JP2013029748A - Aspherical homogenizer and method of designing aspherical lens for homogenizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aspherical homogenizer for use in laser processing or the like, which is hardly affected by tilt errors.SOLUTION: In a homogenizer comprising one lens which refracts and reduces an incident beam which is parallel and has a Gaussian distribution as an energy distribution, to form a beam having a uniform energy distribution in an image surface within a range of a diameter smaller than a diameter of the incident beam, both surfaces of the lens are aspherical, or one surface is aspherical and the other is concave.

Description

  The present invention relates to an aspherical modifier suitable for a high-power laser such as a carbon dioxide laser and a YAG laser used for cutting, welding, and heat treatment of metal, and a design method for an aspherical lens used therefor, in particular, a beam emitted from the laser. The present invention relates to an aspherical homogenizer composed of a single lens that converts the power into a uniform power distribution and a method for designing an aspherical lens for homogenizer.

  The beam output from the laser has a non-uniform power distribution, has a large power at the center, and decreases as it goes to the periphery.

  When such a laser is used for metal processing or the like, only the central portion has a high processing speed, and uniform processing may not be possible. Therefore, in order to process uniformly, it is required that the power is uniform in a certain spatial range. For this reason, there is known a technique in which a beam having a Gaussian distribution (Gaussian beam) is made uniform in a certain range to form a so-called top hat type, but for this purpose, usually two lenses are required.

  Under such circumstances, there has been proposed an optical system (homogenizer) that converts a Gaussian beam emitted from a laser into a top-hat beam using a single aspheric lens (see Patent Document 1).

  In Patent Document 1, the final beam diameter is smaller than the initial Gaussian beam diameter, the phases are not aligned, and it is not parallel light, but it is sufficient for processing applications and the lens is resistant to tilt with respect to the axis. Techniques to do this have been proposed.

Japanese Patent No. 3960295

  Although the above-mentioned homogenizer is strong against tilt, data when tilted to 0.5 degrees is disclosed as an example, but no mention is made of performance changes when tilted beyond that. In general, it is difficult to install the lens in the lens barrel so that the tilt is within 0.5 degrees, and it is necessary to prevent the performance from deteriorating significantly even if the lens is tilted up to about 2 degrees.

  The present invention has been made paying attention to the above-mentioned problems, and is a tilt error reducing aspheric homogenizer comprising a lens in which both surfaces are aspherical or one surface is aspherical and the other surface is concave spherical. The purpose is to provide.

  As a result of intensive studies, the present inventors have found that both surfaces can be aspherical, or that one surface can be aspherical and the other surface can be a concave spherical lens to solve the above problem. The present invention has been completed.

  That is, the homogenizer of the present invention is a method for refracting and reducing an incident beam having a parallel and Gaussian energy distribution to form a uniform energy distribution beam on the image plane in a diameter range smaller than the diameter of the incident beam. In the homogenizer comprising a single lens, the lens is a double-sided aspherical surface.

  In addition, another homogenizer of the present invention refracts and reduces an incident beam having a parallel and Gaussian energy distribution to form a beam having a uniform energy distribution on the image plane in a diameter range smaller than the diameter of the incident beam. The lens is characterized in that the lens is an aspherical surface on one side and a concave spherical surface on the other side.

  The design method of the aspherical lens for homogenizer of the present invention sets the aspherical shape of one surface, divides the other surface into a plurality of regions in a ring shape, and each of the divided regions has a different curvature. It is a spherical surface, and the curvature of the spherical surface is set so that the spherical aberration decreases as it goes from the center, and each region where the curvature of the spherical surface is set is smoothly connected to the spherical surface of the adjacent region. Approximate splicing, single beam can refract and reduce incident beam with parallel and Gaussian energy distribution to form a uniform energy distribution beam on the image plane in a diameter range smaller than the incident beam diameter It is a lens.

  Further, according to another method of designing an aspheric lens for homogenizer of the present invention, a concave spherical shape of one surface is set, the other surface is divided into a plurality of regions in a ring shape, and each of the divided regions is different. A spherical surface having a curvature, the curvature of the spherical surface is set so that the spherical aberration decreases as it goes from the center, and each region where the curvature of the spherical surface is set is smoothly connected to the spherical surface of the adjacent region. A beam of uniform energy distribution on the image plane in the range of diameter smaller than the diameter of the incident beam by refracting and reducing the incident beam that is parallel and Gaussian distribution with a single piece by approximating with an aspherical system. It is characterized by making it a lens which can form.

  According to the design method of the aspherical homogenizer and the aspherical lens for homogenizer of the present invention, it is possible to provide a homogenizer that can reduce the change in performance due to tilt and can irradiate a stable laser beam. Moreover, the aspherical lens used here can be manufactured by this press molding. In that case, the aspherical lens can be easily manufactured with a high yield.

It is the figure which illustrated schematic structure and light power distribution of the 1st homogenizer of the present invention. It is a manufacturing flow of the 1st homogenizer of this invention. It is the figure which illustrated schematic structure and light power distribution of the 2nd homogenizer of this invention. It is a manufacturing flow of the 2nd homogenizer of this invention. It is the figure which showed the relationship between the curvature radius in R2 surface of the 1st homogenizer (Example 1) of this invention, and Seidel's coma aberration coefficient. It is the figure which showed the relationship of the spherical aberration with respect to each ring-shaped area | region of the 1st homogenizer (Example 1) of this invention. It is the figure which showed the light power distribution of the 1st homogenizer (Example 1) of this invention. It is the figure which showed the light power distribution at the time of tilting 0.5 degree | times of the 1st homogenizer (Example 1) of this invention. It is the figure which showed the light power distribution at the time of tilting the 1st homogenizer (Example 1) of this invention twice. It is the figure which showed the relationship of the spherical aberration with respect to each ring-shaped area | region of the 2nd homogenizer (Example 2) of this invention. It is the figure which showed the light power distribution of the 2nd homogenizer (Example 2) of this invention. It is the figure which showed the light power distribution at the time of tilting the 2nd homogenizer (Example 2) of this invention 0.5 degree | times. It is the figure which showed light power distribution at the time of tilting the 2nd homogenizer (Example 2) of this invention twice. It is the figure which showed the light power distribution of the homogenizer of a prior art example. It is the figure which showed the light power distribution at the time of tilting the homogenizer of a prior art example 0.5 degree. It is the figure which showed the light power distribution at the time of tilting the homogenizer of a prior art example twice. It is the figure which showed schematic structure and light power distribution of the homogenizer of this invention designed by the same specification as a prior art example. It is the figure which showed the light power distribution of the homogenizer of this invention designed by the same specification as a prior art example. It is the figure which showed the light power distribution when the homogenizer designed by the design method of this invention so that it may become the same specification as a prior art example is tilted 0.5 degree | times. It is the figure which showed the light power distribution at the time of tilting the homogenizer designed by the design method of this invention twice so that it may become the same specification as a prior art example. It is the figure which showed the relationship between the curvature radius in R22 surface of the homogenizer designed by the design method of this invention so that it might become the same specification as a prior art example, and Seidel's coma aberration coefficient. It is the figure which showed the relationship of the spherical aberration with respect to each ring-shaped area | region of the homogenizer designed with the design method of this invention so that it might become the same specification as a prior art example.

  Hereinafter, the present invention will be described in detail.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of a first homogenizer and a power distribution of light rays according to the present invention. Here, the upper part shows a state in which the laser beam is condensed in addition to the schematic configuration of the homogenizer (FIG. 1 (a-1) is an enlarged view of the lens portion of FIG. 1 (a)), and the lower part is the condensing element. The power distribution at the position is shown (FIG. 1 (b-1) is an enlarged view of the spot portion of FIG. 1 (b)).

  In FIG. 1, a homogenizer 1 is composed of both aspherical lenses 2 and a cover glass 3 housed in a lens barrel (FIG. 1 (a)). In FIG. 1, the left surface (R1 surface) of both aspherical lenses 2 is a convex aspherical surface, and is designed so that the spherical aberration becomes smaller from the center toward the outside at the condensing position. In FIG. 1, the surface on the right side of the lens (R2 surface) is a convex aspheric surface, and is set so that the influence of tilt is minimized.

  As a design method for the R1 surface and the R2 surface, first, the R2 surface is arbitrarily set to an aspherical shape so that the influence of tilt is minimized. At this time, the R1 surface has a spherical shape having a curvature radius obtained when calculating the radius of curvature of the R2 surface. Thereafter, the R1 surface is divided into a plurality of regions (for example, five regions) in a ring shape, and each region is formed into a spherical surface having a different curvature such that the center of curvature is on the optical axis, and as it goes away from the center It is set so that spherical aberration tends to be reduced. Finally, it can be designed as a shape obtained by approximating and joining the regions separated by the R1 surface by an aspherical expression that smoothly connects the surfaces of adjacent regions. Moreover, you may adjust the aspherical shape of R2 surface set initially as needed. The flow of this design method is shown in FIG.

  In order to reduce the influence of tilt on the R2 surface, the radius of curvature is searched for such that the Seidel coma coefficient in the R2 surface is reduced by bending of the R1 surface and the R2 surface, and the curvature radius is set to the non-R2 surface. The aspherical coefficient is determined so as to minimize the spot diameter by setting the paraxial radius of curvature of the spherical surface. When determining the aspherical shape, it is necessary to consider the ease of press molding.

  As a method of dividing into a plurality of regions, if the maximum diameter of the nth region is D (n) max, the beginning of the nth region is D (n−1) max of the n−1th region. This is done by offsetting the nth region in the optical axis direction so as to be connected at the boundary region. However, D (0) = 0. If a user-defined surface “multi-zone surface” of optical design software (manufacturer: Radiant ZEMAX, LLC, trade name: ZEMAX) is used, a plurality of annular zones can be easily set.

  At that time, in order to reduce the spherical aberration in a tendency, the approximate straight line of the distribution composed of the area number (n) and the absolute amount of spherical aberration | SA ′ (n) | The curvature radius of each region is set so that the slope a of y = ax + b is a <0 (negative). If a> 0 (positive), it is determined that the number is increasing.

(Second Embodiment)
FIG. 3 is a diagram illustrating the schematic configuration of the second homogenizer of the present invention and the light power distribution. Here, the upper stage shows a state where the laser beam is condensed in addition to the schematic configuration of the homogenizer (FIG. 3 (a-1) is an enlarged view of the lens portion of FIG. 3 (a)), and the lower stage is at the condensing position. The power distribution is shown (FIG. 3 (b-1) is an enlarged view of the spot portion of FIG. 3 (b)).

  In FIG. 3, the homogenizer 11 includes a single-sided aspherical-single-sided concave spherical lens 12 and a cover glass 13 housed in a lens barrel. In FIG. 3, the surface on the left side of the lens (R11 surface) is a convex aspheric surface, and is designed so that the spherical aberration decreases from the center toward the outside at the condensing position. In FIG. 3, the surface on the right side of the lens (R12 surface) is a concave spherical surface, and is set so that the influence of tilt is minimized.

  As a design method for the R11 surface and the R12 surface, a concave spherical shape is first arbitrarily set so that the influence of the tilt is minimized on the R12 surface. At that time, the R11 surface has a spherical shape having a curvature radius obtained when calculating the curvature radius of the R12 surface. After that, the R11 surface is divided into a plurality of regions (for example, five regions) in a ring shape, and each region is formed into a spherical surface having different curvatures having a center of curvature on the optical axis, and as it goes away from the center. It is set so that spherical aberration tends to be reduced. Finally, it can be designed as a shape obtained by approximating and joining the regions separated by the R11 surface by an aspherical expression that smoothly connects the surfaces of adjacent regions. Moreover, you may adjust the concave spherical surface shape of R12 surface set initially as needed. The flow of this design method is shown in FIG.

  The design of the R11 plane and the R12 plane here may be performed by the same method as in the first embodiment. However, unlike the first embodiment, the R12 surface is a concave spherical surface. In order to reduce the influence of the tilt of this surface, Seidel's coma aberration coefficient on the R12 surface can be reduced by bending the R11 surface and the R12 surface. Finding a radius of curvature such that the radius of curvature is small and setting it as the radius of curvature of the concave spherical surface (R12 surface).

A homogenizer as shown in FIG. 1 was constructed. At this time, the lens 2 is actually designed by the method described in the first embodiment, and the result is shown below.
The distance between the lens shown in FIG. 1 and the condensing position is 75.34 mm, and a cover glass is provided between them. Lens consists refractive index Nd1.58091, the optical glass of the Abbe number Nyudi59.4, the surface anti-reflection coating of magnesium fluoride MgF ₂ is the center wavelength is coated so as to be 1070 nm. The spot diameter of the top hat is 62 μm. The left surface (R1 surface) of FIG. 1 is a convex aspherical surface, the paraxial radius of curvature is 62.5 mm, the conic constant K is 0, and the aspherical expression is as follows.

The design method was as shown in the flow of FIG. In particular,
(1) The method for setting the R2 surface starts by first setting the paraxial radius of curvature, but the curvature radii at which Seidel's coma coefficient is the best are 70 mm and 27.8 mm concave shapes (the lens has a concave and convex shape) ) Is made a convex shape (a biconvex shape as a lens) of −170.59 mm in which the coma aberration coefficient becomes small while facilitating the press molding and the convenience of the shape measurement. FIG. 5 shows the relationship between the radius of curvature in the R2 plane and Seidel's coma coefficient. Next, the aspherical shape of the R2 surface is obtained by adjusting the aspherical coefficient so that the spot diameter is minimized while the above-mentioned paraxial curvature radius is fixed. At this time, the R1 surface has a spherical shape with a radius of curvature obtained together with the R2 surface by bending.

  (2) To divide the R1 surface into a plurality of regions, use a user-defined surface “multi-zone surface” of optical design software (manufacturer: Radiant ZEMAX, LLC, product name: ZEMAX), and the diameter of the division is from the center. 1.5mm, 2.0mm, 3.0mm, 4.5mm, 5.0mm are set, and the radius of curvature of each divided region is the curvature of the R1 surface obtained together with the calculation of the R2 surface in (1) above. A radius of 56.55 mm is given uniformly.

  (3) A method of setting the radius of curvature of each spherical surface so that the divided region is a spherical surface and the spherical aberration is reduced from the center toward the outer side. First, the first radius of curvature is set, and the spherical aberration in the region is SA1. , Where the diameter is D1, the focal length is f, and the spot diameter of the top hat is Ds, the condition that the spot diameter at the condensing position formed in the region of D1 matches Ds, that is, SA1 = f * Adjustment is made so as to roughly match SA1 obtained by Ds / D1. Basically, the second and subsequent curvature radii are adjusted so that the spherical aberration gradually decreases, but finally the adjustment is made so that the light beam power distribution has a desired shape including the first curvature radius. Do. The radius of curvature after adjustment is 62.5 mm, 54.0 mm, 56.0 mm, 54.7 mm, and 56.0 mm from the center. FIG. 6 shows the relationship of the spherical aberration with respect to each zone-shaped region after adjustment of the radius of curvature.

(4) A method of approximating these divided surfaces with an aspherical surface that smoothly connects adjacent surfaces is the following aspherical equation with respect to sag amount data (point cloud data) with respect to the diameter of the shape before approximation. The paraxial curvature radius of the aspherical expression is 62.5 mm, the conic constant K is 0, and the calculation of the aspheric coefficients A1 to A14 is sag. Solves simultaneous equations consisting of sag amount and coefficients A1 to A14 by aspherical component obtained by subtracting spherical component (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 } from quantity Went by things.

Z (y) = (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 }
+ A ₁ · y + A ₂ · y ² + A ₃ · y ³ + A ₄ · y ⁴ + A ₅ · y ⁵
+ A ₆ · y ⁶ + A ₇ · y ⁷ + A ₈ · y ⁸ + A ₉ · y ⁹ + A ₁₀ · y ¹⁰
+ A ₁₁ · y ¹¹ + A ₁₂ · y ¹² + A ₁₃ · y ¹³ + A ₁₄ · y ¹⁴

(R1 surface aspherical)

  The right side surface (R2 surface) of FIG. 1 is also a convex aspherical surface, the paraxial radius of curvature is −170.59 mm, the conic constant K is 0, and the aspherical formula is as follows.

Z (y) = (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 }
+ A ₄ · y ⁴ + A ₆ · y ⁶ + A ₈ · y ⁸ + A ₁₀ · y ¹⁰

(R2 surface aspherical)

In this homogenizer, the power distribution when the tilt of the lens is tilted at 0 degree, 0.5 degree, and 2 degrees is shown in FIGS. 7, 8, and 9, respectively.
Table 3 shows a summary of changes in intensity due to tilt in FIGS. 7 to 9 for the X and Y axes. Note that the Y axis is the tilt axis, and the X axis is the tilt center axis. The intensity change index was defined as the ratio of the amount of intensity change after tilt with respect to the tilt of 0 degree, and was calculated for each of the top hat central portion and the peripheral portion of the light power distribution.

  From Table 3, the homogenizer of this case is tilted because the intensity change is within −4% even when the tilt is 0.5 degrees, and the intensity change in the top hat periphery is within −13% even when the tilt is 2 degrees. It is understood that it is strong. Since the strength of the central portion of the top hat is usually sufficient, there is no problem in processing even if the strength of the central portion changes slightly.

  As Example 2, a case where a lens having one aspherical surface and the other surface having a concave spherical surface described in the second embodiment is used.

A homogenizer as shown in FIG. 3 was constructed. At this time, the lens 12 is actually designed by the method described in the second homogenizer and the result is shown below.
The distance between the lens shown in FIG. 3 and the condensing position is 75.34 mm, and a cover glass is provided between them. Lens consists refractive index Nd1.58091, the optical glass of the Abbe number Nyudi59.4, the surface anti-reflection coating of magnesium fluoride MgF ₂ is the center wavelength is coated so as to be 1070 nm. The spot diameter of the top hat is 62 μm. The left surface (R11 surface) of FIG. 3 is a convex aspherical surface, the paraxial radius of curvature is 28.03 mm, the conic constant K is 0, and the aspherical formula is as follows.

The design method was as shown in the flow of FIG. In particular,
(1) The R12 surface is set to have a concave shape with a radius of curvature of 70 mm, which gives the best Seidel coma aberration coefficient. FIG. 5 shows the relationship between the radius of curvature on the R12 surface and the Seidel coma aberration coefficient. At this time, the R11 surface has a spherical shape with a radius of curvature obtained together with the R12 surface by bending.

  (2) To divide the R11 surface into a plurality of regions, use a user-defined surface “multi-zone surface” of optical design software (manufacturer: Radiant ZEMAX, LLC, product name: ZEMAX), and the diameter of the division is from the center. 2.0 mm, 3.0 mm, 3.5 mm, 4.0 mm, 5.0 mm are set, and the radius of curvature of each divided area is the curvature of the R11 surface obtained together with the calculation of the R12 surface in (1) above. A radius of 26.93 mm is given temporarily.

  (3) A method of setting the radius of curvature of each spherical surface so that the divided region is a spherical surface and the spherical aberration decreases as going from the center to the outside. First, the first radius of curvature is set to the spherical aberration of the region. When SA1, the diameter is D1, the focal length is f, and the spot diameter of the top hat is Ds, the condition that the spot diameter at the condensing position formed in the region of D1 matches Ds, that is, SA1 = f * Adjust so that it roughly matches SA1 obtained by Ds / D1. Basically, the second and subsequent curvature radii are adjusted so that the spherical aberration gradually decreases, but finally the adjustment is made so that the light beam power distribution has a desired shape including the first curvature radius. Do. The radius of curvature after adjustment is 28.03 mm, 27.12 mm, 27.33 mm, 27.19 mm, 27.25 mm from the center, and FIG. 10 shows the relationship of the spherical aberration with respect to each ring-shaped region after adjustment of the radius of curvature.

(4) A method of approximating these divided surfaces with an aspherical surface that smoothly connects adjacent surfaces is the following aspherical equation with respect to sag amount data (point cloud data) with respect to the diameter of the shape before approximation. The paraxial radius of curvature of the aspherical formula is 28.03 mm in the first region, the conic constant K is 0, and the calculation of the aspherical coefficients A1 to A14 is sag. Solves simultaneous equations consisting of sag amount and coefficients A1 to A14 by aspherical component obtained by subtracting spherical component (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 } from quantity Went by things.

Z (y) = (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 }
+ A ₁ · y + A ₂ · y ² + A ₃ · y ³ + A ₄ · y ⁴ + A ₅ · y ⁵
+ A ₆ · y ⁶ + A ₇ · y ⁷ + A ₈ · y ⁸ + A ₉ · y ⁹ + A ₁₀ · y ¹⁰
+ A ₁₁ · y ¹¹ + A ₁₂ · y ¹² + A ₁₃ · y ¹³ + A ₁₄ · y ¹⁴

(R11 surface aspherical)

  The right side surface (R12 surface) of FIG. 3 is a concave spherical surface, and R is 70 mm.

In this homogenizer, the power distribution when the tilt of the lens is tilted at 0, 0.5, and 2 degrees is shown in FIGS. 11, 12, and 13, respectively.
Table 5 summarizes the intensity changes due to tilt in FIGS. 11 to 13 for the X-axis and Y-axis. Note that the Y axis is the tilt axis, and the X axis is the tilt center axis. The intensity change index was defined as the ratio of the amount of intensity change after tilt with respect to the tilt of 0 degree, and was calculated for each of the top hat central portion and the peripheral portion of the light power distribution.

  From Table 5, the homogenizer of this case is tilted because the intensity change is within -4% even when the tilt is 0.5 degrees, and the intensity change in the periphery of the top hat is within -25% even when the tilt is 2 degrees. It is understood that it is strong. Since the strength of the central portion is sufficient, there is no problem in processing even if the strength change in the central portion changes somewhat.

Comparative example

  With respect to the lens (single-sided aspherical surface, single-sided flat surface) of Example 1 of Patent Document 1, the power distribution when the tilt is tilted at 0 degree, 0.5 degree, and 2 degrees is shown in FIGS. 16 shows.

  Table 6 shows a summary of changes in intensity due to tilt in FIGS. 14 to 16 for the X and Y axes. Note that the Y axis is the tilt axis, and the X axis is the tilt center axis. The intensity change index was defined as the ratio of the intensity change amount after tilt with respect to the tilt of 0 degree, and was calculated for each of the central portion and the peripheral portion of the top hat portion.

(Example 3)
On the other hand, a biconvex aspherical lens having the same characteristics as the lens of Patent Document 1 was designed by the design method of the present invention, and its schematic configuration and light power distribution are shown in FIG. Here, the upper stage shows a state where the laser beam is condensed in addition to the schematic configuration of the homogenizer (FIG. 17 (a-1) is an enlarged view of the lens portion of FIG. 17 (a)), and the lower stage is at the condensing position. The power distribution is shown (FIG. 17 (b-1) is an enlarged view of the spot portion of FIG. 17 (b)).

  18, 19, and 20 show power distributions when the tilt of the lens is tilted at 0 degree, 0.5 degree, and 2 degrees, respectively.

The distance between the lens shown in FIG. 17 and the condensing position is 53 mm, the lens is made of optical glass having a refractive index of nd1.445846 and an Abbe number νd67.8, and an antireflection coating of magnesium fluoride MgF ₂ is formed on the surface. It is coated so that the center wavelength is 355 nm. The spot diameter of the top hat is 30 μm. In FIG. 17, the surface on the left side of the lens (R21 surface) is a convex aspherical surface, the paraxial radius of curvature is 33.5 mm, the conic constant K is 0, and the aspherical formula is as shown below.

The design method was the same as in Example 1. In particular,
(1) The method of setting the R22 surface starts by first setting the paraxial radius of curvature, but the radius of curvature at which Seidel's coma aberration coefficient is the best is a concave shape of 50 mm and 18 mm (concave and convex as a lens). A certain point is set to a convex shape of 156.21 mm (a biconvex shape as a lens) in which the coma coefficient becomes small while making the press molding easy and the convenience of shape measurement. FIG. 21 shows the relationship between the radius of curvature on the R22 surface and Seidel's coma aberration coefficient. Next, the aspherical shape of the R22 surface is obtained by adjusting the aspherical coefficient so that the spot diameter is minimized while the above paraxial curvature radius is fixed. At this time, the R21 surface has a spherical shape having a radius of curvature obtained together with the R22 surface by bending.

  (2) To divide the R21 surface into a plurality of regions, use the user-defined surface “multi-zone surface” of the optical design software (manufacturer: Radiant ZEMAX, LLC, product name: ZEMAX), and the diameter of the division starts from the center. 2.0 mm, 4.0 mm, 6.0 mm, 8.0 mm, and 10.0 mm are set, and the radius of curvature of each divided region is the curvature of the R21 surface obtained together with the calculation of the R22 surface in (1) above. A radius of 33.5 mm is given uniformly.

  (3) A method of setting the radius of curvature of each spherical surface so that the divided region is a spherical surface and the spherical aberration decreases as going from the center to the outside. First, the first radius of curvature is set to the spherical aberration of the region. When SA1, the diameter is D1, the focal length is f, and the spot diameter of the top hat is Ds, the condition that the spot diameter at the condensing position formed in the region of D1 matches Ds, that is, SA1 = f * Adjust so that it roughly matches SA1 obtained by Ds / D1. Basically, the second and subsequent curvature radii are adjusted so that the spherical aberration gradually decreases, but finally the adjustment is made so that the light beam power distribution has a desired shape including the first curvature radius. Do. The radius of curvature after adjustment is 33.5 mm, 33.49 mm, 33.484 mm, 33.485 mm, 33.43 mm from the center, and FIG. 22 shows the relationship of the spherical aberration with respect to each ring-shaped region after adjustment of the radius of curvature.

(4) A method of approximating these divided surfaces with an aspherical surface that smoothly connects adjacent surfaces is the following aspherical equation with respect to sag amount data (point cloud data) with respect to the diameter of the shape before approximation. The paraxial radius of curvature of the aspherical formula is 33.5 mm, the conic constant K is 0, and the calculation of the aspherical coefficients A1 to A14 is sag. Solves simultaneous equations consisting of sag amount and coefficients A1 to A14 by aspheric component obtained by subtracting spherical component (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 } from quantity Went by things.

Z (y) = (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 }
+ A ₁ · y + A ₂ · y ² + A ₃ · y ³ + A ₄ · y ⁴ + A ₅ · y ⁵
+ A ₆ · y ⁶ + A ₇ · y ⁷ + A ₈ · y ⁸ + A ₉ · y ⁹ + A ₁₀ · y ¹⁰
+ A ₁₁ · y ¹¹ + A ₁₂ · y ¹² + A ₁₃ · y ¹³ + A ₁₄ · y ¹⁴

(R21 surface aspherical)

  In FIG. 17, the surface on the right side of the lens (R22 surface) is also a convex aspherical surface, the paraxial radius of curvature is −156.21 mm, the conic constant K is 0, and the aspherical expression is as follows.

Z (y) = (y ² / r) / {1 + ((1−K) · y ² / r ² ) ^1/2 }
+ A ₄ · y ⁴ + A ₆ · y ⁶ + A ₈ · y ⁸ + A ₁₀ · y ¹⁰

(R22 surface aspherical)

  Table 9 summarizes the intensity changes due to tilt in FIGS. 18 to 20 for the X-axis and Y-axis. Note that the Y axis is the tilt axis, and the X axis is the tilt center axis. The intensity change index was defined as the ratio of the intensity change amount after tilt with respect to the tilt of 0 degree, and was calculated for each of the central portion and the peripheral portion of the top hat portion.

  From the comparison between Table 6 and Table 9, the homogenizer of Example 1 of Patent Document 1 cited as a comparative example has a strength change ratio of more than double at the center of the X section compared to the homogenizer of the present case designed with the same specifications. It is large and it is understood that it is weak against tilt as compared with the present invention.

  The aspherical lens of Example 1 was manufactured by press molding using an existing method (for example, the method described in Japanese Patent Application Laid-Open No. 2011-132059), incorporated into a homogenizer and evaluated, and it was confirmed that design performance was obtained.

  In the first embodiment described above, an aspheric surface having one convex surface is a convex aspheric surface on the other surface, but the present invention is not limited to this. The combination of the aspheric surfaces on each surface is convex-convex, convex-concave It is also possible to design a concave-convex shape. Similarly, in Example 2, the aspherical surface having one convex surface is a concave spherical surface, but the present invention is not limited to this, and the design is possible even when the aspherical surface is concave.

  As described above, according to the present invention, a homogenizer with little fluctuation in output characteristics even when the lens is tilted was obtained. Furthermore, since the lens of the present invention can be manufactured accurately at low cost by press molding, it can contribute to the cost reduction of the laser processing apparatus.

  The homogenizer of the present invention is used in a processing apparatus using a laser beam.

DESCRIPTION OF SYMBOLS 1 ... Aspherical homogenizer, 2 ... Double-sided aspherical lens, 3 ... Cover glass, 11 ... Aspherical homogenizer, 12 ... Single-sided aspherical lens, 13 ... Cover glass, 21 ... Aspherical homogenizer, 22 ... Double-sided aspherical lens

Claims (6)

This is a homogenizer consisting of a single lens for refracting and reducing a parallel incident beam with a Gaussian energy distribution to form a uniform energy distribution beam on the image plane in a diameter range smaller than the diameter of the incident beam. And
An aspherical homogenizer, wherein the lens is a double-sided aspherical surface. This is a homogenizer consisting of a single lens for refracting and reducing a parallel incident beam with a Gaussian energy distribution to form a uniform energy distribution beam on the image plane in a diameter range smaller than the diameter of the incident beam. And
An aspheric homogenizer, wherein the lens is an aspherical surface on one side and a concave spherical surface on the other side.   The aspherical surface on one side of the lens is formed of spherical surfaces each having a different curvature divided into a plurality of regions in a ring shape, and the spherical aberration is designed to decrease as the spherical surface goes away from the center, 3. The aspherical homogenizer according to claim 1 or 2, wherein the respective regions are connected by approximation with an aspherical expression that smoothly connects the spherical surfaces of adjacent regions.   The aspherical homogenizer according to any one of claims 1 to 3, wherein the lens is obtained by press molding. Set an arbitrary aspheric shape on one side,
The other surface is divided into a plurality of regions in a ring shape,
Each of the divided areas is a spherical surface having a different curvature, and the curvature of the spherical surface is set so that the spherical aberration decreases as going outward from the center,
Approximately connecting each region where the curvature of the spherical surface is set with an aspherical expression that smoothly connects the spherical surfaces of adjacent regions,
A single lens that refracts and reduces an incident beam that is parallel and has a Gaussian energy distribution to form a lens with a uniform energy distribution on the image plane in a diameter range smaller than the diameter of the incident beam. Design method of aspherical lens for homogenizer. Set an arbitrary concave spherical shape on one side,
The other surface is divided into a plurality of regions in a ring shape,
Each of the divided areas is a spherical surface having a different curvature, and the curvature of the spherical surface is set so that the spherical aberration decreases as going outward from the center,
Approximately connecting each region where the curvature of the spherical surface is set with an aspherical expression that smoothly connects the spherical surfaces of adjacent regions,
A single lens that refracts and reduces an incident beam that is parallel and has a Gaussian energy distribution to form a lens with a uniform energy distribution on the image plane in a diameter range smaller than the diameter of the incident beam. Design method of aspherical lens for homogenizer.

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