A telecentric dispersive objective lens

Abstract

This invention discloses a telecentric dispersive objective lens for spectral dispersive beam focusing. The lens employs a hybrid spherical and aspherical structure. From the incident light side, the lens consists of an aperture stop, a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with negative optical power, a sixth lens with positive optical power, and a seventh lens with positive optical power. The second, fourth, fifth, and sixth lenses are spherical lenses; the first, third, and seventh lenses are aspherical lenses, and all three satisfy the aspherical equation. Due to its reasonable optical power distribution, this imaging lens can achieve spectral dispersive beam focusing, and all wavelengths exhibit diffraction-limited focusing levels.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and more particularly to a dispersive lens for non-contact measurement. Background Technology

[0002] Spectroscopic confocal three-dimensional surface topography measurement technology is based on confocal microscopy and introduces a color-coded optical method, thereby increasing the measurement depth of field and solving the problem of small focusing depth in traditional confocal microscopy. This allows it to be applied to three-dimensional surface topography measurement while retaining the high resolution advantage of classic confocal microscopy. The core component of the spectral confocal measuring instrument is a dispersive objective lens, which focuses different wavelengths of light to different distances.

[0003] Currently, dispersive objectives cannot achieve diffraction-limited focusing at all wavelengths. Summary of the Invention

[0004] This invention provides a telecentric dispersive objective lens for dispersive focusing of the 450-650 nm spectrum, achieving diffraction-limited focusing at all wavelengths.

[0005] This invention provides a telecentric dispersion objective lens with a hybrid spherical and aspherical structure. From the incident light side, the lens comprises, in sequence: an aperture stop, a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with negative optical power, a sixth lens with positive optical power, and a seventh lens with positive optical power. The second, fourth, fifth, and sixth lenses are spherical lenses; the first, third, and seventh lenses are aspherical lenses, and all three lenses satisfy the aspherical equation.

[0006]

[0007] Where z is the surface elevation, r is the radial radius, c is the curvature, k is the conic coefficient, and A, B, C, D, E, F, G, and H are aspheric coefficients.

[0008] The first lens is made of an Abbe number greater than or equal to 15 and less than or equal to 35. Both surfaces are aspherical. The radius of curvature of the front surface is greater than 0 and bends toward the aperture stop. The absolute value of the radius of curvature of the rear surface is greater than that of the front surface.

[0009] The optical power of the second lens is less than 0.001.

[0010] The third lens is made of an Abbe number greater than or equal to 50 and less than or equal to 70. Both surfaces are aspherical. The radius of curvature of the front surface is less than 0 and it bends away from the direction of the aperture stop. The radius of curvature of the rear surface is greater than 0 and it bends towards the direction of the aperture stop.

[0011] The fourth lens has a front surface radius of curvature greater than 0 and bends towards the aperture stop, while the rear surface radius of curvature is less than 0 and bends away from the aperture stop. The absolute value of the front surface radius of curvature is greater than that of the rear surface radius of curvature.

[0012] The radius of curvature of the front surface of the fifth lens is less than 0 and it bends away from the aperture stop. The radius of curvature of the rear surface is also less than 0 and it bends away from the aperture stop. The absolute value of the radius of curvature of the front surface is less than the absolute value of the radius of curvature of the rear surface.

[0013] The radius of curvature of the front surface of the sixth lens is less than 0 and it bends away from the aperture stop. The radius of curvature of the rear surface is less than 0 and it bends away from the aperture stop. The absolute value of the radius of curvature of the front surface is greater than the absolute value of the radius of curvature of the rear surface.

[0014] Both surfaces of the seventh lens are aspherical. The radius of curvature of the front surface is greater than 0 and bends toward the aperture stop. The radius of curvature of the rear surface is greater than 0 and bends toward the aperture stop. The radius of curvature of the front surface is smaller than that of the rear surface.

[0015] The first lens, the third lens, the fourth lens, the fifth lens, and the sixth lens each satisfy the following conditions:

[0016] 0.9 f1 / f 1.6

[0017] -1.5 f3 / f -0.4

[0018] 0.35 f4 / f 0.8

[0019] -1.2 f5 / f -0.5

[0020] 2 f6 / f 2.8

[0021] f is the focal length of the lens; f1 is the focal length of the first lens; f3 is the focal length of the third lens; f4 is the focal length of the fourth lens; f5 is the focal length of the fifth lens; and f6 is the focal length of the sixth lens.

[0022] The telecentric dispersive objective lens formed in this embodiment of the invention has a reasonable optical power distribution. It uses a hybrid structure of spherical and aspherical surfaces to disperse and focus the 450-650 nm spectrum. All wavelengths have diffraction-limited focusing levels. Therefore, it is possible to design a telecentric dispersive objective lens with a scanning field of view width of 0-12 mm, a measurement depth of field of 0-8 mm, and a numerical aperture of 0-0.4, so as to realize the wide application of optical measurement. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a dispersive objective lens according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of the dispersive objective lens according to Embodiment 1 of the present invention;

[0025] Figure 3 This is a schematic diagram of the dispersive objective lens according to Embodiment 2 of the present invention;

[0026] Figure 4 This is a schematic diagram of the dispersive objective lens according to Embodiment 3 of the present invention. Detailed Implementation

[0027] The following is in conjunction with the appendix Figure 1 The following is a detailed description of a specific implementation of a dispersive objective lens provided in the embodiments of the present invention. In the figure, reference numeral 9 indicates the 450 nm focusing position and reference numeral 10 indicates the 650 nm focusing position.

[0028] This invention provides a dispersive objective lens with a hybrid spherical and aspherical structure. From the light-incident side, the lens comprises an aperture stop 8, a first lens 1 with positive optical power, a second lens 2 with positive optical power, a third lens 3 with negative optical power, a fourth lens 4 with positive optical power, a fifth lens 5 with negative optical power, a sixth lens 6 with positive optical power, and a seventh lens 7 with positive optical power. The second lens 2, fourth lens 4, fifth lens 5, and sixth lens 6 are spherical lenses; the first lens 1, third lens 3, and seventh lens 7 are aspherical lenses, and all three satisfy the aspherical equation.

[0029]

[0030] Where z is the surface elevation, r is the radial radius, c is the curvature, k is the conic coefficient, and A, B, C, D, E, F, G, and H are aspheric coefficients.

[0031] Aperture 8 is placed at the very front of the lens, which helps to achieve a telecentric optical path.

[0032] The first lens 1 has a front surface radius of curvature greater than 0 and bends towards the aperture stop, while the absolute value of the rear surface radius of curvature is greater than that of the front surface. Both surfaces of this lens are aspherical, which helps to eliminate aperture-related aberrations such as spherical aberration and coma. The positive lens is made of a low Abbe number material, with an Abbe number greater than or equal to 15 and less than or equal to 35, which helps to produce dispersive beams.

[0033] The second lens 2 has an optical power of less than 0.001 and is mainly used to eliminate chromatic aberration due to magnification.

[0034] The third lens 3 has a front surface radius of curvature less than 0 and bends away from the aperture stop 8, while its rear surface radius of curvature is greater than 0 and bends toward the aperture stop 8. Both surfaces of this lens are aspherical, which helps to eliminate spherical aberration, coma, and aperture-related aberrations. The lens is made of a high Abbe number material with an Abbe number greater than or equal to 50 and less than or equal to 70, which helps to produce dispersive spectral dispersion.

[0035] The fourth lens 4 has a front surface radius of curvature greater than 0, curving towards the aperture stop 8, and a rear surface radius of curvature less than 0, curving away from the aperture stop 8. The absolute value of the front surface radius of curvature is greater than that of the rear surface radius of curvature. This lens is mainly used to eliminate spherical aberration, coma, and astigmatism.

[0036] The fifth lens 5 has a front surface radius of curvature less than 0, curving away from the aperture stop 8, and a rear surface radius of curvature less than 0, also curving away from the aperture stop 8. The absolute value of the front surface radius of curvature is smaller than the absolute value of the rear surface radius of curvature. This lens is mainly used to eliminate spherical aberration, coma, and astigmatism.

[0037] The sixth lens 6 has a front surface radius of curvature less than 0, curving away from the aperture stop 8, and a rear surface radius of curvature less than 0, also curving away from the aperture stop 8. The absolute value of the front surface radius of curvature is greater than the absolute value of the rear surface radius of curvature. This lens is mainly used to eliminate spherical aberration and coma.

[0038] The seventh lens 7 has a front surface with a radius of curvature greater than 0, curving towards the aperture stop 8, and a rear surface with a radius of curvature greater than 0, also curving towards the aperture stop 8. The radius of curvature of the front surface is smaller than that of the rear surface. Both surfaces of this lens are aspherical, primarily used to control distortion and help different wavelengths focus to the same image height.

[0039] Lens 1 (first lens), 3 (third lens), 4 (fourth lens), 5 (fifth lens), and 6 (sixth lens) respectively satisfy the following conditions:

[0040] 0.9 f1 / f 1.6

[0041] -1.5 f3 / f -0.4

[0042] 0.35 f4 / f 0.8

[0043] -1.2 f5 / f -0.5

[0044] 2 f6 / f 2.8

[0045] f is the focal length of the lens; f1 is the focal length of the first lens; f3 is the focal length of the third lens; f4 is the focal length of the fourth lens; f5 is the focal length of the fifth lens; and f6 is the focal length of the sixth lens.

[0046] The lens designed in this invention features a reasonable power distribution and employs a hybrid spherical and aspherical structure for dispersive focusing of the 450-650 nm spectrum, achieving diffraction-limited focusing levels for all wavelengths. This allows for the design of telecentric dispersion objectives with a scanning field of view of 0-12 mm, a depth of field measurement (difference between the 650 nm and 450 nm focusing distances) of 0-8 mm, and a numerical aperture of 0-0.4, enabling the lens to be widely used.

[0047] The present invention has designed three specific embodiments, which are described one by one.

[0048] In the design table of each specific embodiment, surface number OBJ represents the object, STOP represents the aperture stop, and surface numbers 1 to 14 represent the front and rear surfaces of the first lens to the seventh lens, respectively.

[0049] Example 1:

[0050] The specific design parameters are shown in Table 1, and the conic coefficient and aspheric coefficient are shown in Table 2.

[0051]

[0052]

[0053] The telecentric dispersive objective lens designed in Example 1 is as follows: Figure 2 As shown, the lens has a focal length of f=133mm, an effective focal length to effective aperture diameter ratio of F / #=4, a field of view (FOV) of 10mm, a depth of field (DOF) of 7mm, a numerical aperture (NA) of 0.125, and a telecentricity of 0.04. It exhibits diffraction-limited imaging quality in the spectral range of 450-650nm.

[0054] Example 2:

[0055] The specific design parameters are shown in Table 3, and the conic coefficient and aspheric coefficient are shown in Table 4.

[0056]

[0057]

[0058] The telecentric dispersive objective lens designed in Example 2 is as follows: Figure 3As shown, the lens has a focal length of f=110mm, an effective focal length to effective aperture diameter ratio of F / #=3, a field of view (FOV) of 4mm, a depth of field (DOF) of 5mm, a numerical aperture (NA) of 0.25, and a telecentricity of 0.029. It exhibits diffraction-limited imaging quality in the spectral range of 450-650nm.

[0059] Example 3:

[0060] The specific design parameters are shown in Table 5, and the conic coefficient and aspheric coefficient are shown in Table 6.

[0061]

[0062]

[0063] The telecentric dispersive objective lens designed in Example 3 is as follows: Figure 4 As shown, the lens has a focal length of f=68.85mm, an effective focal length to effective aperture diameter ratio of F / #=1.5, a field of view (FOV) of 0.6mm, a depth of field (DOF) of 1.85mm, a numerical aperture (NA) of 0.32, and a telecentricity of 0.049. It exhibits diffraction-limited imaging quality in the spectral range of 450-650nm.

[0064] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A telecentric dispersive objective lens, characterized in that: The lens employs a hybrid spherical and aspherical structure. From the light-incident side, the lens comprises, in sequence: an aperture stop, a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with negative optical power, a sixth lens with positive optical power, and a seventh lens with positive optical power. The second, fourth, fifth, and sixth lenses are spherical lenses; the first, third, and seventh lenses are aspherical lenses, and all three satisfy the aspherical equation. ; Where z is the surface elevation, r is the radial radius, c is the curvature, k is the conic coefficient, and A, B, C, D, E, F, G, and H are aspheric coefficients; The first lens is made of material with an Abbe number greater than or equal to 15 and less than or equal to 35, both surfaces are aspherical, the radius of curvature of the front surface is greater than 0 and bends toward the aperture, and the absolute value of the radius of curvature of the rear surface is greater than the radius of curvature of the front surface. The optical power of the second lens is less than 0.001; The third lens is made of material with an Abbe number greater than or equal to 50 and less than or equal to 70. Both surfaces are aspherical. The radius of curvature of the front surface is less than 0 and it bends away from the direction of the aperture stop. The radius of curvature of the rear surface is greater than 0 and it bends towards the direction of the aperture stop. The fourth lens has a front surface radius of curvature greater than 0 and bends toward the aperture, while its rear surface radius of curvature is less than 0 and bends away from the aperture. The front surface radius of curvature is greater than the absolute value of the rear surface radius of curvature. The radius of curvature of the front surface of the fifth lens is less than 0 and it bends away from the direction of the aperture stop. The radius of curvature of the rear surface is less than 0 and it bends away from the direction of the aperture stop. The absolute value of the radius of curvature of the front surface is less than the absolute value of the radius of curvature of the rear surface. The radius of curvature of the front surface of the sixth lens is less than 0 and it bends away from the direction of the aperture stop. The radius of curvature of the rear surface is less than 0 and it bends away from the direction of the aperture stop. The absolute value of the radius of curvature of the front surface is greater than the absolute value of the radius of curvature of the rear surface. Both surfaces of the seventh lens are aspherical. The radius of curvature of the front surface is greater than 0 and it bends toward the aperture. The radius of curvature of the rear surface is greater than 0 and it bends toward the aperture. The radius of curvature of the front surface is smaller than that of the rear surface. The first lens, the third lens, the fourth lens, the fifth lens, and the sixth lens each satisfy the following conditions: 0.9 f1 / f 1.6 -1.5 f3 / f -0.4 0.35 f4 / f 0.8 -1.2 f5 / f -0.5 2 f6 / f 2.8 f is the focal length of the lens; f1 is the focal length of the first lens; f3 is the focal length of the third lens; f4 is the focal length of the fourth lens; f5 is the focal length of the fifth lens; and f6 is the focal length of the sixth lens.

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