Chapter 9: The Ammonia Maser & Energy Transitions

The Hamiltonian equations are used to show how these energy levels are affected by the introduction of an external electric field (denoted as E). This effect, related to the Stark effect, causes the energy levels to split, where the splitting initially depends linearly on E and then quadratically for stronger fields. The practical operation of the maser is detailed by explaining how the two energy states are physically separated. An ammonia molecular beam is passed through an electric field region that deflects molecules based on their energy, allowing only those in the higher energy state (State I or ∣I⟩) to enter the resonant maser cavity. Once inside the cavity, these molecules interact with a time-dependent oscillating electric field. The probability of transition (from State I to the lower State II) is maximized when the frequency of the oscillating field (omega) matches the characteristic resonance frequency (omega zero equals 2A/h-bar). When a transition occurs, the molecule releases its excess energy into the cavity field, generating an amplification effect and sustaining oscillation. This demonstration of stimulated emission under resonance conditions provides a framework for understanding the general quantum theory of light absorption and emission, relating the physical mechanism to the dipole matrix element.