Sample interview questions: How would you describe the concept of population inversion in laser systems?
Sample answer:
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Population Inversion Defined:
Population inversion, a fundamental concept in laser systems, refers to a non-equilibrium condition where more atoms or molecules occupy higher energy states than lower energy states. This state is a prerequisite for achieving laser action. -
Spontaneous and Stimulated Emission:
- Spontaneous Emission: In the absence of external stimulation, an excited atom or molecule spontaneously decays to a lower energy state, emitting a photon with a specific wavelength.
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Stimulated Emission: When an excited atom or molecule interacts with an incident photon of matching energy, it is stimulated to decay to a lower energy state, emitting a photon identical to the incident one in terms of wavelength, phase, and direction.
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Population Inversion and Laser Action:
- Achieving Population Inversion: Population inversion is typically achieved through various methods, such as optical pumping, electrical discharge, or chemical reactions, which excite atoms or molecules to higher energy states.
- Stimulated Emission Dominance: With population inversion, stimulated emission becomes more probable than spontaneous emission. This results in a cascading effect, where emitted photons stimulate further stimulated emissions, leading to a rapid amplification of light at a specific wavelength.
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Laser Output: The amplified light is directed through a partially reflective mirror, allowing a portion of the light to exit as a laser beam, while the rest is reflected back to further stimulate emission.
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Significance of Population Inversion:
- Coherence: Population i… Read full answer