What is Raman Spectroscopy?
Raman spectroscopy is a non-destructive chemical analysis technique that offers detailed information regarding chemical structure, phase and polymorphic crystallinity, and molecular interactions. It is ideal for sample identification and quantification processes.
Raman spectroscopy works by shining a monochromatic light source—usually a laser—onto a sample and detecting the scattered light. Most scattered light is at the same frequency as the excitation source and does not offer helpful information, this is known as either Rayleigh or elastic scattering.
A small amount of the scattered light shifts in energy from the laser frequency because of interactions between the incident electromagnetic waves and the vibrational energy levels of the molecules in the sample. Plotting the intensity of the shifted light against the frequency produces a Raman spectrum of the sample.
Raman spectra are usually plotted according to the laser frequency. On this scale, the band positions sit at the frequencies corresponding to the energy levels of varying functional group vibrations.
What Information Does Raman Spectroscopy Provide?
Raman spectroscopy gives insight into the chemical structure and identity of a material, as well as its phase and polymorphism, intrinsic stress/strain, and contamination and impurity. Raman spectroscopy can also be employed for both qualitative and quantitative applications. Spectra are specific and chemical identifications can be carried out by using search algorithms against digital databases. Band areas are proportional to concentration, meaning Raman spectroscopy is amenable to straightforward quantitative analysis.
Benefits of Raman Spectroscopy
Raman spectra usually depict a distinct chemical fingerprint for a specific molecule or material, which can identify the material or distinguish it from others quickly. Alongside mapping (or imaging) Raman systems, images can be created based on the sample’s Raman spectrum. 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 0.5–1 µm using a Raman microscope. The Raman microscope combines a Raman spectrometer with a standard microscope and enables both high magnification visualization of a sample and Raman analysis using a microscopic laser spot.
Raman spectroscopy enables 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 frequently used for the analysis of solids, powders, liquids, gels, inorganic/organic and biological materials, pure chemicals, mixtures and solutions, as well as metallic oxides and their corrosions.
Raman spectroscopy is often used in art and archeology to characterize pigments, ceramics and gemstones. It is also used in geology to identify minerals and their distribution, fluid inclusions and phase transitions. Raman spectroscopy can also be used for disease diagnoses, ensuring uniformity and component distribution in pharmaceuticals and monitoring chemical reactions.
Lasers Suitable for Raman Spectroscopy
The laser excitation needs to be in the wavelength range 400–800 nm. The power required depends largely on the analysis that is being performed and the area of sample being excited. 532, 473 and 660nm are commonly used wavelengths. The bandwidth of the excitation beam can be a limiting factor in the resolution of the Raman system with lower bandwidths producing higher resolution. Single longitudinal mode lasers provide the highest resolution, but can introduce variation if they are not locked to that single mode.
Ruggedness and stability of the system are also factors to be considered when selecting the right laser for any application. Many lasers produced by Laser Quantum are suited perfectly to the needs of Raman spectroscopy and microscopy.
- gem family – 473, 532, 660 & 671 nm ideal for OEM integration
- ventus family – 473, 532, 660 & 671 nm ideal for scientific and research applications
- ventus solo – 532 nm, bandwidth narrowed to increase resolution
- torus family – 532 or 660 nm. Perfect for the highest resolution with stability from the mode locking
Other posts on our blog consider this subject, such as “Which Laser for Raman Spectroscopy?”
To request more information or a quotation for these or other Laser Quantum products, contact IL Photonics.