JP4917123B2 - Laser beam optical system and laser processing apparatus - Google Patents

Description

  The present invention relates to a laser beam optical system for controlling the intensity distribution of a laser beam. The present invention also relates to a laser processing apparatus for performing processing such as drilling, cutting, and welding using a laser beam.

  A conventional laser processing apparatus for an electronic substrate uses a single aspheric lens in order to shape the beam intensity distribution into a concave shape (see Patent Document 1).

JP 2001-129679 A (page 4, page 7, FIG. 1, FIG. 10)

  When performing laser processing, it is desirable that the intensity distribution of the beam irradiated to the workpiece can be controlled to an arbitrary profile according to the processing content, the shape and material of the workpiece.

  In the conventional laser processing apparatus, when it is desired to change the beam intensity distribution on the workpiece, it is necessary to replace the aspherical lens with another aspherical lens. In addition, in the case of an aspherical lens that shapes the beam intensity distribution into a concave shape, the ratio of the intensity at the edge and the intensity at the center of the beam intensity distribution is fixed for each individual lens. Even if you want to change it, you need to replace it with another aspherical lens.

  In general, lens replacement requires re-adjustment of the optical system, which increases maintenance costs and reduces the operating rate of the laser processing apparatus.

  Further, if the performance of the laser oscillator take-off mirror fluctuates due to dimensional error or thermal distortion, the divergence angle of the beam emitted from the laser oscillator fluctuates, so that a beam having a predetermined beam diameter is not input to the aspherical lens. Then, the beam intensity distribution shaped by the aspherical lens may change or become unstable over time.

  An object of the present invention is to provide a laser beam optical system and a laser processing apparatus using the same, which enable stable processing even if the divergence angle of the beam emitted from the resonator varies.

A laser beam optical system according to the present invention includes a beam intensity distribution conversion element of an aspheric lens that converts the intensity distribution of a laser beam emitted from a take-out mirror of a laser oscillator into a shape of a top hat shape and a concave shape range ,
A transfer optical system provided between the take-out mirror and the beam intensity distribution conversion element and for transferring a beam image on the take-out mirror onto the beam intensity distribution conversion element ;
The transfer optical system is characterized in that the B element of the ray matrix ABCD is zero .

A laser beam optical system according to the present invention includes an aspherical lens beam intensity distribution conversion element that converts the intensity distribution of a laser beam emitted from a take-out mirror of a laser oscillator into a shape in a top hat shape and a concave shape range. ,
A beam profile provided between the take-out mirror and the beam intensity distribution conversion element and having a beam profile within a range of 1 / 0.1411 (m) to 1 / 0.0411 (m) in front of the take-off mirror And a transfer optical system for transferring onto the conversion element.

  According to the present invention, even if the performance of the laser oscillator take-off mirror fluctuates due to dimensional error or thermal distortion, and the divergence angle of the beam emitted from the laser oscillator fluctuates, the transfer optical system in front of the beam intensity distribution conversion element Since the beam diameter on the beam intensity distribution conversion element does not fluctuate, stable laser processing can be performed.

It is a block diagram which shows 1st Embodiment of this invention. FIG. 4 is an explanatory diagram showing functions of an aspheric lens 4. It is explanatory drawing which shows the function of the aspherical lens. It is explanatory drawing which shows the state which the aspherical lens 5 moved back. It is explanatory drawing which shows the design method of the aspherical lens. It is explanatory drawing which shows the design method of the aspherical lens. It is a block diagram which shows 2nd Embodiment of this invention. FIG. 4 is an explanatory diagram showing functions of a transfer optical system 17. FIG. 3 is a configuration diagram illustrating an example of a transfer optical system 17. It is a block diagram which shows 3rd Embodiment of this invention. FIG. 4 is an explanatory diagram showing functions of a transfer optical system 24. 2 is a configuration diagram illustrating an example of a transfer optical system 24. FIG. It is a block diagram which shows 4th Embodiment of this invention. It is explanatory drawing which shows the design method of Fresnel lens 4a, 5a. It is a block diagram which shows 5th Embodiment of this invention. It is explanatory drawing which shows the design method of phase shift mask 4b, 5b.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram showing a first embodiment of the present invention. The laser processing apparatus includes a laser oscillator 1 such as a gas laser or a solid laser, and a laser beam optical system LA for transmitting a laser beam emitted from the laser oscillator 1 to a workpiece to be processed.

  The laser oscillator 1 includes a laser medium and an optical resonator, and an optical amplifier for improving the output is incorporated as necessary. FIG. 1 shows an extraction mirror 2 for outputting a laser beam to the outside. Yes.

  The laser beam optical system LA includes a transfer lens system 3, an aspheric lens 4 that functions as a first beam intensity distribution conversion element, an aspheric lens 5 that functions as a second beam intensity distribution conversion element, and a lens 6. The variable magnification transfer optical system 7, the mask 8, the processing lens 9, and the like are arranged in tandem along the optical axis of the laser beam. In addition, a folding mirror for bending the optical axis or a relay lens for adjusting the optical path length may be interposed as required.

  The transfer lens system 3 includes a plurality of lenses and transmits the laser beam from the laser oscillator 1 to the aspherical lens 4. The aspheric lenses 4 and 5 convert a laser beam having a Gaussian-shaped intensity distribution into a laser beam having a non-Gaussian-shaped intensity distribution. The lens 6 is disposed at the image plane position of the aspherical lens 4 and converts the wavefront curvature of the laser beam.

  The variable magnification transfer optical system 7 is composed of a variable magnification beam expander or the like. The variable magnification transfer optical system 7 enlarges or reduces the beam intensity distribution on the lens 6 at a desired magnification and transfers it onto the mask 8. The mask 8 has a circular or rectangular aperture, and performs beam shaping by partially blocking the laser beam. The processing lens 9 is an objective lens disposed immediately before the workpiece W, and reduces and transfers the beam that has passed through the mask 8.

  With this configuration, the beam profile at the extraction mirror 2 of the laser oscillator 1 is transferred onto the aspherical lens 4 by the transfer lens system 3, and the beam profile at the aspherical lens 4 is transferred onto the lens 6 by the aspherical lens 5. A shaped beam profile is formed, and the beam profile at the lens 6 is transferred onto the mask 8 by the variable magnification transfer optical system 7, and the beam profile at the mask 8 is transferred onto the workpiece W by the processing lens 9. .

  FIG. 2 is an explanatory diagram showing the function of the aspheric lens 4. Here, in order to explain the function of the aspheric lens 4 itself, a state where the aspheric lens 5 does not exist is shown.

  The laser beam input from the transfer lens system 3 shows a Gaussian-shaped beam intensity distribution Pi on the aspherical lens 4. The aspherical lens 4 is designed so that one or both surfaces of the lens are aspherical, and at the position of the lens 6 arranged at a predetermined distance by positively utilizing optical aberrations such as spherical aberration. It can be converted into an arbitrary beam intensity distribution Po.

  Here, as shown in FIG. 2, a beam having a uniform intensity distribution in the radial direction is obtained by shaping the beam intensity distribution Po in a top hat shape at the position of the lens 6.

  FIG. 3 is an explanatory diagram showing the function of the aspheric lens 5. Here, a state where an aspherical lens 5 movable in the optical axis direction is interposed between the aspherical lens 4 and the lens 6 is shown.

  As described above, the laser beam input from the transfer lens system 3 exhibits a Gaussian-shaped beam intensity distribution Pi on the aspherical lens 4. Similarly to the aspherical lens 4, the aspherical lens 5 is also designed so that one or both surfaces of the lens are aspherical. By actively utilizing optical aberrations such as spherical aberration, the aspherical lens 5 is used. The above beam intensity distribution Pm can be converted into an arbitrary beam intensity distribution Po different from the intensity distribution converted by the aspherical lens 4 alone at the position of the lens 6.

  Here, as shown in FIG. 3, by combining the aspherical lens 4 and the aspherical lens 5, the beam intensity distribution Po at the position of the lens 6 is shaped from the top hat shape shown in FIG. A profile is realized in which the light intensity is higher near the beam edge than the beam center.

  FIG. 4 is an explanatory diagram showing a state in which the aspheric lens 5 has moved rearward. When the aspherical lens 5 moves from the initial position shown in FIG. 3 to the lens 6 side, the beam intensity distribution Po at the position of the lens 6 changes from the concave shape shown in FIG. 3 to the top hat shape shown in FIG. It becomes an intermediate shape. Further, when the aspherical lens 5 moves rearward and completely coincides with the position of the lens 6 in the optical theory, it becomes the same as the optical system shown in FIG. 2, and the beam intensity distribution Po at the position of the lens 6 is obtained. Corresponds to the top hat shape shown in FIG. Since an actual lens has a certain lens thickness, the aspherical lens 5 is brought as close to the lens 6 as possible.

  Accordingly, the beam intensity distribution Po at the image plane position of the aspheric lens 4 is continuously changed from the initial profile by continuously changing the position of the aspheric lens 5 along the optical axis with reference to the initial position. Can do. As a result, the beam intensity distribution on the workpiece W can be controlled to a desired profile, and optimization of the beam intensity distribution can be easily achieved in accordance with the machining content, workpiece shape, material, and the like.

Next, a design method for the aspheric lenses 4 and 5 will be described. First, with respect to the first aspheric lens 4, as shown in FIG. 5A, the position of the aspheric lens 4 is A, and the image plane position of the aspheric lens 4 (the position of the lens 6) is B. _Let L _AB be the distance between A and position B.

  FIG. 5B shows a state before and after the conversion of the beam intensity distribution. The horizontal axis is the radial position from the beam center, and the vertical axis is the light intensity. Here, for easy understanding, an example in which the beam intensity distribution is axially symmetric is shown, but it is also possible to design the X direction and the Y direction perpendicular to the optical axis independently.

Beam intensity distribution I _A at position A, can be expressed by a function f (r _A) of the radial position r _A at position A, the beam intensity distribution I _B at position B, the radial position r _B at position B Can be expressed by a function f (r _B ). FIG. 5B shows a case where the function f (r _A ) is a Gaussian function and a function f (r _B ) rectangle function, but both the functions f (r _A ) and f (r _B ) are arbitrary. It can be set to a function.

Therefore, when the beam intensity distributions I _A and I _B are integrated in the radial direction from the beam center, energy functions E _A and E _B as shown in FIG. 5C are obtained. If the conversion efficiency is 100%, both energy functions E _A and E _B are normalized to 1.

Position A, the amplitude _u A in B, _{u B} is represented by the formula (3) (4). However, j is an imaginary unit, and Φ _A and Φ _B are phases.

The energy functions E _A and E _B are integral values of the beam intensity distributions I _A and I _B , and E _A (r _1A ) and E _B (r _1B ) are energy contents from the beam center to the respective radial positions r _1A and r _1B. Indicates the rate.

Here, the relationship between r _1A and r _1B when the energy contents are equal is expressed by Expression (7).

Since E _A and E _B are both monotonically increasing functions, r _1B can be represented by a function h of E _B and further represented by a function of r _1A .

Next, if the inclination of the light beam propagating from r _1A to r _1B is θ, Equation (9) is established, and when this is rewritten, Equation (10) is obtained.

At this time, the phase Φ ₁ is expressed by Expression (11), and Expressions (12) and (13) are obtained by rewriting using Expression (10).

Expression (12) can be obtained by numerical calculation, that is, design is possible if the shape of E _A (r _A ) is known, and the phase distribution at position A is converted to Φ ₁ by converting the phase distribution at position A to Φ ₁ . it is possible to convert the beam intensity distribution I _B into an arbitrary shape.

Next, a design method for the second aspheric lens 5 will be described. As shown in FIG. 6A, the aspherical lens 5 is disposed at a position C between the position A of the aspherical lens 4 and the image plane position B, and as shown in FIG. Consider setting the beam intensity distribution I _B at B to a beam intensity distribution different from that described above. Here, the distance between the position C and the position B is _LCB .

  At this time, the amplitude at the position C is expressed by the following formula (14) using the Fresnel diffraction formula in an axially symmetric cylindrical coordinate system.

Here, the conversion from the beam intensity distribution I _{C at the} position _C to the beam intensity distribution I ′ _B at the position B is considered as in the equations (1) to (13). Beam intensity distribution I _C may be represented by a function f _{C (r C)} of the radial position r _C at position C, the new beam intensity distribution I _'B at position B, the radial position r _B at position B Can be expressed by a function f ′ _B (r _B ).

Position C, the amplitude _u C in B, u _'B is represented by the formula (17) (18). Here, j is an imaginary unit, and Φ _C and Φ ′ _B are phases.

The following E _C (r _2C ) and E ′ _B (r _2B ) indicate energy contents from the beam center to the radial positions r _2C and r _2B .

Here, I _'B shows the beam intensity distribution can be in position B by one sheet and the second sheet of the aspheric lens, a different intensity distribution and I _B shown in Formula (1) - (13) is there. Considering the same as in the cases (1) to (13), since the energy content is a monotonically increasing function, r _2B can be represented by a function g of E ′ _B.

Solving in the same manner as equations (9) to (12), the phase distribution Φ ₂ required at the position of C is expressed by equation (20b).

Therefore, by using the second aspherical lens 5 and converting the phase distribution from Φ _C to Φ ₂ , a desired beam intensity distribution I ′ _B can be obtained at the position B.

  In the present embodiment, the example in which the two aspherical lenses 4 and 5 are used as the beam intensity distribution conversion element has been described. However, it is possible to use three or more aspherical lenses.

Embodiment 2. FIG.
FIG. 7 is a block diagram showing a second embodiment of the present invention. The laser processing apparatus includes a laser oscillator 1 such as a gas laser or a solid laser, and a laser beam optical system LA for transmitting a laser beam emitted from the laser oscillator 1 to a workpiece to be processed.

  The laser oscillator 1 includes a laser medium and an optical resonator, and an optical amplifier for improving the output is incorporated as necessary. FIG. 1 shows an extraction mirror 2 for outputting a laser beam to the outside. Yes.

  The laser beam optical system LA includes a transfer optical system 17, an aspheric lens 4 that functions as a first beam intensity distribution conversion element, an aspheric lens 5 that functions as a second beam intensity distribution conversion element, and a lens 6. The variable magnification transfer optical system 7, the mask 8, the processing lens 9, and the like are arranged in tandem along the optical axis of the laser beam. In addition, a folding mirror for bending the optical axis or a relay lens for adjusting the optical path length may be interposed as required.

  The transfer optical system 17 includes a plurality of lenses, and transmits the laser beam from the laser oscillator 1 to the aspherical lens 4. The aspheric lenses 4 and 5 convert a laser beam having a Gaussian-shaped intensity distribution into a laser beam having a non-Gaussian-shaped intensity distribution. The lens 6 is disposed at the image plane position of the aspherical lens 4 and converts the wavefront curvature of the laser beam.

  The variable magnification transfer optical system 7 is composed of a variable magnification beam expander or the like. The variable magnification transfer optical system 7 enlarges or reduces the beam intensity distribution on the lens 6 at a desired magnification and transfers it onto the mask 8. The mask 8 has a circular or rectangular aperture, and performs beam shaping by partially blocking the laser beam. The processing lens 9 is an objective lens disposed immediately before the workpiece W, and reduces and transfers the beam that has passed through the mask 8.

  With this configuration, the beam profile at the extraction mirror 2 of the laser oscillator 1 is transferred onto the aspheric lens 4 by the transfer optical system 17, and the beam profile at the aspheric lens 4 is transferred onto the lens 6 by the aspheric lens 5. A shaped beam profile is formed, and the beam profile at the lens 6 is transferred onto the mask 8 by the variable magnification transfer optical system 7, and the beam profile at the mask 8 is transferred onto the workpiece W by the processing lens 9. .

  FIG. 8 is an explanatory view showing the function of the transfer optical system 17. When the extraction mirror 2 of the laser oscillator 1 has a lens effect due to a change in refractive index due to heat or the like, the divergence angle of the laser beam emitted from the extraction mirror 2 varies. The beam 18 shown in FIG. 8 is an initial beam, and the beam 19 is a beam whose divergence angle fluctuates due to the lens effect. In addition, the divergence angle of the laser beam may fluctuate even when the light absorption rate varies due to manufacturing errors or contamination of the extraction mirror 2.

  Next, a design method for the transfer optical system 17 will be described. The transfer optical system 17 has a function of transferring the beam immediately after the take-out mirror 2 to the aspherical lens 4 at the subsequent stage, and is an optical system in which the B element of the ray matrix ABCD has a value of zero.

The beam parameter Q ₀ at the position of the extraction mirror 2 is converted into the beam parameter Q ₁ in the aspherical lens 4 by the following equation (21) using the matrix ABCD. The beam parameter Q is expressed by the laser wavelength λ, the beam curvature radius R, the beam radius ω, and the imaginary unit j as shown in the equation (22), and is further rewritten by the parameters P and Ω.

Therefore, Equation (22) is substituted into Equation (21), and the parameter Ω ₁ at the position of the aspherical lens 4 is arranged.

Here, Ω ₀ means the beam diameter immediately after the extraction mirror, P ₀ means the beam divergence angle immediately after the extraction mirror, and Ω ₁ means the beam diameter at the position of the aspherical lens 4.

In the case of the transfer optical system 17, since the B element of the light beam matrix ABCD is zero, the beam diameter Ω ₁ is determined by the beam diameter Ω ₀ and the A element of the matrix ABCD. This is, as shown in FIG. 8, which means that the divergence angle of the laser beam emitted from the pickup mirror 2 even fluctuates, the beam diameter Omega ₁ to be transferred to the aspherical lens 4 is not changed.

  Therefore, even if the performance of the extraction mirror 2 of the laser oscillator 1 varies due to dimensional errors and thermal distortion, and the divergence angle of the beam emitted from the extraction mirror 2 varies, by adopting the transfer optical system 17, an aspheric surface is obtained. The beam diameter at the lens 4 can be kept constant, and the beam shape shaped by the aspherical lenses 4 and 5 can also be stabilized.

FIG. 9 is a configuration diagram illustrating an example of the transfer optical system 17. Transfer optical system 17 is constituted by a two lenses 22 and 23, set the distance between the lens 22 and the lens 23 to _{L 2,} the distance between the extraction mirror 2 and the lens 22 to _{L 1} set, and setting the distance between the lens 23 and the aspherical lens 4 to L _3.

Here, assuming that the focal length of the lens 22 is f ₁ and the focal length of the lens 23 is f ₂ , the distances L ₁ , L ₂ , L ₃ and the focal lengths f ₁ , f so that the following expression (24) is established. By determining ₂ , it is possible to realize a transfer optical system that can eliminate the influence of fluctuations in the beam divergence angle.

  In the present embodiment, the example in which the two lenses 22 and 23 are used as the transfer optical system 17 has been described, but it is also possible to use three or more lenses.

Embodiment 3 FIG.
FIG. 10 is a block diagram showing a third embodiment of the present invention. As in FIG. 7, the laser processing apparatus of the present embodiment includes a laser oscillator 1 including a take-out mirror 2, a laser beam optical system LA, and the like. The laser beam optical system LA includes a transfer optical system 24 having optical characteristics different from those of the transfer optical system 17 shown in FIG. 7, an aspherical lens 4, an aspherical lens 5, a lens 6, and a magnification shown in FIG. The variable transfer optical system 7, the mask 8, the processing lens 9, and the like are arranged in a column along the optical axis of the laser beam.

FIG. 11 is an explanatory diagram showing the function of the transfer optical system 24. Transfer optical system 24 is configured to transfer the beam profile at the position VI to spaced forwardly from extraction mirror 2 by a distance L _VI on aspheric lens 4. In FIG. 11, reference numeral 20 denotes a beam wavefront curvature immediately before the influence of heat, that is, immediately after the oscillator extraction mirror of the initial beam 18, and immediately after the oscillator extraction mirror of the beam 19 in which the wavefront curvature fluctuates due to the influence of the heat of the oscillator extraction mirror. The geometrical-optical beam propagation state of a beam having an average wavefront curvature with the beam wavefront curvature is shown. The focal position before this oscillator take-out mirror of the geometric optical beam 20 having this wavefront curvature is denoted by VI. That is, it is assumed that there is no oscillator takeout mirror at this time. Reference numeral 21 denotes a geometrical optical beam in which the beam 20 emitted from one point of the position of VI passes through the transfer optical system 24 and is focused on one point on the aspherical lens 4. That is, the transfer optical system 24 is an optical system that transfers the beam profile at the position VI to the aspherical lens.

  Since the beam indicated by reference numeral 20 has an average wavefront curvature of the initial beam 18 and the beam 19 whose wavefront curvature has changed, when the beam changes from reference numeral 18 to reference numeral 19, the change in the beam profile is caused by the resonator extraction mirror. This is the smallest at the VI position. In other words, by adopting the transfer optical system 24 that transfers the beam at the position VI to the aspherical lens, the variation of the beam diameter on the aspherical lens can be minimized.

Next, a design method for the transfer optical system 24 will be described. Distance _{L VI} to the mirror 2 is taken out from the position VI is represented by the following formula (25). However, the wavefront curvature of the initial beam 18 is P ₀ , and the wavefront curvature of the beam 19 affected by the heat of the extraction mirror 2 is P ₁ .

If the influence of heat extraction mirror 2 is small, the value of P ₁ may employ a value of P _0. In this case, Expression (25) is 1 / L _VI = −P ₀ . Further, the ray matrix ABCD of the transfer optical system 24 satisfies the following formula (26).

For example, when P ₀ = 0.1411 (m ⁻¹ ) and P ₁ = 0.0411 (m ⁻¹ ), L _VI = −10.98 m. In this case, the following equation (27) holds for the equation (26).

The value of L _VI, the range satisfying _{^{-1 (m -1) ≦ 1 /}} L VI ≦ 1 (m -1) is preferred.

FIG. 12 is a configuration diagram illustrating an example of the transfer optical system 24. Transfer optical system 24 is constituted by a two lenses 25 and 26, set the distance between the lens 25 and the lens 26 to _{L 2,} the distance between the extraction mirror 2 and the lens 25 to _{L 1} set, and setting the distance between the lens 26 and the aspherical lens 4 to L _3.

Here, assuming that the focal length of the lens 25 is f ₁ and the focal length of the lens 26 is f ₂ , the distances L ₁ , L ₂ , L ₃ and the focal lengths f ₁ , f so that the following expression (28) is established. By determining ₂ , it is possible to realize a transfer optical system that can eliminate the influence of fluctuation of the beam divergence angle.

  In this embodiment, the example in which the two lenses 25 and 26 are used as the transfer optical system 24 has been described. However, it is possible to use three or more lenses.

Embodiment 4 FIG.
FIG. 13 is a block diagram showing a fourth embodiment of the present invention. As in FIG. 1, the laser processing apparatus of the present embodiment includes a laser oscillator 1 including a take-out mirror 2, a laser beam optical system LA, and the like. The laser beam optical system LA includes a transfer optical system 3 shown in FIG. 1, a Fresnel lens 4a that functions as a first beam intensity distribution conversion element, a Fresnel lens 5a that functions as a second beam intensity distribution conversion element, Hereinafter, the lens 6, the variable magnification transfer optical system 7, the mask 8, the processing lens 9, and the like illustrated in FIG. 1 are arranged in a column along the optical axis of the laser beam.

  The Fresnel lens 4a has the same function as the aspherical lens 4 shown in FIG. 1, the Fresnel lens 5a has the same function as the aspherical lens 5 shown in FIG. 1, and these Fresnel lenses 4a and 5a are The laser beam having a Gaussian intensity distribution is converted into a laser beam having a non-Gaussian intensity distribution.

  In such a configuration, the beam profile at the extraction mirror 2 of the laser oscillator 1 is transferred onto the Fresnel lens 4a by the transfer lens system 3, and the beam profile at the Fresnel lens 4a is transferred onto the lens 6 by the Fresnel lens 5a. The beam profile at the lens 6 is transferred onto the mask 8 by the variable magnification transfer optical system 7, and the beam profile at the mask 8 is transferred onto the workpiece W by the processing lens 9.

  FIG. 14 is an explanatory diagram showing a design method for the Fresnel lenses 4a and 5a. FIG. 14A shows an example of the aspherical shape of the lens, and shows a state where light having a wavefront curvature of zero is incident with an equiphase wavefront at intervals of 2π. When the lens surface shape peak is used as a reference position, the lens surface is cut into circles with equiphase wavefronts at intervals of 2π, and the divided lens thickness is subtracted by an integral multiple of the phase period, and then joined again within the range from the reference position to one period. When the cross-sectional shape shown in FIG. 14B is obtained and the remaining lens surfaces are formed in a flat shape, a Fresnel lens having a cross-sectional shape as shown in FIG. 14C is obtained. When viewed from the front, the Fresnel lens has a large number of ring-shaped curved surfaces centered on the optical axis, and these have a light-collecting action equivalent to that of a single lens.

  Accordingly, the Fresnel lens 4 a can shape a laser beam having a Gaussian-shaped beam intensity distribution into a top-hat-shaped beam intensity distribution Po at the position of the lens 6, similarly to the aspherical lens 4. Similarly to the aspherical lens 5, the Fresnel lens 5 a shapes the beam intensity distribution Po at the position of the lens 6 into a concave shape in combination with the Fresnel lens 4 a so that the light intensity is near the beam edge from the beam center. A higher profile can be realized. Furthermore, by continuously changing the position of the Fresnel lens 5a along the optical axis with reference to the initial position, the beam intensity distribution Po at the image plane position of the Fresnel lens 4a can be continuously changed from the initial profile. . As a result, the beam intensity distribution on the workpiece W can be controlled to a desired profile, and optimization of the beam intensity distribution can be easily achieved in accordance with the machining content, workpiece shape, material, and the like.

  Further, since the Fresnel lenses 4a and 5a can reduce the thickness of the optical element itself, the entire optical system can be reduced in size and weight.

  In the present embodiment, the example in which the two Fresnel lenses 4a and 5a are used as the beam intensity distribution conversion element has been described. However, it is possible to use three or more Fresnel lenses, and further, an aspheric lens, a Fresnel lens, Combinations of these are also possible.

Embodiment 5 FIG.
FIG. 15 is a block diagram showing a fifth embodiment of the present invention. As in FIG. 1, the laser processing apparatus of the present embodiment includes a laser oscillator 1 including a take-out mirror 2, a laser beam optical system LA, and the like. The laser beam optical system LA includes a transfer optical system 3 shown in FIG. 1, a phase shift mask 4b that functions as a first beam intensity distribution conversion element, and a phase shift mask 5b that functions as a second beam intensity distribution conversion element. Hereinafter, the lens 6, the variable magnification transfer optical system 7, the mask 8, the processing lens 9, and the like shown in FIG. 1 are arranged in a column along the optical axis of the laser beam.

  The phase shift mask 4b has the same function as the aspherical lens 4 shown in FIG. 1, and the phase shift mask 5b has the same function as the aspherical lens 5 shown in FIG. 1, and these phase shift masks 4b. , 5b converts a laser beam having a Gaussian-shaped intensity distribution into a laser beam having a non-Gaussian-shaped intensity distribution.

  In such a configuration, the beam profile at the extraction mirror 2 of the laser oscillator 1 is transferred onto the phase shift mask 4b by the transfer lens system 3, and the beam profile at the phase shift mask 4b is transferred onto the lens 6 by the phase shift mask 5b. After being transferred, the beam profile at the lens 6 is transferred onto the mask 8 by the variable magnification transfer optical system 7, and the beam profile at the mask 8 is transferred onto the workpiece W by the processing lens 9.

  FIG. 16 is an explanatory diagram showing a design method of the phase shift masks 4b and 5b. FIG. 16A shows an example of the aspherical shape of the lens, and the appearance of light having a wavefront curvature of zero is shown as an equiphase wavefront with π intervals. When the lens surface shape peak is used as a reference position, the lens surface is cut into circles with equiphase wavefronts at intervals of 3π, and the divided lens thickness is subtracted by an integral multiple of the phase period, and then joined again within the range from the reference position to one period. The cross-sectional shape shown in FIG. 16B is obtained. Furthermore, a curved surface in the range from the reference position to the phase π is converted into a plane at the reference position, and a curved surface in the range from the phase π to the phase 2π is converted into a plane at the position of the phase π, and the phase from the phase 2π to the phase When a curved surface in the range up to 3π is converted into a plane at the position of phase 2π, the cross-sectional shape shown in FIG. 16C is obtained. When the light emission surface is formed in a planar shape, a phase shift mask having a cross-sectional shape as shown in FIG. The phase shift mask is made of a transparent material having a predetermined refractive index, and when viewed from the front, a large number of ring-shaped planes centered on the optical axis are formed. Have

  Therefore, the phase shift mask 4b can shape a laser beam having a Gaussian-shaped beam intensity distribution into a top-hat-shaped beam intensity distribution Po at the position of the lens 6, as with the aspherical lens 4. Similarly to the aspheric lens 5, the phase shift mask 5b shapes the beam intensity distribution Po at the position of the lens 6 into a concave shape in combination with the phase shift mask 4b, so that the light intensity is higher than the beam center. A profile that increases in the vicinity of the edge can be realized. Further, the beam intensity distribution Po at the image plane position of the phase shift mask 4b is continuously changed from the initial profile by continuously changing the position of the phase shift mask 5b along the optical axis with reference to the initial position. Can do. As a result, the beam intensity distribution on the workpiece W can be controlled to a desired profile, and optimization of the beam intensity distribution can be easily achieved in accordance with the machining content, workpiece shape, material, and the like.

  Further, since the phase shift masks 4b and 5b and the optical element itself can be reduced in thickness, the entire optical system can be reduced in size and weight.

  In the present embodiment, an example in which two phase shift masks 4b and 5b are used as the beam intensity distribution conversion element has been described. However, three or more phase shift masks can be used, and an aspheric lens, Fresnel A combination of lens and phase shift mask is also possible.

In each embodiment, a high output laser beam can be obtained by using a CO ₂ laser, a YAG laser, a YAG _second harmonic laser, a YAG third harmonic laser, a YAG fourth harmonic laser, or the like as the laser oscillator 1. Therefore, the working efficiency of laser processing can be greatly improved.

1 laser oscillator, 2 extraction mirror, 3 transfer lens system,
4,5 aspherical lens, 4a, 5a Fresnel lens,
4b, 5b phase shift mask, 6 lens, 7 magnification variable transfer optical system,
8 mask, 9 processing lens, 17, 24 transfer optical system,
18, 19, 20, 21 beams, 22, 23, 25, 26 lenses,
LA laser beam optical system, W work.

Claims (3)

A beam intensity distribution conversion element of an aspheric lens that converts the intensity distribution of the laser beam emitted from the take-out mirror of the laser oscillator into a shape in a range of a top hat shape and a concave shape ;
A transfer optical system provided between the take-out mirror and the beam intensity distribution conversion element and for transferring a beam image on the take-out mirror onto the beam intensity distribution conversion element ;
The transfer optical system is a laser beam optical system characterized in that the B element of the ray matrix ABCD is zero . A beam intensity distribution conversion element of an aspheric lens that converts the intensity distribution of the laser beam emitted from the take-out mirror of the laser oscillator into a shape in a range of a top hat shape and a concave shape ;
A beam profile provided between the take-out mirror and the beam intensity distribution conversion element and having a beam profile within a range of 1 / 0.1411 (m) to 1 / 0.0411 (m) in front of the take-off mirror A laser beam optical system comprising: a transfer optical system for transferring onto the conversion element. A laser oscillator for generating a laser beam;
A laser beam optical system according to claim 1 or 2 ,
A laser processing apparatus , wherein the laser oscillator includes a CO ₂ laser, a YAG laser, a YAG _second harmonic laser, a YAG third harmonic laser, or a YAG fourth harmonic laser .

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