Final answer:
Atoms emit radiation when they make a transition from an excited state to a lower energy state, typically by the emission of a photon. The uncertainty in the frequency of emitted photons suggests the radiation is not purely monochromatic. This process is essential in applications such as atomic clocks, where microwave frequency is finely tuned to trigger atomic transitions in cesium atoms.
Step-by-step explanation:
When we discuss an 'Atomic Frequency Comb' regarding when an atom is emitted, we are referring to the concept that an atom emits radiation when it undergoes a transition from an excited state to a lower energy state, often a ground state, releasing a photon. This emission occurs because an excited electron drops to a lower energy level within the atom. The uncertainty in the frequency (Δf) of the emitted photon can be estimated considering that an atom typically exists in an excited state for about ×10-8 seconds. According to the Heisenberg uncertainty principle, this leads to a certain breadth of frequency range for the emitted photons, contradicting the notion of purely monochromatic radiation.
Variables such as atomic transitions, stimulated emission, and the application of quantum mechanics to predict these processes provide a detailed insight into how the atomic standard is used to calibrate clocks, as with cesium atoms in atomic clocks. The microwave frequency applied to supercooled cesium atoms in a vacuum chamber needs to be precise for the atoms to absorb the right amount of energy and undergo an electronic transition. The subsequent decay from the higher-energy state back to a lower-energy state emits radiation that is used to measure time accurately. Similarly, an atom can be excited several steps above the ground state by the absorption of a high-energy UV photon, leading to atomic fluorescence.