CN114019676A - Optical imaging system aberration correction method based on coherent light imaging accurate calculation - Google Patents
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Abstract
The invention discloses an optical imaging system aberration correction method based on coherent light imaging accurate calculation. The ideal phase distribution of the imaging system image light field is accurately calculated, and the ideal phase distribution is subtracted from the actual phase distribution acquired by the actual digital holographic imaging system, so that the aberration phase is obtained. The aberration correction method has the advantages that the aberration phase is loaded on the spatial light modulator in the actual imaging system after being processed, the aberration of the imaging system is corrected, the structure of an optical system to be corrected is not changed, complicated light path setting and fitting calculation are not needed, and the purpose of correcting the aberration can be achieved only by changing the phase distribution of an incident light field by using the spatial light modulator.
Description
Technical Field
The invention relates to the technical field of diffraction calculation and digital holographic detection, in particular to an optical imaging system aberration correction method based on coherent light imaging accurate calculation.
Background
The coherent light imaging accurate calculation theory is used for accurately calculating the complex amplitude of an image light field of an optical system under coherent light illumination, the traditional coherent light imaging theory is obtained based on a linear system theory and certain approximation, the imaging system is regarded as an aberration-free linear space invariant system in the method, however, the actual imaging system is not the linear space invariant system, and therefore a certain error exists in the traditional coherent light imaging calculation method for calculating the complex amplitude of the image light field of the optical imaging system in the calculation process; the problem is well solved by the accurate coherent light imaging calculation theory, and the complex amplitude distribution of an image light field of a digital holographic imaging system can be accurately calculated.
With the continuous development of optical imaging systems, people have higher and higher requirements on the precision of a correction method for aberration of the optical imaging system; the digital holography technology has good application prospect in the correction of the optical imaging system aberration because of the advantages of being capable of recording the complex amplitude of the optical field and high detection precision. The conventional method for correcting aberration of an optical imaging system by using a digital holography technology is roughly divided into a data fitting method and an experimental processing method, wherein the data fitting method is to directly process the phase of a reproduced image by a computer, the conventional data fitting method comprises least square fitting, Zernike polynomial fitting and the like, the experimental processing method is realized by adopting different experimental means in the recording process of a hologram, and a double exposure method and a telecentric optical structure are commonly adopted. The method of fitting by a polynomial requires a high-order polynomial to ensure the accuracy of fitting, and the method relying only on experiments has high requirements on experimental environments. The method provided by the invention does not need to carry out fitting calculation of a large amount of data and complex experimental means, reduces experimental requirements and has no influence on the structure of an optical system.
Disclosure of Invention
The invention aims to provide an optical imaging system aberration correction method based on coherent light imaging accurate calculation, which aims to correct the aberration of an optical imaging system on the basis of digital holography and coherent light imaging accurate calculation, and specifically comprises the following steps:
(1) electrifying the hollow spatial light modulator and loading a pair of completely black gray-scale images, keeping the initial object light without adding extra phase, and reconstructing the acquired hologram to obtain the actual phase condition of the digital holographic imaging system
(2) Measuring actual parameters of the digital holographic imaging system in the process of recording the holographic image, wherein the actual parameters mainly comprise laser wavelength and the distance from an imaging object to a CCD camera, and other parameters can be obtained according to the object-image relationship;
(3) simulating the coherent light imaging process of the imaging system according to actual parameters to obtain the complex amplitude U of the image plane light field under the condition of no aberrationc(x, y), the specific calculation formula is as follows:
in the above formula, j is an imaginary unit, wave vector k is 2 pi/lambda, lambda is the wavelength, diIs an image distance, F-1{. represents the inverse Fourier transform, F {. represents the Fourier transform, and the lateral magnification of the image
A＝di/do，doIs an object distance, U0(x, y) is the complex amplitude of the object plane light field, Uc(x, y) is the complex amplitude of the image plane light field, P (x, y) is the pupil function, x and y are the spatial coordinates of the image light field, fxAnd fyIs the frequency domain coordinates of the image light field;
(4) from complex amplitude Uc(x, y) to obtain an ideal phase without aberration
In the above formula
Representing the calculated ideal phase, Im (-) represents the imaginary part, and Re (-) represents the real part;
(5) using the calculated ideal phase and the actual phase of the reconstructed image of the actual hologram
Subtracting to obtain aberration phase caused by system aberration
(6) The spatial light modulator and the CCD are connected into the same computer, images are collected in time, and the calculated aberration phase position
The system aberration is corrected by processing the compensation phase required by correcting the system aberration and loading the processed compensation phase on a spatial light modulator in an experimental light path.
Preferably, in step 1 of the present invention, the digital holographic imaging system includes a laser 1, a polarizer 2, a first beam splitter 3, a first pinhole filter 4, a first collimating lens 5, a second beam splitter 6, a spatial light modulator 7, an imaging object 8, an optical system to be corrected 9, a third beam splitter 10, a CCD camera 11, a computer 12, a first reflector 13, a second collimating lens 14, and a second pinhole filter 15, wherein a light beam emitted from the laser 1 is modulated to a suitable polarization state by the polarizer 2, and then is split into two laser beams with the same polarization state by the first beam splitter 3, wherein one of the laser beams is expanded and collimated into parallel light by the first pinhole filter 4 and the first collimating lens 5, and then enters the spatial light modulator 7 for phase modulation by the second beam splitter 6 and then illuminates the imaging object 8, the light transmitted through the imaging object 8 is collected by the optical system to be corrected 9 and then directly transmits through the third beam splitter 10, vertically irradiating into the CCD camera 11 to form object light; the other beam of light is expanded and collimated into parallel light by a second pinhole filter 15 and a second collimating lens 14, the parallel light is irradiated to the CCD camera 11 through a first reflecting mirror 13 and a third beam splitter 10 to form reference light, and the reference light and the object light are interfered to obtain a hologram, and the hologram is recorded by the CCD camera 11.
The method of the invention can be applied to aberration detection of basic optical elements, such as spherical lenses, aspherical lenses and the like, and can also be applied to combined lens systems, such as micro-objectives, projection objectives, telecentric lens groups, zoom or variable power lens groups and the like.
The invention has the beneficial effects that:
compared with the prior art, the method does not change the structure of the original optical system, reduces the requirement of experimental environment, avoids a large amount of data fitting calculation processes, and can well correct the aberration of the system on the basis of only using the spatial light modulator to change the phase of incident light.
Drawings
FIG. 1 is an imaging system aberration correction optical path for use with the present invention;
FIG. 2 is a process flow diagram of the present invention;
FIG. 3 shows the actual phases collected in the experiment of example 1;
fig. 4 is an ideal phase calculated by coherent light accurate imaging according to actual experimental parameters in example 1;
FIG. 5 shows the aberration phase of the optical system obtained by the method of the present invention in example 1.
In fig. 1: 1-a laser; 2-a polarizing plate; 3-a first beam splitter; 4-a first pinhole filter; 5-a first collimating lens; 6-a second beam splitter; 7-a spatial light modulator; 8-imaging the object; 9-an optical system to be corrected; 10-a third beam splitter; 11-a CCD camera; 12-a computer; 13-a first mirror; 14-a second collimating lens; 15-second pinhole filter.
Detailed Description
The invention will be described in more detail with reference to the following figures and examples, but the scope of the invention is not limited thereto.
The digital holographic imaging system used in embodiments 1-2 of the present invention includes a laser 1, a polarizer 2, a first beam splitter 3, a first pinhole filter 4, a first collimating lens 5, a second beam splitter 6, a spatial light modulator 7, an imaging object 8, an optical system to be corrected 9, a third beam splitter 10, a CCD camera 11, a computer 12, a first reflector 13, a second collimating lens 14, and a second pinhole filter 15, wherein a light beam from the laser 1 is modulated to a suitable polarization state by the polarizer 2, and then is split into two laser beams having the same polarization state by the first beam splitter 3, wherein one of the laser beams is expanded and collimated into parallel light by the first pinhole filter 4 and the first collimating lens 5, and then enters the spatial light modulator 7 for phase modulation by the second beam splitter 6 and then illuminates the imaging object 8, and the light transmitted through the imaging object 8 is collected by the optical system to be corrected 9 and then directly transmits through the third beam splitter 10, vertically irradiating into the CCD camera 11 to form object light; the other beam of light is expanded and collimated by the second pinhole filter 15 and the second collimating lens 14 into parallel light, the parallel light is irradiated to the CCD camera 11 by the first reflecting mirror 13 and the third beam splitter 10 to form reference light, and a hologram is obtained by interference of the reference light and the object light, and the hologram is recorded by the CCD camera 11, as shown in fig. 1.
Example 1
An optical imaging system aberration correction method based on coherent light imaging accurate calculation is specifically used for aberration correction of an optical system of a microscope objective, specifically, an optical system 9 to be corrected in a digital measurement holographic imaging system is replaced by the microscope objective, an imaging object 8 in the embodiment is empty, and the method specifically comprises the following steps:
(1) before the experiment, the hollow spatial light modulator is electrified and a pair of completely black gray-scale images is loaded, the initial object light is kept without adding extra phase, and the actual phase of the digital holographic imaging system is obtained by reconstructing the collected hologramBit condition
As shown in fig. 4.
(2) The main process of correcting the actual aberration of the microscope objective by using the method of the invention is as follows:
the method is characterized in that actual parameters in the process of recording the holographic image by the digital holographic imaging system are measured, the laser wavelength is 632nm, the distance from an imaging object to a CCD camera is 270mm, and other parameters can be obtained according to the object-image relationship.
Secondly, simulating the imaging process of coherent light of the imaging system according to actual parameters to obtain the complex amplitude U of the light field of the image plane under the condition of no aberrationc(x, y), the specific calculation formula is as follows:
in the above formula, j is an imaginary unit, wave vector K is 2 pi/lambda, lambda is wavelength, d isiIs an image distance, F-1{. represents the inverse Fourier transform, F {. represents the Fourier transform, and the transverse magnification A of the image is di/do，doIs an object distance, U0(x, y) is the complex amplitude of the object plane light field, Uc(x, y) is the complex amplitude of the image plane light field, P (x, y) is the pupil function, x and y are the spatial coordinates of the image light field, fxAnd fyIs the frequency domain coordinate of the image light field.
③ complex amplitude Uc(x, y) to obtain an ideal phase without aberration
In the above formula
Representing calculated theoryPhase, Im (·) represents imaginary part, Re (·) represents real part; as shown in fig. 5.
(3) Using the calculated ideal phase and the actual phase of the reconstructed image of the actual hologram
Subtracting to obtain aberration phase caused by system aberration
(4) The spatial light modulator and the CCD are connected into the same computer, images are collected in time, and the calculated aberration phase position
The compensation phase required by correcting the system aberration is processed and loaded on the spatial light modulator in the experimental light path, the system aberration is corrected, and the spatial light modulator 7 continuously loads the processed compensation phase in the correction process.
Example 2
The present embodiment is the same as embodiment 1, except that the method is used for correcting a digital micro-holographic super-resolution imaging system, specifically, an optical system 9 to be corrected in a digital measurement holographic imaging system is replaced by a micro objective lens, and an imaging object 8 used in the present embodiment selects a siemens star-shaped resolution plate, and specifically includes the following steps:
(1) 6 oblique stripes are loaded through a spatial light modulator respectively to change the phase structure of the illumination object light; obtaining the holograms under the condition of 6 kinds of oblique object light illumination, and obtaining the actual aberration condition of the system by a method of synthesizing a frequency spectrum
(2) The main process for correcting the actual aberration of the digital microscopic holographic super-resolution imaging system by using the method is as follows:
the method is characterized in that actual parameters in the process of recording the holographic image by the digital holographic imaging system are measured, the actual parameters mainly comprise that the laser wavelength is 632nm, the distance from an imaging object to a CCD camera is 270mm, the inclination amount of inclined illumination object light on a frequency domain, and other parameters can be obtained according to the object-image relationship.
Simulating a coherent light imaging process of the imaging system according to actual parameters, wherein six oblique illumination object lights are used in the process, and the expression is as follows:
Us＝exp[-jk(x*cosα+y*cosβ)]
in the above formula, j is an imaginary unit, wave vector k is 2 pi/lambda, lambda is the wavelength, x and y are the spatial coordinates of the image light field, and the corresponding value relationship between alpha and beta is obtained by the corresponding calculation of the following table
a is the amount of tilt of the tilted illumination object light in the frequency domain.
Thirdly, simulating the coherent light imaging process of the six oblique illumination object lights according to actual parameters to obtain six image plane light field complex amplitude distributions, and then carrying out frequency spectrum synthesis on the six image plane light field complex amplitudes to obtain super-resolution image plane light field complex amplitude U under the condition of no aberrationc(x, y), the specific calculation formula is as follows:
in the above formula, j is an imaginary unit, wave vector k is 2 pi/lambda, lambda is the wavelength, diIs an image distance, F-1{. represents the inverse Fourier transform, F {. represents the Fourier transform, and the transverse magnification A of the image is di/do，doIs an object distance, U0(x, y) is the complex amplitude of the object plane light field, Uc(x, y) is the complex amplitude of the image plane light field, P (x, y) is the pupil function, x and y are the spatial coordinates of the image light field, fxAnd fyIs likeFrequency domain coordinates of the light field.
Fourthly, the complex amplitude U under the super-resolution conditionc(x, y) to obtain an ideal phase without aberration
In the above formula
Representing the calculated ideal phase, Im (-) represents the imaginary part, and Re (-) represents the real part; as shown in fig. 5.
(3) Using the calculated ideal phase and the actual phase of the reconstructed image of the actual hologram
Subtracting to obtain aberration phase caused by system aberration
(4) The spatial light modulator and the CCD are connected into the same computer, images are collected in time, and the calculated aberration phase position
The compensation phase required by correcting the system aberration is processed and loaded on the spatial light modulator in the experimental light path, the system aberration is corrected, and the spatial light modulator 7 continuously loads the processed compensation phase in the correction process.
Claims (2)
1. An optical imaging system aberration correction method based on coherent light imaging accurate calculation is characterized by comprising the following steps:
(1) electrifying the hollow spatial light modulator and loading a pair of completely black gray-scale images, keeping the initial object light without adding extra phase, and reconstructing the acquired hologram to obtain the actual phase condition of the digital holographic imaging system
(2) Measuring actual parameters of the digital holographic imaging system in the process of recording the holographic image, wherein the actual parameters mainly comprise laser wavelength and the distance from an imaging object to a CCD camera, and other parameters can be obtained according to the object-image relationship;
(3) simulating the coherent light imaging process of the imaging system according to actual parameters to obtain the complex amplitude U of the image plane light field under the condition of no aberrationc(x, y), the specific calculation formula is as follows:
in the above formula, j is an imaginary unit, wave vector k is 2 pi/lambda, lambda is the wavelength, diIs an image distance, F-1{. represents the inverse Fourier transform, F {. represents the Fourier transform, and the transverse magnification A of the image is di/do，doIs an object distance, U0(x, y) is the complex amplitude of the object plane light field, Uc(x, y) is the complex amplitude of the image plane light field, P (x, y) is the pupil function, x and y are the spatial coordinates of the image light field, fxAnd fyIs the frequency domain coordinates of the image light field;
(4) from complex amplitude Uc(x, y) to obtain an ideal phase without aberration
The upper typeIn
Representing the calculated ideal phase, Im (-) represents the imaginary part, and Re (-) represents the real part;
(5) using the calculated ideal phase and the actual phase of the reconstructed image of the actual hologram
Subtracting to obtain aberration phase caused by system aberration
(6) The spatial light modulator and the CCD are connected into the same computer, images are collected in time, and the calculated aberration phase position
The system aberration is corrected by processing the compensation phase required by correcting the system aberration and loading the processed compensation phase on a spatial light modulator in an experimental light path.
2. The method for correcting the aberration of the optical imaging system based on the precise calculation of the coherent light imaging according to claim 1, wherein: the digital holographic imaging system in the step (1) comprises a laser (1), a polaroid (2), a first beam splitter (3), a first pinhole filter (4), a first collimating lens (5), a second beam splitter (6), a spatial light modulator (7), an imaging object (8), an optical system to be corrected (9), a third beam splitter (10), a CCD camera (11), a computer (12), a first reflector (13), a second collimating lens (14) and a second pinhole filter (15), wherein after being modulated to a proper polarization state by the polaroid (2), a light beam coming out of the laser (1) is divided into two laser beams with the same polarization state by the first beam splitter (3), wherein the light beam is expanded and collimated into parallel light by the first pinhole filter (4) and the first collimating lens (5), enters the spatial light modulator (7) by the second beam splitter (6) to be subjected to phase modulation, and then is illuminated on the object to be imaged (8), the light penetrating through the object (8) to be imaged is collected by the optical system (9) to be corrected, then penetrates through a third beam splitter (10) directly and vertically irradiates into a CCD camera (11) to form object light; the other beam of light is expanded and collimated into parallel light by a second pinhole filter (15) and a second collimating lens (14), the parallel light is irradiated to a CCD camera (11) through a first reflecting mirror (13) and a third beam splitter (10) to form reference light, a hologram is obtained through interference of the reference light and object light, and the hologram is recorded by the CCD camera (11).
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