CN108152267A - A kind of method of efficient excitation metallized optical fibre Surface enhanced Raman scattering - Google Patents

Abstract

The invention relates to a method for efficiently exciting metallized optical fiber surface-enhanced Raman scattering, using a columnar vector light field as excitation light to induce metallized optical fiber surface-enhanced Raman scattering (SERS) effect from the inside of the optical fiber. Using a metallized tapered optical fiber with high SERS activity as a probe, compared with linearly polarized light excitation, the columnar vector light field can significantly enhance the electromagnetic field and thus improve the SERS detection sensitivity. The columnar vector light field is transmitted from the inside of the fiber to the end of the probe. When the columnar vector light field and the surface plasmons meet the wave vector matching, localized surface plasmon resonance is realized at the end of the metal-coated fiber tip. Then the intensity of the excited Raman signal is increased, wherein the columnar vector light field is directly generated in the optical fiber by using an electrically controlled tunable acoustic grating. The invention has the advantages of simple operation, remarkable Raman enhancement effect, simple device and easy integration, and can be used for Raman signal detection of three systems of solid powder, liquid and gas.

Description

A method for efficiently exciting surface-enhanced Raman scattering of metallized optical fibers

technical field

The invention belongs to surface-enhanced Raman, and the field relates to a method for efficiently exciting metallized optical fiber surface-enhanced Raman scattering.

Background technique

Surface-enhanced Raman spectroscopy (SERS) has become an important tool for analyzing and detecting molecules because of its ability to significantly enhance the intrinsic Raman signal of materials, and has been widely used in many fields such as chemistry, biology, and food safety. Surface-enhanced Raman is usually achieved by localized surface plasmon resonance (LSPR). Localized surface plasmon resonance (LSPR) can generate a significant electric field enhancement effect in the subwavelength scale, enhance the interaction between light and matter, and thus realize the enhancement of Raman signal. Many nanoscale noble metal structures are used to produce the LSPR effect, including nanospheres, metallized fiber probes, nanorods, and nanogratings. Among them, the metallized optical fiber has excellent anti-interference and low noise characteristics, and is easy to integrate. It can simplify the optical excitation and collection system while improving the detection sensitivity.

The SERS performance is related to many factors such as the polarization state of the excitation light, the substrate, and the system signal collection method, among which the polarization state of the excitation light is one of the key factors. Radially polarized vector light and angularly polarized vector light, two typical columnar vector lights, have been widely concerned because of their special polarization characteristics. Radially polarized vector light can generate extremely strong longitudinal electric field components at the focal point under tight focusing, and has many applications in super-resolution imaging, particle trapping, and Raman scattering enhancement. Considering that the surface-enhanced Raman is mainly caused by the localized surface plasmon resonance (LSPR) of the nanostructure, and the symmetry, specificity and similarity of the cross-sectional polarization distribution of the angular vector light and the radial vector light, in addition , the metallized optical fiber has the characteristics of anti-interference, low noise, and easy integration, so the radial polarization vector light and angular vector light used to excite the Raman scattering of the metallized optical fiber inside have great potential in improving the detection sensitivity of SERS. It is necessary to find a method suitable for the generation and transmission of vector light in optical fibers, and to optimize the geometric structure and surface morphology of metallized optical fibers to match the vector light mode to obtain the best excitation efficiency.

Contents of the invention

technical problem to be solved

In order to avoid the disadvantages of the prior art, the present invention proposes a method for efficiently exciting metallized optical fiber surface-enhanced Raman scattering.

Technical solutions

A method for efficiently exciting metallized optical fiber surface enhanced Raman scattering, characterized in that the steps are as follows:

Step 1. Use the tunable acoustic grating method to directly generate columnar vector light in the optical fiber: place the optical fiber 5 on the optical path of the front objective lens 4, and the incident optical path of the front objective lens 4 is sequentially provided with a linearly polarized light source 1 and a bandpass filter 2 And half-wave plate 3; Mode filter 6 is located at optical fiber 5 and is positioned at front objective lens 4 one ends, and the output end of ultrasonic generator 8 is loaded in the middle part of optical fiber 5, and its input end connects radio frequency generator 7;

Start the linearly polarized light source 1 and the radio frequency generator 7, and the ultrasonic wave generated by the ultrasonic generator is coupled to the optical fiber for transmission, and a linear polarization grating is formed in the optical fiber for modulation, and the polarization direction of the light emitted by the light source is adjusted by rotating the half-wave plate 3. The frequency of the radio frequency generator 7 is until the mode matching is satisfied, thereby converting the vector fundamental mode in the fiber core into a columnar vector light field;

Step 2, using the flame tapering method and light-induced chemical deposition method to prepare metallized optical fiber probes: using the flame tapering method to prepare an optical fiber taper at one end of the optical fiber 5, and then using the light-induced electroless deposition method to plate noble metal on the surface of the tapered optical fiber, Obtain the metallized optical fiber probe 9 at one end of the optical fiber 5;

Step 3. Use the columnar vector light in the optical fiber to excite the surface-enhanced Raman spectrum of the metallized optical fiber: vertically immerse the metallized optical fiber probe 9 in the liquid containing the substance to be measured, or coat the liquid or solid powder containing the substance to be measured On the metallized fiber probe 9 surface, the optical fiber 5 with the metallized fiber probe 9 is placed on the optical path of the front objective lens 4 of the optical path described in step 1, the front end of the metallized fiber probe 9 is provided with a rear objective lens 10, and the rear objective lens 10 A long-wave pass band-edge filter 11, an optical fiber adapter 12 and a Raman spectrometer 13 are arranged in sequence on the exit optical path;

Start the linearly polarized light source 1 and the radio frequency generator 7, and the ultrasonic wave generated by the ultrasonic generator is coupled to the optical fiber for transmission, and a linear polarization grating is formed in the optical fiber for modulation, and the polarization direction of the light emitted by the light source is adjusted by rotating the half-wave plate 3. The frequency of the radio frequency generator 7 is until the mode matching is satisfied, thereby converting the vector fundamental mode in the fiber core into a columnar vector light field; the outgoing signal of the metallized fiber optic probe 9 is collimated by the rear objective lens 10, and is filtered by the long-wave pass band edge The chip 11 filters the excitation light, and the generated Raman signal is collected by the fiber optic adapter 12 and processed by the Raman spectrometer 13 .

The taper angle of the fiber taper is 30 degrees.

The method for metallizing the surface of the tapered optical fiber by the light-induced electroless deposition method is: using linearly polarized light with a power less than 1mW as the inductive light, vertically immersing the optical fiber taper prepared by the flame tapering method into the chemical reaction solution that produces noble metal , light plating 5-60min.

The precious metal is gold, silver or copper.

The size of the nanoparticles on the surface of the noble metal layer coated with the noble metal does not exceed the size of the excitation light wavelength.

Beneficial effect

A method for efficiently exciting metallized optical fiber surface-enhanced Raman scattering proposed by the present invention uses a columnar vector light field as excitation light to induce the metallized optical fiber surface-enhanced Raman scattering (SERS) effect from the inside of the optical fiber. Using metallized tapered fiber with high SERS activity as a probe, compared with linearly polarized light excitation, the columnar vector light field can significantly enhance the electromagnetic field and thus improve the SERS detection sensitivity. The columnar vector light field is transmitted from the inside of the fiber to the end of the probe. When the columnar vector light field and the surface plasmons meet the wave vector matching, localized surface plasmon resonance is realized at the end of the metal-coated fiber tip. Then the intensity of the excited Raman signal is increased, wherein the columnar vector light field is directly generated in the optical fiber by using an electrically controlled tunable acoustic grating. The invention has simple operation, remarkable Raman enhancement effect, simple device and easy integration, and can be used for Raman signal detection of three systems of solid powder, liquid and gas.

Description of drawings

Figure 1: Optical path system for exciting Raman spectroscopy on metallized optical fiber surface using cylindrical radial vector light in optical fiber

Figure 2: Optical fiber cones prepared by the flame tapering method

Fig. 3: the silver layer surface that embodiment silver-plates tapered optical fiber probe obtains

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

The present invention aims to provide a method for efficiently exciting Raman scattering on the surface of a metallized optical fiber by using cylindrical vector light in an optical fiber. The concept is as follows:

Using columnar vector light as the excitation light to excite the SERS effect on the surface of the metallized optical fiber from the inside of the optical fiber, a more significant Raman enhancement effect can be obtained than that excited by linearly polarized light. Using the metallized tapered optical fiber as the probe, the columnar vector light is transmitted to the end of the probe, which excites the local surface plasmon resonance and surface plasmon polaritons at the metal-medium interface, thereby enhancing the interaction between light and matter, and achieving pull Mann scattering enhancement.

According to this idea, the present invention takes following technical scheme:

The columnar vector light is directly generated in the fiber by using the tunable acoustic grating method, and the phase matching is realized by adjusting the polarization direction of the incident light field and the refractive index modulation degree of the electrically controlled tunable grating to generate the columnar vector light field in the fiber.

A metallized tapered optical fiber with high SERS activity was used as a probe. The preparation of the metallized tapered optical fiber probe is tapered first, and then coated with a noble metal layer. Optical fiber tapering adopts thermal tapering method or chemical method; the metallization process of optical fiber adopts light-induced electroless deposition method, and the surface shape of metal-clad optical fiber is controlled by optimizing the induced light power and deposition time in the process of light-induced electroless deposition. appearance.

Specific examples:

1. Use the tunable acoustic grating method to directly generate columnar vector light in the optical fiber:

As shown in Figure 1, a linearly polarized light source 1 produces linearly polarized light, a bandpass filter 2 limits the width of the outgoing light, a half-wave plate 3 adjusts the polarization direction of the linearly polarized light, and an objective lens 4 couples spatial light into an optical fiber 5 , the light transmitted in the optical fiber is filtered by the mode filter 6 to filter out high-order modes, and then the ultrasonic generator 8 loads the acoustic wave signal, wherein the acoustic wave signal is generated by the radio frequency signal generated by the radio frequency generator 7 to drive the ultrasonic transducer. The ultrasonic wave generated by the sonotrode is coupled to the optical fiber for transmission, and a linear polarization grating is formed in the optical fiber for modulation, thereby converting the vector fundamental mode in the fiber core into a columnar vector light field.

2. Preparation of silver-coated fiber optic probes with high SERS activity by using the flame taper method and light-induced chemical deposition method:

First, the fiber taper is prepared by the flame tapering method, and the taper angle is controlled by controlling the drawing speed, so that the taper angle is about 10 degrees, as shown in Figure 2. Secondly, light-induced electroless deposition is used to plate silver on the surface of the tapered optical fiber to prepare silver-coated optical fiber probe 9. 400uW linearly polarized light is used as the induction light, and the 1:1 mixture of potassium sodium tartrate and silver ammonia solution is used as the reaction solution. The cone was vertically immersed in the reaction solution, and the light was plated for 20 minutes. The surface of the prepared silver layer is rough, and the diameter of silver nanoparticles is about 300 nm, as shown in FIG. 3 .

3. Use the cylindrical radial vector light in the fiber to excite the Raman spectrum on the surface of the silver-coated fiber:

Soak the silver-plated optical fiber cone vertically in the alcohol dispersion of malachite green for 5 minutes. The columnar radial vector light generated in the optical fiber is used to excite the Raman signal of the malachite green molecule attached to the surface of the tapered optical fiber probe with high SERS activity. As shown in FIG. 1 , after the outgoing signal is collimated by the objective lens 10 , the excitation light is filtered out by a long-wave pass band-edge filter 11 . The Raman signal is collected by the fiber optic adapter 12 and then entered into the Raman spectrometer 13 for collection. In the case of the same excitation power and fiber probe, the integration time of the Raman spectrometer is the same, and the SERS signal intensity of columnar vector light and linearly polarized excitation is compared. The results of columnar vector light, including radial vector light and angular vector light, compared Polarized excitation can further significantly increase the Raman scattering intensity on the fiber surface.

Claims (5)

1. A kind of 1. method of efficient excitation metallized optical fibre Surface enhanced Raman scattering, it is characterised in that step is as follows：

   Step 1 causes raster method directly to generate column vector light in a fiber using adjustable pictophonetic characters：Optical fiber (5) is placed in preceding object lens (4) in light path, linear polarization light source (1), band pass filter (2) and half-wave plate are equipped in the input path of preceding object lens (4) successively (3)；For mode filter (6) set on optical fiber (5) positioned at preceding object lens (4) one end, the output terminal of supersonic generator (8) loads on optical fiber (5) middle part, input terminal connection radio-frequency signal generator (7)；

   Start linear polarization light source (1) and radio-frequency signal generator (7), passed in the ultrasonic wave-coupled to optical fiber that supersonic generator generates It is defeated, linear polarization grating is formed in a fiber and is modulated, by rotatable halfwave plate (3) to adjust the polarization side of light source emergent light To, while the frequency of radio-frequency signal generator (7) is adjusted until meeting pattern match, so as to which the vector basic mode in fibre core is converted to column Shape vectorial field；

   Step 2 draws cone method and photoinduction chemical deposition to prepare metallized optical fibre probe using flame：Cone method is drawn to exist using flame One end of optical fiber (5) prepares optical taper, then plates noble metal on conical fiber surface using photoinduction electroless deposition processes, obtains optical fiber (5) the metallized optical fibre probe (9) of one end；

   Step 3 excites metallized optical fibre Surface enhanced Raman spectroscopy using column vector light in optical fiber：By metallized optical fibre probe (9) it immerses vertically in the liquid containing measured matter or the liquid containing measured matter or solid powder is coated in metal Change optical fiber probe (9) surface, the optical fiber (5) with metallized optical fibre probe (9) is placed in the preceding object lens of light path described in step 1 (4) in light path, metallized optical fibre probe (9) front end is equipped with rear object lens (10), is equipped with successively in the injection light path of rear object lens (10) Long wave passband side filter plate (11), fiber adapter (12) and Raman spectrometer (13)；

   Start linear polarization light source (1) and radio-frequency signal generator (7), passed in the ultrasonic wave-coupled to optical fiber that supersonic generator generates It is defeated, linear polarization grating is formed in a fiber and is modulated, by rotatable halfwave plate (3) to adjust the polarization side of light source emergent light To, while the frequency of radio-frequency signal generator 7 is adjusted until meeting pattern match, so as to which the vector basic mode in fibre core is converted to column Vectorial field；After the outgoing signal of metallized optical fibre probe (9) is collimated by rear object lens (10), by long wave passband side filter plate (11) exciting light is filtered out, the Raman signal of generation is collected through fiber adapter (12), by Raman spectrometer (13) processing.
2. 2. the method for metallized optical fibre Surface enhanced Raman scattering is efficiently excited according to claim 1, it is characterised in that：Institute The cone angle for stating optical taper is 30 degree.
3. 3. the method for efficient excitation metallized optical fibre Surface enhanced Raman scattering according to claim 1 or claim 2, feature exist In：The photoinduction electroless deposition processes are in the method for conical fiber surface metalation：Made with linearly polarized light of the power less than 1mW To induce light, the optical taper that flame draws cone method to prepare is immersed vertically in the chemical reaction liquid for generating noble metal, thang-kng plating 5- 60min。
4. 4. according to the method for the efficient excitation metallized optical fibre Surface enhanced Raman scattering of claim 1 or 3, feature exists In：The noble metal is gold, silver or copper.
5. 5. according to the method for the efficient excitation metallized optical fibre Surface enhanced Raman scattering of claim 1 or 3, feature exists In：The layer of precious metal nano surface granular size of the plating noble metal is no more than excitation wavelength size.