Application of Optical Spectroscopy in Biological Systems

Conceptually, a typical spectroscopic experiment is extremely simple. Electromagnetic radiation at a certain nominal wavelength λ is allowed to impinge on the sample. Then some properties of the radiation that emerges from the sample are measured. One of the simplest properties is the fraction of the incident radiation absorbed or dissipated by the sample. (Typical techniques are optical absorption spectroscopy, some modes of NMR spectrometry and various elastic scattering techniques.) Instead, one can examine the radiation emitted by the samples at wavelength other than that used for excitation. (Fluorescence, Phosphorescence, Raman scattering and inelastic light scattering are examples.) Not only the emergent intensity, but also the distribution of emergent frequencies, is sources of information. In more complex techniques, not just intensity is detected, but also the kind and degree of polarization of the radiation emitted by a sample. (ORD, CD and fluorescence polarization fit into this category.)