CN118129627B - High-sensitivity mirror deformation measurement system and method based on speckle interference - Google Patents
High-sensitivity mirror deformation measurement system and method based on speckle interference Download PDFInfo
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- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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Abstract
The invention provides a high-sensitivity mirror deformation measuring system and a method based on speckle interference, which relate to an optical measuring system, and the system comprises an imaging element and a laser; a first beam splitter prism for splitting a laser beam generated by the laser into reflected light and transmitted light; the transmitted light passes through the projection lens and is reflected by the polarized light splitting flat sheet and the smooth surface to be detected in sequence and then irradiates on the rough surface to form diffuse reflection light; part of the diffuse reflection light is reflected by the smooth surface to be detected, sequentially passes through the polarization beam splitting flat plate, the first diaphragm and the imaging lens, is reflected by the second beam splitting prism and irradiates on the imaging element; part of the reflected light passes through the second beam splitting prism after being reflected by the first reflecting mirror and irradiates on the imaging element; the focus position of the projection lens and the center position of the hole in the first diaphragm are symmetrically arranged relative to the polarization beam splitting flat sheet; the measuring system provided by the invention can be used for high-precision measurement and dynamic measurement of the deformation of the smooth surface to be measured.
Description
Technical Field
The invention relates to an optical measurement system, in particular to a high-sensitivity mirror deformation measurement system and method based on speckle interference.
Background
The surface profile accuracy of smooth surfaces in optical elements is critical for high accuracy optical systems. And the factors such as assembly stress, ambient temperature and the like can cause the change of the surface shape. Therefore, it is important to accurately measure the surface deformation of the smooth surface of the optical element during the assembly process and in the use environment.
The interferometer is adopted to respectively carry out high-precision surface shape measurement on the optical element before and after deformation, and high-precision surface deformation parameters can be obtained after comparison. The existing interferometer mainly comprises structural forms of a Taman Green interferometer, a Michelson interferometer, a Fidelity interferometer and the like, and can achieve high measurement accuracy.
However, the interferometer has high accuracy, but the factors affecting the accuracy are large. Since the measurement principle of the laser interferometer is to measure the difference in surface shape of the measured optical element and the reference optical element, the difference in surface shape is expressed in the form of a phase, i.e., a fringe pattern. Firstly, in order to ensure the accuracy of measurement, the surface accuracy of the reference optical element must be higher than that of the measured element, which means that the higher the measurement accuracy is, the higher the reference optical surface is required, and the cost of the measurement system is definitely greatly improved; secondly, the reference optical element must be matched with the measured optical element to a certain extent, otherwise, the optical path difference caused by the surface shape difference of the reference optical element and the measured optical element is too large, so that the surface shape difference is difficult to be calculated due to the too large phase fringe density. In particular, a specific reference mirror is required for measuring spherical, aspherical, free-form and other elements. For example, when measuring spherical objects, it is generally required that the difference between the radius of curvature of the spherical standard mirror and the radius of curvature of the sample surface cannot be too large, and excessive difference can bring additional non-common optical path errors, which affects high-precision testing. When measuring a free-form surface object, as no corresponding spherical standard mirror corresponds to the free-form surface object, the interferometer generally adopts sub-aperture splicing or a calculation hologram to reconstruct an aspherical wavefront, however, the sub-aperture splicing efficiency is low, the calculation hologram is expensive and can only be customized for a specific surface; finally, in order to avoid phase errors caused by non-coaxial light paths, the measuring light beam needs to be precisely aligned with the measured object in multiple degrees of freedom, the moving range of the measured mirror surface is greatly limited while the adjusting process is complicated, and the measuring efficiency is reduced.
In order to perform deformation measurement of a smooth surface, some of the prior art have also performed deformation measurement of a smooth surface by speckle interferometry.
For example, rene Skov Hansen in 2004 proposed a compact robust smooth surface object deformation measurement speckle interference system. The system is the same as the traditional speckle interference system, and mainly comprises a laser, a camera, a phase shifting device, a reference glass flat sheet and the like; the laser is not directly irradiated to the smooth surface to be detected after being emitted from the laser, but is irradiated to the rough frosted glass, scattered reflection is generated on the rough frosted glass to generate speckle and irradiate to the smooth surface to be detected, a transparent glass plate is placed in front of the smooth surface to be detected, light beams diffusely reflected by the rough frosted glass are incident on the transparent glass plate, a part of the light beams are reflected to form reference light, a part of the reference light passes through the transparent glass plate and irradiates on a smooth surface object to be reflected by the transparent glass plate, and a phase shifting device is arranged on the transparent glass plate to control the front-back movement of the glass plate, so that the phase of the reference light is controlled, and periodic phase change is realized. After the light irradiated onto the object with the smooth surface through the transparent glass plate is reflected by the object, the light finally interferes with the reference light on the target surface of the camera through the transparent glass plate.
However, the speckle interference system proposed by Hansen can only adopt a time phase shift phase extraction method to carry out relevant measurement, and a plurality of speckle interference patterns must be acquired, cannot carry out dynamic measurement and is easily influenced by environmental disturbance; meanwhile, when the direction of the smooth surface to be measured is changed, the position of the rough surface and the direction of the light beam irradiating the rough surface must be adjusted simultaneously, and the whole illumination light path is complicated to adjust, so that the rapid measurement is not facilitated; in the technical scheme, the measuring light book is emitted once, and the optical path change and the deformation of object light caused by deformation of the smooth surface to be measured are in a double relation, so that the phase difference of an interferogram caused by deformation is in direct proportion to the double of the deformation, and the corresponding relation of the phase delta and the optical path difference d is as follows:
wherein: λ is the laser wavelength and α is the angle between the incident light and the normal of the smooth surface.
Second, tu Saiqi, university of the combined fertilizer industry, 2018, et al, propose another speckle interferometry system that can measure smooth surface deformations, which also uses ground glass to produce speckle to meet the measurement requirements of speckle interferometry. The method is different from the Hansen scheme in that laser irradiates the smooth surface to be measured after being scattered by the frosted glass, but irradiates the smooth surface directly after beam expansion, and irradiates the frosted glass after being reflected by the laser, and the deformation of the smooth surface causes the phase change of the light field irradiated on the frosted glass; the speckle interference system images ground glass directly, rather than a smooth surface to be measured. The system adopts a space carrier phase extraction method, and can acquire the phase by only one speckle interference pattern, thereby realizing dynamic detection and improving the detection efficiency.
However, the transmission frosted glass type mirror deformation measurement system proposed by Tu Saiqi et al is used for directly imaging frosted glass, the mapping relation between the image pixel position and the spatial position of the measured surface is complex, the measured interference phase diagram and the spatial position of the measured mirror surface do not have a direct corresponding relation, and especially, the mapping between the interference phase diagram and the spatial position of the measured mirror surface is more serious when measuring a non-planar mirror surface, and the defects of complex distortion, difficult correction and the like exist.
Therefore, it is needed to provide a smooth surface deformation measurement system to solve the problems of high requirements on reference optical elements, complicated adjustment of illumination light paths, no direct correspondence between measured interference images and the spatial positions of the mirror surfaces to be measured and the like in the smooth surface deformation measurement system in the prior art.
Disclosure of Invention
(One) solving the technical problems
Aiming at the defects of the prior art, the invention provides a high-sensitivity mirror deformation measuring system and method based on speckle interference, which are used for solving the technical problems of high requirements on reference optical elements, complicated illumination light path adjustment and the like in the prior art.
(II) technical scheme
In order to achieve the above purpose, the invention is realized by the following technical scheme:
the invention provides a high-sensitivity mirror deformation measurement system based on speckle interference, which comprises an imaging element and a laser, wherein the imaging element is arranged on the mirror deformation measurement system;
A first beam splitter prism for splitting a laser beam generated by the laser into reflected light and transmitted light;
the transmitted light passes through the projection lens and is reflected by the polarized light splitting flat sheet and the smooth surface to be detected in sequence and then irradiates on the rough surface to form diffuse reflection light;
Part of the diffuse reflection light is reflected by the smooth surface to be detected, sequentially passes through the polarization beam splitting flat plate, the first diaphragm and the imaging lens, is reflected by the second beam splitting prism and irradiates on the imaging element;
part of the reflected light passes through the second beam splitting prism after being reflected by the first reflecting mirror and irradiates on the imaging element;
The focus position of the projection lens and the center position of the hole in the first diaphragm are symmetrically arranged relative to the polarization beam splitting flat sheet;
The first reflecting mirror is vertically connected with the piezoelectric ceramic actuator.
Further, a second mirror is included for reflecting the laser beam to the first beam splitting prism.
The collimating beam expander is arranged between the second reflecting mirror and the first beam splitter prism;
The second diaphragm is arranged between the collimation beam expander and the first beam splitter prism.
Further, the method further comprises the following steps:
the first half wave plate is arranged between the first beam splitting prism and the projection lens;
The second half wave plate is arranged between the first beam splitting prism and the first reflecting mirror.
Further, the method further comprises the following steps:
the first collimating mirror is arranged between the second half-wave plate and the first reflecting mirror;
the second collimating mirror is arranged between the first reflecting mirror and the second beam splitting prism;
The propagation distance of the light beam between the first collimating mirror and the second collimating mirror is the sum of the focal lengths of the first collimating mirror and the second collimating mirror.
Further, the optical system further comprises a third diaphragm arranged between the first collimating mirror and the first reflecting mirror.
Further, the method further comprises the following steps:
the polarizing plate is arranged between the second beam splitting prism and the second collimating mirror;
And the attenuation sheet is arranged between the polaroid and the second beam splitting prism.
Further, the first diaphragm is an adjustable diaphragm.
In a second aspect of the present invention, there is further provided a method for performing high-precision measurement of mirror deformation by using the high-sensitivity mirror deformation measurement system based on speckle interference, where the method includes performing high-precision measurement of mirror deformation by using a time phase shift phase extraction method.
In a third aspect of the present invention, there is further provided a method for dynamically measuring the deformation of a mirror by using the high-sensitivity mirror deformation measurement system based on speckle interference, where the method includes using a spatial carrier phase extraction method to dynamically measure the deformation of the mirror.
(III) beneficial effects
Compared with the prior art, the high-sensitivity mirror deformation measuring system and method based on speckle interference have the following beneficial effects:
1. the measuring light path has simple structure, does not need to be provided with a high-precision reference optical element, and avoids the defect of the arrangement of the reference optical element.
2. The illumination light path is simple to adjust, and the complexity of equipment operation is reduced.
3. The reference light is not affected by the smooth surface to be measured, and the illumination light path and the imaging light path are completely coaxial, so that the adjustment difficulty of the measuring system is further reduced, and meanwhile, the deformation sensitivity is effectively improved.
4. The measuring beam is reflected twice by the smooth surface to be measured, and the measuring sensitivity is doubled compared with the traditional speckle interference technology.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a high-sensitivity mirror deformation measurement system based on speckle interference in an embodiment;
FIG. 2 is a diagram showing the illumination path versus the measurement path in an embodiment;
fig. 3 is a schematic diagram of the optical path change before and after deformation of the smooth surface to be measured in the embodiment.
In the figure:
1. A laser; 2. a first beam-splitting prism; 3. a projection lens; 4. polarizing beam splitting flat sheet; 5. a roughened surface; 6. a first diaphragm; 7. an imaging lens; 8. a second light splitting prism; 9. a first mirror; 10. a piezoelectric ceramic actuator; 11. an imaging element; 12. a second mirror; 13. collimation beam expander; 14. a second diaphragm; 15. a first half-wave plate; 16. a second half-wave plate; 17. a first collimating mirror; 18. a second collimating mirror; 19. a third diaphragm; 20. a polarizing plate; 21. an attenuation sheet.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Examples
In order to solve the problems that the smooth surface deformation measuring system in the prior art has high requirements on a reference optical element, complicated illumination light path adjustment, no direct corresponding relation between a measured interference image and the spatial position of a measured smooth surface and the like, the main solution thinking of the application is as follows:
A high sensitivity mirror deformation measurement system based on speckle interference is provided for performing mirror deformation measurements.
Referring to fig. 1, the deformation measuring system comprises an imaging element 11, a laser 1, a first beam splitter prism 2, a projection lens 3, a polarization beam splitter plate 4, a rough surface 5, a first diaphragm 6, an imaging lens 7, a second beam splitter prism 8, a first reflecting mirror 9 and a piezoceramic actuator 10.
Wherein the laser 1 is used for generating a laser beam.
Based on the relative positional relationship between the laser 1 and the first prism 2, the laser beam is irradiated onto the first prism 2 and then split into reflected light and transmitted light by the first prism 2.
Based on the relative positional relationship among the first dichroic prism 2, the first reflecting mirror 9, the second dichroic prism 8, and the imaging element 11, the reflected light is firstly irradiated on the first reflecting mirror 9, is reflected by the first reflecting mirror 9, is irradiated on the second dichroic prism 8, is divided into a reflection portion and a transmission portion by the second dichroic prism 8, wherein the transmission portion is irradiated on the imaging element 11 after exiting the dichroic prism (wherein the light beam from the first dichroic prism 2→the first reflecting mirror 9→the second dichroic prism 8→the imaging element 11 is the reference light).
Based on the relative positional relationship among the first beam splitter prism 2, the projection lens 3, the polarization beam splitter flat 4, the smooth surface to be measured, the rough surface 5, the first diaphragm 6, the imaging lens 7, the second beam splitter prism 8 and the imaging element 11, the transmitted light is emitted from the first beam splitter prism 2, passes through the projection lens 3, irradiates on the polarization beam splitter flat 4, wherein a part of the transmitted light is reflected by the polarization beam splitter flat 4 to the smooth surface to be measured and totally reflected by the smooth surface to be measured to the rough surface 5 (i.e. the rough surface 5 can receive all light reflected by the smooth surface to be measured), diffuse reflection occurs on the rough surface 5 to form diffuse reflection light, and speckle is generated.
Wherein, part of diffuse reflection light irradiates on the smooth surface to be measured (wherein, the layout position of the rough surface 5 can not influence the light path of the subsequent polarization beam splitter flat 4 to the smooth surface to be measured and the smooth surface to be measured to the polarization beam splitter flat 4), and is reflected on the polarization beam splitter flat 4 by the smooth surface to be measured. A part of the diffuse reflection light passes through the polarization beam splitter plate 4 and is emitted by the polarization beam splitter plate 4, sequentially passes through the first diaphragm 6 and the imaging lens 7, irradiates on the second beam splitter prism 8, and is reflected by the second beam splitter prism 8 to the imaging element 11 (wherein, the light beam of the first beam splitter prism 2, the projection lens 3, the polarization beam splitter plate 4, the smooth surface to be measured, the rough surface 5, the smooth surface to be measured, the polarization beam splitter plate 4, the first diaphragm 6, the imaging lens 7, the second beam splitter prism 8 and the imaging element 11 is measuring light).
The measurement light and the reference light interfere with each other in the imaging element 11 to form an interference pattern for subsequent correlation measurement.
In order to meet the requirement of high-precision measurement in the later stage, in the application, a piezoelectric ceramic actuator 10 (hereinafter abbreviated as PZT) is connected with the first reflecting mirror 9 and is used for driving the first reflecting mirror 9 to linearly reciprocate in the direction perpendicular to the mirror surface.
Secondly, in order to form a measurement system, in the present application, the focal position of the projection lens 3 and the center position of the hole in the first diaphragm 6 are symmetrically disposed about the polarization beam splitter plate 4 (in this embodiment, the included angle between the axis of the hole in the first diaphragm 6 and the polarization beam splitter plate 4 is 45 °, and the included angle therebetween may be other angles, so as to meet the beam propagation requirement).
Based on the above arrangement, referring to fig. 2, in the present application, light emitted to the polarization beam splitter plate 4 at the focal point of the projection lens 3 is reflected by the polarization beam splitter plate 4 to be irradiated on the smooth surface to be measured, and then reflected by the smooth surface to be measured to the rough surface 5, and light paths a 1 and a 2 (shown in the left side of fig. 2) are formed in the process.
The light generated by the diffuse reflection is returned according to the original path of the incident path (the path of the light reflected by the smooth surface to be measured to the rough surface 5) and is reversely irradiated on the smooth surface to be measured, and then is reflected by the smooth surface to be measured to the polarization beam splitter plate 4, wherein a part of the light is transmitted through the polarization beam splitter plate 4 and then is injected into the hole in the first diaphragm 6, and in the process, the light paths A 21 and A 11 are formed (the right side content in FIG. 2).
The relative positional relationship of the projection lens 3, the polarization splitting plate 4 and the first diaphragm 6 is combined, and the optical path A 1＝A11 and the optical path A 2＝A21 are obtained.
Based on the above features, the principle of the present application that can achieve the relevant measurement will be described below.
Referring to fig. 3, before deformation of the smooth surface to be measured, the focus I of the projection lens 3 emits light in the IF direction (F is any point on the smooth surface to be measured) (the wave vector in the light direction is) After reflection at the point F, the rough surface 5 is irradiated (the wave vector in the light direction is) Diffuse reflection occurs to form diffuse reflection light; part of the diffuse reflection light returns to the first diaphragm 6 according to the original incident light path (combining the above, the same as returning to the focus I of the projection lens 3, the generated light direction is opposite to the incident light direction, and the wave vector of the obtained light direction is in turnAnd)。
After the smooth surface to be measured is deformed, the point F generates out-of-plane displacementPost-shifting to F'; then, light in the IF' direction is emitted at the focal point I of the projection lens 3 (the wave vector in the light ray direction is) After reflection at point F', the rough surface 5 is irradiated (the wave vector in the light direction is) Diffuse reflection occurs; the light generated by the diffuse reflection returns to the first diaphragm 6 according to the original path of the incident light path (combining the above, the same as returning to the focus I of the projection lens 3, the generated light is opposite to the incident light, and the wave vector of the obtained light is in turnTo the point of)。
Because the deformation of the smooth surface to be measured before and after deformation is extremely small, the smooth surface to be measured can be deformedAnd is also provided with
In combination with the foregoing, in the measurement system provided by the present application, the illumination beam (the focal point of the projection lens 3→the polarization splitting plate 4→the rough surface 5) and the imaging beam (the rough surface 5→the polarization splitting plate 4→the first diaphragm 6) are overlapped, so that the measurement light is reflected twice.
Then there are:
delta is the phase change quantity of the measuring beam caused by deformation at the midpoint F of the smooth surface to be measured, As the deformation sensitivity vector at point F,Is the deformation vector at point F.
And is also provided with
Wherein,As the wave vector of the reflected wave,Is the wave vector of the incident wave.
Because the smooth surface to be measured only deforms out of plane, the methodUnit vector parallel to the normal to the mirror plane at point FSince a smooth surface follows the reflection theorem of light, it is possible to:
Then there are:
While And is also provided withK isIs provided for the length of (a),Is a unit vector in the direction of the reflected wave, and λ is the wavelength of the laser beam.
It is possible to obtain a solution,Simultaneously eliminating K and multiplying the two sides by pointThe method can obtain the following steps:
In combination with the availability of the foregoing,
In the above-mentioned method, the step of,For the out-of-plane deformation d of the smooth surface to be measured in the direction of the mirror surface normal at the point F, the included angle alpha between the IF and the mirror surface normal at the point F and the included angle alpha 'between the IF' and the mirror surface normal at the point F 'can be regarded as the same, namely alpha is approximately equal to alpha', then
Then there are:
By combining the above, the sensitivity of the measurement system provided by the application is doubled compared with that of the traditional speckle interference technology.
When the measurement system provided by the application is used for high-precision measurement, a time phase shift phase extraction method is used for high-precision measurement, and the PZT is controlled to generate periodic motion in the measurement process so as to realize phase shift.
Namely: before deformation of a smooth surface to be measured, collecting a speckle interference pattern obtained by interference of measuring light and reference light, wherein the intensity expression I (x, y) is as follows:
Where a (x, y) is the sum of the intensities of the measurement light and the reference light, b (x, y) is the contrast of the resulting interferogram, A phase difference between the reference light and the measurement light; (x, y) represents the spatial coordinates on the smooth surface to be measured.
When the phase is extracted by adopting a time phase shift method, a plurality of pairs of speckle interference patterns are obtained by gradually moving the PZT and introducing the periodic phase, an equation set is formed to solve the phase information, and various methods such as a three-step phase shift method, a four-part phase shift method, a five-step phase shift method and the like are developed in the time phase shift method so far. The phase calculation principle is described by taking the most common four-step phase shift method as an example.
In the four-step time phase shift algorithm, the phase introduced by each movement of the PZT is pi/2, the speckle interference pattern obtained in the initial state is used as a first speckle interference pattern, one interference pattern is recorded by each movement of the PZT, and the intensity of the four speckle interference patterns obtained after three movements is as follows:
I 1 (x, y) is obtained in an initial state, and I 2(x,y)、I3 (x, y) and I 4 (x, y) are obtained after each phase shift movement respectively.
The phase information before deformation can be obtained by carrying out combination operation on the above components
After the smooth surface to be measured is deformed, the same image information acquisition and processing are carried out, and the deformed phase information can be obtainedSubtracting the phases before and after deformation to obtain a phase difference corresponding to the deformation of the smooth surface to be measured;
the time phase shift method needs that the smooth surface to be measured is unchanged in the process of collecting speckle interference images by the PZT continuous motion, so that the method is not suitable for the smooth surface to be measured which dynamically changes.
In the above process, the first diaphragm 6 needs to have a larger diameter structure to ensure enough luminous flux.
When the measuring system is used for dynamic measurement (when continuous deformation is generated on the smooth surface to be measured, the dynamic measurement is needed), a spatial carrier phase extraction method is used for relevant measurement.
Specific: the spatial carrier method can extract phase information from a single picture, and the reference light can carry carrier frequency by adjusting the inclination angle of the first reflecting mirror 9, so that the obtained speckle interference image intensity expression is:
where f is the carrier frequency introduced by the first mirror 9 controlling the deflection of the reference light, for simplicity, it is assumed that the first mirror 9 deflects only in the X direction, i.e. only the carrier frequency in the X direction is introduced, and the above formula is developed according to the euler formula:
Assume that Fourier transforming the above, the following can be obtained:
FI(fx,fy)＝FA(fx,fy)+FB(fx+f,fy)+FC(fx-f,fy)
Where c=b *, FI, FA, FB, FC are each the fourier transforms of I, a, B, C.
From the above equation, the frequency domain of the speckle interference pattern is divided into three parts. Wherein, FA (f x,fy) is located in the low frequency part of the frequency domain, and FB (f x+f,fy) and FC (f x-f,fy) are both located in the high frequency part of the frequency domain and are symmetrical about the center of the frequency domain. The cut-off frequencies of FB and FC are controlled by adjusting the size of the first diaphragm 6 (also by changing the first diaphragm), and the frequency size of the incoming carrier is controlled by adjusting the first mirror 9, so that the three spectra are completely separated. Let D (x, y) =b (x, y) e i2πfx, extract FB (f x+f,fy) by using a suitable band-pass filter for FI, perform inverse fourier transform to obtain D (x, y), and calculate the phase by the following formula:
After the smooth surface to be measured is deformed, a pair of speckle interference patterns are collected and subjected to the same data processing, so that deformed phase information can be obtained:
The phase difference of the deformation of the smooth surface to be measured can be obtained by subtracting the two formulas:
that is, the measuring system designed by the application can be used for high-precision measurement and dynamic measurement.
In addition, the application does not need to set a high-precision reference optical element, has simple structure of an illumination light path, does not need to carry out complicated adjustment, and directly corresponds to the measured interference image and the spatial position of the measured mirror surface, thereby effectively solving the technical problem existing in the prior art when the smooth surface deformation measurement is carried out, and improving the measurement precision.
In order to facilitate setting the aperture of the first diaphragm 6 according to the requirement, in this embodiment, the first diaphragm 6 is an adjustable diaphragm.
Second, in order to facilitate adjustment and control of the laser beam incident on the first beam splitter prism 2, a second reflecting mirror 12 is further provided; as shown in fig. 1, the laser beam generated by the laser 1 irradiates on the second reflecting mirror 12, and irradiates on the first beam splitter prism 2 after being reflected by the second reflecting mirror 12, so that the angle of the laser beam injected into the first beam splitter prism 2 can be adjusted by adjusting the angle of the second reflecting mirror 12, thereby being convenient for realizing effective adjustment of the optical path.
In order to ensure the collimation of the laser beam emitted to the first beam-splitting prism 2, in this embodiment, a collimation beam-expanding lens 13 is further disposed between the second reflecting mirror 12 and the first beam-splitting prism 2; that is, the laser beam reflected by the second reflecting mirror 12 is first incident into the collimating and beam expanding mirror 13, and the collimating and beam expanding mirror 13 expands the incident light spot while maintaining the collimation of the laser beam.
In order to facilitate adjustment of the size of the laser beam entering the first beam splitter prism 2, a second diaphragm 14 is further disposed between the collimating and beam expander 13 and the first beam splitter prism 2, so that the beam passing through the second diaphragm 14 can be spatially filtered to achieve a desired parameter corresponding to the beam entering the first beam splitter prism 2.
In order to reduce the clutter effect, in this embodiment, a first half-wave plate 15 and a second half-wave plate 16 are also provided.
The first half-wave plate 15 is disposed between the first beam splitter prism 2 and the projection lens 3, and is used for adjusting the polarization state of the light beam emitted by the first beam splitter prism 2 and directed to the projection lens 3.
The second half-wave plate 16 is disposed between the first beam splitter prism 2 and the first reflecting mirror 9, and is used for adjusting the polarization state of the light beam emitted by the first beam splitter prism 2 and directed to the first reflecting mirror 9.
In order to adjust the alignment state of the light beam between the second half-wave plate 16 and the first reflecting mirror 9 and between the first reflecting mirror 9 and the second beam splitting prism 8, in this embodiment, a first collimating mirror 17 and a second collimating mirror 18 are further provided.
The first collimating mirror 17 is disposed between the second half-wave plate 16 and the first reflecting mirror 9, and is used for performing collimation state adjustment on the light beam emitted by the second half-wave plate 16 and directed to the first reflecting mirror 9.
The second collimating mirror 18 is disposed between the first reflecting mirror 9 and the second beam splitter prism 8, and is used for adjusting the collimation state of the light beam emitted by the first reflecting mirror 9 and directed to the second beam splitter prism 8.
In order to ensure the collimation state of the reflected light, the propagation distance of the light beam between the first collimating mirror 17 and the second collimating mirror 18 is the sum of the focal lengths of the two, so that the emergent light of the second collimating mirror 18 is ensured to be parallel light; and when the focal length of the second collimating mirror 18 is N times that of the first collimating mirror 17, the diameter of the parallel light beam emitted from the second collimating mirror 18 is N times that of the incident parallel light of the first collimating mirror 17.
In order to adjust the parameters of the light beam emitted by the first collimator mirror 9 and directed towards the first mirror 9, a third diaphragm 19 is also arranged between the first collimator mirror 17 and the first mirror 9 for spatially filtering the light beam emitted by the first collimator mirror 17.
In order to adjust parameters related to the light beam emitted from the second collimator lens 18 and incident on the second beam splitter prism 8, a polarizing plate 20 and an attenuation plate 21 are further provided.
The polarizing plate 20 is disposed between the second collimator 18 and the second beam splitter prism 8, and the attenuation plate 21 is disposed between the polarizing plate 20 and the second beam splitter prism 8.
The polarizer 20 and the attenuator 21 are arranged to adjust parameters such as the intensity of the reference light entering the imaging element 11, and finally to make the intensity of the reference light close to that of the measurement light.
In the application, the polarization direction of the transmitted light can be controlled by adjusting the first half-wave plate 15, so that the transmitted light can be completely changed into S light to be reflected by the polarization beam splitting flat plate 4, thereby being beneficial to improving the light utilization rate.
By adjusting the second half-wave plate 16 and the polaroid 20, on one hand, the light intensity ratio of the obtained reference light to the measuring light can be adjusted, which is helpful for improving the imaging signal-to-noise ratio; on the other hand, the reference light and the measuring light can be in the same polarization state, and the interference quality can be improved.
And the aperture of the first diaphragm 6 is set to be adjustable so that the system can adjust the size of the aperture of the first diaphragm 6 as required to limit the spectral width of the resulting speckle interference pattern, etc.
By controlling the inclination angle of the first mirror 9, the angle at which the reference light is introduced can be controlled so as to realize the aforementioned separation of FA (f x,fy)、FB(fx+f,fy) and FC (f x-f,fy) in cooperation with the first diaphragm 6.
In the system, according to the reversibility principle of light transmission, by means of the symmetrical arrangement of the focus of the projection lens 3 and the central point of the hole in the first diaphragm 6 relative to the polarization beam splitting flat sheet 4, the complete coaxiality of an observation light beam (rough surface, smooth surface to be detected, polarization beam splitting flat sheet, first diaphragm) and an illumination light beam (focus of the projection lens, polarization beam splitting flat sheet, smooth surface to be detected and rough surface) is realized.
The direction of the light reflected by the polarization beam splitting flat sheet 4 and irradiated to the smooth surface to be detected is coincident with the direction of the light imaged on the smooth surface.
In summary, the high-sensitivity mirror deformation measurement system and method based on speckle interference have the following beneficial effects compared with the prior art:
1. The application is based on the principle that coherent light irradiates on a smooth surface to be measured to generate specular reflection, a rough surface 5 is placed beside the smooth surface to be measured, the rough surface 5 receives coherent light beams reflected by the smooth surface to be measured, so that scattered reflection occurs on the surface of the rough surface 5 to generate speckles, the generated scattered reflection light is reflected by the smooth surface to be measured again to a measuring system to form measuring light, and the measuring light interferes with reference light which is additionally introduced, so that the speckle interference of the smooth surface to be measured is finally realized.
2. Through the design of a coaxial illumination light path, laser beams are emitted from a measuring system and then irradiated to a smooth surface to be measured, the laser beams are reflected back to the measuring system by the smooth surface to be measured after being diffusely reflected by a rough surface 5, and the focus of a projection lens 3 in the illumination light path and the center of a hole in a first diaphragm 6 are symmetrically arranged relative to a polarization beam splitting flat sheet 4, so that the illumination light beam and an imaging light beam are completely overlapped, the measuring light beam is reflected by the smooth surface to be measured twice according to the same incidence angle, when any point of the smooth surface to be measured is deformed, the optical path difference caused by deformation of the point is 4 times of the deformation, and compared with the arrangement that the measuring light beam is reflected only once in the traditional speckle interference technology, the deformation sensitivity of the invention is doubled compared with the traditional speckle interference.
3. By adopting the combination of the polarizing optical elements such as the polarizing plate 20, the half wave plate, the polarizing beam splitting flat plate 4 and the like, the light utilization rate of the system can be improved, and meanwhile, the light intensity ratio of the reference light to the measuring light can be finely adjusted, thereby being beneficial to improving the signal to noise ratio of later imaging.
4. Based on the coaxial illumination light path, the illumination light path coincides with the measurement light path, so that the measurement system is easy to adjust, only the transmission light reflected by the smooth surface to be measured can be completely irradiated on the rough plane, and the positions of the smooth surface to be measured and the rough surface 5 relative to the measurement system can be adjusted according to the actual measurement environment (the rough surface 5 does not influence the view field light path).
5. By designing the trend of the light path, the invention can effectively avoid parasitic light crosstalk caused by the surface reflection of the optical element.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A high-sensitivity mirror deformation measurement system based on speckle interference comprises an imaging element, and is characterized by further comprising a laser;
A first beam splitter prism for splitting a laser beam generated by the laser into reflected light and transmitted light;
the transmitted light passes through the projection lens and is reflected by the polarized light splitting flat sheet and the smooth surface to be detected in sequence and then irradiates on the rough surface to form diffuse reflection light;
Part of the diffuse reflection light is reflected by the smooth surface to be detected, sequentially passes through the polarization beam splitting flat plate, the first diaphragm and the imaging lens, is reflected by the second beam splitting prism and irradiates on the imaging element;
part of the reflected light passes through the second beam splitting prism after being reflected by the first reflecting mirror and irradiates on the imaging element;
The focus position of the projection lens and the center position of the hole in the first diaphragm are symmetrically arranged relative to the polarization beam splitting flat sheet;
The first reflecting mirror is vertically connected with the piezoelectric ceramic actuator.
2. The high sensitivity specular distortion measurement system of claim 1, further comprising a second mirror for reflecting the laser beam to the first beam splitter prism.
3. The high-sensitivity mirror deformation measurement system based on speckle interference of claim 2, further comprising a collimating and beam expanding lens arranged between the second reflecting mirror and the first beam splitting prism;
The second diaphragm is arranged between the collimation beam expander and the first beam splitter prism.
4. A high sensitivity specular distortion measurement system based on speckle interferometry as set forth in claim 1, further comprising:
the first half wave plate is arranged between the first beam splitting prism and the projection lens;
The second half wave plate is arranged between the first beam splitting prism and the first reflecting mirror.
5. A high sensitivity specular distortion measurement system based on speckle interferometry as set forth in claim 4, further comprising:
the first collimating mirror is arranged between the second half-wave plate and the first reflecting mirror;
the second collimating mirror is arranged between the first reflecting mirror and the second beam splitting prism;
The propagation distance of the light beam between the first collimating mirror and the second collimating mirror is the sum of the focal lengths of the first collimating mirror and the second collimating mirror.
6. The speckle-interference-based high-sensitivity specular deformation measurement system of claim 5, further comprising a third diaphragm disposed between the first collimating mirror and the first reflecting mirror.
7. A high sensitivity specular distortion measurement system based on speckle interferometry as set forth in claim 6, further comprising:
the polarizing plate is arranged between the second beam splitting prism and the second collimating mirror;
And the attenuation sheet is arranged between the polaroid and the second beam splitting prism.
8. A high sensitivity mirror deformation measuring system based on speckle interference according to claim 1, wherein the first diaphragm is an adjustable diaphragm.
9. A method for high-precision measurement of mirror deformation using a high-sensitivity mirror deformation measurement system based on speckle interferometry according to any of claims 1-8, wherein the method comprises using a time-phase-shift phase extraction method to make the high-precision measurement of mirror deformation.
10. A method for dynamic measurement of mirror deformation using a high sensitivity mirror deformation measurement system based on speckle interferometry according to any of claims 1-8, wherein the method comprises using spatial carrier phase extraction for dynamic measurement of mirror deformation.
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| CN108106556A (en) * | 2018-02-02 | 2018-06-01 | 上海交通大学 | Based on the curved face object of digital speckle interference from face distortion measurement method and device |
| CN113847880A (en) * | 2021-07-28 | 2021-12-28 | 合肥工业大学 | High-precision measuring method for three-dimensional deformation of mirror surface |
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| DE4446887A1 (en) * | 1994-12-28 | 1996-07-04 | Wolfgang Prof Dr Ing Steinchen | Non-destructive surface inspection by shearing speckle interferometry |
| US20160320176A1 (en) * | 2013-12-20 | 2016-11-03 | Oakland University | Digital shearography ndt system for speckless objects |
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| CN108106556A (en) * | 2018-02-02 | 2018-06-01 | 上海交通大学 | Based on the curved face object of digital speckle interference from face distortion measurement method and device |
| CN113847880A (en) * | 2021-07-28 | 2021-12-28 | 合肥工业大学 | High-precision measuring method for three-dimensional deformation of mirror surface |
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