Near-resonant excitation refers to the process of applying a frequency of light or other electromagnetic radiation to a two-level system that is close to, but not exactly at, the resonant frequency of the system. This can result in interesting phenomena and effects, such as Rabi oscillations and Autler-Townes splitting.
A two-level system is a physical system that can exist in one of two distinct energy states. This can be a simple quantum mechanical system, such as an atom or a spin, or a macroscopic system with only two distinguishable states, such as a switch or a qubit in a quantum computer.
Near-resonant excitation can induce transitions between the two energy states of a two-level system. When the frequency of the applied radiation is close to the resonant frequency of the system, the system's response can be significantly altered, leading to effects such as population inversion, energy level splitting, and coherent oscillations.
Near-resonant excitation of a two-level system has many practical applications. It is the basis of many laser technologies, such as dye lasers and semiconductor lasers. It is also used in optical pumping, nuclear magnetic resonance (NMR) spectroscopy, and quantum computing, among others.
The near-resonant excitation of a two-level system is influenced by several factors, including the intensity and frequency of the applied radiation, the energy difference between the two states of the system, and the lifetime of the excited state. Additionally, the presence of other nearby energy levels and external perturbations can also affect the excitation process.