CN114184575A - Liquid refractive index sensing system and method based on metal grating terahertz super surface - Google Patents
Liquid refractive index sensing system and method based on metal grating terahertz super surface Download PDFInfo
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- 239000007788 liquid Substances 0.000 title claims abstract description 70
- 239000002184 metal Substances 0.000 title claims abstract description 58
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims description 13
- 238000001228 spectrum Methods 0.000 claims abstract description 32
- 238000001514 detection method Methods 0.000 claims abstract description 31
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 27
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 27
- 239000010703 silicon Substances 0.000 claims abstract description 27
- 230000035945 sensitivity Effects 0.000 claims abstract description 13
- 238000012805 post-processing Methods 0.000 claims abstract description 8
- 230000008878 coupling Effects 0.000 claims abstract description 3
- 238000010168 coupling process Methods 0.000 claims abstract description 3
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- 238000012545 processing Methods 0.000 claims abstract description 3
- 238000002310 reflectometry Methods 0.000 claims description 17
- 238000004364 calculation method Methods 0.000 claims description 11
- 238000006073 displacement reaction Methods 0.000 claims description 7
- 238000005102 attenuated total reflection Methods 0.000 claims description 5
- 239000010931 gold Substances 0.000 claims description 5
- 230000003287 optical effect Effects 0.000 claims description 5
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 4
- 229910052737 gold Inorganic materials 0.000 claims description 4
- 230000004044 response Effects 0.000 claims description 3
- 238000010521 absorption reaction Methods 0.000 abstract description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 5
- 238000000985 reflectance spectrum Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
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- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000010146 3D printing Methods 0.000 description 2
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- 238000001755 magnetron sputter deposition Methods 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
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- 230000005540 biological transmission Effects 0.000 description 1
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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
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
-
- 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
- G01N21/4133—Refractometers, e.g. differential
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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
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N2021/0106—General arrangement of respective parts
- G01N2021/0112—Apparatus in one mechanical, optical or electronic block
Abstract
The invention relates to a liquid refractive index sensing system based on a metal grating terahertz super surface, which comprises a high-resistance silicon prism coupling type metal grating terahertz super surface sensing device for detecting the liquid refractive index and a post-processing system for visualizing and processing the detected terahertz spectrum information in real time. According to the invention, the metal grating terahertz super surface is used as a carrier, a high-momentum Surface Plasmon Polariton (SPP) wave on the metal grating terahertz super surface is excited by the high-resistance silicon prism coupler, and the sensing detection of the refractive index of the liquid sample to be detected in the groove on the surface of the metal grating is realized by utilizing the extremely strong dielectric sensitivity of the SPP wave, so that the sensing sensitivity of a sensing system is greatly improved, the strong absorption of the terahertz wave by polar liquid is relieved to the greatest extent, and the effective sensing detection of the refractive index of the liquid sample is realized.
Description
Technical Field
The invention belongs to the field of terahertz liquid refractive index sensing, and particularly relates to a liquid refractive index sensing system and method based on a metal grating terahertz super surface.
Background
The terahertz super surface with the metal microstructure can change the spatial distribution in the transmission process of terahertz waves and support the generation of surface plasmons, so that the sub-wavelength constraint of a terahertz electromagnetic field in metal is realized, and a remarkable electric field enhancement effect is brought. The important characteristic is very favorable for enhancing the interaction between the terahertz waves and the sample, and can carry out qualitative or quantitative sensing detection on the trace sample. Therefore, the terahertz sensor is very suitable for serving as a platform for terahertz sensing detection. The terahertz super-surface sensor has been regarded as an exciting innovation in the field of biomedical engineering because of its real-time, nondestructive, label-free and high-sensitivity detection characteristics.
At present, the existing terahertz super-surface sensing system generally adopts a terahertz super-surface based on a complex geometric metal surface structure, and the discrete electric field enhancement distribution is limited, so the sensing sensitivity of the system is very limited. Secondly, most terahertz super-surface sensing systems adopt a sensing mode of directly irradiating and exciting SPP waves, and are only limited to sensing detection of low-loss solid samples or dehydration and drying treatment of the samples before detection. Since polar liquids such as water cause severe attenuation or even complete absorption of the incident terahertz wave energy when the detection sample has a high loss, effective refractive index sensing detection cannot be performed. Therefore, how to efficiently develop a high-sensitivity terahertz super-surface sensing system capable of meeting the use requirement of liquid sensing detection becomes a key for further development and application of the terahertz sensing technology.
Disclosure of Invention
In view of this, the invention aims to provide a liquid refractive index sensing system and method based on a metal grating terahertz super surface, which not only greatly improve the sensing sensitivity of the sensing system, but also maximally relieve the strong absorption of the polar liquid to the terahertz wave, and realize effective sensing detection of the refractive index of the liquid sample.
In order to achieve the purpose, the invention adopts the following technical scheme:
a liquid refractive index sensing system based on a metal grating terahertz super surface comprises a high-resistance silicon prism coupling type metal grating terahertz super surface sensing device for detecting the liquid refractive index and a post-processing system for visualizing and processing detected terahertz spectrum information in real time.
Furthermore, the terahertz super-surface sensing device comprises a sensing device control system, a metal grating terahertz super-surface, a high-resistance silicon prism, a terahertz transmitter and a terahertz detector; the terahertz super surface of the metal grating is used as a carrier for carrying a liquid sample to be tested and exciting an SPP wave; the high-resistance silicon prism is arranged between the terahertz transmitter and the terahertz detector and is used as a coupler to realize high momentum matching between incident terahertz waves and SPP waves supported by the terahertz super surface of the metal grating; and the sensing device control system is respectively connected with the linear displacement platform, the terahertz emitter and the terahertz detector.
Furthermore, the metal grating terahertz super surface comprises a surface of a wiener wavelength groove array structure and a gold film plated on the surface of the wiener wavelength groove array structure.
Furthermore, the period of the groove structure unit is 60 mu m, the width is 20-30 mu m, and the groove depth is 90 mu m
Furthermore, the high-resistance silicon prism is shaped like a triangular prism and adopts a refractive index np3.416.
A method for measuring a liquid refractive index sensing system based on a metal grating terahertz super surface comprises the following steps:
step S1: the method comprises the following steps that a high-resistance silicon prism is installed and fixed between a terahertz transmitter and a terahertz detector, high momentum matching between incident terahertz waves and Surface Plasmon Polaritons (SPPs) supported by a terahertz super surface of a metal grating is realized as a coupler, a high momentum SPP wave mode is excited, a terahertz attenuated total reflection time domain spectrum detection optical path is formed, and terahertz signals obtained by detection of the detection optical path are used as reference signals;
step S2: loading a liquid sample to be detected in a surface groove micro-channel of the terahertz super-surface by taking the terahertz super-surface of the metal grating as a carrier;
step S3: the terahertz super surface of the metal grating is sent to a specified detection position by using a linear displacement platform;
step S4: respectively starting a terahertz transmitter and a terahertz detector by using a sensing device control system, transmitting a terahertz pulse spectrum signal, and detecting the reflected terahertz pulse spectrum signal;
step S5: and transmitting the detected terahertz sample signal carrying the electromagnetic response of the liquid sample and the reference signal in the step S1 to a post-processing system, and calculating the refractive index of the liquid sample.
Further, a specific momentum matching formula for realizing high momentum matching by the high-resistance silicon prism is as follows:
wherein k isSPPSPP wave vector, k, supported by terahertz super surface of metal grating||Parallel component of terahertz wave in internal wave vector of high-resistance silicon prism, npIs the refractive index of the high-resistance silicon prism, omega is the frequency of the terahertz wave, c is the speed of light in vacuum, thetainIs the internal incidence angle of the terahertz wave in the high-resistance silicon prism.
Further, the step S5 specifically includes:
step S51: converting the terahertz time-domain pulse signal obtained by detection into a terahertz frequency-domain amplitude spectrum signal through fast Fourier transform;
step S52: calculating the reflectivity spectrum of the liquid sample to be measured by adopting a sample reflectivity spectrum calculation formula so as to obtain the resonant frequency of the sampleRate fsI.e. the frequency of the lowest point of the reflectivity spectrum;
step S53: and finally, calculating the reflectivity of the sample by using a refractive index calculation formula of the liquid sample to be measured.
Further, the calculation formula of the reflectivity spectrum of the liquid sample to be measured in step S52 is as follows:
wherein Es(omega) and ErefAnd (omega) are terahertz frequency domain amplitude spectra of the sample and the reference respectively.
Further, the calculation formula of the refractive index of the liquid sample to be measured in step S53 is as follows:
wherein f issIs the resonant frequency of the sample, frefTo be referenced to the resonance frequency, SnIs the sensing sensitivity of the sensing system.
Compared with the prior art, the invention has the following beneficial effects:
1. the terahertz liquid sensor is stable in performance and high in sensing sensitivity, and can support terahertz sensing detection of polar liquid such as water;
2. according to the invention, the metal grating terahertz super surface is used as a carrier, a high-momentum Surface Plasmon Polariton (SPP) wave on the metal grating terahertz super surface is excited by the high-resistance silicon prism coupler, and the sensing detection of the refractive index of the liquid sample to be detected in the groove on the surface of the metal grating is realized by utilizing the extremely strong dielectric sensitivity of the SPP wave, so that the sensing sensitivity of a sensing system is greatly improved, the strong absorption of the terahertz wave by polar liquid is relieved to the greatest extent, and the effective sensing detection of the refractive index of the liquid sample is realized.
Drawings
FIG. 1 is a schematic view of the detection principle of the present invention;
FIG. 2 is a schematic diagram of the control system of the present invention;
FIG. 3 is a performance test reflectance spectrum of an embodiment of the present invention;
in the figure: 1-a metal grating terahertz super surface; 2-liquid sample to be tested; 3-a linear displacement platform; 4-terahertz transmitter; 5-incident terahertz pulses; 6-high-resistance silicon prism; 7-terahertz evanescent field; 8-SPP waves; 9-reflecting the terahertz pulse; 10-terahertz detector; 11-terahertz signal post-processing system.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
Referring to fig. 1, the invention provides a liquid refractive index sensing system based on a metal grating terahertz super-surface, which comprises a metal grating terahertz super-surface 1, a liquid sample to be measured 2, a linear displacement platform 3, a terahertz transmitter 4, an incident terahertz pulse 5, a high-resistance silicon prism 6, a terahertz evanescent field 7, an SPP wave 8, a reflected terahertz pulse 9, a terahertz detector 10 and a terahertz signal post-processing system 11.
In this embodiment, preferably, the metal grating terahertz super-surface 1 is processed by combining a 3D printing technology and a magnetron sputtering coating technology, and is first printed by using the 3D printing technology to form a one-dimensional sub-wavelength groove array structure surface, preferably, the groove structure unit period is 60 μm, the width is 20-30 μm, and the groove depth is 90 μm, that is, the grating structure surface, and then, by using the magnetron sputtering technology, gold (Au) is selected as a target material, and a gold film with a thickness of 500 μm is plated on the grating structure surface, so as to finally form the metal grating terahertz super-surface. It is used as a carrier for loading the liquid sample 2 to be measured and exciting the SPP wave 8.
Preferably, the high-resistance silicon prism 6 is made of high-refractive-index, np3.416, to provide greater momentum matching.
In this embodiment, a method for measuring a liquid refractive index sensing system based on a metal grating terahertz super surface includes the following steps:
and S1, installing and fixing the high-resistance silicon prism 6 between the terahertz transmitter 4 and the terahertz detector 10 to serve as a coupler to realize high momentum matching between the incident terahertz wave 5 and the SPP wave 8 supported by the metal grating terahertz super surface 1, exciting a high momentum SPP wave 8 mode, and forming a terahertz attenuated total reflection time domain spectrum detection optical path.
And S2, loading the liquid sample 2 to be detected in a surface groove micro-channel of the metal grating terahertz super-surface 1 by taking the metal grating terahertz super-surface 1 as a carrier in the established terahertz attenuated total reflection time domain spectrum detection light path when sensing and detecting the liquid sample.
Step S3, sending an instruction through a control system, as shown in figure 2, and sending the metal grating terahertz super surface loaded with the liquid sample 2 to be detected to a specified detection position by using the linear displacement platform 3;
and step S4, respectively starting the terahertz transmitter 4 and the terahertz detector 10 through the control system, transmitting the incident terahertz pulse 5, and detecting the reflected terahertz pulse 9. Incident terahertz waves 5 emitted by the terahertz emitter 4 are incident in parallel from one surface of the high-resistance silicon prism 6, attenuated total reflection occurs in the prism, a terahertz evanescent field 7 is formed at the bottom of the prism, SPP waves 8 are excited and react with the liquid sample 2 after high momentum matching is completed, and then the terahertz evanescent waves are emitted from the other surface of the high-resistance silicon prism 6.
And S5, transmitting the detected reflected terahertz pulse 9 sample signal carrying the electromagnetic response of the liquid sample to a post-processing system by using a control system, and calculating the refractive index of the liquid sample.
In this embodiment, the specific calculation algorithm and flow of the refractive index of the liquid sample to be measured are as follows:
step S41: converting the terahertz time-domain pulse signal obtained by detection into a terahertz frequency-domain amplitude spectrum signal through Fast Fourier Transform (FFT);
step S42: calculating the reflectivity spectrum of the liquid sample to be measured by adopting a sample reflectivity spectrum calculation formula so as to obtain the resonant frequency f of the samplesI.e. the frequency of the lowest point of the reflectivity spectrum. The calculation formula of the reflectivity spectrum of the liquid sample to be detected is as follows:
wherein Es(omega) and ErefAnd (omega) are terahertz frequency domain amplitude spectra of the sample and the reference respectively.
Step S43: and finally, calculating the reflectivity of the sample by using a refractive index calculation formula of the liquid sample to be measured. Wherein, the calculation formula of the refractive index of the liquid sample to be measured is as follows:
wherein f issIs the resonant frequency of the sample, frefTo be referenced to the resonance frequency, SnIs the sensing sensitivity of the sensing system.
In the embodiment, the performance evaluation of the terahertz super-surface sensing system is as follows:
the performance evaluation of the developed liquid refractive index sensing system based on the terahertz super surface of the metal grating is that nitrogen and purified water are respectively loaded in grooves on the surface of the metal grating, and then the nitrogen and the purified water are respectively conveyed to an appointed detection position by utilizing a linear moving platform.
And performing sensing representation according to the change delta n of the refractive index of the liquid sample to be detected and the movement delta f of the frequency of the lowest point of the reflectivity spectrum calculated according to the terahertz frequency domain amplitude spectrum of the liquid sample to be detected under different frequencies. Sensing sensitivity S for performance of terahertz super-surface sensing systemnRepresents: sn＝Δf/Δn。
According to the performance evaluation of the terahertz super-surface sensing system, the performance test result of the embodiment of the invention is shown in the following fig. 3. From the experimental reflectance spectrum, it can be seen that compared to nitrogen, due to the higher refractive index and loss of water, its reflectance spectrum appears to be significantly red-shifted and broadened, with the lowest point frequency of the reflectance spectrum shifted from the original 0.745THz to 0.345 THz. The remarkable changes prove that the SPP wave supported by the terahertz super-surface of the metal grating is extremely sensitive to the change of the surrounding dielectric environment, namely the embodiment of the invention has higher sensing sensitivity,calculated sensing sensitivity SnUp to 0.37 THz/RIU. Meanwhile, the obvious reflectivity spectrum profile caused by water also shows that the sensing system of the embodiment of the invention can relieve the strong absorption of polar liquid to terahertz waves and can effectively realize the refractive index sensing detection of a liquid sample. Therefore, the terahertz super-surface sensing system has a good application prospect.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (10)
1. A liquid refractive index sensing system based on a metal grating terahertz super surface is characterized by comprising a high-resistance silicon prism coupling type metal grating terahertz super surface sensing device for detecting the liquid refractive index and a post-processing system for visualizing and processing detected terahertz spectrum information in real time.
2. The liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 1, wherein the terahertz super surface sensing device comprises a sensing device control system, a metal grating terahertz super surface, a high-resistance silicon prism, a terahertz transmitter and a terahertz detector; the terahertz super surface of the metal grating is used as a carrier for carrying a liquid sample to be tested and exciting an SPP wave; the high-resistance silicon prism is arranged between the terahertz transmitter and the terahertz detector and is used as a coupler to realize high momentum matching between incident terahertz waves and SPP waves supported by the terahertz super surface of the metal grating; and the sensing device control system is respectively connected with the linear displacement platform, the terahertz emitter and the terahertz detector.
3. The liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 2, wherein the metal grating terahertz super surface comprises a surface of a wiener wavelength groove array structure and a gold film plated on the surface of the wiener wavelength groove array structure.
4. The liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 3, wherein the groove structure unit period is 60 μm, the width is 20-30 μm, and the groove depth is 90 μm.
5. The liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 1, wherein the high-resistance silicon prism is shaped like a triangular prism and adopts a refractive index np3.416.
6. The method for measuring the liquid refractive index sensing system based on the metal grating terahertz super surface according to any one of claims 1 to 5, characterized by comprising the following steps:
step S1: the method comprises the following steps that a high-resistance silicon prism is installed and fixed between a terahertz transmitter and a terahertz detector, high momentum matching between incident terahertz waves and Surface Plasmon Polaritons (SPPs) supported by a terahertz super surface of a metal grating is realized as a coupler, a high momentum SPP wave mode is excited, a terahertz attenuated total reflection time domain spectrum detection optical path is formed, and terahertz signals obtained by detection of the detection optical path are used as reference signals;
step S2: loading a liquid sample to be detected in a surface groove micro-channel of the terahertz super-surface by taking the terahertz super-surface of the metal grating as a carrier;
step S3: the terahertz super surface of the metal grating is sent to a specified detection position by using a linear displacement platform;
step S4: respectively starting a terahertz transmitter and a terahertz detector by using a sensing device control system, transmitting a terahertz pulse spectrum signal, and detecting the reflected terahertz pulse spectrum signal;
step S5: and transmitting the detected terahertz sample signal carrying the electromagnetic response of the liquid sample and the reference signal in the step S1 to a post-processing system, and calculating the refractive index of the liquid sample.
7. The method for measuring the liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 6, wherein a specific momentum matching formula for realizing high momentum matching by the high-resistance silicon prism is as follows:
wherein k isSPPSPP wave vector, k, supported by terahertz super surface of metal grating||Parallel component of terahertz wave in internal wave vector of high-resistance silicon prism, npIs the refractive index of the high-resistance silicon prism, omega is the frequency of the terahertz wave, c is the speed of light in vacuum, thetainIs the internal incidence angle of the terahertz wave in the high-resistance silicon prism.
8. The method for measuring the liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 6, wherein the step S5 specifically comprises:
step S51: converting the terahertz time-domain pulse signal obtained by detection into a terahertz frequency-domain amplitude spectrum signal through fast Fourier transform;
step S52: calculating the reflectivity spectrum of the liquid sample to be measured by adopting a sample reflectivity spectrum calculation formula so as to obtain the resonant frequency f of the samplesI.e. the frequency of the lowest point of the reflectivity spectrum;
step S53: and finally, calculating the reflectivity of the sample by using a refractive index calculation formula of the liquid sample to be measured.
9. The method for measuring the liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 7, wherein the liquid sample reflectivity spectrum to be measured in the step S52 is calculated according to the formula:
wherein Es(omega) and ErefAnd (omega) are terahertz frequency domain amplitude spectra of the sample and the reference respectively.
10. The method for measuring the liquid refractive index sensing system based on the metal grating terahertz super surface according to claim 7, wherein the calculation formula of the refractive index of the liquid sample to be measured in the step S53 is as follows:
wherein f issIs the resonant frequency of the sample, frefTo be referenced to the resonance frequency, SnIs the sensing sensitivity of the sensing system.
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