fourier transform objective

Abstract

The application relates to the technical field of optical imaging, and provides a Fourier transform objective lens. The Fourier transform objective lens is applied to numerical aperture testing of an illumination system, comprises a plurality of lenses, and the plurality of lenses comprise a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in sequence along an optical axis direction from an object side to an image side. The first lens and the fourth lens both have negative optical power, and the second lens, the third lens, the fifth lens and the sixth lens all have positive optical power. The first lens, the second lens and the third lens form a front group reverse telephoto configuration with positive optical power, and the fourth lens, the fifth lens and the sixth lens form a rear group reverse telephoto configuration. The Fourier transform objective lens provided by the application embodiment can be increased while reducing the image plane size, so that the Fourier transform objective lens can match a CCD image sensor with a smaller target surface size, and the hardware cost and volume of the illumination system are reduced.

Description

Technical Field

[0001] This application relates to the field of optical imaging technology, and in particular to a Fourier transform objective lens. Background Technology

[0002] In recent years, with the continuous development of high-precision optical measurement and detection technology in industrial manufacturing and scientific research, the demand for rapid and accurate measurement of the numerical aperture (NA) of illumination systems has been increasing. Fourier transform objectives can linearly map the angular information of the incident beam onto the spatial position of the image plane through the Fourier transform principle. By detecting the distribution range of the light spot on the image plane using a CCD image sensor, the NA value of the beam can be calculated.

[0003] The object-side field of view of a Fourier transform objective represents the maximum angular range that the objective can receive a beam of light. The NA value of the illumination system under test is determined by its beam divergence angle. Therefore, the NA value of the illumination system under test can only be fully measured when the object-side field of view of the objective is greater than or equal to the beam divergence angle. However, the larger the object-side field of view, the larger the calculated image height, resulting in a larger overall image plane size. This necessitates the use of a larger CCD image sensor, leading to higher hardware costs.

[0004] Therefore, how to increase the object-side field of view of a Fourier transform objective while reducing the image plane size has become a problem to be solved. Summary of the Invention

[0005] This application provides a Fourier transform objective lens that can increase the object-side field of view of the Fourier transform objective lens while reducing the image plane size.

[0006] This application provides a Fourier transform objective lens for numerical aperture testing of an illumination system. The Fourier transform objective lens includes multiple lenses, which include:

[0007] The first lens, second lens, third lens, fourth lens, fifth lens, and sixth lens are arranged sequentially from the object side to the image side along the optical axis. The first and fourth lenses have negative optical power, while the second, third, fifth, and sixth lenses have positive optical power.

[0008] The first, second, and third lenses form the front group of the telephoto lens configuration, and the fourth, fifth, and sixth lenses form the rear group of the telephoto lens configuration. The front group of the telephoto lens configuration has positive optical power.

[0009] The Fourier transform objective lens provided in this application forms a front-group anti-telephoto configuration by using a first lens with negative optical power and a second and third lens with positive optical power. The first lens with negative optical power can initially deflect large-angle beams from the object side, allowing the beam to enter the illumination system more smoothly. The second and third lenses with positive optical power can converge the deflected beams and initially correct aberrations caused by large-angle incidence. Therefore, by setting up the front-group anti-telephoto configuration, the range of beam angles that the Fourier transform objective lens can clearly receive and process is expanded, thereby improving the object-side field of view of the Fourier transform objective lens.

[0010] Simultaneously, a rear-group telephoto configuration is formed by setting a fourth lens with negative optical power and a fifth and sixth lens with positive optical power. The fourth lens with negative optical power can diverge the beam that has already been converged in the front-group telephoto configuration, making the beam's propagation path smoother relative to the optical axis. The fifth and sixth lenses with positive optical power can refocus the diverged beam onto the image plane and further correct residual aberrations, ensuring image quality. The diverging effect of the fourth lens, combined with the converging effect of the fifth and sixth lenses, shifts the image principal plane of the illumination system to the image side, thereby reducing the total effective focal length of the Fourier transform objective lens while maintaining a large object-side field of view, thus reducing the image plane size.

[0011] Therefore, by combining the two sets of anti-telephoto configurations, the Fourier transform objective lens provided in this application embodiment can increase the object-side field of view while reducing the image plane size, thereby enabling the Fourier transform objective lens to match CCD image sensors with smaller target plane sizes, which is beneficial to reducing the hardware cost and size of the illumination system.

[0012] In some embodiments, the object-side field of view of the Fourier transform objective lens is greater than 40°.

[0013] In some embodiments, the first lens and the second lens are both meniscus lenses, both the first lens and the second lens have concave surfaces on the object-facing side, and both the first lens and the second lens have convex surfaces on the image-facing side; the third lens is a biconvex lens.

[0014] In some embodiments, the fourth lens is a biconcave lens, the fifth lens is a biconvex lens, and the sixth lens is a plano-convex lens, with the convex surface of the plano-convex lens facing the fifth lens.

[0015] In some embodiments, each lens is a spherical mirror.

[0016] In some embodiments, the effective focal length of the first lens is F1, and F1 satisfies the following condition:

[0017] -1.2≤F1 / F≤-1.1;

[0018] In the formula, F is the total effective focal length of the Fourier transform objective lens.

[0019] In some embodiments, the holographic height of the Fourier transform objective is IC, the total length is TTL, the total effective focal length is F, and the back intercept is OBFL. IC, TTL, F, and OBFL satisfy the following condition:

[0020] 0.6 ≤ IC / TTL ≤ 0.8;

[0021] 1.8≤TTL / F≤2;

[0022] 0.45≤OBFL / TTL≤0.85.

[0023] In some embodiments, the first lens and the fourth lens are made of a first lens material, and the second lens, the third lens, the fifth lens and the sixth lens are made of a second lens material;

[0024] The first lens material has a refractive index of Nd1 and an Abbe constant of Vd1. Nd1 and Vd1 satisfy the following condition:

[0025] 1.65≤Nd1≤1.85;

[0026] 30≤Vd≤50;

[0027] The refractive index of the second lens material is Nd2, and the Abbe constant is Vd2. Nd2 and Vd2 satisfy the following condition:

[0028] 1.5≤Nd1≤1.75;

[0029] 50≤Vd1≤70.

[0030] In some embodiments, the difference between the design image height and the Abbe sine image height of the Fourier transform objective is less than 1 μm.

[0031] In some embodiments, the centering coefficient of the first lens is Z, where 0.05 ≤ Z ≤ 0.08.

[0032] In some embodiments, the effective focal length of the second lens is F2, and the effective focal length of the third lens is F3, where F2 and F3 satisfy the following condition:

[0033] 1.65≤F² / F≤1.75;

[0034] 1.3≤F3 / F≤1.4, and 0.75≤F3 / F2≤0.85;

[0035] In the formula, F is the total effective focal length of the Fourier transform objective lens.

[0036] In some embodiments, the effective focal length of the fifth lens is F5, and the effective focal length of the sixth lens is F6, where F5 and F6 satisfy the following condition:

[0037] 2.6≤F6 / F5≤2.8.

[0038] In some embodiments, the sum of the center thicknesses of all lenses in the Fourier transform objective along the optical axis is ∑CT, and the total optical length of the Fourier transform objective is TTL, where TTL is equal to ∑CT and TTL satisfies the following condition:

[0039] 0.8≤∑CT / TTL≤0.9.

[0040] In some embodiments, the total optical length of the Fourier transform objective is less than 30 mm.

[0041] In some embodiments, the center air gap between the first and second lenses is TH12, the center air gap between the second and third lenses is TH23, the center air gap between the third and fourth lenses is TH34, the center air gap between the fourth and fifth lenses is TH45, and the center air gap between the fifth and sixth lenses is TH56, wherein:

[0042] 0.1mm≤TH12≤1mm;

[0043] 0.1mm≤TH23≤1mm;

[0044] 1mm≤TH34≤1.5mm;

[0045] 1mm ≤ TH45 ≤ 1.6mm;

[0046] 0.1mm≤TH56≤0.5mm. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the optical path of a Kohler lighting system;

[0049] Figure 2 A schematic diagram of the Fourier transform objective lens provided in the embodiments of this application;

[0050] Figure 3 A schematic diagram of the Fourier transform objective lens structure provided in the embodiments of this application;

[0051] Figure 4 The MTF of the Fourier transform objective lens at a working wavelength of 436±2nm;

[0052] Figure 5 The MTF of the Fourier transform objective lens at a working wavelength of 486±2nm;

[0053] Figure 6 The MTF of the Fourier transform objective lens at a working wavelength of 555±2nm;

[0054] Figure 7 The MTF of the Fourier transform objective lens at a working wavelength of 656±2nm;

[0055] Figure 8 The MTF of the Fourier transform objective lens at a working wavelength of 1002±2nm;

[0056] Figure 9 The maximum field-of-view aberration of the Fourier transform objective at a working wavelength of 555±2nm;

[0057] Figure 10 Waveform diagrams of each field of view of the Fourier transform objective lens when the working wavelength is 555±2nm;

[0058] Figure 11 A schematic diagram of the Fourier transform objective lens with F2 / F = 1.64.

[0059] Figure label:

[0060] 100-Fourier transform objective lens;

[0061] 10-Front group reverse telephoto configuration;

[0062] 11-First lens;

[0063] 12-Second lens;

[0064] 13-Third lens;

[0065] 20-rear group reverse telephoto configuration;

[0066] 21-Fourth lens;

[0067] 22-Fifth lens;

[0068] 23 - Sixth lens. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] To facilitate understanding, the relevant technical terms involved in the embodiments of this application will first be explained and described.

[0071] Numerical aperture (NA) is a physical quantity that characterizes the light-gathering ability and spatial resolution of an illumination system (such as a lens, optical fiber, or microscope objective).

[0072] The target surface refers to the photosensitive surface of an image sensor. The larger the target surface, the greater the amount of light the image sensor can capture, and the higher the image height.

[0073] Focal length, also known as focal length, is a measure of the convergence or divergence of light in an illumination system. It refers to the perpendicular distance from the optical center of a lens or lens group to the focal plane when a distant object is projected into a sharp image on the focal plane. From a practical perspective, it can be understood as the distance from the center of the lens (lens assembly) to the image plane.

[0074] The optical axis refers to the straight line that passes through the center of each lens element in a lens assembly.

[0075] Optical power is the ability of a lens to refract a parallel beam of light incident on the ground; it is also called refractive power.

[0076] Positive focal length means that the lens has a positive focal length and has the effect of converging light beams.

[0077] Negative power means that the lens has a negative focal length, which has the effect of diverging the beam of light.

[0078] The field of view (FOV) is the angle between the two edges of the lens assembly, which is the maximum range through which the image of the subject can pass through the lens assembly, with the lens assembly as the vertex.

[0079] The object side, also known as the object side, is the side where the subject is located, with the lens assembly as the boundary. The side of the lens in the lens assembly that faces the object side is the object side of the lens.

[0080] The image side, also known as the image plane, is the side where the image of the subject is located, with the lens assembly as the boundary. The side of the lens in the lens assembly that faces the image side is the image plane of the lens.

[0081] Image height (IH), also known as holographic height, refers to the height of the holographic image formed by the lens assembly.

[0082] The image plane, defined by the lens assembly, is the plane in the image space where the converged light beams from the lens assembly form a sharp image of the subject. The image plane typically coincides with the target surface of the image sensor.

[0083] The principal plane of an image refers to the virtual plane perpendicular to the optical axis formed by the intersection of the backward extension of the outgoing beam and the extension of the incident beam after refraction by the illumination system.

[0084] The focal point is the point where the outgoing beam (or its backward extension) of an incident beam parallel to the optical axis intersects the optical axis after refraction by the lighting system.

[0085] Aberration refers to the deviation between the image formed on the image plane and the ideal image of the subject, caused by limitations in lens material, surface shape, and optical design in an illumination system.

[0086] Reverse telephoto configuration is an optical lens design where the total optical length of the lens assembly (the distance from the object side of the first lens element to the image plane) is greater than the total effective focal length of the lens assembly.

[0087] The Abbe number, also known as the dispersion coefficient, is the ratio of the difference in refractive index of an optical material at different wavelengths, indicating the degree of dispersion of the material.

[0088] The R-number is the ratio of the radius of curvature (R) of a lens to its effective aperture (D), i.e., R-number = R / D. The R-number is used to quantitatively describe the curvature of an optical lens surface. The smaller the R-number, the greater the curvature of the lens surface (i.e., the more curved the surface); the larger the R-number, the smaller the curvature of the lens surface (i.e., the flatter the surface).

[0089] The centering coefficient is a quantitative indicator used to measure the ease of assembly and adjustment of spherical optical lenses. It is defined as one-quarter of the sum of the absolute values ​​of the eccentricity coefficients of the two optical surfaces of the lens. The smaller the centering coefficient, the more difficult it is to align the geometric center of the lens with the optical axis, the higher the required assembly and adjustment precision, and the higher the processing cost. The larger the centering coefficient, the easier it is to assemble and align the lens.

[0090] NIR (Near-Infrared) wavelengths are typically defined as 780nm to 2500nm.

[0091] VIS (Visible) refers to visible light, with a wavelength range typically defined as 380nm to 780nm.

[0092] NUV (Near-Ultraviolet) wavelengths are typically defined as ranging from 200 nm to 380 nm.

[0093] The entrance pupil diameter refers to the diameter of the image formed in object space by the aperture stop (which determines how much light enters the system) of an optical system.

[0094] The half-height of the image plane refers to the radial distance on the image plane of the optical system from the center of the optical axis to the circumference of the imaging point with the maximum field of view, which is half the size of the imaging target surface required.

[0095] Wavefront aberration refers to the optical path difference between the actual optical wavefront (the equiphase surface of a beam) and the ideal spherical wavefront.

[0096] A CCD (Charge-Coupled Device) image sensor is used for photoelectric conversion and image acquisition. It consists of multiple photosensitive units (pixels) arranged in a matrix. Each photosensitive unit can convert the energy of incident photons into and store a corresponding number of charges. By applying clock pulse voltages in a specific time sequence, these charge packets can be sequentially transferred to the output terminal, ultimately forming an electrical signal corresponding to the optical image plane.

[0097] Figure 1 This is a schematic diagram of the optical path of a Kohler lighting system.

[0098] Please refer to Figure 1 With the continuous development of high-precision optical measurement and detection technology in industrial manufacturing and scientific research, the demand for rapid and accurate measurement of the numerical aperture (NA) of illumination systems is increasing. Fourier transform objectives can linearly map the angular information of the incident beam onto the spatial position of the image plane using the Fourier transform principle. By detecting the distribution range of the light spot on the image plane using a CCD image sensor, the NA value of the beam can be calculated.

[0099] The object-side field of view of a Fourier transform objective represents the maximum angular range that the objective can receive a beam of light. The NA value of the illumination system under test is determined by its beam divergence angle. Therefore, the NA value of the illumination system under test can only be fully measured when the object-side field of view of the objective is greater than or equal to the beam divergence angle. However, the larger the object-side field of view, the larger the calculated image height, resulting in a larger overall image plane size. This necessitates the use of a larger CCD image sensor, leading to higher hardware costs.

[0100] Taking the Kohler lighting system as an example, the numerical aperture (NA) of the lighting system varies at each port, including the input light source, aperture stop, and output lighting field of view. Furthermore, the numerical aperture and wavelength of the light source also differ for different lighting systems. If the Fourier transform objective lens used has a small object-side field of view and a single wavelength, it cannot meet the needs of different application scenarios, requiring frequent switching between lenses with different numerical apertures and wavelengths for inspection.

[0101] In view of this, embodiments of this application provide a Fourier transform objective lens, which forms a front anti-telephoto configuration by setting a first lens with negative optical power and a second and third lens with positive optical power. A rear anti-telephoto configuration is formed by setting a fourth lens with negative optical power and a fifth and sixth lens with positive optical power. By combining these two anti-telephoto configurations, the object-side field of view θ can be increased while the image plane size is reduced. This allows the Fourier transform objective lens to be matched with CCD image sensors with smaller target plane sizes, which is beneficial for reducing the hardware cost and size of the illumination system.

[0102] The Fourier transform objective lens provided in the embodiments of this application will be described below with reference to the accompanying drawings.

[0103] Figure 2 This is a schematic diagram of the Fourier transform objective lens 100 provided in an embodiment of this application. Figure 3 This is a schematic diagram of the Fourier transform objective lens 100 provided in an embodiment of this application.

[0104] Please refer to Figure 2 and Figure 3 This application provides a Fourier transform objective lens 100 for numerical aperture testing of an illumination system.

[0105] The Fourier transform objective lens 100 provided in this embodiment includes multiple lenses, which include a first lens 11, a second lens 12, a third lens 13, a fourth lens 21, a fifth lens 22, and a sixth lens 23 arranged sequentially from the object side to the image side along the optical axis.

[0106] Specifically, the first lens 11 and the fourth lens 21 both have negative optical power, while the second lens 12, the third lens 13, the fifth lens 22, and the sixth lens 23 all have positive optical power. The first lens 11, the second lens 12, and the third lens 13 form the front group anti-telephoto configuration 10, and the fourth lens 21, the fifth lens 22, and the sixth lens 23 form the rear group anti-telephoto configuration 20, wherein the front group anti-telephoto configuration 10 has positive optical power.

[0107] Please refer to Figure 2 and Figure 3In the front-group anti-telephoto configuration 10, the first lens 11, with negative optical power, is the lens closest to the object side. When a large-angle incident beam reaches the first lens 11, its negative optical power causes the beam to deflect, changing its propagation direction. This makes the beam, which was originally incident at a large angle towards the optical axis, more gradual and more parallel to the optical axis. Next, the second lens 12, with positive optical power, receives the beam from the first lens 11, which has changed direction, and causes the beam to begin bending towards the optical axis. The third lens 13 further receives the beam from the second lens 12, causing it to continue bending towards the optical axis, ultimately converging the beam. By changing the beam direction with the first lens 11 and converging the beam with the second and third lenses 13, the front-group anti-telephoto configuration 10 can receive large-angle beams from the object side and guide them to the image side, thereby increasing the large object-side field of view θ of the Fourier transform objective lens 100.

[0108] Please refer to Figure 2 and Figure 3 In the rear telephoto configuration 20, the fourth lens 21, which has negative optical power, receives the converging beam from the front telephoto configuration 10. When the converging beam reaches the fourth lens 21, the negative optical power of the fourth lens 21 can exert a diverging effect on the beam, causing the parts of the beam that originally tended to converge towards a point above the optical axis to propagate in a direction further away from the optical axis.

[0109] Please refer to Figure 2 and Figure 3 A fifth lens 22 with positive optical power is disposed adjacent to the fourth lens 21 and is used to receive the diverging beam from the fourth lens 21. When the diverging beam reaches the fifth lens 22, the positive optical power of the fifth lens 22 begins to exert a converging effect on the beam, canceling out part of the divergence effect caused by the fourth lens 21, causing the propagation direction of the beam to deflect back toward the optical axis, but the beam is still in a divergent state at this time.

[0110] Please refer to Figure 2 and Figure 3 A sixth lens 23 with positive optical power is disposed adjacent to the fifth lens 22 to receive the still diverging light beam from the fifth lens 22. The positive optical power of the sixth lens 23 exerts a final converging effect on the light beam, causing the light beam to converge completely and ultimately positioning the convergence point precisely on the image plane of the Fourier transform objective lens 100.

[0111] Specifically, the negative optical power of the fourth lens 21 causes the light beam from the front telephoto configuration 10 to diverge first, increasing the wavefront curvature radius of the light beam. Subsequently, the positive optical power of the fifth lens 22 and the sixth lens 23 converge the diverged light beam in sequence, ultimately converging the light beam onto the image plane.

[0112] According to the principles of geometrical optics imaging, the image-side principal plane is determined by the backward extension of the outgoing rays from the parallel light rays incident from the image side, after passing through the entire illumination system. Since the negative optical power of the fourth lens 21 is located at the front of the optical path, the diverging effect of the fourth lens 21 causes the backward extension of the outgoing rays to travel a longer distance towards the image side before intersecting with the incident parallel light rays. This results in the image-side principal plane of the Fourier transform objective 100 shifting towards the image side. With a fixed image-side focal point, this shift of the image-side principal plane towards the image side reduces the total effective focal length of the Fourier transform objective 100, thereby reducing the image size.

[0113] Therefore, by combining the two sets of anti-telephoto configurations, the Fourier transform objective lens 100 provided in this embodiment can increase the object-side field of view angle θ while reducing the image plane size, thereby enabling the Fourier transform objective lens 100 to match CCD image sensors with smaller target plane sizes, which is beneficial to reducing the hardware cost and size of the illumination system.

[0114] Please refer to Figure 2 and Figure 3 In some embodiments, the object-side field of view θ of the Fourier transform objective 100 is greater than 40°. This enables the Fourier transform objective 100 to detect illumination systems with higher numerical aperture (NA), expanding its application range. Simultaneously, by configuring the front anti-telephoto configuration 10 and the rear anti-telephoto configuration 20, a large object-side field of view θ can be achieved while reducing the total effective focal length of the Fourier transform objective 100. According to the Fourier transform principle, with a fixed object-side field of view θ, the image plane size is proportional to the objective lens focal length. Therefore, a shorter focal length allows for a smaller image plane size corresponding to a large object-side field of view θ, thereby reducing the requirements for the target surface size of the CCD image sensor. This allows for the selection of a lower-cost, smaller image sensor, reducing hardware costs.

[0115] In some embodiments, the first lens 11 and the second lens 12 are both meniscus lenses, both having a concave surface on the object-facing side and a convex surface on the image-facing side. The third lens 13 is a biconvex lens.

[0116] Specifically, the first lens 11 adopts a meniscus structure with a concave object side and a convex image side. When a large-angle incident beam reaches the concave object side of the first lens 11, the concave surface of the first lens 11 can cause the beam to be gently deflected, making the beam more inclined to propagate in a direction parallel to the optical axis. This reduces the incident angle of the beam relative to the surface of the first lens 11, while also reducing the reflection loss of the large-angle beam on the surface of the first lens 11, thereby improving the light transmission efficiency of the Fourier transform objective lens 100.

[0117] Meanwhile, by setting the first lens 11 to a meniscus structure, the divergence effect of the negative optical power of the first lens 11 on the beam and the aberration correction requirements can be balanced, thereby providing a good beam shape for subsequent lenses.

[0118] Similar to the first lens 11, in this embodiment, the second lens 12 also adopts a meniscus structure with a concave object side and a convex image side. The concave object side of the second lens 12 allows it to smoothly receive the diverging light beam from the first lens 11, enabling the beam to be incident at an angle closer to the normal, thereby reducing reflection loss and aberrations caused by large-angle incident light, and ensuring that light energy is transmitted to the interior of the second lens 12 efficiently and with low distortion.

[0119] Meanwhile, by adjusting the curvature of the object-side concave surface and the image-side convex surface of the second lens 12, the deflection characteristics of the light beam when passing through the second lens 12 can be controlled, thereby reducing the focusing difference of the light beam in different directions, making the shape of the light spot closer to a circle, improving the image point clarity, making the image points in the field of view more evenly distributed, and improving the imaging quality of the edge field of view.

[0120] Please refer to Figure 2 and Figure 3 In this embodiment, the third lens 13 is a biconvex lens structure. The biconvex surface can exert a strong converging effect on the light beam from the second lens 12, thereby further converging the light beam and compressing the beam aperture. This is beneficial for reducing the size of subsequent lenses in the Fourier transform objective 100, and also for correcting the spherical aberration of the Fourier transform objective 100.

[0121] Specifically, both convex surfaces of the third lens 13 can exert a deflection force on the light beam in the direction of the optical axis. When the light beam passes through the third lens 13, the light rays at the edge of the beam undergo stronger deflection than those at the center, causing the beam diameter to decrease rapidly as it propagates, thereby compressing the beam aperture. The reduction in beam aperture means that the effective light transmission aperture required by subsequent lenses can be reduced, which is beneficial for reducing the size of subsequent lenses.

[0122] Meanwhile, by adjusting the curvature combination of the two convex surfaces, the position of the convergence point of light rays at different incident heights in the beam can be adjusted, so that the convergence point of the edge rays and paraxial rays tends to be consistent, thereby achieving the correction of 100° spherical aberration of the Fourier transform objective lens.

[0123] Please refer to Figure 2 and Figure 3 In some embodiments, the fourth lens 21 is a biconcave lens, the fifth lens 22 is a biconvex lens, and the sixth lens 23 is a plano-convex lens, with the convex surface of the plano-convex lens facing the fifth lens 22.

[0124] Specifically, when the converging beam reaches the fourth lens 21, the biconcave surface causes the parts of the beam that were originally inclined to converge to propagate in a direction further away from the optical axis, thereby increasing the wavefront curvature radius of the beam.

[0125] The biconvex surface of the fifth lens 22 can converge the diverging beam from the fourth lens 21. The biconvex surface of the fifth lens 22 can deflect the propagation direction of the beam back toward the optical axis, begin to cancel the divergence effect caused by the fourth lens 21, and perform preliminary correction of the residual aberration of the Fourier transform objective lens 100.

[0126] The sixth lens 23 adopts a plano-convex lens structure with its convex surface facing the fifth lens 22, which can exert the final converging effect on the beam from the fifth lens 22, so that the beam is completely converged and precisely positioned on the image plane of the Fourier transform objective lens 100.

[0127] Please refer to Figure 2 and Figure 3 In some embodiments, each lens is a spherical mirror.

[0128] Specifically, using spherical lenses reduces the difficulty of lens processing and manufacturing costs. Compared to aspherical lenses, which require sophisticated processing and testing equipment, spherical lenses can be mass-produced using existing standardized grinding and polishing processes. This allows the Fourier Transform Objective 100 to achieve a large field of view while reducing its production costs.

[0129] Please refer to Figure 2 and Figure 3 In some embodiments, the effective focal length of the first lens 11 is F1, and F1 satisfies Formula 1.

[0130] -1.2≤F1 / F≤-1.1 (Formula 1)

[0131] In Formula 1, F is the total effective focal length of Fourier transform objective lens 100.

[0132] Specifically, if the value of F1 is less than -1.2F, such as -1.3F, -1.4F or -1.5F, then the absolute value of F1 is too large, the negative light focal length is too weak, the first lens 11 has insufficient ability to deflect edge light rays, and it is difficult to fully expand the object-side field of view θ, resulting in the Fourier transform objective lens 100 being unable to accept incident light beams at a larger angle.

[0133] If the value of F1 is greater than -1.1F, such as -1.0F, -0.8F or -0.5F, the absolute value of F1 is too small, the negative optical power is too strong, which can easily lead to excessive aberrations, increase the curvature and distortion of the image plane, and make it difficult to correct aberrations with subsequent positive optical power lenses, resulting in poor final image quality.

[0134] Therefore, by setting the value of F1 to between -1.2F and -1.1F, such as -1.13F, -1.15F, or -1.18F, it is possible to ensure that the first lens 11 provides a sufficiently strong negative optical power to effectively deflect large-angle light rays and increase the object-side field of view θ, while ensuring that the aberrations generated by the first lens 11 are within the correction range of the subsequent positive optical power lenses, thereby ensuring the imaging quality of the Fourier transform objective lens 100.

[0135] Please refer to Figure 2 and Figure 3 In some embodiments, the holographic height of the Fourier transform objective is IC, the total length is TTL, the total effective focal length is F, and the back intercept is OBFL. IC, TTL, F, and OBFL satisfy Formulas 2, 3, and 4.

[0136] 0.6≤IC / TTL≤0.8 (Formula 2)

[0137] 1.8≤TTL / F≤2 (Formula 3)

[0138] 0.45≤OBFL / TTL≤0.85 (Formula 4)

[0139] Specifically, if the IC / TTL value is less than 0.6, such as 0.5, 0.55 or 0.58, the image plane size IC is too small relative to the total lens length TTL, and the total effective focal length F of the Fourier transform objective lens 100 is too short. This can easily lead to an overly concentrated distribution of optical power, thereby increasing the difficulty of subsequent lens correction and resulting in poor image quality.

[0140] If the IC / TTL value is greater than 0.8, such as 0.85, 0.9 or 0.95, then the image plane size IC is too large relative to the total lens length TTL, and the total effective focal length F of the Fourier transform objective lens 100 is too long. This can easily lead to an increase in the target size of the required matching image sensor, thereby increasing hardware costs.

[0141] Therefore, by setting the IC / TTL value between 0.6 and 0.8, such as 0.65, 0.70, or 0.75, it is possible to achieve a smaller image plane size to reduce sensor costs while avoiding the introduction of uncorrectable aberrations due to excessively short focal length, thus ensuring the imaging effect of the Fourier transform objective 100.

[0142] At the same time, if the TTL / F value is less than 1.8, such as 1.6, 1.7 or 1.75, the total lens length TTL is too short relative to the focal length F, making it difficult to accommodate a sufficient number of lenses to effectively correct the astigmatism and field curvature introduced by the large field of view, and also unable to provide sufficient back clipping space for the image side.

[0143] If the TTL / F value is greater than 2, such as 2.1, 2.2 or 2.3, the total lens length TTL is too long relative to the focal length F, which can easily lead to an excessively large physical size of the lens, making it difficult to achieve the lightweight design of the Fourier transform objective lens 100.

[0144] Therefore, by setting the TTL / F value between 1.8 and 2, such as 1.85, 1.90, or 1.95, it is possible to ensure that the lens has sufficient reverse telephoto characteristics to provide a large field of view and a long back focal length while maintaining the compactness of the overall lens length, which is beneficial to achieving the lightweighting of the Fourier Transform Objective 100.

[0145] Furthermore, if the OBFL / TTL value is less than 0.45, such as 0.3, 0.35 or 0.4, the back intercept OBFL is too short, resulting in insufficient space between the sixth lens 23 and the image plane, making it difficult to install optical components such as narrowband filters. At the same time, the lens is prone to collision with the image sensor, resulting in poor safety of the Fourier transform objective lens 100.

[0146] If the OBFL / TTL value is greater than 0.85, such as 0.9, 0.95 or 1.0, the back intercept OBFL is too long, resulting in a looser structure and larger volume of the Fourier transform objective lens 100, which is not conducive to miniaturization design.

[0147] Therefore, by keeping the OBFL / TTL value between 0.45 and 0.85, such as 0.5, 0.6 or 0.7, sufficient working space can be reserved on the image side to facilitate the integration of other optical components, while avoiding an excessive increase in the overall length of the lens, thus ensuring the practicality and compactness of the Fourier Transform Objective 100.

[0148] Please refer to Figure 2 and Figure 3 In some embodiments, the first lens 11 and the fourth lens 21 are made of a first lens material, and the second lens 12, the third lens 13, the fifth lens 22 and the sixth lens 23 are made of a second lens material.

[0149] The first lens material has a refractive index of Nd1 and an Abbe constant of Vd1. Nd1 and Vd1 satisfy Equation 5 and Equation 6.

[0150] 1.65≤Nd1≤1.85 (Formula 5)

[0151] 30≤Vd≤50 (Formula Six)

[0152] Specifically, if the refractive index Nd1 of the first lens material is less than 1.65, such as 1.50, 1.55, or 1.60, then due to the excessively low refractive index, the radius of curvature of the lens needs to be designed to be even smaller to achieve the required negative optical power, resulting in a lens shape tending towards a hemispherical shape. This is not only detrimental to manufacturing but also introduces spherical aberration and higher-order aberrations, thereby increasing the difficulty of aberration correction.

[0153] If the refractive index Nd1 is greater than 1.85, such as 1.90, 1.95 or 2.0, although the curvature of the lens can be reduced, materials with higher refractive indices are usually more expensive and have lower transmittance, which significantly increases the manufacturing cost of the Fourier transform objective 100 and reduces the light transmission efficiency of the Fourier transform objective 100.

[0154] If the Abbe constant Vd1 of the first lens material is less than 30, such as 20, 25 or 28, the material's dispersion capability is too strong, which can easily lead to an increase in the second-order spectrum generated by the lens. Consequently, when the Fourier transform objective lens 100 works in a wide band, the focal points of different wavelengths of light cannot be completely superimposed, thus aggravating chromatic aberration and affecting image clarity.

[0155] If the Abbe constant Vd1 of the first lens material is greater than 50, such as 55, 60 or 65, the material's dispersion capability is too weak, resulting in insufficient dispersion difference between the first lens 11 and the fourth lens 21 and the second lens material. This makes it difficult to effectively correct the axial chromatic aberration of the Fourier transform objective lens 100, resulting in blurred images.

[0156] Therefore, by ensuring that the refractive index Nd1 of the first lens material is between 1.65 and 1.85, such as 1.72, 1.75, or 1.80, and the Abbe constant Vd1 is between 30 and 50, such as 33, 40, or 45, it is possible to ensure that the first lens 11 and the fourth lens 21 have appropriate refractive indices to maintain a reasonable surface curvature for easy processing, while also possessing certain dispersion characteristics. This allows the first lens 11 and the fourth lens 21 to form sufficient dispersion difference with the positive power lens to correct the positional chromatic aberration of the Fourier transform objective lens 100, while also controlling the second-order spectrum of the Fourier transform objective lens 100 within an acceptable range.

[0157] Please refer to Figure 2 and Figure 3 The refractive index of the second lens material is Nd2, and the Abbe constant is Vd2. Nd2 and Vd2 satisfy Equation 7 and Equation 8.

[0158] 1.5≤Nd1≤1.75 (Formula 7)

[0159] 50≤Vd1≤70 (Formula 8)

[0160] Specifically, if the refractive index Nd2 of the second lens material is less than 1.5, such as 1.45, 1.48, or 1.49, the refractive index is too low. To achieve the positive optical power required for a Fourier transform objective lens of 100, the radius of curvature of the lens needs to be designed to be even smaller, resulting in a lens shape that tends towards a hemispherical shape. This is not only detrimental to manufacturing but also introduces spherical aberration and higher-order aberrations, thereby increasing the difficulty of aberration correction.

[0161] If the refractive index Nd2 of the second lens material is greater than 1.75, such as 1.80, 1.85 or 1.90, although the curvature of the lens can be reduced, materials with higher refractive indices are usually more expensive and have lower transmittance, which significantly increases the manufacturing cost of the Fourier transform objective 100 and reduces the light transmission efficiency of the Fourier transform objective 100.

[0162] If the Abbe constant Vd2 of the second lens material is less than 50, such as 45, 48 or 49, the material has a strong dispersion ability, resulting in insufficient dispersion difference between the second lens 12, the third lens 13, the fifth lens 22 and the sixth lens 23 and the first lens material. It is difficult to form a sufficient dispersion difference for correction, thus causing different wavelengths of light to fail to converge at the same point.

[0163] If the Abbe constant Vd2 of the second lens material is greater than 70, such as 72, 75 or 80, the material's dispersion capability is weak, which can easily lead to insufficient axial chromatic aberration correction of the Fourier transform objective lens 100. The focal positions of different wavelengths of light on the image plane are too separated, resulting in blurred imaging and an inability to obtain a clear Fourier spectrum in a wide band.

[0164] Therefore, by ensuring that the refractive index Nd2 of the second lens material is between 1.5 and 1.75, such as 1.52, 1.60, or 1.70, and the Abbe constant Vd2 is between 50 and 70, such as 55, 60, or 65, it is possible to ensure that the lens with positive power has a moderate refractive index to maintain a reasonable surface curvature while possessing certain dispersion characteristics. This allows the second lens 12, the third lens 13, the fifth lens 22, and the sixth lens 23 to form sufficient dispersion difference with the first lens 11 and the second lens 12 to effectively correct the axial and positional chromatic aberration of the Fourier transform objective lens 100, while also facilitating the control of the second-order spectrum and ensuring the imaging effect of the Fourier transform objective lens 100.

[0165] Please refer to Figure 2 and Figure 3 In some embodiments, the difference between the design image height of the Fourier transform objective 100 and the Abbe sine image height is less than 1 μm.

[0166] Specifically, the difference between the designed image height and the Abbe sine image height of the Fourier transform objective 100 indicates the accuracy of the angle detection of the Fourier transform objective 100. If the difference is too large, such as 10μm, 20μm, or 50μm, it means that the actual convergence point of the light rays deviates from the theoretically calculated position, resulting in an error in the correspondence between the angle and the image point position, leading to inaccurate measurement results from the Fourier transform objective 100.

[0167] Therefore, by controlling the difference between the design image height of the Fourier transform objective 100 and the Abbe sine image height to less than 1 μm, it is possible to ensure that each incident angle corresponds to a precise image point position, ensuring the accuracy of the angle-to-space conversion, enabling the Fourier transform objective 100 to achieve high-precision and high-reliability detection of the numerical aperture of the illumination system.

[0168] In some embodiments, the difference between the design image height and the Abbe sine image height of the Fourier transform objective 100 is less than 0.7 μm, so as to further improve the accuracy and precision of the numerical aperture of the illumination system by the Fourier transform objective 100.

[0169] In some embodiments, the centering coefficient of the first lens 11 is Z, where 0.05 ≤ Z ≤ 0.08.

[0170] Specifically, if the centering coefficient Z of the first lens 11 is less than 0.05, such as 0.02, 0.03, or 0.04, it indicates that the curvature centers of the two optical surfaces of the first lens 11 are very close, and the lens shape is approximately hemispherical or hyperspherical. Thus, when the first lens 11 is being ground and centered, its geometric center is not easily aligned with the optical axis. Even a slight misalignment will cause the optical axis to shift. This not only significantly increases processing time and cost but also affects the imaging effect of the Fourier transform objective lens 100.

[0171] If the centering coefficient Z of the first lens 11 is greater than 0.08, for example, 0.09, 0.10, or 0.12, it means that the optical surface of the first lens 11 is very flat, or the aperture of the first lens 11 is relatively large compared to its radius of curvature. This results in a weaker ability of the first lens 11 to deflect light. Therefore, in order to achieve the total optical power required by the Fourier transform objective lens 100, subsequent lenses need to bear a higher optical power, which forces subsequent lenses to use curved surfaces, increases the processing difficulty and aberrations of subsequent lenses, and thus affects the performance and manufacturing cost of the entire Fourier transform objective lens 100.

[0172] Please refer to Figure 2 and Figure 3Therefore, by controlling the centering coefficient Z of the first lens 11 between 0.05 and 0.08, such as 0.06, 0.065 or 0.07, it is possible to ensure that the first lens 11 has effective optical power to participate in aberration correction, while ensuring that the first lens 11 has good manufacturing feasibility and ensuring the performance stability of the Fourier transform objective lens 100.

[0173] In some embodiments, the effective focal length of the second lens 12 is F2, and the effective focal length of the third lens 13 is F3, where F2 and F3 satisfy Formula 9 and Formula 10.

[0174] 1.65≤F² / F≤1.75 (Formula Nine)

[0175] 1.3≤F3 / F≤1.4 (Formula 10)

[0176] 0.75≤F3 / F2≤0.85 (Formula Eleven)

[0177] In the formula, F is the total effective focal length of the Fourier transform objective lens 100.

[0178] Specifically, if F2 / F is less than 1.65, such as 1.60, 1.62 or 1.63, then F2 is too small and the optical focal length of the second lens 12 is too strong. This makes the second lens 12 too strong in converging the light beam from the first lens 11, resulting in an increased incident angle of the light beam on the surface of the second lens 12. This can easily lead to severe spherical aberration and coma, increasing the difficulty of subsequent aberration correction.

[0179] If F2 / F is greater than 1.75, such as 1.78, 1.80 or 1.82, then F2 is too large, the optical power of the second lens 12 is too weak, the second lens 12 has insufficient ability to converge the beam, and it is difficult to effectively counteract the divergence effect generated by the first lens 11, forcing subsequent lenses to bear a stronger optical power, which easily increases the design burden.

[0180] Figure 11 This is a schematic diagram of the Fourier transform objective lens 100 when F2 / F is 1.64.

[0181] Please refer to Figure 11 When F2 / F is 1.64, there will be overlap between the lenses, which will not meet the design requirements of the Fourier transform objective lens 100.

[0182] If F3 / F is less than 1.3, such as 1.25, 1.27 or 1.28, then F3 is too small and the optical focal length of the third lens 13 is too strong, which will excessively converge the beam, causing the focal front of the Fourier transform objective 100 to shift and introducing higher-order aberrations, resulting in image quality deterioration.

[0183] If F3 / F is greater than 1.4, such as 1.43, 1.45 or 1.48, then F3 is too large and the optical focal length of the third lens 13 is too weak. It cannot exert enough converging effect on the beam and it is difficult to complete the shape transformation required to send the beam into the rear group, resulting in an unsatisfactory final imaging effect.

[0184] If F3 / F2 is less than 0.75, such as 0.70, 0.72 or 0.73, it indicates that the optical power of the third lens 13 is too strong relative to the second lens 12. The optical power matching between the third lens 13 and the second lens 12 is unbalanced, resulting in an unstable beam convergence process and poor aberration correction effect.

[0185] If F3 / F2 is greater than 0.85, such as 0.90 or 0.92, it indicates that the optical power of the third lens 13 is too weak compared to the second lens 12, and it cannot effectively receive and further converge the beam.

[0186] Therefore, by setting the F2 / F value between 1.65 and 1.75, such as 1.68, 1.70, or 1.72, the F3 / F value between 1.3 and 1.4, such as 1.33, 1.35, or 1.37, and the F3 / F2 value between 0.75 and 0.85, such as 0.78, 0.80, or 0.82, the matching of the optical power between the second lens 12 and the third lens 13 can be ensured. This allows the second lens 12 to smoothly converge the beam and initially correct aberrations, while the third lens 13 can apply a moderately strong converging effect on the basis of the second lens 12. Ultimately, the beam is smoothly and with low aberrations transmitted to subsequent lenses, ensuring the imaging quality of the Fourier transform objective lens 100.

[0187] Please refer to Figure 2 and Figure 3 In some embodiments, the effective focal length of the fifth lens 22 is F5, and the effective focal length of the sixth lens 23 is F6, where F5 and F6 satisfy Formula Twelve.

[0188] 2.6≤F6 / F5≤2.8 (Formula 12)

[0189] Specifically, if F6 / F5 is less than 2.6, such as 2.4, 2.5, or 2.55, then F6 is too small relative to F5. This means the focal length F6 of the sixth lens 23 is too short compared to the focal length F5 of the fifth lens 22. Since focal length is inversely proportional to optical power, the optical power of the sixth lens 23 is much stronger than that of the fifth lens 22, leading to an imbalance in optical power. This causes the beam converging pressure to be excessively concentrated on the sixth lens 23. This necessitates that the surface curvature of the sixth lens 23 be close to hemispherical, resulting in excessive processing difficulty and high manufacturing costs. Simultaneously, the excessive optical power causes severe refraction of light on the surface of the sixth lens 23, leading to an increased spot size and energy dispersion on the image plane, affecting the imaging quality and measurement accuracy of the Fourier transform objective lens 100.

[0190] If F6 / F5 is greater than 2.8, such as 2.9, 3.0 or 3.2, it means that the optical power of the sixth lens 23 is too weak compared to the fifth lens 22. This results in the sixth lens 23 having insufficient final focusing ability for the light beam, and it cannot accurately converge the light beam that has been converged by the previous lenses to the predetermined position on the image plane. Consequently, the light in the edge field of view of the image plane cannot be focused, resulting in blurred image edges, uneven illumination, and the inability to form a clear and complete Fourier spectrum, thus causing the angle measurement to fail.

[0191] Therefore, by controlling F6 / F5 between 2.6 and 2.8, such as 2.65, 2.70, or 2.75, a good match can be made between the optical power of the fifth lens 22 and the sixth lens 23. In this way, the fifth lens 22 can undertake the main converging function, while the sixth lens 23 is used to provide moderate and accurate final convergence and aberration balance. This ensures that the beam is smoothly and with low aberration converged to the image plane, obtaining a clear spectrum for high-precision angle measurement. At the same time, it avoids the processing difficulties and performance degradation caused by excessive or insufficient optical power of a single lens, thus ensuring the overall performance and mass production feasibility of the Fourier transform objective lens 100.

[0192] Please refer to Figure 2 and Figure 3 In some embodiments, the sum of the center thicknesses of each lens in the Fourier transform objective 100 along the optical axis is ∑CT, and the total optical length of the Fourier transform objective 100 is TTL, where TTL is ∑CT and TTL satisfies Formula Thirteen.

[0193] 0.8≤∑CT / TTL≤0.9 (Formula Thirteen)

[0194] Specifically, the total optical length of the Fourier transform objective lens 100 is the straight-line distance along the optical axis from the object side of the first lens 11 to the image side of the sixth lens 23.

[0195] If the value of ∑CT / TTL is less than 0.8, such as 0.75, 0.76, or 0.78, then the sum of the center thicknesses of all lenses, ∑CT, is too small relative to the total optical length, TTL, meaning that the air gap between the lenses is too large. An excessively large air gap will lengthen the optical path, making it difficult to shorten the length of the Fourier transform objective lens 100. It will also increase the number of reflections of light at the air-glass interface, leading to increased light energy loss and reduced light transmission efficiency of the objective lens.

[0196] If the value of ∑CT / TTL is greater than 0.9, such as 0.92, 0.94, or 0.95, then the sum of the center thicknesses of all lenses, ∑CT, is too large relative to the total optical length, TTL, meaning that the air gap between the lenses is too small. Insufficient air gaps result in narrow space at the lens edges, increasing installation difficulty. Furthermore, insufficient lens gaps limit the degrees of freedom for aberration correction, leading to a decrease in image quality.

[0197] Therefore, by controlling the value of ∑CT / TTL between 0.8 and 0.9, such as 0.82, 0.85, or 0.88, a reasonable center thickness can be allocated to the lens under the condition of a fixed total optical length TTL, and necessary air gaps can be reserved between the lenses. This ensures the compactness of the Fourier transform objective 100, provides sufficient optimization space for aberration correction, and is also conducive to controlling stray light, ensuring that the Fourier transform objective 100 can achieve good image quality and stable performance while realizing miniaturization.

[0198] Please refer to Figure 2 and Figure 3 In some embodiments, the total optical length of the Fourier transform objective 100 is less than 30 mm.

[0199] Specifically, if the total optical length of the Fourier transform objective 100 is too large, such as 35mm, 40mm or 45mm, it will result in a large volume and increased weight of the entire Fourier transform objective 100, thereby occupying too much space in the testing equipment and reducing the portability and integration of the Fourier transform objective 100.

[0200] Therefore, by controlling the total optical length to within 30mm, such as 28mm, 25mm or 22mm, the physical size and weight of the Fourier transform objective 100 can be significantly reduced, enabling the Fourier transform objective 100 to be integrated into inspection equipment of various sizes, thus improving the applicability of the Fourier transform objective 100.

[0201] Please refer to Figure 2 and Figure 3In some embodiments, the central air gap between the first lens 11 and the second lens 12 is TH12, the central air gap between the second lens 12 and the third lens 13 is TH23, the central air gap between the third lens 13 and the fourth lens 21 is TH34, the central air gap between the fourth lens 21 and the fifth lens 22 is TH45, and the central air gap between the fifth lens 22 and the sixth lens 23 is TH56, wherein:

[0202] 0.1mm≤TH12≤1mm;

[0203] 0.1mm≤TH23≤1mm;

[0204] 1mm≤TH34≤1.5mm;

[0205] 1mm ≤ TH45 ≤ 1.6mm;

[0206] 0.1mm≤TH56≤0.5mm.

[0207] Specifically, the first lens 11, the second lens 12, and the third lens 13 together constitute the front anti-telephoto configuration 10. Therefore, by controlling TH12 and TH23 to be between 0.1mm and 1mm, the front anti-telephoto configuration 10 can maintain a compact overall structure, which is beneficial for shortening the optical path, reducing the aberrations generated by the front anti-telephoto configuration 10, and providing the necessary operating space for light deflection between the lenses in the front anti-telephoto configuration 10 to balance aberrations, while avoiding unnecessary increase in the total optical length of the Fourier transform objective lens 100 due to excessive spacing.

[0208] TH34 is the transition zone between the image side of the front anti-telephoto configuration 10 and the object side of the rear anti-telephoto configuration 20. By controlling TH34 between 1mm and 1.5mm, the beam can smoothly transition from the converging state of the front anti-telephoto configuration 10 to the diverging state of the anti-telephoto configuration, which is beneficial to improving the imaging quality.

[0209] TH45 is the main aberration correction range between the negative optical power fourth lens 21 and the positive optical power fifth lens 22 in the rear telephoto configuration 20. By controlling TH45 to 1.6mm, a balanced space can be provided for the light deflection and aberration correction of the fourth lens 21 and the fifth lens 22, while ensuring that there is a distance for installation and adjustment between the lenses.

[0210] TH56 is the central air gap between the fifth lens 22 and the sixth lens 23. Since the fifth lens 22 and the sixth lens 23 form the terminal converging portion of the rear-group telephoto configuration 20, a small air gap needs to be maintained between them to ensure strong coupling of optical power. This allows the fifth lens 22 and the sixth lens 23 to efficiently correct higher-order aberrations such as spherical aberration and chromatic aberration. Simultaneously, this also shortens the back intercept, controls the overall optical length of the Fourier transform objective 100, and achieves miniaturization and weight reduction of the Fourier transform objective 100.

[0211] It should be noted that in this embodiment, TH1, TH23 and TH56 are all greater than 0.1mm, in order to leave a safe gap during the assembly of the lenses, so as to avoid the lenses from contacting each other during assembly and adjustment, which could cause the lens edges to bump and affect the image quality.

[0212] Figure 4 The MTF of the Fourier transform objective lens at a working wavelength of 436±2nm. Figure 5 The MTF of the Fourier transform objective lens at a working wavelength of 486±2nm. Figure 6 The MTF of the Fourier transform objective lens at a working wavelength of 555±2nm. Figure 7 The MTF of the Fourier transform objective lens at a working wavelength of 656±2nm. Figure 8 The MTF of the Fourier transform objective lens at a working wavelength of 1002±2nm. Figure 9 The maximum field-of-view aberration of the Fourier transform objective at a working wavelength of 555±2nm. Figure 10 A series of wave points in each field of view of the Fourier transform objective lens when the working wavelength is 555±2nm.

[0213] Please refer to Figures 4 to 10 To verify the technical effect of this embodiment, the design specifications of the Fourier transform objective lens 100 provided in this embodiment are shown in Table 1, and the lens design parameters are shown in Table 2.

[0214]

[0215] Table 1

[0216] The working band is from near ultraviolet to near infrared, and the MTF index display bands are selected as near ultraviolet light (438±2nm), blue light (486±2nm), green light (555±2nm), red light (656±2nm), and infrared light (1002±2nm).

[0217] Specifically, MTF (modulation transfer function) represents the ability of the Fourier transform objective 100 to transfer the contrast of an object to the image plane, and "close to the diffraction limit" means that the imaging quality of the Fourier transform objective 100 provided in this embodiment is close to the optimal level in physical theory, with extremely strong image detail resolution.

[0218]

[0219] Table 2

[0220] Among them, the radius of curvature determines the degree of curvature of the lens surface, and the net aperture is the effective light-transmitting aperture of the optical element.

[0221] Tables 1 and 2 together provide the specific design specifications and implementation parameters of the Fourier transform objective lens 100 in this embodiment. To verify whether the Fourier transform objective lens 100 provided in this embodiment can simultaneously achieve high imaging accuracy, good manufacturability, and structural non-obviousness, the following further elaborates on this through aberration data, manufacturability analysis, and comparative embodiments.

[0222] Table 3 shows the difference between the designed image height and the sinusoidal image height.

[0223]

[0224] Table 3

[0225] Table 3 quantitatively verifies the imaging accuracy by comparing the differences between the "designed image height" (actual image point position) and the "sine image height" (theoretical image point position). The data shows that the absolute deviation is less than 0.7 μm in all fields of view, proving that the actual imaging accuracy of this embodiment is better than the design requirement of 1 μm, ensuring the linearity and accuracy of angle measurements.

[0226] Table 4 shows the lens manufacturability parameters in this embodiment.

[0227]

[0228] Table 4

[0229] Among them, the R number of the S1 surface is the R number of the object side of the lens, and the R number of the S2 surface is the R number of the image side of the lens.

[0230] Specifically, Table 4 evaluates the manufacturability of the lenses, with key parameters including the "R-number" which measures the difficulty of processing and the "centering coefficient" which measures the ease of assembly and adjustment. Data shows that the centering coefficient of all lenses is greater than 0.06, indicating reasonable R-numbers. This demonstrates that the optical design of the Fourier transform objective lens 100 provided in this application not only boasts excellent performance but also that the shapes of each lens are within a good manufacturable range, possessing good process feasibility.

[0231] Table 5 presents the feasibility analysis of lens processing in related technology 1.

[0232]

[0233] Table 5

[0234] Where R1 / D1 is the R number on the object side of the lens, and R2 / D2 is the R number on the image side of the lens.

[0235] As can be seen from Table 5, the centering coefficients of the first, third, and fourth lenses in related technology 1 are much less than 0.05, and the lens R number is close to 0.5, which makes processing and testing very difficult, resulting in low feasibility of the solution in related technology 1.

[0236] Table 6 shows the comparative examples, simulating the design parameters when F1 / F equals 1.205.

[0237]

[0238] Table 6

[0239] Table 6 shows that when F1 / F does not satisfy -1.2≤F1 / F≤-1.1, the image height of the lens cannot be less than 11μm under the condition that other performance indicators are met, and the image height is 13.05μm.

[0240] Table 7 compares the actual image height with the image height that satisfies the sinusoidal condition in related technology 2.

[0241]

[0242] Table 7

[0243] Wherein, absolute deviation is the absolute value of the difference between the observed value and the corresponding theoretical value, and relative deviation is the ratio of absolute deviation to the selected reference value.

[0244] Table 8 shows the results of spectral point position tracking on the spectral surface in related technology 3.

[0245]

[0246] Table 8

[0247] Wherein, absolute deviation is the absolute value of the difference between the observed value and the corresponding theoretical value, and relative deviation is the ratio of absolute deviation to the selected reference value.

[0248] As shown in Tables 7 and 8, the difference between the image height design value in Table 7 and the sinusoidal image height value is 90 μm, and the difference between the image height design value in Table 8 and the sinusoidal image height value is 208 μm. The design accuracy is too low and cannot meet the usage requirement shown in Table 1 of this embodiment that the sinusoidal image height is less than 1 / 10 of the pixel size.

[0249] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0250] In the description of this invention, it should be understood that the terms “comprising” and “having” as used herein, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0251] Unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can be a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0252] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Fourier transform objective lens, characterized in that, For numerical aperture testing of lighting systems, the Fourier transform objective includes multiple lenses, wherein the multiple lenses include: A first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens are arranged sequentially from the object side to the image side along the optical axis. The first lens and the fourth lens both have negative optical power, while the second lens, the third lens, the fifth lens, and the sixth lens all have positive optical power. The first lens, the second lens, and the third lens form a front-group telephoto configuration, and the fourth lens, the fifth lens, and the sixth lens form a rear-group telephoto configuration, wherein the front-group telephoto configuration has positive optical power.

2. The Fourier transform objective lens according to claim 1, characterized in that, The Fourier transform objective lens has an object-side field of view greater than 40°.

3. The Fourier transform objective lens according to claim 1, characterized in that, Both the first and second lenses are meniscus lenses, and both have concave surfaces on the side facing the object, and both have convex surfaces on the side facing the image; the third lens is a biconvex lens.

4. The Fourier transform objective lens according to claim 3, characterized in that, The fourth lens is a biconcave lens, the fifth lens is a biconvex lens, and the sixth lens is a plano-convex lens, with the convex surface of the plano-convex lens facing the fifth lens.

5. The Fourier transform objective lens according to claim 4, characterized in that, Each of the lenses is a spherical lens.

6. The Fourier transform objective lens according to claim 1, characterized in that, The effective focal length of the first lens is F1, and F1 satisfies the following condition: ； In the formula, F is the total effective focal length of the Fourier transform objective lens.

7. The Fourier transform objective lens according to claim 1, characterized in that, The Fourier transform objective lens has a holoimage height of IC, a total length of TTL, a total effective focal length of F, and a back intercept of OBFL. IC, TTL, F, and OBFL satisfy the following condition: ； ； 。 8. The Fourier transform objective lens according to any one of claims 1-7, characterized in that, The first lens and the fourth lens are made of a first lens material, and the second lens, the third lens, the fifth lens and the sixth lens are made of a second lens material; The refractive index of the first lens material is Nd1, and the Abbe constant is Vd1. Nd1 and Vd1 satisfy the following condition: ； ； The refractive index of the second lens material is Nd2, and the Abbe constant is Vd2. Nd2 and Vd2 satisfy the following condition: ； 。 9. The Fourier transform objective lens according to claim 8, characterized in that, The difference between the designed image height and the Abbe sine image height of the Fourier transform objective is less than 1 μm.

10. The Fourier transform objective lens according to any one of claims 1-7, characterized in that, The centering coefficient of the first lens is Z, where 0.05 ≤ Z ≤ 0.

08.

11. The Fourier transform objective lens according to any one of claims 1-7, characterized in that, The effective focal length of the second lens is F2, and the effective focal length of the third lens is F3. F2 and F3 satisfy the following condition: ； ,and ; In the formula, F is the total effective focal length of the Fourier transform objective lens.

12. The Fourier transform objective lens according to claim 11, characterized in that, The effective focal length of the fifth lens is F5, and the effective focal length of the sixth lens is F6. F5 and F6 satisfy the following condition: 。 13. The Fourier transform objective lens according to any one of claims 1-7, characterized in that, The sum of the center thicknesses of all the lenses in the Fourier transform objective along the optical axis is ∑CT, and the total optical length of the Fourier transform objective is TTL, where TTL is equal to ∑CT and TTL satisfies the following condition: 。 14. The Fourier transform objective lens according to claim 13, characterized in that, The total optical length of the Fourier transform objective is less than 30 mm.

15. The Fourier transform objective lens according to claim 14, characterized in that, The center air gap between the first lens and the second lens is TH12, the center air gap between the second lens and the third lens is TH23, the center air gap between the third lens and the fourth lens is TH34, the center air gap between the fourth lens and the fifth lens is TH45, and the center air gap between the fifth lens and the sixth lens is TH56, wherein: ； ； ； ； 。

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