JPH11326616A - Mirror and optical condensing system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize efficient machining by using a mirror whose angle of inclination of the reflection face at each position of the mirror is designed corresponding to the spot shape and intensity distribution of a laser beam and to those of a beam emitted to an irradiated face. SOLUTION: A rectangular coordinate system, where an optical axis is the origin and the direction of an uniform intensity distribution to be converted is taken as a (y)-axis and the direction orthogonal to it is taken as an (x)-axis, is defined on a plane which includes a point S and is orthogonal to the optical axis of incident light. Assuming that a reflected light 4 from an arbitrary point P of a mirror 1 arrives at an irradiation position 5 and arrives at a point Q on the plane orthogonal to the optical axis in the irradiation position 5, it is sufficient if the point Q is so determined that a desired beam profile 6 which has a uniform intensity distribution with respect to a uniaxial direction be obtained in this position. In order to make the reflected light 4 of the mirror 1 arrive at a position corresponding to the point Q, it is sufficient if the normal of the curved surface at the point P of the mirror 1 divides ∠SPQ equally into two.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror for converting the intensity distribution of a laser beam into a desired intensity distribution in one axial direction, and to a focusing optical system using the mirror.

[0002]

2. Description of the Related Art When laser processing is performed using a laser oscillator, it is general to simply focus a laser beam into a circular shape and irradiate the laser beam to a processing surface. However, depending on the object to be processed, it may be desirable that the spot shape is other than a circle such as a rectangle and the intensity distribution is as uniform as possible. In that case, a rectangular spot is obtained by enlarging the laser beam, passing through a rectangular opening, and converging with a lens.

[0003]

However, according to this conventional method, only the high-intensity portion at the center of the beam is taken out of the aperture, so that the light beam outside the aperture does not contribute to the generation of energy, so that the efficiency is low. There was such a problem. In addition, the intensity distribution tends to be non-uniform depending on the shape of the opening.

On the other hand, when a linear spot is to be obtained, a laser beam is narrowed down by a combination of cylindrical mirrors for irradiation. However, according to this, there is a defect that only an elliptical spot can be obtained and the intensity gradually decreases toward the periphery.

There is also a method of scanning a laser beam focused on a point on a line, but the mechanism tends to be complicated, and it has been difficult to apply the method to a high-output CO ₂ laser.

The present invention has been made in view of such circumstances, and a main object of the present invention is to convert a laser beam having a certain shape and intensity distribution into a linear laser beam having a desired intensity distribution. An object of the present invention is to provide a mirror capable of converting light with high efficiency and a condensing optical system using the mirror.

[0007]

In order to achieve the above object, according to the present invention, a mirror for converting the intensity distribution of a laser beam into a desired intensity distribution in one axial direction is provided at an arbitrary point on the mirror. The inclination angle of the reflection surface with respect to the mirror bottom surface at P is an angle determined from a point Q obtained on the irradiation surface from the intensity distribution of the laser beam and a desired intensity distribution to be converted. The point S on the line is on a plane orthogonal to the incident optical axis, the point Q is on the irradiation plane, and the orthogonal coordinates (y and y 'axes are the directions of the desired intensity distributions to be converted with the optical axis as the origin, respectively) x,
y) and (x ', y') are defined, the beam cross section is divided into two regions by a straight line passing through the point S and parallel to the x-axis, and the ratio of the integrated values of the intensities in each region is calculated. The y 'coordinate of the point that internally divides the width of the desired intensity distribution is defined as the y' coordinate of the point Q, and the x coordinate of the point S is defined as the x 'coordinate of the point Q. Or the intensity of the laser beam is determined such that the normal of the curved surface at the point P divides ∠SPQ into two in a plane including As two mirrors for converting the distribution into a desired intensity distribution in the uniaxial direction,
The inclination angle of the reflection surface with respect to the mirror bottom surface at an arbitrary point P on the first mirror located on the light emitting source side of the mirrors is determined based on the intensity distribution of the laser beam and a desired intensity distribution to be converted. An angle determined from a point T obtained on the reflection surface of the second mirror located on the irradiation surface side of the two mirrors, and the inclination of the reflection surface on the second mirror at the point T The angle is the point P on the first mirror
And the angle determined by the point Q obtained on the irradiation surface, wherein the point T internally divides the beam width of the desired intensity distribution and the point Q internally divides the beam width of the desired intensity distribution. The ratio is the same value, and in a plane including the straight line SP and the straight line PT, the reflection of the first mirror is set so that the normal of the curved surface at the point P divides the ∠SPT into two equal parts. In the plane including the straight line PT and the straight line TQ, the inclination angle of the surface is determined,
It is provided that the inclination angle of the reflection surface of the second mirror is determined such that the normal of the curved surface at the point T divides ΔPTQ into two equal parts. In particular, a cylindrical mirror or a parabolic mirror that focuses in an axial direction perpendicular to the axis as a focal length at a distance from a position where a desired intensity distribution is obtained in a uniaxial direction, the mirror according to claim 1 or the parabolic mirror according to claim 2 The second mirror is arranged between the position of the second mirror described above and a position at which a desired intensity distribution is obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings.

FIG. 1 schematically shows a first embodiment of a condensing optical system for converting a laser beam into a uniform intensity distribution by a mirror according to the present invention.

As a light source of the light 2 incident on the mirror 1, a CO ₂ laser for laser processing with an average output of 10 to 20 kW is used. The light is incident on the mirror 1 with its optical axis aligned with the center of the mirror 1. The incident light 2 has a donut shape when irradiated on a plane orthogonal to the optical axis, and its intensity distribution I (r) is
Assuming that the distance from the center is r, the coefficient is a, and the beam radius is ω, the beam profile 3 has a pseudo TEM ₀₁ ^* ring mode intensity distribution as shown in the following equation.

[0011]

I (r) = a (r / ω) ² exp (r ² / ω ² )

FIG. 2 is a diagram viewed from a direction perpendicular to the optical axis of the light 2 incident on the mirror 1. The mirror 1 is formed from a copper base material into a sectional shape shown in FIG. 2 by machining or wire electric discharge machining. Here, assuming that the reflected light 4 from an arbitrary point P of the mirror 1 reaches the irradiation position 5 and reaches the point Q in a plane orthogonal to the optical axis at the irradiation position 5, it is uniform in the uniaxial direction. The point Q may be determined so that a desired beam profile 6 having an appropriate intensity distribution is obtained at that position. Then, in order for the reflected light 4 of the mirror 1 to reach the position corresponding to the point Q, the normal of the curved surface at the point P of the mirror 1 may be set so as to bisect ∠SPQ.

The relationship between the points P and Q for obtaining a uniform beam profile 6 at the irradiation position 5 with the intensity distribution in the direction orthogonal to the incidence plane is determined as follows. That is, in FIG. 2, the orthogonal coordinate system including the point S and orthogonal to the optical axis of the incident light including the point S is defined as a coordinate having the y-axis as the direction of the uniform intensity distribution to be converted with the optical axis as the origin and the x-axis as the direction orthogonal thereto. The beam cross section is divided into two regions by a straight line passing through the point S (x ₀ , y ₀ ) and parallel to the x-axis, and the integral values m and n of the intensity in each region are defined as The y coordinate of the point obtained by internally dividing the straight line with the ratio of the following formula is orthogonal to the plane including the point Q and orthogonal to the optical axis of the reflected light 4 with the direction of the intensity distribution to be transformed with the optical axis as the origin as the y 'axis. The coordinates are defined as the y 'coordinates of the defined point Q,
The coordinates of the point S are determined to be the x 'coordinates of the point Q.

[0014]

(Equation 2)

[0015]

(Equation 3)

That is, the coordinates of the point Q are given by the following equations.

[X ₀ , y ₀ {m / (m + n) -1/2}]

Hereinafter, the angle of inclination of the reflecting surface of the mirror 1 at the point P may be determined so that the incident light 2 at the point P of the mirror 1 is reflected and the reflected light 4 reaches the point Q. The sectional shape of the mirror 1 is obtained by integrating the inclination of the reflection surface.

The intensity of light passing through the irradiation position 5 integrated with respect to the x 'coordinate while keeping the y' coordinate constant is as follows:
The intensity distribution in the direction parallel to the y 'axis becomes uniform.

The direction of curvature in the direction of incidence in the plane of incidence is
When a cylindrical mirror 7 having a focal length of up to a distance between the mirror 1 and the irradiation position 5 is arranged, the reflected light 8 focuses the light in a direction parallel to the y-axis and the y'-axis. Then, a spot of the beam profile 6 having a constant intensity is obtained at any position on the line.

A parabolic mirror can be used instead of the cylindrical mirror 7. In this case, the position of the point Q may be determined in consideration of the fact that the parabolic mirror has a curvature in the y-axis direction.

As described above, by determining the angle of inclination at each position of the reflection surface of the mirror 1 in accordance with the intensity distribution of the incident light 2, the irradiation position 5 when combined with the cylindrical mirror 7 or the parabolic mirror is determined. In this case, the line profile can be focused with the beam profile 6 having a uniform intensity distribution. Surface processing can be performed using such a laser beam.

FIG. 3 schematically shows a second embodiment of the present invention in which beam shaping is performed by two mirrors 1 and 11. In the present embodiment, a second mirror 11 for reducing, enlarging, or parallelizing the width of a beam in a direction perpendicular to the incident surface is disposed between the mirror 1 and the irradiation position 5 in the first embodiment. Accordingly, the reflected light 4 of the first mirror 1 is converted into a parallel light having a predetermined width by the reflected light 12 of the second mirror 11. Further, by disposing the cylindrical mirror 7 or the parabolic mirror and the plane mirror 13 between the second mirror 11 and the irradiation position 5, the reflected light 14 of the plane mirror 13 and the reflected light 8 of the cylindrical mirror 7 Thus, a spot of the beam profile 6 focused in a line shape is obtained in the same manner as described above. FIG. 4 shows how light rays are converted at that time. Also in this case, the inclination and the shape of the reflection surface of the second mirror 11 are determined in the same manner as in the mirror 1 of the first embodiment.

FIG. 5 is a schematic view similar to FIG. 1 showing a third embodiment of the present invention for performing beam conversion into a catenary intensity distribution having both ends high and a center low, and FIG. 6 shows a mirror. 2
FIG. 2 is a diagram viewed from a direction orthogonal to an optical axis of incident light 2 to the light source 1. Here, the beam profile 3 of the incident light 2 on the mirror 21 has the same TEM ₀₁ ^* ring mode intensity distribution I (r) as shown in the above equation (1).

The reflected light 24 from an arbitrary point P on the mirror 21
Arrives at the irradiation position 25, and reaches a point Q in a plane orthogonal to the optical axis at the irradiation position 25, it is assumed that a catenary beam profile having both ends high and a center low intensity distribution at that position. The point Q may be determined so that 26 is obtained. In order for the light beam to reach the position corresponding to the point Q, the normal of the curved surface at the point P of the mirror 21 may divide the ∠SPQ into two equal parts.

The relationship between the points P and Q for obtaining a catenary beam profile 26 whose intensity distribution in the direction perpendicular to the plane of incidence at the irradiation position 25 is determined as follows. That is, in FIG. 6, orthogonal coordinates having the optical axis as the origin and the direction of the desired intensity distribution to be converted as the y-axis and the direction orthogonal thereto as the x-axis are orthogonal to the optical axis of the incident light including the point S. Defined on a plane that passes through the point S (x ₀ , y ₀ )
The beam cross section is divided into two regions by a straight line parallel to the axis, and the integrated values m and n of the intensities in each region are calculated by using the ratios of Expressions 1 and 2 as described in the first embodiment. The y coordinate y ₁ of a point that internally divides the catenary intensity distribution with respect to the y-axis direction is converted into a desired intensity distribution to be converted using the optical axis as an origin on a plane including the point Q and orthogonal to the optical axis of the reflected light 24. The coordinates are determined so that the orthogonal coordinates having the direction as the y 'axis are the y' coordinates of the defined point Q, and the coordinates of the point S are the x 'coordinates of the point Q. That is, assuming that the catenary intensity distribution function is I = f (y), y ₁ is determined so as to satisfy the following equation.

[0026]

(Equation 5)

[0027]

(Equation 6)

The coordinates of the point Q are given by (x ₀ , y ₁ ).

Hereinafter, the reflected light 24 from the point P of the mirror 21 will be described.
May be determined so that the angle of the reflection surface at the point P of the mirror 21 reaches the point Q. The cross-sectional shape of the mirror 21 is obtained by integrating the inclination of the reflection surface.

The intensity of light passing through the irradiation position 25 is represented by y ′
Keeping the coordinates constant and integrating about the x 'coordinate,
A catenary intensity distribution is given in a direction parallel to the y 'axis.

A curvature is given in the direction in the incident plane, and the irradiation position 2
Cylindrical mirror 2 with focal length up to 5
When the mirror 7 is disposed between the mirror 21 and the irradiation position 25, the reflected light 28 focuses the line in a direction parallel to the y-axis and the y′-axis. As for the intensity distribution on the line, a catenary beam profile 26 is obtained.

A parabolic mirror can be used in place of the cylindrical mirror 27. In this case, the position of Q may be determined in consideration of the fact that the parabolic mirror has a curvature in the y-axis direction.

As described above, the inclination angle at each position of the reflection surface of the mirror 21 is determined according to the intensity distribution of the incident light 2, so that the irradiation position 25 when combined with the cylindrical mirror 27 or the parabolic mirror is used. In this case, it is possible to perform line focus with the beam profile 26 having a desired catenary intensity distribution. Surface processing can be performed using such a laser beam.

FIG. 7 schematically shows a fourth embodiment of the present invention in which beam shaping is performed by two mirrors 21 and 31.
In the present embodiment, a second mirror 31 for reducing / enlarging or parallelizing the width of a beam in a direction perpendicular to the incident surface is disposed between the mirror 21 and the irradiation position 25 in the third embodiment. Accordingly, the reflected light 24 of the first mirror 21 is converted into parallel light of a predetermined width by the reflected light 32 of the second mirror 31. Further, by arranging the cylindrical mirror 27 or the parabolic mirror and the plane mirror 33 between the second mirror 31 and the irradiation position 25, irradiation of the beam profile 26 focused in a line shape in the same manner as described above. A light spot is obtained. FIG. 8 shows how light rays are converted at that time. Also in this case, similarly to the first mirror 21, the inclination angle and the shape of the reflection surface of the second mirror 31 are determined.

[0035]

As is apparent from the above description, according to the present invention, the spot shape and intensity distribution of the laser beam emitted from the laser oscillator correspond to the spot shape and intensity distribution of the beam irradiated on the irradiation surface. By using a mirror in which the inclination angle of the reflection surface at each position of the mirror is designed and a condensing optical system using the mirror, the intensity distribution focused in a linear shape is uniform or a desired catenary laser beam is provided. Can be obtained easily and with low energy loss, which makes the laser processing process advantageous and enables highly efficient processing.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a condensing optical system according to the present invention.

FIG. 2 is a schematic diagram showing how a laser beam is reflected by a mirror shown in FIG. 1 when viewed from a direction orthogonal to an incident surface.

FIG. 3 is a schematic view showing a second embodiment of the light collecting optical system of the present invention.

FIG. 4 is a schematic diagram of a state in which a laser beam is reflected by two mirrors in FIG. 3 when viewed from a direction orthogonal to an incident surface.

FIG. 5 is a schematic view showing a third embodiment of the light collecting optical system of the present invention.

FIG. 6 is a schematic diagram showing how a laser beam is reflected by a mirror shown in FIG. 5 when viewed from a direction orthogonal to an incident surface.

FIG. 7 is a schematic view showing a fourth embodiment of the light collecting optical system of the present invention.

FIG. 8 is a schematic diagram showing how a laser beam is reflected by two mirrors in FIG. 7 as viewed from a direction orthogonal to the incident surface.

[Explanation of symbols]

 1, 21 Mirror 2 Incident light to mirror 3 Beam profile of incident light 4, 24 Reflected light from mirror 5, 25 Irradiation position 6, 26 Desired beam profile 7, 27 Cylindrical mirror 8, 28 Reflected light from cylindrical mirror 11 , 31 second mirror 12, 32 reflected light from second mirror 13, 33 plane mirror 14 reflected light from plane mirror

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuji Yamamoto 1-1, Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works (72) Inventor, Kazushi Maruyama 1st, Tobata-cho, Tobata-ku, Kitakyushu No. 1 Inside Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. A mirror for converting an intensity distribution of a laser beam emitted from a laser oscillator into a desired intensity distribution in a uniaxial direction, wherein a reflection surface with respect to a mirror bottom surface at an arbitrary point P on the mirror. Is an angle determined from a point Q obtained on the irradiation surface from the intensity distribution of the laser beam and a desired intensity distribution to be converted, and a point S on a light ray incident on the point P is defined as an incident optical axis. And orthogonal coordinates (x, y), (x ', y'), where the direction of the desired intensity distribution to be transformed with the optical axis as the origin is the y-axis and the y'-axis, respectively. y '), the cross section of the beam is divided into two regions by a straight line passing through the point S and parallel to the x-axis, and the width of the desired intensity distribution is determined by the ratio of the integrated value of the intensity in each region. The y ′ coordinate of the internally divided point is defined as the y ′ coordinate of the point Q, and The x-coordinate of the point S is determined to be the x'-coordinate of the point Q, and in the plane including the straight line SP and the straight line PQ, the point P
2. The mirror according to claim 1, wherein the angle of inclination of the reflecting surface is determined so that the normal of the curved surface in [1] bisects [Sigma] SPQ. 2. A two-mirror for converting an intensity distribution of a laser beam emitted from a laser oscillator into a desired intensity distribution in one axial direction, wherein the two mirrors are located on a light source side of the two mirrors. The angle of inclination of the reflection surface with respect to the mirror bottom surface at an arbitrary point P on the first mirror is determined based on the intensity distribution of the laser beam and the desired intensity distribution to be converted, on the irradiation surface side of the two mirrors. Is the angle determined from the point T obtained on the reflection surface of the second mirror located at the position of the second mirror, and the inclination angle of the reflection surface at the point T on the second mirror is a point on the first mirror. P and an angle determined by a point Q obtained on the irradiation surface, and a ratio that the point T internally divides a beam width of a desired intensity distribution;
The ratio at which the point Q internally divides the beam width of the desired intensity distribution is the same value, and in the plane including the straight line SP and the straight line PT, the point P
The angle of inclination of the reflecting surface of the first mirror is determined so that the normal of the curved surface at the point divides ∠SPT into two equal parts, and at the point T in the plane including the straight line PT and the straight line TQ. The two mirrors are characterized in that the inclination angle of the reflection surface of the second mirror is determined so that the normal of the curved surface that divides it divides the PTQ into two equal parts. 3. The mirror according to claim 1, wherein a cylindrical mirror or a parabolic mirror that focuses in an axial direction perpendicular to the axis with a focal length being a distance from a position at which a desired intensity distribution is obtained in one axial direction. 3. A condensing optical system, wherein the condensing optical system is arranged between the position of the second mirror described in item 2 and a position at which a desired intensity distribution is obtained.