Terahertz imaging lens

Abstract

The application discloses a terahertz imaging lens, and belongs to the technical field of optical imaging. The terahertz imaging lens comprises a first lens and a second lens. The first lens has a first incident surface and a first exit surface, and at least one of the first incident surface and the first exit surface is an even aspheric surface. The first lens and the second lens are sequentially arranged along an optical axis. The second lens has a second incident surface and a second exit surface, and at least one of the second incident surface and the second exit surface is an even aspheric surface. The terahertz imaging lens is configured to adjust the combined focal length by adjusting the principal point distance between the first lens and the second lens. The terahertz imaging lens is composed of only two lenses, i.e. the first lens and the second lens, thereby reducing the number of optical interfaces, lowering the Fresnel reflection loss of terahertz waves at the interfaces, and improving the energy utilization rate.

Description

Technical Field

[0001] This application belongs to the field of optical imaging technology, specifically relating to a terahertz imaging lens. Background Technology

[0002] Terahertz (THz) waves, due to their unique advantages such as strong penetrability, non-ionizing radiation, and the ability to identify material fingerprint spectra, have broad application prospects in fields such as security inspection, biomedical imaging, non-destructive testing, and aerospace. A terahertz imaging system typically consists of three parts: a terahertz source, an optical system, and a detector. The performance of the imaging lens directly determines the energy harvesting efficiency, imaging resolution, and signal-to-noise ratio of the final image of the optical system.

[0003] In related technologies, terahertz imaging lenses employ a multi-element transmission structure with three or more lenses. However, multiple optical interfaces are formed between the three lenses, and terahertz waves undergo Fresnel reflection loss at each interface, resulting in significant energy loss after superposition. Summary of the Invention

[0004] One of the objectives of this application is to provide a terahertz imaging lens that reduces Fresnel reflection loss of terahertz waves at the interface and improves energy utilization, thereby at least partially solving the above-mentioned technical problems.

[0005] To achieve the above objectives, this application provides a terahertz imaging lens, comprising:

[0006] The first lens has a first incident surface and a first exit surface, wherein at least one of the first incident surface and the first exit surface is an even-order aspherical surface.

[0007] The second lens, the first lens and the second lens are arranged sequentially along the optical axis, the second lens has a second incident surface and a second exit surface, at least one of the second incident surface and the second exit surface is an even-order aspherical surface;

[0008] The terahertz imaging lens is configured to adjust the combined focal length by adjusting the principal point spacing between the first and second lenses.

[0009] In one or more embodiments of this application, the terahertz imaging lens at least satisfies the following formula:

[0010] ;

[0011] Where f is the combined focal length, f1 is the focal length of the first lens, f2 is the focal length of the second lens, and d t The distance between the main points.

[0012] In one or more embodiments of this application, the combined focal length is between 70mm and 100mm; or,

[0013] The combined focal length is between 80mm and 180mm.

[0014] In one or more embodiments of this application, the terahertz imaging lens is configured such that the principal point spacing is continuously adjustable between 50mm and 120mm to achieve continuous adjustment of the combined focal length between 70mm and 100mm.

[0015] In one or more embodiments of this application, the terahertz imaging lens is configured such that the principal point spacing is continuously adjustable between 75mm and 250mm to achieve continuous adjustment of the combined focal length between 80mm and 180mm.

[0016] In one or more embodiments of this application, the focal length of the first lens is greater than the focal length of the second lens.

[0017] In one or more embodiments of this application, the focal length of the first lens is 160mm, and the focal length of the second lens is 80mm; or,

[0018] The focal length of the first lens is 300mm, and the focal length of the second lens is 80mm.

[0019] In one or more embodiments of this application, both the first incident surface and the second incident surface are even-order aspherical surfaces; or,

[0020] The first incident surface, the first exit surface, and the second incident surface are all even-order aspherical surfaces.

[0021] In one or more embodiments of this application, even-order aspherical surfaces satisfy the following formula:

[0022] ;

[0023] Where z is the sag from the vertex of the aspherical surface to any radius r, c is the curvature of the vertex of the aspherical surface, k is the conic coefficient, and a1, a2, a3, a4, a5, and a6 are the coefficients of even-order terms of the 2nd, 4th, 6th, 8th, 10th, and 12th orders, respectively.

[0024] In one or more embodiments of this application, the material of the first lens includes at least one selected from polytetrafluoroethylene, polymethylpentene, high-density polyethylene, and polypropylene, such that the transmittance of the first lens for the operating wavelength of the terahertz imaging lens is not less than 70%; and / or,

[0025] The material of the second lens includes at least one of polytetrafluoroethylene, polymethylpentene, high-density polyethylene, and polypropylene, so that the transmittance of the second lens to the working band of the terahertz imaging lens is not less than 70%.

[0026] In one or more embodiments of this application, the coefficient of the fourth even-order term of the first incident surface is 7.3096 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface is -1.5533 × 10⁶. -13 The coefficient of the 8th even-order term of the first incident surface is -2.1125 × 10⁸. -16 The coefficient of the 10th even-order term of the first incident surface is 4.6656 × 10⁻⁶. -20 The coefficient of the 12th even-order term of the first incident surface is -2.4606 × 10⁻⁶. -24 ;or,

[0027] The coefficient of the fourth even-order term of the first incident surface is -1.801 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface is -7.323 × 10⁶. -14 The coefficient of the 8th even-order term of the first incident surface is -4.709 × 10⁸. -17 The coefficient of the 10th even-order term of the first incident surface is 4.615 × 10⁻⁶. -21 The coefficient of the 12th even-order term of the first incident surface is -1.306 × 10⁻⁶. -25 The coefficient of the fourth even-order term of the first exit surface is -2.250 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first exit surface is -2.159 × 10⁶. -12 The coefficient of the 8th even-order term of the first exit surface is 1.764 × 10⁸. -16 The coefficient of the 10th even-order term of the first exit surface is 6.924 × 10⁻⁶. -21 The coefficient of the 12th even-order term of the first exit surface is -8.996 × 10⁻⁶. -26 .

[0028] In one or more embodiments of this application, the coefficient of the fourth even-order term of the second incident surface is -3.8904 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the second incident surface is -9.2115 × 10⁶. -11 The coefficient of the 8th even-order term of the second incident surface is -2.6503 × 10⁸. -13 The coefficient of the 10th even-order term of the second incident surface is 1.7052 × 10⁻⁶. -16 The coefficient of the 12th even-order term of the second incident surface is -4.0047 × 10⁻⁶. -20 .

[0029] In one or more embodiments of this application, the aperture of the terahertz imaging lens is not less than 60 mm, and the F-number of the terahertz imaging lens is not greater than 2.0.

[0030] Compared with the prior art, the terahertz imaging lens of this application consists of only two lenses, a first lens and a second lens, which reduces the number of optical interfaces, thereby reducing Fresnel reflection loss of terahertz waves at the interfaces and improving energy utilization. Attached Figure Description

[0031] 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 only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the optical path of a terahertz imaging lens in one embodiment of this application, wherein the combined focal length is 70mm;

[0033] Figure 2 for Figure 1 A schematic diagram of the optical path of a mid-terahertz imaging lens, where the combined focal length is 100mm;

[0034] Figure 3 This is a schematic diagram of the optical path of a terahertz imaging lens in another embodiment of this application, wherein the combined focal length is 80mm;

[0035] Figure 4 for Figure 3 A schematic diagram of the optical path of a mid-terahertz imaging lens, where the combined focal length is 180mm;

[0036] Figure 5 for Figure 1 Transmission curve of a mid-terahertz imaging lens;

[0037] Figure 6 for Figure 2 Transmission curve of a mid-terahertz imaging lens;

[0038] Figure 7 for Figure 1 Dot diagram of a mid-terahertz imaging lens;

[0039] Figure 8 for Figure 2 Dot diagram of a mid-terahertz imaging lens;

[0040] Figure 9 for Figure 1 Light trail diagram of a mid-terahertz imaging lens;

[0041] Figure 10 for Figure 2 Light trail diagram of a mid-terahertz imaging lens;

[0042] Figure 11 for Figure 1 Field curvature / F-Tan (Theta) distortion diagram of a mid-terahertz imaging lens;

[0043] Figure 12 for Figure 2 Field curvature / F-Tan (Theta) distortion diagram of a mid-terahertz imaging lens;

[0044] Figure 13 for Figure 1 Geometric image analysis diagram of a mid-terahertz imaging lens;

[0045] Figure 14 for Figure 2 Geometric image analysis diagram of a mid-terahertz imaging lens;

[0046] Figure 15 for Figure 3 Transmission curve of a mid-terahertz imaging lens;

[0047] Figure 16 for Figure 4 Transmission curve of a mid-terahertz imaging lens;

[0048] Figure 17 for Figure 3 Dot diagram of a mid-terahertz imaging lens;

[0049] Figure 18 for Figure 4 Dot diagram of a mid-terahertz imaging lens;

[0050] Figure 19 for Figure 3 Light trail diagram of a mid-terahertz imaging lens;

[0051] Figure 20 for Figure 4 Light trail diagram of a mid-terahertz imaging lens;

[0052] Figure 21 for Figure 3 Field curvature / F-Tan (Theta) distortion diagram of a mid-terahertz imaging lens;

[0053] Figure 22 for Figure 4 Field curvature / F-Tan (Theta) distortion diagram of a mid-terahertz imaging lens;

[0054] Figure 23 for Figure 3 Geometric image analysis diagram of a mid-terahertz imaging lens;

[0055] Figure 24 for Figure 4 Geometric image analysis diagram of a mid-terahertz imaging lens. Detailed Implementation

[0056] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0057] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0058] like Figures 1 to 4 As shown, this application provides a terahertz imaging lens, including a first lens 1 and a second lens 2.

[0059] In this embodiment, the terahertz imaging lens uses only two lenses, resulting in a significantly fewer optical interfaces compared to traditional three-, four-, or five-element terahertz zoom lenses. This minimizes Fresnel reflection losses, ensuring sufficient light energy reaches the detector even with limited terahertz source power and insufficient detector sensitivity, thus achieving high signal-to-noise ratio imaging.

[0060] In this embodiment, the terahertz imaging lens consists of only two lenses, the first lens 1 and the second lens 2, which reduces the number of optical interfaces, thereby reducing Fresnel reflection loss of terahertz waves at the interfaces and improving energy utilization.

[0061] For example, the two-piece structure is simple, uses low-cost polymer materials with good processing performance, and can be manufactured by diamond turning or injection molding. System assembly and adjustment only require controlling the relative positions of the two lenses, which is much less difficult than multi-element lenses, thus helping to reduce the overall cost and promote widespread adoption.

[0062] In some embodiments, the first lens 1 has a first incident surface 11 and a first exit surface 12. The first lens 1 and the second lens 2 are arranged sequentially along the optical axis, and the second lens 2 has a second incident surface 21 and a second exit surface 22.

[0063] In this embodiment, the terahertz wave is incident from the first incident surface 11 of the first lens 1, and exits from the first exit surface 12 to the second incident surface 21 of the second lens 2, and then exits from the second exit surface 22 of the second lens 2.

[0064] In some embodiments, at least one of the first incident surface 11 and the first exit surface 12 is an even-order aspherical surface. At least one of the second incident surface 21 and the second exit surface 22 is an even-order aspherical surface.

[0065] In this embodiment, at least one surface of the first lens 1 and the second lens 2 is designed as an even-order aspherical surface, allowing for good correction of aberrations (such as spherical aberration and coma) in each individual lens. Based on this, when adjusting the focal length in combination, the aberrations of the system are effectively controlled throughout the adjustment range, ensuring image sharpness. Furthermore, each individual lens of the lens employs an even-order aspherical design, resulting in good aberration correction. By adjusting the spacing to achieve zoom, the optimized design ensures good control of system aberrations and high image sharpness throughout the entire focal length adjustment range.

[0066] In some embodiments, the terahertz imaging lens is configured to: adjust the principal point spacing d between the first lens 1 and the second lens 2. t This allows for adjustment of the combined focal length f.

[0067] In this embodiment, the terahertz imaging lens can adapt to different imaging distances and field-of-view requirements without changing the lens, improving the flexibility and efficiency of the terahertz imaging system. By adjusting the combined focal length f (which can be continuous or discrete), zoom functionality is achieved. Thus, an adjustable lens spacing design is realized in the terahertz band, achieved by changing the principal point spacing d between the two lenses. t It can continuously or discretely adjust the combined focal length, which can cover the application requirements of different imaging distances and fields of view, without the need for frequent lens changes, thus improving the adaptability of the terahertz imaging system.

[0068] In some embodiments, a terahertz imaging lens satisfies at least the following formula:

[0069] (1)

[0070] Where f is the combined focal length, f1 is the focal length of the first lens 1, f2 is the focal length of the second lens 2, and d t The distance between the main points.

[0071] In this embodiment, after satisfying formula (1), the terahertz imaging lens can achieve a zoom imaging lens consisting of only two lenses in the terahertz band. Formula (1) provides a precise mathematical basis for focal length adjustment, allowing the focal length to be adjusted by changing d. t The combined focal length f can be changed according to a predetermined pattern (e.g., when d...). t When the focal length f changes continuously within a certain range, the combined focal length f also changes continuously, thus breaking through the technical limitation that existing terahertz imaging lenses can only achieve a fixed focal length.

[0072] In this embodiment, due to the combined focal length f and the principal point spacing d t The above formula (1) is satisfied between the two, and d is adjusted continuously or discretely. tThis allows the lens to cover a wide range of focal lengths. This enables the same lens to adapt to different imaging distances and fields of view, eliminating the need for frequent lens changes and improving the adaptability and efficiency of the terahertz imaging system. For example, a shorter focal length can be used to acquire a wide field of view in security inspection scenarios, while a longer focal length can be used to acquire a magnified local image in detail observation scenarios.

[0073] In this embodiment, according to formula (1), after selecting the focal length f1 of the first lens and the focal length f2 of the second lens, the principal point spacing d required to achieve the target combined focal length f can be accurately calculated. t This allows for the design of the mechanical structure. Based on this, it is possible to provide a variety of zoom range adaptation combinations (such as 70mm-100mm, 80mm-180mm, etc.) to meet the differentiated needs of different application scenarios.

[0074] In some embodiments, the combined focal length f is between 70mm and 100mm.

[0075] In this embodiment, the zoom range of 70mm to 100mm is suitable for medium-range dynamic imaging scenarios such as security inspection imaging and non-destructive testing of materials (the working distance is usually 1-3 meters). Moreover, the zoom ratio of 70mm to 100mm is approximately 1.43x, which is suitable for fine-tuning the field of view.

[0076] In other embodiments, the combined focal length f is between 80mm and 180mm.

[0077] In this embodiment, the zoom range of 80mm to 180mm is suitable for long-distance imaging scenarios such as space exploration and long-distance target recognition (working distance can reach more than 5 meters). Moreover, the zoom ratio of 80mm to 180mm is 2.25x, which can realize a large-scale switching from wide-area search to local magnification.

[0078] In some embodiments, the terahertz imaging lens is configured such that the principal point spacing d t The focal length f can be continuously adjusted between 50mm and 120mm to achieve a combined focal length f between 70mm and 100mm.

[0079] In this embodiment, the spacing d between the main points is... t Continuous adjustment within the range of 50mm to 120mm allows for any combination of focal length f-stops between 70mm and 100mm, without being limited to a few discrete stops. Users can continuously adjust according to the actual working distance to obtain the best imaging effect.

[0080] In this embodiment, the spacing d between the principal points t Adjustment range 50mm-120mm (stroke 70mm), corresponding to the actual distance d between the two lenses. tThe zoom range is approximately 3.8mm-58.7mm. The zoom mechanism is simple in design and has a fast response, making it suitable for integration into portable or automated testing equipment.

[0081] In this embodiment, according to formula (1), the spacing d between the principal points is... t It exhibits a definite monotonic relationship with the combined focal length f (principal point spacing d). t Increasing the focal length f increases the combined focal length f. The user or control system can accurately calculate the required principal point spacing d based on the combined focal length f. t This value enables precise open-loop control.

[0082] In some embodiments, the terahertz imaging lens is configured such that the principal point spacing d t The focal length f can be continuously adjusted between 75mm and 250mm to achieve a combined focal length f between 80mm and 180mm.

[0083] In this embodiment, the spacing d between the main points is continuously adjusted. t It can achieve any focal length within the range of 80mm-180mm, making it suitable for scenarios that require continuous tracking and magnification of distant targets (such as security monitoring and astronomical observation).

[0084] In this embodiment, the spacing d between the principal points t With an adjustment range of 75mm-250mm (travel of 175mm), the longer mechanical travel results in higher resolution focal length control and sub-millimeter positioning accuracy, which is beneficial for precision imaging.

[0085] In this embodiment, the zoom range is used in conjunction with a large-aperture first lens 1 (e.g., aperture = 300mm), and the principal point spacing d t Its wide adjustment range ensures that sufficient light energy transmittance is maintained even at the telephoto end.

[0086] In some embodiments, the focal length f1 of the first lens 1 is greater than the focal length f2 of the second lens 2.

[0087] In this embodiment, according to formula (1), when the optical power of the first lens 1 is small (i.e., the focal length is large) and the optical power of the second lens 2 is large (i.e., the focal length is small), the combined focal length f is relative to d. t The changes are more sensitive. That is, the smaller the principal point spacing d t The change can result in a large variation in the combined focal length f, which is beneficial for realizing a compact zoom mechanism.

[0088] For example, the telephoto lens (i.e., the first lens 1) is placed on the object side, where the incident rays are nearly parallel, which is beneficial for correcting spherical aberration; the short focal length lens (i.e., the second lens 2) is placed on the image side, which undertakes the task of convergence and corrects residual aberration. The two lenses work together to ensure stable image quality throughout the zoom range.

[0089] In some embodiments, the focal length f1 of the first lens 1 is 160mm, and the focal length f2 of the second lens 2 is 80mm.

[0090] In other embodiments, the focal length f1 of the first lens 1 is 300mm and the focal length f2 of the second lens 2 is 80mm.

[0091] In this embodiment, the two sets of adapter combinations (i.e., the zoom range of 70mm to 100mm and the zoom range of 80mm to 180mm) share the same second lens 2 (80mm short focal length lens), making manufacturing and inventory management more convenient. Users only need to replace the first lens 1 (e.g., 160mm or 300mm) to switch between mid-range and long-range zoom modes without having to redesign the entire lens system.

[0092] In this embodiment, the short focal length lens (i.e., the second lens 2) of 80mm can effectively cover the target surface size of common terahertz detectors. If the focal length is less than 60mm, the edge illumination may be insufficient or aberrations may be difficult to correct due to the excessive field of view. Therefore, the second lens 2 with a focal length of 80mm is an optimal value between ensuring detector coverage and imaging quality.

[0093] For example, a combination of a first lens with a focal length of 160mm and a second lens with a focal length of 80mm provides a zoom range of 70mm to 100mm (e.g., suitable for mid-range zoom imaging). A combination of a first lens with a focal length of 300mm and a second lens with a focal length of 80mm provides a zoom range of 80mm to 180mm (e.g., suitable for long-range zoom imaging). The zoom ranges of the two types partially overlap (80mm to 100mm), and users can choose between a lightweight type (160mm focal length first lens 1) or a long-stroke type (300mm focal length first lens 1) according to their actual needs.

[0094] like Figure 1 and Figure 2 This embodiment provides a terahertz imaging lens, wherein the first lens 1 has a focal length f1 = 160mm and the second lens 2 has a focal length f2 = 80mm. The principal point spacing d between the first lens 1 and the second lens 2 is... t Continuous adjustment within the range of 50mm to 120mm allows for continuous variation of the combined focal length f within the range of 70mm to 100mm.

[0095] Table 1 shows the principal point spacing d corresponding to several combined focal lengths f. t and the actual distance d between the first exit surface 12 and the second incident surface 21 t (For example, the actual air gap distance between the first lens 1 and the second lens 2).

[0096] Table 1

[0097]

[0098] As can be seen from Table 1, the spacing d between the principal points t It is monotonically positively correlated with the combined focal length f: when the principal point spacing d t When the focal length is increased from 57.14mm to 112.00mm, the combined focal length f increases from 70mm to 100mm. The user or control system can accurately calculate the required principal point spacing d using formula (1) based on the desired combined focal length. t The value is determined and the stepper motor or manual adjustment mechanism is driven to achieve positioning.

[0099] like Figure 3 and Figure 4 This embodiment provides another terahertz imaging lens, wherein the first lens 1 has a focal length f1 = 300mm and the second lens 2 has a focal length f2 = 80mm. The principal point spacing d between the first lens 1 and the second lens 2 is... t Continuous adjustment within the range of 75mm to 250mm allows for continuous variation of the combined focal length f within the range of 80mm to 180mm.

[0100] Table 2 shows the principal point spacing d corresponding to several combined focal lengths f. t and the actual distance d between the first exit surface 12 and the second incident surface 21 t '.

[0101] Table 2

[0102]

[0103] As can be seen from Table 2, the spacing d between the principal points t It is monotonically positively correlated with the combined focal length f: when the principal point spacing d t When the combined focal length f increases from 80mm to 246.67mm, the combined focal length f increases from 80mm to 180mm. The user or control system can accurately calculate the required principal point spacing d using formula (1) based on the desired combined focal length f. t The value is determined and the stepper motor or manual adjustment mechanism is driven to achieve positioning.

[0104] In some embodiments, the first incident surface 11 and the second incident surface 21 are both even-order aspherical surfaces.

[0105] In this embodiment, for the first lens 1 with a relatively short focal length (160mm) and the second lens 2 with a short focal length (80mm), simply setting the first incident surface 11 and the second incident surface 21 as even-order aspherical surfaces is sufficient to meet the aberration correction requirements and reduce processing costs. Thus, processing costs are reduced while ensuring image quality.

[0106] In other embodiments, the first incident surface 11, the first exit surface 12, and the second incident surface 21 are all even-order aspherical surfaces.

[0107] In this embodiment, for the first lens 1 with a relatively long focal length (300mm), both the first incident surface 11 and the first exit surface 12 need to be set as even-order aspherical surfaces to correct more complex aberrations, thereby improving imaging performance. This provides a higher aberration correction capability to accommodate long-focal-length, large-aperture lenses.

[0108] Relatively speaking, the fewer even-order aspherical surfaces there are, the lower the processing cost. The more even-order aspherical surfaces there are, the better the performance. Users can choose flexibly according to their actual application scenarios.

[0109] In some embodiments, even-order aspherical surfaces satisfy the following formula:

[0110] (2)

[0111] Where z is the vector height from the vertex of the aspherical surface to any radius r, c is the curvature of the vertex of the aspherical surface (c=1 / radius of curvature), k is the conic coefficient, and a is the higher-order coefficient, for example: a1, a2, a3, a4, a5, and a6 are the coefficients of even-order terms of the 2nd, 4th, 6th, 8th, 10th, and 12th orders, respectively.

[0112] In this embodiment, by introducing even-order coefficients from the 2nd to the 12th order, aberrations of different orders can be allocated to independent coefficients for optimization. Specifically: the 4th and 6th order terms mainly correct spherical aberration and fundamental coma, controlling the focusing quality of the central field of view; the 8th and 10th order terms compensate for mid-to-high-order aberrations (such as astigmatism and field curvature), significantly improving off-axis field of view resolution; and the 12th order term finely corrects surface shape deviations, effectively suppressing residual distortion and high-order stray light. This hierarchical synergistic strategy allows a single lens to achieve the aberration balance level of a traditional multi-spherical lens group.

[0113] For example, since the terahertz imaging lens of this application needs to be within the zoom range (principal point spacing d) t To maintain image quality, the introduction of higher-order aspherical coefficients (i.e., even-order coefficients) provides more degrees of freedom for optimization, enabling the system to maintain low aberrations at different spacings.

[0114] In some embodiments, the material of the first lens 1 includes at least one of polytetrafluoroethylene, polymethylpentene, high-density polyethylene and polypropylene, so that the transmittance of the first lens 1 to the working band of the terahertz imaging lens is not less than 70%.

[0115] In some embodiments, the material of the second lens 2 includes at least one of polytetrafluoroethylene, polymethylpentene, high-density polyethylene, and polypropylene, so that the transmittance of the second lens 2 for the working band of the terahertz imaging lens is not less than 70%.

[0116] In this embodiment, the first lens 1 and / or the second lens 2 are made of polymer materials (e.g., the first lens 1 and the second lens 2 are made of polymer materials), which include one or more of polytetrafluoroethylene (PTFE), polymethylpentene (PMP, e.g., TPX), high-density polyethylene (HDPE), and polypropylene (PP).

[0117] In this embodiment, the polymer material has naturally high transmittance (i.e., transmittance not less than 70%, for example, more than 80%) in the terahertz band (i.e., the working band, for example, 0.1THz-3THz) and low refractive index (e.g., 1.4-1.5), so the Fresnel reflection loss at the air-lens interface is small.

[0118] For example, compared to high-resistivity silicon (refractive index 3.42, single-sided reflection loss of about 30%), the single-sided reflection loss of this application is only about 3%-4%, and the total reflection loss of the two lenses with a total of 4 interfaces can be controlled within 15%, and the total transmittance can reach more than 56%.

[0119] For example, the density of polymer materials is approximately 0.9-1.0 g / cm³. 3 It is lower than that of silicon (2.33 g / cm³). 3 Furthermore, it can be mass-produced using injection molding or diamond turning, effectively reducing costs compared to silicon lenses. Materials such as high-density polyethylene possess good mechanical strength and toughness, facilitating the processing of large-diameter lenses (e.g., 300mm aperture) and reducing breakage.

[0120] In some embodiments, the coefficients of the fourth even-order terms of the first incident surface 11 are 7.3096 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface 11 is -1.5533 × 10⁶. -13 The coefficient of the 8th even-order term of the first incident surface 11 is -2.1125 × 10⁸. -16 The coefficient of the 10th even-order term of the first incident surface 11 is 4.6656 × 10⁻⁶. -20 The coefficient of the 12th even-order term of the first incident surface 11 is -2.4606 × 10⁻⁶. -24 .

[0121] For example, the specific parameters of the first lens 1 (i.e., f1 = 160 mm) can be shown in Table 3:

[0122] Table 3

[0123]

[0124] In some embodiments, the coefficient of the fourth even-order term of the first incident surface 11 is -1.801 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface 11 is -7.323 × 10⁶. -14 The coefficient of the 8th even-order term of the first incident surface 11 is -4.709 × 10⁸. -17 The coefficient of the 10th even-order term of the first incident surface 11 is 4.615 × 10. -21 The coefficient of the 12th even-order term of the first incident surface 11 is -1.306 × 10⁻⁶. -25 The coefficient of the fourth even-order term of the first exit surface 12 is -2.250 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first exit surface 12 is -2.159 × 10⁶. -12 The coefficient of the 8th even-order term of the first exit surface 12 is 1.764 × 10⁸. -16 The coefficient of the 10th even-order term of the first exit surface 12 is 6.924 × 10. -21 The coefficient of the 12th even-order term of the first exit surface 12 is -8.996 × 10⁻⁶. -26 .

[0125] For example, the specific parameters of the first lens 1 (i.e., f1 = 300 mm) can be shown in Table 4:

[0126] Table 4

[0127]

[0128] In this embodiment, by precisely defining the coefficients of higher-order even-order terms, the first lens 1 itself possesses low aberrations, and when combined with the second lens 2, it maintains excellent image quality throughout the entire zoom range. For example, the first incident surface conicity of the first lens 1 with a focal length of 160mm is -0.941 (close to a parabola), effectively correcting spherical aberration. The first exit surface conicity of the first lens 1 with a focal length of 300mm is 80.112 (hyperboloid), compensating for the field curvature of the telephoto lens.

[0129] In some embodiments, the coefficient of the fourth even-order term of the second incident surface 21 is -3.8904 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the second incident surface 21 is -9.2115 × 10⁶. -11 The coefficient of the 8th even-order term of the second incident surface 21 is -2.6503 × 10⁸. -13The coefficient of the 10th even-order term of the second incident surface 21 is 1.7052 × 10⁻⁶. -16 The coefficient of the 12th even-order term of the second incident surface 21 is -4.0047 × 10⁻⁶. -20 .

[0130] For example, the specific parameters of the second lens 2 (f2=80mm) are shown in Table 5:

[0131] Table 5

[0132]

[0133] In this embodiment, the second lens 2 serves as a common component for both zoom combinations, with fixed parameters to ensure interchangeability and consistency in mass production. Specific coefficients (e.g., the radius of curvature of the second incident surface 21 is 50.169 mm, the conic coefficient of the second incident surface 21 is -0.209, etc.) have been optimized so that the second lens 2 can achieve good image quality when paired with the first lens 1 with a focal length of 160 mm or 300 mm.

[0134] In this embodiment, the same parameters of the second lens 2 operate within the zoom ranges of 70mm to 100mm and 80mm to 180mm, respectively, and both meet the indicators such as MTF≥0.3 and distortion<1.5%, demonstrating that the design of the second lens 2 has wide adaptability.

[0135] In some embodiments, the aperture of the terahertz imaging lens is not less than 60 mm, and the F-number of the terahertz imaging lens is not greater than 2.0.

[0136] In this embodiment, the aperture is not less than 60mm and the F-number is not greater than 2.0 (the F-number can be as low as 0.59 at some focal lengths), so that the terahertz imaging lens can still collect enough energy to reach the detector when the output power of the terahertz source is only at the milliwatt level, thus achieving high signal-to-noise ratio imaging.

[0137] For example, when the zoom range is between 70mm and 100mm, the F-number is between 0.5 and 2.0, and the aperture is between 100mm and 180mm. When the zoom range is between 80mm and 180mm, the F-number is between 0.5 and 2.0, and the aperture is between 160mm and 310mm.

[0138] For example, the aperture can be adjusted by setting an adjustable stop between the first lens 1 and the second lens 2.

[0139] For example, with a combined focal length of f=70mm, the f-number is 0.64 and the aperture is 110mm. With a combined focal length of f=100mm, the f-number is 0.59 and the aperture is 170mm. With a combined focal length of f=180mm, the aperture can reach 310mm. These values ​​are far superior to typical terahertz fixed focal length lenses (e.g., f-number >2).

[0140] like Figure 5 , Figure 6 , Figure 15 and Figure 16 In the MTF transfer curve diagram, the MTF curves of the entire field of view at each zoom focal length maintain a high value and decrease gently. The consistency of the curves of each field of view is good, indicating that through the above combination optimization of curvature, conic coefficient and higher-order aspherical coefficient, the system effectively corrects spherical aberration, coma and higher-order residual aberration, with high imaging resolution, strong detail transfer capability, and uniform and stable imaging quality of the center and edge fields of view.

[0141] like Figure 7 , Figure 8 , Figure 17 and Figure 18 In the dot plots, the light spots at different fields of view at each zoom position are compact and concentrated, symmetrical in shape, and have small blur spots, with no obvious divergence, trailing, or distortion. This indicates that the parameters of this embodiment can continuously suppress aberrations within the zoom range, resulting in high energy concentration of the imaging light spot and clear, sharp imaging. In the upper right corner of each dot plot: 0,0 indicates that the X-axis field of view is 0° and the Y-axis field of view is 0°; 0,4 indicates that the X-axis field of view is 0° and the Y-axis field of view is 4°; 0,2 indicates that the X-axis field of view is 0° and the Y-axis field of view is 2°; 0,-2 indicates that the X-axis field of view is 0° and the Y-axis field of view is -2°; 0,-4 indicates that the X-axis field of view is 0° and the Y-axis field of view is -4°. Figure 7 and Figure 17 In the diagram, the vertical axis label 4000.00 represents the physical size scale value of the light spot coordinates on the image plane, in micrometers (μm), which is 4 mm. Figure 8 and Figure 18 In the figure, 2000.00 on the vertical axis represents the physical size scale value of the spot coordinates on the image plane, in micrometers (μm), which is 2 mm.

[0142] like Figure 9 , Figure 10 , Figure 19 and Figure 20In the light trail diagrams, the light propagation paths are regular, and both paraxial and off-axis rays converge well without significant deflection or focusing deviation. This demonstrates that the curvature, thickness, and spacing parameters of the two lens sets are reasonably matched, ensuring accurate focusing of large-aperture light even during zooming. In the upper right corner of each light trail diagram: 0,0 indicates an X-axis field of view of 0° and a Y-axis field of view of 0°; 0,4 indicates an X-axis field of view of 0° and a Y-axis field of view of 4°; 0,2 indicates an X-axis field of view of 0° and a Y-axis field of view of 2°; 0,-2 indicates an X-axis field of view of 0° and a Y-axis field of view of -2°; 0,-4 indicates an X-axis field of view of 0° and a Y-axis field of view of -4°.

[0143] like Figure 11 , Figure 12 , Figure 21 and Figure 22 In the field curvature / F-Tan (Theta) distortion diagram, the field curvature curve is flat overall, the focal planes of different fields of view are at the same height, the distortion curve is close to the zero distortion line, and the distortion value is controlled at an extremely low level. This intuitively demonstrates that this embodiment achieves accurate correction of field curvature and distortion through high-order even-order aspherical coefficients, resulting in accurate geometric imaging. It is suitable for high-precision imaging and size detection scenarios.

[0144] like Figure 13 , Figure 14 , Figure 23 and Figure 24 In the geometric aberration analysis diagram, the main aberrations such as spherical aberration, coma, and astigmatism are all suppressed evenly across the entire field of view, without any local sudden increase or imbalance. This proves that the radius of curvature, conic coefficient, and coefficients of the 4th to 12th order even terms defined in this embodiment work together to achieve optimal aberration balance across the entire field of view and aperture of the zoom system, enabling the two-element minimalist structure to achieve or even surpass the imaging level of traditional multi-element zoom lenses.

[0145] In addition, the coefficients of higher-order even-order terms have been precisely matched and synergistically optimized, which can be visually verified from the figure: the MTF curve is high and flat, the spot pattern is concentrated, the distortion is low, and the geometric aberration is evenly suppressed.

[0146] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0147] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0148] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0149] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A terahertz imaging lens, characterized in that, include: A first lens has a first incident surface and a first exit surface, wherein at least one of the first incident surface and the first exit surface is an even-order aspherical surface. The second lens, wherein the first lens and the second lens are arranged sequentially along the optical axis, the second lens has a second incident surface and a second exit surface, and at least one of the second incident surface and the second exit surface is the even-order aspherical surface; The terahertz imaging lens is configured to adjust the combined focal length by adjusting the principal point spacing between the first lens and the second lens.

2. The terahertz imaging lens as described in claim 1, characterized in that, The terahertz imaging lens must satisfy at least the following formula: ； Where f is the combined focal length, f1 is the focal length of the first lens, f2 is the focal length of the second lens, and d t The distance between the main points is denoted as .

3. The terahertz imaging lens as described in claim 1, characterized in that, The combined focal length is between 70mm and 100mm; or, The combined focal length is between 80mm and 180mm.

4. The terahertz imaging lens as described in claim 1, characterized in that, The terahertz imaging lens is configured such that the principal point spacing is continuously adjustable between 50mm and 120mm, so as to achieve continuous adjustment of the combined focal length between 70mm and 100mm.

5. The terahertz imaging lens as described in claim 1, characterized in that, The terahertz imaging lens is configured such that the principal point spacing is continuously adjustable between 75mm and 250mm, so as to achieve continuous adjustment of the combined focal length between 80mm and 180mm.

6. The terahertz imaging lens as described in claim 1, characterized in that, The focal length of the first lens is greater than the focal length of the second lens.

7. The terahertz imaging lens as described in claim 1, characterized in that, The first lens has a focal length of 160mm, and the second lens has a focal length of 80mm; or, The first lens has a focal length of 300mm, and the second lens has a focal length of 80mm.

8. The terahertz imaging lens as described in claim 1, characterized in that, Both the first incident surface and the second incident surface are said to be even-order aspherical surfaces; or, The first incident surface, the first exit surface, and the second incident surface are all even-order aspherical surfaces.

9. The terahertz imaging lens as described in claim 1, characterized in that, The even-order aspherical surface satisfies the following formula: ； Where z is the sag from the vertex of the aspherical surface to any radius r, c is the curvature of the vertex of the aspherical surface, k is the conic coefficient, and a1, a2, a3, a4, a5, and a6 are the coefficients of even-order terms of the 2nd, 4th, 6th, 8th, 10th, and 12th orders, respectively.

10. The terahertz imaging lens as described in claim 1, characterized in that, The first lens is made of at least one of polytetrafluoroethylene, polymethylpentene, high-density polyethylene, and polypropylene, such that the transmittance of the first lens for the operating wavelength of the terahertz imaging lens is not less than 70%; and / or, The material of the second lens includes at least one of polytetrafluoroethylene, polymethylpentene, high-density polyethylene and polypropylene, so that the transmittance of the second lens for the operating band of the terahertz imaging lens is not less than 70%.

11. The terahertz imaging lens as described in claim 9, characterized in that, The coefficients of the fourth even-order term of the first incident surface are 7.3096 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface is -1.5533 × 10⁶. -13 The coefficient of the 8th even-order term of the first incident surface is -2.1125 × 10⁸. -16 The coefficients of the 10th even-order term of the first incident surface are 4.6656 × 10⁻⁶. -20 The coefficient of the 12th even-order term of the first incident surface is -2.4606 × 10⁻⁶. -24 ; or, The coefficients of the fourth even-order term of the first incident surface are -1.801 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first incident surface is -7.323 × 10⁶. -14 The coefficient of the 8th even-order term of the first incident surface is -4.709 × 10⁸. -17 The coefficients of the 10th even-order term of the first incident surface are 4.615 × 10⁻⁶. -21 The coefficient of the 12th even-order term of the first incident surface is -1.306 × 10⁻⁶. -25 The coefficient of the fourth even-order term of the first exit surface is -2.250 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the first exit surface is -2.159 × 10⁶. -12 The coefficient of the 8th even-order term of the first exit surface is 1.764 × 10⁸. -16 The coefficient of the 10th even-order term of the first exit surface is 6.924 × 10⁻⁶. -21 The coefficient of the 12th even-order term of the first exit surface is -8.996 × 10⁻⁶. -26 .

12. The terahertz imaging lens as described in claim 9, characterized in that, The coefficient of the fourth even-order term of the second incident surface is -3.8904 × 10⁻⁶. -8 The coefficient of the 6th even-order term of the second incident surface is -9.2115 × 10⁶. -11 The coefficient of the 8th even-order term of the second incident surface is -2.6503 × 10⁸. -13 The coefficient of the 10th even-order term of the second incident surface is 1.7052 × 10⁻⁶. -16 The coefficient of the 12th even-order term of the second incident surface is -4.0047 × 10⁻⁶. -20 .

13. The terahertz imaging lens as described in claim 1, characterized in that, The aperture of the terahertz imaging lens is not less than 60mm, and the F-number of the terahertz imaging lens is not greater than 2.0.

Images