Spectroscopy Series VOL. 2: Components of a Raman Spectrometer

Hello friends who love science in this opportunity I want to present the continuation of my previous post where I talked about the theory involved in the phenomenon Raman. Where I am going to show the components used to describe the Raman spectroscopy and in the passing of days and I will explain different important spectroscopy techniques to measure this phenomenon and obtain spectra of different materials.

As mentioned in my previous post, Raman spectroscopy provides us with very important information about molecular vibrations within the crystalline structure of a material, which can be used both for the identification and for the quantification of samples of different materials that we wish to characterize.

The basic principle of this technique refers to the illumination by means of a monochromatic light source in the material and detecting said scattered light, this light has the same frequency as the source of excitation, that is, most of the scattered light and this is known as the Rayleigh line or elastic dispersion, the small portion of scattered light that remains moves in energy from the frequency of the laser light due to electromagnetic interactions or vibrations within the molecule of the characterized material. After having happened all this phenomenon and when the intensity of the light changes in function of the frequency, we obtain the spectrum that we are looking for, that is denominated Raman spectrum.

Next I will present the appropriate equipment to measure raman spectroscopy, explaining in detail each component that make up this device.

Components used in Raman spectroscopy

Laser

We can say that it is the main component for the operation of this technique, since it is the source of excitation, without it the light could not be dispersed. For this technique, it is recommended to use the Helium-Neon laser. although there is a great variety. This type of laser has a great power so it is the right one to produce the Raman scattering, since the intensity is very weak, this laser helps to intensify it even more so it needs a very powerful source of excitation, that is to say that the intensities are greater than the noise of the equipment. The He-Ne laser has a large wavelength of approximately 630 nm, making it the most used source, due to its high degree of phase coherence, which makes it very monochromatic. Other types of laser used are those of Ar that have a wavelength of around 500 nm.

Optical fiber

This element consists of the medium through which the laser light travels, towards the sample of the material that it is desired to characterize and later to excite it. There are two ways in which light travels through fiber optic cabling, the first is the light is guided to the optical head of the spectrometer, and the other is the one that collects and transports the laser light to the monochromator. Normally in the experiments when we assemble the equipment a length greater than 10 meters with a diameter of 110 μm is used.

Optical head

Presents various components that form the optical head:

Camera, This device allows to control the area where the incidence of the laser is correctly produced, it consists of a small camera that provides adequate information on the sample image of the material and presents a mirror where the operator can place it in the way he wishes and It is controlled through a movable screw.

The filter, where the wavelength interference occurs, its main function is to allow the laser to pass to the frequency that we want. It is composed of the nocht and edge filters, which eliminate all contact information during the procedure in order to avoid errors in the measurements.

^{Components of the optical head of a spectrometer}

Lens, focuses the concentration of laser light in the area where the sample is analyzed, is also responsible for collecting all the scattered light and then perform the corresponding analysis.

The mirror, allows you to create the bidirectional path between light and excitation, its objective is to reflect the light that goes to the sample to be characterized, and then the information is collected again through the optical fiber.

Monochromator

^{Scheme of the spectrometer shows the function performed by the monochromatorLicensed Creative Commons by Sobarwiki}

The main function of this component is to capture the signal sent by the laser, this happens when the light is captured by the optical head of the spectrometer, which is taken by means of the fiber optic cable, where the signal finally reaches the monochromator. This component is formed by input and output slots, mirrors and collimator.

Coupled charging device

It is a capacitor that converts the photons sent by the laser through the optical fiber, after passing through the mirrors in a similar signal, the CCD is responsible for capturing this signal, it receives it digitizes the sent data and finally sends it to a computer that shows the light spectra of the material.

Software

Finally, after carrying out the entire process previously explained with the various devices that make up the spectrometer, we get to the computer software where we can obtain the spectrum and perform its subsequent qualitative analysis. Through this computer program you can visualize the obtained spectral pattern, there is a great variety of programs that help to analyze this type of information, the most used are the LabSpec or the SpectraPro, it allows to observe and identify bands in the vibrations modes , spectral lines, Fourier transforms, etc.

Soon to share with you all more interesting topics about the world of spectroscopy.

Until next time...

If you want more information about the subject you can visit the following links:

^{The Raman Spectrophotometer}

^{Components of a Raman Spectrometer}

^{Raman scattering}

^{What is the Raman effect?}

^{Raman spectroscopy}

^{Article researchgate Raman}

Video credits @gtg

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