A large-range liquid refractive index measuring instrument and measuring method based on static entities

Abstract

The present invention provides a large-range liquid refractive index measuring instrument and measuring method based on a static entity to solve the technical problems existing in the existing measurement methods for liquid refractive index, such as low measurement accuracy, high cost of required optical elements, complex formula and large error in the measurement calculation process, limited measurement range, and limited application range. The measuring instrument includes a light source and a pre-optical collimation system, a static interferometer system, a sample cell, a Fourier transform objective lens, and a planar array detector arranged in sequence along the optical path; the light emitted by the light source is compressed and collimated by the pre-optical collimation system and then vertically incident on the static interferometer system to form two parallel light beams with a transverse shear amount; the reflected light after beam splitting is incident on the sample cell, and together with the transmitted light, it is incident on the Fourier transform objective lens, and then focused on the focal plane of the planar array detector to form interference fringes. When the liquid to be measured is added to the sample cell, the interference fringes shift, and the large-range liquid refractive index is measured through the shift amount.

Description

Technical Field

[0001] The present invention relates to a liquid refractive index measuring instrument and a measuring method, and particularly to a large-range liquid refractive index measuring instrument and a measuring method based on a static entity. Background Art

[0002] The ratio of the speed of light in vacuum to the speed of light in a certain medium is called the absolute refractive index of this medium. In industrial and agricultural production and scientific research, the liquid refractive index is a physical constant characterizing the optical properties of transparent liquid materials. From aqueous solutions to ionic liquids, from the control and detection of production products to the improvement of management levels in the production process, the measurement of refractive index is indispensable. The liquid refractive index can be used to detect the purity of substances, which is more reliable than the boiling point of liquids, and can also be used to determine the composition of liquid mixtures. Among various liquid substances, the refractive index changes with physical quantities such as concentration, temperature, and density. Therefore, the composition and properties of substances can be analyzed by the change of refractive index to identify unknown compounds. If a compound is a pure substance, the unknown compound can be identified by measuring its refractive index to rule out compounds. In addition to detecting the purity of substances, the refractive index can also be used to analyze the composition of liquid mixtures. For example, when distilling a liquid mixture of two or more liquids with close boiling points, the refractive index can be used to determine the composition of the distillate. Because when the structures and polarities of components are similar, there is often a linear relationship between the refractive index of the mixture and the molar composition.

[0003] In the fields of optics and materials, the research value of the refractive index of optical media is becoming increasingly high. In other fields, other physical quantities related to the refractive index are often involved. There are many methods for measuring the refractive index. The refractive index of a liquid can be measured using the properties of the liquid and some simple physical methods. The main measurement methods include the minimum deviation angle method, the critical angle method, the diffraction grating method, the total reflection method, and the fiber optic Young's interference method, etc. However, they all have certain defects. The minimum deviation angle method has a relatively high measurement accuracy for the refractive index, but it also has high requirements for the triangular prism, requiring high precision for both the apex angle and the plane, and the measurement cost is relatively high. When using the critical angle method for measurement, it can retain up to 4 significant figures, but the calculation formula is relatively complex, there are many factors causing errors, and the measured refractive index range is relatively small (from 1.3 to 1.7), and it cannot be used for some samples with relatively high refractive indices. When calculating the refractive index of the liquid sample to be measured using the diffraction grating method, only the spot spacing needs to be measured, but the data obtained during the measurement of the spot spacing has relatively large errors, and the influence of the glass cell on the light beam is not considered, resulting in low accuracy of the refractive index of the liquid obtained. The total reflection method cannot achieve non-contact measurement of the refractive index of the liquid, and it is easy to cause environmental pollution and damage to human health or cause unnecessary waste for toxic or precious liquids, and the measurement accuracy for semi-transparent liquids basically cannot meet the requirements. When measuring the refractive index of a liquid using the fiber optic Young's interference method, due to the relatively large error in measuring the width of the interference fringes, the measured value of the refractive index of the liquid deviates greatly from the theoretical value. In addition, the stability of the experimental instrument will also affect the measured refractive index value.

[0004] The common refractometer on the market at present is the Abbe refractometer, which is often used in industrial production and laboratories. Its measurement range is 1.3 - 1.7, but the measurement accuracy for the refractive index of volatile liquids is not high. The refractive index of common liquids in life is approximately around 1.3 - 1.6. However, with the continuous emergence of new varieties of liquid materials such as ionic liquids and liquid polymers, the refractive index range of liquid materials has been continuously expanded to 1.8 and even higher. Obviously, it is necessary to develop refractive index detection products with a higher measurement range to meet the actual application requirements. Summary of the Invention

[0005] The purpose of the present invention is to solve the technical problems existing in the existing measurement methods for the refractive index of liquids, such as low measurement accuracy, or high cost of the required optical components, or complex calculation formulas and large errors in the measurement calculation process, limited measurement range, and limited application range, etc., and to provide a large-range liquid refractive index measuring instrument and measurement method based on a static entity.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A large-range liquid refractive index measuring instrument based on a static entity, characterized in that:

[0008] It includes a light source, a pre - optical collimation system, a static interferometer system, a sample cell, a Fourier - transform objective lens, a planar array detector, and a computer connected to the planar array detector, which are arranged in sequence along the optical path;

[0009] The light emitted by the light source is compressed and collimated by the pre - optical collimation system to form collimated light. The collimated light is perpendicularly incident on the static interferometer system. The static interferometer system splits the collimated incident light and deflects the optical path to form two parallel beams with a transverse shear amount;

[0010] One of the beams with a transverse shear amount is perpendicularly incident on the sample cell. After passing through the sample cell, it is incident on the Fourier - transform objective lens together with the other beam with a transverse shear amount. It is focused on the focal plane of the planar array detector to form interference fringes. The planar array detector transmits the interference fringes to the computer for processing to form a spectral image. By injecting the liquid sample to be measured into the sample cell, the interference fringes shift, and the moving distance of the interference fringes is obtained, thereby realizing the measurement of the refractive index of a large - range liquid.

[0011] Furthermore, it also includes a temperature control unit. The static interferometer system and the sample cell are arranged in the temperature control unit. The temperature control unit is used to control the temperatures of the static interferometer system and the sample cell, so that the temperature of the static interferometer system is constant before and after injecting the sample into the sample cell.

[0012] Furthermore, the static interferometer system includes a right - angled trapezoidal prism and a parallelogram prism made of the same material; the length of the hypotenuse waist of the right - angled trapezoidal prism is equal to the length of one side of the parallelogram prism, and the two equal - length sides are glued together to form a glued surface;

[0013] The collimated light is perpendicularly incident on the surface of the parallelogram prism adjacent to the glued surface and is split into transmitted light and reflected light by the glued surface;

[0014] The transmitted light perpendicularly exits through the surface of the right - angled trapezoidal prism opposite to the glued surface, forming transmitted light with a transverse shear amount;

[0015] The reflected light is reflected by the plane of the parallelogram prism opposite to the glued surface and perpendicularly exits through the surface adjacent to the glued surface to form reflected light with a transverse shear amount, which is incident on the sample cell;

[0016] The transmitted light with a transverse shear amount is parallel to the transmitted light with a transverse shear amount;

[0017] The transmitted light with a transverse shear amount and the transmitted light with a transverse shear amount are incident on the Fourier - transform objective lens.

[0018] Furthermore, a non - polarized beam - splitting film is plated on the glued surface, and the beam - splitting ratio is 50%:50%.

[0019] Further, a high-reflection film is coated on one side of the parallelogram prism opposite to the bonding surface;

[0020] Anti-reflection films are coated on the two sides of the parallelogram prism adjacent to the bonding surface and on the side of the right trapezoidal prism opposite to the bonding surface.

[0021] Further, the light source is a composite light source with stable intensity, and a halogen lamp or an LED lamp is adopted;

[0022] The area array detector is a rectangular area array detector, a CCD area array camera or a CMOS area array camera.

[0023] The present invention also provides a method for measuring the refractive index of a large-range liquid based on a static entity, which adopts the above-mentioned measuring instrument for the refractive index of a large-range liquid based on a static entity, and is characterized by including the following steps:

[0024] Step 1: Turn on the light source, and the emitted light of the light source is compressed and collimated by the pre-optical collimation system to form collimated light;

[0025] Step 2: The collimated light is vertically incident on the static interferometer system, and after passing through the static interferometer system, it is split into two parallel beams with a transverse shear amount;

[0026] Step 3: Make one of the beams with a transverse shear amount vertically incident on the sample cell without adding the liquid sample to be measured;

[0027] Step 4: The Fourier transform objective lens focuses the beam with a transverse shear amount and the other beam with a transverse shear amount on the target surface of the area array detector to form an image with interference fringes;

[0028] Step 5: Adjust the position of the area array detector to make the interference fringes in the image located on one side of the target surface of the area array detector, and record the pixel position a where the interference fringes are located through a computer 1 ;

[0029] Step 6: Add the liquid sample to be measured to the sample cell. The change in the optical path difference after refraction by the liquid sample to be measured causes the interference fringes to shift, and record the pixel position a where the interference fringes are located through a computer 2 ;

[0030] Step 7: Obtain the moving distance of the interference fringes on the target surface of the area array detector according to the pixel position a 1 and the pixel position a 2 and calculate the refractive index n of the liquid sample to be measured added to the sample cell 3 .

[0031] Further, Step 2 is specifically as follows: After the collimated light is vertically incident on the static interferometer system, it is divided into transmitted light and reflected light by the glued surface of the right-angled trapezoidal prism and the parallelogram prism; the transmitted light is vertically emitted from the right-angled trapezoidal prism to form transmitted light with a transverse shear amount, and the reflected light is reflected by the parallelogram prism and vertically emitted to form reflected light with a transverse shear amount, and the reflected light with a transverse shear amount is parallel to the transmitted light with a transverse shear amount;

[0032] Step 3 is specifically as follows: Make the reflected light with a transverse shear amount vertically incident on the sample cell without adding the liquid sample to be measured;

[0033] Step 4 is specifically as follows: The Fourier transform objective lens focuses the reflected light with a transverse shear amount and the transmitted light with a transverse shear amount on the target surface of the area array detector to form an image with interference fringes;

[0034] Step 8 is specifically as follows: Calculate the refractive index n of the liquid sample to be measured added to the sample cell 3 :

[0035]

[0036] wherein, f is the focal length of the Fourier transform objective lens; s is the transverse shear amount of the reflected light and the transmitted light emitted by the static interferometer system; e is the interval between each pixel on the target surface of the area array detector;

[0037] n 0 is the refractive index of the right-angled trapezoidal prism and the parallelogram prism; n 1 is the refractive index of the cell wall of the sample cell; n 2 is the refractive index in the environment where the static interferometer system is placed; d is the thickness of the cell wall of the sample cell; c is the distance between the inner walls of the two cell walls of the sample cell;

[0038] GF is the side length of the emitted side of the parallelogram prism of the reflected light with a transverse shear amount; BD is the upper base side length of the right-angled trapezoidal prism.

[0039] Further, in Step 5 and Step 6, the specific method for recording the pixel positions where the interference fringes are located is: Record the pixel positions where the middle bright fringe of the interference fringes is located.

[0040] Further, in Step 6, the temperature control unit monitors the temperatures of the static interferometer system and the sample cell, so that the temperature of the static interferometer system is constant before and after injecting the sample into the sample cell.

[0041] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0042] 1. The large-range liquid refractive index measuring instrument based on a static entity provided by the present invention has a low cost of optical components and high system stability when measuring the refractive index of a large-range liquid. Compared with the existing measurement system, it only needs to fill different liquids to be measured in the sample cell and change the parameters of the sample cell to obtain the refractive index of the sample to be measured. The measurement range is wider and is not affected by the refractive index of other optical components in the system.

[0043] 2. The large-range liquid refractive index measurement method based on a static entity provided by the present invention can measure the refractive index of all light-transmitting liquids by filling different liquids to be measured in the sample cell, with a wide application range and strong versatility.

[0044] 3. In the large-range liquid refractive index measurement method based on a static entity provided by the present invention, in order to improve the detection accuracy, by adjusting the side length of the parallelogram prism through which the incident light enters in the static interferometer system, the lateral shear amount generated by the static interferometer system is increased or decreased, thereby realizing precise control of the width of the interference fringes on the target surface of the area array detector and improving the refractive index measurement accuracy.

[0045] 4. The large-range liquid refractive index measurement method based on a static entity provided by the present invention can obtain the refractive index of the sample to be measured only by changing the parameters of the sample cell. The formula in the calculation process is simple and the calculation amount is small, greatly reducing the calculation error. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic structural diagram of an embodiment of the large-range liquid refractive index measuring instrument based on a static entity of the present invention;

[0047] Figure 2 It is the interference fringe pattern on the target surface of the area array detector in the embodiment of the present invention;

[0048] Figure 3 It is a schematic structural diagram of the sample cell in the embodiment of the present invention;

[0049] REFERENCE SIGNS:

[0050] 1 - Light source, 2 - Pre - optical collimation system, 3 - Static interferometer system, 4 - Sample cell, 5 - Fourier transform objective lens, 6 - Temperature control unit, 7 - Area array detector, 8 - Computer;

[0051] 31 - Right - angled trapezoidal prism, 32 - Parallelogram prism. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] To make the objectives, advantages, and features of the present invention clearer, the following further elaborates in detail on a large-range liquid refractive index measuring instrument and measuring method based on static entities proposed by the present invention in combination with the accompanying drawings and specific embodiments. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0053] As Figure 1 shown, a large-range liquid refractive index measuring instrument based on static entities provided in this embodiment includes a light source 1, a pre-optical collimation system 2 arranged in sequence along the optical path, a static interferometer system 3 and a sample cell 4 arranged in a temperature control unit 6, a Fourier transform objective lens 5, a area array detector 7, and a computer 8 connected to the temperature control unit 6 and the area array detector 7.

[0054] The light source 1 is a polychromatic light source with stable intensity, and a halogen lamp or an LED lamp can be used. The uniformly emitted light emitted by the light source 1 is compressed and collimated by the pre-optical collimation system 2 and then vertically incident on the static interferometer system 3. The static interferometer system 3 splits the collimated incident light and deflects the optical path to form two parallel light beams with a transverse shear amount. The reflected light after splitting is vertically incident on the sample cell 4 filled with the liquid to be measured. After passing through the sample cell 4, it is incident on the Fourier transform objective lens 5 together with the transmitted light after splitting. It is focused on the focal plane of the area array detector 7 by the Fourier transform objective lens 5 to form interference fringes. The area array detector 7 receives the interference fringes with information of the liquid to be measured and then forms a spectral image after being processed by the computer 8. The temperature control unit 6 is used to realize the temperature control of the static interferometer system 3 and the sample cell 4 through the computer 8 to ensure that the temperature of the static interferometer system 3 is constant before and after injecting the sample into the sample cell 4.

[0055] The static interference system 3 is composed of a right trapezoidal prism 31 and a parallelogram prism 32 made of the same material. In the right trapezoidal prism 31, the upper base BD is parallel to the lower base AC, that is, BD / / AC, and ∠ACD = ∠BDC = 90°.

[0056] The length of the hypotenuse waist AB of the right trapezoidal prism 31 is equal to the length of the side HG of the parallelogram prism 32. The length of the hypotenuse waist AB of the right trapezoidal prism 31 is glued to the side HG of the parallelogram prism 32 to form a glued surface. A non-polarizing beam splitter film is plated on the glued surface to make the intensity ratio of the transmitted light to the reflected light after splitting the incident light 50%:50%.

[0057] After being compressed and collimated by the pre - placed optical collimation system 2, the incident light is perpendicularly incident on the side EH of the parallelogram prism 32, and after transmission, it is incident on the bonding surface. After passing through the non - polarized beam - splitting film, reflected light and transmitted light with equal light intensities are formed. The reflected light is reflected by the side EF of the parallelogram prism 32 and transmitted through the side FG, and then is incident on the sample cell 4 filled with the liquid to be measured. After passing through the liquid to be measured in the sample cell 4, it is incident on the Fourier - transform objective lens 5; the transmitted light after beam - splitting is perpendicularly emitted from the right - angled waist CD of the right - angled trapezoid prism 31 and then is incident on the Fourier - transform objective lens 5.

[0058] After the two beams of light are split by the first bonding surface, a lateral shear amount is formed. They are focused on the focal plane of the area array detector 7 by the Fourier - transform objective lens 5 to form interference fringes. As Figure 2 shown, the interference fringes are a set of bright and dark alternating fringes, with the middle bright and gradually darkening on both sides. During actual measurement, only the position of the middle bright fringe needs to be recorded.

[0059] Anti - reflection films are coated on the right - angled waist CD of the right - angled trapezoid prism 31, and the sides EH and GH of the parallelogram prism 32. A high - reflection film is coated on the side EF of the parallelogram prism 32.

[0060] The area array detector 7 is a large - area rectangular detector, which can be a CCD area array camera or a CMOS area array camera.

[0061] As Figure 3 shown, the sample cell 4 is a cuboid, its cell wall thickness is d, and the distance between the inner walls of the two cell walls is c.

[0062] The present invention also provides a method for measuring the refractive index of a large - range liquid based on a static entity, including the following steps:

[0063] Step 1: Turn on the light source 1, and the light emitted with uniform intensity is compressed and collimated by the pre - placed optical collimation system 2;

[0064] Step 2: The collimated light is perpendicularly incident on the static interferometer system 3. After passing through the static interferometer system 3, it is divided into reflected light and transmitted light with the same light intensity, forming two parallel light beams with a lateral shear amount s;

[0065] The collimated incident light is divided into reflected light and transmitted light with the same light intensity on the bonding surface coated with a beam - splitting film in the right - angled trapezoid prism 31 and the parallelogram prism 32 of the static interferometer system 3; the transmitted light is emitted from the side CD of the right - angled trapezoid prism 31, and the reflected light is reflected by the side EF opposite to the bonding surface of the parallelogram prism 32 and emitted from the side GF; the lateral shear amount s generated by the static interference system 3 is related to the side length of the side HE (GF) of the parallelogram prism 32;

[0066] Step 3: Make the reflected light after beam - splitting perpendicularly incident on the sample cell 4 without filling the liquid to be measured;

[0067] Step 4: The Fourier transform objective lens 5 focuses the reflected light and the transmitted light with a lateral shear amount s on the target surface of the area array detector 7 to form an image with interference fringes.

[0068] Step 5: Adjust the position of the area array detector 7 so that the interference fringes in the image are located on one side of the target surface of the area array detector 7, and record the pixel position a of the middle bright fringe through the computer 8. 1 ; During actual measurement, only the position of the middle bright fringe needs to be recorded.

[0069] Step 6: Pour the liquid sample to be measured into the sample cell 4. Since the optical path difference of the system changes, the interference fringes shift, and record the pixel position a of the middle bright fringe of the interference fringes on the computer 8 again. 2 ;

[0070] In Step 6, it is necessary to monitor the temperatures of the static interferometer system 3 and the sample cell 4 through the temperature control unit 6, and control the temperatures of both to ensure that the temperature of the static interferometer system 3 is constant before and after injecting the sample into the sample cell 4.

[0071] Step 7: According to the pixel positions of the middle bright fringes of the interference fringes recorded twice and moving on the target surface of the area array detector 7, the moving distance y of the interference fringes can be calculated as y = a 2 -a 1 ;

[0072] Step 8: Calculate the refractive index n of the liquid sample to be measured poured into the sample cell 4. 3 .

[0073] According to the relationship satisfied by the Fourier transform objective lens 5: ΔL = (s * e * (a 2 -a 1 )) / f;

[0074] In this embodiment, if the side length of the incident parallelogram prism 32 is not equal to the upper base side length of the right trapezoidal prism 31, the optical path difference generated by the reflected light and the transmitted light in the static interferometer system 3 is: ΔL = (GF - BD) * n 0 + BD * n 2 + 2dn 1 + cn 3 , where n 0 is the refractive index of the right trapezoidal prism 31 and the parallelogram prism 32; n 1 is the refractive index of the cell wall of the sample cell 4; n 2is the refractive index in the environment where the static interferometer system 3 is located; d is the thickness of the cell wall of the sample cell 4; c is the distance between the inner walls of the two cell walls of the sample cell 4.

[0075] Then, the refractive index n of the liquid sample to be measured filled in the sample cell 4 3 :

[0076]

[0077] where f is the focal length of the Fourier transform objective lens 5; e is the interval between each pixel on the target surface of the area array detector 7.

[0078] If the side length of the incident parallelogram prism 32 is equal to the upper base side length of the right trapezoidal prism 31 and is equal to half of the lower base side length, that is, HE = GF = BD = CD = (1 / 2)AC, then the optical path difference generated by the reflected light and the transmitted light in the static interferometer system 3 is: ΔL = BD * n 2 + 2dn 1 + cn 3 Then, the refractive index n of the liquid sample to be measured filled in the sample cell 4 3 :

[0079]

[0080] The present invention preliminarily determines the size parameters of the sample cell according to the refractive index range of the liquid to be measured, and realizes the measurement of the refractive index of all transparent liquids by filling different liquids to be measured in the sample cell. During the measurement process, the side length of the incident parallelogram prism of the incident light in the static interferometer system can be adjusted to increase or decrease the lateral shear amount generated by the static interferometer system, thereby realizing the precise control of the interference fringe width on the target surface of the area array detector and improving the refractive index measurement accuracy.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A large-range liquid refractive index measuring instrument based on a static entity, characterized in that: it includes a light source (1) and a pre-optical collimation system (2), a static interferometer system (3), a sample cell (4), a Fourier transform objective lens (5), a planar array detector (7), and a computer (8) connected to the planar array detector (7) arranged in sequence along the optical path; The light emitted by the light source (1) is compressed and collimated by the pre-optical collimation system (2) to form collimated light, and the collimated light is perpendicularly incident on the static interferometer system (3). The static interferometer system (3) splits the collimated incident light and deflects the optical path to form two mutually parallel beams with a transverse shear amount; One of the beams with a transverse shear amount is perpendicularly incident on the sample cell (4), and after passing through the sample cell (4), it is incident on the Fourier transform objective lens (5) together with the other beam with a transverse shear amount. After being focused by the Fourier transform objective lens (5) onto the focal plane of the planar array detector (7), interference fringes are formed. The planar array detector (7) transmits the interference fringes to the computer (8) for processing to form a spectral image, and by injecting the liquid sample to be measured into the sample cell (4) to cause the interference fringes to shift, the moving distance of the interference fringes is obtained, thereby realizing the measurement of the large-range liquid refractive index; The static interferometer system (3) includes a right-angled trapezoidal prism (31) and a parallelogram prism (32) made of the same material; the length of the hypotenuse waist of the right-angled trapezoidal prism (31) is equal to the length of one side of the parallelogram prism (32), and the two sides with equal lengths are glued together to form a glued surface; The collimated light is perpendicularly incident on the surface of the parallelogram prism (32) adjacent to the glued surface, and is divided into transmitted light and reflected light by the glued surface; The transmitted light perpendicularly exits through the surface of the right-angled trapezoidal prism (31) opposite to the glued surface, forming transmitted light with a transverse shear amount; the reflected light is reflected by the plane of the parallelogram prism (32) opposite to the glued surface and perpendicularly exits through the surface adjacent to the glued surface to form reflected light with a transverse shear amount, and is incident on the sample cell (4); The transmitted light with a transverse shear amount is parallel to the transmitted light with a transverse shear amount; the transmitted light with a transverse shear amount and the transmitted light with a transverse shear amount are incident on the Fourier transform objective lens (5).

2. The large-range liquid refractive index measuring instrument based on a static entity according to claim 1, characterized in that: it further includes a temperature control unit (6). The static interferometer system (3) and the sample cell (4) are arranged in the temperature control unit (6). The temperature control unit (6) is used to control the temperature of the static interferometer system (3) and the sample cell (4) so that the temperature of the static interferometer system (3) is constant before and after injecting the sample into the sample cell (4).

3. The large-range liquid refractive index measuring instrument based on a static entity according to claim 2, characterized in that: a non-polarizing beam-splitting film is plated on the glued surface, and the beam-splitting ratio is 50%:50%.

4. The large-range liquid refractive index measuring instrument based on a static entity according to claim 3, characterized in that: a high-reflection film is plated on the surface of the parallelogram prism (32) opposite to the glued surface; Both two sides of the parallelogram prism (32) adjacent to the cemented surface and the side of the right trapezoid prism (31) opposite to the cemented surface are coated with an anti-reflection film.

5. The large-range liquid refractive index measuring instrument based on static entities according to claim 4, characterized in that: the light source (1) is a polychromatic light source with stable intensity, and a halogen lamp or an LED lamp is adopted; the area array detector (7) is a rectangular area array detector, a CCD area array camera or a CMOS area array camera.

6. A method for measuring the large-range liquid refractive index based on static entities, adopting the large-range liquid refractive index measuring instrument based on static entities according to any one of claims 1-5, characterized in that, it includes the following steps: Step 1: Turn on the light source (1), and the emitted light of the light source (1) is compressed and collimated by the pre-optical collimation system (2) to form collimated light; Step 2: The collimated light is vertically incident on the static interferometer system (3), and after passing through the static interferometer system (3), it is split into two parallel beams with a transverse shear amount; Step 3: Make one of the beams with a transverse shear amount vertically incident on the sample cell (4) without adding the liquid sample to be measured; Step 4: The Fourier transform objective lens (5) focuses the beam with a transverse shear amount and the other beam with a transverse shear amount on the target surface of the area array detector (7) to form an image with interference fringes; Step 5: Adjust the position of the area array detector (7) so that the interference fringes in the image are located on one side of the target surface of the area array detector (7), and record the pixel position a where the interference fringes are located through the computer (8). 1 ; Step 6: Add the liquid sample to be measured to the sample cell (4), and the change in the optical path difference after refraction by the liquid sample to be measured causes the interference fringes to shift, and the computer (8) records the pixel position a2 where the interference fringes are located; Step 7: According to the pixel position a 1 and the pixel position a 2 obtain the moving distance of the interference fringe on the target surface of the area array detector (7), and calculate the refractive index n of the liquid sample to be measured filled in the sample cell (4) 3 .

7. The method for measuring the large-range liquid refractive index based on static entities according to claim 6, characterized in that, Step 2 is specifically: after the collimated light is vertically incident on the static interferometer system (3), it is divided into transmitted light and reflected light by the cemented surface of the right trapezoid prism (31) and the parallelogram prism (32); the transmitted light is vertically emitted from the right trapezoid prism (31) to form transmitted light with a transverse shear amount, and the reflected light is reflected by the parallelogram prism (32) and vertically emitted to form reflected light with a transverse shear amount, and the reflected light with a transverse shear amount is parallel to the transmitted light with a transverse shear amount; Step 3 is specifically: make the reflected light with a transverse shear amount vertically incident on the sample cell (4) without adding the liquid sample to be measured; Step 4 is specifically: the Fourier transform objective lens (5) focuses the reflected light with a transverse shear amount and the transmitted light with a transverse shear amount on the target surface of the area array detector (7) to form an image with interference fringes; Step 8 specifically is: calculating the refractive index n of the liquid sample to be measured filled in the sample cell (4) 3 :[[]]END]] wherein, f is the focal length of the Fourier transform objective lens (5); s is the transverse shear amount of the reflected light and the transmitted light emitted from the static interferometer system (3); e is the interval between each pixel on the target surface of the area array detector (7); n 0 is the refractive index of the right trapezoidal prism (31) and the parallelogram prism (32); n 1 is the refractive index of the cell wall of the sample cell (4); n 2 is the refractive index in the environment where the static interferometer system (3) is placed; d is the thickness of the cell wall of the sample cell (4); c is the distance between the inner walls of the two cell walls of the sample cell (4); GF is the side length of the emitted side of the reflected light with a transverse shear amount from the parallelogram prism (32); BD is the upper base side length of the right trapezoid prism (31).

8. The method for measuring the large-range liquid refractive index based on static entities according to claim 7, characterized in that: In Step 5 and Step 6, the specific position of the pixel where the interference fringe is recorded is: recording the position of the pixel where the middle bright fringe of the interference fringe is located.

9. The method for measuring the refractive index of a large-range liquid based on a static entity according to claim 7, characterized in that: In Step 6, the temperature control unit (6) monitors the temperature of the static interferometer system (3) and the sample cell (4) so that the temperature of the static interferometer system (3) is constant before and after injecting the sample into the sample cell (4).

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