A method and application for measuring small optical rotation angles using in-plane spatial spin splitting displacement

Abstract

The present invention belongs to the field of optics and relates to a method for measuring the optical rotation of a chiral substance, and in particular to a method and application for measuring a small optical rotation angle using in-plane spatial spin splitting displacement. This application establishes a theoretical correspondence database of optical rotation angle and in-plane spatial spin splitting displacement change based on the theoretical relationship model between in-plane spatial spin splitting displacement and optical rotation angle; then measures the in-plane spatial spin splitting displacement generated by the reflected light beam when the incident light beam is reflected on the interface of a sample cell without an object; then places the object to be measured into the sample cell, and measures the in-plane spatial spin splitting displacement generated by the reflected light beam at this time; calculates the change in in-plane spatial spin splitting displacement caused by the optical rotation angle; and then compares and calculates with the theoretical correspondence database to obtain the target value. The present invention utilizes the excellent sensitivity of in-plane spatial spin splitting displacement to optical rotation angle to achieve high-resolution measurement of small optical rotation angles.

Description

Technical Field

[0001] The present invention belongs to the field of optics and relates to a method for measuring the optical rotation of a chiral substance, in particular to a method and application for measuring a small optical rotation angle by utilizing in-plane spatial spin splitting displacement. Background Art

[0002] With the widespread application of chiral substances in medicine, pesticides, food additives, and electromagnetic materials, they have become a research hotspot in pharmacology and biochemistry. The rapid development of chiral substances, in particular, has directly impacted people's daily lives. Optical rotation angle is one of the key characteristic parameters of chiral substances. Accurate measurement technology for optical rotation angle has important applications in scientific research, industry, and medicine, such as solution concentration measurement, chemical substance identification, material structure research, crystal birefringence analysis, and fiber-optic current mutual inductance detection. Currently, many instruments are available for measuring optical rotation, such as the Shanghai Shenguang SGW-1 automatic polarimeter and the PerkinElmer 341 / 343 automatic precision polarimeter. These instruments achieve a maximum accuracy of 0.002°, which is sufficient for conventional applications with low precision requirements, but falls short of the requirements of some high-precision measurement applications. Furthermore, Chinese patent application No. 201110173321.8 discloses a simple measurement device for detecting optical rotation angle. This measurement method uses the principle of a three-dimensional field of view based on the measured light intensity signal to identify the optical rotation through the human eye. However, since the human eye is very insensitive to strong light, observation is difficult. The transition from a three-dimensional field of view to a uniform field of view is also difficult, and there is also a certain degree of subjectivity, which leads to inaccurate optical rotation measurements. This is especially true for chiral substances with very small optical rotations, which inevitably leads to inaccurate measurement results. With the continuous advancement of industry, higher requirements are being placed on the measurement of optical rotation angles of chiral substances, requiring not only simple and convenient measurement methods, but also real-time detection and high accuracy. Therefore, the research and development of new high-resolution methods for measuring small optical rotation angles is of great significance in both scientific research and application.

[0003] The photon spin Hall effect refers to the phenomenon that when a linearly polarized light beam passes through an inhomogeneous medium and its left-handed and right-handed components are reflected / refracted from a planar interface, the left-handed and right-handed components of the reflected / refracted light beam will split in a direction perpendicular to the refractive index gradient. This spin splitting shift is closely related to the polarization direction of the incident light. Under certain conditions, a slight change in the polarization state of the light beam can cause a change in the spin splitting shift. The measurement of the optical rotation of a chiral substance is essentially to measure the rotation angle of the polarization direction of a linearly polarized light beam after it passes through a chiral solution. In previous studies, we found that under the same parameter conditions, the in-plane photon spin splitting shift is usually much larger than the out-of-plane photon spin splitting shift. This means that compared to the out-of-plane photon spin splitting shift, parameter measurements based on the in-plane photon spin splitting shift will have higher sensitivity or higher resolution. In order to further improve the accuracy and sensitivity of measuring the optical rotation angle of chiral substances, this application conducted the following research. Summary of the Invention

[0004] To address these technical issues, the present invention proposes a new method based on in-plane spatial spin splitting displacement, enabling high-resolution measurement of small optical rotation angles. Furthermore, this method maintains excellent stability and accuracy, as all system components remain stationary during the measurement process.

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

[0006] A method for measuring small optical rotation angles using in-plane spatial spin splitting displacement comprises the following steps:

[0007] (1) Based on the theoretical relationship model between the in-plane spatial spin splitting displacement and the optical rotation angle, a theoretical correspondence database is established between the optical rotation angle and the change in the in-plane spatial spin splitting displacement caused by the incident light beam passing through the object under test at an arbitrary initial polarization angle and being reflected at a certain reflective interface at an arbitrary incident angle;

[0008] (2) Measure the in-plane spatial spin splitting displacement generated by the reflected light beam when the incident light beam passes through a sample cell without the object being measured at a certain initial polarization angle and is reflected at a certain interface at a certain incident angle;

[0009] (3) While keeping the parameters in step (2) unchanged, the object to be measured is placed in the sample cell, and the in-plane spatial spin splitting displacement generated by the reflected light beam is measured;

[0010] (4) subtracting the in-plane spatial spin splitting displacements obtained in step (3) from the in-plane spatial spin splitting displacements obtained in step (2) to obtain a change in the in-plane spatial spin splitting displacement caused by the optical rotation angle;

[0011] (5) Compare and calculate the change in the in-plane spatial spin splitting displacement obtained in step (4) with the theoretical corresponding relationship database established in step (1) to obtain the value of the small optical rotation angle caused by the object being measured.

[0012] The theoretical relationship model between the in-plane spatial spin splitting displacement and the optical rotation angle in the above step (1) is:

[0013]

[0014] In formula ①,

[0015] Here, α represents the angle of optical rotation, which means the angle by which the polarization direction of the incident light beam rotates after passing through the object being measured; γ i represents the polarization angle of the incident light beam before it passes through the object being measured; σ = + and σ = - represent the left-handed component and right-handed component of the light beam respectively; θ represents the incident angle of the incident light; r p and r s They represent the reflection coefficients of the p-light component and the s-light component of the light beam respectively; A∈{p,s}, Re means taking the real part of the complex number, Im means taking the imaginary part of the complex number; w0 represents the waist of the incident beam; It represents the wave number of the incident light in the propagation medium, ε represents the relative dielectric constant of the propagation medium, and λ is the wavelength of the incident light in the propagation medium.

[0016] Furthermore, the incident light beam in step (1) is an incident light beam with any wavelength and any beam waist, and the certain reflection interface is an arbitrary interface.

[0017] Preferably, the in-plane spatial spin splitting displacement variation is the in-plane spatial photon spin splitting displacement variation of the left-handed component or the right-handed component of the light beam.

[0018] Furthermore, the initial polarization angle in step (2) is any angle between 0° and 90°, and the incident angle is any angle between 0° and 90°.

[0019] Furthermore, the comparison calculation in step (5) is based on a linear interpolation method to calculate the optical rotation angle value.

[0020] Furthermore, the comparison calculation in step (5) is performed directly by comparison, and the optical rotation angle value corresponding to the theoretical value that is close to or equal to the measured value is selected as the measurement result.

[0021] Preferably, the analyte is a solution, a solid or a gaseous substance.

[0022] The above method is used to measure the small optical rotation angle of chiral substances.

[0023] The present invention has the following beneficial effects:

[0024] This method leverages the excellent sensitivity of in-plane spatial spin splitting displacement to optical rotation angles, enabling high-resolution measurement of minute optical rotation angles. Since all system components remain stationary during the measurement process, this method offers excellent stability and measurement accuracy, making it suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 Schematic diagram of the device for measuring in-plane spatial spin splitting displacement in the present invention, wherein 1-laser light source, 2-focusing lens I, 3-polarizer I, 4-sample cell, 5-reflection interface, 6-polarizer II, 7-focusing lens II, 8-photosensitive imaging device, and 9-computer.

[0027] Figure 2 Schematic diagram of the polarization direction of the light beam before and after passing through the object to be measured in the present invention.

[0028] Figure 3 Schematic diagram of the in-plane spatial spin splitting of a light beam when it is reflected at an interface in the present invention.

[0029] Figure 4 The graph is a theoretical relationship curve between the in-plane spatial spin splitting displacement and the optical rotation angle of the left-handed component of the reflected light at different incident angles of the light beam in the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Since the photon spin splitting displacement is usually in the nanometer range, the observation of the photon spin splitting displacement usually requires first amplifying it and then dividing it by the magnification factor to obtain the corresponding photon spin splitting displacement value. Figure 1As shown. This device is a conventional and universal device for realizing photon spin splitting displacement based on weak measurement amplification technology. The linearly polarized light beam emitted by the laser light source 1 passes vertically through the focusing lens Ⅰ2 and then vertically through the polarizer Ⅰ3. At this time, the polarization angle of the light beam is γ i , and then after passing through the sample pool 4 containing the sample solution to be measured, the polarization direction of the light beam will rotate by an angle α, as shown in Figure 2 As shown, the polarization angle of the light beam will become γ i +α, then the light beam is incident on the reflective interface 5 at a certain angle θ, and in-plane spatial spin splitting occurs here, as shown in Figure 3 As shown in the figure, the light beam reflected by the reflective interface 5 passes vertically through the polarizer II 6 and the focusing lens II 7 in sequence, and finally vertically enters the photosensitive surface of the photosensitive imaging device 8. The photosensitive imaging device 8 sends the captured light intensity image to the computer 9, which then performs a series of processing and calculations on the obtained light intensity image to obtain the centroid coordinates of this light intensity image. The centroid coordinates minus the origin coordinates can be used to obtain the weak measurement amplified displacement Aw·δx after amplification by the weak measurement device. The weak measurement amplified displacement is divided by the magnification A of the measurement system. w , we can get the value of the in-plane spatial spin splitting displacement δx at this time. By changing the focal length of the focusing lens Ⅰ2, the size of the beam waist w0 can be changed; adjusting the polarizer Ⅰ3 can change the initial polarization state γ of the beam. i By adjusting the polarizer II6, the weak measurement magnification angle Δ can be adjusted. Focusing lens I2 and focusing lens II7 form a confocal cavity. By adjusting the focal length ratio of the two, the propagation magnification F of the measurement system can be adjusted. The overall magnification A of the measurement system w ≈F / Δ. In this embodiment, by setting a suitable weak measurement magnification angle Δ and a propagation magnification F, a suitable magnification A is formed. w , so that the measurement system can achieve a measurement resolution of 1 nanometer for the in-plane spatial spin splitting displacement.

[0032] In-plane spatial spin splitting displacement The theoretical relationship model with the optical rotation angle α after the linearly polarized light beam passes through the chiral substance solution is:

[0033]

[0034] in,

[0035] Here, α i It represents the angle of optical rotation, that is, the angle at which the polarization direction of the incident light beam rotates after passing through the object being measured; γ i represents the polarization angle of the incident light beam before it passes through the object being measured; σ = + and σ = - represent the left-handed component and right-handed component of the light beam respectively; θ represents the incident angle of the incident light; rp and r s They represent the reflection coefficients of the p-light component and the s-light component of the light beam respectively; A∈{p,s}, Re means taking the real part of the complex number, Im means taking the imaginary part of the complex number; w0 represents the waist of the incident beam; It represents the wave number of the incident light in the propagation medium, ε represents the relative dielectric constant of the propagation medium, and λ is the wavelength of the incident light in the propagation medium.

[0036] Reflection coefficient r p and r s According to the Fresnel equation, we can get:

[0037] r p =(ε2k 1z -ε1k 2z ) / (ε2k 1z +ε1k 2z )

[0038] r s =(k 1z -k 2z ) / (k 1z +k 2z )

[0039] in, Here, i represents 1 and 2 respectively, where 1 represents medium 1 and 2 represents medium 2, ε1 and ε2 represent the relative dielectric constants of medium 1 and medium 2 respectively, λ is the wavelength of the incident light, and θ is the angle of incidence.

[0040] According to equation ①, we can get the initial incident polarization state γ at each incident angle θ i Under the in-plane spatial spin splitting displacement One-to-one correspondence with the optical rotation angle α. Figure 4 is the initial polarization state γ i =0°, and the incident angles are θ=54.5°, θ=55°, θ=55.5°, θ=56°, and θ=56.5° (i.e., the incident angle is near the Brewster angle), the in-plane spatial spin splitting displacement of the left-handed component of the reflected beam is The relationship between the optical rotation angle α. Figure 4 It can be clearly seen that no matter the incident angle θ=54.5°, θ=55°, θ=55.5°, θ=56° and θ=56.5°, the in-plane spatial spin splitting displacement There is a strict one-to-one correspondence with the optical rotation angle α and has good linearity. Therefore, if the in-plane spatial spin splitting displacement is measured at this time According to equation ①, the unique corresponding small optical rotation angle value α can be determined.

[0041] The specific implementation process of the present invention is described in detail below with reference to the accompanying drawings.

[0042] Example

[0043] (1) According to the theoretical relationship model between the in-plane spatial spin splitting displacement and the optical rotation angle, that is, according to equation ①, the beam wavelength is 632.8nm, the beam waist w0 is 15μm, and the initial polarization angle γ of polarizer I3 is established. i =0°, the incident angle θ=56.5°, and the reflection interface is the air / glass interface. The theoretical correspondence database between the optical rotation angle and the change in the in-plane spatial spin splitting displacement of the left-handed component of the reflected light beam is shown in Table 1:

[0044] Table 1 Theoretical correspondence between the optical rotation angle and the change in the in-plane spatial spin splitting displacement of the left-handed component

[0045]

[0046] (2) A helium-neon laser is used as the light source. The wavelength of the light beam emitted by this light source is 632.8 nm. A focusing lens I2 with an appropriate focal length is selected so that the beam waist w0 of the light beam passing vertically through the focusing lens I2 is 15 μm. The polarizer I3 is rotated so that the initial polarization angle γ of the light beam passing vertically through the rotating polarizer I3 is i =0°. Then let the light beam pass vertically through the transparent sample pool 4 that is not filled with the solution to be tested. At this time, the polarization state of the light beam is still 0°. Then let the light beam be incident on the air / glass reflection interface at an angle of 56.5° and reflect. The left-handed and right-handed components of the reflected light beam will be split and displaced at the reflection interface. The reflected light beam passes vertically through the polarizer Ⅱ6 and the focusing lens Ⅱ7 in turn, and is vertically irradiated on the photosensitive surface of the photosensitive imaging device 8. The photosensitive imaging device 8 transmits the captured light intensity image to the computer 9, and the computer 9 performs a series of processing and calculations on the obtained light intensity image to obtain the center of mass coordinate x0 in the x direction of this light intensity image. Because when the initial polarization angle γ i = 0°, in-plane spatial spin splitting displacement is 0, so let the centroid coordinate x0 be the coordinate origin.

[0047] (3) The substance to be tested is prepared into a solution of standard concentration and poured into the transparent sample pool 4. At this time, the polarization angle of the light beam passing through the sample pool 4 will become γ i +α. Due to γ i= 0°, the polarization state of the light beam passing through the sample cell 4 will become α. The light intensity image captured by the photosensitive imaging device 8 is transmitted to the computer 9, which then performs a series of processing and calculations on the obtained light intensity image to obtain the centroid coordinate x1 of this light intensity image. Subtract the origin coordinate x0 from the centroid coordinate x1 of this light intensity image and divide it by the magnification A of the measurement system. w , we can get the in-plane spatial spin splitting displacement at this time Assuming that the measured

[0048] (4) Subtract the in-plane spatial spin splitting displacements obtained in step (3) from those obtained in step (2) to obtain the change in the in-plane spatial spin splitting displacement caused by the rotation of the polarization direction of the incident light beam by an angle α after passing through the measured material.

[0049] (5) According to the established database, the spatial spin splitting displacement in the plane can be determined by querying the database and calculating the corresponding difference. When the value of the optical rotation angle α. According to Table 1, it can be seen that when When the corresponding optical rotation angle α is between 0.03 and 0.04, then, through linear interpolation, we can get When the optical rotation angle α is:

[0050]

[0051] It can be seen from Table 1 that if the measurement resolution of the measurement system for the in-plane spin splitting displacement is 1 nm, then the measurement resolution Δα of the optical rotation angle is approximately: Δα≈0.5 / 6552=8×10 -5 degrees. That is, the resolution can reach 10 -5 Compared with current measuring instruments, the measurement resolution of this method is improved by about 1 to 2 orders of magnitude.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for measuring small optical rotation angles using in-plane spatial spin splitting displacement, characterized in that: The following steps are involved: (1) Based on the theoretical relationship model between the in-plane spatial spin splitting displacement and the optical rotation angle, a theoretical correspondence database is established between the optical rotation angle and the change in the in-plane spatial spin splitting displacement caused by the incident light beam passing through the object under test at an arbitrary initial polarization angle and being reflected at a certain reflective interface at an arbitrary incident angle; (2) Measure the in-plane spatial spin splitting displacement generated by the reflected light beam when the incident light beam passes through a sample cell without the object being measured at a certain initial polarization angle and is reflected at a certain interface at a certain incident angle; (3) While keeping the parameters in step (2) unchanged, the object to be measured is placed in the sample cell, and the in-plane spatial spin splitting displacement generated by the reflected light beam is measured; (4) subtracting the in-plane spatial spin splitting displacements obtained in step (3) from the in-plane spatial spin splitting displacements obtained in step (2) to obtain a change in the in-plane spatial spin splitting displacement caused by the optical rotation angle; (5) Comparing and calculating the change in the in-plane spatial spin splitting displacement obtained in step (4) with the theoretical corresponding relationship database established in step (1) to obtain the value of the small optical rotation angle caused by the object being measured; the theoretical relationship model between the in-plane spatial spin splitting displacement and the optical rotation angle in step (1) is: In formula ①, Here, α represents the angle of optical rotation, which means the angle by which the polarization direction of the incident light beam rotates after passing through the object being measured; γ i represents the polarization angle of the incident light beam before it passes through the object being measured; σ = + and σ = - represent the left-handed component and right-handed component of the light beam respectively; θ represents the incident angle of the incident light; r p and r s They represent the reflection coefficients of the p-light component and the s-light component of the light beam respectively; A∈{p,s}, Re means taking the real part of the complex number, Im means taking the imaginary part of the complex number; w0 represents the waist of the incident beam; It represents the wave number of the incident light in the propagation medium, ε represents the relative dielectric constant of the propagation medium, and λ is the wavelength of the incident light in the propagation medium.

2. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 1, characterized in that: The incident light beam in the step (1) is an incident light beam with any wavelength and any beam waist, and the certain reflection interface is any interface.

3. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 2, characterized in that: The in-plane spatial spin splitting displacement variation is the in-plane spatial photon spin splitting displacement variation of the left-handed component or the right-handed component of the light beam.

4. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 3, wherein: The initial polarization angle in the step (2) is any angle between 0° and 90°, and the incident angle is any angle between 0° and 90°.

5. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 4, characterized in that: The comparison calculation in step (5) is based on a linear interpolation method to calculate the optical rotation angle value.

6. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 4, wherein: The comparison calculation in step (5) is performed directly by comparison, and the optical rotation angle value corresponding to the theoretical value that is close to or equal to the measured value is selected as the measurement result.

7. The method for measuring small optical rotation angles using in-plane spatial spin splitting displacement according to claim 5 or 6, characterized in that: The analyte is a solution, solid or gaseous substance.

8. Use of the method according to claim 7 in measuring small optical rotation angles of chiral substances.

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