Every object in the universe is made up of atoms.
Electrons are the negatively charged particles and protons are the positively charged particles. Neutrons have no charge.
Hence, neutrons are referred as neutral particles. The strong nuclear force between the protons and neutrons makes them stick together to form the nucleus. The electrons revolving around the nucleus have different energy levels based on the distance from the nucleus.
The electrons revolving very close to the nucleus have lowest energy level whereas the electrons revolving at the farthest distance from nucleus have highest energy level. For example, if the lowest energy level is E 1 the next energy level is E 2 and next is E 3 , E 4 and so on. The electrons in the lower energy state E 1 needs extra energy to jump into next higher energy state E 2.
This energy can be supplied in the form of the electric field, heat or light. After a short period, they again fall back to the lower energy level by losing their energy.
Difference Between Spontaneous and Stimulated Emission
The electrons in the higher energy level or higher energy state lose energy in the form of light before they fall back to the lower energy state. In lasers, the way light or photons interact with atoms plays an important role in its operation. The photons interact in three ways with the atoms:.
Difference between Spontaneous and Stimulated Emission of Radiation
The process of absorbing energy from photons is called absorption of radiation. It is well known that there are different energy levels in an atom. The electrons that are very close to the nucleus have lowest energy level. These electrons are also known as ground state electrons. Let us consider that the energy level of ground state electrons or lower energy state electrons is E 1 and the next higher energy level or higher energy state is E 2.
When ground state electrons or lower energy state electrons E 1 absorbs sufficient energy from photons, they jump into the next higher energy level or higher energy state E 2. In other words, when the ground state electrons absorb energy which is equal to the energy difference between the two energy states E 2 — E 1 , the electrons jumps from ground state E 1 to the excited state or higher energy level E 2.
The electrons in the higher energy level are called excited electrons. The light or photons energy applied to excite the electrons can be mathematically written as.
Absorption of radiation, Spontaneous emission and Stimulated emission
Absorption occurs only if the energy of photon exactly matches the difference in energy between the two electron shells or orbits. The process by which excited electrons emit photons while falling to the ground level or lower energy level is called spontaneous emission.
Electrons in the atom absorb energy from various sources such as heat, electric field, or light. The electrons in the excited state do not stay for a long period because the lifetime of electrons in the higher energy state or excited state is very small, of the order of 10 -8 sec.
Hence, after a short period, they fall back to the ground state by releasing energy in the form of photons or light. The energy of the emitted photon is directed proportional to the energy gap of the material. The materials with large energy gap will emit high-energy photons or high-intensity light whereas the materials with small energy gap will emit low energy photons or low-intensity light.
The energy of released photon is equal to the difference in energies between the two electron shells or orbits. The energy of the excited electrons can also be released in other forms such as heat. In spontaneous emission, the electrons changing from one state higher energy state to another state lower energy state occurs naturally. So the photon emission also occurs naturally or spontaneously.
They flow in the random direction. Unlike the spontaneous emission, in this process, the light energy or photon energy is supplied to the excited electrons instead of supplying energy to the ground state electrons. The stimulated emission is not a natural process it is an artificial process. In stimulated emission, the electrons in the excited state need not wait for natural spontaneous emission to occur.
An alternative method is used to stimulate excited electron to emit photons and fall back to ground state.
The incident photon stimulates or forces the excited electron to emit a photon and fall into a lower state or ground state. The energy of a stimulating or incident photon must be equal to the energy difference between the two electron shells. In this process, the excited electron releases an additional photon of same energy same frequency, same phase, and in the same direction while falling into the lower energy state.
Thus, two photons of same energy are released while electrons falling into the ground state. In stimulated emission process, each incident photon generates two photons. The photons emitted in the stimulated emission process will travel in the same direction of the incident photon.
Many ways exist to produce light, but the stimulated emission is the only method known to produce coherent light beam of photons with the same frequency. All the photons in the stimulated emission have the same frequency and travel in the same direction. Skip to content.
May 15, September 8, Asif Shaik absorption of light or radiation , spontaneous emission , stimulated emission. The photons interact in three ways with the atoms: Absorption of radiation or light Spontaneous emission Stimulated emission Absorption of radiation or light The process of absorbing energy from photons is called absorption of radiation. Spontaneous emission The process by which excited electrons emit photons while falling to the ground level or lower energy level is called spontaneous emission.