Reflection-mode dark-field imaging method and system based on fourier conjugate plane modulation

Abstract

The application relates to the field of optical imaging technology and discloses a reflection type dark field imaging method and system based on Fourier conjugate plane modulation, the method comprising the following steps: controlling a first spatial light modulator to load a dynamic ring-shaped illumination pattern and projecting the dynamic ring-shaped illumination pattern to a back focal plane of an objective lens; utilizing the objective lens to separate light field distribution formed by scattered signal light and ring-shaped reflected light at the back focal plane; relaying the light field distribution to a conjugate plane where a second spatial light modulator is located through a second relay optical path; and controlling the second spatial light modulator to load a dynamic blocking pattern, shielding the ring-shaped reflected light and making the scattered signal light pass through, and finally imaging. Through the adoption of two electronic synchronous spatial light modulators, dynamic illumination light field and adaptive spatial filtering are respectively constructed, the illumination pattern and the blocking pattern are matched in cooperation, optical chromatic aberration is actively compensated, the problem of background leakage under wide spectrum illumination is solved, and a high numerical aperture objective lens lacking a dark field channel is compatible.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical imaging technology, in particular to a reflection type dark field imaging method and system based on Fourier conjugate plane modulation. BACKGROUND

[0002] Reflection type dark field imaging is an optical microscopy technique, the core of which is to collect only the scattered signal light generated by the microstructure of the sample, while blocking the strong background reflected light from the sample surface, thereby highlighting the sample information on a dark background. Fourier optical principle reveals that the back focal plane of the objective lens is the Fourier transform plane of the sample plane. On this Fourier transform plane, the scattered signal light and the background reflected light of the sample will be separated in space according to the spatial frequency characteristics.

[0003] The existing reflection type dark field imaging technology mainly relies on specific optical hardware configuration to realize the separation of the illumination beam and the collection light path. A mainstream commercial solution adopts a special objective lens with a built-in dark field channel, and uses the annular mirror structure integrated in the objective lens to form a hollow light cone illumination. Other technical solutions are realized by arranging optical elements outside the objective lens, such as using a reflective parabolic condenser to illuminate the sample from the side at a large angle, or using an annular diaphragm in the condenser system to form a transmission type dark field. In addition, there are integrated optical path designs that realize dark field function by mechanically switching light blocking plates or adding external lens barrels.

[0004] The deficiencies of the prior art are due to the dependence of the implementation method on specific hardware configuration and physical space. On the one hand, the most optimal commercial dark field module solution binds the function with the depth of the objective lens, resulting in the fact that the commercial solution cannot be applied to conventional objective lenses that do not integrate the dark field channel. On the other hand, the solution using external illumination has strict requirements on the working distance of the objective lens. The working distance of a high numerical aperture objective lens is usually very short, and this physical limitation will cause the external illumination light path to be blocked by the objective lens housing and fail. The above dependence on the type or working distance of the objective lens ultimately results in the fact that many high numerical aperture, short working distance objective lenses, especially high performance oil immersion objective lenses, cannot realize reflection type dark field imaging, forming a technical deficiency. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a reflection type dark field imaging method based on Fourier conjugate plane modulation, aiming to solve the problem that the existing dark field technology relies on specific objective lens hardware or working distance, resulting in the inability to be compatible with high numerical aperture objective lenses, especially high performance oil immersion objective lenses.

[0006] To achieve the above purpose, the present application is implemented by the following technical solutions:

[0007] The present application provides a reflection type dark field imaging method based on Fourier conjugate plane modulation.

[0008] The core idea of the method is to use Fourier optics principle, replace the static physical mask with a programmable spatial light modulator on the back focal plane (Fourier transform plane) of the objective lens and its conjugate plane, to realize the double dynamic spatial modulation of the illumination light field and the imaging light field. The method comprises:

[0009] The first spatial light modulator is controlled to load a dynamic annular illumination pattern, and the dynamic annular illumination pattern is projected to the back focal plane of the objective lens through the first relay optical path. The objective lens performs inverse Fourier transform on the annular light field located on the back focal plane thereof, to form a hollow light cone illumination on the sample plane.

[0010] The step of controlling the first spatial light modulator to load a dynamic annular illumination pattern specifically comprises: according to the light wavelength information of the light source, actively adjusting the dynamic annular illumination pattern loaded on the first spatial light modulator, to compensate for the optical chromatic aberration of the objective lens.

[0011] Subsequently, the objective lens collects the scattered signal light and the annular reflected light generated by the sample, and performs Fourier transform again on the total collected light field. In this transformation, the scattered signal light carrying the high-resolution information of the sample is converged in the central region of the back focal plane of the objective lens; and the annular reflected light of the background interference is re-converged to the edge ring of the back focal plane of the objective lens. This step realizes the effective separation of the signal light and the background light in space on the back focal plane (Fourier plane).

[0012] Then, the second relay optical path relays the light field distribution on the back focal plane to the conjugate plane where the second spatial light modulator is located.

[0013] The key step of the method is to control the second spatial light modulator to load a dynamic blocking pattern. The pattern is matched with the illumination pattern and is configured to shield the annular reflected light (i.e. background) in the light field distribution with high precision, while allowing the scattered signal light (i.e. signal) in the central region to pass through.

[0014] The step of controlling the second spatial light modulator to load a dynamic blocking pattern specifically comprises: according to the pattern parameters on the first spatial light modulator, the first magnification of the first relay optical path and the second magnification of the second relay optical path, calculating and generating the dynamic blocking pattern.

[0015] Finally, the fifth lens converges the filtered scattered signal light, and generates a final dark-field image on the camera.

[0016] One core innovation point of the method is the dynamic chromatic aberration compensation and adaptive synchronous filtering mechanism.

[0017] In a preferred embodiment, to solve the chromatic aberration problem under wide spectrum illumination, the control system can actively and dynamically adjust the dynamic annular illumination pattern loaded on the first spatial light modulator according to the real-time light wavelength information of the light source (for example, obtained through a sensor or a preset value). For example, when the wavelength becomes shorter, the diameter of the illumination annular band is correspondingly reduced to ensure that the light of different wavelengths forms the same parameter hollow cone illumination on the sample plane after being dispersed by the objective lens. This step realizes active chromatic aberration compensation on the illumination side.

[0018] To respond to the dynamic adjustment on the illumination side and realize accurate background suppression, the step of loading the dynamic blocking pattern on the second spatial light modulator must work in coordination with the first spatial light modulator. Specifically, the control system can calculate and generate the matching dynamic blocking pattern in real time through a preset function model according to the real-time pattern parameters on the first spatial light modulator, the first magnification of the first relay optical path, and the second magnification of the second relay optical path.

[0019] This electronic synchronization mechanism of the illumination pattern and the blocking pattern is the key to distinguish the present application from the prior art. It ensures that the blocking annular band on the filtering side can always accurately match the changes in the illumination annular band due to chromatic aberration compensation (or switching of the objective lens) in real time, thereby effectively shielding the strong background reflected light and maintaining a very high background suppression ratio under wide spectrum conditions.

[0020] To further optimize the system performance, the present application also provides the following technical solutions:

[0021] In an embodiment, the values of the first magnification (illumination relay) and the second magnification (imaging relay) can be set to be unequal. This asymmetric magnification design provides an additional optimization degree of freedom for the system, for example, when the pixel size or effective area of the first and second spatial light modulators are different, the optical flux and resolution of the two can be matched through the asymmetric magnification design.

[0022] To ensure that the real dark field condition (i.e., the illumination light does not directly enter the detector) is realized, when the dynamic annular illumination pattern is projected to the back focal plane of the objective lens, its spatial frequency (i.e., the position of the annular band) needs to meet strict constraint conditions:

[0023] The numerical aperture of the inner edge of the dynamic annular illumination pattern after being projected through the first relay optical path must be greater than the nominal collection numerical aperture of the objective lens.

[0024] At the same time, its outer edge does not exceed the physical aperture of the back focal plane of the objective lens.

[0025] In a preferred optical path configuration, a light splitting element can be used to spatially separate the illumination path from the imaging path. For example, a polarizing beam splitter can be used as the light splitting element to reflect the dynamic annular illumination pattern to the back focal plane of the objective lens. Meanwhile, a quarter wave plate is arranged between the polarizing beam splitter and the objective lens. After the illumination light passes through the quarter wave plate twice, its polarization state is rotated by 90 degrees, so that it can efficiently pass through the polarizing beam splitter and enter the second relay optical path, achieving efficient separation of the illumination light and the signal light.

[0026] In the imaging step, the second spatial light modulator (i.e., the Fourier filtering plane) can be precisely arranged on the front focal plane of the fifth lens. According to Fourier optics, the fifth lens will perform inverse Fourier transform on the scattered signal light (i.e., the filtered Fourier spectrum) from its front focal plane, thereby reconstructing the real-space dark-field image of the sample on the camera.

[0027] The first spatial light modulator and the second spatial light modulator can be selected from liquid crystal spatial light modulators (LC-SLMs) or digital micromirror devices (DMDs) with fast response speed and high resolution, to achieve high-speed dynamic pattern loading and cooperation.

[0028] The second aspect of the present application provides a reflection-type dark-field imaging system based on Fourier conjugate plane modulation, which is configured to perform the above method, and the system comprises:

[0029] a dynamic illumination module configured to control the first spatial light modulator to load a dynamic annular illumination pattern and project the pattern to the back focal plane of the objective lens through the first relay optical path;

[0030] The dynamic illumination module is configured to actively adjust the dynamic annular illumination pattern loaded on the first spatial light modulator according to the light wavelength information of the light source, to compensate for the optical chromatic aberration of the objective lens.

[0031] a light field separation and relay module configured to use the objective lens to spatially separate the scattered signal light and the annular reflected light on the back focal plane of the objective lens, form a light field distribution, and relay the light field distribution to the conjugate plane through the second relay optical path;

[0032] an adaptive filtering and imaging module configured to control the second spatial light modulator arranged on the conjugate plane to load a dynamic blocking pattern, to filter out the annular reflected light and allow the scattered signal light to pass through, and to generate a final dark-field image on the camera through the fifth lens;

[0033] The adaptive filtering and imaging module is configured to calculate and generate the dynamic blocking pattern according to the pattern parameters on the first spatial light modulator, the first magnification of the first relay optical path, and the second magnification of the second relay optical path.

[0034] The cooperative control system is configured to generate a first control signal according to wavelength information of a light source to control the dynamic illumination module, and in response to a change in the first control signal, to generate a second control signal in real time to control the adaptive filtering and imaging module, so as to realize electronic synchronization of the dynamic annular illumination pattern and the dynamic blocking pattern.

[0035] In summary, by using two spatial light modulators that are electronically synchronized, the dynamic illumination and adaptive filtering are realized on the Fourier conjugate plane of the objective lens, which not only overcomes the limitations of a static mask, but more importantly, provides an effective way to actively compensate for optical chromatic aberration, and can maintain a very high background suppression effect when a wide-spectrum light source is used.

[0036] The application provides a reflection type dark field imaging method and system based on Fourier conjugate plane modulation.

[0037] 1、The application introduces a first spatial light modulator and a second spatial light modulator, and configures a cooperative control system, so that the dynamic annular illumination pattern on the first spatial light modulator can be actively adjusted according to the wavelength information of the light source, and a matching dynamic blocking pattern can be calculated and generated in real time and loaded to the second spatial light modulator. This mechanism realizes electronic synchronization of the illumination pattern and the blocking pattern, solves the problem of background leakage caused by optical chromatic aberration under wide-spectrum illumination of a traditional fixed mask, and can maintain a high signal-to-noise ratio under wide-spectrum conditions compared with the prior art.

[0038] 2、The application uses programmable spatial light modulators to replace static physical masks, which are respectively used to construct dynamic illumination and realize adaptive filtering. This design enables the adjustment of the illumination numerical aperture and the filtering numerical aperture (for example, the setting of the inner diameter and the outer diameter of the ring) to be completed by modifying the pattern parameters in real time through the control system without the need to replace any physical hardware. This way improves the adaptability of the system to different objective lenses and different samples, and simplifies the process of optical path calibration and experimental operation.

[0039] 3、The application adopts an optical structure comprising a first relay optical path and a second relay optical path, and allows the first magnification of the first relay optical path and the second magnification of the second relay optical path to take different values. This asymmetric magnification design provides independent optimization degrees of freedom for the illumination light path and the imaging filter light path, for example, the magnification can be adjusted to match the different pixel sizes or effective areas of the two spatial light modulators, thereby optimizing the light energy utilization efficiency and the quality of the projected pattern while ensuring the system resolution. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A flow chart of the method of the application;

[0041] Figure 2 A system framework diagram of the application;

[0042] Figure 3 A dark field scattering light path diagram of the application;

[0043] Figure 4 A comparison diagram of bright field and dark field imaging effects of the application and a commercial objective lens;

[0044] wherein, Figure 4 a-f are the imaging effects of a commercial Olympus objective lens (100x / 0.9NA), Figure 4 g-l are the imaging effects of the application combined with an objective lens (50x / 0.95NA); specifically, Figure 4 a, c, e and Figure 4 g, i, k are bright field images, Figure 4 b, d, f and Figure 4 h, j, l are dark field images; in addition, Figure 4 a, b, g, h, the samples shown in a, b, g, h are 150nm gold ball particles;

[0045] Figure 5 A bright field and dark field imaging effect diagram of the application under an oil immersion objective lens;

[0046] wherein, the left image is the bright field imaging effect under the oil immersion objective lens, and the right image is the dark field imaging effect under the oil immersion objective lens.

[0047] wherein, 1, light source; 2, optical fiber; 3, collimating lens; 4, first spatial light modulator; 5, first lens; 6, second lens; 7, objective lens; 8, light splitting element; 9, third lens; 10, fourth lens; 11, second spatial light modulator; 12, fifth lens; 13, camera. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the specification of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0049] Please refer to the drawings in the specification of the present application Figures 1-5 The embodiment of the present application provides a reflection type dark field imaging method based on Fourier conjugate plane modulation, comprising the following steps:

[0050] S1: Construction and projection of a dynamic annular illumination field

[0051] The first spatial light modulator 4 is controlled to load an annular illumination pattern. The loaded annular illumination pattern can be further actively adjusted based on the wavelength information of the light source 1 to compensate for the optical chromatic aberration of the objective lens 7.

[0052] The dynamically adjusted annular illumination pattern is reflected by the light splitting element 8 through the first relay optical path composed of the first lens 5 and the second lens 6, is projected and imaged to the back focal plane of the objective lens 7. The objective lens 7 performs Fourier transform on the annular illumination field on the back focal plane to form a hollow light cone illumination in the sample plane.

[0053] The step of controlling the first spatial light modulator to load a dynamic annular illumination pattern specifically comprises: actively adjusting the dynamic annular illumination pattern loaded on the first spatial light modulator according to the light wavelength information of the light source, to compensate for the optical chromatic aberration of the objective lens;

[0054] S2: Collection and Fourier transform separation of sample light field

[0055] Based on the hollow light cone illumination formed in the S1 step, the objective lens 7 collects the scattering signal light and the annular reflected light generated by the sample. The objective lens 7 performs Fourier transform again on the total collected light field to form a light field distribution on the back focal plane BFP of the objective lens 7. In the light field distribution, the scattering signal light is concentrated in the central region, and the annular reflected light is distributed in the edge annular band.

[0056] S3: Light field relay and adaptive spatial filtering

[0057] Based on the light field distribution formed on the back focal plane BFP in the S2 step, the light field distribution is relayed and imaged to the conjugate plane where the second spatial light modulator 11 is located through the second relay optical path composed of the third lens 9 and the fourth lens 10.

[0058] The magnification of the second relay optical path can be set independently of the magnification of the first relay optical path to achieve asymmetric amplification. In cooperation with the annular illumination pattern loaded in the S1 step, the second spatial light modulator 11 is controlled to load a dynamic blocking pattern that is electronically synchronized and matched with it. The blocking pattern is used to block the annular reflected light of the relay imaging, and allows the signal light in the central region to pass through.

[0059] The step of controlling the second spatial light modulator to load a dynamic blocking pattern specifically includes: calculating and generating the dynamic blocking pattern according to the pattern parameters on the first spatial light modulator, the first magnification of the first relay optical path, and the second magnification of the second relay optical path;

[0060] S4: The dark field image is generated based on the filtered signal light obtained in the S3 step, the signal light is converged by the fifth lens 12, and the final dark field image is generated on the photosensitive surface of the camera 13.

[0061] The contents of the steps of the method of the present application will be described in detail below:

[0062] The step S1 of the method of the embodiment of the present application, i.e. the construction and projection of the dynamic annular illumination field, will be described in detail below.

[0063] Specifically, the step S1 includes the following sub-steps:

[0064] In S101, first, the light from the light source 1 is transmitted through an optical fiber 2, and the light beam is collimated into a parallel light beam by a collimating lens 3. The parallel light beam then enters the position of the first spatial light modulator 4, and a digital annular illumination pattern is loaded on the first spatial light modulator 4 through a control system.

[0065] The first spatial light modulator 4 is a programmable optical element, such as a liquid crystal spatial light modulator LC-SLM or a digital micromirror device DMD. The control system inputs a digital mask signal to the first spatial light modulator 4 to control the light transmittance or reflection state of each pixel point thereon, thereby forming an annular transparent region with a specific inner diameter and an outer diameter The remaining area is not transparent or deflects the light out of the optical path. The inner diameter and the outer diameter can be dynamically adjusted in real time by the control system as needed.

[0066] In an embodiment, when a light source 1 or other wide-spectrum light source is used, the objective lens 7 will exhibit chromatic aberration, i.e. different wavelengths The effective position or magnification of the light on the back focal plane BFP of the objective 7 differs for different wavelengths. To compensate for this chromatic aberration, the control system can store the chromatic aberration data of the objective 7 in advance. In a preferred embodiment, the chromatic aberration data can be obtained by a pre-calibration step, for example by testing the light of different wavelengths one by one and recording the parameters of the best annular spot on the BFP.

[0067] In operation, the control system adjusts the diameter of the annular pattern loaded on the first spatial light modulator 4 according to the wavelength of the light emitted by the light source 1 information, by means of a filter wheel or tunable light source synchronized with the light source 1, the current wavelength is obtained, and the diameter of the annular pattern loaded on the first spatial light modulator 4 is actively adjusted so that the inner diameter and the outer diameter become a function of the wavelength, i.e. and In this way, it is ensured that the light of different wavelengths, after being projected, can all form annular spots on the correct position of the back focal plane BFP of the objective 7, which meet the dark-field condition.

[0068] In another embodiment, the method of the present application is also applicable to monochromatic light sources (such as lasers or multi-color discrete light sources), in which case the dynamic programmability of the first spatial light modulator 4 can be used to change the numerical aperture NA of the illumination ring in real time according to experimental requirements, without the need for chromatic aberration compensation.

[0069] In S102, the dynamic annular illumination pattern formed on the first spatial light modulator 4 is projected to the back focal plane of the objective 7 through the first relay optical path.

[0070] The first relay optical path comprises a first lens 5 with a focal length of and a second lens 6 with a focal length of .

[0071] In an embodiment, the first lens 5 and the second lens 6 can be a single lens (such as a plano-convex lens), but in a preferred embodiment, the first lens 5 and / or the second lens 6 can be an achromatic lens or a more complex lens group to reduce the chromatic aberration and aberration of the relay optical path itself.

[0072] The first spatial light modulator 4 is arranged on the front focal plane of the first lens 5. The distance between the first lens 5 and the second lens 6 is set to the sum of the focal lengths of the two lenses .

[0073] The back focal plane BFP of the objective 7 coincides with the back focal plane of the second lens 6.

[0074] The illumination projection magnification of this first relay optical path is defined as follows:

[0075] ;

[0076] wherein The magnification of the first relay optical path composed of the first lens 5 and the second lens 6; The focal length of the first lens 5; The focal length of the second lens 6.

[0077] In one embodiment, an asymmetric design can be adopted, i.e. For example, the following conditions can be set So that A reduced relay projection system is formed. The design of the reduced projection allows a larger physical size of the annular pattern to be generated on the first spatial light modulator 4, and more modulator pixels are used to define the annulus, thereby reducing the influence of pixelation on the quality of the projected light ring.

[0078] To achieve effective dark-field illumination, the size of the annular light spot projected onto the back focal plane of the objective 7 needs to match the back aperture of the objective 7 (i.e. the back hole). Assuming that the back aperture of the objective 7 is D3, and the corresponding diameter of the nominal collection numerical aperture NA (i.e. the central signal collection region outside which the dark-field illumination light ring must be projected) on the back focal plane is Then the parameters of the annular pattern loaded on the first spatial light modulator 4 , and the focal length parameters of the first relay optical path , need to satisfy the following constraint conditions:

[0079] ;

[0080] ;

[0081] In the formula, is the inner diameter of the annular pattern on the first spatial light modulator 4; is the outer diameter of the annular pattern on the first spatial light modulator 4; is the physical aperture of the back focal plane of the objective 7; is the diameter corresponding to the nominal collection numerical aperture of the objective 7; is the focal length of the first lens 5; is the focal length of the second lens 6.

[0082] Satisfying the above conditions can ensure that the illumination numerical aperture corresponding to the inner edge of the projected ring is greater than the collection numerical aperture of the objective, and the outer edge of the projected ring does not exceed the physical aperture of the objective.

[0083] In S103, the objective 7 Fourier transforms the annular illumination field on the back focal plane to form a hollow cone illumination on the sample plane.

[0084] The back focal plane BFP of the objective 7 is the Fourier conjugate plane of the sample plane. According to the principle of Fourier optics, the annular light field distribution on the back focal plane, after the Fourier transform action of the objective 7, will form a converging hollow light cone illumination on the front focal plane of the objective 7, i.e. the sample plane.

[0085] The convergence angle of the hollow light cone is determined by the size of the projected ring. Since the light cone is hollow, the illumination beam does not directly enter the collection aperture of the objective 7, thereby creating the necessary illumination conditions for subsequent dark-field imaging.

[0086] Specifically, step S2 includes the following sub-steps:

[0087] At S201, the sample located in the sample plane interacts with the hollow light cone illumination formed in step S1. The objective 7 is responsible for collecting the total light field returned from the sample plane.

[0088] The total collected light field collected in S201 generally contains two main components:

[0089] The first part is the scattered signal light. The scattered signal light is formed by the scattering, diffraction or refraction of the illumination light cone by the microstructure of the sample, and carries the structural information of the sample.

[0090] The second part is the annular reflected light. The annular reflected light is formed by the direct reflection of the illumination light cone by the optical interface of the sample surface or sample slide, and is regarded as background interference light in the present application.

[0091] At S202, the objective 7 performs a second Fourier transform on the total collected light field collected in S201.

[0092] Since the back focal plane BFP of the objective 7 and the front focal plane sample plane are Fourier conjugate planes, the total light field returned in S201 is transformed by the objective 7 to form a separation distribution based on spatial frequency space again on the back focal plane BFP.

[0093] Specifically, the first part of the scattered signal light is mainly composed of a low numerical aperture scattering component. According to the principle of Fourier optics, the low numerical aperture scattered signal light is converged to the central region on the back focal plane BFP, i.e. within the nominal collection aperture defined by the diameter in the S1 step.

[0094] At the same time, the second part of the annular reflected light retains the high numerical aperture characteristic of the hollow light cone illumination in the S1 step. The high numerical aperture annular reflected light is re-converged to the edge ring region of the back focal plane BFP after the Fourier transform action of the objective 7.

[0095] The position and size of the edge annulus region are determined by the pattern parameters D1, D2 loaded on the first spatial light modulator 4 in the S1 step and the magnification of the first relay optical path are jointly determined.

[0096] The second Fourier transform performed by the objective 7 spatially separates the scattered signal light carrying the sample information from the background interfering annular reflected light in the edge annulus on the back focal plane BFP of the objective 7.

[0097] Specifically, the step S3 comprises the following sub-steps:

[0098] In S301, the total light field comprising the scattered signal light in the central region and the annular reflected light in the edge annulus on the back focal plane BFP of the objective 7 achieved in the S2 step passes through the light splitting element 8 and enters the subsequent adaptive filtering optical path.

[0099] In one embodiment, the light splitting element 8 can be a non-polarization splitting cube NPBS or a broadband thin film light splitting element.

[0100] In a preferred embodiment, when the first spatial light modulator 4 and / or the second spatial light modulator 11 is a polarization-sensitive element such as LCOS-SLM, the light splitting element 8 is preferably a polarization beam splitter PBS.

[0101] In this embodiment, a quarter-wave plate QWP can be additionally arranged between the light splitting element 8 and the objective 7 to convert the linearly polarized illumination light reflected through the PBS in the step S1 into circularly polarized light. After being reflected by the sample, the circularly polarized light passes through the quarter-wave plate again, and the polarization state is rotated by 90 degrees to become linearly polarized light, which is then transmitted by the polarization beam splitter PBS, thereby ensuring the optical path efficiency of the steps S2 and S3.

[0102] In S302, the total light field passing through the light splitting element 8 enters a second relay optical path. The function of the second relay optical path is to relay and image the back focal plane BFP of the objective 7 to the conjugate plane where the second spatial light modulator 11 is located.

[0103] In one embodiment, the second relay optical path comprises a third lens 9 with a focal length of and a fourth lens 10 with a focal length of to form a relay system. Similar to the first relay optical path, the third lens 9 and the fourth lens 10 can preferably be achromatic lenses or lens groups to ensure that the back focal plane BFP of the objective 7 can be relayed and imaged with high fidelity and without chromatic aberration onto the second spatial light modulator 11.

[0104] The back focal plane BFP of the objective 7 is located on the front focal plane of the third lens 9. The second spatial light modulator 11 is disposed on the back focal plane of the fourth lens 10. The distance between the third lens 9 and the fourth lens 10 is set as the sum of the focal lengths of the two lenses .

[0105] The filtered projection magnification of the second relay optical path is defined as follows:

[0106] ;

[0107] wherein, is the magnification of the second relay optical path composed of the third lens 9 and the fourth lens 10; is the focal length of the third lens 9; is the focal length of the fourth lens 10.

[0108] In one embodiment, the value of is different from the value of (i.e. ), to achieve the asymmetric magnification design of the illumination optical path and the imaging filtered optical path, providing additional degrees of freedom for system optimization such as matching different element pixel sizes.

[0109] In S303, a control system (which can be the same system as in S101) loads a digital dynamic blocking pattern to the second spatial light modulator 11.

[0110] The second spatial light modulator 11 is a programmable optical element, such as a liquid crystal spatial light modulator LC-SLM or a digital micromirror device DMD.

[0111] The dynamic blocking pattern is functionally matched with the annular illumination pattern loaded on the first spatial light modulator 4 in S1.

[0112] Specifically, the dynamic blocking pattern is an annular region that is opaque or deflects light out of the optical path, used to accurately block the annular reflected light in the relay imaging in S302. At the same time, the central region of the dynamic blocking pattern remains transparent to allow the scattered signal light in the relay imaging in S302 to pass unhindered.

[0113] In S304, the control system performs electronic synchronization control on the first spatial light modulator 4 and the second spatial light modulator 11.

[0114] When the parameters (e.g. ) of the annular illumination pattern are actively adjusted in S1 step to compensate for chromatic aberration or other purposes, the position of the annular reflected light on the BFP in S2 step will also change.

[0115] At this time, the control system will calculate the matching blocking pattern parameters according to the change of the illumination pattern in S1, and update the dynamic blocking pattern loaded on the second spatial light modulator 11 in real time.

[0116] Specifically, the inner and outer diameter parameters of the blocking pattern loaded on the second spatial light modulator 11 are functions of the pattern parameters on the first spatial light modulator 4, the magnification of the first relay optical path and the magnification of the second relay optical path .

[0117] This synchronous control mechanism ensures that the illumination annulus and the blocking annulus are always accurately matched in the optical path, thereby realizing adaptive spatial filtering and effectively removing the background interference annular reflected light, and only retaining the scattered signal light carrying sample information.

[0118] Specifically, step S4 includes the following sub-steps:

[0119] In S401, only the scattered signal light carrying sample information is emitted from the second spatial light modulator 11 after being dynamically filtered by the second spatial light modulator 11 in the S3 step.

[0120] As in S3, the second spatial light modulator 11 is located on a conjugate plane, so the light field emitted from the second spatial light modulator 11 is the filtered spatial frequency spectrum k-space of the sample.

[0121] In S402, the emitted scattered signal light enters a fifth lens 12 for imaging. In an embodiment, the second spatial light modulator 11 is precisely arranged on the front focal plane of the fifth lens 12.

[0122] In S403, the fifth lens 12 performs an inverse Fourier transform on the scattered signal light from its front focal plane. According to the Fourier optics principle, the function of the fifth lens 12 is to convert the spatial frequency domain signal located on the Fourier conjugate plane in S401 back to the spatial domain real space, thereby reconstructing the real space image of the sample.

[0123] In S404, a camera 13 is arranged on the back focal plane of the fifth lens 12. The real space image formed by the inverse Fourier transform in S403, i.e. the magnified real image of the sample, is clearly imaged on the photosensitive plane of the camera 13. This photosensitive plane is the conjugate image plane of the sample plane S.

[0124] In an embodiment, the camera 13 can be a CCD charge-coupled device camera, a CMOS complementary metal-oxide-semiconductor camera, or other high-speed and high-sensitivity photoelectric detection devices, for capturing the final image.

[0125] Due to the adaptive spatial filtering in S3, the high intensity annular reflected light background interference light has been completely filtered out from the optical path, thus only the scattered signal light carrying the sample microstructure information can reach the photosensitive plane of the camera 13 and participate in the imaging process in S403.

[0126] Finally, the camera 13 captures and generates a final dark-field image with dark background and bright signal on the photosensitive plane.

[0127] Total magnification of the whole imaging system , the focal length of the objective lens 7 and the focal length of the fifth lens 12 together determine, specifically expressed as:

[0128] ;

[0129] In the formula, is the total magnification of the whole imaging system; is the focal length of the fifth lens 12; is the focal length of the objective lens 7.

[0130] In summary, step S4 completes the conversion from the spatial frequency domain (i.e. the Fourier conjugate plane where the second spatial light modulator 11 in S401 is located) to the real space domain (i.e. the conjugate image plane where the camera 13 in S404 is located).

[0131] Referring to the accompanying drawings Figures 1-2 , the present application provides a reflection type dark-field imaging system based on Fourier conjugate plane modulation, which comprises:

[0132] a dynamic illumination module for receiving a first control signal and controlling the first spatial light modulator 4 to load a dynamic annular illumination pattern according to the first control signal, and then projecting the pattern to the back focal plane of the objective lens 7 through the first relay optical path composed of the first lens 5 and the second lens 6;

[0133] Wherein, the dynamic illumination module is configured to actively adjust the dynamic annular illumination pattern loaded on the first spatial light modulator 4 according to the light wavelength information of the light source 1 to compensate for the optical chromatic aberration of the objective lens 7;

[0134] a light field separation and relay module for performing Fourier transform on the illumination light and the collected sample light field from the dynamic illumination module by the objective lens 7, spatially separating the scattered signal light and the annular reflected light on the back focal plane BFP of the objective lens 7, and relaying the light field distribution on the back focal plane BFP to a conjugate plane through the second relay optical path composed of the third lens 9 and the fourth lens 10;

[0135] an adaptive filtering and imaging module for receiving the second control signal and controlling the second spatial light modulator 11 disposed on the conjugate plane to load a dynamic blocking pattern according to the second control signal, so as to filter out the annular reflected light and allow the scattered signal light to pass, and finally generate a final dark-field image on the camera 13 through the fifth lens 12;

[0136] wherein the adaptive filtering and imaging module is configured to calculate and generate the dynamic blocking pattern according to the pattern parameters on the first spatial light modulator 4, the first magnification of the first relay optical path, and the second magnification of the second relay optical path;

[0137] a cooperative control system for generating the first control signal according to the wavelength information of the light source 1 to compensate for the optical chromatic aberration of the objective lens 7, and in response to the change of the first control signal, generating a matching second control signal in real time to realize the electronic synchronization of the dynamic annular illumination pattern and the dynamic blocking pattern.

Claims

1. A reflective dark-field imaging method based on Fourier conjugate surface modulation, characterized in that, include: A dynamic ring illumination pattern is loaded by controlling the first spatial light modulator, and the dynamic ring illumination pattern is projected onto the back focal plane of the objective lens through the first relay optical path to form a hollow light cone illumination on the sample plane. The step of controlling the first spatial light modulator to load a dynamic ring illumination pattern specifically includes: actively adjusting the dynamic ring illumination pattern loaded on the first spatial light modulator according to the light wavelength information of the light source to compensate for the optical chromatic aberration of the objective lens; The objective lens is used to collect the scattered signal light and the ring-shaped reflected light generated by the sample, and the scattered signal light and the ring-shaped reflected light are spatially separated according to spatial frequency on the back focal plane of the objective lens to form a light field distribution; The light field distribution is relayed and imaged onto the conjugate plane where the second spatial light modulator is located via the second relay optical path; The second spatial light modulator is controlled to load a dynamic blocking pattern as an adaptive spatial filter to block the annular reflected light in the light field distribution and allow the scattered signal light to pass through; The step of controlling the second spatial light modulator to load a dynamic blocking pattern specifically includes: calculating and generating the dynamic blocking pattern based on the pattern parameters on the first spatial light modulator, the first amplification of the first relay optical path, and the second amplification of the second relay optical path; The scattered signal light, after being converged and filtered by the fifth lens, undergoes an inverse Fourier transform, generating the final dark-field image on the camera.

2. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 1, characterized in that, The values ​​of the first magnification and the second magnification are not equal.

3. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 1, characterized in that, When the dynamic annular illumination pattern is projected onto the back focal plane of the objective lens, the following constraints are satisfied: After the dynamic ring illumination pattern is projected through the first relay optical path, the illumination numerical aperture corresponding to the inner edge is larger than the nominal collection numerical aperture of the objective lens. After the dynamic ring illumination pattern is projected through the first relay optical path, its outer edge does not exceed the physical aperture of the back focal plane of the objective lens.

4. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 1, characterized in that, The method further includes: A beam splitter is used to reflect the dynamic ring illumination pattern to the back focal plane of the objective lens; The light field distribution passes through the beam splitter and enters the second relay optical path.

5. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 4, characterized in that, The beam splitting element is configured as a polarizing beam splitter, and a quarter-wave plate is arranged between the polarizing beam splitter and the objective lens.

6. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 1, characterized in that, The specific steps of performing an inverse Fourier transform on the scattered signal light after it has been converged and filtered by the fifth lens include: The second spatial light modulator is positioned on the front focal plane of the fifth lens; The fifth lens performs an inverse Fourier transform on the scattered signal light from its front focal plane.

7. The reflective dark-field imaging method based on Fourier conjugate surface modulation according to claim 1, characterized in that, At least one of the first spatial light modulator and the second spatial light modulator is a liquid crystal spatial light modulator or a digital micromirror device.

8. A reflective dark-field imaging system based on Fourier conjugate surface modulation, characterized in that, include: The dynamic illumination module is configured to: control the first spatial light modulator to load a dynamic ring illumination pattern, and project the pattern onto the back focal plane of the objective lens through the first relay optical path; The dynamic illumination module is configured to actively adjust the dynamic ring illumination pattern loaded on the first spatial light modulator according to the light wavelength information of the light source, so as to compensate for the optical chromatic aberration of the objective lens. The light field separation and relay module is configured to: use the objective lens to spatially separate the scattered signal light and the ring-shaped reflected light on the back focal plane of the objective lens to form a light field distribution, and relay the light field distribution to the conjugate plane through the second relay optical path; The adaptive filtering and imaging module is configured to: control a second spatial light modulator deployed on the conjugate plane to load a dynamic blocking pattern as an adaptive spatial filter and perform an inverse Fourier transform on the filtered scattered signal light through a fifth lens to generate the final dark field image on the camera; The adaptive filtering and imaging module is configured to calculate and generate the dynamic blocking pattern based on the pattern parameters on the first spatial light modulator, the first magnification of the first relay optical path, and the second magnification of the second relay optical path. The collaborative control system is configured to: generate a first control signal based on the wavelength information of the light source, control the dynamic lighting module, and generate a matching second control signal in real time in response to changes in the first control signal.

Images