Terahertz circular polarization system for detecting chiral substances

Abstract

The invention relates to the technical field of chiral substance detection, and discloses a terahertz circular polarization system for detecting chiral substances. The invention provides a terahertz circular polarization system for detecting chiral substances. The terahertz circular polarization system comprises a terahertz emitter, a terahertz detector, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, a first polaroid, a third polaroid, a second polaroid and a quarter-wave plate. The terahertz circular polarization system for detecting the chiral substance provided by the invention can stably and accurately detect the chiral substance.

Description

Technical Field

[0001] The present invention relates to the technical field of chiral substance detection, and in particular to a terahertz circular polarization system for detecting chiral substances. Background Art

[0002] Vibrations in simple lattices, usually described as longitudinal and transverse phonons, usually consist of oscillatory displacements of atoms parallel or perpendicular to the direction of propagation. As the complexity of the lattice increases, the normal modes of phonons may become chiral modes due to the contribution of optical rotation components. In addition to their fundamental significance, chiral phonons that favor left-handed and right-handed modes of specific mirror symmetries can be uniquely suitable for a wide range of emerging chiral optical technologies, including biomedical spectroscopy and photonics. In the early 21st century, strong vibrational modes attributed to phonons were observed in macroscopic biological crystals of deoxyribonucleic acid, bovine human serum albumin, collagen, and benzoic acid. These studies were facilitated by the rapid development of terahertz (THz) spectroscopy, which enabled measurements in the photon energy range from 0.001 to 0.010 eV. Since then, a large number of studies have been carried out on crystals of amino acids (AAs), peptides, proteins, and sugars. Although some phonon resonances in the THz range are eliminated, the attribution of these peaks to specific lattice vibrational chirality is limited due to the difficulties in the practical implementation of THz circular dichroism (TCD) spectroscopy. TCD can also effectively resolve the peak assignments of enantiomers and racemates in crystals that may have different space groups, but whether it is possible to distinguish between L- and D-enantiomers in biological crystals remains unresolved. Summary of the invention

[0003] The purpose of the present invention is to provide a terahertz circular polarization system for detecting chiral substances, wherein the terahertz circular polarization system can stably and accurately detect chiral substances.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention:

[0006] A terahertz circular polarization system for detecting chiral substances, comprising:

[0007] A terahertz emitter and a terahertz detector are used to emit terahertz rays and detect terahertz waveforms; the orientation of the terahertz rays emitted by the terahertz emitter is fixed at a horizontal orientation relative to the optical test board, defined as the x-axis; the terahertz detector is fixed at a vertical orientation relative to the optical test board, defined as the y-axis;

[0008] A first off-axis parabolic mirror, a second off-axis parabolic mirror, a third off-axis parabolic mirror and a fourth off-axis parabolic mirror are used to generate collimated terahertz rays;

[0009] A first polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the x-axis;

[0010] A third polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the y-axis so that it is cross-polarized with the first polarizer and the terahertz emitter;

[0011] A second polarizer is disposed between the first polarizer and the third polarizer, and its transmission axis can be rotated to different orientations to determine the complete polarization state of the transmitted electric field;

[0012] The quarter wave plate is arranged between the first polarizer and the second polarizer, and is used for modulating the linearly polarized terahertz ray into terahertz circularly polarized light, and focusing the terahertz circularly polarized light on the detection crystal.

[0013] Furthermore, the terahertz emitter and the terahertz detector are implemented by a standard time-domain terahertz spectrometer using a photoconductive antenna and a 1560nm pulsed laser.

[0014] Furthermore, the first off-axis parabolic mirror, the second off-axis parabolic mirror, the third off-axis parabolic mirror and the fourth off-axis parabolic mirror are made of metal aluminum, with a diameter of 2 inches and a focal length of 50 mm.

[0015] The second technical solution of the present invention:

[0016] A method for detecting chiral substances comprises the following steps:

[0017] Using the above-mentioned terahertz circular polarization system for detecting chiral materials, the chiral materials were placed in polarization states of (-45, -45), (+45, +45), (+45, -45), and (-45, +45) for detection, and the terahertz time domain diagram was obtained. Afterwards, the terahertz time domain signal was Fourier transformed to obtain amplitude transmission spectra and phase transmission spectra in two directions. The orthogonal circular polarization state spectra can be obtained by calculation and analysis.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The terahertz circular polarization system for detecting chiral substances provided by the present invention can detect chiral substances stably and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0021] Figure 1 is a schematic diagram of a terahertz circular polarization system for detecting chiral substances according to the present invention;

[0022] Figure 2 Polarization waveform obtained for 0-180° linear polarization light path;

[0023] Figure 3 This is a waveform comparison chart of the 45° linear polarization optical path measurement and calculation simulation;

[0024] Figure 4 is the electric field vector diagram of left-handed circularly polarized light and right-handed circularly polarized light;

[0025] Figure 5 It is the terahertz time-domain spectra of left-handed circularly polarized light and right-handed circularly polarized light;

[0026] Figure 6 is the orthogonal circular polarization spectrum of D-valine;

[0027] Figure 7 is the orthogonal circular polarization spectrum of L-valine. DETAILED DESCRIPTION

[0028] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0029] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0031] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0032] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0033] Example 1

[0034] A terahertz circular polarization system for detecting chiral substances

[0035] Combination Figure 1 , this embodiment provides a terahertz circular polarization system for detecting chiral substances, including:

[0036] A terahertz emitter and a terahertz detector are used to emit terahertz rays and detect terahertz waveforms; the orientation of the terahertz rays emitted by the terahertz emitter is fixed at a horizontal orientation relative to the optical test board, defined as the x-axis; the terahertz detector is fixed at a vertical orientation relative to the optical test board, defined as the y-axis;

[0037] The emission and detection of terahertz rays were accomplished with a standard time-domain terahertz spectrometer (TeraSmart, (Menlo Systems)) using a photoconductive antenna and a 1560 nm pulsed laser;

[0038] A first off-axis parabolic mirror, a second off-axis parabolic mirror, a third off-axis parabolic mirror and a fourth off-axis parabolic mirror are used to generate collimated terahertz rays;

[0039] The first off-axis parabolic mirror, the second off-axis parabolic mirror, the third off-axis parabolic mirror and the fourth off-axis parabolic mirror are made of metal aluminum, have a diameter of 2 inches and a focal length of 50 mm;

[0040] A first polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the x-axis;

[0041] A third polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the y-axis so that it is cross-polarized with the first polarizer and the terahertz emitter;

[0042] A second polarizer is disposed between the first polarizer and the third polarizer, and its transmission axis can be rotated to different orientations to determine the complete polarization state of the transmitted electric field;

[0043] The transmission axis of the second polarizer is rotated to be along the y direction, which is defined as 0°. At this time, the second polarizer is co-polarized with the first polarizer. The sample to be tested is placed between the quarter-wave plate and the second polarizer, and the y component of the electromagnetic wave transmitted through the sample to be tested is measured;

[0044] The transmission axis of the second polarizer is rotated to +45° or -45°, and the x component is calculated by subtracting the two x components θ+45° or θ-45°;

[0045] Since any electric field can be decomposed into two perpendicular components, the complete polarization state of the transmitted electric field can be determined by three measurements (+45°, 0°, and -45°);

[0046] A quarter wave plate is disposed between the first polarizer and the second polarizer, and is used to modulate the linearly polarized terahertz ray into terahertz circularly polarized light, and focus the terahertz circularly polarized light on the detection crystal;

[0047] Typically, the p-polarization and s-polarization components of a terahertz wave are measured by utilizing the complex amplitude ratio of the p-polarization and s-polarization reflected at different times to extract the ellipsometric parametric spectrum at a specific frequency point; however, a wire grid polarizer cannot remove the intensity and phase noise in the incident terahertz wave, and a traditional terahertz signal source is usually very weak, resulting in a very small dynamic range at both ends of the spectrum, which reduces the signal-to-noise ratio and greatly reduces the frequency range of a reliable spectrum. Therefore, the present invention arranges a quarter-wave plate between the first polarizer and the second polarizer to modulate the linearly polarized terahertz ray into terahertz circularly polarized light, and focuses the terahertz circularly polarized light on a detection crystal, thereby increasing the frequency range of a reliable spectrum.

[0048] Example 2

[0049] Linear polarization light path correction analysis

[0050] The terahertz circular polarization system has very high requirements on the orientation accuracy of the polarizer. Ideally, it is necessary to measure the X polarization of the terahertz pulse and the full response of the DX detector at the same time, while blocking the Y polarization and high extinction ratio;

[0051] In order to check the high isolation of DX and DY polarization responses to linear polarized electric fields, a first polarizer is placed in the terahertz parallel beam between the first off-axis parabolic mirror and the second off-axis parabolic mirror as a polarizer, so that the terahertz pulse light originally propagating in all directions becomes light propagating in only one direction; a second polarizer and a third polarizer are placed in the terahertz parallel beam between the third off-axis parabolic mirror and the fourth off-axis parabolic mirror (the second polarizer is close to the third off-axis parabolic mirror, and the third polarizer is close to the fourth off-axis parabolic mirror), and the second polarizer polarizes the terahertz field along the 45° direction, and the third polarizer is orthogonal to the first polarizer;

[0052] Align the first polarizer and the third polarizer so that the transmission axes of the first polarizer and the third polarizer are parallel and perpendicular to the incident plane respectively, rotate the second polarizer (0-180°), and detect the light intensity, such as Figure 2 As shown, when the measured light intensity is maximum, the transmission axis of the second polarizer is 45° to the axis aligned with the first polarizer and the third polarizer, and 45° to the incident plane; Figure 3 As shown, the 45° linear polarization light path conforms to the theoretical light path model, and the measured field peak value is consistent with the calculated result.

[0053] Example 3

[0054] Circular polarization light path correction analysis

[0055] The terahertz ray is vertically incident on the first polarizer, and the terahertz ray is converted into linearly polarized light. Then, the linearly polarized light is incident on the quarter wave plate, and the output light is elliptically polarized light. The characteristic of the quarter wave plate is that it produces a phase delay of an odd multiple of π / 2. When the linearly polarized light is vertically incident on the quarter wave plate, and the polarization of the light forms an angle θ with the optical axis plane of the wave plate, the linearly polarized light becomes elliptically polarized light after output. In particular, when θ=±45°, the output light is circularly polarized light. Its long axis direction and rotation direction are determined by the angle between the polarization direction of the polarizer and the fast axis direction of the quarter wave plate. The slow axis and the fast axis of the wave plate are orthogonal and form an angle of 45° with the linear polarization direction. When the angle between the fast axis of the wave plate and the polarization direction of the polarizer is +45°, the output light beam is left-handed circularly polarized light. When the angle between the fast axis of the wave plate and the polarization direction of the polarizer is -45°, the output light beam is right-handed circularly polarized light.

[0056] The light intensity attenuation ratio is related to the polarization state of the incident light. A quarter wave plate is added under the premise of a 45° linear polarization optical path. When the first polarizer polarizes the electric field along the x direction and forms a 45° angle with the fast axis direction of the quarter wave plate, the corresponding second polarizer also maintains a 45° polarization direction, and the polarization state of the circularly polarized light is checked. Similarly, the -45° polarization measurement method is consistent with the above.

[0057] Angular misalignment between the first polarizer and the second polarizer can lead to incorrect orientation of the optical waveplate, resulting in inaccurate polarization measurement of the detector, which affects the determination of the system measurement results;

[0058] The theoretical relationship between the polarization angle β of the second polarizer and the two orthogonal terahertz electric fields is given by the following equation:

[0059] EY = EWG2sinβcosβ;

[0060] EY = EWG2sinβsinβ;

[0061] Among them, EWG2 is the electric field after the second polarizer, and the values ​​of two orthogonal electric fields in the time domain are measured;

[0062] Figure 4 is the electric field vector diagram of left-handed circularly polarized light and right-handed circularly polarized light;

[0063] Figure 5 It is the terahertz time-domain spectra of left-handed circularly polarized light and right-handed circularly polarized light;

[0064] Depend on Figure 4 and Figure 5 It can be seen that the experimental and theoretical results are in good agreement. With the modulation of the angle, the phase difference is π / 2, and the intensity remains consistent, which verifies the feasibility of terahertz left-handed circularly polarized light and right-handed circularly polarized light.

[0065] Example 4

[0066] Chiral Substance Detection of D-Valine and L-Valine

[0067] 30 mg of D-valine and 30 mg of L-valine were weighed, mixed with 120 mg of polyethylene powder, and then ground. The mixed powder was pressed at a pressure of 10 MPa for 5 minutes to obtain tablets with a diameter of 13 mm, of which the thickness of D-valine was 1.311 mm and the thickness of L-valine was 1.308 mm.

[0068] The test samples (D-valine tablets and L-valine tablets) were placed in the polarization states of (-45, -45), (+45, +45), (+45, -45), and (-45, +45) for detection, and the terahertz time domain diagram was obtained. After that, the terahertz time domain signal was Fourier transformed to obtain the amplitude transmission spectrum and phase transmission spectrum in two directions. The orthogonal circular polarization state spectrum can be obtained by calculation and analysis, as shown in Figure 6 and Figure 7 As shown;

[0069] Depend on Figure 6 and Figure 7 It can be seen that in the case of left-handed and right-handed polarization components, a reversal occurs, which explains the characteristics of the circularly polarized light path and identifies chiral substances.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A terahertz circular polarization system for detecting chiral substances, characterized in that: The terahertz circular polarization system for detecting chiral substances comprises: A terahertz emitter and a terahertz detector are used to emit terahertz rays and detect terahertz waveforms; the orientation of the terahertz rays emitted by the terahertz emitter is fixed at a horizontal orientation relative to the optical test board, defined as the x-axis; the terahertz detector is fixed at a vertical orientation relative to the optical test board, defined as the y-axis; A first off-axis parabolic mirror, a second off-axis parabolic mirror, a third off-axis parabolic mirror and a fourth off-axis parabolic mirror are used to generate collimated terahertz rays; A first polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the x-axis; A third polarizer is disposed in front of the terahertz emitter and has its transmission direction fixed to the y-axis so that it is cross-polarized with the first polarizer and the terahertz emitter; A second polarizer is disposed between the first polarizer and the third polarizer, and its transmission axis can be rotated to different orientations to determine the complete polarization state of the transmitted electric field; The quarter wave plate is arranged between the first polarizer and the second polarizer, and is used for modulating the linearly polarized terahertz ray into terahertz circularly polarized light, and focusing the terahertz circularly polarized light on the detection crystal.

2. A terahertz circular polarization system for detecting chiral substances according to claim 1, characterized in that: The terahertz emitter and terahertz detector were implemented with a standard time-domain terahertz spectrometer using a photoconductive antenna and a 1560 nm pulsed laser.

3. The terahertz circular polarization system for detecting chiral substances according to claim 1, characterized in that: The first off-axis parabolic mirror, the second off-axis parabolic mirror, the third off-axis parabolic mirror and the fourth off-axis parabolic mirror are made of metal aluminum, have a diameter of 2 inches and a focal length of 50 mm.

4. A method for detecting chiral substances, characterized in that: The following steps are involved: Using the terahertz circular polarization system for detecting chiral substances as described in claims 1 to 3, the chiral substance is placed in the polarization states of (-45, -45), (+45, +45), (+45, -45), and (-45, +45) for detection, and a terahertz time domain diagram is obtained. After that, the terahertz time domain signal is Fourier transformed to obtain amplitude transmission spectra and phase transmission spectra in two directions, and the orthogonal circular polarization state spectrum can be obtained by calculation and analysis.

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