Absorption measurements using low coherence interferometry

The basic use of Low Coherence Interferometry is measuring the intensity of light reflected from defined depths in a partially transparent object. The light back-scattered from a certain depth in the object carries information about the medium that it has passed through. Absorption and scattering attenuate the intensity of the light, and will thus reduce the interference signal from a given depth. One single interference measurement will not discriminate between attenuation due to absorption and scattering. However, by measuring the interference signal at several different wavelengths, discrimination between the two parameters is possible, if they vary differently with wavelength. Especially when measurements are performed in a wavelength region where the scattering coefficient is constant, measurements at two different wavelengths will give the difference in absorption at the two wavelengths. We present preliminary measurements on scattering and absorbing solutions showing a qualitative difference in absorption measured at 810 and 830 nm. As an absorbing solution we used a commercially available dye with an absorption maximum at 800 nm while intralipid was used to introduce scattering. The aim of our work is to measure the oxygenation saturation of blood through absorption measurements at different wavelengths using Low Coherence Interferometry.