TWI620384B - Power balance device for laser beam, laser machining device - Google Patents

Abstract

An object of the present invention is to obtain a laser processing device that can easily perform stable laser processing of a workpiece and a power balancing device for laser light used in the laser processing device. The power balance device for laser light is provided with: a polarizing retardation plate, which is attached to one of the main surfaces of the pair of front and back surfaces, and is formed with a plurality of convex portions made of the same material as the substrate The setting periods P are linear diffraction gratings each extending linearly in parallel, and are formed such that the structural birefringence of the diffraction gratings can be utilized to enter the laser light of far infrared rays, and the period P of the diffraction gratings Satisfy P <λ / n (λ is the wavelength of the incident light, n is the refractive index of the aforementioned substrate material); and the rotation mechanism rotates the polarized retardation plate.

Description

Power balance device and laser processing device for laser light

The present invention relates to a laser processing device for performing hole processing on a workpiece such as a printed circuit board, in particular to a power balancing device for laser light and a laser processing device using the power balancing device.

Regarding the productivity improvement method of the CO ₂ laser processing device for performing hole processing on printed substrates and the like, there is a method of dividing a laser light generated by a laser oscillator into a plurality of holes while simultaneously drilling holes A method of machining multiple holes. In this method, when the energy of the divided laser light is not uniform, the processing quality such as the processing aperture may be inconsistent.

Therefore, in the method disclosed in Patent Document 1 described below, a polarizer for polarization azimuth angle adjustment having a rotation adjustment mechanism is provided around the optical axis further upstream of the optical path than the polarizer for light splitting. In addition, by adjusting the polarization azimuth of the transmitted P wave, the balance of the polarization direction P wave component and the polarization direction S wave component incident on the polarization polarizer for adjustment can be adjusted to uniformly adjust The energy of the P-wave component and the laser light of the S-wave component reflected by the polarizer for splitting.

An example of adjusting the power balance of YAG (Yttrium Aluminum Garnet) laser light is described in Patent Document 2 below. A transmission type 1/4 wavelength (π / 2) phase difference plate with a rotation adjustment mechanism for rotation adjustment is provided on the optical axis as the center of the optical path upstream of the polarizing member for splitting. By adjusting the incident polarized light for splitting The P-wave component in the polarization direction and the S-wave component in the polarization direction of the sub are used to uniformly adjust the processing energy.

The following Patent Document 3 prevents the generation of a thermal lens by providing a polarization azimuth adjustment mechanism using only S-polarized light without using transmitted light.

In recent years, laser processing machines such as printed circuit boards have increased the laser light output due to the high energy processing and / or processing speed of through holes and the like.

(Prior technical literature) (Patent Literature)

Patent Literature 1: International Publication No. 2003/082510 Manual

Patent Document 2: Japanese Patent Laid-Open No. 9-108878 (Figure 1)

Patent Document 3: Japanese Patent Laid-Open No. 2011-251306

Patent Document 4: Japanese Patent Laid-Open No. 2014-29467

In the above-described conventional technology, for example, the configuration disclosed in Patent Document 1 described above transmits the P-wave component transmitted through the polarizer for polarizing azimuth angle adjustment to the downstream of the optical path. Therefore, if the power of the laser light incident on the polarizer is When it is high, the beam diameter of the laser light changes due to the thermal lens effect of the substrate material of the polarizer, and the energy intensity of the laser light passing through the shield is less consistent than that without the thermal lens effect. Therefore, there is a problem that the processing quality of the workpiece is degraded or unstable.

In addition, when the polarizer is rotated and adjusted during polarization azimuth adjustment, there is a slight shift in the center of the optical axis due to light diffraction, which may cause a problem that the processing quality of the workpiece is deteriorated.

In addition, the configuration disclosed in the above-mentioned Patent Document 2 is for YAG laser light with a wavelength of 1 μm, and cannot transmit far-infrared light. The birefringent material that transmits far infrared rays has cadmium sulfide (CdS), but it is a poison and difficult to handle.

In addition, the configuration disclosed in the above-mentioned Patent Document 3 does not use transmitted light but only uses S-polarized light, so the efficiency is not good.

The present invention has been developed in view of the above-mentioned problems, and its object is to obtain a laser processing device that can easily perform stable laser processing of a workpiece and a laser light power used in the laser processing device Balance device.

The method of the present invention is a power balancing device for laser light, which includes a polarizing retardation plate attached to one of the main surfaces of a pair of front and back surfaces, and is formed with a substrate material A plurality of convex portions composed of the same material each extend linearly parallel to each other with a set period P, and are formed to be able to utilize the structural birefringence of the aforementioned diffraction grating, and incident far-infrared laser light, and Make the aforementioned diffraction The period P of the grid satisfies P <λ / n (λ is the wavelength of incident light, n is the refractive index of the substrate material); and the rotation mechanism rotates the polarized retardation plate.

The present invention provides a laser processing device that can easily perform stable laser processing of a workpiece and a power balancing device for laser light used in the laser processing device.

1‧‧‧Laser oscillator

2‧‧‧Laser

2a, 2b‧‧‧‧Laser 2 polarized azimuth at the position shown

4‧‧‧mask

5‧‧‧beam variable section

6‧‧‧Reflecting mirror

7‧‧‧ Polarized beam splitter

8A, 8B‧‧‧Disperse laser light

9A, 9B‧‧‧ Separation direction

10Ax, 10Ay, 10Bx, 10By‧‧‧‧ current scanner

11A, 11B‧‧‧f θ lens

12A 、 12B‧‧‧XY platform

13A, 13B‧‧‧Workpiece

17‧‧‧ Polarizer

100‧‧‧Laser processing device

200‧‧‧ Polarized phase difference plate

201‧‧‧ Diffraction grid

202‧‧‧ substrate

203‧‧‧Convex

206‧‧‧Conical shape

207‧‧‧reflective film

210‧‧‧bronze mirror

211‧‧‧O-ring

212‧‧‧Press plate

213‧‧‧rotating mechanism

214‧‧‧Mirror support

220‧‧‧rotating mechanism

300‧‧‧Power balance device

A1, A2, A3 ‧‧‧ laser beam intensity distribution

B1, B2, B3 ‧‧‧ laser beam intensity distribution

FIG. 1 is a diagram showing an example of the configuration of a laser processing apparatus according to Embodiment 1 of the present invention.

Fig. 2 is a perspective view showing an example of a polarizing retardation plate constituting the sub-wavelength grid structure of Fig. 1;

FIG. 3 is a diagram showing an example of the configuration of a laser processing apparatus according to Embodiment 2 of the present invention.

Fig. 4 is a perspective side view showing an internal exploded structure of an example of the laser power balance device of Fig. 3;

FIG. 5 is a perspective side view showing an internal exploded structure of another example of the laser power balance device of FIG. 3. FIG.

FIG. 6 is a diagram for explaining the influence of the thermal lens phenomenon of the present invention.

FIG. 7 is a diagram for explaining the suppression effect of the thermal lens phenomenon of the present invention.

The present invention, by the sub-wavelength grid structure (sub-wavelength lattic structure), which can constitute a power balance device using high-transmittance materials under far-infrared, so it provides: prevention of thermal lens and even under high output beam A laser processing device with high processing quality and a power balance device for laser light used in the laser processing device are obtained.

Hereinafter, a laser light adding device according to the present invention and a power balance device for laser light used in the laser light adding device according to the present invention will be described using drawings. In addition, in each embodiment, substantially the same or corresponding parts are denoted by the same symbols, and repeated description is omitted.

Embodiment 1

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 device)

The laser processing apparatus 100 splits one laser beam 2 into two scattered laser beams 8A and 8B by a polarization beam splitter 7 belonging to a beam splitter. In general, the two scattered laser beams 8A and 8B are scanned independently, and finally through the f θ lens (LENS), the two processed objects 13A and 13B on the XY stages 12A and 12B are simultaneously opened. Hole processing.

The current scanner (GALVANO SCANNER) 10Ax moves the scattered laser light 8A with respect to the irradiation position of the workpiece 13A in the X direction, and the current scanner 10Ay moves the scattered laser light 8A with respect to the irradiation position of the workpiece 13A toward Y Direction of movement. In the same manner, the current scanner 10Bx directs the irradiation position of the scattered laser light 8B with respect to the workpiece 13B toward the X side The current scanner 10By moves the scattered laser light 8B in the Y direction with respect to the irradiation position of the workpiece 13B. The X direction and the Y direction are the coordinates orthogonal to each other in the plane of the workpieces 13A and 13B as in the XY stage, and are different from the xyz direction of the polarizing retardation plate 200 described later.

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

(Polarized retardation plate with sub-wavelength grid structure)

The polarizing retardation plate 200 having a sub-wavelength grid structure that can transmit far infrared rays has, for example, a structure also shown in Patent Document 4 described above. FIG. 2 is a perspective view showing an example of the configuration of a polarizing retardation plate 200 having a sub-wavelength grid structure in FIG. 1. The polarized retardation plate 200 to which the laser light is incident includes a substrate 202 and a diffraction grid 201 which is formed on one of the main surfaces of the pair of front and back sides of the substrate 202 and is connected to the substrate 202 Formed by the same material. The diffractive grid 201 displays a plurality of convex portions 203 that extend linearly in parallel with the x direction in the x, y, and z directions with the x and y directions as the substrate surfaces and are orthogonal to each other. The direction is formed by forming a line in a set interval at a set period P.

When light enters the above-mentioned diffraction grating 201 in the z direction, there is an effective refractive index with respect to the polarization component in the x direction (TE polarization) and an effective refractive index with respect to the polarization component in the y direction (TM polarization) Be the other This difference results in so-called constructive birefringence. As a result, a difference in transmission speed occurs between TE polarized light and TM polarized light, and elliptically polarized light occurs due to retardation corresponding to the difference in transmission speed.

P <λ / n (1)

P: period (interval) of the diffraction grid

λ: wavelength of incident light

n: refractive index of the basic material

As long as the condition of the above formula (1) is satisfied in advance, it can be seen that the loss of high-order diffracted light can be prevented even if the light is normally incident. The cross-sectional shape of the convex portion 203 is formed into a tapered shape 206 that forms an angle α from the bottom to the top.

Specifically, the substrate material of the substrate 202 is zinc sulfide (ZnS), the height H (that is, the depth of the groove) of the convex portion 203 is 4.01 μm, the inclination angle α of the tapered shape 206 is 22.2 degrees, and the filling factor ) f is 0.468, and the phase difference is λ / 8 (= π / 4).

In addition, the fill factor f is the ratio of the width W of the convex portion 203 at a position (H / 2) of the height H of the convex portion 203 to the period P, that is, the value of f = W / P.

The other main surface of the substrate 202 without the diffraction grating 201 is provided with an anti-reflection film 207. The material of the anti-reflection film 207 is germanium (GERMANIUM).

(Linear polarized light of the oscillator)

The laser oscillator 1 is a laser device that emits laser light 2 (λ = 9.29 μm) composed of CO ₂ laser light that belongs to far infrared rays such as linearly polarized light as a pulse wave. The laser light 2 emitted from the laser oscillator 1 is guided to the polarizing retardation plate 200 belonging to the sub-wavelength grating retardation plate through one or a plurality of reflecting mirrors 6. The reflecting mirror 6 is a mirror body that reflects the laser light 2 or disperses the laser light 8A and 8B and guides the light path downstream. The reflector 6 is arranged at various positions on the optical path in the laser processing apparatus 100.

(Polarized beam splitter)

The polarizing beam splitter 7 belonging to the polarizing beam splitter for splitting is a polarizer such as a beam splitter that splits a single beam of laser light 2 into two beams of dispersed laser light 8A, 8B. The polarizing beam splitter 7 transmits the P wave component of the laser light 2 and has the property of reflecting the S wave component.

(Operation of laser processing device)

Next, the operation processing procedure of the laser processing apparatus 100 will be described. The laser light 2 of the polarized azimuth angle θ guided from the laser oscillator 1 passes through the polarized retardation plate 200 of the sub-wavelength grid structure, and is then guided to the reticle 4 via a beam variable part 5 .

The photomask 4 transmits only the desired part of the laser light 2, thereby shaping the laser light 2 into a beam pattern shape suitable for laser processing. The laser light 2 shaped by the reticle 4 is reflected by one or a plurality of reflecting mirrors 6 to be guided to the polarizing beam splitter 7.

In the polarized light beam splitter 7, the P-wave polarized light component of the laser light 2 is transmitted through the polarized light beam splitter 7 and the dispersed laser light 8A is emitted. In addition, the laser light The S-wave polarized light component of 2 is reflected by the polarized beam splitter 7 and emits scattered laser light 8B. In order to prevent the quality of the processed holes of the two workpieces 13A and 13B from being inconsistent, the energy of the scattered laser light 8A and the energy of the scattered laser light 8B must be equal.

(Thermal lens)

The thermal lens effect is a phenomenon as follows: when higher-power laser light passes through the base material of the polarizing retardation plate 200 of the sub-wavelength grid structure of the first figure belonging to the polarizer, the local temperature rise of the base material causes The refractive index distribution of the polarizer is generated, thereby causing the polarizer to have a lens effect.

In addition, for example, in the case of the above-mentioned Patent Document 1, the polarizing member for polarizing azimuth angle adjustment generates a thermal lens effect.

(The influence of thermal lens on 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 polarizing retardation plate 200 of the present invention is guided downstream of the optical path of the polarizer 17. Fig. 6 (a) shows the intensity distribution of the laser beam when the thermal lens phenomenon does not occur. In addition, Fig. 6 (b) shows the laser beam intensity distribution when the thermal lens phenomenon occurs.

When the thermal lens phenomenon does not occur in FIG. 6 (a), the laser light emitted from the laser oscillator 1 has a laser beam intensity distribution A1. In addition, when the thermal lens phenomenon occurs in FIG. 6 (b), 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.

Also, the laser light 2 from the laser oscillator 1 is transmitted Polarizer 17. Here, the polarizer 17 is arranged at the same position as the conventional polarization azimuth adjustment device, for example. At this time, if the thermal lens phenomenon does not occur, the laser beam of the laser beam intensity distribution A1 passes through the polarizer 17, thereby forming the laser beam of the laser beam intensity distribution A2. In addition, if the thermal lens phenomenon occurs, the laser beam of the laser beam intensity distribution B1 passes through the polarizer 17, thereby forming the laser beam of the laser beam intensity distribution B2 different from the laser beam intensity distribution A2.

As shown in FIG. 6 (b), when the polarizer 17 has a thermal lens phenomenon, compared with the case where the polarizer 17 has no thermal lens phenomenon as shown in FIG. 6 (a), the lightening of the photomask 4 is changed. The beam diameter of the emitted light (beam diameter). The degree of the thermal lens phenomenon depends on the power of the laser light incident on the polarizer 17. Therefore, the beam energy of the laser light transmitted through the photomask 4 changes when the thermal lens phenomenon occurs and when it does not occur. Therefore, when the thermal lens phenomenon occurs and when it does not occur, the energy of the laser light reaching the workpieces 13A and 13B in FIG. 1 may be inconsistent. Specifically, when the thermal lens phenomenon does not occur, the laser light of the laser beam intensity distribution A3 is guided downstream of the optical path. In addition, when the thermal lens phenomenon occurs, laser light having a laser beam intensity distribution B3 different from the laser beam intensity distribution A3 is guided downstream of the optical path. As a result, when the thermal lens phenomenon occurs and when it does not occur, the quality of the processed hole of the workpiece is different.

(I found the problem of absorption by TFP (Thin-Film Polarizers). It can also be implemented in the transmission type)

In the first embodiment, as in the above-mentioned Patent Document 1, the point at which laser light passes through a substrate having a thickness in the polarizing retardation plate 200 is the same. Therefore, according to the temperature gradient in the diameter direction of the substrate, it can be assumed that the thermal lens phenomenon occurs in the same manner.

In view of this, as a result of the investigation of the present invention, the TFP (thin film polarizer) used in the polarized beam splitter of the above-mentioned Patent Document 1 actually used ThF ₄ (thorium fluoride) with a thickness of 1 μm or more. Stacked several layers of structure. Specifically, four or more layers of ThF ₄ (thorium fluoride) are deposited. The measurement of the absorption coefficient in the state of ThF ₄ film was 19 [cm ^-1 ], which was 38,000 times that of ZnSe (zinc selenide) (5e ^-4 [cm ^-1 ]) belonging to the parent material. When the total thickness of the ThF ₄ film is about 5 μm and the thickness of the ZnSe substrate is 5 mm, ThF ₄ absorbs 38 times the laser light. The heat absorbed in the TFP is poor in thermal conductivity in the radial direction because of the thin film, and a temperature difference in the radial direction occurs. That is, it can be known that the influence caused by the heat absorption of TFP is dominant.

(The function and effect of subwavelength grid structure)

On the other hand, in the first embodiment, by using the power balance device of the polarizing retardation plate 200 of the sub-wavelength grid structure, in far infrared ray, it is composed only of the substrate material with high transmittance, and TFP can be eliminated . As a result, processing holes with stable processing quality can be formed in the workpieces 13A and 13B without being affected by the thermal lens phenomenon.

Furthermore, in the first embodiment, the base material (that is, the material) of the substrate 202 of the polarizing retardation plate 200 shown in FIG. 2 uses ZnS (zinc sulfide). In the infrared transmission material, ZnS with a small refractive index is used on the substrate, thereby preventing Fresnel (Fresnel) reflection, even if YF ₃ (yttrium fluoride, yttrium fluoride), etc. are provided on the grid, the absorption rate is high The film of the material can also absorb less ZnS single material to constitute the wavelength plate (that is, constitute the polarizing retardation plate 200), and can suppress the occurrence of the thermal lens.

In addition, the thermal conductivity of ZnSe is 18 [W / (mK)], and the thermal conductivity of ZnS is 27.2 [W / (mK)], which makes it difficult to generate a temperature distribution and suppress the occurrence of thermal lenses.

As an example, FIG. 7 shows the results of evaluating the influence of the thermal lens phenomenon in the case where the polarizer of the polarizer for adjusting the polarization azimuth angle disclosed in Patent Document 1 is used when the power balance device of the laser processing device is provided. The case of the angle adjustment device and the case of the power balance device provided with the polarizing retardation plate 200 using the sub-wavelength grid structure. The power balance device of the laser processing apparatus is arranged at the same position as in the first embodiment. The laser light from the laser oscillator 1 is configured to pass through the power balance device, pass through the light beam variable section 5, and pass through only the desired portion in the mask 4.

Fig. 7 (a): With respect to the power balance device of the laser processing device, when the conventional polarization position adjustment device disclosed in Patent Document 1 is provided, the frequency of the pulse generation of the laser oscillator is relatively reached The measurement result of the rate of change of the laser beam energy intensity of the workpiece. The horizontal axis shows the frequency (pulse frequency) at which the pulses of the laser oscillator occur, and the vertical axis shows the rate of change of the energy intensity of the laser light reaching the workpiece (processing point energy change rate).

The higher the pulse frequency, the higher the power of the laser light incident on the power balancing device. The energy change rate of the processing point is the energy of the processing point when the pulse frequency is about 200Hz is lower as the denominator, which is set under each pulse frequency The energy at the processing point is a numerator, and the value is calculated by division. When the pulse frequency is low, the energy change rate of the processing point decreases, and as the pulse frequency becomes higher, the energy change rate of the processing point increases. This shows that the higher the power of the laser light transmitted through the polarization azimuth adjustment device, the greater the thermal lens effect, and the change rate of the energy intensity of the laser light transmitted through the reticle increases.

Figure 7 (b) is the power balance device of the laser processing device. When the power balance device using the polarizing retardation plate 200 of the sub-wavelength grid structure is provided, the frequency of the pulse of the laser oscillator is relatively The measurement result of the rate of change of the energy intensity of the laser light reaching the workpiece. Variation range of processing point energy change rate when pulse flat rate is changed from 200Hz to 2400Hz: about 7.5% when the conventional polarization azimuth adjustment device is installed, and the power balance of the polarized retardation plate 200 using the sub-wavelength grid structure The case of the device is about 6%, which shows that the power balance device using the polarizing retardation plate 200 of the sub-wavelength grid structure is used in the laser processing device, thereby suppressing the occurrence of the thermal lens.

Figure 7 shows that the pulse frequency is proportional to the energy change rate of the processing point. When the pulse frequency of the laser light from the laser oscillator 1 is higher, the power of the laser light is higher, so by using the sub-wavelength grid The greater the suppression effect of the thermal lens of the power balance device of the polarized retardation plate 200 constructed, the higher processing quality is obtained even with a high output beam.

(Other advantages of the transmission phase difference plate method)

The downstream optical axis changes in accordance with the rotation angle around the optical axis of the polarization azimuth adjusting device in the above-mentioned Patent Document 1, and changes in accordance with the angle of the reflecting surface with respect to the optical axis in the above-mentioned Patent Document 3. , But the actual form In the configuration of state 1, the optical axis of the transmitted light does not change with the eccentricity or tilt of the polarized retardation plate 200. Therefore, a low-precision rotating mechanism can be used, and the cost can be reduced.

(The effect of making the phase difference less than π / 2 (90 degrees), the problem of applying a sub-wavelength grid)

The phase difference plate of the above-mentioned Patent Document 2 discloses examples of π and π / 2. In order to obtain a phase difference of π or π / 2 in the sub-wavelength grid structure, there is a problem that it is difficult to process because a fine structure with a high aspect ratio that is both narrow and deep is required.

Next, the phase difference required for power balance adjustment is calculated.

Let the separation directions shown in 9A and 9B of the polarized beam splitter (PBS) 7 shown in FIG. 1 be directions a and b, and the polarization azimuth angle of linearly polarized light incident on the polarized beam splitter 7 be The phase difference of the polarized phase difference plate 200 is , And the fast axis angle in the direction of TM polarization in Figure 2 is At this time, the incident light e0 is expressed by the following formula (1).

The light e1 after the incident light e0 passes through the polarizing retardation plate 200 has the following formula (2).

e 1 = Rot (ψ) Re (Φ) Rot (-ψ) e0 (2)

The light e1 is split by the polarizing beam splitter 7. The separated polarized light components e1a and e1b are represented by the following formula (3).

The power difference ΔP of each polarized light with respect to the power of incident light is expressed by the following equation (4).

According to the above formula (4), by changing The adjustment range of ΔP obtained is that the second term is a fixed value, and the first term cos (4 -2 θ ) takes a value of -1 to 1, so the following formula (5) is formed.

For the adjustment of the power balance of the laser processing device, an adjustment range of ± 10% is sufficient. According to the equations (4) and (5) above, the phase difference required by the polarizing phase difference plate 200 as follows.

> 0.64rad = 37 degrees

In this way, only the power balance device is even less than 90 degrees There is no practical problem with the phase difference. Therefore, the depth of the groove part belonging to the height H of the convex part 203 of the polarizing phase difference plate 200 can be made shallow, and it can be manufactured.

In addition, the phase difference The smaller it is, the narrower the adjustment width at the time of rotation, that is, the deviation of the balance change from the rotation angle position is smaller, so there is also an advantage that the rotation mechanism can be manufactured at a low cost.

In the first embodiment, the polarizing retardation plate 200 with the sub-wavelength grid structure and the rotation mechanism 220 constitute a laser power balance device.

Embodiment 2

FIG. 3 is a diagram showing an example of the configuration of a laser processing apparatus according to Embodiment 2 of the present invention. FIG. 4 is a perspective side view showing the internal structure of an example of the laser power balance device 300 in FIG. 3. The laser processing apparatus of the second embodiment in FIG. 3 is provided with a laser power balancing device 300 that collects polarized phases including the sub-wavelength grid structure of the first embodiment in FIG. 1 The function of the difference plate 200 and the rotation selection mechanism 220. As shown in FIG. 4, the laser power balance device 300 has the following structure: above the copper mirror 210 belonging to the mirror body, the grating structure is superimposed so that the grating structure faces the surface with the polarization retardation of the sub-wavelength grating structure The plate 200 is accommodated in the lens holder 214, and then the O-ring 211 is inserted and clamped between the pressing plate 212 of the lens holder 214 and the surface of the polarized retardation plate 200.

The incident laser light 2 passes through the polarized retardation plate 200 of the sub-wavelength grid structure, is reflected by the surface of the copper mirror 210, and passes through the polarized retardation plate 200 of the sub-wavelength grid structure again. As above, two The polarizing retardation plate 200 is transmitted twice, so the phase difference of the polarizing retardation plate 200 may be half.

In addition, the mirror support 214 is provided with a rotation mechanism 213 that can rotate the entire mirror support 214 around the normal line of the reflection surface of the copper mirror 210.

The other basic configuration is the same as the above-mentioned first embodiment in FIG.

(Effect of overlapping lens body and wavelength version)

According to the structure as shown in FIG. 4, since the back surface of the polarizing retardation plate 200 of the sub-wavelength grid structure is in contact with the reflecting surface of the copper mirror 210, the heat absorbed in the polarizing retardation plate 200 flows toward the copper mirror 210 and is cooled Polarized phase difference plate 200. The direction of heat flow is not the diameter direction but the optical axis direction as indicated by the arrow HE, so the occurrence of temperature gradient in the diameter direction can be suppressed. As a result, the occurrence of thermal lenses can be prevented, and high power laser processing can be performed.

FIG. 5 is a transmission side view showing another example of the laser power balance device 300 of FIG. 3. In FIG. 5, the convex side of the polarizing retardation plate 200 of the sub-wavelength grid structure is directed to the surface side of the copper mirror 210, and above the copper mirror 210, the main surface opposite to the grid structure is overlapped so as to face the surface. The polarization retardation plate 200 of the wavelength grid structure is housed in the lens holder 214. At this time, since the grid is not in contact with the air, it is possible to prevent the adhesion of foreign materials such as waste materials.

According to the present invention described above, the sub-wavelength grid structure can constitute a power balance device and a laser processing device that use materials with higher transmittance in far infrared rays, thus preventing thermal lenses even with high output beams Obtain higher processing quality.

In addition, by setting the phase difference of the polarizing retardation plate to be π / 2 or less, the aspect ratio of the grid of the polarizing retardation plate is reduced, and manufacturing is facilitated.

In addition, the material of the polarizing retardation plate is ZnS, so the occurrence of thermal lenses can be prevented.

In addition, the mirror body is superposed on the polarizing retardation plate, so that the back surface of the polarizing retardation plate can be contacted with the mirror body to cool, so that the occurrence of the thermal lens can be prevented. In addition, the phase difference of the polarizing retardation plate 200 may be half.

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

(Industry availability)

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

Claims (9)

A power balancing device for laser light, comprising: a polarizing retardation plate, which is attached to one of the main surfaces of a pair of front and back surfaces, and is formed with a plurality of convex portions made of the same material as the substrate The setting periods P are linear diffraction gratings each extending linearly in parallel, and are formed such that the structural birefringence of the diffraction gratings can be utilized to enter the laser light of far infrared rays, and the period P of the diffraction gratings Satisfy P <λ / n (λ is the wavelength of the incident light, n is the refractive index of the substrate material); and the rotation mechanism rotates the polarizing retardation plate around the optical axis of the laser light. According to the power balance device for laser light described in item 1 of the patent application range, the phase difference of the polarizing retardation plate is π / 2 or less. As in the power balance device for laser light as described in item 1 of the patent scope, the material of the polarizing retardation plate includes ZnS. According to the power balance device for laser light described in item 2 of the patent application range, the material of the polarizing retardation plate includes ZnS. The power balance device for laser light as described in item 1 of the patent application scope is provided with a mirror body superimposed on the main surface of the polarized retardation plate. The power balance device for laser light as described in item 2 of the patent application scope is provided with a mirror body superimposed on the main surface of the polarized retardation plate. The power balance device for laser light as described in item 3 of the patent application scope is provided with a mirror body superimposed on the main surface of the polarized retardation plate. The power balance device for laser light as described in item 4 of the patent application scope is provided with a mirror body superimposed on the main surface of the polarized retardation plate. A laser processing device is provided with: a power balance device for laser light as described in any one of claims 1 to 8; and the laser light is generated to a polarizing retardation plate of the power balance device A laser oscillator; and a beam splitter that splits the laser light into two beams of laser light on the optical path from the polarized retardation plate to the workpiece.