An optical path compensation and reference mirror adjustable interferometer

Abstract

The application relates to an interference objective with adjustable optical path compensation and reference mirror, which comprises an equal-ratio light splitting prism, a one-dimensional micro linear displacement table, a detection arm and a reference arm, one end of the detection arm and one end of the reference arm are arranged towards the light splitting prism, and the detection arm and the reference arm are arranged perpendicularly to each other; the detection arm comprises a detection objective, the reference arm comprises a reference objective, the equal-ratio light splitting prism has a light splitting surface, the light splitting surface is arranged at an angle of 45 degrees, and the distance between the light splitting surface of the equal-ratio light splitting prism and the detection objective or the reference objective is adjusted through the one-dimensional micro linear displacement table; the distance between the 45-degree light splitting surface of the equal-ratio light splitting prism and one of the objectives is changed through the one-dimensional micro linear displacement table, the back focal surfaces of the reference objective and the detection objective are symmetrical relative to the 45-degree light splitting surface in space, white light interference zero optical path difference adjustment is realized, the adjustment is convenient and fast, and the one-dimensional micro linear displacement table adjusting mechanism is locked after interference zero adjustment, so that the interference objective and the optical system can stably work.

Description

Technical Field

[0001] This application relates to the field of optical instrument technology, and in particular to an interference objective with optical path compensation and an adjustable reference mirror. Background Technology

[0002] White light interferometry is a topography measurement technique that utilizes a light source of a certain bandwidth, which is split, transmitted, and coherently coherently formed into interference fringes. These fringes are then altered by vertical scanning for analysis. As a high-precision, non-contact measurement technique that does not damage the sample surface, it is widely used in mechanical, electronic, optical, and materials science fields. Its core component is the interferometer objective. The performance parameters of the interferometer objective, such as magnification, field of view number, numerical aperture, working distance, reference mirror material, and reflectivity, respectively affect the lateral resolution, the non-stitched measurement range, the measurable slope angle, the non-stitched vertical scanning range, and the range of measurable sample materials, thus influencing the performance, efficiency, and adaptability of the white light interferometry system.

[0003] Most current white-light interferometry systems utilize interferometric objectives from Michelson and Mirau. While Michelson objectives are simple in principle, their beam-splitting system is located in the object-side optical path, resulting in a shorter effective working distance. This limits their use to low-magnification objectives with long working distances, typically less than 10x, failing to meet higher-precision measurement requirements and thus limiting their application. Existing white-light interferometry systems often employ Mirau objectives from Nikon, Japan. However, Mirau objectives require integrating the beam-splitting system and reference mirror internally, inevitably limiting the numerical aperture and working distance, and the reference mirror cannot be replaced. When the reflectivity of the reference mirror differs significantly from that of the measured sample, the interference signal-to-noise ratio decreases, affecting measurement accuracy. Therefore, standardized interferometric objectives limit the types of samples that can be measured, making it difficult to meet diverse measurement needs. Furthermore, Mirau objectives are more difficult to design and manufacture, resulting in lower production volumes and higher costs compared to standard objectives.

[0004] Another type of interferometer objective, the Linnik, has received less attention. Its characteristic is that the entire interferometer requires a pair of matching objective lenses to form the reference and detector arms. Therefore, it allows for the use of objective lenses with better parameters to improve the overall performance of the interferometer objective, including the field of view, numerical aperture, and working distance. However, because the reference and detector arms are separate and long, they are susceptible to external interference, leading to poor interference stability. Furthermore, the beam-splitting system at the rear focal plane of the objective is sealed within the structure, and the symmetrical design of the structure alone cannot guarantee equal optical path differences between the two arms. Therefore, the application of Linnik interferometer objectives is not as widespread as that of Michelson and Mirau interferometer objectives. Summary of the Invention

[0005] Therefore, it is necessary to provide an interferometer objective with optical path compensation and an adjustable reference mirror, including an equal beam division prism, a one-dimensional miniature linear displacement stage, a probe arm, and a reference arm. One end of the probe arm and one end of the reference arm are respectively arranged towards the equal beam division prism, and the probe arm and the reference arm are arranged perpendicular to each other. The probe arm includes a probe objective, and the reference arm includes a reference objective. The equal beam division prism has a beam splitting surface, which is arranged at 45°. The distance between the beam splitting surface of the equal beam division prism and the probe objective or the reference objective is adjusted by the one-dimensional miniature linear displacement stage.

[0006] The one-dimensional micro linear displacement stage is equipped with an adjustment knob for moving the one-dimensional micro linear displacement stage in a direction away from or close to the reference arm.

[0007] The reference arm includes a reference mirror, a first fixing member, and an adjustment member. The reference mirror is fixed to the first fixing member, which is installed at the other end of the reference objective. The adjustment member includes multiple screws, which are used to adjust the distance and pitch angle of the first fixing member relative to the reference objective.

[0008] The light beam is split into two beams of equal energy by the beam splitting surface of the beam splitting prism. The first beam is reflected back to the beam splitting surface by the reference objective and the reference mirror to obtain the reference light path. The second beam is reflected back to the beam splitting surface by the probe objective and the surface of the sample to be tested to obtain the probe light path.

[0009] It also includes a mounting base, in which the equal beam division prism and the one-dimensional miniature linear displacement stage are mounted; the reference arm includes a base, one end of the reference objective lens is mounted on the base, the base and the mounting base are connected by a connector, and the angle of the reference arm relative to the probe arm can be adjusted by the connector.

[0010] The base has multiple threaded holes spaced apart, and the mounting base also has threaded holes on the side facing the base. The connector includes a set screw, which is used to fix the base and the mounting base through the threaded holes on the base and the mounting base.

[0011] The reference arm includes a housing, and the base, the housing, and the adjustment member enclose a dustproof space, within which the reference objective, the reference lens, and the fixing member are located.

[0012] A partition is provided between the reference objective and the first fixing member. An adjustment space is formed between the partition, the adjusting member, and the outer shell. The first fixing member and the reference objective are located within the adjustment space. The adjusting member is connected to the screw through an elastic connecting mechanism. One end of the elastic connecting mechanism abuts against the first fixing member, and the other end is connected to the screw. By adjusting the screw, the elastic force exerted by the elastic connecting mechanism on the first fixing member is adjusted, thereby changing the distance and pitch angle of the first fixing member relative to the reference objective.

[0013] The adjustment component has a central hole that connects to the adjustment space, through which the reference mirror can be replaced.

[0014] Compared with the prior art, the advantages of the present invention are as follows: This invention provides an interferometer objective with optical path compensation and an adjustable reference mirror. When performing white light interferometry, firstly, based on the sample being measured and the measurement requirements, a pair of matching objective lenses with suitable parameters, and a lens of suitable material and reflectivity are determined as the reference objective, detector objective, and reference mirror, respectively, and installed. The sample being measured is placed facing the detector objective. After the light source beam enters the interferometer objective, it is split into two beams of equal energy by the 45° beam-splitting surface of the equal beam-splitting prism. In this embodiment, the horizontal beam is reflected back to the 45° beam-splitting surface of the equal beam-splitting prism by the reference objective and reference mirror, thus obtaining the reference optical path; the vertical beam... A beam of light in the direction of the test is reflected back to the same beam-splitting surface by the detector objective and the surface of the sample under test, thus obtaining the detector light path. Since the reference light path and the detector light path come from the same light source, they coherently form interference fringes. Structurally, by changing the distance of the 45° beam-splitting surface of the beam-splitting prism relative to one of the objectives by a one-dimensional miniature linear displacement stage, the back focal planes of the reference objective and the detector objective are spatially symmetrical relative to the 45° beam-splitting surface, thereby achieving zero optical path difference adjustment for white light interference. The adjustment is convenient and fast. After the interference is zeroed, the one-dimensional miniature linear displacement stage adjustment mechanism is locked to ensure the stable operation of the interference objective and the optical system. Attached Figure Description

[0015] 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 of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the disassembled structure of the interference objective lens according to an embodiment of this application; Figure 2 This is a cross-sectional structural diagram of the reference arm according to an embodiment of this application; Figure 3This is a cross-sectional structural diagram of the reference arm according to an embodiment of this application.

[0017] Explanation of reference numerals in the attached figures: 1. Equal beam prism; 2. Fixing component two; 3. One-dimensional miniature linear displacement stage; 4. Mounting base; 401. Through hole; 5. Base; 501. Screw hole; 6. Housing; 7. Adjusting component; 8. Elastic connection mechanism; 9. Fixing component one; 10. Screw; 11. Probe objective; 12. Reference objective; 13. Reference mirror; 14. Reference mirror retaining ring; 15. Adjustment knob. Detailed Implementation

[0018] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0019] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0020] Furthermore, 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0022] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0023] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0024] An interferometer objective with optical path compensation and adjustable reference mirror includes an equal-splitting beam splitter 1, a one-dimensional miniature linear displacement stage 3, a probe arm, and a reference arm. The beam splitting surfaces of the equal-splitting beam splitter 1 are arranged at 45°. One end of the probe arm and one end of the reference arm are respectively arranged towards the equal-splitting beam splitter 1 and perpendicular to each other. The probe arm includes a probe objective 11, and the reference arm includes a reference objective 12 and a reference mirror 13. The light beam passes through the beam splitter and enters the probe objective 11 and the reference objective 12 respectively. The distance between the equal-splitting beam splitter 1 and the probe objective 11 or the reference objective 12 is adjusted by the one-dimensional miniature linear displacement stage 3, so that the rear surfaces of the reference objective 12 and the probe objective 11 are spatially symmetrical with respect to the beam splitter, realizing zero optical path difference adjustment of white light interference. After the interference is zeroed, the adjustment mechanism of the one-dimensional miniature linear displacement stage 3 is locked to ensure stable operation of the interferometer objective and the optical system.

[0025] When performing white light interferometry, this optical path-compensated and reference-mirror-adjustable interferometer objective lens first determines a pair of matching objective lenses with suitable parameters, as well as lenses of suitable material and reflectivity, based on the sample being measured and the measurement requirements. These are then used as the reference objective lens 12, the detector objective lens 11, and the reference mirror 13, respectively, and installed. The sample being measured is placed facing the detector objective lens 11. After the light source beam enters the interferometer objective lens, it is split into two beams of equal energy by the 45° beam-splitting surface of the equal beam-splitting prism 1. In this embodiment, the horizontal beam is reflected back to the 45° beam-splitting surface of the equal beam-splitting prism 1 by the reference objective lens 12 and the reference mirror 13, thus obtaining the reference optical path; the vertical beam... A beam of light is reflected back to the same beam-splitting surface by the detector objective 11 and the surface of the sample being tested, thus obtaining the detector light path. Since the reference light path and the detector light path come from the same light source, they coherently form interference fringes. Structurally, by changing the distance of the 45° beam-splitting surface of the beam-splitting prism relative to one of the objectives by the one-dimensional miniature linear displacement stage 3, the back focal planes of the reference objective 12 and the detector objective 11 are spatially symmetrical relative to the 45° beam-splitting surface, thereby achieving zero optical path difference adjustment for white light interference. The adjustment is convenient and fast. After the interference is zeroed, the adjustment mechanism of the one-dimensional miniature linear displacement stage 3 is locked to ensure the stable operation of the interference objective and the optical system.

[0026] In this embodiment, the interference objective includes a mounting base 4, an equal-division beam splitter 1, a fixing component 2 for fixing the equal-division beam splitter 1, and a one-dimensional miniature linear displacement stage 3, all of which are mounted in the mounting base 4. The fixing component 2 has a mounting groove, and the equal-division beam splitter 1 can be detachably fixed in the mounting groove to avoid displacement of the equal-division beam splitter 1 during white light interference measurement, which would cause errors in the adjusted zero optical path difference. The one-dimensional miniature linear displacement stage 3 has an adjustment knob 15 for moving the one-dimensional miniature linear displacement stage 3 in a direction away from or close to the reference arm. The fixing component 2 is connected to or mounted on the one-dimensional miniature linear displacement stage 3. When the one-dimensional miniature linear displacement stage 3 moves, it drives the fixing component 2 and the equal-division beam splitter 1 to move, thereby realizing the movement of the equal-division beam splitter 1 and adjusting the displacement between the beam splitter surface of the equal-division beam splitter 1 and the reference objective 12. The distance between the equal-division beam splitter 1 and the probe arm remains unchanged. Only by adjusting the distance between the equal-division beam splitter 1 and the reference objective 12, the zero optical path difference adjustment of white light interference is achieved, and the adjustment speed is faster.

[0027] In this embodiment, the mounting base 4 is provided with through holes 401 for the light beam to pass through the reference objective lens 12 and the probe objective lens 11. The light beam is split into two beams of equal energy by the 45° beam splitting surface of the beam splitting prism 1, and enters the reference objective lens 12 and the probe objective lens 11 through the two through holes 401 respectively.

[0028] In this embodiment, the reference arm includes a housing 6, a base 5, a reference objective lens 12, a reference lens 13, a fixing component 9, an adjusting component 7, and a retaining ring 14. The base 5, housing 6, and adjusting component 7 enclose a dustproof space. The reference objective lens 12, reference lens 13, and fixing component 9 are all installed in the dustproof space, making the reference arm sealed and dustproof, reducing external interference.

[0029] In this embodiment, one end of the reference objective lens 12 is mounted on the base 5. The base 5 is provided with a plurality of spaced screw holes 501. The side of the mounting base 4 facing the base 5 is also provided with corresponding screw holes 501. By adjusting the mounting positions of the base 5 and the mounting base 4, the angle of the reference arm relative to the probe arm is adjusted. After the adjustment is completed, the mounting base 4 is connected by a connector, which includes a set screw. The set screw passes through the screw holes 501 of the mounting base 4 and the base 5 respectively, and the set screw is locked to fix the base 5 and the mounting base 4, thereby ensuring the stability of the reference arm structure and preventing displacement relative to the probe objective lens 11.

[0030] The adjusting component 7 is connected to a screw 10 via an elastic connecting mechanism 8. One end of the screw 10 adjusts the distance and pitch angle between the fixing component 9 and the reference objective lens 12. In this embodiment, a partition is provided between the reference objective lens 12 and the fixing component, forming an adjustment space between the partition and the adjusting component 7. The fixing component 9 and the reference objective lens 13 are located within the adjustment space. The fixing component 9 has a mounting groove in its middle, into which the reference objective lens 13 is installed. The retaining ring 14 limits the reference objective lens 13 within the mounting groove. The inner end of the screw 10 is embedded in the adjustment space, and the elastic connecting mechanism 8 abuts against the fixing component 9. By adjusting the length of the inner end of the screw 10 embedded in the adjustment space, the distance and pitch angle between the fixing component 9 and the reference objective lens 12 are adjusted, thereby adjusting the distance and pitch angle between the reference objective lens 13 and the reference objective lens 12 to adjust the clarity and density of the interference fringes and obtain higher quality white light interference fringes.

[0031] In this embodiment, the adjustment component 7 has a central hole that connects to the adjustment space. When the reference mirror 13 needs to be replaced, the retaining ring 14 is removed from the central hole, and then the reference mirror 13 is removed. This allows for the replacement of lenses with different materials, coatings, and reflectivities, thus enabling a wider selection of reference mirrors 13 in the white light interferometry system to adapt to a wider range of test samples and measurement needs. Furthermore, this structural design ensures that the operation of replacing the reference mirror 13 does not affect other components in the reference arm, thereby not changing the adjusted optical path difference.

[0032] The optical path compensation and adjustable reference mirror interference objective of this invention fully utilize the advantages of Linnik interference objectives. Specifically, the objective lens used performs better than standard Michelson and Mirau interference objectives under the same magnification conditions, enabling the white light interferometry system to have a larger non-stitched measurement range, a larger measurable angle, or a longer non-stitched scanning range. This invention also proposes a modular design for easy installation and disassembly. The housing 6 seals the reference arm for dust protection, reducing external interference to the reference objectives 12 and 13, resulting in more accurate measurements. The adjustment mechanism in the reference arm allows for the replacement of the reference mirror, and the distance and pitch angle between the reference mirror and the reference objective are adjustable and can be locked. The adjustment mechanism of the beam splitting system, a one-dimensional miniature linear displacement stage, makes it easy to adjust and lock the zero optical path difference in white light interference. Therefore, compared to traditional Linnik interference objectives, this invention more easily obtains higher quality interference fringes. Furthermore, this invention features structural stability, easy zeroing of the optical path difference, adjustable reference mirror, high cost-effectiveness, and strong adaptability to the measurement requirements of the tested samples.

[0033] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An interference objective with adjustable optical path compensation and reference mirror, characterized in that, The device includes an equal-division beam splitter prism, a one-dimensional miniature linear displacement stage, a probe arm, and a reference arm. One end of the probe arm and one end of the reference arm are respectively arranged facing the equal-division beam splitter prism, and the probe arm and the reference arm are arranged perpendicular to each other. The probe arm includes a probe objective lens, and the reference arm includes a reference objective lens. The equal-division beam splitter prism has a beam splitting surface, which is arranged at 45°. The distance between the beam splitting surface of the equal-division beam splitter prism and the probe objective lens or the reference objective lens is adjusted by the one-dimensional miniature linear displacement stage. The reference arm includes a reference mirror, a first fixing member, and an adjustment member. The reference mirror is fixed to the first fixing member, which is installed at the other end of the reference objective. The adjustment member includes multiple screws, which are used to adjust the distance and pitch angle of the first fixing member relative to the reference objective. It also includes a mounting base, in which the equal beam division prism and the one-dimensional miniature linear displacement stage are mounted; the reference arm includes a base, one end of the reference objective lens is mounted on the base, the base and the mounting base are connected by a connector, and the angle of the reference arm relative to the probe arm can be adjusted by the connector. The reference arm includes a housing, and the base, the housing, and the adjustment component enclose a dustproof space, within which the reference objective lens, the reference lens, and the fixing component are located. A partition is provided between the reference objective and the first fixing member. An adjustment space is formed between the partition, the adjusting member, and the outer shell. The first fixing member and the reference objective are located within the adjustment space. The adjusting member is connected to the screw through an elastic connecting mechanism. One end of the elastic connecting mechanism abuts against the first fixing member, and the other end is connected to the screw. By adjusting the screw, the elastic force exerted by the elastic connecting mechanism on the first fixing member is adjusted, thereby changing the distance and pitch angle of the first fixing member relative to the reference objective.

2. The interference objective lens with adjustable optical path compensation and reference mirror according to claim 1, characterized in that, The one-dimensional micro linear displacement stage is equipped with an adjustment knob for moving the one-dimensional micro linear displacement stage in a direction away from or close to the reference arm.

3. The interference objective lens with adjustable optical path compensation and reference mirror according to claim 1, characterized in that, The light beam is split into two beams of equal energy by the beam splitting surface of the beam splitting prism. The first beam is reflected back to the beam splitting surface by the reference objective and the reference mirror to obtain the reference light path. The second beam is reflected back to the beam splitting surface by the probe objective and the surface of the sample to be tested to obtain the probe light path.

4. The interference objective lens with adjustable optical path compensation and reference mirror according to claim 1, characterized in that, The mounting base has a screw hole on the side facing the base, and the base has a plurality of screw holes arranged at intervals. The connector includes a set screw, which is used to fix the base to the mounting base through the screw holes on the base and the screw holes on the mounting base.

5. An interference objective with adjustable optical path compensation and reference mirror according to claim 1, characterized in that, The adjustment component has a central hole that connects to the adjustment space, through which the reference mirror can be replaced.

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