 2, and is amplified by the laser gas excited in the discharge space S. A portion of the amplified laser light A is output from the outer surface 11 of the output mirror 1 and extracted.

[0015] The heat exchanger 4 cools the laser gas excited in the discharge space S. The blower 5 is disposed to circulate the laser gas in the discharge space S, and generates a gas flow F which is a flow of the laser gas. The laser gas cooled by the heat exchanger 4 is blown by the blower 5, and circulated and supplied back to the discharge space S.

[0016] FIG. 3 is a plan view showing an optical resonator of a comparative example. FIG. 4 is a front view showing an optical resonator of a comparative example. FIG. 3 and FIG. 4 show an example in which laser light A oscillates along the z-axis, which is the optical axis, in the optical resonator 100A. As shown in FIG. 4, the outer surface 11 of the output mirror 1 in the comparative example is inclined with respect to the xy plane perpendicular to the z-axis, which is the optical axis. The inclination direction of the outer surface 11 of the output mirror 1 is defined as the direction of the straight line included in the outer surface 11 that has the maximum inclination angle with respect to the xy plane. The maximum inclination angle is defined as θ. The straight line included in the outer surface 11 of the output mirror 1 that has the maximum inclination angle with respect to the xy plane and intersects with the z-axis, which is the optical axis, is referred to as the inclined straight line here. In FIG. 4, the inclined straight line exists in the yz cross section. The inclined straight line in this case is referred to as "inclined in the y-axis direction". The inclination direction of the outer surface 11 and the inclination direction of the inclined straight line are the same.

[0017] FIG. 5 is a front view showing a state in which parasitic oscillation light is generated between the outer surface of the output mirror, the inner surface of the reflecting mirror, and the electrode in the optical resonator of the comparative example. As shown in FIG. 5, in the optical resonator 100A of the comparative example, the inclined straight line included in the outer surface 11 of the output mirror 1 is inclined in the y-axis direction, so that the light reflected by the outer surface 11 of the output mirror 1 heads toward the electrode 3, is reflected by the electrode 3, and becomes unnecessary parasitic oscillation light B between the outer surface 11 of the output mirror 1, the inner surface 20 of the reflecting mirror 2, and the electrode 3. That is, the parasitic oscillation light B is not aligned with the z-axis, which is the optical axis of the optical resonator 100A. In this way, in the optical resonator 100A of the comparative example, the parasitic oscillation light B, which is unnecessary oscillation, causes deterioration of the transverse mode, which is the intensity distribution, and the output of the laser light A is reduced.

[0018] FIG. 6 is a plan view showing an optical resonator of the laser oscillator according to the first embodiment. FIG. 7 is a front view showing an optical resonator of the laser oscillator according to the first embodiment. FIG. 6 and FIG. 7 show an example in which the laser light A oscillates along the z-axis, which is the optical axis, in the optical resonator 100. As shown in FIG. 6, the optical resonator 100 of the laser oscillator 200 according to the first embodiment has the outer surface 11 of the output mirror 1 inclined in the x-axis direction, unlike the outer surface 11 of the output mirror 1 inclined in the y-axis direction shown in FIG. 4 as a comparative example. In other words, among the straight lines existing in the outer surface 11 of the output mirror 1, an inclined straight line exists in the xz cross section, which is a straight line having a maximum inclination angle with respect to the xy plane and which is a straight line intersecting with the z-axis, which is the optical axis.

[0019] 8 is a plan view showing the reflected light reflected by the outer surface of the output mirror in the optical resonator of the laser oscillator according to the first embodiment. As shown in FIG. 8, in the optical resonator 100 of the laser oscillator 200 according to the first embodiment, the inclined straight line included in the outer surface 11 of the output mirror 1 is inclined in the x-axis direction. Therefore, the reflected light C reflected by the outer surface 11 of the output mirror 1 does not head toward the electrode 3, but passes through between the electrodes 3 arranged in pairs to the outside of the optical resonator 100. That is, in the laser oscillator 200 according to the first embodiment, the reflected light C reflected by the outer surface 11 of the output mirror 1 is not reflected by the electrode 3.

[0020] The inclination angle θ at which the reflected light C, which is reflected by the outer surface 11 of the output mirror 1 without being reflected by the electrode 3, exits the optical resonator 100 while traveling back and forth within the optical resonator 100 may satisfy the following formula (1). However, the requirement for satisfying the inclination angle θ is not limited to formula (1).

[0021]

number

[0022] In this way, in the laser oscillator 200 of the first embodiment, parasitic oscillation light B due to reflection at the electrode 3 as shown in FIG. 5 is not generated, so that the transverse mode, which is the intensity distribution, can be improved and a decrease in the output of the laser light A can be suppressed.

[0023] FIG. 9 is an explanatory diagram showing the output mirror as viewed from the y-axis direction. FIG. 10 is an explanatory diagram showing an enlarged view of a part of the outer surface of the output mirror as viewed from the white arrow X shown in FIG. 9. In FIG. 10, an inclined straight line 12 is indicated by an arrow. As shown in FIG. 9, the outer surface 11 of the output mirror 1 is inclined at an inclination angle θ with respect to the xy plane 13. The example shown in FIG. 10 shows a state in which the inclined straight line 12, which is the line on the outer surface 11 of the output mirror 1 that has the maximum inclination angle with respect to the xy plane 13 and intersects with the z-axis, which is the optical axis, is rotated by an angle α from the y-axis. The angle α shown in FIG. 10 is π / 2 radians.

[0024] As shown in Fig. 9, when the output mirror 1 is viewed on a plane where the inclined line 12 and the z-axis exist, that is, on the xz cross section, the direction of the arrow of the inclined line 12 shown in Fig. 10 indicates the direction away from the intersection point P when the inner surface 10 and the outer surface 11 of the output mirror 1 are extended. Therefore, the optical resonator 100 can suppress the parasitic oscillation light B shown in Fig. 5 by rotating the inclined line 12, which indicates the inclination direction of the outer surface 11 of the output mirror 1, by π / 2 radians with respect to the y-axis along which the electrodes 3 face each other.

[0025] The inclined straight line 12 shown in Fig. 10 is rotated counterclockwise by π / 2 radians from the y-axis, but may be rotated clockwise by π / 2 radians from the y-axis. In this case, the angle α is -π / 2 radians. In the optical resonator 100A of the comparative example shown in Figs. 3 to 5, the angle α between the inclined straight line in the outer surface 11 and the y-axis is 0 radians, so that the light reflected by the outer surface 11 of the output mirror 1 travels toward the electrode 3 and is reflected by the electrode 3 to become unnecessary parasitic oscillation light B.

[0026] FIG. 11 shows the state in which the electrodes of the laser oscillator according to the first embodiment are viewed from the z-axis direction, and the angle α of the inclined straight line is expressed as tan -112 is an explanatory diagram showing a state in which the electrode of the laser oscillator according to the first embodiment is viewed from the z-axis direction, and the angle α of the inclined straight line is π-tan -1 11 and 12 are arranged in pairs and face each other at a distance D in the y-axis direction. The length of each electrode 3 in the x-axis direction is W.

[0027] 11 and 12, in order to suppress the parasitic oscillation light B shown in Fig. 5, the inclined line 12 indicating the inclination direction of the outer surface 11 of the output mirror 1 is made not to intersect with the electrode 3 so that the reflected light C reflected by the outer surface 11 of the output mirror 1 is not reflected to the electrode 3. In other words, the angle α between the inclined line 12 and the y-axis should be set to satisfy the following formula (2).

[0028]

number

[0029] 11 and 12 show a state in which the inclined straight line 12 is rotated counterclockwise by the angle α, but it may be rotated clockwise by the angle α. In this case, the angle α between the inclined straight line 12 and the y-axis is given by the following formula (3).

[0030]

number

[0031] For example, when W = 9 mm and D = 12.9 mm, the range of formula (2) is 0.61 radians (35 degrees) < α < 2.53 radians (145 degrees). The range of formula (3) is -2.53 radians (-145 degrees) < α < -0.61 radians (-35 degrees).

[0032] For example, when W=38 mm and D=12.9 mm, the range of formula (2) is 1.24 radians (71 degrees) < α < 1.90 radians (109 degrees). The range of formula (3) is -1.90 radians (-109 degrees) < α < -1.24 radians (-71 degrees).

[0033] For example, when W=50 mm and D=12.9 mm, the range of formula (2) is 1.32 radians (76 degrees) < α < 1.82 radians (105 degrees). The range of formula (3) is -1.82 radians (-105 degrees) < α < -1.32 radians (-76 degrees).

[0034] In addition, when the angle α of the inclined straight line 12 is π / 2 radians (90 degrees) or −π / 2 radians (−90 degrees), which are the median values ​​of the ranges of equations (2) and (3), the parasitic oscillation light B can be further suppressed.

[0035] As described above, the laser oscillator 200 according to the first embodiment includes the output mirror 1 from which the laser light A is output, the reflecting mirror 2 which reflects the laser light A output from the output mirror 1, and the electrodes 3 which are arranged in pairs at a distance D in the direction of the y-axis which is an axis perpendicular to the z-axis which is the optical axis of the laser light A, and have a length W in the direction of the x-axis which is an axis perpendicular to the z-axis and the y-axis. An optical resonator is formed by the inner surface 10 of the output mirror 1 and the inner surface 20 of the reflecting mirror 2 which faces the inner surface 10 of the output mirror 1. The outer surface 11 of the output mirror 1 is an inclined surface which is inclined with respect to the xy plane 13 which is perpendicular to the z-axis. If the angle between the y-axis and the inclined straight line 12 which is a straight line in the outer surface 11 of the output mirror 1 that intersects with the optical axis and which makes the maximum angle θ with the xy plane 13 is defined as angle α, the angle α can be expressed as tan -1 (W / D) is greater than π-tan -1 (W / D) or less than tan -1 (W / D)-π or greater, -tan -1 Less than (W / D).

[0036] That is, in the laser oscillator 200 according to the first embodiment, the angle α between the inclined straight line 12 and the y-axis is set so that the inclined straight line 12 indicating the inclination direction of the outer surface 11 of the output mirror 1 does not intersect with the electrode 3. As a result, the reflected light C reflected by the outer surface 11 of the output mirror 1 is not reflected by the electrode 3 and passes outside the optical resonator 100, so that the parasitic oscillation light B generated due to the reflection by the electrode 3 can be suppressed. Therefore, the transverse mode, which is the intensity distribution, can be improved, and a decrease in the output of the laser light A can be suppressed.

[0037] Fig. 13 is a perspective view showing an optical resonator of Modification 1 of the laser oscillator according to the first embodiment. As shown in Fig. 13, in the optical resonator 100 of the first embodiment, a folding mirror 6 that defines the polarization of the laser light A may be provided on the optical path of the laser light A between the inner surface 10 of the output mirror 1 and the inner surface 20 of the reflecting mirror 2. For example, a coating having polarization dependency may be applied to the reflecting surface 60 of the folding mirror 6 so that the laser light A has a desired polarization.

[0038] FIG. 14 is an explanatory diagram showing an output mirror in Modification 2 of the laser oscillator according to the first embodiment. The inner surface 10 of the output mirror 1A in the modification shown in FIG. 14 is a spherical surface with a radius of curvature R1 and centered at O1. For example, by setting the radius of curvature R1 of the inner surface 10 of the output mirror 1A to a radius of curvature R1 that satisfies the stability condition shown in the following formula (4), a stable optical resonator can be constructed and the output of the laser light A can be stabilized. In formula (4), R2 is the radius of curvature of the inner surface 20 of the reflecting mirror 2, and L c is the resonator length. The resonator length is the distance between the inner surface 10 of the output mirror 1A and the inner surface 20 of the reflecting mirror 2. In addition, in Fig. 14, the outer surface 11 of the output mirror 1A is illustrated as a flat surface, but it is not limited to a flat surface and may be a curved surface or a surface having another shape.

[0039]

number

[0040] Embodiment 2 Next, a laser oscillator according to the second embodiment will be described. FIG. 15 is an explanatory diagram showing an output mirror of the laser oscillator according to the second embodiment. As shown in FIG. 15, the output mirror 1B of the laser oscillator according to the second embodiment has an outer surface 11 that is a spherical surface with a curvature radius r1 with O2 as the center of curvature. The other configurations are the same as those of the first embodiment. By setting the curvature radius r1 such that an optical resonator is not formed between the outer surface 11 of the output mirror 1B and the inner surface 20 of the reflecting mirror 2, parasitic oscillation can be suppressed. For example, the curvature radius r1 can be set so that the stability condition expressed by the formula (4) is not satisfied by replacing R1 with r1 in the above formula (4), thereby suppressing the parasitic oscillation light B. Note that a stable resonator can also be constructed by satisfying the above formula (4) for the inner surface 10 of the output mirror 1B. In this case, since the inner surface 10 of the output mirror 1B is a flat surface in the above formula (4), the curvature radius R1 can be considered to be infinite, and (1-L c / R1) becomes 1.

[0041] In addition, in the output mirror 1B shown in Fig. 15, the tilt direction of the outer surface 11 is defined as follows. Of the straight lines included in tangent plane 14 tangent to the intersection of outer surface 11 and the z-axis, the direction of the straight line that has the maximum tilt angle with respect to xy plane 13 is defined as the tilt direction, and this maximum tilt angle is defined as θ. Of the straight lines included in tangent plane 14 tangent to the intersection of outer surface 11 and the z-axis, the straight line that has the maximum tilt angle with respect to xy plane 13 and intersects with the z-axis, which is the optical axis, is called the tilt straight line. The tilt straight line in output mirror 1B shown in Fig. 15 exists in the xz cross section, and is tilted in the x-axis direction.

[0042] Similarly to the optical resonator 100 in the first embodiment, the angle α between the y-axis and an inclined line, which is a line that has the maximum inclination angle with respect to the xy plane 13 and intersects with the z-axis, on the outer surface 11 of the output mirror 1B should satisfy the above formulas (2) and (3). Thus, in the laser oscillator according to the second embodiment, the inclined line indicating the inclination direction of the outer surface 11 of the output mirror 1B can be prevented from intersecting with the electrode 3 even by making the angle α satisfy the above formulas (2) and (3), so that the parasitic oscillation light B can be suppressed.

[0043] In the laser oscillator according to the second embodiment, R1 may be replaced with r1 in the above formula (4) so ​​as not to satisfy the stability condition expressed by formula (4), and the angle α may satisfy the above formulas (2) and (3). In addition, in Fig. 15, the inner surface 10 of the output mirror 1B is illustrated as a flat surface, but it is not limited to a flat surface, and may be a curved surface or a surface having another shape.

[0044] Fig. 16 is an explanatory diagram showing an output mirror as a modified example of the laser oscillator according to the second embodiment. In the modified output mirror 1C shown in Fig. 16, the inner surface 10 is a spherical surface with a radius of curvature R1 and a center of curvature at O1, and the outer surface 11 is a spherical surface with a radius of curvature r1 and a center of curvature at O2. In the output mirror 1C shown in Fig. 16, for example, by setting the radius of curvature R1 of the inner surface 10 to a radius of curvature R1 that satisfies the above formula (4), the stability as an optical resonator can be improved and the output of the laser light A can be stabilized.

[0045] Embodiment 3 Next, a laser oscillator 200 according to the third embodiment will be described. FIG. 17 is a perspective view showing an optical resonator of the laser oscillator according to the third embodiment. In the optical resonator 101 of the laser oscillator 200 shown in FIG. 17, a retroreflective mirror 7 is used as the reflecting mirror 2. The retroreflective mirror 7 is a mirror in which a first reflecting mirror surface 70 and a second reflecting mirror surface 71 intersect at a right angle. The retroreflective mirror 7 has a valley line 72 which is an intersection line between the first reflecting mirror surface 70 and the second reflecting mirror surface 71. The retroreflective mirror 7 is disposed, for example, such that the valley line 72 is parallel to the y axis. In this case, the direction of the valley line 72 is perpendicular to the x axis which is the direction of the gas flow F in the discharge space S and the z axis which is the optical axis of the laser light A. By using the retroreflective mirror 7, the optical resonator 101 can suppress the optical axis of the laser light A output from the output mirror 1 from being changed by the gas flow F, thereby realizing stable oscillation.

[0046] FIG. 18 is a graph showing the power of light reflected by the output mirror, the electrodes, and the retroreflective mirror when the angle α is changed in the laser oscillator according to the third embodiment. The vertical axis is the power of light reflected between the outer surface 11 of the output mirror 1, the electrode 3, and the reflecting surfaces of the first reflecting mirror surface 70 and the second reflecting mirror surface 71 of the retroreflective mirror 7. The horizontal axis is the angle α. In FIG. 18, in order to illustrate the ease with which parasitic oscillation light B occurs in the optical resonator 101, the power of the reflected light is calculated and normalized at a value of α=0. Hereinafter, the power of the reflected light normalized at a value of α=0 is simply referred to as normalized power. It means that the larger the normalized power, the more likely parasitic oscillation light B is to occur.

[0047] The solid line shown in Fig. 18 is a calculation example when the length W of electrode 3 in the x-axis direction is 9 mm. The dashed line shown in Fig. 18 is a calculation example when the length W of electrode 3 in the x-axis direction is 38 mm. The dotted line shown in Fig. 18 is a calculation example when the length W of electrode 3 in the x-axis direction is 50 mm. In all of the solid line, dashed line, and dotted line shown in Fig. 18, the distance D of electrodes 3 in the y-axis direction is 12.9 mm.

[0048] The normalized power shown in Fig. 18 decreases as |α|, the absolute value of the angle α, increases from 0 radians (0 degrees) and tends to decrease until it approaches 1.57 radians (90 degrees) in all cases of the solid line, dashed line, and dotted line. Furthermore, the normalized power shown in Fig. 18 has a graph shape that is symmetrical with respect to |α| being 1.57 radians (90 degrees).

[0049] The normalized power shown in FIG. 18 is small near 1.57 radians (90 degrees), and there is a range where it does not change significantly even if the angle |α| changes. In this range, not only can the parasitic oscillation light B be suppressed, but the normalized power does not change significantly even if the angle |α| changes, so the margin for suppressing the parasitic oscillation light B is large. When W=9 mm, this range is 1.05 radians (60 degrees)<|α|<2.09 radians (120 degrees). When W=38 mm, it is 1.40 radians (80 degrees)<|α|<1.75 radians (100 degrees). When W=50 mm, it is 1.40 radians (80 degrees)<|α|<1.75 radians (100 degrees).

[0050] The smaller the length W of the electrode 3 in the x-axis direction, the wider the range of |α| becomes, and the range of |α| does not change even if the value of W is greater than 38 mm. If the range of |α| where the parasitic oscillation light B can be suppressed and the suppression margin is large is rewritten as the range of α, then when W=9 mm, 1.05 radians (60 degrees)<α<2.09 radians (120 degrees), -2.09 radians (-120 degrees)<α<-1.05 radians (-60 degrees). When W=38 mm, 1.40 radians (80 degrees)<α<1.75 radians (100 degrees), -1.75 radians (-100 degrees)<α<-1.40 radians (-80 degrees). When W = 50 mm, 1.40 radians (80 degrees) < α < 1.75 radians (100 degrees), and -1.75 radians (-100 degrees) < α < -1.40 radians (-80 degrees).

[0051] The range of |α| becomes wider as the length W of the electrode 3 in the x-axis direction becomes smaller. Furthermore, the range of |α| does not change when the length W of the electrode 3 in the x-axis direction is 38 mm or more. Therefore, for example, a common range of α that is independent of the length W of the electrode 3 in the x-axis direction may be 1.40 radians (80 degrees) < α < 1.75 radians (100 degrees) or -1.75 radians (-100 degrees) < α < -1.40 radians (-80 degrees).

[0052] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or the embodiments may be combined with each other. Also, parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0053] 1,1A,1B,1C output mirror, 2 reflecting mirror, 3 electrode, 4 heat exchanger, 5 blower, 6 folding mirror, 7 retroreflective mirror, 10,20 inner surface, 11,21 outer surface, 12 inclined straight line, 13 xy plane, 14 tangential plane, 60 reflecting surface, 70 first reflecting mirror surface, 71 second reflecting mirror surface, 72 valley line, 100,100A,101 optical resonator, 200 laser oscillator, A laser light, B parasitic oscillation light, C reflected light, S discharge space.

Claims

1. an output mirror from which the laser light is output; a reflecting mirror that reflects the laser light output from the output mirror; a pair of electrodes arranged at an interval D along a y-axis direction perpendicular to a z-axis direction which is an optical axis of the laser light, the pair of electrodes having a length W along an x-axis direction which is perpendicular to the z-axis and y-axis; an optical resonator is formed by an inner surface of the output mirror and an inner surface of the reflecting mirror opposed to the inner surface of the output mirror, an outer surface of the output mirror is an inclined surface inclined with respect to an xy plane perpendicular to the z axis, Let α be the angle between the y-axis and an inclined straight line that intersects with the optical axis on the outer surface of the output mirror and that has the maximum angle with the xy plane. The angle α is expressed in radians as tan －１ (W / D) is larger than π-tan －１ (W / D) or less than tan －１ (W / D)-π or more, -tan －１ (W / D) is smaller than A laser oscillator characterized by:

2. an output mirror from which the laser light is output; a reflecting mirror that reflects the laser light output from the output mirror; and electrodes arranged in pairs at intervals along a y-axis direction perpendicular to a z-axis which is the optical axis of the laser light; an optical resonator is formed by an inner surface of the reflecting mirror and an inner surface of the output mirror opposed to the inner surface of the reflecting mirror, an outer surface of the output mirror is a spherical surface having a radius of curvature, and a tangent plane that is a plane tangent to an intersection point between the outer surface of the output mirror and the optical axis is formed so as to be inclined with respect to an xy plane perpendicular to the z axis; A laser oscillator characterized by:

3. The electrodes are arranged in pairs at an interval D in the y-axis direction, and have a length W in the x-axis direction, which is perpendicular to the z-axis and y-axis. Let α be the angle between the y-axis and an inclined straight line that intersects with the optical axis in the tangential plane and has the maximum angle with the xy plane. The angle α is expressed in radians as tan －１ (W / D) is larger than π-tan －１ (W / D) or less than tan －１ (W / D)-π or more, -tan －１ (W / D) is smaller than 3. The laser oscillator according to claim 2.

4. The reflecting mirror has two reflecting surfaces that are orthogonal to each other.

2. The laser oscillator according to claim 1.

5. The reflecting mirror has two orthogonal reflecting surfaces.

3. The laser oscillator according to claim 2.

6. The reflecting mirror has two orthogonal reflecting surfaces.

4. The laser oscillator according to claim 3.

7. A valley line, which is an intersection line of the two reflecting surfaces, is parallel to the y-axis.

5. The laser oscillator according to claim 4.

8. A valley line, which is the intersection line of the two reflecting surfaces, is parallel to the y-axis.

6. The laser oscillator according to claim 5.

9. A valley line, which is the intersection line of the two reflecting surfaces, is parallel to the y-axis.

7. The laser oscillator according to claim 6.

10. the angle α is greater than 1.40 radians and less than 1.75 radians, or greater than −1.75 radians and less than −1.40 radians; 8. The laser oscillator according to claim 7.

11. The angle α is π / 2 radians or −π / 2 radians.

10. The laser oscillator according to claim 1, 3, 4, 6, 7 or 9.

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