When an atom in an excited state E2 jumps to lower energy state E1 emitting a photon, without any external influence. Then this transition is called spontaneous emission.
When an atom in an excited state E2 jumps to lower energy state E1 emitting a photon, it emits an additional photon of same frequency of incident photon. This transition is known as stimulated emission.
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The emitted photon can move in any random direction.
The emitted photon travels in the same direction in which the incident photon is moving.
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Emission of photons takes place without energy.
Emission of photons takes place with energy.
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The radiation given out by such a source will be incoherent.
The radiation given out by such a source will be highly intense, monochromatic and coherent.
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Polychromatic radiation.(having many wavelength).
Monochromatic radiation.( having a single wavelength )
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Low intense
High intense
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Less directionality and having more angular spread during propagation.
High directionality and less angular spread during propagation.
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Example: Light from sodium or mercury vapour lamp.
