JP3221338U - F-theta lens - Google Patents

Abstract

The present invention provides an f-theta lens for focusing a high-power laser, which can be used in a scanning device for laser material processing. A first single lens L1 as a planar-concave lens having a focal length f1 and a concave-convex-lens having a focal length f2 disposed behind the first single lens L1. And a second single lens L2 as the second single lens L2 and a third single lens L3 as a double convex lens having a focal length f3 disposed behind the second single lens L2, and an f-theta lens The ratio of the focal lengths f1 to f3 to the total focal length f satisfies the following condition. -1.0 <f1 / f <-0.8, -2.2 <f2 / f <-1.9, +0.3 <f3 / f <+0.6. [Selected figure] Figure 1

Description

  The present invention relates to an f-theta (fθ) lens for focusing high power lasers, such as can be used in scanning devices for laser material processing.

  The f-theta lens focuses the laser beam, which is scanned and abuts against the optical axis of the f-theta lens by a scanning angle range of +/− θ, on a flat image field plane (image plane BE). Within this scanning angle range, the ratio of the scanning angle to the distance of the impingement point of the laser beam from the optical axis in the image plane follows a linear function. That is, a laser beam scanned at a constant angular velocity generates a focal point moving at a constant velocity in the image plane. At that time, the size of the focus should be constant at all places in the image plane. The size of the focus is determined depending on the purpose of laser material processing, such as writing, film removal, cutting.

  Based on the wavelength-dependent refraction of the laser beam as it passes through the f-theta lens, the f-theta lens is corrected to the wavelength of the working laser beam used to achieve high focus properties. That is, the lens provides an optical imaging that produces a significant change in the size of the focal spot for the set wavelength and the set laser beam diameter, within the tolerance temperature error, for the set size of the image plane. It is calculated so as not to generate errors or to generate very small coupling errors. Especially for use in laser material processing, f-theta lenses have a large image plane and a large total focal length.

  The object of the present invention is to provide an f-theta lens for a high-power laser with a wavelength of 1064 nm and a total focal length of 410-430 mm, which enables imaging without back reflection of the laser beam.

This task is solved by the features of claim 1 with respect to the f-theta lens. Advantageous embodiments are set forth in the dependent claims.

  Next, the present invention will be described in detail based on the drawings.

FIG. 3 is a geometrical optical view of the lens according to the invention for the case of a maximum scanning angle showing the beam path along the optical axis A.

The f-theta lens according to the present invention has an entrance pupil EP spaced apart in front of the f-theta lens. This entrance pupil can be arranged in the plane provided with one scanning mirror or, in the case of using two scanning mirrors, arranged in the plane provided with the calculated substitute plane for it It is. F-theta lens has three single lens L ₁ ~L ₃ disposed on a common optical axis A. The three single lens L ₁ ~L ₃ is formed so as to form a "negative - - negative positive" lens column. That is, the first two single lenses L ₁ , L ₂ have a negative focal length, while the third lens L ₃ has a positive focal length.

At that time, the first lens L ₁ is a plan - a lens, a second lens L ₂ is concave - - concave is a lens, the third lens L ₃ is convex - - convex convex - lens (double Convex lens).

The focal lengths of the three single lenses satisfy the following requirements.
The focal length ratio of the focal length _{f 1} of the first lens _{L 1} to the total focal length f _is -1.0 <f 1 /f<-0.8.
The focal length ratio of the focal length _{f 2} of the second lens _{L 2} to the total focal length f _is -2.2 <f 2 /f<-1.9.
The focal length ratio of the focal length _{f 3} of the third lens _{L 3} to the total focal length f _is + 0.3 <f 3 /f<+0.6.

The protective glass SG can be disposed in front of the _three single lenses L _{1 to} L ₃ .

The beneficial effects achieved by the f-theta lens according to the invention are suitable for high-power lasers and corrected for a wavelength of 1064 nm by means of _three single lenses L ₁ -L 3 consisting of quartz glass, The reason is that an f-theta lens having a total focal length of 423 mm is produced. The parameters of the f-theta lens are such that the optically effective surfaces of the lenses L ₁ -L ₃ and possibly the back reflection generated by the protective glass SG are arranged around the surface of the lenses L ₁ -L ₃ or around the entrance pupil EP It is formed not to be focused by the mirror. There is no back reflection in the lens material. There is no back reflection at the optical surface and no back reflection at the recommended scan position. The specific structure and parameters of such an embodiment of the f-theta lens will now be described.

F-theta entrance pupil EP of data lens, the first lens L ₁ having a thickness of d _2, i.e. the plane - concave - located in front of the distance d ₁ of the front vertex of the lens, the front surface of the first lens radius having r _1, the surface of the rear has a radius _{r 2.} At a gap d ₃ from the first lens L _1, second lens L ₂ of the thickness d _4, i.e. a concave - convex - lens is provided, the radius r ₃ is the front surface of the second lens a surface of the rear has a radius r _4. At a gap d _5, the third lens L ₃ of the thickness d _6, i.e. convex - convex - lens or a double convex lens is provided. Front surface of the third lens has a radius r _5, the surface of the rear has a radius r _6. At a gap d _7, protective glass SG parallel plane of thickness d ₈ is provided. The image plane BE occurs at a distance d _{9 to} the protective glass SG. Quartz glass with a refractive index n is selected as the material for all single lenses L ₁ -L ₃ and the protective glass SG.

The radii, thicknesses and distances d of the single lenses L _{1 to} L ₃ are listed in the following table.

Distance and thickness is represented by d in the same way, serial numbers attached to the beam passing direction in the order along the optical axis A of the f-theta lens, is described as d ₁ to d ₉ in Figure 1. The "front" and "back" surfaces described relate to the beam passing direction. The radii r _{1 to} r ₆ can be assigned reliably by reference to the corresponding lenses L _{1 to} L ₃ and the protective glass SG and are therefore not described in FIG. 1 for the sake of clarity.

Depending on the refractive index of the single lens L _{1 to} L ₃ depending on the material, and in relation to the radius of curvature r _{1 to} r ₆ of the single lens, the thickness d of the single lens L _{1 to} L _{3 2} , d ₄ and d ₆ respectively determine focal lengths f _{1 to} f ₃ of the single lenses L _{1 to} L ₃ . The focal distances f _{1 to} f ₃ , which indicate the distance of the focal point from the principal plane of the single lenses L _{1 to} L ₃ respectively, are not described in FIG. The reason is that the main planes of the single lenses L _{1 to} L ₃ are not drawn in order to make them easy to see. Likewise, the total focal length f representing the distance of the image plane BE from the substitute principal plane of the f-theta lens is also not described.

For f-theta lens with the parameters described herein, the focal length f ₁ of the first lens L ₁ having a ratio of -0.9 for all the focal length f occurs, -2 relative to the total focal length. the focal length _{f 2} of the second lens _{L 2} is generated with a 07 ratio of the focal length _{f 3} of the third lens _{L 3} having a ratio of -0.48 for all the focal length f occurs.

From the arrangement before and after the lens _L 1 ~L ₃ associated with the gap _d 3, _{d 5,} occurs all the focal length f of 423Mm. The f-theta lens is corrected to a wavelength of 1064 nm.

d1 EP and L1 distance d2 L1 thickness d3 L1 and L2 distance d4 L2 thickness d5 L2 and L3 distance d6 L3 thickness d7 L3 and protective glass (SG) spacing d8 protective glass thickness d9 Distance between protective glass and image plane (BE)

Claims (3)

Plane has a focal length f ₁ - concave - the first single lens L ₁ as a lens, a concave having a focal length f ₂ - convex - a second single lens L ₂ as a lens, the focal length f double convex having ₃ - and a third single lens L ₃ as a lens L _3, and there at f-theta lens with three single lenses having a total focal length f of the f-theta lens The ratio of the focal lengths f _{1 to} f ₃ to the total focal length f is the following condition −1.0 / f ₁ /f<−0.8
−2.2 <f ₂ /f<−1.9
+0.3 <f ₃ /f<+0.6
To satisfy
The above F theta lens. f-theta lens according to claim 1, characterized in that the f ₁ /f=-0.9,f ₂ /f=-2.07,f ₃ /f=+0.48. Wherein the first front of the single lens L _1, at a distance d ₁ of 30 mm, f-theta lens according to claim 2, characterized in that the entrance pupil EP of the f-theta lens is provided.