Raman imaging guide
The basic principle of Raman imaging
Raman imaging is what?
Basic knowledge of Raman spectra
Raman imaging based on two powerful analysis technology of organic combination of Raman spectroscopy and microscopy.
In the Raman spectra, inelastic scattering of monochromatic light (laser) carries information used study the chemical properties of matter.Typically, the process condition is even contact.
Basic knowledge of Raman microscope
Traditionally, optical microscope to observe a very small sample.Imagine, use 100 x object lens to see 1 microns diameter of particles.
If in the microscope/Raman spectrometer, to the small particles for chemical analysis.If you put these spectral data with 2 d or 3 d space information together, get the Raman imaging we said.
About Raman imaging
Now, first select the microscope photograph of a small point on the sample photos as a measurement point, and then on the sample of the measurement point moves to objective measure below.
According to the step size of sample machine, will produce the sample space resolution spectral information.And if the execution of "grid" measurement, such as the size of a 10 x 10 microns "grid", now has generated is called the Raman imaging.
The basic principle of Raman imaging
Containing molecular chemistry every pixel in the image.In the Raman image, the pixel is madeThe completeRaman spectra.This means that Raman image contains a lot of chemical analytical spectral data, can be a false color image can be traced to strengthen represent the character such as chemical structure and composition of the sample.
In order to answer some problem analysis, spectral data can be parsed by a variety of ways.For example, a typical application is by generating false color images can be characterized the characteristics of the sample.It's more clearly shows the sample chemical structure and composition distribution.
The generation of Raman imaging
Main used for Raman micro Raman imaging tests, and the specific measurement process is very simple.Raman spectrum in the test area defined in a certain distance for point by point sampling interval, the Raman data obtained contains spatial information.In the whole test process, the laser focus has always been the focus in on a single point on the sample test, the sample is below the point move to the laser, until the interested region is "imaging".
Spatial information can be obtained is one-dimensional, two-dimensional or three-dimensional, so even for chemical exploration sample in advanced!In this way, we found that the analysis question answered, including the uniformity of coating characterization, access to information elements distribution or particles and other pollutants.
Raman imaging of frequently asked questions (FAQ)
Common problems about Raman imaging
Micro Raman spatial resolution
The confocal micro Raman spectrometer optical element of the Raman signal filtering.Therefore, confocal pinhole size determines the measurement point of collecting Raman signal and improve the spatial resolution.
Elaborate the spatial resolution of the confocal micro Raman eventually by light diffraction limit:
- dradial= 0.61 lambda /NA
- daxial= 1.4 lambda/NA
Therefore, confocal microscopic Raman can realize the analysis and characterization of the characteristics of the sample, the spatial resolution can be as low as half a micron.
The basic principle of Raman imaging
Raman imaging is a use of generate the image spectral and spatial information technology.Acquisition of Raman spectra from the different space position, then each spectrum was reduced to only one value of the corresponding pixel then each Raman spectrum represented as a value for the pixel.
The most common method is to use the peak intensity of Raman imaging chemical distribution and concentration.Multiple peak intensity and peak displacement, peak ratio and peak width is also used to generate Raman images in a variety of circumstances.Pixel values are usually displayed as gray or false color.
The length of the Raman imaging need
Raman imaging to gather a lot of Raman spectra.Accordingly, to contain thousands or even millions of Raman spectra of the image, the total measurement time may be very long.
Sensitivity is vital for generating Raman image, it can shorten the Raman spectra of each acquisition time.Therefore, we should optimize the target samples, laser power and the choice of optical efficiency, to speed up the image acquisition.
The surface of the micro Raman can test the following features
Yes, confocal microscopic Raman in both horizontal and vertical spatial resolution is limited by diffraction.As a result, the laser scattering and Raman scattering is not material under the condition of strong absorption, longitudinal depth analysis and three villa Raman imaging can be used to analysis chemical distribution under the surface of the sample.
Micro Raman analysis of fluid samples
Compared with the Fourier infrared, Raman spectroscopy is one of the main advantages of water of the Raman signal is very weak, can measure the water dissolved compounds and are not subject to the strong interference.
The droplets can be placed on a glass slide is measured directly.Samples for evaporation, quartz glass or recessed slide rail with quartz cover glass allows Raman measurement of liquid in a closed container, have no background signal contribution.For volatile sample, quartz color dish or concave with a quartz glass cover can slide in the absence of background signal in an airtight container liquid Raman measurement directly.
