CN116147497A - Common-path shearing interference imaging system and method with independently adjustable shearing and carrier frequency - Google Patents
Common-path shearing interference imaging system and method with independently adjustable shearing and carrier frequency Download PDFInfo
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- CN116147497A CN116147497A CN202310003555.0A CN202310003555A CN116147497A CN 116147497 A CN116147497 A CN 116147497A CN 202310003555 A CN202310003555 A CN 202310003555A CN 116147497 A CN116147497 A CN 116147497A
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01B11/161—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge by interferometric means
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
- G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
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Abstract
The invention discloses a shearing and carrier frequency independent adjustable common-path shearing interference imaging system and method, comprising a coherent light source, wherein the light beam of the coherent light source is emitted to the surface of an object to be detected through a beam expander, and the object to be detected, a first lens, an aperture, a second lens, a Wollaston prism, a polaroid, an imaging lens and a camera are sequentially arranged on the same axis with the object to be detected. The invention also discloses a common-path shearing interference imaging method with independently adjustable shearing and carrier frequency. The invention adopts the common-path shearing interference imaging system and the method with the shearing and carrier frequency being independently adjustable, the shearing quantity and the space carrier frequency in the imaging system are controlled to be distributed to different parts of the imaging system, and the shearing force which is small enough is provided by the adjustable near-zero shearing quantity so as to ensure that complex surface shapes or deformation can be solved; the separate control of the spatial carriers further ensures a well-distributed spatial spectrum when configuring the required near zero amount of shear.
Description
Technical Field
The invention relates to the technical field of optical interferometry, in particular to a common-path shearing interference imaging system and method with independently adjustable shearing and carrier frequencies.
Background
The shearing interference technology is characterized in that laser is used as a measuring tool, the laser irradiates the surface of an object after beam expansion, reflected light/diffuse reflected light is collected by a detector after passing through a system, the collected object light is sheared by a shearing unit to form two beams of same object light with transverse displacement, then a shearing interference pattern is formed on the detector, and a phase diagram of the shearing interference can be obtained after algorithm processing, wherein the phase diagram represents the phase distribution of the surface to be measured. Wherein, for an optically smooth surface, the phase diagram characterizes its geometry for measuring its surface geometry errors; for optically rough surfaces, the displacement gradient of the surface due to the associated deformation can be obtained by subtracting the two phase maps acquired before and after the deformation. The technology is a nondestructive testing technology and is commonly used for detection in the fields of aerospace, mechanical manufacturing, optical processing and the like.
In the shear interferometry technique, the "shear volume" is defined as the displacement between two beams of transverse shear images, which is one of the characteristic parameters of a shear interference imaging system and determines to some extent the performance of the shear measurement system. In optically smooth surfaces with complex surface shape distribution, optically rough surfaces with complex deformation distribution, and nondestructive inspection with high rate of change, a sufficiently small amount of shear (near zero amount of shear) is required and preferable. On the one hand, the profile relief or deformation distribution can only exist at one extreme point in the shearing quantity range, which requires that the shearing quantity is sufficiently small. On the other hand, near zero shear slows down the decorrelation process between the two beams of shear light, providing a large dynamic range, especially in applications with high rates of change.
Meanwhile, phase shifting in a temporal or spatial manner is an indispensable technique for realizing a quantitative shearing interference imaging system. For measurements in recent years, a large number of measurements require a relatively high time resolution, so that the spatial carrier frequency method is preferred because the spatial carrier frequency method can retrieve the phase map by means of only one shearing interferogram.
Compared with a shearing interference system based on Michelson and Mach-Zehnder configuration, the collinear common-path system is beneficial to the construction of the system, and the robustness and the stability of the system are further enhanced. All optical devices in the collinear system are concentric and collinear at the same time, and two mutually-tangential object lights propagate along the same light path, so that interference and noise in the light path are counteracted. However, in the existing collinear common-path system, the shearing amount is entangled with the spatial carrier frequency, and independent control cannot be realized. In practice, small amounts of shear lead to high accuracy and large measurement ranges. Furthermore, for effective measurement, only one extreme point of deformation or profile distribution is required within the amount of shear, which requires that the amount of shear be small enough. However, co-linear, co-routed shear imaging systems, while having unique co-linear characteristics, often have difficulty achieving independent control of the adjustable arbitrary small shear and carrier frequency.
Disclosure of Invention
The invention aims to provide a common-path shearing interference imaging system and method with independently adjustable shearing and carrier frequencies, which solve the problems in the background art.
In order to achieve the above purpose, the invention provides a common-path shearing interference imaging system with independently adjustable shearing and carrier frequencies, which comprises a coherent light source, wherein the light beam of the coherent light source is emitted to the surface of an object to be detected through a beam expander, and the object to be detected, a lens I, an aperture, a lens II, a Wollaston prism, a polaroid, an imaging lens and a camera are sequentially arranged on the same axis as the object to be detected.
The invention also provides a common-path shearing interference imaging method with independently adjustable shearing and carrier frequency, which comprises the following steps:
step one, adjusting an imaging system to obtain a desired amount of shear and a desired spatial spectral distribution;
step two, the surface of the object to be detected is irradiated by a coherent light source, the imaging system collects the light returned from the surface of the object to be detected, and the object to be detected is imaged on a camera;
step three, a camera collects the shearing interference pattern and performs Fourier transformation;
introducing a spatial carrier frequency, selecting components in the spatial frequency spectrum subjected to Fourier transform, and performing inverse Fourier transform on the components to obtain complex amplitude;
step five, calculating the phase angle of the complex amplitude, removing carrier frequency for the obtained phase angle, obtaining phase distribution, and obtaining the surface relief height gradient of the measured surface;
step six, for surface displacement gradient measurement, carrying out the step one to the step five before and after deformation respectively, obtaining the surface height gradient of the front and the back twice and making difference.
Preferably, in the first step, the imaging system is adjusted, and the distance between the Wollaston prism and the intermediate real image surface is controlled so as to obtain the desired shearing amount; the image distance of the imaging system is adjusted to obtain the desired spatial spectral distribution.
Preferably, in the second step, the surface of the object to be measured is illuminated at a certain angle after the beam is expanded by the beam expander, the light returned from the surface of the object to be measured is collected by the imaging system and imaged on the intermediate real image surface, two beams of misplaced object light are generated by splitting by the Wollaston prism, the intermediate real image surface is imaged by the imaging lens, the imaged image is positioned on the photosensitive surface of the camera, and the wavefront of the two sheared object light is
u 1 (x,y)＝|u 1 (x,y)exp{i[φ(x,y)]}
u 2 (x,y)＝|u 1 (x+δ x ,y)exp{i[φ(x+δ x ,y)+2πf 0 x]}
Wherein (x, y) describes camera photosurface coordinates, phi is the phase from the surface of the object to be measured, delta x F is the amount of shear applied 0 For the introduced spatial carrier frequency.
Preferably, in the third step, the camera acquires a shearing interference pattern, and the intensity of the shearing interference pattern is recorded as
Wherein, asterisks indicate complex conjugate operation;
fourier transforming the shearing interference pattern collected by the camera, and recording as
Wherein the method comprises the steps of
Representing the fourier transform operation, DC represents the low frequency spectrum of the background light intensity, and uppercase letter U represents the fourier transform of each complex amplitude in the formula of step two.
Preferably, in the fourth step, by introducing the spatial carrier frequency, the three components in the spatial spectrum diagram shown in the formula in the third step are separated from different positions of the spatial spectrum, and are selected from the spectrum
A component; performing inverse Fourier transform on the selected component to obtain complex amplitude +.>
Is marked as
Wherein the method comprises the steps of
Representing an inverse fourier transform operation. />
Preferably, in the fifth step, the phase angle of the obtained complex amplitude is obtained and recorded as
Wherein Im is the operation of taking the imaginary part, and Re is the operation of taking the real part;
removing carrier frequency from the obtained phase angle to obtain phase distribution phi (x, y), calculating according to the following formula to obtain surface relief height gradient of the measured surface, and recording as
Where θ is the angle between the incident light and the normal to the surface of the object under test.
Therefore, the system and the method for common-path shearing interference imaging with independently adjustable shearing and carrier frequencies have the following beneficial effects:
1. the invention provides a convenient system installation mode by adopting a collinear common-path system, and has potential to operate in an industrial environment due to the excellent noise resistance;
2. the shearing interference imaging system provided by the invention is particularly suitable for measuring complex surface distribution or complex deformation, and the adjustable near-zero shearing quantity provides small shearing force enough to ensure that complex surface shape or deformation can be solved.
3. The control of the amount of shear and the spatial carrier frequency in the imaging system of the present invention is distributed to different parts of the imaging system, and the separate control of the spatial carrier further ensures a well-distributed spatial spectrum when configuring the required near-zero amount of shear.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a schematic diagram of an imaging system of the present invention;
FIG. 2 is a flow chart of the steps of the imaging method of the present invention;
FIG. 3 is a schematic diagram of an imaging system according to an embodiment of the invention.
Reference numerals
1. A coherent light source; 2. a beam expander; 3. an object to be measured; 4. a first lens; 5. an aperture; 6. a second lens; 7. wollaston prism; 8. a polarizing plate; 9. an imaging lens; 10. and a camera.
Detailed Description
The technical scheme of the invention is further described below through the attached drawings and the embodiments.
Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. The terms "first," "second," and the like, as used herein, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The word "comprising" or "comprises", and the like, means that elements or items preceding the word are included in the element or item listed after the word and equivalents thereof, but does not exclude other elements or items. The terms "disposed," "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. "upper", "lower", "left", "right", etc. are used merely to indicate relative positional relationships, which may also be changed when the absolute position of the object to be described is changed.
Examples
FIG. 1 is a schematic diagram of an imaging system of the present invention; FIG. 2 is a flow chart of the steps of the imaging method of the present invention; FIG. 3 is a schematic diagram of an imaging system according to an embodiment of the invention.
As shown in fig. 1, the common-path shearing interference imaging system with independently adjustable shearing and carrier frequencies comprises a coherent light source 1, wherein light beams of the coherent light source 1 are emitted to the surface of an object to be detected 3 through a beam expander 2, and the object to be detected 3, a first lens 4, an aperture 5, a second lens 6, a Wollaston prism 7, a polaroid 8, an imaging lens 9 and a camera 10 are sequentially arranged on the same axis with the object to be detected 3.
An optical system is built according to the illustration of fig. 3, laser is selected as a coherent light source 1, the laser enters the surface of an object to be detected 3 at an angle theta, a first lens 4 is L1, a second lens 6 is L2, an imaging lens 9 is L3, the lenses L1 and L2 are the same in focal length f, and the distance between the two lenses is kept to be 2f. In this case, the distance between the surface of the object 3 to be measured and the intermediate real image surface is 4f. The diaphragm 5 is placed at the common focal position of the lenses L1 and L2, and holds the lenses L1, L2 and the diaphragm 5 as a whole so as to be freely slidable within a distance of 4f from the surface of the object 3 to be measured to the intermediate real image surface. A wollaston prism 7 is placed near the intermediate real image plane, and the beam splitting angle of the wollaston prism 7 is alpha. An imaging lens L3 is placed behind the wollaston prism 7 to image the intermediate real image plane RI onto the photosurface of the camera 10. A polarizer 8 is placed in front of the camera 10 so that two beams of orthogonally polarized light exiting the wollaston prism 7 interfere at the surface of the camera 10.
The aperture 5 is modulated to the maximum opening and the axial position of the wollaston prism 7 is adjusted to obtain a suitable amount of shear at the plane of the camera 10. The Wollaston prism 7 is fixed, the aperture 5 is properly adjusted, the L1, the L2 and the aperture 5 are taken as a whole, the whole is moved, and meanwhile, the spatial frequency of the shearing interference pattern acquired by the camera 10 is observed, so that the left side lobe and the right side lobe in the spatial frequency spectrum are completely separated from the central fundamental frequency. And (3) finishing the adjustment of the imaging system, and finishing the measurement according to the steps.
As shown in fig. 3, the shearing interference imaging system provided by the invention has the following characteristics: 1. controlling the space carrier frequency independently; 2. an adjustable near zero shear amount; 3. embedding a 4f imaging system; 4. the 4f imaging system comprises a movable aperture 5; 5. an intermediate real image plane RI exists in the imaging system; 6. all optical elements are coaxially placed except for the illumination light path. The object light is collected by a 4f imaging system (L1 and L2) and imaged in an intermediate real image plane (RI). One Wollaston prism 7 is placed near the middle realizing surface RI, and after passing through the Wollaston prism 7, the light beam is split into two object lights with symmetrical inclination angles, and the two object lights are imaged on the photosensitive surface IP of the camera 10 through the imaging lens L3, and adjustable near zero shearing is generated. A 4f imaging system embeds a variable position, variable opening size aperture 5 to provide independent control of spatial carrier frequency. The control of the amount of clipping and the spatial carrier frequency is distributed to different parts of the imaging system. The co-linear co-channel system provides a convenient way of system installation and has the potential to operate in an industrial environment due to its excellent noise immunity. The shearing interference imaging system provided by the invention is particularly suitable for measuring complex surface distribution or complex deformation. The adjustable near zero shear provides a sufficiently small shear force to ensure that complex surface shapes or deformations are resolvable. At the same time, the individual control of the spatial carriers further ensures a well-distributed spatial spectrum when configuring the required near zero amount of shearing.
The surface of the object 3 to be measured is irradiated by the extended coherent light source 1. The light returned by the object is collected by a set of lenses L1 and L2 to form an intermediate real image at the plane RI, where the aperture has the function of controlling the spatial carrier frequency. A wollaston prism 7 (WP) is placed in the adjacent region of the intermediate real image plane RI to produce a cut and form two identical but laterally displaced twin images on the photosurface of the camera 10 through the imaging lens L3. A polarizer P is placed in front of the camera 10 to interfere with the orthogonal polarization from the wollaston prism 7.
The generation of near zero shear is dependent on the generation of the intermediate real image plane RI. Imaging the surface of the object 3 to be measured at the intermediate real image plane by the 4f imaging system can be regarded as mapping the surface of the object 3 to be measured to the intermediate real image plane, and the generation of the intermediate real image plane provides enough operation space for the shearing device (i.e. the Wollaston prism 7). Assuming that the amount of shear is in the x-direction, the amount of shear delta of the imaging system is shown in FIG. 3 x Can be expressed as
Where α is the beam splitting angle provided by Wollaston prism 7, f img Q is the focal length of the imaging lens L3 r For the image distance of the imaging lens L3, L w Is the distance of the Wollaston prism 7 from the intermediate real image plane RI. The amount of shear decreases as the Wollaston prism 7 slides towards the intermediate real image plane RI, and near zero shear occurs when the Wollaston prism 7 is sufficiently close to the intermediate real image plane. In the extreme case, when the Wollaston prism 7 is just located on the intermediate real image plane RI, accurate zero shear will be obtained, and at this time, the two beams of object light coincide again on the photosensitive surface of the camera 10, which makes it possible to realize white light interference by using the present imaging system.
In order to obtain carrier frequency independent control, let 4f beThe two lenses in the image system have the same focal length f. The axial distance between the two lenses L1 and L2 is set to a constant value of 2f, and the aperture 5 is placed between them, at a distance L from L2 a Is a distance of (3). In order to keep the position of the intermediate real image plane RI fixed, the object distance of the 4f lens group is set to 4f. In this configuration, the lens group can slide within a distance of 4f while the object imaging relationship remains unchanged. The spatial carrier is characterized by its center frequency, which determines the position of the spatial carrier in the spatial spectrum.
In the imaging system proposed by the present invention, the center frequency of the carrier frequency can be expressed as
Wherein lambda is the wavelength of the laser, p r And q r For the object distance and image distance, L, of the imaging lens L3 a For the distance between the aperture 5 and L2, L w Q is the distance between Wollaston prism 7 and the intermediate real image plane o Is the image distance (distance of L2 from the intermediate real image plane) of the 4f imaging system. From the aforementioned shear quantity delta x The formula shows that the shearing amount of the imaging system is represented by l w And (5) controlling. Therefore, to realize independent control of carrier frequency, other imaging system parameters are selected to control in the formula of the center frequency of the carrier frequency. In general, the aperture 5 position l can be controlled by a And 4f imaging system image distance q o And controlling the space carrier frequency. Note that when the diaphragm 5 is deviated from the midpoint position (L) of L1 and L2 a Not f), the aperture 5 itself becomes a field stop of the imaging system, causing the aperture 5 to block the field of view. Thus, when near zero shear configuration is complete, it means l w Has been fixed by varying the distance q between the lens groups L1 and L2 and the intermediate real image plane o To control spatial carrier frequencies.
The invention relates to a common-path shearing interference imaging method with independently adjustable shearing and carrier frequencies, which comprises the following steps:
step one, an imaging system is adjusted to control the distance between the Wollaston prism 7 and the intermediate real image surfaceFrom l w To obtain a desired amount of shear; adjusting the image distance q of a 4f imaging system o To obtain the desired spatial spectral distribution.
Step two, the coherent light source 1 is a laser, the outgoing laser is expanded by the beam expander 2 and then irradiates the surface of the object to be measured 3 at a certain angle, the light returned from the surface of the object to be measured 3 is collected by the 4f imaging system and imaged on the intermediate real image surface RI, two beams of misplaced object light are generated by splitting by the Wollaston prism 7, the intermediate real image surface is imaged by the imaging lens L3, the imaged object light is positioned on the photosensitive surface of the camera 10, and the wave fronts of the two sheared object light are
u 1 (x,y)＝|u 1 (x,y)|exp{i[φ(x,y)]}
u 2 (x,y)＝|u 1 (x+δ x ,y)|exp{i[φ(x+δ x ,y)+2πf 0 x]}
Where (x, y) describes the camera 10 photosurface coordinates, phi being the phase, delta, from the surface of the object 3 to be measured x F is the amount of shear applied 0 For the introduced spatial carrier frequency.
Step three, the camera 10 collects the shearing interferograms and performs a fourier transform.
The camera 10 acquires a shearing interferogram whose intensity is noted as
Wherein, asterisks indicate complex conjugate operation;
fourier transforming the shearing interferogram acquired by camera 10, denoted as
Wherein the method comprises the steps of
Representing the Fourier transform operation, DC represents the low frequency spectrum of the background light intensity, and capital U represents the Fourier transform of each complex amplitude in the formula of step twoAnd (5) changing.
Step four, through the introduction of the spatial carrier frequency, three components in the spatial spectrum diagram displayed by the Fourier transform formula in step three are separated from different positions of the spatial spectrum, and the three components are selected from the spectrum
A component; performing inverse Fourier transform on the selected component to obtain complex amplitude +.>
Is marked as
Wherein the method comprises the steps of
Representing an inverse fourier transform operation.
And fifthly, calculating the phase angle of the complex amplitude, removing carrier frequency for the obtained phase angle, obtaining phase distribution, and obtaining the surface relief height gradient of the measured surface.
The phase angle of the obtained complex amplitude is calculated and recorded as
Where Im is the operation of taking the imaginary part and Re is the operation of taking the real part.
Removing carrier frequency from the obtained phase angle to obtain phase distribution phi (x, y), calculating according to the following formula to obtain surface relief height gradient of the measured surface, and recording as
Where θ is the angle between the incident light and the normal to the surface of the object 3 to be measured.
Step six, for the surface displacement gradient measurement, the first step to the fifth step are respectively carried out before and after deformation, the surface height gradient of the front and the rear two times is obtained, and the difference is carried out, so that the first derivative information of the out-of-plane displacement can be obtained.
Therefore, the invention adopts the common-path shearing interference imaging system and the method with the shearing and carrier frequency being independently adjustable, the control of the shearing quantity and the space carrier frequency in the imaging system is distributed to different parts of the imaging system, and the shearing force which is small enough is provided by the adjustable near-zero shearing quantity so as to ensure that complex surface shapes or deformation can be solved. The separate control of the spatial carriers further ensures a well-distributed spatial spectrum when configuring the required near zero amount of shear.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting it, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that: the technical scheme of the invention can be modified or replaced by the same, and the modified technical scheme cannot deviate from the spirit and scope of the technical scheme of the invention.
Claims (7)
1. A shearing and carrier frequency independently adjustable common-path shearing interference imaging system is characterized in that: the device comprises a coherent light source, wherein light beams of the coherent light source are emitted to the surface of an object to be detected through a beam expander, and the object to be detected, a first lens, an aperture, a second lens, a Wollaston prism, a polaroid, an imaging lens and a camera are sequentially arranged on the same axis with the object to be detected.
2. The common-path shearing interference imaging method with independently adjustable shearing and carrier frequencies as claimed in claim 1, wherein: the method comprises the following steps:
step one, adjusting an imaging system to obtain a desired amount of shear and a desired spatial spectral distribution;
step two, the surface of the object to be detected is irradiated by a coherent light source, the imaging system collects the light returned from the surface of the object to be detected, and the object to be detected is imaged on a camera;
step three, a camera collects the shearing interference pattern and performs Fourier transformation;
introducing a spatial carrier frequency, selecting components in the spatial frequency spectrum subjected to Fourier transform, and performing inverse Fourier transform on the components to obtain complex amplitude;
step five, calculating the phase angle of the complex amplitude, removing carrier frequency for the obtained phase angle, obtaining phase distribution, and obtaining the surface relief height gradient of the measured surface;
step six, for surface displacement gradient measurement, carrying out the step one to the step five before and after deformation respectively, obtaining the surface height gradient of the front and the back twice and making difference.
3. The shearing and carrier frequency independently adjustable common-path shearing interference imaging method as claimed in claim 2, wherein: step one, an imaging system is adjusted, and the distance between the Wollaston prism and the intermediate real image surface is controlled to obtain a desired shearing amount; the image distance of the imaging system is adjusted to obtain the desired spatial spectral distribution.
4. A common-path shearing interference imaging method with independently adjustable shearing and carrier frequencies as defined in claim 3, wherein: in the second step, the emergent light of the coherent light source is expanded by the beam expander to illuminate the surface of the object to be measured at a certain angle, the returned light of the surface of the object to be measured is collected by the imaging system and imaged on the middle real image surface, two staggered beams of the object light are generated by splitting by the Wollaston prism, the middle real image surface is imaged by the imaging lens, the imaged image is positioned on the photosensitive surface of the camera, and the wave fronts of the two sheared object light are
u 1 (x,y)＝|u 1 (x,y)|exp{i[φ(x,y)]}
u 2 (x,y)＝|u 1 (x+δ x ,y)|exp{i[φ(x+δ x ,y)+2πf 0 x]}
Wherein (x, y) describes camera photosurface coordinates, phi is the phase from the surface of the object to be measured, delta x F is the amount of shear applied 0 For the introduced spatial carrier frequency.
5. The shearing and carrier frequency independently adjustable common-path shearing interference imaging method as defined in claim 4, wherein: in the third step, the camera collects a shearing interference pattern, and the intensity of the shearing interference pattern is recorded as
Wherein, asterisks indicate complex conjugate operation;
fourier transforming the shearing interference pattern collected by the camera, and recording as
Wherein the method comprises the steps of
Representing the fourier transform operation, DC represents the low frequency spectrum of the background light intensity, and uppercase letter U represents the fourier transform of each complex amplitude in the formula of step two.
6. The shearing and carrier frequency independently adjustable common-path shearing interference imaging method as defined in claim 5, wherein: in the fourth step, three components in the spatial spectrum diagram shown in the formula in the third step are separated from different positions of the spatial spectrum by introducing spatial carrier frequency, and are selected from the spectrum
A component; performing inverse Fourier transform on the selected component to obtain complex amplitude +.>
Is marked as
Wherein the method comprises the steps of
Representing an inverse fourier transform operation.
7. The shearing and carrier frequency independently adjustable common-path shearing interference imaging method as defined in claim 6, wherein: step five, the phase angle of the obtained complex amplitude is calculated and recorded as
Wherein Im is the operation of taking the imaginary part, and Re is the operation of taking the real part;
removing carrier frequency from the obtained phase angle to obtain phase distribution phi (x, y), calculating according to the following formula to obtain surface relief height gradient of the measured surface, and recording as
Where θ is the angle between the incident light and the normal to the surface of the object under test.
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