TWI729554B - Reentrant optical resonator - Google Patents

Abstract

The present invention provides a reentrant optical resonator that is less likely to cause damage to the lens. The front mirror of the foldback optical resonator is composed of a concave mirror, the back mirror has two planar reflection areas in a positional relationship that intersect each other, and the foldback mirror arranged on the optical axis between the front mirror and the back mirror is composed of a concave mirror.

Description

Reentrant optical resonator

The present invention relates to a reentrant optical resonator.

The laser oscillator is equipped with an optical resonator for blocking light, a discharge electrode part for exciting the laser gas, and a laser gas circulation part. The optical resonator includes a front mirror and a rear mirror. The light enclosed in the optical resonator is amplified, and part of it is radiated to the outside through the front mirror. There is known a folding optical resonator in which a folding mirror is arranged on the optical axis of the optical resonator in order to control the polarization direction of the laser beam. In order to suppress the generation of high-order lateral modes and improve the modal stability, there is also known an optical resonator that uses an orthogonal lens having two reflective surfaces orthogonal to each other as a rear mirror (for example, Patent Document 1) .

[Prior Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent No. 5220198

If a concave mirror is used for the front mirror to form a hemispherical resonator, the beam diameter at the position of the folding mirror or the rear mirror becomes smaller, and therefore the energy density at that position becomes higher. Therefore, damage to the reentrant mirror or rear mirror is likely to occur. In particular, in the folding mirror, two reflections are generated during the period when the laser beam goes back and forth in the optical resonator once, so the risk of damage is high.

The object of the present invention is to provide a reentrant optical resonator that is less likely to cause damage to the lens.

According to an aspect of the present invention, there is provided a fold-back optical resonator, which has: a front mirror composed of a concave mirror; a rear mirror having two planar reflection areas in a positional relationship that intersect each other; and a fold-back mirror disposed in the foregoing On the optical axis between the front mirror and the aforementioned rear mirror, it is composed of a concave mirror, and the angle formed by the two reflecting surfaces of the aforementioned rear mirror is greater than 90°.

According to another aspect of the present invention, a foldback optical resonator is provided, which has: a front mirror composed of a concave mirror; a rear mirror having two planar reflection regions in a positional relationship intersecting each other; and a foldback mirror arranged in the foregoing The optical axis between the front mirror and the rear mirror is formed by a concave mirror; and a fine adjustment mechanism for fine-tuning the angle formed by the two reflection areas of the rear mirror.

According to another aspect of the present invention, there is provided a fold-back optical resonator, which has: a front mirror composed of a concave mirror; a rear mirror having two planar reflection areas in a positional relationship that intersect each other; and a fold-back mirror disposed at The front mirror and the rear mirror are located on the optical axis and are composed of a concave mirror, and the front mirror, the rear mirror, and the folding mirror are each one.

By setting the rear mirror to have a structure with two planar reflection areas in a positional relationship that intersect each other, the modal stability of the laser beam can be improved. By setting the foldback mirror as a concave mirror, the beam profile at the position of the foldback mirror or the rear mirror becomes larger, so that it is not easy to cause damage to the foldback mirror or the rear mirror.

10: Chamber

11: Optical room

12: Blower room

13: Upper and lower partitions

13A, 13B: opening

14: bottom plate

15: partition

16: chamber support member

21: discharge electrode

22, 23: Discharge electrode support member

24: discharge area

25: Foldback optical resonator

25F: Front mirror

25M: Folding mirror

25R: Rear mirror

26: Common support member

27: Optical resonator supporting member

28: light window

29F: front aperture

29R: rear aperture

30: beam waist

30x: beam waist on xz profile

30y: beam waist on the yz profile

40: reflective surface

41: The first member

42: Support surface

43: reflective surface

44: The second member

45: lever member

46, 47: Fixture

48: Gasket

50: Blower

51: The 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: workbench

73: control device

75: Object to be processed

[Fig. 1] is a cross-sectional view of the optical axis in the discharge area including the gas laser device equipped with the folding optical resonator according to the embodiment.

[Fig. 2] is a cross-sectional view of a gas laser device equipped with a folding optical resonator based on this embodiment perpendicular to the optical axis in the discharge area.

[Fig. 3] A schematic plan view of the folding optical resonator based on this embodiment.

[Fig. 4] A schematic plan view of a folding optical resonator based on a comparative example.

[Fig. 5] The outline of the reentrant optical resonator based on the embodiment shown in Fig. 3 Top view and schematic side view.

Fig. 6 is a schematic plan view of a folding optical resonator based on another embodiment.

[Fig. 7] is a cross-sectional view showing the fine adjustment mechanism of the rear mirror of the folding optical resonator based on the embodiment shown in Fig. 6. [Fig.

[Fig. 8] A schematic plan view of a folding optical resonator based on another embodiment.

[Fig. 9] A schematic diagram of a laser processing device.

1 to 3, the gas laser device equipped with the reentrant optical resonator based on the embodiment and the reentrant optical resonator will be described.

FIG. 1 is a cross-sectional view of a gas laser device equipped with a folding optical resonator based on an embodiment including an optical axis in a discharge area. The xyz orthogonal coordinate system is defined by assuming that the optical axis direction in the discharge area is the z-axis direction and the vertical upward is the x-axis direction.

The laser gas is contained in the chamber 10. The internal space of the chamber 10 is divided into an optical chamber 11 relatively located on the upper side in the vertical direction and a blower room 12 relatively located on the lower side in the vertical direction. The optical chamber 11 and the blower chamber 12 are separated by upper and lower partitions 13. In addition, the upper and lower partition plates 13 are provided with openings to allow the laser gas to circulate between the optical chamber 11 and the blower chamber 12. The bottom plate 14 of the optical chamber 11 protrudes from the side wall of the blower chamber 12 to 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 on the bottom plate 14 of the optical chamber 11 by the chamber support member 16 to the light. Learn pedestal.

A pair of discharge electrodes 21 are arranged in the optical chamber 11. The pair of discharge electrodes 21 are supported on the bottom plate 14 with the discharge electrode supporting members 22 and 23 interposed therebetween, respectively. The pair of discharge electrodes 21 are arranged with an interval in the x-axis direction to define a discharge area 24 therebetween. The discharge electrode 21 excites the laser gas by generating a discharge in the discharge area 24. As described later with reference to FIG. 2, the laser gas flows through the discharge area 24 in a direction perpendicular to the paper surface of FIG. 1.

The reentrant optical resonator 25 is supported on the common support member 26 arranged in the optical chamber 11.

The reentrant optical resonator 25 is composed of a front mirror 25F, a reentrant mirror 25M, and a rear mirror. The rear mirror is not shown in the section shown in FIG. 1. The optical axis between the front mirror 25F and the folding mirror 25M is parallel to the z-axis and passes through the discharge area 24. The common support member 26 is supported on the bottom plate 14 with the optical resonator support member 27 interposed therebetween. At the intersection of the extension line extending the optical axis of the folding optical resonator 25 on the side of the front mirror 25F (the left side in FIG. 1) and the wall surface of the optical chamber 11, a transparent window 28 for transmitting the laser beam is installed. The laser beam excited in the folding optical resonator 25 is radiated to the outside through the light transmission window 28.

A blower 50 is arranged in the blower room 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 a gas laser device equipped with a folding optical resonator 25 (FIG. 1) based on this embodiment. The internal space of the chamber 10 is divided into an upper optical chamber 11 and a lower blower chamber 12 by the upper and lower partitions 13. A common supporting member 26 supporting a pair of discharge electrodes 21 and a folding optical resonator 25 (FIG. 1) is arranged in the optical chamber 11. Delineated between discharge electrodes 21 Discharge area 24.

A partition 15 is arranged in the optical chamber 11. The separator 15 defines a first gas flow path 51 from the opening 13A provided in the upper and lower separators 13 to the discharge area 24, and a second gas flow from the discharge area 24 to the other opening 13B provided in the upper and lower separators 13 Road 52. The laser gas flows through the discharge area 24 in a direction (y-axis direction) orthogonal to the optical axis. The discharge direction (x-axis direction) is orthogonal to two directions, 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 area 24, and the second gas flow path 52 constitute a circulating flow path through which the laser gas circulates. The blower 50 generates a laser gas flow in such a way that the laser gas circulates in the circulating flow path.

A heat exchanger 56 is housed in the circulation flow path in the blower chamber 12. The laser gas heated in the discharge area 24 is cooled by the heat exchanger 56, and the cooled laser gas is supplied to the discharge area 24 again.

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

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

The front mirror 25F is composed of a concave mirror. The rear mirror 25R has two planar reflection areas in a positional relationship intersecting each other. For example, as the rear mirror 25R, a roof mirror having two reflective surfaces that cross each other can be used. The two reflecting surfaces do not need to intersect at the intersection with a geometric angle in the strict sense. For example, within a range that does not affect the optical properties, two reflective surfaces can be connected via a cylindrical surface with a small radius of curvature. In addition, a small gap may be provided between the two reflecting surfaces. The folding 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 disposing the folding mirror 25M, the linearly polarized laser light is selectively oscillated in the folding optical resonator 25. As the polarization direction of the laser light in the folding optical resonator 25, the direction of S-polarized light or the direction of P-polarized light with respect to the folding mirror 25M is selected. Which direction is selected as the polarization direction of the laser light depends on the reflection characteristics of the folding mirror 25M. In this embodiment, the laser light having linear polarization is oscillated in a direction (direction parallel to the x-axis) that becomes S-polarized light with respect to the folding 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 light. In this embodiment, the polarization direction of the laser light and the valley line of the rear mirror 25R are parallel to the x-axis.

A front diaphragm 29F is arranged between the discharge area 24 and the front mirror 25F, and a rear diaphragm 29R is arranged between the discharge area 24 and the return mirror 25M. The front aperture 29F and the rear aperture 29R shield excess light propagating away from the optical axis.

A beam waist 30 is formed between the front mirror 25F and the folding mirror 25M. The beam waist 30 is located in the discharge area 24.

Next, one side compares with the reentrant optical resonator based on the comparative example shown in Fig. 4 For comparison, the excellent effects of this embodiment will be described.

FIG. 4 is a schematic plan view of the folding optical resonator 25 based on the comparative example. In the comparative example, the folding mirror 25M is composed of a flat mirror. The front mirror 25F is composed of a concave mirror like the embodiment shown in FIG. 3. Therefore, the folded-back optical resonator 25 based on the comparative example performs light confinement based on the same principle as the hemispherical resonator. Therefore, at the position of the folding mirror 25M or the rear mirror 25R, the beam diameter becomes smaller. As a result, the energy density becomes high, and the folding mirror 25M or the rear mirror 25R is easily damaged. By making the reflecting surface of the rear mirror 25R a concave surface, the increase in energy density can be improved, but it is difficult to make the two reflecting surfaces of the roof mirror that cross each other concave.

In this embodiment, the folding mirror 25M (FIG. 3) is constituted by a concave mirror. Therefore, the beam diameter at the positions of the folding mirror 25M and the rear mirror 25R becomes larger than that of the comparative example in FIG. 4. As a result, the increase in energy density is improved, and the effect that the return mirror 25M and the rear mirror 25R are not easily damaged can be obtained.

In addition, in this embodiment, the rear mirror 25R is constituted by a roof mirror, so that the excitation of high-order lateral modes can be suppressed, and the modal stability can be improved.

As an example, in the folding optical resonator 25 based on the embodiment shown in FIG. 3, when the radius of curvature of the front mirror 25F is set to 20m and the radius of curvature of the folding mirror 25M is set to 10m, it can be taken out as shown in FIG. 4 In the comparative example shown, the radius of curvature of the front mirror 25F is set to a laser beam with the same divergence angle when the radius of curvature is 5 m.

Next, a modification of the above-mentioned embodiment will be described.

In the above-mentioned embodiment, the laser beam having the polarization direction of S polarization with respect to the folding mirror 25M is oscillated, but the reflection characteristics of the folding mirror 25M may be adjusted to oscillate the laser beam having the polarization direction of P polarization. this In this case, it is preferable to arrange the rear mirror 25R in a posture in which the valley line of the reflecting surface is parallel to the polarization direction of the P-polarized light.

Next, referring to FIGS. 5 to 7, a foldback optical resonator 25 based on another embodiment will be described. Hereinafter, the description of the structure common to the folding optical resonator 25 based on the embodiment shown in FIG. 3 is omitted. Before describing this embodiment, the problem of the folding optical resonator 25 based on the embodiment shown in FIG. 3 will be described. In this embodiment, this problem is solved.

FIG. 5 is a schematic plan view and a schematic side view of the folding optical resonator 25 based on the embodiment shown in FIG. 3 as viewed from the y-axis direction. The folding mirror 25M is arranged obliquely with respect to the optical axis of the laser beam. Therefore, the radius of curvature of the folding mirror 25M on the yz cross-section is different from the curvature radius of the folding mirror 25M on the xz cross-section. As a result, the position of the beam waist 30y on the yz section is different from the position of the beam waist 30x on the xz section. Therefore, the beam cross section becomes an ellipse in the vicinity of the beam waists 30x and 30y.

FIG. 6 is a schematic plan view of the folded optical resonator 25 based on this embodiment. In this embodiment, the angle θr formed by the two reflecting surfaces of the rear mirror 25R is greater than 90°. The rear mirror 25R has a fine adjustment mechanism that finely adjusts the size 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 reflective surface 40 and a second member 44 having the other reflective surface 43. The first member 41 has a reflective surface 40 and a supporting surface 42 provided at a lower position than the reflective surface 40. A step difference occurs between the reflecting surface 40 and the supporting surface 42.

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

The lever member 45 is arranged on the support surface 42 with its bottom surface facing the support surface 42. The tip that 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 abuts on the step provided on the first member 41. The lever is composed of a first member 41, a second member 44, and a lever member 45. The tip of the lever member 45 becomes the fulcrum PP of the lever.

The edge of the lever member 45 on the side opposite to the tip end floats from the support surface 42, and a spacer 48 is inserted between the bottom surface of the lever member 45 and the support surface 42. The contact portion of the lever member 45 and the spacer 48 becomes the force 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 the contact portion becomes the point of action PL of the lever. The second member 44 is fixed to the first member 41 by a fixing tool 46 such as a bolt. The lever member 45 is fixed to the first member 41 by 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 of the point of application PL is smaller than the displacement of the point of force PE. If the spacer 48 is inserted to displace the point of application PL, the angle θr formed by the two reflection surfaces 40 and the reflection surface 43 changes. In a state where the angle θr is changed, if the second member 44 is fixed to the first member 41 by the fixture 46, the angle θr formed by the two reflection surfaces 40 and the reflection surface 43 is fixed.

Next, the excellent effects of the embodiment shown in FIGS. 5 to 7 will be described.

In this embodiment, by setting the angle θr formed by the two reflecting surfaces of the rear mirror 25R to be greater than 90°, the curvature of the xz section of the folding mirror 25M can be reduced. The influence of the difference between the radius and the radius of curvature on the yz section can make the position of the beam waist 30y (Figure 5) on the yz section close to the position of the beam waist 30x (Figure 5) on the xz section. As a result, the beam cross section near the beam waist can be made close to a perfect circle.

Furthermore, with the fine adjustment mechanism that finely adjusts the angle θr formed by the two reflecting surfaces of the rear mirror 25R, the size of the angle θr can be adjusted with fine resolution and high accuracy. The optimal value of the angle θr can be determined by performing evaluation experiments on the shape of the beam profile near the beam waist for various angles θr.

Next, referring to FIG. 8, a foldback optical resonator 25 based on another embodiment will be described. Hereinafter, the description of the structure common to the folding optical resonator 25 based on the embodiment shown in FIG. 3 is omitted.

FIG. 8 is a schematic plan view of the folded optical resonator 25 based on this embodiment. In the embodiment shown in FIG. 3, the incident angle of the light enclosed between the front mirror 25F and the rear mirror 25R to the folding mirror 25M is 45°. In contrast, in this embodiment, the incident angle θi is less than 45°. The posture of the rear mirror 25R is adjusted so that the optical axis between the folding mirror 25M and the rear mirror 25R bisects the angle formed by the two reflecting surfaces of the rear mirror 25R.

Next, the excellent effect of the embodiment shown in FIG. 8 will be described.

In this embodiment, if the incident angle θi is set to be less than 45°, the difference between the radius of curvature on the yz section of the folding mirror 25M and the radius of curvature on the xz section becomes smaller. As a result, the shape of the beam cross-section near the beam waist can be made closer to a perfect circle from the ellipse.

Next, a modification of this embodiment will be described. In this embodiment, the incident angle θi of the reverse mirror 25M is set to be less than 45°, and the reverse mirror 25R The angle formed by the two reflecting surfaces is set to 90° as in the embodiment shown in FIG. 3. In this embodiment, as in the embodiment shown in FIG. 6, the angle θr formed by the two reflecting surfaces of the rear mirror 25R can be set to be greater than 90°. Thereby, the beam profile near the beam waist can be brought closer to a perfect circle.

Next, referring to FIG. 9, a laser processing apparatus equipped with a folded optical resonator 25 based on any one of the above-mentioned embodiments will be described.

Fig. 9 is a schematic diagram of a laser processing device. The laser oscillator 70 outputs a pulsed laser beam according to an instruction from the control device 73. The pulsed laser beam output from the laser oscillator 70 enters the object 75 to be processed through the beam shaping scanning optical system 71. The beam shaping scanning optical system 71 shapes the beam cross-sectional shape of the laser beam, and scans the laser beam in a two-dimensional direction.

The object 75 to be processed is, for example, a printed circuit board, and is held by the table 72. The table 72 can move the object 75 to be processed in two directions parallel to the surface to be processed in accordance with instructions from the control device 73. This laser processing device is used for drilling processing of a processing object 75 based on a pulsed laser beam.

The laser oscillator 70 uses the folding optical resonator 25 based on any one of the above-mentioned embodiments. Therefore, it is possible to suppress the generation of high-order transverse modes of the pulsed laser beam output from the laser oscillator 70, and it is possible to improve the roundness of the beam spot. As a result, the processing quality of drilling can be improved. Furthermore, it is possible to obtain an excellent effect that the lens of the reentrant optical resonator is not easily damaged.

The foregoing embodiments are only examples, and of course, the structures shown in different embodiments may be partially replaced or used in combination. Regarding the same effect based on the same structure of the plural embodiments, it is not in each actual The examples are explained one by one. Furthermore, the present invention is not limited to the above-mentioned embodiment. For example, the present invention can be subjected to various changes, improvements, and combinations, which are obvious to those having ordinary knowledge in the technical field to which the present invention belongs.

24: discharge area

25: Foldback optical resonator

25F: Front mirror

25M: Folding mirror

25R: Rear mirror

29F: front aperture

29R: rear aperture

30: beam waist

x: x axis

y: y axis

z: z axis

Claims (3)

A refolding optical resonator, which has: a front mirror composed of a concave mirror; a rear mirror having two planar reflection areas in a positional relationship that intersect each other; and a refolding mirror arranged between the front mirror and the rear mirror On the optical axis of, and is composed of a concave mirror, the angle formed by the two reflective surfaces of the aforementioned rear mirror is greater than 90°. A foldback optical resonator, which has: a front mirror, which is composed of a concave mirror; a back mirror, which has two planar reflection areas in a positional relationship that cross each other; a foldback mirror, which is arranged between the front mirror and the rear mirror On the optical axis, it is composed of a concave mirror; and a fine-tuning mechanism for fine-tuning the angle formed by the two reflection areas of the rear mirror. The reentrant optical resonator according to claim 2, wherein the fine adjustment mechanism includes a lever, configured such that the displacement of the point of application is smaller than the displacement of the point of force, and the angle formed by the two reflection areas of the rear mirror depends on the point of application And the fixture, in a state where force is applied to the force point of the lever and the point of action is displaced, and the angle formed by the two reflection areas is fixed.

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