Question

Eienstein coefficients for spontaneous and stimulated emission

Answer 1

Answer:

The three processes are referred to as spontaneous emission, stimulated emission, and absorption. With each is associated an Einstein coefficient, which is a measure of the probability of that particular process occurring.

Explanation:

Answer 2

Answer:

Einstein showed the interaction of radiation with matter with the help of three processes called stimulated absorption, spontaneous emission and stimulated emission. He showed in 1917 that for proper description of radiation with matter,the process of stimulated emission is essential.Let us first derive the Einstein coefficient relation on the basis of above theory:

Explanation:

Let N1 be the number of atoms per unit volume in the ground state E1 and these atoms exist in the radiation field of photons of energy E2-E1 =h v such that energy density of the field is E.

Let R1 be the rate of absorption of light by E1 -> E2 transitions by the process called stimulated absorption

This rate of absorption R1 is proportional to the number of atoms N1 per unit volume in the ground state and proportional to the energy density E of radiations.

That is                                    R1∞ N1 E

Or                                          R1 = B12N1 E                                               (1)

Where B12 is known as the Einstein’s coefficient of stimulated absorption and it represents the probability of absorption of radiation. Energy density e is defined as the incident energy on an atom as per unit volume in a state.

Now atoms in the higher energy level E2 can fall to the ground state E1 automatically after 10-8 sec by the process called spontaneous emission.

The rate R2 of spontaneous emission E2-> E1 is independent of energy density E of the radiation field.