JPH02190816A - Linear image forming lens - Google Patents

Abstract

PURPOSE:To reduce residual aberration and to obtain the fine line width extending over the whole length of a linear image by changing a condensing distance in a cross section in one direction with respect to a condensed light, and specifying the radius of curvature of the incident surface and the emitting surface in a cross section in the other direction. CONSTITUTION:In (xy) surface, a lens 2 works as a concave lens, and a condensing distance of a focusing incident light which is emitted from a condensing lens 1 and forms a condensing point on an image forming surface 3a is lengthened so that the width of a luminous flux on the image forming surface 3a becomes large. Also, in the (xz) surface, the lens 2 does not have a condensing or divergent function, and an incident convergent light forms a condensing point on the image forming surface 3a. In this case, the incident surface 21 and the emitting surface of the lens 2 have a curvature like a concentric circle, and each radius of curvature is set to 1.2-1.4 folds of distanes A1, A2 extending from each surface to the image forming surface 3a. In such a manner, the aberration is corrected satisfactorily extending over the whole area in the longitudinal direction of a linear image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lens in a line imaging optical system for forming a linear image of a light beam with high energy density, such as a laser beam. The present invention is particularly effective for excitation light sources for generating X-ray lasers.

[Conventional technology]

Conventionally, optical systems for forming a line image of a light beam with high energy density such as a laser beam have used the following lenses in order to form a linear image of the light beam.

That is, in the first conventional example, as shown in Fig. 5, in a cross section including a line image (xy plane in Fig. 5), a parallel light beam is set to a predetermined radius of curvature that determines the length of the line image. (hereinafter abbreviated as R), and a cross section perpendicular to this cross section (xz plane in Figure 5) has a surface with R that serves as a convex lens to condense light onto the line image forming surface. A line image was formed by entering a toric lens having a

In addition, as a second conventional example, as shown in Fig. 6, the beam that has been converged to one point by the previous optical system is The lens is passed through a cylindrical lens 2b having a surface with a predetermined radius that determines the length of the line image, and having no radius in the cross section in the direction perpendicular to this cross section (xz plane in FIG. 6). line image 3 was formed.

[Problem that the invention is trying to solve] However,
In the case of the first conventional example, R in the cross section orthogonal to the line image is
It is largely determined by the focal length of the toric lens, and it is difficult to correct aberrations in the direction orthogonal to the line image by changing this R. Residual aberrations occur due to insufficient correction, and the width of the line image increases. could not be made smaller.

Furthermore, in the second conventional example, the light ray 5 that enters the paraxial region of the silitorical lens 2b has little aberration. However, since the ray 4, which is far from the paraxial axis and has a large incident height, originally has an optical path length to be condensed at the condensing point 3b, it is refracted in the y direction in the drawing, so that the condensing point goes beyond the imaging plane. End aberration occurs. Therefore, as shown in the figure, there is a drawback that the line width at the end of the line image becomes wider.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a lens that makes it possible to see fine lines throughout the entire line image.

[Means and effects for solving the problem] The present invention provides a linear imaging lens having a function of changing the condensing distance within a cross section in one direction for linear imaging, on the entrance and exit surfaces of the lens. By giving a predetermined curvature in the cross section in the other direction perpendicular to the cross section in one direction so that the incident condensed light beam enters at an appropriate angle, the residual aberration is reduced (so that a line image in a thin line can be obtained). Specifically, in the embodiment described later, the incident surface and the exit surface have a radius of curvature that is 1.2 to 1.4 times the distance to the condensing position of the condensed light in the other direction cross section. I'm doing it like that.

〔Example〕

FIGS. 1 and 2 show a side view and a top view of an optical system for explaining an embodiment of the present invention. 1 is a condenser lens for condensing an incident parallel light beam onto a point on an imaging plane 3a; 2 is a lens for linear imaging; 3a is an imaging plane; and 3 is a linear image.

In the first drawing (in the xy plane), the lens 2 acts as a concave lens, and increases the condensing distance of the convergent incident light that should be emitted from the condenser lens and form a condensing point on the imaging plane 3a, The width of the light beam on the imaging plane 3a is made to be large.

In the second drawing (in the xz plane), the lens 2 does not have a condensing or diverging function, and the incident convergent light forms a condensing point on the imaging plane 3a. The entrance surface 21 and the exit surface 22 of the lens 2 have concentric curvatures, and each radius of curvature is set to 1.2 to 1.4 times the distance A1°A2 from each surface to the imaging surface 3a. has been done. By setting the curvature in this manner, aberrations are favorably corrected over the entire length of the line image. FIG. 3 shows the condensing state of the optical system at this time.

Numerical examples proving the effectiveness of the present invention are shown below.

The lens data of this example is shown below.

35.0 50.72 7.3 1.458631 56.87 34.0 14.58 Here, the combined focal length of the optical system in the xz plane f = 100m
m (at wavelength λ = 0.248 μ) b, f, = 77.72 mm (=A 2) The first surface 11 is an aspheric surface, H is the radius from the optical axis, and X is the coordinate in the X direction, then B It can be expressed as =-3,062279x 10-' C=-2,127008X 1O-1ffi. This is data when the radius of curvature of the surfaces 21 and 22 in the xz plane is approximately 1.26 times the distance to the imaging plane.

FIGS. 4(a), (b), (C), and (d) show the radius of curvature of the entrance surface 23 of the lens 2 and the exit surface 22 in the xz plane by 1.0 of the distance to the imaging surface 3a. 1.1. 1.2.
1.4. y=o, 10, 12.25 on the imaging plane 3a when the magnification is 1.5 times and the optimum value is 1,26 times.
．． 15 is a graph showing the state of lateral aberration on a line of 15 mm. The lens data with a radius of curvature of 1.26 is as described above, and when using lenses with other radii of curvature, the lens data should be the same as the data described above except for the radius of curvature in the xz plane of surface 21.22. be. The horizontal axis represents the position in two directions, and the vertical axis represents the magnitude of lateral aberration Δzk at multiple positions in each of the two directions.
' indicates. As you can see from this figure, by making the radius of curvature of the entrance and exit surfaces 1.2 to 1.4 times the distance to the imaging plane, the value of lateral aberration can be reduced for any value of y. It is possible to make the light smaller and condense the light onto the imaging plane 3a in a shape closer to a linear shape.

In this embodiment, a good line image can be easily obtained from a parallel laser beam using only a normal condensing system and one toric lens, especially a two-lens system. High-power laser light, such as ultraviolet laser light or UV laser light, is easily absorbed by lenses, and there is a problem in that the amount of irradiated laser light decreases when many lenses are used in an optical system. This embodiment also has the advantage that good line imaging can be obtained without reducing the amount of irradiated laser light.

〔Effect of the invention〕

As shown above, after condensing the beam at one point, the condensing distance is changed within the cross section in one direction, and the radius of curvature of the entrance surface and the exit surface is set to 1.2 to 1.2 of the distance to the condensing position within the cross section in the other direction. A good linear imaging optical system was obtained by increasing the magnification to 1.4 times.

[Brief explanation of the drawing]

1 is a side view of the optical system according to the first embodiment of the present invention, FIG. 2 is a top view of the same optical system, FIG. 3 is a perspective view showing the condensing state of the optical system, and FIG.
Figures (a), (b), (c), and (d) are the second
A graph showing the state of lateral aberration at each radius of curvature of the entrance/exit surface of the lens. FIGS. 5 and 6 are perspective views of an optical system showing a conventional example. In the figure, 1...Condensing lens 2...Line imaging lens 3a...Imaging surface.

Claims (1)

[Claims] It is arranged on the rear side of the condensing optical system, changes the condensing distance of the condensed light from the condensing optical system within a cross section in one direction, and changes the condensing distance of the condensed light from the condensing optical system within a cross section in another direction perpendicular to the cross section in one direction. and each have a radius of curvature that is 1.2 to 1.4 times the distance to the condensing position of the condensed light.