Polarization State Modulation-Type Nanoscale Thin Film Refractive Index Measurement Method Based on In-Plane Photon Spin Hall Effect and Its Application

Abstract

The present invention belongs to the field of precision measurement, and relates to a method for measuring the refractive index of a nanoscale thin film with polarization state modulation based on the in-plane photon spin Hall effect and its application. By establishing a database of the in-plane photon spin splitting displacement varying with the incident polarization state at each refractive index for thin film materials with different thicknesses; placing the nanoscale thin film to be detected on the sample stage, and at a certain incident angle, successively collecting the measurement data of the in-plane photon spin splitting displacement at different incident polarization states. Comparing the measurement data with the corresponding theoretical data in the database, and then determining the refractive index of the measured nanoscale thin film. The detection system of the present invention has a simple structure and is easy to operate, and during the measurement, it is the incident polarization state that is modulated rather than the incident angle. Therefore, the eccentricity error caused by the variation of the incident angle will not be introduced during the measurement process. In addition, what this method measures is the offset of the spot centroid, which is not affected by ambient light. Therefore, this method has the advantages of high measurement accuracy and good stability.

Description

Technical Field

[0001] The present invention belongs to the field of precision measurement, and relates to a polarization state modulation type nano-thin film refractive index measurement method based on the in-plane photon spin Hall effect and its application. Background Technique

[0002] With the development of current science and technology, various devices and instruments are becoming more and more miniaturized, which promotes the production and manufacturing technology of thin films to reach the nanometer scale. Nano-thin films have many peculiar properties compared with bulk materials: size effect, surface effect, interface effect, etc., making them have unique electrical, optical and mechanical properties, and are widely used in microelectronics, optoelectronics, aerospace, bioengineering, weaponry, food science, medical instruments and polymer materials and other fields. The refractive index of nano-thin films is the basic optical constant of thin films, reflecting the interaction between light and thin films. On the one hand, in optical devices, optoelectronic devices, semiconductor devices and other devices, the refractive index of nano-thin films is a basic parameter for the optical analysis and optimal design of related devices, affecting the performance of various devices. On the other hand, the refractive index of nano-thin films is different from that of bulk materials and is affected by factors such as deposition methods, process parameters and material properties. Even thin film materials with the same chemical composition have different refractive indices under different deposition processes and preparation conditions. Therefore, there is a certain error between the reference refractive index given in the material library or packaging label and the actual value. Therefore, accurately measuring the refractive index of nano-thin films is of great significance for the design, manufacture and application of new materials and their related devices.

[0003] At present, the methods for measuring the refractive index of nanoscale thin films mainly include transmission / reflection spectroscopy, ellipsometry, surface plasmon resonance method, etc. Both the transmission / reflection spectroscopy and ellipsometry belong to the light intensity modulation type measurement methods and are affected by the stability of the light source and background light. In the surface plasmon resonance method, although the phase modulation type is not affected by the stability of the light source and background light, it can only detect the refractive index of metal thin films and cannot detect non-absorbing thin films. The photon spin Hall effect refers to the fact that when a polarized light beam is reflected or refracted at an interface with a refractive index gradient, the left-handed and right-handed components of the light beam will produce spin-related splitting displacements in the direction perpendicular to the refractive gradient. Spin splitting displacements occur both in the plane parallel to and perpendicular to the plane of incidence. Usually, the former is called the in-plane spin splitting displacement, and the latter is called the out-of-plane spin splitting displacement. Because the photon spin Hall effect is extremely sensitive to the property changes of the reflection / refraction interface, the parameter changes of the nanoscale thin film can cause changes in its in-plane and out-of-plane spin splitting displacements. Therefore, the photon spin Hall effect has good application prospects in the field of nanoscale thin film parameter detection. For example, a Chinese invention patent with the patent number ZL201910681547.5 discloses a method for measuring the thickness of a nanoscale thin film using the photon spin Hall effect. Based on the out-of-plane spin splitting displacement, it can achieve the measurement of the thickness of the nanoscale thin film. From the cause of the photon spin Hall effect, it can be seen that it originates from the refractive index gradient difference existing at the interface where the light beam acts during the reflection / refraction process of the light beam, which means that the photon spin Hall effect is very sensitive to the change of the refractive index of the interface material. In previous studies, we found that usually under the same parameter conditions, the in-plane photon spin splitting displacement is much larger than the out-of-plane photon spin splitting displacement. This means that compared with the out-of-plane photon spin splitting displacement, the parameter measurement based on the in-plane photon spin splitting displacement will have higher sensitivity or higher resolution, which will lead to inaccurate detection results. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a polarization state modulation type nanoscale thin film refractive index measurement method and its application based on the in-plane photon spin Hall effect. The detection system structure of this method is simple and easy to operate, and during the measurement, the incident polarization state is modulated instead of the incident angle. Therefore, the eccentricity error caused by the change of the incident angle will not be introduced during the measurement process. In addition, this method measures the offset of the centroid of the light spot and is not affected by ambient light. Therefore, this method has the advantages of high measurement accuracy and good stability.

[0005] The technical solution of the present invention is realized as follows:

[0006] A polarization state modulation type nanoscale thin film refractive index measurement method based on the in-plane photon spin Hall effect includes the following steps:

[0007] (1) According to the theoretical relationship model between the in-plane photon spin splitting displacement and the refractive index of the thin film, establish a data set of the theoretical correspondence between the incident polarization state and the in-plane photon spin splitting displacement corresponding to each refractive index of the thin film when the incident light beam is reflected from the surface of nano-scale thin films with different thicknesses at any incident angle.

[0008] (2) Incident the incident light at a certain incident angle and a certain initial incident polarization state onto the material to be measured, and use the method of measuring the in-plane photon spin splitting displacement to obtain the in-plane photon spin splitting displacement in this polarization state.

[0009] (3) Referring to the method in step (2), sequentially change the incident polarization state to obtain a set of measurement data of the in-plane photon spin splitting displacement under a set of incident polarization states.

[0010] (4) Compare, analyze and calculate the measurement data set obtained in step (3) with the theoretical correspondence data set obtained in step (1), and finally determine the refractive index of the nano-scale thin film.

[0011] The theoretical relationship model between the in-plane photon spin splitting displacement and the refractive index of the thin film in step (1) above is:

[0012]

[0013]

[0014] Among them,

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021] Here, represents the in-plane spatial spin splitting displacement, represents the in-plane angular spin splitting displacement; σ represents the spin quantity of the light beam, σ = + represents the left-handed component of the light beam, σ = - represents the right-handed component of the light beam; n represents the refractive index of the thin film to be measured; a p = cos(γ i ), a s = sin(γ i ), γ is the polarization angle of the incident light; R p and R s respectively represent the reflection coefficients rp and r s modulus value; φ p and φ s respectively represent the reflection coefficient r p and r s phase; r p and r s are respectively the reflection coefficients of the horizontal and vertical components of the incident light during reflection; A ∈ {p, s}, Re represents taking the real part of a complex number, Im represents taking the imaginary part of a complex number; θ is the angle of incidence; z R = k i ω0 2 / 2 represents the Rayleigh length, ω0 is the waist of the Gaussian beam; k i = 2πn1 / λ, n1 represents the refractive index of the first layer of medium in the reflection interface, λ is the wavelength of the incident light propagating in the first medium.

[0022] The above reflection coefficients r p and r s When affected by the refractive index of the measured nanoscale thin film, the reflection coefficients r p and r s can be obtained from the Fresnel equations. The calculation formulas for the reflection coefficients r p and r s are as follows:

[0023]

[0024]

[0025]

[0026]

[0027] where r 12 is the reflection coefficient at the interface between the first layer of medium and the nanoscale thin film, r 23 is the reflection coefficient at the interface between the nanoscale thin film and the third layer of medium; i represents the imaginary number, n3 represents the refractive index of the third layer of medium in the reflection interface; n2 represents the refractive index of the measured nanoscale thin film in the reflection interface; the superscript letters p and s respectively represent the horizontal and vertical components of the reflected light, d represents the thickness of the measured thin film, m represents the number of layers of the medium in the reflection interface, k0 = 2π / λ represents the wave number of the incident light in vacuum.

[0028] In the above step (1), the incident polarization state is linearly polarized or elliptically polarized, and the in-plane photon spin splitting displacement is the in-plane photon spin splitting displacement of the left-handed or right-handed component of the light beam.

[0029] In the above step (2), a certain angle of incidence is any angle in 0 - 90°.

[0030] Preferably, the method for measuring the in-plane photon spin splitting displacement is the quantum weak measurement method.

[0031] In the above step (3), changing the incident polarization state means changing the incident polarization angle, changing the incident polarization phase, or changing both the incident polarization angle and the incident polarization phase simultaneously.

[0032] The operations of comparison analysis and calculation in the above step (4) are as follows: First, calculate the sum of the squares of the residuals between the measurement data set and the theoretical corresponding relationship data sets at each refractive index. The refractive index value corresponding to the theoretical data set when the sum of the squares of the residuals is the smallest is the refractive index value of the measured thin film.

[0033] Furthermore, the thin film is a thin film of any material, and the thin film has a single-layer or multi-layer structure.

[0034] Application of the above polarization state modulation type nano-scale thin film refractive index measurement method in measuring the offset of the centroid of the measurement spot.

[0035] The present invention has the following beneficial effects:

[0036] 1. Based on the in-plane photon spin splitting displacement, the present invention modulates the polarization state of the incident light, and based on the dependence relationship between the in-plane photon spin splitting displacement and the refractive index of the nano-scale thin film, realizes non-contact, non-destructive, highly sensitive and highly stable measurement of the refractive index of the nano-scale thin film, and the detection system has a simple structure and is easy to operate.

[0037] 2. The present application establishes a database of the in-plane photon spin splitting displacement varying with the incident polarization state at each refractive index for thin film materials of different thicknesses; places the nano-scale thin film to be detected on the sample stage, and at a certain incident angle, sequentially collects the measurement data of the in-plane photon spin splitting displacement at different incident polarization states. Compare this measurement data with the corresponding theoretical data in the database, and then determine the refractive index of the measured nano-scale thin film. The detection system of the present invention has a simple structure and is easy to operate, and when measuring, it modulates the incident polarization state rather than the incident angle. Therefore, the eccentricity error caused by the change of the incident angle will not be introduced during the measurement process. In addition, this method measures the offset of the centroid of the light spot, which is not affected by ambient light, so this method has the advantages of high measurement accuracy and good stability. Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 Schematic diagram of in-plane spatial spin splitting of light beam on the surface of the sample to be measured in the present invention.

[0040] Figure 2 Graph of the change of the in-plane spatial spin splitting displacement of the left-handed component of the reflected light corresponding to the refractive index of 1 - 2 RIU of the nanoscale thin film of the present invention with the polarization angle.

[0041] Figure 3 Graph of the change of the in-plane spatial spin splitting displacement of the left-handed component of the reflected light corresponding to the refractive index of 2 - 4 RIU of the nanoscale thin film of the present invention with the polarization angle.

[0042] Figure 4 Graph of the change of the in-plane spatial spin splitting displacement of the left-handed component of the reflected light corresponding to the refractive index of 4 - 6 RIU of the nanoscale thin film of the present invention with the polarization angle.

[0043] Figure 5 Schematic diagram of the device for measuring the in-plane photon spin splitting displacement of the present invention; where 1 - laser, 2 - half-wave plate, 3 - polarizer Ⅰ, 4 - sample to be measured, 5 - sample stage, 6 - lens, 7 - polarizer Ⅱ, 8 - imaging device, 9 - computer.

[0044] Figure 6 Graph of the refractive index fitting result based on the in-plane spatial spin splitting displacement of the present invention

[0045] Figure 7 Schematic diagram of the in-plane angular spin splitting of light beam on the surface of the sample to be measured in the present invention.

[0046] Figure 8 Graph of the refractive index fitting result based on the in-plane angular spin splitting displacement of the present invention. Detailed implementation manners

[0047] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0048] Embodiment 1

[0049] In this embodiment, the incident polarization angle γ is modulated i , and based on the in-plane spatial spin splitting displacement δ xMeasure the refractive index of the thin film under test. In this embodiment, the incident light beam used is a Gaussian beam with a wavelength of 632.8 nm and a beam waist ω0 of 10 μm. The beam is incident on the surface of the nanoscale thin film sample under test at an incident angle θ = 70°, and the thickness of the thin film is 100 nm.

[0050] The theoretical relationship model between the refractive index of the thin film and the in-plane spatial spin splitting displacement is:

[0051]

[0052] Where,

[0053]

[0054]

[0055]

[0056]

[0057] Here, σ represents the spin quantity of the light beam, σ = + represents the left-handed component of the light beam, and σ = - represents the right-handed component of the light beam; a p = cos(γ i ), a s = sin(γ i ), γ is the polarization angle of the incident light; R p and R s respectively represent the modulus values of the reflection coefficients r p and r s ; φ p and φ s respectively represent the phases of the reflection coefficients r p and r s ; r p and r s are the reflection coefficients of the p-component and s-component of the incident light during reflection, respectively; A ∈ {p, s}, Re represents taking the real part of a complex number, and Im represents taking the imaginary part of a complex number; θ is the incident angle; z R = k i ω0 2 / 2 represents the Rayleigh length, ω0 is the beam waist of the Gaussian beam; k i = 2πn1 / λ, n1 represents the refractive index of the first layer of medium in the reflection interface, and λ is the wavelength of the incident light when propagating in the first medium;

[0058] The reflection coefficients r p and r s are affected by the refractive index of the nanoscale thin film under test. According to the Fresnel equation:

[0059]

[0060]

[0061]

[0062]

[0063] r 12 is the reflection coefficient at the interface between the first-layer medium and the nanoscale thin film, and r 23 is the reflection coefficient at the interface between the nanoscale thin film and the third-layer medium. i represents the imaginary number, and n3 represents the refractive index of the third-layer medium (substrate) in the reflection interface; n2 represents the refractive index of the measured nanoscale thin film in the reflection interface.

[0064] As can be seen from Equation ①, the change in the refractive index of the nanoscale thin film will cause the change of the reflection coefficients r p and r s , and then cause the change of the in-plane spatial spin splitting displacement. And for different refractive indices, the in-plane spatial spin splitting displacement δ i corresponding to the incident polarization angle γ xm is also different, that is, the [γ im , δ xm arrays are different under different thin film refractive indices. To theoretically verify the feasibility of this method, we plotted the relationship curve between the in-plane spatial spin position of the left-handed component of the reflected beam and the incident light polarization angle under different thin film refractive indices when the thickness of the measured thin film is 100 nm, as shown in Figures 2 - 4 shown. As can be seen from Figure 2 , even if the refractive index of the thin film changes by 0.1 RIU, different curves have good distinguishability. Therefore, by comparing and analyzing the theoretical data and the measured data, the refractive index of the measured thin film can be determined.

[0065] Next, in combination with the attached drawings, the specific measurement process of the refractive index of the nanoscale thin film will be described in detail.

[0066] (1) According to Equation ①, establish a theoretical database of the in-plane spatial spin splitting displacement corresponding to the thickness of each thin film, the incident angle, and each incident polarization angle under different refractive indices.

[0067] (2) Select the incident light as linearly polarized light, adjust the polarization angle γ i of the incident light to -10°, and let the incident light enter the surface of the measured thin film at an incident angle of 70°. The left-handed component and the right-handed component of the reflected beam will undergo in-plane spatial photon spin splitting at the thin film interface, as shown in Figure 1 , and then we use the quantum weak measurement method to measure the in-plane spatial photon spin splitting displacement at this time. The schematic diagram of the device for measuring the in-plane spatial photon spin splitting displacement by quantum weak measurement is shown in Figure 5As shown. The laser 1 generates a linearly polarized light beam, which successively passes through a half-wave plate 2 and a polarizer I 3, and then is incident on the surface of the measured nanoscale thin film sample 4, and reflection occurs at this interface. Due to the refractive index gradient existing at the reflection interface, the in-plane photon spin Hall effect is caused, and further, the in-plane spatial spin splitting of the left-handed and right-handed components of the reflected light beam occurs. The reflected light beam vertically passes through a lens 6 and a polarizer II 3, and finally the light beam is vertically incident on a photosensitive imaging device 8, and the spot image information presented by the imaging device 8 is transmitted to a computer 9. By using this spot image, the centroid displacement of the spot in the image is obtained, and finally the value δ of the spatial displacement of the left-handed component is obtained. x Rotating the polarizer I 3 can change the polarization angle γ of the incident light beam. i In this embodiment, the initial polarization angle γ of the polarizer I 3 i =-10°. The thickness of the measured thin film is 100 nm. The measured sample 4 is placed on the sample stage 5. Rotating the sample stage 5 can adjust the angle at which the light beam is incident on the surface of the measured thin film sample 4. In this embodiment, the incident angle θ = 70°. The lens 6 is used to collimate the light beam. Rotating the polarizer II 3 can adjust the post-selection state of the weak measurement.

[0068] (3) Rotate the polarizer I 3 successively at intervals of 1°, and record the corresponding in-plane spatial spin splitting displacement δ im under the corresponding polarization angle γ xm . Until the polarization angle γ of the incident light i = 10°. In this way, a set of [γ im , δ xm data can be obtained, where m = 1, 2, ……, 21. The specific data is shown in Table 1.

[0069] Table 1: Measurement and calculation data under different incident polarization angles

[0070]

[0071] (4) According to the theoretical data corresponding to the refractive indices of each thin film in step (1) and the measurement data set [γ im , δ xm in step (3), calculate the sum of the squared residuals between the measurement data and the theoretical data [γ itm , δ xtm under each refractive index. When the sum of the squared residuals is the smallest, the refractive index corresponding to [γ itm , δ xtm is the refractive index of the measured thin film. The specific data is shown in Table 1.

[0072] The specific calculation method of the sum of the squared residuals is as follows:

[0073]

[0074] Sum of squared residuals In the formula, l m represents the measured data δ xm , y m represents the theoretical data δ xtm , v m represents the residual error (abbreviated as residual).

[0075] After calculation and analysis, when the refractive index is 1.7662, the sum of squared residuals between the theoretical value of the in-plane spatial spin splitting displacement and the measured data is the smallest. Therefore, 1.7662 is the measured value of the refractive index of the thin film to be measured. Figure 6 It is a fitting result diagram of the refractive index based on the in-plane spatial spin splitting displacement. The black curve is the theoretical relationship curve between the in-plane spatial spin splitting displacement and the polarization angle when the refractive index is 1.7662, and the black circles are the measured data. The current optical constant handbook shows that the refractive index of the solid substance Al2O3 at a wavelength of 632.8 nm is about 1.77, while the refractive index of the 100-nm-thick Al2O3 thin film measured in this embodiment is 1.7662. Therefore, the measurement method mentioned in the present invention is feasible.

[0076] Example 2

[0077] In this embodiment, the refractive index of the thin film to be measured is measured based on the in-plane angular spin splitting displacement Θ x , and the theoretical relationship model between the thin film refractive index and the in-plane angular spin splitting displacement is as follows:

[0078]

[0079] Among them,

[0080]

[0081]

[0082] The meanings of the parameter letters in Equation ② are as described in Example 1. It can be seen from Equation ② that the change in the refractive index of the nanoscale thin film will cause the change of the reflection coefficients r p and r s , and further cause the change of the in-plane angular spin splitting displacement. Moreover, for different refractive indices, the array of the in-plane angular spin splitting displacements Θ i corresponding to the incident polarization angles γ x is also different, that is, the [γ im , Θ xm arrays under different thin film refractive indices are different. Therefore, by comparing and analyzing the theoretical data and the measured data, the refractive index of the thin film to be measured can be determined.

[0083] Next, in combination with the accompanying drawings, the specific measurement process of the refractive index of the nanoscale thin film will be described in detail.

[0084] (1) According to Equation ②, establish a theoretical database of the in-plane angular spin splitting displacement corresponding to the thickness of each thin film, the incident angle, and each incident polarization angle at different refractive indices.

[0085] (2) Select linearly polarized light as the incident light and adjust the polarization angle γ i of the incident light to -10°, and let the incident light be incident on the surface of the thin film to be measured at an incident angle of 70°. The left-handed and right-handed components of the reflected light beam will undergo in-plane angular spin splitting at the thin film interface, as Figure 7 shown. Then, we use the quantum weak measurement method to measure the in-plane angular photon spin splitting displacement at this time. The schematic diagram of the device for measuring the in-plane angular photon spin splitting displacement using quantum weak measurement is as Figure 5 shown.

[0086] (3) Rotate the polarizer Ⅰ3 in steps of 1° and record the corresponding in-plane spatial spin splitting displacement Θ im at the corresponding polarization angle γ xm . Until the polarization angle γ i of the incident light = 10°. In this way, a set of [γ im , Θ xm data can be obtained, where m = 1, 2, ……, 21.

[0087] (4) According to the theoretical data corresponding to the refractive indices of each thin film in step (1) and the measurement data set [γ im , Θ xm in step (3), calculate the sum of the squares of the residuals between the measurement data and the theoretical data [γ itm , Θ xtm at each refractive index. When the sum of the squares of the residuals is the smallest, the refractive index corresponding to [γ itm , Θ xtm is the refractive index of the thin film to be measured. The specific calculation method of the sum of the squares of the residuals is the same as that in Example 1.

[0088] Through calculation and analysis, when the refractive index is 1.7665, the sum of the squares of the residuals between the theoretical value of the in-plane angular spin splitting displacement and the measurement data is the smallest. That is, the measurement result of the refractive index of the thin film to be measured is 1.7665. Figure 8 is the refractive index fitting result graph based on the in-plane angular spin splitting displacement. The black curve in this graph is the theoretical relationship curve between the in-plane angular spin splitting displacement and the polarization angle when the refractive index is 1.7665, and the black circles are the measurement data. The current optical constant handbook shows that the refractive index of the solid substance Al2O3 at a wavelength of 632.8 nm is about 1.77, while the refractive index of the 100-nm-thick Al2O3 thin film measured in this example is 1.7665. Therefore, the measurement method mentioned in the present invention is feasible.

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the refractive index of a nanoscale thin film with a polarization state modulation type based on the in-plane photonic spin Hall effect, characterized in that It includes the following steps: (1) According to the theoretical relationship model between the in-plane photon spin splitting displacement and the refractive index of the thin film, establish a theoretical correspondence data set of the incident polarization state and the in-plane photon spin splitting displacement corresponding to each refractive index of the thin film when the incident light beam is reflected on the surface of nanoscale thin films with different thicknesses at an arbitrary incident angle. (2) Incident the incident light at a certain incident angle and a certain initial incident polarization state onto the material to be measured, and use the method of measuring the in-plane photon spin splitting displacement to obtain the in-plane photon spin splitting displacement in this polarization state. (3) Referring to the method in step (2), sequentially change the incident polarization state to obtain a set of measurement data of the in-plane photon spin splitting displacement under a set of incident polarization states. (4) Compare, analyze and calculate the measurement data set obtained in step (3) with the theoretical correspondence data set obtained in step (1), and finally determine the refractive index of the nanoscale thin film.

2. The polarization state modulation type nanoscale thin film refractive index measurement method based on the in-plane photonic spin Hall effect according to claim 1, wherein In step (1), the in-plane photon spin splitting displacement refers to the in-plane spatial spin splitting displacement or the in-plane angular spin splitting displacement. The theoretical relationship model between the in-plane spatial spin splitting displacement and the refractive index of the thin film is: The theoretical relationship model between the in-plane angular spin splitting displacement and the refractive index of the thin film is: Wherein, Here, represents the in-plane spatial spin splitting displacement, represents the in-plane angular spin splitting displacement; σ represents the spin amount of the light beam, σ = + represents the left-handed component of the light beam, σ = - represents the right-handed component of the light beam; n represents the refractive index of the thin film to be measured; a p = cos(γ i ), a s = sin(γ i ), γ is the polarization angle of the incident light; R p and R s respectively represent the modulus values of the reflection coefficients r p and r s ; φ p and φ s respectively represent the phases of the reflection coefficients r p and r s ; r p and r s are respectively the reflection coefficients when the horizontal component and the vertical component of the incident light are reflected; A ∈ {p, s}, Re represents taking the real part of a complex number, Im represents taking the imaginary part of a complex number; θ is the incident angle; z R = k i ω0 2 / 2 represents the Rayleigh length, ω0 is the waist of the Gaussian beam; k i = 2πn1 / λ, n1 represents the refractive index of the first layer of medium in the reflection interface, λ is the wavelength of the incident light when propagating in the first medium.

3. The method for measuring the refractive index of a nanoscale thin film with a polarization state modulation type based on the in-plane photonic spin Hall effect according to claim 2, wherein The said r p and r s are calculated as follows: where r 12 is the reflection coefficient at the interface between the first layer of medium and the nanoscale film, and r 23 is the reflection coefficient at the interface between the nanoscale film and the third layer of medium; i represents the imaginary number, n3 represents the refractive index of the third layer of medium in the reflection interface; n2 represents the refractive index of the measured nanoscale film in the reflection interface; the superscript letters p and s represent the horizontal and vertical components of the reflected light respectively, d represents the thickness of the measured film, m represents the number of layers of medium in the reflection interface, and k0 = 2π / λ represents the wave number of the incident light in vacuum.

4. The method for measuring the refractive index of a nanoscale thin film with polarization state modulation based on the in-plane photonic spin Hall effect according to claim 2 or 3, characterized in that: In step (1), the incident polarization state is a linear polarization or an elliptical polarization state, and the in-plane photon spin splitting displacement is the in-plane photon spin splitting displacement of the left-handed component or the right-handed component of the light beam.

5. The method for measuring the refractive index of a nanoscale thin film with polarization state modulation based on the in-plane photonic spin Hall effect according to claim 4, wherein: In step (2), a certain incident angle is any angle in the range of 0 - 90°.

6. The polarization state modulation type nanoscale thin film refractive index measurement method based on the in-plane photon spin Hall effect according to claim 5, wherein: The method of measuring the in-plane photon spin splitting displacement is the quantum weak measurement method.

7. The polarization state modulation type nanoscale thin film refractive index measurement method based on the in-plane photonic spin Hall effect according to claim 6, characterized in that: In step (3), changing the incident polarization state means changing the incident polarization angle, changing the incident polarization phase, or changing both the incident polarization angle and the incident polarization phase simultaneously.

8. The method for measuring the refractive index of a nanoscale thin film with polarization state modulation based on the in-plane photonic spin Hall effect according to claim 7, characterized in that, The operation of the comparison, analysis and calculation in step (4) is: first calculate the sum of the squares of the residuals between the measurement data set and the theoretical correspondence data sets at each refractive index. The refractive index value corresponding to the theoretical data set when the sum of the squares of the residuals is the smallest is the refractive index value of the thin film to be measured.

9. The method for measuring the refractive index of a nanoscale thin film with polarization state modulation based on the in-plane photonic spin Hall effect according to any one of claims 5-8, characterized in that: The thin film is a thin film of any material, and the thin film is a single-layer or multi-layer structure.

10. Application of the method for measuring the refractive index of a polarization state modulation type nanoscale thin film according to claim 9 in measuring the offset of the centroid of the measurement spot.

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