Gold layer thickness measurement method based on surface plasmon resonance holographic microscopy

Abstract

The present invention belongs to the field of optical measurement technology, and specifically relates to a gold layer thickness measurement method based on surface plasmon resonance holographic microscopy. The method has the characteristics of ultra-high response sensitivity to small changes in the thickness of the gold layer based on the phase information of the reflected light wave when the surface plasmon resonance occurs. The surface plasmon resonance holographic microscopy system is used to measure the phase change curve of the reflected light wave during the volatilization of the dielectric droplet and combined with the theoretical model to achieve quantitative characterization of the thickness of the gold layer. The method can provide a high-precision, non-destructive, fast and low-cost measurement means and technology for the measurement of the thickness of the gold layer, and finally achieve non-destructive, fast, high-precision nanometer-level precision measurement of the thickness of the gold layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and specifically relates to a method for measuring the thickness of a gold layer based on surface plasmon resonance holographic microscopy. The method has the advantage of ultra-high sensitivity to slight changes in the thickness of the gold layer by utilizing the phase information of reflected light waves when surface plasmon resonance occurs, thereby achieving high-precision and rapid measurement of the thickness of the gold layer. Background Art

[0002] Surface plasmon resonance technology has a wide range of applications in the fields of dielectric property measurement and biological cell dynamic monitoring. It can not only detect small changes in the refractive index and concentration of samples in the near-field area of ​​the metal interface with high sensitivity, but also respond to changes in the thickness of metal thin layers, especially gold layers, with high sensitivity. Surface plasmon resonance is generally excited by a Kretschmann structure, including a prism-gold layer-dielectric layer, such as Figure 1 As shown. When a beam of p-polarized light waves passes through a prism and is incident on the surface of the gold layer at a specific angle, the free electrons on the surface of the gold layer will collectively oscillate, the energy of the incident light wave is coupled into the surface plasma wave, and the intensity and phase of the reflected light wave also change significantly accordingly, and surface plasmon resonance occurs at this time. It is worth noting that when surface plasmon resonance occurs, the phase information of the reflected light wave has a higher response sensitivity to small changes in the sample in the near field region than the intensity information of the reflected light wave.

[0003] The thickness of the gold layer is crucial to the excitation efficiency of surface plasmon resonance. At a specific excitation wavelength, a gold layer that is too thin or too thick will reduce the efficiency of exciting surface plasmon resonance. Especially for phase detection technology, the thickness of the gold layer directly determines the gradient and range of the phase change of the reflected light wave. Therefore, in order to obtain the optimal gold layer thickness and efficiently excite surface plasmon resonance, it is very necessary to measure and characterize the thickness of the gold layer with high precision. The step meter is a commercial instrument used to measure the thickness of thin films. It measures the thickness of the gold layer by lightly touching the surface of the sample, but the contact used by the step meter is relatively hard and may cause damage to the sample surface. Ellipsometer is another effective means to characterize the thickness of the gold layer, but it has the disadvantages of complex optical path structure and data post-processing process and limited measurement accuracy.

[0004] In the prior art, researchers have proposed a sensor based on surface plasmon resonance technology (ZL201610576077.2), which measures the thickness of double or multi-layer metal thin layers by obtaining the difference in the phase change of two orthogonal polarized light waves as the incident angle changes. It cannot directly measure a single gold layer, and there are problems such as cumbersome measurement process and limited measurement accuracy. Furthermore, surface plasmon resonance holographic microscopy combines the advantages of digital holography, which can perform wide-field dynamic measurement of light wave complex amplitude, and high sensitivity of surface plasmon resonance, and can simultaneously obtain intensity and phase images in the near-field region. In ZL201710613735.5, the thickness of the dielectric thin layer above the gold layer can be measured by simultaneously demodulating the surface plasmon resonance intensity and phase images, but the thickness of the gold layer cannot be measured. In CN202211232389.3, surface plasmon resonance holographic microscopy can also measure the thickness of metal thin layers, but it is only applicable to models where both metal layers exist, and it cannot directly measure the thickness of a single gold layer.

[0005] In summary, although there are a variety of existing technologies that have achieved the measurement of gold layer thickness, none of them can directly measure the thickness of a single gold layer non-destructively, quickly, simply and with high precision, and there is a problem of complex subsequent data processing. At present, there is still a lack of a direct, non-invasive, pre-processing-free, nanometer-level precision gold layer thickness measurement characterization method. Therefore, it is of great significance to develop a quick and simple gold layer measurement method with nanometer-level measurement accuracy. Summary of the invention

[0006] Technical issues to be solved

[0007] In order to solve the shortcomings of the prior art, the present invention proposes a method for measuring the thickness of a gold layer based on surface plasmon resonance holographic microscopy. The method experimentally records the phase change curve of the reflected light wave during the volatilization of the ethanol solution when surface plasmon resonance occurs, and combines the theoretical curve of the reflection phase shift changing with the refractive index of the dielectric, and finally achieves high-precision and rapid measurement of the thickness of the gold layer.

[0008] Technical Solution

[0009] The idea of ​​the present invention is to first establish a surface plasmon resonance model including a prism-gold layer-dielectric solution layer, and experimentally use a surface plasmon resonance holographic microscope system to record in real time a digital hologram of the ethanol solution volatilization process when the surface plasmon resonance occurs and perform numerical reconstruction to obtain a phase change curve of the reflected light wave. When other parameters of the model are known and only the thickness of the gold layer is unknown, the thickness of the gold layer can be uniquely determined by the phase curve measured experimentally, thereby achieving high-precision measurement of the thickness of the gold layer.

[0010] The present invention provides a method for measuring the thickness of a gold layer based on surface plasmon resonance holographic microscopy, comprising the following steps:

[0011] Step 1: In the prism structure, no ethanol solution sample is dropped, and a background hologram without sample information is recorded using a surface plasmon resonance holographic microscopy system;

[0012] Step 2: titrate a drop of ethanol solution on the surface of the gold layer, and then continuously record the sample hologram containing the ethanol solution using a surface plasmon resonance holographic microscopy system until the ethanol solution evaporates into pure water;

[0013] Step 3: Measurement of experimental curve:

[0014] The background hologram and sample hologram recorded by the image acquisition device are numerically reconstructed to obtain the surface plasmon resonance phase image of the ethanol solution with the background phase removed. A rectangular area is selected in the ethanol solution sample area and the average is taken to obtain the experimental curve of the phase value as the ethanol solution evaporates.

[0015] Three characteristic parameters are obtained based on the experimental curve;

[0016] Step 4: Drawing of theoretical curve:

[0017] Using the theoretical formula, the reflection phase shift difference of the reflected light wave in the surface plasmon resonance model is calculated. The theoretical curve of the change of dielectric refractive index n3, the reflection phase shift difference It is defined as the difference in the reflection phase shift of the corresponding reflected light wave when the dielectric layer is ethanol solution and air respectively;

[0018] Based on the theoretical curve, three characteristic parameters are obtained;

[0019] Step 5: Demodulation of gold layer thickness:

[0020] The three characteristic parameters of the experimental curve measured by the surface plasmon resonance holographic microscopy system and the theoretical curve calculated by the surface plasmon resonance model are respectively equal, and the thickness of the gold layer is demodulated by the characteristic parameters.

[0021] Furthermore, the process of drawing the theoretical curve in step 4 is as follows:

[0022] In the surface plasmon resonance model, the reflection coefficient of the reflected light wave is expressed as:

[0023]

[0024] Among them, r j,N is the reflection coefficient between the jth and Nth layers of media;

[0025] j represents the jth layer of medium;

[0026] N represents the total number of layers included in the surface plasmon resonance model. For the three-layer model, j = 1 and N = 3;

[0027] r j,j+1 is the reflection coefficient between two adjacent layers of media;

[0028] r j+1,N is the reflection coefficient between the j+1th and Nth layers of media;

[0029] d j+1 is the thickness of the j+1th layer;

[0030] k zj is the wave vector of the light wave along the z direction in the jth layer of the medium;

[0031] k z(j+1) is the wave vector of the light wave along the z direction in the j+1th layer of the medium;

[0032] is the ratio of the dielectric constant of the j-th layer of medium to the wave vector of the light wave along the z direction in the j-th layer of medium;

[0033] is the ratio of the dielectric constant of the j+1th layer of medium to the wave vector of the light wave along the z direction in the j+1th layer of medium;

[0034] is the dielectric constant of the jth layer;

[0035] and θ are the wavelength and angle of incidence of the incident light wave respectively;

[0036] Reflection phase shift of reflected light wave The calculation is as follows:

[0037]

[0038] Among them, Im(r 1,3 ) and Re(r 1,3 ) represent the reflection coefficient r 1,3 The imaginary and real parts of

[0039] Using the above formula, the reflection phase shift difference of the reflected light wave in the surface plasmon resonance model is calculated: Theoretical curve as a function of dielectric refractive index n3.

[0040] Furthermore, the volume ratio of the ethanol solution in step 2 is , the refractive index is 1.3440 RIU, and the refractive index of the pure water in step 2 is 1.3317 RIU.

[0041] Furthermore, the hologram numerical reconstruction in step 3 is based on scalar diffraction theory and convolution method; and the surface plasmon resonance phase image of the ethanol solution is obtained based on the double exposure method.

[0042] Furthermore, the phase value of step 3 and the reflected phase shift difference of step 4 are equal.

[0043] Furthermore, the characteristic parameters of steps 3 and 4 are: the reflection phase shift difference at the initial moment of ethanol drop volatilization , the reflection phase shift difference when the solution evaporates to pure water , and the range of the reflection phase shift difference at the initial and final moments .

[0044] Furthermore, the step 5 of demodulating the thickness of the gold layer by the characteristic parameter is as follows:

[0045] Step 5.1: For a certain range of reflection phase shift difference There are two sets of solutions for the thickness of the gold layer d2;

[0046] Step 5.2: Plot the two sets of gold layer thickness to solve for the reflection phase shift difference Theoretical curve of the change of dielectric refractive index n3, using and Determine the thickness of the gold layer.

[0047] Beneficial Effects

[0048] Compared with the prior art, this application has at least the following beneficial effects:

[0049] 1. The method for measuring the thickness of the gold layer proposed in the present invention is based on the characteristic that the phase information of the reflected light wave when surface plasmon resonance occurs has a high sensitivity response to the change of the thickness of the gold layer in the near field area. The phase change curve of the reflected light wave during the volatilization of the ethanol solution is measured by a surface plasmon resonance holographic microscopy system, and the thickness of the gold layer can be quantitatively determined, thereby finally realizing non-destructive, rapid, and nanometer-level precision measurement of the thickness of the gold layer.

[0050] 2. Figure 5 The demodulation results of two gold layer thicknesses (46 nm and 43 nm, respectively) are shown. Therefore, the results show that the high-precision, non-destructive and rapid measurement of gold layer thickness can be achieved by dynamically monitoring the evaporation process of ethanol solution using a surface plasmon resonance holographic microscopy system and combining it with a theoretical model. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is the Kretschmann structure for exciting surface plasmon resonance involved in the background technology of the present invention.

[0052] In the figure: the surface plasmon resonance model includes: 1-prism, 2-gold layer, 3-dielectric layer.

[0053] Figure 2 It is a theoretical curve of the reflection phase shift difference of the reflected light wave under the surface plasma resonance model calculated by using the Fresnel formula in the technical solution of the present invention as the refractive index of the dielectric layer changes.

[0054] In the figure: represents the reflection phase shift difference of the reflected light wave; n3 represents the refractive index of the third dielectric layer; It represents the variation range of the reflection phase shift difference when n3 is 1.3440 RIU and 1.3317 RIU respectively; t0 and t1 represent the initial moment and final moment of the volatilization process of the ethanol solution sample respectively.

[0055] FIG. 3( a ) is a diagram of the present invention based on Figure 2 The phase curve shown is obtained Theoretical curves as the thickness of the gold layer changes;

[0056] Figure 3(b) is When the value is determined, one of the corresponding sets of theoretical curves of reflection phase shift difference changing with the refractive index of the dielectric;

[0057] Figure 3(c) is When the value is determined, one of the corresponding sets of theoretical curves of reflection phase shift difference changing with the refractive index of the dielectric;

[0058] In the figure: d2 represents the thickness of the gold layer.

[0059] Figure 4 (a) is a background hologram measured by a surface plasmon resonance holographic microscopy system in an embodiment of the present invention;

[0060] Figure 4(b) is an ethanol solution ( ; RI = 1.3440) sample hologram containing solution information at the initial moment of the volatilization process;

[0061] Figure 4(c) is an ethanol solution ( ; RI = 1.3440) sample hologram containing solution information at the final moment of the volatilization process;

[0062] Figure 5 is the ethanol solution measured by the surface plasmon resonance holographic microscopy system in the embodiment of the present invention ; RI=1.3440) reflection phase shift difference change curve during volatilization and the corresponding two gold layer thickness measurement results. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0064] The present invention will now be further described with reference to the embodiments and the accompanying drawings:

[0065] A high-precision gold layer thickness measurement method based on surface plasmon resonance holographic microscopy, the steps are as follows:

[0066] Step 1: In the Kretschmann structure, when no ethanol solution sample is dripped, that is, the dielectric above the gold layer is air, a background hologram without sample information is recorded using a surface plasmon resonance holographic microscopy system. At this time, the four-layer surface plasmon resonance model includes: prism, gold layer, and air layer.

[0067] Step 2: Titrate a drop of ethanol solution on the surface of the gold layer, where , the refractive index is 1.3440 RIU, and then the surface plasmon resonance microscopy system is used to continuously record the digital hologram containing the ethanol solution until the ethanol solution evaporates into pure water, wherein the refractive index of pure water is 1.3317 RIU. At this time, the four-layer surface plasmon resonance model includes: prism, gold layer, and ethanol droplet layer.

[0068] Step 3: Measurement of experimental curve:

[0069] The background hologram and the sample hologram recorded by the image acquisition device are numerically reconstructed. Preferably, the numerical reconstruction is performed based on scalar diffraction theory and convolution method.

[0070] Based on the double exposure method, the surface plasmon resonance phase image of the ethanol solution with the background phase removed is obtained. A rectangular area is selected in the ethanol solution sample area and the average is taken to obtain the experimental curve of the phase value as the ethanol solution evaporates. Three characteristic parameters can be obtained from the experimental curve.

[0071] Step 4: Drawing of theoretical curve:

[0072] In the surface plasmon resonance model, the reflection coefficient of the reflected light wave is expressed as:

[0073]

[0074] Among them, r j,N is the reflection coefficient between the jth and Nth layers of media;

[0075] j represents the jth layer of medium;

[0076] N represents the total number of layers included in the surface plasmon resonance model. For the three-layer model, j = 1 and N = 3;

[0077] r j,j+1 is the reflection coefficient between two adjacent layers of media;

[0078] r j+1,N is the reflection coefficient between the j+1th and Nth layers of media;

[0079] d j+1 is the thickness of the j+1th layer;

[0080] k zj is the wave vector of the light wave along the z direction in the jth layer of the medium;

[0081] k z(j+1) is the wave vector of the light wave along the z direction in the j+1th layer of the medium;

[0082] is the ratio of the dielectric constant of the j-th layer of medium to the wave vector of the light wave along the z direction in the j-th layer of medium;

[0083] is the ratio of the dielectric constant of the j+1th layer of medium to the wave vector of the light wave along the z direction in the j+1th layer of medium;

[0084] and θ are the wavelength and angle of incidence of the incident light wave respectively;

[0085] Reflection phase shift of reflected light wave The calculation is as follows:

[0086] ;

[0087] Among them, Im(r 1,3 ) and Re(r 1,3 ) represent the reflection coefficient r 1,3 The imaginary and real parts of .

[0088] Using the above formula, the reflection phase shift difference of the reflected light wave in the surface plasmon resonance model can be calculated: The theoretical curve of the difference in the reflected phase shift of the reflected light wave when the dielectric layer is ethanol solution and air respectively as the dielectric refractive index n3 changes, such as Figure 2 It should be noted that the phase value of step 3 is different from the reflected phase shift of step 4. Furthermore, three characteristic parameters can be obtained from the above theoretical curve.

[0089] For the ethanol solution sample used in the technical method of the present invention, for its volatilization process, three characteristic parameters can be obtained from the curve, namely, the reflection phase shift difference at the initial moment of volatilization of the ethanol droplet (refractive index 1.3440 RIU) , the reflection phase shift difference when the final solution evaporates to pure water (refractive index 1.3317 RIU) , and the range of the reflection phase shift difference at the initial and final moments .

[0090] Step 5: Demodulation of gold layer thickness:

[0091] The three characteristic parameters of the experimental curve measured by the surface plasmon resonance holographic microscopy system and the theoretical curve calculated by the surface plasmon resonance model are respectively equal. The thickness of the gold layer is uniquely determined by the characteristic parameters, thereby achieving high-precision measurement of the thickness of the gold layer.

[0092] Based on the above phase curve, The theoretical curve of the change of the gold layer thickness is shown in Figure 3(a). It can be seen that for a certain There are two sets of solutions for the thickness of the gold layer. In order to finally determine the thickness of the gold layer, a theoretical curve of the reflection phase shift difference changing with the refractive index of the dielectric under the two sets of solutions for the thickness of the gold layer can be drawn, as shown in Figure 3(b) and 3(c) As shown in the figure, the corresponding ethanol solution volatilization at the initial and final moments of the two groups of solutions and Therefore, it can be used and The thickness of the gold layer is further determined. In summary, when the characteristic parameter of the surface plasmon resonance phase curve , and When all are known, the thickness of the gold layer can be uniquely determined.

[0093] In the experiment, surface plasmon resonance holographic microscopy can be used to measure the phase difference of the reflected light wave when the dielectric is air and ethanol solution, which is equal to the reflection phase shift difference of the reflected light wave under the surface plasmon resonance model. Therefore, using the experimentally measured surface plasmon resonance phase curve and its characteristic parameters ( , and ) can uniquely determine the thickness of the gold layer, that is, achieve high-precision measurement of the thickness of the gold layer.

[0094] The workflow of the gold layer thickness measurement method of this application is as follows:

[0095] First, a surface plasmon resonance holographic microscopy system was built, which includes a prism structure (Kretschmann structure) for exciting surface plasmon resonance. A collimated laser beam (wavelength: 632.8 nm) was incident on the gold layer from the hypotenuse of the prism and excited the surface plasmon resonance. After being reflected by the gold layer, part of the laser beam carried the sample information and became the object light wave, while the other part served as the reference light wave. The object light wave and the reference light wave interfered after passing through the beam splitter prism, and the interference fringes were finally recorded by the image acquisition device to form a digital hologram.

[0096] Using the above system, in the Kretschmann structure, when the dielectric above the gold layer is air, a background hologram is taken using an image acquisition device. Subsequently, a drop of ethanol solution ( ), using an image acquisition device to continuously record a digital hologram containing an ethanol solution until the ethanol solution evaporates into pure water. Using a numerical reconstruction algorithm, a surface plasmon resonance phase image containing the ethanol solution is demodulated from the digital hologram.

[0097] FIG. 4( a ) is a background hologram measured by a surface plasmon resonance holographic microscopy system in an embodiment of the present invention.

[0098] Figure 4(b) and Figure 4(c) show the background hologram and sample hologram recorded by the system at the initial and final moments of the ethanol solution volatilization process. In the phase image reconstructed from the hologram, a rectangular area at the ethanol solution is selected and averaged, and the surface plasmon resonance phase change curve of the ethanol solution from the initial moment (refractive index 1.3340) to the volatilization to pure water (refractive index 1.3317) can be further obtained, as shown in Figure 4(b) and Figure 4(c) Figure 5 From the measured phase curve, the reflection phase shift difference at the initial and final moments of the ethanol solution volatilization process is further obtained. and , and the change in the reflection phase shift difference at the initial and final moments The thickness of the gold layer can be finally determined by combining the surface plasmon resonance model and the Fresnel formula.

[0099] Figure 5 The demodulation results of two gold layer thicknesses (46 nm and 43 nm, respectively) are shown. Therefore, by dynamically monitoring the volatilization process of the ethanol solution using the surface plasmon resonance holographic microscopy system and combining it with the theoretical model, the high-precision, non-destructive and rapid measurement of the gold layer thickness can be achieved.

[0100] In summary, the method for measuring the thickness of the gold layer proposed in the present invention is based on the characteristic that the phase information of the reflected light wave when the surface plasmon resonance occurs has a high sensitivity response to the change of the thickness of the gold layer in the near field region. The surface plasmon resonance holographic microscopy system is used to measure the phase change curve of the reflected light wave during the volatilization of the ethanol solution, and the thickness of the gold layer can be quantitatively determined, and finally the non-destructive, rapid, nanometer-level precision measurement of the thickness of the gold layer can be achieved. The results show that by dynamically monitoring the volatilization process of the ethanol solution using the surface plasmon resonance holographic microscopy system and combining it with the theoretical model, the high-precision, non-destructive and rapid measurement of the thickness of the gold layer can be achieved.

[0101] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for measuring the thickness of a gold layer based on surface plasmon resonance holographic microscopy, characterized in that The steps include: Step 1: In the prism structure, a surface plasmon resonance model including a prism-gold layer-dielectric solution layer is established, and no ethanol solution sample is dropped, and a background hologram containing no sample information is recorded using a surface plasmon resonance holographic microscopy system; Step 2: titrate a drop of ethanol solution on the surface of the gold layer, and then continuously record the sample hologram containing the ethanol solution using a surface plasmon resonance holographic microscopy system until the ethanol solution evaporates into pure water; Step 3: Measurement of experimental curve: The background hologram and sample hologram recorded by the image acquisition device are numerically reconstructed to obtain the surface plasmon resonance phase image of the ethanol solution with the background phase removed. A rectangular area is selected in the ethanol solution sample area and the average is taken to obtain the experimental curve of the phase value as the ethanol solution evaporates. Three characteristic parameters are obtained based on the experimental curve; Step 4: Drawing of theoretical curve: Using the theoretical formula, the reflection phase shift difference of the reflected light wave in the surface plasmon resonance model is calculated. With the dielectric refractive index n 3 changes in the theoretical curve, the reflection phase shift difference It is defined as the difference in the reflection phase shift of the corresponding reflected light wave when the dielectric layer is ethanol solution and air respectively; Based on the theoretical curve, three characteristic parameters are obtained; Step 5: Demodulation of gold layer thickness: The three characteristic parameters of the experimental curve measured by the surface plasmon resonance holographic microscopy system and the theoretical curve calculated by the surface plasmon resonance model are respectively equal. When the refractive index of the model dielectric solution layer is known and only the thickness of the gold layer is unknown, the thickness of the gold layer is demodulated by the characteristic parameters. The characteristic parameters are: the reflection phase shift difference at the initial moment of ethanol drop volatilization , the reflection phase shift difference when the solution evaporates to pure water , and the range of the reflection phase shift difference at the initial and final moments ; The phase value of step 3 and the reflected phase shift difference of step 4 equal.

2. The method for measuring the thickness of the gold layer according to claim 1, characterized in that: The drawing process of the theoretical curve in step 4 is as follows: In the surface plasmon resonance model, the reflection coefficient of the reflected light wave is expressed as: ； ； ； ； in, r j,N For the j Layer and N Reflection coefficient between layers of media; j Representative j Layer medium; N Represents the total number of layers included in the surface plasmon resonance model. For a three-layer model, j =1, N =3; r j,j+1 is the reflection coefficient between two adjacent layers of media; r j+1,N For the j +1st level and N Reflection coefficient between layers of media; d j+1 For the j +1 layer thickness; k zj is the wave vector of the light wave along the z direction in the jth layer of the medium; k z(j+1) For light waves j +1 layer of dielectric center edge z Direction of the wave vector; For the j The dielectric constant of the layer medium is related to the light wave j Layer dielectric edge z The ratio of the wave vectors of the directions; For the j The dielectric constant of the +1 layer medium is related to the light wave in the j +1 layer of dielectric center edge z The ratio of the wave vectors of the directions; For the j The dielectric constant of the layer; and are the wavelength and incident angle of the incident light wave respectively; Reflection phase shift of reflected light wave The calculation is as follows: ； Among them, Im( r 1,3 ) and Re( r 1,3 ) represent the reflection coefficients r 1,3 The imaginary and real parts of Using the above formula, the reflection phase shift difference of the reflected light wave in the surface plasmon resonance model is calculated: With the dielectric refractive index n 3 Theoretical curve of changes.

3. The method for measuring the thickness of the gold layer according to claim 1, characterized in that: The volume ratio of the ethanol solution in step 2 is , the refractive index is 1.3440 RIU, and the refractive index of the pure water in step 2 is 1.3317 RIU.

4. The method for measuring the thickness of the gold layer according to claim 1, characterized in that: The hologram numerical reconstruction in step 3 is based on scalar diffraction theory and convolution method; and the surface plasma resonance phase image of the ethanol solution is obtained based on the double exposure method.

5. The method for measuring the thickness of the gold layer according to claim 1, characterized in that: The step 5 of demodulating the thickness of the gold layer by the characteristic parameter is as follows: Step 5.1: For a certain range of reflection phase shift difference There are two sets of gold layer thickness d Solution of 2; Step 5.2: Plot the two sets of gold layer thickness to solve for the reflection phase shift difference With the dielectric refractive index n 3 Theoretical curve of change, using and Determine the thickness of the gold layer.

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