A method of measuring the thickness profile and refractive index dispersion curve of a liquid film

Abstract

A method for measuring thickness distribution and refractive index dispersion curve of a liquid film, comprising: covering the liquid film on a SPR sensing module; irradiating a wide-spectrum linearly polarized parallel light beam on the SPR sensing module to obtain reflected light through total reflection, the wide-spectrum linearly polarized parallel light beam exciting SPR mode and / or PWR mode on the SPR sensing module through total reflection; receiving the reflected light carrying information of the liquid film by a hyperspectral imager to obtain a hyperspectral image, pixels in the hyperspectral image corresponding to positions on the liquid film one by one; determining at least three measured resonance wavelengths at a target position corresponding to a target pixel according to the hyperspectral image; obtaining the liquid film thickness at the target position and the refractive index dispersion curve of the liquid film according to the at least three measured resonance wavelengths at the target position; obtaining the liquid film thickness at other positions according to the refractive index dispersion curve of the liquid film at the target position and the measured resonance wavelengths at the other positions; and obtaining the thickness distribution of the liquid film according to the thickness of the liquid film at all positions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision detection, and particularly relates to a method for measuring thickness distribution and refractive index dispersion curve of liquid film. BACKGROUND

[0002] Liquid film has important applications in many fields such as environmental protection, petroleum chemical industry, chemical bionics, medicine and health, organic synthesis, analytical chemistry, gas separation, etc. Liquid film is widely used in mechanical sealing and bearing lubrication, which can improve the sealing performance, reduce friction and prolong the service life of mechanical devices; liquid film is also often used to protect solid surfaces from oxidation, improve the optical and mechanical properties of solid surfaces, and is used for waterproofing, thermal insulation and ultraviolet protection; liquid film has fast mass transfer rate and good molecular selectivity, and is often used for selective absorption and separation of gas molecules; liquid film plays an important role in biological organisms, for example, tears form a uniform liquid film on the corneal surface, which reduces the scattering of light and improves the visual efficiency; liquid film also has important applications in biochemical sensing field, and using liquid film as a sensitive film has the advantages of simple film formation, easy updating, reusable substrate and improved sensor selectivity. For example, using an ionic liquid film as a sensor sensitive film can realize specific detection of heavy metal mercury ions. Liquid film is also an indispensable preliminary state in the process of preparing solid film by chemical method, and is an important research object in the field of chemical film preparation technology. Thickness distribution and refractive index dispersion curve are two important parameters of liquid film, and accurate measurement of the thickness and two-dimensional distribution of liquid film helps to establish controllable preparation method of liquid film and optimize the performance of liquid film in different applications. Accurate measurement of the refractive index dispersion curve of liquid film can effectively evaluate the changes of optical properties and chemical composition of liquid film in use. Simultaneous measurement of the thickness distribution and the refractive index dispersion curve of liquid film can help us more comprehensively analyze the physical and chemical properties of liquid film in use.

[0003] Optical measurement method has the advantages of accuracy, rapidity, non-destructiveness and easy implementation, and is the main method for measuring the thickness and refractive index of liquid film. At present, the optical instruments commonly used for measuring liquid refractive index include ellipsometer, Abbe refractometer, optical waveguide sensor and SPR sensor. These optical instruments have high sensitivity and can accurately measure the thickness or refractive index of liquid film, but they have single function and are not suitable for simultaneous measurement of the thickness and refractive index of liquid film, not to mention the two-dimensional distribution of liquid film thickness and the refractive index dispersion curve of liquid film. There is a lack of advanced methods and tools for simultaneously measuring the thickness distribution and the refractive index dispersion curve of liquid film in real life. SUMMARY

[0004] Therefore, in order to solve the above problems, a method for measuring the thickness distribution and the refractive index dispersion curve of liquid film is provided.

[0005] As an aspect of the present application, a method for measuring a liquid film thickness distribution and a refractive index dispersion curve of a liquid film is provided, the method is implemented based on a hyperspectral SPR imaging device, the hyperspectral SPR imaging device comprises an SPR sensing module, and the method comprises:

[0006] covering the liquid film on the SPR sensing module;

[0007] irradiating a wide spectral line polarized parallel light beam onto the SPR sensing module and causing total reflection to obtain reflected light, the wide spectral line polarized parallel light beam excites an SPR mode and / or a PWR mode on the SPR sensing module through total reflection, and the reflected light carries information of the liquid film through interaction of the SPR mode and / or the PWR mode with the liquid film; wherein the reflected light is received by a hyperspectral imager to obtain a hyperspectral image, and pixels in the hyperspectral image correspond one-to-one to positions on the liquid film;

[0008] determining at least three measured resonance wavelengths at a target position corresponding to a target pixel according to the hyperspectral image, the measured resonance wavelengths at the target position being resonance wavelengths of the SPR mode and / or the PWR mode;

[0009] obtaining a liquid film thickness at the target position and a refractive index dispersion curve of the liquid film according to the at least three measured resonance wavelengths at the target position;

[0010] obtaining a liquid film thickness at each other position on the liquid film according to the refractive index dispersion curve of the liquid film and the measured resonance wavelength at the other position, the other position being any position on the liquid film except the target position;

[0011] obtaining a thickness distribution of the liquid film according to the liquid film thicknesses at all positions on the liquid film.

[0012] According to an embodiment of the present application, the SPR sensing module comprises a substrate and a metal thin film located on the substrate, the substrate is a prism, and the metal thin film is deposited on a bottom surface of the prism; or

[0013] the substrate is a combination of a prism and a transparent substrate in close contact with a bottom surface of the prism, and the metal thin film is deposited on a surface of the transparent substrate away from the prism;

[0014] the liquid film is arranged on a surface of the metal thin film;

[0015] the SPR mode is excited at an interface between the metal thin film and the substrate;

[0016] the PWR mode is excited in the liquid film.

[0017] According to an embodiment of the present application, a cover layer is further formed on the liquid film;

[0018] According to the at least three measured resonance wavelengths at the target position, the liquid film thickness at the target position and the refractive index dispersion curve of the liquid film are obtained, comprising:

[0019] The refractive index of the substrate, the refractive index and thickness of the metal thin film, and the refractive index of the cover layer above the liquid film are brought into the Fresnel reflection formula of the four-layer structure, the at least three measured resonance wavelengths of the liquid film at the target position are simulated and fitted to obtain a first relationship curve at each measured resonance wavelength at the target position, wherein the first relationship curve is a relationship curve between the refractive index of the liquid film and the liquid film thickness at the target position, and the at least three measured resonance wavelengths correspond to at least three first curves;

[0020] According to the Cauchy dispersion formula and the at least three first relationship curves of the liquid film at the target position, the liquid film thickness at the target position and the refractive index dispersion curve of the liquid film are obtained.

[0021] According to an embodiment of the present application, according to the refractive index dispersion curve of the liquid film and the measured resonance wavelength at each other position, the liquid film thickness at the other position is obtained, comprising:

[0022] The measured resonance wavelength at the other position is obtained by using the hyperspectral image;

[0023] According to the refractive index dispersion curve of the liquid film, the refractive index of the liquid film at the measured resonance wavelength at the other position is determined;

[0024] According to the refractive index of the liquid film at the measured resonance wavelength at the other position and the Fresnel reflection formula of the four-layer structure, the liquid film thickness at the other position is obtained.

[0025] According to an embodiment of the present application, the Cauchy dispersion formula is expressed as follows:

[0026]

[0027] wherein, , is a parameter, represents the refractive index of the liquid film at wavelength λ;

[0028] According to the Cauchy dispersion formula and the at least three first relationship curves of the liquid film at the target position, the liquid film thickness at the target position and the refractive index dispersion curve of the liquid film are obtained, comprising:

[0029] At least two second relation curves of the parameter b and the liquid film thickness at the target position are obtained according to the Cauchy dispersion formula and the at least three first relation curves, and all the second curves intersect at a point;

[0030] The intersection of the at least two second relation curves is calculated to obtain the value of the parameter b and the liquid film thickness at the target position;

[0031] According to the value of the parameter b and the liquid film thickness at the target position, the value of the parameter a is obtained in combination with any one of the at least three first relation curves; and the Cauchy dispersion formula is brought into the values of the parameters a and b to obtain the refractive index dispersion curve of the liquid film.

[0032] According to an embodiment of the present application, the Fresnel reflection formula of the four-layer structure is represented as follows:

[0033] R= r 1234 ·r 1234 *

[0034]

[0035]

[0036]

[0037] Wherein, R represents the reflectivity of the four-layer structure composed of the substrate, the metal film, the liquid film and the cover layer, the substrate, the metal film, the liquid film and the cover layer are the 1st layer, the 2nd layer, the 3rd layer and the 4th layer from bottom to top, respectively, r 1234 represents the reflection coefficient of the four-layer structure, r 1234 * represents the complex conjugate of r 1234 , D2 is the thickness of the 2nd layer, D3 is the thickness of the 3rd layer, k2 and k3 represent the vertical components of the propagation constants of the wide spectral line polarized parallel light beam in the 2nd layer and the 3rd layer, respectively; r 234 represents the reflection coefficient of the three-layer structure composed of the 2nd layer, the 3rd layer and the 4th layer, r ij represents the interface reflection coefficient of the ith layer and the jth layer, i=1, 2 or 3, j=2, 3 or 4, λ is the wavelength of light in vacuum, n i represents the refractive index of the ith layer at the wavelength λ.

[0038] According to an embodiment of the present application, the wide spectral line polarized parallel light beam is s-polarized light or p-polarized light or other linearly polarized light which can be decomposed into s-polarized component and p-polarized component.

[0039] According to an embodiment of the present application, when the wide spectral line polarized parallel light beam is s-polarized light, r ij is obtained by the following formula:

[0040]

[0041] when the wide spectral line polarized parallel light beam is p-polarized light, r ij is obtained by the following formula:

[0042]

[0043] where θ i and θ j respectively represent the corresponding incident angle and refraction angle of the wide spectral line polarized light when it is incident on the jth layer from the ith layer, n j is the refractive index of the jth layer, k i and k j respectively represent the vertical components of the propagation constants of the light in the ith layer and the jth layer.

[0044] According to an embodiment of the present application, the metal thin film, when covered by the liquid film, does not fall off and does not change in physical and chemical properties; and the liquid film remains stable within the test time.

[0045] According to an embodiment of the present application, the at least three measured resonance wavelengths at the target position are obtained by one high-spectral imaging measurement or by multiple high-spectral imaging measurements under different conditions.

[0046] The basic method for measuring the thickness of the liquid film and the refractive index of the liquid film in the embodiments of the present application is the surface plasmon resonance (SPR) sensing method and the plasmonic waveguide resonance (PWR) sensing method. SPR is a mature high-sensitivity biochemical sensing method. However, the detection depth of the SPR sensor is small, and in the visible light band, it can at most detect a liquid film of 300 nm thick. With the increase of the thickness of the liquid film (from hundreds of nanometers to microns), PWR mode will gradually appear in the liquid film. Therefore, PWR mode can be used to measure thicker (micron-level thickness) liquid films, and SPR mode can be used to measure thinner (a few nanometers to tens of nanometers thick) liquid films.

[0047] According to embodiments of the present invention, the thickness and refractive index dispersion curve of the liquid film include multiple unknowns. Therefore, when simultaneously measuring the thickness distribution and refractive index dispersion curve of the liquid film, multiple unknowns need to be determined. This requires experimentally obtaining the resonance wavelengths of at least three SPR and / or PWR modes at the target location corresponding to the target pixel in the hyperspectral image. For the target pixel, the three measured resonance wavelengths can be used as known quantities to measure the liquid film thickness and refractive index dispersion curve at the target location. The thickness of the liquid film changes with position, but the dispersion curve of the liquid film does not change with position; the refractive index dispersion curve at the target location is the refractive index dispersion curve of the liquid film. Only one unknown, namely the thickness, needs to be measured at each other location on the liquid film. Therefore, for other locations of the liquid film, the liquid film thickness at that location can be measured using the measured resonance wavelength and refractive index dispersion curve. Therefore, embodiments of the present invention can achieve simultaneous measurement of the thickness distribution and refractive index dispersion curve of the liquid film. Attached Figure Description

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0049] Figure 1 A schematic diagram of the hyperspectral SPR imaging device provided in an embodiment of the present invention is shown;

[0050] Figure 2 A flowchart of a method for measuring the thickness distribution and refractive index dispersion curve of a liquid film according to an embodiment of the present invention is shown.

[0051] Figure 3 A flowchart of a method for measuring the thickness distribution and refractive index dispersion curve of a liquid film according to another embodiment of the present invention is provided.

[0052] Figure 4A Experimental and simulated spectra of target pixels on hyperspectral images of silicone oil films provided according to embodiments of the present invention are shown;

[0053] Figure 4B It shows the result of Figure 4A Two-dimensional distribution diagrams of the measured resonant wavelengths of the five PWR modes were obtained.

[0054] Figure 4C It shows that according to Figure 4A The three first curves obtained from three of the resonant wavelengths;

[0055] Figure 4D It shows that according to Figure 4C The three first curves are used to obtain the two second curves at the target location.

[0056] Figure 5 The thickness distribution of the silicone oil film measured according to the embodiment of the present application is shown;

[0057] Figure 6 The comparison of four experimental spectra and the corresponding simulated spectra extracted from other four pixels on the hyperspectral image of the measured silicone oil film according to the embodiment of the present application is shown;

[0058] Figure 7 The refractive index dispersion curve of the silicone oil film measured according to the embodiment of the present application is shown;

[0059] Figure 8A The experimental spectrum and the simulated spectrum extracted from the target pixel on the hyperspectral image of the measured glycerol film according to the embodiment of the present application are shown;

[0060] Figure 8B The four PWR modes obtained are shown. Figure 8A The two-dimensional distribution map of the measured resonance wavelength of each of the four PWR modes is shown;

[0061] Figure 9A The refractive index dispersion curve of the glycerol film measured according to the embodiment of the present application is shown;

[0062] Figure 9B The thickness distribution of the dry oil film measured according to the embodiment of the present application is shown.

[0063] BRIEF DESCRIPTION OF DRAWINGS

[0064] 1-linear polarizer;

[0065] 2-SPR sensing module;

[0066] 21-substrate;

[0067] 211-prism;

[0068] 212-glass substrate;

[0069] 22-metal thin film;

[0070] 3-liquid film;

[0071] 4-broadband light source;

[0072] 5-imaging lens;

[0073] 6-hyperspectral imager;

[0074] 7-cover layer. DETAILED DESCRIPTION

[0075] In order to make the objects, technical solutions and advantages of the present application clearer, the following further describes the present application with reference to the embodiments and the accompanying drawings. However, the present application can be implemented in different forms and should not be interpreted as being limited to the embodiments presented herein. On the contrary, the embodiments are presented to make the present application thorough and complete and to fully convey the scope of the present application to those skilled in the art. In the accompanying drawings, the sizes and relative sizes of layers and regions can be exaggerated for clarity, and the same reference signs are used throughout to denote the same elements.

[0076] The terms used herein are merely used to describe specific embodiments and are not intended to limit the present application. The terms "comprise", "include" and the like as used herein indicate the presence of the stated features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0077] Figure 1 A schematic diagram of a hyperspectral SPR imaging device is given.

[0078] As shown in Figure 1 The hyperspectral SPR imaging device comprises an SPR sensing module 2, a liquid film 3 located on the SPR sensing module 2, a broadband light source 4 and a hyperspectral imager 6 arranged on both sides of the SPR sensing module 2, a linear polarizer 1 arranged between the broadband light source 4 and the SPR sensing module 2, and an imaging lens 5 arranged between the SPR sensing module 2 and the hyperspectral imager 6. The hyperspectral SPR imaging device is used to realize the simultaneous measurement of the thickness distribution of the liquid film 2 and the refractive index dispersion curve of the liquid film 2.

[0079] Figure 2 A flowchart of a method for measuring the thickness distribution and the refractive index dispersion curve of a liquid film according to an embodiment of the present application is shown. Referring to Figure 1 and Figure 2 The method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film 3 comprises operations S1-S6.

[0080] In operation S1, the liquid film 3 is overlaid on the SPR sensing module.

[0081] In operation S2, a broadband linearly polarized parallel light beam is irradiated onto the SPR sensing module 2 and total reflection occurs to obtain reflected light. The broadband linearly polarized parallel light beam excites SPR mode and / or PWR mode on the SPR sensing module 2 through total reflection, and the reflected light carries information of the liquid film 3 through the interaction of the SPR mode and / or the PWR mode with the liquid film 3. The broadband linearly polarized parallel light beam is obtained by passing through the linear polarizer 1 after being emitted by the broadband light source 4 of the hyperspectral SPR imaging device. The reflected light is received by the hyperspectral imager 6 after passing through the imaging lens 5, and a hyperspectral image is obtained. The pixels in the hyperspectral image correspond one-to-one to the positions on the liquid film.

[0082] In operation S3, at least three measured resonance wavelengths at the target position corresponding to the target pixel are determined according to the hyperspectral image, the measured resonance wavelengths at the target position being resonance wavelengths of the SPR mode and / or the PWR mode. The target pixel is, for example, a pixel at the center of the field of view of the hyperspectral imager 6.

[0083] In operation S4, the liquid film thickness at the target position and the refractive index dispersion curve of the liquid film are obtained according to the at least three measured resonance wavelengths at the target position.

[0084] In operation S5, the liquid film thickness at each other position is obtained according to the refractive index dispersion curve of the liquid film and the measured resonance wavelength at the other position, the other position being any position on the liquid film except the target position.

[0085] In operation S6, the distribution of the liquid film thickness is obtained according to the liquid film thickness at all positions on the liquid film 3.

[0086] The basic method for measuring the liquid film thickness and the liquid film refractive index in the embodiments of the present application is the surface plasmon resonance (SPR) sensing method and the plasmonic waveguide resonance (PWR) sensing method. The SPR is a mature high-sensitivity biochemical sensing method. However, the detection depth of the SPR sensor is small, and in the visible light band, it can at most detect a liquid film with a thickness of 300 nm. As the liquid film thickness increases (hundreds of nanometers to microns), the PWR mode will gradually appear in the liquid film. Therefore, the PWR mode can be used to measure a thicker (micron-level thickness) liquid film, and the SPR mode can be used to measure a thinner (a few nanometers to tens of nanometers thick) liquid film. The embodiments of the present application can realize both the surface plasmon resonance (SPR) and the plasmonic waveguide resonance (PWR), so the embodiments of the present application can realize the detection of a thinner (a few nanometers to tens of nanometers) liquid film, and also realize the detection of a thinner (hundreds of nanometers to a few microns) liquid film.

[0087] According to the embodiment of the present application, the thickness and the refractive index dispersion curve of the liquid film include a plurality of unknown quantities, and therefore a plurality of unknown quantities need to be determined when the thickness distribution and the refractive index dispersion curve of the liquid film are measured synchronously. This requires that the experimental apparatus obtains at least three resonance wavelengths of the SPR mode and / or the PWR mode at the target position corresponding to the target pixel in the hyperspectral image. For the target pixel, the three measured resonance wavelengths can be used as known quantities to measure the thickness and the refractive index dispersion curve at the target position. The thickness of the liquid film changes with the position, but the dispersion curve of the liquid film does not change with the position. The refractive index dispersion curve at the target position is the refractive index dispersion curve of the liquid film. Only one unknown quantity, i.e., the thickness, needs to be determined at each other position on the liquid film. Therefore, for the other positions on the liquid film, the measured resonance wavelength and the refractive index dispersion curve of the position can be used to measure the thickness of the liquid film at the position. Therefore, the embodiment of the present application can realize the synchronous measurement of the thickness distribution of the liquid film and the refractive index dispersion curve of the liquid film.

[0088] According to the embodiment of the present application, the liquid constituting the liquid film 3 must be a stable and uniform liquid. The liquid film 3 is a relatively thin liquid film with a thickness ranging from 1 to 10 microns. The specific thickness range is related to the hyperspectral SPR imaging device, and it is only required to ensure that the PWR mode can be generated and at least three resonance peaks of the PWR mode are formed in the measured spectral range (400-10000 nm). The liquid film 3 can be prepared by natural diffusion method, spin coating method, etc.

[0089] According to the embodiment of the present application, the SPR sensing module 2 includes a substrate 21 and a metal film 22 on the substrate 21. In the first embodiment, a first Kretschmann prism coupling structure is used, in which the substrate 21 is a prism, and the material can be glass. The metal film 22 is deposited on the bottom surface of the glass prism. Figure 2As shown, the second Kretschmann prism coupling structure is adopted, wherein the substrate 21 is a combination of a prism 211 and a glass substrate 212 in close contact with the bottom surface of the prism 211. The metal film 22 is deposited on the surface of the glass substrate 212 away from the bottom surface of the prism 211, and the glass substrate 212 is in close contact with the bottom surface of the prism 211 through a high refractive index coupling liquid. The liquid film 3 is arranged on the surface of the metal film 22 and exposed on the outermost side. The thickness of the metal film is between 10 nm and 100 nm, and the optimal thickness is 50 nm when the metal film 22 is a gold film. The wide spectral line polarized parallel light beam passes through the substrate 21, and total reflection occurs at the glass and metal interface of the SPR sensing module 2. The reflected light beam is emitted from the side of the prism 211, passes through the imaging lens 5, and is then received by the hyperspectral imager 6. The evanescent field generated with the total reflection penetrates the metal film 22 and excites the SPR mode at the interface between the metal film 22 and the substrate 21 and / or excites the PWR mode in the liquid film. Both the SPR mode and the PWR mode can interact with the liquid film, so that the reflected light carries the information of the liquid film 3.

[0090] According to the embodiment of the present application, when the SPR sensing module 2 in Figure 1 combination with the Kretschmann prism coupling structure, the wideband light emitted by the wideband light source 4 such as a halogen tungsten lamp becomes a s-polarized or p-polarized parallel light beam through the multimode quartz optical fiber, the prism 211 and the linear polarizer 1, and then is incident on the prism at an angle θ, which can be adjusted by the rotating device turntable. The wide spectral line polarized parallel light beam entering the prism 211 is totally reflected at the interface between the glass substrate 212 and the metal film 22 of the SPR sensing module 2, and the reflected light passes through the imaging prism 5 and is incident on the hyperspectral imager 6. The evanescent field generated with the total reflection can excite the PWR mode in the liquid film 3 or excite the SPR mode at the interface between the metal film 22 and the liquid film 3. When the evanescent field generated with the total reflection excites the PWR in the liquid film 3, the reflected spectrum presents multiple troughs, so that the wavelength corresponding to the trough in each pixel spectrum in the hyperspectral image recorded by the hyperspectral imager 6 is the resonance wavelength λ R of the PWR mode. In addition to the Kretschmann prism, it is clear to those skilled in the art that the Otto prism coupling structure can also be used to obtain the hyperspectral image of the liquid film, which will not be described in detail here.

[0091] According to the embodiment of the present application, when the liquid film 3 is very thin, only the SPR mode can be excited at the interface between the metal film 22 and the liquid film 3, and as the thickness of the liquid film increases, the PWR mode is gradually excited. When only the SPR mode is excited at the interface between the metal film 22 and the liquid film 3, the target pixel of each hyperspectral image can only obtain the resonance wavelength at the target position. Or when the thickness of the liquid film is not enough, although the PWR mode can be excited, each hyperspectral image can only obtain less than three resonance wavelengths at the target pixel.

[0092] The cover layer 7 is also formed on the liquid film 3. In order to obtain at least three measured resonance wavelengths at the target position corresponding to the target pixel, different hyperspectral images can be obtained by changing the test conditions, so as to obtain three resonance wavelengths at the target position. Changing the test conditions may, for example, include changing the material of the cover layer 7, or changing the polarization direction of the wide-spectrum linearly polarized parallel light beam.

[0093] For example, the reflected light can be hyperspectrally imaged under different (at least three) cover layers 7 respectively, to obtain at least three hyperspectral images, and at least three measured resonance wavelengths at the target position can be obtained according to the obtained at least three hyperspectral images. For example, when the cover layer 7 on the liquid film 3 is air, water, and a solid plate with a smooth surface, respectively, the reflected light can be hyperspectrally imaged, to obtain a hyperspectral image corresponding to each cover layer 7, so as to obtain at least three measured resonance wavelengths at the target position according to the hyperspectral images corresponding to all cover layers 7.

[0094] According to the embodiment of the present application, three resonance wavelengths at the target position can also be obtained by changing the polarization direction of the wide-spectrum linearly polarized parallel light beam while changing the cover layer 7. Or three resonance wavelengths at the target position can be obtained by only changing the polarization direction of the wide-spectrum linearly polarized parallel light beam. For example, the material of the cover layer 7 is unchanged, and the reflected light can be hyperspectrally imaged when the polarization direction of the wide-spectrum linearly polarized parallel light beam is different (S direction or P direction), to obtain a hyperspectral image corresponding to each polarization direction. According to the hyperspectral images corresponding to each polarization direction under the condition of multiple cover layers 7, at least three measured resonance wavelengths at the target position can be obtained.

[0095] No matter which of the above cases is used to obtain at least three resonance wavelengths, the obtained at least three resonance wavelengths can be used as known quantities to determine the refractive index dispersion curve and the thickness distribution.

[0096] According to the embodiment of the present application, when the thickness of the liquid film 3 is large enough to support at least three PWR modes, at least three resonance wavelengths at the target position can be obtained by one hyperspectral imaging measurement, and therefore, the measurement of the liquid film can be realized by using one hyperspectral image obtained by imaging the reflected light once.

[0097] According to an embodiment of the present application, the PWR mode generates a plurality of orders, each order corresponding to a resonance wavelength, the resonance wavelength being related to the thickness of the liquid film and the refractive index dispersion curve of the liquid film. Under the PWR mode, the resonance wavelengths of the plurality of orders (corresponding to different orders of the PWR mode) at the target position of the liquid film can be used as a plurality of known quantities to simultaneously calculate the refractive index dispersion curve of the liquid film and the thickness at the target position. When combined with the hyperspectral image, since the hyperspectral image can obtain the resonance spectrum of tens of thousands of pixels of the liquid film, the large number of resonance peaks of the tens of thousands of pixels can solve the distribution of the thickness of the liquid film of the refractive index dispersion curve.

[0098] According to an embodiment of the present application, operation S4, obtaining the thickness of the liquid film at the target position and the refractive index dispersion curve of the liquid film according to at least three measured resonance wavelengths at the target position, includes sub-operation S41 to sub-operation S42.

[0099] In sub-operation S41, the refractive index of the substrate, the refractive index and thickness of the metal thin film, and the refractive index of the cover layer 7 above the liquid film are brought into the Fresnel reflection formula of the four-layer structure, and at least three measured resonance wavelengths of the liquid film at the target position are simulated and fitted to obtain a first relationship curve at each measured resonance wavelength at the target position, wherein the first relationship curve is a relationship curve of the refractive index of the liquid film and the thickness of the liquid film at the target position, and the at least three measured resonance wavelengths correspond to at least three first curves.

[0100] In sub-operation S42, the thickness of the liquid film at the target position and the refractive index dispersion curve of the liquid film are obtained according to the Cauchy dispersion formula and the at least three first relationship curves of the liquid film at the target position.

[0101] According to an embodiment of the present application, the Cauchy dispersion curve is expressed as formula (1).

[0102] (1).

[0103] wherein, is a parameter, represents the refractive index of the liquid film at a wavelength of λ.

[0104] In sub-operation S42, the thickness of the liquid film at the target position and the refractive index dispersion curve of the liquid film are obtained according to the Cauchy dispersion formula and the at least three first relationship curves of the liquid film at the target position, including sub-operation S421 to sub-operation S423.

[0105] Sub-operation S421, based on the Cauchy dispersion formula and at least three first relationship curves, obtains at least two second relationship curves at the target location. The second relationship curves are the relationship curves between parameter b and the liquid film thickness at the target location. Since both parameter b and liquid film thickness are independent of wavelength (i.e., parameter b and liquid film thickness are independent of wavelength), all (at least two) second relationship curves obtained at the target location must intersect at a single point.

[0106] Sub-operation S422 obtains the value of parameter b and the liquid film thickness at the target location by finding the intersection of at least two second relationship curves.

[0107] Sub-operation S423: Based on the value of parameter b and the liquid film thickness at the target location, and combining any one of at least three first curves (the relationship curve between refractive index and liquid film thickness at the target location), the value of parameter a is obtained; the values ​​of parameters a and b are substituted into the Cauchy dispersion formula to obtain the refractive index dispersion curve of liquid film 3. According to an embodiment of the present invention, when determining the refractive index dispersion curve of liquid film 3 using the Cauchy dispersion formula, there are two unknown parameters, namely parameters a and b. At the target location of liquid film 3, in addition to parameters a and b, the thickness at that location also needs to be measured. Therefore, three unknowns need to be measured. Thus, when obtaining the refractive index dispersion curve of liquid film 3 using the Cauchy dispersion formula, three resonance wavelengths at the target location need to be obtained. To improve the accuracy of solving for parameters a and b and the liquid film thickness at the target location, when determining at least three measured resonance wavelengths in a spectrum with three or more PWR resonance peaks, at least three measured resonance wavelengths are selected according to the principle of maximizing the wavelength interval.

[0108] The following section provides a detailed explanation of the measurement principle of liquid film thickness distribution and refractive index dispersion curve using Cauchy's formula.

[0109] Taking the calculation of the thickness and refractive index dispersion curves at the target location using three measured resonant wavelengths of the target pixel as an example. The three measured resonant wavelengths of the target pixel are, for example,... , and Substituting the refractive index of substrate 21, the refractive index and thickness of metal thin film 22, and the refractive index of the capping layer 7 above the liquid film into the Fresnel reflection formula for a four-layer structure, simulation fitting was performed on each measured resonant wavelength of liquid film 3 at the target location to obtain at least three first curves. That is, the first curve is... Down The relationship with T, the second curve is Down The relationship with T, the third curve is Down The relationship with T. for The refractive index below for The refractive index below, and for The refractive index below.

[0110] According to formula (1),

[0111] (8)

[0112] (9)

[0113] (10)

[0114] According to (8)~(9), we can obtain:

[0115] (11)

[0116] According to (9)~(10), we can obtain:

[0117] (12)

[0118] Will Relationship with T Relationship with T Substituting the relationship between b and T into (11) and (12) respectively, we obtain two curves showing the relationship between b and T. The intersection of these two curves represents the values ​​of b and T. Based on Cauchy's formula, we can then calculate a. Once a and b are determined, the refractive index dispersion curve can be determined.

[0119] According to an embodiment of the present invention, in operation S5, the thickness of the liquid film at other locations is obtained based on the refractive index dispersion curve of the liquid film and the measured resonant wavelength at each other location, which can be divided into sub-operations S51 to S53.

[0120] Sub-operation S51 uses the measured hyperspectral image to obtain other measured resonance wavelengths at other locations.

[0121] Sub-operation S52 determines the refractive index of the liquid film at other locations at the measured resonant wavelength based on the refractive index dispersion curve of the liquid film.

[0122] Sub-operation S53 obtains the thickness of the liquid film at other locations based on the measured resonant wavelength of the liquid film at other locations and the Fresnel reflection formula for the four-layer structure.

[0123] According to an embodiment of the present invention, the Fresnel formula for the four-layer structure is expressed as equation (2 to equation (5).

[0124] R= r 1234 ·r 1234* (2)

[0125] (3)

[0126] (4)

[0127] (5)

[0128] wherein R represents the reflectivity of a four-layer structure composed of a substrate, a metal thin film, a liquid film and a cover layer, the substrate, the metal thin film, the liquid film and the cover layer being the 1st layer, the 2nd layer, the 3rd layer and the 4th layer from bottom to top, respectively, r 1234 represents the reflection coefficient of the four-layer structure, r 1234 * represents the complex conjugate of r 1234 , D2 is the thickness of the 2nd layer, D3 is the thickness of the 3rd layer, k2 and k3 represent the vertical components of the propagation constant of a broad spectral line polarized parallel light beam in the 2nd layer and the 3rd layer, respectively; r 234 represents the reflection coefficient of a three-layer structure composed of the 2nd layer, the 3rd layer and the 4th layer, r ij represents the reflection coefficient of the interface between the i-th layer and the j-th layer, i = 1, 2 or 3, j = 2, 3 or 4, λ is the wavelength of light in vacuum, n i represents the refractive index of the i-th layer at the wavelength λ.

[0129] The broad spectral line polarized parallel light beam can be s-polarized light or p-polarized light or other linearly polarized light which can be decomposed into s-polarized component and p-polarized component.

[0130] When the broad spectral line polarized parallel light beam is s-polarized light, r ij is obtained from the following formula: r ij is obtained from formula (6).

[0131] (6)

[0132] When the broad spectral line polarized parallel light beam is p-polarized light, r ij is obtained from the following formula. (7)

[0133] For other linearly polarized light, it can be decomposed into s-polarized component and p-polarized component, and then synthesized after calculation. i and θ j represent the corresponding incident angle and refraction angle when light is emitted from the i-th layer to the j-th layer, n j is the single-wavelength refractive index of the j-th layer, k i and k j represent the vertical components of the propagation constant of light in the i-th layer and the j-th layer, respectively.

[0134] According to the embodiment of the present application, the metal thin film 22 needs to be able to excite SPR mode on its surface, which is usually gold, silver, aluminum or titanium.

[0135] When the metal thin film 22 is covered by the liquid film, it is required that no peeling occurs, and no change in physical and chemical properties occurs; the liquid film is required to remain stable within the test time.

[0136] The hyperspectral imager 6 may be, for example, a line scanning hyperspectral imager based on grating spectrometer, or a hyperspectral imager based on wavelength scanning of light source.

[0137] Figure 3 A flow chart of the method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film according to another embodiment of the present application is shown.

[0138] The method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film according to the present application will be described in detail below. Figure 1 and Figure 3 The method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film according to the present application will be described in detail below.

[0139] As shown in Figure 1 , the hyperspectral SPR imaging device comprises an SPR sensing module 2, a liquid film 3 located on the SPR sensing module 2, a broadband light source 4 and a hyperspectral imager 6 respectively arranged on the two sides of the SPR sensing module 2, a linear polarizer 1 arranged between the broadband light source 4 and the SPR sensing module 2, and an imaging lens 5 arranged between the SPR sensing module 2 and the hyperspectral imager 6. The hyperspectral SPR imaging device is used to realize the simultaneous measurement of the thickness distribution of the liquid film 2 and the refractive index dispersion curve of the liquid film 2.

[0140] As shown in Figure 3 , the method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film comprises steps A to H. In step A, the liquid film 3 is covered on the SPR sensing module 2.

[0141] In step B, a wide-spectrum linearly polarized parallel light beam is irradiated onto the SPR sensing module 2 to cause total reflection, and reflected light is obtained. The wide-spectrum linearly polarized parallel light beam excites SPR mode and / or PWR mode on the SPR sensing module 2 through total reflection, and the reflected light carries information of the liquid film 3 through the interaction of the reflected light with the liquid film 3 through the SPR mode and / or the PWR mode; the reflected light is received by the hyperspectral imager 6 to obtain a hyperspectral image, and the pixels in the hyperspectral image correspond one-to-one to the positions on the liquid film 3. The wide-spectrum linearly polarized parallel light beam is obtained by passing through the linear polarizer 1 after being emitted by the broadband light source 4 of the hyperspectral SPR imaging device.

[0142] Step C, determining at least three measured resonance wavelengths at the target position corresponding to the target pixel according to the hyperspectral image output by the hyperspectral imager 6, the measured resonance wavelengths at the target position being resonance wavelengths of the SPR mode and / or the PWR mode. The target pixel is, for example, a pixel at the center of the field of view of the hyperspectral imager 6. The at least three measured resonance wavelengths at the target position can be obtained by one hyperspectral imaging measurement or by multiple hyperspectral imaging measurements under different conditions.

[0143] Step D, bringing the refractive index of the substrate, the refractive index and thickness of the metal thin film, and the refractive index of the covering layer above the liquid film into the Fresnel reflection formula of the four-layer structure, simulating and fitting the at least three measured resonance wavelengths of the liquid film at the target position to obtain at least three first relationship curves at the target position, where the first relationship curve is a relationship curve of the refractive index of the liquid film and the thickness of the liquid film at the target position, and each first curve corresponds to each measured resonance wavelength.

[0144] Step E, obtaining at least two second relationship curves at the target position according to the Cauchy dispersion formula n(λ) = a + bλ -2 and the at least three first relationship curves obtained, where the second relationship curve is a relationship curve of the parameter b and the thickness of the liquid film at the target position, and then obtaining the intersection of the at least two second relationship curves to obtain the value of the parameter b and the thickness of the liquid film at the target position. Since the parameter b and the thickness of the liquid film are not dependent on the wavelength, multiple second relationship curves obtained at the same position must intersect at one point.

[0145] Step F, obtaining the value of the parameter a according to the value of the parameter b obtained and the thickness of the liquid film at the target position, in combination with any one of the at least three first relationship curves obtained; bringing the values of the parameters a and b into the Cauchy dispersion formula to obtain the refractive index dispersion curve of the liquid film. Since the liquid film at the target position and the liquid film at other positions belong to the same material, the refractive index dispersion curve obtained by using the multiple first relationship curves and the multiple second relationship curves at the target position is applicable to the entire liquid film 3.

[0146] Step G, determining the measured resonance wavelengths at other positions according to the hyperspectral image output by the hyperspectral imager 6, and then determining the refractive index of the liquid film at the measured resonance wavelengths at other positions according to the refractive index dispersion curve of the liquid film obtained, and obtaining the thickness of the liquid film at other positions according to the refractive index of the liquid film at the measured resonance wavelengths at other positions and the Fresnel reflection formula of the four-layer structure.

[0147] Step H, obtaining the thickness distribution of the liquid film according to the thickness of the liquid film at all positions obtained. Here, all positions include the target position and other positions except the target position.

[0148] The basic method for measuring the thickness distribution of the liquid film 3 and the refractive index dispersion curve of the liquid film 3 in the embodiment of the present application is a hyperspectral surface plasmon resonance (SPR) imaging sensing method and a hyperspectral plasmonic waveguide resonance (PWR) imaging sensing method. SPR is a mature high-sensitivity biochemical sensing method. However, the detection depth of the SPR sensor is small, and in the visible light band, the liquid film can be detected at most to 300 nm thick. With the increase of the thickness of the liquid film (hundreds of nanometers to microns), the PWR mode will gradually occur in the liquid film. Therefore, the PWR mode can be used to measure the liquid film with a relatively large thickness (micron level), and the SPR mode can be used to measure the liquid film with a relatively small thickness (a few nanometers to tens of nanometers).

[0149] According to the embodiment of the present application, the thickness and the refractive index dispersion curve of the liquid film 3 include a plurality of unknown quantities, and therefore when the thickness distribution and the refractive index dispersion curve of the liquid film 3 are measured synchronously, a plurality of unknown quantities need to be determined. This requires that at least three resonance wavelengths of the SPR mode and / or the PWR mode at the target position corresponding to the target pixel in the hyperspectral image are obtained by the experiment, and for the target pixel, the three measured resonance wavelengths can be used as known quantities to measure the thickness and the refractive index dispersion curve at the target position. The thickness of the liquid film 3 changes with the position, but the dispersion curve of the liquid film 3 does not change with the position, and the refractive index dispersion curve at the target position is the refractive index dispersion curve of the liquid film 3. Only one unknown quantity, i.e., the thickness, needs to be determined at each other position on the liquid film 3. Therefore, for other positions of the liquid film 3, the measured resonance wavelength and the refractive index dispersion curve of the position can be used to measure the thickness of the liquid film at the position. Therefore, the embodiment of the present application can realize the synchronous measurement of the thickness distribution and the refractive index dispersion curve of the liquid film 3.

[0150] So far, the method for measuring the actual refractive index dispersion curve and the thickness of the liquid film in the embodiment has been introduced. In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application will be further described in detail below in combination with specific examples and with reference to the accompanying drawings.

[0151] The following examples one and two are used to illustrate the actual measurement method for measuring the thickness distribution and the refractive index dispersion curve of the liquid film. In the two examples, the broadband light source 14 includes a halogen tungsten lamp, a focusing lens and a linear polarizer 1. The metal film is selected as a gold film, and the thickness of the gold film is about 50 nm. The hyperspectral SPR imaging sensing device uses a Kretschmann prism coupling structure. In example one, a silicon oil film is selected to be described in detail, and in example two, a glycerol film is selected to be described in detail.

[0152] Example one

[0153] In the method for measuring the liquid film thickness distribution and the actual refractive index dispersion curve, the liquid film 3 is a silicone oil film prepared on a glass substrate with a 50 nm gold film sputtered thereon using a spin coating method. The method for measuring the refractive index dispersion curve of the silicone oil film and the thickness distribution thereof includes:

[0154] A hyperspectral image of the silicone oil film is obtained using the hyperspectral SPR imaging device.

[0155] First, the glass substrate is fixed as a whole to the spin coating platform, and an appropriate amount of silicone oil is dropped at the center of the substrate. The spin coating platform is set to rotate at a speed of 2000 rpm, and the silicone oil film is obtained by spin coating for 120 s. Subsequently, the substrate with the silicone oil spin coated thereon is fixed to the bottom surface of the glass prism, and the upper surface of the silicone oil is exposed to the air, that is, the corresponding cover layer is air at this time.

[0156] Second, the linear polarizer 1 is adjusted so that the incident broadband linearly polarized light beam is p-polarized light, and the hyperspectral imaging device 6 is used to record the hyperspectral image of the reflected p-polarized light on the SPR resonance module 2 at an incident angle of 50°.

[0157] Figure 4A The experimental spectrum and the simulated spectrum of a target pixel on the hyperspectral image of the silicone oil film are shown;

[0158] As Figure 4A shown, the spectrum of the target pixel obtained at an incident angle of 50° of the p-polarized light, and the simulation result of the spectrum at the target pixel. The spectrum of the target pixel includes a plurality of measured resonance wavelengths of the measured SPR mode and / or PWR mode, and the measured resonance wavelength and the simulated resonance wavelength are the same.

[0159] Five measured resonance wavelengths (or simulated resonance wavelengths) of the measured SPR mode and / or PWR mode which are less affected by the spectrum of the broadband light source 14 are selected for fitting. The five resonance wavelengths are the first resonance wavelength, the second resonance wavelength, the third resonance wavelength, the fourth resonance wavelength, and the fifth resonance wavelength. From Figure 4A it can be determined that the five more obvious resonance wavelengths (measured resonance wavelengths or simulated resonance wavelengths) λ R of this pixel are 527.7 nm, 563.9 nm, 606.9 nm, 655.7 nm, and 714.0 nm, respectively. After determining the five measured resonance wavelengths (or simulated resonance wavelengths) of the pixel, the two-dimensional distribution diagram of the measured resonance wavelengths of the five measured SPR modes and / or PWR modes can be drawn. Figure 4B The two-dimensional distribution diagram of the measured resonance wavelengths of the five SPR modes and / or PWR modes obtained from Figure 4A is shown.

[0160] The thickness at the target location (the center of the hyperspectral image) and the refractive index dispersion curve of the liquid film are obtained based on five measured resonance wavelengths. Given the resonance wavelengths, the thickness is scanned, and a series of refractive indices are obtained by fitting the Fresnel formula.

[0161] Figure 4C It shows that according to Figure 4A The three first curves were obtained from three of the resonant wavelengths.

[0162] like Figure 4C As shown, it is by Figure 4A The refractive index-thickness simulation curves at the target location were plotted using the 3rd, 4th, and 5th resonance wavelengths. Since the 3rd, 4th, and 5th resonance wavelengths are different, the refractive indices corresponding to these three resonance peaks are not the same, therefore these three curves do not intersect. However, the refractive indices corresponding to each of these three resonance peaks conform to the Cauchy dispersion formula. Based on formulas (11) and (12), the refractive index of the liquid film can be converted into the parameter b of the Cauchy dispersion formula, thereby plotting the refractive index parameter b-thickness curve.

[0163] Figure 4D It shows that according to Figure 4C The three first curves are used to obtain the two second curves at the target location.

[0164] like Figure 4D As shown, based on formulas (11) to (12), according to Figure 4C The two refractive index parameter-thickness curves (two second curves) obtained from the refractive index-thickness simulation curves at the 3rd, 4th, and 5th resonance wavelengths are used to visually depict the method for solving the initial thickness of the pixel at the target location under the experimental conditions, since the liquid film thickness at this target location is fixed with respect to the refractive index parameter. The initial thickness of the liquid film at the target location can be obtained from the position of the intersection point. nm.

[0165] Figure 5 The thickness distribution of the silicone oil film provided according to an embodiment of the present invention is shown.

[0166] like Figure 5 As shown, the thickness distribution of the silicone oil film is in the range of 3900-4100 nm.

[0167] Figure 6 The diagram shows a comparison between the simulated spectrum and the experimental spectrum obtained from the other four pixels of a hyperspectral image formed by a silicone oil film provided according to an embodiment of the present invention.

[0168] like Figure 6As shown, the simulation spectrum of the four pixels is compared with the experimental spectrum, respectively as shown in Figure 5 As shown in part (a), part (b), part (c) and part (d), the simulated resonance wavelength obtained by simulating the spectrum of the other four pixels (except the target pixel) is in good agreement with the measured resonance wavelength of the SPR mode and / or PWR mode. The refractive index dispersion curve of the silicone oil film is shown in Figure 7 As shown in the dispersion curve obtained in the present example is .

[0169] Example Two

[0170] Different from Example One, the liquid film in the present example is a glycerol film. In the present embodiment, the hyperspectral SPR image of the glycerol film is measured at an incident angle of 52° for a wide-spectrum linearly polarized parallel light beam in the p-polarization direction. Since the glycerol film is thinner than the silicone oil film in Example One, the PWR resonance order is less, and only four resonance wavelengths are selected for fitting for each pixel, and a resonance wavelength distribution graph is drawn.

[0171] Figure 8A The experimental spectrum and the simulation spectrum of the target pixel on the hyperspectral image of the glycerol film provided by the embodiment of the present application are shown.

[0172] As shown in Figure 8A , the resonance wavelength of the central pixel (target pixel) is still preferentially fitted, and the preliminary fitting result is shown in Figure 8A . The four resonance wavelengths are 500.1 nm, 566.8 nm, 631.1 nm and 729.7 nm, respectively. The single-wavelength refractive index of the pixel obtained by the preliminary fitting is , and the thickness at the target position is nm. Figure 8B The two-dimensional distribution graph of the measured resonance wavelength of each of the four SPR modes and / or PWR modes obtained by Figure 8A is shown.

[0173] The refractive index dispersion curve of the glycerol film is shown in Figure 9A , and the thickness distribution of the glycerol film is shown in Figure 9B , and the dispersion curve in the present example is .

[0174] As can be seen from the above technical solutions, the method for determining the refractive index dispersion curve and the thickness distribution of the liquid film of the present application has low equipment cost and simple operation, the theory involved in the simulation fitting is not complex, and the refractive index dispersion curve and the thickness distribution of the liquid film can be obtained at the same time. It has very important practical significance for quickly and accurately obtaining multiple parameters of various liquid films at the same time.

[0175] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described is only a specific embodiment of the present application and is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for measuring the thickness distribution and refractive index dispersion curve of a liquid film, the method being implemented based on a hyperspectral SPR imaging device, the hyperspectral SPR imaging device comprising an SPR sensing module, the SPR sensing module comprising a substrate and a metal thin film located on the substrate, and a capping layer further formed on the liquid film; the method comprising: Cover the SPR sensing module with a liquid film; A broadband linearly polarized parallel beam is irradiated onto the SPR sensing module and undergoes total internal reflection to obtain reflected light. The broadband linearly polarized parallel beam excites the SPR mode and / or PWR mode on the SPR sensing module through total internal reflection. The reflected light carries information about the liquid film through the interaction between the SPR mode and / or PWR mode and the liquid film. The reflected light is received by a hyperspectral imager to obtain a hyperspectral image, and the pixels in the hyperspectral image correspond one-to-one with the positions on the liquid film. Based on the hyperspectral image, at least three measured resonance wavelengths at the target location corresponding to the target pixel are determined, wherein the measured resonance wavelengths at the target location are the resonance wavelengths of SPR mode and / or PWR mode. The refractive index of the substrate, the refractive index and thickness of the metal thin film, and the refractive index of the overlying layer above the liquid film are substituted into the Fresnel reflection formula for a four-layer structure. Simulation fitting is performed on at least three measured resonant wavelengths of the liquid film at the target location to obtain a first relationship curve for each measured resonant wavelength at the target location. The first relationship curve is the relationship curve between the refractive index of the liquid film and the thickness of the liquid film at the target location. At least three measured resonant wavelengths correspond to at least three first relationship curves. Based on at least three first relationship curves of the liquid film at the target location, the thickness of the liquid film at the target location and the refractive index dispersion curve of the liquid film are obtained; The thickness of the liquid film at other locations is obtained based on the refractive index dispersion curve of the liquid film and the measured resonant wavelength at each other location. The other locations are any locations on the liquid film other than the target location. The thickness distribution of the liquid film is obtained based on the thickness of the liquid film at all locations.

2. The method according to claim 1, wherein, The substrate is a prism, and the metal thin film is deposited on the bottom surface of the prism; or The substrate is a combination of a prism and a transparent substrate in close contact with the bottom surface of the prism, and the metal film is deposited on the surface of the transparent substrate away from the prism; The liquid film is disposed on the surface of the metal thin film; The SPR mode is excited at the interface between the metal thin film and the substrate; The PWR mode is activated within the liquid film.

3. The method according to claim 1, wherein, Based on at least three first relationship curves of the liquid film at the target location, the thickness of the liquid film at the target location and the refractive index dispersion curve of the liquid film are obtained, including: Based on the Cauchy dispersion formula and at least three first relationship curves of the liquid film at the target location, the thickness of the liquid film at the target location and the refractive index dispersion curve of the liquid film are obtained.

4. The method according to claim 3, wherein, Based on the refractive index dispersion curve of the liquid film and the measured resonant wavelength at each other location, the thickness of the liquid film at the other locations is obtained, including: The measured resonance wavelengths at the other locations are obtained using the hyperspectral image; Based on the refractive index dispersion curve of the liquid film, determine the refractive index of the liquid film at the measured resonant wavelength at the other locations; The thickness of the liquid film at the other locations is obtained based on the refractive index of the liquid film at the measured resonant wavelength at the other locations and the Fresnel reflection formula of the four-layer structure.

5. The method according to claim 3, wherein, The Cauchy dispersion formula is expressed as follows: in, , For parameters, This represents the refractive index of the liquid film at wavelength λ; Based on the Cauchy dispersion formula and at least three first relationship curves of the liquid film at the target location, the thickness of the liquid film at the target location and the refractive index dispersion curve of the liquid film are obtained, including: Based on the Cauchy dispersion formula and the at least three first relationship curves, at least two second relationship curves are obtained at the target position. The second relationship curves are the relationship curves between the parameter b and the liquid film thickness at the target position. All the second relationship curves intersect at one point. The value of parameter b and the liquid film thickness at the target location are obtained by finding the intersection of at least two second relationship curves. Based on the value of parameter b and the thickness of the liquid film at the target location, and combined with any one of the at least three first relationship curves, the value of parameter a is obtained; the values ​​of parameter a and parameter b are substituted into the Cauchy dispersion formula to obtain the refractive index dispersion curve of the liquid film.

6. The method according to claim 3, wherein, The Fresnel reflection formula for the four-layer structure is expressed as follows: R= r 1234 ·r 1234 * Wherein, R represents the reflectivity of the four-layer structure consisting of the substrate, the metal thin film, the liquid film, and the capping layer, and the substrate, the metal thin film, the liquid film, and the capping layer are, from bottom to top, layer 1, layer 2, layer 3, and layer 4, respectively. 1234 The reflection coefficient of the four-layer structure, r 1234 * Indicates r 1234 The complex conjugate of , D2 is the thickness of the second layer, D3 is the thickness of the third layer, and k2 and k3 represent the vertical components of the propagation constant of the broadband linearly polarized parallel beam in the second and third layers, respectively; r 234 The reflection coefficient r represents the reflection coefficient of light in a three-layer structure consisting of layers 2, 3, and 4. ij This represents the reflection coefficient of the interface between the i-th and j-th layers, where i = 1, 2, or 3, j = 2, 3, or 4, λ is the wavelength of light in vacuum, and n i This represents the refractive index of the i-th layer at wavelength λ.

7. The method according to claim 6, wherein, The broadband linearly polarized parallel beam is s-polarized light, p-polarized light, or other linearly polarized light that can be decomposed into s-polarized and p-polarized components.

8. The method according to claim 7, wherein, When the broadband linearly polarized parallel beam is s-polarized light, r ij Obtained from the following formula: When the broadband linearly polarized parallel beam is p-polarized light, r ij Obtained from the following formula: Where, θ i and θ j Representing the incident angle and refraction angle respectively when broadband linearly polarized light travels from the i-th layer to the j-th layer, n j The refractive index of the j-th layer, k i and k j These represent the vertical components of the propagation constant of light in the i-th and j-th layers, respectively.

9. The method according to claim 1, wherein, The metal film does not peel off or undergo any changes in physical or chemical properties after being covered by the liquid film; and the liquid film remains stable during the test period.

10. The method according to claim 1, wherein, The at least three measured resonant wavelengths at the target location are obtained through a single hyperspectral imaging measurement or through multiple hyperspectral imaging measurements under different conditions.

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