CN111579441A - Digital holographic particle measuring device and method based on diaphragm spatial modulation - Google Patents
Digital holographic particle measuring device and method based on diaphragm spatial modulation Download PDFInfo
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- CN111579441A CN111579441A CN202010505333.5A CN202010505333A CN111579441A CN 111579441 A CN111579441 A CN 111579441A CN 202010505333 A CN202010505333 A CN 202010505333A CN 111579441 A CN111579441 A CN 111579441A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
- G01N15/0205—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging
- G01N15/0227—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging using imaging, e.g. a projected image of suspension; using holography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/021—Interferometers using holographic techniques
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
- G01N15/0205—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging
- G01N2015/0233—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging using holography
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/02—Investigating particle size or size distribution
- G01N15/0205—Investigating particle size or size distribution by optical means, e.g. by light scattering, diffraction, holography or imaging
- G01N2015/0238—Single particle scatter
Abstract
The invention discloses a digital holographic particle measuring device based on diaphragm spatial modulation, which comprises the following components: a laser light source; the spatial filtering beam expanding unit comprises a spatial filter and a beam expander; the measuring area is distributed with particles to be measured; the diaphragm modulation unit comprises a first lens, a diaphragm and a second lens, wherein the first lens, the diaphragm and the second lens are sequentially arranged by object light; an image recording unit including a CCD or CMOS digital camera; a data processing unit. The invention also discloses a digital holographic particle measuring method based on diaphragm space modulation, which comprises the following steps: a laser light source and a spatial filtering beam expanding unit are utilized to generate a particle field of collimated light beams irradiating a measuring area; performing spatial modulation on the particulate light by using a diaphragm modulation unit; recording a particle holographic interference fringe image by using a CCD or CMOS digital camera; and reconstructing and analyzing the recorded particle holographic interference fringe image to obtain particle information. The device and the method provided by the invention can realize rapid monitoring of the particle size of the particles and reduce mutual overlapping and interference among the particles.
Description
Technical Field
The invention relates to the field of measuring a particle field by an advanced optical method, in particular to a digital full-particle measuring device and method based on diaphragm spatial modulation.
Background
The particles have an important position in the industries of energy, materials, chemical industry, environment, aerospace and the like. Solid particles such as pulverized coal particles in a coal-fired power plant are transported and combusted, fluidized bed particles are circulated and the like, liquid particles such as internal combustion engine spray combustion, liquid rocket engine atomization mixed combustion propulsion and the like, and bubble particles such as boiling heat transfer and mass transfer, turbine blade cavitation and the like. The method has great scientific significance and wide industrial application prospect for the research of the particles, and has very important significance for the accurate measurement of key parameters such as the positions, the particle sizes and the like of the particles and the high-efficiency safe production.
Particle testing techniques can be largely classified into conventional contact mechanical methods, non-contact electrical and acoustic methods, and advanced optical methods. From the development trend, the process of obtaining non-contact, on-line, multi-parameter and multi-dimensional transient measurement from contact time, off-line, single-parameter and single-point measurement is experienced. In the conventional particle measurement, such as the instantaneous sampling method for measuring particle concentration, the sieving method for measuring particle size, etc., the measurement result is easily influenced by the operation technique of an operator, the sampling method, time, etc., and the method itself has the limitation of off-line application, and has been gradually replaced at present.
The electrical method mainly includes an electrostatic method and a capacitance method, which are easily interfered by external environments such as a complex electromagnetic field and the like, and the application difficulty is high. The acoustic method is mainly an ultrasonic method, and a typical application is an ultrasonic attenuation particle analyzer. The precise measurement of ultrasonic waves is a difficult problem, errors are difficult to control, and the ultrasonic wave is easily influenced by factors such as temperature and the like. In the above methods, the particle group is measured as a whole, and the obtained result is the average particle size, and the particle size and position information of a single particle cannot be accurately obtained.
In the optical method, the laser particle analyzer has high measurement speed and accurate result, and is widely applied. However, the laser particle analyzer is expensive, has high requirements on the environment, is easy to pollute optical elements of the instrument, and has poor industrial field adaptability due to complex installation.
The digital holography technology is a three-dimensional measurement technology, and can conveniently record and store the hologram by adopting digital recording and digital reconstruction. Unlike the electrical and acoustic methods described above, the digital holography measures the particle field by measuring each particle in the particle field, and obtains the geometric information and the position information of each particle. However, laser beams and area-array cameras are widely used for measuring the particle size by using a digital holographic technology at present, so that recorded holograms contain three-dimensional data, the data volume is large, the processing speed is low during reconstruction, the difficulty is large, and the measurement instantaneity is poor. In the case of a high-concentration particle field, dense particles exist on the holographic optical path, and the measured particle holograms have the problem of mutual overlapping and interference among the particles, which brings great inconvenience to data processing processes such as hologram reconstruction and particle identification, and results in low measurement precision of the high-concentration particle field.
Disclosure of Invention
The invention aims to solve the problem of providing a digital holographic particle measuring device and a measuring method based on diaphragm space modulation aiming at the defects of the current particle holographic measuring method; the particle size can be rapidly monitored by reducing the data size through reducing the dimension of the collected and reconstructed data; the object light in the required direction is modulated through the diaphragm space, and the mutual overlapping and interference among particles can be reduced.
A digital holographic particle measurement apparatus based on spatial modulation of an aperture, the apparatus comprising:
a laser light source for generating a laser beam of adjustable intensity;
the spatial filtering beam expanding unit comprises a spatial filter and a beam expander and is used for expanding and collimating the laser beam to form a collimated beam;
the device comprises a measuring area, a light source and a control unit, wherein particles to be measured are distributed in the measuring area, the collimated light beam irradiates the measuring particles, the particles are scattered to form object light, and unscattered straight light is used as reference light;
the diaphragm modulation unit comprises a first lens, a diaphragm and a second lens which are sequentially arranged for object light to spatially modulate the object light so that part of the object light and the reference light pass through;
the image recording unit comprises a CCD or CMOS digital camera and is used for recording a holographic interference fringe image formed by the interference of object light and reference light of the particles;
and the data processing unit is used for acquiring and reconstructing the particle hologram recorded by the image recording unit to obtain the information of the detected particles, wherein the information comprises the particle size and the three-dimensional position.
The apparatus provided by the invention further comprises an optical bench system for adjusting the light path and the laser incidence position: height, level, angle, etc. The diaphragm modulation unit is used for modulating and suppressing partial holographic interference fringes of the particles. The hologram was reconstructed using hologram reconstruction software.
The laser light source is a monochromatic solid laser, and the laser wavelength range is 350nm to 700 nm.
The diaphragm modulation unit is located between the measuring area and the image recording unit, the back focal plane of the first convex lens coincides with the front focal plane of the second convex lens, and the diaphragm is placed on the coincident focal plane of the first convex lens and the second convex lens. The first convex lens and the second convex lens are arranged on the optical sliding guide rail; preferably the aperture is a horizontal line aperture. The reference light is approximate to plane light and is not influenced by the diaphragm; the object light is circumferential scattered light, only the object light in the horizontal direction and the object light close to the horizontal direction can pass through the diaphragm, and the scattered object light in other directions can be filtered by adjusting the size of the diaphragm.
The first convex lens and the second convex lens have the same diameter and the same focal length, and the diaphragm modulation unit has no zooming effect on the object image; or the diameters of the first convex lens and the second convex lens are different, the focal lengths are different, and the diaphragm modulation unit has a zooming effect on the object image; the diaphragm slit width is adjustable, and the slit width is 5-200 mu m.
The diaphragm modulation unit has the following relationship with the image recording unit and the particles: the distance between the plane of the particles and the recording plane (conjugate plane) is denoted as recording distance z, and the distance d between the recording plane and the first lens is denoted as0The distance from the second lens to the CCD or CMOS is d, f1、f2The focal lengths of the first lens and the second lens are respectively, the distance from the plane of the particles to the first lens is x, and the expression of the recording distance z can be obtained by a lens formula or matrix optical derivation: z ═ f (x, d)0,d,f1,f2). If the first lens and the second lens in the diaphragm modulation unit are the same, i.e. f1＝f2F, then z is x-d0＝z-(2f-d)。
The laser light source, the spatial filtering and beam expanding unit, the measuring area, the diaphragm modulating unit and the image recording unit are positioned on the same axis to form a coaxial holographic system, and the object light is particle horizontal scattered light.
The laser light source, the spatial filtering beam expanding unit and the measuring area are positioned on the same axis, the diaphragm modulating unit and the image recording unit are perpendicular to the measuring area to form an off-axis holographic system, and the object light is 90-degree scattered light of particles; a spectroscope is arranged between the spatial filtering beam expanding unit and the measuring area, and collimated light beams are incident between the diaphragm modulating unit and the image recording unit as reference light after being split.
And for an on-axis holographic system or an off-axis holographic system, an optical filter is arranged between the diaphragm modulation unit and the image recording unit. An optical filter is added in front of the digital camera to reduce the background light power received at the detector, thereby reducing ambient light scatter and background radiation induced noise. More preferably, the bandwidth of the filter is as narrow as possible under the condition of ensuring the laser to transmit, so that the detector is in a good working state.
The detected light intensity of CCD or CMOS is fed into computer. The holographic data processing unit consists of a computer with a digital holographic reconstruction program, and the program algorithm comprises a positioning part, an identification part and a particle size calculation part
The invention also provides a digital holographic particle measuring method based on the diaphragm space modulation, and the digital holographic particle measuring device using the diaphragm space modulation comprises the following steps:
(1) generating a collimated light beam by using a laser light source and a spatial filtering beam expanding unit, and enabling the collimated light beam to irradiate a particle field of a measuring area;
(2) the aperture modulation unit is adopted to perform spatial modulation on the particle light, so that part of the object light passes through;
(3) recording a particle holographic interference fringe image by using a CCD or CMOS digital camera;
(4) and reconstructing and analyzing the recorded holographic interference fringe image of the particle particles to obtain particle information including particle size and position information.
In the step (1), the process of generating the collimated light beam is as follows: laser beams generated by the laser light source sequentially pass through the spatial filter and the beam expander in the spatial filtering beam expanding unit to form collimated cylindrical light beams, when the particle field is irradiated, part of light is scattered through particles to form object light, and the other part of laser without the particles is used as reference light.
The process of spatially modulating the particle light by the diaphragm modulation unit in the step (2) is as follows: the back focal plane of the first convex lens and the front focal plane of the second convex lens are adjusted to coincide, the diaphragm is placed on the coincidence plane, the slit width of the diaphragm is adjusted, and when collimated light beams sequentially pass through the first convex lens, the diaphragm and the second convex lens, scattered object light in the vertical direction of the slit of the diaphragm can be filtered, and spatial modulation of the object light is achieved. By controlling the aperture width of the lens focal plane, scattered object light in other directions can be filtered, and the object light in the required direction can be kept to pass through.
The forming process of the particle holographic fringes in the step (3) is as follows: one part of light is scattered by the particles to form object light O, the other part of unscattered straight transmission light is used as reference light R, and the modulated object light and the reference light are interfered again to form holographic fringes:
IH＝|O+R|2＝IO+IR+OR*+O*R (1)
the reconstruction analysis of the holographic fringes in the step (4) comprises a particle positioning process, a particle identification process and a particle size calculation process. The reconstruction can adopt an angular spectrum reconstruction algorithm, and the calculation formula of the light intensity of the reconstructed image is as follows:
where λ is the wavelength, fxIs the spatial frequency, F-1Is an inverse fourier transform. Besides the angular spectrum reconstruction algorithm, algorithms such as Fresnel integral reconstruction, convolution reconstruction, wavelet reconstruction and the like can be adopted.
Aiming at the defects of various existing particle measuring methods, the invention provides a digital holographic particle measuring method and a digital holographic particle measuring device based on diaphragm space modulation.
The invention has the beneficial effects that:
the digital holographic particle measuring device and method based on diaphragm space modulation can reduce the recorded particle holographic information data from two-dimensional holographic fringes to one-dimensional holographic fringes, can remarkably reduce the calculation amount of holographic digital reconstruction and information processing, and is beneficial to realizing real-time reconstruction and processing of particle holograms; the invention modulates the particle scattered object light through the diaphragm, realizes the recording of the particle holographic partial interference fringes, reduces the recording of redundant information, greatly reduces the mutual superposition and interference of different particle holographic interference fringes, is beneficial to realizing the holographic three-dimensional measurement of a high-concentration particle field, and provides powerful technical means and data support for applying the digital holographic technology to the high-concentration particle field.
Drawings
FIG. 1 is a schematic diagram of the overall structure of the coaxial holographic system;
FIG. 2 is a schematic diagram of the overall structure of the off-axis holographic optical system.
Detailed Description
In order to make the technical means, creation features, working flow field and use method of the present invention easy to understand, the following will further explain the specific embodiments of the present invention with reference to the drawings.
As shown in fig. 1, the digital holographic particle measuring device based on aperture spatial modulation provided by the present invention includes a laser light source 1, a spatial filter 2, a beam expander 3, a measuring region 4, a convex lens 5, an aperture 6, a convex lens 7, an optical filter 8, and a digital camera 9. The elements are arranged on the same axis according to the arrangement sequence, are in a coaxial holographic form, and are fixed and position-adjusted by using an optical guide rail.
As shown in fig. 2, the diaphragm modulation unit and the image recording unit are arranged perpendicular to the laser axis, a part of the reference light is led out by the spectroscope, a certain deflection angle exists between the reference light and the object light to form an off-axis holographic system, the spectroscope 11, the light splitting environment 12 and the reflector 13 together form a reference light path, and the object light is 90-degree scattered light of particles.
The laser, preferably a 532nm semiconductor continuous laser, has adjustable light intensity.
As shown in fig. 1, the back focal plane of the convex lens 5 coincides with the front focal plane of the convex lens 7, and a slit diaphragm 6 is installed on the coincident focal plane to perform spatial modulation on the object light, and the object light and the digital camera form a fourier optical imaging system. The diaphragm is used for enabling only object light with the incident direction parallel to and close to the main optical axis to pass through, so that the object light in other directions is filtered, and spatial modulation of particle scattering light (object light) is achieved.
The lens diameter is 100mm, and the focal length f is 150 mm.
The diaphragm is an adjustable slit diaphragm, and the slit width is 5-200 mu m.
The image element size of the area array CCD or CMOS digital camera is 7.4 μm, and the number of pixels is 2048 × 2048.
In order to improve the signal-to-noise ratio and reduce the influence of external stray light on the quality of the hologram, a neutral density filter 8 is installed in front of the digital camera. And a height adjusting rod is arranged at the lower part of the digital camera shell and is used for modulating the coincidence of the receiving part of the detector and the laser.
The digital holographic particle measurement method based on the diaphragm space modulation comprises the following implementation steps:
step 1: and starting a laser light source to generate a laser beam.
Step 2: and adjusting the spatial filter and the beam expander to proper positions, and filtering and expanding the laser to form a collimated cylindrical laser beam.
And step 3: the elements of the diaphragm space modulation unit are adjusted to proper positions, so that the collimated laser beams can pass through without being influenced by the diaphragm.
And 4, step 4: and focusing the digital camera, and adjusting the position to enable the camera chip to coincide with the laser. And shooting a background hologram after the adjustment is finished.
And 5: the particles 10 to be measured are introduced into the measurement area, the width of the slit of the diaphragm is adjusted, only object light which is parallel to the optical axis and close to parallel at a certain angle (the angle is less than 0.04 DEG according to the optimal focal length of the lens and the slit width) passes through the diaphragm, and after the adjustment is finished, the digital camera is controlled to shoot the holographic fringes of the particles. While transmitting the holographic fringe data to a computer.
Step 6: and analyzing by utilizing a hologram reconstruction program to obtain the particle size and position information of the particles. The treatment process comprises the following steps: removing the background of the holographic fringe image; carrying out particle positioning and particle identification to obtain particle position information; and calculating to obtain particle size information.
In summary, the digital holographic particle measurement method and device based on aperture spatial modulation of the invention realize the recording of the holographic partial interference fringes of the particles by modulating the scattered object light of the particles through the aperture, so as to reduce the recording of redundant information, greatly reduce the mutual superposition and interference of the holographic interference fringes of different particles, and facilitate the realization of the holographic three-dimensional measurement of a high-concentration particle field. Meanwhile, the invention can reduce the recorded particle holographic information data from two-dimensional holographic fringes to one-dimensional holographic fringes, can obviously reduce the calculation amount of holographic digital reconstruction and information processing, and is beneficial to realizing the real-time reconstruction and processing of particle holograms.
Claims (10)
1. A digital holographic particle measurement device based on spatial modulation of a diaphragm, the device comprising:
a laser light source for generating a laser beam of adjustable intensity;
the spatial filtering beam expanding unit comprises a spatial filter and a beam expander and is used for expanding and collimating the laser beam to form a collimated beam;
the device comprises a measuring area, a light source and a control unit, wherein particles to be measured are distributed in the measuring area, the collimated light beam irradiates the measuring particles, the particles are scattered to form object light, and unscattered straight light is used as reference light;
the diaphragm modulation unit comprises a first lens, a diaphragm and a second lens which are sequentially arranged for object light to spatially modulate the object light so that part of the object light and the reference light pass through;
the image recording unit comprises a CCD or CMOS digital camera and is used for recording a holographic interference fringe image formed by the interference of object light and reference light of the particles;
and the data processing unit is used for acquiring and reconstructing the particle hologram recorded by the image recording unit to obtain the information of the detected particles, wherein the information comprises the particle size and the three-dimensional position.
2. The digital holographic particle measurement device based on optical diaphragm spatial modulation of claim 1, wherein the optical diaphragm modulation unit is located between the measurement area and the image recording unit, a back focal plane of the first convex lens coincides with a front focal plane of the second convex lens, and the optical diaphragm is placed at a coincident focal plane of the first convex lens and the second convex lens.
3. The digital holographic particle measurement device based on the diaphragm spatial modulation of claim 2, wherein the first convex lens and the second convex lens have the same diameter and the same focal length, and the diaphragm modulation unit has no zooming effect on the object image; or the diameters of the first convex lens and the second convex lens are different, the focal lengths are different, and the diaphragm modulation unit has a zooming effect on the object image; the diaphragm slit width is adjustable, and the slit width is 5-200 mu m.
4. The digital holographic particle measuring device based on the spatial modulation of the diaphragm, as claimed in claim 1, wherein the laser source, the spatial filtering and beam expanding unit, the measuring area, the diaphragm modulation unit and the image recording unit are located on the same axis to form a coaxial holographic system, and the object light is horizontally scattered light of particles.
5. The digital holographic particle measurement device based on the diaphragm spatial modulation is characterized in that the laser light source, the spatial filtering and beam expanding unit and the measurement area are positioned on the same axis, the diaphragm modulation unit and the image recording unit are perpendicular to the measurement area to form an off-axis holographic system, and the object light is 90-degree scattered light of particles; a spectroscope is arranged between the spatial filtering beam expanding unit and the measuring area, and collimated light beams are incident between the diaphragm modulating unit and the image recording unit as reference light after being split.
6. The digital holographic particle measurement device based on the spatial modulation of the diaphragm, according to the claim 4 or 5, is characterized in that a filter is arranged between the diaphragm modulation unit and the image recording unit.
7. A digital holographic particle measurement method based on diaphragm spatial modulation is characterized by comprising the following steps:
(1) generating a collimated light beam by using a laser light source and a spatial filtering beam expanding unit, and enabling the collimated light beam to irradiate a particle field of a measuring area;
(2) the aperture modulation unit is adopted to perform spatial modulation on the particle light, so that part of the object light passes through;
(3) recording a particle holographic interference fringe image by using a CCD or CMOS digital camera;
(4) and reconstructing and analyzing the recorded holographic interference fringe image of the particles to obtain particle information including particle size and position information.
8. The digital holographic particle measurement method based on spatial modulation of diaphragm of claim 7, wherein in the step (1), the process of generating the collimated light beam is as follows: laser beams generated by the laser light source sequentially pass through the spatial filter and the beam expander in the spatial filtering beam expanding unit to form collimated cylindrical light beams, when the particle field is irradiated, part of light is scattered through particles to form object light, and the other part of laser without the particles is used as reference light.
9. The digital holographic particle measurement method based on the diaphragm spatial modulation of claim 7, wherein the process of spatially modulating the particle light by the diaphragm modulation unit in the step (2) is as follows: the back focal plane of the first convex lens and the front focal plane of the second convex lens are adjusted to coincide, the diaphragm is placed on the coincidence plane, the slit width of the diaphragm is adjusted, and when collimated light beams sequentially pass through the first convex lens, the diaphragm and the second convex lens, scattered object light in the vertical direction of the slit of the diaphragm can be filtered, and spatial modulation of the object light is achieved.
10. The digital holographic particle measurement method based on spatial modulation of optical diaphragm of claim 7, wherein the reconstruction analysis of the holographic fringes in the step (4) comprises a particle location process, a particle identification process and a particle size calculation process.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112749507A (en) * | 2020-12-29 | 2021-05-04 | 浙江大学 | Method for deep learning holographic online measurement of coal and biomass coupling power generation blending ratio |
| CN116026729A (en) * | 2023-03-03 | 2023-04-28 | 浙江大学 | Portable microplastic detection device based on digital coaxial holographic microscopy |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112749507A (en) * | 2020-12-29 | 2021-05-04 | 浙江大学 | Method for deep learning holographic online measurement of coal and biomass coupling power generation blending ratio |
| CN112749507B (en) * | 2020-12-29 | 2022-07-12 | 浙江大学 | Method for holographic online measurement of coal and biomass coupling power generation blending ratio |
| CN116026729A (en) * | 2023-03-03 | 2023-04-28 | 浙江大学 | Portable microplastic detection device based on digital coaxial holographic microscopy |
| CN116026729B (en) * | 2023-03-03 | 2024-03-15 | 浙江大学 | Portable microplastic detection device based on digital coaxial holographic microscopy |
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