Question

How did Einstein expand the light quantum theory in 1917?

Answer 1

Let us go to the basics first .

This question is based on the concept of

1. Light quantum theory 1917

2. Quantum of energy

3. Spontaneous emission

4. Cascading effect of emission

The detail is as per following:

Einstein expanded light quantum theory in 1917 by suggesting:

1. Albert Einstein first broached the possibility of stimulated emission in a 1917 paper.

2. Einstein devised an improved fundamental statistical theory of heat, embracing the quantum of energy.

3. First, Einstein proposed that an excited atom in isolation can return to a lower energy state by emitting photons, a process he dubbed spontaneous emission.

4. Atoms will only absorb photons of the correct wavelength: the photon disappears and the atom goes to a higher energy state, setting the stage for spontaneous emission.

5. Second, his theory predicted that as light passes through a substance, it could stimulate the emission of more light.

6. Einstein postulated that photons prefer to travel together in the same state. If one has a large collection of atoms containing a great deal of excess energy, they will be ready to emit a photon randomly.

7. However, if a stray photon of the correct wavelength passes by (or, in the case of a laser, is fired at an atom already in an excited state), its presence will stimulate the atoms to release their photons early–and those photons will travel in the same direction with the identical frequency and phase as the original stray photon.

8. A cascading effect ensues: as the crowd of identical photons moves through the rest of the atoms, ever more photons will be emitted from their atoms to join them.

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