CN118295145A - Device and test method for adjusting and controlling partial coherent light field to improve imaging resolution limit - Google Patents
Device and test method for adjusting and controlling partial coherent light field to improve imaging resolution limit Download PDFInfo
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 3
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- CPBQJMYROZQQJC-UHFFFAOYSA-N helium neon Chemical compound [He].[Ne] CPBQJMYROZQQJC-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention relates to the technical field of optical imaging, in particular to a device and a testing method for regulating and controlling a partial coherent light field to improve imaging resolution limit. The method is that the coherence of a light field of a high-coherence light beam scattered by a dynamic scatterer is regulated and controlled by setting the rotation speed of the dynamic scatterer in an illumination optical system and the position of the scatterer between the light source and a lens so as to obtain the coherence of a target light source. The device has simple structure, easy operation and low cost, and can generate stable partial coherent light field after the system is determined. The method is simple and easy to implement, and can adapt to different imaging requirements and conditions from complete coherence to complete incoherent or any coherence state between the two in the coherence process of the optical imaging system.
Description
Technical Field
The invention relates to the technical field of optical imaging, in particular to a device and a test method for regulating and controlling a partial coherent light field to improve imaging resolution limit.
Background
Optical imaging is not a "point-to-point" image reproduction in the spatial dimension, even if noise and other random disturbances are not considered, because of diffraction effects during light wave propagation, the ideal aberration-free converging lens does not image a far point source of light into a geometric point without size, but a spot with a certain spread in space, i.e., an Airy diffraction spot, due to high frequency component loss.
As is well known, the laser source has the advantages of high coherence, good directivity, high brightness and the like, and is widely applied to the fields of scientific research, medical health, national defense science and technology and the like. However, in the fields of laser atmospheric optical communication, inertial confinement nuclear fusion and the like, high coherence is rather detrimental. The high coherence light irradiates dust, small bubbles and other defects on the surface of the optical lens, and then generates speckle noise and other interference gain to impair imaging quality. In imaging resolution systems, the high coherence of the illumination distribution may instead reduce the resolution of the imaging system, which is disadvantageous for practical applications. In this case, it becomes important how to reduce the coherence of the light source to increase the resolution of the imaging system. The partially coherent light can also generate far field distribution with uniform irradiance and high directivity, and the problems of fuzzy image point distance, incapability of measurement, inconvenience in resolution and the like caused by interference fringes can be avoided.
In the application document of application number 2009101108987, named "a method for reducing laser coherence and a phase modulator thereof", an electro-optic phase modulator with a waveguide structure made of electro-optic material is used to obtain high-frequency phase modulation, so that the phase is disordered to reduce the laser coherence. This method reduces laser coherence by a phase modulator, but has problems of a relatively complex structure and a complex modulation. In the document entitled "2018108953032", a device and a method for reducing coherence of laser light ", a method for reducing coherence of a light source by adjusting a width of a light spot and controlling a degree of scattering is proposed. The method can regulate and control the coherence of the light field in real time, but still has the problems of complex light path, complex modulation, higher requirements on instruments and equipment and higher implementation difficulty.
In summary, with the breakthrough progress of the light field regulation technology and the prolongation of the partial coherence theory structure, it is possible to improve the two-point resolution limit by optimizing the classical optical imaging system by using the controllable light field spatial fluctuation distribution.
Disclosure of Invention
The invention provides a method and a device for regulating and controlling a partially coherent light field to improve imaging resolution limit, which are used for solving the problems of complex structure and high implementation difficulty in the prior art.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows: the system for regulating and controlling the partial coherent light field to improve the imaging resolution limit comprises a coherent light source, a collimating lens and a CMOS camera, wherein the collimating lens comprises a first collimating lens and a second collimating lens, and the first collimating lens, a dynamic scatterer, the second collimating lens, an object, the imaging lens and the CMOS camera are positioned on an emergent optical axis of the coherent light source; the dynamic scatterer is arranged on a linear displacement platform, and the linear displacement platform is controlled by a motor.
Further, one surface of the dynamic scattering body is polished, and the other surface is a quartz crystal with fine sand of 120 meshes and roughness of 125 mu m.
Further, the dynamic scattering body is ground glass.
Furthermore, an attenuation sheet is arranged at the exit of the coherent light source.
Further, the test method of the system for improving the imaging resolution limit based on the regulation and control of the light field coherence comprises the following steps,
Step one: the coherent light source emits laser to irradiate on the dynamic scattering body, and the light beam scattered by the dynamic scattering body illuminates an object to be imaged on the CMOS camera after passing through the imaging lens;
Step two: according to the coherence of the required optical imaging system, setting the rotation parameters of a stepping motor in the illumination optical system to control the rotation speed of the dynamic scatterer, so as to realize control operations such as speed increasing, speed reducing, reversing and the like;
Step three: according to the rotation speed of the dynamic scatterer, the coherence of the light field of the high-coherence light beam scattered by the dynamic scatterer is regulated and controlled to obtain the coherence of the target light source;
step four: the method comprises the steps of utilizing a microcontroller chip to acquire the rotating speed information of a dynamic scatterer in real time;
step five: changing the position of the dynamic scatterer between the coherent light source and the second collimating lens, increasing or reducing the modulation quantity of the partial coherent light, and obtaining a partial coherent modulation light spot with high coherence or low coherence;
Step six: obtaining interference fringe patterns in the image plane light intensity distribution of an imaging system through a CMOS camera;
Step seven: the coherence of the optical imaging system can be verified by calculating the contrast of the interference fringes, and the rotation speed relation with the dynamic scatterer is determined;
Step eight: and (3) adjusting rotation and position parameters of the dynamic scatterer, and repeating the steps three to seven until a target coherent light field is obtained.
Compared with the prior art, the invention has the advantages that:
1. The optical imaging system is simple in structure and easy to operate, the size of the coherence of the light source is reduced by controlling the stepping motor to rotate the dynamic scattering body, the spot modulation quantity of the coherent modulator is regulated and controlled by moving the scattering body to be away from the position between the light source and the lens, the problem that the coherence of the imaging system is difficult to regulate and control is solved, the coherence is difficult to change after the system is determined, and a stable partial coherent light field can be generated. Meanwhile, the requirements on the precision of the parts are low, the manufacturing cost is low, the requirements on the use environment are also low, and the use cost is low.
2. In the method provided by the invention, the coherence of the light field and the coherence modulation quantity of the illumination system are regulated and controlled by changing the rotation speed of the scatterer and the position between the scatterer and the light source and the lens, and the coherence of the optical imaging system can be tested by measuring the 'unclear' interference fringe pattern generated by the intensity distribution of the light on the image plane of the imaging system. The method for realizing the coherence of the optical imaging system is simple and flexible, and the coherence of the light field of the high-coherence light beam scattered by the dynamic scatterer can be regulated and controlled only by setting the rotation parameter of the stepping motor to control the rotation speed of the dynamic scatterer, so that the coherence of the target light source is obtained. From fully coherent to fully incoherent, or any coherent state in between, to accommodate different imaging requirements and conditions.
Drawings
FIG. 1 is a schematic diagram of a structure for adjusting coherence of an optical imaging system;
fig. 2 is a graph of the results of a partially coherent light illuminated two-point imaging system with the parameter μ= 0.4524 in a specific embodiment;
Fig. 3 is a graph of the results of a partially coherent light illuminated two-point imaging system with the parameter μ= 0.8688 in a specific embodiment.
The reference numerals are as follows:
1-a coherent light source; 2-a first collimating lens; 3-dynamic scatterers; 4-a stepping motor; 5-a linear displacement stage; 6-a second collimating lens; 7-an object; 8-an imaging lens; 9-CMOS camera.
Detailed Description
The invention is described in further detail below with reference to the drawings and examples.
Referring to fig. 1, the system for adjusting and controlling a partially coherent light field to improve imaging resolution limit provided by the invention comprises a coherent light source 1, a collimating lens and a CMOS camera 9, wherein the collimating lens comprises a first collimating lens 2 and a second collimating lens 6, the first collimating lens 2, a dynamic scatterer 3, the second collimating lens 6, an object 7, an imaging lens 8 and the CMOS camera 9 are positioned on an emergent optical axis of the coherent light source 1, wherein the coherent light source 1, the first collimating lens 2, the second collimating lens 6 and the object 7 form an illumination optical system, and a rotation speed of dynamic ground glass in the illumination optical system can be set to adjust and control the coherence of the light field of the high coherent light beam scattered by the dynamic ground glass so as to obtain the coherence of a target light source. The dynamic scatterer 3 is arranged on a linear displacement table 5, the linear displacement table 5 is controlled by a stepping motor 4, and the dynamic scatterer 3, the linear displacement table 5 and the stepping motor 4 form a coherent modulator; the imaging lens 8 and the CMOS camera 9 form a two-point imaging resolution system, interference fringe patterns in the light intensity distribution of the imaging system image surface can be obtained, and the coherence of the optical imaging system can be verified by calculating the contrast of interference fringes.
One surface of the dynamic scattering body 3 is polished, and the other surface is fine ground with 120 meshes and has quartz crystal with roughness of 125 mu m. Ground glass was selected in this example.
An attenuation sheet is arranged at the emergent port of the coherent light source 1 to absorb laser density. When the light intensity is strong, the light intensity can be selected.
In this embodiment: helium-neon laser with output power of 5.0mW and wavelength of 632.8nm is selected as coherent light source, and an attenuation sheet with OD=1.0 is added in front of the light source, which can absorb 90% of laser density. And a dynamic scattering body 3 is designed, which is ground on one surface and ground on the other surface, and is fine ground with 120 meshes, and has a roughness of 125 mu m, and is used for scattering coherent light to generate a partial coherent light beam to illuminate the two-point imaging resolution system. The experiment selects an imaging lens 8 with a diffraction aperture of 2σ=25.4 mm and a focal length of f=50 mm.
In this embodiment, the object 7 is an opaque light shielding plate made by laser drilling, and is provided with two small holes with the same size, the diameter of the small holes is 0.1mm, and the two holes are small enough to be equivalent to two self-luminous point light sources in object space, so that light beams can only pass through the two holes.
Object distance f p =50 mm and image distance f q =50 mm in the two-point imaging and imaging resolution system; a CMOS camera 9 having a resolution of 1920 (H) ×1200 (V).
When the fringe contrast is 0, the system is a completely incoherent optical imaging system; when the contrast of the stripes is 1, the stripe is a completely coherent optical imaging system; when the stripe contrast is between 0 and 1, the partial coherent optical imaging system is provided, and the higher the numerical value is, the stronger the coherence of the optical imaging system is; when the contrast of the fringes is between-1 and 0, the optical imaging system is still a partially coherent optical imaging system, the smaller the value is, the stronger the coherence of the optical imaging system is, and the "-" indicates that the phase difference of two light waves emitted after passing through two holes is 180 degrees different.
A test method of a system for improving imaging resolution limit based on the regulation and control of a partially coherent light field comprises the following specific steps:
Step one: the helium-neon laser emits laser to irradiate on the frosted glass, and the light beam scattered by the frosted glass illuminates an object to be imaged on the CMOS camera 9 after being transmitted through the imaging lens 8;
step two: setting the rotation parameters of a stepping motor 4 in the illumination optical system to control the rotation speed of the dynamic ground glass according to the coherence of the required optical imaging system, so as to realize control operations such as speed increasing, speed reducing, reversing and the like;
Step three: according to the rotation speed of the setting frosted glass, the coherence of the light field of the high-coherence light beam scattered by the dynamic frosted glass is regulated so as to obtain the coherence of the target light source;
Step four: a microcontroller chip (MCU chip) is utilized to send out accurate control instructions to each module, and the rotating speed information of ground glass is collected in real time, so that real-time rotating speed parameters can be read through an OLED display screen;
Step five: changing the position of the frosted glass between the light source and the lens, increasing or reducing the modulation quantity of the partially coherent light (when the modulation quantity is larger, the low-rotation-speed dynamic scattering body breaks up the coherent light and can also generate the partially coherent light with low coherence, and when the modulation quantity is smaller, the higher-rotation-speed dynamic scattering body breaks up the coherent light and can generate the partially coherent light with low coherence), so as to obtain the partially coherent modulation light spots with high coherence or low coherence;
Step six: obtaining interference fringe patterns in the image plane light intensity distribution of the imaging system through the CMOS camera 9;
Step seven: the coherence of the optical imaging system can be verified by calculating the contrast of the interference fringes, and the rotation speed relation with ground glass is determined;
Step eight: and (3) adjusting rotation and position parameters of the frosted glass, and repeating the steps three to seven until a target coherent light field is obtained.
In the embodiment, two partial coherent illumination two-point imaging system result diagrams of parameters (the coherence degree is 0.4524) and (the coherence degree is 0.8688) are respectively acquired, and are shown in fig. 2 and 3.
When the coherence is 0.4524, the distance of the modulation light path is 105mm, wherein the distance from the laser light source to the dynamic scattering body 3 is 10mm, and the distance from the dynamic scattering body 3 to the object is 55mm. The modulated incident light spots are smaller, and the modulation quantity is smaller. When the rotation speed of the coherent modulator is 32rpm, the phenomenon of image quality impairment such as image distortion caused by interference noise such as "speckle" generated by high coherent light is hardly seen. The contrast of the interference fringes is lower, and the corresponding light field coherence is also lower, and belongs to a low-coherence partially coherent light field.
When the coherence is 0.8688, the distance of the modulation light path is 115mm, wherein the distance from the laser light source to the dynamic scattering body 3 is 10mm, and the distance from the dynamic scattering body 3 to the object is 65mm. The modulated incident light spots are larger, and the modulation quantity is larger. When the rotation speed of the coherent modulator is 2rpm, the phenomenon of "speckle" or the like generated by high coherent light is not seen. The contrast of the interference fringes is very high, and the coherence of the corresponding light field is also very high, and the interference fringes belong to a high-coherence partially coherent light field.
The present invention is not limited to the preferred embodiments, but can be modified in any way according to the technical principles of the present invention, and all such modifications, equivalent variations and modifications are included in the scope of the present invention.
Claims (5)
1. The system for regulating and controlling the partial coherent light field to improve the imaging resolution limit comprises a coherent light source (1), a collimating lens and a CMOS camera (9), and is characterized in that the collimating lens comprises a first collimating lens (2) and a second collimating lens (6), and the first collimating lens (2), a dynamic scatterer (3), the second collimating lens (6), an object (7), an imaging lens (8) and the CMOS camera (9) are positioned on an emergent optical axis of the coherent light source (1); the dynamic scattering body (3) is arranged on the linear displacement table (5), and the dynamic scattering body (3) is controlled by the stepping motor (4).
2. The system for improving imaging resolution limit of a regulated partially coherent light field according to claim 1, wherein one surface of the dynamic scattering body (3) is polished, and the other surface is a quartz crystal with 120 meshes of fine frosting and 125 μm of roughness.
3. A system for adjusting and controlling the resolution limit of imaging of a partially coherent light field according to claim 2, wherein said dynamic scatterer (3) is ground glass.
4. A system for adjusting and controlling the partial coherent light field to improve the imaging resolution limit according to claim 2 or 3 is characterized in that an attenuation sheet is arranged at the emergent port of the coherent light source (1).
5. The method for testing the system for adjusting and controlling the imaging resolution limit of the partially coherent light field according to claim 1, wherein the method comprises the following steps: comprises the following steps
Step one: the coherent light source (1) emits laser to irradiate on the dynamic scattering body (3), and the light beam scattered by the dynamic scattering body (3) illuminates an object to be imaged on the CMOS camera (9) after being transmitted through the imaging lens (8);
Step two: according to the coherence of the required optical imaging system, setting the rotation parameters of a stepping motor (4) in the illumination optical system to control the rotation speed of the dynamic scatterer (3) so as to realize control operations such as speed increasing, speed reducing, reversing and the like;
Step three: according to the rotation speed of the dynamic scatterer (3), the coherence of a light field of the high-coherence light beam scattered by the dynamic scatterer (3) is regulated and controlled to obtain the coherence of a target light source;
Step four: the microcontroller chip is utilized to immediately acquire the rotating speed information of the dynamic scatterer (3);
Step five: changing the position of the dynamic scattering body (3) between the coherent light source (1) and the second collimating lens (6), increasing or reducing the modulation quantity of the partial coherent light, and obtaining a partial coherent modulation light spot with high coherence or low coherence;
Step six: obtaining interference fringe patterns in the image plane light intensity distribution of an imaging system through a CMOS camera (9);
Step seven: the coherence of the optical imaging system can be verified by calculating the contrast of the interference fringes, and the rotation speed relation with the dynamic scatterer (3) is determined;
step eight: and (3) adjusting rotation and position parameters of the dynamic scatterer (3), and repeating the steps three to seven until a target coherent light field is obtained.
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