In a laser, light is produced by
Correct answer: B. stimulated emission, in which a passing photon triggers an identical photon from an excited atom
- A. spontaneous emission only
- B. stimulated emission, in which a passing photon triggers an identical photon from an excited atom
- C. heating a filament
- D. the photoelectric effect
Explanation
The triggered photon matches the original in frequency, phase and direction, so the beam is coherent and highly directional, which is what distinguishes laser light from that of a lamp. Achieving it requires a population inversion, with more atoms excited than in the ground state, maintained by pumping. Metastable states are needed so that atoms remain excited long enough.
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About Atomic Spectra
Atoms emit or absorb light at specific wavelengths because electrons occupy quantized energy levels and change levels by absorbing or releasing photons. The topic covers emission and absorption spectra, spectral series, hydrogen’s line spectrum, energy-level transitions, and the relation between wavelength, frequency and photon energy.
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