A measurement device for high-steepness continuous phase element and its application method

Abstract

The present invention discloses a measuring device for a high-steepness continuous phase element and an application method thereof. The measuring device of the present invention comprises a laser interferometer, a reflector and a fixture. A compensating mirror and a measured continuous phase element are arranged on the fixture. The compensating mirror is arranged between the interferometer and the measured continuous phase element. The surface shape of the compensating mirror is complementary to the standard surface shape of the measured continuous phase element. The surface shape of the compensating mirror is between negative 60% and negative 50% of the standard surface shape of the measured continuous phase element to compensate for the interference fringe density of the local high-steepness surface shape of the continuous phase element. The laser beam emitted by the laser interferometer passes through the compensating mirror and the measured continuous phase element in sequence and then reaches the reflector, and then is reflected by the reflector to form interference for detection. The present invention aims to solve the problem that the interference measurement loses data due to the interference fringe density of the local high-steepness surface shape being too high to be recorded and solved, and finally the surface shape cannot be accurately measured, resulting in a great increase in the number and time of subsequent processing.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element measurement, and in particular to a measuring device for a high-steepness continuous phase element and an application method thereof. Background Art

[0002] The continuous phase element (CPP) is a typical diffractive optical element, whose surface is designed as a continuous three-dimensional relief profile. The incident wavefront is modulated into an ideal output wavefront after passing through the relief profile. It has broad application prospects in beam shaping, compensation and modulation. With the continuous iteration and upgrading of the controlled inertial confinement fusion system, the new generation of laser systems require that the focal spot intensity distribution of the laser beam has flat top, steep edges and no side lobes. However, this requires the continuous phase element to have a smaller spatial period and a higher modulation depth, which undoubtedly brings great challenges to the surface quality detection of the continuous phase plate. Interferometry is a high-precision optical element surface shape measurement method, which is mainly used for the quality inspection of the finishing stage and finished optical components. At present, the maximum gradient of the continuous phase element designed in China has reached 8λ / cm, and the gradient resolution of the commonly used laser interferometer is usually 2λ / cm. As the surface steepness of the continuous phase element continues to increase, the change of the surface gradient of the continuous phase element may cause the interference fringes to be too dense, resulting in the detector being unable to distinguish and thus unable to distinguish the phase, which exceeds the dynamic range of the laser interferometer. Therefore, the interference measurement method will be unable to record and solve due to the high density of the interference fringes, and there will be data missing in the local high-steepness surface shape, which cannot be accurately measured. The surface gradient and spatial period of the high-steepness (surface gradient exceeds 2λ / cm) continuous phase element are small and may also cause some light to escape the laser interferometer. When measuring the high-steepness continuous phase element with traditional interferometry, a curve obtained by taking a horizontal line will find that a lot of data is missing at this position. The measurement feedback accuracy of the surface error will directly determine the processing efficiency and final accuracy of the continuous phase element. If the surface shape of the continuous phase element cannot be measured, it can only rely on the operator's experience to try blindly, lacking processing basis, and the surface error of this part of the missing result will greatly increase the number and time of repeated processing. Summary of the invention

[0003] Technical problem to be solved by the present invention: In view of the above-mentioned problems in the prior art, a measuring device for a high-steepness continuous phase element and an application method thereof are provided. The present invention aims to solve the problem that in interference measurement, the interference fringes density is too high due to the local high-steepness surface shape, which cannot be recorded and solved and data is lost, and ultimately the surface shape cannot be accurately measured, resulting in a significant increase in the number and time of subsequent processing. Without changing the original laser interferometer optical path, the measurement of the local steepness surface error of the high-steepness continuous phase element is achieved.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A measuring device for a high-steepness continuous phase element comprises a laser interferometer, a reflector and a fixture arranged at one side of the laser interferometer, wherein a compensating mirror and a measured continuous phase element are arranged on the fixture, wherein the compensating mirror and the measured continuous phase element are arranged in parallel and the compensating mirror is arranged between the laser interferometer and the measured continuous phase element, wherein the surface shape of the compensating mirror and the standard surface shape of the measured continuous phase element complement each other so that the highest point of the surface shape of the compensating mirror corresponds to the lowest point of the standard surface shape of the measured continuous phase element, and the lowest point of the surface shape of the compensating mirror corresponds to the highest point of the standard surface shape of the measured continuous phase element, and the surface shape of the compensating mirror takes a specified percentage of the standard surface shape of the measured continuous phase element to compensate for the interference fringe density of the local high-steepness surface shape of the continuous phase element, wherein the laser beam emitted by the laser interferometer passes through the compensating mirror and the measured continuous phase element in sequence and then reaches the reflector, and then is reflected by the reflector and returns to pass through the measured continuous phase element and the compensating mirror to form interference with the laser beam emitted by the laser interferometer to be detected by the laser interferometer.

[0006] Optionally, the specified percentage ranges from negative 60% to negative 50%.

[0007] Optionally, the fixture includes a base, on which a connecting support plate and two clamping arms are provided, wherein both ends of the connecting support plate are connected to a clamping arm respectively, and two positioning grooves are provided on the top of the connecting support plate and the opposite sides of the two clamping arms to respectively clamp and fix the compensation mirror and the continuous phase element to be measured.

[0008] Optionally, a dovetail groove is provided on the base, and the connecting support plate and the two clamping arms are inserted into the dovetail groove of the base through a dovetail tenon at the bottom.

[0009] In addition, the present invention also provides an application method of the aforementioned high-steepness continuous phase element measurement device, comprising:

[0010] S1, using laser interferometer to measure the compensation mirror alone to obtain the full-aperture surface error distribution;

[0011] S2, using a laser interferometer to measure the surface data of the measured continuous phase element after compensation by a compensation mirror;

[0012] S3, subtracting the surface shape data of the compensation mirror from the surface shape data of the measured continuous phase element after compensation by the compensation mirror, to obtain the complete surface shape data of the measured continuous phase element.

[0013] Optionally, before step S1, the process also includes preparing a compensation mirror: obtaining a standard surface shape of the continuous phase element to be measured; multiplying the standard surface shape of the continuous phase element to be measured by a specified percentage to obtain a standard surface shape of the compensation mirror, and the standard surface shape of the compensation mirror and the standard surface shape of the continuous phase element to be measured are complementary so that the highest point of the surface shape of the compensation mirror corresponds to the lowest point of the standard surface shape of the continuous phase element to be measured, and the lowest point of the surface shape of the compensation mirror corresponds to the highest point of the standard surface shape of the continuous phase element to be measured; and iteratively processing the surface shape of the compensation mirror through a deterministic shaping process until the surface shape meets the requirements.

[0014] Optionally, the iterative processing of the surface shape of the compensation mirror by a deterministic shaping process refers to iterative processing of the surface shape of the compensation mirror by a combined process of small grinding head polishing and magnetorheological shaping.

[0015] Optionally, the combined process of small grinding head polishing and magnetorheological shaping refers to first using a small grinding head for smoothing and then using magnetorheological shaping.

[0016] Optionally, when the surface shape of the compensation mirror is iteratively processed by a combined process of small grinding head polishing and magnetorheological shaping, both the small grinding head polishing and magnetorheological shaping processes have two removal functions of different sizes, and during processing, a larger removal function is first used to remove most of the material, and then a smaller removal function is used for shaping, and the proportion of time occupied by the smaller removal function in any one of the processing processes is positively correlated with the number of iterations.

[0017] Compared with the prior art, the present invention mainly has the following advantages: Compared with the traditional continuous phase element measurement device, the high-steepness continuous phase element measurement device of the present invention needs to add a compensation mirror, which is manufactured based on the designed surface shape of the continuous phase element to be measured, and can compensate for part of the surface shape information in the measurement optical path, thereby avoiding the problem that the high-steepness surface shape of the optical element cannot be measured. The present invention can measure the local steepness surface shape error of the high-steepness continuous phase element without changing the original measurement optical path. The structure is relatively simple, and no complex full-aperture mechanical scanning structure is required, retaining the high precision of interference measurement. The high-steepness continuous phase element measurement device of the present invention can effectively reduce the number and time required for subsequent continuous phase element processing by accurately measuring the surface shape of the continuous phase element. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the three-dimensional structure of a measuring device in an embodiment of the present invention.

[0019] Figure 2 Schematic diagram of the working principle of the measuring device in an embodiment of the present invention.

[0020] Figure 3 Schematic diagram of the detection surface shape obtained by the measuring device in an embodiment of the present invention after removing the compensation mirror.

[0021] Figure 4 Schematic diagram of the detection surface shape obtained by the measuring device in an embodiment of the present invention when using a compensation mirror.

[0022] Legend: 1. Laser interferometer; 2. Fixture; 21. Base; 22. Connecting support plate; 23. Clamping arm; 3. Compensation mirror; 4. Continuous phase element; 5. Reflector. DETAILED DESCRIPTION

[0023] The present invention aims to solve the problem that the interference fringe density of the local high-steepness surface is too high, and the data cannot be recorded and solved, which leads to the loss of data, and ultimately the surface cannot be accurately measured, resulting in a great increase in the number and time of subsequent processing. Without changing the original laser interferometer optical path, the local steepness surface error of the high-steepness continuous phase element can be measured. Figure 1 and Figure 2 As shown, this embodiment provides a measuring device for a high-steepness continuous phase element, comprising a laser interferometer 1, a reflector 5, and a fixture 2 arranged on one side of the laser interferometer 1, wherein a compensation mirror 3 and a continuous phase element 4 to be measured are arranged on the fixture 2, wherein the compensation mirror 3 and the continuous phase element 4 to be measured are arranged in parallel, and the compensation mirror 3 is arranged between the laser interferometer 1 and the continuous phase element 4 to be measured, wherein the surface shape of the compensation mirror 3 and the standard surface shape of the continuous phase element 4 to be measured are complementary, so that the highest point of the surface shape of the compensation mirror 3 corresponds to the lowest point of the standard surface shape of the continuous phase element 4 to be measured The lowest point of the surface shape of the compensating mirror 3 corresponds to the highest point of the standard surface shape of the continuous phase element 4 to be measured. The compensating mirror 3 takes a specified percentage of the standard surface shape of the continuous phase element 4 to be measured to compensate for the interference fringe density of the local high-steepness surface shape of the continuous phase element 4. The laser light beam emitted by the laser interferometer 1 passes through the compensating mirror 3 and the continuous phase element 4 to be measured in turn and reaches the reflecting mirror 5. After being reflected by the reflecting mirror 5, it returns and passes through the continuous phase element 4 to be measured and the compensating mirror 3, and then interferes with the laser light beam emitted by the laser interferometer 1 to be detected by the laser interferometer 1. Undoubtedly, the above-mentioned specified percentage can be specified according to actual needs, as long as it can compensate for the interference fringe density of the local high-steepness surface shape of the continuous phase element 4, it can meet the needs. As an optional implementation method, the specified percentage in this embodiment is negative 50%. Taking the negative means reversing the standard surface shape, that is, the surface shape of the compensation mirror 3 and the standard surface shape of the measured continuous phase element 4 complement each other so that the highest point of the surface shape of the compensation mirror 3 corresponds to the lowest point of the standard surface shape of the measured continuous phase element 4, and the lowest point of the surface shape of the compensation mirror 3 corresponds to the highest point of the standard surface shape of the measured continuous phase element 4. Sometimes, when the modulation depth of the measured continuous phase element 4 is too large and the period is too small, the ratio can be increased accordingly, for example, increased to negative 30%.

[0024] like Figure 1As shown, in this embodiment, the fixture 2 includes a base 21, on which a connecting support plate 22 and two clamping arms 23 are provided, and both ends of the connecting support plate 22 are connected to a clamping arm 23, and two positioning grooves are provided on the top of the connecting support plate 22 and the opposite sides of the two clamping arms 23 to respectively bond and clamp the compensation mirror 3 and the measured continuous phase element 4. As an optional embodiment, in this embodiment, plasticine is used for bonding to facilitate disassembly, and other adhesive materials can also be used as needed.

[0025] like Figure 1 As shown, in this embodiment, a dovetail groove is provided on the base 21, and the connecting support plate 22 and the two clamping arms 23 are arranged in the dovetail groove of the base 21 through the dovetail tenon at the bottom. As an optional embodiment, in this embodiment, the base 21 and the laser interferometer 1 are arranged on an air floating platform. In order to improve the measurement accuracy, it is also necessary to ensure that the test environment is stable, the temperature change is small, and the air flow disturbance is low.

[0026] In addition, this embodiment also provides an application method of the aforementioned high-steepness continuous phase element measurement device, including:

[0027] S1, using laser interferometer 1 to measure compensation mirror 3 alone to obtain full-aperture surface error distribution;

[0028] S2, using a laser interferometer 1 to measure the surface shape data of the measured continuous phase element 4 after compensation by the compensation mirror 3;

[0029] S3, subtracting the surface shape data of the compensation mirror 3 from the surface shape data of the measured continuous phase element 4 after compensation by the compensation mirror 3, so as to obtain the complete surface shape data of the measured continuous phase element 4.

[0030] In this embodiment, before step S1, the method also includes preparing the compensation mirror 3: obtaining the standard surface shape of the continuous phase element 4 to be measured; multiplying the standard surface shape of the continuous phase element 4 to be measured by a specified percentage to obtain the standard surface shape of the compensation mirror 3, and the standard surface shape of the compensation mirror 3 and the standard surface shape of the continuous phase element 4 to be measured are complementary so that the highest point of the surface shape of the compensation mirror 3 corresponds to the lowest point of the standard surface shape of the continuous phase element 4 to be measured, and the lowest point of the surface shape of the compensation mirror 3 corresponds to the highest point of the standard surface shape of the continuous phase element 4 to be measured; and iteratively processing the surface shape of the compensation mirror 3 through a deterministic shaping process until the surface shape meets the requirements. As an optional implementation, in this embodiment, the standard surface shape of the measured continuous phase element 4 is multiplied by -50% (-0.5) to obtain the standard surface shape of the compensation mirror 3 (the standard surface shape of the compensation mirror 3 and the standard surface shape of the measured continuous phase element 4 are complementary so that the highest point of the surface shape of the compensation mirror 3 corresponds to the lowest point of the standard surface shape of the measured continuous phase element 4, and the lowest point of the surface shape of the compensation mirror 3 corresponds to the highest point of the standard surface shape of the measured continuous phase element 4), which is etched as the standard surface shape of the compensation mirror 3, and at the same time, the pattern of the compensation mirror 3 is opposite to that of the continuous phase element (equivalent to the high and low points of the two mirrors being interchanged). According to the deterministic shaping principle, detection and processing are continuously iterated to complete the production of the compensation mirror with the established requirements.

[0031] Since the surface structure of the continuous phase element is complex and the local morphology changes greatly, the present embodiment adopts a combined process of small grinding head polishing and magnetorheological modification to achieve high-precision processing of the compensation mirror 3. In the present embodiment, iteratively processing the surface shape of the compensation mirror 3 by a deterministic modification process means iteratively processing the surface shape of the compensation mirror 3 by a combined process of small grinding head polishing and magnetorheological modification, and the combined process of small grinding head polishing and magnetorheological modification means first using a small grinding head for smoothing and then using magnetorheological modification.

[0032] Since the surface features of the measured continuous phase element 4 are relatively complex and the RMS value can reach 3 wavelengths, the actual amount of material removal will still be large, so when making the compensation mirror 3, the actual amount of material removal will also be large. If the size of the removal function selected during development is small, although the development accuracy is high, the development time is very long due to the low removal efficiency; when the size of the removal function is large, the development efficiency is high, but the residual error after development is relatively large. Taking both factors into consideration, when developing the compensation mirror 3, a large-sized removal function is first used to remove a large amount of material to process the basic surface shape of the measured continuous phase element 4, and then a small removal function is used for precise shaping, so as to take into account both efficiency and accuracy and achieve the purpose of convergent development. As an optional implementation, in this embodiment, when a combined process of small grinding head polishing and magnetorheological shaping is used to iteratively process the surface shape of the compensation mirror 3, both the small grinding head polishing and magnetorheological shaping processes have two removal functions of different sizes, and during processing, a larger removal function is first used for processing, and then a smaller removal function is used for processing, and the proportion of time occupied by the smaller removal function in any processing process is positively correlated with the number of iterations. For example, as an optional implementation, the number of iterations can be multiplied by a constant as a percentage increment on the basis of 50%, and the proportion of time occupied by the smaller removal function can be obtained by accumulating the increments, so that the proportion of time occupied by the smaller removal function is positively correlated with the number of iterations, thereby making the processing accuracy higher and higher, and improving the processing efficiency and processing quality.

[0033] Figure 3 Schematic diagram of the detection surface shape obtained by the measuring device in this embodiment after removing the compensation mirror 3, Figure 3 The high steepness leads to missing data. The black spots in the square color map are the data missing areas. Once this happens, the number and time of repeated processing will increase greatly. Due to missing data, the obtained surface features, such as the peak-to-valley value (PV), cannot accurately reflect the surface shape. Here, the PV is about 4.29λ. Figure 4 Schematic diagram of the detection surface shape obtained by the measuring device in this embodiment when using the compensation mirror 3. Figure 3 and Figure 4 It can be seen that by adding the compensation mirror 3 to measure the continuous phase element surface data, the PV value is reduced to 3.29λ, and the area with missing data is greatly reduced, which can effectively guide the subsequent process flow.

[0034] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. An application method of a high-steepness continuous phase element measurement device, characterized in that: The measuring device of the high-steepness continuous phase element comprises a laser interferometer (1), a reflector (5) and a fixture (2) arranged on one side of the laser interferometer (1); the fixture (2) is provided with a compensation mirror (3) and a continuous phase element (4) to be measured; the compensation mirror (3) and the continuous phase element (4) to be measured are arranged in parallel, and the compensation mirror (3) is arranged between the laser interferometer (1) and the continuous phase element (4) to be measured; the surface shape of the compensation mirror (3) and the standard surface shape of the continuous phase element (4) to be measured complement each other so that the highest point of the surface shape of the compensation mirror (3) corresponds to the lowest point of the standard surface shape of the continuous phase element (4) to be measured, and the compensation mirror (3) corresponds to the lowest point of the standard surface shape of the continuous phase element (4) to be measured. The lowest point of the surface shape of the mirror (3) corresponds to the highest point of the standard surface shape of the continuous phase element (4) to be measured, and the surface shape of the compensation mirror (3) takes a specified percentage of the standard surface shape of the continuous phase element (4) to be measured so as to compensate for the interference fringe density of the local high-steepness surface shape of the continuous phase element (4). The laser beam emitted by the laser interferometer (1) passes through the compensation mirror (3) and the continuous phase element (4) to be measured in sequence and then reaches the reflection mirror (5), and then is reflected by the reflection mirror (5) and returns to pass through the continuous phase element (4) to be measured and the compensation mirror (3), and then forms interference with the laser beam emitted by the laser interferometer (1) to be detected by the laser interferometer (1); The application method comprises: S1, using a laser interferometer (1) to measure the compensation mirror (3) alone to obtain the full-aperture surface error distribution; S2, using a laser interferometer (1) to measure the surface shape data of the measured continuous phase element (4) after compensation by the compensation mirror (3); S3, subtracting the surface shape data of the compensation mirror (3) from the surface shape data of the measured continuous phase element (4) after compensation by the compensation mirror (3), so as to obtain the complete surface shape data of the measured continuous phase element (4).

2. The application method of the high-steepness continuous phase element measuring device according to claim 1, characterized in that: The specified percentage ranges from negative 60% to negative 50%.

3. The application method of the high-steepness continuous phase element measuring device according to claim 1, characterized in that: The clamp (2) comprises a base (21), on which a connecting support plate (22) and two clamping arms (23) are provided, wherein two ends of the connecting support plate (22) are respectively connected to a clamping arm (23), and two positioning grooves are provided on the top of the connecting support plate (22) and on opposite sides of the two clamping arms (23) to respectively clamp, bond and fix the compensation mirror (3) and the measured continuous phase element (4).

4. The application method of the high-steepness continuous phase element measuring device according to claim 3 is characterized in that: The base (21) is provided with a dovetail groove, and the connecting support plate (22) and the two clamping arms (23) are arranged in the dovetail groove of the base (21) through dovetail tenons at the bottom.

5. The application method of the high-steepness continuous phase element measuring device according to claim 3 is characterized in that: The base (21) is placed on an air-floating platform.

6. The application method of the high-steepness continuous phase element measuring device according to claim 1, characterized in that: Before step S1, the method further includes preparing a compensation mirror (3): obtaining a standard surface shape of the continuous phase element (4) to be measured; multiplying the standard surface shape of the continuous phase element (4) to be measured by a specified percentage to obtain a standard surface shape of the compensation mirror (3), wherein the standard surface shape of the compensation mirror (3) and the standard surface shape of the continuous phase element (4) to be measured are complementary so that the highest point of the surface shape of the compensation mirror (3) corresponds to the lowest point of the standard surface shape of the continuous phase element (4) to be measured, and the lowest point of the surface shape of the compensation mirror (3) corresponds to the highest point of the standard surface shape of the continuous phase element (4) to be measured; and iteratively processing the surface shape of the compensation mirror (3) through a deterministic shaping process until the surface shape meets the requirements.

7. The application method of the high-steepness continuous phase element measuring device according to claim 6, characterized in that: The surface shape of the compensation mirror (3) is iteratively processed by a deterministic shaping process, which refers to the surface shape of the compensation mirror (3) being iteratively processed by a combination of a small grinding head polishing and a magnetorheological shaping process.

8. The application method of the high-steepness continuous phase element measuring device according to claim 7, characterized in that: The combined process of small grinding head polishing and magnetorheological shaping refers to first using a small grinding head for smoothing and then using magnetorheological shaping.

9. The application method of the high-steepness continuous phase element measuring device according to claim 8, characterized in that: When the surface shape of the compensation mirror (3) is iteratively processed by the combined process of small grinding head polishing and magnetorheological shaping, both the small grinding head polishing and magnetorheological shaping processes have two removal functions of different sizes, and during processing, a larger removal function is first used to remove most of the material, and then a smaller removal function is used for shaping, and the proportion of time occupied by the smaller removal function in any one of the processing processes is positively correlated with the number of iterations.

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