KR20190001936U - F-theta objective - Google Patents

Abstract

First individual lens (L _1), the focal length (f ₂₎ for having a concave as the negative lens-second individual lens (L _2), the focal length as a convex lens (f ₃₎ concave having the focal length (f ₁₎ A third individual lens L ₃ which is a convex-convex lens with a focal length f ₄ and an individual lens with a fourth individual lens L ₄ as a convex-convex lens with a focal length f ₄ . The f-theta lens has a total focal length f of the f-theta lens and the ratio between the total focal length f and the focal distances 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

The F-theta objective &lt; RTI ID = 0.0 &gt;

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

An F-theta lens focuses an incident laser beam into a flat image field while scanning a scanning angle range of +/-? Relative to the optical axis of the F-theta lens, and in this case, within this scanning angle range, The ratio of the distance between the incident points of the laser beam and the scanning angle follows a linear function. That is, the laser beam scanned at a constant angular velocity forms a focus in the image field, and the focus moves at a constant speed. In this case, the magnitude of the focus at each position within the image field may be constant. The magnitude of the focus is determined by laser material processing, for example labeling, decoating or cutting.

Due to the wavelength-dependent refraction of the laser beam in the transmission of the F-theta lens, the F-theta lens is corrected to the wavelength of the working laser beam used to achieve high focus quality, i. E. The lens is pre- Is calculated so as to have no optical imaging error or only a very small optical imaging error in the image field of a predetermined size within the allowed temperature tolerance for the diameter, . Especially for use in laser material processing, the F-setter lens has a large image field and a large overall focal length.

It is an object of the present invention to provide an F-theta lens for high power lasers having a wavelength of 355 nm and a total focal length of 50 to 60 mm, which enables back reflex free imaging of laser radiation. The above problem is solved by an F-setter lens comprising the features of claim 1

Preferred embodiments are described in the dependent claims.

The invention will now be described with reference to the drawings.

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

The fftera lens according to the present invention comprises an entrance pupil (EP) spaced apart in front of an F-numbered lens, said entrance pupil being calculated for one scanner mirror or for use with two scanner mirrors And the Fresceller lenses include 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.

A first lens (L ₁₎ is in this case a concave-concave-lens (biconcave lens) and the second lens (L ₂₎ has a concave-and lens, the third lens (L ₃₎ is a convex-convex convex-lens (Double-side convex lens), and the fourth lens L ₄ is also a convex-convex lens (double-side convex lens).

The focal length of the four individual lenses meets the following requirements:

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

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

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

The total focal length (f) for the fourth focal length ratio of the focal length (f ₄₎ of the 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-setter lens according to the present invention is that it is suitable for high power lasers by means of four individual lenses (L ₁ -L ₄ ) made of quartz glass and is corrected for a wavelength of 355 nm, An Efceta lens having a distance is formed. The Fresnel lens is configured such that the back reflection that occurs on the optically working surface of the lenses L ₁ -L ₄ and occasionally on the protective glass SG is reflected by the parameters on the surfaces of the lenses L ₁ -L ₄ , And is not focused on a mirror arranged around the incident copper EP. No back reflection is made in the material of the lens. Back reflection at the optical surface and no back reflection at the point of the recommended scanner position. The specific structure and parameters of the embodiment for such an F-theta lens will be described subsequently.

The entrance pupil EP of the F-theta lens is located at a distance d ₁ before the front vertex of the concave-concave lens having the first lens L ₁ , that is, the thickness d ₂ , ₁ ), and the rear surface of the lens has a radius r ₂ . The first with a lens the air gap (d ₃₎ followed by (L ₁₎ a second lens (L _2), that is concave with a thickness (d ₄₎ - convex - front surface of the lens is the continuous, the lens radius ( r ₃ , and the rear surface of the lens has a radius r ₄ . A convex-convex lens or a double-convex lens having a third lens L ₃ , that is, a thickness d ₆ , is continuous with an air gap d ₅ , the front surface of the lens has a radius r ₅ , rear surface of the lens has a radius (r _6). With an air gap (d ₇₎ the fourth lens (L _4), that is convex with a thickness (d ₈₎ - convex - front surface of the lens, or a biconvex lens is the continuous, the lens has a radius (r ₇₎ , And the rear surface of the lens has a radius r ₈ . A planar parallel protective glass SG having a thickness d ₁₀ is continued with the air gap d ₇ therebetween. The image field (BE) is formed at an interval of d ₁₁ from the protective glass (SG). A quartz glass having a refractive index (n) is selected as a 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 ), the thickness of the lenses and the spacing (d) are shown in the following table.

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 r ₆ -43 air 0.3 L ₄ r ₇ 74 8 1.460081 L ₄ r ₈ -227 air d ₇ 2 SG
SG
air r ₉
r ₁₀
∞
∞
d ₈

d ₉ 3

63 1.460081

The intervals and thicknesses are equally represented by d, the order of which is numbered in the beam transmission direction along the optical axis A of the F-setter lens, denoted d ₁ to d ₁₁ in FIG. The expressions &quot; before &quot; and &quot; after &quot; are associated with the beam transmission direction. The radii r ₁ -r ₁₀ can be clearly assigned with respect to the lenses L ₁ -L ₄ and the protective glass SG, and therefore are not specified in FIG. 1 for clarity. Each lens (L ₁ -L ₄₎ of the material-dependent refractive index (n) individual lenses (L ₁ -L ₄₎ the thickness _{(d 2, d 4, d} 6, d 8) of the radius of curvature of the individual lens according to ( (f ₁ -f ₄ ) of the individual lenses (L ₁ -L ₄ ) with respect to the respective focal lengths (r ₁ -r ₈ ). Since the main planes of the individual lenses L _{1 to} L ₄ are not shown for clarity, FIG. 1 shows a focal length f (x, y) representing the distance between the main plane and the focal point of the individual lenses L _{1 to} L _{4 1} -f ₄ ) are not specified. Also, the total focal length f indicating the distance between the alternate main plane and the image field BE for the F-theta lens is not specified.

In the case of the F-theta lens with the parameters set forth herein the first lens (L ₁₎ 2.47 for the ratio, the second lens (L ₂₎ of the total focal length (f) for the focal length (f ₁₎ of about -0.66 the total focal length (f) for the focal length (f ₂₎ ratio, a third lens (L ₃₎ the total focal length (f) for a focal length of 1.44 on a (f ₃₎ ratio, and a fourth lens (L of ₄ ), the ratio of the total focal length (f) to the focal length (f ₄ ) of 2.12 is given.

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

d1 interval EP-L1
d2 thickness L1
d3 interval L1-L2
d4 thickness L2
d5 interval L2-L3
d6 Thickness L3
d7 interval L4-L4
d8 thickness L4
d9 interval L4-protective glass
d10 Thick protective glass
d11 gap protection glass - image plane

Claims (3)

First individual lens (L _1), the focal length (f ₂₎ for having a concave as the negative lens-second individual lens (L _2), the focal length as a convex lens (f ₃₎ concave having the focal length (f ₁₎ And an individual lens having a fourth individual lens L ₄ as a convex-convex lens having a focal length f ₄ and a third individual lens L ₃ as a convex-convex lens having a focal length f ₄ , Wherein 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 2. The f ∙ sheath lens according to claim 1, wherein f ₁ / f = -0.66, f ₂ / f = +2.47, f ₃ / f = +1.44, and f ₄ / f = +2.12. 3. The Freset lens according to claim 2, wherein the entrance pupil (EP) of the F-theta lens is located at an interval (d ₁ ) of 23 mm in front of the first individual lens (L ₁ ).

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