A high-precision small F-number divergent interferometer standard lens and optical interferometer

Abstract

This invention relates to a high-precision small F-number divergent interferometer standard lens and an optical interferometer. The lens comprises, from left to right, a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens. The entire lens uses a double Gaussian configuration, where incident parallel light first converges and then diverges. The lens aperture gradually decreases from the first lens to the fourth lens and then gradually increases from the fourth lens to the seventh lens. The first surface of the seventh lens is aspherical. This invention is rationally designed, highly manufacturable, and its small F-number characteristic allows for the interferometer to detect lens surfaces with a wider range of R-numbers. The divergent lens reduces the working length of the interferometer and provides a relatively ideal wavefront value.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology, and in particular to a high-precision small F-number divergent interferometer standard lens and an optical interferometer. Background Technology

[0002] Optical interferometry is a metrological testing method based on the principle of light wave interference and using the wavelength of light as the unit. It is recognized as one of the most effective and accurate means of inspecting optical systems and components, playing a crucial role in optical processing and measurement. Interferometers feature non-contact testing, enabling high-speed, non-contact acquisition of measured information, and outperform other types of optical measuring instruments in terms of sensitivity and accuracy. The standard reference lens is a vital component of the interferometer. It converts the plane wave output by the interferometer into a high-precision spherical wave for measuring the surface shape of spherical components. Simultaneously, it separates the output laser beam into a reference beam and a measurement beam. The measurement beam passes perpendicularly through the reference surface, illuminates the surface of the component under test, reflects off the surface, returns to the reference surface, and passes perpendicularly through it again, being received by the interferometer's internal detector along with the reference wavefront. Since the measurement wavefront carries the surface shape information of the component under test, the surface shape of the component can be obtained through data processing.

[0003] The F-number of a standard reference mirror is defined as the working focal length of the standard reference mirror divided by its entrance pupil diameter. The R-number of a spherical element is defined as the radius of the sphere divided by its actual aperture. When measuring the surface shape of an element using an interferometer, the aperture of the element can only be fully measured if the F-number of the standard reference mirror is less than the R-number of the element being measured. Because small F-number standard reference mirrors bend light rays at large angles, their design and manufacturing difficulty increases rapidly. Currently, most reference mirrors used in interferometers are high-F-number converging lenses, or a few low-F-number converging lenses. However, when using a converging standard reference mirror for high-precision interferometric testing of a concave spherical surface with a long radius of curvature, the required optical cavity length is the sum of the back focal length of the reference lens and the radius of curvature of the test surface. In this case, using a diverging reference lens can effectively shorten the length of the test optical cavity, improve the repeatability of the test, and facilitate the use of the translational-rotational absolute detection method for reference surface error calibration. Therefore, it is urgent to solve the problem of how to provide a high-precision small F-number divergent interferometer standard lens to shorten the cavity length for detecting long-radius concave spherical surfaces and improve measurement accuracy. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a high-precision small F-number divergent interferometer standard lens and optical interferometer. The divergent standard lens helps to shorten the working distance.

[0005] The present invention adopts the following technical solution:

[0006] A high-precision small F-number divergent interferometer standard lens, the lens comprising, from left to right, an aperture stop, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7, wherein the aperture stop coincides with the first surface of the first lens L1;

[0007] The center thicknesses of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, and seventh lens L7 along the optical axis are set to TC1, TC2, TC3, TC4, TC5, TC6, and TC7, respectively. The air gaps between the lenses along the optical axis are set to TA1, TA2, TA3, TA4, TA5, and TA6, respectively. The relationship between the center thicknesses of each lens along the optical axis is as follows:

[0008] TC1 / TA1>5, TC2 / TA2<0.6, TC3 / TA3<0.75, TC4 / TA4>0.55, TC5 / TA5<0.7, TC6 / TA6>6, the total thickness of each lens on the optical axis is TLC, the total air gap of the system is TLA, and TLC and TLA satisfy the following relationship: TLC / TLA>1;

[0009] The first lens L1 and the second lens L2 are meniscus-shaped, with the convex surface facing the incident light side and the concave surface facing the outgoing light side; the third lens L3 and the fourth lens L4 are negative lenses, with the lens shape being meniscus-shaped or biconcave; the fifth lens L5, the sixth lens L6, and the seventh lens L7 are meniscus-shaped, with the convex surface facing the outgoing light side and the concave surface facing the incident light side.

[0010] The focal lengths of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, and seventh lens L7 are set to f1, f2, f3, f4, f5, f6, and f7 respectively, with the total focal length set to f. The relationship between the focal lengths of each lens is as follows: -6 <f1 / f<-5.5、-5<f2 / f<-3.5、0.5<f3 / f< 1、0.3<f4 / f<0.6、1<f5 / f<1.3、2.5<f6 / f<4。

[0011] An optical interferometer, comprising the aforementioned high-precision small F-number divergent interferometer standard lens.

[0012] Compared with the prior art, the present invention has the following advantages: the light aperture gradually decreases and then increases again, the light path transitions smoothly, the design is reasonable and the processability is strong, the F number is small, the range of detectable concave spherical surfaces is large, the divergent standard mirror can effectively reduce the working distance of the measured part, the total RMS of the standard mirror is less than 1 / 100λ, and the measurement accuracy is high. Attached Figure Description

[0013] The invention will be further described below with reference to the accompanying drawings.

[0014] Figure 1 A schematic diagram of the structure of a high-precision small F-number divergent interferometer standard lens according to the present invention;

[0015] Figure 2 Schematic diagram of the optical path of this invention;

[0016] Figure 3 Wavefront diagram of Embodiment 1 of the present invention;

[0017] Figure 4 Wavefront diagram of Embodiment 2 of the present invention; Detailed Implementation

[0018] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0019] like Figure 1 As shown, the high-precision small F-number divergent interferometer standard lens of the present invention includes: an aperture stop, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6 and a seventh lens L7 arranged sequentially from left to right, wherein the aperture stop coincides with the first surface of the first lens L1, i.e. the surface facing the light incident side.

[0020] In this embodiment, the center thicknesses of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, and seventh lens L7 along the optical axis are set to TC1, TC2, TC3, TC4, TC5, TC6, and TC7, respectively. The air gaps between the lenses along the optical axis are TA1, TA2, TA3, TA4, TA5, and TA6, respectively. The relationship between the center thicknesses of each lens along the optical axis is as follows:

[0021] TC1 / TA1>5, TC2 / TA2<0.6, TC3 / TA3<0.75, TC4 / TA4>0.55, TC5 / TA5<0.7, TC6 / TA6>6, the total thickness of each lens on the optical axis is TLC, the total air gap of the system is TLA, and TLC and TLA satisfy the following relationship: TLC / TLA>1.

[0022] In this embodiment, the first lens L1 and the second lens L2 are meniscus-shaped, with the convex surface facing the incident light side and the concave surface facing the outgoing light side. The third lens L3 and the fourth lens L4 are negative lenses, and their shapes can be either meniscus-shaped or biconcave lenses depending on the optical power. The fifth lens L5, the sixth lens L6, and the seventh lens L7 are also meniscus-shaped, with the convex surface facing the outgoing light side and the concave surface facing the incident light side. The entire lens uses a double Gaussian configuration, where the incident parallel light first converges and then diverges. The lens aperture gradually decreases from the first lens to the fourth lens and then gradually increases from the fourth lens to the seventh lens.

[0023] In this embodiment, the focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 are set to f1, f2, f3, f4, f5, f6, and f7 respectively, and the total focal length is set to f. The relationship between the focal lengths of each lens is as follows: -6 <f1 / f<-5.5、-5<f2 / f<-3.5、0.5<f3 / f<1、0.3<f4 / f<0.6、1<f5 / f<1.3、2.5<f6 / f<4。

[0024] In this embodiment, the first surface of the seventh lens, i.e., the surface facing the incident light, is an aspherical surface. The equation for an aspherical surface is:

[0025] ,

[0026] Where: z is the aspherical elevation, c is the curvature of the aspherical vertex, and k is the cone coefficient. Let be the radial distance from the lens surface coordinates to the vertex of the aspherical surface. is the surface coefficient.

[0027] In this embodiment, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are all made of H-ZK8 optical glass, and the seventh lens L7 is made of Corning 7980 lens.

[0028] In this embodiment, the last surface of the standard mirror, facing the outgoing light side, is the reference surface. It is set in a confocal relationship with the surface being measured. The surface shape and machining accuracy of this surface determine the measurement accuracy of the standard mirror. Therefore, the last lens of the standard mirror needs to use a more stable and easier-to-manufacture lens material. Other lenses besides the last lens of the standard mirror can use lens materials with higher refractive index to reduce lens curvature and reduce manufacturing difficulty.

[0029] The process of decreasing and then increasing the aperture of each curved surface of the standard mirror has two advantages: first, the light transition is smooth, making it easier to achieve a more ideal wavefront value; second, the resulting optical structure is easier to design with a corresponding mechanical structure.

[0030] Tables 1-1 and 1-2, and Tables 2-1 and 2-2 provide specific lens parameters for a standard lens, which meet the above requirements.

[0031] Table 1-1 Parameter Table of the First Embodiment

[0032]

[0033] Each lens corresponds to two surfaces, which are described according to the direction of the incident light to the outgoing light. For example, for lens L1, S2 is the side closer to the incident light and S3 is the side closer to the outgoing light. The radius of curvature of the lens is negative if the center of the sphere is facing the direction of the incident light, and positive if the center of the sphere is facing the direction of the outgoing light.

[0034] Table 1-2 Aspheric coefficients of the first embodiment

[0035]

[0036] The lens has a total focal length of f = -57.25mm, a radius of curvature R = -95mm for the standard surface (light exit surface) of the seventh element, a standard surface aperture D = 147mm, a total length TTl = 249.85mm, and an f-number of 0.647. Figure 3 The wavefront diagram shown is from this embodiment, with an RMS of 0.0009λ, where λ is the incident light wavelength (typically 632.8 nm in the interferometer). The materials of the first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, and sixth lens L6 have a refractive index of 1.614 and an Abbe number of 55.116. The material of the seventh lens L7 has a refractive index of 1.458 and an Abbe number of 67.821. (See Table 1-2.) The value is 0.

[0037] Table 2-1 Parameter Table of the Second Embodiment

[0038]

[0039] Table 2-2 Aspheric coefficients of the second embodiment

[0040]

[0041] The lens has a focal length of f = -52.16mm, a standard surface radius of curvature R = -98.5mm for the seventh lens element, a standard surface aperture D = 152.4mm, a total length TTl = 275.09mm, and an f-number of 0.647. Figure 4 The wavefront diagram shown in this embodiment is 0.0022λ, where λ is the incident light wavelength (typically 632.8 nm in the interferometer). In Table 2-2, The value is 0.

[0042] In the two parameter embodiments above, the F-number of the standard connector is less than 0.65, the wavefront error RMS of the standard lens is less than 1 / 100λ, and the focal point of the emitted light coincides with the center of the sphere of the second surface of the seventh lens, i.e., the reference surface (the surface closer to the emitted light side).

[0043] The present invention also provides an optical interferometer, including the above-mentioned high-precision small F-number divergent interferometer standard lens.

[0044] Unless otherwise stated, if any of the technical solutions disclosed in this invention specify a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely one among many feasible numerical values ​​that has a more obvious or representative technical effect. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0045] If the terms "first" or "second" are used in this document to specify components, those skilled in the art should know that the use of "first" or "second" is merely for the purpose of distinguishing components in description, and unless otherwise stated, the above terms have no special meaning.

[0046] 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 preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A high-precision small F-number divergent interferometer standard lens, characterized in that: The lens consists of an aperture stop, a first lens element (L1), a second lens element (L2), a third lens element (L3), a fourth lens element (L4), a fifth lens element (L5), a sixth lens element (L6), and a seventh lens element (L7) arranged from left to right, wherein the aperture stop coincides with the first surface of the first lens element (L1); The center thicknesses of the first lens (L1), second lens (L2), third lens (L3), fourth lens (L4), fifth lens (L5), and sixth lens (L6) along the optical axis are set as TC1, TC2, TC3, TC4, TC5, and TC6, respectively. The air gaps between the lenses along the optical axis are set as TA1, TA2, TA3, TA4, TA5, and TA6, respectively. The relationship between the center thicknesses of each lens along the optical axis is as follows: TC1 / TA1>5, TC2 / TA2<0.6, TC3 / TA3<0.75, TC4 / TA4>0.55, TC5 / TA5<0.7, TC6 / TA6>6, the total thickness of each lens on the optical axis is TLC, the total air gap of the system is TLA, and TLC and TLA satisfy the following relationship: TLC / TLA>1; The first lens (L1) and the second lens (L2) are meniscus-shaped, with the convex surface facing the incident light side and the concave surface facing the outgoing light side; the third lens (L3) and the fourth lens (L4) are negative lenses, with the third lens (L3) being biconcave and the fourth lens (L4) being meniscus-shaped, with the convex surface facing the outgoing light side and the concave surface facing the incident light side; the fifth lens (L5), the sixth lens (L6), and the seventh lens (L7) are also meniscus-shaped, with the convex surface facing the outgoing light side and the concave surface facing the incident light side. The focal lengths of the first lens (L1), second lens (L2), third lens (L3), fourth lens (L4), fifth lens (L5), and sixth lens (L6) are set to f1, f2, f3, f4, f5, and f6 respectively, with the total focal length set to f. The relationship between the focal lengths of each lens is as follows: -6 <f1 / f<-5.5、-5<f2 / f<-3.5、0.5<f3 / f< 1、0.3<f4 / f<0.6、1<f5 / f<1.3、2.5<f6 / f<4。 2. The high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that: The first surface of the seventh lens, the side facing the incident light, is an aspherical surface. The equation for an aspherical surface is: ， Where: z is the aspherical elevation, c is the curvature of the aspherical vertex, and k is the cone coefficient. Let be the radial distance from the lens surface coordinates to the vertex of the aspherical surface. is the surface coefficient.

3. The high-precision small F-number divergent interferometer standard lens according to claim 2, characterized in that: ， ， ， ， ， ， 。 4. The high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The first lens (L1), second lens (L2), third lens (L3), fourth lens (L4), fifth lens (L5) and sixth lens (L6) have a refractive index of 1.614 and an Abbe number of 55.

116.

5. The high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The seventh lens (L7) has a refractive index of 1.458 and an Abbe number of 67.

821.

6. The high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), and the sixth lens (L6) are all made of H-ZK8 optical glass, while the seventh lens (L7) is made of Corning 7980 lens.

7. A high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The standard lens has an F-number of less than 0.65, and the focal point of the emitted light coincides with the center of the sphere of the second surface of the seventh lens, i.e., the reference surface.

8. A high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The total focal length of the standard lens is f=-57.25mm.

9. A high-precision small F-number divergent interferometer standard lens according to claim 1, characterized in that, The total focal length of the standard lens is f=-52.16mm.

10. An optical interferometer, characterized in that, Includes a high-precision small F-number divergent interferometer standard lens according to any one of claims 1-9.

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