What Is Raman Spectroscopy?

Raman spectra is a type of scattering spectrum. Raman spectroscopy is based on the Raman scattering effect discovered by Indian scientist CV Raman, and analyzes the scattering spectrum with a frequency different from the incident light to obtain information on molecular vibration and rotation, and is applied to the study of molecular structure An analytical method.

Raman spectra is a type of scattering spectrum. Raman spectroscopy is based on the Raman scattering effect discovered by Indian scientist CV Raman, and analyzes the scattering spectrum with a frequency different from the incident light to obtain information on molecular vibration and rotation, and is applied to the study of molecular structure An analytical method.
Chinese name
Raman spectroscopy
Foreign name
Raman spectra
Category
Scattering spectrum
Use
An analytical method for molecular structure research

Raman spectrum history

192
Raman spectroscopy
The 8-year CV Raman experiment found that when light passes through a transparent medium and is scattered by molecules, the frequency changes. This phenomenon is called Raman scattering, and it was also observed in the Soviet Union and France later in the same year. In the scattering spectrum of a transparent medium, a component having the same frequency as the incident light frequency 0 is called Rayleigh scattering; a spectral line or a frequency band symmetrically distributed on both sides of 0 0 ± 1 is a Raman spectrum, where The smaller frequency component 0 - 1 is also called Stokes line, and the larger frequency component 0 + 1 is also called anti-Stokes line. The spectral lines near the sides of the Rayleigh scattering line are called small Raman spectra; the spectral lines appearing at the sides far from the Rayleigh line are called large Raman spectra. The intensity of the Rayleigh scattering line is only 10 -3 of the intensity of the incident light, and the intensity of the Raman spectrum is only about 10 -3 of the Rayleigh line. The small Raman spectrum is related to the molecular rotation energy level, and the large Raman spectrum is related to the molecular vibration-rotation energy level. The theoretical explanation of Raman spectroscopy is that inelastic scattering occurs between incident photons and molecules. The molecules absorb photons with a frequency of 0 and emit photons of 0- 1 ( that is, the absorbed energy is greater than the released energy ), and the molecules are from a low energy state. Transition to a high energy state (Stokes line); the molecule releases a photon with a frequency of 0 and emits a photon of 0 + 1 ( that is, the energy released is greater than the energy absorbed ), while the molecule transitions from a high energy state to a low energy state ( Anti-Stokes line). The transition of molecular energy levels involves only rotational energy levels and emits small Raman spectra; it involves vibration-rotational energy levels and emits large Raman spectra. Unlike molecular infrared spectroscopy, both polar and non-polar molecules can produce Raman spectroscopy. The advent of the laser has provided high-quality, high-intensity monochromatic light, which has strongly promoted the research and application of Raman scattering. Raman spectroscopy has applications in chemistry, physics, biology, and medicine, and is of great value for purely qualitative analysis, highly quantitative analysis, and determination of molecular structure.

Information about Raman spectroscopy

Electrochemical in situ Raman spectroscopy is a method that uses the scattering phenomenon of material molecules to significantly change the frequency of incident light. Monochromatic incident light (including circularly polarized light and linearly polarized light) is used to excite the electrode modulated by the electrode potential. On the surface, the relationship between the scattered Raman spectrum signal (changes in frequency, intensity, and polarization performance) and electrode potential or current intensity is measured. The Raman spectrum of general substance molecules is very weak. In order to obtain an enhanced signal, the electrode surface can be roughened to obtain a Surface Enhanced Raman Scattering (SERS) spectrum with an intensity of 10 4 -10 7 times higher. When a molecule with a resonance Raman effect is adsorbed on a roughened electrode surface, a surface-enhanced resonance Raman scattering (SERRS) spectrum is obtained, and its intensity can be increased by 10 2 -10 3 .
The measurement device of electrochemical in situ Raman spectroscopy mainly includes two parts: a Raman spectrometer and an in situ electrochemical Raman cell. The Raman spectrometer consists of a laser source, a collection system, a spectroscopic system, and a detection system.The light source generally uses a laser with high energy concentration and high power density.The collection system consists of a lens group. In addition to Rayleigh scattering and stray light, the spectroscopic detection system uses a photomultiplier tube detector, a semiconductor array detector, or a multi-channel charge coupling device. The in situ electrochemical Raman cell generally has a working electrode, an auxiliary electrode and a reference electrode, and a ventilation device. To prevent corrosive solutions and gases from attacking the instrument, the Raman cell must be equipped with a sealed system of optical windows. When the experimental conditions allow, in order to avoid the interference of the solution signal as much as possible, a thin layer solution (the distance between the electrode and the window is 0.1 to 1 mm) should be used. This is very important for the micro Raman system, and the optical window or the solution layer is too thick It will cause the optical path of the microscope system to change, which will reduce the collection efficiency of surface Raman signals. The most common method for electrode surface roughening is the electrochemical oxidation-reduction cycle (ORC) method, which can generally be performed in situ or ex situ ORC.
At present, the research progress of electrochemical in situ Raman spectroscopy is mainly as follows: First, the test system has been broadened to transition metal and semiconductor electrodes through surface enhancement treatment. Although electrochemical in situ Raman spectroscopy is a more sensitive method for on-site detection, only silver, copper, and gold electrodes can give strong SERS in the visible light region. Many scholars have tried to achieve surface-enhanced Raman scattering on transition metal electrodes and semiconductor electrodes with important application backgrounds. The second is to analyze the structure, orientation of the species adsorbed on the electrode surface and the relationship between the SERS spectrum of the object and the electrochemical parameters, and to describe the electrochemical adsorption phenomenon at the molecular level. Third, by changing the frequency of the modulation potential, a "time-resolved spectrum" can be obtained that changes at two potentials to analyze the relationship between the SERS peak of the system and the potential, and solve the problem that the SERS active site on the electrode surface changes with the potential. Bring problems.

Raman spectrum meaning

Elastic and inelastic scattering occurs when light hits a substance. Elastically scattered scattered light is the same component as the wavelength of the excitation light. Inelastically scattered scattered light has longer and shorter components than the wavelength of the excitation light, collectively known as the Raman effect. . The Raman effect is the result of the interaction of photons with optically supported phonons.
Raman spectroscopy-Principles The Raman effect originates from molecular vibrations (and lattice vibrations) and rotation, so knowledge of molecular vibrational levels (lattice vibrational levels) and rotational energy level structures can be obtained from Raman spectra. The Raman effect can be illustrated with the concept of an imaginary upper level:
It is assumed that the scatterer molecules were originally in the ground electron state, and the vibration energy levels are shown in the figure. When irradiated with incident light, the polarization caused by the interaction of the excitation light with this molecule can be regarded as a virtual absorption, expressed as an electron transition to a virtual state, and the electrons on the virtual energy level immediately transition to the lower energy level. Luminescence is the scattered light. Suppose that it still returns to the original electronic state, there are three cases as shown in the figure. Therefore, the scattered light has both the same spectral line as the frequency of the incident light and different spectral lines from the frequency of the incident light. The former is called the Rayleigh line and the latter is called the Raman line. In Raman lines, the spectral lines with frequencies lower than the frequency of incident light are called Stokes lines, and the spectral lines with frequencies greater than the frequency of incident light are called Anti-Stokes lines.
The additional frequency value related to the vibration energy level is called the large Raman displacement, and the rotation energy level in the same vibration energy level is called the small Raman displacement:
Large Raman displacement: (band frequency of vibration energy level)
Small Raman shift: (where B is the rotation constant)
Simple Derivation of Small Raman Shifts: Using Rotation Constants

Raman spectral characteristics

Raman scattering spectrum has the following obvious features
a. Although the wave number of the Raman scattering line varies with the wave number of the incident light, for the same sample, the displacement of the same Raman line is independent of the wavelength of the incident light, and is only related to the vibrational energy level of the sample;
b. On the Raman spectrum with the wave number as a variable, the Stokes and anti-Stokes lines are symmetrically distributed on both sides of the Rayleigh scattering line. This is because in the above two cases, the corresponding Or lost a quantum energy of vibration.
c. In general, the Stokes line is stronger than the anti-Stokes line. This is because of the Boltzmann distribution, the number of particles in the vibrational ground state is much larger than the number of particles in the vibrational excited state.

Raman spectroscopy

Spectral plots made by experiments (see attached picture, in wavelengths)
Standard spectrum (below, in wave numbers)
Spectral analysis through structural analysis:
The molecule has a tetrahedral structure with one carbon atom at the center and four chlorine atoms at the four vertices of the tetrahedron. When a tetrahedron rotates a certain angle around its own axis, or after a memory inversion (r--r), or rotation plus inversion, the operation of the molecule's geometric configuration is not called a symmetry operation, and its rotation axis becomes symmetrical axis. CCI 4 has 13 axes of symmetry, and there are cases where 4 symmetrical operations can be checked. We know that a molecule composed of N atoms has (3N-6) internal vibrational degrees of freedom. So the molecule can have 9 (3 × 5-6) degrees of freedom, or 9 independent normal vibrations. According to the symmetry of the molecules, these nine kinds of normal vibrations can be summarized into the following four categories:
In the first type, there is only one type of vibration. The four chlorine atoms vibrate in the direction of the line with the C atom, which is denoted as v1, which indicates non-degenerate vibration.
In the second type, there are two modes of vibration. Two adjacent pairs of CI atoms move in the opposite direction at the same time with the C atom, or in the direction perpendicular to the connection line. They are recorded as v2, which indicates double degenerate vibration.
In the third type, there are three vibration modes. Four CI and C atoms move in the opposite direction, denoted as v3, which means triple degenerate vibration.
In the fourth category, there are three modes of vibration. The adjacent pair of CI atoms makes stretching motion, and the other pair makes compression motion, denoted as v4.
The above-mentioned "degenerate" means that in the same type of vibration, although they contain different vibration modes, they have the same energy, and they correspond to the same spectral line in the Raman spectrum. Therefore, the molecular vibration Raman spectrum should have 4 basic spectral lines, and the relative intensity of each spectral line measured in the experiment is v1> v2> v3> v4 in this order. The spectrum of benzene is also shown in the drawing, and the analysis is similar, so it will not be repeated here.

Superiority of Raman spectroscopy

Advantages of Raman spectroscopy
Provides fast, simple, repeatable, and heavier
Raman spectroscopy
What is needed is qualitative and quantitative analysis without damage. It does not require sample preparation. The sample can be measured directly through the fiber optic probe or through glass, quartz, and fiber optics. Besides
1 Because the Raman scattering of water is very weak, Raman spectroscopy is an ideal tool for studying biological samples and chemical compounds in aqueous solutions.
2 Raman can cover the range of 50-4000 wave numbers at the same time, which can analyze organic and inorganic substances. Conversely, if the infrared spectrum covers the same interval, the grating, beam splitter, filter, and detector must be changed.
3 Raman spectrum peaks are clear and sharp, which is more suitable for quantitative research, database search, and qualitative research using difference analysis. In chemical structure analysis, the intensity of independent Raman intervals can be related to the number of functional groups.
4 Because the diameter of the laser beam is usually only 0.2-2 mm at its focal point, conventional Raman spectroscopy requires only a small number of samples to obtain it. This is a great advantage of Raman spectroscopy over conventional infrared spectroscopy. Moreover, Raman microscope objectives can further focus the laser beam to 20 microns or smaller, allowing analysis of smaller areas of samples.
5 The resonance Raman effect can be used to selectively enhance the vibration of specific chromophores of large biomolecules. The Raman intensity of these chromophores can be selectively increased by 1000 to 10,000 times.

Raman spectroscopy

Raman spectroscopy

Raman spectrometer is generally composed of the following five parts.
Raman spectroscopy

Raman spectrum light source

Its function is to provide incident light with good monochromaticity, high power, and preferably multi-wavelength operation. At present, all the light sources of Raman spectroscopy experiments have replaced the mercury lamps used in history with lasers. For conventional Raman spectroscopy experiments, common gas lasers can basically meet the needs of the experiment. In some Raman spectroscopy experiments, the intensity of the incident light is required to be stable, which requires the output power of the laser to be stable.

Raman spectrum external light path

The external light path part includes light collecting, light collecting and sample holder. Filtering and polarization components.
(1) Condensing: Use one or two converging lenses with appropriate focal length to place the sample at the waist of the converging laser beam to increase the irradiation power of the sample light. Enhance 105 times.
(2) Light collection: commonly used lens groups or reflective concave mirrors are used to collect scattered light. It usually consists of a lens with a relative aperture value of about 1. In order to collect more scattered light, for some experimental samples, a mirror can be added on the opposite side of the collector and the direction of illumination light propagation.
(3) Sample holder: The design of the sample holder should ensure the most effective illumination and the least stray light, especially to prevent the incident laser from entering the entrance slit of the spectrometer. For this reason, for a transparent sample, the optimal sample arrangement scheme is to make the illuminated portion of the sample a long cylinder in the shape of an entrance slit of a spectrometer, and make the direction of the collected light perpendicular to the propagation direction of the incident light. See the figure on the right for the space configuration of several typical sample racks.
(4) Filtering: The main purpose of the filter is to suppress stray light and improve the signal-to-noise ratio of Raman scattering. In front of the sample, typical filters are front monochromators or interference filters, which filter out most of the light energy at non-laser frequencies in the light source. The small aperture light barrier has a good effect on filtering out the plasma lines generated by the laser. Behind the sample, a suitable interference filter or absorption box can filter a large part of the energy of unwanted Rayleigh lines, and increase the relative intensity of Raman scattering.
(5) Polarization: When measuring the polarization spectrum, a polarizing element must be inserted in the external optical path. Adding a polarization rotator can change the polarization direction of the incident light; adding an analyzer before the entrance slit of the spectrometer can change the polarization of the scattered light entering the spectrometer; setting a polarization scrambler behind the analyzer can eliminate the depolarization interference of the spectrometer .

Raman spectral dispersion system

Dispersion systems separate Raman scattered light by wavelength in space, and usually use a monochromator. Because the intensity of Raman scattering is very weak, a good level of stray light is required for the Raman spectrometer. Defects of various optical components, especially those of gratings, are the main source of stray light for instruments. When the stray light power of the instrument is less than 10-4, it can only be used for Raman spectrum of gas, transparent liquid and transparent crystal.
Raman spectroscopy

Raman spectrum receiving system

There are two types of Raman scattered signal reception: single-channel and multi-channel. Photomultiplier tube reception is single-channel reception.

Raman spectroscopy information processing

In order to extract Raman scattering information, the common electronic processing methods are DC amplification, frequency selection and photon counting, and then use a recorder or computer interface software to draw a spectrum.

Raman spectrum Raman effect

Elastic and inelastic scattering occurs when light hits a substance. Elastically scattered scattered light is the same component as the wavelength of the excitation light. Inelastically scattered scattered light has longer and shorter components than the wavelength of the excitation light, collectively known as the Raman effect .
When irradiating a gas, liquid or transparent sample with a monochromatic light having a wavelength much smaller than the particle size of the sample, most of the light will be transmitted in the original direction, while a small part will be scattered at different angles, resulting in Scattered light. When viewed in the vertical direction, in addition to the Rayleigh scattering with the same frequency as the original incident light, there are a series of symmetrically distributed several very weak Raman spectral lines that are shifted from the frequency of the incident light. This phenomenon is called Raman effect. Due to the number of Raman spectral lines, the magnitude of the displacement, and the length of the spectral lines are directly related to the vibration or rotational energy levels of the sample molecules. Therefore, similar to infrared absorption spectroscopy, the study of Raman spectroscopy can also obtain information about molecular vibration or rotation. At present, Raman spectroscopy technology has been widely used in the identification of substances and the study of spectral characteristics of molecular structures.

Raman spectroscopy

Raman spectrum types

Several important Raman spectroscopy techniques
1.Raman spectroscopy analysis technology for single channel detection
Raman spectroscopy
2.Raman spectrum analysis technology of multi-channel detectors represented by CCD
3.FT-Raman spectral analysis technology using Fourier transform technology
4.Resonance Raman spectroscopy analysis technology
5. Surface enhanced Raman effect analysis technology
Advantages and disadvantages of Raman spectroscopy for analysis

Raman spectroscopy advantages

1.The advantages of Raman spectroscopy for analysis
The analysis method of Raman spectroscopy does not require pretreatment of the sample, and there is no sample preparation process, which avoids the generation of some errors, and it is easy to operate in the analysis process, with short measurement time and high sensitivity.

Insufficient Raman spectrum

2.Insufficient Raman spectroscopy for analysis
(1) Raman scattering area
(2) The overlap of different vibration peaks and the intensity of Raman scattering are easily affected by factors such as optical system parameters
(3) Interference of fluorescence phenomenon on Fourier transform Raman spectrum analysis
(4) When performing Fourier transform spectrum analysis, the problem of nonlinearity of the curve often occurs.
(5) The introduction of any substance will cause a certain degree of pollution to the system of the subject, which is equivalent to introducing the possibility of some errors, which will have a certain impact on the results of the analysis.

Raman spectral signal selection

Selection of Raman signals
The power of the incident laser, the thickness of the sample cell, and the parameters of the optical system also have a great impact on the intensity of the Raman signal. Therefore, a substrate that can generate a strong Raman signal and whose Raman peak does not overlap with the Raman peak to be measured is often used. Or the molecules of the external substance are used as internal standards for correction. The internal standard selection principles and quantitative analysis methods are basically the same as other spectral analysis methods.
Stokes line energy decreases and wavelength becomes longer
Anti-Stokes line energy increases and wavelength decreases

Application of Raman spectroscopy

Application of Raman spectroscopy
By analyzing the Raman spectrum, you can know the vibrational energy level of the substance, so that you can identify the substance and analyze the nature of the substance. Here are some examples:
The Raman spectrum of natural heliotrope and imitation heliotrope are essentially different. The former is mainly Raman spectroscopy and cinnabar, and the latter is mainly Raman spectroscopy of organic matter. The Raman spectrum can be used to distinguish the two.
Raman Spectrum of Natural Soapstone:
Raman Spectrum of Natural Soapstone
Raman spectrum of imitation heliotrope:
In the two pictures above, a is the ground (black) and b is the blood (red)
After consulting the data and comparing the Raman spectra of different substances, it can be known that the main component of natural heliotrope "ground" is diketone, and the natural bloodstone sample "blood" has both cinnabar and diketone. A collection of ground stone. The main component of the imitation heliotrope "ground" is polystyrene-acrylonitrile, Raman spectrum of "blood" and a red organic dye called PermanentBordo
Raman spectrum of mimicry
Basically match.
Drug identification: Drugs and certain white powders were analyzed using Raman spectroscopy. The spectra are as follows:
Common drugs have quite abundant Raman characteristic shift peaks, and the signal-to-noise ratio of each peak is relatively high, indicating that the method of component analysis of drugs using Raman spectroscopy is feasible and the quality of the obtained spectra is high. Because the laser Raman spectrum has the function of micro-area analysis, even if drugs and other white powdery substances are mixed together, they can be identified by microscopic analysis technology, and the Raman spectra of drugs and other white powders can be obtained.
Raman spectroscopy can be used to monitor the preparation of materials: Supported molybdenum sulfide and tungsten sulfide catalysts are prepared by heating the corresponding supported metal oxides in H2 and H2S atmospheres, and are mainly used in the industry for hydrofining catalyst. In such an industry
Raman spectroscopy analyzes drugs and certain white powders
Under these conditions, two-dimensional surface metal oxides are transformed into two-dimensional or three-dimensional metal sulfides. Compared with supported metal oxides, the Raman spectroscopy of supported metal sulfides is relatively rare. This is because the black sulfides have relatively strong absorption of visible light, resulting in weaker signals. However, Raman spectroscopy can easily detect small metal sulfide crystallites. The figure below shows the Raman spectrum of the unsupported crystalline phase MoS 2
(Picture) Raman spectrum of unsupported crystalline phase MoS 2
At 380 and 450 cm -1 , two spectral peaks belonging to the crystalline phase sum appear, and the spectral peak of the supported crystal phase molybdenum sulfide is much wider than that of the crystal phase molybdenum sulfide. The addition of cobalt auxiliary causes the spectrum peak of molybdenum sulfide to shift and weaken, which is caused by the formation of phases and black phases.
Raman spectroscopy can monitor pesticide residues on fruit surfaces
Tear a small piece of peel on the surface of the treated fruit, and drop a drop of different pesticides on the surface of the fruit, and the pesticide will infiltrate the peel. Wipe the pesticide liquid on the peel with absorbent paper, then press the peel with the pesticide remaining into the small groove of the aluminum sheet to ensure that the surface of the peel of the remaining pesticide appears outside the small groove of the aluminum sheet, and then absorb the pressed juice with water Wipe the paper clean. Spectrum such as
Raman spectrum of unsupported crystalline phase MoS2
under:
Raman spectra obtained by plant protection postdoctoral drops on the surface of different kinds of fruits (see picture on the left). Obviously, in addition to the original Raman peak of the fruit, the characteristic peaks of Dr. Plant Protection were 993cm -1 , 1348cm -1 , and 1591cm -1 all appeared. Because the method of simulated pesticide spraying in the experiment was much less than the actual pesticide spray Despite this, pesticide residues are still clearly displayed, indicating that the method is sensitive and applicable. Quantitative analysis of pesticide residues can be obtained from the relative intensity ratio of pesticide characteristic lines and fruit characteristic lines.
Application of laser Raman spectroscopy
There are several applications of laser Raman spectroscopy: applications in organic chemistry, applications in polymers, applications in biology, applications in surfaces and films.
Organic chemistry: Raman spectroscopy is mainly used as a means of structural identification in organic chemistry. The magnitude, intensity, and shape of Raman peaks of Raman shifts are important bases for chemical bonds and functional groups. Using polarization characteristics, Raman spectroscopy can also be used as a basis for judging cis-trans structure.
Polymers: Raman spectroscopy can provide structural information about carbon chains or rings. In determining the isomers (single rest isomerism, position
Raman spectra obtained by dripping plant protection on different types of fruits
Isomerization, geometrical isomerism, and spatial stereoisomerism, etc.) Raman spectroscopy can play its unique role. The research of electroactive polymers such as polypyrrole and polythiophene often uses Raman spectroscopy as a tool. In the industrial production of polymers, such as the observation of the shape of extruded linear polyethylene and the observation of tight bundle molecules in high-strength fibers Raman spectroscopy has been used in the measurement of the crystallinity of polyethylene wear debris.
Biology: Raman spectroscopy is a powerful method for studying biological macromolecules. Because the Raman spectrum of water is very weak and the spectrum is simple, Raman spectroscopy can study the structure of biological macromolecules and their activities in a state close to nature and activity. Variety. The application of Raman spectroscopy in the study of protein secondary structure, the role of DNA and carcinogens, the structural changes of rhodopsin in the light cycle, the calcification deposition in arteriosclerosis and the red blood cell membrane have been applied in the literature. Report.
There are many successful examples of using FT-Raman to eliminate fluorescence interference of biological macromolecules.
Surfaces and films
In terms of materials research, Raman spectroscopy can do many examples in the topics of phase composition interface and grain boundary.
Recently, the interest of domestic and foreign scholars on the application of Raman spectroscopy in the research of diamond and diamond-like diamond films has continued to increase.
Raman spectroscopy has become a detection and identification method for thin films prepared by CVD (chemical vapor deposition).
In addition, Raman spectroscopy studies of LB films and Raman spectroscopy studies of silicon nitride films have been reported.
Although Raman scattering is weak and Raman spectroscopy is usually not sensitive enough, the sensitivity of Raman spectroscopy can be greatly enhanced by using resonance or surface enhanced Raman techniques. Surface enhanced Raman spectroscopy (SERS) has become an active area in Raman spectroscopy research.
development of
The traditional grating spectroscopic Raman spectrometer is a point-by-point scanning and single-channel recording method, which is a waste of time. In addition, the laser used in the laser Raman spectrometer can easily excite fluorescence and affect the determination. To avoid the disadvantages of traditional laser spectrometers, two new spectrometers have recently been developed:
Fourier transform near-infrared laser Raman spectrometer and confocal laser spectrometer.
The Fourier Raman spectrometer consists of a laser light source, a sample chamber, a Michelson interferometer, a special filter, and a detector.
The Fourier Raman spectrometer and optical path are similar to the optical path of a Fourier infrared spectrometer. The detected signal is collected and processed by a computer through an amplifier.

Development prospects of Raman spectroscopy

Raman spectroscopy laser technology

Raman spectroscopy has developed rapidly in recent years. It should benefit from two aspects.
Raman spectroscopy
On the one hand, the development of laser technology, I recently participated in the 21st International Raman Spectroscopy Conference held in London, England, and felt that now the ultra-fast laser-based nonlinear Raman spectroscopy technology has become more and more mature. This kind of highly sophisticated technology that requires expensive equipment was originally only available in a few units. In particular, the laser part is built by itself, and it has to be adjusted every day, which is very unstable. This situation no longer exists, and the price of the instrument is relatively low. The ultra-fast (femtosecond or picosecond) lasers currently engaged in the research of nonlinear spectroscopy are now internationally mature and can be purchased in sets and are relatively stable. Non-linear Raman spectroscopy has played its unique and important role in life science research. For example, Professor Xie Xiaoliang of Harvard University in the United States has achieved a series of important results in pioneering and using coherent anti-Stokes Raman spectroscopy microscopy (CARS Microscopy) to study the three-dimensional structure inside living cells. I think high-quality ultrafast lasers have also promoted another promising surface spectroscopy technology, which is the development of combined frequency (SFG) technology. As a non-linear spectral method with unique interface selectivity, it has been applied to interfaces and surfaces. Science, materials and even research in the field of life play an increasingly important role.

Raman spectroscopy nanotechnology

The second important aspect is the rapid development of nanotechnology, which has made surface-enhanced Raman spectroscopy (SERS) and needle-enhanced Raman spectroscopy (TERS) based on nanostructures have made great progress in ultra-high sensitivity detection, promoting Raman. Spectroscopy has hitherto been one of the few technologies that can reach the level of single molecule detection. Now, whether it is a Raman spectroscopy publication or a Raman spectroscopy conference, SERS is one of the most concerned content. In recent international Raman spectroscopy conferences, SERS chapters are the largest chapters. In recent years, the number of papers on SERS has also increased significantly. SERS and TERS will have great development potential not only in the field of surface science research, but also in the field of life sciences, which can contribute to the research of various important life science systems and solve basic problems. One of the advantages of Raman spectroscopy over infrared spectroscopy is that it is more convenient to use Raman to study aqueous solutions, and many researches in life science often require aqueous environments. Resonance Raman, surface-enhanced Raman and non-linear Raman spectroscopy and their combination will become important research methods in the frontiers of life sciences. Because the 21st century is the century of life sciences, I think it is also the technology of nanotechnology and laser technology. century.

Raman spectroscopy related technologies

Raman spectroscopy surface enhancement

Since 1974, Fleischmann et al. Found that the pyridine molecules adsorbed on the roughened Ag electrode exhibited a large Raman scattering phenomenon. In addition, the surface of the active support selected the adsorption molecules to suppress the fluorescence emission.
Raman spectroscopy
The signal-to-noise ratio of laser Raman spectroscopy is greatly improved. This surface enhancement effect is called surface enhanced Raman scattering (SERS). SERS technology is a new surface testing technology that can study the structural information of material molecules at the molecular level.

Raman spectroscopy

High-temperature laser Raman technology is used in metallurgy, glass, geochemistry, crystal growth and other fields. It is used to study the high-temperature phase transition process of solids and the bond structure of melts. However, these tests need to be performed at high temperatures, and conventional Raman instruments must be technically modified.

Raman spectroscopy

When the laser resonance Raman spectroscopy (RRS) generates a laser frequency that is close to or coincides with an electronic absorption peak of a molecule to be measured, the intensity of one or more characteristic Raman bands of this molecule can reach 104 in the normal Raman band. 106 times, and observed the overtone and combined vibration spectrum which are hard to appear in the normal Raman effect and whose intensity is comparable to the fundamental frequency. Compared with normal Raman spectroscopy, resonance Raman spectroscopy has high sensitivity. Combined with surface enhancement technology, the sensitivity has reached single molecule detection.

Raman spectroscopy confocal microscopy

Micro Raman spectroscopy is an application technology that combines Raman spectroscopy and microanalysis. Compared with other traditional technologies, it is easier to directly obtain a lot of valuable information. Confocal microscopic Raman spectroscopy not only has the characteristics of conventional Raman spectroscopy, but also has its own unique advantages. Complemented by a high-power optical microscope, it has the characteristics of micro, in-situ, polyphase, good stability, and high spatial resolution. It can realize point-by-point scanning and obtain high-resolution three-dimensional images. It has a wide range of applications in tumor detection, cultural relics archeology, public security law and other fields.

Raman spectroscopy Fourier transform

Fourier transform Raman spectroscopy is a new technology developed in the 1990s. In 1987, Perkin Elmer introduced the first near-infrared excited Fourier transform Raman spectroscopy (NIR FT-R) instrument, which uses Fourier transform technology to collect signals. , Accumulate multiple times to improve the signal-to-noise ratio, and irradiate the sample with a near-infrared laser of 1064mm, which greatly reduces the fluorescent background. Since then, Fr-Raman has shown tremendous vitality in the non-destructive structural analysis of chemical, biological, and biomedical samples.

Raman spectroscopy fiber method

The introduction of optical fiber makes it possible for Raman spectrometers to be used in industrial online analysis and field telemetry analysis. Huy et al. Used two 10 m long and 100 m diameter fibers with a laser wavelength of 514.5 nm to analyze a benzene / heptane mixture, and obtained very good results. Benoit et al. Used an optical fiber sensor in a Raman spectrometer to increase the Raman signal of a liquid sample by a factor of 50. Cooney et al. Compared the results of a single fiber with multiple fibers in a Raman spectrometer and found that the application of multiple fibers will improve the effectiveness of collecting Raman light. Cooper et al. Used fiber-optic remote-controlled Raman technology to analyze the xylene isomers in petroleum dyes. In recent years, foreign countries have applied 1550nm fiber laser and EDFA fiber amplifier technology to Raman scattering type distributed fiber temperature sensor systems, and achieved good results. Distributed fiber Raman photon temperature sensor has become the development trend of fiber sensing technology and detection technology. Because of its unique performance, it has become a new detection device in industrial process control and developed into an industrial automation measurement network.

Raman spectroscopy solid photoacoustic method

Photoacoustic Raman technology is a non-linear optical storage technology that uses photoacoustic methods to directly detect energy stored in a sample due to coherent Raman processes. The photoacoustic Raman signal is proportional to the imaginary part of the third-order Raman polarizability of the solid medium. The shortcomings of Rayleigh scattering and Brillouin scattering interference, have high sensitivity (can detect the Raman coefficient of 10-6cm-1), high resolution and basically no optical background and other advantages. In gas
Raman spectroscopy
The ideal results were obtained in the detection and analysis of liquid samples. Because it does not have strict phase matching angle requirements like the coherent Stokes Raman process, it is also suitable for studying the properties of solid media. Barrett et al. Theoretically analyzed the photoacoustic Raman spectroscopy process in a gas sample, but in contrast, the photoacoustic Raman effect of a solid medium is coupled by the local thermal energy generated by the coherent Raman gain process to the vibration of the sample itself The thermoelastic process of the mode, for the anisotropic structure of the medium, the third-order nonlinear Raman polarizability tensor form shows symmetry, so the situation is much more complicated. The parallel model and thermoelastic theory are used to derive the solid medium sample. Analytical expressions of the mid-photoacoustic Raman signal analyze some characteristics of the photoacoustic Raman effect in solids.

Raman spectroscopy

In the past two years, Raman has been used in combination with many other micro-analysis and testing instruments, including: Raman-SEM; Raman and Atomic Force Microscopy AFM / NSOM); Raman-infrared (Raman-iR); Raman-laser scanning confocal microscope (Raman-CLSM). The focus of these combinations is in-situ detection of micro-regions. Get more information and improve reliability through combination. [1]

Raman spectroscopy analysis

1.Raman spectroscopy analysis technology for single channel detection
2.Raman spectrum analysis technology of multi-channel detectors represented by CCD
3.FT-Raman spectral analysis technology using Fourier transform technology
4.Resonance Raman spectroscopy analysis technology
5. Surface enhanced Raman effect analysis technology

IN OTHER LANGUAGES

Was this article helpful? Thanks for the feedback Thanks for the feedback

How can we help? How can we help?

RELATED ARTICLES