CN114322863A - A method for far-field illumination and detection of objects that break the diffraction limit - Google Patents

Abstract

An embodiment of the present application provides a method for far-field illumination and detection of an object that breaks through the diffraction limit. The method includes: a wave source emits a wave to the object, the wave is scattered by the object to generate an evanescent field, and is excited by the evanescent field to generate a transmittable field. To the wave signal in the far field, there is a corresponding relationship between the characteristic size of the object and the time-varying wave intensity of the wave signal; the wave intensity detector detects the time-varying wave intensity; the computing unit obtains the time-varying wave intensity and correspondence and determine the characteristic size of the object based on the two. The technical solutions of the embodiments of the present application break through the limitation of diffraction effects, and objects of any size can be detected based on the above correspondence.

Description

A method for far-field illumination and detection of objects that break the diffraction limit

technical field

The invention relates to the field of object detection, in particular to a method for far-field super-resolution detection of microscopic objects that break through the diffraction limit.

Background technique

When the object is detected, the high spatial frequency information of the detected object less than one-half wavelength (also known as the information beyond the diffraction limit) is carried by the evanescent field, but this evanescent field is limited to the detected object. near the surface and cannot propagate into the far field. Therefore, the limit of spatial imaging resolution that can be detected by the usual far-field detection technology is about half the wavelength of the incident wave.

Existing technologies for detecting information beyond the diffraction limit of objects mainly include near-field scanning microscopy, superlens detection technology based on artificial microstructure materials, and fluorescence microscopy detection based on fluorescent labels.

In near-field scanning microscopy, the wave source or detector is placed in the near field of the detected object, and the evanescent field of the detected object is scanned point by point in the near field, which not only makes the imaging speed slow, but also inevitably destroys the need for The information of the detected target object is prone to false images.

In the detection technology based on the artificial microstructure material superlens, the lens is placed in the near field of the detected object, so that the detected object needs to be placed close to the lens; , the achievable spatial resolution is strictly limited by the fine microstructure of the lens, its complexity (limited by micromachining techniques), absorption losses, etc.

In fluorescence microscopy based on fluorescent labeling, the nonlinear effects of materials are exploited, high power lasers and nonlinearly responsive materials (fluorescent labels) are required; and point-to-point scanning or the capture of hundreds or thousands of raw images is required for imaging reconstruction, resulting in a complex and slow imaging process.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is that the existing technology for detecting information beyond the diffraction limit of an object has the disadvantages of slow detection speed, easy generation of false images, spatial resolution limited by the fine microstructure of the lens, etc., and the need to use nonlinear materials and high-power lasers. and other defects.

In order to solve the above technical problems, the embodiments of the present invention provide a method for far-field illumination and detection of objects that break through the diffraction limit. The field excitation generates a wave signal that can be transmitted to the far field, and there is a correspondence between the characteristic size of the object and the time-varying wave intensity of the wave signal; the wave intensity detector detects the time-varying wave intensity; the computing unit obtains the time-varying wave intensity; The varying wave intensities and correspondences and based on both determine the characteristic size of the object.

Optionally, the waves are electromagnetic waves, elastic waves or sound waves in any frequency band.

Optionally, both the wave source and the wave intensity detector are located in the far field, which is the region where the distance to the surface of the object is greater than the wavelength of the wave.

Optionally, the wave has a single wavelength, and the wavelength of the wave is a single wavelength; or, the wave includes a plurality of discrete wavelengths, and the wavelength of the wave is any one of the plurality of discrete wavelengths.

Optionally, the computing unit is adapted to perform Fourier transform on the time-varying wave intensity to obtain the characteristic vibration frequency, and obtain the characteristic size of the object based on the characteristic vibration frequency and the corresponding relationship, and the corresponding relationship is:

P _s =λ/(1+f _s /f ₀ ),

where P _s is the characteristic size, λ is the wavelength of the wave, f _s is the characteristic vibration frequency, and f ₀ is the center frequency of the wave.

Optionally, the above-mentioned method comprises: selecting the corresponding wave source based on the estimated size of the object; judging whether the characteristic vibration frequency can be obtained; if so, instruct the computing unit to calculate the characteristic size based on the characteristic vibration frequency and the corresponding relationship, if otherwise, select different. Wave source of wavelength, repeating the above judgment steps until the characteristic vibration frequency is obtained, and instructing the calculation unit to calculate the characteristic size based on the characteristic vibration frequency and the corresponding relationship.

Optionally, the characteristic size is the distance between adjacent parts of the surface of the object, or the actual size of the object.

Optionally, the feature size is the distance between two places inside the object, and the two places scatter the waves emitted by the wave source to obtain the corresponding evanescent field, which excites the corresponding wave signal propagating to the far field, and the time-varying wave signal is After the wave intensity is Fourier transformed, it has a characteristic vibration frequency in the frequency domain.

Optionally, the wave signal generated by the evanescent field excitation that can be transmitted to the far field is calculated by the formula of the complex amplitude of the wave signal as follows:

Among them, ψ _s (z, t) is the complex amplitude of the wave signal, i is the imaginary unit, t is the transmission time of the wave signal, z is the propagation distance of the wave signal, ω _s is the characteristic angular frequency of the wave signal, and ω is the wave source The angular frequency of , c is the transmission speed of the wave in free space, k _⊥ is the wave number of the evanescent field, Θ(tz/c) is the switching function, the switching function is 0 when t≦z/c When >z/c, the value is 1.

Compared with the prior art, the technical solutions of the embodiments of the present invention have at least the following beneficial effects.

For example, in the prior art, the wave emitted by the wave source to the object is scattered by the object to generate an evanescent field, which is located in the near field and thus cannot be detected in the far field. In the technical solution of the embodiment of the present invention, the wave emitted by the wave source to the object is scattered by the object to generate an evanescent field, which is excited to generate a wave signal that can be transmitted to the far field; due to the characteristic size of the object and the variation of the wave signal with time There is a correspondence between the varying wave intensities, so the characteristic size of the object can be determined based on the correspondence and the wave intensities detected by the wave intensity detector. The technical solution of the embodiment of the present invention can detect the wave signal excited by the evanescent field, which not only breaks through the limitation of the diffraction effect (super-diffraction limit), but also can detect an object of any size based on the above-mentioned corresponding relationship, for example, by detecting the object feature size.

For another example, in the existing near-field scanning microscopy technology, the wave source or detector needs to be placed in the near field of the object to be detected to directly detect the evanescent field. In the superlens detection technology based on artificial microstructured materials, it is necessary to The lens is placed in the near field of the object to be detected, and converts the evanescent field into a propagating field to the far field for detection; this makes it difficult to set up a wave source, detector or lens, and requires strict requirements on the fine microstructure of the lens, absorption loss, etc. , and the detection operation is complicated. In the technical solution of the embodiment of the present invention, the detection is excited by the evanescent field to generate a wave signal that can be transmitted to the far field. During the detection process, both the wave source and the detector can be placed in the far field, which makes the wave source The setup of the detector and the detector are easy, and the operation of the detector is simple.

For another example, in the existing fluorescence microscopy techniques, not only the nonlinear effects of materials are utilized, but high-power lasers and nonlinear response materials, such as fluorescent markers, are required, and there is no physical mechanism to detect super-resolution objects in principle; And it still needs to scan point-to-point or take hundreds or thousands of original images for image reconstruction, which makes the imaging process complicated and slow. However, in the technical solution of the embodiment of the present invention, without relying on additional marking materials and nonlinear effects, a linear method for detecting super-resolution objects is directly provided in principle.

Description of drawings

1 is a schematic structural diagram of a device for performing far-field illumination and detection on objects that break through the diffraction limit in an embodiment of the present invention;

2 is another schematic structural diagram of a device for performing far-field illumination and detection on objects that break through the diffraction limit in an embodiment of the present invention;

Fig. 3 is the schematic diagram of the wave intensity that changes with time and its corresponding frequency spectrum in the embodiment of the present invention;

4 is a schematic diagram of detecting the characteristic size of an object that breaks through the diffraction limit in an embodiment of the present invention, wherein the characteristic size represents the fluctuation of the surface of the object;

5 is a schematic diagram of detecting the characteristic size of an object that breaks through the diffraction limit in an embodiment of the present invention, wherein the characteristic size represents the actual size of the object;

6 is a schematic diagram of detecting the characteristic size of an object that breaks through the diffraction limit in an embodiment of the present invention, wherein the characteristic size represents the internal structure of the object;

FIG. 7 is a flowchart of a method for far-field illumination and detection of objects that break through the diffraction limit in an embodiment of the present invention.

Detailed ways

In order to make the above objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Embodiments of the present invention provide a device for far-field illumination and detection of objects that break through the diffraction limit.

As shown in Figures 1, 2, 4 to 6, devices 100, 200, 300, 400, 500 are used for far-field illumination and far-field detection of objects. The devices 100 , 200 , 300 , 400 , 500 may include a wave source 110 , a wave intensity detector 120 and a computing unit 130 .

The wave source 110 may emit waves towards the object.

A wave may have a single wavelength (ie, a wave having only one frequency), in which case the wavelength λ of the wave is the single wavelength. The wave may also include multiple discrete wavelengths (ie, waves having multiple frequencies), and in this case, the wavelength λ of the wave is any one of the discrete multiple wavelengths.

In a specific implementation, the wave source 110 can be an electromagnetic field source, and the waves it emits are electromagnetic waves, such as radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, and gamma rays; the waves emitted by the wave source 110 can also be elastic wave sources, which emit The waves are elastic waves, such as body waves and boundary waves; the waves emitted by the wave source 110 can also be sound wave sources, and the waves emitted by the wave source 110 are sound waves, such as infrasound waves, audible sound waves, ultrasonic waves, and supersonic waves.

The object scatters the waves emitted by the wave source 110, resulting in evanescent and propagating fields.

In the embodiment of the present invention, when the object scatters the waves emitted by the wave source 110, evanescent fields of different frequencies are generated, and the evanescent fields of different frequencies are excited and generate wave signals that can be transmitted to the far field, and the wave signals generate The principle can be expressed by the formula of the complex amplitude of the wave signal as follows:

Among them, ψ _s (z, t) is the complex amplitude of the wave signal, i is the imaginary unit, t is the transmission time of the wave signal, z is the propagation distance of the wave signal, ω _s is the characteristic angular frequency of the wave signal, and ω is the wave source The angular frequency of , c is the transmission speed of the wave in free space, k _⊥ is the wave number of the evanescent field, Θ(tz/c) is the switching function, the switching function is 0 when t≦z/c When >z/c, the value is 1.

The above formula establishes a correlation between an evanescent field (eg its wavenumber k _⊥ ) and its excitation-generated wave signal [eg, its complex amplitude ψ _s (z,t)] that can be transmitted to the far field.

In the above formula, when other parameters are known, as the propagation distance z of the wave signal increases gradually, the complex amplitude ψ _s (z, t) of the wave signal gradually decreases.

In the embodiment of the present invention, the scattering of the wave by the object includes transmission type scattering and reflection type scattering. Among them, the transmission type scattering means that the incident wave irradiates on the surface, edge or internal structure of the object and is scattered, and the wave generated after the scattering can pass through the object and reach the wave intensity detector 120 located on the back side of the object; the reflection type scattering means , after the incident wave is irradiated on the surface, edge or internal structure of the object, scattering occurs, and the wave generated after the scattering is reflected and reaches the wave intensity detector 120 located on the front side of the object.

As shown in FIG. 1 , the device 100 performs far-field illumination and far-field detection on the object 11 . The object 11 can scatter the waves in a transmission type, and the waves generated after the scattering pass through the object 11 and reach the wave intensity detector 120 located on the rear side of the object 11 .

As shown in FIG. 2 , device 200 performs far-field illumination and far-field detection of object 12 . The object 12 can perform reflective scattering on the waves, and the waves generated after the scattering pass through the object 12 and are reflected to reach the wave intensity detector 120 located on the front side of the object 12 .

The wave intensity detector 120 can detect a wave signal that is excited by the evanescent field to generate a wave signal that can be transmitted to the far field, and the wave signal is a time-varying wave intensity signal.

In some embodiments, the wave intensity detector 120 may be a known illuminometer, wave intensity meter, amplitude real part detection device, etc., which converts the wave intensity of the wave signal into a current of corresponding intensity, and based on the measured The current determines the size of the corresponding detected physical quantity.

The wave intensity detector 120 can also measure the wave intensities of different wavelengths (or different frequencies) respectively.

The wave intensity can vary with time, and the wave intensity detector 120 can detect the wave intensity in real time, so as to obtain the distribution of the wave intensity in the time domain.

In the embodiment of the present invention, the wave emitted by the wave source has a wavelength λ, a region with a distance to the surface of the detected object less than λ can be called a near field, and a region with a distance from the surface of the detected object greater than λ can be called a far field field.

When the apparatuses 100, 200, 300, 400, 500 perform far-field illumination and far-field detection on an object, the wave source 110 and the wave intensity detector 120 are both located in the far-field.

In one embodiment, as shown in sub-figure 3a of FIG. 3, the wave intensity detector 120 detects the time-varying distribution of the wave intensity in real time.

The time-varying wave intensity distribution can be Fourier transformed to obtain a frequency spectrum, the abscissa of which is the frequency domain corresponding to the wave intensity distribution, as shown in sub-figure 3b of FIG. 3 .

In this spectrum, there is a characteristic vibrational frequency f _s .

The object may be a solid or a liquid, wherein it may have a characteristic dimension P _s , which corresponds to the characteristic vibrational frequency f _s in the above-mentioned frequency spectrum.

The characteristic dimension _Ps of an object is less than the diffraction limit, eg its length, width, height, diameter or the distance between the two most distant points on its surface may be less than half the wavelength λ of the wave.

In some embodiments, the feature size P _s may represent the magnitude of the fluctuation of the surface of the object.

As shown in FIG. 4 , the device 300 performs far-field illumination and far-field detection of the object 13 . The surface of the object 13 has portions adjacent to each other, such as adjacent peaks A and valleys B, wherein the peaks A and the valleys B can be compared with each other so as to have opposite peaks and valleys, respectively . The peaks A and the valleys B adjacent to each other are similar to a grating structure, and the waves emitted by the wave source 110 are scattered to obtain a corresponding evanescent field, which excites a corresponding wave signal propagating to the far field, and the wave signal has a time-varying wave signal. The wave intensity of , which after Fourier transform, has a frequency (eigen vibration frequency) f _s of high amplitude in the frequency domain, as shown in FIG. 3 . The characteristic dimension P _s represents the distance between the peak A and the valley B, that is, the distance between the peak of the peak A and the valley bottom of the valley B.

In other embodiments, the characteristic size P _s may represent the actual size of the object.

As shown in FIG. 5 , device 400 performs far-field illumination and far-field detection of object 14 . The actual size of the object 14 can be represented by the edge locations C and D where its surfaces are farther or farthest apart. The object 14 is located between edge positions C and D, which is similar to a grating structure, and scatters the waves emitted by the wave source 110 to obtain a corresponding evanescent field, which excites a corresponding wave signal propagating to the far field, and the wave signal has a change in time. The changing wave intensity, which after Fourier transform, has a frequency (eigen vibration frequency) f _s with high amplitude in the frequency domain, is shown with reference to FIG. 3 . The characteristic size P _s represents the distance between the edge positions C and D, ie the actual size of the object 14 .

In yet other embodiments, the feature size _Ps may represent the internal structure of the object.

As shown in FIG. 6 , device 500 performs far-field illumination and far-field detection of object 15 . The two locations E, F inside the object 15 have different materials, densities, textures, concentrations or other physical properties. The part of the object 15 between the two places E and F is similar to a grating structure, and the wave emitted by the wave source 110 is scattered to obtain a corresponding evanescent field, which excites a corresponding wave signal propagating to the far field, and the wave signal has a corresponding evanescent field. The time-varying wave intensity, after Fourier transform, has a frequency (eigen vibration frequency) f _s with a high frequency amplitude in the frequency domain, as shown with reference to FIG. 3 . The feature size P _s represents the distance between the two locations E and F.

The above-mentioned embodiments related to the feature size P _s are described above with reference to FIGS. 4 to 6 . Although FIGS. 4 to 6 illustrate transmission-type scattering, it should be understood that the above-mentioned embodiments related to the feature size P _s can also be applied to reflective-type scattering scenarios. .

The computing unit 130 may acquire the time-varying wave intensity and the corresponding relationship and determine the feature size of the object based on the two.

In an embodiment of the present invention, there is a correspondence between the size of the object and the time-varying wave intensity of the wave signal.

Specifically, the calculation unit 130 may receive the time-varying wave intensity output by the wave intensity detector 120, and may perform Fourier transform on the time-varying wave intensity distribution to obtain a corresponding frequency spectrum. Therefore, the correspondence between the characteristic size of the object and the time-varying wave intensity of the wave signal can be expressed as the correspondence between the characteristic size of the object and the corresponding frequency spectrum, which is expressed by the following formula:

P _s =λ/(1+f _s /f ₀ ),

where P _s is the characteristic size, λ is the wavelength of the wave, f _s is the characteristic vibration frequency, and f ₀ is the center frequency of the wave.

When the wave has a single wavelength, the wavelength λ of the wave in the above formula takes the single wavelength. When the wave includes a plurality of discrete wavelengths, for example, λ ₁ and λ ₂ , the wavelength λ of the wave in the above formula can take any one of the plurality of discrete wavelengths, such as λ ₁ or λ ₂ .

The calculation unit 130 can obtain the corresponding relationship between the size of the object and the corresponding frequency spectrum or the corresponding relationship between the characteristic size P _s of the object and the characteristic vibration frequency f _s , and the corresponding relationship can be pre-stored in a memory, which can be set in the calculation unit 130 Internal or external. When the calculation unit 130 performs the calculation, the corresponding relationship can be read from the memory.

Theoretically, through the corresponding relationship between the characteristic size P _s of the object and the characteristic vibration frequency f _s , based on the wavelength λ of the wave emitted by the wave source 110, the characteristic vibration frequency f _s and the center frequency f ₀ of the wave, the calculation unit 130 can calculate any arbitrary The characteristic dimension P _s of an object of size.

In the detection of actual experiments, the characteristic size P _s of the detectable object is determined by the detection accuracy of the wave intensity detector 120 . According to the detection accuracy of the self-owned detector in this embodiment, the characteristic size P _s of the detectable object can reach one-sixth of the wavelength λ of the wave, breaking the diffraction limit (which is about one-half of the wavelength) .

In the numerical simulation experiment, the corresponding relationship between the characteristic size P _s of the object and the characteristic vibration frequency f _s is calculated, and the characteristic size P _s of the detectable object can reach one-thirtieth of the wavelength λ of the wave, which is far far beyond the diffraction limit.

During actual detection, the device for performing far-field illumination and far-field detection on an object may include a control unit, and the wave source may be selectively set. For example, several wave sources with different wavelengths can be controlled by the control unit to selectively emit waves to the object, and the control unit can select one of the wave sources to emit waves to the object.

Specifically, first, the size of the detected object can be estimated, and then the control unit selects a corresponding wave source based on the estimated size. For example, based on the input estimated size a of the detected object, the control unit selects a wave source whose emission wave has a wavelength of 2a.

Next, the control unit judges whether the characteristic vibration frequency f _s can be determined in the corresponding frequency spectrum obtained by Fourier transforming the wave intensity distribution. If the characteristic vibration frequency f _s can be determined, the control unit instructs the calculation unit to calculate the characteristic size P _s of the object based on the characteristic vibration frequency f _s and the corresponding relationship. If the characteristic vibrational frequency _fs cannot be determined, the control unit may select wave sources of different wavelengths; the control unit repeats this step until the characteristic vibrational frequency _fs can be determined in the frequency spectrum, and calculates the characteristic size of the object based on the characteristic vibrational frequency _fs P _s .

In the embodiment of the present invention, the computing unit 130 and the control unit may be processors, such as a central processing unit (Central Processing Unit, CPU), a general-purpose processor, a microprocessor, and a digital signal processor (Digital Signal Processor, DSP) , Application Specific Integrated Circuit (ASIC), off-the-shelf Programmable Gate Array (Field Programmable Gate Array, FPGA), other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components, etc.

Embodiments of the present invention also provide a method for far-field illumination and detection of objects that break through the diffraction limit.

As shown in FIG. 7 , the method 600 for far-field illumination and detection of objects that break through the diffraction limit includes: step S610, a wave source emits a wave to the object, the wave is scattered by the object to generate an evanescent field, and is excited by the evanescent field to generate a transmittable To the wave signal in the far field, there is a corresponding relationship between the characteristic size of the object and the wave intensity of the wave signal that changes with time; step S620, the wave intensity detector detects the wave intensity that changes with time; The time-varying wave intensities and correspondences and based on both determine the characteristic size of the object.

In a specific implementation, the method 600 may be performed based on any one of the above-mentioned devices 100 , 200 , 300 , 400 , and 500 .

In a specific implementation, the computing unit performs Fourier transform on the wave intensity that changes with time to obtain the characteristic vibration frequency, and the corresponding relationship is:

P _s =λ/(1+f _s /f ₀ ),

where P _s is the characteristic size, λ is the wavelength of the wave, f _s is the characteristic vibration frequency, and f ₀ is the center frequency of the wave.

In specific implementation, the control unit can perform the following steps: select the corresponding wave source based on the estimated size of the object; determine whether the characteristic vibration frequency can be obtained; if so, instruct the calculation unit to calculate the characteristic size based on the characteristic vibration frequency and the corresponding relationship, if Otherwise, select a wave source with a different wavelength, repeat the above judgment steps until the characteristic vibration frequency is obtained, and instruct the calculation unit to calculate the characteristic size based on the characteristic vibration frequency and the corresponding relationship.

In a specific implementation, the waves are electromagnetic waves, elastic waves or sound waves in any frequency band.

In a specific implementation, both the wave source and the wave intensity detector are located in the far field, and the far field is the region where the distance to the surface of the object is greater than the wavelength of the wave.

In a specific implementation, the wave has a single wavelength, and the wavelength of the wave is a single wavelength; or, the wave includes multiple discrete wavelengths, and the wavelength of the wave is any one of the multiple discrete wavelengths.

In a specific implementation, the characteristic size is the distance between adjacent parts of the surface of the object, or the actual size of the object.

In the specific implementation, the feature size is the distance between two places inside the object, and the two places scatter the waves emitted by the wave source to obtain the corresponding evanescent field, which excites the corresponding wave signal propagating to the far field, and the wave signal changes with time. After Fourier transform, the wave intensity has characteristic vibration frequency in the frequency domain.

In a specific implementation, the wave signal that can be transmitted to the far field generated by the evanescent field excitation is calculated by the formula of the complex amplitude of the wave signal as follows:

Among them, ψ _s (z, t) is the complex amplitude of the wave signal, i is the imaginary unit, t is the transmission time of the wave signal, z is the propagation distance of the wave signal, ω _s is the characteristic angular frequency of the wave signal, and ω is the wave source The angular frequency of , c is the transmission speed of the wave in free space, k _⊥ is the wave number of the evanescent field, Θ(tz/c) is the switching function, the switching function is 0 when t≦z/c When >z/c, the value is 1.

For the specific principles, implementations, etc. of the method 600 for performing far-field illumination and far-field detection on an object, reference may be made to the above-mentioned related descriptions of the device for performing far-field illumination and far-field detection on an object in conjunction with FIGS. Repeat.

Although the present invention is disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be based on the scope defined by the claims.

Claims (9)

1. a method for far-field illumination and detection to an object breaking through the diffraction limit, is characterized in that, comprising: The wave source emits a wave to the object, and the wave is scattered by the object to generate an evanescent field, which is excited by the evanescent field to generate a wave signal that can be transmitted to the far field. The characteristic size of the object is related to the wave signal. There is a corresponding relationship between the wave intensities that vary with time; A wave intensity detector detects the time-varying wave intensity; The computing unit acquires the time-varying wave intensity and the corresponding relationship and determines a characteristic size of the object based on the two. 2 . The method according to claim 1 , wherein the waves are electromagnetic waves, elastic waves or acoustic waves in any frequency band. 3 . 3. The method of claim 1, wherein both the wave source and the wave intensity detector are located in a far field, and the far field is a distance from the surface of the object greater than the wavelength of the wave. area. 4. The method according to claim 1, wherein the wave has a single wavelength, and the wavelength of the wave is the single wavelength; or, the wave comprises a plurality of discrete wavelengths, and the wavelength of the wave is is any one of the discrete wavelengths. 5. The method according to claim 1, wherein the calculation unit is adapted to perform Fourier transform on the time-varying wave intensity to obtain a characteristic vibration frequency, and based on the characteristic vibration frequency and the The characteristic size of the object is obtained by the corresponding relationship, and the corresponding relationship is: P _s =λ/(1+f _s /f ₀ ), Wherein, P _s is the characteristic size, λ is the wavelength of the wave, f _s is the characteristic vibration frequency, and f ₀ is the center frequency of the wave. 6. The method of claim 5, comprising: selecting a corresponding wave source based on the estimated size of the object; Determine whether the characteristic vibration frequency can be obtained; If yes, instruct the calculation unit to calculate the characteristic size based on the characteristic vibration frequency and the corresponding relationship, if otherwise, select a wave source with a different wavelength, repeat the above judgment steps until the characteristic vibration frequency is obtained, and instruct the The calculation unit calculates the characteristic size based on the characteristic vibration frequency and the corresponding relationship. 7. The method of claim 5, wherein the characteristic size is the distance between adjacent portions of the surface of the object, or the actual size of the object. 8. The method according to claim 5, wherein the feature size is the distance between two places inside the object, and the two places scatter the wave emitted by the wave source to obtain a corresponding evanescent field, which excites The corresponding wave signal propagated to the far field has the characteristic vibration frequency in the frequency domain after the time-varying wave intensity of the wave signal is Fourier transformed. 9. The method according to claim 1, wherein the wave signal that can be transmitted to the far field is generated by the evanescent field excitation and is calculated by the formula of the complex amplitude of the wave signal:

Among them, ψ _s (z, t) is the complex amplitude of the wave signal, i is the imaginary unit, t is the transmission time of the wave signal, z is the propagation distance of the wave signal, and ω _s is the wave signal , ω is the angular frequency of the wave source, c is the transmission speed of the wave in free space, k _⊥ is the wave number of the evanescent field, Θ(tz/c) is the switching function, the The switching function takes a value of 0 when t≦z/c and 1 when t>z/c.

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