Stimulated and spotaneous emission

In summary, the light emitted in spontaneous emission is polychromatic because it involves a variety of energy levels and produces multiple photons. However, in stimulated emission, the light can be made to be monochromatic by controlling the parameters and selecting a specific pair of energy levels to use. This is why devices that rely on stimulated emission, such as lasers, are designed to be as monochromatic as possible.
  • #1
ajayguhan
153
1
Why the light emitted in spontaneous emission is poly chromatic whereas the light in stimulated emissions is monochromanti?

If E1 and E2 be two energy level such that E2 >E1, in both emission the energy difference is fixed, so the frequency and so the wavelength thus the light emitted in both case should be monochromatic but why the light emitted in stimulidated emission is alone monochromatic ?
 
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  • #2
It's not. They may both be polychromatic if you want it to be.

A transition between a particular pair of energy states will always give the same wavelength ... but you don't normally get just one pair of energy states or just one photon.

You get a variety of colors when there are many different pairs of states involved producing lots of photons.

We usually build the devices relying on stimulated emission to be as monochromatic as possible.
With stimulated emission you can select which pair of states to use - the effect is particularly strong when your feed some of the stimulated photons back through the medium - as in a laser.

He-Ne gas (for instance) can be made to lase at a variety of different frequencies and steps have to be taken to suppress lasing at some of them.
 
  • #3
ajayguhan said:
If E1 and E2 be two energy level such that E2 >E1, in both emission the energy difference is fixed, so the frequency and so the wavelength thus the light emitted in both case should be monochromatic

Yes, that is true. Assuming a jump between two specific energy levels, the frequency of the light be identical in both cases (monochromatic).

In spontanious emission the phase and the direction will be random. In simulated emission they are the same.

Maybe you can get various other frequencies from spontanious emission because other energy levels are involved. This does not happen with stimulated emission because the parameters are set (controlled) for only a single frequency.

[Edit] Didn't see Simon's post when I replied. What he said...
 

What is stimulated emission?

Stimulated emission is a process in which an atom or molecule, already in an excited state, is further excited by an incoming photon, causing it to emit a second photon with the same energy, phase, and direction as the incoming photon.

What is spontaneous emission?

Spontaneous emission is a process in which an atom or molecule, in an excited state, spontaneously emits a photon without any external stimulation. This process occurs randomly and is responsible for the emission of light from light sources such as stars and light bulbs.

What is the difference between stimulated and spontaneous emission?

The main difference between stimulated and spontaneous emission is that stimulated emission is triggered by an external photon, while spontaneous emission occurs randomly without any external stimulation. Additionally, stimulated emission produces a photon with the same properties as the incoming photon, while spontaneous emission produces a photon with random properties.

How are stimulated and spontaneous emission related to lasers?

Lasers work by using stimulated emission to produce a coherent and intense beam of light. The atoms or molecules in a laser medium are first excited by an external energy source, then stimulated emission occurs, causing the emission of photons with the same properties. These photons then bounce back and forth between mirrors, causing further stimulated emission and amplification of the light, resulting in a laser beam.

What are some practical applications of stimulated and spontaneous emission?

Stimulated and spontaneous emission have many practical applications, including in lasers for cutting, welding, and medical procedures, in fiber-optic communication, and in fluorescence microscopy. Additionally, they are crucial in understanding and studying the behavior of atoms and molecules, as well as the properties of light.

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