Interaction of electromagnetic radiation with matter.

Matter can reflect, transmit, or absorb electromagnetic (radiant) energy (Figure 1 above). If matter is transparent to radiant energy, the energy will pass through it unchanged. If matter is a perfect reflector, the energy will not be changed except to change the direction in which it is moving. If electromagnetic radiation is absorbed by matter, then there is a transfer of energy from the radiant energy to the medium that is doing the absorbing. This may result in an increase in the vibrational energy of the molecules of the absorbing medium if it is a solid, or increased molecular velocities if the medium is a gas, or chemical change if the radiant energy is of sufficiently high energy (high frequency) to break chemical bonds or change the energy level of electrons. In general all of these types of absorption results in a rise in temperature of the absorbing medium.