On interaction of matter with a beam of radiation, the radiation may be transmitted, absorbed, polarized, reflected, refracted, diffracted, scattered, or it may excite fluorescence (Fig. 1). Transmission is the interaction of radiation with matter without loss of energy while absorption involves attenuation of radiation energy. Polarization takes place when one of the radiation components is filtered. Emission of lower energy radiation compared with incident radiation is referred to as fluorescence. Radiation is said to undergo reflection when it is deflected in the direction of the radiation source, refraction when it bends on passing into different media, and diffraction when radiation bends around obstacles and spread out of small openings. Deflection of radiation in random directions is called scattering.