JP7076914B2 - Folded optical resonator - Google Patents

Description

The present invention relates to a folded optical resonator.

The laser oscillator includes an optical resonator that confine light, a discharge electrode portion for exciting the laser gas, and a laser gas circulation portion. The optical resonator includes a front mirror and a rear mirror, and the light confined in the optical resonator is amplified and a part of the light is transmitted to the outside through the front mirror. A folded optical resonator in which a folded mirror is arranged on the optical axis of the optical resonator in order to control the polarization direction of the laser beam is known. Further, in order to suppress the occurrence of higher-order transverse modes and improve mode stability, an optical resonator using an orthogonal mirror having two reflecting surfaces orthogonal to each other as a rear mirror is known (for example,). Patent Document 1).

Japanese Patent No. 5220198

When a hemispherical resonator is configured by using a concave mirror for the front mirror, the beam diameter at the position of the folded mirror or the rear mirror becomes small, so that the energy density becomes high at that position. Therefore, the folded mirror and the rear mirror are liable to be damaged. In particular, in the folded mirror, there is a high risk of damage because the laser beam is reflected twice while making one round trip in the optical resonator.

An object of the present invention is to provide a folded optical resonator in which damage to the mirror is less likely to occur.

According to one aspect of the invention
A front mirror composed of concave mirrors and
A rear mirror with two planar reflection regions that intersect each other,
Provided is a folded optical resonator having a folded mirror arranged on an optical axis between the front mirror and the rear mirror and composed of a concave mirror.

The mode stability of the laser beam can be improved by configuring the rear mirror with two planar reflection regions that are in a positional relationship that intersects each other. By making the folded mirror a concave mirror, the beam cross section at the position of the folded mirror and the rear mirror becomes large, and the folded mirror and the rear mirror are less likely to be damaged.

FIG. 1 is a cross-sectional view including an optical axis in a discharge region of a gas laser apparatus equipped with a folded optical resonator according to an embodiment. FIG. 2 is a cross-sectional view perpendicular to the optical axis in the discharge region of the gas laser apparatus equipped with the folded optical resonator according to the present embodiment. FIG. 3 is a schematic plan view of the folded optical resonator according to the present embodiment. FIG. 4 is a schematic plan view of a folded optical resonator according to a comparative example. FIG. 5 is a schematic plan view and a schematic side view of the folded optical resonator according to the embodiment shown in FIG. FIG. 6 is a schematic plan view of the folded optical resonator according to another embodiment. FIG. 7 is a cross-sectional view showing a fine adjustment mechanism of the rear mirror of the folded optical resonator according to the embodiment shown in FIG. FIG. 8 is a schematic plan view of the folded optical resonator according to still another embodiment. FIG. 9 is a schematic view of the laser processing apparatus.

The gas laser apparatus equipped with the folded-back optical resonator according to the embodiment and the folded-back optical resonator will be described with reference to FIGS. 1 to 3.
FIG. 1 is a cross-sectional view including an optical axis in a discharge region of a gas laser apparatus equipped with a folded optical resonator according to an embodiment. A xyz orthogonal coordinate system is defined in which the optical axis direction in the discharge region is the z-axis direction and the vertical upper direction is the x-axis direction.

Laser gas is housed in the chamber 10. The internal space of the chamber 10 is divided into an optical chamber 11 located relatively above in the vertical direction and a blower chamber 12 located relatively below in the vertical direction. The optical chamber 11 and the blower chamber 12 are partitioned by an upper and lower partition plate 13. The upper and lower partition plates 13 are provided with an opening for allowing laser gas to flow between the optical chamber 11 and the blower chamber 12. The bottom plates 14 of the optical chamber 11 project from the side wall of the blower chamber 12 on both sides in the z-axis direction, and the length of the optical chamber 11 in the z-axis direction is longer than the length of the blower chamber 12 in the z-axis direction. The chamber 10 is supported by the optical base by the chamber support member 16 in the bottom plate 14 of the optical chamber 11.

A pair of discharge electrodes 21 are arranged in the optical chamber 11. The pair of discharge electrodes 21 are supported by the bottom plate 14 via the discharge electrode support members 22 and 23, respectively. The pair of discharge electrodes 21 are arranged at intervals in the x-axis direction, and a discharge region 24 is defined between them. The discharge electrode 21 excites the laser gas by causing a discharge in the discharge region 24. As will be described later with reference to FIG. 2, the laser gas flows through the discharge region 24 in the direction perpendicular to the paper surface of FIG.

The folded optical resonator 25 is supported by the common support member 26 arranged in the optical chamber 11. The folded-back optical resonator 25 is composed of a front mirror 25F, a folded-back mirror 25M, and a rear mirror. The rear mirror does not appear in the cross section shown in FIG. The optical axis between the front mirror 25F and the folded mirror 25M is parallel to the z-axis and passes through the discharge region 24. The common support member 26 is supported by the bottom plate 14 via the optical resonator support member 27. A light transmission window 28 for transmitting a laser beam is attached at an intersection of an extension line extending the optical axis of the folded optical resonator toward the front mirror 25F (left side in FIG. 1) and the wall surface of the optical chamber 11. .. The laser beam excited in the folded optical resonator 25 passes through the light transmitting window 28 and is radiated to the outside.

A blower 50 is arranged in the blower chamber 12. The blower 50 circulates the laser gas between the optical chamber 11 and the blower chamber 12.

FIG. 2 is a cross-sectional view perpendicular to the z-axis of the gas laser apparatus on which the folded optical resonator 25 (FIG. 1) according to the present embodiment is mounted. The internal space of the chamber 10 is divided into an upper optical chamber 11 and a lower blower chamber 12 by an upper and lower partition plate 13. A pair of discharge electrodes 21 and a common support member 26 for supporting the folded optical resonator 25 (FIG. 1) are arranged in the optical chamber 11. A discharge region 24 is defined between the discharge electrodes 21.

A partition plate 15 is arranged in the optical chamber 11. The partition plate 15 is a first gas flow path 51 from the opening 13A provided in the upper and lower partition plates 13 to the discharge region 24, and a second gas flow from the discharge region 24 to another opening 13B provided in the upper and lower partition plates 13. The road 52 is defined. The laser gas flows in the discharge region 24 in a direction orthogonal to the optical axis (y-axis direction). The discharge direction (x-axis direction) is orthogonal to both the direction in which the laser gas flows (y-axis direction) and the optical axis direction (z-axis direction). The blower chamber 12, the first gas flow path 51, the discharge region 24, and the second gas flow path 52 form a circulation path through which the laser gas circulates. The blower 50 generates a flow of the laser gas so that the laser gas circulates in this circulation path.

The heat exchanger 56 is housed in the circulation path in the blower chamber 12. The laser gas heated in the discharge region 24 is cooled by passing through the heat exchanger 56, and the cooled laser gas is resupplied to the discharge region 24.

The upper and lower partition plates 13 are provided with an outflow hole 58 for allowing laser gas to flow out from the blower chamber 12 to the optical chamber 11. A part of the laser gas contained in the flow of the laser gas toward the first gas flow path 51 by the blower 50 passes through the outflow hole 58 and flows out to the optical chamber 11. The outflow hole 58 is provided with a filter 59 for removing particles. For example, the filter 59 closes the outflow hole 58, and the laser gas flowing out from the blower chamber 12 to the optical chamber 11 is filtered by passing through the filter 59.

FIG. 3 is a schematic plan view of the folded optical resonator 25 according to the present embodiment. The folded optical resonator 25 includes a front mirror 25F, a rear mirror 25R, and a folded mirror 25M. The optical axis between the front mirror 25F and the folded mirror 25M is parallel to the z-axis, and the optical axis between the folded mirror 25M and the rear mirror 25R is parallel to the y-axis. The optical axis between the front mirror 25F and the folded mirror 25M passes through the discharge region 24.

The front mirror 25F is composed of a concave mirror. The rear mirror 25R has two planar reflection regions that are in a positional relationship that intersects each other. For example, as the rear mirror 25R, a roof mirror having two mutually intersecting reflecting surfaces can be used. The two reflective surfaces do not have to intersect at exactly geometrical angles at the intersections. For example, two reflecting surfaces may be connected via a cylindrical surface having a small radius of curvature as long as the optical properties are not affected. Further, a minute gap may be provided between the two reflecting surfaces. The folded mirror 25M is arranged on the optical axis between the front mirror 25F and the rear mirror 25R, and is composed of a concave mirror.

By arranging the folded mirror 25M, the linearly polarized laser light is selectively oscillated in the folded optical resonator 25. As the polarization direction of the laser beam in the folded optical resonator 25, the direction of S polarization or the direction of P polarization with respect to the folded mirror 25M is selected. Which direction is selected as the polarization direction of the laser beam depends on the reflection characteristics of the folded mirror 25M. In this embodiment, the laser beam having linear polarization in the direction of S polarization (direction parallel to the x-axis) oscillates with respect to the folded mirror 25M. The rear mirror 25R is held in a posture in which the valley lines of the two reflecting surfaces are parallel to the polarization direction of the laser beam. In this embodiment, the polarization direction of the laser beam and the valley line of the rear mirror 25R are parallel to the x-axis.

The front iris 29F is arranged between the discharge area 24 and the front mirror 25F, and the rear iris 29R is arranged between the discharge area 24 and the folded mirror 25M. The front iris 29F and the rear iris 29R block extra light propagating away from the optical axis.

A beam waist 30 is formed between the front mirror 25F and the folded mirror 25M. The beam waist 30 is located within the discharge region 24.

Next, the excellent effect of this embodiment will be described while comparing with the folded-back optical resonator according to the comparative example shown in FIG.

FIG. 4 is a schematic plan view of the folded optical resonator 25 according to a comparative example. In the comparative example, the folded mirror 25M is composed of a plane mirror. The front mirror 25F is composed of a concave mirror as in the embodiment shown in FIG. Therefore, the folded optical cavity 25 according to the comparative example performs optical confinement by the same principle as the hemispherical cavity. Therefore, the beam diameter becomes smaller at the positions of the folded mirror 25M and the rear mirror 25R. As a result, the energy density becomes high, and the folded mirror 25M and the rear mirror 25R are easily damaged. By making the reflective surface of the rear mirror 25R concave, the increase in energy density can be improved, but it is difficult to make the two reflective surfaces intersecting each other of the roof mirror concave.

In this embodiment, since the folded mirror 25M (FIG. 3) is composed of a concave mirror, the beam diameters at the positions of the folded mirror 25M and the rear mirror 25R are larger than those in the comparative example of FIG. As a result, it is possible to improve the increase in energy density and obtain the effect that the folded mirror 25M and the rear mirror 25R are less likely to be damaged.

Further, in this embodiment, since the rear mirror 25R is composed of a roof mirror, it is possible to suppress the excitation in the higher-order transverse mode and improve the mode stability.

As an example, in the folded optical resonator 25 according to the embodiment shown in FIG. 3, when the radius of curvature of the front mirror 25F is 20 m and the radius of curvature of the folded mirror 25M is 10 m, the front mirror is shown in the comparative example shown in FIG. A laser beam having the same spread angle as when the radius of curvature of 25F is 5 m can be taken out.

Next, a modification of the above embodiment will be described.
In the above embodiment, the laser beam having the polarization direction of S polarization oscillates with respect to the folded mirror 25M, but the reflection characteristic of the folded mirror 25M is adjusted so that the laser beam having the polarization direction of P polarization oscillates. You may. In this case, the rear mirror 25R may be arranged in a posture in which the valley line of the reflecting surface is parallel to the polarization direction of the P polarization.

Next, the folded-back optical resonator 25 according to another embodiment will be described with reference to FIGS. 5 to 7. Hereinafter, the description of the configuration common to the folded-back optical resonator 25 according to the embodiment shown in FIG. 3 will be omitted. Before explaining this embodiment, the problem of the folded-back optical resonator 25 according to the embodiment shown in FIG. 3 will be described. In this embodiment, this problem is solved.

FIG. 5 is a schematic plan view of the folded optical resonator 25 according to the embodiment shown in FIG. 3, and a schematic side view seen from the y-axis direction. Since the folded mirror 25M is arranged obliquely with respect to the optical axis of the laser beam, the radius of curvature of the folded mirror 25M in the yz cross section and the radius of curvature of the folded mirror 25M in the xz cross section are different. As a result, the position of the beam waist 30y in the yz cross section and the position of the beam waist 30x in the xz cross section are different. Therefore, the beam cross section becomes elliptical in the vicinity of the beam waists 30x and 30y.

FIG. 6 is a schematic plan view of the folded optical resonator 25 according to the present embodiment. In this embodiment, the angle θr formed by the two reflecting surfaces of the rear mirror 25R is larger than 90 °. The rear mirror 25R is provided with a fine adjustment mechanism for finely adjusting the magnitude of the angle θr formed by the two reflecting surfaces.

FIG. 7 is a cross-sectional view showing a fine adjustment mechanism included in the rear mirror 25R. The rear mirror 25R includes a first member 41 having one reflecting surface 40 and a second member 44 having the other reflecting surface 43. The first member 41 has a reflection surface 40 and a support surface 42 provided at a position lower than the reflection surface 40. There is a step between the reflective surface 40 and the support surface 42.

The second member 44 is arranged on the reflective surface 40 so as to be in contact with the reflective surface 40, and a part thereof extends above the support surface 42. A gap is formed between the support surface 42 and the second member 44.

A lever member 45 is arranged on the support surface 42 with its bottom surface facing the support surface 42. The tip, which is one edge of the lever member 45, is inserted into the gap between the support surface 42 and the second member 44, and the tip is pressed against the step provided in the first member 41. The lever is composed of the first member 41, the second member 44, and the lever member 45. The tip of the lever member 45 serves as the fulcrum PP of the lever.

The edge opposite to the tip of the lever member 45 is raised from the support surface 42, and the shim 48 is inserted between the bottom surface of the lever member 45 and the support surface 42. The contact point between the lever member 45 and the shim 48 becomes the power point PE of the lever. A part of the upper surface of the lever member 45 is in contact with a part of the second member 44, and this contact point becomes the point of action PL of the lever. The second member 44 is fixed to the first member 41 with a fixing tool 46 such as a bolt. The lever member 45 is fixed to the first member 41 with a fixing tool 47 such as a bolt.

In the lever composed of the first member 41, the second member 44, and the lever member 45, the displacement amount of the action point PL is smaller than the displacement amount of the force point PE. When the point of action PL is displaced with the shim 48 in between, the angle θr formed by the two reflecting surfaces 40 and 43 changes. When the second member 44 is fixed to the first member 41 by the fixing tool 46 in a state where the angle θr is changed, the angle θr formed by the two reflecting surfaces 40 and 43 is fixed.

Next, the excellent effects of the examples shown in FIGS. 5 to 7 will be described.
In this embodiment, by making the angle θr formed by the two reflecting surfaces of the rear mirror 25R larger than 90 °, the influence of the difference between the radius of curvature in the xz cross section and the radius of curvature in the yz cross section of the folded mirror 25M is mitigated. The position of the beam waist 30y (FIG. 5) in the yz cross section can be brought close to the position of the beam waist 30x (FIG. 5) in the xz cross section. As a result, the beam cross section in the vicinity of the beam waist can be made closer to a perfect circle.

Further, the fine adjustment mechanism for finely adjusting the angle θr formed by the two reflecting surfaces of the rear mirror 25R makes it possible to finely adjust the magnitude of the angle θr with a fine resolution. The optimum value of the angle θr can be determined by conducting an evaluation experiment for observing the shape of the beam cross section in the vicinity of the beam waist at various angles θr.

Next, the folded-back optical resonator 25 according to still another embodiment will be described with reference to FIG. Hereinafter, the description of the configuration common to the folded-back optical resonator 25 according to the embodiment shown in FIG. 3 will be omitted.

FIG. 8 is a schematic plan view of the folded optical resonator 25 according to the present embodiment. In the embodiment shown in FIG. 3, the angle of incidence of the light confined between the front mirror 25F and the rear mirror 25R on the folded mirror 25M is 45 °. On the other hand, in this embodiment, the incident angle θi is smaller than 45 °. The posture of the rear mirror 25R is adjusted so that the optical axis between the folded mirror 25M and the rear mirror 25R bisects the angle formed by the two reflecting surfaces of the rear mirror 25R.

Next, the excellent effects of the examples shown in FIG. 8 will be described.
In this embodiment, when the incident angle θi is smaller than 45 °, the difference between the radius of curvature in the yz cross section of the folded mirror 25M and the radius of curvature in the xz cross section becomes small. As a result, the shape of the beam cross section in the vicinity of the beam waist can be made closer to a perfect circle from an ellipse.

Next, a modified example of this embodiment will be described. In this embodiment, the angle of incidence θi on the folded mirror 25M is smaller than 45 °, and the angle formed by the two reflecting surfaces of the rear mirror 25R is 90 °, as in the embodiment shown in FIG. Also in this embodiment, the angle θr formed by the two reflecting surfaces of the rear mirror 25R may be larger than 90, as in the embodiment shown in FIG. As a result, the beam cross section in the vicinity of the beam waist can be made closer to a perfect circle.

Next, with reference to FIG. 9, a laser processing apparatus equipped with a folded optical resonator 25 according to any one of the plurality of embodiments will be described.

FIG. 9 is a schematic view of the laser processing apparatus. The laser oscillator 70 outputs a pulsed laser beam based on a command from the control device 73. The pulsed laser beam output from the laser oscillator 70 passes through the beam shaping scanning optical system 71 and is incident on the workpiece 75. The beam shaping scanning optical system 71 shapes the beam cross-sectional shape of the laser beam and scans the laser beam in the two-dimensional direction.

The object to be processed 75 is, for example, a printed circuit board, and is held on the stage 72. The stage 72 can move the object to be machined 75 in two directions parallel to the surface to be machined by a command from the control device 73. This laser processing device is used for drilling a hole in the object to be machined 75 by using a pulsed laser beam.

As the laser oscillator 70, the folded optical resonator 25 according to any one of the plurality of embodiments described above is used. Therefore, it is possible to suppress the generation of the high-order transverse mode of the pulsed laser beam output from the laser oscillator 70 and to increase the roundness of the beam spot. As a result, it becomes possible to improve the processing quality of the drilling process. Further, the excellent effect that the mirror of the folded optical resonator is not easily damaged can be obtained.

It goes without saying that each of the above embodiments is exemplary and the configurations shown in different examples can be partially replaced or combined. Similar actions and effects due to the same configuration of a plurality of examples will not be mentioned sequentially for each example. Furthermore, the present invention is not limited to the above-mentioned examples. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

10 Chamber 11 Optical chamber 12 Blower chamber 13 Upper and lower partition plates 13A, 13B Opening 14 Bottom plate 15 Partition plate 16 Chamber support member 21 Discharge electrode 22, 23 Discharge electrode support member 24 Discharge region 25 Folded optical cavity 25F Front mirror 25M Folded mirror 25R Rear mirror 26 Common support member 27 Resonator support member 28 Light transmission window 29F Front iris 29R Rear iris 30 Beam waist 30 x xz Beam waist 30 in cross section Beam waist 40 Reflective surface 41 First member 42 Support surface 43 Reflective surface 44 No. 2 members 45 Nest members 46, 47 Fixtures 48 Shim 50 Blower 51 First gas flow path 52 Second gas flow path 56 Heat exchanger 58 Outflow hole 59 Filter 70 Laser oscillator 71 Beam shaping scanning optical system 72 Stage 73 Control device 75 Object to be processed

Claims (4)

A front mirror composed of concave mirrors and
A rear mirror with two planar reflection regions that intersect each other,
A folded optical resonator having a folded mirror arranged on an optical axis between the front mirror and the rear mirror and composed of a concave mirror. The folded optical resonator according to claim 1, wherein the angle of incidence of the light confined between the front mirror and the rear mirror on the folded mirror is smaller than 45 °. The folded optical resonator according to claim 1 or 2, wherein the angle formed by the two reflecting surfaces of the rear mirror is larger than 90 °. Further, it has a fine adjustment mechanism for finely adjusting the angle formed by the two reflection regions of the rear mirror.
The fine adjustment mechanism is
A lever configured such that the displacement amount of the action point is smaller than the displacement amount of the force point, and the angle formed by the two reflection regions of the rear mirror changes depending on the displacement of the action point.
The folded optical resonator according to claim 3, further comprising a fixture that fixes the angle formed by the two reflection regions in a state where a force is applied to the force point of the lever to displace the action point.

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