Microscope objective

Abstract

The application discloses a microscope objective lens and relates to the technical field of microscope objective lenses, wherein the microscope objective lens has a first lens group, a second lens group, a third lens group and a fourth lens group along an optical axis from an object plane to an image plane, and the microscope objective lens has the following relationships: 1<=-f1 / f<3; 3<=f2 / f<5; 12<=f3 / f<20; 1.5<=f4 / f<4; NA=0.8; 0.7<=d0 / f<1; wherein f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, f4 is the combined focal length of the fourth lens group, f is the combined focal length of the whole microscope objective lens, d0 is the distance from the object plane to the object plane side lens surface of the first lens group, and NA is the object side numerical aperture of the microscope objective lens; in the application, the inherent contradiction between a large numerical aperture and a long working distance, which cannot be solved for a long time in the prior art, is broken through by new refractive power global distribution and front group optical configuration innovation.

Description

Technical Field

[0001] This invention relates to the field of microscope objectives, and particularly to a microscope objective. Background Technology

[0002] Optimized for silicon penetration testing in semiconductors, a numerical aperture (NA) of 0.65 can be achieved, but the maximum working distance is only 5mm. For dedicated models with a working distance (WD) ≥10mm, the NA is only up to 0.45, failing to balance high resolution and a long safe working distance, representing a core bottleneck in advanced packaging and testing production lines. Existing technologies cannot simultaneously meet the four core requirements of "large NA, long WD, wide-spectrum diffraction-limited imaging, and industrial mass production adaptability," exhibiting four inherent defects that cannot be resolved through conventional optimization. Existing long-WD SWIR objectives suffer from insufficient aberration correction across the entire field of view, with wavelet aberration RMS generally >λ / 4 (λ=1.55μm), far below the diffraction-limited standard; the MTF at the Nyquist frequency is <0.3 across the entire field of view, resulting in poor imaging contrast, insufficient signal-to-noise ratio for small defects, and false negative and false positive rates far exceeding the semiconductor mass production standard of ≤0.1%.

[0003] The wavelength of SWIR band is 2 to 4 times that of visible light. To achieve the same level of diffraction-limited resolution as visible light, a higher aperture (NA) is required. However, increasing the NA depends on increasing the aperture angle of the front objective lens, which requires placing the front lens extremely close to the sample, resulting in a drastic reduction in the working distance. To extend the working distance, a negative optical power front lens must be introduced, and the lens spacing must be increased, which in turn leads to an exponential increase in off-axis aberrations and a significant reduction in the upper limit of NA. Summary of the Invention

[0004] The main objective of this invention is to propose a microscope objective that addresses the inherent contradiction between large numerical aperture and long working distance, a problem that traditional microscope objectives cannot solve.

[0005] To achieve the above objectives, the microscope objective proposed in this invention comprises, along the optical axis from the object plane to the image plane, a first lens group, a second lens group, a third lens group, and a fourth lens group, and the microscope objective has the following relationship: 1 ≤ -f1 / f < 3; 3≤f² / f<5; 12≤f3 / f<20; 1.5 ≤ f4 / f < 4; NA=0.8; 0.7 ≤ d0 / f < 1; Wherein, f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, f4 is the combined focal length of the fourth lens group, f is the combined focal length of the entire microscope objective, d0 is the distance from the object surface to the object-side mirror of the first lens group, and NA is the object-side numerical aperture of the microscope objective.

[0006] In one embodiment, the second lens group includes at least one cemented lens, and the cemented lens in the second lens group includes a positive lens and a negative lens, satisfying the following relationship: Nmt-Npt>0.25, Vdpt-Vdmt>30; Wherein, Nmt is the refractive index of the negative lens in the cemented lens of the second lens group, Npt is the refractive index of the positive lens in the cemented lens of the second lens group, Vdmt is the dispersion coefficient of the negative lens in the cemented lens of the second lens group, and Vdpt is the dispersion coefficient of the positive lens in the cemented lens of the second lens group.

[0007] In one embodiment, the third lens group includes at least one cemented triplet lens, and the cemented triplet lens of the third lens group includes a positive lens, a negative lens, and a positive lens arranged sequentially from the object plane to the image plane; At least one positive lens in the third group of cemented triplet lenses satisfies the following relationship: Vdt>80; Wherein, Vdt is the positive lens dispersion coefficient of the triplet lens in the third lens group.

[0008] In one embodiment, the third lens group further includes a cemented doublet lens, which is disposed on the image plane side of the cemented triplet lens of the third lens group.

[0009] In one embodiment, the microscope objective further includes an aperture stop; The aperture is positioned between the second lens group and the third lens group.

[0010] In one embodiment, the light refraction angle ratio of the first lens group, the second lens group, the third lens group, and the fourth lens group is -0.5:0.6:0.7:0.8; and / or, The optical power of the first lens group, the second lens group, the third lens group, and the fourth lens group satisfies the following relationship: φ1 = (1 - 2tan(u1) / tan(u0))φ total ;φ2= φ total / (1+L total φ total ); φ3 = (tan(u2) / tan(u0))φ total;φ4= (tan(u2) / tan(u0))φ total ; where φ total L represents the total optical power of the microscope objective lens. total The total length of the microscope objective lens is given. φ1, φ2, φ3, and φ4 are the optical powers of the first lens group, the second lens group, the third lens group, and the fourth lens group, respectively. u0 is the paraxial ray aperture angle on the object side, u1 is the ray aperture angle of the first lens group, and u2 is the ray aperture angle of the second lens group.

[0011] In one embodiment, the optical power of the first lens group is negative, and the first lens group includes a first lens, a second lens, and a third lens arranged sequentially from the object plane to the image plane; The first lens has a positive optical power, and the second and third lenses together form a cemented lens with a negative optical power.

[0012] In one embodiment, the optical power of the second lens group is positive, and the second lens group includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens; The fourth and fifth lenses are cemented lenses with positive optical power, and the sixth and seventh lenses are cemented lenses with positive optical power.

[0013] In one embodiment, the optical power of the third lens group is positive, and the third lens group includes an eighth lens, a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens; The eighth, ninth, and tenth lenses are cemented lenses with positive optical power, while the eleventh and twelfth lenses are cemented lenses with negative optical power.

[0014] In one embodiment, the fourth lens group comprises a thirteenth lens and a fourteenth lens, wherein the optical power of the thirteenth lens is positive and the optical power of the fourteenth lens is positive.

[0015] This invention overcomes the inherent contradiction between large numerical aperture and long working distance, which has long been a problem in existing technologies, through a novel global allocation of optical power and innovative front-group optical configuration. It achieves a simultaneous balance between the two, completely solving a bottleneck pain point in the industry. By optimizing the combination of low-dispersion and low-thermal-optical-coefficient optical materials and designing a global aberration balance across the entire field of view, it can effectively address, to a certain extent, the core defects of existing technologies, namely the inability to simultaneously achieve broadband chromatic aberration correction and thermal stability, and insufficient aberration correction. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 A schematic diagram of an embodiment of the optical lens arrangement in a microscope objective provided by the present invention; Figure 2 for Figure 1 Light path propagation diagram of a medium-sized microscope objective lens; Figure 3 for Figure 1 RMS wavefront aberration vs. field of view of medium microscope objectives; Figure 4 for Figure 1 MTF diagram of polychromatic light diffraction under a medium microscope objective; Figure 5 for Figure 1 Field curvature and distortion diagram of a medium-sized microscope objective.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] Optimized for silicon penetration testing in semiconductors, a numerical aperture (NA) of 0.65 can be achieved, but the maximum working distance is only 5mm. For dedicated models with a working distance (WD) ≥10mm, the NA is only up to 0.45, failing to balance high resolution and a long safe working distance, representing a core bottleneck in advanced packaging and testing production lines. Existing technologies cannot simultaneously meet the four core requirements of "large NA, long WD, wide-spectrum diffraction-limited imaging, and industrial mass production adaptability," exhibiting four inherent defects that cannot be resolved through conventional optimization. Existing long-WD SWIR objectives suffer from insufficient aberration correction across the entire field of view, with wavelet aberration RMS generally >λ / 4 (λ=1.55μm), far below the diffraction-limited standard; the MTF at the Nyquist frequency is <0.3 across the entire field of view, resulting in poor imaging contrast, insufficient signal-to-noise ratio for small defects, and false negative and false positive rates far exceeding the semiconductor mass production standard of ≤0.1%.

[0023] The wavelength of SWIR band is 2 to 4 times that of visible light. To achieve the same level of diffraction-limited resolution as visible light, a higher aperture (NA) is required. However, increasing the NA depends on increasing the aperture angle of the front objective lens, which requires placing the front lens extremely close to the sample, resulting in a sharp decrease in the working distance. To extend the working distance, a negative optical power front lens must be introduced, and the lens spacing must be increased, which in turn leads to an exponential increase in off-axis aberrations and a significant decrease in the upper limit of NA.

[0024] This invention proposes a microscope objective.

[0025] Please see Figures 1 to 5In one embodiment of the present invention, the microscope objective has a first lens group, a second lens group, a third lens group, and a fourth lens group along the optical axis from the object plane to the image plane. The microscope objective has the following relationships: 1≤-f1 / f<3; 3≤f2 / f<5; 12≤f3 / f<20; 1.5≤f4 / f<4; NA=0.8; 0.7≤d0 / f<1; where f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, f4 is the combined focal length of the fourth lens group, f is the combined focal length of the entire microscope objective, d0 is the distance from the object plane to the object plane side mirror of the first lens group, and NA is the object-side numerical aperture of the microscope objective.

[0026] The microscope objective is a microscopic imaging optical objective operating in the short-wave infrared (SWIR) band. Its lens groups, arranged sequentially along the optical axis from the object plane (the plane containing the sample) to the image plane (the plane containing the detector's photosensitive surface), form a complete imaging optical path. The first, second, third, and fourth lens groups are four independent optical sub-objectives arranged sequentially along the optical axis, each consisting of one or more lens elements. The combined focal length refers to the equivalent focal length of all lens elements within each lens group as a whole, and its sign represents the positive or negative optical power of the lens group. The object-side numerical aperture NA is the core parameter characterizing the objective's light-gathering capability, defined as NA = n·sin(θ), where n is the refractive index of the object-side medium, and θ is the angle between the object-side edge ray and the optical axis. d0 is the working distance of the microscope objective, characterizing the spatial distance between the front surface of the objective and the sample being tested.

[0027] In the given formula, a negative value for f1 (represented by -f1 / f) indicates that the optical power of the first lens group is negative, meaning the first lens group is a divergent lens group. The upper and lower limits of each focal length ratio collectively define the reasonable distribution range of optical power for the four lens groups: the focal length ratio range for the first lens group is 1 ≤ -f1 / f < 3, corresponding to the absolute value of the negative optical power of the first lens group being between 1 / 3 and 1 times the overall optical power of the objective lens; the focal length ratio range for the second lens group is 3 ≤ f2 / f < 5, indicating that the second lens group has positive optical power; the focal length ratio range for the third lens group is 12 ≤ f3 / f < 20, indicating that the third lens group has positive optical power; and the focal length ratio range for the fourth lens group is 1.5 ≤ f4 / f < 4, indicating that the fourth lens group has positive optical power. NA = 0.8 indicates that the numerical aperture of the objective lens in the object-side air medium is fixed at 0.8, corresponding to an object-side edge ray aperture angle of approximately 53.1°. The working distance ratio 0.7≤d0 / f<1 is used to normalize and constrain the working distance based on the overall focal length of the objective lens.

[0028] In the field of short-wave infrared microscopy, since the wavelength of SWIR (1.05μm~1.55μm) is 2 to 4 times that of visible light, a larger numerical aperture (NA) is required to achieve the same diffraction-limited resolution as visible light. However, increasing the NA requires increasing the object-side aperture angle, which necessitates placing the front lens group as close to the sample as possible, resulting in a drastic reduction in the working distance. Conversely, introducing a negative optical power front lens group and increasing the lens spacing to extend the working distance would cause an exponential increase in off-axis aberrations, significantly reducing the upper limit of the NA. This is the inherent contradiction that has long existed in current technologies: a strong negative correlation between a large NA and a long working distance.

[0029] This embodiment employs a negative-positive-positive-positive four-group reverse telephoto structure, overcoming the aforementioned contradictions through the global allocation of optical power across the four lens groups. The first lens group uses negative optical power. On one hand, this reduces the incident height of subsequent lens groups after the large aperture angle beam diverges, suppressing higher-order spherical aberrations. On the other hand, the reverse telephoto effect of the negative optical power group shifts the rear focal point forward, achieving large NA light collection without shortening the working distance. The lower limit of the focal length ratio of the first lens group avoids excessive spherical aberration, coma, and chromatic aberration that are difficult to correct in subsequent lens groups due to excessive negative optical power; the upper limit avoids excessive higher-order spherical aberrations and second-order spectral distortion when the negative optical power is too weak. The second lens group, as the main converging element, undertakes the core function of converting diverging beams into convergent beams. Its focal length ratio ensures sufficient refractive power to compress the beam diameter while avoiding large angular aberrations caused by excessive single-group optical power. The third lens group uses a weak positive optical power to perform fine aberration correction after the main beam convergence is complete, especially to balance and compensate for residual spherical aberration, coma, and axial chromatic aberration. The positive optical power of the fourth lens group is used to control the exit pupil position and image-side telecentricity of the microscope objectives. Its lower limit avoids overly irregular lens shapes that are difficult to manufacture, as well as excessive spherical aberration and field curvature; its upper limit avoids insufficient refractive power that leads to a bulky structure and difficulties in comprehensive aberration correction. The constraint of the working distance ratio ensures that the objectives have sufficient safe operating space, avoiding the risk of lens collision during the inspection process, while preventing the working distance from being too short, which would cause a sharp increase in spherical aberration and chromatic aberration, complicating the structure of the microscope objectives.

[0030] Through the aforementioned global optical power allocation strategy, the microscope objective lens can simultaneously achieve a large numerical aperture (NA) of 0.8 and a long working distance of no less than 7 mm in the 1.05 μm to 1.55 μm short-wave infrared band. The full-field wave aberration RMS can reach below λ / 30 (λ=1.55 μm), and the full-field MTF at the Nyquist frequency is ≥0.5, meeting the high-resolution transmission imaging requirements for 1 μm-level micro-defects in advanced semiconductor packaging inspection.

[0031] In one specific embodiment, the overall combined focal length of the microscope objectives is f=10mm, the working wavelength is 1.05μm~1.55μm, the object-side numerical aperture NA=0.8, and the object height is 0.5mm. The combined focal length f1 of the first lens group is negative, satisfying 1≤-f1 / f<3, i.e., -f1 is in the range of 10mm to 30mm; the combined focal length f2 of the second lens group satisfies 3≤f2 / f<5, i.e., f2 is in the range of 30mm to 50mm; the combined focal length f3 of the third lens group satisfies 12≤f3 / f<20, i.e., f3 is in the range of 120mm to 200mm; and the combined focal length f4 of the fourth lens group satisfies 1.5≤f4 / f<4, i.e., f4 is in the range of 15mm to 40mm. The working distance d0 satisfies 0.7≤d0 / f<1, i.e., d0 is in the range of 7mm to 10mm. Under this parameter combination, the polychromatic light diffraction MTF of the microscope objective is close to the diffraction limit, the RMS wavefront aberration is less than the diffraction limit standard in the entire field of view, and the field curvature and distortion are well controlled. It can be used with a short-wave infrared detector to achieve high-contrast imaging of dislocations, hidden cracks and chip packaging defects in silicon wafer penetration detection.

[0032] In some embodiments, such as Figure 1 and Figure 2 As shown, the second lens group includes at least one cemented lens, and the cemented lens in the second lens group includes one positive lens and one negative lens, satisfying the following relationships: Nmt-Npt>0.25, Vdpt-Vdmt>30; where Nmt is the refractive index of one negative lens in the cemented lens group, Npt is the refractive index of one positive lens in the cemented lens group, Vdmt is the dispersion coefficient of one negative lens in the cemented lens group, and Vdpt is the dispersion coefficient of one positive lens in the cemented lens group.

[0033] The cemented lens refers to a composite optical element in which two or more lens elements are bonded together using an optical adhesive, sharing a common bonding surface. The positive lens is a lens element with positive optical power, which converges light beams; the negative lens is a lens element with negative optical power, which diverges light beams. The refractive index refers to the refractive index value of the lens material at a specific reference wavelength, characterizing the material's ability to deflect light. The dispersion coefficient (Abbe number) is a parameter characterizing the dispersion properties of optical glass; a larger dispersion coefficient indicates less dispersion, and vice versa.

[0034] The relationship Nmt-Npt>0.25 defines the lower limit of the refractive index difference between the negative and positive lenses in the cemented lens group of the second lens group, requiring that the refractive index of the negative lens is at least 0.25 higher than that of the positive lens. The relationship Vdpt-Vdmt>30 defines the lower limit of the difference between the dispersion coefficients of the positive and negative lenses, requiring that the dispersion coefficient of the positive lens is at least 30 greater than that of the negative lens, i.e., the positive lens uses a low-dispersion material and the negative lens uses a high-dispersion material. The phrase "at least one cemented lens" indicates that the second lens group may contain one or more cemented lenses that satisfy the above conditions.

[0035] In short-wave infrared broadband (1.05μm~1.55μm) imaging microscope objectives, axial chromatic aberration correction (especially in the second-order spectrum) is a core challenge in achieving diffraction-limited imaging. The second lens group, as the main converging lens group, has a relatively high incident height of light, making its contribution to chromatic aberration most significant. By employing a combination of materials with high refractive index difference and large dispersion coefficient difference in the cemented lens of the second lens group, sufficient dispersion compensation can be generated at the cemented surface: the positive lens uses a low-dispersion (high Abbe number) material for converging, while the negative lens uses a high-dispersion (low Abbe number) and high-refractive-index material to cancel and correct the chromatic aberration introduced by the positive lens at the cemented surface. A refractive index difference greater than 0.25 ensures that the cemented surface has sufficient optical power to correct spherical aberration, and a dispersion coefficient difference greater than 30 ensures that the difference in dispersion characteristics between the positive and negative lenses is sufficient to compensate for axial chromatic aberration across the broadband spectrum, especially showing a significant suppression effect on second-order chromatic aberration. This material pairing strategy enables the second lens group to achieve efficient beam convergence while keeping the chromatic aberration contribution at an extremely low level, laying the foundation for fine aberration balance in subsequent lens groups.

[0036] In some embodiments, the third lens group includes at least one cemented triplet lens, and the cemented triplet lens of the third lens group includes a positive lens, a negative lens, and a positive lens arranged sequentially from the object plane to the image plane; At least one positive lens in the third group of cemented triplet lenses satisfies the following relationship: Vdt>80; Where Vdt is the positive lens dispersion coefficient of the triplet lens in the third lens group.

[0037] The term "cemented lens" refers to a composite optical element consisting of three lens elements sequentially bonded together using optical adhesive, forming two bonding surfaces. The third lens group of the cemented lens group consists of a positive lens, a negative lens, and a positive lens arranged sequentially from the object plane to the image plane, forming a positive-negative-positive symmetrical configuration. The dispersion coefficient Vdt > 80 indicates that the optical material used in the positive lens is extremely low dispersion glass, meaning that the refractive index of this material changes very little with wavelength within the operating wavelength range.

[0038] The phrase "at least one cemented lens" indicates that the third lens group may contain one or more cemented lens structures. The requirement that at least one positive lens satisfy Vdt>80 indicates that one or both positive lenses in the cemented lens group must have a dispersion coefficient greater than 80. A dispersion coefficient of 80 is a typical threshold value for extremely low dispersion optical glass; optical materials exceeding this value are typically fluoride glass or special crown glass, which have near-linear dispersion curves in the short-wave infrared band and are key materials for achieving apochromatic designs.

[0039] The third lens group performs fine aberration correction. Its optical power is relatively weak (focal length ratio 12 ≤ f3 / f < 20), and its main function is to balance and compensate for residual aberrations after passing through the first and second lens groups. A positive-negative-positive triple-cemented configuration is adopted. On the one hand, the symmetrical structure automatically eliminates the contribution of odd-order aberrations (coma, distortion, etc.); on the other hand, the two cemented surfaces provide more design freedom, allowing for simultaneous joint correction of spherical aberration, coma, and axial chromatic aberration.

[0040] In broadband apochromatic design, the simultaneous elimination of first-order chromatic aberration and second-order spectral distortion requires the use of optical materials with special dispersion characteristics. Based on the Buchdahl dispersion model, the dispersion vector and G0 of the microscope objective lens must approach zero to achieve apochromatic distortion. The positive lens in the triplet lens assembly uses an extremely low dispersion material with a dispersion coefficient greater than 80. Its dispersion vector direction differs significantly from conventional glass, allowing it to effectively counteract the dispersion vector contributions of other lenses in the microscope objective as an anomalous dispersion glass. This makes the overall dispersion vector of the microscope objective approach zero, thereby simultaneously eliminating first-order chromatic aberration and second-order spectral distortion across the entire 1.05μm~1.55μm wavelength range. Building upon the chromatic aberration correction foundation of the second-group cemented lens, the triplet lens assembly of the third-group further compresses the residual axial chromatic aberration across the entire wavelength range to an extremely low level, ensuring that the RMS of the full-field wave aberration reaches the λ / 30 level, achieving diffraction-limited imaging.

[0041] Specific optimizations include: Apochromatic aberration based on color difference and aberration formulas: (1) First-order positional color difference coefficient: CI = Σ (i = 1 to J)h i ²φ i ν i P λ,i (2) First-order magnification color difference coefficient: CII = Σ (i=1 to J)h i h ’ i φ i ν i P λ,i (3) Dispersion relative coefficient (shortwave infrared correction): Pλ = (n F -n λ ) / (n F -n C ) (4) Third-order spherical aberration coefficient: SI = Σ (i=1 to J)h i 4 φ i ³ i +2Σ(i=1 to J)h i 4 φ i ³Y i N i + ... Where J represents the total number of optical surfaces of the microscope objective, i is the surface number, and h is the number of optical surfaces. i Let h be the paraxial on-axis ray height of the i-th face. ’ i Let ν be the height of the paraxial off-axis principal ray on the i-th surface. i Let P be the Abbe number of the glass corresponding to the i-th face. λ n is the relative dispersion coefficient. F The refractive index of the short-wavelength characteristic spectrum, n C The refractive index of the long-wavelength characteristic spectrum, n λ denoted as the refractive index of the target characteristic spectrum.

[0042] Based on the Buchdahl dispersion model; N(ω) = N0 + υ1ω + υ2ω 2 ; The sum of the dispersive vectors of the microscope objectives is: G0 = Σ(j = 1 to n)α j G j α j = (y j 2 φ j ) / (y1 2 φ1); Calculate the glass dispersion vector G j The preferred glass combination has |G0| close to 0 to suppress the secondary spectrum and achieve apochromaticity.

[0043] Where N(ω) is the wavelength-dependent glass refractive index, ω is the Buchdahl normalized wavelength variable, N0 is the base refractive index at the reference wavelength, and G... j Let α be the eigendispersion vector of the j-th glass element. j Let y be the weighting coefficient for the j-th glass piece. j Let φ be the paraxial ray height on the j-th lens. j Let be the optical power of the j-th lens.

[0044] In Zemax, set multi-wavelength weighted constraints (1050nm / 1200nm / 1350nm / 1550nm weights 1:1:2:1): C I =0、C II =0 (achromatic), C I For first-order dispersion, C II It is a secondary spectrum.

[0045] S I ≤0.01, S II ≤0.01 (spherical aberration / coherence correction), S I S is the primary spherical aberration Seidel coefficient. II Seidel coefficient of primary coma Field curvature ≤2μm, distortion ≤0.5% (flat field low distortion), please refer to the following for details. Figures 3 to 5 .

[0046] By varying the curvature, thickness, spacing, and material, and through global optimization combined with local damped least squares iteration, the MTF is brought close to the diffraction limit across the entire wavelength range.

[0047] In some embodiments, the third lens group further includes a cemented doublet lens, which is disposed on the image plane side of the cemented triplet lens of the third lens group.

[0048] The cemented doublet lens refers to a composite optical element in which two lens elements are bonded together by an optical adhesive and have a bonding surface. The cemented doublet lens of the third lens group is located on the image plane side of the cemented triplet lens, that is, along the optical axis, the cemented doublet lens is located behind the cemented triplet lens (closer to the image plane side).

[0049] The third lens group comprises two sub-units: a cemented triplet lens and a cemented doublet lens. These two sub-units are arranged sequentially along the optical axis, with the cemented triplet lens in front (closer to the object plane) and the cemented doublet lens behind (closer to the image plane). An air gap exists between the cemented doublet lens and the cemented triplet lens, together forming the complete optical structure of the third lens group.

[0050] The third lens group employs a combination of cemented triplicate and cemented doubly lenses, creating a collaborative layout for aberration correction. The cemented triplicate lens primarily handles apochromatic and coma correction. After achieving fine chromatic aberration balance, the beam exiting through the cemented triplicate lens still exhibits some residual spherical aberration and field curvature. The cemented doubly lens, positioned on the image plane side of the cemented triplicate lens, further compensates for residual spherical aberration and field curvature based on the chromatic aberration correction already achieved by the cemented triplicate lens. Simultaneously, it finely adjusts the Petzvar of the microscope objective to control image plane curvature. This cascaded configuration allows the third lens group to simultaneously achieve multi-dimensional fine correction of chromatic aberration, spherical aberration, coma, and field curvature within the constraint of overall weak positive optical power, avoiding overcorrection or imbalance caused by relying on a single lens unit to handle too much correction work.

[0051] Depend on Figures 3 to 5 It is evident that the microscope objective of this invention maintains meridional and sagittal field curvatures within ±2 μm and distortion within 0.5% across the entire field of view. A field curvature less than 2 μm indicates excellent image plane flatness, with minimal shift in the optimal focal plane across the entire field of view. This ensures that all pixels of the planar short-wave infrared detector are simultaneously within the depth of focus of the objective, achieving uniform and clear imaging across the entire field of view without the need for field curvature compensation. This avoids the problem of blurred edges due to excessive field curvature. Furthermore, the good consistency between meridional and sagittal field curvatures (with minimal difference) indicates extremely low residual astigmatism in the microscope objective, further guaranteeing the uniformity of imaging quality across the entire field of view.

[0052] With distortion controlled within 0.5%, the objective lens of this invention exhibits extremely high fidelity in reproducing the geometric morphology of the sample. The shape and size proportions of objects in the image are highly consistent with the actual sample, and there is no obvious barrel or pincushion distortion. For semiconductor inspection applications, the low distortion characteristic directly ensures the accuracy of defect localization and the precision of dimensional measurement, avoiding defect coordinate offset or critical dimension (CD) measurement errors caused by image geometric deformation, thus meeting the stringent requirements for sub-micron precision measurement in advanced semiconductor packaging inspection.

[0053] In some embodiments, such as Figure 1 and Figure 2 As shown, the microscope objective also includes an aperture stop; the aperture stop is located between the second lens group and the third lens group.

[0054] The aperture stop is a physical opening that limits the aperture of the on-axis point imaging beam. In a microscope objective, it simultaneously limits the numerical aperture of the microscope objective and controls aberrations. The aperture stop is located between the second and third lens groups, that is, the aperture stop plane is located in the air gap after the last optical surface of the second lens group and before the first optical surface of the third lens group.

[0055] The position of the aperture directly affects the aberration correction effect and telecentric characteristics of the microscope objective. The aperture is located between the second and third lens groups, meaning it is positioned slightly forward of the center of the objective's optical path, at the node after most light rays have converged and before fine aberration correction. The aperture size corresponds to the object-side numerical aperture NA = 0.8 and is determined by the optical design parameters of the microscope objective.

[0056] In large numerical aperture microscope objectives, the position of the aperture has a decisive influence on the control of higher-order aberrations. The aperture, positioned between the second and third lens groups, offers the following design advantages: the first and second lens groups are located on the object plane side of the aperture, undertaking the collection and initial convergence of the large-aperture angle beam; the aperture is precisely located in the region after beam diameter compression, where the incident height of edge rays reaches its maximum, effectively blocking stray light and ensuring precise control of the microscope objective's numerical aperture. Simultaneously, the aperture divides the microscope objective into two semi-symmetrical sub-objectives: the off-axis aberrations (coma, distortion, etc.) mainly generated by the front group (first and second lens groups) can be naturally compensated by the rear group (third and fourth lens groups) in a nearly symmetrical optical path. This centrally located aperture layout facilitates the global balance correction of higher-order aberrations. In addition, the centrally located aperture makes the tilt angle distribution of the principal ray more uniform on both the object and image sides, which helps to control aberration consistency across the entire field of view and minimize the difference in imaging quality between the edge and center fields of view.

[0057] In some embodiments, the ratio of the light refraction angles of the first lens group, the second lens group, the third lens group, and the fourth lens group is -0.5:0.6:0.7:0.8; and / or, the optical power of the first lens group, the second lens group, the third lens group, and the fourth lens group satisfies the following relationship: φ1= (1-2tan(u1) / tan(u0))φ total ;φ2=φ total / (1+L total φ total ); φ3 = (tan(u2) / tan(u0))φ total ;φ4= (tan(u2) / tan(u0))φ total ; where φ totalL represents the total optical power of the microscope objective lens. total The total length of the microscope objective lens is given. φ1, φ2, φ3, and φ4 are the optical powers of the first lens group, the second lens group, the third lens group, and the fourth lens group, respectively. u0 is the paraxial ray aperture angle on the object side, u1 is the ray aperture angle of the first lens group, and u2 is the ray aperture angle of the second lens group.

[0058] The light refraction angle refers to the change in the direction of paraxial light rays after passing through each lens group, characterizing the contribution of each lens group to the deflection of the light propagation direction. The optical power is a measure of the refractive power of a lens or lens group, equal to the reciprocal of the focal length; a positive value indicates convergence, and a negative value indicates divergence. The negative sign in the light refraction angle ratio -0.5:0.6:0.7:0.8 indicates that the first lens group diverges the light rays away from the optical axis (opposite to the converging direction of the latter three groups). The total optical power φ of the microscope objectives... total This is the reciprocal of the focal length of the entire objective lens assembly. The total length L of the microscope objective lens... total The distance from the object-side mirror of the first mirror group to the image-side mirror of the fourth mirror group is the optical axis distance. The paraxial aperture angle u0 on the object side is the angle between the paraxial marginal ray emitted from a point on the object side axis and the optical axis.

[0059] The light refraction angle ratio is a relative ratio of the refraction angles of each lens group, not an absolute value of the refraction angle. In the optical power formula, φ3 and φ4 use the same expression (tan(u2) / tan(u0)). total This indicates that the optical power of the third and fourth lens groups is determined by the same parameter relationship, and they have similar refractive power distributions. The aperture angles u0, u1, and u2 in each formula are light angle parameters under paraxial conditions, used to characterize the changes in the divergence / convergence state of light after passing through each lens group.

[0060] In large numerical aperture optical microscope objectives, the degree to which each lens group deflects light directly determines the magnitude of aberrations—the larger the deflection angle of the lens group, the more severe the aberrations (especially higher-order spherical aberration and coma). Therefore, rationally allocating the proportion of light deflection angles among the lens groups is the core design strategy for controlling microscope objective aberrations.

[0061] The light deflection angle ratio of -0.5:0.6:0.7:0.8 reflects the design philosophy of suppressing large-angle aberrations: the first lens group bears the smallest proportion of deflection (absolute value 0.5), avoiding the burst of higher-order spherical aberrations caused by large deflection angles in the first group; the deflection amounts of the subsequent three lens groups gradually increase (0.6, 0.7, 0.8), distributing the gradual change in light direction across multiple lens groups, keeping the aberration load borne by each lens group within a correctable range. This gradual allocation avoids the formation of uncorrectable higher-order aberrations due to excessively large deflection angles in any one lens group, while ensuring that the total refractive power of the microscope objectives is sufficient to achieve a large numerical aperture of NA=0.8.

[0062] The optical power relationship, based on aberration theory, provides a quantitative relationship between the optical power of each lens group and the microscope objective parameters: the expression for the optical power φ1 of the first lens group incorporates the aperture angle ratio 2tan(u1) / tan(u0), ensuring that the negative optical power of the first lens group does not generate excessive divergence aberration while extending the working distance by controlling the matching relationship between the optical power of the first lens group and the object-side aperture angle; the optical power φ2 of the second lens group is related to the total length L of the microscope objective. total The correlation reflects the physical constraint that the refractive power of the main converging lens group must be compatible with the length of the microscope objective tube. The optical power of the third and fourth lens groups is determined by the product of tan(u2) / tan(u0) and the total optical power of the microscope objectives, ensuring that the optical power allocation of the latter two groups matches the beam state of the former group during the aberration correction stage. The above optical power allocation scheme is a quantitative method for constructing the initial structure based on aberration theory. It can directly guide the parameter initialization of optical design, significantly improve optimization efficiency, and ensure that the final design converges to the global optimum.

[0063] In some embodiments, such as Figure 1 and Figure 2 As shown, the first lens group has a negative optical power and includes a first lens, a second lens, and a third lens arranged sequentially from the object plane to the image plane; the first lens has a positive optical power, and the second lens and the third lens together form a cemented lens with a negative optical power.

[0064] The first lens group consists of three lens elements arranged sequentially along the optical axis from the object plane to the image plane. Its overall optical power is negative, meaning the first lens group diverges the incident light beam. The first lens is an independent single lens with positive optical power; the second and third lenses are cemented together as a doublet, resulting in negative optical power when combined. In the first lens group, the first lens is in front (closest to the object plane), and the cemented lens consisting of the second and third lenses is behind.

[0065] The overall negative optical power of the first lens group is determined by the combination of the optical power of each lens within the group: the first lens provides positive optical power, the cemented lens of the second and third lenses provides negative optical power, and the first lens group exhibits negative optical power when the absolute value of the negative optical power of the negative cemented lens is greater than the positive optical power of the first lens. The first lens is an independent single lens, with an air gap between it and the cemented lens behind it.

[0066] The first lens group, as the front group of the objectives closest to the sample, directly faces the large aperture angle beam (approximately 53.1°) corresponding to object-side NA=0.8, and bears the greatest light deflection pressure among the microscope objectives. The structural design of the first lens group needs to simultaneously achieve two contradictory functional goals: first, to diverge the beam with negative optical power, producing a reverse telephoto effect to extend the working distance; second, to control the spherical aberration and chromatic aberration generated during the divergence process within an acceptable range.

[0067] The configuration of a positive lens in front and a negative cemented lens behind embodies a convergent-divergent optical path strategy: the first lens, with positive optical power, initially converges the large-aperture-angle beam on the object side, reducing the tilt angle of the light relative to the optical axis and decreasing the incident angle of the light on subsequent optical surfaces, thereby suppressing the generation of higher-order spherical aberrations caused by large incident angles. Subsequently, the negative-optical-power cemented lens, composed of the second and third lenses, diverges the beam based on the partially converged beam by the positive lens. At this point, the light angle has been reduced, and the aberrations generated by the negative cemented lens are much smaller than those generated by directly applying negative optical power to a large-aperture-angle beam. Simultaneously, the cemented surface of the cemented lens provides an additional degree of freedom for chromatic aberration correction, allowing for preliminary compensation for the chromatic aberration introduced by the first lens. This "positive + negative" cemented configuration allows the first lens group to achieve overall negative optical power while controlling the generation of spherical and chromatic aberrations within the correctable range of subsequent lens groups, avoiding the problem of excessive aberration accumulation in the preceding group leading to difficulties in overall correction of the microscope objectives.

[0068] In some embodiments, the optical power of the second lens group is positive, and the second lens group includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens; The fourth and fifth lenses are cemented lenses with positive optical power, and the sixth and seventh lenses are cemented lenses with positive optical power.

[0069] An air gap exists between the two cemented lenses in the second lens group, each independently performing the beam converging function. Both cemented lenses have positive optical power, indicating that the total positive optical power of the second lens group is shared by the two sub-units, with each cemented lens undertaking a portion of the refractive task. Each cemented lens is internally composed of a positive lens and a negative lens, achieving chromatic aberration correction through positive-negative pairing while maintaining an overall positive optical power.

[0070] The second lens group is the main converging unit of the entire objective lens, specifically the micro objective lens. It needs to refocus the beam that has diverged after passing through the first lens group, transforming it from a divergent state to a convergent state. Under the large beam aperture condition corresponding to NA=0.8, if a single lens undertakes the entire converging function, it will inevitably lead to an excessively large refraction angle of the light rays on the lens surface, resulting in severe spherical aberration and coma. By using two positive power cemented lenses to share the converging task, the large refraction angle of the light rays is dispersed to the four refractive surfaces and the two cemented surfaces, effectively reducing the contribution of single-surface aberrations.

[0071] Meanwhile, the pairing of positive and negative lenses within each cemented lens provides chromatic aberration correction. Under broad spectral operating conditions of 1.05μm to 1.55μm, the chromatic aberration introduced by the positive lens is canceled out at the cemented surface by the corresponding negative lens, achieving a synergistic design of simultaneous convergence and chromatic aberration cancellation. The tandem configuration of the two cemented lens groups further provides redundant degrees of freedom for spherical aberration and chromatic aberration correction, allowing for fine control of first-order chromatic aberration and second-order spectral aberration across the entire wavelength range. Since the incident height of light in the second lens group is relatively large (the light transmission radius reaches near the maximum value of the microscope objective), the chromatic aberration contribution is most significant at this point. Therefore, it is essential to arrange two cemented lenses in the second lens group for dual chromatic aberration correction. This structure allows the second lens group to achieve primary convergence while keeping spherical aberration and axial chromatic aberration at extremely low levels, providing a good aberration foundation for the subsequent fine correction of the third lens group.

[0072] In some embodiments, the third lens group has positive optical power, and the third lens group includes an eighth lens, a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens; the eighth lens, the ninth lens, and the tenth lens are cemented lenses with positive optical power, and the eleventh lens and the twelfth lens are cemented lenses with negative optical power.

[0073] The third lens group consists of five lens elements, arranged sequentially from the object plane to the image plane along the optical axis: the eighth, ninth, tenth, eleventh, and twelfth lens. The eighth, ninth, and tenth lenses are cemented together to form a cemented triplet lens, which has positive optical power. The eleventh and twelfth lenses are cemented together to form a cemented doublet lens, which has negative optical power. The overall optical power of the third lens group is positive, determined by the net value of the positive-power cemented triplet lens and the negative-power cemented doublet lens.

[0074] An air gap exists between the cemented triplet lenses (eighth, ninth, and tenth lenses) and the cemented doublet lenses (eleventh and twelfth lenses), allowing each lens to independently perform different aberration correction functions. The third lens group as a whole exhibits positive optical power, indicating that the positive optical power of the cemented triplet lenses is greater than the absolute value of the negative optical power of the cemented doublet lenses. Within the third lens group, the coexistence of positive and negative optical power creates an "overcorrection-compensation" effect in optical power, providing ample design freedom for fine-tuning aberrations.

[0075] The third lens group is located after the aperture stop in the microscope objective lens and is responsible for finely balancing and correcting the residual aberrations of the first two groups. Its focal length ratio is 12≤f3 / f<20, which is a weak positive power configuration. This means that the third lens group does not focus on convergence as its primary task, but rather on aberration correction as its core function.

[0076] It should be noted that the overall structure of the microscope objective can be referred to... Figure 1 and Figure 2 To understand the relevant structure, in the corresponding Figure 1 and Figure 2 In the specific attached diagram, L1, L2, L3, L4, L5, L6, L7, L8, L9, L10, L11, L12, L13, and L14 represent the first to fourteenth lenses mentioned above. S1 to S22 are the surface structure identifiers formed by the 14 lenses mentioned above, and their corresponding numerical information, including the radius of curvature and the light transmission radius, can be found in Table 1 below. The aperture stop is located between the seventh and eighth lenses and is indicated by "stop". G1, G2, G3, and G4 represent the first, second, third, and fourth lens groups mentioned above, respectively.

[0077] The triplet lens employs a positive-negative-positive configuration, with three lens elements providing two cemented surfaces for a total of four refractive surfaces, offering ample design freedom. The positive-negative-positive symmetrical configuration naturally possesses anti-coma properties, and the two cemented surfaces can respectively correct spherical aberration and chromatic aberration: the front cemented surface primarily compensates for spherical aberration left over from the previous group, while the rear cemented surface primarily compensates for higher-order chromatic aberration (second-order spectrum). At least one of the positive lenses uses an extremely low dispersion material with a dispersion coefficient greater than 80 as an anomalous dispersion glass, making the overall dispersion vector of the microscope objective approach zero, achieving apochromatic aberration across the entire 1.05μm~1.55μm wavelength range.

[0078] The cemented doublet lens, possessing negative optical power, is positioned on the image plane side of the cemented triplet lens. Its functions are twofold: first, to compensate for the positive patellar effect and contribution introduced by the cemented triplet lens through negative optical power, thereby optimizing image plane flatness and suppressing field curvature; second, to provide final fine compensation for the minute residual spherical aberration after correction by the cemented triplet lens. The cascaded combination of the positive optical power cemented triplet lens and the negative optical power cemented doublet lens, under the overall constraint of the weak positive optical power of the third lens group, achieves simultaneous multi-dimensional fine correction of spherical aberration, coma, chromatic aberration, and field curvature, enabling the RMS of aberrations across the entire field of view to reach the λ / 30 level.

[0079] like Figure 1 , Figure 3 and Figure 5 As shown, the RMS wavefront difference of the microscope objective lens in the working band of 1.05μm~1.55μm is less than λ / 30 (λ=1.55μm) in the entire field of view (from the on-axis 0 field of view to the maximum field of view of 0.5mm object height at the edge), which is far better than the diffraction-limited imaging standard defined by the Mareschal criterion (RMS≤λ / 14). Compared to the current technology where the RMS of aberrations across the entire field of view of long-working-distance SWIR objectives is generally greater than λ / 4 (λ=1.55μm) and far from reaching the diffraction limit, this embodiment achieves a comprehensive control of the entire field of view aberrations within several times the diffraction limit through the synergistic effect of various techniques, including global allocation of optical power in a negative-positive-positive-positive four-group optical system, a combination of cemented lenses with high refractive index difference / large dispersion coefficient difference in the second lens group, an apochromatic design of a positive-negative-positive triple cemented lens in the third lens group, and fine aberration correction using a double cemented lens cascade. This demonstrates that all aberrations, such as spherical aberration, coma, astigmatism, and chromatic aberration, at each field of view of the microscope objective are fully and evenly corrected, resulting in highly consistent imaging quality between the central and peripheral fields of view. Diffraction-limited imaging is achieved across the entire field of view, overcoming the shortcomings of insufficient aberration correction and drastic degradation of imaging quality in the peripheral fields of view in existing technologies.

[0080] Depend on Figures 3 to 5It is evident that, under broadband polychromatic illumination of 1.05μm~1.55μm, the modulation transfer function (MTF) curves of the microscope objective of this invention closely approximate the diffraction-limited curves at all spatial frequencies across the entire field of view, with a full-field MTF value ≥0.5 at the Nyquist frequency. Compared to existing technologies where the full-field MTF at the Nyquist frequency is generally below 0.3, insufficient imaging contrast leads to poor signal-to-noise ratio for minute defects, and false negative and false positive rates far exceeding the semiconductor mass production standard of ≤0.1%, the MTF performance of the objective of this invention represents a qualitative improvement. A high MTF value signifies that the objective has excellent contrast transmission capability for sample microstructures (such as 1μm-level dislocations, hidden cracks, and chip packaging defects), effectively ensuring that defect signals are clearly distinguished from background noise, significantly improving detection sensitivity and signal-to-noise ratio, and meeting the stringent requirement of a false negative rate of ≤0.1% for advanced semiconductor packaging testing lines. Meanwhile, the separation of the MTF curves in the meridional and sagittal directions at all frequencies across the entire field of view is extremely small, indicating that the astigmatism of the microscope object is well controlled, the imaging resolution in all directions is uniform and consistent, and there is no directional resolution degradation.

[0081] In some embodiments, the fourth lens group comprises a thirteenth lens and a fourteenth lens, wherein the optical power of the thirteenth lens is positive and the optical power of the fourteenth lens is positive.

[0082] The fourth lens group consists of two independent lens elements, namely the thirteenth lens and the fourteenth lens, arranged sequentially from the object plane to the image plane along the optical axis. Both have positive optical power, meaning they both converge the light beam. The thirteenth and fourteenth lenses are non-cemented independent single lenses, with an air gap between them.

[0083] Both lenses in the fourth lens group are positive optical power, and the overall optical power of the fourth lens group is also positive, corresponding to the constraint range of focal length ratio 1.5 ≤ f4 / f < 4. As the last group of microscope objectives closest to the image plane, the fourth lens group is the last optical sub-microscope objective before the beam is finally focused and imaged, and its outgoing beam is directly transmitted to the image plane (detector photosensitive surface).

[0084] The fourth mirror group is located at the end of the optical path. After the convergence and aberration correction of the first three groups, the beam is in a converged state with a smaller aperture. The core functions of the fourth mirror group are: first, to complete the final focusing of the beam, projecting the converged beam after the correction of the first three groups onto the image plane at a suitable angle, ensuring the image-side telecentric or near-telecentric characteristics, so that the main rays received by each pixel of the detector are almost perpendicular to the photosensitive surface, avoiding the decrease in light energy efficiency and vignetting unevenness caused by oblique incidence; second, to perform a final compensation for the trace residual aberrations left by the previous groups (mainly higher-order spherical aberration and field curvature).

[0085] The use of two independent positive lenses instead of a cemented lens configuration allows for flexible distribution of aberration contribution between the two lenses in the fourth lens group: the thirteenth lens bears the main positive power, completing the final focusing of the beam; the fourteenth lens performs terminal fine-tuning of aberrations with a moderate positive power, and the air gap between them provides additional degrees of freedom for spherical aberration correction. This simple double positive lens configuration ensures sufficient refractive power while avoiding increased processing and assembly difficulties caused by overly complex lens group structures, which is beneficial for controlling mass production consistency. Simultaneously, the fourth lens group avoids focal length ratios exceeding the upper limit (f4 / f<4), ensuring sufficient refractive power for smooth beam focusing and imaging without structural bulkiness; and avoids focal length ratios below the lower limit (f4 / f≥1.5), preventing excessive lens curvature that would lead to processing difficulties and excessive spherical aberration and field curvature.

[0086] The optical parameters of the above lenses are shown in Table 1.

[0087] Table 1:

[0088] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A microscope objective lens, comprising, sequentially from the object plane to the image plane along the optical axis, a first lens group, a second lens group, a third lens group, and a fourth lens group, characterized in that, The microscope objective lens has the following relationship: 1 ≤ -f1 / f < 3; 3≤f² / f<5; 12≤f3 / f<20; 1.5 ≤ f4 / f < 4; NA=0.8; 0.7 ≤ d0 / f < 1; Wherein, f1 is the combined focal length of the first lens group, f2 is the combined focal length of the second lens group, f3 is the combined focal length of the third lens group, f4 is the combined focal length of the fourth lens group, f is the combined focal length of the entire microscope objective, d0 is the distance from the object surface to the object-side mirror of the first lens group, and NA is the object-side numerical aperture of the microscope objective.

2. The microscope objective lens as described in claim 1, characterized in that, The second lens group includes at least one cemented lens, and the cemented lens in the second lens group includes one positive lens and one negative lens, and satisfies the following relationship: Nmt-Npt>0.25, Vdpt-Vdmt>30; Wherein, Nmt is the refractive index of the negative lens in the cemented lens of the second lens group, Npt is the refractive index of the positive lens in the cemented lens of the second lens group, Vdmt is the dispersion coefficient of the negative lens in the cemented lens of the second lens group, and Vdpt is the dispersion coefficient of the positive lens in the cemented lens of the second lens group.

3. The microscope objective lens as described in claim 1, characterized in that, The third lens group includes at least one cemented triplet lens, and the cemented triplet lens of the third lens group includes a positive lens, a negative lens, and a positive lens arranged sequentially from the object plane to the image plane; At least one positive lens in the third group of cemented triplet lenses satisfies the following relationship: Vdt>80; Wherein, Vdt is the positive lens dispersion coefficient of the triplet lens in the third lens group.

4. The microscope objective lens as described in claim 3, characterized in that, The third lens group also includes a cemented doublet lens, which is disposed on the image plane side of the cemented triplet lens of the third lens group.

5. The microscope objective lens as described in claim 1, characterized in that, The microscope objective also includes an aperture stop; The aperture is positioned between the second lens group and the third lens group.

6. The microscope objective as described in claim 1, characterized in that, The ratio of the light refraction angles of the first lens group, the second lens group, the third lens group, and the fourth lens group is -0.5:0.6:0.7:0.8; and / or, The optical power of the first lens group, the second lens group, the third lens group, and the fourth lens group satisfies the following relationship: φ1 = (1 - 2tan(u1) / tan(u0))φ total ;φ2= φ total / (1+L total φ total ); φ3=(tan(u2) / tan(u0))φ total ;φ4= (tan(u2) / tan(u0))φ total ; where φ total L represents the total optical power of the microscope objective lens. total The total length of the microscope objective lens is given. φ1, φ2, φ3, and φ4 are the optical powers of the first lens group, the second lens group, the third lens group, and the fourth lens group, respectively. u0 is the paraxial ray aperture angle on the object side, u1 is the ray aperture angle of the first lens group, and u2 is the ray aperture angle of the second lens group.

7. The microscope objective lens as described in claim 1, characterized in that, The first lens group has a negative optical power and includes a first lens, a second lens, and a third lens arranged sequentially from the object plane to the image plane. The first lens has a positive optical power, and the second and third lenses together form a cemented lens with a negative optical power.

8. The microscope objective lens as described in claim 1, characterized in that, The second lens group has a positive optical power and includes a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The fourth and fifth lenses are cemented lenses with positive optical power, and the sixth and seventh lenses are cemented lenses with positive optical power.

9. The microscope objective lens as described in claim 1, characterized in that, The optical power of the third lens group is positive, and the third lens group includes an eighth lens, a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens; The eighth, ninth, and tenth lenses are cemented lenses with positive optical power, while the eleventh and twelfth lenses are cemented lenses with negative optical power.

10. The microscope objective as claimed in claim 1, characterized in that, The fourth lens group consists of a thirteenth lens and a fourteenth lens, wherein the optical power of the thirteenth lens is positive and the optical power of the fourteenth lens is positive.

Images