CN113125386B - Method for generating chiral plasmon based on carbon nanotube and application - Google Patents
Method for generating chiral plasmon based on carbon nanotube and application Download PDFInfo
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Abstract
The invention provides a method for generating chiral plasmons based on carbon nano tubes, which comprises the step of generating the chiral plasmons by the action of intermediate infrared laser pulses and the carbon nano tubes, and also provides application of the chiral plasmons. Based on the effect of the mid-infrared laser and the carbon nano tube, chiral plasmons are generated, and the method is simple and efficient. The chirality of the plasmons can be conveniently changed by changing the polarization direction of the laser.
Description
Technical Field
The invention relates to the field of interaction of light and substances, in particular to a method for generating chiral plasmons based on a carbon nano tube and application of the method.
Background
Chirality, the concept originally derived from the greek word (kheir), is used to describe the difference between the left and right hands, i.e. mirror images of each other but not coincident. The chirality of a substance is of only two types: left and right handedness. Chiral materials in nature are ubiquitous, such as amino acids, nucleic acids, and proteins. Their twin molecules look very similar, but the properties may be completely different. Some drug molecules can cure the disease, but its mirror image molecule may be a toxic drug. Therefore, chiral identification of biomolecules is very important. The unique optical response of chiral materials makes it an effective means to identify and characterize their complex structures and physical properties. It is well known that most biomolecules are difficult to detect due to their too weak chiral response intensity and very small diameter. The surface plasmon breaks through the characteristics of diffraction limit propagation and local electric field enhancement, so that the surface plasmon becomes a very important means in the field of research of chiral materials.
Recently, chiral plasmons have been used to differentially identify different chiral molecules in various fields, such as physics, biology, chemistry, and drug development. In these studies, various structures composed of metamaterials have exhibited many novel phenomena in generating chiral responses to light, but the preparation processes thereof are very complicated. Chiral plasmons also appear in the noble metal silver nanowires, but the noble metal silver nanowires only play the role of ideal conductors in the visible light region, and the chiral response range is far away from the infrared response region of most biomolecules.
Therefore, a new simple and easy excitation method of chiral plasmons is needed to be found, which can conveniently and efficiently detect the chirality of most biomolecules.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and discloses a method for generating chiral plasmons based on the action of mid-infrared laser and carbon nanotubes. In order to achieve the above purpose, the present invention provides a method for generating chiral plasmons based on carbon nanotubes and applications thereof.
To achieve the above objects, a first aspect of the present invention provides a method for generating chiral plasmons based on carbon nanotubes, the method comprising the steps of:
(1) Focusing the intermediate infrared laser pulse by using a convex lens to form a light spot;
(2) And (3) enabling the focused light spots in the step (1) to act with the carbon nano tubes to generate chiral plasmons.
The method according to the first aspect of the present invention, wherein in the step (1), the focal length of the convex lens is 1 to 5cm, preferably 3cm.
The method according to the first aspect of the present invention, wherein, in the step (1), the wave number of the mid-infrared laser pulse is 400 to 2000cm -1 Preferably 840 to 1600cm -1 。
The method according to the first aspect of the present invention, wherein in the step (1), the spot beam waist size of the mid-infrared laser pulse is 0.5 to 2.0 μm, preferably 0.5 to 1.5 μm, and most preferably 1.0 μm.
The method according to the first aspect of the present invention, wherein, in the step (1), the polarization angle of the mid-infrared laser pulse is 0 ° to 360 °, preferably, the polarization angle of the mid-infrared laser pulse is not 0 °, 90 °, 180 °, or 270 °, and most preferably, the polarization angle of the mid-infrared laser pulse is 45 ° or 135 °.
The method according to the first aspect of the present invention, wherein, in the step (1), the mid-infrared laser pulse is a paraxial approximate gaussian beam. The method according to the first aspect of the present invention, wherein, in the step (2), the diameter of the carbon nanotube is 1 to 6 nm, preferably 2.5 to 4.5 nm.
The method according to the first aspect of the present invention, wherein, in the step (2), the carbon nanotubes are single-walled carbon nanotubes.
The method according to the first aspect of the present invention, wherein the method controls the excitation pattern of the carbon nanotube plasmon by the incident polarization angle of the mid-infrared laser pulse to regulate the chirality of the carbon nanotube plasmon.
A second aspect of the present invention provides a method for detecting a chiral molecule, the method comprising the method for generating a chiral plasmon based on a carbon nanotube according to the first aspect.
The method for generating chiral plasmons based on the carbon nanotubes can have the following beneficial effects:
(1) Based on the effect of the mid-infrared laser and the carbon nano tube, chiral plasmons are generated, and the method is simple and efficient.
(2) The chirality of the plasmons can be conveniently changed by changing the polarization direction of the laser.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic diagram of a nanotube plasmon detection structure using near-field optical techniques provided by the present invention.
Fig. 2 is a distribution of an electric field for exciting plasmon of three modes in cross section, provided in embodiment 1 of the present invention, where fig. 2 (a) shows a plasmon electric field distribution of an m =0 mode, fig. 2 (b) shows a plasmon electric field distribution of an m =1 mode, and fig. 2 (c) shows a plasmon electric field distribution of an m = -1 mode.
Fig. 3 is a distribution of electric fields superimposed on top views for exciting plasmons of three modes provided in embodiment 1 of the present invention, where fig. 3 (a) shows an electric field distribution of a right-handed plasmon, fig. 3 (b) shows an electric field distribution of a left-handed plasmon, fig. 3 (c) shows electric field distributions of superimposed plasmons of m =0 and m =1, and fig. 3 (d) shows an electric field distribution of a plasmon of m = -1.
FIG. 4 is an electric field distribution across a cross-section of a nanotube taken at 40nm intervals as provided in example 1 of the present invention.
Description of reference numerals:
1. mid-infrared laser pulses; 2. a carbon nanotube; 3. a plasmon; 4. electric field distribution of plasmons of m =0 mode on a cross section; 5. electric field distribution of plasmons of m =1 mode on a cross section; 6. electric field distribution of plasmons of m = -1 mode on the cross section; 7. the polarization direction of the incident laser light is 45 degrees; 8. polarization direction of incident laser-45 °; 9. the polarization direction of the incident laser is 0 degree; 10. the polarization direction of the incident laser is 90 degrees; 11. electric field distribution of plasmons on a plan view when the polarization direction of incident laser light is 45 °; 12. electric field distribution of plasmons on a top view when the polarization direction of incident laser is-45 degrees; 13. electric field distribution of plasmons on a plan view when the polarization direction of the incident laser light is 0 °; 14. electric field distribution of the plasmon on a plan view when the polarization direction of the incident laser light is 90 °;15-20, intercepting the electric field distribution on the cross section of the nanotube plasmon electric field at intervals of 40 nm; 21. the direction of rotational propagation of the helical surface plasmon wave.
Detailed Description
The invention is further illustrated by the following specific examples, which, however, are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
This section generally describes the materials used in the testing of the present invention, as well as the testing methods. Although many materials and methods of operation are known in the art for the purpose of carrying out the invention, the invention is nevertheless described herein in as detail as possible. It will be apparent to those skilled in the art that the materials and methods of operation used in the present invention are well within the skill of the art in this context, if not specifically mentioned.
Example 1
This example serves to illustrate the method of the present invention for detecting nanotube plasmons using near-field optical techniques.
FIG. 1 is a schematic diagram of a nanotube plasmon detection structure using near-field optical techniques provided by the present invention. The inventor uses commercial software COMSOL based on finite element method to numerically simulate chiral plasmons which can be excited in the carbon nanotube, and uses a mode analysis module to analyze the plasmon mode of the nanotube, and tries to find a waveguide mode which can be excited in a middle infrared band of the carbon nanotube, so that the electric field distribution of the carbon nanotube can be known.
The inventors have placed carbon nanotubes in a Boron Nitride (BN) dielectric environment. The electrical conductivity of a carbon nanotube is given by the Random Phase Approximation (RPA) of the local limit (q → 0):
where ω is the frequency, E F Is the fermi level and τ is the scattering time of the carriers in the nanotube. Vertically irradiating a paraxial approximate Gaussian beam (mid-infrared laser pulse) with the beam waist size of 1.0 mu m of light spot on the surface of the carbon nano tube by a convex lens with the focal length of 3cm, wherein the diameter of the carbon nano tube is 2.5-4.5 nanometers, and the wave number of the mid-infrared laser pulse is 840-1600 cm -1 . The angle (alpha) between the polarization direction of the excitation light and the nanotube axis. When light is rotated counterclockwise along the nanotube axis, α is defined as positive. With respect to the setting of the time-harmonic field, the inventors herein have recognized that
As an electric field component of the excitation light, E 0 In order to be a spatial distribution of the incident field,
the phase of the incident field. To excite a certain mode of plasmon, it is necessary to require overlap of the incident field with the field component of the plasmon mode, and only then this mode can be formed. Then, in order to make the excitation efficiency high, the overlapped portion is increased by some means.
When the nanotube is illuminated with excitation light having an incident polarization parallel to the nanotube axis, m =0 mode 4 and m = -1 mode 6 may be excited simultaneously. And when the instantaneous phase of the excitation light is 0, there is exactly an overlap with the m =0 mode 4 (fig. 2 a); when the excitation light continues to propagate with a momentary phase of pi/2, it just overlaps with the m = -1 mode 6 (fig. 2 c). The excitation light polarization is then changed to be orthogonal to the nanotube axis and the instantaneous phase is 0, the instantaneous electric field overlaps with the m =1 mode 5 (fig. 2 b). When the incident angle polarization angle is 0 ° < α <90 °, there are both parallel and perpendicular components, and thus, m =0,m = ± 1 three plasmon modes can be excited at the same time. Wherein the m =0 mode is an electron density wave vibration along the carbon nanotube axis direction, and m = ± 1 is an electron density wave vibration perpendicular to the carbon nanotube axis direction, and their vibration directions are perpendicular to each other.
It can be seen from the electric field diagrams of fig. 3b and 3c that the vibrations of the two modes are perpendicular to each other, and it can be known from the circularly polarized light forming mechanism that when the amplitudes of the two modes are equal and the phase difference is ± pi/2, circularly polarized surface plasmons can be formed. Like circularly polarized light, circularly polarized surface plasmons carry an angular momentum σ ± . It has been mentioned above that when an excitation beam of arbitrary polarization strikes a carbon nanotube, three plasmon modes are excited simultaneously. Reference numerals 7 to 10 in fig. 3 show different polarization directions of incident laser light, and when the polarization of incident light is 45 °, two modes of m = ± 1 are superimposed to form a circular polarization plasmon, and at this time, a mode of m =0 is also excited, and when it is superimposed with the circular polarization plasmon, it appears on the cross section of the nanotube that coherent phase is long on one side and coherent phase is cancelled on the other side, so that a spiral electric field distribution is formed, as shown in fig. 3a, which is called chiral surface plasmon. Whereas when the excitation polarization direction is changed to-45 ° (i.e., 315 °), the helical directions of the chiral plasmons are completely opposite, as shown in fig. 3 b. This is because the chirality of the plasmon, i.e., the helical direction, is controlled by the phase difference between m = ± 1 two modes, and when the phase difference between the two modes is positive, the circular polarization direction is clockwise rotation, i.e., the surface plasmon of the right chirality, and vice versa, the surface plasmon of the left chirality.
In fig. 4, reference numerals 15 to 20 denote cross sections obtained by cutting the nanotube plasmon electric field at intervals of 40nm, and the spiral near-field distribution and the time-averaged electric field intensity can be seen more clearly. White arrows 21 in the figure indicate the rotational propagation direction of the helical surface plasmon wave. The purpose of generating the plasmon with chirality based on the carbon nano tube is achieved by adjusting the polarization of incident light.
Although the present invention has been described to a certain extent, it is apparent that appropriate changes in the respective conditions may be made without departing from the spirit and scope of the present invention. It is to be understood that the invention is not limited to the described embodiments, but is to be accorded the scope consistent with the claims, including equivalents of each element described.
Claims (15)
1. A method of generating chiral plasmons based on carbon nanotubes, the method comprising the steps of:
(1) Focusing the intermediate infrared laser pulse by using a convex lens to form a light spot;
(2) The focused light spots in the step (1) act with the carbon nano tubes to generate chiral plasmons; wherein the content of the first and second substances,
in the step (1), the incident polarization angle of the mid-infrared laser pulse is 0-360 degrees and is not 0 degrees, 90 degrees, 180 degrees or 270 degrees.
2. The method according to claim 1, wherein in the step (1), the focal length of the convex lens is 1-5 cm.
3. The method according to claim 2, wherein in step (1), the focal length of the convex lens is 3cm.
4. The method according to claim 1, wherein in step (1), the wave number of the mid-infrared laser pulse is 400-2000 cm -1 。
5. The method according to claim 4, wherein in step (1), the wavenumber of the mid-infrared laser pulse is 840-1600 cm -1 。
6. The method according to claim 1, wherein in step (1), the beam waist size of the spot formed by focusing the mid-infrared laser pulse is 0.5-2.0 μm.
7. The method according to claim 6, wherein in step (1), the beam waist size of the spot formed by focusing the mid-infrared laser pulse is 0.5-1.5 μm.
8. The method of claim 7, wherein in step (1), the beam waist size of the spot formed by focusing the mid-IR laser pulse is 1.0 μm.
9. The method according to claim 1, wherein in step (1), the polarization angle of the mid-infrared laser pulses is 45 ° or 315 °.
10. The method according to claim 1, wherein in step (1), the mid-infrared laser pulse is a paraxial approximation gaussian beam.
11. The method of claim 1, wherein in step (2), the carbon nanotubes have a diameter of 1 to 6 nm.
12. The method of claim 11, wherein in step (2), the carbon nanotubes have a diameter of 2.5 to 4.5 nm.
13. The method of claim 1, wherein in step (2), the carbon nanotubes are single-walled carbon nanotubes.
14. The method of claim 1, wherein the method controls the excitation pattern of the carbon nanotube plasmons by the incident polarization angle of the mid-infrared laser pulse to modulate the chirality of the carbon nanotube plasmons.
15. A method for detecting chiral molecules, comprising the method for generating chiral plasmons based on carbon nanotubes according to any one of claims 1 to 14.
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