KR200496448Y1 - F-theta objective - Google Patents

Abstract

A first individual lens (L ₁ ) as a concave-concave lens having a focal length (f ₁ ), a second individual lens (L ₂ ) as a concave-convex lens having a focal length (f ₂ ), and a focal length (f ₃ ) An f theta lens including individual lenses having a third individual lens (L ₃ ) as a convex-convex lens having a focal length (f ₄ ) and a fourth individual lens (L ₄ ) as a convex-convex lens having a focal length (f 4 ) is described. . The f theta lens has the total focal length f of the f theta lens, and the ratio between the total focal length f and the focal lengths f ₁ -f ₄ satisfies the following conditions:
-8.0 < f ₁ /f < -0.50
+2.10 < f ₂ /f < +2.70
+1.20 < f ₃ /f < +1.60
+2.00 < f ₄ /f < +2.40

Description

F-theta lens {F-theta objective}

The present invention relates to an F-theta objective for focusing a high power laser such as may be used in a scanning device for laser material processing.

The f theta lens focuses an incident laser beam into a flat image field while scanning a scanning angular range of +/-θ with respect to the optical axis of the f theta lens, in this case within this scanning angular range the optical axis and the optical axis within the image field The ratio of the distance between the incident points of the laser beam and the scanning angle follows a linear function. That is, a laser beam scanned at a constant angular velocity forms a focal point within an image field, and the focal point moves at a constant velocity. In this case, the size of the focal point at each position within the image field may be constant. The size of the focus is determined by laser material processing, eg labeling, decoating or cutting.

Due to the wavelength-dependent refraction of the laser beam upon transmission of the f-theta lens, the f-theta lens is calibrated to the wavelength of the processing laser beam used in order to achieve a high focus quality, i.e., the lens has a predetermined wavelength and a predetermined laser beam Calculated to have no or only very small optical imaging errors for an image field of a predetermined size within the temperature tolerance allowed for the diameter, such that the error is less than the appreciable size of the focal point. cause change Especially for use in laser material processing, F-theta lenses have a large image field and a large overall focal length.

An object of the present invention is to provide an F-theta lens for a high-power laser with a wavelength of 355 nm and a total focal length of 50 to 60 mm, enabling back reflex free imaging of laser radiation. This problem is solved by an F theta lens comprising the features of claim 1

Preferred embodiments are described in the dependent claims.

The invention continues to be described with reference to the drawings.

1 shows a geometrical optical diagram of a lens according to the invention with an indication of the beam path along the optical axis A at maximum scanning angle.

The f theta lens according to the present invention includes an entrance pupil (EP) spaced apart in front of the f theta lens, the entrance pupil calculated for this when one scanner mirror is placed or when two scanner mirrors are used. It can be arranged in the plane in which the alternate plane lies, and the f theta lens comprises four individual lenses (L ₁ -L ₄ ) arranged on a common optical axis (A). The four individual lenses (L ₁ -L ₄ ) are configured to form a “negative-positive-positive-positive” lens sequence. That is, the single first lens (L ₁ ) has a negative focal length, while the other three lenses (L ₂ -L ₄ ) have a positive focal length.

The first lens L ₁ is in this case a concave-concave-lens (biconcave lens), the second lens L ₂ is a concave-convex-lens and the third lens L ₃ is a convex-convex-lens. (biconvex lens), and the fourth lens (L ₄ ) is also a convex-convex-lens (biconvex lens).

The focal lengths of the four individual lenses meet the following requirements:

The focal length ratio of the total focal length f to the focal length f ₁ of the first lens L ₁ is -8.0 < f ₁ /f < -0.50.

The ratio of the total focal length (f) to the focal length (f ₂ ) of the second lens (L ₂ ) is 2.10 < f ₂ /f < 2.70.

The ratio of the total focal length (f) to the focal length (f ₃ ) of the third lens (L ₃ ) is 1.20 < f ₃ /f < 1.60.

The ratio of the total focal length (f) to the focal length (f ₄ ) of the fourth lens (L ₄ ) is 2.00 < f ₄ /f < 2.40.

A protective glass (SG) may be disposed behind the four individual lenses (L ₁ -L ₄ ).

A preferred effect achieved by the f theta lens according to the present invention is suitable for high-power lasers by means of four individual lenses (L ₁ -L ₄ ) made of quartz glass, corrected for a wavelength of 355 nm and having a total focus of 56 mm An F theta lens with a distance is formed. According to the parameters of the f-theta lens, the rear reflection generated on the optical working surfaces of the lenses (L ₁ -L ₄ ) and in some cases on the protective glass (SG) is reflected on the surface of the lenses (L ₁ -L ₄ ) or It is configured not to focus on mirrors disposed around the entrance pupil EP. There is no back reflection in the material of the lens. No dorsal reflections at optical surfaces and no dorsal reflections at the points of the recommended scanner position. The specific structure and parameters of an embodiment for this F theta lens are described subsequently.

The entrance pupil (EP) of the f-theta lens is located in front of the front apex of the first lens (L ₁ ), that is, the concave-concave lens having the thickness (d ₂ ) at a distance of d ₁ , and the front surface of the lens has a radius (r). ₁ ), and the rear surface of the lens has a radius r ₂ . Following the first lens (L ₁ ), a second lens (L ₂ ), that is, a concave-convex-lens having a thickness (d ₄ ) continues with an air gap (d ₃ ), and the front surface of the lens has a radius ( r ₃ ), and the rear surface of the lens has a radius r ₄ . A third lens (L ₃ ), that is, a convex-convex-lens or a biconvex lens having a thickness (d ₆ ) is continuous with an air gap (d ₅ ), and the front surface of the lens has a radius (r ₅ ), The rear surface of the lens has a radius r ₆ . A fourth lens (L ₄ ), that is, a convex-convex-lens or a biconvex lens having a thickness (d ₈ ) is continuous with an air gap (d ₇ ), and the front surface of the lens has a radius (r ₇ ) , the rear surface of the lens has a radius r ₈ . A plane-parallel protective glass (SG) having a thickness (d ₁₀ ) is continuous with an air gap (d ₇ ) therebetween. The image field BE is formed at a distance of d ₁₁ from the protective glass SG. Quartz glass with a refractive index n is selected as the material for all the individual lenses L ₁ -L ₄ and the protective glass SG.

The radii of the individual lenses L ₁ -L ₄ , their thickness and spacing d are given in the table below.

media radius
[mm] thickness
[mm] N air d ₁ 23 L ₁ r ₁ -23 d ₂ 3 1.460081 L ₁ r ₂ 77 air d ₃ 8 L ₂ r ₃ -94 d ₄ 12 1.460081 L ₂ r ₄ -40 air d ₅ 0.3 L ₃ r ₅ 345 d ₆ 8 1.460081 L _{3 r6} -43 air 0.3 L _{4 r7} 74 8 1.460081 L _{4 r8} -227 air d ₇ 2 SG
SG
air r ₉
r ₁₀
∞
∞
d ₈

d ₉ 3

63 1.460081

The spacings and thicknesses are identically denoted by d, the order of which is numbered in the beam transmission direction along the optical axis A of the f theta lens, designated d ₁ to d ₁₁ in FIG. 1 . The expressions “front” and “back” planes relate to the beam transmission direction. The radii r ₁ -r ₁₀ can be clearly assigned in relation to the corresponding lenses L ₁ -L ₄ and the protective glass SG, and are therefore not specified in FIG. 1 for clarity. Depending on the material-dependent refractive index (n) of the individual lenses (L ₁ -L ₄ ), the thickness (d ₂ , d ₄ , d ₆ , d ₈ ) of the individual lenses (L ₁ -L ₄ ) is the radius of curvature ( Determine the respective focal lengths (f ₁ -f ₄ ) of the individual lenses (L ₁ -L ₄ ) in terms of r ₁ -r ₈ . Since the main planes of the individual lenses (L ₁ -L ₄ ) are not _shown for clarity, in FIG. ₁ the focal lengths (f ₁ -f ₄ ) is not specified. Also, the total focal length f representing the distance between the image field BE and the alternate main plane for the f theta lens is not specified.

For an f theta lens with the parameters specified herein, the ratio of total focal length (f) to focal length (f ₁ ) of -0.66 for the first lens (L ₁ ) and 2.47 for the second lens (L ₂ ) The ratio of the total focal length (f) to the focal length (f ₂ ) of, the ratio of the total focal length (f) to the focal length (f ₃ ) of 1.44 for the third lens (L ₃ ), and the fourth lens (L ₄ ) gives a ratio of total focal length (f) to focal length (f ₄ ) of 2.12.

The successive arrangement of the lenses L ₁ -L ₄ with respect to the air gaps d ₃ , d ₅ , d ₇ gives a total focal length f of 56 mm. The f theta lens is calibrated for a wavelength of 355 nm.

d1 spacing EP-L1
d2 thickness L1
d3 spacing L1-L2
d4 thickness L2
d5 interval L2-L3
d6 thickness L3
d7 spacing L4-L4
d8 thickness L4
d9 spacing L4 - protective glass
d10 thick protective glass
d11 spacing protective glass - image plane

Claims (3)

A first individual lens (L ₁ ) as a concave-concave lens having a focal length (f ₁ ), a second individual lens (L ₂ ) as a concave-convex lens having a focal length (f ₂ ), and a focal length (f ₃ ) An f theta lens including individual lenses having a third individual lens (L ₃ ) as a convex-convex lens having and a fourth individual lens (L ₄ ) as a convex-convex lens having a focal length (f ₄ ), An f theta lens that has the total focal length f of the theta lens, and the ratio between the total focal length f and the focal lengths f ₁ -f ₄ satisfies the following conditions:
-8.0 < f ₁ /f < -0.50
+2.10 < f ₂ /f < +2.70
+1.20 < f ₃ /f < +1.60
+2.00 < f ₄ /f < +2.40 The f theta lens according to claim 1, wherein f ₁ /f = -0.66, f ₂ /f = +2.47, f ₃ /f = +1.44, f ₄ /f = +2.12. The f-theta lens of claim 2, wherein the entrance pupil (EP) of the f-theta lens is positioned at a distance (d ₁ ) of 23 mm in front of the first individual lens (L ₁ ).

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