KR20220148158A - Beam splitter and split ratio adjustment method - Google Patents

Abstract

On the path of the laser beam incident on the polarizing beam splitter, a first reflecting mirror, a second reflecting mirror, and a third reflecting mirror are sequentially disposed in the forward direction of the laser beam. The first reflecting mirror is supported by the first adjusting mechanism so as to be tilt-adjustable in a direction for changing the angle between the polarization plane of the light incident on the first reflecting mirror and the optical axis of the reflected light reflected by the first reflecting mirror. When the posture of the first reflecting mirror is changed by the first adjusting mechanism, the state in which the reflected light of the first reflecting mirror is incident on the second reflecting mirror and the state in which the reflected light of the second reflecting mirror is incident on the third reflecting mirror is maintained. A second reflecting mirror is supported by the second adjusting mechanism so that it is possible and tilt-adjustable. It becomes possible to fine-tune the polarization direction of the laser beam incident on the polarization beam splitter without increasing the number of optical components inserted into the optical path of the laser beam.

Description

Beam splitter and split ratio adjustment method

The present invention relates to a beam splitter for splitting a laser beam and a method for adjusting a branch ratio.

In order to increase the efficiency of laser processing, a biaxial laser processing apparatus that cuts out two pulses from one pulse of a pulsed laser beam output from a laser oscillator and performs processing with two laser beams is known (for example, the following patent See document 1). In the laser processing apparatus disclosed in Patent Document 1, one pulse of a pulsed laser beam is divided into two pulses on a time axis by an acoustooptic element, and the two pulses propagate through different optical paths, respectively. The acousto-optical element has a function of cutting out a processing pulse from one pulse, and a function of branching one optical path into two optical paths.

Patent Document 1: Japanese Patent Application Laid-Open No. 2013-71136

The angle formed by the two optical paths branched by the acoustooptic device is small. For this reason, it becomes easy to spatially interfere with the optical component to be arrange|positioned in the two optical paths after branching, and the position which arrange|positions an optical component is restricted. By using a polarization beam splitter that splits the laser beam into two paths according to the polarization direction instead of the acousto-optical element, it is possible to branch one optical path into two optical paths.

Due to the manufacturing non-uniformity of the polarizing beam splitter, the laser beam divergence ratio is non-uniform among individuals. In order to set the intensity of the two diverged laser beams to a target value, the polarization direction of the laser beam incident on the polarization beam splitter must be finely adjusted, and the intensity ratio of the P-polarization component and the S-polarization component must be finely adjusted. The intensity ratio of the P-polarization component and the S-polarization component can be adjusted using the Brewster window. If a Brewster window is inserted into the optical path of the laser beam only for adjusting the intensity ratio of the P-polarized light component and the S-polarized light component, the number of optical components increases. The increased optical component exerts various adverse effects such as thermal lensing effect on the convergence and divergence of the laser beam.

An object of the present invention is to provide a beam splitter capable of finely adjusting the polarization direction of a laser beam incident on a polarization beam splitter and a method for adjusting the split ratio without increasing the number of optical components inserted into the optical path of the laser beam. will be.

According to one aspect of the present invention,

A polarization beam splitter that splits the linearly polarized laser beam;

and a polarization direction adjustment optical system for guiding the incident laser beam to the polarization beam splitter,

The polarization direction adjustment optical system,

A first reflector, a second reflector, and a third reflector are sequentially disposed in the forward direction of the laser beam on the path of the laser beam incident on the polarization beam splitter;

a first adjusting mechanism for supporting the first reflecting mirror so as to be tilt-adjustable in a direction for changing an angle between the polarization plane of the light incident on the first reflecting mirror and the optical axis of the reflected light reflected from the first reflecting mirror;

When the posture of the first reflecting mirror is changed by the first adjusting mechanism, the reflected light of the first reflecting mirror is incident on the second reflecting mirror, and the reflected light of the second reflecting mirror is incident on the third reflecting mirror There is provided a beam splitter having a second adjusting mechanism for supporting the second reflecting mirror so as to be movable and tilt-adjustable in the direction of holding the .

According to another aspect of the present invention,

A first reflector, a second reflector, and a third reflector are sequentially formed in the forward direction of the laser beam on the path of the laser beam incident on the polarization beam splitter, which branches the linearly polarized laser beam by changing the branching ratio according to the polarization direction. place it,

performing tilt adjustment of the first reflecting mirror in a direction in which an angle between the polarization plane of the incident light to the first reflecting mirror and the optical axis of the reflected light reflected by the first reflecting mirror is changed,

Even after changing the posture of the first reflecting mirror by adjusting the movement and tilt of the second reflecting mirror, the state in which the reflected light of the first reflecting mirror is incident on the second reflecting mirror, and the reflected light of the second reflecting mirror 3 A branch ratio adjustment method for maintaining a state of being incident on a reflector is provided.

By performing the tilt adjustment of the first reflecting mirror and the movement and tilt adjustment of the second reflecting mirror, the polarization direction of the laser beam incident on the polarizing beam splitter can be adjusted without increasing the number of optical components.

1 is a schematic perspective view of a beam splitter according to an embodiment.
Fig. 2A is a schematic plan view showing the arrangement of each optical component of the beam splitter and the positional relationship of the optical axis of the laser beam, and Fig. 2B is the arrangement of each optical component and the positional relationship of the optical axis of the laser beam It is a schematic side view.
It is a schematic front view of a 2nd adjustment mechanism.
Fig. 4 is a schematic diagram of a laser processing apparatus according to a modification of the embodiment shown in Figs.
Fig. 5 is a schematic diagram showing the positional relationship between the first reflecting mirror, the second reflecting mirror, and the third reflecting mirror of the polarization direction adjusting optical system according to another embodiment.

A beam splitter according to an embodiment will be described with reference to FIGS. 1 to 3 .

1 is a schematic perspective view of a beam splitter according to an embodiment. On the optical platen 10, a laser light source 20, a polarization direction adjustment optical system 30, and a polarization beam splitter 40 are supported. The polarization direction adjustment optical system 30 includes a first reflecting mirror 31 , a second reflecting mirror 32 , a third reflecting mirror 33 , a first adjusting mechanism 36 , and a second adjusting mechanism 37 . An xyz orthogonal coordinate system is defined in which the upper surface of the optical surface plate 10 is the xy surface, and the normal direction of the image surface of the optical surface plate 10 is the z-axis direction. For example, the xy plane is a horizontal plane, and the z-axis is directed vertically upward.

Fig. 2A is a schematic plan view showing the arrangement of each optical component and the positional relationship of the optical axis of the laser beam, and Fig. 2B is the arrangement of each optical component and the positional relationship of the optical axis of the laser beam when viewed along the x-axis. It is a schematic side view showing In the following description, with reference to FIG. 1, reference is made to 2A and 2B of FIG. 2 as necessary.

The laser light source 20 outputs a linearly polarized laser beam. The optical axis of the laser beam output from the laser light source 20 is parallel to the upper surface of the optical surface plate 10 . For example, the optical axis of the laser beam output from the laser light source 20 is parallel to the xy plane, and the laser beam propagates in the negative direction of the x-axis. In this specification, the xy plane is referred to as a reference plane. The polarization direction (PD) of this laser beam is parallel to the y-axis. That is, the polarization plane is parallel to the xy plane. The laser beam output from the laser light source 20 is sequentially reflected by the first reflecting mirror 31 , the second reflecting mirror 32 , and the third reflecting mirror 33 to be incident on the polarizing beam splitter 40 .

The first reflecting mirror 31 is a polarization plane of an incident laser beam (hereinafter, referred to as incident light) and a laser beam reflected (hereinafter, The laser beam is reflected in the direction in which the optical axis of the reflected light becomes oblique. For example, the optical axis of the reflected light by the first reflecting mirror 31 is oblique to either the reference plane (xy plane) or the zx plane (see 2B in FIG. 2 ). In addition, the optical axis of the reflected light of the first reflecting mirror 31 is orthogonal to the optical axis of the incident light. That is, the optical axis of the reflected light of the first reflecting mirror 31 is parallel to the yz plane (see 2A in FIG. 2 ).

The first adjustment mechanism (36) is a tilt-adjustable first in a direction for changing an angle between the polarization plane of the incident light to the first reflecting mirror (31) and the optical axis of the reflected light reflected by the first reflecting mirror (31). The reflector 31 is supported (refer to 2B in FIG. 2). When the tilt adjustment of the first reflecting mirror 31 is performed, the optical axis of the reflected light by the first reflecting mirror 31 changes within a plane parallel to the yz plane, and the inclination angle from the reference plane (xy plane) (hereinafter referred to as elevation angle θ) do) is changed.

The optical axis of the light reflected by the second reflecting mirror 32 is perpendicular to the reference plane (xy plane) (see 2B in FIG. 2 ). In the second adjustment mechanism 37 , even when tilt adjustment of the first reflecting mirror 31 is performed, the reflected light of the first reflecting mirror 31 is incident on the second reflecting mirror 32 , and the second reflecting mirror 32 is The second reflecting mirror 32 is supported so as to be movable and tilt adjustable in a direction in which the reflected light is kept incident on the third reflecting mirror 33 (see 2B in FIG. 2 ). Even if the second reflecting mirror 32 moves, the position of the reflected light of the second reflecting mirror 32 in the xy plane of the optical axis does not change.

The third reflecting mirror 33 is fixed to the optical surface plate 10 . The optical axis of the reflected light of the third reflecting mirror 33 is parallel to the reference plane (xy plane), and the reflected light propagates in the positive direction of the x-axis (refer to 2A in Fig. 2). That is, the propagation direction of the reflected light of the third reflecting mirror 33 is antiparallel to the propagating direction of the incident light of the first reflecting mirror 31 . The reflected light of the third reflector 33 is incident on the polarization beam splitter 40 . The polarization direction PD of the reflected light of the third reflecting mirror 33 is inclined with respect to the xy plane according to the elevation angle θ (refer to 2B in FIG. 2 ). For example, when the elevation angle θ is 45°, the polarization plane of the reflected light of the third reflecting mirror 33 is inclined by 45° with respect to the xy plane.

The polarization beam splitter 40 splits the incident laser beam into two optical paths: an optical path parallel to the x-axis and an optical path parallel to the z-axis. The branch ratio depends on the polarization direction of the incident laser beam. When the polarization plane of the reflected light of the third reflection mirror 33 is inclined by 45° with respect to the xy plane, the split ratio of the laser beam by the polarization beam splitter 40 is approximately 1:1.

3 : is a schematic front view of the 2nd adjustment mechanism 37. As shown in FIG. A support member 51 is fixed to the optical surface plate 10 . The support member 51 has a guide surface parallel to the yz plane. On the guide surface of the support member 51, the lifting member 53 and the positioning block 52 are mounted so as to be movable in the z-axis direction. For example, the positioning block 52 is screwed to the support member 51 through a long hole 55 in the z-axis direction. The elevating member 53 is screwed to the support member 51 through a plurality of elongated holes 56 long in the z-axis direction. When positioning the lifting member 53 , first, the positioning block 52 is fixed to the support member 51 , and the downwardly facing surface of the lifting member 53 is the upper surface of the positioning block 52 . make contact with

A mirror holder 54 is mounted on the lifting member 53 . On the mirror holder 54, a second reflecting mirror 32 is supported so as to be tilt-adjustable.

Next, the excellent effect of the above embodiment will be described.

In the above embodiment, the tilt adjustment of the first reflecting mirror 31 is performed by the first adjusting mechanism 36, and by adjusting the elevation angle θ (2B in FIG. 2), the laser beam incident on the polarization beam splitter 40 is adjusted. The polarization direction can be adjusted. That is, the intensity ratio of the P-polarization component and the S-polarization component with respect to the polarization beam splitter 40 can be adjusted. Thereby, the individual difference in the branch ratio due to the non-uniformity in manufacturing of the polarization beam splitter 40 can be absorbed, and the intensity of the two branched laser beams can be made equal.

Next, the range of the tilt adjustment of the first reflecting mirror 31 and the movement range of the second reflecting mirror 32 in the x-axis direction will be described. What is necessary is just to set the range of the tilt adjustment of the 1st reflecting mirror 31 depending on the magnitude|size of the nonuniformity of the branch ratio of the polarization beam splitter 40 between individuals. If the range of the tilt adjustment of the first reflecting mirror 31 is enlarged, it is possible to cope with a larger non-uniformity of the branch ratio of the polarization beam splitter 40 between individuals. For example, in order to be able to cope with the normal non-uniformity between objects of the branching ratio of the general polarization beam splitter 40, the adjustable range of the elevation angle θ (2B in FIG. 2) includes the range of 45°±1°. , the range of the tilt adjustment of the first reflector 31 may be set.

The adjustable range of the elevation angle [theta] is sufficient as long as it can absorb the individual nonuniformity of the branch ratio of the polarization beam splitter 40, and it is not necessary to make it excessively large. When the adjustable range of the elevation angle θ (2B in FIG. 2) is increased, the movable range of the second reflecting mirror 32 is maintained in order to maintain the state in which the reflected light of the first reflecting mirror 31 is incident on the second reflecting mirror 32. should be large That is, the adjustable range by the support member 51 or the mirror holder 54 (FIG. 3) for movably supporting the second reflecting mirror 32 should be increased. If the movable range of the second reflecting mirror 32 is excessively large, it becomes difficult to respond by the support member 51 or the mirror holder 54 . For this reason, what is necessary is just to set the range of the tilt adjustment of the 1st reflecting mirror 31 so that the elevation angle θ can be adjusted within the range of 45°±5°.

If the interval between the optical axis of the incident light of the first reflecting mirror 31 and the optical axis of the reflected light of the third reflecting mirror 33 is expressed as L, the height from the third reflecting mirror 33 to the second reflecting mirror 32 is L×tanθ do. When the elevation angle θ can be adjusted within the range of 45°±5°, the height of the second reflecting mirror 32 may be movable within the range of L×tan40° to L×tan50°. If the second reflecting mirror 32 is movable within this range, even if the tilt adjustment of the first reflecting mirror 31 is performed, the state in which the reflected light of the first reflecting mirror 31 is incident on the second reflecting mirror 32 can be maintained. have. As an example, when the space|interval L is 143 mm, what is necessary is just to make it possible to adjust the height from the 3rd reflecting mirror 33 to the 2nd reflecting mirror 32 in the range of 120.0 mm or more and 170.4 mm or less.

In addition, the first reflecting mirror 31, the second reflecting mirror 32, and the third reflecting mirror 33 used in the above embodiment generally set the polarization direction of the laser beam output from the laser light source 20 to 45 ° It is an optical component necessary for turning. In the above embodiment, it is possible to fine-tune the polarization direction without additionally disposing a dedicated optical component for fine-tuning the polarization direction, for example, a Brewster window or the like on the optical axis of the laser beam. For this reason, the influence, etc. on the convergence divergence of a laser beam due to an increase in the number of optical components can be reduced.

Further, in the above embodiment, the optical axis of the laser beam between the second reflecting mirror 32 and the third reflecting mirror 33 even when the elevation angle θ (2B in FIG. 2) is changed by adjusting the tilt of the first reflecting mirror 31. does not move in the xy-plane direction. For this reason, it is not necessary to perform position adjustment or tilt adjustment of the third reflecting mirror 33 at the time of adjustment of the polarization direction. Further, even when the tilt adjustment of the first reflecting mirror 31 is performed, the interval between the optical axis of the laser beam output from the laser light source 20 and the optical axis of the laser beam incident on the polarization beam splitter 40 remains unchanged. Therefore, even if the polarization direction is adjusted, it is not necessary to adjust the relative positional relationship between the laser light source 20 and the polarization beam splitter 40 .

Next, a modified example of the above embodiment will be described.

In the above embodiment, the polarization direction of the laser beam output from the laser light source 20 is parallel to the y-axis direction, but may be parallel to the z-axis direction. Further, in the above embodiment, although the propagation direction of the laser beam output from the laser light source 20 and the propagation direction of the laser beam incident on the polarization beam splitter 40 are antiparallel, both may be parallel.

In the above embodiment, the optical axis of the laser beam reflected by the polarization beam splitter 40 is parallel to the z-axis, but it may be parallel to the y-axis. Incidentally, although the optical axis of the reflected light of the first reflecting mirror 31 is changed in the yz plane in the above embodiment, it may be changed in a plane inclined with respect to the x-axis.

Next, with reference to FIG. 4, a laser processing apparatus according to another embodiment will be described.

Fig. 4 is a schematic diagram of a laser processing apparatus according to the present embodiment. A laser light source 20 , a polarization direction adjustment optical system 30 , a polarization beam splitter 40 , and a fold mirror 23 are supported on the upper surface of the optical platen 10 . However, if necessary, an optical component for adjusting the beam diameter or divergent convergence of the laser beam, for example, an aperture, a beam expander, and the like is disposed. The polarization direction of the laser beam output from the laser light source 20 is adjusted by the polarization direction adjustment optical system 30 and is incident on the polarization beam splitter 40 . As the polarization direction adjustment optical system 30, the polarization direction adjustment optical system 30 according to the embodiment shown in Figs.

The laser beam whose polarization direction is adjusted in the polarization direction adjustment optical system 30 is split into two by the polarization beam splitter 40 . The laser beam reflected by the polarization beam splitter 40 passes through an opening provided in the optical platen 10 and is incident on the beam injector 24A disposed under the optical platen 10 . The laser beam traveling straight through the polarization beam splitter 40 is reflected downward by the fold mirror 23 , passes through an opening provided in the optical surface plate 10 , and a beam injector 24B disposed under the optical surface plate 10 . ) is entered into

The laser beam scanned by the beam scanners 24A and 24B passes through the condensing lenses 25A and 25B, respectively, and is incident on the objects 60A and 60B. The objects to be processed 60A and 60B are, for example, printed wiring boards, and drilling is performed by the incident of a laser beam.

The objects to be processed 60A and 60B are held movably in the inward direction of the substrate by the moving mechanism 70 . A power meter 26 is attached to the moving mechanism 70 . By making one of the two laser beams incident on the power meter 26, the power of the laser beam can be measured. The control device 71 controls the laser light source 20 , the beam scanners 24A and 24B, and the moving mechanism 70 .

Next, the excellent effect of this embodiment is demonstrated.

By adjusting the polarization direction of the laser beam incident on the polarization beam splitter 40 by the polarization direction adjustment optical system 30 while measuring the respective powers of the two laser beams with the power meter 26, power can be equal. As the polarization direction adjustment optical system 30, since the polarization direction adjustment optical system 30 according to the embodiment shown in Figs. It is possible to fine-tune the polarization direction without arranging the light beam on the optical axis of the laser beam.

Next, a modified example of the above embodiment will be described. In the above embodiment, one power meter 26 is used to measure the respective powers of the two laser beams, but as a modification, the moving mechanism 70 may be equipped with two power meters. If two power meters are installed, the power of two laser beams can be measured simultaneously. For this reason, the effect that the adjustment of the polarization direction adjustment optical system 30 for making the power of two laser beams equal becomes easy is acquired.

Next, a polarization direction adjustment optical system according to another embodiment will be further described with reference to FIG. 5 . Hereinafter, a description of the configuration common to the polarization direction adjustment optical system 30 according to the embodiment shown in FIGS. 1 to 3 will be omitted.

5 is a schematic diagram showing the positional relationship between the first reflecting mirror 31, the second reflecting mirror 32, and the third reflecting mirror 33 of the polarization direction adjusting optical system 30 according to the present embodiment. In the embodiment shown in Fig. 2B, the moving direction of the second reflecting mirror 32 is parallel to the z-axis. For this reason, when the tilt adjustment of the first reflecting mirror 31 is performed, the optical path length between the first reflecting mirror 31 and the second reflecting mirror 32 and the second reflecting mirror 32 and the third reflecting mirror 33 are adjusted. both of the optical path lengths of On the other hand, in the present embodiment, when the tilt of the first reflecting mirror 31 is adjusted, the second reflecting mirror 32 moves along a circular arc 38 centering on the incident point of the laser beam of the third reflecting mirror 33 . . For this reason, even if the polarization direction is adjusted, the optical path length between the second reflecting mirror 32 and the third reflecting mirror 33 does not change, and the distance between the first reflecting mirror 31 and the second reflecting mirror 32 is not changed. Only the light path length changes.

Next, the excellent effect of this embodiment is demonstrated.

In this embodiment, as in the embodiment shown in Figs. 1 to 3, a dedicated optical component for finely adjusting the polarization direction, for example, a Brewster window, etc., is not disposed on the optical axis of the laser beam, and the polarization direction It is possible to fine-tune the

Next, a modified example of the above embodiment will be described.

In the above embodiment, when the tilt adjustment of the first reflecting mirror 31 is performed, the optical path length between the second reflecting mirror 32 and the third reflecting mirror 33 is not changed, and the first reflecting mirror 31 and the second reflecting mirror 31 are not changed. The optical path length between the reflecting mirrors 32 is changed. Conversely, even with a configuration in which the optical path length between the second reflecting mirror 32 and the third reflecting mirror 33 is changed without changing the optical path length between the first reflecting mirror 31 and the second reflecting mirror 32, do.

Each of the above-described embodiments is an example, and it goes without saying that partial substitutions or combinations of configurations shown in different embodiments are possible. The same operation and effect due to the same configuration of the plurality of embodiments will not be separately mentioned for each embodiment. In addition, the present invention is not limited to the above-described embodiment. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like are possible.

10 optical plate
20 laser light source
23 fold mirror
24A, 24B beam syringe
25A, 25B condensing lens
26 power meter
30 Polarization direction adjustment optical system
31 first reflector
32 second reflector
33 third reflector
36 first adjustment mechanism
37 second adjustment mechanism
38 arc
40 Polarizing Beam Splitter
51 support member
52 positioning block
53 Elevating member
54 mirror holder
55, 56 long hole
60A, 60B processing object
70 moving mechanism
71 control

Claims (8)

A polarization beam splitter that splits the linearly polarized laser beam;
and a polarization direction adjustment optical system for guiding the incident laser beam to the polarization beam splitter,
The polarization direction adjustment optical system,
A first reflector, a second reflector, and a third reflector are sequentially disposed in the forward direction of the laser beam on the path of the laser beam incident on the polarization beam splitter;
a first adjusting mechanism for supporting the first reflecting mirror so as to be tilt-adjustable in a direction for changing an angle between the polarization plane of the light incident on the first reflecting mirror and the optical axis of the reflected light reflected from the first reflecting mirror;
When the posture of the first reflecting mirror is changed by the first adjusting mechanism, the reflected light of the first reflecting mirror is incident on the second reflecting mirror, and the reflected light of the second reflecting mirror is incident on the third reflecting mirror A beam splitter having a second adjusting mechanism for supporting the second reflecting mirror so as to be movable and tilt-adjustable in a direction for maintaining the . According to claim 1,
the first adjusting mechanism supports the first reflecting mirror so as to be tilt-adjustable in a direction for changing the optical axis of the reflected light in a plane perpendicular to the optical axis of the incident light to the first reflecting mirror;
The second adjustment mechanism is movable and tilt adjustable in a direction to change at least one of an optical path length from the first reflecting mirror to the second reflecting mirror and an optical path length from the second reflecting mirror to the third reflecting mirror A beam splitter for supporting the second reflector. 3. The method of claim 1 or 2,
The optical axis of the light incident on the first reflecting mirror and the optical axis of the reflected light of the third reflecting mirror are parallel to the reference plane. 4. The method of claim 3,
An optical axis of the laser beam from the second reflecting mirror to the third reflecting mirror is perpendicular to the reference plane,
The second adjusting mechanism is a beam splitter for supporting the second reflecting mirror so as to be movable in a direction orthogonal to the reference plane. A first reflector, a second reflector, and a third reflector are sequentially formed in the forward direction of the laser beam on the path of the laser beam incident on the polarization beam splitter, which branches the linearly polarized laser beam by changing the branching ratio according to the polarization direction. place it,
performing tilt adjustment of the first reflecting mirror in a direction in which an angle between the polarization plane of the incident light to the first reflecting mirror and the optical axis of the reflected light reflected by the first reflecting mirror is changed,
Even after changing the posture of the first reflecting mirror by adjusting the movement and tilt of the second reflecting mirror, the state in which the reflected light of the first reflecting mirror is incident on the second reflecting mirror, and the reflected light of the second reflecting mirror 3 A branch ratio adjustment method that maintains the state of being incident on the reflector. 6. The method of claim 5,
When the tilt adjustment of the first reflecting mirror is performed, the optical axis of the reflected light is changed in a plane perpendicular to the optical axis of the incident light to the first reflecting mirror;
Branch ratio adjustment for changing at least one of the optical path length from the first reflecting mirror to the second reflecting mirror and the optical path length from the second reflecting mirror to the third reflecting mirror when the second reflecting mirror is moved and tilted Way. 7. The method according to claim 5 or 6,
An optical axis of the light incident on the first reflecting mirror and the optical axis of the reflected light of the third reflecting mirror are parallel to a reference plane. 8. The method of claim 7,
An optical axis of the laser beam from the second reflecting mirror to the third reflecting mirror is perpendicular to the reference plane,
A branch ratio adjusting method of moving the second reflecting mirror in a direction perpendicular to the reference plane when the position and posture of the second reflecting mirror are changed.

Images