What Is a Raman Spectrometer?
A Raman spectrometer is a device that can analyze chemical structures and evaluate physical properties by measuring the light scattered when a substance is irradiated with light.
Scattered light contains light of various wavelengths, with a light of the same wavelength as the incident light being called Rayleigh scattered light and light of a different wavelength being called Raman scattered light. The Raman spectrometer analyzes and evaluates by detecting the Raman scattered light.
The Raman spectrometer consists of a laser light source, a diffraction grating, and a sensitive detector for detecting weak Raman scattered light. It can measure the structure of almost any material, regardless of whether it is a gas, liquid, or solid, without any preprocessing.
In addition, Raman spectrometers are used in many fields because they can identify molecules in a non-contact and non-destructive manner.
Uses of Raman Spectrometers
Raman spectrometers are used in a great many fields, including batteries, displays, food science, and the medical and pharmaceutical fields, as instruments for analyzing chemical and molecular structures, regardless of whether they are organic or inorganic materials.
It can be used to analyze the life, performance, and degradation state of batteries, as well as quantitative analysis of proteins, lipids, and food dyes contained in food products. In pharmaceuticals, Raman spectroscopy can be used to examine crystal structures, which are then used to determine solubility and efficacy.
Principle of Raman Spectrometers
Raman spectrometer is a device to evaluate the structure and physical properties of a substance by detecting Raman scattered light from the substance. It consists of a light source, a spectrometer for extracting Raman scattered light from scattered light, and a detector for detecting Raman scattered light.
1. Light Source
A light source with a single wavelength and high light intensity is used as a light source. This is because the narrower the line width of the light source, the higher the resolution of the analysis, and because the Raman scattering light is a weak signal. In most cases, solid-state lasers are used.
2. Spectroscope
A monochromator emitting light at a single wavelength or a polychromator emitting light at a fixed wavelength is used. Spectroscopy is performed using a diffraction grating contained in the spectrometer. The diffraction grating is a glass substrate engraved with microscopic grooves at equal intervals, and is an element that uses the diffraction phenomenon of light to perform spectroscopy.
3. Detector
Since Raman scattered light is very weak, a highly sensitive detector is used. It is desirable to detect many spectrally separated wavelengths simultaneously. Therefore, a linear image sensor is used.
Other Information on Raman Spectrometers
1. Comparison With Infrared Spectrometer
Infrared spectrometers are often compared to Raman spectrometers. Both instruments are capable of analyzing chemical structures and evaluating physical properties based on the vibrational spectra of molecules. However, there are differences in the spectra that can be measured.
The Raman spectrometer analyzes scattered light, while the infrared spectrometer analyzes based on the optical absorption of a substance, so the spectra that can be measured by both are different. Other comparative features are shown below.
Features of Raman Spectrometer
- Sample size can be as small as 1μm
- Capable of measuring samples in glass containers
- Measurement in aqueous solution is possible.
- No pre-treatment such as dilution is required
- Expensive equipment
- Sample may be damaged by measurement
Features of Infrared Spectrometer
- Sample size can be as small as 10 μm
- Cannot measure in glass containers
- Measurement in aqueous solution is limited
- Sample identification is easy
- Inexpensive equipment
- Sample is not easily damaged by measurement
2. Raman Scattering Light to Be Detected
Raman spectrometer analyzes and evaluates materials by shining light on them and detecting the scattered light. There are two types of scattered light: elastic scattering and inelastic scattering.
Elastic scattering produces scattered light with the same wavelength as the light before scattering, while inelastic scattering produces scattered light with a wavelength different from that before scattering. The light detected by a Raman spectrometer is Raman scattered light produced by inelastic scattering. The Raman scattering light is generated based on the vibrational and rotational levels of the material.
Since these levels are molecular-specific energy levels, the Raman scattered light is a molecule-specific spectrum. Therefore, by detecting the Raman scattered light, the Raman spectrometer can measure the wavelength deviation from the incident light and identify the molecule.