A method for correcting chromatic aberration of a tomographic microscope

Abstract

The present invention relates to the field of optical imaging technology, and specifically to a method for correcting chromatic aberration of a tomographic microscope, comprising the following steps: S1: adding a quadratic phase grating, a blazed grating, a reflector, and a tube lens to the imaging optical path of the microscope; wherein the blazed grating includes multiple parts corresponding to the diffraction orders of the quadratic phase grating; S2: placing the sample to be observed at the object-side focal plane of the microscope objective, and placing the quadratic phase grating at the image-side focal plane of the microscope objective; S3: incident light first passes through the microscope objective and then sequentially enters the quadratic phase grating, the blazed grating, the reflector, and the tube lens, and finally forms an image on a CCD detector; the light wave at the quadratic phase grating is split into three diffracted light waves and projected onto the upper, middle, and lower portions of the blazed grating, respectively, to achieve chromatic aberration correction through dispersion subtraction. The present invention has a simple structure, low manufacturing cost, good chromatic aberration correction effect, and high light wave projection energy.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a chromatic aberration correction method for a tomographic microscope. Background Art

[0002] Optical image tomography technology has been widely applied in various fields, especially in disease detection. The use of optical image tomography microscopes is quite common in disease detection. Currently, tomography microscopes based on the principle of quadratic phase grating spectroscopy can achieve real-time acquisition of multi-layer image information of biological samples. Compared with the traditional method of staining and sectioning followed by sequential microscopic observation, tomography microscopes have the following advantages: 1. Real-time 3D imaging without the need for reconstruction algorithms; 2. Applicable for observation of living cells; 3. Simple structure with no moving parts.

[0003] However, as the core component of a tomographic microscope, the quadratic phase grating follows the grating equation for its spectroscopic principle. Since the light that the human eye can perceive is polychromatic light, incident light of different wavelengths will have different diffraction angles due to the difference in wavelength after being split by the grating, resulting in chromatic aberration. The existence of chromatic aberration will cause images of different wavelengths to overlap, greatly affecting the observation results. Therefore, the chromatic aberration of the tomographic microscope needs to be corrected.

[0004] Currently, the following methods are mainly used for chromatic aberration correction of tomographic microscopes:

[0005] 1. Use a bandpass filter: This filter confines the incident light passing through the quadratic phase grating to a very narrow wavelength range, significantly reducing the difference in diffraction angles and thus reducing chromatic aberration. This method is simple to operate, does not affect the optical structure of the imaging system, and is highly effective in correcting chromatic aberration. However, the low light flux of the bandpass filter significantly reduces the light energy output by the system, making it unsuitable for high-magnification microscopic imaging.

[0006] 2. Use prisms for correction: A prism is composed of a prism and a grating. Two prisms are usually required to form a prism pair. The function of the prism pair is to artificially create chromatic aberration in the incident light. This part of the chromatic aberration is called pre-dispersion. The pre-dispersed light is then passed through a secondary phase grating. By adjusting the parameters of the secondary phase grating, the chromatic aberration produced by the secondary phase grating and the pre-dispersion are subtracted, thereby achieving chromatic aberration correction.

[0007] This method preserves light of all wavelengths and has minimal energy loss. However, the parameters of the prism pairs and the quadratic phase grating in the optical path require very precise matching. If there are discrepancies in the matching, chromatic aberration correction will still be impossible. At the same time, there are very high requirements for the relative positions of the various components in the optical path. Any discrepancies in the position adjustment will also affect the chromatic aberration correction results.

[0008] 3. Combining a blazed grating and a prism: This approach utilizes the dispersion of the blazed grating and the prism to compensate for the chromatic aberration of the secondary phase grating while simultaneously achieving tomographic image separation. Compared to solutions using prisms for correction, this method offers a simpler optical path structure, eliminates one grating, achieves higher projected light energy, and facilitates parameter matching. However, in practical applications, the Abbe number of the prism material found may differ from the calculated Abbe number, significantly affecting the effectiveness of chromatic aberration correction.

[0009] In summary, how to design a chromatic aberration correction method for a tomographic microscope that can achieve good light flux, low parameter matching difficulty, and strong chromatic aberration correction while maintaining a simple microscope structure is an urgent problem that needs to be solved. Summary of the Invention

[0010] In order to solve the above problems, the present invention provides a method for correcting chromatic aberration of a tomographic microscope.

[0011] To achieve the above object, the present invention proposes the following technical solution: a method for correcting chromatic aberration of a tomographic microscope, comprising the following steps:

[0012] S1: Adding a quadratic phase grating, a blazed grating, a reflector, and a tube lens to the imaging optical path of the microscope; wherein the blazed grating includes multiple parts corresponding to the diffraction orders of the quadratic phase grating;

[0013] S2: Place the sample to be observed at the object focal plane of the microscope objective lens, and place the secondary phase grating at the image focal plane of the microscope objective lens;

[0014] S3: The incident light first passes through the microscope objective lens and then enters the secondary phase grating, blazed grating, reflector and tube lens in sequence, and finally forms an image on the CCD detector.

[0015] Preferably, the blazed grating in step S1 is divided into three parts: an upper part, a middle part, and a lower part, wherein the central periods of the upper and lower parts of the blazed grating are the same and are the same as the central period of the quadratic phase grating; the orders of the upper and lower parts of the blazed grating are +1 and -1, respectively, corresponding to the -1 diffraction order and +1 diffraction order of the quadratic phase grating, respectively; and the middle part of the blazed grating is a region without grating stripes, that is, a 0-order grating-free dispersion region.

[0016] Preferably, the optical path of the light wave in S3 is specifically:

[0017] S31: The incident light wave enters from the object focal plane of the microscope objective;

[0018] S32: The incident light wave entering the microscope objective then enters the secondary phase grating;

[0019] S33: The light wave at the quadratic phase grating is split into three diffracted light waves and projected onto the upper, middle, and lower parts of the blazed grating, respectively. At this point, the three images entering the blazed grating are separated from each other on the blazed grating surface.

[0020] S34: After passing through the blazed grating, the three diffracted light beams all have the same diffraction angle and are projected onto the reflector in parallel. The three diffracted light waves correspond to three different reflectors, and the direction of the light path is controlled by adjusting the inclination angle of the reflector.

[0021] S35: The three diffracted light waves are projected onto the cylindrical mirror through the reflector;

[0022] S36: The three diffracted light waves enter the CCD detector through the cylindrical lens and form an image.

[0023] Preferably, the blazed grating is placed at the object-side focal plane of the tube lens, and the CCD detector is placed at the image-side focal plane of the tube lens; a distance is left between the secondary phase grating and the blazed grating.

[0024] Preferably, the quadratic phase grating and the blazed grating are made of the same material, and the distance between the quadratic phase grating and the blazed grating is adjusted according to the size of the object-side line field of view.

[0025] Preferably, assuming that the aperture on the blazed grating surface is D′, the incident angle of the edge field chief ray on the quadratic phase grating is θ, and the spacing between the quadratic phase grating and the blazed grating is L, to ensure that the three images entering the blazed grating are separated from each other on the blazed grating surface, the following conditions must be met:

[0026]

[0027] Preferably, the focal length of the microscope objective is f1′ and the object side half-line field of view is y:

[0028] Preferably, the aperture of the microscope objective lens is D, and the object side numerical aperture of the microscope is N. A :D=2f1′·N A +2y.

[0029] Preferably,

[0030] Preferably, assuming that the central wavelength of the incident light is λ, the central period of the quadratic phase grating is d, the diffraction angle of the edge field main light on the quadratic phase grating is θ′: d(sinθ′-sinθ)=-λ.

[0031] The beneficial effects of the present invention are:

[0032] 1. Based on the tomographic microscope, the present invention adopts a blazed grating to compensate for the chromatic aberration of the secondary phase grating, adopts a reflector to separate the tomographic image, and corrects the chromatic aberration by dispersion subtraction, which can improve the effectiveness of chromatic aberration correction and increase the projection energy of light waves.

[0033] 2. In the present invention, the blazed grating is configured as an upper portion, a middle portion, and a lower portion. The upper and lower portions have the same central period, and the orders of the upper and lower portions are +1 and -1, respectively, corresponding to the -1 and +1 diffraction orders of the quadratic phase grating. The middle portion of the blazed grating is a region without grating stripes, i.e., a 0-order grating-free dispersion region. The light waves at the quadratic phase grating are split into three diffracted light waves and projected onto the upper, middle, and lower portions of the blazed grating, respectively. This allows for chromatic aberration correction to be achieved while obtaining three clear tomographic images.

[0034] 3. The quadratic phase grating and the blazed grating are made of the same material, so there is no difference in Abbe number between the materials for chromatic aberration correction.

[0035] 4. The inclination angle of the reflector is adjustable, and the direction of the light path can be controlled by adjusting the inclination angle of the reflector. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the optical path structure provided by an embodiment of the present invention. Figure 1 .

[0037] Figure 2 It is a schematic diagram of the overall principle of the tomography microscope system provided by an embodiment of the present invention.

[0038] Figure 3 Schematic diagram of the achromatic principle of the tomographic microscope system provided by an embodiment of the present invention.

[0039] Figure 4 This is a schematic diagram of the optical path structure provided by an embodiment of the present invention. Figure 2 .

[0040] Figure 5 This is a schematic diagram of the optical path structure provided by an embodiment of the present invention. Figure 3 .

[0041] Figure numerals: microscope objective 1, secondary phase grating 2, blazed grating 3, reflecting mirror 4, tube lens 5, upper part 6, middle part 7, lower part 8, +1 order light beam 9, 0 order light beam 10, -1 order light beam 11, CCD detector 12. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clear, the following Figure 1-5It should be understood that the specific embodiments described herein are only used to illustrate the present invention and do not constitute a limitation of the present invention.

[0043] A method for correcting chromatic aberration of a tomographic microscope comprises the following steps:

[0044] S1: If Figure 1 、 2 As shown, a secondary phase grating 2, a blazed grating 3, a reflector 4 and a tube lens 5 are added to the imaging optical path of the microscope; the blazed grating 3 is used to compensate for chromatic aberration, and the reflector 4 is used to separate the tomographic images; the secondary phase grating 2 and the blazed grating 3 are made of the same material.

[0045] The blazed grating 3 includes multiple parts corresponding to the diffraction orders of the secondary phase grating 2; specifically: Figure 2 As shown, the blazed grating 3 is divided into three parts: an upper part 6, a middle part 7 and a lower part 8, wherein the central periods of the upper part 6 and the lower part 8 of the blazed grating 3 are the same and are the same as the central period of the quadratic phase grating 2; the orders of the upper part 6 and the lower part 8 of the blazed grating 3 are +1 and -1 respectively and correspond to the -1 diffraction order and +1 diffraction order of the quadratic phase grating 2 respectively; the middle part 7 of the blazed grating 3 is a region without grating stripes, that is, a 0-order grating-free dispersion region.

[0046] S2: Place the sample to be observed at the object focal plane of the microscope objective 1, and place the secondary phase grating 2 at the image focal plane of the microscope objective 1; at the same time, in order to improve the efficiency of chromatic aberration compensation, it is preferred to place the blazed grating 3 at the object focal plane of the tube lens 5, and place the CCD detector 12 at the image focal plane of the tube lens 5; leave a gap between the secondary phase grating 2 and the blazed grating 3, and the distance between the secondary phase grating 2 and the blazed grating 3 is adjusted according to the size of the object line field of view.

[0047] S3: The incident light first passes through the microscope objective lens 1 and then enters the secondary phase grating 2, the blazed grating 3, the reflector 4 and the tube lens 5 in sequence, and finally forms an image on the CCD detector 12.

[0048] The optical path of the light wave is specifically:

[0049] S31: The incident light wave enters from the object focal plane of microscope objective 1;

[0050] S32: The incident light wave entering the microscope objective 1 then enters the secondary phase grating 2;

[0051] S33: The light wave at the secondary phase grating 2 is divided into three diffracted light waves and projected onto the upper part 6, the middle part 7 and the lower part 8 of the blazed grating 3 respectively. Figure 1-3As shown, the three diffracted light waves are +1 order light beam 9, 0 order light beam 10, and -1 order light beam 11. At this time, the three images entering the blazed grating 3 are separated from each other on the surface of the blazed grating 3.

[0052] S34: After passing through the blazed grating 3, the +1-order light beam 9, the 0-order light beam 10, and the -1-order light beam 11 all have the same diffraction angle and are projected parallel to the reflector 4. The three diffracted light waves correspond to three different reflectors 4, and the direction of the light path can be controlled by adjusting the inclination angle of the reflector 4.

[0053] S35: The three diffracted light waves are projected onto the tube mirror 5 via the reflector 4;

[0054] S36: The three diffracted light waves enter the CCD detector 12 through the cylindrical lens 5 and form an image.

[0055] To ensure that the three images entering the blazed grating 3 are separated from each other on the blazed grating 3, as shown in FIG. Figure 4 and Figure 5 As shown, assuming that the aperture on the blazed grating 3 is D′, the incident angle of the edge field chief ray on the quadratic phase grating 2 is θ, and the spacing between the quadratic phase grating 2 and the blazed grating 3 is L, it must satisfy:

[0056] At the same time, other variables should satisfy the following relationships:

[0057] Assume that the focal length of microscope objective 1 is f1′ and the object side half-line field of view is y:

[0058] Assume that the aperture of microscope objective 1 is D and the object side numerical aperture of microscope is N. A :D=2f1′·N A +2y.

[0059]

[0060] Assume that the central wavelength of the incident light is λ, the central period of the quadratic phase grating 2 is d, and the diffraction angle of the edge field main light on the quadratic phase grating 2 is θ′: d(sinθ′-sinθ)=-λ.

[0061] When in use, the central period of the secondary phase grating 2 used is 40μm. It is known that the focal length of the microscope objective lens 1 used is 4.5mm, the object numerical aperture is 0.3, the magnification is 40, the central wavelength of the incident light wave is 550nm, and the object line field is 0.025mm.

[0062] Calculation shows that the object-side aperture is 2.9 mm, the aperture on the three surfaces of the blazed grating is 4.85 mm, and the angle of incidence is 0.3183°. The three beams of light passing through the blazed grating 3 are given different angles by the reflector 4, and each beam of light corresponds to a reflector 4. The direction of the light is controlled by changing the inclination angle of different reflectors 4. At this time, the angles corresponding to the +1-level beam 9, the 0-level beam 10, and the -1-level beam 11 are 21.5°, 22°, and 22.5°, respectively.

[0063] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art may make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0064] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for correcting chromatic aberration of a tomographic microscope, characterized in that: The steps include: S1: A quadratic phase grating (2), a blazed grating (3), a reflector (4) and a tube mirror (5) are added to the imaging optical path of the microscope; wherein the blazed grating (3) includes a plurality of parts corresponding to the diffraction orders of the quadratic phase grating (2); The secondary phase grating (2) and the blazed grating (3) are made of the same material, the blazed grating 3 is used to compensate for chromatic aberration, and the reflector 4 is used to separate the tomographic images; S2: placing the sample to be observed at the object focal plane of the microscope objective (1), and placing the secondary phase grating (2) at the image focal plane of the microscope objective (1); S3: The incident light first passes through the microscope objective lens (1) and then enters the secondary phase grating (2), the blazed grating (3), the reflector (4) and the tube lens (5) in sequence, and finally forms an image on the CCD detector (12); The optical path of the light wave in step S3 is specifically: S31: The incident light wave enters from the object focal plane of the microscope objective (1); S32: The incident light wave entering the microscope objective (1) then enters the secondary phase grating (2); S33: The light wave at the secondary phase grating (2) is divided into three diffracted light waves and projected onto the upper part (6), middle part (7) and lower part (8) of the blazed grating (3) respectively. At this time, the three images entering the blazed grating (3) are separated from each other on the surface of the blazed grating (3); S34: After passing through the blazed grating (3), the three diffracted light beams all have the same diffraction angle and are projected onto the reflector (4) in parallel; the three diffracted light waves correspond to three different reflectors (4), and the direction of the light path is controlled by adjusting the inclination angle of the reflector (4); S35: The three diffracted light waves are projected onto the cylindrical mirror (5) via the reflector (4); S36: The three diffracted light waves enter the CCD detector (12) through the cylindrical mirror (5) and form an image.

2. The method for correcting chromatic aberration of a tomographic microscope according to claim 1, wherein: The blazed grating (3) in step S1 is set to be composed of three parts: an upper part (6), a middle part (7) and a lower part (8), wherein the central periods of the upper part (6) and the lower part (8) of the blazed grating (3) are the same and are the same as the central period of the secondary phase grating (2); the orders of the upper part (6) and the lower part (8) of the blazed grating (3) are +1 and -1 respectively and correspond to the -1 diffraction order and +1 diffraction order of the secondary phase grating (2) respectively; the middle part (7) of the blazed grating (3) is a grating-free stripe area, that is, a 0-order grating-free dispersion area.

3. The method for correcting chromatic aberration of a tomographic microscope according to claim 2, wherein: The blazed grating (3) is placed at the object side focal plane of the tube lens (5), and the CCD detector (12) is placed at the image side focal plane of the tube lens (5); a distance is left between the secondary phase grating (2) and the blazed grating (3).

4. The method for correcting chromatic aberration of a tomographic microscope according to claim 3, wherein: The distance between the secondary phase grating (2) and the blazed grating (3) is adjusted according to the size of the object line field of view.

5. The method for correcting chromatic aberration of a tomographic microscope according to any one of claims 1 to 4, characterized in that: Assume that the aperture of the blazed grating (3) is , the incident angle of the edge field principal ray on the secondary phase grating (2) is θ , the spacing between the secondary phase grating (2) and the blazed grating (3) is L , in order to ensure that the three images entering the blazed grating (3) are separated from each other on the surface of the blazed grating (3), it is necessary to satisfy: 。 6. The method for correcting chromatic aberration of a tomographic microscope according to claim 5, characterized in that: Assume that the focal length of the microscope objective (1) is , the object side half-line field of view is y: .

7. The method for correcting chromatic aberration of a tomographic microscope according to claim 6, characterized in that: Assume that the aperture of the microscope objective (1) is D , the object numerical aperture of the microscope is : .

8. The method for correcting chromatic aberration of a tomographic microscope according to claim 7, characterized in that: 。 9. The method for correcting chromatic aberration of a tomographic microscope according to claim 8, wherein: Assume that the central wavelength of the incident light is λ , the central period of the secondary phase grating (2) is d , the diffraction angle of the edge field principal ray on the secondary phase grating (2) is : .

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