Quantum scattering

The structure of matter is particulate and comprises atoms and molecules at the fundamental level. Atoms, in turn, have a nucleus with electrons orbiting around. The atom is electrically neutral though internally the positive and the negative charges are spatially segregated. Measurements are related to electronic transitions alone, the nucleus being stable with respect to a majority of external perturbations. When light falls on matter, photons may be absorbed by the medium, raising electrons to a higher energy level. Since the residence time of electrons diminishes with increase in energy, electrons invariably return to their original state, called the ground state . This transition is accompanied by the release of photons of appropriate frequency/wavelength and forms the measurement step in an experiment. The properties of the photon thus released may depend on the properties of the incident radiation and the material properties or any one of them.