JPWO2007119838A1 - YAG laser, fiber laser lens and laser processing apparatus - Google Patents

Abstract

A glass lens or a quartz lens is used as a lens that refracts and condenses the beams of the YAG laser and the fiber laser. Lenses of these materials may not be able to properly give the front and back curved surfaces when performing a specific function of a single lens. Large aberrations may occur with glass and quartz lenses. When a single fθ lens is used, a beam refracted to the periphery may be deformed into an elliptical shape when a YAG or fiber laser beam having a circular cross section is scanned and applied to the lens. As a solution, a lens is manufactured using ZnSe as a material. Since ZnSe has a refractive index about 1 higher than that of glass or quartz, the curvature of the curved surface before and after the lens can be reduced and the aberration can be reduced. When the fθ lens is used, the elliptical cross section of the beam refracted to the peripheral portion can be reduced.

Description

  The present invention relates to a lens for a YAG laser or a fiber laser and a laser processing apparatus using the same. The wavelength of the YAG laser is 1.06 μm, which is near infrared light. The wavelength of the fiber laser is 0.9 μm, 1.06 μm, 1.11 μm, or the like. Although there are others, the wavelength of the fiber laser is near infrared light of 0.8 μm to 1.2 μm. As an optical system for the YAG laser and the fiber laser, a lens of ordinary optical glass (crown glass or flint glass) or a quartz lens can be used. The absorption of the optical glass is small and the transmittance is close to 100%. When a YAG or fiber laser beam is condensed and focused on the object to be processed to process the object to be processed, a group of lenses made of two to five optical glasses or quartz is used.

Japanese Patent Laid-Open No. 2003-164985 guides YAG laser light through an optical fiber, converts it into parallel light through a glass lens, diffracts it by a ZnSe diffractive optical component (DOE), and divides and shapes it into a plurality of beams having a desired shape. It is squeezed with a lens made by irradiating the transparent / opaque resin, which is the object, to melt the opaque resin instantly and bond it to the transparent resin. The front and rear glass lenses convert YAG light guided by a fiber into a parallel beam, put it in a diffractive optical component, collect the split beam, and irradiate the object. The diffractive optical component is divided vertically and horizontally and has pixels with different thicknesses, and a single parallel incident beam is converted into a number of beams. It is not mechanically vibrated like a galvanometer mirror and swings the beam back and forth. The beam is divided statically so that a strong beam can be irradiated to many points at the same time. The optical component for splitting the beam is a ZnSe diffractive optical component. Since heat is generated here, a cooling mechanism is provided to cool ZnSe. Resins (objects) to be cured are polypropylene, polycarbonate polyamide, polybutylene terephthalate, and the like. The cross section of the beam produced by the diffractive optical component may be a band, a ring, a quadrilateral ring, a lattice point, or the like. It depends on the resin distribution of the object. The reason why ZnSe is cooled with cooling water or the like is that it absorbs YAG light and generates heat.
Japanese Patent Laid-Open No. 2003-232993 combines four types of lenses having different refractive indexes in order to cancel out aberrations in an optical system composed of an imaging lens group, a field lens group, and a relay lens group of a camera mounted on an artificial satellite. Aberrations include spherical aberration, astigmatism, coma aberration, field curvature, distortion, etc. In order to cancel these aberrations, it is necessary to combine several lenses having different refractive indexes. Therefore, Japanese Patent Application Laid-Open No. 2003-232993 uses an optical system of an artificial satellite camera by combining eight lenses of four kinds of materials having different refractive indexes such as SLAH65, quartz, ZnSe, and ZnS. It receives infrared light from space and mainly receives light having a near infrared wavelength (980 nm to 1020 nm) in the 1 μm band so as to form an accurate image on the image plane. Not for laser.
Japanese Patent Application Laid-Open No. 2001-05191 is suitable for two-dimensional scanning with a strong pulsed light of a carbon dioxide laser with a wavelength of 10.6 μm with a galvanometer, etc. An fθ lens is provided. The lens material is ZnSe or Ge because it must pass strong light with a wavelength of 10.6 μm from a carbon dioxide laser. A first group of positive lenses convex on the object side, a second group of negative lenses concave on the object side, a positive lens alone or a positive / negative lens, or a combination of positive and negative lenses has a positive refractive index as a whole. Composed of the third group, the total focal length is f, the distance from the front focal point to the rear focal point is d, −2.2 ≦ f ₂ /f≦−0.3, 0.4 ≦ f ₃ / f ≦ 0.9, 1.8 ≦ d / f ≦ 2.4.

An optical glass lens or quartz is used to collect the light from the YAG laser and the fiber laser. This lens has a long track record and is suitable for a YAG of 1.06 μm and a fiber laser of 0.80 μm to 1.20 μm. The lens manufacturing method and polishing method are also mature. The material cost is low and useful. Even when a plurality of lenses are combined to suppress aberrations, the cost of material for each lens is low, so the cost does not increase so much even if a compound lens is used.
Glass lenses (crown glass, flint glass, etc.) can be made into a suitable shape by melting them and putting them in a mold. Although it is polished to a suitable surface, it is excellent in terms of cost and hardly absorbs. In view of cost, in the case of a combined lens in which a plurality of lenses are combined, an optical glass lens is suitable for a YAG laser and a fiber laser. Quartz has a track record as a YAG and fiber laser lens.
However, quartz and optical glass have a drawback that the refractive index is low. The optical glass has a refractive index n = 1.4 to 1.6 for YAG of 1.06 μm and fiber laser of 0.80 μm to 1.20 μm. Since the refractive index is low, the condensing diameter may be distorted and enlarged. In order to give the same light collecting performance to a lens having a lower refractive index, it is necessary to make the unevenness stronger. In other words, the curvature of the lens surface must be increased.
In particular, when the number of lenses used in the scanning optical system is small, the light condensing performance may be deteriorated outside the area if the refractive index is low. A scanning optical system is an optical system that scans a beam back and forth with a galvano mirror that reciprocally swings and a rotating prism mirror. When the beam is reflected by the galvanometer mirror and scanned left and right, the beam passes not only through the center of the lens but also around the periphery. Although the beam passing through the central part is well collected in a circular shape, the beam passing through the peripheral part spreads in an elliptical shape. That is inconvenient.
If the number of lenses is increased, such deformation of the beam shape can be prevented. Various aberrations can be canceled out by increasing the number of lenses. The above-mentioned Japanese Patent Application Laid-Open No. 2003-232993 also constitutes a refractive optical system having excellent imaging performance with few aberrations by combining 8 to 9 lenses. In the case of a camera mounted on an artificial satellite, there is no need to reduce the cost, so there may be a large number of lenses. However, in the case of consumer equipment, there are cases where low-cost demands are strong.
As for the fθ lens for the carbon dioxide laser, it is preferable to make an optical system with less aberration by combining two or more lenses as described in JP-A-2001-05191. If the aberration is large, uniform processing cannot be performed over the entire surface.
The YAG and fiber laser lens of the present invention is a lens using ZnSe. One or two to five minority lenses made of ZnSe. In the case of a plurality of lenses, ZnSe may be used for one or more of them, but it is suitable for a single fθ lens. Since the refractive index is higher than that of glass, folding can be reduced. Therefore, aberration can be suppressed. The desired effect can be increased with a few lenses. When a single fθ lens is used, the curvature of the concave surface on the front surface can be increased, and the elliptical distribution of the power distribution of the beam spot irradiated on the image surface can be prevented. A single fθ lens with good performance can be provided.
The present invention uses a ZnSe lens instead of an optical glass (flint glass, crown glass) lens or quartz lens to focus the beam of 1.06 μm of YAG laser and 0.80 μm to 1.20 μm of fiber laser. ing. Since ZnSe has a refractive index about 1 higher than that of glass, it has a high refractive power. Since the refractive index is high, the curvature can be reduced even when the same focal length is given. FIG. 10 schematically shows the relationship between the curvature 1 / R ₁ of the front surface of the lens that gives the same focal length (positive in the convex case) and the curvature 1 / R _{2 of the} rear surface (positive in the convex case). It is a graph to show. The solid line shows the case of a quartz lens. Both the curvature of the front surface (first surface) and the rear surface (second surface) are large. A broken line is a case of a ZnSe lens. The curvature is small on both the front and rear surfaces. The small curvature is easy to make because the curvature radius is large.
If the curvature is small, it is easy to make a lens. In addition, aberration is reduced. Therefore, even with a single lens or a simple lens group, beam distortion at the peripheral portion can be reduced. In the case of a single lens made of normal glass or quartz, the curvature is large, so that aberrations are large. In the case of a single lens, if a ZnSe lens is used, the beam distortion at the peripheral portion can be reduced to about 1/2 to 1/4 as compared with a glass lens. A scanning system lens that also uses the periphery of the lens, and a lens made of ZnSe as the lens in the case of a branched beam system using diffractive optical components are optimal.
I am worried about absorption. However, ZnSe has almost no absorption at the wavelength of 1.06 μm of the YAG laser and 0.80 μm to 1.20 μm of the fiber laser, and is almost the same as a glass lens.
Since ZnSe is more expensive than optical glass, the material cost increases. However, it is also possible to configure a single lens that is equivalent to a combination of two to four glass lenses so far. Including the mount often has a cost advantage. Similarly, with a single lens, ZnSe is more useful because it has less beam distortion at the periphery.

FIG. 1 is a schematic configuration diagram of an optical system in which a YAG laser beam is scanned by two galvanometer mirrors G and condensed on an image plane by a single fθ lens.
FIG. 2 is a diagram showing the intensity distribution of the beam spots at the center and the periphery on the image plane I when a quartz glass lens and a ZnSe lens are used as the single fθ lens N. FIG. On the image plane, a 15 mm, 30 mm, 45 mm, 60 mm, and 75 mm square area is assumed, and the beam power distribution at the outermost corner is indicated by contour lines.
FIG. 3 is an explanatory diagram of an optical system showing beam paths on a galvano mirror (light source point) G, an fθ lens N, and an image plane I, which are beam swing points, for explaining the focusing action of a single fθ lens N. It is.
FIG. 4 shows a case where the paraxial ray has a long focal length and is focused on the image plane I in the single lens fθ lens N, but the far-axis ray has a short focal length and therefore is condensed on the lens side from the image plane I and has no aberration. FIG. 5 is an optical system explanatory diagram showing beam paths in a galvanometer mirror (light source point) G, an fθ lens N, and an image plane I for explaining that the image can be made to have fθ characteristics from the center.
FIG. 5 shows that in the single-lens fθ lens N, the far-axis ray is incident on the front surface (R1) of the lens obliquely and is projected onto the image plane I by a beam that is assumed to start from the image point. FIG. 4 is a perspective view of a light source point G, an fθ lens N, and a light beam on the image plane I for explaining that the image plane I becomes an ellipse extending in the radial direction.
In FIG. 6, in the single-lens fθ lens N, the curvature radius R1 of the front surface of the lens is much longer than the distance a between the light source and the lens, so that the parallel circular section beam from the light source point G is incident on the front surface R1 obliquely. FIG. 3 is an optical system configuration diagram for explaining that an elliptical cross section is formed on a surface, which becomes a right cylindrical beam from an image point H and is narrowed down by a lens to become an elliptical cross section spot on an image plane I;
Figure 7 is parallel cylindrical section from the light source point G beam S _G is out of the elliptical cross-section at the front of the lens point E gradually beam S beam from _E next image point H is reduced elliptical cross-section with the lens as an ellipse S _H section It is beam sectional drawing for demonstrating that the cross section of the cylindrical beam used as spot beam _SJL changes.
FIG. 8 illustrates that when a single fθ lens N is made of a quartz lens and a ZnSe lens, it is difficult to make the front surface a strong concave shape in order to prevent elliptic distortion of the beam cross section. It is lens sectional drawing for. 8A is a quartz lens, and FIG. 8B is a cross section of a ZnSe lens.
FIG. 9 is a diagram showing cross sections of a quartz lens and a ZnSe lens for having the same focal length f in the case of a biconvex lens. The quartz lens is stronger and enlarged at the center. The ZnSe lens has a small bulge at the center.
FIG. 10 is a graph showing values that the front / rear surface curvatures 1 / R ₁ and 1 / R ₂ should satisfy when the convex shape is positive, the radii of curvature of the rear surface of the front surface of the lens are R ₁ and R ₂ , and the focal lengths are the same. It is. It can be seen that the quartz lens has a total curvature more than three times that of the ZnSe lens and is difficult to form.
In FIG. 11, the 10.6 μm light of the carbon dioxide laser and the 1.06 μm light of the YAG laser are superimposed on the same optical axis by a mixing filter, and the carbon dioxide laser and the YAG laser beam are emitted by a ZnSe lens. It is a block diagram of the laser processing apparatus which squeezed and irradiated to a target object so that both cutting and welding could be performed.

The case of a lens used for a YAG laser will be described below. The same applies to fiber lasers. An fθ lens can be approximated using a single convex lens. Unlike those using three to five lenses as disclosed in JP-A-2001-05191, various aberrations cannot be canceled. However, since it functions as an fθ lens, it can be a low-cost fθ lens. What kind of arrangement is the fθ lens? First, I will explain that. FIG. 1 shows the structure of the embodiment, which will be described later but will be briefly described here. The YAG laser beam is shaped into a parallel beam having a wide diameter by a collimator (not shown). Collimated beam is y direction scanning by the first galvanometer mirror M _1, the x-direction scan in the second galvanometer mirror M _2. The scanning beam is condensed by a lens N supported by the mount MT and irradiated to a point J having an image plane I. Since scanning is performed in the xy direction, the point J moves back and forth. Since it is a pulse laser, it becomes a remote irradiation point.
In the following, explanations will be made so that the comparison becomes clear with some bold assumptions and approximations, including mathematical formulas. I think there are some points that are not theoretical, but I think they are good for understanding the image.
fθ lens becomes a problem from the second galvanometer mirror M ₂ or later. This point is hereinafter referred to as G. FIG. 3 is a schematic diagram of an fθ lens optical system including a galvanometer mirror G, a convex lens N, and an image plane I. The galvanometer mirror G, the center K of the lens N, and the center O of the image plane I are aligned on the z-axis direction. The optical axis can be expressed by GKO. Y-direction galvano mirror G is a two, if adapted to swing in the x direction, where may be considered only galvanometer mirror M ₂ towards the back. The center of oscillation of the galvanometer mirror is G. The distance between the lens N and the image plane I is f. It is assumed that the parallel laser beam is reflected by the galvanometer mirror G in the direction of θ. The beam is GE.
Therefore, ∠EGK = θ. This is refracted by the lens N and hits point J on the image plane I. A straight line KJ drawn from the lens center K to the irradiation point J forms an angle θ with the optical axis KO. ∠ JKO = θ. The distance between the lens center K and the image plane center O is the focal length f. OJ = ftan θ.
The distance from the lens center K to the galvanometer mirror G is assumed to be a. The light source point G (a) is closer to the lens than the front focal point. The position of the image with respect to it is set as H point. This is simply called an image point H. The image plane I and the image point H are completely different. Do not confuse. This can be at a position farther backward from the lens K than the light source point G. The distance of the image point H from the lens center K is b. Since b is intuitively easy to understand, b takes a positive value.
The light emitted from G is refracted by the lens N and reaches the point J on the image plane I. OJ = x = ftanθ. The image point H can be an erect virtual image. It seems that a straight beam HEJ comes out from the H point. In the triangle HKJ, GE and KJ are parallel. In the triangle HJO, EK and JO are parallel.
a: b = GK: HK = EJ: HJ = KO: HO = f: (f + b) (1)
It becomes. From here bf = a (f + b) (2)
But the whole is divided by abf,
1 / a-1 / b = 1 / f (3)
It becomes. This is equivalent to the relationship between the light source / lens / image distances a and b of the thin lens and the focal length f. Since KO = f, the parallel beam can be converged on the image plane. If the arrangement is such that the light source is closer to the lens than the front focal point (a <f) and a virtual image (b> a) is formed in front of the lens and before the light source, the parallel beam is shaken back and forth and the image is It can be converged on plane I. However, it only becomes an ftan θ lens. Nevertheless, by appropriately controlling the movement of the galvanometer mirror G, the beam spots can be applied to the image plane at equal intervals. When the movement of the galvanometer mirror G is an equiangular velocity, in order to draw spots on the image plane I at equal intervals, ftanθ is not sufficient, and an fθ lens must be used.
It is easy to give fθ property when a plurality of lenses are combined. Even if one lens is made aspherical, it is possible. However, aspheric surfaces are expensive. Here, it is considered that a spherical lens is used as close as possible to fθ without using an aspherical surface. The thin lens formula (3) is an approximation that holds for paraxial rays, and shifts for far-axis rays. Since the far-axis ray is strongly refracted by the lens, the focal point also approaches the lens side.
Paraxial ray GE ₁ constituting the optical axis and theta ₁ as shown in FIG. 4 as converging to a point J ₁ of the image plane I, the far axis ray GE ₂ J ₂ constituting the optical axis and theta ₂ is closer than Q Converges at ₂ points. That is, the focal length is effectively shortened. Because it is ∠P ₂ KO = θ _2, it is an OP ₂ = ftanθ 2. If the far-axis ray Without shortening of the focal length should leading to P ₂ point is ∠P _{2 KO} = θ 2. However, since the focal length of the far-axis ray is shortened, the far-axis ray follows the path GE ₂ Q _{2 and} is condensed at the point Q ₂ . Therefore, the irradiation point on the image plane I becomes J ₂ and is closer to the center O than P ₂ . Therefore, the distance OJ ₂ from the center of the incident point is closer to fθ than to ftanθ. This is the reason why even a single spherical lens can be used as an approximate fθ lens. Among them, it is necessary to appropriately determine the distance a between the swing point G and the lens center K in order to approach the fθ lens.
The image plane I is the beginning of the diverging from made in front of the converging point Q _2. As such, the focal point of the paraxial ray (Gauss image plane) is far, and the focal point of the far axis ray is near. In practice, the focal length f may be an intermediate distance rather than the focal point of the paraxial ray. In that case, KO means an average focal length <f>.
The present invention claims that when a YAG laser optical system is constituted by a single lens, a ZnSe lens is superior to quartz because of less distortion. In the case of a single fθ lens, even if the spot interval satisfies the fθ property, there is a problem that the beam cross section of the far-axis ray at the irradiation point is distorted into an ellipse.
The reason why the projection of the far-axis ray on the image plane I is distorted into an ellipse will be described with reference to FIG. This is a perspective view of the optical system of FIGS. Although the lens center K and the image plane center O are further away from each other, they are drawn close to each other for easy understanding of the beam shape. The galvanometer mirror G is a parallel beam (S _G ) having a circular cross section. FIG. 7 (1) shows an _SG beam cross section. The parallel circular cross-section beam is incident on the lens N at an angle θ. Non-normal incidence is made on the front surface of the lens N. Since the angle formed with the front surface of the lens (the radius of curvature R ₁ ) is not 90 degrees, an ellipse (S _E ) extending in the radial direction is formed. 7 (2) shows a cross-section of _{S E.}
Image point a S _E stroking it becomes S _H been growing rays from H so H. The cross section _SH is shown in FIG. The beam is converged with the cross section. S _{JS on the} image plane. Although this is small and difficult to understand, the lens action is a reduction action, so it should be similar to the ellipse S _JL determined by the intersection of the elliptic cylinder extending from the image point H and the image plane I. An enlarged S _JL is shown in FIG. The reason why this becomes an ellipse having a higher eccentricity is that the angle formed by the beam from the image point H and the image plane I is deviated from a right angle.
From FIG. 5, the ovalization of the far-axis ray on the image plane I is that the angle formed by the beam GE from the point G and the front surface of the lens N (first surface: radius of curvature R ₁ ) is greatly deviated from a right angle. It can be seen that this is caused by There are caused to other, is the largest cause is that GE and the first surface R ₁ intersects obliquely. Since there are differences in the lens incident point on the upright normal and incident ray (incident angle of the lens Υ is not 0) S _E has an elliptical.
The incident angle at the lens surface (the angle of the normal to the incident beam) and Υ the lens surface R ₁ extending at a rate of 1 / cosΥ radially. Since it does not change in the circumferential direction, it becomes an ellipse. This means that ovalization can be prevented by making the incident angle Υ closer to zero. GK = a a (light source lens distance), the radius of curvature of the first surface is _{R 1.} This makes the case of a concave surface positive. The deviation from the center of the incident point on the lens surface is h (h = KE). Υ is an approximate expression Υ = (h / a) − (h / R ₁ ) (4)
It can be expressed as follows. If R ₁ = a, the GE line and the first lens surface are orthogonal and Υ = 0. In that case _{S E} becomes a circle.
However, a is a very small distance, and it is impossible to make a lens having a remarkable curvature such that R ₁ = a. R ₁ > a is always satisfied.
By bringing R1 as close as possible to a, elliptic distortion of the far-axis ray (h is large) can be reduced. By making the first surface of the lens N a strong concave surface, the problem of elliptic distortion can be reduced as R ₁ → a.
However, the desired focal length f is given first. Although approximate, the focal length f, the refractive index n, and between the front and rear curvature radii R ₁ and R ₂ of the lens (1 / R ₂ ) − (1 / R ₁ ) = 1 / (n−1) f (5)
There is such a relationship. R ₁ and R ₂ are the curvature radii of the front and rear surfaces, and (1 / R ₁ ) and (1 / R ₂ ) are the curvatures of the front and rear surfaces. Since R ₁ is concave and R ₂ is positive, the sign of (5) is different. The right side of (5) is inversely proportional to the refractive index n minus 1. In the case of quartz, (n-1) is approximately 0.45, and (5) the right side is 2.2 / f and becomes large. I want to make R ₁ small, but then (1 / R ₁ ) becomes large. That is why 1 / R ₂ is significantly increased. Increasing the curvature 1 / R ₂ of the rear surface of the lens means making the lens enlarged. It is difficult to make, but it can be made to some extent. However, there are still limitations.
However, when ZnSe is used as a lens, (n-1) is about 1.5, and (5) the right side is about 0.66 / f, which is small. About 1/3. Therefore, even if 1 / R ₁ is increased, 1 / R ₂ does not have to be increased too much. In this way, a large 1 / R ₁ and 1 / R ₂ can be easily produced.
8A and 8B show cross sections of a quartz lens and a ZnSe lens that give the same focal length f. The first surface R ₁ is a concave surface. In the case of a quartz lens, the second surface has a large curvature (1 / R ₂ ) and is an enlarged lens. On the other hand, ZnSe has an advantage that the first surface can be a concave surface with a considerably large curvature, and the curvature of the second surface does not have to be so large.
Because so there is 1 / _{R 2} limit, it can not be increasing the curvature 1 / _{R 1} of the first surface when the quartz can be increased ZnSe in 1 / _{R 1.} That can reduce the distortion of the far-axis ray.
What has been described above is the case of a single fθ lens. However, the present invention is not limited to this, and since ZnSe can lower the curvatures 1 / R ₁ and 1 / R ₂ of the front and rear surfaces compared to quartz and glass, it is easy to manufacture and also has a small aberration.
FIG. 9 shows an example of a biconvex lens. This is also an enlarged lens type in the case of a quartz lens. In the case of ZnSe, the curvature can be further reduced even in the case of biconvexity. In this case, assuming that the curvature radii of the front and rear surfaces are R ₁ and R ₂ and both are convex, it is approximated to the same degree as before (1 / R ₂ ) + (1 / R ₁ ) = 1 / ( n-1) f (6)
It becomes. In the case of ZnSe, the right side is small, so the left side may be small. Therefore, it is a ZnSe lens with a small curvature.
FIG. 10 is a graph showing a relationship that the front surface curvature 1 / R ₁ (positive convexity) and the rear surface curvature 1 / R ₂ of a quartz lens and a ZnSe lens having the same focal length should be satisfied. This is the case of a lens having positive refractive power with a positive focal length because a 45 degree straight line crosses the first quadrant. ZnSe can reduce the absolute value of the curvature on both the front and rear surfaces. A small curvature means that it is easy to manufacture. In addition, the aberration is small when the curvature is small.
In the case of a single fθ lens, it is desired to reduce the radius of curvature of the concave surface (R ₁ <0) on the front surface. Instead of FIG. 10, two graphs crossing the third quadrant can be written. This is the case of a concave lens as a whole and having a negative refractive power. Even in that case, ZnSe has a smaller absolute value of curvature and is easier to make, and aberrations are also smaller.

二種類のレンズの曲率半径、厚み、直径などは次のようである。レンズの曲率半径の符号は、左に中心があり右に円弧を書いたときＲを正にする。だからここではＲ_１については凹面が正に、Ｒ_２については凸面が正になる。
合成石英レンズＮ_１
入射面側曲率半径Ｒ_１＝１９２．７１ｍｍ（凹面）
出射面側曲率半径Ｒ_２＝ ５０．５３ｍｍ（凸面）
中心厚み Ｈ_１＝ ７．２ｍｍ
レンズ直径 Ｄ_１＝ ４０ｍｍ
ＺｎＳｅレンズＮ_２
入射面側曲率半径Ｒ_１＝ ８２．２８ｍｍ（凹面）
出射面側曲率半径Ｒ_２＝ ６２．８４ｍｍ（凸面）
中心厚み Ｈ_２＝ ６．４ｍｍ
レンズ直径 Ｄ_２＝ ４０ｍｍ
図８に石英、ＺｎＳｅレンズの断面概略を示す。これは厚み方向を誇張して書いてある。そのような光学系とレンズ系によってＹＡＧレーザビームを左右前後に走査する。この例で石英レンズの前面曲率半径と後面曲率半径の比率は３．８倍である。ＺｎＳｅレンズの前面曲率半径と後面曲率半径の比率は１．３倍である。曲率半径の比率はＺｎＳｅの場合２以下にすることができる。前後どちらが大きい場合もあるので前面曲率半径絶対値｜Ｒ_１｜と後面曲率半径絶対値｜Ｒ_２｜の比｜Ｒ_１｜／｜Ｒ_２｜を０．５〜２の間に納めることができる。さらに好ましくは、比｜Ｒ_１｜／｜Ｒ_２｜を０．７〜１．４の間とすることができる。
像面Ｉにおけるビームパワー分布を測定し等高線によってパワーを表現したものが図２である。中央部や周辺部でのビームパワー分布を示す。それらは９重の同心の環を持つ等高線であるが中央のパワー密度を１として、中央から順に０．９、０．８、０．７、０．６、０．５、０．４、０．３、０．２、０．１のパワー密度の点を結んだものである。
合成石英レンズでもＺｎＳｅレンズでも、初めの段に示す像面中央部（ｘ＝０、ｙ＝０）でのパワー分布はきれいな円筒対称である。歪みなくビームがうまく集光されているということが分かる。
次の段に示すのは、像面Ｉの１５ｍｍ角最外点（ｘ＝７．５ｍｍ、ｙ＝−７．５ｍｍ）でのパワー分布である。石英レンズでもＺｎＳｅレンズでも等方的な９重の同心円となりビームは歪みなく集光される。
３段目に示すのは、像面Ｉの３０ｍｍ角最外点（ｘ＝１５ｍｍ、ｙ＝−１５ｍｍ）でのパワー分布である。石英レンズでもＺｎＳｅレンズでも均一の９重の同心円となり歪みはない。
４段目に示すのは、像面Ｉの４５ｍｍ角最外点（ｘ＝２２．５ｍｍ、ｙ＝−２２．５ｍｍ）でのパワー分布である。石英レンズの場合、パワー密度が歪みｘ−ｙ方向（右下方向）に長くなっている。ｘｙ方向（右上方向）に比べ約１．５倍に伸びている。ＺｎＳｅレンズの場合は殆ど歪みはなくて同心のパワー分布となっている。
５段目に示すのは、像面Ｉの６０ｍｍ角最外点（ｘ＝３０ｍｍ、ｙ＝−３０ｍｍ）でのパワー分布である。石英レンズの場合、パワー密度が歪みｘ−ｙ方向に長くなっている。ｘｙ方向に比べ約１．９倍に伸びている。またパワーが分散しており等高線の間隔が広がっている。ＺｎＳｅレンズも歪みが現れｘｙの方向に伸びている。しかし石英レンズに比べてパワー分布の広がりは小さい。ｘｙ（右上）方向の伸び及びｘ−ｙ（右下）方向の伸びで比較すると約６０％程度である。周辺へ向かうビームに対してＺｎＳｅレンズの集光性の方が優れていることが分かる。
６段目に示すのは、像面Ｉの７５ｍｍ角最外点（ｘ＝３７．５ｍｍ、ｙ＝−３７．５ｍｍ）でのパワー分布である。石英レンズの場合、パワー密度が歪みｘ−ｙ方向に一段と長くなっている。ｘｙ方向に比べ約１．９倍に伸びている。またパワーが分散しており等高線の間隔が広がり中央でのパワー広がりに比べてｘｙ方向で約２．４倍、ｘ−ｙ方向で約４．５倍に広がっている。ＺｎＳｅレンズも歪みが現れｘｙの方向に伸びている。ＺｎＳｅの中央部でのパワー広がりに比べ、ｘｙ方向には殆ど違いがない。ｘ−ｙ方向には２．５倍程度広がっている。しかし石英レンズに比べてパワー分布の広がりは小さい。ｘｙ（右上）方向の伸びで比較すると４５％程度、ｘ−ｙ（右下）方向の伸びで比較すると約５３％程度である。大体半分の広がりであり面積にすると約１／４の広がりである。特性が改善されている。周辺へ向かうビームに対して石英レンズより、ＺｎＳｅレンズの方が集光性において格段に優れていることが分かる。
ガルバノミラーＧでビームを左右前後に揺動するのだから中央部分のみ集光性がよくても何にもならない。周辺部での集光性がよいということが重要である。その点でＺｎＳｅレンズが石英レンズよりも好適だということである。
以上は１枚ｆθレンズを例にとって説明したが、複数枚からなる組レンズにおいてもそのうちの１枚以上をＺｎＳｅとすることで特性を向上させ得ることは、その原因が屈折率が高いことである故に明らかである。[Example 1: Example of one fθ lens]
The pulsed YAG laser beam was scanned by two galvanometer mirrors G oscillating in two directions of the x axis and the y axis, condensed by one fθ lens, and irradiated onto the image plane I in a spot shape. Then, the power distribution of the spot beam in the central part and the peripheral part was examined. The YAG laser beam is a Gaussian beam, and its beam diameter is φ5 mm when the position at which it attenuates to 1 / e ² of the peak power is taken as the periphery. FIG. 1 is a schematic diagram of an optical system.
Providing the first galvanometer mirror M ₁ for y-direction scanning by reflecting a laser beam in front of the YAG laser (M1 across). The mirror is swung around an axis parallel to the z axis to perform sub-scanning. X-direction from M _1, the distance by further reflecting the laser beam at the position of L ₁ providing the second galvanometer mirror M ₂ for x-direction scanning. The mirror is swung around an axis parallel to the y axis to perform main scanning. The beam reflected for the second time is a parallel beam that remains φ5 mm. Providing a mount MT to the position of the forward (z-direction) _{L 2} of the second galvanometer mirror _{M 2.} A single fθ lens N is provided on the mount MT.
As described with respect to Japanese Patent Laid-Open No. 2001-05191, it is common that the fθ lens is formed by combining four, five, and six lenses to cancel out aberrations. Originally, it is somewhat impossible to make an fθ lens with one lens, but here a single lens is used for cost reduction. Both material cost and production cost can be reduced, and the structure of the mount MT can be simplified. On the other hand, large aberrations appear.
Here, since xy scanning is performed by the galvanometer mirror G, the distortion of the beam at the peripheral portion increases. It must be possible to suppress beam distortion at the periphery.
there is an image plane I to the position of the z-direction forward distance L ₄ of the fθ lens. By oscillating the galvanometer mirror G, the image plane I is irradiated with a pulse laser at a plurality of points. Table 1 shows the parameters of the optical system and the lens. The unit of length is mm.
A synthetic quartz lens N ₁ and a ZnSe lens N ₂ were used.
For YAG laser light (1.06 μm)
Refractive index of synthetic quartz n ₁ = 1.44963
ZnSe refractive index n ₂ = 2.48196
It is. There is a difference of about 1.0 in refractive index. Although it is a single fθ lens and it is preferable to use an aspherical surface in order to suppress aberrations, a spherical lens is used instead of an aspherical surface in consideration of cost. In the case of a spherical lens, the lens surface can be formed by a general-purpose device, so that the cost can be reduced. Here, all are concave-convex lenses. Table 1 shows the arrangement of the optical system, ZnSe, and parameters of the quartz lens.
Table 1

The radius of curvature, thickness, diameter, etc. of the two types of lenses are as follows. The sign of the radius of curvature of the lens makes R positive when the center is on the left and an arc is written on the right. So where concave positive for R ₁ is convex is positive for R _2.
Synthetic quartz lens N ₁
Incident surface side radius of curvature R ₁ = 192.71 mm (concave surface)
Output surface side radius of curvature R ₂ = 50.53 mm (convex surface)
Center thickness H ₁ = 7.2 mm
Lens diameter D ₁ = 40 mm
ZnSe lens N ₂
Incident surface side radius of curvature R ₁ = 82.28 mm (concave surface)
Output surface side radius of curvature R ₂ = 62.84 mm (convex surface)
Center thickness H ₂ = 6.4 mm
Lens diameter D ₂ = 40 mm
FIG. 8 shows a schematic cross section of a quartz and ZnSe lens. This is exaggerated in the thickness direction. With such an optical system and a lens system, a YAG laser beam is scanned back and forth. In this example, the ratio of the front curvature radius and the rear curvature radius of the quartz lens is 3.8 times. The ratio of the front curvature radius and the rear curvature radius of the ZnSe lens is 1.3 times. The ratio of the radius of curvature can be 2 or less in the case of ZnSe. Since the front and rear may be larger, the ratio of the absolute value of the front curvature radius | R ₁ | to the absolute value of the rear curvature radius | R ₂ | | R ₁ | / | R ₂ | . More preferably, the ratio | R ₁ | / | R ₂ | can be between 0.7 and 1.4.
FIG. 2 shows the beam power distribution on the image plane I and the power expressed by contour lines. The beam power distribution at the center and the periphery is shown. They are contour lines with 9-fold concentric rings, but the power density at the center is 1, and 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0 in order from the center. .3, 0.2, 0.1 power density points are connected.
In both the synthetic quartz lens and the ZnSe lens, the power distribution at the center of the image plane (x = 0, y = 0) shown in the first stage is clean cylindrical symmetry. It can be seen that the beam is well focused without distortion.
The next stage shows the power distribution at the 15 mm square outermost point (x = 7.5 mm, y = −7.5 mm) of the image plane I. Both the quartz lens and the ZnSe lens are isotropic nine-fold concentric circles, and the beam is collected without distortion.
The power distribution at the 30 mm square outermost point (x = 15 mm, y = −15 mm) of the image plane I is shown in the third row. Both the quartz lens and the ZnSe lens are uniform nine-fold concentric circles and have no distortion.
The fourth row shows the power distribution at the 45 mm square outermost point (x = 22.5 mm, y = −22.5 mm) of the image plane I. In the case of a quartz lens, the power density is longer in the strain xy direction (lower right direction). It extends about 1.5 times compared to the xy direction (upper right direction). In the case of a ZnSe lens, there is almost no distortion and the power distribution is concentric.
The power distribution at the 60 mm square outermost point (x = 30 mm, y = −30 mm) of the image plane I is shown in the fifth row. In the case of a quartz lens, the power density is long in the strain xy direction. It extends about 1.9 times compared to the xy direction. Moreover, the power is dispersed and the interval between the contour lines is widened. The ZnSe lens also shows distortion and extends in the xy direction. However, the spread of power distribution is small compared to quartz lenses. When compared with the elongation in the xy (upper right) direction and the elongation in the xy (lower right) direction, it is about 60%. It can be seen that the light collecting property of the ZnSe lens is superior to the beam toward the periphery.
The sixth stage shows the power distribution at the 75 mm square outermost point (x = 37.5 mm, y = -37.5 mm) of the image plane I. In the case of a quartz lens, the power density is further increased in the strain xy direction. It extends about 1.9 times compared to the xy direction. In addition, the power is dispersed, the interval between contour lines is widened, and is about 2.4 times in the xy direction and about 4.5 times in the xy direction compared to the power spread in the center. The ZnSe lens also shows distortion and extends in the xy direction. Compared to the power spread in the central part of ZnSe, there is almost no difference in the xy direction. It expands about 2.5 times in the xy direction. However, the spread of power distribution is small compared to quartz lenses. Compared with the elongation in the xy (upper right) direction, it is about 45%, and compared with the elongation in the xy (lower right) direction, it is about 53%. The area is roughly half of the area, and the area is about 1/4. The characteristics have been improved. It can be seen that the ZnSe lens is much more excellent in the light condensing performance than the quartz lens with respect to the beam toward the periphery.
Since the beam is swung back and forth by the galvanometer mirror G, nothing will happen even if the central portion has good light collecting properties. It is important that the light collecting property at the peripheral part is good. In this respect, the ZnSe lens is more suitable than the quartz lens.
In the above description, a single fθ lens has been described as an example. However, even in a combination lens composed of a plurality of lenses, it is possible to improve the characteristics by using one or more of them as ZnSe because the refractive index is high. Therefore it is clear.

[Example 2 (an optical system sharing a YAG laser and a carbon dioxide laser; FIG. 11)]
FIG. 11 shows an optical system including a YAG laser sharing a ZnSe lens and a carbon dioxide laser. A ZnSe mixing filter 8 is provided at an angle of 45 degrees on the beam axis of the carbon dioxide laser. In front of the mixing filter 8, a convex flat lens 9 having a convex ZnSe incident side and a flat exit side is provided. The convex lens has a diameter of 50.8 mm and an edge thickness of 7.87 mm. Images of the carbon dioxide laser beam and the YAG laser beam by the convex flat lens 9 can be made at the distances WD1 and WD2 in front of them. The carbon dioxide laser and YAG laser may be continuous wave (CW) or pulsed.
The mixing filter 8 passes light of 45 ° incident carbon dioxide laser (10.6 μm) well (transmittance of 90% or more) and reflects light of 45 ° incident YAG laser (1.06 μm) well (reflectance). 90% or more). The ZnSe lens 9 following the mixing filter allows YAG (1.06 μm) and carbon dioxide laser (10.6 μm) to pass well without reflection. An antireflection film (AR) is coated to reduce reflection. This is different from the antireflection film of only YAG. It is also different from the anti-reflective coating made of carbon dioxide laser only. It is an antireflection film for both YAG and carbon dioxide laser. The carbon dioxide laser transmittance of the ZnSe lens 9 is 95% or more, and the YAG laser transmittance is 90% or more.
The refractive index of ZnSe with respect to the carbon dioxide laser is n = 2.403. The refractive index for a YAG laser (1.06 μm) is n = 2.4819. Carbonate Gasure the refractive index is different - image position WD ₁ and YAG laser image position WD of THE are different. WD ₁ = 186.8 mm and WD ₂ = 176.7 mm. Since the optical system of the carbon dioxide laser and the YAG laser can be assembled on the same optical axis in this way, the object is placed at the position of the image plane, for example, cutting such that one beam is used for preheating, It can be set as the apparatus for welding.
So far, the description has been made mainly on the YAG laser, but it can also be applied to a fiber laser. The wavelength of the fiber laser is 800 nm to 1200 nm, such as 900 nm (0.9 μm), 1060 nm (1.06 μm), 1110 nm (1.11 μm), and is similar to the oscillation wavelength of the YAG laser. ZnSe has a small absorption and a high refractive index with respect to 0.8 μm to 1.2 μm. So it can be used for both YAG lasers and fiber lasers.
When the ZnSe lens described in the example was used with a 1.06 μm fiber laser as a light source, it was confirmed that the same characteristics as those of the YAG laser were exhibited. All that has been said about the YAG laser so far applies to fiber lasers of 0.8 μm to 1.2 μm.

Claims (5)

A YAG laser or fiber laser lens containing ZnSe as a material for refracting and condensing a beam of a YAG laser having a wavelength of 1.06 μm or a fiber laser having a wavelength of 0.80 μm to 1.20 μm. 2. The YAG laser and fiber laser lens according to claim 1, wherein the lens is a fθ lens comprising one lens and having a concave front surface and a convex rear surface. The ratio of the absolute value | R ₁ | of the curvature radius of the front surface to the absolute value | R ₂ | of the curvature radius of the rear surface is 0.5 to 2; lens. A laser processing apparatus characterized in that a carbon dioxide laser beam and a YAG laser beam are combined by a mixing filter so as to enter a ZnSe lens along the same optical axis and irradiate an object. 5. The laser processing apparatus according to claim 4, wherein an antireflection film for light from both a carbon dioxide laser and a YAG laser is formed on both surfaces of the ZnSe lens.

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