For 10 points, identify this condition that occurs when more particles are found in an excited state than at their lower energy levels, vital to the workings of a laser.
Composite pulses can be used to facilitate this process and enhance spin-spin NMR, while water and dust around AGNs can experience this process, accounting for the exceptionally strong 22 GHz spectral line. This state may be quenched when a gas overheats, thus leading to radiation trapping. Einstein's A and B coefficients imply that this state cannot be achieved in a (*) two-level system because the rate of absorption and downward transitions are equal. For a helium-neon system, this state occurs because of the very-fast transition between metastable and higher-energy states, which results in 1.15 nanometer visible light. Energy is introduced into the gain medium via "pumping" to achieve this state, a precondition for stimulate emission. For 10 points, identify this condition that occurs when more particles are found in an excited state than at their lower energy levels, vital to the workings of a laser.
Composite pulses can be used to facilitate this process and enhance spin-spin NMR, while water and dust around AGNs can experience this process, accounting for the exceptionally strong 22 GHz spectral line.
population inversion