Raman Spectroscopy: Overview and Forensic Investigation Applications

Raman spectroscopy is a useful technique for the identification of a wide range of substances: solids, liquids, and gases. It is a straightforward and non-destructive technique. “Raman effect” was observed in practice for the first time in 1928 by C.V. Raman. This scientist was awarded the Nobel Prize in 1930 for this invention. Raman spectroscopy is frequency shifted by this Raman effect in the studied material or substance. Such spectroscopy is one of the vibrational spectroscopic techniques used to provide information on molecular vibrations and crystal structures. This method uses a fiber laser light source to irradiate a sample and generates an infinitesimal amount of Raman scattered light. The aforementioned type of spectroscopy involves illuminating a sample with monochromatic light and using a spectrometer to examine light scattered by the sample.

Raman spectrometry is a well-known, extremely precise analytical technique. This technique can be used to evaluate suspensions, slurries, and aqueous compounds. Raman spectroscopy uses a method known in science as vibrational spectroscopy, which is based on utilizing sensitivity to vibrations in molecules, and then this information is used to name the compound. Infrared (IR) spectroscopy also used the method of vibrational sensitivity and so, IR and Raman are popular forensic methods in laboratories. In laboratory conditions or out in the field Raman spectroscopy can accomplish successful identification of a variety of forensic sample types. Such popularity and continuous use throughout time is a result of their low false positive rates and high specificity.

As a consequence of Raman spectroscopy being specific to the chemical structure of a sample. It doesn’t destroy the sample in the process of its identification. In comparison with other analytical techniques, this feature is a great advantage. Narcotics are an example of organically-based chemical compounds. As they have specific molecules which vibrate at different frequencies, they can be differentiated from one other. The amount and wavelength of a molecule vibration are reliant on the number of atoms which are contained within the chemical compound and in what way they interact with different types of chemical bonds. The analysis of the vibrations can be used to identify the compound in a sample.

The spectrum of the scattered Raman signal is created from a sample by pointing a laser beam onto it in Raman spectrometers. The typical laser used for Raman spectroscopy is the 785 nm excitation system because it presents an optimal sensitivity to fluorescence, the balance of signal, overall function, and cost. In Raman spectroscopy laser excitation system of 1064 mn is used for sample analysis.

Raman spectrometers can come in portable and handheld sizes for in the field applications and quick screening. There are also a variety of laser excitation options that allow for the best-suited system to evaluate different sample types. Raman fiber optic probes are miniaturized without compromising their performance, which is enabled by the technology of direct deposition of the dielectric filters at the fiber end faces. It results in a small, cost-effective Raman probe for endoscopic and other applications.

Optromix provides fiber optic Raman probes, which are produced for multi-wave excitations in the range 690-785 nm, e.g. @785nm – “Fingerprint” spectral range with fluorescence reduction, and @690nm – “High wavenumber” spectral range for conventional Raman spectrometers. If you would like to buy fiber optic Raman probes, please contact us at info@optromix.com

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