CN110954504B - Element for detecting refractive index of film by using terahertz wave - Google Patents
Element for detecting refractive index of film by using terahertz wave Download PDFInfo
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- CN110954504B CN110954504B CN201811127905.XA CN201811127905A CN110954504B CN 110954504 B CN110954504 B CN 110954504B CN 201811127905 A CN201811127905 A CN 201811127905A CN 110954504 B CN110954504 B CN 110954504B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/063—Illuminating optical parts
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Abstract
The invention discloses an element for detecting the refractive index of a film by utilizing terahertz waves, which comprises: the terahertz wave resonant cavity comprises a resonant cavity and a super-surface structure, wherein the super-surface structure is arranged in the resonant cavity and can enable terahertz waves entering the resonant cavity to generate a strong local electric field; when the element detects the film to be detected, the film to be detected covers the super-surface structure. The invention arranges the super-surface structure in the resonant cavity, and utilizes the local enhancement of the super-surface structure to the electromagnetic field and the sensitivity to the surrounding medium to ensure that the refractive index detection element can also shift the transmission peak frequency of the transmission signal under the condition that the thickness of the film to be detected is in micron/ten micron order, thereby detecting the refractive index of the film to be detected.
Description
Technical Field
The invention relates to the field of terahertz wave photoelectricity, in particular to an element for detecting the refractive index of a film by utilizing terahertz waves.
Background
Terahertz (THz) waves generally refer to electromagnetic radiation having a frequency within the range of 0.3-3.0THz (corresponding to a wavelength of 100-. In the electromagnetic spectrum, terahertz waves lie between infrared and microwave. Terahertz waves have many unusual characteristics, such as wide frequency band, high transmittance to dielectric materials, low photon energy, and covering of rotation and vibration frequencies of many molecular atoms, and are widely applied to the fields of wireless communication, security inspection and explosion prevention, nondestructive inspection, medical imaging and the like.
Terahertz radiation has strong penetrating power to nonpolar substances (such as plastics, paper, cloth and the like), so that the terahertz radiation can be widely applied to substance detection. For example, to verify the authenticity of a material, one common way of verifying is to: the method comprises the steps of placing a material to be detected in the center of a pair of Bragg reflectors, irradiating the material with a beam of terahertz continuous wave with tunable frequency, and searching for a transmission peak value (a transmission peak below) of terahertz waves of the material to be detected by detecting a transmission signal. And under the condition that the thickness of the material to be detected is known, the refractive index of the material to be detected can be obtained. And (3) comparing the refractive indexes of the material to be detected and the contrast material in the terahertz wave band to obtain an authenticity result.
However, the above examination method requires a material thickness in the range of several hundreds of micrometers to several millimeters, so that there is a significant transmission peak shift. When the thickness of the material to be detected is in the range of micron/ten micron, the transmission peak shift is no longer sensitive in the above-mentioned inspection mode, so that it is necessary to develop a new element for detecting the refractive index of the film by using terahertz waves.
Disclosure of Invention
In order to achieve the purpose, the invention adopts the following technical scheme:
an element for detecting a refractive index of a thin film using a terahertz wave, comprising: the terahertz wave detector comprises a resonant cavity and a super-surface structure, wherein the super-surface structure is arranged in the resonant cavity and can enable terahertz waves entering the resonant cavity to generate a strong local electric field; when the element detects the film to be detected, the film to be detected covers the super-surface structure.
Preferably, the super-surface structure comprises a plurality of metal pattern layers arranged in an array.
Preferably, the metal pattern layer comprises at least two metal layers, and the metal layers are arranged in a laminated manner; wherein the materials of at least two metal layers are different from each other.
Preferably, the resonant cavity comprises two bragg reflectors which are oppositely arranged and a substrate which is clamped between the two bragg reflectors, and the super-surface structure is formed on the surface of the substrate facing one of the two bragg reflectors; when the element detects the thin film to be detected, the projection of one of the two Bragg reflectors on the substrate covers the thin film to be detected.
Preferably, the bragg reflector includes a plurality of plate groups stacked in a direction toward the substrate, each of the plate groups including a first plate facing the substrate and a second plate disposed on a surface of the first plate facing the substrate.
Preferably, the second flat sheet has a through hole therein, and a projection of the through hole on the substrate is located inside the super-surface structure.
Preferably, the first and second plates are made of quartz.
Preferably, the projection of the bragg mirror on the substrate is located inside the substrate.
Preferably, the substrate is made of quartz.
Preferably, the edge of the bragg reflector is fixed to the substrate by bonding with glue.
The invention arranges the super-surface structure in the resonant cavity, and utilizes the local enhancement of the super-surface structure to the electromagnetic field and the sensitivity to the surrounding medium to ensure that the refractive index detection element can also shift the transmission peak frequency of the transmission signal under the condition that the thickness of the film to be detected is in micron/ten micron order, thereby detecting the refractive index of the film to be detected.
Drawings
FIG. 1 is a schematic diagram of a standby state of a detecting element according to the present invention;
FIG. 2 is a schematic structural diagram of the working state of the detecting element of the present invention;
FIG. 3 is a schematic view of a super-surface structure of a detection element of the present invention;
FIG. 4 is a schematic view of an exemplary super-surface structure of the present invention;
FIG. 5 is a schematic diagram of the test element shown in FIG. 4;
FIG. 6 is a schematic diagram showing the change rate of the transmission peak frequency of the detecting element when the size of the metal pattern layer is changed.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the invention shown in the drawings and described in accordance with the drawings are exemplary only, and the invention is not limited to these embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
As shown in FIG. 1 and FIG. 2, the present invention provides an element for detecting refractive index of a thin film by using terahertz waves, comprising a resonant cavity A and a component arranged in the resonant cavity AAnd (B) a super-surface structure in the A. The super-surface structure B can enable terahertz waves entering the resonant cavity A to generate a strong local electric field. The resonant cavity a includes two bragg reflectors 2 arranged oppositely and a substrate 3 sandwiched between the two bragg reflectors 2, and the super-surface structure B is formed on a surface of the substrate 3 facing one of the two bragg reflectors 2. Preferably, the size of the super surface structure B is 16-25 mm 2 The size of the substrate 3 is 100-400 mm 2 The thickness is 80-85 μm, and the material is quartz or sapphire. Wherein the substrate 3 has an electromagnetic wave absorption coefficient in the terahertz wave band of less than 10cm -1 。
Referring to fig. 1, the bragg reflector 2 includes a plurality of quartz flat plate groups stacked in a direction toward the substrate 3. Each set of plates comprises a first plate 21 and a second plate 22. The first flat sheet 21 faces the substrate 3, and the second flat sheet 22 is disposed on a surface of the first flat sheet 21 facing the substrate 3. The second slab 22 has a through hole 22a therein, and the through hole 22a forms an air layer, so that the bragg reflector 2 and the substrate 3 are attached to each other (the bragg reflector holds the substrate, or the bragg reflector is adhered to both sides of the substrate by glue) to form the resonant cavity a. Preferably, the number of the first flat sheet 21 and the second flat sheet 22 is 4-10, and the size is 300-400 mm 2 . The thickness of the first flat sheet 21 is 40-45 μm, and the thickness of the second flat sheet 22 is 85-90 μm.
Further, as shown in fig. 3 to 5, the super-surface structure B includes a plurality of metal pattern layers 1 arranged in an array. The metal pattern layer 1 can change the effective dielectric constant and magnetic permeability of the detection object, so that the transmission peak can be obviously shifted even though the refractive index difference between the material to be detected and the contrast material is small. Specifically, as shown in fig. 4, as an example of the present invention, the super-surface structure B includes a plurality of metal pattern layers 1 arranged in a matrix, the metal pattern layers 1 are square, and have a size of 30 μm × 30 μm, and a pitch between any two adjacent metal pattern layers 1 is 5 μm. Fig. 5 shows the results of the detection element of the present example testing a plurality of films to be tested having a thickness of 5 μm (transmittance in the figure refers to the transmittance of terahertz waves for the entire detection element including the films to be tested, and the numerical value at the top of the peak of each curve is the refractive index of the films to be tested corresponding to each curve). In fig. 5, it can be seen that the transmittance of the whole detection element at the peak of the transmission curve can reach more than 50%, and it can be obtained that when the refractive index of the film to be detected is different, the frequency of the terahertz wave corresponding to the peak position of the transmission peak (the highest transmittance point) is sensitively shifted.
Further, the metal pattern layer 1 includes at least two metal layers stacked one on another, the metal layers are made of any one of Al, Ag, Cu, Au, Ti, and Ni, and the materials of the at least two metal layers are different from each other. Preferably, the overall size of the super-surface structure B is 16-25 mm 2 . The thickness of the metal pattern layer 1 is 60-200 nm, and the size is 1 multiplied by 10 2 ～1×10 4 μm 2 Conductivity greater than 4X 10 7 S/m, the metal pattern layer 1 is preferably a two-layer structure composed of a Ti layer and an Au layer.
The relationship between the size of the metal pattern layer 1 and the terahertz wave transmittance is explained below by test data.
As shown in fig. 6, the test includes 3 detection elements. The metal pattern layers 1 of the 3 detection elements are all square, wherein the sizes of the metal pattern layers 1 are respectively 30 micrometers multiplied by 30 micrometers, 20 micrometers multiplied by 20 micrometers and 10 micrometers multiplied by 10 micrometers, and the space between every two adjacent metal pattern layers 1 is respectively 5 micrometers, 15 micrometers and 25 micrometers. As can be seen in fig. 6, as the size of the metal pattern layer 1 increases, the rate of change in the transmission peak frequency (the slope of each curve in fig. 6) also increases, which is advantageous for the detection of a minute change in the refractive index of the material.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. An element for detecting a refractive index of a thin film using a terahertz wave, comprising: the terahertz wave detector comprises a resonant cavity (A) and a super-surface structure (B), wherein the super-surface structure (B) is arranged in the resonant cavity (A) and can enable terahertz waves entering the resonant cavity (A) to generate a strong local electric field; when the element detects a film to be detected, the film to be detected covers the super-surface structure (B);
the super-surface structure (B) comprises a plurality of metal pattern layers (1) which are arranged in an array mode, and the metal pattern layers (1) can change the effective dielectric constant and the magnetic permeability of the film to be tested;
the metal pattern layer (1) comprises at least two metal layers, and the metal layers are arranged in a laminated mode; wherein the materials of at least two metal layers are different from each other;
the resonant cavity (A) comprises two Bragg reflectors (2) which are arranged oppositely and a substrate (3) which is clamped between the two Bragg reflectors (2), and the super-surface structure (B) is formed on the surface, facing any one of the two Bragg reflectors (2), of the substrate (3); when the element detects a film to be detected, the projection of any one of the two Bragg reflectors (2) on the substrate (3) covers the film to be detected;
wherein the Bragg reflector (2) comprises a plurality of flat sheet groups which are arranged in a stacked manner in a direction towards the substrate (3), each flat sheet group comprising a first flat sheet (21) and a second flat sheet (22), the first flat sheet (21) facing the substrate (3), the second flat sheet (22) being arranged on a surface of the first flat sheet (21) facing the substrate (3);
wherein the second flat sheet (22) has a through hole (22 a) therein, and the projection of the through hole (22 a) on the substrate (3) is positioned inside the super-surface structure (B).
2. Element according to claim 1, characterized in that said first flat sheet (21) and said second flat sheet (22) are made of quartz.
3. Element according to claim 1, characterized in that the projection of the bragg mirror (2) on the substrate (3) is located inside the substrate (3).
4. Element according to claim 1, characterized in that the substrate (3) is made of quartz.
5. Element according to claim 1, characterized in that the edge of the bragg mirror (2) is fixed adhesively to the substrate (3) by means of glue.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201811127905.XA CN110954504B (en) | 2018-09-27 | 2018-09-27 | Element for detecting refractive index of film by using terahertz wave |
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| CN201811127905.XA CN110954504B (en) | 2018-09-27 | 2018-09-27 | Element for detecting refractive index of film by using terahertz wave |
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| CN110954504A CN110954504A (en) | 2020-04-03 |
| CN110954504B true CN110954504B (en) | 2022-09-27 |
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| CN103972791B (en) * | 2014-05-15 | 2017-02-08 | 中国科学院上海微系统与信息技术研究所 | Terahertz quantum cascading laser device of distributed Bragg reflection structure |
| CN105093777B (en) * | 2015-07-23 | 2017-11-07 | 北京大学 | A kind of Meta Materials microcavity composite construction and its production and use |
| CN106645016A (en) * | 2016-11-23 | 2017-05-10 | 电子科技大学 | Transmission type terahertz microfluidic channel sensor based on L-shaped structured metamaterial |
| CN107064052B (en) * | 2017-04-26 | 2019-12-27 | 中国计量大学 | Terahertz fingerprint detection sensitivity enhancement method based on microcavity resonance mode |
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