Laser physics basics: Identify the process that produces the first photons. Once a laser’s active medium is excited (population inversion initiated), which fundamental process produces the initial photons that start the light amplification? Choose the correct physical process.

GivenA laser medium after excitation/population inversion.

Concept/ApproachLaser action begins when an excited atom decays spontaneously, emitting a photon that then triggers stimulated emission in other excited atoms, leading to coherent amplification.

SequenceExcitation → Spontaneous emission (seed photon) → Stimulated emission (amplification).

Final AnswerSpontaneous emission.