Large-view-field low-distortion infrared telecentric scanning objective lens

Abstract

The invention discloses a large-view-field low-distortion infrared telecentric scanning objective lens which comprises a lens body, the lens body is composed of a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged along an axis, the first lens is a positive lens, the second lens is a negative lens, the third lens is a negative lens, the fourth lens is a meniscus positive lens, and the fifth lens is a negative lens. The fifth lens is a positive lens, and the first lens and the second lens are cemented lenses. According to the invention, through combination of a plurality of lenses and the balsaming lens, high optical index, good temperature adaptability, low distortion, large target surface and large entrance pupil diameter are realized; by reasonably distributing the focal power of each lens and adopting the combination of optical materials with specific refractive index and Abbe number, various aberrations such as spherical aberration, curvature of field, chromatic aberration and the like are effectively corrected, so that high-quality imaging with system RMS wavefront less than 0.02 lambda is realized, the distortion is strictly controlled below 0.02%, and the imaging quality is greatly improved. And a sub-pixel-level accurate positioning capability is realized for high-precision machine vision and measurement detection.

Description

Technical Field

[0001] This invention belongs to the field of high-precision optical scanning lenses, and specifically relates to an infrared large field-of-view f-theta scanning objective that combines temperature adaptability and low distortion. Background Technology

[0002] With the rapid development of precision manufacturing and microfabrication technologies, the industrial sector is increasingly demanding technologies such as laser precision machining, additive manufacturing, semiconductor direct writing, high-precision marking, and micro / nano structure manufacturing. These applications place extremely high demands on processing accuracy, speed, and the ability to generate complex patterns, which traditional optical scanning and processing methods can no longer meet. Galvanometer scanning systems, as a core technology for achieving high-speed, high-precision laser processing, have been widely applied in these fields. Their core principle lies in controlling the laser beam to rapidly scan and position itself within a two-dimensional plane by deflecting two high-speed galvanometers.

[0003] In a galvanometer scanning system, the f-theta lens, as a key optical component connecting the galvanometer and the processing plane, directly determines the processing accuracy, speed, and quality of the entire system. The core function of the f-theta lens is to linearly convert the angular deflection of the galvanometer into displacement on the image plane, ensuring a constant movement speed of the scanning spot on the image plane, thereby achieving distortion-free image processing. To meet the demands of high-precision processing, an ideal f-theta lens must possess several stringent optical characteristics: it must strictly adhere to the f-theta linear relationship to ensure distortion-free scanned images; it must achieve flat-field focusing throughout the entire scanning field of view to ensure consistent spot size and energy density at the edges and center; it needs a high numerical aperture to obtain a small spot size, thereby improving processing resolution; furthermore, to eliminate positioning errors caused by minute changes in the height of the processing surface, the lens is typically designed with an image-side telecentric structure.

[0004] Domestic and international research institutions have conducted extensive work on the design of f-theta lenses. Early designs often employed simple positive lens groups, which, while structurally concise, struggled to simultaneously correct field curvature, astigmatism, and distortion over a wide field of view. Modern high-performance f-theta lenses generally utilize complex structures combining multiple lenses, achieving coordinated correction of various aberrations through the rational allocation of positive and negative optical power and the use of specialized optical materials. However, existing designs still face challenges in simultaneously achieving a large field of view, high numerical aperture, low distortion, and good telecentricity, especially in applications requiring both long working distances and compact structures, where the design difficulty increases significantly. Furthermore, the diversification of processing materials and techniques places higher demands on the wavelength adaptability, thermal stability, and assembly tolerance of f-theta lenses. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a large field-of-view, low-distortion infrared telecentric scanning objective, thereby achieving good thermal stability and better, more stable image quality while simultaneously pursuing a large field of view, high numerical aperture, low distortion, and good telecentricity.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: The present invention provides a large field-of-view, low-distortion infrared telecentric scanning objective lens, which comprises a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged coaxially from the object side to the image side. The first lens is a biconvex lens with positive optical power. The second lens is a biconcave lens with negative optical power; The first lens and the second lens constitute a cemented doublet lens, and the combined optical power of the cemented doublet lens is positive. The third lens is a biconcave lens, with the side closest to the object being concave, and its optical power is negative. The fourth lens is a meniscus lens, with the side closest to the object being concave, and its optical power is positive. The fifth lens is a biconvex lens with positive optical power; Light rays emitted from the object side are incident sequentially on a doublet consisting of a first lens and a second lens at an angle parallel to the optical axis. Refraction occurs at the first lens, causing the parallel light to initially converge. The light then diverges sequentially through the second and third lenses, and then converges sequentially through the fourth and fifth lenses, making the sum of the distortion coefficients of each lens zero. This allows the light to converge and form an image on the focal plane of the infrared telecentric scanning objective, thereby forming the target imaging light within the corresponding wavelength range.

[0007] The large field-of-view, low-distortion infrared telecentric scanning objective of this invention is characterized by designating any one of the five lenses as the i-th lens, and using equation (1) to obtain the constraints between the lenses: (1) In equation (1), Let be the distortion coefficient of the i-th lens, and we have: (2) In equation (2), Let be the optical power of the i-th lens. The incident height of the principal ray on the i-th lens, Let be the angle of the principal ray incident on the i-th lens. Let f be a function of the Abbe number of the i-th lens material.

[0008] Furthermore, the light rays refracted by each lens satisfy the law of refraction shown in equation (3): (3) In equation (3), The refractive index of the medium on the incident side of the light rays for each lens. The refractive index of the medium on the exit side of each lens. Let be the angle of incidence of the light at the interface between the incident and exiting media. Let α be the angle of incidence of the light ray at the interface between the incident and exiting media; and when the light ray is refracted at the interface between air and the lens material, both the angle of incidence α and the angle of refraction β satisfy 0° ≤ , ≤20°.

[0009] Furthermore, the working wavelength of the infrared telecentric scanning objective is 1525nm-1575nm, and the material of the lens selected for the infrared telecentric scanning objective should meet the thermal difference condition shown in equation (4): (4) In equation (4), Let be the optical power of the i-th lens. The total optical power of the infrared telecentric scanning objective lens. Given the relative thermal difference, we have: (5) In equation (5), It is the temperature coefficient of the refractive index of the material. It is the coefficient of linear expansion of the i-th lens material. is the refractive index of the i-th lens material at the reference temperature, t represents the ambient temperature, and t∈[0℃,100℃].

[0010] Furthermore, the ideal lateral resolution of the infrared telecentric scanning objective under the Rayleigh criterion... Satisfy the constraints shown in equation (6): (6) In equation (6), NA is the image-side numerical aperture of the infrared telecentric scanning objective. For the operating wavelength, This is the highest limit for the ideal horizontal resolution, and <16μm.

[0011] Furthermore, at ambient temperature t, when light of each wavelength within the working band propagates in the infrared telecentric scanning objective, the modulation transfer function of each lens imaging at its respective focal plane satisfies the constraint shown in equation (7): (7) In equation (7), For the infrared telecentric scanning objective at the j-th working wavelength Modulation transfer function under the theoretical diffraction limit. For the infrared telecentric scanning objective at the j-th working wavelength The modulation transfer function for actual imaging.

[0012] Furthermore, the working distance between the last refractive surface of the fifth lens (5) in the large field-of-view, low-distortion infrared telecentric scanning objective and the convergence point on the focal plane is greater than 90 mm.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By selecting materials, this invention achieves an overall system distortion of less than 0.02% under ideal conditions when the incident wavelength is in the range of 1525nm-1575nm. The maximum position deviation is <6μm across the entire field of view, enabling sub-pixel level precise positioning. It is applicable to scenarios with top-level precision requirements, such as semiconductor lithography and detection, and high-precision metrology and measurement.

[0014] 2. This invention optimizes the imaging quality of the large field-of-view f-theta scanning objective at 0℃-100℃, giving the scanning objective an ultra-wide temperature adaptability. The imaging quality is superior at 0℃-100℃, and the modulation transfer function of each band is close to the diffraction limit, thus avoiding the interference of ambient temperature on measurement accuracy.

[0015] 3. By optimizing the wavelength, material selection, and structure of the large field-of-view f-theta scanning objective, the present invention achieves a telecentricity better than 0.05%, thereby enabling the large field-of-view f-theta scanning objective to have high measurement accuracy.

[0016] 4. The large field-of-view f-theta scanning objective of this invention has a mirror height greater than 28mm. While ensuring f-theta distortion is less than 0.02%, it possesses a large field of view. To achieve a given working area, using an objective with a large scanning range reduces the dependence on the travel and accuracy of mechanical moving parts (such as a large-format moving stage). This objective architecture can be more compact, lighter, more reliable, and easier to maintain.

[0017] 5. To achieve stable imaging of a large field-of-view f-theta scanning objective over a wide temperature range, this invention requires effective compensation for thermally induced aberrations. Since the thermal characteristics of a single optical glass (dependent on refractive index and temperature) are limited, it cannot achieve good thermal stability independently. Therefore, a combination of multiple glass materials is necessary to achieve passive thermal compensation through the mutual cancellation of their thermal parameters. However, too many material types significantly increase material control and processing costs. Therefore, this invention uses a combination of four types of optical glass (less than five). This approach overcomes the limitations of single-material thermal performance and effectively suppresses system thermal drift while avoiding the economic decline caused by too many material types, thus achieving a good balance between optical performance (low distortion, low telecentricity, and temperature adaptability) and manufacturing costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the optical structure of the optical system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the overall f-theta distortion in an embodiment of the present invention; Figure 3 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 0°C and 1525nm-1575nm. Figure 4 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 20°C and 1525nm-1575nm. Figure 5 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 40°C and 1525nm-1575nm. Figure 6 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 60°C and 1525nm-1575nm. Figure 7 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 80°C and 1525nm-1575nm. Figure 8 This is a graph showing the actual imaging modulation transfer function of an embodiment of the present invention at 100℃ and 1525nm-1575nm. The lenses in the diagram are labeled as follows: 1. First lens, 2. Second lens, 3. Third lens, 4. Fourth lens, and 5. Fifth lens. Detailed Implementation

[0019] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0020] In this embodiment, a large field-of-view, low-distortion infrared telecentric scanning objective lens, such as... Figure 1As shown, it comprises a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a fifth lens 5 arranged coaxially from the object side to the image side.

[0021] The first lens 1 is a biconvex lens with positive optical power; in this embodiment, the refractive index n1 of the first lens 1 satisfies 1.8≤n1≤1.9, and the center thickness is 16.5mm. The second lens 2 is a biconcave lens with negative optical power; in this embodiment, the refractive index n2 of the second lens 2 satisfies 1.6≤n2≤1.7, and the center thickness is 5mm; the air gap between the center of the cemented doublet lens and the center of the third lens 3 is 11mm.

[0022] A cemented doublet 1 is formed by a first lens 1 and a second lens 2, and the combined optical power of the cemented doublet is positive. The third lens 3 is a biconcave lens, with the side closest to the object being concave, and its optical power is negative. In this embodiment, the refractive index n3 of the third lens 3 satisfies 1.6≤n3≤1.7, the center thickness is 15.1mm, and the air gap between the center of the third lens 3 and the center of the fourth lens 4 is 5mm.

[0023] The fourth lens 4 is a meniscus lens with a concave surface on the object side and positive optical power. In this embodiment, the refractive index n4 of the fourth lens 4 satisfies 1.8≤n4≤1.9, the center thickness is 10.5mm, and the air gap between the center of the fourth lens 4 and the center of the fifth lens 5 is 1.5mm. The fifth lens 5 is a biconvex lens with positive optical power; in this embodiment, the refractive index n5 of the fifth lens 5 satisfies 1.9≤n5≤2.1, and the center thickness is 17.

[0024] Light rays with a wavelength range of 1525nm-1575nm emitted from the object side are sequentially incident on a cemented doublet consisting of a first lens 1 and a second lens 2 at an angle parallel to the optical axis. Refraction occurs at the first lens 1, causing the parallel light to initially converge. Then, the light rays are sequentially incident on the second lens 2 for divergence, the third lens 3 for divergence, the fourth lens 1 for convergence, and the fifth lens 5 for convergence. This process corrects aberrations, controls lens distortion and telecentricity, and converges to form an image on the focal plane, creating the target imaging light of the corresponding wavelength.

[0025] In this embodiment, the first lens is made of biconvex lanthanum flint glass (low dispersion), and is combined with a second lens of biconcave special flint glass (high dispersion) to form a double-cemented structure, satisfying equations (1)-(3): ,2(1) (2) (3) In equations (1)-(3), Indicates the optical power of a cemented doublet lens. , These represent the optical power of the first lens 1 and the second lens 2, respectively. , These represent the Abbe numbers of the first lens 1 and the second lens 2, respectively. This double-cemented structure is a classic achromatic combination that can effectively correct axial chromatic aberration (positional chromatic aberration). The cemented surface provides additional degrees of freedom, which can simultaneously correct spherical aberration and coma, and also reduce reflection loss and improve light transmittance.

[0026] In this embodiment, any one of the five lenses is denoted as the i-th lens, and the constraints between the lenses are obtained using equation (4): (4) In equation (4), Let be the distortion coefficient of the i-th lens, and its specific expression is given by equation (5): (5) In equation (5), Let be the optical power of the i-th lens. The incident height of the principal ray on the i-th lens, Let be the angle of the principal ray incident on the i-th lens. Let be a function of the Abbe number of the i-th lens material. When the lens group satisfies This means that the sum of the positive and negative distortion coefficients generated by all lenses in a large field-of-view, low-distortion infrared telecentric scanning objective must cancel each other out.

[0027] In this embodiment, the distortion of this large field-of-view, low-distortion infrared telecentric scanning objective is as follows: Figure 2 As shown, the f-θ distortion of the objective lens at its maximum field of view is less than 0.03%.

[0028] In this embodiment, all five lenses are made of high-refractive-index glass, three of which are special lanthanum flint glass. The lenses in the dispersive objective lens use fewer than five different types of materials.

[0029] In this embodiment, the large field-of-view, low-distortion infrared telecentric scanning objective adopts a "positive-negative-negative-meniscus-positive" structure, providing abundant degrees of freedom for aberration correction. The second lens 2 and the third lens 3 both employ a negative optical power design, effectively compensating for the inherent pincushion distortion of the positive lens. The fourth lens 4 adopts a meniscus design, precisely correcting astigmatism and coma. Finally, the fifth lens 5 performs aberration balancing and field flattening. The use of a high-refractive-index meniscus design in the fourth lens 4 and a highly refractive-index biconvex design in the fifth lens ensures excellent image-side telecentricity, ultimately enabling the system to achieve an ultra-low f-theta distortion of 0.02%, close to the theoretical limit.

[0030] In this embodiment, in the large field-of-view, low-distortion infrared telecentric scanning objective, after the parallel beam is incident from the object side, the light refracted on each lens satisfies the refraction law shown in equation (6): (6) In equation (6), The refractive index of the medium on the incident side of the light rays for each lens. The refractive index of the medium on the exit side of each lens. Let be the angle of incidence of the light at the interface between the incident and exiting media. Let α be the angle of incidence of the light ray at the interface between the incident and exiting media; and when the light ray is refracted at the interface between air and the lens material, both the angle of incidence α and the angle of refraction β satisfy 0° ≤ , ≤20°.

[0031] In this embodiment, the operating wavelength of the large field-of-view f-theta scanning objective is 1525nm-1575nm, and the material of the lens selected should meet the system's thermal degradation requirements. (7) In equation (7), Let be the optical power of the i-th lens. The total optical power of the system, The relative thermal difference of the system represents the relative rate of change of the material's contribution to "optical power" when the temperature changes. Its defining equation is: (8) In equation (8), It is the temperature coefficient of the refractive index of the material. It is the coefficient of linear expansion of the i-th lens material. is the refractive index of the i-th lens material at the reference temperature, t represents the ambient temperature, and t∈[0℃,100℃].

[0032] In this embodiment, the first lens 1, the fourth lens 4, and the fifth lens 5 adopt a medium-low resolution. The series of glass, the second lens 2 and the third lens 3 adopt medium and high quality. The series of glass, through the coordination of optical power distribution and air gaps, cancels out these two trends, keeping the total optical power and image plane position of the system stable over a wide temperature range.

[0033] In this embodiment, the material of the fifth lens 5 has extremely low... This makes its optical power least sensitive to temperature, and as the last lens in the system, its stable output ensures a constant image plane position. Its extremely high refractive index allows for the use of a relatively gentle surface while contributing the necessary optical power, reducing the temperature sensitivity of advanced aberrations. Furthermore, it has a higher [performance / quality] than the preceding lenses. The second lens 2 and the third lens 3 form a "high and low" combination, which effectively suppresses the overall thermal focal length drift of the system.

[0034] In this embodiment, the ideal lateral resolution of the infrared telecentric scanning objective under the Rayleigh criterion is... Satisfy the constraints shown in equation (9): (9) In equation (9), NA is the image-side numerical aperture of the infrared telecentric scanning objective. For the operating wavelength, This is the highest limit for the ideal horizontal resolution, and <16μm.

[0035] In this embodiment, at ambient temperature t, when light of each wavelength in the working band propagates in the infrared telecentric scanning objective, the modulation transfer function of each lens imaging at its respective focal plane satisfies the constraint shown in equation (7): (10) In equation (7), For a large field-of-view f-theta scanning objective at the j-th operating wavelength Modulation transfer function under the theoretical diffraction limit. For a large field-of-view f-theta scanning objective at the j-th operating wavelength The modulation transfer function of actual imaging.

[0036] In this embodiment, the working distance between the last refractive surface of the fifth lens 5 in the large field-of-view, low-distortion infrared telecentric scanning objective and the convergence point on the focal plane is greater than 90 mm.

[0037] The specific parameters of each lens in the optical system of this embodiment are shown in Table 1: Table 1

[0038] like Figure 3 The dispersive objective lens shown exhibits good image quality at 0℃ and wavelengths of 1525nm-1575nm, with the actual imaging modulation transfer function approaching that at the diffraction limit. The lens in this embodiment demonstrates good adaptability to low temperatures.

[0039] like Figure 4 The dispersive objective shown has good imaging quality at 20℃ and wavelengths of 1525nm-1575nm, and the actual imaging modulation transfer function is close to the modulation transfer function under the diffraction limit.

[0040] like Figure 5 The dispersive objective shown has good imaging quality at 40℃ and wavelengths of 1525nm-1575nm, and the actual imaging modulation transfer function is close to the modulation transfer function under the diffraction limit.

[0041] like Figure 6 The dispersive objective shown has good imaging quality at 60℃ and wavelengths of 1525nm-1575nm, and the actual imaging modulation transfer function is close to the modulation transfer function under the diffraction limit.

[0042] like Figure 7 The dispersive objective lens shown exhibits good image quality at 80℃ and wavelengths of 1525nm-1575nm, with the actual imaging modulation transfer function approaching the modulation transfer function under diffraction-limited conditions. The lens in this embodiment demonstrates good adaptability to high temperatures.

[0043] like Figure 8 The dispersive objective lens shown exhibits good image quality at 100℃ and wavelengths of 1525nm-1575nm, with the actual imaging modulation transfer function approaching the modulation transfer function under diffraction-limited conditions. The lens in this embodiment demonstrates good adaptability to high temperatures.

Claims

1. An infrared telecentric scanning objective with large field of view and low distortion, characterized in that The application relates to a large-view-field low-distortion infrared telecentric scanning objective lens. The first lens (1) is a biconvex lens and has positive refractive power. The second lens (2) is a biconcave lens and has negative refractive power. The first lens (1) and the second lens (2) form a double cemented lens (1), and the combined refractive power of the double cemented lens (1) is positive. The third lens (3) is a biconcave lens, and the side close to the object side is a concave surface, and the refractive power is negative. The fourth lens (4) is a meniscus lens, and the side close to the object side is a concave surface, and the refractive power is positive. The fifth lens (5) is a biconvex lens and has positive refractive power. The light emitted from the object side is incident on the double cemented lens (1) composed of the first lens (1) and the second lens (2) at an angle parallel to the optical axis, is refracted at the first lens (1), is then incident on the second lens (2) and the third lens (3) to be diverged, and is then incident on the fourth lens (4) and the fifth lens (5) to be converged, so that the sum of the distortion coefficients of the lenses is zero, and the light is converged on the focal plane of the infrared telecentric scanning objective lens to form an image of a target in a corresponding wavelength range. Any one of the five lenses is recorded as the ith lens, and the constraint between the lenses is obtained by using formula (1):

2. The large field of view, low distortion, infrared telecentric scanning objective of claim 1, wherein, The refracted light on each lens satisfies the refraction law shown in formula (3): (1) In formula (1), is the distortion coefficient of the i-th lens and has: (2) in formula (2), is the power of the i-th lens, is the entrance height of the chief ray on the i-th lens, is the chief ray angle of incidence to the i-th lens, is a function of the Abbe number of the i-th lens material.

3. The large field of view, low distortion, infrared telecentric scanning objective of claim 1, wherein, The working wavelength range of the infrared telecentric scanning objective lens is 1525nm-1575nm, and the material of the selected lens of the lens should satisfy the athermalization condition shown in formula (4): (3) In formula (3), is the refractive index of the medium on the light-incident side of each lens, is the refractive index of the medium on the light-incident side of each lens, is the incident angle of the light at the interface between the medium on the light-incident side and the medium on the light-incident side, is the incident angle of the light at the interface between the medium on the light-incident side and the medium on the light-incident side; and when the light is refracted at the interface between air and the lens material, both the incident angle a and the refracted angle b satisfy 0°≤a, b≤20°. , 20°.

4. The large field of view, low distortion, infrared telecentric scanning objective of claim 1, wherein, At the ambient temperature t, the modulation transfer function of the imaging of each lens at the respective focal plane when the light of each wavelength in the working wavelength range propagates in the infrared telecentric scanning objective lens satisfies the constraint shown in formula (7): (4) In formula (4), is the optical power of the i-th lens, is the total optical power of the infrared telecentric scanning objective, is the relative thermal difference of and has: (5) In formula (5), is the temperature coefficient of the refractive index of the material, is the linear expansion coefficient of the i-th lens material, is the refractive index of the i-th lens material at the reference temperature, t denotes the ambient temperature, and t e [0 °C, 100 °C].

5. The large field of view, low distortion, infrared telecentric scanning objective as claimed in claim 1, wherein, Ideal lateral resolution of the infrared telecentric scanning objective under the Rayleigh criterion satisfies the constraint shown in equation (6): (6) In formula (6), NA is a numerical aperture on an image side of the infrared telecentric scanning objective, is a working wavelength, is a highest limit value of an ideal lateral resolution, and < 16 μm.

6. The large field of view, low distortion, infrared telecentric scanning objective of claim 1, wherein, The working distance between the last refractive surface of the fifth lens (5) in the large-view-field low-distortion infrared telecentric scanning objective lens and the converging point on the focal plane is greater than 90mm. (7) in formula (7), Mtfj is the modulation transfer function of the infrared telecentric scanning objective at the jth working wavelength Mtfj is the modulation transfer function of the infrared telecentric scanning objective at the jth working wavelength Mtfj is the modulation transfer function of the infrared telecentric scanning objective at the jth working wavelength Mtfj is the modulation transfer function of the infrared telecentric scanning objective at the jth working wavelength 7. The large field of view, low distortion, infrared telecentric scanning objective as claimed in claim 1, wherein, ​

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