Device and method for measuring specific rotation and circular dichroism spectrum of chiral substance

Abstract

The present invention discloses a device and method for measuring the specific rotation and circular dichroism spectrum of chiral substances. The device includes a narrow linewidth laser, a single-mode fiber, a quarter-wave plate, a half-wave plate, a polarization beam splitter, a convex lens group, a ring cavity, a photodetector, and a calculation module, which are arranged in sequence along the light propagation direction. When measuring, the chiral substance to be measured is located in the ring cavity, and the laser passes through the single-mode fiber, the quarter-wave plate, the half-wave plate, the polarization beam splitter, the convex lens group, and the ring cavity in sequence and enters the photodetector. The calculation module fits the free spectral range (FSR) of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth according to the optical signal detected by the photodetector, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured. The present invention is simple, fast, and accurate.

Description

Technical Field

[0001] The present invention relates to the field of optical precision measurement, and particularly to an apparatus and method for measuring the specific rotation and circular dichroism of chiral substances. Background Art

[0002] Chirality plays an important role in daily life. Many basic biomolecules, such as amino acids, nucleic acids, enzymes, and carbohydrates, may have two enantiomers that are mirror images of each other, and they may exhibit two different or even opposite biochemical properties and functions. Therefore, the analysis of the absolute configuration of chiral molecules is of great significance in fields such as food, medicine, and drug development. The optical chirality of substances can usually be characterized by specific rotation and circular dichroism. A polarimeter is an instrument for measuring the specific rotation of substances, which can be used for sugar determination in industrial production, or for product analysis in the pharmaceutical industry and ribonucleic acid research in life sciences. Circular dichroism is the most widely used optical tool for studying the structure of enantiomers, which reflects the difference in absorption of left-circularly polarized light and right-circularly polarized light by chiral molecules. Circular dichroism has been widely used in the determination of the absolute configuration of various chiral molecules, such as chiral sulfoxides, spiro compounds, insect pheromones, alkaloids, and polysaccharides and proteins. General polarimeters are composed of optical, mechanical, and electronic detection parts. Such instruments have factors such as large measurement error changes caused by mechanical wear. At the same time, during the measurement process, it is necessary to observe with the human eye to distinguish the fields of view with consistent brightness, so the accuracy is very low. Good circular dichroism spectrometers are also scarce in the market and are very expensive, costing more than 2 million yuan each. Therefore, how to simply, quickly, and accurately measure specific rotation and circular dichroism is very important, which can solve problems in many fields such as medicine, food, chemical industry, and scientific research.

[0003] Some researchers have also proposed to measure the specific rotation using the method of cavity-enhanced chiral polarization determination (see [Nature 514, 76 - 79 (2014), Sci. Adv. 8, eabm3749 (2022)]). This scheme has a low cost and uses a ring cavity to amplify weak chiral signals. Its sensitivity for detecting specific rotation is several orders of magnitude higher than that of a polarization measuring instrument. However, this scheme requires recording signals multiple times and requires additional modulation during the measurement process, and the measurement process is relatively complex. Summary of the Invention

[0004] Object of the Invention: Aiming at the problems existing in the prior art, the present invention provides an apparatus and method for measuring the specific rotation and circular dichroism of chiral substances with simplicity, rapidity, and small error.

[0005] Technical solution: The device for measuring the specific rotation and circular dichroism spectrum of chiral substances according to the present invention includes a narrow linewidth laser, a single-mode optical fiber, a quarter-wave plate, a half-wave plate, a polarization beam splitter, a convex lens group, a ring cavity, a photodetector, and a calculation module arranged in sequence along the light propagation direction. When measuring, the chiral substance to be measured is located in the ring cavity, and the laser passes through the single-mode optical fiber, the quarter-wave plate, the half-wave plate, the polarization beam splitter, the convex lens group, and the ring cavity in sequence and enters the photodetector. The calculation module is used to fit the free spectral range FSR, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the linewidth of the ring cavity according to the optical signal detected by the photodetector, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured.

[0006] Further, the calculation module specifically includes:

[0007] A fitting unit, which is used to fit the resonance peaks of the optical signal received by the photodetector to obtain a cavity transmission spectrum, and then obtain the free spectral range FSR, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the linewidth of the ring cavity according to the cavity transmission spectrum;

[0008] A specific rotation calculation unit, which is used to calculate the specific rotation of the chiral substance to be measured at the laser wavelength according to the FSR, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the length and concentration of the chiral substance to be measured according to the following formula:

[0009]

[0010] In the formula, α is the specific rotation, (ν R -ν L ) is the difference between the left-handed polarized light resonance peak frequency ν L and the right-handed polarized light resonance peak frequency ν R , FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured;

[0011] A circular dichroism spectrum calculation unit, which is used to calculate the circular dichroism spectrum of the chiral substance to be measured at the laser wavelength according to the FSR, the linewidths of the left-handed and right-handed polarized light resonance peaks, and the length and concentration of the chiral substance to be measured according to the following formula:

[0012]

[0013] In the formula, Δε is the circular dichroism spectrum, (δ L -δ R ) is the difference between the left-handed polarized light resonance peak linewidth δ L and the right-handed polarized light resonance peak linewidth δ R .

[0014] Further, the quarter-wave plate and the half-wave plate are installed on a rotating rack, and the angle of the main axis of the rotating rack is adjustable.

[0015] Further, the annular cavity is composed of a first concave mirror, a second concave mirror, a first plane mirror, and a second plane mirror. Light enters the annular cavity from the first concave cavity mirror, and the light propagates in the direction of the first concave mirror, the second concave mirror, the first plane mirror, the second plane mirror, and the first concave mirror, and is output from the second concave cavity mirror. The light field resonates with the annular cavity.

[0016] Further, the convex lens group includes a first convex lens and a second convex lens arranged in sequence along the light propagation direction. The focal length of the first convex lens is 100 mm, and the focal length of the second convex lens is 150 mm.

[0017] The method for measuring the specific rotation and circular dichroism spectrum of a chiral substance according to the present invention is realized based on the above device, and the method includes:

[0018] (1) Place the chiral substance to be measured in the annular cavity;

[0019] (2) Turn on the narrow linewidth laser, adjust the quarter-wave plate and half-wave plate, and by rotating the angles of the quarter-wave plate and half-wave plate, make the light beam obtain the maximum light intensity after passing through the polarization beam splitter;

[0020] (3) Scan the frequency of the narrow linewidth laser to make the annular cavity have a stable cavity mode output;

[0021] (4) The photodetector receives the optical signal output from the annular cavity;

[0022] (5) The calculation module fits the optical signal received by the photodetector to obtain the cavity transmission spectrum, and then obtains the free spectral range FSR of the annular cavity, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the linewidth from the cavity transmission spectrum, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured.

[0023] Further, change the laser wavelength emitted by the narrow linewidth laser, and repeat (3)-(5), so as to obtain the specific rotation and circular dichroism spectrum of the chiral substance to be measured at different wavelengths.

[0024] Further, step (1) specifically includes:

[0025] (1-1) If the chiral substance to be measured is a crystal, insert it between the first concave cavity mirror and the second concave cavity mirror of the annular cavity, and anti-reflection films are coated on both sides of the chiral substance to be measured;

[0026] (1-2) If the chiral substance to be measured is a solution, place the solution in a T-shaped tube, and insert the T-shaped tube between the first concave cavity mirror and the second concave cavity mirror. Window plates with single-sided coating are provided on both sides of the T-shaped tube, and a broadband anti-reflection film is coated on the side facing the air.

[0027] Further, step (5) specifically includes:

[0028] (5-1) The calculation module fits the resonance peaks of the optical signal received by the photodetector to obtain the cavity transmission spectrum, and then obtains the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth based on the cavity transmission spectrum;

[0029] (5-2) According to the FSR, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured, the specific rotation of the chiral substance to be measured at this laser wavelength is calculated according to the following formula:

[0030]

[0031] In the formula, α is the specific rotation, (ν R -ν L ) is the difference between the resonance peak frequency ν L of left-handed polarized light and the resonance peak frequency ν R of right-handed polarized light, FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured;

[0032] (5-3) According to the FSR, the linewidths of the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured, the circular dichroism spectrum of the chiral substance to be measured at this laser wavelength is calculated according to the following formula:

[0033]

[0034] In the formula, Δε is the circular dichroism spectrum, (δ L -δ R ) is the difference between the linewidth δ L of the resonance peak of left-handed polarized light and the linewidth δ R of the resonance peak of right-handed polarized light.

[0035] Advantageous effects: Compared with the prior art, the remarkable advantages of the present invention are as follows: The device of the present invention is simple and low-cost. When measuring, only the cavity transmission spectrum signal of the linearly polarized light exiting from the ring cavity needs to be recorded once, and no additional modulation is required during the measurement process. The measurement is simple, fast, accurate, and has high precision and wide applicability. In addition, the present invention first proposes a method based on cavity enhancement to simultaneously measure the specific rotation and circular dichroism spectrum of chiral substances. Description of the Drawings

[0036] Figure 1 is a structural diagram of an embodiment of the device for measuring the specific rotation and circular dichroism spectrum of chiral substances provided by the present invention;

[0037] Figure 2 are the cavity transmission spectrum (a), specific rotation (b) and (d), and circular dichroism (c) and (e) obtained by fitting when measuring quartz crystals;

[0038] Figure 3 They are the cavity transmission spectra (a), specific rotation (b) and (d), and circular dichroism (c) and (e) obtained by fitting when measuring sucrose solutions. Specific implementation manners

[0039] Example 1

[0040] This example provides a device for measuring the specific rotation and circular dichroism spectrum of chiral substances, as Figure 1As shown, it includes a tunable narrow-linewidth laser 1, a single-mode optical fiber 2, a quarter-wave plate 3, a half-wave plate 4, a polarization beam splitter 5, a convex lens group (composed of a first convex lens 6-1 and a second convex lens 6-2), a high-quality ring cavity 7 (composed of a first concave mirror 7-1, a second concave mirror 7-2, a first plane mirror 7-3, and a second plane mirror 7-4), a photodetector 9, and a calculation module (not shown in the figure). Among them, the narrow-linewidth light source 1 is a narrow-linewidth light source with a central wavelength of 790 nm, a linewidth less than 100 KHz, a power of 90 mW, a wavelength tuning range of 760 - 810 nm, and the emitted light is linearly polarized light. The single-mode optical fiber 2 shapes the linearly polarized light emitted by the narrow-linewidth light source 1 into single-mode circularly polarized light, and the length of the single-mode optical fiber 2 is two meters. The quarter-wave plate 3 converts the circularly polarized light emitted from the single-mode optical fiber 2 into linearly polarized light, and the half-wave plate 4 rotates the polarization direction of the converted linearly polarized light to the horizontal direction. The polarization beam splitter 5 further purifies the polarization state of the laser (horizontal linear polarization). The quarter-wave plate 3 and the half-wave plate 4 are installed on a rotating rack, and the angle of the main axis of the rotating rack is adjustable. By rotating the angles of the quarter-wave plate 3 and the half-wave plate 4, the light beam can obtain the maximum light intensity after passing through the polarization beam splitter 5. The horizontally polarized light emitted from the polarization beam splitter 5 can be regarded as composed of two circularly polarized lights with equal amplitudes (left-handed and right-handed circularly polarized lights). They are coupled into the high-quality ring cavity 7 through the first convex lens 6-1 and the second convex lens 6-2. The focal length of the first convex lens is 100 mm, and the focal length of the second convex lens is 150 mm. The linearly polarized light enters from the first concave mirror 7-1, is reflected in turn by the second concave mirror 7-2, the first plane mirror 7-3, the second plane mirror 7-4, and the first concave mirror 7-1, and exits from the second concave mirror 7-2. The optical field forms resonance with the ring cavity. The incident plane of the first concave cavity mirror is coated with an antireflection film with a transmittance of 99.9%, and the other side is coated with a reflection film with a reflectivity of 97%. The exit plane of the second concave cavity mirror is coated with an antireflection film with a transmittance of 99.9%, and one side of the ring cavity is coated with a reflection film with a reflectivity of 97%. The first plane cavity mirror and the second plane mirror are total reflection mirrors. The chiral substance 8 to be measured is placed between the first concave mirror 7-1 and the second concave mirror 7-2, and it can be a crystal, a solution, etc. The photodetector 9 is a silicon-based amplified photodetector with a response range of 400 - 1000 nm, and is used to detect and receive the light output from the high-quality ring cavity 7. The calculation module is used to fit the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of the left-handed and right-handed polarized lights, and the linewidth according to the optical signals detected by the photodetector, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured.

[0041] The calculation module specifically includes a fitting unit, a specific rotation calculation unit, and a circular dichroism calculation unit. The fitting unit is used to fit the resonance peaks of the optical signals received by the photodetector to obtain the cavity transmission spectrum, and then obtain the free spectral range (FSR) of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the line width based on the cavity transmission spectrum. The specific rotation calculation unit is used to calculate the specific rotation of the chiral substance to be measured at this laser wavelength according to the FSR, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured according to the following formula:

[0042]

[0043] In the formula, α is the specific rotation, (ν R -ν L ) is the difference between the resonance peak frequency ν L of left-handed polarized light and the resonance peak frequency ν R of right-handed polarized light, FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured. The circular dichroism calculation unit is used to calculate the circular dichroism of the chiral substance to be measured at this laser wavelength according to the FSR, the line widths of the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured according to the following formula:

[0044]

[0045] In the formula, Δε is the circular dichroism, (δ L -δ R ) is the difference between the line width δ L of the resonance peak of left-handed polarized light and the line width δ R of the resonance peak of right-handed polarized light.

[0046] Example 2

[0047] This example provides a method for measuring the specific rotation and circular dichroism of a chiral substance. This method is based on the device of Example 1, and the substance to be measured is a quartz crystal with a length of 6 mm. The specific measurement method is as follows:

[0048] (1) Insert the chiral substance to be measured between the first concave mirror and the second concave mirror of the ring cavity, and anti-reflection films with a transmittance of 99.9% are coated on both sides of the chiral substance to be measured;

[0049] (2) Turn on the narrow linewidth laser, adjust the quarter-wave plate and half-wave plate, and by rotating the angles of the quarter-wave plate and half-wave plate, make the light beam obtain the maximum light intensity after passing through the polarization beam splitter;

[0050] (3) Scan the frequency of the narrow linewidth laser to make the ring cavity have a stable cavity mode output; in this example, the scanned frequency is around 790 nm;

[0051] (4) The photodetector receives the optical signal output from the ring cavity;

[0052] (5) The calculation module fits the optical signal received by the photodetector to obtain the free spectral range FSR of the ring cavity, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the line width, thereby calculating the specific rotation and circular dichroism spectrum of the chiral substance to be measured; specifically including:

[0053] (5-1) The calculation module fits the resonance peaks of the optical signal received by the photodetector to obtain the cavity transmission spectrum, and then obtains the free spectral range FSR of the ring cavity, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the line width according to the cavity transmission spectrum;

[0054] (5-2) According to the FSR, the frequency difference between the left-handed and right-handed polarized light resonance peaks, and the length and concentration of the chiral substance to be measured, the specific rotation of the chiral substance to be measured at this laser wavelength is calculated according to the following formula (as shown in Figure 2 (b)):

[0055]

[0056] In the formula, α is the specific rotation, (ν R -ν L ) is the difference between the left-handed polarized light resonance peak frequency ν L and the right-handed polarized light resonance peak frequency ν R , FSR is the free spectral range of the ring cavity, and l is the length of the chiral substance to be measured;

[0057] (5-3) According to the FSR, the line widths of the left-handed and right-handed polarized light resonance peaks, and the length and concentration of the chiral substance to be measured, the circular dichroism spectrum of the chiral substance to be measured at this laser wavelength is calculated according to the following formula (as shown in Figure 2 (c)):

[0058]

[0059] In the formula, Δε is the circular dichroism spectrum, (δ L -δ R ) is the difference between the left-handed polarized light resonance peak line width δ L and the right-handed polarized light resonance peak line width δ R .

[0060] (6) Change the laser wavelength emitted by the narrow line width laser and repeat (3)-(5), thereby obtaining the specific rotation and circular dichroism spectrum of the chiral substance to be measured at different wavelengths, as shown in Figure 2 (d) and (e).

[0061] In this embodiment, the specific rotation of the quartz crystal at a wavelength of 790 nm is finally calculated to be -11.737±0.086 deg.mm-1 , the circular dichroism is 0.004 ± 0.0014 dm -1 , as Figure 2 shown in (b) and (c).

[0062] Example 3

[0063] This example provides another method for measuring the specific rotation and circular dichroism spectrum of chiral substances. The substance to be measured is a sucrose solution. This method is the same as the other parts of Example 2, except that when measuring, the sucrose solution is placed in a T-tube, and window plates with single-sided coatings are provided on both sides of the T-tube. The side facing the air is coated with a broadband antireflection film. The calculation formulas for the specific rotation and circular dichroism spectrum of the sucrose solution are respectively:

[0064]

[0065] In the formula, α is the specific rotation, Δε is the circular dichroism, (ν R -ν L ) is the frequency difference between the resonance peaks of left-handed and right-handed polarized light, (δ L -δ R ) is the difference between the linewidth δ L of the resonance peak of left-handed polarized light and the linewidth δ R of the resonance peak of right-handed polarized light, FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured.

[0066] The cavity transmission spectrum fitted in this example is as Figure 3 shown in (a), the specific rotation and circular dichroism spectrum are respectively as Figure 3 shown in (b) and (c). By changing the wavelength of the narrow-linewidth laser, the specific rotation and circular dichroism spectrum of the substance at different wavelengths are as Figure 3 shown in (d) and (e).

[0067] The specific rotation of the sucrose solution at a wavelength of 790 nm finally calculated in this example is -32.2 ± 0.16 deg.dm -1 g -1 / ml, and the circular dichroism is 0.012 ± 0.00025 dm -1 g -1 / ml.

[0068] Example 4

[0069] This example provides a method for measuring the specific rotation and circular dichroism spectrum of chiral substances. The substance to be measured is a protein molecule or a nucleic acid molecule. This method is the same as the other parts of Example 3, except that when measuring, the protein molecule or nucleic acid molecule is dissolved in a solvent and then placed in a T-tube. This example can be widely used for the detection and analysis of proteins or nucleic acids in foods and drugs.

[0070] The working principle of the present invention is as follows: The linearly polarized light incident on the high-quality ring cavity can be regarded as composed of two circularly polarized lights (left-handed and right-handed circular polarizations) with equal amplitudes. When it passes through the chiral substance, it has different refractive indices and absorption coefficients. Therefore, the resonance frequencies and line widths of the left-circularly polarized light and the right-circularly polarized light in the ring cavity are different. By fitting the cavity transmission spectra of the left-circularly polarized light and the right-circularly polarized light, the specific rotation and circular dichroism of the chiral substance to be measured can be calculated. The cavity transmission spectrum of this system can be expressed as:

[0071]

[0072] where the first term and the second term on the left side of the equation respectively represent the cavity transmission spectra of the left-circularly polarized light and the right-circularly polarized light. ν L and ν R respectively represent the frequencies of the resonance peaks of the left-handed and right-handed polarized lights, and δ L =(2κ1 + κ i + κ L ) and δ R =(2κ1 + κ i + κ R ) respectively represent the line widths of the resonance peaks of the left-handed and right-handed polarized lights.

[0073] The device disclosed by the present invention enhances the measurement of specific rotation and circular dichroism through the ring cavity, and has higher precision compared with traditional polarimeters and circular dichroism spectrometers. This device can automatically fit the transmission spectra of the left-circularly polarized light and the right-circularly polarized light, and directly calculate the specific rotation and circular dichroism of the chiral substance to be measured. Moreover, when measuring the chiral substance with this device, only the cavity transmission signal needs to be recorded, and no additional modulation is required during the measurement process. The measurement is simple, fast and has very small errors. The device of the present invention is a simple butterfly cavity, with a wide range of applications, not affected by the spectral band of the light source. As long as there is a suitable light source, it can be measured in the range from ultraviolet to infrared.

[0074] The above-disclosed is only a preferred embodiment of the present invention, and it cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. An apparatus for measuring the specific rotation and circular dichroism spectrum of chiral substances, characterized in that: It includes a narrow-linewidth laser, a single-mode optical fiber, a quarter-wave plate, a half-wave plate, a polarization beam splitter, a convex lens group, a ring cavity, a photodetector and a calculation module, which are arranged in sequence along the light propagation direction. When measuring, the chiral substance to be measured is located in the ring cavity. The laser passes through the single-mode optical fiber, the quarter-wave plate, the half-wave plate, the polarization beam splitter, the convex lens group, and the ring cavity in sequence and enters the photodetector. The calculation module fits the light signal detected by the photodetector to obtain the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured; Among them, the ring cavity is composed of a first concave mirror, a second concave mirror, a first plane mirror and a second plane mirror. Light enters the ring cavity from the first concave mirror and propagates in the direction of the first concave mirror, the second concave mirror, the first plane mirror, the second plane mirror, and the first concave mirror, and exits from the second concave mirror. The light field forms resonance with the ring cavity. The incident plane of the first concave mirror is coated with an antireflection film with a transmittance greater than the first preset threshold, and the other side is coated with a reflection film with a reflectance greater than the second preset threshold but less than 100%. The exit plane of the second concave mirror is coated with an antireflection film with a transmittance greater than the first preset threshold. One side in the ring cavity is coated with a reflection film with a reflectance greater than the second preset threshold but less than 100%. The first plane cavity mirror and the second plane mirror are total reflection mirrors.

2. The device for measuring the specific rotation and circular dichroism spectrum of chiral substances according to claim 1, wherein: The calculation module specifically includes: A fitting unit, which is used to fit the resonance peaks of the light signal received by the photodetector to obtain the cavity transmission spectrum, and then obtain the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth according to the cavity transmission spectrum; A specific rotation calculation unit, which is used to calculate the specific rotation of the chiral substance to be measured according to the FSR, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured according to the following formula: where α is the specific rotation, (ν R - ν L ) is the difference between the resonance peak frequencies ν L of left-handed polarized light and ν R of right-handed polarized light, FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured; A circular dichroism spectrum calculation unit, which is used to calculate the circular dichroism spectrum of the chiral substance to be measured according to the FSR, the linewidths of the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured according to the following formula: where Δε is the circular dichroism spectrum, (δ L - δ R ) is the difference between the resonance peak linewidth δ L of the left-handed polarized light and the resonance peak linewidth δ R of the right-handed polarized light.

3. The device for measuring the specific rotation and circular dichroism spectrum of chiral substances according to claim 1, characterized in that: The quarter-wave plate and the half-wave plate are installed on a rotating rack, and the angle of the main axis of the rotating rack is adjustable.

4. The device for measuring the specific rotation and circular dichroism spectrum of chiral substances according to claim 1, wherein: The convex lens group includes a first convex lens and a second convex lens arranged in sequence along the light propagation direction.

5. A method for measuring the specific rotation and circular dichroism spectrum of chiral substances, characterized in that: This method is implemented based on the device described in claim 1, and this method includes: (1) Place the chiral substance to be measured in the ring cavity; (2) Turn on the narrow-linewidth laser, adjust the quarter-wave plate and the half-wave plate, and by rotating the angles of the quarter-wave plate and the half-wave plate, make the light beam obtain the maximum light intensity after passing through the polarization beam splitter; (3) Scan the frequency of the narrow-linewidth laser to make the ring cavity have a stable cavity mode output; (4) The photodetector receives the light signal output by the ring cavity; (5) The calculation module fits the light signal received by the photodetector to obtain the cavity transmission spectrum, and then obtains the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth according to the cavity transmission spectrum, so as to calculate the specific rotation and circular dichroism spectrum of the chiral substance to be measured.

6. The method for measuring the specific rotation and circular dichroism spectrum of a chiral substance according to claim 5, wherein: Change the laser wavelength emitted by the narrow linewidth laser, and repeat steps (3)-(5), so as to obtain the specific rotation and circular dichroism spectrum of the chiral substance to be measured at different wavelengths.

7. The method for measuring the specific rotation and circular dichroism spectrum of a chiral substance according to claim 5, characterized in that: Step (1) specifically includes: (1-1) If the chiral substance to be measured is a crystal, insert it between the first concave mirror and the second concave mirror of the ring cavity, and anti-reflection films are coated on both sides of the chiral substance to be measured; (1-2) If the chiral substance to be measured is a solution, place the solution in a T-shaped tube, and insert the T-shaped tube between the first concave mirror and the second concave mirror. Window plates with single-sided coating are provided on both sides of the T-shaped tube, and a broadband anti-reflection film is coated on the side facing the air.

8. The method for measuring the specific rotation and circular dichroism spectrum of a chiral substance according to claim 5, characterized in that: Step (5) specifically includes: (5-1) The calculation module fits the resonance peaks of the optical signals received by the photodetector to obtain the cavity transmission spectrum, and then obtains the free spectral range FSR of the ring cavity, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the linewidth according to the cavity transmission spectrum; (5-2) According to the FSR, the frequency difference between the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured, calculate the specific rotation of the chiral substance to be measured according to the following formula: In the formula, α is the specific rotation, (ν R - ν L ) is the difference between the resonance peak frequency ν L of the left-handed polarized light and the resonance peak frequency ν R of the right-handed polarized light, FSR is the free spectral range of the ring cavity, l is the length of the chiral substance to be measured, and M is the concentration of the chiral substance to be measured; (5-3) According to the FSR, the linewidths of the resonance peaks of left-handed and right-handed polarized light, and the length and concentration of the chiral substance to be measured, calculate the circular dichroism spectrum of the chiral substance to be measured according to the following formula: where Δε is the circular dichroism spectrum, and (δ L −δ R ) is the difference between the resonance peak linewidth δ L of the left-handed polarized light and the resonance peak linewidth δ R of the right-handed polarized light.

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