JPWO2017126363A1 - Power balance device and laser processing device for laser light - Google Patents

Abstract

A laser processing apparatus capable of easily performing stable laser processing on a workpiece and a power balance apparatus for laser light used in the laser processing apparatus are obtained. A diffraction grating in which a plurality of convex portions made of the same material as the substrate material extend linearly in parallel with each other at a set period P is formed on one main surface side of a pair of opposing main surfaces. A polarization phase difference plate formed by using birefringence and receiving a far-infrared laser beam, wherein the period P of the diffraction grating is P <λ / n (λ is a wavelength of incident light, n is a power balance device for laser light that includes a material that satisfies the refractive index of the substrate material) and a rotation mechanism that rotates the polarization phase difference plate.

Description

  The present invention relates to a laser processing apparatus for drilling a workpiece such as a printed circuit board, and more particularly to a power balance apparatus for laser light and a laser processing apparatus using the power balance apparatus.

As a method of improving the productivity of a CO ₂ laser processing apparatus that drills a workpiece such as a printed circuit board, one laser beam generated by a laser oscillator is divided into a plurality of holes, and a plurality of holes are drilled simultaneously. There is a way. In this method, when the energy of each of the divided laser beams is not uniform, the processing quality such as the processing hole diameter varies.

  For this reason, in the method described in Patent Document 1 below, a polarization azimuth adjusting polarizer having a rotation adjusting mechanism about the optical axis is provided upstream of the spectral polarizer in the optical path. Then, by adjusting the polarization azimuth angle of the transmitted P wave, the balance between the polarization direction P wave component and the polarization direction S wave component incident on the spectroscopic polarizer is adjusted, and the P wave transmitted through the spectroscopic polarizer. The energy of the laser beam divided into the component and the S wave component reflected by the spectroscopic polarizer is uniformly adjusted.

  Patent Document 2 below describes an example of adjusting the power balance of YAG laser light. A transmission type ¼ wavelength (π / 2) phase difference plate having a rotation adjusting mechanism for adjusting the rotation about the optical axis is provided upstream of the optical polarizer for the spectroscopic polarizer and is incident on the spectroscopic polarizer. By adjusting the polarization direction P wave component and the polarization direction S wave component, the processing energy is adjusted uniformly.

  In Patent Document 3 below, the generation of a thermal lens is prevented by using a polarization azimuth adjustment mechanism that uses only S-polarized light without using transmitted light.

  In recent years, in a drilling machine such as a printed circuit board, the output of laser light has been improved due to high energy processing such as through holes and improvement in processing speed.

International Publication No. 2003/085221 Pamphlet JP-A-9-108878 (FIG. 1) JP 2011-251306 A JP 2014-29467 A

In the above conventional technique, for example, in the configuration described in Patent Document 1, the P wave component transmitted through the polarization azimuth adjusting polarizer is propagated downstream in the optical path. For this reason, when the power of the laser beam incident on the polarizer is high, the beam diameter of the laser beam changes due to the thermal lens effect of the substrate material of the polarizer, and the mask is transmitted through the mask compared to the case where the thermal lens effect does not occur. The energy intensity of the laser beam to be scattered varies. Thereby, there existed a problem that the processing quality of a to-be-processed object deteriorated or became unstable.
Further, when the polarizer is rotated and adjusted at the time of adjusting the polarization azimuth angle, there is a problem that a slight shift occurs in the center of the optical axis due to light refraction, and the processing quality of the workpiece may be deteriorated.
The configuration described in Patent Document 2 is for YAG laser light having a wavelength of about 1 μm and cannot transmit far-infrared light. Birefringent materials that transmit far-infrared light include cadmium sulfide (CdS), but they are poisonous and difficult to handle.
Further, in the configuration described in Patent Document 3, only transmitted light is used and only S-polarized light is used, which is inefficient.

  The present invention has been made in view of the above, a laser processing apparatus capable of easily performing stable laser processing on a workpiece, and a power balance for laser light used in the laser processing apparatus. The object is to obtain a device.

  According to the present invention, a diffraction grating in which a plurality of convex portions made of the same material as the substrate material extend linearly in parallel with each other at a set period P is formed on one main surface side of a pair of opposing main surfaces, A polarization phase difference plate formed by using structural birefringence of a grating and receiving laser light of far-infrared light, wherein the period P of the diffraction grating is P <λ / n (λ is incident) A power balance device for laser light and the like, which includes a light wavelength (n is the refractive index of the substrate material) and a rotation mechanism that rotates the polarization phase difference plate.

  The present invention provides a laser processing apparatus capable of easily performing stable laser processing on a workpiece and a power balance apparatus for laser light used in the laser processing apparatus.

It is a figure which shows an example of a structure of the laser processing apparatus by Embodiment 1 of this invention. It is a perspective view which shows the structure of an example of the polarization phase difference plate of the subwavelength grating structure of FIG. It is a figure which shows an example of a structure of the laser processing apparatus by Embodiment 2 of this invention. It is a see-through | perspective side view which shows the internal division structure of an example of the power balance apparatus for lasers of FIG. It is a see-through | perspective side view which shows the internal distribution structure of another example of the power balance apparatus for lasers of FIG. It is a figure for demonstrating the influence of the thermal lens phenomenon which concerns on this invention. It is a figure for demonstrating the effect of suppression of the thermal lens phenomenon which concerns on this invention.

  According to the present invention, a power balance device using a material having a high transmittance in far infrared light can be configured by the sub-wavelength grating structure, thereby preventing a thermal lens and obtaining a high processing quality even with a high output beam. And the power balance apparatus for the laser beam used with this laser processing apparatus is provided.

  Hereinafter, a laser processing apparatus according to the present invention and a power balance apparatus for laser light used in the laser processing apparatus will be described with reference to the drawings according to each embodiment. In each embodiment, basically, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

Embodiment 1 FIG.
FIG. 1 is a diagram showing an example of the configuration of a laser processing apparatus according to Embodiment 1 of the present invention.
<Configuration of laser processing equipment>
The laser processing apparatus 100 splits one laser beam 2 into two dispersed laser beams 8A and 8B by a polarization beam splitter 7 serving as a spectroscopic unit. In general, the two dispersed laser beams 8A and 8B are scanned independently, and finally the two workpieces 13A and 13B on the XY tables 12A and 12B are passed through the fθ lenses 11A and 11B. Drill holes at the same time.
The irradiation position of the dispersed laser beam 8A on the workpiece 13A is moved by the galvano scanner 10Ax in the X direction, and the galvano scanner 10Ay is moved in the Y direction. Similarly, the irradiation position of the dispersed laser beam 8B on the workpiece 13B is moved by the galvano scanner 10Bx in the X direction, and the galvano scanner 10By is moved in the Y direction. The X direction and the Y direction are coordinates orthogonal to each other in the plane of the workpieces 13A and 13B, as in the XY table, and are different from the xyz direction in the polarization phase difference plate 200 described later.

  In the laser processing apparatus 100 according to the first embodiment, a polarization phase difference plate 200 having a sub-wavelength grating structure is disposed upstream of the polarization beam splitter 7 in the optical path. The polarization phase difference plate 200 is configured to be rotatable around the optical axis by a rotation mechanism 220.

<Sub-wavelength grating polarization plate>
The polarization phase difference plate 200 having a sub-wavelength grating structure capable of transmitting far-infrared light has a structure as shown in Patent Document 4, for example. FIG. 2 is a perspective view showing an example of the configuration of a polarization phase difference plate 200 having a sub-wavelength grating structure shown in FIG. The polarization phase difference plate 200 on which the laser light is incident includes a substrate 202 and a diffraction grating 201 formed of the same material as the substrate 202 on one main surface of a pair of opposing main surfaces of the substrate 202. The diffraction grating 201 sets, along the y direction, a plurality of convex portions 203 extending linearly in parallel to the x direction in the x, y, and z directions indicating directions orthogonal to each other with the x and y directions as the substrate surface. Aligned and formed at set intervals according to the period P.

When light enters the diffraction grating 201 along the z direction,
an effective refractive index for the polarization component in the x direction (TE polarization);
an effective refractive index for the polarization component in the y direction (TM polarization);
Become different from each other, and so-called structural birefringence occurs. As a result, a propagation speed difference occurs between the TE polarized light and the TM polarized light, and elliptically polarized light is generated according to the phase difference (retardation) corresponding to the propagation speed difference.

P <λ / n (1)
P: Period (interval) of diffraction grating
λ: wavelength of incident light n: refractive index of substrate material

It is known that if the above formula (1) is satisfied, loss of high-order diffracted light can be prevented even with vertically incident light. The cross-sectional shape of the convex portion 203 is formed into a tapered shape 206 having an angle α from the bottom to the top.
In particular,
The substrate material of the substrate 202 is zinc sulfide (ZnS),
The height H of the convex portion 203, that is, the depth of the groove is 4.01 μm,
The inclination angle α of the tapered shape 206 is 22.2 degrees.
The filling factor f is 0.468,
The retardation is λ / 8 (= π / 4).
The filling factor f is a ratio of the width W of the convex portion 203 to the period P at a position (H / 2) that is half the height H of the convex portion 203, that is, a value of f = W / P.
An antireflection film 207 is provided on the other main surface of the substrate 202 without the diffraction grating 201. The material of the antireflection film 207 is germanium.

<Linear polarization of oscillator>
The laser oscillator 1 is a laser device that emits laser light 2 (λ = 9.29 μm), which is far-infrared light, for example, linearly polarized CO ₂ laser light, as a pulse wave. The laser light 2 emitted from the laser oscillator 1 is guided to a polarization phase difference plate 200 that is a sub-wavelength grating phase difference plate via one or a plurality of reflection mirrors 6. The reflection mirror 6 is a mirror that reflects the laser beam 2 and the dispersed laser beams 8A and 8B and guides them downstream in the optical path. The reflection mirror 6 is disposed at various positions on the optical path in the laser processing apparatus 100.

<Polarized beam splitter>
A polarizing beam splitter 7 which is a polarizing beam splitter for spectroscopy is a polarizer such as a beam splitter that splits one beam-like laser beam 2 into two dispersed laser beams 8A and 8B. The polarization beam splitter 7 has a property of transmitting the P wave component of the laser light 2 and reflecting the S wave component.

<Operation of laser processing equipment>
Next, an operation processing procedure of the laser processing apparatus 100 will be described. The laser beam 2 having the polarization azimuth angle θ guided from the laser oscillator 1 is transmitted through the polarization phase difference plate 200 having the sub-wavelength grating structure and then guided to the mask 4 through the beam variable unit 5.
In the mask 4, only a desired portion of the laser beam 2 is transmitted to shape the laser beam 2 into a beam mode shape suitable for laser processing. The laser beam 2 shaped by the mask 4 is reflected by one or a plurality of reflecting mirrors 6 and guided to the polarization beam splitter 7.
In the polarization beam splitter 7, the P-wave polarization component of the laser beam 2 passes through the polarization beam splitter 7 and is emitted as the dispersed laser beam 8 </ b> A. Further, the S-wave polarization component of the laser beam 2 is reflected by the polarization beam splitter 7 and emitted as a dispersed laser beam 8B. In order not to cause variations in the quality of the processed holes of the two workpieces 13A and 13B, it is necessary that the energy of the dispersed laser light 8A and the energy of the dispersed laser light 8B are equal.

<Thermal lens>
The thermal lens effect is caused by the fact that the substrate material locally rises in temperature when high-power laser light is transmitted through the substrate material of the polarization phase difference plate 200 having the sub-wavelength grating structure of FIG. This is a phenomenon in which the refractive index distribution of the polarizer is generated, and thereby the polarizer acts as a lens.
For example, in the case of the above-mentioned Patent Document 1, the thermal lens effect is derived from the polarization azimuth adjusting polarizer.

<Influence on thermal lens processing>
FIG. 6 is a diagram for explaining the thermal lens phenomenon when the P wave component transmitted through the conventional polarizer 17 corresponding to the polarization phase difference plate 200 according to the present invention is guided downstream of the optical path of the polarizer 17. . FIG. 6A shows the laser beam intensity distribution when the thermal lens phenomenon does not occur. FIG. 6B shows the laser beam intensity distribution when the thermal lens phenomenon occurs.

  When the thermal lens phenomenon shown in FIG. 6A does not occur, the laser light emitted from the laser oscillator 1 has a laser beam intensity distribution A1. When the thermal lens phenomenon shown in FIG. 6B occurs, the laser light emitted from the laser oscillator 1 has a laser beam intensity distribution B1. The laser beam intensity distribution B1 has the same intensity distribution as the laser beam intensity distribution A1.

  Then, the laser beam 2 from the laser oscillator 1 passes through the polarizer 17. Here, for example, the polarizer 17 is disposed at the same position as that of a conventional polarization azimuth adjusting device. At this time, if the thermal lens phenomenon does not occur, the laser beam having the laser beam intensity distribution A1 is transmitted through the polarizer 17 to become a laser beam having the laser beam intensity distribution A2. If the thermal lens phenomenon has occurred, the laser beam with the laser beam intensity distribution B1 passes through the polarizer 17 and becomes a laser beam with a laser beam intensity distribution B2 different from the laser beam intensity distribution A2.

  When the thermal lens phenomenon occurs in the polarizer 17 as shown in FIG. 6B, compared to the case where the thermal lens phenomenon does not occur in the polarizer 17 as shown in FIG. The beam diameter of the laser beam on the mask 4 changes. Since the degree of the thermal lens phenomenon depends on the power of the laser light incident on the polarizer 17, the beam energy of the laser light transmitted through the mask 4 varies depending on whether the thermal lens phenomenon occurs or not. Therefore, the energy of the laser light reaching the workpieces 13A and 13B in FIG. 1 varies depending on whether the thermal lens phenomenon occurs or not. Specifically, when the thermal lens phenomenon does not occur, the laser beam having the laser beam intensity distribution A3 is guided downstream in the optical path. When the thermal lens phenomenon occurs, the laser beam having a laser beam intensity distribution B3 different from the laser beam intensity distribution A3 is guided downstream in the optical path. As a result, there is a difference in the quality of the processed hole of the workpiece depending on whether the thermal lens phenomenon occurs or not.

<Discovering the problem of absorption by TFP. Can also be used with transmission type>
In the first embodiment, similarly to the above-mentioned Patent Document 1, the point that the laser beam is transmitted through the thick substrate in the polarization phase difference plate 200 is the same, so that the thermal gradient is similarly caused by the temperature gradient in the radial direction of the substrate. It is thought that the lens phenomenon occurs.
On the other hand, as a result of the investigation according to the present invention, the TFP (thin film polarizer) used in the polarizing beam splitter according to Patent Document 1 is actually used as a ThF having a thickness of 1 μm or more. ₄ (Thorium fluoride) was stacked in layers. Specifically, four or more ThF ₄ (thorium fluoride) layers are stacked. As a result of measuring the absorption coefficient of ThF _{4 in} the film state, it was 19 [cm ⁻¹ ], which was 38000 times that of the base material ZnSe (zinc selenide) (5e ⁻⁴ [cm ⁻¹ ]). When the total film thickness of ThF ₄ is about 5 μm and the substrate thickness of ZnSe is 5 mm, ThF ₄ absorbs laser light 38 times. Since the heat absorbed by the TFP is a thin film, the thermal conductivity in the radial direction is poor and a temperature difference in the radial direction is generated. That is, it was found that the influence of heat absorption in TFP is dominant.

<Operation and effect of sub-wavelength grating structure>
On the other hand, in the first embodiment, the power balance device using the polarization phase difference plate 200 having the sub-wavelength grating structure can be configured only with a substrate material having a high transmittance in far-infrared light. Can be eliminated. As a result, it is possible to form the machining holes with stable machining quality in the workpieces 13A and 13B without being affected by the thermal lens phenomenon.
Further, in the first embodiment, ZnS (zinc sulfide) is used as a base material, that is, a material of the substrate 202 of the polarization phase difference plate 200 shown in FIG. Among infrared transmitting materials, ZnS with a low refractive index is used for the substrate to prevent Fresnel reflection, and a film of a material having a high absorption rate such as YF ₃ (yttrium fluoride) is not provided on the lattice. However, the wavelength plate, that is, the polarization phase difference plate 200 can be formed of a single material with little absorption of ZnS, and generation of a thermal lens can be suppressed.
Further, the thermal conductivity of ZnSe is 18 [W / (mK)], whereas the thermal conductivity of ZnS is as large as 27.2 [W / (mK)]. Can be suppressed.

  As an example, when a polarization azimuth adjusting device using a conventional polarization azimuth adjusting polarizer described in Patent Document 1 is installed as a power balance device of a laser processing device, a polarization phase difference plate having a sub-wavelength grating structure FIG. 7 shows the result of evaluating the influence of the thermal lens phenomenon when a power balance device using 200 is installed. The power balance device of the laser processing apparatus is disposed at the same position as in the first embodiment. The laser beam from the laser oscillator 1 is transmitted through the power balance device, and then is transmitted through the beam variable unit 5 only through a desired portion through the mask 4.

  (A) of FIG. 7 arrives at the workpiece with respect to the pulse generation frequency of the laser oscillator when the conventional polarization azimuth adjusting device described in Patent Document 1 is installed as the power balance device of the laser processing device. It is a measurement result of the change rate of the energy intensity of a laser beam. The horizontal axis shows the pulse generation frequency (pulse frequency) of the laser oscillator, and the vertical axis shows the rate of change of the energy intensity of the laser beam reaching the workpiece (working point energy change rate).

  The higher the pulse frequency, the higher the power of the laser light incident on the power balance device. The machining point energy change rate is a value obtained by dividing the machining point energy when the pulse frequency is as low as about 200 Hz as a denominator and the machining point energy at each pulse frequency as a numerator. When the pulse frequency is low, the machining point energy change rate is small, and as the pulse frequency increases, the machining point energy change rate increases. This indicates that the higher the power of the laser light transmitted through the polarization azimuth adjusting device, the greater the thermal lens effect and the greater the rate of change in the energy intensity of the laser light transmitted through the mask.

  FIG. 7B shows a workpiece for the frequency of pulse generation of the laser oscillator when a power balance device using the polarization phase difference plate 200 having a sub-wavelength grating structure is installed as the power balance device of the laser processing device. It is a measurement result of the change rate of the energy intensity of the laser beam which reaches | attains. When the pulse frequency is changed from 200 Hz to 2400 Hz, the change range of the processing point energy change rate is about 7.5% when a conventional polarization azimuth adjusting device is installed, and a polarization phase difference plate with a sub-wavelength grating structure When the power balance device using 200 is installed, it is about 6%, and the generation of the thermal lens is suppressed by using the power balance device using the polarization phase difference plate 200 having the sub-wavelength grating structure in the laser processing device. It has been shown.

  FIG. 7 shows a proportional relationship between the pulse frequency and the processing point energy change rate. The higher the pulse frequency of the laser light from the laser oscillator 1 and the higher the power of the laser light, the higher the polarization phase difference of the sub-wavelength grating structure. The effect of suppressing the thermal lens by the power balance device using the plate 200 is increased, and high processing quality can be obtained even with a high output beam.

<Other merits of transmission type retardation plate method>
In Patent Document 1, the downstream optical axis changes depending on the rotation angle around the optical axis of the polarization direction adjusting device, and in Patent Document 3 depends on the angle of the reflecting surface with respect to the optical axis. The optical axis of the transmitted light does not change due to the misalignment or inclination of the polarization phase difference plate 200. For this reason, a rotation mechanism with low precision may be sufficient, and cost can be reduced.

<Effect of making retardation less than π / 2 (90 degrees), subject of subwavelength grating application>
For the retardation plate of Patent Document 2, examples of π and π / 2 are disclosed. In the subwavelength grating structure, in order to obtain retardation of π or π / 2, a thin and deep high-aspect-ratio fine structure is required, so that there is a problem that processing is difficult.

The retardation required for power balance adjustment is calculated below.
The separation directions indicated by 9A and 9B of the polarization beam splitter (PBS) 7 shown in FIG.
The polarization azimuth angle of linearly polarized light incident on the polarization beam splitter 7 is θ,
The retardation of the polarization phase difference plate 200 is φ,
The fast axis angle which is the TM polarization direction of FIG.
Then, the incident light e0 is

Indicated by The light e1 after the incident light e0 passes through the polarization phase difference plate 200 is

It becomes. The light e1 is separated by the polarization beam splitter 7. The separated polarization components e1a and e1b are

It becomes.
The difference ΔP of the power of each polarized light with respect to the power of incident light is

It becomes.
From the above equation (5), the adjustment range of ΔP by changing ψ is that the second term is a fixed value and cos (4ψ-2θ) of the first term takes a value from −1 to 1,

It becomes.

  An adjustment range of about ± 10% is sufficient for adjusting the power balance of the laser processing apparatus. From the above formulas (5) and (6), the retardation φ required for the polarization phase difference plate 200 is

  φ> 0.64 rad = 37 degrees

It becomes.
Thus, in the case of a power balance device only, a retardation much smaller than 90 degrees has no practical problem, so that the depth of the groove, which is the height H of the convex portion 203 of the polarization phase difference plate 200, can be reduced. Can be shallow and can be manufactured.
Further, the smaller the retardation φ, the narrower the adjustment width when rotated, that is, the smaller the fluctuation of the balance with respect to the rotational angle position deviation, so there is also an advantage that the rotating mechanism can be manufactured at low cost.
In the first embodiment, the polarization phase difference plate 200 having a sub-wavelength grating structure and the rotation mechanism 220 constitute a power balance device for laser.

Embodiment 2. FIG.
FIG. 3 is a diagram showing an example of the configuration of a laser machining apparatus according to Embodiment 2 of the present invention. FIG. 4 is a perspective side view showing an internal configuration of an example of the laser power balance apparatus 300 of FIG. In the laser processing apparatus of the second embodiment shown in FIG. 3, the laser power balance apparatus 300 including the functions of the polarization phase difference plate 200 and the rotating mechanism 220 having the sub-wavelength grating structure of the first embodiment shown in FIG. Is provided. As shown in FIG. 4, the laser power balance device 300 has a polarization retardation plate 200 having a sub-wavelength grating structure superimposed on a copper mirror 210 as a mirror so that the grating structure faces the front. The O-ring 211 is inserted between the holding plate 212 of the mirror holder 214 and the surface of the polarization phase difference plate 200 and fixed so as to be sandwiched.

The incident laser beam 2 is transmitted through the polarization phase difference plate 200 having the sub-wavelength grating structure, reflected by the surface of the copper mirror 210, and once again transmitted through the polarization phase difference plate 200 having the sub-wavelength grating structure. Thus, since the light passes through the polarization phase difference plate 200 twice, the retardation of the polarization phase difference plate 200 may be half.
Further, the mirror holder 214 includes a rotation mechanism 213 that can rotate the entire mirror holder 214 around the normal line of the reflection surface of the copper mirror 210.
Other basic configurations are the same as those of the first embodiment shown in FIG.

<Effect of overlapping mirror and wave plate>
With the configuration as shown in FIG. 4, the back surface of the polarization phase difference plate 200 having the sub-wavelength grating structure and the reflection surface of the copper mirror 210 are in contact with each other, so that the heat absorbed by the polarization phase difference plate 200 flows in the direction of the copper mirror 210. The polarization phase difference plate 200 is cooled. Since the direction of heat flow is not the radial direction but the optical axis direction as indicated by the arrow HE, the occurrence of a temperature gradient in the radial direction can be suppressed. As a result, generation of a thermal lens can be prevented, and further high-power laser processing can be performed.

  FIG. 5 is a perspective side view showing another example of the laser power balance apparatus 300 of FIG. In FIG. 5, the convex side of the polarization retardation plate 200 having the sub-wavelength grating structure is directed to the surface side of the copper mirror 210, and the polarization retardation plate 200 having the sub-wavelength grating structure is opposite to the grating structure on the copper mirror 210. It is stored in the mirror holder 214 so that the main surface faces the front. In this case, since the lattice is not in contact with air, it is possible to prevent foreign matters such as dust from adhering.

As described above, according to the present invention, a power balance device and a laser processing device using a material having a high transmittance in far-infrared light can be configured by the sub-wavelength grating structure, thereby preventing a thermal lens and high processing even with a high output beam. Quality is obtained.
In addition, by setting the retardation of the polarization phase difference plate to less than π / 2, the aspect ratio of the grating of the polarization phase difference plate is reduced, and the manufacture is facilitated.
Moreover, since the material of the polarization phase difference plate is ZnS, the generation of a thermal lens can be prevented.
In addition, since the back of the polarization phase difference plate is brought into contact with the mirror and cooled by overlapping the mirror on the polarization phase difference plate, generation of a thermal lens can be prevented, and the retardation of the polarization phase difference plate 200 may be halved. .

  The power balance device and laser processing device for laser light according to the present invention are not limited to the above embodiments.

Industrial applicability

  The power balance device and laser processing apparatus according to the present invention can be applied to laser processing in many fields.

  DESCRIPTION OF SYMBOLS 1 Laser oscillator, 2 Laser beam, 4 Mask, 5 Beam variable part, 6 Reflecting mirror, 7 Polarizing beam splitter, 8A, 8B Dispersed laser beam, 10Ax, 10Ay, 10Bx, 10By Galvano scanner, 11A, 11B f (theta) lens, 12A, 12B XY table, 13A, 13B Workpiece, 17 Polarizer, 100 Laser processing device, 200 Polarization phase difference plate, 201 Diffraction grating, 202 Substrate, 203 Convex part, 206 Taper shape, 207 Antireflection film, 210 Copper mirror, 211 O-ring, 212 pressure plate, 213 rotation mechanism, 214 mirror holder, 220 rotation mechanism, 300 power balance device.

Claims (5)

A diffraction grating in which a plurality of convex portions made of the same material as the substrate material extend linearly in parallel with each other at a set period P is formed on one main surface side of a pair of opposing main surfaces. A polarization phase difference plate formed by using birefringence and receiving a far-infrared laser beam, wherein the period P of the diffraction grating is P <λ / n (λ is a wavelength of incident light, n satisfies the refractive index of the substrate material),
A rotation mechanism for rotating the polarization phase difference plate;
A power balance device for laser light.   The power balance device for laser light according to claim 1, wherein the retardation of the polarization phase difference plate is less than π / 2.   The power balance device for laser light according to claim 1 or 2, wherein a material of the polarization phase difference plate is made of ZnS.   The power balance device for laser light according to any one of claims 1 to 3, further comprising a mirror superimposed on a main surface of the polarization phase difference plate. A power balance device for laser light according to any one of claims 1 to 4,
A laser oscillator that generates the laser light with respect to a polarization phase difference plate of the power balance device;
A spectroscopic unit that splits the laser beam into two laser beams on an optical path from the polarization phase difference plate to the workpiece;
A laser processing apparatus comprising:

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