CN111896557A - A three-dimensional measurement device and method for dark-field microscopic defects with structured light modulation - Google Patents

Abstract

The invention discloses a three-dimensional measurement device and method for dark-field microscopic defects with structured light modulation. The three-dimensional measurement device comprises a light source, a spatial light modulator, a first lens, a beam splitter, a microscope objective lens, a second lens, a third lens Three lenses, a filter, a fourth lens and a CCD; the spatial light modulator is used to receive the light emitted by the light source and modulate it into structured light; the structured light modulated by the spatial light modulator passes through the first lens, the beam splitter and the display in sequence. The micro-objective lens is miniature projected onto the sample and reflected on the sample to form zero-order light and first-order light; the zero-order light passes through the microscope objective lens, the second lens and the third lens in turn to reach the filter; the first-order light passes through the The microscope objective, the second lens, the third lens and the fourth lens reach the CCD for imaging. The invention solves the problem that the illumination background light and the defocused light interfere with the imaging of the scattered light of the defect in the existing non-destructive testing method.

Description

A three-dimensional measurement device and method for dark-field microscopic defects with structured light modulation

technical field

The invention relates to the field of material detection, in particular to a three-dimensional measurement device and method for dark field microscopic defects modulated by structured light.

Background technique

Accurate measurement of the three-dimensional morphology of defects in transparent optical materials is one of the keys to obtaining high-quality and low-defect optical components. Existing defect detection methods can be divided into two categories: destructive testing and non-destructive testing. Destructive detection methods (such as cross-section microscopy, angle polishing, ion beam etching, and magnetorheological polishing spots) expose and expand the internal structure of defects by means of etching, polishing, etc., and detect the depth information of defects. The detection accuracy is high, but it will cause damage or failure of optical components, and can only be used as a sampling method. Non-destructive testing methods do not damage optical components, and have high efficiency and low cost, and have become an inevitable development trend in defect detection.

Among non-destructive testing methods, dark-field imaging has high sensitivity, but it can only measure the two-dimensional structure of defects and lack the ability to detect longitudinal depths. Non-destructive 3D micro-defect detection methods mainly include white light interference, atomic force microscopy, confocal scanning microscopy, optical coherence tomography, digital holographic microscopy, total internal reflection dark field microscopy and other technologies. It can detect the three-dimensional topography of surface defects. Several other methods have the ability of three-dimensional detection of surface and internal defects at the same time, but there is a problem that illumination background light and defocused light interfere with the imaging of scattered light of defects.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a structured light-modulated dark-field microscopic defect three-dimensional measuring device, which solves the problem of the existing non-destructive testing methods that the illumination background light and the defocused light interfere with the scattered light imaging of the defect.

In addition, the present invention also provides a method based on the above-mentioned measuring device.

The present invention is achieved through the following technical solutions:

A structured light-modulated dark-field microscopic defect three-dimensional measurement device, comprising a light source, a spatial light modulator, a first lens, a beam splitter, a microscope objective lens, a second lens, a third lens, a filter, a fourth lens and a CCD ;

The spatial light modulator is used for receiving the light emitted by the light source and modulating it into structured light;

The structured light modulated by the spatial light modulator is micro-projected onto the sample through the first lens, the beam splitter and the microscope objective lens in turn, and is reflected on the sample to form zero-order light and first-order light;

The zero-order light reaches the filter through the microscope objective lens, the second lens and the third lens in sequence;

The first-order light passes through the microscope objective lens, the second lens, the third lens and the fourth lens in sequence to reach the CCD imaging.

The microscope objective lens of the present invention is both an illumination lens and an imaging objective lens, and the CCD is a charge-coupled element, which can be called a CCD image sensor.

The zero-order light is most of the illumination background light, the first-order light contains a small part of the illumination background light and part of the defect scattered light, and most of the illumination background light can be removed by using an external filter.

The separation of in-focus light and defocused light is achieved by high-frequency structured light field illumination and subsequent modulation degree analysis algorithms. This high-frequency structured light field means that the modulated structured light of the spatial light modulator must be high-frequency The separation effect is the best when the focused light and the defocused light are separated. Specifically, when the frequency of the structured light is half of the specific system cutoff frequency, the separation effect is the best.

The system cut-off frequency f _c =2NA/λ, where NA is the numerical aperture of the microscope objective, and λ is the wavelength of the illumination light.

To sum up, the present invention uses high-frequency structured light field illumination defects, separates on-focus light and defocused light by means of structured light frequency-domain modulation, and uses an external frequency-domain filter to remove most of the illumination background light, which can eliminate the illumination background. The interference of light and defocused light interference improves imaging sensitivity.

Further, a filter is interposed between the third lens and the fourth lens.

Further, the back focal plane of the third lens and the front focal plane of the fourth lens overlap to form a spectrum plane, and the filter is located on the spectrum plane.

Further, the size of the filter is smaller than the aperture size of the CCD.

That is, the blocking objects on the optical path cannot completely block the imaging format of the CCD, and the first-order light and the light scattered by the defects can partially enter the imaging format of the CCD.

Further, a displacement mechanism for installing the sample is also included, and the displacement mechanism is used for the sample to move in the direction of the optical axis.

In this way, during detection, the sample to be tested is installed on the displacement mechanism, and the displacement mechanism drives the sample to be tested to move in the direction of the optical axis for testing, so as to realize axial three-dimensional scanning of sample defects.

Preferably, the direction in which the displacement mechanism drives the sample to be tested is parallel to the optical axis of the coaxial optical path.

Further, the sample is mounted near the focal plane of the microscope objective.

Further, the sample is a transparent material.

Further, the light source is an LED light source.

A measurement method of a structured light-modulated dark-field microscopic defect three-dimensional measurement device, comprising the following steps:

S1. Install the sample to be tested near the focal plane of the microscope objective lens;

S2, adjust the sample so that the area to be measured of the sample enters the imaging field of view of the microscope objective lens, and set the fringe frequency, phase shift step size and phase shift step number of the spatial light modulator;

S3. Activate the light source, the spatial light modulator and the CCD, pause at each axial position and collect a dark-field microscopic image of the set phase-shift fringes.

Further, it also includes:

S4. Use the phase shift modulation degree analysis method to calculate the modulation degree of each axial position to obtain the axial modulation degree curve. The calculation formula is as follows:

In the formula, N represents the number of phase shift steps, and I _i represents the light intensity value of a certain point during the i-th phase shift;

S5. Perform three-dimensional reconstruction of the defects on the sample according to the axial modulation curve.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The three-dimensional measurement device of the present invention improves the sensitivity of defect imaging through high-frequency structured light modulation and external frequency domain filters, while eliminating the interference of illumination background light and defocused light.

2. The present invention can be effectively used for three-dimensional defect detection of transparent materials, and meets the detection requirements of the three-dimensional structure of the surface and internal defects of transparent materials in the fields of optical manufacturing and the like.

Description of drawings

The accompanying drawings described herein are used to provide further understanding of the embodiments of the present invention, and constitute a part of the present application, and do not constitute limitations to the embodiments of the present invention. In the attached image:

FIG. 1 is a schematic structural diagram of a three-dimensional measurement device;

FIG. 2 is a measurement flow chart of the three-dimensional measurement device.

The marks in the attached drawings and the corresponding parts names:

1-light source, 2-spatial light modulator, 3-first lens, 4-beamsplitter, 5-microscopic objective, 6-sample, 7-defect, 8-displacement mechanism, 9-second lens, 10-th Three lenses, 11-filter, 12-fourth lens, 13-CCD, 14-zeroth-order light, 15-first-order light.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. as a limitation of the present invention.

Example 1:

As shown in Figure 1, a structured light modulation dark field microscopic defect three-dimensional measurement device includes a light source 1, a spatial light modulator 2, a first lens 3, a beam splitter 4, a microscope objective lens 5, a second lens 9, The third lens 10, the filter 11, the fourth lens 12 and the CCD13;

The spatial light modulator 2 is used for receiving the light emitted by the light source 1 and modulating it into structured light;

The structured light modulated by the spatial light modulator 2 is micro-projected onto the sample 6 through the first lens 3, the beam splitter 4 and the microscope objective lens 5 in turn, and is reflected on the sample 6 to form the zero-order light 14 and the first-order light 15. The sample 6 is installed near the focal plane of the microscope objective lens 5, and the sample 6 is a transparent material;

The zero-order light 14 passes through the microscope objective lens 5, the second lens 9 and the third lens 10 in sequence to reach the filter 11. The back focal plane of the third lens 10 and the front focal plane of the fourth lens 12 overlap to form a spectrum plane. , the filter 11 is located on the spectrum plane, and the size of the filter 11 is smaller than the aperture size of the CCD 13;

The primary light 15 sequentially passes through the microscope objective lens 5 , the second lens 9 , the third lens 10 and the fourth lens 12 to reach the CCD 13 for imaging.

As shown in Figure 2, the measurement method of this embodiment includes the following steps:

S1, the sample 6 to be tested is installed near the focal plane of the microscope objective lens 5;

S2, adjust the sample 6 so that the area to be measured of the sample 6 enters the imaging field of view of the microscope objective lens 5, and set the fringe frequency, phase shift step length and phase shift step number of the spatial light modulator 2;

S3, start the light source 1, the spatial light modulator 2 and the CCD 13, pause at each axial position and collect the dark field microscopic images of the set phase shift fringes;

Specifically: the light emitted by the light source 1 is incident on the spatial light modulator 2 at a specific angle and is modulated into structured light by the spatial light modulator 2, and then passes through the first lens 3, the beam splitter 4 and the microscope objective lens 5 and is then miniature projected to the sample 6 It is reflected on the sample 6 to form zero-order light 14 and first-order light 15. The zero-order light 14 passes through the microscope objective lens 5, the second lens 9 and the third lens 10 in turn to reach the filter 11, and the first-order light 15 sequentially After the microscope objective lens 5 , the second lens 9 , the third lens 10 and the fourth lens 12 reach the CCD13 for imaging; if there is a defect in the sample 6 , the scattered light from the defect and the primary light 15 reach the CCD13 for imaging.

S4. Use the phase shift modulation degree analysis method to calculate the modulation degree of each axial position to obtain the axial modulation degree curve. The calculation formula is as follows:

In the formula, N represents the number of phase shift steps, and I _i represents the light intensity value of a certain point during the i-th phase shift;

S5. Perform three-dimensional reconstruction of the defect 7 on the sample 6 according to the axial modulation curve:

Extract the axial modulation curve corresponding to the same position of the defect, and use the center of gravity method or the fitting method to calculate the position of the optical axis direction corresponding to the peak of the curve, which is the focal plane of the defect.

This embodiment uses the high-frequency structured light field illumination defect, separates the in-focus light and the defocused light by means of frequency-domain modulation of the structured light, and uses an external frequency-domain filter to remove the illumination background light, which can exclude the illumination background light and the defocused light. The interference of light interference improves the imaging sensitivity.

Example 2:

As shown in FIG. 1 , this embodiment is based on Embodiment 1, and further includes a displacement mechanism 8 for installing the sample 6 , the displacement mechanism 8 is used for moving the sample 6 in the direction of the optical axis, and the light source 1 is an LED light source.

The displacement mechanism 8 in this embodiment is a commonly used moving device in the prior art, such as but not limited to using a transport line, a transmission device, etc., as long as it can drive the sample 6 to move in the direction of the optical axis, which is not used in this embodiment. Describe its structure.

The specific embodiments described above further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A dark field microscopic defect three-dimensional measuring device for structured light modulation is characterized by comprising a light source (1), a spatial light modulator (2), a first lens (3), a spectroscope (4), a microscope objective (5), a second lens (9), a third lens (10), a filter (11), a fourth lens (12) and a CCD (13);

the spatial light modulator (2) is used for receiving light emitted by the light source (1) and modulating the light into structured light;

the structured light modulated by the spatial light modulator (2) is subjected to micro projection on a sample (6) through a first lens (3), a spectroscope (4) and a microscope objective (5) in sequence and is reflected on the sample (6) to form zero-order light (14) and first-order light (15);

the zero-order light (14) sequentially passes through the microscope objective (5), the second lens (9) and the third lens (10) to reach the filter (11);

the primary light (15) sequentially passes through the microscope objective (5), the second lens (9), the third lens (10) and the fourth lens (12) to reach the CCD (13) for imaging.

2. The three-dimensional measurement device for the structured light modulated dark-field microscopic defect according to claim 1, characterized in that the filter (11) is disposed between the third lens (10) and the fourth lens (12).

3. The three-dimensional measurement device for the structured light modulated dark-field microscopic defect according to claim 2, characterized in that the back focal plane of the third lens (10) and the front focal plane of the fourth lens (12) are coincident to form a spectral plane, and the filter (11) is located on the spectral plane.

4. The three-dimensional measurement device for the structured light modulated dark-field microscopic defect according to claim 1, characterized in that the size of the filter (11) is smaller than the aperture size of the CCD (13).

5. The three-dimensional measurement device for the structured light modulated dark-field microscopic defect of claim 1, further comprising a displacement mechanism (8) for mounting the sample (6), wherein the displacement mechanism (8) is used for moving the sample (6) in the optical axis direction.

6. The three-dimensional measurement device for the structured light modulated dark-field microscopic defect according to claim 1, characterized in that the specimen (6) is mounted near the focal plane of the microscope objective (5).

7. The three-dimensional measurement device for the structured light modulated dark-field microscopic defects according to any one of claims 1 to 6, wherein the sample (6) is a transparent material.

8. The three-dimensional measurement device for the structured light modulated dark-field microscopic defects according to any one of claims 1 to 6, wherein the light source (1) is an LED light source.

9. The measurement method of the structured light modulated dark field microscopic defect three-dimensional measurement device based on any one of claims 1 to 8 is characterized by comprising the following steps:

s1, installing the sample (6) to be measured near the focal plane of the microscope objective (5);

s2, adjusting the sample (6), enabling the area to be measured of the sample (6) to enter the imaging field of the microscope objective (5), and setting the fringe frequency, the phase shift step length and the phase shift step number of the spatial light modulator (2);

s3, starting a light source (1), a spatial light modulator (2) and a CCD (13), pausing at each axial position and acquiring a dark field microscopic image with set phase shift stripes.

10. The measurement method of the structured light modulated dark field microscopic defect three-dimensional measurement device according to claim 9, further comprising:

s4, calculating the modulation degree of each axial position by using a phase shift modulation degree analysis method to obtain an axial modulation degree curve, wherein the calculation formula is as follows:

in which N represents the number of phase shift steps, I_iRepresenting the light intensity value at a point at the ith phase shift;

and S5, performing three-dimensional reconstruction on the defect (7) on the sample (6) according to the axial modulation degree curve.

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