JP2022015941A - Iris and laser oscillator - Google Patents

Abstract

To provide an iris for an optical resonator capable of suppressing collapse of a beam cross section from a true circle.SOLUTION: An iris is arranged in a path of a laser beam confined in an optical resonator. The iris defines a passage region through which the laser beam confined in the optical resonator passes and a light shielding region arranged around the passage region. An aspect ratio, which is a ratio of dimensions of passage regions in two directions orthogonal to each other in the plane orthogonal to an optical axis of the optical resonator, is variable.SELECTED DRAWING: Figure 5

Description

The present invention relates to an iris arranged in an optical resonator and a laser oscillator equipped with the iris.

The laser oscillator includes an optical resonator composed of a front mirror and a rear mirror, and an excitation mechanism such as a discharge electrode. Generally, the front iris, the rear iris, or both are arranged on the optical axis of the optical resonator. By arranging the iris, the cross section of the beam can be shaped into a perfect circle, the spread angle can be suppressed, and the parasitic oscillation can be suppressed. In order to extract a laser beam having a circular beam cross section, a metal plate provided with a perfect circular opening is used as an iris (see, for example, Patent Document 1 below).

Japanese Unexamined Patent Publication No. 61-276387

Even if the beam cross section is shaped using an iris having a perfect circular aperture, the shape of the beam cross section of the laser beam output from the laser oscillator may collapse from the perfect circle and become elliptical.

An object of the present invention is to provide an iris capable of suppressing a collapse of a beam cross section from a perfect circle. Another object of the present invention is to provide a laser oscillator capable of suppressing the collapse of the beam cross section from a perfect circle.

According to one aspect of the invention
An iris placed in the path of a laser beam confined in an optical cavity.
A passing region through which the laser beam confined in the optical resonator passes and a light-shielding region arranged around the passing region are defined, and each other is defined in a plane orthogonal to the optical axis of the optical resonator. An iris having a variable aspect ratio, which is the ratio of the dimensions of the passage area in two orthogonal directions, is provided.

According to another aspect of the invention
An optical resonator that traps the laser beam,
A passing region through which the laser beam confined in the optical resonator passes and a light-shielding region arranged around the passing region are defined, and are orthogonal to each other in a plane orthogonal to the optical axis of the optical resonator. An iris with a variable aspect ratio, which is the ratio of the dimensions of the passage area in two directions.
The optical resonator, the iris, and the chamber accommodating the laser medium gas,
Provided is a laser oscillator having an aspect ratio changing mechanism for changing the aspect ratio of the passing region of the iris by operating from outside the chamber.

By changing the aspect ratio of the passage region of the iris, the shape of the beam cross section can be adjusted and the collapse from the perfect circle can be suppressed.

FIG. 1 is a schematic view of a laser processing apparatus equipped with a laser oscillator according to the present embodiment. FIG. 2 is a cross-sectional view including an optical axis of the laser oscillator according to the embodiment. FIG. 3 is a cross-sectional view perpendicular to the optical axis of the laser oscillator according to the embodiment. FIG. 4 is a diagram showing the positional relationship of the discharge electrode, the electrode box, and the iris when viewed from the front. 5A is a perspective view of the iris, and FIGS. 5B and 5C are front views of the first member and the second member of the iris. FIG. 6 is a graph showing the results of an evaluation experiment in which the beam diameter of the beam spot of the laser beam is measured at a position advanced by a certain optical path length from the light transmission window of the laser oscillator by changing the repetition frequency of the pulse. FIG. 7 is a cross-sectional view perpendicular to the optical axis of the laser oscillator according to another embodiment. FIG. 8 is a perspective view of an iris used in the laser oscillator according to still another embodiment.

A laser oscillator according to an embodiment will be described with reference to FIGS. 1 to 6.
FIG. 1 is a schematic view of a laser processing apparatus equipped with a laser oscillator according to the present embodiment. The laser processing apparatus includes a laser oscillator 12 and a processing apparatus 80.

The laser oscillator 12 is supported on the gantry 11, and the gantry 11 is fixed to the common base 100. The processing apparatus 80 includes a beam shaping optical system 81 and a stage 82. The object to be machined 90 is held on the stage 82. The beam shaping optical system 81 and the stage 82 are fixed to the common base 100. The beam profiler 50 can be arranged in the path of the laser beam between the laser oscillator 12 and the beam shaping optical system 81. During laser processing, the beam profiler 50 is retracted from the path of the laser beam. The common base 100 is, for example, a floor.

The laser oscillator 12 outputs a pulsed laser beam. As the laser oscillator 12, for example, a carbon dioxide laser oscillator is used. As the laser oscillator 12, another gas laser oscillator, for example, an excimer laser oscillator may be used. The pulsed laser beam output from the laser oscillator 12 has its beam profile shaped by the beam shaping optical system 81, and is incident on the object to be machined 90.

FIG. 2 is a cross-sectional view including an optical axis of the laser oscillator 12 according to the embodiment. The laser oscillator 12 includes a chamber 15 that houses a laser medium gas, an optical resonator 20, and the like. The internal space of the chamber 15 is divided into an optical chamber 16 located relatively above and a blower chamber 17 located relatively below. The optical chamber 16 and the blower chamber 17 are partitioned by an upper and lower partition plate 18. The upper and lower partition plates 18 are provided with an opening for allowing the laser medium gas to flow between the optical chamber 16 and the blower chamber 17. The bottom plate 19 of the optical chamber 16 projects from the side wall of the blower chamber 17 in the direction of the optical axis 20A of the optical resonator 20, and the length of the optical chamber 16 in the optical axis direction is the length of the blower chamber 17 in the optical axis direction. It's longer than that.

The bottom plate 19 of the chamber 15 is supported by the gantry 11 (FIG. 1) at four support points 45. The four support points 45 are arranged at positions corresponding to the four vertices of the rectangle in a plan view.

A pair of discharge electrodes 21 and a pair of resonator mirrors 25 are arranged in the optical chamber 16. Each of the pair of discharge electrodes 21 is fixed to the electrode box 22. The pair of electrode boxes 22 are supported by the bottom plate 19 via a plurality of electrode support members 23. The pair of discharge electrodes 21 are arranged at intervals in the vertical direction, and a discharge region 24 is defined between them. The discharge electrode 21 excites the laser medium gas by causing a discharge in the discharge region 24. The pair of resonator mirrors 25 constitutes an optical resonator 20 having an optical axis 20A passing through the discharge region 24. As will be described later with reference to FIG. 3, the laser medium gas flows through the discharge region 24 in the direction perpendicular to the paper surface of FIG.

The pair of resonator mirrors 25 are fixed to a common resonator base 26 arranged in the optical chamber 16. The resonator base 26 is a plate-shaped member long in the direction of the optical axis 20A, and is supported by the bottom plate 19 via a plurality of optical resonator support members 27.

The light generated in the discharge region 24 is repeatedly reflected between the pair of resonator mirrors 25, and the wavelength is standing in the region 20B between the pair of resonator mirrors 25 according to the optical path length between the resonator mirrors 25. Waves are generated. In this way, the laser beam is confined in the region 20B between the pair of resonator mirrors 25. A part of the laser beam confined in the optical resonator 20 passes through one of the resonator mirrors 25 (the resonator mirror 25 on the left side in FIG. 2) and is output to the outside. Two irises 60 and 70 are arranged in the path of the laser beam confined in the optical resonator 20. The irises 60 and 70 are supported by the resonator base 26. The two irises 60 and 70 are arranged at positions sandwiching the discharge region 24 in the direction of the optical axis 20A.

A light transmission window 28 for transmitting a laser beam is attached to an intersection of an extension line extending the optical axis 20A of the optical resonator 20 in one direction (left direction in FIG. 1) and the wall surface of the optical chamber 16. .. The laser beam excited in the optical resonator 20 passes through the light transmission window 28 and is radiated to the outside. The iris 60 arranged on the light transmitting window 28 side may be referred to as a front iris, and the other iris 70 may be referred to as a rear iris.

A blower 29 is arranged in the blower chamber 17. The blower 29 circulates the laser medium gas between the optical chamber 16 and the blower chamber 17.

FIG. 3 is a cross-sectional view perpendicular to the optical axis 20A (FIG. 2) of the laser oscillator 12 according to the embodiment. As described with reference to FIG. 2, the internal space of the chamber 15 is divided into an upper optical chamber 16 and a lower blower chamber 17 by the upper and lower partition plates 18. A pair of discharge electrodes 21 and a resonator base 26 are arranged in the optical chamber 16. Each of the pair of discharge electrodes 21 is fixed to the electrode box 22. The electrode box 22 is supported by a plurality of electrode support members 23 on the bottom plate 19 (FIG. 2) of the chamber 15. A discharge region 24 is defined between the pair of discharge electrodes 21. The resonator base 26 is supported by a plurality of optical resonator support members 27 on the bottom plate 19 (FIG. 2) of the chamber 15. Since the electrode support member 23 and the optical resonator support member 27 are arranged at positions deviated from the cross section shown in FIG. 3, the electrode support member 23 and the optical resonator support member 27 are represented by broken lines in FIG. ..

A partition plate 40 is arranged in the optical chamber 16. The partition plate 40 is a first gas flow path 41 from the opening 18A provided in the upper and lower partition plates 18 to the discharge region 24, and a second gas flow from the discharge region 24 to another opening 18B provided in the upper and lower partition plates 18. The road 42 is defined. The laser medium gas flows in the discharge region 24 in a direction orthogonal to the optical axis 20A (FIG. 2). The discharge direction is orthogonal to both the direction in which the laser medium gas flows and the optical axis 20A. The blower chamber 17, the first gas flow path 41, the discharge region 24, and the second gas flow path 42 form a circulation path through which the laser medium gas circulates. The blower 29 generates a flow of the laser medium gas indicated by an arrow so that the laser medium gas circulates in this circulation path.

The heat exchanger 43 is housed in the circulation path in the blower chamber 17. The laser medium gas heated in the discharge region 24 is cooled by passing through the heat exchanger 43, and the cooled laser medium gas is resupplied to the discharge region 24.

FIG. 4 shows the positional relationship of the discharge electrode 21, the electrode box 22, and the iris 60 when viewed from the front. In FIG. 4, the electrode box 22 is hatched. A pair of discharge electrodes 21 facing each other in the vertical direction are fixed to the electrode box 22. The partition plate 40 attached to the electrode box 22 defines the first gas flow path 41 and the second gas flow path 42 of the laser medium gas. Note that FIG. 3 schematically shows the partition plate 40, and the shape of the partition plate 40 shown in FIG. 4 is different from the shape of the partition plate 40 schematically shown in FIG.

The laser medium gas flows from the first gas flow path 41 through the space between the pair of electrode boxes 22 toward the second gas flow path 42. In FIG. 4, the flow of the laser medium gas is indicated by an arrow. The space between the pair of electrode boxes 22 includes a discharge region 24. A straightening vane 44 is arranged at the inflow end of the laser medium gas into the space between the pair of electrode boxes 22.

The iris 60 is arranged at a position overlapping the discharge region 24. When viewed from the front, the iris 60 includes a passing region 60A through which the laser beam passes and a light shielding region 60B arranged around the passing region 60A. The passage region 60A is included in the discharge region 24 when viewed from the front. The ratio of the dimensions of the passage region 60A in two directions orthogonal to each other in the plane orthogonal to the optical axis 20A (FIG. 2) of the optical resonator 20 is variable. The passing region of the other iris 70 (FIG. 2) is a perfect circle, and its size does not change.

For example, the direction in which the laser medium gas flows (horizontal direction in FIG. 4) is defined as the first direction D1, and the direction in which the pair of discharge electrodes 21 are separated (vertical direction in FIG. 4) is defined as the second direction D2. The dimension of the first direction D1 of the passage region 60A is variable, and the dimension of the second direction D2 is fixed. When the dimension of the first direction D1 of the passing region 60A changes, the ratio between the dimension of the first direction D1 of the passing region 60A and the dimension of the second direction D2 (hereinafter referred to as an aspect ratio) changes. In FIG. 4, the passing region 60A in which the dimension of the first direction D1 is smaller than that of the passing region 60A shown by the solid line is shown by a broken line.

Next, the configuration of the iris 60 will be described with reference to FIGS. 5A to 5C.
FIG. 5A is a perspective view of the iris 60. The iris 60 includes a first member 61 and a second member 62. The second member 62 includes two parts 62A and 62B. The first member 61 is a plate material (for example, a metal plate) arranged perpendicular to the optical axis 20A of the optical resonator 20 (FIG. 2), and the plate material is provided with an opening 63 that overlaps with the path of the laser beam. There is. The size of the opening 63 is invariant.

The two parts 62A and 62B of the second member 62 are arranged at positions sandwiching the optical axis 20A in the first direction D1 when viewed from the front. Each of the two parts 62A and 62B is a plate material arranged perpendicular to the optical axis 20A. The facing edges of the two parts 62A and 62B are curved inwardly.

The two parts 62A and 62B of the second member 62 are movably supported in the first direction D1 by the slide mechanism 65. The guide surface of the slide mechanism 65 is fixed to the resonator base 26 (FIG. 2). The two parts 62A and 62B can move independently in the first direction D1. When the two parts 62A and 62B are moved in the first direction D1, the relative positional relationship between the opening 63 of the first member 61 and the two parts 62A and 62B changes when viewed from the front. When the two parts 62A and 62B are moved in a direction approaching the optical axis 20A from the state where the two parts 62A and 62B do not overlap with the opening 63, the two parts 62A and 62B overlap with a part of the opening 63 and the opening 63. Is closed from both sides of the first direction D1. For example, the two parts 62A, 62B block an area that has entered inward from the edge of the opening 63. The area of the closed area of the opening 63 is changed by moving the two parts 62A and 62B of the second member 62.

5B and 5C are front views of the first member 61 and the second member 62. FIG. 5B shows a state in which the two parts 62A and 62B of the second member 62 do not overlap with the opening 63 of the first member 61. At this time, the opening 63 of the first member 61 coincides with the passing region 60A of the iris 60.

FIG. 5C shows a state in which the two parts 62A and 62B of the second member 62 overlap with a part of the opening 63 of the first member 61. The region of the opening 63 that does not overlap with the second member 62 corresponds to the passage region 60A of the iris 60. The two parts 62A and 62B of the second member 62 close a part of the opening 63, so that the dimension of the first direction D1 of the passage region 60A becomes smaller. The dimension of the second direction D2 of the passage region 60A is equal to the dimension of the second direction D2 of the opening 63 and is invariant.

Next, the excellent effect of the above embodiment will be described.
When a pulsed laser beam output from a laser oscillator is incident on an object to be machined to form a plurality of holes, the pulsed laser beams are sequentially incident on a plurality of positions where the holes should be formed. If the distance from the hole machined immediately before to the hole to be machined next becomes long, the moving distance of the incident position of the pulsed laser beam becomes long, and the time from the previous shot to the next shot may become long. Therefore, the repetition frequency of the pulse fluctuates due to the influence of the distribution of holes to be formed. In order to make the shape of the hole to be formed uniform, it is preferable that the shape of the beam spot does not change even if the repetition frequency of the pulse fluctuates.

The inventors of the present application change the repetition frequency of the pulse of the laser oscillator 12 to form the shape of the beam spot of the laser beam at a position advanced by a certain optical path length from the light transmission window 28 (FIG. 2) of the laser oscillator 12. An evaluation experiment was conducted to observe. In the evaluation experiment, the passing region 60A of the iris 60 was set as a perfect circle.

FIG. 6 is a graph showing the results of the evaluation experiment. The horizontal axis represents the pulse repetition frequency in the unit "kHz", and the vertical axis represents the dimensions of the beam spots in the first direction D1 and the second direction D2 as relative values. The circle symbol and the triangle symbol in the graph indicate the dimension of the first direction D1 and the dimension of the second direction D2, respectively. Regardless of the value of the pulse repetition frequency, the dimension of the beam cross section in the first direction D1 is larger than the dimension of the second direction D2. As described above, although the irises 60 and 70 having a perfect circular passage region are used, the beam cross section does not become a perfect circle but becomes horizontally long. This is because the oscillation situation differs between the first direction D1 and the second direction D2 due to the influence of the flow of the laser medium gas and the spatial non-uniformity of the discharge.

Decreasing the pulse repetition frequency increases the size of the beam cross section. However, the amount of increase in the dimension of the first direction D1 is larger than the amount of increase in the dimension of the second direction D2. This is because the non-uniformity of the discharge state with respect to the flow direction of the laser medium gas (first direction D1) is more affected by the change in the repetition frequency of the pulse than the non-uniformity of the discharge state with respect to the second direction D2. This is to receive a large amount. As the pulse repetition frequency decreases, the shape of the beam cross section collapses from a perfect circle.

In this embodiment, the shape of the beam cross section can be made closer to a perfect circle by changing the dimension of the first direction D1 of the passing region 60A of the iris 60. For example, when the repetition frequency of the pulse is lowered and the beam cross section becomes longer in the first direction D1, the dimension of the first direction D1 of the passing region 60A may be reduced.

By adjusting the aspect ratio of the passing region 60A according to the repetition frequency of the pulse, the beam cross section can be maintained in a substantially perfect circle even if the repetition frequency of the pulse is changed.

Further, in this embodiment, since a part of the opening 63 (FIG. 5A) of the first member 61 is closed from both sides of the first direction D1, even if the dimension of the first direction D1 of the passing area 60A is changed, the passing area 60A The geometric center position of is not moved. Therefore, even if the dimension of the first direction D1 of the passing region 60A is changed, the deviation of the central axis of the laser beam does not occur.

Next, a modification of the above embodiment will be described.
In the above embodiment, the aspect ratio of the passing area 60A (FIG. 4) of the iris 60 (FIG. 2) on the front side is variable, but the aspect ratio of the passing area of the iris 70 on the rear side may be variable. Further, the aspect ratio of the passing regions of the two irises 60 and 70 may be variable.

In the above embodiment, the dimension of the second direction D2 of the passage region 60A of the iris 60 is fixed and the dimension of the first direction D1 is variable, but conversely, the dimension of the first direction D1 is fixed and the second direction is fixed. The dimension of the direction D2 may be variable. In this case, the opening 63 (FIG. 5A) provided in the first member 61 may be an ellipse long in the second direction D2, and the second member 62 may be composed of two members divided in the second direction. As the repetition frequency of the pulse is lowered, the dimension of the second direction D2 of the passing region 60A may be increased. As a result, it is possible to reduce the collapse of the beam cross section from the perfect circle.

Further, both the dimension of the first direction D1 and the dimension of the second direction D2 of the passing region 60A may be variable. This makes it possible to increase the degree of freedom in adjusting the shape of the beam cross section.

In the above embodiment, the pair of resonator mirrors 25 constitutes an optical resonator 20 having one linear optical axis 20A (FIG. 2), but various other reflecting mirrors are further arranged and folded back. An optical resonator may be configured. In this case, the optical resonator has, for example, a broken line optical axis, and the laser beam is confined along the broken line optical axis between the pair of resonator mirrors at both ends. The iris may be placed at any position in the path of the line-shaped laser beam confined in the optical cavity.

Next, a laser oscillator according to another embodiment will be described with reference to FIG. 7. Hereinafter, the description of the common configuration with the laser oscillator according to the embodiment shown in FIGS. 1 to 6 will be omitted.

FIG. 7 is a cross-sectional view perpendicular to the optical axis 20A of the laser oscillator according to the present embodiment. The first member 61 of the iris 60 is fixed to the resonator base 26. The two parts 62A and 62B of the second member 62 are supported by the resonator base 26 via the slide mechanism 65. Rods 66A and 66B are connected to the two parts 62A and 62B of the second member 62, respectively. The rods 66A and 66B extend from the two parts 62A and 62B in the first direction D1, respectively, pass through the side wall of the chamber 15, and are pulled out to the outside of the chamber 15. Airtightness is ensured at the locations where the rods 66A and 66B each penetrate the side wall of the chamber 15 by the sealing structures 67A and 67B including the O-ring.

When the rods 66A and 66B are operated from outside the chamber 15 and moved in the first direction D1, the two parts 62A and 62B of the second member 62 move in the first direction D1. As a result, the aspect ratio of the passing region 60A changes. The rods 66A and 66B have a function as an aspect ratio changing mechanism for changing the aspect ratio of the passing region 60A.

Next, the excellent effect of this embodiment will be described.
In this embodiment, the two parts 62A and 62B of the second member 62 can be moved from the outside of the chamber 15 to the first direction D1 via the rods 66A and 66B. Therefore, with the laser oscillator 12 oscillating, the aspect ratio of the passage region 60A of the iris 60 can be adjusted while observing the shape of the beam cross section with the beam profiler 50 (FIG. 1). This makes it easy to make adjustments to bring the beam cross section closer to a perfect circle.

Next, a laser oscillator according to still another embodiment will be described with reference to FIG. Hereinafter, the description of the common configuration with the laser oscillator according to the embodiment shown in FIGS. 1 to 6 will be omitted.

FIG. 8 is a perspective view of the iris 60 used in the laser oscillator according to the present embodiment. In the embodiment shown in FIGS. 1 to 6, the second member 62 (FIG. 5A) is divided into two in the first direction D1. On the other hand, in this embodiment, neither the first member 61 nor the second member 62 is divided. Like the first member 61, the second member 62 is made of a plate material having an opening 64. The first member 61 and the second member 62 are independently movably supported in the first direction D1 by the slide mechanism 65.

The region where the opening 63 of the first member 61 and the opening 64 of the second member 62 overlap when the iris 60 is viewed from the front corresponds to the passage region 60A of the iris 60. When the relative positional relationship between the first member 61 and the second member 62 in the first direction D1 is changed, the dimension of the first direction D1 of the passing region 60A changes. The dimension of the second direction D2 of the passing region 60A also changes, but since the amount of change is small, the aspect ratio of the passing region 60A changes. Further, if the first member 61 and the second member 62 are moved in opposite directions by an equidistant distance, the dimension of the passing region 60A in the first direction changes while the center position of the passing region 60A is fixed. do.

Next, the excellent effect of this embodiment will be described.
Also in this embodiment, by changing the aspect ratio of the passage region 60A of the iris 60, the beam cross section is almost a perfect circle even if the pulse repetition frequency is changed, as in the examples shown in FIGS. 1 to 6. The state of can be maintained.

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.

11 Stand 12 Laser oscillator 15 Chamber 16 Optical room 17 Blower room 18 Upper and lower partition plates 18A, 18B Opening 19 Bottom plate 20 Optical cavity 20A Optical axis 20B Area where light is confined between a pair of resonator mirrors 21 Discharge electrode 22 Electrode box 23 Electron support member 24 Discharge area 25 Resonator mirror 26 Resonator base 27 Optical cavity support member 28 Light transmission window 29 Blower 40 Partition plate 41 First gas flow path 42 Second gas flow path 43 Heat exchanger 44 Rectifier plate 45 Support point 50 Beam profiler 60 Iris 60A Passing area 60B Shading area 61 First member 62 Second member 62A, 62B Second member part 63 First member opening 64 Second member opening 65 Slide mechanism 66A, 66B Rod 67A, 67B Sealed structure 70 Iris
80 Machining equipment 81 Beam shaping optical system 82 Stage 90 Machining object 100 Common base

Claims (8)

An iris placed in the path of a laser beam confined in an optical cavity.
A passing region through which the laser beam confined in the optical resonator passes and a light-shielding region arranged around the passing region are defined, and each other is defined in a plane orthogonal to the optical axis of the optical resonator. An iris having a variable aspect ratio, which is the ratio of the dimensions of the passage area in two orthogonal directions. The dimension of the passage region in the first direction is variable among the two directions orthogonal to each other in the plane orthogonal to the optical axis of the optical resonator, and the passage in the second direction orthogonal to the first direction. The iris according to claim 1, wherein the dimensions of the area are fixed. The first member with an opening that is invariant in size,
A second member that is movably supported by the first member in the first direction and that closes a part of the area that has entered inward from the edge of the opening of the first member by moving in the first direction. Including
The iris according to claim 2, wherein a region of the opening of the first member that is not blocked by the second member is the passage region. The second member includes two parts divided in the first direction, and the two parts of the second member close a part of the opening of the first member from both sides in the first direction. The iris described in 3. An optical resonator that traps the laser beam,
A passing region through which the laser beam confined in the optical resonator passes and a light-shielding region arranged around the passing region are defined, and are orthogonal to each other in a plane orthogonal to the optical axis of the optical resonator. An iris with a variable aspect ratio, which is the ratio of the dimensions of the passage area in two directions.
The optical resonator, the iris, and the chamber accommodating the laser medium gas,
A laser oscillator having an aspect ratio changing mechanism that changes the aspect ratio of the passing region of the iris by operating from outside the chamber. The dimension of the passage region in the first direction is variable among the two directions orthogonal to each other in the plane orthogonal to the optical axis of the optical resonator, and the passage in the second direction orthogonal to the first direction. The laser oscillator according to claim 5, wherein the dimensions of the region are fixed. The iris is
The first member with an opening that is invariant in size,
A second member that is movably supported by the first member in the first direction and that closes a part of the area that has entered inward from the edge of the opening of the first member by moving in the first direction. Including
The laser oscillator according to claim 6, wherein the aspect ratio changing mechanism moves the second member in the first direction with respect to the first member. The second member includes two parts divided in the first direction, and the two parts of the second member close the opening of the first member from both sides in the first direction.
The laser oscillator according to claim 7, wherein the aspect ratio changing mechanism moves the two parts of the second member in the first direction, respectively.

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