The device which produces highly coherent sources is
A
Fresnel biprism
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B
Young's double sit
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C
Laser
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D
Lloyd's mirror
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Solution
The correct option is C Laser The atoms in the laser medium are pumped up energetically by an external power source, producing a population inversion of atomic energies. The pumped-up atoms can return to lower energy levels by emitting light at only certain frequencies, depending on the particular medium, which can be a solid (e.g. laser diode), a liquid (e.g. dye laser) or a gas (e.g. helium-neon laser).
We get temporal coherence because the excited atoms emit only at that preferred frequency.