Achromatic telecentric field lens

Abstract

The invention relates to the technical field of laser optics, and discloses an achromatic telecentric field lens, which comprises a plurality of lenses and plane mirrors which are coaxially arranged, incident light sequentially reaches the first face and the second face of each lens in the incidence direction. The plurality of lenses and plane mirrors comprise a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth plane mirror of which incident light is sequentially arranged from the object space to the image space along the incident direction; wherein the fifth lens is a Fresnel lens. The Fresnel lens carries out directional compensation on the vertical axis chromatic aberration generated by femtosecond laser spectrum broadening, the broadening spectrum of the ultraviolet band is converged to the same focal plane through the discrete phase modulation capability of the Fresnel lens, and the aberration of the telecentric field lens light path is ensured to be effectively corrected by combining the cooperative aberration correction of the first four lenses.

Description

Technical Field

[0001] The present invention relates to the field of laser optics technology, in particular to an achromatic telecentric field mirror. Background Art

[0002] Femtosecond laser has the characteristics of extremely short pulse width and extremely high peak power. The extremely short pulse width can generate extremely high power in an instant, so no excess heat is generated, thereby avoiding material cracking, breakage, melting and other phenomena during the processing process, and thus obtaining very high-quality processing results.

[0003] The existing field mirrors used in the field of high-energy lasers are usually designed for a single wavelength and have no achromatic effect. Femtosecond lasers are lasers that can generate ultra-short laser pulses at the femtosecond level. They have the characteristics of short pulse width, high peak power, small focused spot, and high precision. They are usually used in relatively high-end processing fields, and the focusing effect of the spot is required to be relatively strict. The output light of a femtosecond laser has a spectral broadening phenomenon, that is, the femtosecond laser is not a single wavelength, but has a certain spectral width. Therefore, when using existing field mirrors, the output light will be incident on the field mirror and will produce serious chromatic aberration, making it impossible for the output light of the field mirror to converge on the same point. In particular, the vertical axis chromatic aberration causes the output light spot of the field mirror to become larger and more elliptical after focusing, affecting the uniformity and ellipticity of the output light spot, and thus affecting the laser processing effect. However, femtosecond lasers are usually used in relatively high-end processing fields, and the focusing effect of the spot is required to be relatively strict. The field mirrors of related technologies are difficult to meet this demand. Summary of the Invention

[0004] In view of this, the present invention provides an achromatic telecentric field mirror to solve the problem of affected marking effect of femtosecond laser.

[0005] The present invention provides an achromatic telecentric field mirror, comprising:

[0006] A plurality of lenses and plane mirrors are coaxially arranged; incident light reaches the first surface and the second surface of each lens in sequence along the incident direction; the plurality of lenses and plane mirrors include a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth plane mirror arranged in sequence from the object side to the image side along the incident direction of the incident light; wherein the fifth lens is a Fresnel lens.

[0007] In some optional embodiments, the Abbe number of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth plane mirror is 67.8, and the refractive index is 1.458.

[0008] In some optional embodiments, the first lens is a biconcave spherical negative lens, the absolute value of the radius of curvature of the first surface of the first lens is smaller than the absolute value of the radius of curvature of the second surface of the first lens, the radius of curvature of the first surface of the first lens is -32.15, the radius of curvature of the second surface of the first lens is 149, and the thickness of the first lens is 4 mm.

[0009] In some optional embodiments, the second lens is a meniscus spherical positive lens, the second surface of the first lens is close to the first surface of the second lens, the absolute value of the radius of curvature of the first surface of the second lens is greater than the absolute value of the radius of curvature of the second surface of the second lens, the radius of curvature of the first surface of the second lens is -81.67, the radius of curvature of the second surface of the second lens is -37.68, and the thickness of the second lens is 14 mm.

[0010] In some optional embodiments, the third lens is an aspheric positive lens, the first surface of the third lens is close to the second surface of the second lens, the absolute value of the radius of curvature of the first surface of the third lens is greater than the absolute value of the radius of curvature of the second surface of the third lens, the radius of curvature of the first surface of the third lens is -164.9, the radius of curvature of the second surface of the third lens is -46.3, and the thickness of the third lens is 12 mm.

[0011] In some optional embodiments, the fourth lens is a meniscus positive lens, the second surface of the third lens is close to the first surface of the fourth lens, the absolute value of the radius of curvature of the first surface of the fourth lens is greater than the absolute value of the radius of curvature of the second surface of the fourth lens, the radius of curvature of the first surface of the fourth lens is -449.8, the radius of curvature of the second surface of the fourth lens is -134.6, and the thickness of the fourth lens is 6.5 mm.

[0012] In some optional embodiments, the radius of curvature of the first surface of the fourth lens is -449.8, the radius of curvature of the second surface of the fourth lens is -134.6, and the thickness of the fourth lens is 6.5 mm.

[0013] In some optional embodiments, the radius of curvature of the first surface of the fifth lens is 131, the radius of curvature of the second surface of the fifth lens is 287, the thickness of the fifth lens is 3 mm, the material of the sixth plane mirror is fused quartz glass material, and the thickness of the sixth plane mirror is 3 mm.

[0014] In some optional embodiments, the first lens has negative optical power, the second lens has positive optical power, the third lens has positive optical power, the fourth lens has positive optical power, and the fifth lens has positive optical power.

[0015] In some optional embodiments, the first lens is used to diverge the incident light; the second lens and the fourth lens are used to deflect the incident light and balance the aberration generated by the first lens; the third lens is used to reduce the spherical aberration of the optical path of the incident light; and the fifth lens is used to correct chromatic aberration.

[0016] The achromatic telecentric field mirror provided by an embodiment of the present invention comprises: a plurality of coaxially arranged lenses and a plane mirror; incident light sequentially strikes the first and second surfaces of each lens along the incident direction; the plurality of lenses and plane mirrors comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth plane mirror, sequentially arranged along the incident direction from the object side to the image side; wherein the fifth lens is a Fresnel lens. The Fresnel lens provides directionally compensated vertical axial chromatic aberration caused by the broadening of the femtosecond laser spectrum. Its discrete phase modulation capability converges the broadened spectrum in the ultraviolet band to a common focal plane. Combined with the synergistic aberration correction of the first four lenses, this ensures that the aberrations of the lens optical path are effectively corrected. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 is a schematic diagram of an achromatic telecentric field mirror according to an embodiment of the present invention;

[0019] Figure 2 is a dispersion pattern at different field angles according to an embodiment of the present invention;

[0020] Figure 3 is a distortion map according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0022] Femtosecond lasers are specialized lasers that produce ultrafast pulses of extremely short duration. Their short pulse width allows them to concentrate energy within a very short time, generating peak power. Their interaction with matter is also extremely brief, minimizing thermal effects. This makes femtosecond lasers highly advantageous in fields such as precision micromachining, ophthalmic surgery, biomedical imaging, the study of ultrafast phenomena, and fundamental physics research.

[0023] Existing fused silica telecentric field lenses are primarily used to provide wide-range, distortion-free flat-field focusing in laser scanning processes, maintaining the beam's telecentricity perpendicular to the processing plane during scanning. Their optical design is typically highly optimized for a single, specific operating wavelength. Under single-wavelength conditions, they can precisely correct monochromatic aberrations such as spherical aberration, astigmatism, field curvature, and coma. Femtosecond lasers exhibit spectral broadening. This means that femtosecond lasers have a spectral width rather than a single wavelength. Therefore, when using existing telecentric field lenses, the light source will experience chromatic aberration as it passes through the lens. The ideal small spot of light that could be focused at a single wavelength is significantly enlarged due to the dispersion of different wavelength components in the focal plane. The energy density of the beam is the core driving force of laser processing, and an increase in the spot size means a sharp decrease in energy density. Vertical chromatic aberration can manifest differently in different directions, causing the spot to become elliptical instead of the ideal circular shape. This shape distortion disrupts the symmetry and uniformity of the energy distribution. Femtosecond laser applications typically require a stable spot size at the micron or even submicron level, with a highly symmetrical shape and consistency across the entire processing area. Deterioration in spot quality can lead to increased edge roughness, feature size deviations, changes in sidewall taper, an expansion of the heat-affected zone, and even process failure. Consequently, current telecentric field lenses struggle to meet the demands of femtosecond laser applications.

[0024] Based on this, the present invention provides an achromatic telecentric field mirror that can be used in the field of ultraviolet femtosecond laser applications.

[0025] According to an embodiment of the present invention, an embodiment of an achromatic telecentric field mirror is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0026] In this embodiment, an achromatic telecentric field mirror is provided, comprising: a plurality of lenses and a plane mirror arranged coaxially; an incident light ray sequentially reaches a first surface and a second surface of each of the lenses along an incident direction;

[0027] The multiple lenses and plane mirrors include a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth plane mirror arranged in sequence from the object side to the image side along the incident direction of the incident light; wherein the fifth lens is a Fresnel lens.

[0028] Figure 1 is an achromatic telecentric field mirror according to an embodiment of the present invention, such as Figure 1 As shown, the first lens L1 is the first lens that enters the field lens system. Along the incident direction of the incident light, from the object side to the image side, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth plane mirror L6 are arranged in sequence. Among them, the fifth lens is a Fresnel lens.

[0029] Among them, the first lens is the first lens through which light enters the field lens system. After the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are arranged in sequence. These lenses cooperate with each other to further modulate the light through their respective optical properties, such as correcting aberrations and adjusting focal length, and jointly achieve the optical performance requirements of an achromatic telecentric field lens. The fifth lens is a Fresnel lens, and the Fresnel structure on its surface helps to improve the focusing performance of light and increase the uniformity of light. After the fifth lens, a sixth plane mirror L6 is arranged to change the propagation direction of light and adjust the optical path layout to make the entire optical system more compact or adapt to specific application scenarios.

[0030] The achromatic telecentric field mirror provided by an embodiment of the present invention comprises: a plurality of coaxially arranged lenses and a plane mirror; incident light sequentially strikes the first and second surfaces of each lens along the incident direction; the plurality of lenses and plane mirrors comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth plane mirror, sequentially arranged along the incident direction from the object side to the image side; wherein the fifth lens is a Fresnel lens. The Fresnel lens provides directionally compensated vertical axial chromatic aberration caused by the broadening of the femtosecond laser spectrum. Its discrete phase modulation capability converges the broadened spectrum in the ultraviolet band to a common focal plane. Combined with the synergistic aberration correction of the first four lenses, this ensures that the aberrations of the lens optical path are effectively corrected.

[0031] In some optional embodiments, the Abbe number of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth plane mirror is 67.8, and the refractive index is 1.458.

[0032] In some optional embodiments, the first lens has negative optical power, the second lens has positive optical power, the third lens has positive optical power, the fourth lens has positive optical power, and the fifth lens has positive optical power. The first lens is used to diverge the incident light, the second lens and the fourth lens are used to deflect the incident light and balance the aberrations generated by the first lens, the third lens is used to reduce spherical aberration of the optical path of the incident light, and the fifth lens is used to correct chromatic aberration.

[0033] Optical focal length is a physical quantity that describes the ability of an optical system to converge or diverge light. The negative optical focal length of the first lens is used to correct the initial aberration of the incident light, so that the main surface of the lens optical path moves backward and the working distance of the lens is increased. The second lens has positive optical focal length, and its function is to converge light and provide most of the positive optical focal length required. The third lens to the fifth lens all have positive optical focal length, and by gradually increasing the convergence ability, the beam diameter is further compressed and the plane position is adjusted. The telecentric field mirror provided in an embodiment of the present invention can offset or compensate for various aberrations generated by different lenses by reasonably allocating the optical focal length and position of each lens, thereby minimizing the comprehensive aberration of the entire optical system and achieving the expected imaging quality.

[0034] In some optional embodiments, the first lens is a biconcave spherical negative lens, the absolute value of the radius of curvature of the first surface of the first lens is smaller than the absolute value of the radius of curvature of the second surface of the first lens, the radius of curvature of the first surface of the first lens is -32.15, the radius of curvature of the second surface of the first lens is 149, and the thickness of the first lens is 4 mm.

[0035] The second lens is a meniscus spherical positive lens. The second surface of the first lens is close to the first surface of the second lens. The absolute value of the radius of curvature of the first surface of the second lens is greater than the absolute value of the radius of curvature of the second surface of the second lens. The radius of curvature of the first surface of the second lens is -81.67, the radius of curvature of the second surface of the second lens is -37.68, and the thickness of the second lens is 14 mm.

[0036] The third lens is an aspheric positive lens. The first surface of the third lens is close to the second surface of the second lens. The absolute value of the radius of curvature of the first surface of the third lens is greater than the absolute value of the radius of curvature of the second surface of the third lens. The radius of curvature of the first surface of the third lens is -164.9, the radius of curvature of the second surface of the third lens is -46.3, and the thickness of the third lens is 12 mm.

[0037] The fourth lens is a meniscus positive lens. The second surface of the third lens is close to the first surface of the fourth lens. The absolute value of the radius of curvature of the first surface of the fourth lens is greater than the absolute value of the radius of curvature of the second surface of the fourth lens. The radius of curvature of the first surface of the fourth lens is -449.8, the radius of curvature of the second surface of the fourth lens is -134.6, and the thickness of the fourth lens is 6.5 mm.

[0038] The curvature radius of the first surface of the fifth lens is 131, the curvature radius of the second surface of the fifth lens is 287, the thickness of the fifth lens is 3 mm, the material of the sixth plane mirror is fused quartz glass, and the thickness of the sixth plane mirror is 3 mm.

[0039] In some optional embodiments, the fifth lens is a Fresnel lens. By simplifying a continuously curved lens into a concentric ring-shaped structure, the Fresnel lens significantly reduces thickness and weight while retaining focusing performance, achieving lightweight and low-cost manufacturing. Its jagged cross-section, composed of precisely calculated ring-shaped zones, not only focuses light like a convex lens, but also resists deformation and is easy to process.

[0040] Fresnel lenses utilize the discrete phase modulation properties of their ring-shaped structure to differentially refract light of different wavelengths in the ultraviolet band. Short-wavelength light is more strongly deflected at the edges of the ring-shaped structure, thereby converging all wavelengths of the broadened spectrum onto the same focal plane, eliminating focus drift caused by chromatic aberration. Furthermore, Fresnel lenses utilize mature diamond turning technology, ensuring effective cost and quality control.

[0041] The specific parameters are shown in the table below. The table below shows the radius of curvature, thickness, refractive index, and Abbe number of each lens in the achromatic telecentric field mirror provided in this embodiment. Here, radius of curvature 1 is the first surface of the lens along the incident direction, and radius of curvature 2 is the second surface of the lens along the incident direction. The sign in the radius of curvature indicates the direction of curvature: a positive value indicates curvature toward the object, and a negative value indicates curvature toward the image.

[0042] Lens number Curvature radius 1 Curvature radius 2 thickness Refractive index Abbe number First spherical lens -32.15 149 4 1.458 67.8 Second spherical lens -81.67 -37.68 14 1.458 67.8 The third aspheric lens -164.9 -46.3 12 1.458 67.8 Fourth spherical lens -449.8 -134.6 6.5 1.458 67.8 Fifth Fresnel lens 131 INF 3 1.458 67.8 Sixth protective plane mirror INF INF 3 1.458 67.8

[0043] In some optional embodiments, the first lens is used to diverge the incident light, the second lens and the fourth lens are used to deflect the incident light and balance the aberration produced by the first lens, the third lens is used to reduce the spherical aberration of the optical path of the incident light, and the fifth lens is used to correct chromatic aberration.

[0044] Specifically, the first lens is a biconcave spherical negative lens. As the starting element of the optical path, its biconcave structure diverges incident parallel light, providing suitable incident conditions for the subsequent convergence of the positive lens, thereby preventing premature focusing of the light beam and the accumulation of aberrations. Made of fused quartz, which has extremely high transmittance in the visible and near-infrared bands, it effectively reduces light absorption losses within the lens, ensuring that more light can be transmitted smoothly through the lens. The negative optical power shifts the system's main surface backward, extending the working distance while reducing the risk of interference between the front of the lens and the subject.

[0045] The second lens is a positive spherical meniscus lens. Its curvature radius allows for precise control of the light deflection angle, simultaneously bending the light to form a preliminary real image. Combined with the first lens, it corrects for axial chromatic aberration and spherical aberration, balancing the aberrations introduced by the first spherical negative lens and improving central resolution.

[0046] The third lens is an aspheric positive lens. The aspheric surface can precisely control the angle of light deflection, eliminate the spherical aberration of traditional spherical lenses, and make the edge light and the axial light focus on the same point, significantly improving the resolution. The aspheric design can reduce the number or thickness of lenses and achieve miniaturization of the lens.

[0047] The fourth lens is a meniscus spherical positive lens, which works together with the second lens to further balance the residual chromatic aberration and astigmatism. By adjusting the curvature of the meniscus lens, the light beam convergence angle can be finely controlled to ensure the accuracy of the final image plane position.

[0048] The fifth lens is a Fresnel lens, which can correct the chromatic aberration caused by the broadening of the ultrafast laser spectrum. It is used in F-theta field mirrors with different focal lengths. The Fresnel lens is processed by diamond turning, which has a mature processing technology and can well control the cost and quality.

[0049] Furthermore, the first lens, the second lens, the third aspheric lens, the fourth lens, the fifth lens, and the sixth plane mirror are all made of fused quartz glass.

[0050] The third aspheric lens is along the incident direction. From left to right, the first surface is spherical and the second surface is aspherical. The aspheric equation is:

[0051]

[0052] Where Z is the sag in the direction of the optical axis, C is the inverse of the radius of curvature, k is the cone coefficient, r is the radial coordinate of the coordinate axis, a1, a2, a3, a4, a5, a6, a7, a8 are the high-order coefficients, dimensionless. The following table shows the high-order coefficients of the aspheric surface in the third aspheric lens:

[0053]

[0054] The conic coefficient k of an aspheric surface is 0.

[0055] The equation of the Fresnel surface in the fifth Fresnel lens is:

[0056]

[0057] Where Z is the sag of the optical axis, C is the inverse of the radius of curvature, k is the cone coefficient, r is the radial coordinate of the coordinate axis, a1, a2, a3, a4, a5, a6, a7, a8 are the coefficients of higher-order terms and are dimensionless;

[0058] The following table shows the high-order coefficients of the aspheric surface in the fifth Fresnel lens:

[0059]

[0060] The cone coefficient k in the Fresnel surface is 0.

[0061] like Figure 1 As shown, the telecentric field mirror provided by the present invention uses a multi-stage, alternating combination design to collaboratively correct chromatic aberration in a wide spectral range (covering the broadened spectrum of femtosecond laser). Among them, the vertical axis chromatic aberration caused by the broadening of the femtosecond laser spectrum is directionally compensated by the Fresnel lens, and its discrete phase modulation capability converges the broadened spectrum of the ultraviolet band to the same focal plane. Combined with the collaborative aberration correction of the first four lenses, it ensures that the aberration of the lens optical path is effectively corrected.

[0062] Figure 2 The diffuse spot diagrams under different field angles are shown in the figure below. The upper left diagram is the focus spot diagram at a field angle of 0 degrees, the upper right diagram is the focus spot diagram at a field angle of 8 degrees, the lower left diagram is the focus spot diagram at a field angle of 16 degrees, and the lower right diagram is the focus spot diagram at a field angle of 19 degrees. By combining different lens materials to eliminate chromatic aberration and combining aspheric surfaces to correct spherical aberration, as shown in the figure below. Figure 2 As shown in the figure, the diffuse spot of the lens is close to the diffraction limit, and the focused spot emitted by the lens has good roundness and uniformity.

[0063] Figure 3 This is a distortion diagram. The lens has small distortion and is suitable for linear scanning marking. Figure 3 The vertical axis is the field of view angle, and the horizontal axis is the F-theta field lens distortion value. The figure shows the F-theta field lens distortion at different field angles.

[0064] The achromatic telecentric field mirror provided by an embodiment of the present invention comprises: a plurality of coaxially arranged lenses and a plane mirror; incident light sequentially strikes the first and second surfaces of each lens along the incident direction; the plurality of lenses and plane mirrors comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth plane mirror, sequentially arranged along the incident direction from the object side to the image side; wherein the fifth lens is a Fresnel lens. The Fresnel lens provides directionally compensated vertical axial chromatic aberration caused by the broadening of the femtosecond laser spectrum. Its discrete phase modulation capability converges the broadened spectrum in the ultraviolet band to a common focal plane. Combined with the synergistic aberration correction of the first four lenses, this ensures that the aberrations of the lens optical path are effectively corrected.

[0065] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the present invention.

Claims

1. An achromatic telecentric field lens, characterized in that: include: A plurality of lenses and plane mirrors are coaxially arranged; incident light sequentially reaches the first surface and the second surface of each lens along the incident direction; The multiple lenses and plane mirrors include a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth plane mirror arranged in sequence from the object side to the image side along the incident direction of the incident light; wherein the fifth lens is a Fresnel lens.

2. The achromatic telecentric field mirror according to claim 1, characterized in that: The Abbe number of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth plane mirror is 67.8, and the refractive index is 1.

458.

3. The achromatic telecentric field mirror according to claim 1, characterized in that: The first lens is a biconcave spherical negative lens, the absolute value of the curvature radius of the first surface of the first lens is smaller than the absolute value of the curvature radius of the second surface of the first lens, the curvature radius of the first surface of the first lens is -32.15, the curvature radius of the second surface of the first lens is 149, and the thickness of the first lens is 4 mm.

4. The achromatic telecentric field mirror according to claim 1, characterized in that: The second lens is a meniscus spherical positive lens, the second surface of the first lens is close to the first surface of the second lens, the absolute value of the curvature radius of the first surface of the second lens is greater than the absolute value of the curvature radius of the second surface of the second lens, the curvature radius of the first surface of the second lens is -81.67, the curvature radius of the second surface of the second lens is -37.68, and the thickness of the second lens is 14 mm.

5. The achromatic telecentric field mirror according to claim 1, characterized in that: The third lens is an aspheric positive lens, the first surface of the third lens is close to the second surface of the second lens, the absolute value of the curvature radius of the first surface of the third lens is greater than the absolute value of the curvature radius of the second surface of the third lens, the curvature radius of the first surface of the third lens is -164.9, the curvature radius of the second surface of the third lens is -46.3, and the thickness of the third lens is 12 mm.

6. The achromatic telecentric field mirror according to claim 1, characterized in that: The fourth lens is a meniscus positive lens, the second surface of the third lens is close to the first surface of the fourth lens, and the absolute value of the curvature radius of the first surface of the fourth lens is greater than the absolute value of the curvature radius of the second surface of the fourth lens.

7. The achromatic telecentric field mirror according to claim 6, characterized in that: The curvature radius of the first surface of the fourth lens is -449.8, the curvature radius of the second surface of the fourth lens is -134.6, and the thickness of the fourth lens is 6.5 mm.

8. The achromatic telecentric field mirror according to claim 1, characterized in that: The curvature radius of the first surface of the fifth lens is 131, the curvature radius of the second surface of the fifth lens is 287, the thickness of the fifth lens is 3 mm, the material of the sixth plane mirror is fused quartz glass, and the thickness of the sixth plane mirror is 3 mm.

9. The achromatic telecentric field mirror according to claim 1, characterized in that: The first lens has negative refractive power, the second lens has positive refractive power, the third lens has positive refractive power, the fourth lens has positive refractive power, and the fifth lens has positive refractive power.

10. The telecentric field mirror according to claim 1, characterized in that: The first lens is used to diverge the incident light; the second lens and the fourth lens are used to deflect the incident light and balance the aberration generated by the first lens; the third lens is used to reduce the spherical aberration of the optical path of the incident light; The fifth lens is used to correct chromatic aberration.

Images