Ultraviolet femtosecond achromatic telecentric field lens

Abstract

The invention relates to the technical field of laser optics, and discloses an ultraviolet femtosecond achromatic telecentric field lens which comprises a plurality of lenses and diffractive optical elements which are coaxially arranged, and the diffractive optical elements are used for correcting chromatic aberration. The lens comprises a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror which are sequentially arranged from the object space to the image space along the incident direction of incident light; the diffractive optical element is arranged between the third lens and the fifth lens. According to the femtosecond laser, the lenses and the diffractive optical elements are coaxially arranged, chromatic aberration correction is achieved through the diffractive optical elements, it is ensured that laser beams can be accurately focused, and the machining precision and quality of the femtosecond laser are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser optics, in particular to a kind of ultraviolet femtosecond achromatic telecentric field lens. BACKGROUND

[0002] High-energy laser is a kind of laser with high energy density, high focusing degree, high light intensity characteristics, and has wide application in industry, medical treatment, communication, scientific research and many other fields.The field lens of the existing high-energy laser use field is usually designed for single wavelength, and the lens material is fused quartz, and this type of field lens is only suitable for picosecond, nanosecond laser.The femtosecond laser is a kind of laser capable of generating femtosecond-level ultrashort laser pulses, with the characteristics of short pulse width, high peak power, small focused spot and high precision, and is usually applied to relatively high-end processing field, and the focusing effect of light spot is required to be more strict.Femtosecond laser has spectral broadening, i.e.1-2nm will be widened near the center wavelength, and the off-axis field angle of general field lens is large, and the laser emission light incident into the field lens will produce serious chromatic aberration, so that the emission light of the field lens cannot be converged on the same point, which affects the uniformity and ellipticity of the emission light spot, and affects the marking effect. SUMMARY

[0003] Therefore, the present application provides an ultraviolet femtosecond achromatic telecentric field lens to solve the problem that the marking effect of femtosecond laser is affected.

[0004] The present application provides an ultraviolet femtosecond achromatic telecentric field lens, comprising:

[0005] A plurality of lenses and a diffractive optical element coaxially arranged, the diffractive optical element is used for correcting chromatic aberration;

[0006] The lens comprises a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror arranged in order along the incident direction of incident light from the object side to the image side;

[0007] The diffractive optical element is arranged between the third lens and the fifth lens.

[0008] The ultraviolet femtosecond achromatic telecentric field lens provided in the embodiment comprises a plurality of lenses and a diffractive optical element coaxially arranged, the diffractive optical element is used for correcting chromatic aberration;The lens comprises a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror arranged in order along the incident direction of incident light from the object side to the image side;The diffractive optical element is arranged between the third lens and the fifth lens.Through coaxial arrangement of a plurality of lenses and a diffractive optical element, the diffractive optical element is used to correct chromatic aberration, so as to ensure that the laser beam can be accurately focused, and the processing precision and quality of femtosecond laser are improved.

[0009] In some alternative embodiments, the refractive index and the Abbe number of the lens and the diffractive optical element are the same.

[0010] In some alternative embodiments, the incident light rays reach the first and second surfaces of each lens in turn along the incident direction.

[0011] The first lens is a plano-concave negative lens, the second lens is a meniscus positive lens, the second surface of the first lens is close to the first surface of the second lens, the second surface of the first lens is a plane, and the absolute value of the radius of curvature of the first surface of the second lens is greater than the absolute value of the radius of curvature of the second surface of the second lens.

[0012] In some alternative embodiments, the radius of curvature of the first surface of the first lens is -40.7, the radius of curvature of the first surface of the second lens is -276.7, the radius of curvature of the second surface of the second lens is -44.4, the thickness of the first lens is equal to the thickness of the second lens, and the thickness of the first lens and the thickness of the second lens are 15 mm.

[0013] In some alternative embodiments, the third lens is an aspheric positive lens, the first surface of the third lens is close to the second surface of the second lens, and the absolute value of the radius of curvature of the first surface of the third lens is less than the absolute value of the radius of curvature of the second surface of the third lens.

[0014] In some alternative embodiments, the radius of curvature of the first surface of the third lens is 164.4, the radius of curvature of the second surface of the third lens is -567.8, and the thickness of the third lens is 13 mm.

[0015] In some alternative embodiments, the fifth lens is a double-concave negative lens, and the sixth lens is a meniscus positive lens.

[0016] The second surface of the fifth lens is close to the first surface of the sixth lens, the absolute value of the radius of curvature of the first surface of the fifth lens is less than the absolute value of the radius of curvature of the second surface of the fifth lens, and the absolute value of the radius of curvature of the first surface of the sixth lens is less than the absolute value of the radius of curvature of the second surface of the sixth lens.

[0017] The first surface of the seventh plane mirror is close to the second surface of the sixth lens, and the seventh plane mirror is a glass protective plane mirror.

[0018] In some alternative embodiments, the first surface of the fifth lens has a radius of curvature of -156.06, the second surface of the fifth lens has a radius of curvature of 910.67; the first surface of the sixth lens has a radius of curvature of 90.4, the second surface of the sixth lens has a radius of curvature of 221.5; the thickness of the fifth lens is 9mm, the thickness of the sixth lens is 7.8mm, and the thickness of the seventh plane mirror is 3mm.

[0019] In some alternative embodiments, the first lens, the second lens, the third lens, the diffractive optical element, the fifth lens, the sixth lens and the seventh plane mirror are made of fused silica glass material.

[0020] In some alternative embodiments, the first lens is configured to diverge the incident light rays; the second lens is configured to fold the incident light rays and balance the aberration generated by the negative lens of the first lens; the third lens is configured to reduce the spherical aberration of the optical path; the fifth lens is configured to balance the aberration of the optical path; and the sixth lens is configured to reduce the telecentric angle of the lens optical path. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 is a schematic diagram of an ultraviolet femtosecond achromatic telecentric field lens according to an embodiment of the present application;

[0023] Figure 2 is a spot diagram under different field angles according to an embodiment of the present application;

[0024] Figure 3 is a distortion diagram according to an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0026] The current telecentric field lens is designed for a single working wavelength, while the femtosecond laser has a spectrum broadening phenomenon, that is, the femtosecond laser is not a single wavelength, but has a certain spectrum width, so when the existing field lens is used, the light source will produce chromatic aberration after passing through the field lens, especially the vertical axis chromatic aberration, which will cause the focused spot of the field lens to become large and elliptical, affecting the laser processing effect. Based on this, the application provides a kind of ultraviolet femtosecond achromatic telecentric field lens.

[0027] According to the embodiment of the application, an ultraviolet femtosecond achromatic telecentric field lens is provided. It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0028] In this embodiment, an ultraviolet femtosecond achromatic telecentric field lens is provided, which comprises a plurality of lenses and a diffractive optical element arranged coaxially, wherein the diffractive optical element is used to correct chromatic aberration. The lenses include a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror arranged in order from the object side to the image side along the incident direction of the incident light. The diffractive optical element is arranged between the third lens and the fifth lens.

[0029] Figure 1 The ultraviolet femtosecond achromatic telecentric field lens according to the embodiment of the application is shown in Figure 1 The first lens L1 is the first lens through which the light enters the field lens system, and is arranged in order from the object side to the image side along the incident direction of the incident light as the first lens L1, the second lens L2, the third lens L3, the diffractive optical element L4, the fifth lens L5, the sixth lens L6 and the seventh plane mirror L7.

[0030] The diffractive optical element (DOE) is an optical element that works based on the principle of light diffraction. The diffractive optical element L4 is arranged between the third lens L3 and the fifth lens L5, which can be used to compensate for the chromatic dispersion caused by the front refractive lens. When light of different wavelengths passes through the refractive lens, there will be different focal positions, while the chromatic dispersion of the DOE is opposite, which can adjust the focal points of different wavelengths to make them coincide, thereby eliminating chromatic aberration. Therefore, the diffractive optical element L4 arranged between the third lens L3 and the fifth lens L5 is beneficial to the effect of eliminating chromatic aberration of the diffractive optical element, and can also compensate for other aberrations.

[0031] In the embodiment, the optical power distribution of the lens optical path is negative, positive, positive, positive, negative and positive in sequence according to the order of light propagation, and the aberration of the lens optical path is effectively corrected by reasonable optical power distribution. Specifically, the first optical power section is negative, used for diverging light, adjusting the incidence angle and position of light, and providing suitable incidence conditions for subsequent lenses. The second, third and fourth optical power sections are positive, used for converging light, focusing light, and the three positive optical power sections respectively undertake different aberration correction tasks in the process of converging light. For example, the second optical power section can be responsible for correcting field curvature, the third optical power section can further correct spherical aberration and astigmatism, and the fourth optical power section can balance the aberration of the lens optical path. The fifth optical power section can be used to reduce the telecentric angle of the lens optical path and ensure the telecentricity of the lens. The sixth optical power section adjusts the convergence degree and position of light to ensure that the light can form a high-quality and high-precision focused spot at the target position.

[0032] The product parameters of the ultraviolet femtosecond achromatic telecentric field lens provided by the embodiment include: focal length: 103mm; scanning field: 35mm*35mm; scanning angle: ±19 degrees; working wavelength: 343±0.8nm; focused spot: 10um.

[0033] The ultraviolet femtosecond achromatic telecentric field lens provided by the embodiment includes a plurality of lenses and a diffractive optical element coaxially arranged, and the diffractive optical element is used for correcting chromatic aberration. The lens includes a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror arranged in sequence along the incident direction of the incident light from the object side to the image side. The diffractive optical element is arranged between the third lens and the fifth lens. By coaxially arranging a plurality of lenses and a diffractive optical element, the diffractive optical element is used to correct chromatic aberration, so that the laser beam can be accurately focused, and the machining precision and quality of the femtosecond laser are improved.

[0034] In some optional embodiments, the first lens, the second lens, the third lens, the diffractive optical element, the fifth lens, the sixth lens and the seventh plane mirror are fused quartz glass materials. The achromatic effect is realized by using full fused quartz material optical elements, and the damage threshold of the lens is improved.

[0035] In some optional embodiments, the incident light rays reach the first face and the second face of each lens in turn along the incident direction; the first lens is a plano-concave negative lens, the second lens is a meniscus positive lens, the second face of the first lens is close to the first face of the second lens, the second face of the first lens is a plane, and the absolute value of the curvature radius of the first face of the second lens is greater than the absolute value of the curvature radius of the second face of the second lens. The third lens is a positive aspheric lens, the first face of the third lens is close to the second face of the second lens, and the absolute value of the curvature radius of the first face of the third lens is less than the absolute value of the curvature radius of the second face of the third lens. The fifth lens is a double-concave negative lens, the sixth lens is a meniscus positive lens, the second face of the fifth lens is close to the first face of the sixth lens, the absolute value of the curvature radius of the first face of the fifth lens is less than the absolute value of the curvature radius of the second face of the fifth lens, and the absolute value of the curvature radius of the first face of the sixth lens is less than the absolute value of the curvature radius of the second face of the sixth lens. The first face of the seventh plane mirror is close to the second face of the sixth lens, and the seventh plane mirror is a glass protective plane mirror.

[0036] In some optional embodiments, the curvature radius of the first face of the first lens is -40.7, the curvature radius of the first face of the second lens is -276.7, the curvature radius of the second face of the second lens is -44.4, the thickness of the first lens is equal to the thickness of the second lens, and the thickness of the first lens and the thickness of the second lens are 15 mm. The curvature radius of the first face of the third lens is 164.4, the curvature radius of the second face of the third lens is -567.8, and the thickness of the third lens is 13 mm. The curvature radius of the first face of the fifth lens is -156.06, and the curvature radius of the second face of the fifth lens is 910.67. The curvature radius of the first face of the sixth lens is 90.4, and the curvature radius of the second face of the sixth lens is 221.5. The thickness of the fifth lens is 9 mm, the thickness of the sixth lens is 7.8 mm, and the thickness of the seventh plane mirror is 3 mm. The specific parameters are shown in Table 1, which is the curvature radius, thickness, refractive index, and Abbe number of each lens in the ultraviolet femtosecond achromatic telecentric field mirror provided in this embodiment. Among them, curvature radius 1 is the first face of the lens along the incident direction, and curvature radius 2 is the second face of the lens along the incident direction. The positive and negative signs in the curvature radius represent the direction of the curved surface, and the positive value represents the curved surface bending towards the object side, and the negative value represents the curved surface bending towards the image side.

[0037] Table 1: Curvature radius, thickness, refractive index, and Abbe number of each lens in the ultraviolet femtosecond achromatic telecentric field mirror, as follows:

[0038] Lens No. Curvature radius 1 Curvature radius 2 Thickness Refractive index Abbe number First spherical lens -40.7 INF 15 1.458 67.8 Second spherical lens -276.7 -44.4 15 1.458 67.8 Third aspherical lens 164.4 -567.8 13 1.458 67.8 Fourth DOE element INF INF 3 1.458 67.8 Fifth spherical lens -156.06 910.67 8 1.458 67.8 Sixth spherical lens 90.4 221.5 7.8 1.458 67.8 Seventh protective flat mirror INF INF 3 1.458 67.8

[0039] In some optional embodiments, the first lens is used to diverge the incident light, the second lens is used to fold the incident light and balance the aberration generated by the negative lens of the first lens, the third lens is used to reduce the spherical aberration of the optical path, the fifth lens is used to balance the aberration of the optical path, and the sixth lens is used to reduce the telecentric angle of the lens optical path.

[0040] Specifically, the first lens is a flat concave spherical negative lens, which is used to diverge the incident light. Due to the divergence of the light, the principal plane position of the lens optical path moves backward, and the working distance refers to the distance between the last surface of the lens and the imaged object (or focal point). By moving the principal plane backward, the first lens effectively increases the spatial distance between the lens and the processed object or the imaging target, thereby improving the working distance of the lens. This is of great significance for some application scenarios that need to operate in a larger spatial range, such as laser processing of large workpieces.

[0041] The second lens is a meniscus spherical positive lens with positive refractive power, which folds the light rays diverged by the first lens to change the propagation direction of the light rays. By reasonably selecting the curvature radius, refractive index and other parameters of the lens, the second lens can balance the aberration generated by the first lens to a certain extent.

[0042] The third lens is a spherical positive lens, which reduces the spherical aberration to improve the focusing quality of the outgoing light of the lens, makes the focal point clearer and sharper, and makes the lens structure more compact.

[0043] The third aspherical lens has an aspherical surface on the first surface from left to right along the incident direction, and a spherical surface on the second surface, wherein the aspherical surface equations are as follows:

[0044]

[0045] Wherein, Z represents the axial height in the optical axis direction, C represents the reciprocal of the curvature radius, k represents the conic coefficient, r represents the radial coordinate of the coordinate axis, a1, a2, a3, a4, a5, a6, a7, a8 represent the high-order coefficient of the aspherical surface, and the dimensionless. Table 2 shows the high-order coefficients of the aspherical surface of the aspherical positive lens:

[0046]

[0047] The conic coefficient k in the aspherical surface is 0.

[0048] The diffractive optical element utilizes the diffraction principle of light, and through designing specific micro-nano structures on the surface or inside of the element, different degrees of phase modulation are performed on light rays of different wavelengths, so that they can be refocused on the same point after passing through the element, thereby effectively correcting chromatic aberration.

[0049] The fifth lens adopts a double-concave spherical negative lens, and after transmission and processing of the plurality of optical elements in front, some residual aberrations can still exist, the main role of the fifth lens is to further balance and correct the aberrations of the lens optical path, and by reasonably designing the parameters of the lens, various aberrations introduced by the optical elements in front can be compensated, thereby further balancing the aberrations of the lens optical path.

[0050] The sixth lens adopts a meniscus spherical positive lens, the sixth lens can reduce the telecentric angle of the lens optical path by the special meniscus shape and optical parameter design, so that the chief ray is closer to parallel to the optical axis, thereby improving the telecentricity of the lens.

[0051] As shown in Figure 1 , the optical power of each optical element in the lens optical path is reasonably distributed, and by combining the positive and negative optical powers of the elements, the positive lens and the negative lens generate opposite aberrations, which can be mutually offset, thereby effectively reducing the aberrations of the lens optical path.

[0052] The aspherical lens is used in the lens optical path, which can correct the residual spherical aberration of the lens optical path while reducing the spherical aberration of the lens itself. The diffractive optical element mainly compensates the chromatic aberration generated by the fused quartz lens, and can also compensate the residual aberration of the lens optical path. The lens power in the lens optical path presents a feature of being negative in front and positive in back, which can move the rear of the main surface of the lens to the left, which is beneficial to enlarge the working distance of the lens.

[0053] Figure 2 are spot diagrams under different field angles, wherein the upper left diagram is a focused spot diagram under a 0-degree field angle, the upper right diagram is a focused spot diagram under an 8-degree field angle, the lower left diagram is a focused spot diagram under a 16-degree field angle, and the lower right diagram is a focused spot diagram under a 19-degree field angle. Figure 3 is a distortion diagram, the distortion of the lens is small, and the lens is suitable for linear scanning marking. Figure 3 The longitudinal coordinate is a field angle, the horizontal coordinate is an F-theta field lens distortion value, and the diagram shows the distortion of the F-theta field lens under different field angles.

[0054] The ultraviolet femtosecond achromatic telecentric field lens provided by the embodiment of the application uses an aspherical lens to reduce the spherical aberration generated by the optical path, and also makes the lens structure small in size. By means of the diffractive optical element, the chromatic aberration generated by the fused quartz lens is compensated, and the spherical aberration is corrected by the aspherical surface, the spot diagram of the lens is close to the diffraction limit, and the focused spot diagram emitted by the lens has good roundness and uniformity.

[0055] As one or more specific application embodiments of the embodiment of the application, the optimal implementation scheme or the scheme that the inventor most wants to embody is described in combination with a specific application scenario.

[0056] Although embodiments of the present application have been described in conjunction with the accompanying drawings, various modifications and changes can be suggested to one skilled in the art, and it is intended that the present application encompass such modifications and changes as fall within the scope of the appended claims.

Claims

1. A UV femtosecond achromatic telecentric field lens, characterized in that: include: A plurality of lenses and a diffractive optical element arranged coaxially, wherein the diffractive optical element is used to correct chromatic aberration; The lens comprises a first lens, a second lens, a third lens, a fifth lens, a sixth lens and a seventh plane mirror which are arranged in sequence from the object side to the image side along the incident direction of the incident light; The diffractive optical element is arranged between the third lens and the fifth lens.

2. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 1, characterized in that: The lens and the diffractive optical element have the same refractive index and Abbe number.

3. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 1, characterized in that: The incident light reaches the first surface and the second surface of each lens in sequence along the incident direction; The first lens is a plano-concave spherical negative lens, the second lens is a meniscus spherical positive lens, the second surface of the first lens is close to the first surface of the second lens, the second surface of the first lens is a plane, and the absolute value of the curvature radius of the first surface of the second lens is greater than the absolute value of the curvature radius of the second surface of the second lens.

4. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 3, characterized in that: The curvature radius of the first surface of the first lens is -40.7, the curvature radius of the first surface of the second lens is -276.7, the curvature radius of the second surface of the second lens is -44.4, the thickness of the first lens is equal to the thickness of the second lens, and the thickness of the first lens and the thickness of the second lens are 15 mm.

5. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 3, characterized in that: The third lens is an aspheric positive lens, the first surface of the third lens is close to the second surface of the second lens, and the absolute value of the curvature radius of the first surface of the third lens is smaller than the absolute value of the curvature radius of the second surface of the third lens.

6. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 5, characterized in that: The curvature radius of the first surface of the third lens is 164.4, the curvature radius of the second surface of the third lens is -567.8, and the thickness of the third lens is 13 mm.

7. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 3, characterized in that: The fifth lens is a biconcave spherical negative lens, and the sixth lens is a meniscus spherical positive lens; The second surface of the fifth lens is close to the first surface of the sixth lens, the absolute value of the curvature radius of the first surface of the fifth lens is smaller than the absolute value of the curvature radius of the second surface of the fifth lens, and the absolute value of the curvature radius of the first surface of the sixth lens is smaller than the absolute value of the curvature radius of the second surface of the sixth lens; The first surface of the seventh plane mirror is close to the second surface of the sixth lens, and the seventh plane mirror is a glass protection plane mirror.

8. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 7, characterized in that: The radius of curvature of the first surface of the fifth lens is -156.06, and the radius of curvature of the second surface of the fifth lens is 910.67; the radius of curvature of the first surface of the sixth lens is 90.4, and the radius of curvature of the second surface of the sixth lens is 221.5; the thickness of the fifth lens is 9 mm, the thickness of the sixth lens is 7.8 mm, and the thickness of the seventh plane mirror is 3 mm.

9. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 1, characterized in that: The first lens, the second lens, the third lens, the diffractive optical element, the fifth lens, the sixth lens and the seventh plane mirror are made of fused quartz glass.

10. The ultraviolet femtosecond achromatic telecentric field mirror according to claim 1, characterized in that: The first lens is used to diverge the incident light; the second lens is used to deflect the incident light and balance the aberration generated by the negative lens of the first lens; the third lens is used to reduce the spherical aberration of the light path; the fifth lens is used to balance the aberration of the light path; and the sixth lens is used to reduce the telecentric angle of the lens light path.

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