Question

Concepts/Descriptions:

a. List the modes of interaction for photons and electron in a solid.

b. Contrast spontaneous emission and spontaneous emission of photons

Answer 1

Answer a) The behavior of photons in matter is completely different from that of charged particles. In particular, the photon’s lack of an electric charge makes impossible the many inelastic collision with atomic electrons so characteristic of charged particles. For this kind of radiation the most important mechanism of interaction are:

a) Photoelectric effect
b) Compton and Rayleigh scattering
c) Pair production

Answer b) Stimulated emission is the process by which an incoming photon of a specific frequency can interact with an excited atomic electron (or other excited molecular state), causing it to drop to a lower energy level. The liberated energy transfers to the electromagnetic field, creating a new photon with a phase, frequency, polarization, and direction of travel that are all identical to the photons of the incident wave.

Spontaneous emission is the process in which a quantum mechanical system (such as an atom, molecule or subatomic particle) transitions from an excited energy state to a lower energy state (e.g., its ground state) and emits a quantised amount of energy in the form of a photon.