CN108281884B - Raman spectrum detection device adopting Fabry-Perot resonant cavity enhancement mode - Google Patents
Raman spectrum detection device adopting Fabry-Perot resonant cavity enhancement mode Download PDFInfo
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- CN108281884B CN108281884B CN201810056734.XA CN201810056734A CN108281884B CN 108281884 B CN108281884 B CN 108281884B CN 201810056734 A CN201810056734 A CN 201810056734A CN 108281884 B CN108281884 B CN 108281884B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
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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
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
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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
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
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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
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N2021/653—Coherent methods [CARS]
- G01N2021/655—Stimulated Raman
Abstract
According to the Raman signal enhancement device of the Fabry-Perot resonant cavity, the excitation light is reflected back and forth in the Fabry-Perot resonant cavity, the time and the distance of the action of the excitation light on a substance are increased, and the enhanced Raman signal light is obtained through the excitation light high-reflection film screening. On the basis, the Fabry-Perot resonant cavity Raman signal enhancement device is improved, the Fabry-Perot resonant cavity Raman signal enhancement device based on the internally plated metal capillary is provided, the excitation light is bound in the capillary resonant cavity, the interaction between the excitation light and an object to be detected is greatly enhanced, and the enhanced Raman signal is obtained through screening of the excitation light high-reflection film. The device has high sensitivity and high detection speed, can simultaneously detect various liquids/gases to perform qualitative and quantitative analysis on the object to be detected, and has high integration level and simple and convenient operation.
Description
Technical Field
The invention belongs to the field of laser Raman spectrum detection, and particularly relates to a method for Raman-enhancing signals of a Fabry-Perot resonant cavity based on an internally-plated metal capillary tube, so that the sensitivity and accuracy of Raman signal detection of a liquid/gas mixture are improved, and qualitative and quantitative analysis of an object to be detected is performed.
Background
Raman spectroscopy is a spectroscopic method for studying molecular vibration and rotation, and is generated by inelastic scattering of light irradiated on a substance. The Raman spectrum analysis method can research the molecular structure and has the advantages of short analysis time, non-contact to the sample, qualitative and quantitative simultaneous detection of various liquids/gases/solids and the like. The Raman spectrum technology develops rapidly in recent years, is widely applied to various fields such as material analysis, petroleum, chemical engineering, biomedicine, geology and the like, and provides a powerful research method for the development of various disciplines.
However, the raman scattered light intensity is low, the background noise is high, the resolution is difficult, and the sensitivity in detection is low, so that the application of the raman spectrum is limited. How to improve the sensitivity of the Raman signal is a main problem of the current Raman spectrum real-time detection application, and a method for enhancing the Raman scattering signal is realized by adopting a signal light multiple reflection enhanced structure (such as a Fabry-Perot resonant cavity). A fabry-perot resonator, i.e. a parallel plate resonator, is formed by a pair of parallel plates of high reflectivity. The invention discloses a Fabry-Perot resonant cavity Raman signal enhancement device aiming at micro detection of liquid and gas, which can increase the time and distance of the action of excitation light and an object, thereby increasing the intensity of Raman signal light. Meanwhile, the invention provides the Fabry-Perot resonant cavity Raman signal enhancement device based on the internally plated metal capillary tube, which is improved on the basis of the Fabry-Perot resonant cavity Raman signal enhancement device and can improve the sensitivity, accuracy and stability of Raman spectrum detection.
Disclosure of Invention
The invention provides a Raman spectrum detection system based on a Fabry-Perot resonant cavity (F-P cavity) enhancement mode, and aims to enhance the interaction between excitation light and an object to be detected, generate a larger Raman scattering signal, reduce the influence of background noise on the Raman signal, and improve the accuracy and sensitivity of liquid/gas detection by a Raman spectrum method.
The system is characterized in that: the substance to be measured is injected into the resonant cavity, the exciting light is incident into the cavity through the small hole at the high reflecting mirror surface end of the Fabry-Perot resonant cavity and is reflected back and forth to interact with the substance to generate Raman light, and the Raman light can be received by the Raman spectrometer through the filter surface end of the Fabry-Perot resonant cavity. The device increases the time and distance of the action of the substance and the light, so that the generated Raman signal light is enhanced, and a gain medium is not needed in the cavity.
The system structure of the invention comprises a laser, an F-P resonant cavity and a Raman spectrometer, and is shown in the following figure 1. Wherein one end of the F-P resonant cavity is coated with a high reflection film (1) which can reflect the excitation light and the Raman light simultaneously, and the other end is coated with a filter film (3) which is high in reflection to the excitation light and high in transmission to the Raman light, such as a gold or silver film, and the thickness is 0.1 to 10 microns. The excitation light may enter the fabry-perot cavity from a notch through the highly reflective film. When the exciting light is incident into the Fabry-Perot resonant cavity, the light and the substance act to generate Raman light, and the Raman light is received by the spectrograph through the filter film to be analyzed by the detected substance.
The detection device of fig. 2 is designed herein to implement the function of raman detection based on the structural characteristics described above. Plating a high-reflection film (1) on SiO2A notch is formed on the substrate (4) and penetrates through the high-reflection mirror surface to allow the excitation light to pass through; the filter film (3) is coated on a suitable substrate (5). After the excitation light enters the cavity through the notch and reacts with the substance, the generated Raman signal light penetrates through the filter membrane, penetrates through the glass or plastic substrate and enters the Raman spectrometer, and the Raman spectrometer receives the signal light for analysis.
In order to further enhance the raman signal, fig. 2 is modified, and the detection device of fig. 3 is designed to realize raman detection with higher sensitivity. The system structure comprises a laser, a hollow capillary (8), an excitation optical fiber (9), a large-core-diameter optical fiber (10), an inner plating metal capillary (11) and a Raman spectrometer. The corroded exciting optical fiber is inserted into the hollow capillary tube with one end surface plated with the high-reflection film to serve as a light input assembly, and the light receiving assembly is composed of a large-core-diameter optical fiber with one end surface plated with the light filter film. The inner diameter of the hollow capillary is controlled to be at least one order of magnitude smaller than the outer diameter so that more excitation light can be reflected back and forth in the Fabry-Perot cavity. And then the Fabry-Perot resonant cavity is wrapped by the internally plated metal capillary (with the inner wall plated with gold or silver), so that the excitation light cannot be leaked out of the Fabry-Perot resonant cavity to a greater extent, and the generated Raman signal light can be received by the large-core optical fiber to a greater extent.
The Raman spectrum detection method adopting the internally plated metal capillary Fabry-Perot resonant cavity enhancement mode can be packaged into a simple device shown in the figure 6. Under the observation of an optical microscope, firstly inserting an exciting optical fiber with one end being corroded and thinned into the uncoated end of a hollow capillary tube, adhering the exciting optical fiber with the ultraviolet curing adhesive, then respectively inserting the coated ends of the hollow capillary tube and a large-core-diameter optical fiber into two sides of an inner-coated metal capillary tube to be used as two-sided reflectors of a Fabry-Perot resonant cavity, then respectively encapsulating the reflectors in a three-way valve, and introducing an object to be detected from an injection port.
Laser with wavelength of lambda nm emitted by a laser (lambda is in a Raman excitation waveband) is coupled to an excitation optical fiber in a free space, the laser enters a capillary tube with an inner silver coating, and is continuously reflected by a hollow capillary tube (end surface plated with a gold or silver high-reflection coating) and a high-reflectivity coating of a receiving optical fiber end surface (end surface plated with a filter coating which is highly reflective to excitation light and highly transparent to Raman light), the laser is bound in a capillary tube resonant cavity to be continuously enhanced and fully acts with liquid/gas entering the capillary tube from a sample inlet of a three-way valve to generate an enhanced Raman scattering signal, a required Raman signal is obtained by screening the filter coating of the receiving optical fiber end surface, the Raman signal is collected and introduced into a Raman spectrometer, and a Raman spectrogram is analyzed to obtain the component of the object to be.
The invention has the beneficial effects that:
(1) the Raman spectrum detection device adopting the Fabry-Perot resonant cavity enhancement mode realizes the detection of the components of the liquid/gas mixture by utilizing Raman spectrum signals.
(2) The metal capillary tube-Fabry-Perot resonant cavity is plated in the metal capillary tube-Fabry-Perot resonant cavity, so that Raman scattering signals are greatly enhanced, the influence of background noise on the Raman signals is reduced, and the sensitivity of a Raman spectrum detection mixture is further improved.
(3) The Raman spectrum detection device adopting the Fabry-Perot resonant cavity enhancement mode realizes online real-time detection of liquid/gas mixture components, has short detection time, simple structure, high integration level and good sealing property, and can perform qualitative and quantitative analysis on an object to be detected.
Drawings
Figure 1 is a schematic diagram of a fabry-perot resonator enhancement mode.
Fig. 2 is a structural diagram of a fabry-perot resonator enhanced raman detection device.
FIG. 3 is a schematic diagram of the structure of a Fabry-Perot resonant cavity inside a metal-plated capillary.
FIG. 4 is a schematic end view of a Fabry-Perot resonator.
FIG. 5 is a view showing a structure of a coating film formed on the end face of the receiving end.
FIG. 6 is a schematic diagram of the overall design of a Fabry-Perot enhanced Raman spectrum detection device.
FIG. 7 is a spectrum of alcohol detection with 780nm excitation light, wherein the excitation light intensity is 100mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm.
Reference numerals:
1-a highly reflective film, gold (Au) or silver (Ag) film, 0.1 to 10 μm thick, reflecting the excitation light and the raman light;
2-a notch penetrating through the high reflection film, from which the incident light enters the light object action region;
3-a light filtering film which is highly reflective to excitation light and highly transparent to Raman light;
4-substrate of high reflection film, the material is glass or transparent plastic;
5-substrate of the filter film, the material is glass or transparent plastic;
6-high reflection mirror surface, which is composed of high reflection film and substrate;
7-filter mirror surface, which is composed of filter film and substrate;
8-hollow capillary tube with outer diameter of 330um and inner diameter of 30um, one end face is high reflection mirror surface;
9-the outer diameter of the corroded excitation fiber is about 25 um;
10-large core diameter optical fiber with outer diameter of 330um, one end face of which is a filter mirror;
11-inner plating metal capillary with 350um inner diameter, and plating gold or silver on the inner wall;
12-low refractive index layer, SiO being selected as film material2A material;
13-high refractive index layer, the film material is selected from titanium oxide (TiO)2) Tantalum oxide (Ta)2O5) Hafnium oxide (HfO)2) One or a mixture of a certain proportion of the three;
14-Fabry-Perot resonant cavity, which is formed by a high reflection mirror and a filter mirror arranged face to face;
15-three-way valve;
16-sample inlet of the object to be detected;
17-sample outlet for the substance to be measured.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
The specific Fabry-Perot resonant cavity Raman enhancement design is shown in FIG. 2, and comprises a laser, a high-reflection mirror (gold film + substrate), a filter mirror (filter film + substrate), and a Raman spectrometer.
The method mainly comprises the following steps: (gold plating film is exemplified here)
(1) A round glass with smooth and flat surface, 1cm thickness and 3cm diameter is provided with a 1mm round hole in the middle, then the glass is put into a coating instrument, and gold (Au) is coated on the glass with the thickness of 0.1-10 microns by an electron beam evaporation coating method, so that the manufacture of a mirror surface of a Fabry-Perot resonant cavity is completed.
(2) Putting another piece of round glass with smooth and flat surface and thickness of 1cm and diameter of 3cm into a coating instrument to be coated with an excitation light high-reflection film shown in figure 5, specifically: firstly, film system design of 780nm excitation light high-reflection film is carried out, and SiO is selected as film material with low refractive index2High refractive index film material selected titanium oxide (TiO)2) Tantalum oxide (Ta)2O5) Hafnium oxide (HfO)2) One or a mixture of the three or a certain proportion of the three obtains the film system design parameters with the excitation wavelength reflectivity of 99 percent and the Raman optical band reflectivity of less than 20 percent by controlling the single-layer thickness of the low-refractive-index film and the high-refractive-index film and the combined periodicity. And putting the glass into a film plating machine according to the parameters, and plating a 780nm light filtering film.
(3) And forming a Fabry-Perot resonant cavity by the two mirrors, and immersing the Fabry-Perot resonant cavity into a sample to be measured. Laser enters the Fabry-Perot resonant cavity from a notch penetrating through the high-reflection film, is reflected back and forth between the two mirror surfaces to act with a substance, and generated Raman light is received by the Raman spectrometer after penetrating through the filter film for spectral analysis.
The Fabry-Perot resonant cavity Raman enhancement detection device based on the internally plated metal capillary is further improved and designed on the basis of the Fabry-Perot resonant cavity Raman enhancement spectrum detection device, as shown in figure 6, the Fabry-Perot Raman enhancement detection device comprises a laser, a hollow capillary (8) with one end surface plated with a high-reflection film, a 780nm single-mode optical fiber (9), a large-core-diameter optical fiber (10) with one end surface plated with a filter film, an internally plated silver film capillary (11), a three-way valve (15) for sample injection/sample discharge of an object to be detected and a Raman spectrometer. The structure is added with the internally plated metal capillary, so that the excitation light and the Raman light can be better constrained in the Fabry-Perot resonant cavity. Meanwhile, excitation/Raman light is transmitted by adopting optical fibers at two ends of the Fabry-Perot resonant cavity and is packaged by using a three-way valve, so that the system is more portable.
The Raman spectrum detection method of the inner plating metal capillary Fabry-Perot resonant cavity enhancement mode mainly comprises the following steps:
(1) plating a gold (Au) film (high-reflection film) on one end face of the hollow capillary tube, and plating a filter film (the reflectivity is 99% for 780nm and the reflectivity is lower than 20% for 830 and 1100 nm) on one end face of the large-core-diameter optical fiber. Specifically, the method comprises the following steps: the surfaces of the hollow capillary and the large-core-diameter optical fiber are polished and wiped clean under a 400-time magnification system. Then they are clamped by a special coating clamp and put into a coating machine. For plating gold on the surface of a hollow capillary tube, an electron beam evaporation coating method is adopted, and gold is placed into a crucible and then is plated for more than 7 hours in a coating machine. For the end face of the large-core optical fiber to be coated with the filter film, as shown in fig. 5, the method of electron beam evaporation and hall ion source assisted coating is used, the film system design of the filter film with 780nm (or other raman excitation light wave bands) is carried out in advance, and the low-refractive index film material is selected from SiO2High refractive index film material selected titanium oxide (TiO)2) Tantalum oxide (Ta)2O5) Hafnium oxide (HfO)2) One or a mixture of a certain proportion of the three can obtain the design parameters of the filter film system with the excitation wavelength lambda reflectivity of 99 percent by controlling the single-layer thickness of the low-refractive-index film and the high-refractive-index film and the combined period number. According to the parameters, the optical fiber is put into a film coating machine and is coated with the film in a rotating way, the film coating time is 7 hours, so that the reflectivity of 780nm (or other Raman excitation light wave bands) is more than 99 percent, and the reflectivity of the excited Raman light wave band is 20 percentThe following;
(2) the coating layer of the excitation fiber (core diameter 7um, cladding 125 um) was stripped with a fiber stripper and the surface was cleaned with absolute ethanol, and the stripped area was bent in a fume hood and etched in hydrofluoric acid at a temperature of 45 ℃. Inevitably, if the concentration of hydrofluoric acid is high, the surface of the optical fiber after etching has a certain roughness. In order to ensure the smoothness of the outer wall of the optical fiber as much as possible and reduce scattering leakage of the side wall of the optical fiber, hydrofluoric acid with the concentration of 10% is selected, the outer diameter of the optical fiber is observed in real time by combining an optical microscope system, and the exciting optical fiber is corroded to the outer diameter of 25 um;
(3) cleaning the corroded excitation optical fiber by using ultrapure water to cut the optical fiber, wherein the outer diameter of the optical fiber is only 25 mu m, and the optical fiber cutter cannot meet the cutting requirement, so that a cutting platform for the optical fiber with the extremely small outer diameter is designed, and the excitation optical fiber with a flat end face is obtained;
(4) as shown in fig. 3, under an optical microscope, the excitation fiber processed in step (3) is inserted into a hollow capillary tube with an inner diameter of 30um and an outer diameter of 330um, and is bonded by ultraviolet curing glue to enlarge the diameter of the outer wall of the excitation fiber, so as to adapt to the inner diameter of the inner metal plated capillary tube and reduce the leakage of signal light. Then inserting one end of the hollow capillary tube and one end of the large-core-diameter optical fiber coating film from two sides of the internally-coated metal capillary tube respectively to be used as two-sided reflectors of the Fabry-Perot resonant cavity, and finally packaging the two-sided reflectors in a three-way valve by using ultraviolet curing glue to form a structure shown in the figure 6;
(5) coupling the laser free space emitted by a laser to an exciting optical fiber which is thinned by corrosion, enabling the laser to enter a capillary tube with an inner silver coating, continuously reflecting the laser through a hollow capillary tube (the end surface of which is plated with a high-reflection gold coating) and a high-reflectivity coating on the end surface of a receiving optical fiber (the end surface of which is plated with a filter coating), and fully acting with liquid/gas entering the capillary tube from a sample inlet of a three-way valve, enabling the exciting light and generated Raman light to be bound in the capillary tube with the inner wall of which is plated with the silver, continuously enhancing the optical power in unit area, increasing the acting distance between the exciting light and an object, and generating an enhanced Raman scattering signal;
(6) the filter film on the end face of the receiving optical fiber can reflect light with 780nm wavelength and transmit Raman light to serve as a filter to screen out needed Raman signals, the Raman signals are collected and led into a Raman spectrometer, and the components of the object to be measured can be obtained by analyzing a Raman spectrogram.
According to the Raman signal enhancement device of the Fabry-Perot resonant cavity, the excitation light is reflected back and forth in the Fabry-Perot resonant cavity, the time and the distance of the action of the excitation light on a substance are increased, and the enhanced Raman signal light is obtained through the excitation light high-reflection film screening.
On the basis, the Fabry-Perot resonant cavity Raman signal enhancement device is improved, the Fabry-Perot resonant cavity Raman signal enhancement device based on the internally plated metal capillary is provided, the excitation light is bound in the capillary resonant cavity, the interaction between the excitation light and an object to be detected is greatly enhanced, and the enhanced Raman signal is obtained through screening of the excitation light high-reflection film. The device has high sensitivity and high detection speed, can simultaneously detect various liquids/gases to perform qualitative and quantitative analysis on the object to be detected, and has high integration level and simple and convenient operation.
The following are experimental data based on the structure of the Fabry-Perot resonant cavity enhanced Raman detection device of FIG. 2
1. The following table shows 488nm-1064nm excitation light for identifying alcohol (ethanol)C-C-O，-CH 3 ，C-O-H，-CH 2 -CH 3 Radical case (2800-3000 cm)-1：−𝐶H2−𝐶H3Symmetric and asymmetric stretching vibration of the group, 1453 cm-1：−𝐶H3Asymmetric deformation, 1300 cm-1：𝐶−𝑂-H bending vibration, 1000--1：𝐶−𝐶−𝑂Out-of-plane stretching produces Raman characteristic doublet of 884 cm-1：𝐶−𝐶−𝑂In-plane stretching), wherein the cavity length is 1mm, the ethanol is absolute ethanol, the power of a 488nm wavelength laser is 300mW, the power of a 532nm wavelength laser is 150mW, the power of a 780nm wavelength laser is 100mW, and the power of a 1064nm wavelength laser is 450 mW. Laser is vertically incident into the cavity, the end face of the hollow capillary is plated with a high-reflection gold film, and the strength value of each peak is measured as follows:
note that: the Raman spectrometer with different wavelengths measures the Raman peak value intensity without comparative significance.
The following table shows 488nm-1064nm excitation light for identifying C-C-O, -CH in alcohol (ethanol)3，C-O-H，-CH2-CH3Radical case (2800-3000 cm)-1：−𝐶H2−𝐶H3Symmetric and asymmetric stretching vibration of the group, 1453 cm-1：−𝐶H3Asymmetric deformation, 1300 cm-1：𝐶−𝑂-H bending vibration, 1000--1：𝐶−𝐶−𝑂Out-of-plane stretching produces Raman characteristic doublet of 884 cm-1：𝐶−𝐶−𝑂In-plane stretching), wherein the cavity length is 1mm, the ethanol is absolute ethanol, the power of a 488nm wavelength laser is 300mW, the power of a 532nm wavelength laser is 150mW, the power of a 780nm wavelength laser is 100mW, and the power of a 1064nm wavelength laser is 450 mW. Laser is vertically incident into the cavity, the end face of the hollow capillary is plated with a high-reflection silver film, and the strength value of each peak is measured as follows:
2. the table below shows the table of the change of the intensity of the Raman peak of the ethanol with the concentration of 20% -100%, the wavelength of the excitation light is 488nm, the intensity of the excitation light is 300mW, and the cavity length is 1 mm. Laser is vertically incident into the cavity, the end face of the hollow capillary is plated with a gold film, and the strength value of each peak is measured as follows:
"-" represents no data detected.
The following table shows the intensity variation table of 20% -100% concentration ethanol Raman peak, excitation light wavelength is 532nm, excitation light intensity is 150mW, and cavity length is 1 mm. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the following table shows the intensity variation table of 20% -100% concentration ethanol Raman peak, 780nm excitation light wavelength, 100mW excitation light intensity, and 1mm cavity length. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the table below shows the table of the intensity variation of the ethanol Raman peak with the concentration of 20% -100%, the wavelength of the excitation light is 1064nm, the intensity of the excitation light is 450mW, and the cavity length is 1 mm. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
3. the table below shows the intensity change of the ethanol Raman peak when the cavity length is changed from 1mm to 4mm, the excitation light wavelength is 488nm, and the laser power is 300 mW. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the table below shows the change of the intensity of the ethanol Raman peak when the cavity length is changed from 1mm to 4mm, the excitation light wavelength is 532nm, and the laser power is 150 mW. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the table below shows the change of the intensity of the ethanol Raman peak when the cavity length is changed from 1mm to 4mm, the wavelength of the excitation light is 780nm, and the laser power is 100 mW. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the table below shows the change of the intensity of the ethanol Raman peak when the cavity length is changed from 1mm to 4mm, the excitation light wavelength is 1064nm, and the laser power is 450 mW. The laser was vertically incident into the cavity and the intensity values of the individual peaks were measured as follows:
the following experimental data based on fig. 3 and fig. 6 shows the structure of fabry-perot resonator inside the metal-coated capillary:
1. the following table shows 488nm-1064nm excitation light for identifying alcohol (ethanol)C-C-O，-CH 3 ，C-O-H，-CH 2 -CH 3 Radical case (2800-3000 cm)-1：−𝐶H2−H3Symmetric and asymmetric stretching vibration of the group, 1453 cm-1：−𝐶H3Asymmetric deformation, 1300 cm-1：𝐶−𝑂-H bending vibration, 1000--1：𝐶−𝐶−𝑂Out-of-plane stretching to produce Raman feature double, 884 cm-1：𝐶−𝐶−𝑂In-plane expansion):
for different wavelengths, the excitation fibers (3-2) in FIG. 3 are all converted into single-mode fibers with corresponding wavelengths, and 3-4 in FIG. 3 are converted into high-reflectivity films with corresponding wavelengths. From this figure it can be concluded that excitation light between 488nm and 1064nm can identify the groups of the substance using the system proposed herein. Wherein the power of the 488nm wavelength laser is 300mW, the power of the 532nm wavelength laser is 150mW, the power of the 780nm wavelength laser is 100mW, and the power of the 1064nm wavelength laser is 450 mW.
FIG. 7 is a spectrum of alcohol detection with 780nm excitation light, wherein the excitation light intensity is 100mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm.
2. The following table shows the intensity variation table of 10% -100% concentration ethanol Raman peak, the excitation light wavelength is 488nm, the excitation light intensity is 300mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
"-" represents no data detected.
The following table shows the intensity variation table of 10% -100% concentration ethanol Raman peak, excitation light wavelength 532nm, excitation light intensity 150mW, cavity length 2cm, and capillary hollow hole diameter 30 μm:
the following table shows the intensity variation table of 10% -100% concentration ethanol Raman peak, the wavelength of excitation light is 780nm, the intensity of excitation light is 100mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
the following table shows the intensity variation table of 10% -100% concentration ethanol Raman peak, the excitation light wavelength is 1064nm, the excitation light intensity is 450mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
3. the following table shows the intensity change of the ethanol Raman peak when the excitation light power is changed from 30mW to 300mW, the wavelength of the excitation light is 488nm, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
the following table shows the intensity change of the ethanol Raman peak when the excitation light power is changed from 20mW to 150mW, the excitation light wavelength is 532nm, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
the following table shows the intensity change of the ethanol Raman peak when the excitation light power is changed from 20mW to 100mW, the wavelength of the excitation light is 780nm, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
the following table shows the intensity change of the ethanol Raman peak when the excitation light power is changed from 50mW to 450mW, the wavelength of the excitation light is 1064nm, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30 μm:
4. the following table shows the intensity change of the ethanol Raman peak when the cavity length is changed from 1cm to 2cm, the excitation light wavelength is 488nm, the laser power is 300mW, and the diameter of a hollow hole in the capillary is 30 mu m:
the following table shows the intensity change of the ethanol Raman peak when the cavity length is changed from 1cm to 2cm, the excitation light wavelength is 532nm, the laser power is 150mW, and the diameter of a hollow hole in the capillary is 30 mu m:
the following table shows the intensity change of the ethanol Raman peak when the cavity length is changed from 1cm to 2cm, the wavelength of the excitation light is 780nm, the laser power is 100mW, and the diameter of the hollow hole of the capillary is 30 μm:
the following table shows the intensity change of the ethanol Raman peak when the cavity length is changed from 1cm to 2cm, the excitation light wavelength is 1064nm, the laser power is 450mW, and the diameter of the hollow hole of the capillary is 30 μm:
5. the following table shows the Raman peak intensity variation of ethanol under different hollow hole diameters, the excitation wavelength is 488nm, the laser intensity is 300mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30-250 μm:
the following table shows the Raman peak intensity variation of ethanol under different hollow pore diameters, excitation wavelength 532nm, laser intensity 150mW, cavity length 2cm, and hollow pore diameter of the capillary 30 μm-250 μm:
the following table shows the Raman peak intensity variation of ethanol under different hollow hole diameters, with an excitation wavelength of 780nm, a laser intensity of 100mW, a cavity length of 2cm, and a capillary hollow hole diameter of 30 μm-250 μm:
the following table shows the Raman peak intensity variation of ethanol under different hollow hole diameters, the excitation wavelength is 1064nm, the laser intensity is 450mW, the cavity length is 2cm, and the diameter of the hollow hole of the capillary is 30-250 μm:
Claims (13)
1. a Raman spectrum enhancement device of a Fabry-Perot resonant cavity is characterized by comprising an excitation light input assembly and a Raman light receiving assembly, wherein the excitation light input assembly comprises a high-reflection mirror surface which has no selectivity on the reflection of light, a notch penetrating through the mirror surface is reserved on the high-reflection mirror surface, and an optical fiber called as an excitation light optical fiber is inserted into the notch penetrating through the mirror surface reserved on the high-reflection mirror surface; the Raman light receiving assembly comprises a Raman light receiving optical fiber, an end face of the Raman light receiving optical fiber facing the Fabry-Perot resonant cavity and a filter mirror surface which is arranged on the end face and is formed by a filter film which is highly reflective to the exciting light and highly transparent to the Raman light, the highly reflective mirror surface and the filter mirror surface are arranged in a face-to-face mode to form the Fabry-Perot resonant cavity, and the exciting light is guided into the Fabry-Perot resonant cavity by using the exciting light optical fiber.
2. The apparatus of claim 1, wherein the fabry-perot cavity is surrounded by a metal film coated sleeve, and a gap is left between the sleeve and the edges of the high-reflectivity mirror and the filter mirror, through which a sample to be measured enters and exits the fabry-perot cavity.
3. The apparatus of claim 2, wherein a three-way valve is connected to two ends of the sleeve, the exciting light fiber, the raman light receiving fiber, and the sleeve are fixed to the three-way valve, and the sample to be measured enters and exits the fabry-perot resonator through the three-way valve and further through the sleeve.
4. The fabry-perot resonator raman spectrum enhancement device of claim 1, wherein the filter film provided at the end face of the raman light receiving fiber, which is highly reflective to the excitation light and highly transparent to the raman light, is a film highly reflective to 785nm light and highly transparent to the raman light.
5. The Fabry-Perot cavity Raman spectral enhancement device of any of claims 1-4, wherein said highly reflective mirror is a gold or silver plated mirror.
6. The Fabry-Perot cavity Raman spectral enhancement device of claim 5, wherein the thickness of the gold or silver film of the highly reflective mirror is 0.5 to 10 microns.
7. The Fabry-Perot resonant cavity Raman spectrum enhancement device of claim 5, wherein in the preparation of the filter mirror, the low refractive index film material is selected from SiO2, the high refractive index film material is selected from one or a mixture of more of titanium oxide (TiO 2), tantalum oxide (Ta 2O 5) and hafnium oxide (HfO 2) in a certain proportion, and the filter mirror is prepared by controlling the thicknesses of the single layers of the low refractive index film and the high refractive index film and the combined cycle number.
8. The apparatus of claim 7, wherein the filter has a reflectivity of 99% or more with respect to the excitation light and a reflectivity of 20% or less with respect to the stimulated raman wavelength band.
9. The fabry-perot resonator raman spectrum enhancement device of any one of claims 1 to 3, wherein the excitation fiber is etched to a desired thickness with 10% hydrofluoric acid.
10. The fabry-perot resonator raman spectrum enhancement device of claim 9, wherein a temperature of hydrofluoric acid etching the excitation fiber is 45 degrees celsius.
11. The fabry-perot resonator raman spectral enhancement device of claim 9, the excitation fiber having an outer diameter of 30 microns.
12. The apparatus of claim 3, wherein the fiber for transmitting the excitation light, the Raman light receiving fiber, and the sleeve are fixed to the three-way valve by bonding with UV curable adhesive.
13. A method for detecting a gas or liquid sample to be tested by using the fabry-perot resonator raman spectroscopy enhancement device of any one of claims 1 to 12, comprising the steps of:
(1) enabling a gas or liquid sample to be measured to enter the Fabry-Perot resonant cavity;
(2) exciting light is emitted into the Fabry-Perot resonant cavity through an exciting light fiber inserted into a notch which is reserved on the high-reflection mirror surface and penetrates through the mirror surface;
(3) the high-reflection mirror surface at the excitation light input side of the Fabry-Perot resonant cavity reflects excitation light and Raman light in an unselective manner, the filter lens at the Raman light receiving assembly side of the Fabry-Perot resonant cavity reflects the excitation light in a high-reflection manner and transmits the Raman light in a high-transmission manner, and the excitation light and the Raman light generated by excitation are continuously reflected and enhanced in the Fabry-Perot resonant cavity;
(4) and receiving the Raman spectrum signal by using a Raman spectrometer at the Raman light receiving component side, and analyzing the Raman spectrum.
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