Raman Spectroscopy

Raman spectroscopy is a method by which details of the constituents of a molecule can be understood by examining the frequency shift of scattered light after it has impinged on the target material.

This requires the application of the Raman Effect which depends on the nonlinear properties of molecular vibrations. In Raman the electric field of light incident upon the molecule interacts with electric fields of this molecule. The non-linearity causes inelastic scattering of the light resulting in a change in frequency. This so called Raman shift depends quantitatively upon the energy levels of the molecular vibrations specified in wave numbers (1/cm) where:

Wavelength (in micrometers) = 10,000 / wave numbers

Raman scattering is a very weak effect. The strength of the Raman emission is typically a million times less than the strength of the illuminating beam. Thus measuring the Raman-scattered radiation is a challenging task. There are several reasons for this, including the weakness of the scattering, the intensity of the laser light, and often the closeness (in frequency) of the Raman-scattered light to the original laser light.

Instruments require that the laser be of low noise and able to be well focused with a stable spatial beam. More advanced systems require lasers to exhibit narrow frequency bands so that better resolutions can be reached and for this single longitudinal mode lasers are preferred.

Popular wavelengths include 1064nm, 785nm and 532nm. There is also considerable interest in the UV (266nm for example) although this can result in unwanted auto-fluorescence both in the sample and in the optics of the instrument.

KLASTECH lasers such as the Senza^® and Scherzo^® range are already utilized for such applications.