Raman spectroscopy how does it work

These images display distribution of individual chemical components, polymorphs and phases, and variation in crystallinity. Uses of Raman Spectroscopy. Raman spectroscopy can be used in microscopic analysis, with a spatial resolution in the order of 0. The Raman microscope combines a Raman spectrometer with a standard microscope and enables high magnification visualization of a sample and Raman analysis using a microscopic laser spot.

Raman spectroscopy can be used for the analysis of micron size particles of volumes. It can also be used to analyze individual layers within a multilayered sample and pinpoint contaminants and features under the surface of a transparent sample. Raman spectroscopy is often used in art and archeology to characterize pigments, ceramics and gemstones. It can even be used for the analysis of different layers in a multilayered sample e.

Motorized mapping stages allow Raman spectral images to be generated, which contain many thousands of Raman spectra acquired from different positions on the sample. From these beginnings through to the present day, HORIBA Scientific and its associated companies have been at the forefront of the development of Raman spectroscopy.

It developed as the molecular analog of Castaing's electron microscope. As such it provides bonding information on condensed phase materials; in addition to detection of molecular bonding, identification of the crystalline phase and other more subtle effects also proved of significant interest. The microscope was initially integrated with the scanning double grating monochromator c. When high sensitivity, low noise multichannel detectors became available mid s , triple stage spectrographs were introduced with the microscope as an integrated component.

In the holographic notch filters were demonstrated to provide superior laser rejection so that a Raman microscope could be built on a single stage spectrograph and provide enhanced sensitivity. Compared with the original scanning double monochromators, collection times for comparable spectra resolution and signal to noise for a given laser power is now at least two to three orders of magnitude higher than what it was 35 years ago.

These core innovations have been pioneered in the HORIBA Scientific labs in northern France by the scientists and engineers who were trained in Professor Delhaye's laboratory, taking advantage of hardware as it came available. This included holographic gratings, notch filters, air-cooled lasers, multichannel detectors first intensified diode arrays and then CCDs , high power computers, and associated developments in electronics and software.

Because of the leadership that HORIBA Scientific and its associated companies have played in the industry, well- equipped applications laboratories with highly qualified scientists have been employed continuously for more than 30 years in developing the applications of these innovative instruments.

Raman spectra can be acquired from nearly all samples which contain true molecular bonding. This means that solids, powders, slurries, liquids, gels and gases can be analyzed using Raman spectroscopy. He was awarded the physics Nobel Prize for this great discovery. By studying the vibration of the atoms we can discover the chemical composition and other useful information about the material. The Raman effect is very weak; only about 1 part in 10 million of the scattered light has a shifted colour.

This is too weak to see with the naked eye, so we analyse the light with a highly sensitive spectrometer. Raman scattering offers significant advantages for the investigation of materials over other analytical techniques, such as x-raying them or seeing how they absorb light e. Discover more about Raman spectroscopy, what it can tell you and why we use it. Precision measurement and process control. Position and motion control. Request engineer support and learn more about our repair , calibration or refurbishment services.

Therefore, a light wave or photon carries more energy E the larger the frequency or, alternatively, the smaller the wavelength is Equation 2. The wavenumber is directly proportional to the energy of the photon Equation 3 and usually expressed in units of reciprocal centimeters cm —1 to give easy to read numbers. Figure 2: Electromagnetic spectrum: Depending on the energy of the electromagnetic radiation, different processes in atoms and molecules can be induced by the interaction between light and matter.

The above description is valid for a single light wave or photon. However, a light beam consists of many light waves with different frequencies propagating in the same direction.

Each frequency contributes to the beam with intensity I i. The intensity of a light beam is the quantity that is ultimately measured with the detector of a spectrometer. The intensity distribution of all frequencies is called the spectrum of this light beam.

Other spectral regions are e. For Raman spectroscopy, visible light or infrared IR light is used for the excitation. The most important physical parameters and their corresponding equations relevant for Raman spectroscopy are summarized in Table 1. When a light beam hits matter, it will interact with it in a specific way, dependent on the interplay between the light waves and the atoms and molecules that make up the matter. The interaction may leave the energy of matter and light unchanged e.

The processes used in spectroscopy to characterize matter belong to the latter category. The transfer of energy from light to matter leads to an excitation. The following section outlines the most important excitation processes required to understand Raman spectroscopy: absorption, fluorescence, and scattering.

Light energy in some parts of the electromagnetic spectrum is partially transferred to the matter. This means some light waves pass through the matter without modification transmission , while some light is absorbed by the sample. Absorption : Some of the incident wavelengths are partially absorbed in the sample, while other wavelengths are transmitted without much loss in intensity. Figure 3. Matter can reemit absorbed light again by an independent process called fluorescence.

Figure 4. When an intense light source e. However, a tiny fraction of the scattered light interacts with the matter it hits in a way that it exchanges small amounts of energy, which is called inelastic scattering.

The change in energy of the scattered light results in a changed frequency and wavelength. The microscopic origin of this Raman interaction is an excitation or de-excitation of molecular vibrations in the matter. The characteristics of these vibrations determine the wavelength of the inelastically scattered light. From measuring the intensity distribution spectrum of the scattered light it is hence possible to deduce information about the vibrational structure of the substance illuminated.

Therefore, Raman spectroscopy belongs to the group of vibrational spectroscopies. Raman scattering : Most of the incident yellow light is scattered elastically in all directions. Small amounts of light, usually with higher wavelengths orange, red , are also scattered inelastically after interaction with the molecules of the sample.

Figure 5. Each of these processes can be exploited to extract information about the chemical and physical nature of the sample. The exact type and extent of molecular properties deducible depends on the type of spectroscopy used.

The two main vibrational spectroscopies are infrared IR spectroscopy and Raman spectroscopy. Raman spectroscopy employs the Raman effect for the analysis of substances. The basics of Raman scattering are explained below. There are three scattering processes that are important for Raman spectroscopy and Raman imaging techniques: [3].

Anti-Stokes Raman scattering is another inelastic scattering process. Here, a specific amount of energy is transferred from a molecular vibration to the photon.