Tricks of the light

A research team at the University of Southampton has developed a technique for using Raman scattering an optical phenomenon for the rapid detection and identification of minute quantities of molecules in a sample of liquid. Gloucester Hospitals NHS Foundation Trust is conducting trials of the technique as a tool for making differential diagnosis of conjunctivitis from tear fluid.

When monochromatic light, such as from a laser, is focused on a sample, some light is transmitted, some absorbed and some scattered. Most of the scattered light has the same wavelength as the incident light this is known as Rayleigh scattering. A tiny fraction around one in 107 photons is scattered at different wavelengths, characteristic of the molecules contained in the sample.