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Figure b displays spontaneous emission. The inner circle is nucleus. The middle circle is orbit of ground state. The outer circle is orbit of excited state. The electron in orbit of excited state is in form of circle made with dots which is converted into the electron of solid state in orbit of ground state. The arrow displays emission of photons.

Figure c displays stimulated emission. The inner circle is nucleus. The middle circle is orbit of ground state. The outer circle is orbit of excited state. The electron in orbit of excited state is in form of circle made with dots which is converted into the electron of solid state in orbit of ground state. The arrow displays emission of photons. The photons are emitted into electron in excited state and converted to stimulated photon in ground state.