CN113418469B - Spectrum confocal scanning common-path digital holographic measurement system and measurement method - Google Patents
Spectrum confocal scanning common-path digital holographic measurement system and measurement method Download PDFInfo
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- CN113418469B CN113418469B CN202110772709.3A CN202110772709A CN113418469B CN 113418469 B CN113418469 B CN 113418469B CN 202110772709 A CN202110772709 A CN 202110772709A CN 113418469 B CN113418469 B CN 113418469B
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Abstract
The invention discloses a spectral confocal scanning common-path digital holographic measurement system and a measurement method, which overcome the defect that the prior art is only suitable for measuring the phase change formed by the reflection or transmission of the surface of an object to be measured and cannot realize the high-precision, non-contact and synchronous three-dimensional shape measurement of the micro-shape of each layered interface of a transparent object. The device comprises a multispectral light source, a microscope objective, a lens, a first spectroscope, a focusing dispersion lens and an object to be measured, wherein the multispectral light source, the microscope objective, the lens, the first spectroscope, the focusing dispersion lens and the object to be measured are sequentially arranged, the object to be measured is positioned in a focusing range of a focusing dispersion element, a second spectroscope is arranged behind the first spectroscope, an achromatic microscope objective and a fiber optic spectrometer are sequentially arranged in front of the second spectroscope, a bifocal diffractive element is arranged behind the second spectroscope, an image sensor is arranged behind the bifocal diffractive element, the image sensor is arranged in a small focal distance behind the bifocal diffractive element, and the fiber optic spectrometer and the image sensor are respectively connected with a computer.
Description
The technical field is as follows:
the invention belongs to the technical field of digital holographic measurement, and relates to a spectral confocal scanning common-path digital holographic measurement system and a measurement method.
The background art comprises the following steps:
the digital holographic measurement technology achieves the purpose of rapidly recovering the three-dimensional shape of an object to be measured by recording the amplitude and the phase of object light, has the advantages of non-contact, full field, high resolution, rapid reconstruction and the like, and can provide a more effective technical tool for the research in the fields of micro-optical elements, micro-electro-mechanical systems, biomedicine and the like. However, the current digital holography technology is only suitable for measuring the phase change formed by the reflection or transmission of the surface of the object to be measured, is not suitable for reconstructing the three-dimensional structure of the object to be measured, and cannot realize the rapid measurement of the three-dimensional structure aiming at the upper surface, the lower surface and the inner layered microstructure of the object to be measured.
The spectrum confocal scanning technology only detects information on a focal plane by using a precise pinhole filtering technology, so that stray light of a non-focal plane is inhibited to the maximum extent, and the imaging resolution and the signal-to-noise ratio are high; and can carry out nondestructive optical tomography along the axis direction, thereby determining the position information of each layer of the object to be measured.
The invention content is as follows:
the invention aims to provide a spectral confocal scanning common-path digital holographic measurement system and a measurement method, which solve the problems that the prior art is only suitable for phase change measurement formed by reflection or transmission on the surface of an object to be measured and cannot realize high-precision, non-contact and synchronous three-dimensional shape measurement of the micro-shape of each layered interface of a transparent object, and realize high-precision, non-contact and synchronous three-dimensional shape measurement of the micro-shape of each layered interface of the transparent object.
In order to achieve the purpose, the invention adopts the technical scheme that:
the utility model provides a confocal scanning common path digital holographic measurement system of spectrum which characterized in that: the measurement system comprises a measurement system body, wherein the measurement system body comprises a multispectral light source, a microscope objective, a lens, a first spectroscope, a focusing dispersion lens and an object to be measured, the multispectral light source, the microscope objective, the lens, the first spectroscope, the focusing dispersion lens and the object to be measured are sequentially arranged, the object to be measured is located in a focusing range of the focusing dispersion element, a second spectroscope is arranged behind the first spectroscope, an achromatic microscope objective and a fiber optic spectrometer are sequentially arranged in front of the second spectroscope, a bifocal diffractive element is arranged behind the second spectroscope, an image sensor is arranged behind the bifocal diffractive element and is arranged within a small focal distance behind the bifocal diffractive element, and the fiber optic spectrometer and the image sensor are respectively connected with a computer.
Light λ with a minimum wavelength in the focusing range of the focusing dispersion lens min And light of maximum wavelength lambda max Of the focal point.
A measuring method of a spectrum confocal scanning common-path digital holographic measuring system is characterized in that: the method comprises the following steps:
the method comprises the following steps: after the multispectral light source is shaped by the light beams of the microscope objective and the lens, parallel light for working is formed; the parallel light is dispersed after passing through a focusing dispersion lens, so that light rays with different wavelengths are focused at different positions on an optical axis; when the object to be tested is placed in the focusing range, only the light focused on the layered interface of the object to be tested can return to the focusing dispersion lens, at the moment, the object to be tested has several layered interfaces, and then the light with several wavelengths returns to the focusing dispersion lens to form a test light beam;
step two: the test light beam is divided into two beams after passing through the first spectroscope and the second spectroscope, wherein the light reflected by the second spectroscope is coupled to the fiber optic spectrometer through the achromatic microscope objective, and the wavelength existing in the reflected light is determined after the spectral analysis of the fiber optic spectrometer, so that the position of the layered interface of the object to be tested is determined; after the light transmitted by the spectroscope II is focused by the bifocal diffractive element, the transmitted light is divided into two convergent light beam focuses in front of and behind the image sensor, and the convergent light beams form a digital holographic interference pattern on the target surface of the image sensor;
step three: preprocessing the obtained digital holographic interference image; firstly, fourier transform is carried out to obtain a spectrogram, different carriers are introduced into different wavelengths, so that the crosstalk of the frequency spectrum information of the different wavelengths in a frequency domain is small; then, extracting +1 level frequency spectrums with different wavelengths by using a filter window; finally, carrying out inverse Fourier transform on the complex amplitude distribution to obtain complex amplitude distribution of the object light wave;
step four: and respectively obtaining reconstruction phases with different wavelengths by using a digital holographic angular spectrum phase reconstruction algorithm, thereby determining the three-dimensional shapes of different layered interfaces of the object to be measured.
Compared with the prior art, the invention has the following advantages and effects:
1. the measuring method can simultaneously obtain the three-dimensional shapes of different layered interfaces of the object to be measured, thereby greatly improving the measuring efficiency;
2. the measuring method can measure the three-dimensional shapes of different layered interfaces and can determine the position of each layered interface, thereby being beneficial to better analyzing the characteristic parameters of the object to be measured;
3. the measuring device disclosed by the invention is designed to share a light path, is simple in structure, is convenient and fast to operate, and is easy to eliminate the influence of system noise.
Description of the drawings:
FIG. 1 is a schematic structural diagram of a spectral confocal scanning common-path digital holographic measurement system according to the present invention;
FIG. 2 is a schematic diagram of a focusing and dispersing element according to the present invention;
FIG. 3 is a diagram of the holographic interference pattern formed by the reference light and the test light in the present invention, wherein: (a) Schematic representation of interference recording principle, (b) schematic representation of target surface of image sensor;
FIG. 4 is a schematic diagram of the spectrum extraction according to the present invention;
FIG. 5 is a flow chart of hologram preprocessing in the present invention;
FIG. 6 is a flowchart of the digital holographic angular spectrum reconstruction algorithm of the present invention.
In the figure, 1-a multispectral light source, 2-a microscope objective, a 3-lens, a 4-a spectroscope I, a 5-a focusing dispersion lens, 6-an object to be measured, a 7-a spectroscope II, an 8-an achromatic microscope objective, a 9-a fiber optic spectrometer, a 10-bifocal diffractive element, an 11-an image sensor and a 12-a computer.
The specific implementation mode is as follows:
the present invention will be described in detail with reference to specific embodiments. These examples are intended to illustrate the invention and are not intended to limit the scope of the invention. The implementation conditions used in the examples can be further adjusted according to the specific experimental environment, and the implementation conditions not mentioned are generally the conditions in routine experiments.
The invention provides a spectrum confocal scanning common-path digital holographic measuring device and method based on accurate positioning of spectrum confocal so as to realize synchronous three-dimensional detection of the microstructure of each layered interface of an object to be detected.
Referring to fig. 1, the invention comprises a measuring system body, wherein the measuring system body comprises a multispectral light source 1, a microobjective 2, a lens 3, a spectroscope I4, a focusing dispersion lens 5 and an object 6 to be measured which are sequentially arranged, the object 6 to be measured is positioned in the focusing range of the focusing dispersion element 5, a spectroscope II 7 is arranged behind the spectroscope I4, an achromatic microobjective 8 and a fiber optic spectrometer 9 are sequentially arranged in front of the spectroscope II 7, a bifocal diffractive element 10 is arranged behind the spectroscope II 7, an image sensor 11 is arranged behind the bifocal diffractive element 10, the image sensor 11 is arranged within a small focal distance behind the bifocal diffractive element 10, and the fiber optic spectrometer 9 and the image sensor 11 are respectively connected with a computer 12.
The multispectral light source refers to a continuous spectrum light source or a multi-wavelength discontinuous spectrum light source. The multispectral light source 1 irradiates the microobjective 2 and the lens 3 to carry out beam shaping to form a plane beam. The plane beam passes through the beam splitter I4 and then is subjected to chromatic dispersion by the focusing chromatic dispersion element 5, so that the light rays with different wavelengths are focused at different positions on the optical axis. The object 6 to be measured is positioned in the focusing range of the focusing dispersion element 5, focusing reflection is generated at different layered interfaces of the object 6 to be measured, a test light beam is formed, and the test light beam is divided into transmission light and reflection light after passing through the spectroscope I4 and the spectroscope II 7. The reflected light is received by the fiber spectrometer 9 after passing through the achromatic microobjective 8, and the wavelength of the reflected light is determined after spectral analysis, so that the positions of different layered interfaces of the object 6 to be measured are determined. The transmitted light passes through the bifocal diffractive element 10 carrying the carrier frequency to form two convergent beams with different focal lengths, wherein the solid line in the figure represents a small focal length f1 test beam, and the dotted line represents a large focal length f2 reference beam; for the laser with different wavelengths, the two converging light focuses passing through the bifocal diffractive element 10 are the same, so that the test light beam meets the reference light beam to form an interference hologram. The image sensor 11 is arranged in the back f1 of the bifocal diffractive element 10, the image sensor 11 collects a digital holographic interference pattern and transmits the digital holographic interference pattern to the computer 12, and phase data reconstructed at different wavelengths is obtained through a digital holographic angular spectrum phase reconstruction algorithm, so that the three-dimensional morphology of different layered interfaces of the object to be measured is determined.
Fig. 2 is a schematic structural diagram of the focusing and dispersing element 5 according to the present invention. The light with different wavelengths is focused on different positions of points on the axis after being focused by the focusing and dispersing element 5, wherein lambda 1 Focused on the upper surface of the object 6 to be measured, λ 2 Focusing on a layered interface, lambda, at a certain depth of the object 6 to be measured 3 Focused on the lower surface of the object to be measured 6, lambda min And λ max Is the focal range of the focus dispersive element 5.
FIG. 3 shows the holographic interference pattern formed by the reference light and the test light in the present invention. (a) For a schematic diagram of the interference recording principle, the light beam is focused by f1 to form a test light beam, and a reference light beam is formed by f2, and an interference hologram is obtained by the image sensor 11. (b) In order to schematically illustrate the target surface of the image sensor 11, the overlapping area of f1 and f2 interferes, i.e. the interference pattern acquired by the image sensor 11.
The invention also comprises a measuring method based on the spectrum confocal scanning common-path digital holographic measuring system, which comprises the following steps:
the method comprises the following steps: the multispectral light source 1 forms parallel light for work after the light beam of the microscope objective lens 2 and the lens 3 is shaped. The parallel light is dispersed by the focusing dispersion lens 5, so that the light rays with different wavelengths are focused at different positions on the optical axis. When the object 6 to be tested is placed in the focusing range, only the light focused on the layered interface of the object 6 to be tested can return to the focusing dispersion lens 5, at this time, the object 6 to be tested has several layered interfaces, and then the light with several wavelengths returns to the focusing dispersion lens 5 to form a test beam.
Step two: the test light beam is divided into two beams after passing through the first spectroscope 4 and the second spectroscope 7, wherein the light reflected by the second spectroscope 7 is coupled to the fiber optic spectrometer 9 through the achromatic microscope objective 8, and the wavelength existing in the reflected light can be determined after the spectral analysis of the fiber optic spectrometer 9, so that the position of the layered interface of the object to be tested is determined. After the light transmitted by the second beam splitter 7 is focused by the bifocal diffractive element 10, the transmitted light is divided into two converging beam focuses before and after the image sensor 11, and the converging beams form a digital holographic interference pattern on the target surface of the image sensor 11.
Step three: and preprocessing the obtained digital holographic interference pattern. Firstly, fourier transform is carried out to obtain a spectrogram, different carriers are introduced into different wavelengths, so that the crosstalk of the frequency spectrum information of the different wavelengths in a frequency domain is small. Then, a filter window can be used for extracting +1 level frequency spectrums with different wavelengths; and finally, carrying out inverse Fourier transform on the complex amplitude distribution to obtain the complex amplitude distribution of the object light wave.
Referring to fig. 5, fig. 5 is a flow chart of hologram preprocessing in the present invention. The hologram preprocessing process comprises the following steps: fourier transform is carried out on the hologram to obtain a spectrogram, a filtering window is arranged to extract +1 level frequency spectrum, the frequency spectrum is subjected to shift, and inverse Fourier transform is carried out to obtain complex amplitude distribution of object light waves.
Step four: and respectively obtaining reconstruction phases with different wavelengths by using a digital holographic angular spectrum phase reconstruction algorithm, thereby determining the three-dimensional shapes of different layered interfaces of the object to be measured.
Referring to fig. 6, fig. 6 is a flowchart of a digital holographic angular spectrum reconstruction algorithm program in the present invention. The program flow of the digital holographic angular spectrum reconstruction algorithm is as follows: and transforming the reference light subjected to Fourier transform and subjected to point multiplication numerical simulation on the object light wave complex amplitude distribution obtained by preprocessing into a frequency domain to obtain a frequency spectrum of the holographic surface, then performing point multiplication on a frequency domain transfer function, propagating in a frequency domain form to obtain a frequency spectrum of a reproduced image, and performing inverse Fourier transform on the frequency spectrum of the reproduced image to obtain reproduced light field complex amplitude distribution, namely the reproduced image. The light wave field is not approximate in the whole propagation process, and errors can be effectively reduced.
Fig. 4 is a schematic diagram of spectrum extraction in digital holographic reproduction. Setting rectangular filtering window to extract lambda 1 ，λ 2 ，λ 3 And reproducing the corresponding + 1-level spectrogram to obtain the three-dimensional phase reconstruction of the upper surface, the layered interface with a certain depth and the lower surface of the measured object 6 shown in the figure 2.
The above embodiments are merely illustrative of the principles and effects of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept of the present invention, and the scope of the present invention is defined by the appended claims.
Claims (3)
1. The utility model provides a confocal scanning common path digital holographic measurement system of spectrum which characterized in that: the device comprises a measuring system body, wherein the measuring system body comprises a multispectral light source (1), a microscope objective (2), a lens (3), a first spectroscope (4), a focusing dispersion lens (5) and an object to be measured (6) which are sequentially arranged, the object to be measured (6) is positioned in a focusing range of the focusing dispersion lens (5), a second spectroscope (7) is arranged behind the first spectroscope (4), an achromatic microscope objective (8) and a fiber optic spectrometer (9) are sequentially arranged in front of the second spectroscope (7), a bifocal diffractive element (10) is arranged behind the second spectroscope (7), an image sensor (11) is arranged behind the bifocal diffractive element (10), the image sensor (11) is arranged within a small focal length behind the bifocal diffractive element (10), and the fiber optic spectrometer (9) and the image sensor (11) are respectively connected with a computer (12).
2. The spectral confocal scanning common-path digital holographic measurement system according to claim 1, wherein: light lambda of the focusing range of the focusing dispersion lens (5) is the minimum wavelength min And light λ of maximum wavelength max Of the focal point.
3. A measurement method using the spectral confocal scanning common-path digital holographic measurement system of claim 1, wherein: the method comprises the following steps:
the method comprises the following steps: after the multispectral light source (1) is shaped by light beams of the microscope objective (2) and the lens (3), parallel light for working is formed; the parallel light is dispersed after passing through a focusing dispersion lens, so that light rays with different wavelengths are focused at different positions on an optical axis; when the object (6) to be tested is placed in the focusing range, only the light focused on the layered interface of the object (6) to be tested can return to the focusing dispersion lens (5), at the moment, the object (6) to be tested has several layered interfaces, and the light with several wavelengths returns to the focusing dispersion lens (5) to form a test light beam;
step two: the test light beam is divided into two beams after passing through the first spectroscope (4) and the second spectroscope (7), wherein the light reflected by the second spectroscope (7) is coupled to the fiber optic spectrometer (9) through the achromatic microobjective (8), and the wavelength existing in the reflected light is determined after the spectral analysis of the fiber optic spectrometer (9), so that the position of the layered interface of the object to be tested (6) is determined; after the light transmitted by the spectroscope II (7) is focused by the bifocal diffractive element (10), the transmitted light is divided into two convergent light beam focuses in front of and behind the image sensor (11), and the convergent light beams form a digital holographic interference pattern on the target surface of the image sensor (11);
step three: preprocessing the obtained digital holographic interference pattern; firstly, fourier transform is carried out to obtain a spectrogram, different carriers are introduced into different wavelengths, so that the crosstalk of the frequency spectrum information of the different wavelengths in a frequency domain is small; then, extracting +1 level frequency spectrums with different wavelengths by using a filter window; finally, carrying out inverse Fourier transform on the complex amplitude distribution to obtain complex amplitude distribution of the object light wave;
step four: and respectively obtaining reconstruction phases with different wavelengths by using a digital holographic angular spectrum phase reconstruction algorithm, thereby determining the three-dimensional morphology of different layered interfaces of the object to be measured.
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