CN108226170B - Material internal defect detection system based on Michelson shearing speckle interference - Google Patents
Material internal defect detection system based on Michelson shearing speckle interference Download PDFInfo
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- CN108226170B CN108226170B CN201810079279.5A CN201810079279A CN108226170B CN 108226170 B CN108226170 B CN 108226170B CN 201810079279 A CN201810079279 A CN 201810079279A CN 108226170 B CN108226170 B CN 108226170B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
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Abstract
The invention relates to the technical field of shearing speckle interference, and particularly discloses a material internal defect detection system based on Michelson shearing speckle interference. The device comprises a laser, a beam expander, a first lens, a second lens, a first polaroid, a spatial light modulator, a third lens, a second polaroid and a CCD (charge coupled device); laser emitted by the laser sequentially passes through the surface of an object to be measured, the first lens, the first polaroid and the second lens, the SLM modulates Fourier transform of input light of the second lens, phase factors are added to e light signals, e light modulated by the SLM and o light not modulated by the SLM enter the second polaroid through the third lens, and the e light and the o light are projected onto a CCD target surface through a first light beam and a second light beam generated by the second polaroid respectively so as to interfere with each other on the CCD target surface. The detection system overcomes the measurement error caused by manually adjusting the shearing quantity, has low requirement on the reflection angle of the SLM, reduces the difficulty of system adjustment, and has no requirement on a laser light source.
Description
Technical Field
The invention relates to the technical field of shearing speckle interference, in particular to a material internal defect detection system based on Michelson shearing speckle interference.
Background
In the conventional shearing speckle interference, a mirror adjusting frame debugged by a manipulator is generally adopted, and the purpose of adjusting the shearing amount is achieved by adjusting the rotation angle of the adjusting frame in the XY direction. Most of the adjustment quantities are modulated based on the target surface of a charge-coupled device (CCD) image sensor of the same type and the estimation of the detected object and the defect size of the detected object by depending on experience, and when the CCD target surface changes, or the condition of the detected object changes, or the resolution of a display screen changes, misjudgment of the shearing quantity can be caused. If the shearing amount is too small, although the resolution of the stripes is improved, the sensitivity of the detection system is reduced, and small defects or defects deeper from the surface can be ignored; however, if the shearing amount is too large, although the sensitivity of the system is high, the same deformation and the number of fringes increase, and under the condition of a certain resolution of the CCD, the resulting fringe pattern may not be processed, and an ideal experimental result may not be obtained.
Spatial Light Modulator (SLM) technology can be employed in shearing speckle interferometry systems to achieve controllable adjustment of the amount of shearing. At present, shearing speckle interference systems based on the SLM technology all adopt non-coaxial detection light paths, and the SLM reflection angle is required to reach 15 degrees, but the commercially available SLM reflection angle can not meet the requirement, so that the detection system needs to be specially made, and the cost is higher. In addition, due to the problem of long axis deflection of SLM liquid crystal molecules, there is a certain requirement for the polarization direction of laser light emitted from a laser, and thus there is a great difficulty in adjusting the position of the laser. In addition, since the position of the laser is fixed, there is caused a problem that the field of view is illuminated and the light intensity is limited at the time of detection.
Disclosure of Invention
Technical problem to be solved
The invention aims to provide a material internal defect detection system based on Michelson shearing speckle interference, and aims to at least solve one of the technical problems in the prior art or the related art.
(II) technical scheme
In order to solve the technical problem, the invention provides a material internal defect detection system based on michelson shearing speckle interference, which comprises: the device comprises a laser, a beam expander, a first lens, a second lens, a first polaroid, a spatial light modulator, a third lens, a second polaroid and a charge-coupled device image sensor; the spatial light modulator is positioned on a Fourier frequency spectrum plane of the second lens, laser emitted by the laser is incident to the surface of a measured object and is reflected to the first lens through the surface of the measured object, and linear polarized light capable of adjusting the polarization direction is formed through the first polaroid after being focused by the first lens; the linearly polarized light is Fourier transformed by the second lens, the spatial light modulator modulates Fourier transform of input light of the second lens and adds a spatial phase factor to extraordinary light, the extraordinary light modulated by the spatial light modulator and the ordinary light not modulated by the spatial light modulator are focused on a target surface of the CCD image sensor by the third lens, a second polarizer is arranged between the third lens and the CCD image sensor, the polarization direction of the second polarizer forms an included angle alpha with the extraordinary light and the ordinary light, wherein 0 DEG < alpha <90 DEG, and a first light beam generated by the second polarizer and a second light beam generated by the ordinary light are projected on the target surface of the CCD image sensor, so as to form a speckle interference pattern formed by mutual interference of the first light beam and the second light beam on the target surface of the CCD image sensor.
Wherein a half wave plate is arranged between the polarizer and the second lens.
Wherein α is 45 °.
Wherein the spatial light modulator is a liquid crystal type phase adjuster controlled by a computer.
Wherein the spatial light modulator is a reflective phase-type spatial light modulator.
(III) advantageous effects
The material internal defect detection system based on Michelson shearing speckle interference provided by the invention adopts a coaxial light path, so that the requirement on the deflection angle of the SLM is reduced, and the cost is saved under the condition of the same experimental result. And because the coaxial optical path is adopted, in the aspects of optical path adjustment and phase transformation technology, the problem of optical path caused by angles is reduced, the difficulty of optical path adjustment is reduced, and the reliability of results is improved. The detection system overcomes the measurement error caused by manually adjusting the shearing quantity in the prior art, and simultaneously, the detection system achieves balance in two aspects of resolution and sensitivity.
In addition, a method that a polarizing film and a half wave plate are matched together is adopted before the SLM, the polarization direction of input light of the laser is not required, the difficulty of system adjustment is greatly reduced, and the requirements on a laser light source are not required.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a preferred embodiment of a material internal defect detection system based on michelson shearing speckle interference according to the invention.
In the figure, 1: a laser; 2: a measured object; 3: a first lens; 4: a first polarizing plate; 5: a half wave plate; 6: a second lens; 7: a spatial light modulator; 8: a third lens; 9: a second polarizing plate; 10: a charge coupled device image sensor; 11: a beam expander.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.
Fig. 1 shows a preferred embodiment of a michelson shearing speckle interference based material internal defect detection system according to the present invention. As shown in the figure, the system for detecting the internal defect of the shearing speckle interference material comprises a laser 1, a beam expander 11, a first lens 3, a first polaroid 4, a second lens 6, a Spatial Light Modulator (SLM)7, a third lens 8, a second polaroid 9 and a charge-coupled device image sensor 10; the SLM7 is located on a Fourier spectrum plane of the second lens 6, laser emitted by the laser 1 enters the surface of the object 2 to be measured, is reflected to the first lens 3 through the surface of the object 2 to be measured, and forms linearly polarized light capable of adjusting the polarization direction through the first polarizer 4 after being focused by the first lens 3; this linearly polarized light is fourier transformed by the second lens 6, the SLM7 modulates the fourier transform of the light input by the second lens 6, and adds a space phase factor to the extraordinary ray (e-ray), the e-ray modulated by the SLM7 and the ordinary ray (o-ray) not modulated by the SLM7 are focused on the target surface of a charge coupled device image sensor (CCD)10 through a third lens 8, a second polarizer 9 is arranged between the third lens 8 and the ccd image sensor 10, wherein the polarization direction of the second polarizer 9 forms an included angle alpha with the e light and the o light, wherein alpha is 45 degrees, the e light is projected to the target surface of a charge-coupled device image sensor (CCD)10 through a first light beam generated by the second polarizer 9 and a second light beam generated by the o light through the second polarizer 9, to form a speckle interference pattern on the target surface of the CCD10, wherein the first and second light beams interfere with each other.
Further, a half wave plate 5 is preferably arranged between the first polarizer 4 and the second lens 6, and is used for changing the polarization direction of the linearly polarized light generated by the first polarizer 4, so that the included angle between the polarization direction of the linearly polarized light and the liquid crystal molecules of the SLM7 is equal to 45 degrees, the light intensities of the polarized light in the two directions are basically consistent, and therefore good interference on the CCD10 is ensured.
It should be noted that, in this embodiment, the angle α between the polarization direction of the second polarizer 9 and the o-light and the e-light is 45 °. However, it will be appreciated by those skilled in the art that in other embodiments of the invention the second polarizer 9 may have a polarization direction that is at other angles to the o-and e-light, but that 0 < α <90 ° is ensured.
Further, the SLM7 is a liquid crystal type phase adjuster controlled by a computer. The liquid crystal is deflected by an electric control method, the electric control nematic twist effect and the electric control birefringence effect of the liquid crystal are used as the main control principle, the phase of the e light is changed by the liquid crystal, a phase factor is added to the modulated e light in the frequency domain, a translation is generated in a corresponding space domain, and therefore the o light and the e light generate a constant dislocation after passing through the SLM 7.
It should be noted that although in this embodiment SLM7 is a reflective phase type spatial light modulator. However, it will be appreciated by those skilled in the art that SLM7 could also be a transmissive phase type spatial light modulator, etc., in other embodiments of the present invention.
When the device is used, laser beams generated by the laser 1 are directly projected to the surface of the measured object 2 through the beam expander 11, and original linear polarization light is converted into light in all polarization directions due to diffuse reflection on the surface of the measured object 2. The first lens 3 acts as an imaging lens to converge the light beam on the surface of the object 2 to be measured onto the phase plane of the second lens 6. The first polarizing plate 4 serves as a polarizer to change polarized light having any polarization direction passing through the second lens 6 into linearly polarized light having only one polarization direction. The half wave plate 5 between the first polarizer 4 and the second lens 6 is used for changing the polarization direction of the linearly polarized light generated by the first polarizer, so that the angle between the polarization direction of the linearly polarized light and the liquid crystal molecules of the SLM7 is equal to 45 degrees. Since the liquid crystal molecules of SLM7 modulate light with respect to one direction of polarization, light with another direction of polarization is not modulated. The SLM7 is placed in the fourier spectral plane of the second lens 6 and the light is fourier transformed by the second lens 6, resulting in a fourier transform of the input light in the image plane of the second lens 6. The SLM7 modulates the fourier transform of the input light from the second lens 6, adding a phase factor, so that the modulated e-light adds a phase factor in the frequency domain, producing a shift in the spatial domain. The light modulated by the SLM7 enters the third lens 8 to be converged onto the target surface of the CCD 10. And passes through the second polarizer 9 before converging on the target surface of the CCD10, the polarization direction of the second polarizer 9 making an angle of 45 ° with the o and e light, i.e. the polarized light passing through the second polarizer 9 is the sum of the components of the o and e light in this polarization direction. Since the SLM7 is placed on the fourier spectrum plane of the second lens 6, the phase modulation of the e-light is reflected as a shift change in the spatial domain, so that the o-light and the e-light generate a constant misalignment after passing through the SLM 7. And because of the modulation of the second polarizer 9, the o light and the e light have components in a certain polarization direction, and the components are used as the first light beam and the second light beam which interfere with each other, and finally the o light and the e light interfere with each other on the target surface of the CCD 10. And the relative displacement of the surface of the measured object is inversely calculated by recording the phase of the interference fringes. Because the phase difference is constant, the polarization directions are the same, and the frequencies are the same, the two beams of light form an interference phenomenon on the surface of the CCD 10. By analyzing the phase of the interference fringes, corresponding position information can be obtained.
In conclusion, the material internal defect detection system based on Michelson shearing speckle interference provided by the invention reduces the requirement on the deflection angle of the SLM7 by adopting a coaxial optical path, and saves the cost under the condition of the same experimental result. And because of adopting the coaxial light path, in the aspect of the adjustment of the light path and the aspect of the phase transformation technology, the problem of the light path caused by the angle is reduced, the difficulty of the light path adjustment is reduced, and the reliability of the result is improved. The detection system overcomes the measurement error caused by manually adjusting the shearing quantity in the prior art, and simultaneously, the detection system achieves balance in two aspects of resolution and sensitivity. In addition, the method that the first polarizer 4 and the half-wave plate 5 are matched together before the SLM7 is adopted, the polarization direction of input light of the laser 1 is not required, the difficulty of system adjustment is greatly reduced, and the laser light source is not required.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, 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 an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present 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 solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (4)
1. A system for detecting internal defects of a material based on Michelson shearing speckle interference is characterized by comprising: the device comprises a laser, a beam expander, a first lens, a second lens, a first polaroid, a spatial light modulator, a third lens, a second polaroid and a charge-coupled device image sensor; the spatial light modulator is positioned on a Fourier frequency spectrum plane of the second lens, laser emitted by the laser is incident to the surface of a measured object and is reflected to the first lens through the surface of the measured object, and linear polarized light capable of adjusting the polarization direction is formed through the first polaroid after being focused by the first lens; the linearly polarized light is Fourier transformed by the second lens, the spatial light modulator modulates Fourier transform of input light of the second lens and adds a spatial phase factor to extraordinary light, the extraordinary light modulated by the spatial light modulator and the ordinary light not modulated by the spatial light modulator are focused on a target surface of the CCD image sensor by the third lens, a second polarizer is arranged between the third lens and the CCD image sensor, the polarization direction of the second polarizer forms an included angle alpha with the extraordinary light and the ordinary light, wherein 0 DEG < alpha <90 DEG, and a first light beam generated by the second polarizer and a second light beam generated by the ordinary light are projected on the target surface of the CCD image sensor, forming a speckle interference pattern formed by the first light beam and the second light beam through mutual interference on the target surface of the CCD image sensor;
and a half wave plate is arranged between the first polaroid and the second lens.
2. The system for detecting internal defects in a material based on michelson shearing speckle interference as claimed in claim 1, wherein α is 45 °.
3. The system for detecting internal defects of material based on michelson shearing speckle interference according to claim 1, wherein the spatial light modulator is a liquid crystal type phase adjuster controlled by a computer.
4. The system for detecting internal defects of a material based on Michelson shearing speckle interference as claimed in any one of claims 1 to 3, wherein the spatial light modulator is a reflective phase-type spatial light modulator.
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| CN109297931B (en) * | 2018-11-23 | 2020-12-22 | 合肥工业大学 | Three-direction shearing speckle interference system and method based on spatial carrier |
| CN112414941A (en) * | 2020-11-26 | 2021-02-26 | 青岛理工大学 | Complex surface nondestructive detection system and method based on shearing speckle interference technology |
| CN112858344B (en) * | 2021-01-20 | 2022-09-20 | 昆明理工大学 | Nondestructive testing device and method |
| CN113283420A (en) * | 2021-05-20 | 2021-08-20 | 维沃移动通信有限公司 | Electronic device, material detection method, material detection device, and readable storage medium |
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