CN115014242B - Microcosmic surface topography measuring method and device based on parallel multi-slit structure illumination - Google Patents
Microcosmic surface topography measuring method and device based on parallel multi-slit structure illumination Download PDFInfo
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- CN115014242B CN115014242B CN202210584700.4A CN202210584700A CN115014242B CN 115014242 B CN115014242 B CN 115014242B CN 202210584700 A CN202210584700 A CN 202210584700A CN 115014242 B CN115014242 B CN 115014242B
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Abstract
The invention belongs to the field of microscopic surface topography measurement, and particularly discloses a microscopic surface topography measurement method and device based on parallel multi-slit structure illumination, which comprises the following steps: s1, loading a group of structure illumination patterns into a digital micromirror array in sequence; the structure lighting patterns are vertical or inclined stripes with alternate light and shade, and the bright stripes between two adjacent structure lighting patterns move by the width of one bright stripe; s2, relaying the light to a digital micro-mirror array, and modulating the light into structured light in an illumination pattern mode by the digital micro-mirror array; s3, projecting a group of structural illumination patterns to the surface of the sample through an objective lens, collecting a structural light image reflected by the surface of the sample through a camera, and calculating to obtain an optical tomography image of the current position; and S4, adjusting the height of the objective lens, repeating the step S3, and obtaining optical tomography images at different axial positions so as to obtain the three-dimensional surface morphology. The invention can solve the problem of limited optical tomography capability caused by the limitation of the contrast ratio of the projection fringe.
Description
Technical Field
The invention belongs to the field of microscopic surface topography measurement, and particularly relates to a microscopic surface topography measurement method and device based on parallel multi-slit structure illumination.
Background
Optical tomography is a key step in reconstructing the three-dimensional surface topography of an object with high accuracy. The method comprises the steps of sequentially loading required illumination patterns on a projection device, utilizing an optical relay lens group to relay to a sample surface at a preset scaling ratio to excite corresponding sub-field of view, sequentially passing fluorescence signals excited by different illumination patterns in the sub-field of view through the optical relay lens group and relaying to a camera target surface at the preset scaling ratio, achieving acquisition of high-resolution sub-field of view images, and obtaining three-dimensional optical tomographic images of the acquired images by using a structured light tomography algorithm. Chinese patent CN112986195A discloses a three-dimensional wide-field and high-resolution tomography method and device, which loads a structure pattern and a plane pattern on a digital micromirror device, irradiates the digital micromirror device through a light source to sequentially generate structure light and uniform light and relay the structure light and the uniform light to a sample, and collects an excited structure light illumination image and an excited uniform light illumination image; the structured light and uniform light illumination image is divided into a plurality of sub-field-of-view images after passing through the reflection beam splitting device, and the obtained wide-field-of-view optical tomography image is subjected to data reconstruction to obtain a high-resolution wide-field three-dimensional tomography image. The method can be used for three-dimensional rapid imaging of biodynamic processes.
The optical tomography ability of the two optical tomography methods is closely related to the frequency of the projected stripes. Although theoretically, the illumination pattern with the optimal fringe frequency can be used to obtain the optical tomography effect equivalent to that of the confocal microscope, in practice, due to the limitation of the contrast of the projection fringe, only the fringe illumination pattern with the lower frequency can be selected, so that the optical tomography capability is limited, and the high-precision reconstruction of the three-dimensional surface topography of the object is influenced. This effect is more pronounced for low power objective lenses (e.g., 5x, 10x, etc.) with a larger field of view and a smaller numerical aperture. The axial corresponding curves obtained by the two structure lighting methods are analyzed, and the relative effect is poor.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a method and a device for measuring the microscopic surface topography based on parallel multi-slit structure illumination, aiming at solving the problem that the optical tomography capability is limited during the microscopic surface topography measurement due to the limitation of projection fringe contrast and the selection of a fringe illumination pattern with lower frequency.
To achieve the above object, according to an aspect of the present invention, a method for measuring a microscopic surface topography based on parallel multi-slit structure illumination is provided, which comprises the following steps:
s1, sequentially loading a group of parallel multi-slit modulated structure illumination patterns into a digital micromirror array; the structural lighting patterns are alternately bright and dark stripes, and the arrangement sequence of one group of structural lighting patterns is as follows: in the adjacent structure lighting patterns, the bright stripe on the next structure lighting pattern moves to the appointed direction by a distance of one bright stripe width compared with the bright stripe on the previous structure lighting pattern;
s2, relaying the light to a digital micro-mirror array, and modulating the relayed light into structured light in an illumination pattern mode by using the digital micro-mirror array;
s3, sequentially projecting a group of structural illumination patterns to the surface of the sample through an objective lens by using a digital micromirror array, and acquiring a structural light image reflected by the surface of the sample each time by using a camera so as to obtain an optical tomography image of the current position;
and S4, adjusting the height of the objective lens, repeating the step S3 to obtain a plurality of optical tomography images at different axial positions so as to obtain a three-dimensional tomography image stack, and further completing the measurement of the microscopic surface topography of the sample.
As a further preferable mode, the structured illumination pattern employs oblique stripes having an oblique angle of 45 degrees.
As a further preference, in the structured lighting pattern, the width of the bright stripes is the same as the camera pixel size; the ratio of the width of the dark stripe to the width of the light stripe is not less than 5.
More preferably, the maximum value of the intensity value of the structured light image collected by the camera is 85% to 95% of the theoretical maximum value.
Further preferably, in step S3, an optical tomographic image is obtained by an optical tomographic image demodulation method according to a set of structured light images collected by the camera; the optical tomography image demodulation method comprises the following steps:
wherein, I p (u) is the optical tomographic image of the system at the out-of-focus position u,
nth structure collected by cameraLight image, v 2x ,v 2y Representing the optical coordinates on the camera face, N being the amount of lateral shift of the multi-slit illumination mask, av being the amount of shift of the slits along the x-axis,
and acquiring n + k structural light images for the camera, wherein k is an integer not equal to 0, and Z represents an integer.
Preferably, in step S4, according to the three-dimensional tomographic image stack, peak positioning is performed on the axial data of each pixel point, specifically, a gaussian curve fitting method is used to determine a position of the peak, and then a coordinate value of the position of the peak is obtained, that is, the relative height information at the pixel point, so as to achieve measurement of the microscopic surface topography of the sample.
According to another aspect of the present invention, there is provided a micro surface topography measuring apparatus based on parallel multi-slit structure illumination, comprising an optical path system, a digital micromirror array and a CMOS camera, wherein: the light path system comprises a relay light path component and a collection light path component, wherein the relay light path component is used for relaying light onto the digital micromirror array, and the digital micromirror array is used for modulating the relayed light into structured light in an illumination pattern mode according to a parallel multi-slit modulated structured illumination pattern; the collection light path component is used for projecting the structured light to the surface of the sample and reflecting the structured light to the CMOS camera; and measuring the microcosmic surface topography of the sample according to the structured light image acquired by the CMOS camera.
Preferably, the relay optical path component includes an LED lamp, an auxiliary lens, a field stop, a first collecting mirror, an aperture stop, a second collecting mirror, a plane mirror, and a total internal reflection prism; the light emitted by the LED lamp is imaged on the field diaphragm through the auxiliary lens, the image positioned on the field diaphragm reaches the plane mirror after passing through the first light collecting mirror, the aperture diaphragm and the second light collecting mirror, is reflected by the plane mirror and enters the total internal reflection prism, the total internal reflection prism reflects the light to the digital micromirror array, and the light is modulated into structural light corresponding to the illumination pattern by the digital micromirror array;
the collection optical path component comprises a first sleeve lens, a beam splitter prism, an objective lens and a second sleeve lens; the structured light is imaged on a rear focal plane of the objective lens through the first sleeve lens and the beam splitter prism, is converted into parallel light beams through the objective lens to uniformly illuminate an object plane of a sample, and the light reflected by the object plane is imaged on an image plane of the CMOS camera through the beam splitter prism and the second sleeve lens.
Preferably, the surface where the filament of the LED lamp is located, the field diaphragm, the aperture diaphragm and the object surface satisfy a conjugate relation; the plane of the photosensitive element of the CMOS camera and the plane of the digital micro-mirror array are in a conjugate focal plane.
As a further preferred, the device further comprises a device bracket, a screw mechanism, an L-shaped platform and a piezoelectric ceramic driver, wherein: the screw mechanism is fixed at the top of the device bracket, and a slide block is arranged on a screw rod of the screw mechanism; the L-shaped platform is fixed on the sliding block, the optical path system is arranged on the L-shaped platform, the digital micromirror array is installed between the plane mirror and the first sleeve lens, and the CMOS camera is installed behind the second sleeve lens; the piezoelectric ceramic driver is arranged at the bottom of the L-shaped platform and used for driving the objective lens to move up and down.
Generally, compared with the prior art, the technical scheme conceived by the invention mainly has the following technical advantages:
1. compared with the limitation of the contrast of the conventional structured light projection fringe, the method can only select a low-frequency fringe illumination pattern, so that the optical tomography capability is limited, and the high-precision reconstruction of the three-dimensional surface appearance of the object is influenced. According to the invention, through a set of multi-slit illuminating structure illuminating microscope, designed parallel multi-slit structure illuminating patterns are projected on the surface of a sample, an image of the surface to be measured is obtained by using a camera, and the image is demodulated to obtain an optimal optical tomography image, so that the problem that the optical tomography capability is limited due to the limitation of projection stripe contrast and only a stripe illuminating pattern with a lower frequency can be selected is solved; meanwhile, the problem that the modulation contrast of the projection fringe pattern in the illumination microscope with the traditional structure and the frequency of the projection fringe pattern are mutually dependent and difficult to decouple can be effectively solved, so that the microscope objectives under various multiplying powers can obtain the optimal optical tomography capability.
2. Compared with the existing single-point scanning and line scanning mode, the parallel multi-slit structure illumination pattern provided by the invention not only improves the light energy utilization rate of the LED lamp, but also improves the measurement efficiency by adopting the parallel scanning mode.
3. Since the bright and dark stripes are generated by digital micromirror array (DMD) control, the oblique stripes with an oblique angle of 45 degrees are preferably used to generate higher quality tomographic images by fully characterizing the pixelation of the DMD itself.
4. The width of the bright stripes is similar to the size of the pixels of the camera, and the width ratio of the bright stripes to the dark stripes is not less than 5, so that the projected multi-slit pattern can have good modulation contrast.
5. The invention provides a specific optical tomography image demodulation method, which can obtain higher axial resolution, can adjust the axial resolution by controlling parameters, and ensures the signal-to-noise ratio of the whole system, thereby obtaining an optimal optical tomography image and realizing high-precision reconstruction of the three-dimensional surface topography of an object.
6. Compared with the traditional confocal measurement microscope, the measurement device provided by the invention is lack of a pair of conjugate pinholes in an optical path system, so that the device provided by the invention does not need to accurately calibrate the position between the two conjugate pinholes, the requirement on assembly precision in the installation process of the device is reduced, the structure is relatively simple, the cost is relatively low, and meanwhile, the theoretical full width at half maximum of an experimental curve is close to or even superior to that of a point scanning confocal microscope under the same configuration.
7. The plane where the CMOS camera photosensitive element is located and the plane where the DMD is located are located in a conjugate focal plane, and the situation that the clearest position of the stripe is overlapped with the position where an object is in focus can be guaranteed. Meanwhile, the surface where the filament of the LED lamp is located and the aperture diaphragm and the field diaphragm meet the conjugate relation with the object surface, so that the field of view of the object surface can be adjusted by adjusting the size of the field diaphragm, the light intensity on the object surface can be adjusted by the aperture diaphragm, and the illumination effect of the optical system is influenced by the aperture diaphragm and the object surface independently.
Drawings
FIG. 1 is a schematic diagram of an optical path system for a micro surface topography measurement apparatus constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is an elevational view of the general construction of a micro surface topography measurement device constructed in accordance with a preferred embodiment of the present invention;
FIG. 3 is a side cross-sectional view of the general construction of a micro surface topography measurement device constructed in accordance with a preferred embodiment of the present invention;
FIG. 4 is a schematic measurement flow diagram of a parallel multi-slit structured illumination micro-surface topography measurement apparatus constructed in accordance with a preferred embodiment of the present invention;
fig. 5 (a) - (f) are partial schematic diagrams of a set of parallel multi-slit modulated structured illumination patterns constructed according to the preferred embodiment of the present invention;
fig. 6 (a) - (f) are schematic diagrams of the part of the pattern projected onto the sample after the LED light source constructed according to the preferred embodiment of the present invention is modulated into the structured light of the corresponding pattern by DMD;
FIG. 7 is a schematic diagram of a high-precision optical tomographic image calculated by the pattern mode-based optical tomographic image demodulation method according to the preferred embodiment of the present invention;
FIG. 8 is a schematic illustration of a fitted curve obtained by peak location using Gaussian curve fitting on axial data constructed in accordance with a preferred embodiment of the invention.
The same reference numbers will be used throughout the drawings to refer to the same elements or structures, wherein: 1-LED lamp, 2-auxiliary lens, 3-field diaphragm, 4-first condenser, 5-aperture diaphragm, 6-second condenser, 7-plane mirror, 8, 22-DMD, 10-first sleeve lens, 11, 25-CMOS camera, 12-second sleeve lens, 13-beam splitter prism, 14-objective lens back focal plane, 15, 26-objective lens, 16-object plane, 17-device support, 18-lead screw mechanism, 19-object stage, 20-L type platform, 21-optical path system, 23-piezoelectric ceramic driver, 24-motor, 27-slide block.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The microscopic surface topography measuring device based on parallel multi-slit structure illumination provided by the embodiment of the invention is shown in fig. 2 and fig. 3, and comprises a device support 17, a screw mechanism 18, an object placing table 19, an L-shaped platform 20, an optical path system 21, a DMD22, a piezoelectric ceramic driver 23, a motor 24 and a CMOS camera 25, wherein:
the device bracket 17 is arch-shaped and is used for fixing and supporting the whole instrument. A screw mechanism 18 is fixed at the top of the device bracket 17, a slide block 27 is arranged on a screw rod of the screw mechanism 18, the slide block 27 is controlled to move up and down by the positive and negative rotation of the screw rod, and an L-shaped platform 20 is fixed on the slide block 27 arranged on the screw rod mechanism; a motor 24 is fixed to an upper portion of the screw mechanism 18 for controlling the raising and lowering of the L-shaped stage 20, and the optical path system 21 is disposed above the L-shaped stage 20. DMD22 (i.e., DMD8 in fig. 1) is located between the first sleeve lens and the plane mirror in optical path system 21, and modulates the light reflected from the plane mirror into a structured light pattern corresponding to the loading pattern. A piezo ceramic actuator 23 is mounted on the bottom of the L-shaped stage 20 for driving the up and down movement of the objective lens 26 (i.e., the objective lens 15 in fig. 1). A CMOS camera 25 (i.e. the CMOS camera 11 in fig. 1) is mounted behind the second sleeve lens of the optical path system 21 for acquiring an image of the structured light reflected back through the sample surface.
Further, as shown in fig. 1, the optical path system 21 includes an LED lamp 1, an auxiliary lens 2, a field stop 3, a first collecting mirror 4, an aperture stop 5, a second collecting mirror 6, a plane mirror 7, a total internal reflection prism, a first sleeve lens 10, a beam splitter prism 13, an objective lens 15, and a second sleeve lens 12, where:
light emitted by the LED lamp 1 is imaged on a field diaphragm 3 through the auxiliary lens 2, the image on the field diaphragm 3 reaches a plane mirror 7 after passing through a first light collecting mirror 4, an aperture diaphragm 5 and a second light collecting mirror 6, is reflected by the plane mirror 7 and enters a full inner reflection prism, the full inner reflection prism reflects a light source to a DMD8, the light source is modulated into structural light corresponding to a loaded pattern by the DMD8, the structural light is imaged on a rear focal plane 14 of an objective lens through a first sleeve lens 10 and a light splitting prism 13, and finally the structural light is converted into parallel light beams through an objective lens 15 to uniformly illuminate a sample object plane 16. The light reflected by the object plane 16 passes through the beam splitter prism 13 and the second sleeve lens 12 and is finally imaged on the image plane of the CMOS camera 11.
Furthermore, the surface of the LED lamp 1 where the filament is located and the aperture diaphragm 5, and the field diaphragm 3 and the object surface 16 satisfy a conjugate relationship, so that the field of view of the object surface 16 can be adjusted by adjusting the size of the field diaphragm 3, that is, the size of the measured area of the sample object surface is adjusted; the aperture diaphragm 5 can be adjusted to adjust the light intensity on the object plane, and the two independently influence the illumination effect of the optical system.
Furthermore, the plane where the photosensitive element of the CMOS camera is located and the plane where the DMD is located are located on a conjugate focal plane, so that the clearest position of the stripe is ensured to be superposed with the position of an object in focus.
Based on the device, the invention provides a microscopic surface topography measuring method based on a parallel multi-slit structure lighting device, as shown in fig. 4, comprising the following steps:
s1, designing a group of parallel multi-slit modulated structural lighting patterns, wherein the structural lighting patterns consist of light and dark alternate horizontal, vertical or inclined stripes, and the bright stripes between two adjacent lighting patterns move by a distance of one stripe width; more specifically, the arrangement sequence of a group of structured lighting patterns is: in the adjacent structure lighting patterns, the bright stripe on the next structure lighting pattern moves to the appointed direction by a distance of one bright stripe width compared with the bright stripe on the previous structure lighting pattern;
and S2, loading the group of structural illumination patterns into a DMD in sequence, transmitting a light source through an LED lamp, relaying the light onto the DMD by using an auxiliary lens, a field diaphragm, a first light collecting mirror, an aperture diaphragm, a second light collecting mirror and a plane mirror in an optical path system, and modulating the relayed light into the structural light in an illumination pattern mode by using the modulation effect of the DMD.
And S3, sequentially switching the loaded group of structural illumination patterns by the DMD at the same axial position, and collecting a structural light pattern reflected by the surface of the sample by the CMOS camera every time the loaded group of structural illumination patterns are switched. And calculating the optical tomography image at the current position by using an optical tomography image demodulation method based on the pattern mode according to a group of structure illumination patterns acquired by the camera.
Specifically, each time the structured light is projected to the surface of the sample by using the first sleeve lens, the beam splitter prism and the objective lens in the optical path system, the structured light reflected by the surface of the sample is imaged on the photosensitive element of the CMOS camera through the beam splitter prism and the second sleeve lens in the optical path system, and finally is collected by the CMOS camera.
And S4, driving the objective lens to move downwards by a specified distance by using a piezoelectric ceramic driver, repeating the process of the step S3, axially scanning the sample, and calculating an optical tomography image at each axial position to obtain a high-resolution three-dimensional tomography image stack. And according to the calculated high-resolution three-dimensional chromatographic image, carrying out peak positioning on the axial data of each pixel point to obtain a coordinate value at the position of the peak value, namely the relative height information of the pixel point.
Further, since the light and dark stripes are generated by DMD control, it is preferable to use oblique stripes with an oblique angle of 45 degrees to produce higher quality tomographic images by taking advantage of the pixelation feature of the DMD itself.
Further, the ratio of the light and dark stripe widths in the illumination pattern is referred to as the duty cycle. The width of the bright stripes is preferably the width similar to the pixel size of the cmos camera, and the ratio of the width of the dark stripes to the width of the bright stripes, i.e. the duty ratio, is preferably not less than 5, so as to ensure that the projected multi-slit pattern has a good modulation contrast.
Furthermore, the maximum value of the intensity value of the structured light pattern collected by the CMOS camera is kept about 90 percent of the theoretical maximum value by adjusting the light source intensity of the LED lamp, so that the whole dynamic range of the CMOS camera is fully utilized.
Furthermore, when the peak positioning algorithm is used for determining the position of the peak, a Gaussian curve fitting method is preferably adopted for positioning, and the highest-precision surface reconstruction can be realized.
Further, in step S3, an optical tomographic image at the current position is calculated by using the optical tomographic image demodulation method based on the pattern mode proposed by the present invention; the demodulation method is based on the following principle:
assume the use of a structured illumination pattern S (v) 1x ,v 1y ) For a single slit of finite width, infinite length parallel to the Y axis, there are:
wherein, Δ v and v r The displacement and half width of the slit along the x-axis, (v) 1x ,v 1y ) Are the optical coordinates on the DMD surface. Then the defocus response of an ideally uniform plane at each axial position for single slit illumination is:
where C is a constant, the normalized frequency t = f λ/NA, f is the actual spatial frequency, λ is the illumination wavelength, NA is the illumination aperture of the objective lens, and the normalized defocus u =8 π z/λ sin 2 (α/2), z is the actual defocus, α is the illumination aperture half-angle, sine function sin c (x) = sin (π x)/(π x), g (t, u) is the optical transfer function of a weakly scattering object, (v) is the actual defocus 2x ,v 2y ) Are the optical coordinates on the camera face.
The invention uses a method of subtraction of adjacent structure illumination images to obtain an optical tomographic image as shown in equation (3):
by scanning the slit in the X-axis direction and substituting equation (2) into equation (3), equation (4) can be obtained:
however, the method of acquiring optical tomographic images due to the single slit scan described above is inefficient for the measurement task and causes a waste of most of the illumination light energy. Therefore, a good alternative is to use a parallel multi-slit illumination mask, which can be expressed as:
wherein N is s And 2v s Respectively the number and spacing of the slits on the illumination mask. To obtain an optical tomography power comparable to equation (4), equation (3) is restated as:
where N is the number of lateral shifts of the multi-slit illumination mask. Combining equation (5) and equation (6), the defocus response of the system can be obtained:
since the subtraction technique is limited by noise in the acquired image, equation (6) is more sensitive to noise than confocal microscopy, which in some cases may result in a low signal-to-noise ratio. It is further preferred to extend equation (6) to a more general and robust version:
wherein, I p (u) is the optical tomographic image of the system at the out-of-focus position u,
n structured light image, v, collected for camera 2x ,v 2y Representing optical coordinates on the camera surface, N being the number of lateral shifts of the multi-slit illumination maskThe amount of the compound (A) is,
the n + k structural light images are collected by a camera; k is an integer not equal to 0 and can be-2, -1, 2, etc. When the maximum value | k! of the absolute values of all k is max Equal to 1, equation (8) is identical to equation (6). As the value of | k | max becomes larger, equation (8) gradually approximates the variance of the signal and improves robustness to noise at the expense of reduced optical tomography capability. For different imaging applications, the user may adjust the level of slice intensity according to the desired signal-to-noise ratio.
The following are specific examples:
the DMD has the advantages that the number of the micromirrors is 200W, the resolution is 1920 x 1080, the size of each micromirror is 7.4um x 7.4um, and the switching frequency of the structured light pattern can reach 9.5khz.
The pixel of the CMOS camera is 230W, the resolution is 1920 x 1200, the pixel size is 5.86um x 5.86um, the frame rate can reach 164fps, and the external dimension is 25mm x 25mm.
The complete measurement process of the sample comprises the following steps:
1) And designing a group of parallel shift multi-slit modulation structure illumination patterns according to the sizes of the selected CMOS camera and the DMD pixel units. The inclination angle of the stripes in the set of structured lighting patterns is 45 degrees, the width of the bright stripes is 1 pixel width, the width of the dark stripes is 8 pixel width, the duty ratio of the bright and dark stripes is 8, and as shown in fig. 5, the generated patterns are a set of structured lighting patterns described above.
2) The method comprises the steps of switching on a power supply of a DMD (digital micromirror device), a COMS (complementary metal oxide semiconductor) camera, a piezoelectric ceramic driver and a motor, sequentially loading a group of structural lighting patterns generated as shown in figure 5 into a cache of the DMD, turning on a switch of an LED lamp, observing brightness information of the surface of a sample in the CMOS camera, and adjusting the light source intensity of the LED lamp to keep the maximum brightness value in the CMOS camera at about 90 percent of the theoretical maximum value, wherein the maximum brightness value is shown in figure 6 and is an image which is shot by the camera and is reflected by the surface of the sample and contains structural light information.
3) And at the same axial position, the DMD is controlled by an instruction to sequentially switch the parallel shift multi-slit modulated structure illumination patterns loaded into the cache, and the CMOS camera is controlled to synchronously acquire sample surface image information of the corresponding structure illumination patterns by the DMD once switching.
4) From the image information of a set of sample surfaces acquired by the CMOS camera, the shuffled image data is processed as shown in fig. 7 using an optical tomographic image demodulation method based on the pattern. An optical tomographic image of the set of image data is obtained as shown in fig. 8.
5) And (5) driving the objective lens to move downwards by a unit distance by using a piezoelectric ceramic driver, and repeating the step 3) and the step 4) to axially scan the sample and calculate an optical tomography image at each axial position, thereby obtaining a three-dimensional tomography image stack.
6) Extracting axial data of each pixel point according to the three-dimensional chromatographic image stack obtained in the step 5), and performing Gaussian curve fitting on the extracted axial data to obtain a fitting curve, as shown in FIG. 8, according to a parameter value of the fitting curve, obtaining a coordinate value of a position where a peak value is located, and further obtaining a relative height value of the current pixel point position.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A microscopic surface topography measuring method based on parallel multi-slit structure illumination is characterized by comprising the following steps:
s1, sequentially loading a group of parallel multi-slit modulated structure illumination patterns into a digital micromirror array; the structural lighting patterns are alternately bright and dark stripes, and the arrangement sequence of one group of structural lighting patterns is as follows: in the adjacent structure lighting patterns, the bright stripe on the next structure lighting pattern moves to the appointed direction by a distance of one bright stripe width compared with the bright stripe on the previous structure lighting pattern;
s2, relaying the light onto a digital micromirror array, and modulating the relayed light into structured light in an illumination pattern mode by using the digital micromirror array;
s3, sequentially projecting a group of structural illumination patterns to the surface of the sample through an objective lens by using a digital micromirror array, and acquiring a structural light image reflected by the surface of the sample each time by using a camera so as to obtain an optical tomography image of the current position;
and S4, adjusting the height of the objective lens, repeating the step S3 to obtain a plurality of optical chromatographic images at different axial positions so as to obtain a three-dimensional chromatographic image stack, and further completing the measurement of the microscopic surface topography of the sample.
2. The method for measuring the topography of a microscopic surface based on illumination of a parallel multi-slit structure as defined in claim 1, wherein the pattern of structured illumination employs slanted stripes having a slanted angle of 45 degrees.
3. The method of claim 1, wherein the width of the bright stripes in the structured illumination pattern is the same as the camera pixel size; the ratio of the width of the dark stripe to the width of the light stripe is not less than 5.
4. The method for measuring the topography of a microscopic surface based on illumination of a parallel multi-slit structure as claimed in claim 1, wherein the maximum value of the intensity value of the structured light image collected by the camera is 85% -95% of the theoretical maximum value.
5. The method for measuring the shape of the microscopic surface based on the illumination of the parallel multi-slit structure as claimed in claim 1, wherein in step S3, an optical tomographic image is obtained by an optical tomographic image demodulation method based on a set of structured light images collected by a camera; the optical tomography image demodulation method comprises the following steps:
wherein, I p (u) is the optical tomographic image of the system at the out-of-focus position u,
n structured light image, v, collected for camera 2x ,v 2y Representing the optical coordinates on the camera face, N is the amount of lateral shift of the multi-slit illumination mask, av is the amount of shift of the slits along the x-axis,
and acquiring n + k structural light images for the camera, wherein k is an integer not equal to 0, and Z represents an integer.
6. The method for measuring the shape of the microscopic surface based on the illumination of the parallel multi-slit structure as claimed in any one of claims 1 to 5, wherein in step S4, the axial data of each pixel point is subjected to peak positioning according to the three-dimensional tomographic image stack, the position of the peak is determined by using a Gaussian curve fitting method, and then the coordinate value of the position of the peak is obtained, that is, the relative height information of the pixel point, thereby realizing the measurement of the shape of the microscopic surface of the sample.
7. A microscopic surface topography measuring device based on parallel multi-slit structure illumination for implementing the measuring method according to any one of claims 1 to 6, comprising an optical path system, a digital micromirror array and a CMOS camera, wherein: the light path system comprises a relay light path component and a collection light path component, wherein the relay light path component is used for relaying light onto the digital micromirror array, and the digital micromirror array is used for modulating the relayed light into structured light in an illumination pattern mode according to a parallel multi-slit modulated structured illumination pattern; the collection light path component is used for projecting the structured light to the surface of the sample and reflecting the structured light to the CMOS camera; and measuring the microscopic surface topography of the sample according to the structured light image acquired by the CMOS camera.
8. The device for measuring the microscopic surface topography based on the parallel multi-slit structure illumination of claim 7, wherein the relay optical path components comprise an LED lamp (1), an auxiliary lens (2), a field stop (3), a first light-collecting mirror (4), an aperture stop (5), a second light-collecting mirror (6), a plane mirror (7) and a total internal reflection prism; light emitted by the LED lamp (1) is imaged on the field diaphragm (3) through the auxiliary lens (2), an image positioned on the field diaphragm (3) reaches the plane mirror (7) after passing through the first light collecting mirror (4), the aperture diaphragm (5) and the second light collecting mirror (6), is reflected by the plane mirror (7) and enters the total internal reflection prism, the total internal reflection prism reflects the light to the digital micromirror array, and the light is modulated into structural light corresponding to an illumination pattern by the digital micromirror array;
the collection optical path component comprises a first sleeve lens (10), a beam splitter prism (13), an objective lens (15) and a second sleeve lens (12); the structured light is imaged on a rear focal plane of the objective lens through the first sleeve lens (10) and the beam splitter prism (13), is converted into parallel light beams through the objective lens (15) to uniformly illuminate an object plane (16) of the sample, and the light reflected by the object plane (16) is imaged on an image plane of the CMOS camera after passing through the beam splitter prism (13) and the second sleeve lens (12).
9. The device for measuring the microscopic surface topography based on the parallel multi-slit structure illumination is characterized in that the surface of the LED lamp (1) where the filament is located satisfies a conjugate relation with the field diaphragm (3), the aperture diaphragm (5) and the object surface (16); the plane of the CMOS camera photosensitive element and the plane of the digital micromirror array are in a conjugate focal plane.
10. The apparatus for measuring the microscopic surface topography based on the parallel multi-slit structure illumination according to claim 8 or 9, further comprising an apparatus support (17), a screw mechanism (18), an L-shaped platform (20) and a piezoceramic driver (23), wherein: the screw mechanism (18) is fixed at the top of the device bracket (17), and a screw rod of the screw mechanism (18) is provided with a sliding block (27); the L-shaped platform (20) is fixed on the sliding block (27), the optical path system is arranged on the L-shaped platform (20), the digital micromirror array is installed between a plane mirror (7) and a first sleeve lens (10), and the CMOS camera is installed behind a second sleeve lens (12); and the piezoelectric ceramic driver (23) is arranged at the bottom of the L-shaped platform (20) and is used for driving the objective lens (15) to move up and down.
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