Circular Dichroism Spectroscopy Measurement System Based on Heterodyne Phase Modulation

Abstract

This invention relates to a circular dichroism spectroscopy measurement system based on heterodyne phase modulation. It includes a broadband light source, a polarizer, a chiral sample, an α-BBO crystal, a Wollaston prism, two optical fibers, a CCD spectrometer, a data transmission line, and a data processing computer. The broadband light source, polarizer, chiral sample, α-BBO crystal, and Wollaston prism are arranged in a straight line. The system operates by combining incoherent spectral acquisition with heterodyne coherent spectral acquisition. During incoherent spectral acquisition, the polarizer's polarization direction is parallel to the Wollaston prism's optical axis, and the CCD spectrometer acquires coherent spectral information. During heterodyne coherent spectral acquisition, the polarizer's polarization direction forms a 45° angle with the Wollaston prism's optical axis, and the CCD spectrometer acquires coherent spectral information. Finally, the circular dichroism spectrum of the chiral sample is obtained through mathematical calculation. This system further improves the signal-to-noise ratio and optimizes measurement accuracy in circular dichroism spectroscopy.

Description

Technical Field

[0001] This invention relates to the field of optical sample detection, specifically a circular dichroism spectroscopy measurement system based on heterodyne phase modulation. Background Technology

[0002] Circular dichroism spectroscopy is an optical rotation spectrum used to infer the configuration and conformation of chiral molecules. Chiral substances have different absorption coefficients for left-handed and right-handed polarized light, i.e. Using the wavelengths of the left-handed and right-handed polarized light as the abscissa, and the difference in absorptivity ( The spectrum obtained by plotting the wavelength on the vertical axis is the circular dichroism spectrum of the chiral substance. Due to the inconsistency of the absorption coefficients of chiral substances for left-handed and right-handed polarized light, when a circularly polarized beam passes through a chiral substance, it will no longer be circularly polarized light, but will become elliptically polarized light. Therefore, the molar ellipticity θ can also be used as the measurement object of the circular dichroism spectrum. That is, the spectrum obtained by plotting the molar ellipticity θ on the vertical axis and the wavelength on the horizontal axis can characterize the circular dichroism spectrum of the chiral substance. The tangent of the molar ellipticity θ is related to the ratio of the luminous flux of the left-handed and right-handed polarized light.

[0003] For the acquisition of circular dichroism spectra of chiral substances, the published results currently use modulation methods and single-photon counting methods to measure the intensity of left-handed and right-handed polarized light transmitted through the chiral sample. Since the difference in the absorption rate of chiral substances to left-handed and right-handed light is small, the quality of the final circular dichroism spectrum obtained by the system in obtaining the difference in the absorption rate of left-handed and right-handed polarized light is still unable to accurately describe the properties of the chiral substance under test in some cases due to issues such as signal-to-noise ratio. Summary of the Invention

[0004] To further improve the signal-to-noise ratio and optimize the measurement accuracy of circular dichroism spectroscopy, this invention innovatively proposes a circular dichroism spectroscopy measurement system based on heterodyne phase modulation. Utilizing linearly polarized light as the detection source, the phase modulation of linearly polarized light by chiral substances is expressed through spectral coherence via the heterodyne phase modulation principle. Finally, the luminous flux ratio along the orthogonal vector directions is obtained through mathematical calculation, ultimately yielding the circular dichroism spectrum correlated with the molar ellipticity θ.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] The circular dichroism spectroscopy measurement system based on heterodyne phase modulation includes a broadband light source, a polarizer, an α-BBO crystal, and a Wollaston prism arranged in a straight line. It also includes a first optical fiber, a second optical fiber, a CCD spectrometer, a data transmission line, and a data processing computer. One end of each of the first and second optical fibers is connected to the Wollaston prism, and the other end is connected to the CCD spectrometer. The CCD spectrometer is connected to the data processing computer via the data transmission line. A space is provided between the polarizer and the α-BBO crystal for placing the chiral sample to be measured.

[0007] The broadband light source is at least one of LED light source, xenon lamp, mercury lamp, or halogen lamp.

[0008] The CCD spectrometer contains at least two detector arrays.

[0009] The first optical fiber is connected to the top array of the CCD spectrometer, and the second optical fiber is connected to the bottom array of the CCD spectrometer.

[0010] When performing incoherent spectral acquisition, the polarization direction of the polarizer is parallel to the optical axis of the Wollaston prism.

[0011] When performing heterodyne coherent spectroscopy acquisition, the polarization direction of the polarizer makes an angle of 45° with the optical axis of the Wollaston prism.

[0012] The polarizer is mounted on a lens frame that has the degree of freedom to rotate around the direction of light propagation.

[0013] The Wollaston prism is equipped with focusing elements between itself and optical fiber one and optical fiber two, respectively.

[0014] The circular dichroism spectroscopy measurement method based on heterodyne phase modulation includes the following steps: A broadband light beam emitted from a broadband light source is polarized into linearly polarized light by a polarizer and then incident on a chiral test sample. The chiral test sample changes the phase of the linearly polarized light, so that the linearly polarized light transmitted through the chiral test sample acquires orthogonal polarization components. After the light beam transmitted through the chiral test sample passes through an α-BBO crystal, the orthogonal polarization components are time-delayed. The orthogonally polarized light beam with time delay is split into two beams by a Wollaston prism, namely o-ray and e-ray. The o-ray is transmitted to the top array of the CCD spectrometer via a first optical fiber, and the e-ray is transmitted to the bottom array of the CCD spectrometer via a second optical fiber. The CCD spectrometer converts the collected light intensity signal into an electrical signal and transmits it to a data processing computer via a data transmission line.

[0015] The spectral measurement process is divided into an incoherent spectral acquisition process and a heterodyne coherent spectral acquisition process. When performing the incoherent spectral acquisition process, the polarization direction of the polarizer is parallel to the optical axis of the Wollaston prism. When performing the heterodyne coherent spectral acquisition process, the polarization direction of the polarizer is at an angle of 45° to the optical axis of the Wollaston prism.

[0016] The o-beam split by the Wollaston prism needs to be focused during its coupling into the first optical fiber, and the e-beam split by the Wollaston prism needs to be focused during its coupling into the second optical fiber.

[0017] The present invention has the following beneficial effects and advantages:

[0018] This invention innovatively employs heterodyne phase modulation to achieve circular dichroism spectral detection, which further improves the system's measurement signal-to-noise ratio compared to previously published results, and has advantages for small signal measurements. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0020] Figure 2a This is a schematic diagram of the principle of the invention. Figure 1 ;

[0021] Figure 2b This is a schematic diagram of the principle of the present invention (II).

[0022] Among them, 1 is a broadband light source, 2 is a polarizer, 3 is a chiral sample, 4 is an α-BBO crystal, 5 is a Wollaston prism, 6 is optical fiber one, 7 is optical fiber two, 8 is a CCD spectrometer, 9 is a data transmission line, and 10 is a data processing computer. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0024] like Figure 1As shown, this invention includes 1. a broadband light source, 2. a polarizer, 3. a chiral sample to be tested, 4. an α-BBO crystal, 5. a Wollaston prism, 6. a first optical fiber, 7. a second optical fiber, 8. a CCD spectrometer, 9. a data transmission line, and 10. a data processing computer. The broadband light source 1, polarizer 2, chiral sample to be tested 3, α-BBO crystal 4, and Wollaston prism 5 are arranged in a straight line. The system operation includes an incoherent spectral acquisition process and a heterodyne coherent spectral acquisition process. During the incoherent spectral acquisition process, the polarization direction of polarizer 2 is parallel to the optical axis of Wollaston prism 5, and the CCD spectrometer 8 acquires the incoherent spectrum. During the heterodyne coherent spectral acquisition process, the polarization direction of polarizer 2 forms an angle of 45° with the optical axis of Wollaston prism 5, and the CCD spectrometer 8 acquires the coherent spectral information. Finally, the circular dichroism spectrum of the chiral sample to be tested 3 is obtained through mathematical calculation.

[0025] As shown in Figure 2, the present invention includes an incoherent spectral acquisition process and a heterodyne coherent spectral acquisition process during operation. These two processes will be described in detail below with reference to the accompanying drawings.

[0026] like Figure 2a As shown, during the incoherent spectral acquisition process, the polarization direction of polarizer 2 is parallel to the optical axis of Wollaston prism 5. The naturally polarized beam emitted from broadband light source 1 is polarized into a linearly polarized beam by polarizer 2. When the linearly polarized beam passes through chiral sample 3, due to the asymmetry of the molecular structure of chiral sample 3, the linearly polarized beam transmitted through chiral sample 3 exhibits a polarization component in the orthogonal direction of its polarization direction. At this time, the linearly polarized beam is transformed into a polarized beam with orthogonal polarization direction. When the orthogonally polarized beam passes through α-BBO crystal 4, α-BBO crystal 4 polarizes the orthogonally polarized beam. The orthogonal polarization components in the polarized beam have different refractive indices. Therefore, the orthogonal polarization components in the orthogonally polarized beam exhibit different propagation speeds in the α-BBO crystal 4. When the orthogonally polarized beam passes through the α-BBO crystal 4, the orthogonal polarization components in the orthogonally polarized beam exhibit a time delay. Since the optical axis of the Wollaston prism 5 is parallel to the polarization direction of the polarizer 2, the orthogonally polarized beam is split into two beams by the Wollaston prism, and each beam is a beam containing one of the polarization components of the orthogonally polarized beam.

[0027] like Figure 2bAs shown, during heterodyne coherent spectroscopy acquisition, the polarization direction of polarizer 2 makes an angle of 45° with the optical axis of Wollaston prism 5. The naturally polarized beam emitted from broadband light source 1 is polarized into a linearly polarized beam by polarizer 2. When the linearly polarized beam passes through chiral sample 3, due to the asymmetry of the molecular structure of chiral sample 3, the linearly polarized beam transmitted through chiral sample 3 exhibits polarization components in the orthogonal direction of its polarization direction. At this time, the linearly polarized beam is transformed into a polarized beam with orthogonal polarization direction. When the orthogonally polarized beam passes through α-BBO crystal 4, α-BBO crystal 4 has a different refractive index for the orthogonal polarization components in the orthogonal polarized beam. Therefore, the orthogonal polarization components in the orthogonal polarized beam exhibit different propagation speeds in α-BBO crystal 4. After a polarized beam with orthogonal polarization direction is transmitted through α-BBO crystal 4, the orthogonal polarization component in the orthogonal polarized beam exhibits a time delay. Since the angle between the optical axis of Wollaston prism 5 and the polarization direction of polarizer 2 is 45°, the orthogonal polarized beam is split into two beams by Wollaston prism. Each beam represents the component of the orthogonal polarized beam in the optical axis direction of Wollaston prism 5 and the orthogonal direction of Wollaston prism 5. That is, Wollaston prism 5 splits the orthogonal polarized beam with time delay in the direction of Wollaston prism 5 and the orthogonal direction of optical axis. Therefore, the polarization directions of the two beams after splitting are orthogonal to each other, and the vibration modes in each split beam have a time delay. This time delay causes spectral interference between the two vibration modes.

[0028] like Figure 1 As shown, the two beams split by the Wollaston prism 5 are coupled into optical fiber 6 and optical fiber 7, respectively. During the coupling process, a focusing element may be required. Optical fiber 6 and optical fiber 7 synchronously transmit the coupled beams and transmit them to a CCD spectrometer 8. The CCD spectrometer 8 contains at least two array detectors, defined here as a top detector and a bottom detector. The bottom detector and the top detector receive the beams transmitted by optical fiber 6 and optical fiber 7, respectively, and convert them into spectral information through photoelectric conversion. The spectral information formed after photoelectric conversion is transmitted to a data processing computer 10 through a data transmission line 9. The data processing computer completes relevant data calculations and graphic visualization processes.

[0029] The broadband light source can be one or more combinations of LED light sources, xenon lamps, mercury lamps, or halogen lamps.

[0030] The polarizer is mounted on a lens frame that has the degree of freedom to rotate around the direction of light propagation. The rotation of the lens frame can be controlled manually or by a motor.

[0031] During the coupling of the o-ray and e-ray separated by the Wollaston prism into optical fiber one and optical fiber two, focusing may be required.

[0032] The working principle of this invention is as follows:

[0033] This invention includes an incoherent spectral acquisition process and a heterodyne coherent spectral acquisition process. The difference between the two acquisition processes is caused by the difference in the angle between the polarization direction of the polarizer 2 and the optical axis of the Wollaston prism 5. This invention changes the angle between the polarizer 2 and the optical axis of the Wollaston prism 5 by rotating the polarization direction of the polarizer 2.

[0034] like Figure 1 As shown, polarizer 2 is mounted on a frame that has a degree of freedom to rotate around the beam propagation direction. The frame can be manually controlled to rotate or controlled by a motor. During the incoherent spectral acquisition process, the frame is rotated so that the polarization direction of polarizer 2 is parallel to the optical axis of Wollaston prism 5. During the heterodyne coherent spectral acquisition process, the frame is rotated so that the polarization direction of polarizer 2 makes an angle of 45° with the optical axis of Wollaston prism 5.

[0035] In the data calculation process of this invention, the light intensity detected by the detection array in the CCD spectrometer 8 during photoelectric conversion is used as the standard. When the circular dichroism spectral properties of the chiral sample 3 are represented by molar ellipticity θ, the ratio of light flux is a quantitative index of molar ellipticity θ. Therefore, it is necessary to convert the parameters through mathematical calculation. In the mathematical calculation process, each spectral acquisition point is taken as a set of data. In each set of data, the light intensity acquired by the top array of the CCD spectrometer 8 and the light intensity acquired by the bottom array of the CCD spectrometer 8 during heterodyne coherent spectral acquisition are subtracted. The difference is then compared with the light intensity acquired by the top array of the CCD spectrometer 8 during incoherent spectral acquisition. The resulting ratio is the light flux ratio related to molar ellipticity θ.

Claims

1. A circular dichroism spectroscopy measurement system based on heterodyne phase modulation, characterized in that, The device includes a broadband light source (1), a polarizer (2), an α-BBO crystal (4), and a Wollaston prism (5) arranged in a straight line. It also includes a first optical fiber (6), a second optical fiber (7), a CCD spectrometer (8), a data transmission line (9), and a data processing computer (10). One end of the first optical fiber (6) and the second optical fiber (7) are connected to the Wollaston prism (5), and the other end is connected to the CCD spectrometer (8). The CCD spectrometer (8) is connected to the data processing computer (10) through the data transmission line (9). There is a space between the polarizer (2) and the α-BBO crystal (4) for placing the chiral sample (3). When performing incoherent spectral acquisition, the polarization direction of the polarizer (2) is parallel to the optical axis of the Wollaston prism (5); When performing heterodyne coherent spectral acquisition, the polarization direction of the polarizer (2) is at an angle of 45° with the optical axis of the Wollaston prism (5).

2. The circular dichroism spectroscopy measurement system based on heterodyne phase modulation method according to claim 1, characterized in that, The broadband light source (1) is at least one of LED light source, xenon lamp, mercury lamp, or halogen lamp.

3. The circular dichroism spectroscopy measurement system based on heterodyne phase modulation method according to claim 1, characterized in that, The CCD spectrometer (8) contains at least two detector arrays.

4. The circular dichroism spectroscopy measurement system based on heterodyne phase modulation method according to claim 1 or 3, characterized in that, The first optical fiber (6) is connected to the top array of the CCD spectrometer (8), and the second optical fiber (7) is connected to the bottom array of the CCD spectrometer (8).

5. The circular dichroism spectroscopy measurement system based on heterodyne phase modulation method according to claim 1, characterized in that, The polarizer (2) is mounted on a lens frame that has a degree of freedom to rotate around the direction of light propagation.

6. The circular dichroism spectroscopy measurement system based on heterodyne phase modulation method according to claim 1, characterized in that, The Wollaston prism (5) is provided with focusing elements between optical fiber one (6) and optical fiber two (7).

7. A method for measuring circular dichroism spectroscopy based on heterodyne phase modulation, characterized in that, Includes the following steps: The broadband light beam emitted from the broadband light source (1) is polarized into linearly polarized light by the polarizer (2) and then incident on the chiral test sample (3). The chiral test sample (3) changes the phase of the linearly polarized light, so that the linearly polarized light transmitted through the chiral test sample (3) obtains a polarization component with orthogonal polarization direction. After the light beam transmitted through the chiral test sample passes through the α-BBO crystal (4), the orthogonal polarization component generates a time delay. The orthogonally polarized light beam with time delay is split into two beams by the Wollaston prism (5), namely o-light and e-light. The o-light is transmitted to the top array in the CCD spectrometer (8) through the first optical fiber (6), and the e-light is transmitted to the bottom array in the CCD spectrometer (8) through the second optical fiber (7). The CCD spectrometer (8) converts the collected light intensity signal into an electrical signal and transmits it to the data processing computer (10) through the data transmission line (9). The spectral measurement process is divided into an incoherent spectral acquisition process and a heterodyne coherent spectral acquisition process. When the incoherent spectral acquisition process is performed, the polarization direction of the polarizer (2) is parallel to the optical axis of the Wollaston prism (5). When the heterodyne coherent spectral acquisition process is performed, the polarization direction of the polarizer (2) is at an angle of 45° to the optical axis of the Wollaston prism (5).

8. The circular dichroism spectroscopy measurement method based on heterodyne phase modulation according to claim 7, characterized in that, The o-beam split by the Wollaston prism (5) needs to be focused during the coupling of the light into the first optical fiber (6), and the e-beam split by the Wollaston prism (5) needs to be focused during the coupling of the light into the second optical fiber (7).

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