Two-dimensional white light microscopic stitching interferometry apparatus and method

Abstract

The application discloses a two-dimensional white light microscopic splicing interferometer measuring device and method, and belongs to the technical field of precise optical detection. The device comprises a base platform, vertical motion tables arranged on both sides of the base platform, a non-Schlieren interferometer and a white light profiler respectively carried by the vertical motion tables, an X-direction linear guide rail, and a large-scale rotary table assembly and a small-scale rotary table assembly arranged on the X-direction linear guide rail. The method uses the white light profiler and the non-Schlieren interferometer in cooperation, acquires the relative angle difference between sub-apertures in real time, adopts a dynamic angle compensation mechanism, and combines a specific splicing algorithm to realize high-precision fusion of surface shape data. The application effectively solves the angle error accumulation problem in sub-aperture splicing measurement of a small curvature radius curved mirror, realizes sub-nanometer level surface shape measurement precision, and is particularly suitable for high-precision detection of an X-ray curved mirror.

Description

Technical Field

[0001] This invention belongs to the field of precision optical detection technology, specifically relating to a two-dimensional white light microscopic splicing interferometry device and method for X-ray curved surface mirrors with small radius of curvature. Background Technology

[0002] The rapid development of fourth-generation synchrotron radiation sources has placed unprecedented demands on the surface accuracy of X-ray mirrors, requiring sub-nanometer-level surface shape error and nanoradian-level slope error control. With the advancement of optical systems, the length of mirrors has increased to nearly meters, while the radius of curvature has decreased to below 10 meters. This extreme trend in size and curvature presents a severe challenge to traditional detection methods. Currently, laboratories, such as the European Synchrotron Radiation Facility, primarily use Fizeau interferometers for sub-aperture stitching measurements. While this can meet the detection requirements of long planar mirrors, when dealing with curved mirrors with small radii of curvature, the effective interference area is significantly reduced due to the strong curvature, making backlash error and angular accumulation error problems particularly prominent during the measurement process.

[0003] Existing research indicates that even with advanced methods such as relative angle deterministic stitching interferometry and micro-stitching interferometry, when the radius of curvature decreases to within the 10-meter range, the number of sub-apertures increases dramatically, leading to an exponential amplification of errors. This results in measurement repeatability dropping to the 0.5 nm RMS level, making it difficult to consistently achieve sub-nanometer precision. The white-light microspatial stitching scheme proposed by SPring-8 in Japan and Brookhaven National Laboratory in the United States, which introduces auxiliary plane mirrors to record sub-aperture tilt, improves stitching accuracy to some extent, but the final surface shape measurement accuracy remains limited to the 0.3–0.5 nm RMS range. Furthermore, the longitudinal accuracy of traditional Fizeau interferometers is limited by the absolute accuracy of the reference surface and long-path air disturbances, while the lateral spatial resolution is also constrained by the interference optical path structure, typically only reaching the tens of micrometers level, failing to meet the increasingly demanding detection requirements.

[0004] The white-light vertical scanning interferometer, with its narrow coherence gate characteristic, generates interference signals only near zero optical path difference, effectively suppressing errors caused by multiple reflections and long-distance air disturbances, and controlling random noise below 0.1 nm RMS, resulting in higher surface shape measurement accuracy and resolution. Simultaneously, the white-light profilometer supports both phase-shifting interferometry and vertical scanning interferometry, applicable to continuous smooth surfaces and surfaces with discontinuous step structures, respectively. Combined with four-step phase shifting and envelope peak extraction algorithms, it can achieve high-confidence rapid assessment of sub-nanometer surface shape errors. However, using the white-light profilometer alone cannot solve the problem of angular error accumulation during the aperture splicing process of large-size curved mirrors, which has become a major technical bottleneck restricting the high-precision inspection of small radius-of-curvature X-ray mirrors.

[0005] Therefore, developing a white light microscopic stitching interferometry technique that can effectively suppress the accumulation of angular errors and has both high spatial resolution and high measurement accuracy has become a key technical problem that urgently needs to be solved in the field of precision inspection of small radius of curvature X-ray mirrors. Summary of the Invention

[0006] The technical problem to be solved by this invention is: how to effectively suppress the accumulation of angle error and achieve sub-nanometer-level surface shape measurement accuracy in the sub-aperture splicing measurement of small radius curvature surface mirrors.

[0007] In order to achieve the above objectives:

[0008] In a first aspect, the present invention provides a two-dimensional white light microscopic splicing interferometry device, comprising:

[0009] Base platform;

[0010] The first vertical motion stage and the second vertical motion stage are respectively disposed on both sides of the base platform;

[0011] The Fiso interferometer, set on the first vertical motion stage, is used to acquire interference fringe data of the planar reference mirror;

[0012] A white light profilometer, set on the second vertical motion stage, is used to acquire sub-aperture surface shape data of the curved surface mirror to be tested;

[0013] An X-direction linear guide rail is disposed on the base platform and located between the first vertical motion table and the second vertical motion table;

[0014] A large turntable assembly is mounted on the linear guide rail in the X direction. The large turntable assembly is used to support the curved surface mirror to be tested and the planar reference mirror and drive the two to rotate and adjust synchronously.

[0015] A small turntable assembly is disposed on the large turntable assembly. The small turntable assembly is used to support the planar reference mirror and drive the planar reference mirror to rotate and adjust independently relative to the large turntable assembly.

[0016] The surface mirror to be tested is fixedly mounted on the large turntable assembly and located below the field of view of the white light profilometer; the small turntable assembly is located on the side of the large turntable assembly closer to the Fizeau interferometer, and the planar reference mirror is located in front of the field of view of the Fizeau interferometer.

[0017] As an optional implementation, the large turntable assembly includes:

[0018] First large turntable and second large turntable;

[0019] The second large turntable is fixedly mounted on the linear guide rail in the X direction to realize rotational motion around the Z axis.

[0020] The first large turntable is stacked on top of the second large turntable to realize rotational movement around the X-axis;

[0021] Both the curved reflector to be tested and the small turntable assembly are mounted on the first large turntable.

[0022] As an optional implementation, the small turntable assembly includes:

[0023] First small turntable and second small turntable;

[0024] The second small turntable is fixedly mounted on the large turntable assembly;

[0025] The first small turntable is stacked on top of the second small turntable;

[0026] The planar reference mirror is fixedly mounted on the first small turntable;

[0027] The first and second miniature turntables are configured to provide independent angle adjustments about the X-axis and Z-axis, respectively.

[0028] As an optional implementation, the X-direction linear guide is driven by an air-bearing guide and a linear motor, with a stroke configuration of 1200mm;

[0029] The first large turntable, the second large turntable, the first small turntable, and the second small turntable are all equipped with position feedback devices to achieve closed-loop control.

[0030] In a second aspect, the present invention also provides a two-dimensional white light microscopic splicing interferometry method using the apparatus described in the first aspect, comprising the following steps:

[0031] S1. Adjust the orientation of the surface mirror to be tested using the large turntable assembly so that it displays zero stripes in the white light profilometer;

[0032] S2. Adjust the orientation of the planar reference mirror (4) using the small turntable assembly so that it displays zero fringes in the Fizeau interferometer;

[0033] S3. Control the white light profilometer to acquire the surface shape data of the sub-aperture at the current position. And control the Fiso interferometer to acquire the current angle data of the plane reference mirror;

[0034] S4: Control the large turntable assembly to move along the linear guide rail in the X direction to the next sub-aperture position, and adjust the angle of the large turntable assembly so that the next sub-aperture area reappears as zero stripes in the white light profilometer;

[0035] S5: Based on the angle change of the planar reference mirror before and after the movement measured by the Fiso interferometer (1), determine the relative angle difference between the sub-apertures of the surface mirror to be tested;

[0036] S6: Repeat steps S3 to S5 until all sub-aperture data are collected, and then stitch and fuse them based on the relative angle difference.

[0037] As an optional implementation, a reference mirror range reset step is further included between steps S4 and S5:

[0038] Real-time monitoring of the deflection angle of the planar reference mirror relative to the Fizzo interferometer;

[0039] When the deflection angle exceeds a preset threshold, the small turntable assembly is controlled to drive the planar reference mirror to rotate in the opposite direction, so that it returns to the vicinity of the measurement zero position of the Fiso interferometer, and the angle compensation value of the reverse rotation is recorded.

[0040] As an optional implementation, the preset threshold is set to 1×102 -4 rad, the angle of the reverse rotation is set to 2×10 -4 rad.

[0041] As an optional implementation, in step S6, the first splicing data of individual apertures Calculated using the following formula:

[0042] ;

[0043] in, This is the sequence number of the sub-aperture to be spliced;

[0044] The coordinates are the positions in the coordinate system of the adjacent reference sub-apertures;

[0045] For the first The aperture in coordinates Adjusted height data at the location;

[0046] For the first Initial height data function for each aperture;

[0047] and The first The slope adjustment coefficients of the individual aperture in the X and Y directions, the slope adjustment coefficients and The result is calculated based on the relative angle difference determined in step S5;

[0048] For the first Adjustment amount of individual aperture in the height direction;

[0049] and The first The required positional adjustments of each aperture relative to the reference coordinate system in the X and Y directions.

[0050] As an optional implementation, the height adjustment amount Calculated using the least squares method, it satisfies the following minimization condition:

[0051] ;

[0052] in, In order to be with the first The sub-aperture numbers that are adjacent to each other and serve as a reference;

[0053] For the first The aperture in coordinates Height data at the location;

[0054] This indicates the search for a function that minimizes the sum of the squares mentioned above.

[0055] As an optional implementation, the white light profilometer adopts a vertical scanning interference mode, and the stitching and fusion adopts a weighted fusion algorithm based on pixel position.

[0056] This invention uses a Fizeau interferometer to monitor the angle changes of a planar reference mirror in real time, directly obtaining the relative angle difference between sub-apertures. This fundamentally avoids the error accumulation problem caused by traditional methods that calculate angles through overlapping areas. Furthermore, a dynamic angle compensation mechanism is introduced. When the planar reference mirror deflects beyond a preset threshold, it automatically reverses the adjustment, ensuring that the measurement process remains within the instrument's effective range, significantly improving measurement stability and reliability. By directly substituting the measured angle difference into the slope adjustment coefficient calculation of the stitching algorithm, not only is the data processing flow simplified, but more importantly, the stitching accuracy is greatly improved, making sub-nanometer-level surface shape measurement of small-radius X-ray curved mirrors possible. Combined with the nanometer-level positioning and micro-radius-level angle adjustment capabilities provided by a high-precision motion control platform, as well as the height adjustment and weighted fusion algorithm optimized based on the least squares method, measurement repeatability better than 0.5 nm RMS is ultimately achieved. In addition, this invention supports high-precision detection of various complex surfaces such as hyperboloids and tori, breaking through the limitations of traditional methods in terms of application scope and providing reliable technical support for the precision manufacturing and testing of synchrotron radiation optical components. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0058] Figure 1 This is a simplified structural diagram of the two-dimensional white light microscopic splicing interferometry device of the present invention;

[0059] Figure 2 This is a schematic diagram of the assembly structure of the two-dimensional white light microscopic splicing interferometry device of the present invention;

[0060] Figure 3 This is a schematic diagram illustrating the splicing detection using a white light profilometer according to the present invention;

[0061] In the figure: 1. Fiso interferometer; 2. White light profilometer; 3-1. First vertical motion stage; 3-2. Second vertical motion stage; 4. Plane reference mirror; 5. Mirror reflecting the surface to be tested; 6-1. First small turntable; 6-2. Second small turntable; 7-1. First large turntable; 7-2. Second large turntable; 8. Linear guide rail in the X direction; 9. Base platform; 10. Air-bearing vibration isolation bracket. Detailed Implementation

[0062] Example 1:

[0063] like Figure 1 and Figure 2As shown, this embodiment provides a two-dimensional white light microscopic splicing interferometry device specifically for small radius of curvature X-ray curved surface mirror 5. This device is a highly integrated precision optical-mechanical system. Its core design lies in achieving the coordinated operation of the white light profilometer 2 and the Fiso interferometer 1 through specific mechanical layout and motion planning, and ensuring that there is a precise and knowable relative motion relationship between the mirror under test and the reference mirror.

[0064] The entire device is built on a marble base platform 9, which serves as the basic support structure. This platform material possesses excellent thermal and mechanical stability. It is isolated from the ground by four air-bearing vibration isolation supports 10. These supports effectively attenuate low-frequency and high-frequency vibrations from the ground, providing a near-ideal static measurement environment for the entire measurement system. On the upper surface of the base platform 9, an X-direction linear guide rail 8, constituting the core motion axis of the device, is precisely installed. This X-direction linear guide rail 8 is a key component for long-range scanning of the mirror under test. Its specific structure can refer to the mature air-bearing guide rail and linear motor combination scheme in existing technology. This scheme provides frictionless, highly stable linear motion. Its stroke is configured to 1200mm to meet the inspection requirements of meter-long reflectors 5. Closed-loop control is achieved through a high-precision grating ruler, ensuring a straightness better than 5μm throughout the entire stroke, a repeatability accuracy of ±0.5μm, and pitch and yaw errors suppressed within ±0.8μrad. These indicators lay a solid foundation for the subsequent precise stepping positioning of the sub-apertures.

[0065] On the base platform 9, a first vertical motion stage 3-1 and a second vertical motion stage 3-2 are fixedly installed side by side on both sides of the X-direction linear guide rail 8. These two vertical motion stages constitute the Z-axis adjustment mechanism of the device. The top of the first vertical motion stage 3-1 supports the Fizeau interferometer 1, while the top of the second vertical motion stage 3-2 supports the white light profilometer 2. The two motion stages are jointly responsible for adjusting the vertical height of the optical instruments above them to accurately align with their respective target mirror surfaces. These two vertical motion stages themselves can be high-precision electric displacement stages in the prior art, with a resolution better than 50nm and a repeatability accuracy of less than 1μm, which can meet the requirements of initial focusing and coarse positioning in the height direction. The white light profilometer 2, as the principal surface shape measurement sensor, preferably adopts the vertical scanning interferometry mode, which effectively suppresses environmental disturbances by utilizing its narrow coherence gate characteristics, and its vertical resolution can reach the sub-nanometer level. The Fizeau interferometer 1, as the angle change monitoring sensor, functions to accurately capture the minute deflection of the plane reference mirror 4.

[0066] Supported on the slide of the X-direction linear guide 8 is a complex multi-degree-of-freedom attitude adjustment platform system, namely a large turntable assembly. This assembly is the key link connecting the motion axis and the workpiece under test. Specifically, a second large turntable 7-2, serving as the underlying rotary mechanism, is directly fixed to the slide of the X-direction linear guide 8 via its base. This turntable provides rotational motion around the Z-axis, which is perpendicular to the horizontal plane. Its technical implementation can refer to the existing technology of using an air-bearing turntable with an arc motor. This design achieves extremely low friction and extremely high rotational accuracy, with a stroke range meeting the ±2° requirement and a repeatability better than 0.1 μrad. On the rotary platform of the second large turntable 7-2, a first large turntable 7-1 is stacked. This turntable provides rotational motion around the X-axis, parallel to the X-direction linear guide 8. Its high-precision drive can refer to the existing mature linear motor direct-drive rotation scheme, also ensuring a repeatability better than 0.1 μrad. This "rotation-pitch" series configuration allows the surface mirror 5 to be tested, which is fixed on it, to achieve precise attitude adjustment in two degrees of freedom, so as to ensure that it can be adjusted to the optimal measurement attitude perpendicular to the optical axis of the white light profilometer 2 when measuring each sub-aperture.

[0067] Above the large turntable assembly, more specifically, on the upper platform of the first large turntable 7-1 and near the Fizeau interferometer 1, is another precision attitude adjustment mechanism—a small turntable assembly. This assembly is used to support and independently adjust the attitude of the plane reference mirror 4. Its structure is similar to the large turntable assembly but smaller in scale and with higher precision requirements: the base of the second small turntable 6-2 is fixed to the table surface of the first large turntable 7-1, and the first small turntable 6-1 is stacked on top of the second small turntable 6-2. The plane reference mirror 4 is rigidly fixed to the upper surface of the first small turntable 6-1 by a dedicated mirror mount. The first small turntable 6-1 and the second small turntable 6-2 provide independent rotational motions about the X-axis and Z-axis, respectively, and their repeatability is also required to be better than 0.1 μrad. The plane reference mirror 4 is precisely adjusted to be located directly in front of the measurement field of view of the Fizeau interferometer 1 to ensure that the Fizeau interferometer 1 can continuously obtain high-quality interference signals. The curved mirror 5 to be tested is rigidly mounted on the upper platform of the first large turntable 7-1 and close to the white light profilometer 2 via another set of mirror frames. Its surface to be tested is precisely adjusted to be below the field of view of the white light profilometer 2. The key to this layout is that the planar reference mirror 4 and the curved mirror 5 to be tested are mechanically formed into a rigid whole through the first large turntable 7-1 and the second large turntable 7-2. When the large turntable assembly rotates to adjust the attitude of the mirror under test, the planar reference mirror 4 is synchronously driven, and its spatial orientation changes completely in the same way. At the same time, the planar reference mirror 4 can also be independently fine-tuned relative to the large turntable assembly through the small turntable assembly. This design is the basis for realizing the dynamic angle compensation function.

[0068] The motion control system of the entire device employs a fully closed-loop control strategy to eliminate errors. The X-direction linear guide 8 and the second large turntable 7-2 achieve position feedback through optical grating rulers and circular gratings, with resolutions reaching 50 nm and 10 nrad, respectively. The first large turntable 7-1 can achieve nanometer-level closed-loop control using existing technologies such as optical ranging. All these high-precision motion control components work together to form a precision measurement platform capable of achieving nanometer-level positioning and micro-radian-level pointing.

[0069] The two-dimensional white light microscopic stitching interferometry device provided in this embodiment integrates a white light profilometer 2, a Fizeau interferometer 1, a multi-degree-of-freedom precision motion platform, and an air-bearing vibration isolation system with specific positional and connection relationships to construct a complete hardware solution. The core of this device lies in allowing the planar reference mirror 4 and the surface mirror under test to share most of their kinematic chains. This enables the Fizeau interferometer 1 to accurately reflect the attitude changes of the mirror under test by measuring the angle changes of the reference mirror. Simultaneously, an independent small turntable assembly provides the necessary degrees of freedom for the reference mirror to maintain its position within the optimal operating range of the interferometer 1. This design makes it possible to directly and in real-time obtain the relative angle differences between sub-apertures, which are difficult to calculate precisely. This provides a unique hardware foundation for subsequent high-precision data stitching and is particularly suitable for solving the surface shape detection problem of small radius-of-curvature X-ray curved mirrors 5.

[0070] Example 2:

[0071] This embodiment provides a two-dimensional white light microscopic stitching interferometry method using the apparatus described in Embodiment 1. The core idea of ​​this method is to synergistically utilize the high-resolution topography measurement capability of the white light profilometer 2 and the high-precision angle monitoring capability of the Fizeau interferometer 1 to directly acquire the spatial relative position and attitude relationship between adjacent sub-apertures during sub-aperture scanning, and integrate it into a precise mathematical stitching model. This fundamentally suppresses the error accumulation problem caused by relying on overlapping areas to calculate pose in traditional methods, and ultimately achieves high-precision, high-resolution global surface shape reconstruction of the entire curved mirror surface.

[0072] The implementation of the method begins with the system initialization and benchmark establishment phase. First, the operator securely mounts the curved mirror 5 to be tested onto the large turntable assembly, roughly aligning its rightmost end with the center of the field of view of the white light profilometer 2. Then, the system is started, and the height of the white light profilometer 2 is finely adjusted by controlling the second vertical stage 3-2, ensuring its objective lens is aligned with the mirror surface under test and clear interference fringes are obtained. Next, by controlling the first large turntable 7-1 and the second large turntable 7-2, the pitch and roll angles of the curved mirror 5 under test are slowly adjusted, and the interference fringe pattern in the white light profilometer 2 is observed until the fringes are adjusted to their sparsest or even disappearing state, reaching the so-called "zero-fringe" state. This indicates that within the current sub-aperture region, the local normal direction of the mirror surface under test is parallel to the optical axis direction of the white light profilometer 2, indicating an optimal measurement posture. After adjusting and locking the position of the mirror under test (in subsequent sub-aperture measurements, the large turntable will be readjusted to restore zero fringes at each position), an angle monitoring benchmark needs to be established. The height of the Fizeau interferometer 1 is adjusted by controlling the first vertical motion stage 3-1 to ensure that its measurement beam precisely covers the full aperture of the plane reference mirror 4. Then, the pitch and yaw of the plane reference mirror 4 are finely adjusted by operating the first small turntable 6-1 and the second small turntable 6-2 until zero fringes are also observed in the monitoring interface of the Fizeau interferometer 1. At this point, the system has completed the initial calibration, both optical instruments are at the optimal measurement starting point, and the initial surface shape data of the plane reference mirror 4 (which can be regarded as an angular reference) is recorded by the Fizeau interferometer 1 as reference mirror surface shape data one.

[0073] After establishing the baseline, the measurement planning and sub-aperture division stage begins. Based on the physical dimensions of the curved mirror 5 to be tested (e.g., length 100mm, width 50mm) and the magnification of the objective lens used in the white light profilometer 2 (e.g., a 5x objective lens with a 1x eyepiece), the size of the measurement area for a single sub-aperture (e.g., a square area of ​​1.74mm × 1.74mm) is determined, and combined with the preset overlap rate, the total number of sub-apertures to be measured and their arrangement are calculated. The overlap rate is a key parameter to ensure successful stitching; its selection requires a balance between measurement efficiency and stitching reliability, and is typically set to no less than 80%. For example, when the overlap rate is set to 80%, the step distance in the X direction (mirror length direction) is 0.348mm, requiring the measurement of 280 sub-apertures; the step distance in the Z direction (mirror height direction) is also 0.348mm, requiring the measurement of 105 sub-apertures, for a total of 280 × 105 = 29400 sub-aperture data points to be collected. The specific value of the overlap ratio can be adjusted according to the actual detection accuracy requirements. For example, 85% or 90% can be selected, which corresponds to a smaller step distance, a larger number of sub-apertures, and theoretically higher splicing accuracy. The measurement path usually adopts an efficient serpentine scanning method, that is, the first row is from left to right, the second row is from right to left, and so on. Figure 3The sub-apertures are named S in the order indicated by the red arrows. 1.1 S 1.2 , ...,S 1.280 ,S 2.280 S 2.279 , ..., S 2.1 S 3.1 ...until the entire mirror surface is covered.

[0074] Once the planning is complete, the automated data acquisition process is initiated. The system first controls the white light profilometer 2 to acquire the initial position (usually S). 1.1 The surface shape data of the sub-aperture is denoted as Simultaneously, the Fizeau interferometer 1 records the surface shape data of the planar reference mirror 4 at this time (i.e., the aforementioned reference mirror surface shape data one). Subsequently, the system controls the X-direction linear guide 8 to move one step distance (e.g., 0.348 mm), moving the mirror under test to the second sub-aperture S. 1.2 The position of the sub-aperture region is adjusted. Since the mirror body is curved, after movement, the current sub-aperture region is usually no longer perpendicular to the optical axis of the white light profilometer 2. At this point, the system controls the first large turntable 7-1 and the second large turntable 7-2 to readjust the orientation of the curved mirror 5 under test, so that it reappears as a zero-fringe in the white light profilometer 2. Because the plane reference mirror 4 is rigidly connected to the mirror under test, this adjustment will simultaneously change the spatial orientation of the plane reference mirror 4. After the adjustment is complete, the white light profilometer 2 collects the sub-aperture S. 1.2 Surface data Meanwhile, the Fizeau interferometer 1 simultaneously acquires new surface shape data of the planar reference mirror 4 (i.e., the aforementioned reference mirror surface shape data two). The internal processor of the Fizeau interferometer 1 calculates in real time the relative angle difference between reference mirror surface shape data two and reference mirror surface shape data one. That is, the curved surface mirror 5 to be tested has a sub-aperture S. 1.1 With S 1.2 The actual relative deflection angle between them about the X-axis and / or Z-axis.

[0075] The data acquisition process continues along a predetermined path. Each time the data is moved to a new sub-aperture position S... i.j Repeat the above steps: adjust the large turntable to restore zero fringes at the sub-aperture of the mirror under test, and then simultaneously acquire the surface shape data of the sub-aperture. and the angular difference relative to the previous sub-aperture obtained by the Fiso interferometer 1 During this process, the planar reference mirror 4 is continuously deflected in one direction by the large turntable assembly, and its cumulative deflection angle gradually increases. To ensure that the Fizeau interferometer 1 always operates within the linear measurement range, this embodiment introduces a dynamic angle compensation mechanism. The system monitors the deflection angle of the planar reference mirror 4 relative to its initial zero position in real time. When this angle exceeds a preset threshold, for example, reaching 1×10⁻⁶, a dynamic angle compensation mechanism is introduced. -4 Upon reaching rad, the system will pause sub-aperture measurement and control the miniature turntable assembly (first miniature turntable 6-1 and / or second miniature turntable 6-2) to drive the plane reference mirror 4 to rotate in the opposite direction by a specific angle, such as 2×10. - 4 rad. This operation is equivalent to mechanically "resetting" the reference mirror, bringing it back to the vicinity of the zero fringe of the Fizeau interferometer 1. The angle value of this reverse rotation is accurately recorded by the system and subtracted as a compensation amount in subsequent data processing, thereby ensuring the continuity and accuracy of the angle reference in long-distance measurements.

[0076] After measuring all sub-apertures in a row (X direction), the system controls the second vertical motion stage 3-2 carrying the white light profilometer 2 to descend by a vertical step distance (also determined by the sub-aperture size and overlap rate). Then, the X-direction linear guide 8 moves in the opposite direction to begin scanning a new row. This process is repeated until all preset sub-aperture data, including their surface shape data and the angular difference data between adjacent sub-apertures, are collected.

[0077] After all the raw data acquisition is completed, the core data stitching and fusion stage begins. The task of this stage is to integrate the local surface shape data of all sub-apertures. By combining their known relative positions and orientations, and integrating them into a unified global coordinate system, the complete surface shape is reconstructed. The stitching process is essentially a mathematical optimization problem. For any given x... Each sub-aperture, its data is stitched into the adjacent first aperture. When using the aperture as a reference coordinate system, coordinate transformation and attitude adjustment are required. The mathematical expression is:

[0078] .

[0079] In this formula, and Representing the The amount of translation required for each sub-aperture relative to the reference coordinate system in the X and Y directions is usually determined precisely by analyzing the image features of the overlapping area of ​​the two sub-apertures and using existing techniques such as digital image correlation for registration. and These are crucial slope adjustment coefficients, which directly determine the pitch and roll attitude of the sub-aperture after splicing. Their values ​​are not estimated through calculations of the overlapping area, but are directly derived from the relative angle differences measured by the Fiso interferometer 1 during the measurement process. This direct correlation is the key to this method's breakthrough in overcoming the bottlenecks of traditional splicing techniques. This is the adjustment amount in the height direction, used to eliminate the height reference offset between sub-apertures. The solution is achieved through the least squares method, with the goal of making the th... Individual aperture and the first The sum of squared height differences of all pixels within the overlapping region of each reference sub-aperture is minimized, i.e., the minimization condition is satisfied:

[0080] .

[0081] By solving this least squares problem, the optimal solution can be obtained. value.

[0082] After performing the coordinate transformation, attitude adjustment, and height optimization on all sub-apertures sequentially, each sub-aperture has been accurately transformed into a unified global coordinate system. However, in the overlapping areas of sub-apertures, direct stitching may produce "seams" due to measurement noise and minor errors. To obtain a smooth and continuous global surface shape, the final step is data fusion. This method employs a pixel-position-based weighted average fusion algorithm. This algorithm calculates a weight function for each pixel within the overlapping area based on its distance to the center and outer boundary of the current sub-aperture; the closer the pixel is to the center, the greater the weight. The final fused height value of this pixel is the weighted average of its corresponding height values ​​in different sub-apertures. This fusion method effectively smooths the stitching boundaries and maximizes the recovery of the true surface shape information of the measured surface.

[0083] The two-dimensional white light microscopic stitching interferometry method provided in this embodiment directly incorporates the angular difference monitored in real time by the Fiso interferometer 1 into the mathematical model of sub-aperture stitching, replacing the traditional indirect method that relies on overlapping region data for pose estimation. This fundamentally avoids the propagation and accumulation of angular errors. Combined with a dynamic angle compensation mechanism to ensure the stability of long-term measurements, and a precise algorithm based on least squares and weighted fusion, this method can fully leverage the sub-nanometer vertical resolution advantage of the white light profilometer 2, ultimately achieving nanometer-level or even sub-nanometer-level precision surface shape measurement of complex curved surface mirrors 5 with small curvature radii. This effectively solves a long-standing detection problem in the field of high-end optical manufacturing.

Claims

1. A two-dimensional white light microscopic splicing interferometry device, characterized in that, include: Base platform (9); The first vertical motion stage (3-1) and the second vertical motion stage (3-2) are respectively disposed on both sides of the base platform (9); The Fiso interferometer (1) is set on the first vertical motion stage (3-1) and is used to acquire the interference fringe data of the plane reference mirror (4); A white light profilometer (2) is set on the second vertical motion stage (3-2) to acquire the sub-aperture surface shape data of the curved surface mirror (5) to be tested; The X-direction linear guide (8) is set on the base platform (9) and located between the first vertical motion stage (3-1) and the second vertical motion stage (3-2); A large turntable assembly is set on the X-direction linear guide rail (8). The large turntable assembly is used to support the surface mirror (5) to be tested and the plane reference mirror (4) and drive them to rotate and adjust synchronously. A small turntable assembly is disposed on the large turntable assembly. The small turntable assembly is used to support the planar reference mirror (4) and drive the planar reference mirror (4) to rotate and adjust independently relative to the large turntable assembly. The surface mirror (5) to be tested is fixedly mounted on the large turntable assembly and located below the field of view of the white light profilometer (2); the small turntable assembly is located on the side of the large turntable assembly close to the Fizeau interferometer (1), and the plane reference mirror (4) is located in front of the field of view of the Fizeau interferometer (1).

2. The two-dimensional white light microscopic splicing interferometry device according to claim 1, characterized in that, The large turntable assembly includes: First large turntable (7-1) and second large turntable (7-2); The second large turntable (7-2) is fixedly mounted on the X-direction linear guide rail (8) to realize rotational motion around the Z-axis; The first large turntable (7-1) is stacked on top of the second large turntable (7-2) to realize rotational movement around the X-axis; The surface reflector to be tested (5) and the small turntable assembly are both mounted on the first large turntable (7-1).

3. The two-dimensional white light microscopic splicing interferometry device according to claim 1, characterized in that, The small turntable assembly includes: First small turntable (6-1) and second small turntable (6-2); The second small turntable (6-2) is fixedly mounted on the large turntable assembly; The first small turntable (6-1) is stacked on top of the second small turntable (6-2); The planar reference mirror (4) is fixedly mounted on the first small turntable (6-1); The first small turntable (6-1) and the second small turntable (6-2) are configured to provide independent angle adjustments around the X-axis and around the Z-axis, respectively.

4. The two-dimensional white light microscopic splicing interferometry device according to claim 1, characterized in that: The X-direction linear guide (8) is driven by an air-bearing guide and a linear motor, with a stroke configuration of 1200mm; The first large turntable (7-1), the second large turntable (7-2), the first small turntable (6-1), and the second small turntable (6-2) are all equipped with position feedback devices to achieve closed-loop control.

5. A two-dimensional white light microscopic splicing interferometry method using the apparatus described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Adjust the orientation of the surface mirror (5) to be tested by means of the large turntable assembly so that it displays zero stripes in the white light profilometer (2); S2. Adjust the orientation of the planar reference mirror (4) using the small turntable assembly so that it displays zero fringes in the Fizzo interferometer (1); S3. Control the white light profiler (2) to collect the surface shape data of the sub-aperture at the current position. And control the Fiso interferometer (1) to collect the current angle data of the plane reference mirror (4); S4: Control the large turntable assembly to move along the X-direction linear guide rail (8) to the next sub-aperture position, and adjust the angle of the large turntable assembly so that the next sub-aperture area reappears as zero stripes in the white light profiler (2); S5: Based on the angle change of the plane reference mirror (4) before and after movement measured by the Fiso interferometer (1), determine the relative angle difference between the sub-apertures of the surface mirror (5) to be tested; S6: Repeat steps S3 to S5 until all sub-aperture data are collected, and then stitch and fuse them based on the relative angle difference.

6. The two-dimensional white light microscopic splicing interferometry method according to claim 5, characterized in that, Between steps S4 and S5, there is also a reference mirror range reset step: Real-time monitoring of the deflection angle of the planar reference mirror (4) relative to the Fizzo interferometer (1); When the deflection angle exceeds the preset threshold, the small turntable assembly is controlled to drive the plane reference mirror (4) to rotate in the opposite direction, so that it returns to the vicinity of the measurement zero position of the Fiso interferometer (1), and the angle compensation value of the reverse rotation is recorded.

7. The two-dimensional white light microscopic splicing interferometry method according to claim 6, characterized in that, The preset threshold is set to 1×10. -4 rad, the angle of the reverse rotation is set to 2×10 -4 rad.

8. The two-dimensional white light microscopic splicing interferometry method according to claim 5, characterized in that, In step S6, the first splicing data of individual apertures Calculated using the following formula: ； in, This is the sequence number of the sub-aperture to be spliced; The coordinates are those of the adjacent reference sub-aperture coordinate system. For the first The aperture in coordinates Adjusted height data at the location; For the first Initial height data function for each aperture; and The first The slope adjustment coefficients of the individual aperture in the X and Y directions, the slope adjustment coefficients and The result is calculated based on the relative angle difference determined in step S5; For the first Adjustment amount of individual aperture in the height direction; and The first The required positional adjustments of each aperture relative to the reference coordinate system in the X and Y directions.

9. The two-dimensional white light microscopic splicing interferometry method according to claim 8, characterized in that, The height adjustment amount Calculated using the least squares method, it satisfies the following minimization condition: ； in, In order to be with the first The sub-aperture numbers that are adjacent to each other and serve as a reference; For the first The aperture in coordinates Height data at the location; This indicates the search for a function that minimizes the sum of squares.

10. The two-dimensional white light microscopic splicing interferometry method according to claim 5, characterized in that: The white light profilometer (2) adopts a vertical scanning interference mode, and the stitching and fusion adopts a weighted fusion algorithm based on pixel position.

Images