ABSTRACT

All elec tromagnetic radia tion o riginates in t he accelera tion o f charge. In antennas at radio frequencies, the charges are electrons pumped back and forth by the transmitter resulting in a radiated electromagnetic wave as a solution of the Helmholtz vector wave equations. I n o ptical emissio n, t he lig ht p hotons a re emi tted as charge carriers relax (decelerate) from an excited energy state to a lo wer ener gy st ate (F igure 36.1). I n t hermal imagin g, t he emission comes from photons emitted by the relaxation of thermally excited atoms and molecules-that is, from internal thermal energy modes in the material under observation.