Large-angle heterodyne interferometry wavefront control target mirror structure and matching adjustment method

Abstract

The application discloses a large-angle heterodyne interferometric wavefront regulation target mirror structure and a matching adjustment method, and belongs to the technical field of laser interferometry. The target mirror is composed of a coaxial main mirror barrel and an adjusting sleeve. A plano-convex lens and multiple correction lenses are sequentially arranged in the main mirror barrel. A reflecting mirror is arranged in the adjusting sleeve. The axial adjustment and locking of the reflecting mirror can be realized through screw threads or sliding fit. During adjustment and assembly, an evaluation function is constructed based on the light beam center offset, residual exit angle and return light power under different incident angles and axial adjustment amounts. The optimal axial position is selected to complete adjustment and locking. The application utilizes the double-pass propagation of the lens group to suppress the light beam direction offset caused by large-angle deflection, correct optical aberration, determine the reflecting mirror assembly position through quantitative evaluation indexes, compensate for processing and assembly errors, effectively improve the stability and contrast of the interferometric signal under large-angle working conditions, and is suitable for high-precision heterodyne interferometric measurement scenes.

Description

Technical Field

[0001] This invention belongs to the field of laser interferometry technology, and particularly relates to a target mirror structure for wavefront control in large-angle heterodyne interferometry and a matching assembly method. Background Technology

[0002] Laser heterodyne interferometry boasts advantages such as high resolution, high measurement accuracy, fast response speed, and easy phase demodulation, making it widely used in precision displacement detection, attitude measurement, position feedback for ultra-precision motion platforms, and error detection for precision equipment. As precision measurement systems evolve towards higher dynamics, longer strokes, and higher integration, heterodyne interferometry devices not only require high displacement measurement accuracy but also the ability to maintain a stable return measurement beam and effective interference signal even when the measured object exhibits angular deflection, attitude disturbances, or assembly errors.

[0003] In existing heterodyne interferometry devices, the target end typically uses a common plane mirror or other reflective elements as the reflecting device for the measurement beam. This type of target reflection structure is mainly used to reflect the measurement beam back to the interferometry system. It is simple in structure, easy to install, and suitable for measurement scenarios with minimal changes in target attitude. However, when the measured object undergoes pitch, yaw, or other angular deflections during displacement, a common plane mirror will cause the propagation direction of the returned measurement beam to change significantly with the target mirror's attitude. This can easily lead to angular mismatch between the measurement beam and the reference beam, decreased spatial overlap, poor wavefront matching, and reduced interference contrast. In severe cases, it may even be difficult to maintain an effective interference signal.

[0004] In existing technologies, cat-eye retroreflective structures typically consist of a lens and a reflective surface positioned near the focal plane of the lens. They can suppress changes in the direction of the reflected light caused by angular deflection at the target end through the two-way propagation relationship between the lens and the reflective surface. However, traditional cat-eye retroreflective structures are usually used as independent retroreflective optical elements. Their design focuses on geometric retroreflective performance and the stability of the reflected direction, without considering factors such as the interference reception conditions at the target end of heterodyne interferometry, the center offset of the reflected beam, the residual emission angle, the power of the reflected light, the axial matching of the reflective surface, assembly focusing, and locking after adjustment.

[0005] For heterodyne interferometry, the target-end reflective structure not only needs to provide the returned light, but also needs to ensure that the returned measurement light returns in a propagation state suitable for interferometer reception, beam combining, and phase demodulation. If only a common plane mirror or a traditional cat's-eye retroreflective structure is used, the returned measurement light may be difficult to stably participate in the heterodyne interferometry due to factors such as incident position deviation, limited aperture, defocusing of the reflecting surface, lens aberrations, assembly errors, mirror attitude errors, or mismatch of subsequent interferometric optical paths.

[0006] Furthermore, the position of the reflecting surface in traditional cat-eye retroreflective structures is usually determined based on the geometric focal plane, empirical position, or fixed assembly dimensions, without considering the return beam center offset, residual exit angle, and return power in heterodyne interferometry as unified constraints. Even if the reflecting surface is placed near the lens focal plane, errors in lens thickness, lens barrel processing, spacer length, adhesive layer thickness, or assembly may still cause the reflecting surface to deviate from the actual optimal return position. This can increase the residual exit angle of the return beam, increase the beam center offset, or reduce the return power, thereby affecting the interference contrast and phase demodulation stability of the heterodyne interferometry signal.

[0007] Therefore, it is still necessary to propose a wavefront-controlled target mirror structure for use at the target end of heterodyne interferometry, and provide a corresponding axial matching assembly method. This structure should not only have a stable optomechanical assembly relationship between the plano-convex lens, the correction lens group, and the reflector, but also an assembly method that can determine the axial matching position of the reflector based on the heterodyne interferometry return state. Furthermore, through axial adjustment and a locking structure after adjustment, the reflector should be fixed in an axial position that meets the requirements for maintaining the return interferometry. Summary of the Invention

[0008] The purpose of this invention is to provide a target mirror structure and matching method for wavefront modulation in large-angle heterodyne interferometry, to solve the problems that ordinary target reflection structures easily cause changes in the propagation direction of the returned measurement beam when angular deflection occurs, leading to angle mismatch, wavefront mismatch, decreased interference contrast, and insufficient interference retention capability under large-angle conditions. The technical solution adopted by this invention is as follows:

[0009] The wavefront control target mirror structure for large-angle heterodyne interferometry includes a main mirror tube and an adjustment sleeve connected coaxially at the front and back. The main mirror tube contains a plano-convex lens, a fourth correction lens, a third correction lens, a second correction lens, and a first correction lens arranged sequentially from front to back. The adjustment sleeve contains a reflector.

[0010] Furthermore, the convex side of the plano-convex lens is positioned facing forward, the front end pressure ring is threadedly connected to the main lens barrel, the first ball-and-socket spacer is coaxially abutted against the inner hole positioning step of the main lens barrel, the planar side of the plano-convex lens is coaxially abutted against the first ball-and-socket spacer through the second ball-and-socket spacer, and the front end pressure ring is coaxially abutted against the convex side of the plano-convex lens through the third ball-and-socket spacer.

[0011] Furthermore, a reflective pad is provided in the stepped hole of the adjusting sleeve, and the reflective pressure ring is threadedly connected to the adjusting sleeve, pressing the reflector onto the reflective pad.

[0012] Furthermore, the rear of the main lens barrel is provided with an axial adjustment connection part, and the adjustment sleeve is threadedly connected to the axial adjustment connection part.

[0013] Furthermore, the rear of the main lens barrel is provided with an axial adjustment connection part, and the adjustment sleeve slides axially with the axial adjustment connection part, or a glue-filling groove is formed by drilling. The main lens barrel and the adjustment sleeve are fixedly connected by injecting adhesive into the glue-filling groove.

[0014] Furthermore, tool mating holes are provided on the end faces of both the reflective pressure ring and the front pressure ring.

[0015] This invention also provides a method for matching and adjusting a wavefront-controlled target mirror for large-angle heterodyne interferometry, which is based on the aforementioned structure of the wavefront-controlled target mirror for large-angle heterodyne interferometry, and includes the following steps:

[0016] Step 1: Set the incident angle set as Θ, and the axial adjustment range of the reflector as S. Under multiple axial adjustment values ​​s, obtain the center position offset and residual exit angle of the returned measurement beam at each incident angle. and return optical power;

[0017] The set of incident angles Θ is: (1) in, Let N be the i-th incident angle state, and N be the number of incident angle states; Let the axial adjustment amount of the adjusting sleeve relative to the main mirror tube be s, and the axial adjustment range of the reflecting mirror be: (2) Among them, s min s is the lower limit of the axial adjustment of the reflector. max This is the upper limit of the axial adjustment range of the reflector; Under the i-th incident angle and the axial adjustment amount s of the reflector, two detection sections with a mutual spacing of D are selected in the propagation optical path of the returning measurement beam. The center of the returning measurement beam mapped onto the first detection section is... The returning measurement beam is mapped onto the second detection section, with the beam center at [center value missing]. ,in: (3) (4) In the formula, yes x-axis coordinates yes y-axis coordinate, yes x-axis coordinates yes y-axis coordinate; Residual exit angle of the returning measurement beam Calculated using the following formula: (5) Let the ideal receiving center of the receiving area of ​​the heterodyne interferometry device be: (6) Where x0 is the x-axis coordinate of the ideal receiving center, and y0 is the y-axis coordinate of the ideal receiving center; Then the center offset of the returning measurement beam at the i-th incident angle. Calculated using the following formula: (7) Let the return power at the i-th incident angle be... The minimum permissible return optical power is P. min Then the return power constraint term Defined as: (8) Step 2: Based on the residual emission angle Calculation formula, center offset Calculation formula and return power The calculation formula for the return interference preservation evaluation function : (9) in, center offset The corresponding weighting coefficients, For the residual exit angle The corresponding weighting coefficients, For the return power constraint term The corresponding weighting coefficients, To allow for a residual exit angle reference value; The smaller the value, the greater the center offset of the returning measurement beam at that incident angle. Residual exit angle and return optical power The higher the degree to which the receiving requirements of the heterodyne interferometry device are met; Step 3: Determine the optimal axial adjustment amount The reflector is adjusted to the corresponding position through the axial adjustment connection, and the main mirror tube and the adjustment sleeve are locked. To ensure that the target mirror structure has stable return interference retention capability throughout the entire allowable incident angle range, the worst-case evaluation function is defined as follows: (10) In the formula, This is the worst-case evaluation function; The optimal axial adjustment amount of the reflector Calculated using the following formula: (11) in, It is determined when the return interference preservation evaluation function is minimized under the worst-case conditions with multiple incident angles; Let L0 be the initial axial position of the reflecting mirror relative to the plano-convex lens. Then, the final locking position of the reflecting mirror relative to the plano-convex lens is determined by the following formula: (12) Let f be the equivalent focal length formed by the plano-convex lens and the corrector lens group. Then, the defocusing amount of the final locked position of the reflecting mirror relative to the plano-convex lens relative to the equivalent focal plane is... Determined by the following formula: (13) Therefore, the axial matching position of the reflector is determined by the center offset of the returned measurement beam, the residual exit angle, and the returned light power under multiple incident angle conditions.

[0018] Furthermore, when the incident measurement beam is a Gaussian beam, let the beam radius of the incident measurement beam on the incident side of the plano-convex lens be... If the wavelength of the measured light is λ, and the equivalent focal length of the plano-convex lens and the corrective lens group is f, then the radius of the beam waist formed by the lens group near the reflecting mirror can be approximately expressed as: (14) In the formula, Pi; Waist radius w f The corresponding Rayleigh length is determined by the following formula: (15) The beam radius w at the reflecting mirror m It can be represented as: (16) Among them, w f Let z be the waist radius near the focal plane. R w is the Rayleigh length. m Let w be the beam radius at the reflector. From equations (14) to (16), it can be derived that by placing the reflector within the near-focal range characterized by Rayleigh length, the beam radius w at the reflector can be made smaller. m The state of the returning measurement beam meets the receiving requirements of the heterodyne interferometry device.

[0019] Furthermore, let the effective reflection radius of the mirror be... The maximum offset of the beam center at the reflector caused by the deflection or adjustment error of the object under test is: The effective reflection radius of the mirror satisfies the following formula: (17) Wherein, η is the spot coverage coefficient determined according to the allowable light cutoff loss, which is used to characterize the coverage multiple of the effective reflection area or effective light transmission area on the spot radius; Let the effective light transmission radius of the plano-convex lens or the corrective lens group be... The maximum offset of the beam center at the plano-convex lens is The effective light transmission radius is... Satisfy the following formula: (18) Furthermore, for a Gaussian beam, when the aperture radius is a and the beam radius is w, the proportion of optical power T passing through the aperture is expressed as: (19) Since both the incident measurement beam and the returned measurement beam pass through the plano-convex lens and the correction lens group at the target end, the power of the returned measurement beam is expressed as: (20) in, To measure the power of the incident beam, To correct the effective transmission rate of the lens group, The effective transmission rate of the reflector. Let be the reflectivity of the mirror. To measure the power of the returning beam.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs a plano-convex lens, multiple correction lenses, and a reflecting mirror to form a two-way propagation structure. The incident measurement beam, after being corrected by the plano-convex lens and correction lens group at the target end, is reflected by the reflecting mirror. The resulting returning measurement beam, similarly affected by the correction lens group and the plano-convex lens, returns to the heterodyne interferometry measuring device. This structure differs from the simple reflection operation of ordinary plane reflecting mirrors, enabling control over the propagation direction, wavefront state, and beam center position of the returning measurement beam at the target end.

[0021] 2. This invention uses a plano-convex lens as the main wavefront control element and a correction lens group as an auxiliary correction element. This not only highlights the main wavefront control role of the plano-convex lens on the incident beam, but also reduces aberrations and focus shift caused by large-angle incident and wide field of view propagation through multiple correction lenses, thereby improving the quality of the returning beam.

[0022] 3. This invention determines the axial matching position of the reflector through a return-of-focus interference retention evaluation function, avoiding the instability of the returned beam state caused by assembly based solely on geometric focal points or empirical positions. The evaluation function simultaneously considers the return beam center offset, residual emission angle, and returned light power, enabling the axial position of the reflector to be quantitatively determined according to heterodyne interferometry reception requirements.

[0023] 4. The present invention determines the axial adjustment amount of the reflector by minimizing the worst-case evaluation function under multiple incident angle conditions, so that the target mirror structure has good consistency of return interference throughout the entire allowable incident angle range.

[0024] 5. This invention allows the reflector to be axially positioned relative to the plano-convex lens and the correction lens group by adjusting the axial adjustment connection between the adjusting sleeve and the main lens barrel, so as to adjust the reflector to the axial matching position determined by the returning interference preservation evaluation function. This structure can compensate for focal position deviations caused by lens thickness, spacer length, and lens barrel processing and assembly errors.

[0025] 6. This invention uses the glue-filling groove to fix the adjusting sleeve and the main mirror barrel after adjustment, realizing an assembly method of evaluation first, adjustment then locking, which is beneficial to improving the long-term stability of the axial position of the reflector.

[0026] 7. The present invention forms a plano-convex lens fixing assembly by means of a first ball-and-socket spacer, a second ball-and-socket spacer, a third ball-and-socket spacer and a front end pressure ring, so that the plano-convex lens can be stably installed at the front end of the main lens barrel and the impact of assembly errors on optical axis coaxiality and wavefront control effect is reduced.

[0027] 8. The present invention can provide tool mating holes on the reflective pressure ring and the front pressure ring, so that the pressure ring can still be tightened, loosened and locked by external tools under space-constrained conditions, thereby improving the convenience of assembly and maintenance.

[0028] 9. The reflector pad of the present invention can adopt multiple circumferentially spaced support bosses, preferably three support bosses evenly distributed at approximately 120°, to form a stable support and improve the stability of the reflector installation position. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the device of the present invention; Figure 2 This is a schematic diagram of the reflective pressure ring structure; Figure 3 This is a schematic diagram of the propagation optical path of the incident measurement beam and the returning measurement beam before and after the object under test deflects. Figure 4 This is a flowchart of the matching and adjustment method of the present invention; Figure 5This is a simulation test diagram of the present invention.

[0030] In the diagram, 1. Adjusting sleeve, 2. Main lens barrel, 3. Reflection pressure ring, 4. Reflector, 5. Reflection pad, 6. Axial adjustment connection, 7. First correction lens, 8. Second correction lens, 9. Third correction lens, 10. Fourth correction lens, 11. First ball-and-socket spacer, 12. Second ball-and-socket spacer, 13. Plano-convex lens, 14. Third ball-and-socket spacer, 15. Front pressure ring, 16. Glue potting groove, 17. Incident measurement beam, 18. Return measurement beam, 19. Target lens optical axis, 20. Tool mating hole. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0032] The connections mentioned in this invention are divided into fixed connections and detachable connections. Fixed connections, also known as non-detachable connections, include but are not limited to conventional fixed connection methods such as folded connections, riveted connections, adhesive connections, and welded connections. Detachable connections include but are not limited to conventional disassembly methods such as bolted connections, snap-fit ​​connections, pin connections, and hinged connections. When a specific connection method is not explicitly defined, it is assumed that at least one existing connection method can be found to achieve this function, and those skilled in the art can choose according to their needs. For example, a welded connection can be chosen for fixed connections, and a bolted connection can be chosen for detachable connections.

[0033] The present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are explanations of the present invention, but the present invention is not limited to the following embodiments.

[0034] Example 1: As Figures 1-3 As shown, the large-angle heterodyne interferometry wavefront control target mirror structure includes a main mirror tube 2 and an adjustment sleeve 1 connected coaxially at the front and back. The main mirror tube 2 is provided with a plano-convex lens 13, a fourth correction lens 10, a third correction lens 9, a second correction lens 8 and a first correction lens 7 arranged sequentially from front to back. The adjustment sleeve 1 is provided with a reflector 4.

[0035] The main lens barrel 2 is the main support component of the target mirror structure, and the plano-convex lens 13 is the main element for wavefront control. The incident measurement beam 17 enters the target mirror structure from the front, and first undergoes preliminary focusing and wavefront control via the plano-convex lens 13. Subsequently, the incident measurement beam 17 passes sequentially through a correction lens group consisting of a fourth correction lens 10, a third correction lens 9, a second correction lens 8, and a first correction lens 7 for aberration correction and focus position control. After being processed by the correction lens group, the incident measurement beam 17 propagates to the reflecting mirror 4 and is reflected by the reflecting mirror 4 to form a returning measurement beam 18. The returning measurement beam 18 passes sequentially through the first correction lens 7, the second correction lens 8, the third correction lens 9, the fourth correction lens 10, and the plano-convex lens 13 before exiting the target mirror structure.

[0036] The corrective lens group is used to reduce spherical aberration, coma, astigmatism, field curvature, and focal shift of the incident measurement beam 17 after being adjusted by the plano-convex lens 13 during propagation. The optical elements in the corrective lens group can be single lenses, cemented lenses, or compound lens groups as needed. The optical elements in the corrective lens group can be fixed using positioning steps, spacers, pressure rings, retaining rings, lens frames, elastic supports, ball-and-socket spacers, adhesive layers, or combinations thereof within the main lens barrel 2. Adjacent optical elements in the corrective lens group can maintain a predetermined air gap using precision spacers or spacer sleeves to ensure that the actual assembly state matches the optical design state.

[0037] This invention is generally used in conjunction with a heterodyne interferometry device, which can emit a first reference beam and a second reference beam of different frequencies. The first reference beam is separated by a polarizing beam splitter group to form a first measurement beam and a first reference beam. The second reference beam is separated by a polarizing beam splitter group to form a second reference beam and an incident measurement beam 17. The second reference beam and the first measurement beam are coupled together after reflection and / or refraction to form a reference light signal. The returned measurement beam 18 is coupled with the first reference beam after reflection and / or refraction to form a measurement light signal. When the target mirror structure described in this invention is installed on the object under test, and the target mirror structure deflects at an angle with the object under test, the incident measurement beam 17 forms a certain incident angle with respect to the optical axis 19 of the target mirror structure. Since both the incident measurement beam 17 and the returning measurement beam 18 pass through the plano-convex lens 13 and the correction lens group, undergoing two-way propagation, the change in the exit direction of the returning measurement beam 18 caused by the angle deflection of the target mirror structure is suppressed. The returning measurement beam 18, relative to the incident measurement beam 17, exhibits more of a change in optical axis position. Therefore, the angular mismatch and wavefront mismatch between the returning measurement beam 18 and the first reference beam can be reduced, improving the interference preservation capability of the heterodyne interferometry device under large angle conditions.

[0038] Figure 3A schematic diagram of the path changes of the incident measurement beam 17 and the return measurement beam 18 when the target being measured deflects is given. The dashed line represents the initial position of the plano-convex lens 13, the correction lens group, and the reflector 4. The solid line represents the position of the plano-convex lens 13, the correction lens group, and the reflector 4 after deflection. The blue line represents the incident measurement beam 17, the return measurement beam 18, and the optical axis 19 of the target mirror before the target mirror structure deflects. The red line represents the incident measurement beam 17, the return measurement beam 18, and the optical axis 19 of the target mirror after the target mirror structure deflects. When the target mirror structure of the present invention deflects, the incident measurement beam 17 forms a certain angle with the optical axis 19 of the target mirror, but the emission path of the return measurement beam 18 remains parallel to the incident measurement beam 17. The difference is that the emission optical axis of the return measurement beam 18 after the target mirror structure deflects is offset relative to the emission optical axis of the return measurement beam 18 before the target mirror structure deflects.

[0039] The convex side of the plano-convex lens 13 faces forward, and the front end pressure ring 15 is threadedly connected to the main lens barrel 2. The first ball-and-socket spacer 11 is coaxially abutted against the inner hole positioning step of the main lens barrel 2. The planar side of the plano-convex lens 13 is coaxially abutted against the first ball-and-socket spacer 11 through the second ball-and-socket spacer 12. The front end pressure ring 15 is coaxially abutted against the convex side of the plano-convex lens 13 through the third ball-and-socket spacer 14. The first ball-and-socket spacer 11 and the second ball-and-socket spacer 12 cooperate to form a ball-and-socket support structure for the plano-convex lens 13.

[0040] A reflective pad 5 is provided in the stepped hole of the adjusting sleeve 1. The reflective pressure ring 3 is threadedly connected to the adjusting sleeve 1. The reflective pressure ring 3 presses the reflector 4 onto the reflective pad 5. The reflective pad 5 provides support and positioning reference for the reflector 4. The reflective pad 5 can be a continuous annular boss or a boss composed of multiple local protrusions. In this embodiment, the reflective pad 5 is preferably composed of three circumferentially spaced protrusions to form a stable three-point support structure.

[0041] The rear of the main lens barrel 2 is provided with an axial adjustment connection part 6, and the adjustment sleeve 1 is threadedly connected to the axial adjustment connection part 6. By changing the thread engagement depth between the adjustment sleeve 1 and the axial adjustment connection part 6, the adjustment sleeve 1 and the main lens barrel 2 are made to form an axially adjustable connection relationship through the axial adjustment connection part 6, so that the reflecting mirror 4 can move back and forth along the optical axis 19 of the target mirror, thereby adjusting the axial relative position between the reflecting mirror 4, the plano-convex lens 13, and the correction lens group. Thus, the reflecting mirror 4 can be adjusted to the focal point, near-focal surface, or axially matched position determined by the returning interference retention evaluation function of the correction lens group structure.

[0042] Both the reflective pressure ring 3 and the front pressure ring 15 have tool mating holes 20 on their end faces. The tool mating holes 20 are used for inserting external tools to loosen or tighten the reflective pressure ring 3 or the front pressure ring 15. In this embodiment, the tool mating holes 20 are two blind holes symmetrical about the axis of the reflective pressure ring 3 or the front pressure ring 15, so as to cooperate with a double pin wrench or other special tools.

[0043] Example 2: This embodiment describes another method for adjusting the reflector 4, in conjunction with Example 1. The difference from Example 1 is that the rear of the main mirror barrel 2 is provided with an axial adjustment connection part 6. The adjustment sleeve 1 and the axial adjustment connection part 6 are axially slidably engaged. During assembly, the reflector 4 can be adjusted to a predetermined axial position by adjusting the insertion depth of the adjustment sleeve 1 and the main mirror barrel 2, thereby adjusting the axial relative position between the reflector 4, the plano-convex lens 13, and the correction lens group. Alternatively, a glue-filling groove 16 can be drilled to form a glue-filling hole. The main mirror barrel 2 and the adjustment sleeve 1 are fixedly connected by injecting adhesive into the glue-filling groove 16. After the reflector 4 is adjusted to the axial matching position determined by the return interference retention evaluation function, a glue-filling groove 16 is drilled on the side wall of the mating part of the axial adjustment connection part 6 and the adjustment sleeve 1. By injecting adhesive into the glue-filling groove 16, a fixed connection is formed between the adjustment sleeve 1 and the main mirror barrel 2. Therefore, the position of the reflector 4 can be locked after adjustment, preventing the reflector 4 from undergoing axial displacement relative to the plano-convex lens 13 and the correction lens group during the measurement process.

[0044] Example 3: Figures 1-5 As shown, the method for matching and adjusting the target mirror for large-angle heterodyne interferometry wavefront control is based on the large-angle heterodyne interferometry wavefront control target mirror structure described in Example 1 or Example 2, and includes the following steps: Step 1: Set the incident angle set as Θ, and the axial adjustment range of the reflector 4 as S. Under multiple axial adjustment values ​​s, obtain the center position offset and residual exit angle of the return measurement beam 18 at each incident angle. and return optical power; The set of incident angles Θ is: (1) in, Let N be the i-th incident angle state, and N be the number of incident angle states; Let the axial adjustment amount of the adjusting sleeve 1 relative to the main mirror tube 2 be s, and the axial adjustment range of the reflecting mirror 4 be: (2) Among them, s min The lower limit of the 4-axis adjustment range of the reflector, s max This is the upper limit of the 4-axis adjustment range of the reflector; Under the i-th incident angle and the axial adjustment s of the reflector 4, two detection sections with a mutual spacing of D are selected in the propagation optical path of the returning measurement beam 18. The beam center of the returning measurement beam 18 mapped onto the first detection section is... The return measurement beam 18 is mapped onto the second detection section, with the beam center being... ,in: (3) (4) In the formula, yes x-axis coordinates yes y-axis coordinate, yes x-axis coordinates yes y-axis coordinate; The residual exit angle of the return measurement beam 18 Calculated using the following formula: (5) Let the ideal receiving center of the receiving area of ​​the heterodyne interferometry device be: (6) Where x0 is the x-axis coordinate of the ideal receiving center, and y0 is the y-axis coordinate of the ideal receiving center; The center offset of the returned measurement beam 18 under the i-th incident angle state Calculated using the following formula: (7) Let the return power at the i-th incident angle be... The minimum permissible return optical power is P. min Then the return power constraint term Defined as: (8) Step 2: Based on the residual emission angle Calculation formula, center offset Calculation formula and return power The calculation formula for the return interference preservation evaluation function : (9) in, center offset The corresponding weighting coefficients, For the residual exit angle The corresponding weighting coefficients, For the return power constraint term The corresponding weighting coefficients, To allow for a residual exit angle reference value; The smaller the value, the greater the center offset of the returning measurement beam 18 at that incident angle. Residual exit angle and return optical power The higher the degree to which the receiving requirements of the heterodyne interferometry device are met; Step 3: Determine the optimal axial adjustment amount The reflector 4 is adjusted to the corresponding position by means of the axial adjustment connection part 6, and the main mirror tube 2 and the adjustment sleeve 1 are locked. To ensure that the target mirror structure has stable return interference retention capability throughout the entire allowable incident angle range, the worst-case evaluation function is defined as follows: (10) In the formula, This is the worst-case evaluation function; The optimal axial adjustment amount of mirror 4 Calculated using the following formula: (11) in, It is determined when the return interference preservation evaluation function is minimized under the worst-case conditions with multiple incident angles; Let the initial axial position of the reflector 4 relative to the plano-convex lens 13 be L0, then the final locking position of the reflector 4 relative to the plano-convex lens 13 is determined by the following formula: (12) Let f be the equivalent focal length formed by the plano-convex lens 13 and the corrective lens group. Then, the defocusing amount of the final locked position of the reflecting mirror 4 relative to the plano-convex lens 13 relative to the equivalent focal plane is... Determined by the following formula: (13) Therefore, the axial matching position of the reflector 4 is not fixed solely based on the geometric focal plane or empirical position, but is determined jointly based on the center offset of the returned measurement beam 18, the residual exit angle, and the returned light power under multiple incident angle conditions.

[0045] When the incident measurement beam 17 is a Gaussian beam, let the beam radius of the incident measurement beam 17 on the incident side of the plano-convex lens 13 be... If the wavelength of the measured light is λ, and the equivalent focal length of the plano-convex lens 13 and the correction lens group is f, then the radius of the beam waist formed by the lens group near the reflecting mirror 4 can be approximately expressed as: (14) In the formula, π is the ratio of pi to circumference. Waist radius w f The corresponding Rayleigh length is determined by the following formula: (15) The beam radius w at mirror 4 m It can be represented as: (16) Among them, w f Let z be the waist radius near the focal plane. R w is the Rayleigh length. m Let w be the beam radius at mirror 4. From equations (14) to (16), it can be derived that by placing mirror 4 within the near-focal range characterized by Rayleigh length, the beam radius w at mirror 4 can be made smaller. m The state of the return measurement beam 18 meets the receiving requirements of the heterodyne interferometry device.

[0046] Let the effective reflection radius of mirror 4 be a. m The maximum offset of the beam center at point 4 of the reflector caused by the deflection or adjustment error of the object under test is Δ. m Then the effective reflection radius of mirror 4 satisfies the following formula: (17) Wherein, η is the spot coverage coefficient determined according to the allowable light cutoff loss, which is used to characterize the coverage multiple of the effective reflection area or effective light transmission area on the spot radius; Let the effective light transmission radius of the plano-convex lens 13 or the corrective lens group be... The maximum offset of the beam center at point 13 of the plano-convex lens is The effective light transmission radius is... Satisfy the following formula: (18) For a Gaussian beam, when the aperture radius is a and the beam radius is w, the proportion of optical power T passing through the aperture is expressed as: (19) Since both the incident measurement beam 17 and the returned measurement beam 18 pass through the plano-convex lens 13 and the correction lens group at the target end, the power of the returned measurement beam 18 is expressed as: (20) in, To measure the power of incident beam 17, To correct the effective transmission rate of the lens group, The effective transmission rate of reflector 4. The reflectivity of mirror 4 is... The power of the returned measurement beam 18. Since the transmittance of the incident measurement beam 17 and the returned measurement beam 18 differs when passing through the correction lens group, it can also be expressed using the transmittance of the first lens and the transmittance of the second lens, respectively. This is a simplified representation when the two are approximately equal.

[0047] To verify the engineering feasibility of the wavefront-controlled target mirror structure described in this invention, a simulation design was performed on a large-angle return optical path in the visible light band. The design conditions included: the diameter of the incident measurement beam 17 was approximately 2 mm, and the incident angle range was 0°. ° Up to 4 ° The purpose is to ensure that the incident measurement beam 17 at different incident angles returns approximately along the original optical path after passing through the plano-convex lens 13, the correction lens group, and the reflector 4.

[0048] Simulation results show that when the field of view is no greater than 8... ° Under the design condition that the beam diameter is no greater than 4 mm, the target mirror structure of this invention can achieve effective return control of large-angle incident beams. Under specific parameters, the total length of the target mirror structure is approximately 50 mm, and the equivalent focal length is approximately 15.8 mm. ° The collimation of the 18-beam returning to the view within the field of view is approximately 0.36 mrad, which is close to the diffraction limit. Under normal tolerance conditions, the target mirror structure still has the optical performance to meet the requirements of retrace control.

[0049] The above design example is only used to illustrate one feasible implementation of the present invention and does not limit the present invention to using the specific field of view, beam diameter, number of lenses, target mirror structure length, focal length, collimation, or tolerance analysis results described above. Based on the operating wavelength, beam size, allowable incident angle range, receiving range, and assembly conditions of different heterodyne interferometry devices, the structural parameters between the plano-convex lens 13, the correction lens group, and the reflecting mirror 4 can be adjusted accordingly.

[0050] The wavefront-controlled target mirror structure described in this embodiment can be used as an independent optical target mirror module. During use, the main mirror barrel 2, adjusting sleeve 1, or their external structures can be fixed to the object being measured, moving parts, or external carrier using external clamps, adapters, pressure plates, adhesives, threaded connections, or other fixing methods, depending on the actual measurement conditions. This invention does not limit the specific clamping method, installation direction, or usage posture of the target mirror structure; as long as the incident measurement beam 17 can enter from the plano-convex lens 13 side, pass through the plano-convex lens 13 and the correction lens group to reach the reflecting mirror 4, and be reflected back by the reflecting mirror 4 to the heterodyne interferometry measuring device to form an effective interference signal, the target end return measurement function can be realized.

[0051] The above embodiments are merely illustrative examples of the present invention and do not limit its scope of protection. Those skilled in the art can make partial changes to them, as long as they do not exceed the spirit and essence of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for matching and adjusting a target mirror for wavefront control in large-angle heterodyne interferometry is based on a target mirror structure for wavefront control in large-angle heterodyne interferometry. The target mirror structure includes a main mirror tube (2) and an adjustment sleeve (1) connected coaxially at the front and back. The main mirror tube (2) is provided with a plano-convex lens (13), a fourth correction lens (10), a third correction lens (9), a second correction lens (8), and a first correction lens (7) in sequence from front to back. The adjustment sleeve (1) is provided with a reflector (4). The rear part of the main mirror tube (2) is provided with an axial adjustment connection part (6). Its features are, The matching and adjustment method includes the following steps: Step 1: Set the incident angle set as Θ, and the axial adjustment range of the reflector (4) as S. Under multiple axial adjustment values ​​s, obtain the center position offset and residual exit angle β of the return measurement beam (18) under each incident angle state. i (s) and return optical power; The set of incident angles Θ is: θ=θ1,θ2,……,θ N ;(1) Where, θ i Let N be the i-th incident angle state, and N be the number of incident angle states; Let the axial adjustment amount of the adjusting sleeve (1) relative to the main mirror tube (2) be s, and the axial adjustment range of the reflecting mirror (4) be: ；(2) Among them, s min s is the lower limit of the axial adjustment of the reflector (4). max This is the upper limit of the axial adjustment of the reflector (4); Under the i-th incident angle and the axial adjustment amount s of the reflector (4), two detection sections with a mutual spacing of D are selected in the propagation optical path of the return measurement beam (18). The beam center of the return measurement beam (18) mapped onto the first detection section is C. 1,i (s), the return measurement beam (18) is mapped onto the second detection section with the beam center at C. 2,i (s), where: ；(3) ；(4) In the formula, x 1,i (s) is C 1,i x-axis coordinate of (s), y 1,i (s) is C 1,i The y-coordinate of (s), x 2,i (s) is C 2,i x-axis coordinate of (s), y 2,i (s) is C 2,i The y-axis coordinate of (s); The residual exit angle β of the returned measurement beam (18) i (s) is calculated using the following formula: ；(5) Let the ideal receiving center of the receiving area of ​​the heterodyne interferometry device be: C0=(x0,y0); (6) Where x0 is the x-axis coordinate of the ideal receiving center, and y0 is the y-axis coordinate of the ideal receiving center; Then the center offset Δ of the returned measurement beam (18) under the i-th incident angle state i (s) is calculated using the following formula: ；(7) Let P be the reflected light power at the i-th incident angle. i (s), the minimum permissible return optical power is P min Then the return optical power constraint term Q i (s) is defined as: ；(8) Step 2: Based on the residual emission angle β i The formula for calculating (s), and the center offset Δ i The formula for calculating (s) and the return optical power P i The formula for calculating (s) is used to calculate the evaluation function Λ of the return interference preservation function. i (s): ；(9) Where, ω Δ Center offset Δ i The weighting coefficients corresponding to (s), ω β The residual exit angle β i The weighting coefficients corresponding to (s), ω P For the return optical power constraint term Q i (s) corresponds to the weighting coefficient, and β0 is the allowable residual emission angle reference value; Λ i The smaller (s) is, the greater the center offset Δ of the returning measurement beam (18) at that incident angle. i (s), residual emission angle β i (s) and return optical power P i (s) The higher the degree to which the receiving requirements of the heterodyne interferometry measurement device are met; Step 3: Determine the optimal axial adjustment amount s * The mirror (4) is adjusted to the corresponding position by means of the axial adjustment connection (6), and the main mirror tube (2) and the adjustment sleeve (1) are locked. To ensure that the target mirror structure has stable return interference retention capability throughout the entire allowable incident angle range, the worst-case evaluation function is defined as follows: ；(10) In the formula, Λ max (s) is the worst-case evaluation function; The optimal axial adjustment amount s of the reflector (4) * Calculated using the following formula: ；(11) Among them, s * It is determined when the return interference preservation evaluation function is minimized under the worst-case conditions with multiple incident angles; Let the initial axial position of the reflector (4) relative to the plano-convex lens (13) be L0, then the final locking position of the reflector (4) relative to the plano-convex lens (13) is determined by the following formula: ；(12) Let f be the equivalent focal length formed by the plano-convex lens (13) and the corrector lens group. Then the defocusing amount δ of the final locked position of the reflecting mirror (4) relative to the plano-convex lens (13) relative to the equivalent focal plane is... * Determined by the following formula: ；(13) Therefore, the axial matching position of the reflector (4) is determined by the center offset of the return measurement beam (18) under multiple incident angle conditions, the residual exit angle and the return light power.

2. The method for matching and adjusting the target mirror of wavefront-controlled large-angle heterodyne interferometry according to claim 1, characterized in that: The plano-convex lens (13) is set with its convex side facing forward. The front end pressure ring (15) is threadedly connected to the main lens barrel (2). The first ball-and-socket spacer (11) is coaxially abutted against the inner hole positioning step of the main lens barrel (2). The planar side of the plano-convex lens (13) is coaxially abutted against the first ball-and-socket spacer (11) through the second ball-and-socket spacer (12). The front end pressure ring (15) is coaxially abutted against the convex side of the plano-convex lens (13) through the third ball-and-socket spacer (14).

3. The method for matching and adjusting the target mirror of wavefront-controlled large-angle heterodyne interferometry according to claim 2, characterized in that: The stepped hole of the adjusting sleeve (1) is provided with a reflective pad (5), and the reflective pressure ring (3) is threadedly connected to the adjusting sleeve (1). The reflective pressure ring (3) presses the reflector (4) onto the reflective pad (5).

4. The method for matching and adjusting the target mirror of wavefront-controlled large-angle heterodyne interferometry according to claim 3, characterized in that: The adjusting sleeve (1) is threadedly connected to the axial adjusting connection (6).

5. The method for matching and adjusting the target mirror of wavefront-controlled large-angle heterodyne interferometry according to claim 3, characterized in that: The adjusting sleeve (1) and the axial adjusting connection (6) are axially slidingly fitted, or a glue-filling groove (16) is formed by drilling. The main lens tube (2) and the adjusting sleeve (1) are fixedly connected by injecting adhesive into the glue-filling groove (16).

6. The method for matching and adjusting the target mirror of wavefront control in large-angle heterodyne interferometry according to claim 4 or 5, characterized in that: Tool fitting holes (20) are provided on the end faces of both the reflective pressure ring (3) and the front pressure ring (15).

7. The method for matching and adjusting a target mirror in large-angle heterodyne interferometry wavefront control according to claim 1, characterized in that: When the incident measurement beam (17) is a Gaussian beam, let the beam radius of the incident measurement beam (17) on the incident side of the plano-convex lens (13) be w. i If the wavelength of the measured light is λ, and the equivalent focal length of the plano-convex lens (13) and the correction lens group is f, then the radius of the waist formed by the lens group near the reflecting mirror (4) can be approximately expressed as: ； (14) In the formula, π is the ratio of pi to circumference. Waist radius w f The corresponding Rayleigh length is determined by the following formula: ；(15) The beam radius w at the reflector (4) m It can be represented as: ；(16) Among them, w f Let z be the waist radius near the focal plane. R w is the Rayleigh length. m Let w be the beam radius at the reflector (4). From equations (14) to (16), it can be deduced that by placing the reflector (4) within the near-focal range characterized by Rayleigh length, the beam radius w at the reflector (4) can be made smaller. m The state of the return measurement beam (18) meets the receiving requirements of the heterodyne interferometer.

8. The method for matching and adjusting a target mirror with wavefront control in large-angle heterodyne interferometry according to claim 7, characterized in that: Let the effective reflection radius of the mirror (4) be a. m The maximum offset of the beam center at the reflector (4) caused by the deflection or adjustment error of the object under test is Δ. m Then the effective reflection radius of the reflector (4) satisfies the following formula: ；(17) Wherein, η is the spot coverage coefficient determined according to the allowable light cutoff loss, which is used to characterize the coverage multiple of the effective reflection area or effective light transmission area on the spot radius; Let the effective light transmission radius of the plano-convex lens (13) or the corrective lens group be a. l The maximum offset of the beam center at the plano-convex lens (13) is Δ l Then the effective light transmission radius a l Satisfy the following formula: (18)。 9. The method for matching and adjusting a target mirror in large-angle heterodyne interferometry wavefront control according to claim 1, characterized in that: For a Gaussian beam, when the aperture radius is a and the beam radius is w, the proportion of optical power T passing through the aperture is expressed as: ；(19) Since both the incident measurement beam (17) and the returning measurement beam (18) pass through the plano-convex lens (13) and the correction lens group at the target end, the power of the returning measurement beam (18) is expressed as: ； (20) Where P0 is the power of the incident measurement beam (17), and T l To correct the effective transmission rate of the lens group, T m R is the effective transmittance of the reflector (4). m P is the reflectivity of mirror (4). r The power of the return measurement beam (18) is used.

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