CN110715931B - Automatic detection method and detection device for defects of transparent sample - Google Patents
Automatic detection method and detection device for defects of transparent sample Download PDFInfo
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Abstract
The invention discloses a method and a device for automatically detecting defects of a transparent sample. The method comprises the following steps: acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; placing a transparent sample on an objective table, wherein the transparent sample is not coincident with the central axis of an objective lens; the spatial light modulator is arranged on the image surface of the objective lens and is arranged as a grating for collecting interference patterns formed after passing through the spatial light modulator; adjusting the grating period of the spatial light modulator to a first detection grating period; obtaining a first interference image and a first phase distribution; removing the transparent sample to obtain a second phase distribution; and acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution and calculating the refractive index distribution of the transparent sample. The method provided by the embodiment of the invention can eliminate repeated images, is easier to extract the refractive index distribution of the transparent sample, and realizes automatic detection of the transparent samples with different sizes.
Description
Technical Field
The embodiment of the invention relates to the field of optical detection, in particular to a method and a device for automatically detecting defects of a transparent sample.
Background
With the traditional machine vision technology, defects in a micron scale are easy to find. However, if it is a sub-micron defect in a transparent sample, it is difficult to find, and this problem is a critical problem in optical element inspection such as a microlens array. It is therefore necessary to develop new machine vision methods for detecting these invisible defects. In general, in the manufacturing process of optical elements, the refractive index may change due to the cooling rate and pressure, and thus it is necessary to detect such a change in refractive index.
To detect defects in the optical elements on the micrometer scale, a digital holographic method may be used, which may be based on michelson or mach-zehnder interferometers. However, these interferometers tend to be too complicated in optical path structure. The shearing interference has a simple optical path structure and is easy to integrate into a detection system, but since the shearing interference is a self-reference interferometry technique, a hologram obtained by the shearing interference contains a repeated real image, the quality of the real image to be acquired is reduced by the repeated image, and the refractive index distribution information of an object is difficult to extract.
Disclosure of Invention
In order to solve the problems, the invention provides a method and a device for automatically detecting the defects of the transparent sample, which can eliminate repeated images, is easier to extract the refractive index distribution of the transparent sample and realizes the automatic detection of the transparent samples with different sizes.
In a first aspect, an embodiment of the present invention provides an automatic detection method for defects of a transparent sample, where the method includes:
acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample;
placing a transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of an objective lens;
collecting an interference pattern formed after the illumination light beam passes through the transparent sample and the spatial light modulator; the spatial light modulator is placed on the image surface of the objective lens and is set as a grating;
according to the interference pattern, adjusting the grating period of the spatial light modulator to a first detection grating period, so that the overlapping part of the zero-order diffraction beam and the first-order diffraction beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam;
obtaining a first interference image formed after the illumination light beam passes through the transparent sample and the spatial light modulator grating with the first detection grating period, and obtaining a first phase distribution according to the first interference image;
removing the transparent sample, obtaining a second interference image formed after the illumination light beam passes through the spatial light modulator grating of the first detection grating period, and obtaining a second phase distribution according to the second interference image;
acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
In a second aspect, an embodiment of the present invention further provides an apparatus for automatically detecting defects of a transparent sample, where the apparatus includes:
the system comprises a light source, an objective table, an objective lens, a spatial light modulator and an image acquisition device which are sequentially arranged along a light path;
the light source is used for generating an illumination light beam, and the radius of the illumination light beam is R; the objective table is used for bearing a transparent sample, the diameter of the transparent sample is 2R, and the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; the objective lens is positioned on one side of the bearing surface of the objective table; the spatial light modulator is positioned on the image surface of the objective lens and is set as a grating; the central axis of the transparent sample is not coincident with the central axis of the objective lens;
the image acquisition device is used for acquiring an interference pattern formed by the illumination light beam after passing through the transparent sample and the spatial light modulator grating; the system is also used for obtaining a first interference image formed by the illumination beam after passing through the transparent sample and the spatial light modulator grating with the first detection grating period, and obtaining a second interference image formed by the illumination beam after passing through the spatial light modulator grating with the first detection grating period after removing the transparent sample;
the processing device is electrically connected with the image acquisition device and used for adjusting the grating period of the spatial light modulator to a first detection grating period according to the acquired interference pattern, so that the overlapped part of the zero-order diffraction beam and the first-order diffraction beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam; the first phase distribution is acquired according to the first interference image; acquiring a second phase distribution according to the second interference image; obtaining a phase distribution of the transparent sample from the first phase distribution and the second phase distribution, and calculating a refractive index distribution of the transparent sample from the phase distribution of the transparent sample.
According to the embodiment of the application, the transparent sample is placed on the objective table, the diameter of the transparent sample is larger than the radius of the illumination light beam, and the central axis of the transparent sample is not overlapped with the central axis of the objective lens, so that the illumination light beam passing through the transparent sample is divided into two parts, one part contains information of the transparent sample, and the other part does not contain the information of the transparent sample; the spatial light modulator is used as a shearing device and is set as a grating, an illumination beam can generate an interference pattern carrying transparent sample information after passing through the grating, the shearing distance of the interference pattern can be adjusted by adjusting the grating period of the spatial light modulator, so that the overlapped part of a zero-order diffraction beam and a first-order diffraction beam contains all areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam, and the interference between the areas carrying the transparent sample information in the zero-order diffraction beam and the areas carrying the transparent sample information in the first-order diffraction beam in the interference pattern is eliminated, therefore, repeated images are eliminated, the refractive index distribution of a transparent sample is easier to extract, and the defect distribution condition of the transparent sample can be obtained according to the refractive index distribution; meanwhile, aiming at the transparent samples with different sizes, the grating period of the grating of the spatial light modulator can be adjusted digitally through a computer, so that the automatic detection of the transparent samples with different sizes is realized.
Drawings
FIG. 1 is a schematic flow chart of a method for automatically detecting defects of a transparent sample according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of light spots of zero-order diffracted light and first-order diffracted light generated after a probe beam and a reference beam pass through a spatial light modulator grating according to an embodiment of the present invention;
3-5 are schematic diagrams of light spots of zero-order diffracted light and first-order diffracted light at three shearing distances in the embodiments of the present application;
FIG. 6 is a flowchart illustrating a method for adjusting a grating period of a spatial light modulator to a first detected grating period according to an interference pattern according to an embodiment of the present disclosure;
FIG. 7 is a schematic flow chart of another method for automatically detecting defects of a transparent sample according to an embodiment of the present application;
FIG. 8 is a schematic flowchart of a method for obtaining a complex amplitude distribution of a first interference reconstructed image according to a complex amplitude distribution of a reference beam and a light intensity distribution of the first interference image according to an embodiment of the present application;
FIG. 9 is a flowchart illustrating a method for calculating a first phase distribution according to a complex amplitude distribution of a first interference reconstructed image according to an embodiment of the present application;
fig. 10 is a schematic structural diagram of an automatic defect detection apparatus for a transparent sample according to an embodiment of the present disclosure;
FIGS. 11 and 12 are schematic diagrams of raster images of two display states of a spatial light modulator provided by an embodiment of the present application;
fig. 13 is a schematic structural diagram of another automatic defect detection apparatus for a transparent sample according to an embodiment of the present application.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Fig. 1 is a schematic flow chart of an automatic defect detection method for a transparent sample according to an embodiment of the present invention. As shown in fig. 1, the defect detection method specifically includes the following steps:
110, acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample;
120, placing a transparent sample on the stage, the central axis of the transparent sample not coinciding with the central axis of the objective lens;
the light source is a He-Ne laser having a wavelength of 632.8nm, a semiconductor laser having a wavelength of 532nm, or the like.
Specifically, the radius of the illumination beam is not smaller than the diameter of the transparent sample, the central axis of the transparent sample is not coincident with the central axis of the objective lens, so that a part of the illumination beam can penetrate through the transparent sample and enter the objective lens, the part of the illumination beam is called a probe beam, and the other part of the illumination beam does not directly enter the objective lens without passing through the transparent sample and is a reference beam, so that in an interference pattern formed on an image plane of the objective lens, the overlapped part of the zero-order diffracted beam and the first-order diffracted beam contains all the areas carrying the transparent sample information in the zero-order diffracted beam and does not contain the areas carrying the transparent sample information in the first-order diffracted beam.
130, collecting an interference pattern formed after the illumination light beam passes through the transparent sample and the spatial light modulator; the spatial light modulator is placed on the image surface of the objective lens and is set as a grating;
specifically, the spatial light modulator is set as a grating, and then the spatial light modulator plays a role of the grating, so that the detection light beam and the reference light beam are converged to the grating of the spatial light modulator through the objective lens to generate diffraction and generate interference patterns with alternate light and shade, wherein each level of diffraction light beam consists of two parts, namely a region containing transparent sample information and a region not containing transparent sample information, and the distribution of the refractive index of the sample to be detected can be obtained by analyzing the interference of zero-level diffraction light and first-level diffraction light.
Grating diffraction equation:
psinθ＝mλ (1)
where p is the grating period, θ is the angle of the diffracted light with the optical axis, λ is the wavelength of the illumination beam, and m is the order of diffraction. When m is 1, the grating period can be calculated according to the wavelength of the illumination light beam and the included angle between the first-order diffraction light and the optical axis:
p＝λ/sinθ (2)
FIG. 2 is a schematic diagram of light spots of zero-order diffracted light and first-order diffracted light generated after a probe beam and a reference beam pass through a spatial light modulator grating in the embodiment of the present invention. As shown in FIG. 2, the spot 210 of zero-order diffracted light is centered on the optical axis with a grating period of:
p＝λ/sinθ＝λ/sin(tan-1(S/h)) (3)
where S is a distance between a spot center of the zero-order diffracted light 210 and a spot center of the first-order diffracted light 220, that is, a shearing distance, and h is a distance from the image pickup device to the spatial light modulator 230. It can be seen that the smaller the grating period, the larger the shearing distance.
140, adjusting the grating period of the spatial light modulator to a first detection grating period according to the interference pattern, so that the overlapping part of the zero-order diffracted beam and the first-order diffracted beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffracted beam and does not contain the areas carrying the transparent sample information in the first-order diffracted beam;
fig. 3-5 are schematic diagrams of light spots of the zero-order diffracted light and the first-order diffracted light at three shearing distances in the embodiment of the present application. As shown in fig. 3, the shearing distance is S1As shown in fig. 4, the shearing distance is S2As shown in fig. 5, the shearing distance is S3。
S3>S2>S1When the shearing distance is S1At this time, the distance separating the light spot 210 of the zero-order diffraction light and the light spot 220 of the first-order diffraction light is too small, the region of the zero-order diffraction light carrying the transparent sample information interferes with the region of the first-order diffraction light carrying the transparent sample information, a repeated image is generated, and at this time, the grating with a smaller grating period needs to be replaced to obtain a larger shearing distance S2(ii) a When the shearing distance is S2During the process, the area of the zero-order diffraction light carrying the transparent sample information is just not interfered with the area of the first-order diffraction light carrying the transparent sample information, the area of the zero-order diffraction light carrying the transparent sample information is just interfered with the area of the first-order diffraction light not carrying the transparent sample information, the influence of repeated images is eliminated, the grating with a smaller grating period is continuously replaced at the moment, and a larger shearing distance S is obtained3(ii) a When the shearing distance is S3When the area of the zero-order diffraction light carrying the transparent sample information does not interfere with the area of the first-order diffraction light carrying the transparent sample information, and the area of the zero-order diffraction light carrying the transparent sample information just interferes with the area of the first-order diffraction light not carrying the transparent sample information, the influence of repeated images can still be eliminated. However, if the shearing distance is further increased, the region where the zero-order diffracted light carries the transparent sample information cannot be totally interfered with the region where the first-order diffracted light does not carry the transparent sample information, and a part of the transparent sample information is lost. Thus, all information on the transparent sample was obtainedMeanwhile, the influence of repeated images is eliminated, and the shearing distance is required to be greater than or equal to S2Less than or equal to S3That is to say S2And S3The minimum and maximum shearing distances for the transparent sample, respectively.
Therefore, the shearing distance is set to be greater than or equal to S by adjusting the grating period of the spatial light modulator grating to the first detection grating period2Less than or equal to S3Within the range of (1), all information of the transparent sample can be obtained while eliminating the influence of the duplicate image. Transparent samples of different sizes correspond to different S2And S3According to the interference patterns of different transparent samples, the appropriate grating period can be automatically selected for defect detection.
Fig. 6 is a flowchart illustrating a method for adjusting a grating period of a spatial light modulator to a first detected grating period according to an interference pattern according to an embodiment of the present disclosure. As shown in fig. 6, the specific steps include:
610 of the interference pattern, determining whether a region of the zero order diffracted beam carrying the transparent sample information overlaps with a region of the first order diffracted beam carrying the transparent sample information;
the interference pattern is obtained in real time through the image acquisition device, the obtained interference pattern is analyzed in real time through the processing device, the analysis result is fed back to the spatial light modulator, the grating period of the spatial light modulator is adjusted, and the information of the overlapped part of the light spots is monitored in real time, so that the shearing distance is larger than or equal to S2Less than or equal to S3。
620, if yes, reducing the grating period of the spatial light modulator until the area carrying the transparent sample information in the zero-order diffraction beam and the area carrying the transparent sample information in the first-order diffraction beam do not overlap;
if not, judging whether the area of the zero-order diffraction beam carrying the transparent sample information in the interference pattern is completely contained in the area of the first-order diffraction beam not carrying the transparent sample information;
if the zero order diffracted light is carried in the transparentThe area of the sample information is overlapped with the area carrying the transparent sample information in the first-order diffracted light, and the shearing distance is smaller than S2The grating period needs to be reduced so that the shearing distance is increased to be equal to or greater than S2(ii) a If not, the shearing distance is more than or equal to S2And simultaneously determining the shearing distance and S3The magnitude relationship of (1).
640, if yes, it indicates that the overlapping part of the zero-order diffracted beam and the first-order diffracted beam in the interference pattern contains the area of the zero-order diffracted beam carrying all the information of the transparent sample, and does not contain the area of the first-order diffracted beam carrying the information of the transparent sample;
and 650, if not, increasing the grating period of the spatial light modulator until the region carrying the transparent sample information in the zero-order diffracted light is completely contained in the region not carrying the transparent sample information in the first-order diffracted light.
If the region carrying the transparent sample information in the zero-order diffracted light is not completely contained in the region not carrying the transparent sample information in the first-order diffracted light, it indicates that the shearing distance is greater than S3The grating period needs to be increased so that the shearing distance is not more than S3(ii) a If the region carrying the transparent sample information in the zero-order diffracted light is completely contained in the region not carrying the transparent sample information in the first-order diffracted light, the shearing distance is less than or equal to S3. So that the shearing distance not only satisfies the condition of S or more2And satisfies S or less3The grating period of (a) is the first detection grating period.
150, obtaining a first interference image formed after the illumination beam passes through the transparent sample and the spatial light modulator grating with the first detection grating period, and obtaining a first phase distribution according to the first interference image;
160, removing the transparent sample, acquiring a second interference image formed after the illumination beam passes through the spatial light modulator grating of the first detection grating period, and acquiring a second phase distribution according to the second interference image;
170 obtaining a phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
obtaining the complex amplitude distribution of the first interference reconstruction image through low-pass filtering, angular spectrum propagation and inverse Fourier transform according to the complex amplitude distribution of the first interference image and the reference beam, and obtaining a first phase distribution (phi) according to the complex amplitude distribution of the first interference reconstruction image, namely the first phase distribution (phi) when a transparent sample exists on an object plane1(x, y, d); removing the transparent sample, illuminating the same grating with the illuminating beam to obtain a second interference image, obtaining the complex amplitude distribution of the second interference reconstruction image through the same operation according to the complex amplitude distribution information of the second interference image and the reference beam, and obtaining a second phase distribution according to the complex amplitude distribution of the second interference reconstruction image, namely the second phase distribution phi when no transparent sample exists on the object plane2(x, y, d). The phase distribution Δ Φ (x, y, d) of the transparent sample was calculated according to equation (4):
Δφ(x,y,d)＝φ1(x,y,d)-φ2(x,y,d) (4)
180, calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
The refractive index distribution of the transparent sample was calculated according to equation (5):
where Δ Φ (x, y, d) is the phase distribution of the transparent sample, Δ L (x, y, d) is the thickness variation distribution of the transparent sample, and λ is the wavelength of the illumination beam.
According to the embodiment of the application, the transparent sample is placed on the objective table, the diameter of the transparent sample is larger than the radius of the illumination light beam, and the central axis of the transparent sample is not overlapped with the central axis of the objective lens, so that the illumination light beam passing through the transparent sample is divided into two parts, one part contains information of the transparent sample, and the other part does not contain the information of the transparent sample; the spatial light modulator is used as a shearing device and is set as a grating, an illumination beam can generate an interference pattern carrying transparent sample information after passing through the grating, the shearing distance of the interference pattern can be adjusted by adjusting the grating period of the spatial light modulator, so that the overlapped part of a zero-order diffraction beam and a first-order diffraction beam contains all areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam, and the interference between the areas carrying the transparent sample information in the zero-order diffraction beam and the areas carrying the transparent sample information in the first-order diffraction beam in the interference pattern is eliminated, therefore, repeated images are eliminated, the refractive index distribution of a transparent sample is easier to extract, and the defect distribution condition of the transparent sample can be obtained according to the refractive index distribution; meanwhile, aiming at the transparent samples with different sizes, the grating period of the grating of the spatial light modulator can be adjusted digitally through a computer, so that the automatic detection of the transparent samples with different sizes is realized.
Optionally, the spatial light modulator grating is a two-dimensional grating. The grating slit displayed by the spatial light modulator can extend along the horizontal direction and can also extend along the vertical direction, so that the refractive index distribution along the horizontal direction and the refractive index distribution along the vertical direction can be obtained, and the detection results in the two directions are combined, so that a better defect detection effect can be realized.
Fig. 7 is a schematic flow chart of another automatic defect detection method for a transparent sample according to an embodiment of the present application. As shown in fig. 7, the method specifically includes the following steps:
110, acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample;
120, placing a transparent sample on the stage, the central axis of the transparent sample not coinciding with the central axis of the objective lens;
130, collecting an interference pattern formed after the illumination light beam passes through the transparent sample and the spatial light modulator; the spatial light modulator is placed on the image surface of the objective lens and is set as a grating;
140, adjusting the grating period of the spatial light modulator to a first detection grating period according to the interference pattern, so that the overlapping part of the zero-order diffracted beam and the first-order diffracted beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffracted beam and does not contain the areas carrying the transparent sample information in the first-order diffracted beam;
710, obtaining a first interference image formed by the illumination beam passing through the transparent sample and the spatial light modulator grating with the first detection grating period,
720, acquiring the light intensity distribution of the first interference image;
specifically, referring to FIG. 4 or FIG. 5, the complex amplitude distribution of the region 211 where the zero-order diffracted light carries the information of the transparent sample is O1The complex amplitude of the region 212 where zero-order diffracted light does not carry transparent sample information is R1The complex amplitude distribution of the first-order diffracted light carrying transparent sample information area 221 is O2The complex amplitude of the first order diffracted light in the region 222 not carrying information on the transparent sample is R2The complex amplitude distribution of the generated first interference image can be expressed as:
wherein, | O1|2+|R2|2In the form of a direct current term,
is a virtual image and is a virtual image,
is a real image.
730, acquiring the complex amplitude distribution of the first interference reconstruction image according to the complex amplitude distribution of the reference beam and the light intensity distribution of the first interference image;
specifically, fig. 8 is a schematic flowchart of a method for obtaining a complex amplitude distribution of a first interference reconstructed image according to a complex amplitude distribution of a reference beam and a light intensity distribution of the first interference image according to an embodiment of the present application. As shown in fig. 8, the method specifically includes:
731, removing the direct current item and the virtual image of the light intensity in the first interference image through a filtering algorithm, and obtaining the light intensity distribution of the first real image;
namely, the DC term | O of the light intensity distribution in the first interference image is removed by utilizing a low-pass filtering algorithm1|2+|R2|2And virtual images
Leaving only real images
Since only the real image is related to the phase distribution of the transparent sample, the noise can be reduced and effective information can be extracted. Thus, the light intensity distribution of the first real image is obtained as:
732, and superposing the complex amplitude distribution of the reference beam and the first real image to obtain the complex amplitude distribution of the first interference reconstruction image.
According to the complex amplitude distribution of the reference beam and the light intensity distribution of the first real image, the reference beam refers to the part of the illumination beam which is directly incident to the objective lens without passing through the transparent sample, and R is adopted2(x, y) representing the complex amplitude distribution of the reference beam, resulting in a complex amplitude distribution of the first interference reconstructed image:
wherein R is2(x, y) is the complex amplitude of the reference beam.
740, calculating the first phase distribution according to the complex amplitude distribution of the first interference reconstruction image.
Specifically, fig. 9 is a flowchart illustrating a method for calculating a first phase distribution according to a complex amplitude distribution of a first interference reconstructed image according to an embodiment of the present application. As shown in fig. 9, the method specifically includes:
741, obtaining frequency domain complex amplitude distribution of the first interference reconstruction image transmitted to an image plane by using an angular spectrum transmission algorithm;
that is, the frequency domain complex amplitude distribution of the first interference reconstruction image propagated to the image plane is calculated by formula (9):
wherein,
is the frequency domain complex amplitude distribution of the filtered image, fxSpatial frequency in x-direction, fyIn the y-direction, k is the wave number and d represents the propagation distance.
742, obtaining the spatial domain complex amplitude distribution of the first interference reconstruction image transmitted to the image plane by utilizing inverse Fourier transform;
namely, the frequency domain complex amplitude distribution of the first interference reconstruction image after being transmitted to the image plane is obtained through inverse Fourier transform according to the formula (10):
743, extracting a real part and an imaginary part in the spatial domain complex amplitude distribution of the first interference reconstruction image, and calculating the first phase distribution.
I.e. extracting the real part and imaginary part of U (x, y, d), and obtaining the first phase distribution according to equation (11):
where Im [ U (x, y, d) ] is the imaginary part of the spatial domain complex amplitude distribution of the first interference reconstructed image, and Re [ U (x, y, d) ] is the real part of the spatial domain complex amplitude distribution of the first interference reconstructed image.
160, removing the transparent sample, acquiring a second interference image formed after the illumination beam passes through the spatial light modulator grating of the first detection grating period, and acquiring a second phase distribution according to the second interference image;
removing the transparent sample, and enabling the illumination beam to pass through the grating of the spatial light modulator, wherein the grating period of the grating of the spatial light modulator is the same as the grating period of the grating of the spatial light modulator when the transparent sample exists, so that the light intensity distribution of a second interference image is obtained; removing the direct current item and the virtual image of the light intensity in the second interference image through a filtering algorithm to obtain a second real image; superposing the complex amplitude distribution of the reference beam and the light intensity distribution of the second real image to obtain the complex amplitude distribution of the second interference reconstruction image; converting the spatial domain complex amplitude distribution of the second interference reconstruction image into frequency domain complex amplitude distribution through Fourier transform; obtaining the frequency domain complex amplitude distribution of the second interference reconstruction image transmitted to the image plane according to the frequency domain complex amplitude distribution of the second interference reconstruction image by using an angular spectrum transmission algorithm; obtaining the spatial domain complex amplitude distribution of the second interference reconstruction image transmitted to the image plane by utilizing inverse Fourier transform; extracting the real part and the imaginary part in the space-domain complex amplitude distribution of the second interference reconstruction image, and calculating a second phase distribution phi2(x,y,d)。
170 obtaining a phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
180, calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
Based on the same inventive concept, the embodiment of the invention also provides an automatic defect detection device for a transparent sample, which can execute the automatic defect detection method for the transparent sample provided by any embodiment of the invention and has corresponding functions and beneficial effects of the execution method.
Fig. 10 is a schematic structural diagram of an automatic defect detection apparatus for a transparent sample according to an embodiment of the present application. As shown in fig. 10, the detection device includes: a light source 910, an object stage 920, an objective lens 930, a spatial light modulator 940 and an image acquisition device 950 arranged in sequence along an optical path;
the light source 910 is used for generating an illumination beam, wherein the radius of the illumination beam is R; the stage 920 is used for carrying a transparent sample 960, the diameter of the transparent sample is 2R, and the radius R of the illumination beam is not less than the diameter 2R of the transparent sample; the objective lens 930 is located on the bearing surface side of the stage 920; the spatial light modulator 940 is located at the image plane of the objective lens 930 and is arranged as a grating; the central axis of the transparent sample 960 is not coincident with the central axis of the objective lens 930;
the image acquisition device 950 is used for acquiring an interference pattern formed by the illumination beam after passing through the transparent sample 960 and the spatial light modulator 940; the system is further configured to obtain a first interference image formed by the illumination beam passing through the transparent sample 960 and the spatial light modulator 940 with the first detection grating period, and obtain a second interference image formed by the illumination beam passing through the spatial light modulator 940 with the first detection grating period after the transparent sample 960 is removed;
the spatial light modulator 940 is electrically connected with the image acquisition device 950, and the processing device 970 is used for adjusting the grating period of the spatial light modulator 940 to a first detection grating period according to the acquired interference pattern, so that the overlapping part of the zero-order diffracted beam and the first-order diffracted beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffracted light and does not contain the areas carrying the transparent sample information in the first-order diffracted light; the first phase distribution is acquired according to the first interference image; acquiring a second phase distribution according to the second interference image; obtaining the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution, and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample;
specifically, the light source 910 is a He-Ne laser having a wavelength of 632.8nm, a semiconductor laser having a wavelength of 532nm, or the like. Objective table 920 includes a transparent region, and transparent sample 960 is placed in the transparent region, and does not affect the reception of the illumination beam by the transparent sample, and ensures that the beam emitted by the transparent sample contains information of the transparent sample and does not contain information of the objective table, thereby ensuring the accuracy of the detection result.
Optionally, with continued reference to fig. 11, the processing device 970 includes: a first judging module 971, an adjusting module 972 and a second judging module 973;
a first judging module 971, configured to judge whether a region carrying transparent sample information in a zero-order diffraction beam and a region carrying transparent sample information in a first-order diffraction beam in the interference pattern overlap;
a second judging module 973, configured to, when the judgment result of the first judging module 971 is negative, judge whether an area carrying transparent sample information in the zero-order diffraction beam in the interference pattern is completely included in an area not carrying transparent sample information in the first-order diffraction beam;
an adjusting module 972, configured to, when the determination result of the first determining module 971 is yes, decrease the grating period of the spatial light modulator 940 until an area carrying the transparent sample information in the zero-order diffracted beam and an area carrying the transparent sample information in the first-order diffracted beam do not overlap; and is further configured to, when the determination result of the second determining module 973 is negative, increase the grating period of the spatial light modulator 940 until the region carrying the transparent sample information in the zero-order diffracted light is completely included in the region not carrying the transparent sample information in the first-order diffracted light.
Optionally, the spatial light modulator is a two-dimensional spatial light modulator, and is connected to a computer, and the spatial light modulator is set as a two-dimensional grating by the computer.
Fig. 11 and 12 are schematic raster images of two display states of the spatial light modulator according to the embodiment of the present application. As shown in fig. 11, the size of the spatial light modulator pixel 410 is l, the grating period is changed by the number of pixels in an on state in each row, the minimum period is one row of pixels, and the grating period p is 2nl, where n is the number of pixels in an on state in each grating slit along the row direction; the grating shown in fig. 12 is a two-dimensional grating, and the grating periods in the row and column directions may be different. Therefore, the grating period of the spatial light modulator can be controlled by only controlling the number of n, the automation is convenient to realize when the transparent samples with different sizes are detected, the integration and the miniaturization are easy, and the cost of the device is reduced.
Fig. 13 is a schematic structural diagram of another automatic defect detection apparatus for a transparent sample according to an embodiment of the present application. As shown in fig. 13, the detection device includes: a light source 910, a beam expander 981, a reflector 982 stage 920, an objective 930, a spatial light modulator 940 and an image acquisition device 950 which are arranged along an optical path in sequence;
Specifically, when the beam radius of the illumination beam emitted from the light source 910 is small or the diameter of the transparent sample 960 is large and the beam radius is smaller than the diameter of the transparent sample 960, the beam radius of the illumination beam can be enlarged by the beam expander 981 so that the beam radius is not smaller than the diameter of the transparent sample 960. The mirror 982 can change the propagation path of the illumination beam, and when the position of the transparent sample 960 on the stage 920 changes, the path of the illumination beam can be changed by changing the angle of the mirror 982 without moving the light source 910, so as to meet the condition of defect detection.
Illustratively, a linearly polarized He — Ne laser having a wavelength of 632.8nm was selected as the light source, and the output power thereof was 2 mW; the transparent sample is an aspheric collimating objective lens, the radius of the aspheric collimating objective lens is 0.8mm, and the thickness of the aspheric collimating objective lens is 500 mu m; the size of the pixel of the spatial light modulator is 18 micrometers, and the radius of a light spot of an illumination light beam expanded by the beam expander is 4 mm; the right side of the transparent sample coincides with the right boundary of the illumination beam; the distance between the spatial light modulator and the image acquisition device is 500 mm; the image acquisition device selects a CCD camera which has 8-bit dynamic range, pixels are 2048 × 2048, and the pixel size is 7.4 μm × 7.4 μm; the magnification of the objective lens is 2, and the numerical aperture is 0.055.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (10)
1. A method for automatically detecting defects of a transparent sample is characterized by comprising the following steps:
acquiring the radius R of an illumination light beam according to the radius R of the transparent sample, wherein the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample;
placing a transparent sample on an objective table, wherein the central axis of the transparent sample is not coincident with the central axis of an objective lens;
collecting an interference pattern formed after the illumination light beam passes through the transparent sample and the spatial light modulator; the spatial light modulator is placed on the image surface of the objective lens and is set as a grating;
according to the interference pattern, adjusting the grating period of the spatial light modulator to a first detection grating period, so that the overlapping part of the zero-order diffraction beam and the first-order diffraction beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam;
obtaining a first interference image formed after the illumination light beam passes through the transparent sample and the spatial light modulator grating with the first detection grating period, and obtaining a first phase distribution according to the first interference image;
removing the transparent sample, obtaining a second interference image formed after the illumination light beam passes through the spatial light modulator grating of the first detection grating period, and obtaining a second phase distribution according to the second interference image;
acquiring the phase distribution of the transparent sample according to the first phase distribution and the second phase distribution;
and calculating the refractive index distribution of the transparent sample according to the phase distribution of the transparent sample.
2. The automatic detection method according to claim 1, wherein the adjusting the grating period of the spatial light modulator to a first detection grating period according to the interference pattern so that the overlapping portion of the zeroth order diffracted beam and the first order diffracted beam in the interference pattern contains an area of the zeroth order diffracted beam that carries the entire information of the transparent sample and does not contain an area of the first order diffracted beam that carries the information of the transparent sample comprises:
determining whether a region of the interference pattern in which the transparent sample information is carried in the zero-order diffracted beam overlaps with a region of the interference pattern in which the transparent sample information is carried in the first-order diffracted beam;
if so, reducing the grating period of the spatial light modulator until the area carrying the transparent sample information in the zero-order diffraction beam and the area carrying the transparent sample information in the first-order diffraction beam are not overlapped;
if not, judging whether the area of the zero-order diffraction beam carrying the transparent sample information in the interference pattern is completely contained in the area of the first-order diffraction beam not carrying the transparent sample information;
if yes, the overlapping part of the zero-order diffraction beam and the first-order diffraction beam in the interference pattern contains a region carrying all information of the transparent sample in the zero-order diffraction beam and does not contain a region carrying the information of the transparent sample in the first-order diffraction beam;
and if not, increasing the grating period of the spatial light modulator until the region carrying the transparent sample information in the zero-order diffraction beam is completely contained in the region not carrying the transparent sample information in the first-order diffraction beam.
3. The automatic detection method of claim 1, wherein the spatial light modulator grating is a two-dimensional grating.
4. The automatic detection method according to claim 1, wherein the obtaining a first phase distribution from the first interference image comprises:
acquiring the light intensity distribution of the first interference image;
acquiring the complex amplitude distribution of a first interference reconstruction image according to the complex amplitude distribution of the reference light and the light intensity distribution of the first interference image;
and calculating the first phase distribution according to the complex amplitude distribution of the first interference reconstruction image.
5. The automatic detection method according to claim 4, wherein the obtaining the complex amplitude distribution of the first interference reconstructed image according to the complex amplitude distribution of the reference beam and the light intensity distribution of the first interference image comprises:
removing the direct current item and the virtual image of the light intensity in the first interference image through a filtering algorithm to obtain the light intensity distribution of a first real image;
and superposing the complex amplitude distribution of the reference beam and the light intensity distribution of the first real image to obtain the complex amplitude distribution of the first interference reconstruction image.
6. The automatic detection method according to claim 4, wherein said calculating the first phase distribution from the complex amplitude distribution of the first interference reconstructed image comprises:
obtaining frequency domain complex amplitude distribution of the first interference reconstruction image transmitted to an image plane by using an angular spectrum transmission algorithm;
obtaining the spatial domain complex amplitude distribution of the first interference reconstruction image transmitted to the image plane by utilizing inverse Fourier transform;
and extracting a real part and an imaginary part in the spatial domain complex amplitude distribution of the first interference reconstruction image, and calculating the first phase distribution.
7. An automatic defect detection device for a transparent sample, comprising:
the system comprises a light source, an objective table, an objective lens, a spatial light modulator and an image acquisition device which are sequentially arranged along a light path;
the light source is used for generating an illumination light beam, and the radius of the illumination light beam is R; the objective table is used for bearing a transparent sample, the diameter of the transparent sample is 2R, and the radius R of the illumination light beam is not less than the diameter 2R of the transparent sample; the objective lens is positioned on one side of the bearing surface of the objective table; the spatial light modulator is positioned on the image surface of the objective lens and is set as a grating; the central axis of the transparent sample is not coincident with the central axis of the objective lens;
the image acquisition device is used for acquiring an interference pattern formed by the illumination light beam after passing through the transparent sample and the spatial light modulator grating; the system is also used for obtaining a first interference image formed by the illumination beam after passing through the transparent sample and the spatial light modulator grating with the first detection grating period, and obtaining a second interference image formed by the illumination beam after passing through the spatial light modulator grating with the first detection grating period after removing the transparent sample;
the processing device is electrically connected with the image acquisition device and used for adjusting the grating period of the spatial light modulator to a first detection grating period according to the acquired interference pattern, so that the overlapped part of the zero-order diffraction beam and the first-order diffraction beam in the interference pattern contains all the areas carrying the transparent sample information in the zero-order diffraction beam and does not contain the areas carrying the transparent sample information in the first-order diffraction beam; the first phase distribution is acquired according to the first interference image; acquiring a second phase distribution according to the second interference image; obtaining a phase distribution of the transparent sample from the first phase distribution and the second phase distribution, and calculating a refractive index distribution of the transparent sample from the phase distribution of the transparent sample.
8. The automatic detection device according to claim 7, wherein the processing device comprises: the device comprises a first judgment module, an adjustment module and a second judgment module;
the first judging module is used for judging whether a region carrying the transparent sample information in the zero-order diffraction beam and a region carrying the transparent sample information in the first-order diffraction beam in the interference pattern are overlapped;
the second judging module is configured to, when the judgment result of the first judging module is negative, judge whether an area in the interference pattern, where the zero-order diffraction beam carries the transparent sample information, is completely included in an area in the first-order diffraction beam that does not carry the transparent sample information;
the adjusting module is configured to reduce a grating period of the spatial light modulator until an area carrying the transparent sample information in the zero-order diffracted beam and an area carrying the transparent sample information in the first-order diffracted beam do not overlap with each other when the first judging module judges that the transparent sample information is not in the first-order diffracted beam; and the spatial light modulator is further configured to increase a grating period of the spatial light modulator when the judgment result of the second judgment module is negative, until a region carrying the transparent sample information in the zero-order diffraction beam is completely included in a region not carrying the transparent sample information in the first-order diffraction beam.
9. The automatic detection device according to claim 7, wherein the spatial light modulator is connected to a computer, and the spatial light modulator is configured as a two-dimensional grating by the computer.
10. The automatic detection device according to claim 7, further comprising:
a beam expander and a mirror;
the beam expander is positioned between the light source and the reflector; the reflector is used for reflecting the illumination light beams emitted by the light source to the objective table after passing through the beam expander.
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